RELATED APPLICATIONS

[001] Priority is claimed to each of the following United States provisional patent applications: (1) No. 63/474,257, filed August 1, 2022, entitled “Vehicle Guidance System”; (2) No. 63/474,383, filed August 10, 2022, entitled “Vehicle Guidance System”; (3) No. 63/576,322, filed Jan. 30, 2023, entitled “Short-Range Radar for use in Vehicle Lateral Guidance and Control”; (4) No. 63/576,323, filed January 30, 2023, entitled “Vehicle Guidance System”; (5) No. 63/454,669, filed March 25, 2023, entitled “Radar-Based Vehicle Guidance System Using Dihedral Corner Reflector Embedded in Pavement Marker”; (6) No. 63/464,532, filed May 5, 2023, entitled “Vehicle Guidance System”; (7) No. 63/464,527, filed May 5, 2023, entitled “Short-Range Radar for Use in Vehicle Lateral Guidance and Control”; (8) No. 63/466,612, filed May 15, 2023, entitled “Vehicle Guidance System”; and (9) No. 63/469,920, filed May 31, 2023, entitled “Radar-Based Vehicle Guidance Using Corner Reflectors Embedded in Pavement Markers on a Driving Surface.” The entire disclosures of each of the foregoing patent applications are hereby incorporated by reference herein.

TECHNICAL FIELD

[002] The field of this disclosure relates generally to control of an automobile or similar vehicle. More specifically, this disclosure relates to the use of radar (radio detection and ranging) reflectors on or near a roadway or other driving surface to control or assist in controlling a vehicle, especially its lateral positioning.

BACKGROUND INFORMATION

[003] Figures 1A and IB shows typical pavement markers 445 that are currently used on today’s roads. The pavement marker 445 shown in Figure 1 A is rectangular, but pavement markers come in many different shapes and sizes. The pavement marker 445 can be placed on top of the pavement surface, in which case they are called Raised Pavement Markers (RPMs), or can be installed at or slightly below the pavement surface level eg., snow-plowable markers), or below the roadway surface 300 in cut grooves, divots, or slots. The pavement markers 445 are typically installed along the painted lines 305, 307, and 309 on the roadway 300, as shown in Figure IB. The painted line 307 is typically a yellow center line and the painted white lines 305 and 309 mark the sides of the road. The primary function of the pavement marker 445 is to reflect light waves so that the vehicle headlights or sunlight is reflected back to the driver of the vehicle in order for the driver to visually see the location of the road lines, especially in inclement weather. The pavement markers have a visible reflector 275 on one or more sides as shown in Figure 1A. Also, the raised pavement reflectors may act as a rumble guard when the vehicle crosses the roadway lines or pavement markers 445 since the marker 445 are typically 25 mm above the roadway surface and causes the vehicle tire(s) to impact the raised pavement marker. The raised pavement markers 445 have many modifications over the years with various visible reflective properties such as the cat’s eye, LED (light emitting diode) lights, lidar reflection patterns, etc. The pavement markers 445 are very reflective to visible light, but not very reflective to radio frequencies (RF) coming from radar transceivers even though some pavements markers are made of metal. The pavement markers are used typically on highways, but also in parking lots, shipping yards, shipping docks, and other paved and non-paved areas.

OVERVIEW OF DISCLOSURE

[004] This disclosure generally relates to (1) a pavement marker in which is embedded a radar- reflective dihedral corner reflector or other suitably oriented directional reflector that can reflect a radar signal; (2) methods of manufacturing such pavement markers; (3) arrangements of radar-reflective pavement markers on a driving surface, such as a road or a lane of a road, including along or near boundaries of the road or the lane, such as lane lines; (4) methods of installing such pavement markers on a driving surface; (5) radar transceivers on or in a vehicle for sensing the radar-reflective pavement markers and measuring distances from the vehicle to the markers; (6) vehicles equipped with such radar transceivers; and (7) methods of operation of such radar transceivers and uses of the measured distance, such as, for example, controlling or assisting with lateral steering or positioning of a vehicle on a driving surface.

[005] According to one embodiment, a pavement marker is for use on a roadway on which vehicles travel in a direction of travel. The roadway comprises lane lines marked on a top surface of the roadway generally parallel to the direction of travel. The pavement marker comprises an optically reflective surface positioned and oriented to face oncoming vehicles when the pavement marker is affixed to the roadway and a dihedral corner reflector comprising a longitudinal axis and two passive radar-reflective surfaces intersecting at the longitudinal axis. The dihedral corner reflector is positioned and oriented so that the longitudinal axis is generally orthogonal to the optically reflective surface as well as substantially parallel to the direction of travel and substantially parallel to the lane lines when the pavement marker is affixed to the roadway.

[006] Optionally, the dihedral corner reflector is strictly dihedral, and/or the two passive radar-reflective surfaces are at least approximately orthogonal.

[007] Optionally, the pavement marker further comprises a substantially radar- transparent material between the two passive radar-reflective surfaces of the dihedral corner reflector. The substantially radar-transparent material may comprise, for example, a material selected from a group consisting of polytetrafluoroethylene, polypropiolactone, polyvinyl chloride and acrylonitrile butadiene styrene. The substantially radar-transparent material may be adhered to the dihedral corner reflector with a substantially radar-transparent adhesive.

[008] The dihedral corner reflector may comprise, for example, two metal plates or two surfaces coated with radar-reflective coatings. The radar-reflective coatings may be paint, such as a metallic paint, or electroplated.

[009] Optionally, the pavement marker further comprises one or more additional dihedral corner reflectors. The total number of dihedral corner reflectors may be, for example, two or at least four. If two, the two dihedral corner reflectors may form an inverted T-shape with a common vertical element. If two, the two dihedral corner reflectors may be laterally offset from each other, on opposite sides of the pavement marker, and oriented to reflect radar signals in opposite directions horizontally.

[0010] In a pavement marker with at least four dihedral corner reflectors, one of them may be positioned along and proximate each side of the pavement marker.

[0011] Optionally, the pavement marker is snow-plowable and/or one of the radar- reflective surfaces of the dihedral comer reflector is the top surface of the roadway.

[0012] The pavement marker may be, for example, approximately 100 mm wide, approximately 100 mm long, and approximately 25 mm high.

[0013] According to one embodiment, a pavement marker is for use on a roadway on which vehicles travel in a direction of travel. The pavement marker comprises an optically reflective surface positioned and oriented to face oncoming vehicles when the pavement marker is affixed to the roadway and a passive radar-reflective reflector characterized by a reflection direction from which a radar signal incident on the reflector is reflected back toward a source of the radar signal with maximum amplitude. The pavement marker is configured to be affixed to the roadway so that the reflection direction is partially upward from the roadway and substantially orthogonal to the direction of travel.

[0014] Optionally, the roadway comprises lane lines marked on a top surface of the roadway generally parallel to the direction of travel, and the pavement marker is configured to be mounted such that the reflection direction is substantially orthogonal to the lane lines.

[0015] Optionally, the source of the radar signal is a vehicle having a directional radar transmitter having a main beam lobe center axis directed sideways from the vehicle and downward from the vehicle, and the reflector is positioned and oriented to generate a detectable return signal via reflection of an incident radar signal from the vehicle’s radar transmitter directed sideways and downward from the vehicle as the vehicle passes alongside of the pavement marker.

[0016] Optionally, the pavement marker further comprises a substantially radar- transparent material between the reflector and the source. The substantially radar-transparent material may be selected from a group consisting of, for example, polytetrafluoroethylene, polypropiolactone, polyvinyl chloride and acrylonitrile butadiene styrene. The substantially radar-transparent material may be adhered to the reflector with a substantially radar- transparent adhesive.

[0017] The pavement marker comprises, for example, metal or one or more surfaces coated with radar-reflective coatings, which may be paint, such as metallic paint, or electroplated.

[0018] Optionally, the pavement marker further comprises one or more additional radar-reflective reflectors. The total number of reflectors may be, for example, two or at least four. If two, the two reflectors may be horizontally offset from each other, on opposite sides of the pavement marker, and oriented to reflect radar signals in opposite directions horizontally. If at least four, one reflector may be positioned along and proximate each side of the pavement marker.

[0019] Optionally, the pavement marker is snow-plowable; approximately 100 mm wide, approximately 100 mm long, and approximately 25 mm high; further comprises a radar- reflective bottom plate; and/or the reflector is a dihedral corner reflector.

[0020] According to one embodiment, a method makes a pavement marker for use on a roadway on which a vehicle travels in a direction of travel. The method provides on a first exterior side of the pavement marker a visibly reflective part configured to be seen by a driver of the vehicle when driving the vehicle generally toward the pavement marker. The method also embeds within the pavement marker a dihedral corner reflector comprising a longitudinal axis and two passive RF-reflective surfaces intersecting at the longitudinal axis, which is substantially orthogonal to the first exterior side of the pavement marker.

[0021] Optionally, the embedding step comprises placing a substantially radar- transparent material between the two RF-reflective surfaces of the dihedral corner reflector. Optionally, the method further attaches the substantially radar-transparent material to the two RF-reflective surfaces of the dihedral corner reflector. The attaching step may comprise adhering the substantially radar-transparent material to the two RF-reflective surfaces of the dihedral corner reflector with a radar-transparent adhesive. The substantially radar- transparent material may have a quarter-round shape.

[0022] Optionally, the method further comprises forming a dihedral corner reflector by an extrusion process, cutting an output of the extrusion process into segments, and selecting one of the segments to embed in the pavement marker. Optionally, the method further comprises forming the dihedral corner reflector by welding two metal pieces together. Optionally, the method further comprises forming the dihedral corner reflector by bending a flat metal piece. Optionally, the method further comprises forming the dihedral corner reflector by a process comprising applying an RF-reflective paint to one or more of the two passive RF-reflective surfaces. Optionally, the method further comprises forming the dihedral corner reflector by a process comprising electroplating an RF-reflective coating on one or more of the two passive RF-reflective surfaces.

[0023] According to one embodiment, a method makes a radar-reflective pavement marker for use for use on a roadway on which vehicles travel in a direction of travel. The method provides on a first exterior side of the pavement marker a visibly reflective part configured to be seen by a driver of the vehicle when driving the vehicle generally toward the pavement marker. The method also embeds within the pavement marker a passive directional radar reflector positioned and oriented to give a maximum return signal via reflection of an incident radar signal directed partially downward toward the pavement marker and also directed horizontally from a direction substantially orthogonal to both the direction of travel and first exterior side of the pavement marker.

[0024] Optionally, the embedding step comprises placing a substantially radar- transparent material over the reflector. Further, the method may comprises attaching the substantially radar-transparent material to the reflector. The attaching step may comprises, for example, adhering the substantially radar-transparent material to the reflector with a radar- transparent adhesive.

[0025] Optionally, the passive directional radar reflector is a dihedral corner reflector.

[0026] Optionally, the method further comprises forming a radar reflector by an extrusion process, cutting an output of the extrusion process into segments; and selecting one of the segments to embed in the pavement marker. Optionally, the method further comprises forming the radar reflector by welding metal pieces together. Optionally, the method further comprises forming the radar reflector by bending a metal piece. Optionally, the method further comprises forming the radar reflector by a process comprising applying an RF- reflective paint to one or more surfaces of the radar reflector. Optionally, the method further comprises forming the radar reflector by a process comprising electroplating an RF-reflective coating on one or more surfaces of the radar reflector.

[0027] One embodiment is a roadway on which vehicles travel in a direction of travel in a lane. The roadway comprises a set of pavement markers discretely spaced along at least one side of the lane and attached to a top surface of the roadway. Each pavement marker in the set comprises a radar-reflective dihedral corner reflector comprising a longitudinal axis and two passive radar-reflective surfaces intersecting at the longitudinal axis. The pavement markers are affixed to the roadway so that the longitudinal axis is substantially parallel to the direction of travel.

[0028] Optionally, the roadway further comprises lane lines marked on the top surface of the roadway generally parallel to the direction of travel to demark boundaries of the lane, and the pavement markers are affixed to the roadway such that the longitudinal axis of the radar-reflective dihedral corner reflectors are substantially parallel to the lane lines. The pavement markers may be, for example, affixed to the roadway along one of the lane lines.

[0029] A distance between adjacent pavement markers in the set may be, for example, between about 0.3 m (meters) and about 8 m.

[0030] Optionally, the roadway further comprises a second set of pavement markers discretely spaced along a second side of the lane and attached to a top surface of the roadway. Each of the pavement marker in the second set comprises a radar-reflective dihedral corner reflector having a longitudinal axis, the radar-reflective dihedral corner reflector comprising two RF-reflective surfaces orthogonal to one another and intersecting at the longitudinal axis. The pavement markers are affixed to the roadway so that the longitudinal axis is substantially parallel to the direction of travel.

[0031] The roadway may be, for example, a multi-lane roadway or a bidirectional roadway.

[0032] Optionally, the set of pavement markers encodes information about the roadway. For example, the roadway may comprise substantially straight segments and curved segments, and the information encoded in the set of pavement markers comprises data identifying a segment as straight or curved.

[0033] Optionally, the roadway further comprises divots in the surface of the roadway forming rumble strips, wherein at least some of the set of pavement markers are installed in the divots.

[0034] One embodiment is a driving surface on which a vehicle is driven along a path in a direction of travel. The driving surface comprises a set of pavement markers discretely spaced along a side of the path and attached to the driving surface. Each of the pavement marker comprises a passive radar-reflective reflector characterized by a reflection direction from which a radar signal incident on the reflector is reflected back toward a source of the radar signal with maximum amplitude. The pavement marker is affixed to the driving surface so that the reflection direction is partially upward from the driving surface and substantially orthogonal to the direction of travel.

[0035] The driving surface may be, for example, a roadway, such as a multi-lane roadway or a bidirectional roadway, or a parking lot, transportation depot, shipping dock, loading bay, or warehouse lot.

[0036] The driving surface may be, for example, a lane further comprising lane lines marked on the driving surface generally parallel to the direction of travel to demark boundaries of the lane, and the pavement markers are affixed to the roadway such that the reflection directions are substantially orthogonal to the lane lines. In one arrangement, the pavement markers are affixed to the roadway along one of the lane lines.

[0037] A distance between adjacent pavement markers in the set may be, for example, between about 0.3 m and about 8 m.

[0038] Optionally, the driving surface further comprises a second set of pavement markers discretely spaced along a second side of the path and attached to a top surface of the driving surface. Each of the pavement marker in the second set comprises a passive radar- reflective reflector characterized by a reflection direction from which a radar signal incident on the reflector is reflected back toward a source of the radar signal with maximum amplitude. The pavement marker is affixed to the driving surface so that the reflection direction is partially upward from the driving surface and substantially orthogonal to the direction of travel.

[0039] Optionally, the set of pavement markers encodes information about the driving surface.

[0040] Optionally, the radar-reflective reflector is a dihedral corner reflector. [0041] According to one embodiment, a radar transceiver is configured to be installed in or on a land vehicle and for use with radar-reflective pavement markers distributed along a pathway along which the land vehicle can travel. The radar transceiver comprises a radar transmitter and a radar receiver. The radar transmitter is configured to transmit a radar signal having a transmission beam pattern having a center direction of maximum transmission. The radar receiver is configured to receive a radar return reflection signal and to have a reception beam pattern having a center direction of maximum reception. The radar transceiver is also configured to be installed in or on the land vehicle so that the center direction of maximum transmission is downward and sideways from the land vehicle when the radar transceiver is installed on or in the land vehicle and so that the center direction of maximum reception is upward and sideways toward the land vehicle when the radar transceiver is installed on or in the land vehicle.

[0042] Optionally, the radar transceiver operates within a frequency range within a range from about 300 MHz to about I THz, or, for example, within a frequency range from about 77 GHz to about 81 GHz.

[0043] The radar transceiver may be, for example, a frequency-modulated continuous wave radar transceiver, an ultra wideband impulse radar transceiver, or of a type selected from a group consisting of two-frequency phase difference, multiple-frequency radar, orthogonal frequency division multiplex, frequency shift keying, digital code modulation, phase- modulated continuous wave, multiple-input-multiple-output, polarimetric, dual-polarimetric, monopulse, and interferometric synthetic aperture radar.

[0044] The radar transceiver according to claim 81, wherein the radar transceiver is monostatic or bi-static.

[0045] Optionally, the radar transceiver comprises an antenna array. [0046] Optionally, the radar transmitter is configured to transmit a polarized radar signal, and the radar receiver may be configured to detect the radar return reflection signal based on its polarization.

[0047] The radar transceiver may be configured to be placed, for example, within a front bumper of the vehicle or within a vehicle light assembly.

[0048] Optionally, the radar transceiver further comprises a signal processor coupled to the radar receiver, configured to receive signals based on the radar return reflection signal, and configured to determine path lengths from the radar transceiver to the radar-reflective pavement markers. The signal processor may be further configured to process just a portion of the radar return reflection signal received in a window corresponding to an expected range of a reflection target, or to perform a frequency transform of the radar return reflection signal.

[0049] Optionally, the radar-reflective pavement markers comprise dihedral corner reflectors.

[0050] According to one embodiment, a method installs radar-reflective pavement markers on a roadway on which vehicles travel in a direction of travel. A radar-reflective pavement marker comprises a RF-reflective dihedral corner reflector having two radar- reflective surfaces intersecting along a longitudinal axis. The method comprises attaching a plurality of said radar-reflective pavement markers to the roadway in an orientation such that the longitudinal axis of each radar-reflective pavement marker is generally aligned with the direction of travel and such that the longitudinal axes of the plurality of said radar-reflective pavement markers define a desired path of a vehicle on the roadway in the direction of travel.

[0051] According to one embodiment, a method installs radar-reflective pavement markers on a driving surface on which a vehicle is driven. The vehicle has a directional radar transmitter having a main beam lobe center axis directed sideways from the vehicle and downward from the vehicle. The method comprises attaching a plurality of said radar- reflective pavement markers to the driving surface such that each directional radar reflector is positioned and oriented to give a maximum or high return signal via reflection of an incident radar signal from the vehicle’s radar transmitter directed sideways and downward from the vehicle. Optionally, the directional radar reflectors are dihedral corner reflectors.

