TRANSMITTER FOR RECEIVER POSITIONING

BACKGROUND

Field

[0001] Embodiments of the present invention generally relate to radio signal processing and, in particular, to a method and apparatus for processing radio signals to perform receiver positioning.

Description of the Related Art

[0002] Radio transmissions are used in various communications and positioning systems. For example, WiFi, using the IEEE 802.1 la, b, g, n, ac standards, has become ubiquitous for short range data communications. WiFi access points (also referred to as WiFi hotspots) comprise radio transceivers that broadcast 2.4 or 5GHz signals using a narrowband signal (e.g., 20 MHz). These access points can be used for low accuracy position location. Typically, received signal strength measurements of multiple such access point transmissions received at a receiver of a WiFi enabled device can be used by the receiver to estimate its distance from each transmitter, allowing the receiver to determine its approximate position relative to the transmitters through trilateration. Indoor position accuracy is 5-8 meters at best.

[0003] Some WiFi positioning techniques use signal characteristics of wireless access points to position connected devices. By knowing the ground truth position of access points and the signal strength detected by WiFi enabled devices, a receiver can provide location simply by listening to access point signals without connecting to WiFi network. This WiFi location approach has several advantages:

(1) It can work in areas where satellite positioning systems are unreliable, such as in dense urban areas and indoors.

(2) It uses existing Wi-Fi infrastructure to work, without any additional hardware installation, making it an affordable positioning option.

[0004] Some WiFi positioning techniques use signal fingerprint techniques where a database of signal strength measurements at each given location is stored and used to predict future positions. To remove ambiguities in position, multiple non -co-located transmitters are required. [0005] To create a functional positioning system, several WiFi transmitters need to exist in a given location. The narrowband nature of the signals severely constrains the functionality of the receiver when exposed to multipath signals. The reflected narrowband WiFi signals overlap in a multipath situation such that the receiver cannot discriminate between signals arriving directly from a transmitter and those that are reflected from objects or walls. As such, in a severe multipath environment, the receiver may not be able to derive a position at all. Additional transmitters may be required to ensure the receiver also receives signals directly from the transmitter with a very high signal strength. Such additional transmitters adds complexity and cost to the positioning system.

[0006] Therefore, there is a need for a method and apparatus that uses a transmission signal from a single transmitter for receiver positioning.

SUMMARY

[0007] Embodiments of the present invention generally relate to a method and apparatus that uses a transmission from a single transmitter for receiver positioning as shown in and/or described in connection with at least one of the figures.

[0008] According to a first aspect of the present invention there is provided a method for providing a position of a receiver using signals transmitted from a single transmitter, comprising: a) receiving a plurality of signals transmitted from a single transmitter, where each of the plurality of signals has a different propagation path; b) determining a motion of an antenna of the receiver; c) generating a plurality of phasor sequences, where each phasor sequence represents a hypothesis based on antenna motion and a direction of arrival estimate for each of the plurality of the received signals; d) compensating the received signals, a plurality of local signals or correlation results from correlating the received signals with the local signals using the plurality of phasor sequences based on the plurality of hypotheses regarding the receiver motion (e.g. the motion of the antenna of the receiver) and the direction of arrival to generate a plurality of compensated correlation results; e) determining a preferred hypothesis in the plurality of hypotheses for each received signal that optimizes each correlation result in the plurality of compensated correlation results; f) identifying a direction of arrival for the plurality of received signals using the determined hypothesis; and g) determining a position of the receiver from the direction of arrival of each received signal in the plurality of received signals.

[0009] In this way, by identifying a direction of arrival for (each of) the plurality of received signals, the position of the receiver may advantageously be determined using signals received from a single (e.g. WiFi) transmitter that have travelled along different propagation paths between the transmitter and receiver, and therefore have different angles of arrival at the receiver. Additionally, determining a receiver position based on the angle of arrival of a plurality of received signals provides increased positioning accuracy compared to using conventional techniques that are based on signal strength measurements. Through determining receiver position based on signals received from a single transmitter such as a WiFi access point, the present invention finds particular advantage in environments where satellite positioning systems are unreliable, such as dense urban areas and indoor environments.

[0010] The direction of arrival estimate for each phasor sequence may be based on one or more of: a known position of the transmitter, a known building model, an approximate position of the receiver. The approximate position of the receiver may be provided by one or more of: a global navigation satellite receiver, an inertial navigation system, a landmark within the known building model. The known building model may be a map or floor plan of a room, or may be a map of an urban canyon having buildings or other reflective surfaces. Estimating the direction of arrival in this way may be particularly useful to provide an initial estimate for the direction of arrival, such as shortly after initialization of the receiver.