[0052] According to one embodiment, a vehicle can be used on a road along which a plurality of pavement markers have been installed. Each of the pavement markers comprises a radar reflector. The vehicle comprises a radar transceiver and a processor. The radar transceiver is mounted to the vehicle and characterized by a beam pattern having a center aimed towards downward and sideways from the vehicle such that a reflection is detected from a radar reflector embedded in a pavement marker as the vehicle moves forward by the pavement marker on the vehicle’s side. The processor is operatively coupled to the radar transceiver and configured to determine, based on the reflection, a path length from the radar transceiver to the radar reflector embedded in the pavement marker.

[0053] Optionally, the radar transceiver is further characterized by a second beam pattern having a second center downward and in a second sideways direction from the vehicle such that a reflection is detected from a second radar reflector embedded in a second pavement marker as the vehicle moves by the second pavement marker, wherein the second sideways direction is horizontally approximately opposite the sideways direction, and wherein the second pavement marker is on an opposite side of the vehicle from the first pavement marker.

[0054] Optionally, the vehicle further comprising: a second radar transceiver mounted to the vehicle, wherein the second radar transceiver is characterized by a second beam pattern having a second center aimed downward and in a second sideways direction from the vehicle such that a reflection is detected from a radar reflector embedded in a second pavement marker as the vehicle moves forward by the second pavement marker by the pavement marker on the vehicle’s side. [0055] The vehicle may further comprises an exterior light assembly, and the radar transceiver may be located within the exterior light assembly, or the vehicle may further comprises a front bumper, and the radar transceiver is located within the front bumper.

[0056] Optionally, the processor is configured to perform one or more of a lane departure warning function, a lane keeping function, and a lane centering assistance function based on the path length from the radar transceiver to the radar reflector embedded in the pavement marker.

[0057] Optionally, the vehicle further comprises a lateral positioning system independent of the radar transceiver, wherein the radar transceiver and the processor form a redundant lateral positioning system.

[0058] The vehicle may be at least partially autonomous, and the lateral positioning of the vehicle may be performed based at least in part on the path length from the radar transceiver to the radar reflector embedded in the pavement marker.

[0059] Optionally, the radar transceiver is also configured to perform blind-spot detection.

[0060] Optionally, the radar reflector is a dihedral corner reflector.

[0061] According to one embodiment, a method determines a lateral position of a land vehicle along in a pathway. The pathway has radar-reflective pavement markers distributed along the pathway in a direction of vehicle travel. The method transmits downward and sideways from the land vehicle towards a pavement marker mounted on or near the pathway a radar transmit signal as the vehicle passes the pavement marker. The method also receives at the land vehicle a radar reflection signal from a radar reflector embedded within the pavement marker as the vehicle passes by the pavement marker. The method also determines, based on the radar transmit signal and the radar reflection signal, a distance between the land vehicle and the pavement marker. [0062] Optionally, the transmitting, receiving, and determining steps are repeated for every radar-reflective pavement marker that the vehicle passes. The transmitting step, for example, may be repeated periodically at a period selected from a range from about 0.5 milliseconds to about 1 second.

[0063] The radar-reflective pavement markers may be distributed, for example, along one side of the vehicle as the vehicle travels along the pathway or the pathway is one lane of a multi-lane road, and the radar-reflective pavement markers are distributed along a line demarking one side of the pathway.

[0064] Optionally, the pathway is one lane of a multi-lane road, and the radar- reflective pavement markers are distributed along a line demarking one side of a lane adjacent to a lane corresponding to the pathway of the vehicle.

[0065] Optionally, the method further comprises filtering the radar reflection signal based on a range of expected distances between the land vehicle and the pavement marker; performing a frequency transform on the radar reflection signal; and/or using the distance to guide or assist steering the vehicle laterally to follow the pathway.

[0066] Optionally, the method further comprises providing a warning to a driver of the vehicle if the distance exceeds a maximum threshold or is less than a minimum threshold and/or providing a warning external to the vehicle if the distance exceeds a maximum threshold or is less than a minimum threshold. For example, the warning external to the vehicle comprises flashing a blinker.

[0067] Optionally, the method further comprises performing one or more of a lanecentering assistance function and a lane-keeping function based on the distance between the land vehicle and the pavement marker.

[0068] The vehicle may optionally comprise a lateral positioning system independent of the method summarize above, and the method further comprises either using the distance in conjunction with the independent lateral positioning system to improve lateral position determination, using the method’s measured distance to calibrate the independent lateral positioning system.

[0069] Optionally, the radar-reflective pavement markers used with the method comprise dihedral corner reflectors.

[0070] As one skilled in the art will appreciate in light of this disclosure, certain embodiments of the pavement markers, radar reflectors, and radar disclosed herein may be capable of achieving certain advantages, which will be apparent from the following detailed description of example embodiments, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 A is an isometric diagram of a conventional pavement marker.

[0072] Figure IB is a top view of a segment of a road on which conventional pavement markers have been placed.

[0073] Figure 2A is an isometric diagram of a dihedral corner reflector.

[0074] Figure 2B is an isometric diagram of a pavement marker augmented with two dihedral corner reflectors, according to one embodiment.

[0075] Figure 2C is a top view of the pavement marker of Figure 2B.

[0076] Figure 2D is a side view of the pavement marker of Figure 2B.

[0077] Figure 3A is an isometric diagram of a double dihedral corner reflector.

[0078] Figure 3B is an isometric view of a pavement marker augmented with a double dihedral corner reflectors, according to one embodiment.

[0079] Figure 3C is a top view of the pavement marker of Figure 3B.

[0080] Figure 3D is a side view of the pavement marker of Figure 3B. [0081] Figure 4A is a side view of the pavement marker of Figure 2B illustrating a reflection from/to a radar transceiver, according to one embodiment.

[0082] Figure 4B is a side cross-section view of a dihedral corner reflector with dimension labels.

[0083] Figure 4C is an isometric diagram of the dihedral corner reflector of Figure 2A with dimension labels.

[0084] Figure 4D is a side cross-section view of a double dihedral corner reflector with dimension labels.

[0085] Figure 4E is an isometric diagram of the dihedral corner reflector of Figure 3A with dimension labels.

[0086] Figure 5A is a representative plot of a radar cross section of a dihedral corner reflector versus angle of incidence in one dimension, according to one embodiment.

[0087] Figure 5B is a diagram illustrating an angle of incidence of radiation directed at a dihedral corner reflector corresponding to Figure 5A.

[0088] Figure 5C is a diagram illustrating a position of incidence of radiation directed at a dihedral corner reflector along the longitudinal direction of the reflector.

[0089] Figure 5D is a representative plot of a radar cross section of a dihedral corner reflector versus position of incidence along the longitudinal direction of the reflector corresponding to Figure 5C.

[0090] Figure 5E is a diagram illustrating an angle of incidence of radiation directed at a dihedral corner reflector in another dimension, according to one embodiment.

[0091] Figure 5F is a representative plot of a radar cross section of a dihedral corner reflector versus angle of incidence corresponding to Figure 5E. [0092] Figure 6A is an exploded isometric diagram of a pavement marker having two dihedral corner reflectors, according to one embodiment.

[0093] Figure 6B is an exploded isometric diagram of a pavement marker having two dihedral corner reflectors, according to another embodiment.

[0094] Figure 6C is an isometric diagram of the pavement marker having two dihedral corner reflectors, according to another embodiment.

[0095] Figure 7A is an exploded isometric diagram of the pavement marker of Figure 3B.

[0096] Figure 7B is an exploded isometric diagram of another pavement marker having two dihedral comer reflectors, according to another embodiment.

[0097] Figure 7C is an exploded isometric diagram of yet another pavement marker having two dihedral corner reflectors, according to yet another embodiment.

[0098] Figure 7D is an exploded isometric diagram of a pavement marker having four dihedral corner reflectors, according to one embodiment.

[0099] Figure 8A is a front-view diagram of a vehicle equipped with a radar transceiver interacting with a radar-reflective pavement marker on a driving surface, according to one embodiment.

[00100] Figure 8B is a block diagram of a radar-based lateral control system for a vehicle, according to one embodiment.

[00101] Figure 8C is a block diagram of a radar-based LDW system for a vehicle, according to one embodiment.

[00102] Figure 8D is a block diagram of a radar-based LKA/LKS system for a vehicle, according to one embodiment. [00103] Figure 8E is a block diagram of a radar-based autonomous lateral control system for a vehicle, according to one embodiment.

[00104] Figure 9A is a side-view diagram of a vehicle equipped with a radar transceiver interacting with radar-reflective pavement markers on a driving surface, according to one embodiment.

[00105] Figure 9B is a top view of the vehicle of Figure 9A.

[00106] Figure 9C is a top view of a vehicle equipped with radar transceivers on a road having radar-reflective pavement markers, according to one embodiment.

[00107] Figure 10A is a front- view diagram of a vehicle equipped with two radar transceivers interacting with two radar-reflective pavement markers on a driving surface, according to one embodiment.

[00108] Figure 10B is a front-view diagram of a vehicle equipped with a dual-direction radar transceiver interacting with two radar-reflective pavement markers on a driving surface, according to one embodiment.

[00109] Figure 11A is a top-view diagram of two vehicles equipped with radar transceivers interacting with radar-reflective pavement markers on a multi-lane road, according to one embodiment.

[00110] Figure 1 IB is a top-view diagram of a vehicle equipped with radar transceivers interacting with radar-reflective pavement markers on a curved road, according to one embodiment.

[00111] Figure 11C is a top-view diagram of a vehicle equipped with radar transceivers interacting with radar-reflective pavement markers on a curved road, according to another embodiment

[00112] Figure 1 ID is a diagram illustrating a set of radar-reflective pavement markers in a coded arrangement, according to one embodiment. [00113] Figure 11E is a diagram illustrating a set of radar-reflective pavement markers in a coded arrangement, according to another embodiment.

[00114] Figure 1 IF is a diagram illustrating a set of radar-reflective pavement markers in a coded arrangement, according to yet another embodiment.

[00115] Figure 11G is a diagram illustrating a set of radar-reflective pavement markers in a coded arrangement, according to still another embodiment.

[00116] Figure 12A is an isometric diagram of a pavement marker having dihedral corner reflectors, according to one embodiment.

[00117] Figure 12B is an isometric diagram of a pavement marker having dihedral corner reflectors, according to another embodiment.

[00118] Figure 12C is an isometric diagram of a pavement marker having dihedral corner reflectors, according to yet another embodiment.

[00119] Figure 13A is a cross-section view of a pavement marker in a cavity below a driving surface, according to one embodiment.

[00120] Figure 13B is a top view of a section of a road in which pavement markers of Figure 13A have been arranged, according to one embodiment.

[00121] Figure 13C is a top view of a section of a road in which pavement markers of Figure 13A have been arranged, according to another embodiment.

[00122] Figure 14A is a cross-section view of a pavement marker in a cavity below a driving surface, according to another embodiment.

[00123] Figure 14B is a top view of a section of a road in which pavement markers of Figure 14A have been arranged, according to one embodiment.

[00124] Figure 14C is a top view of a section of a road in which pavement markers of Figure 14A have been arranged, according to another embodiment. [00125] Figure 14D is an isometric view of a snow-plowable pavement marker augmented with dihedral corner reflectors, according to one embodiment.

[00126] Figure 14E is a top view of a snow-plowable pavement marker augmented with dihedral corner reflectors, according to another embodiment.

[00127] Figure 14F is a side cross-section view of the snow-plowable pavement marker of Figure 14E.

[00128] Figure 14G is a side cross-section view of a snow-plowable pavement marker augmented with dihedral corner reflectors, according to another embodiment.

[00129] Figure 14H is a side cross-section view of a snow-plowable pavement marker augmented with dihedral corner reflectors, according to yet another embodiment.

[00130] Figure 15A is an isometric view of a dihedral corner reflector along a curb, according to one embodiment.

[00131] Figure 15B is a diagram illustrating a dihedral corner reflector within or behind a curb, according to one embodiment.

[00132] Figure 15C is a diagram illustrating a dihedral corner reflector along a curb, according to another embodiment.

[00133] Figure 16A is an isometric view of a pavement marker or portion thereof having three dihedral corner reflectors, according to one embodiment.

[00134] Figure 16B is an isometric view of a pavement marker or portion thereof having a front dihedral corner reflector at a different vertical angle, according to one embodiment.

[00135] Figure 16C is an isometric view of a pavement marker or portion thereof having a side-facing dihedral corner reflector, according to one embodiment.

[00136] Figure 17 is a block diagram of an UWB impulse radar transceiver, according to one embodiment. [00137] Figure 18 is a block diagram of an impulse radar transceiver with multiple antennas, according to one embodiment.

[00138] Figure 19 is a block diagram of an FMCW radar transceiver, according to one embodiment.

[00139] Figure 20 is a block diagram of an FMCW radar transceiver, according to another embodiment.

[00140] Figure 21 is a block diagram of an dual -frequency radar transceiver, according to one embodiment.

[00141] Figure 22 is a block diagram of a DCM radar transceiver, according to one embodiment.

[00142] Figure 23 is a block diagram of an FMCW radar transceiver with multiple antennas, according to one embodiment.

[00143] Figure 24 is a block diagram of a system that combines multiple detection, guidance, and/or control systems, including a radar-based lateral positioning system, according to one embodiment.

[00144] Figure 25 is a top-view diagram of a vehicle equipped with radar transceivers on a road with radar-reflective pavement markers, according to one embodiment.

[00145] Figure 26 is a table of positions of the pavement markers in Figure 25, according to one embodiment.

[00146] Figure 27 is a block diagram of a system for controlling vehicle speed based on radar-measured positions of pavement markers, according to one embodiment.

[00147] Figure 28 is a block diagram of a longitudinal vehicle position control system, according to one embodiment [00148] Figure 29 is a top-view diagram of a truck and trailers equipped with radar transceivers on a road with radar-reflective pavement markers, according to one embodiment

[00149] Figure 30A is an isometric diagram of a dihedral/trihedral corner reflector, according to one embodiment.

[00150] Figure 30B is an isometric diagram of a double dihedral/trihedral corner reflector, according to one embodiment.

[00151] Figure 31 A is a side-view illustration of a reflection from a dihedral portion of the dihedral/trihedral corner reflector of Figure 30A.

[00152] Figure 31B is a top-view illustration of a reflection from a dihedral portion of the dihedral/trihedral corner reflector of Figure 30A.

[00153] Figure 31C is a top-view illustration of a reflection from a trihedral portion of the dihedral/trihedral corner reflector of Figure 30A using a side-directed radar transceiver.

[00154] Figure 31D is a top-view illustration of a reflection from a trihedral portion of the dihedral/trihedral corner reflector of Figure 30A using a forward-directed radar transceiver.

[00155] Figure 32A is an exploded isometric diagram of a pavement marker having two dihedral/trihedral corner reflectors, according to one embodiment.

[00156] Figure 32B is an exploded isometric diagram of a pavement marker having two dihedral/trihedral corner reflectors, according to another embodiment.

[00157] Figure 33A is an exploded isometric diagram of a pavement marker having a T- shaped double dihedral/trihedral corner reflector, according to one embodiment.

[00158] Figure 33B is an exploded isometric diagram of a pavement marker having a T- shaped double dihedral/trihedral corner reflector, according to another embodiment. [00159] Figure 33C is an exploded isometric diagram of a pavement marker having a T- shaped double dihedral/trihedral corner reflector, according to yet another embodiment.

[00160] Figure 34 is an exploded isometric diagram of a pavement marker having four dihedral/trihedral corner reflectors, according to one embodiment.

[00161] Figure 35A is a top-view diagram of a vehicle equipped with both side-looking and forward-looking radar transceivers on a road with radar-reflective pavement markers, according to one embodiment.

[00162] Figure 35B is a top-view diagram of a vehicle equipped with both side-looking and forward-looking radar transceivers on a road with radar-reflective pavement markers, according to one embodiment.

[00163] Figure 35C is a top-view diagram of a vehicle equipped with both side-looking and forward-looking radar transceivers on a curved road with radar-reflective pavement markers, according to one embodiment.

[00164] Figure 35D is a top-view diagram of a vehicle equipped with both side-looking and forward-looking radar transceivers on a road intersection with radar-reflective pavement markers, according to one embodiment.

[00165] Figure 36 is a top-view diagram of a vehicle equipped with side-looking radar transceivers having multiple antennas on a road with radar-reflective pavement markers, according to one embodiment.

[00166] Figure 37 is a schematic diagram of a radar transceiver with multiple transmit/receive antennas, according to one embodiment.

[00167] Figure 38 is a diagram of an array of radar transceivers, according to one embodiment. DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Preliminary Notes

[00168] Example embodiments are described below with reference to the accompanying drawings. Unless otherwise expressly stated, the sizes, positions, etc., of components, features, elements, etc., as well as any distances therebetween, in the drawings are not necessarily to scale, and may be disproportionate and/or exaggerated for clarity.

[00169] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It should be recognized that the terms “comprise,” “comprises,” comprising, include, includes, including, has, have, and having, when used in this document, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Unless otherwise specified, a range of values, when recited, includes both the upper and lower limits of the range, as well as any sub-ranges therebetween. Unless indicated otherwise, terms such as “first,” “second,” etc., are only used to distinguish one element from another and not to imply any relative order, placement, or ranking. For example, one element could be termed a “first element” and similarly, another element could be termed a “second element,” or vice versa. The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[00170] Unless indicated otherwise, the terms “about,” “thereabout,” “substantially,” “generally,” “approximately,” etc., mean that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error, and the like, and other factors known to those of skill in the art. [00171] Spatially relative terms, such as “right,” “left,” “forward,” “rearward,” “below,” “beneath,” “lower,” “above,” and “upper,” and the like, may be used herein for ease of description to describe one element’s or feature’s relationship to another element or feature, as illustrated in the drawings. It should be recognized that the spatially relative terms are intended to encompass different orientations in addition to the orientation depicted in the drawings. For example, if an object in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the term “below” can, for example, encompass both an orientation of above and below. An object may be otherwise oriented (eg., rotated 90° or at other orientations) and the spatially relative descriptors used herein may be interpreted accordingly.

[00172] The terms “RF” and “radio” are used herein to refer to or imply electromagnetic radiation in the frequency range that can be detected and processed electronically. For example, the RF spectrum includes very low frequencies (VLF, e.g., about 3 kHz) and may extend to just below infrared (e.g., about 300 THz). The RF spectrum includes VLF, low frequency (LF), medium frequency (MF), high frequency (HF), very high frequency (VHF), ultra high frequency (UHF), super high frequency (SHF), and extremely high frequency (EHF) bands. The RF spectrum also includes microwave and millimeter-wave bands.