[0011] A phasor sequence comprises a sequence of phasors that each comprise a phase angle and an amplitude based upon the motion of the antenna at a particular time t. Each phasor sequence is indicative of the phase and/or amplitude changes introduced into the received signal as a result of the component of the antenna motion along a particular direction as a function of time. The phasor sequence may also be indicative of other system parameters such as clock error. A compensated correlation result based on a phasor sequence indicative of the antenna motion along a particular direction (e g. the component of the antenna motion along a particular direction) will exhibit preferential gain for a signal received along that direction in comparison with a signal that is not received along that direction. Therefore, a phasor sequence that represents the component of the antenna motion along a particular direction is indicative of a direction of arrival hypothesis for that direction. For a particular correlation of a local signal with a received signal to produce a correlation result, a phasor sequence may be used to compensate at least one of the local signal, the received signal, and the correlation result, in order to generate a compensated correlation result.

[0012] The local signals may typically be generated using a frequency reference provided by a local oscillator (e.g. a quartz crystal) that may be a constituent component of the receiver.

[0013] The hypotheses may be based on a previously determined preferred hypothesis. The previously determined preferred hypothesis may be determined from a previous repetition of the method (e.g. for a previous epoch). Since the true values of the hypotheses correlate strongly between repetitions, the search space of the hypotheses may be narrowed over time to make the search less intensive while still converging to the true value.

[0014] The hypotheses may be offset from the previously determined preferred hypothesis based on an expected receiver motion. The hypotheses may be centered around a previously determined preferred hypothesis. Since the receiver is expected to move in a manner that obeys the laws of Physics, the hypotheses may be based on the expected (e.g. predicted) receiver motion. In this way, the number of hypotheses that need to be tested before determining the preferred hypothesis may be reduced.

[0015] The hypotheses may be further based on a local oscillator frequency error. The local oscillator frequency error may be referred to herein as the clock error. The local oscillator is typically used to generate the local signals, and is typically a constituent component of the receiver. The clock error is typically common to all the received signals. The hypotheses may therefore compensate or remove the clock error in order to enable calculation of a more accurate receiver position. The clock error may be determined using techniques known in the art.

[0016] Determining the motion of the antenna may include determining one or more of velocity, heading, and/or orientation of the antenna. The motion of the antenna may be measured (e.g. using an inertial navigation system) or estimated (e.g. based on patterns of motion in previous epochs). [0017] The method may further comprise selecting (e.g. reflected) signals based on an angle of reflection of the signal. The angle of reflection is typically defined as the angle between the reflected ray and the normal to the reflecting surface. Preferably, the signals are selected if the signals are determined to have an angle of reflection that is less than 70 degrees, preferably less than 60 degrees, more preferably less than 50 degrees. The selected signals may be used to determine the position of the receiver, with signals not meeting the reflection angle criteria being discarded or otherwise not contributing to the positioning solution Signals with a large angle of reflection (e.g., glancing signals) may be difficult to differentiate from direct signals and may result in erroneous position calculations.

[0018] The preferred hypothesis may correspond to a hypothesis that provides a compensated correlation result with the strongest signal-to-noise ratio or highest power. Determining a preferred hypothesis may include performing a mathematical optimization process across the plurality of compensated correlation results in order to find the compensated correlation result with the strongest signal-to-noise ratio or the highest power (e.g. the optimal or “best” correlation result). This may include producing a joint correlation output as a function (e g., summation) of the plurality of correlation results resulting from all the hypotheses and received transmitter signals.

[0019] The preferred hypothesis may be determined based on a cost function. Preferably, the preferred hypothesis may be determined by minimizing the cost function. The cost function may be applied to each set of correlation values for each received signal to find the optimal (e.g. highest power) correlation output corresponding to a preferred hypothesis or hypotheses. In this way, the direction of arrival for each received signal may be determined based on the preferred hypothesis for that signal.

[0020] The position of the receiver may be determined based on one or more of: a transmission time stamp, a received signal time stamp, an estimated transmission path length, a transmitter position, a reflection position, a building model, a time difference of arrival between received signals, a signal strength of received signals. For example, the direction of arrival may be combined with the room map and the known transmitter location to determine the location of the receiver, such as by using the intersection of the direction of arrival vectors for the received signals. Time of arrival and time difference of arrival techniques can be used to improve the determined receiver position. For example, particular signals may be selected for the time of arrival processing. Signal strength may be used to improve or augment the position calculation using direction of arrival and/or time of arrival.

[0021] The transmitter may have a known location. Preferably, the transmitter is one of: a WiFi transmitter, a Bluetooth transmitter, a cellular transmitter, a communications satellite, or a positioning satellite. The transmitter may be a fixed transmitter (e.g. having a fixed, known location such as a WiFi, Bluetooth or cellular transmitter) or may be a moving transmitter (e.g. having a known trajectory, such as a communications or positioning satellite).

[0022] The method may further comprise performing the steps a) to g) using signals transmitted from a second single transmitter, and (e.g., subsequently) combining the receiver positions determined using each of the single transmitters to provide a receiver position. In this way, the receiver position is independently determined, which may be combined to provide a more accurate receiver position.

[0023] The method may further comprise (e.g. iteratively) repeating steps a) to g) to provide one or more subsequent receiver positions. Accordingly, the position of the receiver may be updated in order to track its position over time. A geocoordinate map may be produced identifying the positions of the receiver as it moves.