[00173] The concepts and innovations described herein with reference to RF or radio radiation and/or radar can also be practiced with other types of radiation or waves, including, for example, infrared, visible, ultraviolet, laser, lidar, and sonar, with suitable modifications to the transceivers and reflectors.

[00174] Unless clearly indicated otherwise, all connections and couplings may be direct (without intermediaries) or indirect (with one or more intermediaries). All operative connections and couplings, unless clearly indicated otherwise, may be electronic via hardware or logical via software. Similarly, unless clearly indicated otherwise, all physical connections and couplings may be rigid or non-rigid, permanent or detachable. [00175] Like numbers refer to like elements throughout. Thus, the same or similar numbers may be described with reference to other drawings even if they are neither mentioned nor described in the corresponding drawing. Also, even elements that are not denoted by reference numbers may be described with reference to other drawings. Additionally, the drawings may include non-essential elements that are included only for the sake of thoroughness. These non-essential elements may be removed entirely or left only in outline form if drawing changes are desired to create greater clarity.

[00176] The embodiments described herein are merely examples, set forth by way of illustration only and not limitation. Those skilled in the art will recognize in light of the teachings herein that there are alternatives, variations and equivalents to the example embodiments described herein and their component parts. For example, other embodiments are readily possible, variations can be made to the embodiments described herein, and there may be equivalents to the components, parts, or steps that make up the described embodiments.

[00177] For the sake of clarity and conciseness, certain aspects of components or steps of certain embodiments are presented without undue detail where such detail would be apparent to those skilled in the art in light of the teachings herein and/or where such detail would obfuscate an understanding of more pertinent aspects of the embodiments.

[00178] The foregoing is illustrative of embodiments of the invention and is not to be construed as limiting thereof. Although a few specific example embodiments have been described, those skilled in the art will readily appreciate that many modifications to the disclosed example embodiments, as well as other embodiments, are possible without materially departing from the novel teachings and advantages of the invention. Accordingly, all such modifications are intended to be included within the scope of the invention as defined in the claims. For example, skilled persons will appreciate that the subject matter of any sentence or paragraph can be combined with subject matter of some or all of the other sentences or paragraphs, except where such combinations are mutually exclusive.

[00179] It will be clear to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the inventions described herein.

Pavement Marker With Embedded Radar Re flector(s)

[00180] Figures 2A-2D illustrate a pavement marker 284 in which is embedded a type of radar reflector called a dihedral corner reflector 287, as shown in Figure 2A. Figure 2B is an isometric view of the pavement marker 284 with dihedral corner reflectors 286 and 287 on opposite sides of the pavement marker 284. The dihedral corner reflector 287 can be constructed in a variety of manners. For example, the dihedral corner reflector 287 may be molded or extruded and cut into segments. The dihedral corner reflector 287 may be, for example, formed by welding or otherwise connecting two slats or flat plats together, or by bending a flat plate.

[00181] Figure 2B shows the incorporation of the dihedral corner reflectors 286 and 287 within a pavement marker 284 which also has an optical reflector 275 for human vision, cameras, and lidar. In this embodiment, the dihedral corner reflectors 286 and 287 are attached to the sides of the pavement marker 284 with the dihedral corner reflector 286 and 287 substantially parallel to the direction of vehicle travel. The method of attachment of the dihedral corner reflector 286 and 287 to the central body portion of the pavement marker 284 may be, for example, glue, adhesive, snap fit, friction fit, fasteners (e.g., screws, rivets, nails, staples), etc.

[00182] The dihedral corner reflector 287 (and 286) consists of two plane reflectors intersecting along an axis where a dihedral angle is formed. The dihedral angle may be 90° or approximately 90° (Ze., at a right angles, orthogonal, perpendicular, or normal). Incident waves entering the aperture so formed with a direction of incidence perpendicular to the edge (Ze., at a direction of incidence that bisects the 90° angle between the two planes), are returned parallel to their direction of incidence. Optionally, the pavement marker 284 may have a bottom plate (not shown).

[00183] A dihedral corner reflector is a passive device used to reflect radio waves back toward the emission source directly. The dihedral corner reflectors 286 and 287 can be a rightangle metal such as aluminum, galvanized steel, copper, brass, magnesium, steel, etc. or any other RF-reflective material. The dihedral comer reflectors 286 and 287 can also consist of metallic or other RF-reflective paint on a non-metallic surface, a metallic other RF-reflective foil, or electroplating a conductive other RF-reflective material on a non-metallic or non-RF- reflective surface such as plastic. A dihedral corner reflector can also be formed with one side being a roadway surface (eg., asphalt, concrete), and other side being a metallic surface, as the road surface may be sufficiently reflective to RF radiation. For example, when a radar signal is transmitted toward the dihedral corner reflectors 287 downward from the side (right, as illustrated in Figure 2A), and the radar signal is directed at a downward angle less than 45°, e.g., 25° (where perfectly horizontal toward the horizon is considered 0° and vertical straight into the ground is 90°), and the radar source mounted low from the ground, eg., 0.3 m, the ground surface acts like a smooth reflective surface to the RF waves and the road surface acts as one side for the dihedral corner reflector. The road surface is more reflective when wet.

[00184] The reflectivity of the road surface can be enhanced by coating portions of the road surface with an RF-reflective adhesive (e.g., conductive epoxy) or RF-reflective paint, (eg, copper, carbon, nickel, and silver conductive paint) below and/or around the pavement marker. For example, MG Chemicals 841AR is an acrylic nickel conductive paint and MG Chemicals 841ER is a nickel conductive epoxy. An RF-reflective adhesive may also be used to adhere the pavement marker, which contains the other surface of the dihedral corner reflector, to the road surface. A dihedral corner reflector can also be formed by painting or coating pertinent sides of an existing pavement marker with perpendicular or nearly perpendicular sides and the road surface near sides with an RF-reflective coating. A dihedral corner reflector can also be formed by painting milled grooves, divots, or cutouts in a roadway surface with RF-reflective coating.

[00185] The pavement marker 284 has an optical reflector 275 similar to current pavement markers to provide optical reflections on the front side facing oncoming vehicles. These optical reflectors in the pavement marker can be used by vision cameras or lidar sensors for further redundancy for lateral guidance.

[00186] Figures 2C and 2D show the top and side view of the pavement marker 284. Typical dimensions of a current raised pavement markers that are installed on the roadways are typically 100 mm x 100 mm x 25 mm. Using these dimensions, the dihedral corner reflectors 286 and 287 can be around 25 mm x 25 mm x 100 mm. These dimensions are for typical current raised pavement markers; longer or higher raised pavement markers can be constructed and installed on the roadways which can have higher Radar Cross-Section (RCS).

[00187] The pavement marker 284 (and the other pavement markers described herein) may be affixed to any driving surface for any vehicle, including roadways such as one-way, bidirectional or multi-lane roads, highways, thoroughfares, lanes, avenues, boulevards, parkways, pathways, byways, streets, paths, trails, and the like, as well as on bridges, in tunnels, parking lots, parking structures, shipping yards, shipping docks, transportation depots, loading/unloading bays, warehouse lots or yards, etc., whether paved (eg., asphalt, concrete, brick, stone) or unpaved. The pavement marker 284 (and the other pavement markers described herein) are preferably affixed to the surface so that the longitudinal axis of a dihedral corner reflector within the pavement marker 284 is generally parallel to the direction of vehicle travel and along one or both sides of the path of travel of the vehicle.

[00188] Figures 3A-3D show another embodiment where the dihedral corner reflector is constructed using a T-shape piece (more precisely, an inverted T-shaped piece) to form two or double dihedral reflectors, facing opposite directions. Figure 3 A shows this T-shape dihedral corner reflector 396 where the RF waves are reflected from both sides of the T-shape material. Figure 3B is an isometric view of the T-shape reflector 396 installed in the middle of the pavement marker with RF-transparent (and thus radar-transparent) material 395 on both sides of the T-shape reflector 396. An optical reflector 275 is installed on the front of the pavement marker 394 facing the oncoming vehicles for viewing by human, vision, or lidar as described above. The T-shape dihedral corner reflector 396 can be any metal or other material that is reflective to RF radiation. Also, the T-shape reflector 396 can be constructed using metallic or other RF-reflective paint or tape or electroplated material on the RF-transparent material 395. RF-transparent materials are materials through which RF radiation can penetrate with little or no dielectric loss factor such as, for example, Teflon®, polypropiolactone (PPL), polyvinyl chloride (PVC), polytetrafluoroethylene (PTFE) or acrylonitrile butadiene styrene (ABS). Plastic materials are lightweight, resistant to rain erosion, and have outstanding dielectric properties. Figures 3C and 3D show the top and side views of the T-shape radar-reflective pavement marker 394.

[00189] The RF-transparent material 395 may be one piece or two pieces. The piece or pieces may be molded, extruded and cut, or manufactured in any other suitable way. If the RF material 395 is a single piece, it may have a channel down the middle to accommodate the top fin of the T-shape reflector 396. The channel may be formed during molding or extrusion, for example, or may be created by a cutting or scarring operation. The RF-transparent material 395 piece(s) may also have a step or shelf cutout or cavity to match the horizontal part of the T-shape reflector 396. The T-shape reflector 396 may be attached to the RF-transparent material 395 piece(s) by, for example, RF-transparent glue or adhesive, friction fit, snap fit, fasteners, etc. An example of an RF-transparent glue is Loctite® 3494, a single component, medium viscosity, UV-cured, acrylic material used for bonding or sealing. Suitable solventbased adhesives include toluene and 1,4-Dioxane. The pavement marker 384 may optionally have a bottom plate (not shown).

[00190] Figures 4A-4E illustrate reflectivity qualities of the raised pavement markers with dihedral corner reflectors. In Figure 4A, the radar transceiver 116 transmits a signal 1119 towards the dihedral corner reflector 287 of the raised pavement marker 284. The dihedral corner reflector 287 reflects back a signal 1118 after the signal is reflected off of two sides and directly back to the radar transceiver 116. The dihedral corner reflector 287 shown in Figures 4B consists of two plane reflectors with dimension “a” forming a dihedral angle of 90°. This type of dihedral corner reflector more strongly returns the beam towards the source if the direction of the incident beam is perpendicular or approximately perpendicular to the line of intersection of the planes. The measured radar distance “d” is from the center point of the dihedral corner reflector 287 to the radar transceiver 116.

[00191] The radar transceiver 116 has both transmission and reception functionality. The radar transceiver 116 may be two separate subsystems (transmitter and receiver) or may be one combined or integrated unit. The term “radar sensor” is sometimes used to refer to a radar transceiver and sometimes just a radar receiver, depending on context.

[00192] Figures 4B-4C illustrate the dimensions of the dihedral comer reflector 287. The short sides have dimension a and the long side, which is substantially parallel to the lane markings, end has dimension b. The RCS of a corner reflector with typically raised pavement marker dimensions (100 mm x 100 mm x 25 mm) at a radar frequency of 77 GHz (which is currently used in automotive applications) can be calculated using the formula for a dihedral corner reflector RCS = 87ta2b2/ A2 where u ~ 3.1416 and X is wavelength of the radar signal. The RCS for this combination is 8*3.1416(0.025)2(0.1)2/(0.003893)2 = 10.36 m ² . The RSC of a vehicle is between 10 and 100 m ² . The RCS can be made larger by extending the dimensions a and/or b and/or by decreasing the wavelength (Ze., increasing the frequency). Figures 4D- 4E illustrate the dimensions of the T-shape dihedral corner reflector 396. The short sides are dimension a and the long side, which is parallel to the lane markings similarly to the single dihedral corner reflector 287, is dimension b.

[00193] Figures 5A-5F show the reflection pattern of the dihedral corner reflectors 286,

287, and 396 in various axes from a radar transceiver 116. Figure 5B shows the rotation of the radar transceiver 116 from the center of the corner reflector. Figures 5A and 5B show the relative RCS over +/-45° of rotation of the radar transceiver 116 from the center of the dihedral corner reflector in one dimension. The RSC represents the returned signal strength of the reflections from the target, in this case, a dihedral corner reflector. As shown in Figure 5B, as long as the position of the radar transceiver 116 is within the right angle (90° quadrant) of the dihedral corner reflector, the signal return is good. If the radar transceiver 116 is past the 45° of rotation and sees the back of the corner reflector 287 but not at a right angle to the back, the signal is not reflected back very well, as illustrated in Figure 5A. This is an advantage of a dihedral corner reflector versus a flat plate or sphere. A flat plate reflects the signal back if the radar transceiver faces the plate or at 90° to the plate, but very little signal returns if the radar transceiver rotates in either direction. A dihedral corner reflector can be made in different sizes to increase or decrease the RCS, and therefore the magnitude of the return signal strength, when the radar transceiver 116 directly faces the dihedral corner reflector, as shown in Figures 5B-5C.

[00194] The dihedral comer reflector angle can be less than 90° or larger than 90°. When the dihedral reflector angle is around 90°, it is an orthogonal dihedral reflector, as described above. An orthogonal dihedral corner reflector reflects back a maximum signal when the radar signal is aimed at the center of the reflector as shown in Fig. 5A. The orthogonal dihedral corner reflector is a preferred embodiment of the dihedral corner reflector, but other embodiments of the dihedral corner reflector with different angles may be used. The received signal strength depends on the angle of the two reflective surfaces, the orientation of the radar sensor in relation to the reflective pavement marker, the type of radar sensor, the sensitivity of the radar receiver, and the number of transmit and receive antennas and their spatial locations and orientations. For the applications described herein, depending on other system parameters, a suitable dihedral corner reflector can be made with an angle ranging from about ±35° of 90° (Ze., from about 55° to about 125°), more preferably ±20° of 90°, even more preferably ±10° of 90°, even more preferably ±5° of 90°, which is approximately or substantially orthogonal.

[00195] A monostatic radar transceiver has a single antenna that is used for both transmitting and receiving or distinct transmit and receive antennas that are co-located or located in close proximity to each other relative to the radar target eg., a dihedral corner reflector). A radar transceiver that is monostatic or has similar characteristics as a monostatic one and a narrow beam may be more sensitive to the angle of a dihedral corner reflector. For example, a Texas Instruments AWR1843AOP radar transceiver chip using a single transmit and receiving antenna and an antenna lens with a beamwidth of 6° yielded a loss of signal strength of about 6-10 dB (decibels) from a dihedral angle around 95° as compared to a dihedral angle of 90°. Similarly, the signal strength from a dihedral angle around 85° was about 6-10 dB less than at 90°. If the dihedral angle was less than 85° or greater than 95°, the signal strength was much less (15-20 dB) than at an angle of 90°.

[00196] For a radar sensor with bi-static characteristics (Ze., where there are distinct transmit and received antennas not collocated), e.g., Texas Instruments AWR1843AOP with the three transmit and four receive antennas, and a wide beamwidth, eg., 60-120°, the signal strength from a dihedral angle at 85° or 95° was about 4-6 dB less than at 90°. If the dihedral angle was greater than 95° but less 110°, then the reflective signal was about 10 dB less. If the dihedral angle was greater than 110° but less than 125°, the reflective signal was much lower than 10 dB. Likewise, if the dihedral angle was less than 85° but greater than 70°, the reflective signal was 10 dB less. If the acute angle was less than 70°, the reflective signal decreased by much more than 10 dB. If a radar sensor has a multiple-antenna array (s) for both transmitting and receiving, the radar signal reflection for the dihedral corner reflector can be higher depending on physical arrangement of the antennas.

[00197] In one embodiment, the sensitivity of the reflected signal can be utilized to execute a lateral position control system. For example, if the radar transceiver 116 is positioned and oriented on a vehicle to provide a maximum return signal from the corner reflector 287 when the vehicle is in the optimal lateral position and the radar system has the requisite sensitivity and the reflectors in the pavement markers have sufficient uniformity, then a simple control system can be designed to minimize the deviation of the return signal from the maximum by laterally adjusting the position of the vehicle. Alternatively, if the radar beam is steerable, it can be swept laterally while the maximum reflection is detected.

[00198] According to another embodiment using sensitivity of the reflected signal, if a radar transceiver 116 is positioned on the vehicle to provide two received signals from two corner reflectors 287 spaced a known lateral distance apart, the ratio of the amplitude of the two received signals can determine the position of the vehicle related to the corner reflectors 287. According to another embodiment using sensitivity of the reflected signal, if two radar transceivers 116 are directed to opposite sides of the vehicle, one on each side, to provide two received signals from two corner reflectors 287 on the opposite sides of the vehicle, then the difference in signal strength can be used to derive the position of the vehicle. When the vehicle is in the optimal lateral position and the radar receiver has the requisite sensitivity, then a simple control system can be designed to minimize the differences of the return signals by laterally adjusting the position of the vehicle. The optimal lateral position, according to these embodiments and in general, may be such that the vehicle is centered in the lane or some desired predetermined or random offset from the center of the lane.

[00199] Figure 5C shows the radar transceiver 116 aimed directly at the dihedral corner reflector 287. The radar transceiver beamwidth 1116 is wide enough to cover the length “b” of the dihedral corner reflector in the direction of travel, “y.” The transmitted signal 1119 is reflected back as the returned signal 1118 for given length of the corner reflector “b” and radar beamwidth 1116. The RCS pattern is shown in Figure 5D. The signal strength is good from the reflector as long as the radar transceiver passes by the dihedral corner reflector. Once the radar transceiver passes the corner reflector, the signal returned drops off significantly. [00200] If the radar transceiver 116 rotates in the direction facing the dihedral corner reflector 287 as shown in Figure 5E, the resulting RCS pattern with rotation shown in Figure 5F for a narrow beamwidth antenna. Multiple antennas and/or antenna(s) with wider beamwidth(s) can have a larger RCS pattern when the radar transceiver 116 is rotated as in Figure 5E. So, when the radar transceiver 116 passes the dihedral corner reflector 287 in the parallel direction to the corner reflector length, the radar transceiver measures the distance from corner reflector center to the radar transceiver antenna. This distance is constant if the radar transceiver 116 is maintained substantially parallel to the dihedral corner reflector 287. If the radar transceiver 116 moves closer to the dihedral corner reflector 287 in the parallel direction, the radar transceiver 116 would measure a closer distance to the corner reflector 287. There is no distance measurement until the radar transceiver beamwidth 1116 is in view of the dihedral corner reflector 287. When in view of the dihedral corner reflector 287, the radar transceiver 116 measures only one distance if the radar transceiver 116 stays substantially parallel for the brief time it is viewing the dihedral corner reflector 287.