[0024] According to second aspect of the present invention there is provided an apparatus for performing signal correlation within a signal processing system, comprising at least one processor and at least one non-transient computer readable medium for storing instructions that, when executed by the at least one processor, causes the apparatus to perform operations comprising: a) receiving a plurality of signals transmitted from a single transmitter, where each of the plurality of signals has a different propagation path; b) determining a motion of an antenna of the receiver; c) generating a plurality of phasors sequences, where each phasor sequence represents a hypothesis based on antenna motion and a direction of arrival estimate for each of the plurality of the received signals; d) compensating the received signals, a plurality of local signals or correlation results from correlating the received signals with the local signals using the plurality of phasor sequences based on the plurality of hypotheses regarding the receiver motion and the direction of arrival to generate a plurality of compensated correlation results; e) determining a preferred hypothesis in the plurality of hypotheses for each received signal that optimizes each correlation result in the plurality of compensated correlation results; f) identifying a direction of arrival for the plurality of received signals using the determined hypothesis; and g) determining a position of the receiver from the direction of arrival of each received signal in the plurality of received signals.

[0025] The apparatus of the second aspect of the invention therefore provides all of the advantages described above with reference to the first aspect. The apparatus may be configured to perform the method of any of the examples discussed above with reference to the first aspect of the invention.

[0026] According to another aspect of the present invention there is provided an apparatus for performing signal correlation within a signal processing system, comprising at least one processor and at least one non-transient computer readable medium for storing instructions that, when executed by the at least one processor, causes the apparatus to perform the method as described above and herein.

[0027] These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] So that the manner in which the above recited features of the present invention can be understood in detail, a particular description of the invention, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0029] FIG. 1 depicts a block diagram of an exemplary scenario having a receiver that determines a receiver position using signals transmitted by a single transmitter in accordance with at least one embodiment of the invention;

[0030] FIG. 2 is a block diagram of the receiver of FIG. 1 in accordance with at least one embodiment of the invention; [0031] FIG. 3 depicts an exemplary scenario of operation of the receiver of FIGs. 1 and 2 in accordance with at least one embodiment of the invention;

[0032] FIG. 4 is a flow diagram of a method of operation for the signal processing software in accordance with at least one embodiment of the invention; and

[0033] FIG. 5 is a flow diagram of a method of operation of the receiver positioning software in accordance with at least one embodiment of the invention.

DETAILED DESCRIPTION

[0034] Embodiments of the present invention comprise apparatus and methods that use a transmission from a single transmitter for receiver positioning. Digital communications systems such as cellular, Bluetooth or WiFi utilize encoded digital signals to improve communication throughput and security. These systems utilize some form of deterministic digital code to facilitate signal acquisition, e.g., acquisition codes. Such a digital code is determined by the receiver and repeatedly broadcast by the transmitter to enable the receivers to acquire and receive the transmitted signals. Using such deterministic codes combined with an accurate motion model of a receiver, embodiments of the invention are useful for isolating a signal propagation path along a specific direction of arrival (DoA). The signal may propagate directly (e.g., line-of-sight (LOS)) or via a reflection (e.g., non-line-of-sight (NLOS)). The technique for performing this DoA determination using receiver motion information is known as SUPERCORRELATION™ and is described in commonly assigned US patent 9,780,829, issued 3 October 2017; US patent 10,321,430, issued 11 June 2019; US patent 10,816,672, issued 27 October 2020; US patent publication 2020/0264317, published 20 August 2020; and US patent publication 2020/0319347, published 8 October 2020, which are hereby incorporated herein by reference in their entireties. In one embodiment, the receiver and transmitter are operating within a room. The receiver uses this DoA data regarding transmissions from a single transmitter in combination with a map (floor plan) of the room and the location of the transmitter within the room to determine the position of the receiver within the room. The computed position of the receiver is relative to the known location of the transmitter. As such, in most situations, the receiver operates substantially horizontal to the transmitter. Consequently, DoA data (i.e., azimuth and elevation) is not necessary, such that, angle of arrival (AoA) data (i.e., azimuth) will suffice for deriving a receiver position. In the following description, the more general DoA data is used, but it should be understood that AoA data may be substituted for DoA data in situations where elevation is not necessary throughout this description.

[0035] In one exemplary embodiment, a receiver may be transported through a room containing a single transmitter (e.g., WiFi, Bluetooth, or cellular) and be able to identify signal propagation paths (LOS and NLOS). In one embodiments, the transmitter transmits a narrow bandwidth signal, e.g., about 20MHz. With knowledge of the location of the transmitter (e.g., a WiFi access point or hotspot) and knowledge of the room dimensions (floor plan), embodiments of the invention determine the propagation paths for LOS and NLOS signals. The receiver isolates the LOS and NLOS signals to use all the signals as if they were transmitted by different transmitters from different directions having different transmission path lengths (i.e., a virtual transmitter is defined at each reflection point of the NLOS signals). Processing of these isolated signals results in a position determination for the receiver. The functions of embodiments of the invention may be embedded into cellular telephones, Internet of Things (loT) devices, mobile computers, tablets, positioning tags and the like. Embodiments find use on any moving receiver that receives signals having a code that can be correlated with a locally generated code. Embodiments may be useful in processing low bandwidth signals that are particularly difficult to use for location purposes. The receiver need only be able to utilize the deterministic acquisition code contained in the received signal. Although the receiver may receive the signal and utilize a full data message of the signal (i .e., WiFi, Bluetooth or cellular enabled), the receiver does not have to be fully enabled.

[0036] As the receiver traverses an area, it collects DoA data for the transmitter and the virtual transmitters formed by signal reflections, i.e, at least two versions of the transmitted signal (two reflected signals, or a direct and reflected signal) are needed to determine a receiver position. The received signals appear to the receiver as multiple signals transmitted from the direct (actual transmitter) and reflection points (synthetic transmitters) where the transmitters use synchronized clocks. As such, the receiver is capable of extracting clock error between the transmitter clock and receiver clock because the clock error is common to all received signals. When the receiver is stationary, the clock error is the only frequency offset that is evident in the correlation results. Consequently, the position error otherwise caused by this clock error can be mitigated (or otherwise removed or compensated) to enable calculation of an accurate receiver position.

[0037] Initially, the receiver knows its approximate position through the use of a global navigation satellite system (GNSS) receiver and/or an inertial guidance system. The receiver may also know an initial position of a door through which the receiver enters a room (or other landmark) and use the door/landmark position as a starting position. From the receiver approximate position, a plurality of DoA vectors, a known location of the transmitter and room dimensions (i.e., room map or floor plan), embodiments of the invention accurately compute the position of the receiver relative to the transmitter location. The relative position within the room can then be translated to a geocoordinate, if desired. As receiver positions are computed, a geocoordinate map may be produced identifying the positions of the receiver as it moves. As such, embodiments of the invention provide a method and apparatus for generating improved simultaneous location and mapping (SLAM) within an indoor space that is served by a single transmitter.

[0038] Although the embodiment described above uses a single transmitter, other embodiments may use multiple transmitters where signals from each transmitter are processed in the manner described for the single transmitter above to determine independent receiver positions. The receiver positions generated by processing the signals from each transmitter may be combined to more accurately determine the receiver position.

[0039] Some embodiments may perform the signal processing locally on the moving platform. In other embodiments, the transmitter location, room dimensions, receiver motion information, and receiver position information may be gathered at the moving platform and communicated (wired or wirelessly) to a server for remote processing in real-time or at a later time.

[0040] FIG. 1A and IB depict a block diagram of an exemplary scenario 100/150 having at least one receiver 102 for receiving signals broadcast from a single transmitter 104 in accordance with at least one embodiment of the invention. FIG. 1A depicts the scenario 100 where at least one receiver 102 has entered a room 106 at position 114. FIG. IB depicts the scenario 150 where the at least one receiver 102 has moved through the room 106 to position 116. As the at least one receiver 102 moves through the room 106, the receiver 102 receives signals from the signal transmitter 104 and determines an accurate receiver position. In the depicted scenario 100/150, the at least one receiver 102 is operating in a high multipath environment such as indoors within a room 106. In other embodiments, the receiver 102 may be operating in an urban canyon having buildings or other reflective structures proximate the receiver 102. Each of the at least one receiver 102 comprises a positioning module 108 configured to receive and process signals transmitted by the transmitter 104.

[0041] In the embodiment shown in FIG. 1A, the receiver 102 enters the room 106 knowing its approximate position either from: (1) a global navigation satellite (GNSS)receiver and/or an inertial navigation system (INS) or (2) position knowledge from a map (e.g., enter through a door 110 or other landmark with a known location within the room 106). The positioning module 108 uses a known location of the transmitter 104 within the room 106, the known receiver initial position, a map or floor plan of the room and receiver motion information (a motion model) in combination with the received signals that arrive directly from the transmitter (LOS signals) and reflected signals (NLOS signals) to determine an accurate receiver position as the receiver traverses the room to position 116 of FIG. IB.

[0042] As described in detail below, the at least one receiver 102 uses a SUPERCORRELATION™ technique as described in commonly assigned US patent 9,780,829, issued 3 October 2017; US patent 10,321,430, issued 11 June 2019; US patent 10,816,672, issued 27 October 2020; US patent publication 2020/0264317, published 20 August 2020; and US patent publication 2020/0319347, published 8 October 2020, which are hereby incorporated herein by reference in their entireties. The technique determines a direction of arrival (DoA) of signals received at a receiver (i.e., received signals) from the transmitter - both LOS and NLOS signals. As the receiver 102 moves (represented by arrow 112), the positioning module 108 computes motion information representing motion of the receiver 102. The motion information is used to perform motion compensated correlation of the received signals. From the motion compensated correlation process, the positioning module 108 estimates the DoA of the received signals. The positioning module 108 uses the room map and the transmitter location along with the DoA data to determine a location of the receiver 102. The intersection of a plurality of DoA vectors generated as the receiver moves along path 112 can be used to identify the location of the receiver 102 as described in detail below. In other embodiments, the DoA vectors are used to isolate received signals and time of arrival (TOA) or time difference of arrival (TDOA) techniques can be used to process correlation results associated with the isolated signals to determine the receiver position. In other embodiments, received signal strength may also be used to improve or augment the position calculation using DoA and/or TOA. Note that, because the positioning module 108 can discern the DoA of the narrowband signals which overlap in a multipath environment, the positioning module can isolate reflected signals and use those signals as if they were transmitted by transmitters located at the image points (i.e., the image points form virtual transmitter locations).