[00201] A dihedral corner reflector may have several advantages in this application over a trihedral corner reflector, which is a corner formed by three orthogonal sides. First, a dihedral corner reflector has two orthogonal or approximately orthogonal sides and can be easily constructed out of right-angle metal, for example, whereas a trihedral corner reflector has three orthogonal sides and requires significant construction effort to attach together at 90°. Second, a dihedral corner reflector can be constructed continuously, such as, for example, by extrusion. With a continuous horizontally facing dihedral corner reflector on an above-road side guard rail, as described in previous literature (cited below), radar guidance systems have been designed and successfully tested with automated vehicles. Trihedral corner reflectors are individual reflectors, do not have this continuous feature, and require additional design and construction techniques to make a viable guidance system. Third, the radar transceiver 116 picks up a distance to the trihedral corner reflector when the radar transceiver 116 is not substantially parallel to the trihedral corner reflector and provides different distance measurements as the radar transceiver approaches and moves away from the trihedral reflector. The closest distance would be when the radar transceiver 116 is parallel to the trihedral corner reflector. A scheme using trihedral corner reflectors may therefore require more processing to measure lateral distance versus a scheme using a dihedral corner reflector. Fourth, ground-lobing i.e., reflection from the ground in the vicinity of the reflector) is more of a concern with a trihedral reflector and decreases the returned signal as compared to a dihedral corner reflector mounted on the ground. Fifth, a dihedral corner reflector reflects the signal back to the source with two bounces from the two dihedral surfaces, as shown in Figure 4A, whereas a trihedral corner reflector reflects the signal back with three bounces. With a polarimetric (polarized) radar, a dihedral corner reflector is therefore easier to distinguish from the ground surface than a trihedral corner reflector based on the polarization of the return signal.

[00202] A dihedral corner reflector as shown and described herein effectively reflects all frequencies back to the radar transceiver equally and it is not tuned to any particular frequency. That is, a dihedral corner reflector may be largely frequency invariant across the bandwidth of operation. This feature allows a dihedral corner reflector to reflect ultra- wideband frequencies, e.g., using current FMCW 77-81 GHz automotive radar sensors with 4 GHz bandwidth, back to the radar sensor effectively equally. There is no appreciable attenuation of any of the frequencies due to the dihedral corner reflector’s characteristics.

[00203] Figures 6A-6C show several constructions of raised pavement markers with two dihedral corner reflectors. Figure 6A shows one embodiment 284 with the main body 290 containing the optical reflector 275, two dihedral corner metal reflectors 286 and 287 and two quarter-round RF transparent materials 291 and 293. The corner reflectors 286 and 287 are attached to the left and right side of the main body 290 with the optical reflector 275 attached to the front as shown in these isometric diagrams. The quarter-round RF transparent materials 291 and 293 are placed inside the corner reflectors 286 and 287, respectively, to provide a protector from road damage. The attachment means for the corner reflectors 286 and 287, the main body 290, and the RF transparent materials 291 and 293 can be glue, screws, rivets, slots, or similar attachment mechanisms.

[00204] Figure 6B shows another raised pavement marker 384 with two dihedral corner reflectors. In this embodiment, the quarter round RF transparent pieces 294 and 295 have a metallic paint or metallic foil sprayed or glued, respectively, on the two flat sides to form the dihedral corner reflectors. The bottom flat plate 277, which may not be necessary, provides a good flat protected surface. Another embodiment (not shown) is to have a the bottom plate TT7 be metallic and the main body 290 to be metallic. With the bottom plate TT7 there is no need for a reflective coating on the bottom sides of the quarter round RF-transparent pieces 294 and 295.

[00205] Figure 6C shows another raised pavement marker 484 with two dihedral corner reflectors. In this embodiment, the main body 290 is made out a molded plastic or similar material that is RF transparent with slots 292 molded into the main body 290. Two metallic corner reflectors 296 and 297 can be pushed into the slots. The optical reflector 275 can be glued on the front of the raised pavement marker 484.

[00206] Figures 7A-7D show several constructions of raised pavement markers with a (inverted) T-shape dihedral corner reflector or double dihedral corner reflector 396. The elements illustrated in Figures 7A-7D but for the optical reflector 275 may be extruded and cut, for example, or made by other techniques. Figure 7A shows one embodiment 584 with the T-shape dihedral comer reflector 396 made of metal or other RF-reflective material in the center of two quarter- round or similarly shaped RF-transparent materials 397 and 398 and the optical reflector 275 attached to the front, forming the pavement marker. The two quarterround RF-transparent materials 397 and 398 are attached to the left and right side of the T- shape dihedral corner reflector 396 with the optical reflector 275 facing the front from the isometric picture. The quarter-round RF transparent materials provide protection from road damage. The attachment means for connecting the T-shape corner reflector 396 to the RF transparent materials 397 and 398 can be glue, screws, rivets, slots, or similar attachment mechanisms.

[00207] Figure 7B shows a construction of another raised pavement marker 684 with a T-shape dihedral corner reflector. In this embodiment, one of the quarter-round RF transparent pieces 1396 has a metallic or other RF-reflective paint or foil sprayed or glued on one side to form the T-shape dihedral corner reflector. The quarter-round RF transparent piece 1396 can be electroplated with a metallic surface on the one side, for example. The bottom flat plate 1300, which may be metallic or another RF-reflective material, forms the bottom of the T-shape corner reflector and provides a good flat protected surface.

[00208] Figure 7C shows a construction of another raised pavement marker 784 with a T-shape dihedral corner reflector. In this embodiment, two molded plastic or similar pieces 1396 and 1397 that are RF transparent are electroplated or sprayed on the sides with metal or other RF-reflective material. The molded plastic piece 1396 is sprayed or electroplated on the bottom side 1302, whereas the molded plastic 1397 is sprayed or electroplated on the two flat sides 1399 and 1304. When the two are glued or mechanically connected together, they form a T-shape dihedral corner reflector. Adding the optical reflector 275 to the front forms the raised pavement marker 784..

[00209] Figure 7D shows a construction of another raised pavement marker 884 with a T-shape dihedral comer reflector 396 made of metal or similar RF-reflective material or conductive coated right-angle material, etc., with two additional L-shape dihedral corner reflectors 286 and 287 on the ends of the pavement marker. The center reflector has two squared-shaped RF-transparent materials 1292 and 1293 on each side of the T-shape reflector 396. And two quarter-round or similarly shaped RF-transparent materials 293 attached to the ends, and the optical reflector 275 attached to the front, forming the pavement marker 884. The two quarter-round RF-transparent materials 293 are attached to the left and right side of the L-shape dihedral corner reflector 286 and 287, respectively, with the optical reflector 275 facing the front from this isometric view. The quarter-round RF transparent materials 293 keep the dihedral corner reflectors 286 and 287 clean and provide protection and structural support for the dihedral corner reflectors 286 and 287 while also reducing the likelihood that the dihedral corner reflectors 286 and 287 damage tires rolling over the pavement marker. The two squared-shaped RF-transparent materials 1292 and 1293 provide similar support and protection. This multi-reflector arrangement provides for a larger RCS than a single dihedral corner reflector. Similarly sized and shaped targets, e.g., dihedral corner reflectors, spaced one, two, or four wavelengths apart can have a significantly larger RCS than an individual target. So, one or more dihedral corner reflectors spaced wavelengths apart can be used in pavement markers to enhance the RCS of the pavement marker to the radar transceiver.

[00210] There are many ways to construct raised pavement markers with dihedral corner reflectors; the above embodiments show some preferred combinations.

Vehicle Guidance Based on Radar-Measured Distances to Pavement Markers

[00211] Figures 8A-8D illustrate several embodiments of a lateral guidance schemes. Figure 8A shows the front view of a vehicle 180 having a radar transceiver 116 mounted on a vehicle 180 as well as installed pavement markers 284 on the roadway with dihedral corner reflectors 286 and 287. The vehicle 180 may be any land vehicle, including, for example, an automobile, truck, bus, van, motorcycle, etc. Figure 8B is a block diagram of a lateral guidance system 810 designed to follow lane markings with no human driver. The front mounted radar transceiver 116 is mounted on a side of the vehicle as shown in Figure 8A, and the pavement marker 284 is mounted on the roadway lane marking or within a set distance from the lane marking on the roadway 300. The pavement marker 284 can be a raised pavement marker or installed at or below the pavement level. The radar transceiver 116 transmits a signal 1119 in the direction of the pavement marker 284 and receives a signal 1118 reflected back from the pavement marker 284 via the dihedral corner reflector 286. The orientation of the pavement marker 284 is such that the dihedral corner reflectors 286 and 287 are approximately parallel to the lane markings and the direction of the vehicle travel, as shown in Figure 8A. This orientation provides the maximum returned signal when the radar transceiver 116 passes by the pavement marker 284.

[00212] The distance between the pavement marker 284 and the radar transceiver 116 is measured by the radar transceiver 116 using well known radar techniques and provided to a lateral guidance controller 800, as shown in Figure 8B. The radar transceiver 116 or an associated processor (which may be a general-purpose processor, signal processor, digital signal processor (DSP) or the like and which may implement its processing in software, hardware, firmware, or some combination of the foregoing) measures the distance du from the dihedral corner reflector 286 embedded in the pavement marker 284. The actual lateral distance from the vehicle 180 to the pavement marker 284 is related the radar s measured distance dR and geometry of the mounting of the radar 116 attached to the vehicle 180. The desired controlled distance de to maintain the vehicle in the center of the lane or at any predetermined distance from the pavement marker and the radar-measured distance di< are inputs to the lateral guidance controller 800. The lateral guidance controller 800 sends a signal to the steering motor or controlled device in the steering mechanism 802. The steering mechanism 802 controls the steering wheels 804. The steering wheels 804 and steering mechanism 802 are for highway vehicles, but the vehicle could be an offroad tracked vehicle and the controller could utilize hydraulic actuators. The desired lateral distance the vehicle 180 maintains from the reflector pavement marker 284 is maintained by controlling the steering wheels 804. Note that in some cases there could be just a single steerable wheel, e.g., bike, trike, three-wheeled forklift, etc.

[00213] The radar transceiver 116 may generate a continuous radar transmission signal and/or monitor continuously for a reflection, or the radar transceiver may periodically and repeatedly transmit a discrete radar signal (e.g., a pulse) and monitor for reflections, depending on the type of radar techniques employed. The radar transmission signal is generally directed partially downward and sideways from the vehicle 180, and pavement marker 284 is designed to reflect the incident radar signal partially upward and sideways back toward the radar signal source (i.e., the transceiver 116) on the vehicle 180.

[00214] The radar transceiver 116 and/or the lateral guidance controller 800 may filter reflections based on range and/or magnitude to distinguish the dihedral corner reflectors 286 and 287 from other objects. The pavement markers 284 are within a known range from the vehicle. Since the radar cross section of the dihedral corner reflector 286 is large for automotive frequencies and since the pavement marker 284 is in close range of the radar transceiver 116, the magnitude of the returned signal is typically notably high compared to the road surface and other road objects, e.g., dead animals, cardboard, rocks, beverage cans, etc. Other radar processing techniques, besides filtering on magnitude and range, can be used to distinguish the pavement markers from the road surface and other objects. For example, polarization can distinguish a dihedral reflector from the road surface and other objects on or near the road. Also, fixed or approximately fixed spacing of the pavement markers can be used to filter out false signals based on time. For example, a reflection arriving between two pavement marker may be excluded as a probable false target. A Kalman filter or other known filtering techniques can filter out reflection signals based on the fixed spacing/time of the pavement markers and/or other known or predictable attributes of the pavement markers. The pavement markers 284 are therefore distinguishable from other objects, and the many pavement markers 284 on a driving surface may be uniformly identical or similar with similar dihedral corner reflectors 286, 287 and similar RCSs.

[00215] Figure 8C is a block diagram of a lateral guidance system 840 that warns the driver if the vehicle leaves its lane with visual, audible, and/or vibration warnings. This embodiment represents a Lane Departure Warning (LDW) system. The radar transceiver 116 transmits a signal 1119 in the direction of the pavement marker 284, in which a reflector may be embedded, and receives a signal 1118 reflected back from the pavement marker 284. The distance between the pavement marker 284 and the radar transceiver 116 is measured by the radar transceiver 116 using well known radar techniques and provided to the lateral guidance controller 820 shown in Figure 8C. The radar transceiver! 16 measures the distance di< from a dihedral corner reflector embedded in the pavement marker 284. The actual lateral distance from the vehicle 180 to the pavement marker 284 is related the radar’s measure distance dR and the geometry of the mounting of the radar transceiver 116 attached to the vehicle 180, as shown in Figure 8A. If the vehicle travels too close to or too far away from the pavement marker 284 eg., is less than a minimum threshold or exceeds a maximum threshold), indicating a lane departure, the guidance controller 820 transmits a sound to a speaker 824 (or plural speakers) to alert the driver of the lane departure, sends a signal to the display 826 to alert the driver of the lane departure visually, and/or controls the vibration 828 of the seat, steering wheel, or other vehicle part. The guidance controller 820 can disable lane-departure alerts if a turn signals 822 is turned on signaling an intent by the driver to initiate a lane change or turn in the direction of the detected lane departure. Whether or not lane-departure alerts are enabled or disabled by a prior turn signal can be a configurable setting set by the driver, factory, or service technician. The guidance controller 820 can also be configured to activate the turn signal indicator 822 eg., blinker) on the side of the vehicle corresponding to the detected lane departure when a lane departure is detected. That can serve as a warning to other drivers, vehicles, pedestrians, cyclists, etc. that a lane departure is occurring or may occur. In this way, safety can be enhanced for others as compared to the case in which no lane-change indication is provided.

[00216] Figure 8D is a block diagram of a lateral guidance system 850 that can warn the driver if the vehicle is leaving its lane with visual, audible, and/or haptic warning, and, if no corrective response is taken by the drive, the system 850 can automatically take steps to maintain the vehicle in its lane. This embodiment represents a Lane Keeping Assist (LKA/LKS) system. The radar transceiver 116 transmits a signal 1119 in the direction of the pavement marker 284 and receives a signal 1118 reflected back from the pavement marker 284. The distance between the pavement marker 284 and the radar transceiver 116 is measured by the radar transceiver 116 using well known radar techniques and provided to a lateral guidance controller 830, as shown in Figure 8D. The radar transceiver! 16 measures the distance du from a dihedral corner reflector embedded in the pavement marker 284. The actual lateral distance from the vehicle 180 to the pavement marker 284 is related the radar’s measured distance dR and the geometry of the mounting of the radar transceiver 116 attached to the vehicle 180. If the vehicle 180 travels too close to or too far away from the pavement markers 284, indicating a lane departure, the guidance controller 830 transmits a sound to a speaker 824 (or plural speakers) to alert the driver on a lane departure and/or sends a signal to the display 826 to alert the driver of the lane departure visually and/or causes vibration or other haptic stimulation to the drive. If no driver response is detected, the controller 830 controls the steering mechanism 802 to control the wheels 804 to keep the vehicle in the lane. The guidance controller 830 may not alert or take action if the turn signals 822 are turned on to signal a lane change or turn in the direction of the detected lane departure.

[00217] Another embodiment similar to the LKA/LKS system shown in Figure 8D can implement Lane Centering Assist (LCA). An LCA system controls steering of the vehicle 180 to keep the vehicle in the lane without the driver’s effort, but the system can be overridden by the driver.

[00218] Figure 8E is a block diagram of a lateral guidance control system 8500 which controls the steering of the vehicle to keep the vehicle in its lane. This embodiment represents an autonomous lateral control system. The radar transceiver 1160 transmits signals in the direction of the pavement markers and receives a signals reflected back from the pavement markers. The distance between the pavement marker and the radar transceiver 1160 is measured by the radar transceiver 1160 using well known radar techniques and provided to the lateral guidance controller 8004 shown in Figure 8E. The radar 1160 measures the distance dR from a dihedral corner reflector embedded in the pavement markers. The actual lateral distance from the vehicle to the pavement marker is related the radar’s measure distance and the geometry of the mounting of the radar transceiver 1160 attached to the vehicle. The desired control distance de from the pavement marker is subtracted by the radar measured distance du to determine an error dERROR which is inputted in the lateral guidance controller 8004. Vehicle speed 8008, road geometry preview information 8006, and wheel angle 8028 are sent to the lateral guidance controller 8004. There may be other sensors, e.g., IMU (Inertial Measurement Unit), GPS (Global Precision System), vision cameras, laser radar, etc. (not shown) that can be used to augment the lateral control system 8500. The output of the guidance controller 8004 controls a steering mechanism 8020, which controls the angle of the wheels and, along with the vehicle dynamics 8040, controls the lateral position of the vehicle in the lane in relation to the pavement markers. The lateral guidance controller system 8500 can have many different embodiments for control algorithms to control the steering of the vehicle along the pavement markers. Some embodiments are Fuzzy control algorithms, PID (Proportional Integral Derivative) control algorithms, adaptive PID control algorithms, Stanley control algorithms, MPG (Model Predictive Control) control algorithms, neural network control algorithms, modified sliding mode control algorithms, multi-rate control algorithms, and LQR (Linear Quadratic Regulator) control algorithms.

[00219] The desired control distance de from the pavement marker may be a predetermined distance based on assumed lane width, vehicle width, and radar transceiver location on the vehicle. Alternatively, the desired control distance de from the pavement marker may be dependent on the approximate location of the vehicle to account for different lane widths and/or different pavement marker locations on different roads. For example, a database may store a set of desired control distances for different roads or geographic locations, and the database may be queried based on the geographic location of the vehicle, such as determined, for example, by GPS, sufficient to determine which road or set of nearby roads the vehicle is traveling on. Additionally, the desired control distance de from the pavement marker may be dependent on the vehicle’s direction of travel, which may be determined from compass sensors and/or GPS measurements, as lane widths and/or pavement marker locations may not be the same in different directions on the same road. [00220] In another embodiment, the desired control distance de may be dynamically determined as the vehicle travels down the road by measuring distances to different, laterally displaced markers. For example, the lane width can be indirectly measured by (a) measuring distance(s) to pavement markers marking an adjacent lane boundary on a given side of the vehicle, (b) measuring distance(s) to pavement markers marking the next lane boundary on the same side of the vehicle, (c) subtracting those measured distances to calculate the adjacent lane width, and assuming that the vehicle’s current lane width is the same. If the vehicle is equipped with right-looking and left-looking radar transceivers, two desired control distances (right and left) can be used, and the control strategy can be to equalize the two distances (.eg., using a zero difference between the right and left distances as the nominal setpoint) so that the vehicle is centered in its lane. Also, the desired control distance de may be offset from the true lane center for different vehicles so that the tire pattern does not wear out the pavement in the same area.

[00221] Figures 9A-9C show different embodiments of the placement of the pavement marker 284 with the dihedral corner reflector on the roadway 300. Figure 9A shows a side view of one embodiment with the pavement markers 284 placed or distributed along the side of the roadway 300 at the same or different distances of separation. The radar transceiver 116 mounted on the vehicle 180 transmits a radar signal 1111 to the pavement marker 284 and receives a return signal 1110 to determine the distance from the pavement marker 284 and the radar transceiver 116. The optical reflectivity is on the front side of the pavement marker 284 as disclosed earlier facing the oncoming vehicle 180 and the dihedral corner reflector is mounted within the pavement marker 284 facing the radar transceiver 116.

[00222] Figure 9B shows a top view of an embodiment with the vehicle 180 where pavement markers 284 and 1284 are installed on both sides of the road at various separation distances. The vehicle 180 has two radar transceivers 116 and 117 mounted to front sides of the vehicle 180. The radar transceiver 116 sees the pavement markers 284 on the right side of the vehicle and the radar transceiver 117 sees the pavement markers 1284 on the left side of the road. If the separation distance between pavement markers is zero, meaning a continuous dihedral corner reflector, the lateral guidance controller in Figure 8B can be similar to the controller used with a guardrail-based radar guidance system developed at the PACCAR Technical Center, as described in “Dual-Mode Truck: Automated and Manual Operation,” by Richard A. Bishel, published as SAE Technical Paper Series #931837 (1994), which is incorporated by reference herein in its entirety, or the controller used with a wire guidance system developed at the Ohio State University, as described in “Fundamental Studies in Automatic Vehicle Control” by R. Fenton, R. Mayhan, R. Bishel, R. Kneifel, R. Magee, S. Murthy, L. Rakocy, R. Smith, and L. Thayer, published as Report No. FHWA/RD-80/198 (Aug. 1981), which is incorporated by reference herein in its entirety. If the pavement markers’ distance separation is around 1- 4 m, the controllers could be similar to the lateral controllers used with embedded magnets in the roadways, as developed by the California Partners for Advanced Transportation Technology (PATH), as described in “The Design of a Look-Down Feedback Adaptive Controller for the Lateral Control of Front- Wheel-Steering Autonomous Highway Vehicles” by Seibum B. Choi, published in IEEE Transactions On Vehicular Tech., Vol. 49, No. 6 (Nov. 2000), which is incorporated by reference herein in its entirety. The lateral controllers from Ohio State University and the PACCAR Technical Center provide good lateral vehicle control at highway speeds without any augmented sensors and just using the radar transceiver alone.

[00223] Embodiments based on a dihedral corner reflector in a pavement marker may have several advantages over the approaches described in the literature cited above. For example, pavement markers mounted on the ground enable a radar transceiver to be mounted low on a vehicle and pointed downward to see the reflector in the pavement markers across multiple lanes even when other vehicles are present in the other lanes. Such pavement markers can be used to provide guidance for vehicles in any lane of a multi-lane road, rather than just a guardrail-adjacent lane. Second, pavement markers in embedded dihedral corner reflectors are significantly low in cost to install, and pavement markers are already widely used throughout the country and the globe with the concomitant existing infrastructure to manufacture and install pavement markers. Indeed, radar-reflective pavement markers described herein can be installed just as conventional pavement markers are currently installed. For example, the radar-reflective pavement markers described herein can be easily and inexpensively installed in between lane markings, as is currently done on multiple-lane highways, and/or along outer or interior lane lines that demark lanes. Moreover, in some cases, multiple discrete radar-reflective pavement markers may be visible to a vehicle and can provide the distances to each pavement marker for lateral control, including selecting which lane in which to drive. Additionally, the radar-reflective pavement markers described herein can be used with many different types of radar transceivers.

[00224] Figure 9C shows another embodiment in which multiple radar transceivers 117 can be installed at several places on the left side of the vehicle 180 and similarly one or more radar transceivers 116 can be installed on the right side the vehicle 180. The radar transceivers 116 and 117 can be installed in side marker lights, headlights, fog lights, daytime running lights, or turn signals on the vehicle for minimum impact on the exterior design. The radar transceivers 116 and 117 can be mounted on or in a bumper (eg., front bumper) of the vehicle 180. The radar transceivers 116 and 117 can be mounted behind the vehicle 180 body exterior made of RF-transparent material typically plastic and/or fiberglass. In another embodiment, one or more radar transceivers 117 would see pavement markers 1284 and one or more radar transceivers 116 would see pavement markers 284. Also, a radar transceiver 119 can be mounted in the center front of the vehicle 180 and see in both directions, right and left side of the vehicle 180, in view of pavement markers 284 and 1284. These additional radar transceivers provide redundancy and more timely distance measurements. There can be many other combinations of mounting one or more radar transceivers on the vehicle 180 to provide for more robust lateral guidance control.

[00225] Figures 10A-10B show embodiments of the radar transceiver(s) mounted on a vehicle 182. Figure 10A is another embodiment of multiple radar transceivers 116 and 117 mounted along the sides and front of the vehicle 182. Having multiple radar transceivers 116 and 117 on each side and in the front provides redundancy. A radar transceiver beamwidth 1106 sent from radar transceiver 116 sees the pavement marker 284 and a radar transceiver beamwidth 1107 sent from radar transceiver 117 sees the pavement marker 1284. The antennas on radar transceivers 116 and 117 can be polarized to prevent multiple vehicles with similar radar transceivers from interfering which each other. The antennas can be horizontally, vertically, right-hand circularly, or left-hand circularly polarized, for example.

[00226] Figure 10B shows another embodiment of the radar transceiver 119 mounted in the front center of the vehicle 182 and sensing the distance to both pavement markers 284 and 1284 on both sides of the vehicle 182 using radar beams having beamwidths 1108 and 1109, respectively. One embodiment of the radar transceiver 119 could have one antenna 1190 right-hand circular polarized (RHCP) and the other antenna 1192 left-hand circular polarized (LHCP) . Another embodiment could feature antenna 1190 horizontally polarized and antenna 1192 vertically polarized to prevent interference of passing vehicles with similar transceivers. Alternatively, the radar transceiver 119 according to another embodiment comprises two independent transceivers, one directed right and one facing left. Mounting the radar transceiver(s) in or near the center of the vehicle 182 provides for additional distance between the radar sensor 119 and the pavement markers 284 and/or 1284. The radar sensors 116, 117, and 119 can be installed any lateral distance along the vehicle front bumper. The tires of the vehicle 182 could cross the pavement markers 284 without loss of the radar signal. If that happens without a turn indicator in the direction of drift having been activated first, detection of crossing of the pavement markers (i.e., drifting into another lane) could trigger a warning to the driver and/or corrective action (e.g., corrective steering, reduction of speed, etc.). The warning may be audible, visual, and/or haptic, for example.

[00227] Figure 11 A shows one embodiment where the left-side and right-side radar transceivers 116 and 117, respectively, on vehicles 180 and 182 may use different antenna polarizations and to see both pavement markers 284 and 1284 via two beamwidths 1106 and 1107, respectively. When the vehicle 180 passes the vehicle 182, the different polarization of the antennas minimizes radio frequency interference. The radar transceiver 119 as in Figure 10B but not shown in Figure 11A sees both pavement markers 284 and 1284 via the two beamwidths 1108, and 1109, respectively. The longer distance allows the vehicle’s tires to cross over the pavement markers 284 and still have a valid distance signal from the pavement markers. In this embodiment, the radar placement provides for larger lateral deviations without loss of valid radar signal. The radar transceivers 116 and 117 can also be mounted anywhere along the front of the vehicle to provide larger lateral deviations without loss of valid radar signal.

[00228] Figures 11A-11C show top views of different configurations of distance separation of pavement markers with dihedral corner reflectors. Figure 11 A is a top view of a multi-lane highway 3000 with two vehicles 180 and 182 in the highway lanes between the painted lines 304 and dihedral corner reflector pavement markers 284 and 1284. The separation distance 190 between pavement markers 284 can be constant or variable. The separation distance 190 may be small (e.g., 0.3 m or continuous) or large (e.g., 22.4 m). Current markers are typically spaced 6.1 m, 12.2 m, or 22.4 m on straight roadways and gradual curves depending on the type of roadway. Current pavement markers are typically spaced 0.3-6.1 m around sharp curves. On a straight highway as shown in Figure 11 A the pavement markers 284 may be separated by a constant distance but offset by half of the separation every other lane. Providing radar transceivers 116 and 117 on both sides of the vehicle 180 allows the radar transceivers to track dihedral corner reflector pavement markers 284 and 1284 on both sides and allows for larger separation distance 190 of the pavement markers 284 on each side. If the lateral controller 800 (in Figure 8B) needs around a minimum of 4 m separation of pavement markers in the lane for good lateral control, similar controller performance can be obtained with 8 m of separation pavement markers 284 or 1284 offset on both sides of the lane. A separation distance 190 from about 0.3 m to about 8.0 m between pavement markers can work well for the lateral controller 800 (in Figure 8B) without any augmented sensors e.g., GPS, IMU, camera, or lidar). Lateral controllers with inputs from other sensors eg., GPS, and IMU) may achieve good performance with larger separation distance 190 (eg., about 12.2 m) similar to currently prevalent pavement marker spacing. In one embodiment, the radar transceiver 116 on the vehicle 180 sees the pavement marker 284 on the right side of the vehicle 180 with the radar beam 1106. The radar transceiver 117 on the same vehicle 180 sees the pavement marker 1284 in the far-left lane with the radar beam 1107. So, the onboard lateral guidance controller in the vehicle 180 can decide to stay in the same highway lane and follow the dihedral comer reflector pavement markers 284 on the right side of the vehicle or make a lane-change maneuver and follow the dihedral corner reflector pavement markers 1284 on the far-left side of the vehicle 180. The vehicle 182 with similar radar transceivers 116 and 117 can follow the same strategy. Another sensor, not shown, e.g., radar, vision, ultrasonic, or lidar, or the same radar transceivers 116 and 117 with vehicle detection capabilities (in addition to providing lateral distance), can determine if there is another vehicle in the left or right lane and allow such a lane-changing maneuver. If the antennas on radar transceiver 116 on the vehicles 180 and 182 are left-hand circular polarized and antennas on radar transceiver 117 on all vehicles 180 and 182 are right-hand circular polarized, then radar signals from radar transceiver 116 on the vehicle 180 will not interfere, because of the different polarizations, with radar signals from radar transceiver 117 on the vehicle 182 as the vehicle 180 passes by the vehicle 182.

[00229] In another embodiment, Figure 11B shows the separation distance 194 between pavement markers 284 may be smaller in a turn on the roadway 301 to allow more radar distance measurements from the radar transceivers 116 and 117 to correct the steering of the vehicle 180 more often to stay in the middle of the lane. When on a straight section or coming out of the curve, a larger separation distance 192 can be used.

[00230] In another embodiment, Figure 11C shows the shows a special arrangement of pavement markers 285 in the beginning of the curve section and at the end of the curve section of the roadway 301. This arrangement of pavement makers 285 which will be referred to as a “coded section” allows for the radar transceiver to pick up additional information to inform the controller (in Figure 8B) that a certain road geometry will be forthcoming. For example, the controller (Figure 8B) could take action upon receiving this information from the coded section to minimize lateral errors coming into and leaving a curve section. The coded section 285 can be used to communicate current or upcoming road geometry e.g., curves or straight sections, narrow lanes), intersections, hazards, road conditions, school zones, hospital zones, construction zones, railroad crossing, road changes, no-stopping areas, speed limits, speed limit changes, or other information. The distance 192 between pavement markers 284 may be smaller in the highway turns 301 to allow more radar distance measurements from the radar transceivers 116 and 117 to correct the steering of the vehicle 180 more often to stay in the middle of the lane. When on a straight section or coming out of the curve, a larger separation distances can be used.

[00231] Figures 11D-11G show different embodiments of the coded section 285. Figure 11D shows one embodiment of the coded section 285 with several pavement markers 284 spaced at shorter distances 2851 and 2852 than larger typical distances 190, 192, or 194. The radar transceiver could, for example, interpret this close spacing and separation as information on an upcoming curve or straight section if within a curve. Figure 11E shows another embodiment of the coded section 285 where not only the distances 2851 and 2852 are shorter between markers 284, but lateral distances 2853 between the pavement markers 284 are different.

[00232] Figure 11F shows another embodiment of the coded section 285 where the pavement markers feature different lengths and spacings. Pavement markers 284 have a common length, but pavement makers 288 have a longer length 2857. The distance 2855 between the pavement markers 284 and 288, respectively, is different than the distance 2856 between pavement markers 288 and 284, respectively. [00233] Figure 11G shows another embodiment of the coded section 285 where the size of the pavement markers 284 and 289 are different and the spacings are different 2851 and 2852. The pavement markers 289 could be smaller or larger (as shown in Figure 11G) than pavement marker 284. In addition, the pavement markers 284 and 289 can have different radar reflective characteristics to provide coded information. That is, one or more of marker/reflector spacing, length, reflectivity, or other detectable factors can be varied to encode information that a controller can decode from characteristics of the reflected signal.

Pavement Marker Variations

[00234] Figures 12A-12C show other embodiments of L-shaped dihedral corner reflector pavement markers. Figure 12A shows the pavement marker 282 with the optical reflector 275 on the front and dihedral corner reflectors 286 and 287 on the sides with one side of the corner reflector generally flat on the ground and the other side of the corner reflector generally perpendicular or transverse to the ground. Figure 12B shows another embodiment of the dihedral corner reflector pavement marker 283 with the similar optical reflector on the front of the marker, but the dihedral corner reflectors 286 and 287 are installed in an angle from the ground or lane surface. The dihedral corner reflectors can be installed at the angle to the direction of travel. Figure 12C shows another embodiment of the dihedral corner reflector pavement marker 288 with the dihedral corner reflectors 286 and 287 facing up at an angle. There are many other possible variations of installing the dihedral corner reflectors 286 and 287 on the pavement markers.

[00235] Figures 13A-13C illustrate embodiments installing T-shaped dihedral corner pavement markers below the driving surface in rumble strips or parallel cut slots, grooves, or divots. Figure 13A illustrates a front side view of a rumble strip 310 which is a cut in the road surface 300 to produce a sound when the tire rides over the rumble strip 310 to alert the driver. The T-shaped dihedral corner reflector pavement marker 394 is installed in the rumble strip 310 with a T-shaped dihedral comer reflector 396. Figure 13B shows the top view of the T- shape dihedral corner reflector pavement marker 394 installed in one of the rumble strips 310 along the roadway with a painted line 910. Figure 13C shows another embodiment where the T-shaped dihedral corner reflector pavement marker 394 is installed in highway slots 312 where existing pavement markers are installed so that snow plows or other equipment will not tear them off the roadway surface.

[00236] Figures 14A-14D illustrate embodiments installing dihedral corner pavement markers below the surface in rumble strips, parallel cut slots, or snow plowable pavement markers. Figure 14A illustrates a front side view of a rumble strip 310 which is a cut in the road surface 300 to produce a sound when the tire rides over the rumble strip 310 to alert the driver. A dihedral corner reflector pavement marker 1288 is installed in the rumble strip 310 with dihedral corner reflectors 1286 and 1287 which are mounted inside rumble strip sides parallel to the vehicle travel on each side of the pavement marker 1288. Figure 14B shows the top view of the dihedral corner reflector pavement marker 1288 installed in one of the rumble strips 310 along the roadway with a painted line 910. Figure 14C shows another embodiment where the dihedral corner reflector pavement marker 1288 is installed in highway slots 312 where existing pavement markers are installed so that snow plows or other equipment will not tear them off the roadway surface. Another embodiment is to use the milled rumble strips as the dihedral corner reflector by spraying conductive paint in the milled rumble strip. Figure 14A shows the milled rumble strip 310 but instead of installing the pavement marker 1288, the milled rumble strip 310 is coated with conductive paint to form the two dihedral reflectors 1286 and 1287. The longer length milled highway slots 312 as shown in Figure 14C can be painted with conductive paint along the entire length of the rumble strip 312. This would provide a larger RCS for a radar transceiver to view.

[00237] Figures 14D-14H show other embodiments in which dihedral corner reflectors are included in a snow-plowable pavement marker. Specifically, Figure 14D shows an isometric view of dihedral corner reflectors 1285 and 1289 installed in a snow-plowable pavement marker 1290. A snow plows rides on the top of sides 1206 and 1208 which are typically metal. An optical reflector 1275, which is typically made of plastic, is installed in the middle of the frame of snow-plowable pavement marker 1290 so that drivers or vision sensors can see the marker 1290. The dihedral corner reflector 1285 reflects RF waves (eg., microwaves) back to a radar sensor from one side of the pavement marker 1290 and the dihedral comer reflector 1285 reflects RF waves back to a radar sensor on the other side of the pavement marker 1290. Snow-plowable markers 1290 may be mounted in a center or interior lane line to be viewed by radar sensors mounted on vehicles in two different lanes. Alternatively, the snow-plowable marker 1290 may be mounted in an exterior road line, in which case the dihedral corner reflector on the interior side may be omitted or not used . The dihedral corner reflectors 1285 and 1289 can be made from right-angle metallic material or a conductive coating on a right-angle surface made from plastic, fiberglass, or composite material or part of the cast iron snow plowable structure. When installed in the roadway, the snowplowable pavement marker 1290 will not only be visible to the drivers, vision sensors, and lidar, but also to radar sensors.

[00238] Figure 14E shows a top view of a snow-plowable marker 1298 according to another embodiment, in which the dihedral reflectors 1285 and 1289 extend the entire length of the snow-plowable pavement marker 1298. The optical reflector 1275 is mounted in the center of the snow-plowable pavement marker 1298. The sides 1208 and 1206 are typically made of cast iron or different types of metal. Figure 14F show a side view of a snow-plowable marker 1298 as in Figure 14E. The right-angle dihedral reflectors 1285 and 1289 are visibly shown in this view.