[0043] In one embodiment, the single transmitter is a WiFi transmitter having transmissions at about 2.4 GHz or 5 GHz with a signal bandwidth of 20 MHz. Other embodiments may operate using other signals such as from Bluetooth (i.e., a 1MHz channel width) or cellular (i.e., ranging from 1 to 20 MHz depending on the standard) transmitters having fixed, known locations. In other embodiments, the single transmitter may have a known moving location (for example a known trajectory). Such examples include a positioning or communications satellite, from which the receiver may receive multiple signals due to reflections (e.g. off building surfaces).

[0044] FIG. 2 is a block diagram of the receiver 102 in accordance with at least one embodiment of the invention. The receiver 102 comprises a mobile platform 200, an antenna 202, receiver front end 204, signal processor 206, and motion module 228. The receiver 102 may form a portion of a laptop computer, mobile phone, tablet computer, Internet of Things (loT) device, purpose built positioning device, etc.

[0045] In the receiver 102, the positioning module 108 and the antenna 202 are an indivisible unit where the antenna 202 moves with the positioning module 108. The operation of the SUPERCORRELATION™ technique operates based upon determining the motion of the signal receiving antenna. Any mention of motion herein refers to the motion of the antenna 202. In some embodiments, the antenna 202 may be separate from the positioning module 108. In such a situation, the motion estimate used in the motion compensated correlation process is the motion of the antenna 202. In most scenarios, the motion of the positioning module 108 is the same as the motion of the antenna 202 and, as such, the following description will assume that the motion of the positioning module 108 and antenna 202 are the same. [0046] The positioning module 108 comprises a receiver front end 204, a signal processor 206 and a motion module 208. The receiver front end 204 downconverts, filters, and samples (digitizes) the received signals in a manner that is well-known to those skilled in the art. The output of the receiver front end 204 is a digital signal containing data. The data of interest is a deterministic training or acquisition code used by the transmitter to synchronize the transmission to a receiver, e.g., a WiFi transceiver.

[0047] The signal processor 206 comprises at least one processor 210, support circuits 212 and memory 214. The at least one processor 210 may be any form of processor or combination of processors including, but not limited to, central processing units, microprocessors, microcontrollers, field programmable gate arrays, graphics processing units, digital signal processors, and the like. The support circuits 212 may comprise well-known circuits and devices facilitating functionality of the processor(s). The support circuits 212 may comprise one or more of, or a combination of, power supplies, clock circuits, analog to digital converters, communications circuits, cache, displays, and/or the like.

[0048] The memory 214 comprises one or more forms of non-transitory computer readable media including one or more of, or any combination of, read-only memory or random-access memory. The memory 214 stores software and data including, for example, signal processing software 216, positioning software 232 and data 218. The data 218 comprises the receiver location 220, direction of arrival (DoA) vectors 222 (collectively, DoA data), transmitter location 224, motion information 226, a room map or floorplan 228, and various other data used to perform the SUPERCORRELATION™ processing. The signal processing software 216, when executed by the one or more processors 210, performs motion compensated correlation upon the received signals to estimate the DoA vectors for the received signals. The motion compensated correlation process is described in detail below.

[0049] As described below in detail, the DoA vectors 222 and receiver position 220 are used by the positioning software 208 to improve the accuracy of the receiver position. The data 218 stored in memory 214 may also include signal estimates, correlation results, motion compensation information, motion information, motion and/or other receiver parameter hypotheses, position information and the like (e g., other data 230). [0050] The motion module 208 generates a motion estimate for the antenna 202. The motion module 208 may comprise an inertial navigation system (INS) 234 as well as a global navigation satellite system (GNSS) receiver 236 such as GPS, GLONASS, GALILEO, DEIBOU, etc. The INS 234 may comprise one or more of, but not limited to, a gyroscope, a magnetometer, an accelerometer, and the like. To facilitate motion compensated correlation, the motion module 208 produces motion information (sometimes referred to as a motion model) comprising at least a velocity of the antenna 202 in the direction of interest, i.e., an estimated direction of a source of a received signal or a reflection point of a received reflected signal. In some embodiments, the motion information may also comprise estimates of platform orientation or heading including, but not limited to, pitch, roll and yaw of the module 200/antenna 202. Generally, as described in more detail below, the receiver 102 may test every direction and iteratively narrow the search to one or more directions of interest. In some embodiments, the receiver 102 uses a priori knowledge of the receiver position, room dimensions, transmitter location, and the like to narrow the range of parameters to be searched.