[00239] Figure 14G shows another embodiment installed in concrete or asphalt pavement 300. The sides 1206 and 1208 are the same as in Figures 14D-14F. The optical reflector 1275 may be larger to fill the entire length of the inside of the snow plowable marker 1295. The dihedral corner reflectors 1285 and 1289 are part of the insert (marker within the snow-plowable structure or frame) with the optical reflector 1275. Figure 14G shows cut slots 1207 and 1280 in the pavement 300 to install the snow-plowable pavement marker 1295 in the pavement 300. As one can see, the snow-plowable pavement marker 1295 is installed at ground level or slightly above ground. The snow-plowable pavement marker 1295 may be glued (eg., using an epoxy glue) or otherwise secured in the cut slots 1207 and 1280. The dihedral corner reflectors 1285 and 1289 are part of the insert (pavement marker within the snow plowable structure or frame) shown installed on the inside of the snow-plowable pavement marker 1295 to reflect RF waves back to a radar sensor. The optical reflector 1275 reflects light waves back to the driver or a vision camera and may also reflects laser waves back to a lidar sensor.

[00240] Figure 14H shows another embodiment of a snow-plowable pavement marker 1308 installed in the pavement 300. In this embodiment, an additional T-shaped comer reflector 1209 is installed in the center of the insert pavement marker and therefore, in the center of the snow-plowable pavement marker 1308. The additional reflector 1209 allows for larger radar cross section of the snow-plowable pavement marker 1308 to a radar sensor. If the spacing between the reflectors is greater than the resolution of the radar sensor, then the T-shaped reflector 1209 would appear as an additional target. This feature can provide additional information, e.g., to determine the type of pavement marker or lane location. Figure 14H shows only one T-shaped corner reflector, but multiple reflectors can be added depending on the desired radar cross section or needed additional information.

[00241] Figures 15A-15C illustrate other embodiments of installing a dihedral corner reflector along a roadside using different types of pavement markers or schemes. Figure 15A shows a sidewalk 1422, a curb 1420, and a painted or installed corner reflector marker 1488 continuously along the road surface 300 or at intervals. Figure 15B shows the corner reflector marker 1584 installed behind a concrete curb 1424. Radar waves can penetrate the concrete and reflect from the metallic corner reflector buried behind the concrete. Figure 15C shows another embodiment where the corner reflector 1684 is installed on the surface of the concrete curb 1424 at various spacings along the curb 1424 or continuously. [00242] Figures 16A-16C show another embodiment where the corner reflector is one, two, three or four sides of the pavement marker. Figure 16A shows the pavement marker 580 with three dihedral corner reflector sides 586, 587, and 589. The front side dihedral corner reflector 589 faces the direction of travel and a front-mounted forward-looking radar can reflect signals from the front reflector 589 to provide lateral and longitudinal information regarding the vehicle relative to the reflector 589. The dihedral corner reflector 589 can be installed at an angle to the direction of travel to provide for both longitudinal and lateral information from the same dihedral corner reflector. Alternatively, a pavement marker can have a parallelogram shape, rather than a rectangular shape, so that the side-facing dihedral corner reflectors remain side-facing while the front-facing reflector(s) is angled slightly toward the center of the lane. Using the measured distance from a front-mounted radar, which could be at the same angle as the dihedral corner reflector for maximum radar reflectivity, and the installed dihedral corner reflector angle, one can calculate the lateral distance from the side of the vehicle to the corner reflector via the law of sines (lateral distance = sin(angle)/measured distance). The longitudinal distance from the front of the vehicle to the corner reflector may be calculated via the law of cosines (longitudinal distance = cosine(angle)/measured distance). Figure 16B shows another embodiment of the pavement marker 582 where the front mount corner reflector 590 is at an angle up from the ground to give a more reflective target for a forward-looking radar. Also, another embodiment, 583 shown in Figure 16C, consists of only one dihedral corner reflector 586 for pavement markers on the side of the road.

Radar Transceiver Architectures and Processing

[00243] Figure 17 shows an embodiment of an Ultra-Wideband (UWB) impulse radar transceiver unit. In this embodiment, the UWB impulse radar unit generates short pulses via a pulse generator 430, amplifies the signal via an amplifier 440, and transmits the short pulses through an antenna 436. The signal 1140 then propagates to the ground surface and the reflector (not shown). When the signal meets the ground surface and reflector, some of the signal is reflected from the ground surface, but significantly more of the signal is reflected from the reflector and propagates back to the antenna 435. The returned ground surface signals can be filtered out by several known methods. One method is to select only signals above a certain amplitude threshold. Another method is to receive signals without the reflector and then use that base signal to filter out the ground surface. There are many other schemes to filter out all or some of the ground surface signals. The signals 1142 from the ground surface and reflector are amplified by an amplifier 449 and sent to a sampler/data acquisition unit 442. The sampler/data acquisition unit 442 samples the received signal 1142 at various times from the initial transmit signal 1140 generated by a computer 428. The computer 428 initiates the pulse via the pulse generator 430, but the computer 428 is also used to generate a timing signal via a timer delay 441 to sample the incoming delays. The incoming signal 1142 is sampled in time at different delays and the amplitude of the incoming signal 1142 is recorded at those different times. At a certain time, the returned signal will be of a certain amplitude representing the returned signal from the reflector. The computer 428 processes the information from the sampler/data acquisition unit 442 to determine, at least approximately, the distance from the radar unit to the reflector via the time delay between the transmitted pulse and received pulse. The time delay between the transmitted signal 1140 and the received signal 1142 is related to the distance between the radar unit and the reflector. The impulse radar uses pulses with short duration and wide frequency band to provide high-resolution distance measurements. Advantages of this embodiment can include high accuracy and low power. If the pulse is or encodes a pseudorandom noise sequence and the computer does a correlation on the transmitted pulse with the received signals, then a noise radar is achieved. Noise radar is useful in interference mitigation.

[00244] Figure 18 shows an impulse radar system 2480 with multiple transmitters and receive antennas 1151-1155 aimed towards a corner reflector 459. In this embodiment, the impulse radar system 2480 comprises an antenna array 1150, an impulse radar subsystem 454, and a computer 480. The antenna array 1150 is composed of multiple antennas 1151-1155, typically between two to several hundred antennas. The antennas can be of any types known in the art such as, for example, printed antennas, waveguide antennas, dipole antennas, or Vivaldi broadband antennas. The antenna array 1150 can be linear or two-dimensional, flat or conformal to the region of interest. The impulse radar system 2480 generates RF signals and transmits the RF signals via the antenna array 1150 consisting of antennas 1151-1155. The output signal is reflected from the corner reflector 459 and back to the antenna array 1150. The impulse radar unit 454 receives the returned signals from the antenna array 1150. The signals can be, for example, pulse signals, stepped-frequency signals, or the like. The generation circuitry within the impulse radar system 2480 can involve oscillators, synthesizers, mixers, or it can be based on pulse-oriented circuits such as logic gates or step-recovery diodes. The conversion of the signals can include down conversions, sampling, and/or the other similar techniques. The impulse radar system 2480 can perform transmission and reception with multiple antennas at a time or select one transmit and one receive antenna at a time. The impulse radar system 2480 preferably has data acquisition capability to collect and digitize the signals from the antenna array 1150. The data acquisitions capability typically includes analog- to-digital converters, data buffers, and filtering functions. The computer 480 may convert the signals 481 into responses characterizing the reflector 459 and perform algorithms for converting the sets of responses into image data (two- or three-dimensional) of the reflector. The reflector 459 image can be determined with respect to the antenna array 1150 alignment; therefore, the orientation of the reflector 459 can be determined with respect to the antenna array 1150.

[00245] Figure 19 shows a Frequency-Modulated Continuous Wave (FMCW) radar transceiver, such as, for example, a Texas Instrument 60 GHz and 77 GHz FMCW radar transceiver. In this embodiment, a processor 425 generates a DC (direct current) signal via a DAC (digital-to-analog converter) 421 to control a VCO (voltage-controlled oscillator) 410. The VCO 410 generates a signal 1130 called a FMCW chirp and sends the signal 1130 through an antenna 414. There is typically a power amplifier prior to antenna 414 to increase the signal strength. A return signal 1132 is received via an antenna 416 and combined by a modulator 418 with the transmitting signal via a path 412. There is typically a low-noise amplifier to boost the received signal level. The modulator 418 is a quadrature modulator and provides both real and imaginary components. The output of the modulator 418, which is at the beat frequency, is amplified and filtered via a filter 419 and sent to a A/D (analog-to-digital) converter 420. The processor 425 receives the signal from the A/D convertor 420 and processes the signal for distance and amplitude information using a frequency transform such as, for example, a Fast-Fourier Transform (FFT). One FFT on the first frequency ramp, which is typically 10-250 microseconds long and called a fast chirp in FMCW modulation, can provide a sufficient lateral distance measurement. This fast chirp allows for distance measurements in short time intervals, e.g., less than one millisecond. Higher distance accuracy can be achieved without significant memory or speed compromises using the Chirp-Z Transform and Zoom FFT. The Chirp-Z Transform is a generalization of the Discrete Fourier Transform (DFT). The Zoom FFT technique only processes the frequency of interest, not the whole spectrum. That is possible in these circumstances because the lateral distance to the vehicle from the pavement markers is roughly known within a range of distances, and that corresponds to a frequency range or band. These techniques can improve the measured distance accuracy and thereby enable or improve lateral control of the vehicle. Other techniques similar to the above can also be used to improve accuracy. The FMCW radar transceiver can derive not only the distance but also velocity, signal amplitude, and phase. With multiple receive antennas, the angle-of-arrival (AoA) can also be determined and therefore, the direction of the object.

[00246] Some automotive radar transceiver types utilize a frame sequence to transmits RF signals. For example, with FMCW there are chirps (ramp of frequencies); with Digital Coded Modulation, DCM, there are sequences of chips (digital coded stream); and with UWB impulse radar, one or more pulses (wideband of frequencies) are transmitted to the objects and reflected signals are received back from various objects. These radar types can differentiate multiple targets and are characterized by frames per second (fps), which can related to the processing speed to derive distance, velocity, and location of the target. The faster the frame rate, the quicker the target can be identified. Typically, frame rates are 8-50 fps for automotive radars, but higher frame rates can be achieved by using shorter chirp, chip, or pulse sequences, respectively. The frame rate may be, for example, as low as 1 fps or as high as 2000 fps. For example, the Texas Instruments IWR1443 in one configuration has a frame rate of 909 fps (1.1 millisecond frame time) for one type of radar application. CW radars transmit a continuous frequency and do not have frames. For example, two-frequency CW or multiple-frequency CW radar continuously transmits and receives signals; there are no frames. However, multiple-frequency CW radars imply much different processing to pick up more than one target.

[00247] For example, for a downward side-looking radar transceiver on a vehicle moving 25 m/s down the roadway, the radar transceiver will be in view of a 0.1 m long dihedral corner reflector pavement marker for about 4 milliseconds (view time = length of dihedral corner reflector/vehicle velocity). In order not to miss the dihedral corner reflector pavement marker by the radar transceiver, the frame rate should be greater than 250 fps (l/0.004s). The length of the dihedral corner reflector can be very short, eg., 0.05 m or very long, e.g., 1 m. Typically, the spacing between the pavement markers on the roadway may be as short as 0.5 m to as long as 25 m.

[00248] To minimize frame rate, one can use synchronous timing of the frames to the velocity and dihedral corner reflector pavement marker spacing. A start time of a frame would be from the end of the spacing time period when the radar transceiver viewed the last dihedral corner reflector pavement marker to the next dihedral corner reflector pavement marker. This spacing time period is equal to pavement marker spacing distance divided by the vehicle average velocity during the period. For example, if the spacing distance between pavement markers is 1 m and vehicle velocity travelling down the road is 25 m/s, the spacing time period, Tsp, is 40 milliseconds (Tsp = pavement marker spacing distance / vehicle road speed). The radar transceiver frame rate would be about 25 fps (1/0.04s) if the radar transceiver starts the frame synchronized with the spacing time period. For example, the Texas Instruments IWR1843BOOST provides the capability to start a frame using either a software start command or a hardware SYNC_IN pin signal. The radar transceiver frame rate can vary based on the vehicle speed and dihedral comer reflector pavement marker spacing. Synchronizing the frames to the beginning of the dihedral corner reflector allows for more radar viewing time on the dihedral corner reflector, no missed dihedral corner reflector pavement markers, and less or no need for high speed radar processing. The frame period may range from about 0.5 milliseconds to about 1 second. A Kalman filter can be used to assist in tracking the pavement markers and to mitigate missing pavement markers.

[00249] Figure 20 shows a radar transceiver with additional synchronization such as a Texas Instrument 60 GHz and 77 GHz FMCW radar transceiver. In this embodiment, the processor 425 generates a DC signal via the DAC 421 to control a VCO 410. The DAC signal is synchronized with an A/D signal via a line 423 to provide high accuracy distance measurements. The VCO 410 generates a signal 1130 and sends the signal 1130 through the antenna 414. The signal 1132 is received via the antenna 416 and combined by the modulator 418 with the transmitting signal via the path 412. The output of the modulator 418 is amplified and filtered via the filter 419 and sent to the A/D converter 420. The processor 425 receives the signal from the A/D convertor 420 and processes the signal for distance, velocity, amplitude and phase information. As mentioned earlier, both the transmit and receive signals at the antennas typically have amplifiers (not shown) to boost the signal strength.

[00250] Another embodiment shown in Figure 21 is a two-frequency radar transceiver that determines the distance of the pavement reflector 284 relative to the vehicle 180 via a phase difference in two received signals. A high-frequency generator 600 is mixed with a lower frequency 602 to form two frequencies fi and f2 using a single-sideband mixer 604. The two frequency signals are combined in a summer 606, amplified via amplifier 607 and sent out a transmitter antenna 608, which aims at the pavement reflector 284 via a signal 1610. A signal 1612 is reflected back to a receiver antenna 610 and amplified via a low-noise amplifier (LNA) 611. The received signal 1612 is mixed with fi and f2 and filtered with filters 616 and 618, respectively. The resulting signals are sent to a phase detector 620, which detects the phase difference of the two signals. The phase difference is related to distance travelled between the two-frequency radar and pavement reflector 284: Phase difference = 4irfd/c where 7t ~ 3.1416, f is the difference frequency, d is the distance, and c is speed of light. The frequencies can be sent out at different time intervals, time-multiplexed or frequency-multiplexed. The difference frequency sets the maximum range and range resolution. The higher the difference frequency, the better the range resolution, but the lower the maximum range. The Ohio State University radar transceiver cited above had a center frequency fi of 10.5 GHz and a difference frequency of 300 MHz. That provided an unambiguous range of 0.5 m and range accuracy of less than 1 centimeter (cm). The PACCAR Technical Center radar used a two-frequency timemultiplex wave radar with a 10.5 GHz center frequency and difference of 20 MHz. That provided an unambiguous range of 7.5 m. To improve range accuracy, the 10.5 GHz cycles were monitored using a quadrature detection scheme and provided a range accuracy of better than 1.5 cm. Another embodiment could transmit and receive multiple frequencies to determine the distance to the reflector 284. Three or more frequencies can be transmitted to the reflector using similar hardware as the two-frequency radar but with more components and frequencies. Two frequencies, such as 77 GHz and 77.01 GHz, can provide an unambiguous range of 15 m and third frequency, such as 78 GHz, provide range accuracy of better than 1 cm.

[00251] Figure 22 shows a Digital Code Modulation (DCM) radar transceiver. A unique digital code, a sequence of chips, is generated by a digital code generator 1421 and mixed using a modulator 1604 with a reference frequency generated from a signal generator, VCO, 410. A chip is a binary value to modulate the phase of the RF sinusoidal signal. This signal is amplified using an RF power amplifier 1607 and transmitted via an antenna 414. The return signal is received by an antenna 416 and amplified by an RF LNA 1611. The return signal is mixed with the reference signal using a modulator 418. The output signal of the modulator 418 is filtered via a filter 419 and sampled via an A/D converter 420. A radar processor 425 receives the signal from the A/D converter 420 and knows the reference code from the digital code generator 1421. By correlating the transmitted code with the received code, the radar processor 425 can determine distance to the corner reflector and velocity. The angle to the target or corner reflector can be determined with multiple transmit and received antennas.

[00252] Figure 23 shows another example of a FMCW radar transceiver but with multiple transmit antennas 414 and multiple receive antennas 416. In particular, Figure 23 shows a FMCW MIMO (multiple-input, multiple-output) radar transceiver. A radar processor 426 drives a synthesizer 411 to provide a chirp or frequency ramp of a transmitting signal. The signal is amplified by RF power amplifiers 413 and sent out via multiple transmit antennas 414. The received signal is captured by antennas 416 and amplified via RF low-noise amplifiers (LNAs) 415. The transmitted signal is quadrature mixed with the received signal using modulators 418 so both the phase and velocity of the signal can be determined. The output of the modulators 418 are filtered by filters 419 and A/D converted via an A/D convertor 420 to a signal read by the radar processor 426. With multiple antennas, the system can determine the angle to the target (Ao A) to help discriminate among different targets.

[00253] Also, if the transmit antennas 414 and receive antennas are polarized, eg., orthogonal linearly-polarized antennas, then the radar system is polarimetric radar with added capability of distinguishing the dihedral corner reflector from other objects such as the ground based on a polarimetric scattering matrix. The radar reflection from a dihedral corner reflector is a double-bounce signal (two reflections from the two dihedral reflective surfaces), as shown in Figure 4A, whereas the reflection from the ground or road surface is only one bounce (one reflection from the ground or road surface). The phase change in the polarized electric fields from a single-bounce reflection and a double-bounce reflection is different, and that difference can be detected to distinguish from a dihedral corner reflector from the ground surface. In particular, with an even number of bounces, such as from a dihedral corner reflector (two reflections from the two dihedral reflective surfaces), the phase in the vertical-to-vertical polarized direction is different from an odd number of bounces eg., one reflection from the ground surface or three bounces from the three reflective surfaces of a trihedral corner reflector). The phase change in the polarized electric fields can therefore distinguish whether a reflection is from the ground surface or a dihedral corner reflector. In addition, an evenbounce reflector always returns the same sense circular polarization as the incident wave. For example, a left-hand circularly polarized wave is reflected as a left-hand circular wave from a dihedral corner reflector, whereas the circular polarized wave is reflected back as a right-hand circular wave from the ground. A dual-polarimetric radar transmits and receives pulses in both a horizontal and vertical polarization dimension. As a result, the returning frequencies provide measurements of the horizontal and vertical dimensions of a pavement marker, providing information on the size and shape of pavement maker and the distance to the pavement marker. With these measurements, the dual-polarization radar can filter out other objects as clutter and provide a more accurate distance to the pavement marker.