[0051] FIG. 3 depicts a scenario 300 of operation of the receiver 102 of FIGs. 1 and 2 in accordance with at least one embodiment of the invention. The scenario 300 comprises the receiver 102 moving through a room 106. As the receiver 102 traverses the area, the receiver 102 computes a DoA vectors 300, 302 and 304 (for clarity only three vectors are depicted). The three DoA vectors 300, 302, 304 intersect at the location of the receiver 102. Receiver position may be calculated with as few as two received signals. In various embodiments, the DoA vectors may be computed periodically, intermittently, or continuously as the receiver moves. Additional vectors may be used to converge the solution onto an accurate receiver location. The DoA vectors may be processed at a remotely located server to improve the accuracy of the position of the receiver 102.

[0052] In an urban environment, some DoA vectors 300 are derived from a combination of line-of-sight (LOS) signals and/or some DoA vectors 302 and 304 are derived from non- line-of-sight (NLOS) signals, i.e., LOS vectors represent signals that are transmitted directly from the transmitter 104 to the receiver 102, while NLOS vectors may be reflected from structures (e.g., walls of a room 106) in the vicinity of the receiver 102. [0053] The structures causing reflections are modeled in a building model - a floorplan or map. The model in conjunction with ray tracing techniques can be used to estimate the DoA of reflected signals. Consequently, the path of the reflected transmitter signal is estimated, and the reflected signals may be used in the receiver’s position calculation. Some signals may be reflected multiple times before being received.

[0054] In other embodiments, one or more receivers 102 may collect all transmitter signals, LOS and NLOS, over a period of time while the receiver(s) are traversing an area. These collected signals may be processed using the receiver positioning techniques described herein to create a signal profile for a region. The signal formula will contain DoA vector intersection regions that identify receiver positions over time.

[0055] Typically, when using a DoA positioning technique, a vector intersection location is not a point, but rather it’s a region or area due to the probabilistic nature of the DoA vectors, i.e., the direction of each vector has an error distribution and the intersection forms a region rather than a point. The region will have a maximum that defines the position of the receiver 102.

[0056] The forgoing embodiment performs the receiver vector and position determination within the receiver 102. In other embodiments, the data (i.e., emitter data) for producing DoA vectors, DoA vectors themselves, position information, etc. may be transmitted from the receiver to a server for processing to produce the receiver positions.

[0057] In operation, the receiver 102 performs the SUPERCORRELATION™ technique to motion compensate the received signals arriving from the transmitter 104. These signals may arrive unimpeded as a direct LOS signal 300. Other signals along paths 302 and 304 reflect from the walls (e.g., 308 and 310) and arrive at the receiver 102. For example, the transmitted radio signal leaves the transmitter 104 and propagates to the wall 308 where the signal contacts the wall 308 and an angle of incidence (<I). The reflected signal leaves the wall 308 and an angle of reflection (<R) that is equal to <1. At a point 312 along the wall, the transmitted signal reflects from the wall and the signal on path 302 impinges upon the receiver antenna. The same reflective process occurs for wall 310 and signal path 304. The DoA of these signals forms the DoA vectors computed by the receiver. To improve clock error and position calculations, the receiver may select signals only having reflection angles in a specific range to ensure the DoA results from a small angle of reflection, e.g., less than 50 degrees with respect to the normal to the reflecting surface. Signals with a large angle of reflection (i.e., glancing signals) may be difficult to differentiate from direct signals and result in erroneous position calculations.

[0058] To determine an accurate receiver position, the receiver 102 has a general understanding of its position from the motion module and has an accurate understanding of the motion of the receiver. The receiver 102 also has knowledge of the floorplan and an accurate location of the transmitter. The receiver 102 receives the signals from the transmitter 104 and correlates those signals with locally generated signals to determine correlation results. In some embodiments, the correlation result of each received signal may be used to produce a time of arrival for each signal. These correlation results are motion compensated using the receiver motion to correct for doppler and doppler rate changes due to the receiver motion and extend the coherent integration period of the receiver such that accurate correlation results are used in determining time of arrival to a sub-wavelength level.

[0059] Since ray tracing provides only an estimate of the DoA, the DoA vectors require processing to enable accurate receiver positioning. The DoA vector estimates are used to define a search space of directions that signals may arrive. The receiver produces a plurality of phasor sequence hypotheses, where each hypothesis represents a phasor sequence of signal phase that may occur for a signal arriving at a particular DoA. By testing each hypothesis, the receiver converges upon an accurate DoA for each signal. As such, a signal arriving from a particular direction can be isolated from other reflected signals and the isolated signal processed with other isolated signals to generate accurate receiver position information that can be used to improve the GNSS/INS generated approximate position. Without the use of a motion compensated correlation technique (e.g., SUPERCORRELATION™) the narrowband signals could not be isolated to enable a single transmitter to facilitate receiver position improvement.