[00254] A typical FMCW radar sensor, such as the Texas Instruments AWR1843AOP, can provide object range by doing an FFT over the processed received signal, the beat frequency. The radar sensor can provide velocity using a second FFT across several sequential received signals (chirps with ramped transmitted frequencies) by detecting the change in phase from one chirp to the next chirp. The radar sensor can provide direction using a third FFT across several received signals from different received antennas using AoA. This result in a radar cube comprising range, velocity, and direction. Using dihedral corner reflectors in pavement markers, an accurate lateral distance to a radar sensor can be determined using a single FFT on first frequency ramp which is typically 10-250 microseconds, which is called a fast chirp in FMCW modulation. This fast chirp allows for distance measurements in short time intervals, e.g., less than one millisecond. Typically, the lateral velocity measurement is small and near zero, therefore, a second FFT is not required. Also, the angle of the maximum received signal to the pavement marker will be facing the corner reflector since the vehicle will be parallel to the pavement marker. The processing software within or in conjunction with the radar sensor can use both techniques: A single FFT on the fast chip for processing accurate lateral distance measurements to the desired reflective pavement markers and multiple FFTs on distance, velocity, and multiple receive antennas for detection of other objects surrounding the vehicle, e.g., blind spot detection or for performing lane changing maneuvers and lane departure detection.

[00255] Deep learning methods may be utilized to enhance detection of the dihedral corner reflector from other objects on the roadway and to thereby decrease the likelihood that a pavement marker is missed in view of other radar clutter. Using Convolution Neural Networks (CNN) or Recurrent Neural Networks (RNN), for example, on the radar cube or just the range and some other properties, e.g., polarization and magnitude, can improve the distance measurements from the desired reflective pavement markers.

[00256] Phase-Modulated Continuous Wave (PMCW) radar, Orthogonal Frequency- Division Multiplexing (OFDM) radar, and other digital radar techniques can also determine the distance to the reflective pavement markers. Combinations of one or more of the above techniques can also be used. For example, an FMCW technique and a PMCW technique could be used in the same radar sensor to determine redundant distances to the reflector. Alternatively, two or more radar transceivers with the same or different characteristics could be used in combination at different distances.

[00257] The radar sensors can be any of the previously described types, e.g., FMCW, PMCW, OFDM, DCM, multiple-frequency radar, multiple-frequency phase radar, MIMO radar, UWB FMCW, UWB impulse radar, FSK (Frequency Shift Keying) radar, monopulse radar, or combination of any of these types. The radar preferably operates at radio frequencies between 0.3 to 1000 GHz (300 MHz to 1 THz).

[00258] The radar beam transmitted by the radar transceiver preferably has a single or dominant lobe characterized by a beam direction and a beam shape. The beam direction is typically characterized by a vector along the center or centroid of the lobe. The radar transceiver is preferably placed and pointed so that the beam direction is toward where the dihedral comer reflector in the pavement marker is expected to be when the vehicle is centered in its lane. The beam shape may be, for example, Gaussian and characterized by a beam width, which is typically measured from half-power points on opposite sides of the beam center. The beam may be circularly symmetrical about the center direction vector or may be asymmetrical. The beam width is preferably narrow enough to only detect one reflector at a time in a given line of reflectors (although reflectors in parallel, more distant lines may also be detected in the beamwidth) but wide enough to capture markers within the expected area of variation based on vehicle drift, tolerance of marker placement, etc. Range-based gating or filtering can be employed to ignore reflection signals from objects outside of the range of interest.

[00259] The beam shape and/or direction may be static or variable. Well-known beam shaping techniques can be applied to alter the beam dynamically or non-dynamically. For example, when the beam is generated from an antenna array, well-known electronic beam steering and beam shaping techniques (eg., delay and sum, windowing, etc.) can be employed to electronically alter (eg., steer) the beam. For example, the beam can switch between a relatively narrow width pointed at a nominal pavement marker location and a relatively broader width pointed more upwardly for blind spot detection, as described in more detail below.

[00260] In some embodiments, mechanical beam shaping devices can be employed. For example, an RF lens can be used to alter a beam’s shape, including its width. If the radar transceiver is located within a vehicle light, then the exterior light cover (or relevant portion thereof) can be shaped and built of a suitable material to be an RF lens. As another example, an RF reflector (eg., horn) may also alter a beam’s shape and/or width. Combinations With Other Automotive Radar Systems

[00261] Another embodiment combines a current automotive radar transceiver that provides object detection on the front, side, and/or rear of the vehicle with a radar transceiver used to detect radar-reflective pavement markers. That is, the same radar transceiver on the vehicle can be used for both object detection and pavement marker ranging. For example, the same side or comer automotive radar can (1) see the reflective pavement marker as a stationary, highly reflective targets and measure the lateral distance to the reflective pavement marker installed on the roadway and also (2) process the other objects along the side such as moving vehicles in a blind spot of the vehicle driver. Not only can the same radar transceiver be used for blind-spot detection, but for cross-traffic alerts, lane-change assistance, and trafficjam assistance using, for example, known beam steering techniques with the multiple antennas on or with the same radar transceiver unit as shown in Figure 23. This could be, for example, a dual-purpose side radar transceiver that processes large above-ground objects, e.g., vehicles in the blind spots, and also processes small on-ground objects, e.g., reflective pavement markers, for lateral distance measurements. Figure 23 shows a typical FMCW radar transceiver that provides object location for objects, both stationary and moving. The FMCW radar transceiver may contain or utilize software to differentiate between targets and to provide the object’s range, the object’s location, the object’s returned signal strength, and/or a relative speed difference between the object and the radar transceiver. Similarly, a front radar can see a combo reflective marker (described below), a marker with multiple dihedral/trihedral reflectors or multiple dihedral reflectors, as the vehicle travels along the roadway in addition to other vehicles in front of the vehicle. The automotive radar can see the other vehicles as moving targets at certain distances ahead of the vehicle and see the combo reflective pavement markers as stationary targets along the roadway on both sides of the lane. The distance to the combo reflective pavement markers can be used to determine the geometry of the roadway ahead of the vehicle. This dual-purpose forward-looking radar transceiver can detect objects in front of the vehicle to avoid or in the case of adaptive cruise control, vehicle to follow, but also provide the road geometry for use in a lateral steering controller as preview information. Likewise, a dual-purpose backward-facing radar transceiver can see other vehicles approaching the vehicle and also see a combo reflective pavement markers for additional information on the roadway geometry.

[00262] In one embodiment, the radar transceiver can be packaged in a turn-signal light, marker light, or other light assembly on the vehicle. For example, the radar transceiver may be integrated with such a light or added as a retro-fit add-on under an existing lights exterior cover.

[00263] When a radar transceiver is used to provide blind-spot monitoring, then a light on the vehicle can be made to turn on or blink (alternately turn on and off) to signal to the person or other vehicle in the blind spot that it has been detected in the blind spot. That is, detection of an object in the blind spot can cause a processor associated with the radar sensor to cause a light on the vehicle to turn on or blink. Alternatively, another indication (visual or audio) can be activated when an object is detected in a blind spot. If the activated light or indication is on the exterior of the vehicle in the vicinity of the blind spot, the light or indication can prompt the other driver, cyclist, or pedestrian, etc. to move relative to the vehicle so as not to be in the vehicle’s blind spot. For example, shorting of a turn-signal light can cause the light to flash at twice the rate as a standard blinking rate that signals an intention to turn or change lanes. An indication can also be generated on the dashboard or elsewhere in or near the driver’s cabin/compartment to indicate to the driver the presence of an object in the blind spot. If the light is a self-powered turn-signal light combined with the radar transceiver, the action to activate the light can happen locally at the light (by a processor therein), with no added load on the vehicle’s computing system. According to another embodiment, when the radar transceiver detects an object in a blind spot, many select pixels per headlamp or turn signal can be activated to project a visual warning, such as a warning symbol in HD quality to warn the driver and other drivers of the blind spot detection. Combinations With Other Automotive Guidance Systems

[00264] For redundancy and/or higher reliability, the radar guidance techniques described herein can be combined with other guidance techniques based on other technologies. For example, the radar transceiver 116 can be integrated with other sensors such as, for example, a GPS receiver 901, lidar sensor 902, vision sensor 903, forward-looking radar 904, or other location sensors 905, as shown in Figure 24. As another example, the processing of signals from a variety of sensors, including the radar sensors described herein, can be performed by a common processor or computer (which may have multiple processors). Joint processing of the various sensor types can improve the performance of any one sensor type alone. For example, the output of an onboard processor 437 using, for example, Kalman filters can provide highly reliable location information 914, steering information 912, and speed information 918.

[00265] Figure 25 shows another embodiment where the dihedral corner pavement markers 2841-2847 and 3841-3846 are placed along the roadway. Pavement markers 2841- 2847 are spaced X21-X27, respectively, along one side of the lane 303. The other side of the lane has pavement markers 3842-3846, which could be spaced similarly. A vehicle 1800 with radar transceivers 1161 and 1171, which are sufficiently directional, and a sufficiently accurate position-determination system {eg., DGPS (differential GPS)) can record the location of the pavement markers as the vehicle 1800 is driven along the lane 303. A recording of the placement of the radar reflector pavement markers using the sufficiently directional radar on vehicle and a sufficiently accurate location sensor can be incorporated in a database of the latitude and longitudinal readings for of each marker along with the distance between the pavement markers, e.g., X21-X27. Figure 26 shows a table of one embodiment of the pavement marker database. In this table, pavement markers are identified as alphanumeric strings using the road name and direction of travel, eg., US30, the direction East, and pavement marker number would be US30E2841. Other methods for identifying the pavement marker with the location can also or alternatively be used. The pavement marker location in this example are latitude and longitudinal coordinates. The distance from previous maker X21 to the next marker X22 could also or alternatively be recorded. Figure 26 could, thus, represent accurate locations of the reflective pavement markers on the road.

[00266] The database of Figure 26 may be augmented with other information, including, for example, the location of known hazards eg., potholes). With an accurate database of the pavement maker locations and known hazards, the speed and positioning of the vehicle can be adjusted to avoid the hazards or to reduce or minimize their effects on a vehicle.

[00267] With an accurate database of the pavement maker locations, the speed and longitudinal location of a vehicle can be determined by the location of the vehicle along the roadway. The vehicle speed can be determined from knowing the distances, eg., X22, between the pavement markers and the time of travel between viewing, via radar transceiver 1161, pavement marker 2841 and pavement marker 2842. This would be the actual speed of the vehicle. One can also get speed from forward looking radar or from the vehicle wheel speed. Figure 27 shows one embodiment of using the location information of the pavement markers to control the vehicle speed. A vehicle speed controller 9080 can control the engine (gas vehicles) or electric motor (electric vehicles) or engine/motor 9020. The engine/motor 9020 drives the vehicle dynamics 9050 which results in vehicle speed. The desired vehicle speed VDESIRED is inputted to the vehicle speed controller 9080. The marker database 9006 can be queried to determine the actual speed from time the radar transceiver 1167 viewed the two markers and the actual distance between the markers in the marker database 9006. The marker database 9006 can have input from other sensors such as the coded markers 9090, GPS receiver 901, and vehicle-to-infrastructure (V2I) communication 9180. The controller 9080 receives the error between the actual speed and the desired speed and derives the proper response to control the engine/motor 9020. The vehicle speed controller 9080 can have input from the other vehicles via vehicle-to-vehicle communication (not shown) to alter the speed based on traffic. [00268] Another embodiment uses the marker database 9006 for longitudinal distance control of the vehicle. Figure 28 shows a longitudinal distance control system which controls the vehicle position travelling along the road. The desired distance, XDESIREE, at any point is determine by a central computer for the vehicle highway via vehicle-to-infrastructure (V2I) communication 9180 or by a vehicle-onboard computer via vehicle-to-vehicle (V2V) communication 9170. If a desired distance is determined by the highway central computer via V2I communication, then the controlled vehicles would be in an automated highway system where all vehicle positions are known along the roadway. If determined by the vehicle onboard computer via V2V communication 9170, then the vehicle is controlled in a platoon with other vehicles. A combination of both schemes can be used to provide platoon of vehicles on the automated highway to improve safety and traffic flow. Figure 28 shows a block diagram for a longitudinal control system where the difference between the desired distance and the actual distance travelled is inputted in a vehicle longitudinal controller 9004. The controller 9004 compensates for vehicle dynamics and roadway conditions and controls the engine/motor mechanism 9120, which in turn controls the vehicle dynamics (transmission and wheels) and is influenced by the road conditions. The actual distance, XACT, is calculated using the radar transceiver 1167 viewing the pavement markers at various times and the marker database 9006 of the pavement markers’ locations. The actual distance XACT can be determined from the pavement markers via the marker database 9006, from forward-looking radar 904, or from a wheel speed sensor 1904. The marker database 9006 may have the actual locations of the pavement markers and determine the location of the vehicle along the highway at any point in time from processing the radar transceiver information from the radar transceiver 1167. The marker database 9006 can have other sensor inputs to help determine the vehicle location, e.g., coded markers 9090, GPS receiver 901, and V2I communication 9180. The vehicle longitudinal controller 9004 could be, for example, similar to the one using discrete embedded magnets as described in “Vehicle Longitudinal Control Using Discrete Markers” by David W. Love and Masayoshi Tomizuka published by California PATH Program of the University of California as California PATH Research Report UCB-ITS-PRR-94-28 (Dec. 1994), which is incorporated by reference herein in its entirety.

[00269] Another embodiment shown in Figure 29 uses the location of pavement markers to determine the position of a trailer on a roadway. Figure 29 shows a tractor-trailer combination with a tractor 1801 and two trailers 1802 and 1804 connected to the tractor 1801. Besides the lateral radar steering transceiver on the front of the tractor to control the lateral movement of the tractor, as described above, the trailers’ positions can be determined using multiple side-looking and downward-looking radar transceivers 9116-9119 with radar beams 9126-9129, respectively, on one side of the trailers viewing the pavement markers 284 on one side and side-looking and downward-looking radar transceivers 9216-9219 with radar beams 9226-9229, respectively, on the other side of trailers viewing other side pavement makers (not shown).

[00270] According to another embodiment, the radar-based measurement and guidance techniques described herein can be used to test or calibrate other guidance systems based on other technologies (eg., lidar, vision, other radar, etc.).

Pavement Marker With Embedded Combination Radar Reflector(s)

[00271] There are many ways to construct raised pavement markers with dihedral corner reflectors. The above embodiments show some preferred combinations. Another embodiment is a combination of one or more dihedral reflectors and one or more trihedral reflectors embedded in a pavement marker. Figure 30A illustrates the dimensions of a dihedral/trihedral combination corner reflector 3287. The combination corner reflector 3287 is dihedral reflector 287 (L-shaped) similar to what is shown in Figures 2A-2D but with an added side reflector element 2287. Adding this element 2287 on the end creates a trihedral corner reflector for one end of the reflector 3287. The side dimensions are “a” and the long end, which is substantially parallel to the lane markings, has dimension “b.” The added element 2287 has similar dimensions “a” for the height and width of the element. Alternatively, the additional element 2287 may have a different shape, such as triangular, for example. The dihedral/trihedral combination corner reflector 3287 differs from a strictly dihedral corner reflector, such as the dihedral corner reflectors illustrated in Figures 2A-4E, for example, in that the latter does not have an end piece such as the side reflector end element 2287 shown in Figure 30A. As used herein, a strictly dihedral comer reflector has exactly two sides and does not include a third side.

[00272] Another embodiment shown in Figure 30B illustrates the dimensions of a T- shape dihedral/trihedral combination corner reflector 2396. The sides have dimension “a” and the long end, which is parallel to the lane markings similarly to the single dihedral corner reflector 287, has dimension “b.” The new element 4396 added to the T-shaped dihedral corner reflector 396 creates the new combination dihedral/trihedral reflector 2396. The dimensions of the element 4396 are “a” in height and “2a” in length. The end element 4396 is attached to the end of the T-shaped dihedral reflector 396 to form the combination dihedral/trihedral reflector 2396.

[00273] Figures 31A-31D show the reflection of the single L-shaped combo dihedral/trihedral corner reflector 3287 in various positions from a radar transceiver 116. The other embodiments have similar results. Figure 31 A shows the radar transceiver 116 aimed at the center of the dihedral corner reflector section, a transmit signal 1119, and a receive signal 1118 similar to the previously described dihedral reflector. A distance “d” can be measured between the radar transceiver 116 and the reflector 3287. As shown earlier in Figure 5A, the relative RCS over +/-45° of rotation of the radar transceiver 116 from the center of the dihedral corner reflector returns a strong signal strength of the reflections from the target, in this case, a dihedral corner reflector. As long as the position of the radar transceiver 116 is within corner reflector right angle, the signal return is very good. If the radar transceiver 116 is past 45° of rotation and sees the back of the combo reflector 3287 but not at a right angle to the back, the signal is not reflected back very well. This is an advantage of a corner reflector versus a flat plate or sphere. A flat plate reflects the signal back if the radar transceiver was facing the plate or at 90° to the plate, but very little signal returns if the radar transceiver rotates in either direction.

[00274] Figure 31B shows a top view of the combo reflector 3287 and shows the radar transceiver 116 aimed directly at the dihedral portion of the combo reflector 3287. The radar transceiver beamwidth is wide enough to cover the length “b” of the dihedral corner reflector in the direction of travel, “y.” The transmitted signal 1119 is reflected back as the returned signal 1118 for a given length of the corner reflector “b” and radar beamwidth. The signal strength is good from the reflector as long as the radar transceiver passes by the dihedral corner reflector. Once the radar transceiver passes the corner reflector, especially the end element 2287, the signal returned drops off significantly. So, when the radar transceiver 116 passes the combo reflector 3287 in the parallel direction to the corner reflector length, the radar transceiver measures the distance from corner reflector to the radar transceiver antenna. This distance is constant for a period of time if the radar transceiver 116 is maintained substantially parallel to the combo reflector 3287. If the radar transceiver 116 moves closer to the combo reflector 3287 in the parallel direction, the radar transceiver 116 would measure a closer distance to the combo reflector 3287.

[00275] Figure 31C shows a top view of the radar transceiver 116 with the radar looking towards the corner formed by the three surfaces of the combo trihedral reflector at a distance away from the combo reflector 3287 and going towards the combo reflector 3287 in a parallel direction to the long section of the combo reflector 3287. The radar transceiver beamwidth is wide enough that the radar transceiver 116 transmits a signal 2119 and receives a signal 2118 from a distance from the combo reflector 3287. The trihedral reflector created by the end element 2287 and dihedral reflector portion provides a strong signal return while the radar transceiver approaches the combo reflector 3287. The distance measured db will vary and decrease as the radar transceiver approaches the combo reflector 3287 until, as shown in Figure 31B, the radar transceiver 116 faces directly across from the combo reflector 3287. Then, the radar transceiver 116 measures the constant distance d for a period of time. When the radar transceiver 116 passes the combo reflector 3287, the signal return will drop off significantly and no short-range distance will be reported.

[00276] Figure 31D shows a top view of a forward-looking radar transceiver 1168 a distance away from the combo reflector 3287. Here the main beam is aimed towards the trihedral corner reflector of the combo reflector 3287. The radar transceiver 1160 transmits a signal 3119 towards the combo reflector 3287 and the trihedral component reflects the signal 3118 back towards the radar transceiver 1160. The distance d _P is measured between the radar transceiver 1168 and the combo reflector 3287.

[00277] The combination dihedral/trihedral corner reflector has several advantages in this application over just a trihedral corner reflector and over a strictly dihedral corner reflector. First, the combination dihedral/trihedral corner reflector provides a constant distance for a period of time similarly to the dihedral corner reflector when viewing the corner reflector sideways, but also allows for a signal return approaching the combo reflector as a trihedral corner reflector. This allows for viewing the combo reflector for a longer time and may reduce the processing needed. A second advantage is that a combo reflector can be seen by a forward-looking radar. This radar system would provide preview information of the road geometry ahead of the vehicle travel. There would be minimal need to store information in a database since the road geometry would be visible when travelling along the road. A third advantage is that the forward-looking radar can provide the location of the vehicle within the lane using the geometry of the various pavement marker locations.

[00278] Figures 32A and 32B show several constructions of raised pavement markers with a combination dihedral/trihedral corner reflector. Figure 32A shows one embodiment with the main body 290 containing the optical reflector 275, two combination dihedral/trihedral corner reflectors or combo corner reflectors 2286 and 2288 and two quarterround RF transparent materials 293 with end caps. The combo corner reflectors 2286 and 2288 are attached to the left and right side of the main body 290 with the optical reflector 275 attached to the front as shown in these isometric diagrams. The quarter-round RF transparent materials 293 are placed inside the combo comer reflectors 2286 and 2288, respectively, to provide a protector from road damage. The attachment means for the combo corner reflectors 2286 and 2288, the main body 290, and the RF transparent materials 293 can be glue, screws, rivets, molded slots, or similar attachment mechanisms.

[00279] Figure 32B shows another embodiment 2384 for constructing raised pavement markers with combination dihedral/trihedral corner reflectors. In this embodiment the quarter round RF transparent materials 1294 and 1296 have a metallic or other RF-reflective paint or foil sprayed or glued, respectively, on the two flat angle-shaped sides to form the dihedral corner reflectors and on the quarter-circle-shaped end cap 1301 to form the trihedral reflector. The bottom sides 1302 and 1303 are also coated with a metallic paint or metallic foil on the quarter round RF transparent materials 1294 and 1296, respectively.

[00280] Figures 33A-33C show several constructions of raised pavement markers with a T-shaped combination dihedral/trihedral corner reflectors. Figure 33A shows one embodiment 1588 with the T-shaped combination dihedral/trihedral corner reflector 2396 made of metal or other RF-reflective material in the center of two quarter-round or similarly shaped RF-transparent materials 397 and 398, and the optical reflector 275 attached to the front, forming the pavement marker 1588. The two quarter-round RF-transparent materials 397 and 398 are attached to the left and right side of the T-shaped combination dihedral/trihedral corner reflector 2396 with the optical reflector 275 facing the front from the isometric picture. The quarter-round RF transparent materials provide protection from road damage. The attachment means for connecting the T-shaped combo corner reflector 2396 to the RF transparent materials 397 and 398 can be glue, screws, rivets, molded slots, or any other suitable attachment mechanism(s).

[00281] Figure 33B shows another embodiment 1688 for constructing raised pavement markers with a T-shaped combo corner reflector. In this embodiment, one of the quarter- round RF-transparent piece 3396 has a metallic or other RF-reflective paint or foil sprayed or glued on one side the combo corner reflector and on the end cap 1301. The other transparent RF-transparent piece 3397 has an end cap 1301 with a similar coating. The quarter-round RF- transparent material 3396 can be electroplated with a metallic surface on the two sides: interior side and end cap. The bottom flat plate 1300, which is metallic or another RF- reflective material, forms the bottom of the T-shape corner reflector and provides a good flat protective surface.

[00282] Figure 33C shows another embodiment 1788 for constructing a raised pavement marker with a T-shaped combo corner reflector. In this embodiment, two molded plastic or similar RF-transparent material 3396 and 3397 that are RF transparent are electroplated or metallic sprayed on the sides. The molded plastic RF-transparent material 3396 is sprayed or electroplated on the bottom side 1303, whereas the molded plastic RF-transparent material 3397 is sprayed or electroplated on the two sides right angle side 1399 and bottom side 1303. When the two are glued or mechanically connected together, they form the T-shape dihedral corner reflector. Adding the optical reflector 275 to the front forms the raised pavement marker 1784.

[00283] Figure 34 shows another embodiment 2888 with a T-shaped dihedral/trihedral corner reflector 2396 made of metal or other RF-reflective material or conductive coated rightangle material, etc., with two additional combo corner reflectors 2286 and 2288 on the ends of the pavement marker. The center reflector has two squared shaped RF-transparent materials 1293 on each side of the T-shaped reflector 2396. And two quarter-round or similarly shaped RF-transparent materials 393, and the optical reflector 275 attached to the front, forming the pavement marker 2888. The two quarter-round RF-transparent materials 393 are attached to the left and right side of the combo corner reflector 2286 and 2288, respectively, with the optical reflector 275 facing the front from the isometric picture. The quarter-round RF transparent material provides protection from road damage. The two-reflector arrangement provides for a larger radar cross section than a single dihedral corner reflector. According to, for example, “Introduction to Radar Systems” by Merrill I. Skolnik (3 ^rd Ed. 2002, publ. by McGraw-Hill), pages 45-46, similar sized and shaped targets, e.g., dihedral corner reflectors, spaced one, two, or four wavelengths apart will have a significantly larger radar cross section from a minimum of zero to maximum of four times the cross section of an individual scatterer. So, one or more dihedral/trihedral corner reflectors spaced wavelengths apart can be used in a pavement marker to enhance the radar cross section of the pavement marker to the radar transceiver.

[00284] There are many ways to construct raised pavement markers with combination dihedral/trihedral corner reflectors. The above embodiments show just some preferred forms. Another embodiment is formed from four vertical RF-reflective plates - two arranged parallel to each other oriented north-south and two arranged parallel to each other oriented east-west - above a RF-reflective bottom plate. This embodiment resembles a tic-tac-toe board from the top view (but typically with a larger center square), and it comprises four strictly trihedral corner reflectors (one in the vicinity of each corner) and multiple combination dihedral/trihedral corner reflectors along the interior portions of each side and along each side of the center square. Such an embodiment can be seen from all directions by a variety of types of directive radar systems on a vehicle, including side-looking, forward-looking, and even rear-looking radar transceivers.

[00285] There are many ways to construct raised pavement markers with dihedral corner reflectors; the above embodiments show just some preferred forms. One advantage of the above embodiments with the combination dihedral/trihedral corner reflectors, 2284, 2384, 1588, 1688, 1788, and 2888, is the ability to use forward-looking radar transceivers 1166, 1170, and 1198 to view the upcoming combo reflector pavement markers as shown, for example, in Figure 35A. As shown in Figure 35A, a vehicle 180 has side-looking radar transceivers 116,117, and 119 mounted on the vehicle 180 to measure lateral distances between the combination dihedral/trihedral pavement markers 2284 and the radar transceivers 116, 117, and 119. But the vehicle 180 also has forward-looking radar transceivers 1166, 1170, and 1198 to measure the distance to the combination dihedral/trihedral pavement markers or combo reflectors pavement makers 2284 in front of the vehicle 180. Knowledge of the distances between the vehicle 180 and the combo reflectors pavement markers 2284 provides advantages. For example, one advantage is that a number of combo reflectors pavement markers 2284 on one side will provide road curvature information along that side of the road/lane and therefore, preview information on the upcoming road geometry. This information can be used by the lateral guidance control to provide a better lateral controller for the vehicle 180 and less error coming into and out of curves. Likewise, the combo reflectors pavement markers 2284 on the other side of the vehicle 180 can provide road curvature information on that side of the road/lane and therefore redundancy in determining the road geometry. Another advantage is that, if the locations of combo reflectors pavement markers 2284 installed on the roadway are known and the forward-looking radar transceivers 1166, 1170, and 1198 measure the forward distance to the combo reflectors, processing this information will provide additional lateral and longitudinal distances which will allow the onboard controller to determine where the vehicle 180 is relative to combo reflectors pavement markers 2284 and the vehicle location within the road 300.

[00286] Figure 35B shows a top view of the forward-looking radar transceiver 1198 viewing several combo reflector pavement markers 2284 and measuring distances di, d2, ds, d4, and ds to combo-reflectors pavement markers 2284. The forward-looking radar transceiver 1198 can be mounted on the left or right side of the bumper. Figure 35B shows the forwardlooking radar mounted in the center of the front of the vehicle. There can be one or more forward-looking radar transceivers mounted on the front of the vehicle to view the comboreflector pavement markers 2284. The forward-looking radar transceiver can also look slightly downward towards the combo-reflector pavement markers 2284 or the beamwidth may be wide enough to view the combo-reflector pavement markers 2284. A typical FMCW radar sensor such as Texas Instrument AWR1843AOP can measure these distances, the velocities to the markers, and the angles to the combo-reflector pavement markers 2284. Using the law of cosines, the angle oci, as shown in Fig. 35B, can be determined using the following formula: oci = arccos[(s _m ² +d2 ² -di ² )/2*s _m *d2] where s _m is the spacing 192 between the markers on this roadway 300, and di and d2 are the radar-measured distances to the markers. Using the law of sines, the lateral distance xi from the combo reflectors pavement markers 2284 on the right side of the vehicle (the side on which the radar sensor 116 is mounted in Figure 35B) or the lane markers can be calculated by using the following formula xi = d2*sin(oci). An accurate lateral distance to the road line or combo reflectors pavement markers 2284 from the radar transceiver 1198 can be determined by using many lane markers on both sides of the vehicle 180 using the geometry and the laws of cosines and sines. Using similar geometry and the law of sines, the longitudinal location of the vehicle 180 relative to the combo reflectors pavement markers 2284 can also be determined. Using a Kalman filter or other filtering techniques on all these lateral distance measurements can provide a more accurate lateral distance and the longitudinal location of the vehicle 180 within the roadway 300.

[00287] Figure 35C shows a top view of the forward-looking radar transceiver 1198 viewing several combo reflectors pavement markers 2284 around a curved section of the roadway 300 and measuring the distances du, di2, dis, du, dis, die, and di? to combo reflectors pavement markers 2284 on both sides of the vehicle. The distances du-di3 to the combo reflectors pavement markers 2284 on the right side of the vehicle (the side on which the radar sensor 116 is mounted in Figure 35C) will show shorter distances than the distances di4-di7 to the combo reflectors pavement markers 2284 on the left side of the vehicle since the roadway 300 curves to the right. Likewise, the opposite is true if the roadway curves to the left. As in this example, the vehicle is travelling in the center of the roadway 300. Compensation to the measurements can be made if the vehicle is travelling closer to either side.

[00288] Figure 35D shows an embodiment using combo pavement reflectors within a roadway intersection. A vehicle 180 with radar transceivers 116, 117, and 1198, respectively, right, left, and front mounted sensors, can select three paths to follow when going through the roadway intersection: (A) right turn, (B) straight, or (C) left turn. If the vehicle 180 follows path A, the radar transceivers 116 and 1198 would follow the combo pavement markers 5284 to the left of the vehicle. The combo pavement markers 5284 are the same as combo-reflector pavement markers 2284, but designate a curve area. Also, the combo pavement markers 5284 are spaced closer together to provide a more continuous RF-reflective path and to minimize any lateral position error from the desired vehicle turn radius.

[00289] If the vehicle 180 follows path B, the radar transceivers 116, 117 and 1198 would be used to go straight through the intersection. Radar sensor 117 would follow combo reflectors pavement markers 2284 in the middle of the lane and then radar sensor 116 would pick up pavement marker 580 on the right side of the vehicle in the middle of the intersection. Pavement marker 580 is a three-sided dihedral reflector same as the pavement marker 580 as shown Fig. 16A. And then radar sensor 117 would pick up the pavement marker 580 on the right side of the vehicle as the vehicle goes through the intersection and then all the radar transceivers 116, 117, and 1198 would sense the combo reflectors pavement markers 2284 again.

[00290] If the vehicle 180 follows path C, then radar sensor 117 would pick up combo reflectors pavement markers 5484 on the far left of vehicle 180 and follow those combo reflectors pavement markers 5484 at a longer distance as the vehicle makes a left turn. Once through the intersection, the radar transceivers 116, 117, and 1198 again would follow combo reflectors pavement markers 2284. The combo reflectors pavement markers 5484 are the same as combo reflectors pavement markers 2284, but more closely spaced. Likewise, combo reflectors pavement markers 5684 and 5884 are installed on the other two curbs. Instead of installing combo reflectors pavement markers 5284, 5484, 5684, and 5884, the curb pavement around the curve may be painted a metallic paint similar to Figs. 15A-15C. The unlabeled markers are all designated as combo reflectors pavement markers 2284 and not shown for clarity. There are other combinations of markers that can be used in the intersection. For example, combo markers can be installed in the intersection to add redundancy for making vehicle maneuvers. Multiple Radar Sensors for Continuous Monitoring

[00291] Another embodiment shown in Figure 36 utilizes multiple radar transceivers or multiple transmit/receive antennas using the same radar transceiver 1165 and 1175 attached to the right and left side of the vehicle 180. Multiple radar transceivers 1165 on the right side of the vehicle 180 see the pavement markers 284 continuously as the vehicle 180 moves in the forward direction. Likewise, multiple radar transceivers 1175 on the left side of the vehicle 180 see the pavement markers 1284 continuously on the left side or driver’s side of the vehicle 180. The spacing between the pavement makers 284 and 1284 is at a distance dm. The array of radar transceivers 1165 and 1175 cover a distance dtotai on the vehicle 180. If the array of radar transceivers! 165 and 1175 spacing dtotai is the same as or greater than the spacing dm of the pavement markers 284 and 1284, respectively, then the lateral distance can be measured continuously or quasi-continuously (discrete measurements taken frequently enough to adequately approximate a continuous measurement) between the vehicle radars and the pavement markers.

[00292] InSAR (Interferometric Synthetic Aperture Radar) is a processing technique to determine the lateral distance using radar images of a target collected by multiple radar transceivers or multiple receive/transmit antennas. InSAR can be applied to pavement markers. Multiple radar images of the same area that collected at different times from similar locations as the vehicle passes the pavement marker can be compared against each other. Movement of the vehicle toward or away from the pavement markers can be measured during the time between the images.

[00293] This embodiment can utilize a lateral controller the same as or similar to ones that have already demonstrated satisfactory control using a continuous marking reference along the roadway. As shown in Figure 36, the spacing of the pavement markers 284 and 1284 alternate in distance such that the right-side pavement marker 284 are seen by multiple radar transceivers! 165 half the time and the left-side pavement markers 1284 are seen by the multiple radar transceivers 1175 the other half of the time. With alternate spacing like this, the number of radars in the radar array is reduced by half.

[00294] Figure 37 shows a schematic view of a radar sensor with multiple transmit/receive antennas. This embodiment can be used with an array of the radar transceivers 1165 and/or 1175. The radar processor 4260 starts a frequency synthesizer 4160 to provide a suitable FMCW signal, which may be amplified by power amplifier/phase shifters 4130 and transmitted to multiple transmit antennas set up in an array of paired antennas spaced at a distance dam apart. The receive antennas may be part of a paired antenna TX/RX (transmit/receive) combo array 4300 and receive return signals, which may be amplified by low noise amplifiers (LNA) 4150. The received signals are mixed with the transmit signal via modulators 4180. The signal output of the modulator 4180 is filtered via the filter block 4190 to provide the beat or immediate frequency from the modulator 4180. The filtered signal is sampled by the A/D converter 4120 and sent to the radar processor 4260 to compute the measured distance, velocity, phase, and/or amplitude. Figure 37 shows only six TX/RX pairs but many more pairs can be created. If only one pair is provided, then more radar transceivers would be needed to provide the array 1165 and/or 1175. The radar processor 4260 can control the power amplifier/phase shifters 4130 to turn on various antennas in time sequence to minimize interference between antenna pairs.

[00295] Figure 38 shows an embodiment of the array of radar transceivers 1165 and/or 1175 where six TX/RX antenna combos 4308 and 4306 are mounted in an array 4302 to form a multiple-antenna array of radars. The spacing 4304 of the six TX/RX combos is at a distance dant, which may be the same length as the width Pw of the pavement marker 284. For example, if the width of the pavement marker is 0.1 m, then the distance may be the same or less than 0.1 m. If the pavement marker separation dm is 3.0 m, then the total array length dtotal may be 3.0 m or longer. If using alternate spacing markers as shown in Figure 36, the array length dtotal would be 1.5 m or longer. With a 3.0 m array length, then 30 3.0 m / 0.1 m) TX/RX combos would be needed to provide continuous lateral distance for the pavement marker.

CONCLUSION

[00296] The foregoing embodiments, descriptions, and terms are set forth by way of illustration and example only and are not meant as limitations. The scope of the invention should be determined only by the following claims, claims presented in a continuing patent application or a post-issuance proceeding, and equivalents to such claims.