[0060] FIG. 4 is a flow diagram of a method 400 of operation for the signal processing software 216 in accordance with at least one embodiment of the invention. The method 400 may be implemented in software, hardware or a combination of both (e.g., using the signal processor 206 of FIG. 2). [0061] The method 400 begins at 402 and proceeds to 404 where signals are received at a receiver from a remote source (e.g., transmitter 104) in a manner as described with respect to FIGs. 1, 2 and 3. Each received signal comprises a synchronization or acquisition code, i.e., a deterministic code, extracted from the radio frequency (RF) signal received at the antenna. The process of downconverting the RF signal and extracting the digital code is well known in the art. At 406, the method 400 receives motion information from the motion module 208 of FIG. 2. The motion information comprises an estimate of the motion of the receiver 102 of FIG. 1, e.g., one or more of velocity, heading, orientation, etc.

[0062] At 408, the method 400 generates a plurality of phasor sequence hypotheses related to a direction of interest of the received signal, e.g., direction of the transmitter or direction of one or more reflections. These hypotheses comprise a plurality of local signals representing code phase estimates. Each phasor sequence hypothesis comprises a series of phase offsets that vary with parameters of the receiver such as motion, frequency, DoA of the received signals, and the like. The signal processing correlates a local code encoded in a local signal with a code encoded in the received RF signal. In one embodiment, the phasor sequence hypotheses are used to adjust, at a sub-wavelength accuracy, the carrier phase of the local code over one or more periods (lengths) of the received code. Such adjustment or compensation may be performed by adjusting a local oscillator signal (e.g. generated by a local signal generator, such as a frequency synthesizer, using a frequency reference provided by a local oscillator of the receiver), the received signal(s), or the correlation result to produce a phase compensated correlation result. The signals and/or correlation results are complex signals comprising in- phase (I) and quadrature phase (Q) components. The method applies each phase offset in the phasor sequence to a corresponding complex sample in the signals or correlation results. If the phase adjustment is or includes an adjustment for receiver motion, then the result is a motion compensated correlation result. For each received signal, at 410, the method 400 correlates the received signals with a set (plurality) of direction hypotheses containing estimates of a phase offset necessary to accurately correlate the received signals arriving from particular directions. There is a set of hypotheses representing a search space for each received signal and each parameter of interest, e.g., motion, frequency, frequency rate, DoA, etc.

[0063] The motion estimates are typically hypotheses of the receiver motion in a direction of interest such as in the direction of the transmitter or a direction of a reflection of interest. At initialization, the direction of interest (e.g., DoA of the received signals) may be inaccurately estimated using ray tracing based on the known position of the transmitter and the known floor plan. Over time, as the hypotheses for DoA are tested, the receiver converges on an accurate DoA. As the receiver moves, the method 400, using the motion information, may anticipate the direction change for the signals and alter the hypothesis search space accordingly. There is very strong correlation between the true values of these hypotheses between code repetition, such that the initial search might be intensive, but subsequent processing only requires tracking of the parameters in the receiver as they evolve. Consequently, subsequent phase compensation is performed over a narrow search space.

[0064] In one embodiment, since the signal is received from a single transmitter, the set of hypotheses for newly received signals from the transmitter include a group of phasor sequence hypotheses using the expected Doppler and Doppler rate and/or last Doppler and last Doppler rate used in receiving the prior signal from that transmitter. The values may be centered around the last values used or the last values used additionally offset by a prediction of further offset based on the expected receiver motion. At 410, the method 400 correlates each received signal with that signal’s set of hypotheses. The hypotheses are used as parameters to form the phase- compensated phasors to phase compensate the correlation process. As such, the phase compensation may be applied to the received signals, the local frequency source (e.g., an oscillator), or the correlation result values. The hypotheses collectively form an N ^v search space, where N is the number of hypotheses and V is the number of variables (parameters) that need to be defined. In addition to searching over the DoA and receiver motion space, the method 400 may also apply hypotheses related to other parameters such as oscillator frequency to correct frequency and/or phase drift, or heading to ensure the correct motion compensation is being applied. The result of the correlation process is a plurality of phase-compensated correlation results - one phase-compensated correlation result value for each hypothesis for each received signal.

[0065] At 412, the method 400 processes the correlation results to find the “best” or optimal result for each received signal, i.e., isolate each signal using an optimal DoA hypothesis. In one embodiment, the method 400 produces a joint correlation output as a function (e g., summation) of the plurality of correlation results resulting from all the hypotheses and received transmitter signals. The joint correlation output may be a single value or a plurality of values that represent the parameter hypotheses (preferred hypotheses) that provide an optimal or best correlation output. In general, a cost function is applied to each set of correlation values for each received signal to find the optimal correlation output corresponding to a preferred hypothesis or hypotheses.

[0066] At 414, the method 400 identifies the DoA vector of each received signal from the optimal correlation result for the signal. The received signals along the DoA vector typically have the strongest signal to noise ratio and represent line of sight (LOS) propagation or NLOS propagation having a single reflection point. As such, using motion compensated correlation enables the receiver 102 to identify the DoA vector of the received signal(s).

[0067] In other embodiments, rather than using the largest magnitude correlation value, other test criteria may be used. For example, the method 400 may monitor the progression of correlations as hypotheses are tested and apply a cost function that indicates the best hypotheses when the cost function reaches a minimum (e g., a small hamming distance amongst peaks in the correlation plots). As such, the joint correlation output may be a joint correlation value or a group of values. In other embodiments, additional hypotheses may be tested in addition to the DoA hypotheses to, for example, ensure the motion compensation (i.e., speed and heading) is correct.

[0068] At 416, the method 400 may use the DoA associated with the preferred hypotheses to isolate a plurality of the received signals and their associated motion compensated correlation results, e g., signals with large angles of reflection (i.e. glancing signals) may be ignored or particular signals may be selected for TOA processing to improve a position attained through DoA intersect processing. These correlation results may be used by the positioning software to improve the current receiver position estimate as described with respect to FIG. 5. The method 400 ends at 416. The angle of reflection of a received signal may be computed using techniques known in the art. For example, one or more of DoA information, time difference of arrival information, and a known location of the single transmitter, may be used to compute the reflection position of a received NLOS signal and hence the angle of reflection.

[0069] FIG. 5 is a flow diagram of a method 500 of operation of the positioning software 232 in accordance with at least one embodiment of the invention. The method 500 may be performed locally within the receiver or may be performed remotely on a server. If performed remotely, the estimated receiver position, correlation results for the isolated received signals, and other information are transmitted from the receiver to the remote server for processing in accordance with method 500.

[0070] The method 500 begins at 502 and proceeds to 504 where the method 500 accesses a receiver position estimate, transmission information and the correlation results for the isolated received signals. The position estimate is the best-known current position of the receiver (i.e., an initial approximate position, the immediately prior position calculation, or an average of several prior position calculations). The transmission information comprises any information regarding the transmitter and the transmission paths of the isolated signals that is required to compute position from the received signals. For example, depending on the method used to compute the position, the transmission information may comprise, but is not limited to, one or more of the following: a transmission time stamp, a received signal time stamp, an estimated transmission path length, a transmitter position, a reflection position, etc.

[0071] At 506, in one embodiment, the method 500 determines a time difference of arrival (TDOA) for the isolated received signals based on the motion compensated correlation results and the transmission information. In lieu of the TDOA information, the method may produce direction or angle of arrival information or time of arrival information, or time of flight, or other positioning metrics known to those skilled in the art. In general, this step produces whatever information is required to compute the receiver position.

[0072] At 508, using the time difference of arrival information for each received signal, the method 500 computes a position of the receiver. In other embodiments, time of arrival or direction/angle of arrival techniques may be used to compute the position. All of these positioning techniques (also known as localization techniques) are well known to those skilled in the art.

[0073] At 510, the method 500 updates the position estimate with the computed receiver position. At 512, the method queries whether the method 500 should continue to determine receiver positions. If the query is affirmatively answered, the method 500 returns to 504 along path 516. If the query is negatively answered, the method 500 ends at 514. [0074] Here multiple examples have been given to illustrate various features and are not intended to be so limiting. Any one or more of the features may not be limited to the particular examples presented herein, regardless of any order, combination, or connections described. In fact, it should be understood that any combination of the features and/or elements described by way of example above are contemplated, including any variation or modification which is not enumerated, but capable of achieving the same. Unless otherwise stated, any one or more of the features may be combined in any order.

[0075] As above, figures are presented herein for illustrative purposes and are not meant to impose any structural limitations, unless otherwise specified. Various modifications to any of the structures shown in the figures are contemplated to be within the scope of the invention presented herein. The invention is not intended to be limited to any scope of claim language.

[0076] Where “coupling” or “connection” is used, unless otherwise specified, no limitation is implied that the coupling or connection be restricted to a physical coupling or connection and, instead, should be read to include communicative couplings, including wireless transmissions and protocols.

[0077] Any block, step, module, or otherwise described herein may represent one or more instructions which can be stored on a non-transitory computer readable media as software and/or performed by hardware. Any such block, module, step, or otherwise can be performed by various software and/or hardware combinations in a manner which may be automated, including the use of specialized hardware designed to achieve such a purpose. As above, any number of blocks, steps, or modules may be performed in any order or not at all, including substantially simultaneously, i.e., within tolerances of the systems executing the block, step, or module.

[0078] Where conditional language is used, including, but not limited to, “can,” “could,” “may” or “might,” it should be understood that the associated features or elements are not required. As such, where conditional language is used, the elements and/or features should be understood as being optionally present in at least some examples, and not necessarily conditioned upon anything, unless otherwise specified. [0079] Where lists are enumerated in the alternative or conjunctive (e.g., one or more of A, B, and/or C), unless stated otherwise, it is understood to include one or more of each element, including any one or more combinations of any number of the enumerated elements (e.g. A, AB, AC, ABC, ABB, etc.). When “and/or” is used, it should be understood that the elements may be joined in the alternative or conjunctive.

[0080] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.