Device and Method for Deploying and Controlling Active Taps

RELATED APPLICATIONS

[0001 ] This application claims the priority of Australian Provisional Patent Application No. 2021903249 in the name of Shaun Cunningham, which was filed on 10 October 2021 , entitled “Device and Method for Deploying and Controlling Active Taps” and the specification thereof is incorporated herein by reference in its entirety and for all purposes.

FIELD OF INVENTION

[0002] The present invention relates generally to signal distribution networks carrying signals on coaxial cables where active taps are introduced to improve network performance and where additional tap functionality needs to be introduced and controlled. The term “active tap” refers to a tap which draws energy from a power source in order to provide amplification, mixing, switching adaptive control, or other processing of signals which are coupled into the tap.

[0003] The invention has been developed primarily for use in Hybrid Fibre Coaxial (HFC) networks and will be described hereinafter with reference to this application. However, it will be appreciated that the invention is not limited to this field of use, and may provide benefits in other network types using other modulation schemes.

BACKGROUND OF THE INVENTION

[0004] As the world’s demand for entertainment and information content increases, new means of distributing this content are being developed. Cable TV (CATV) networks have been deployed since the 1980’s and are an example of a telecommunication network that was built to offer subscribers a significantly increased range of content. Coaxial cable has traditionally been used for such distribution networks because it has relatively low cost and because it simplifies connection to network devices and customers premises. Network coaxial cables consist of outer plastic jacket, a conductive outer sheath, a low loss insulator and central conductor. Although original CATV networks were entirely made from coaxial cables, modern networks often employ a so-called Hybrid Fibre Coax (HFC) structure where connectivity is provided using optical fibres from the core network to Nodes where data is converted to electrical signals and conveyed to customer’s premises using coaxial cables. [0005] Although the content capacity of CATV networks has previously met subscriber’s requirements, there is a growing demand for subscriber customised content, for example in the form of streaming video on demand and other internet related sources of information or entertainment content. As a result, network operators are under increased pressure to make use of the full bandwidth capacities of their networks and/or to increase their network bandwidth capacities by upgrading network elements.

[0006] Figure 1 provides a block diagram of a conventional HFC network architecture. Signals are conveyed to and from a ‘Head End’ installation 100 using optical fibres 101 or satellite links. These links carry data at many gigabits per second and provide connectivity to the internet and other information service providers such as cable TV operators. Signals are then conveyed from the Head End to ‘Nodes’ 102 which are located close to groups of customers. At the Nodes, optical signals are then converted to and from electrical signals 103 which propagates through coaxial cables to and from customers.

[0007] Unlike fibre transmission mediums, coaxial cables are relatively lossy which means that electrical signals quickly degrade when travelling only modest distances through cable. To combat this degradation, network designers install amplifying devices along the cable route to boost signals and overcome degradation due to loss. For example, amplifiers may be installed every 400 metres along the cable path to amplify signals travelling both ‘downstream’ toward the subscribers and ‘upstream’ toward the Head End, i.e., bi-directionally.

[0008] In the portion of the coaxial network closest to the Node, coaxial amplifiers conventionally carry bidirectional signals between two signal ports without any splitting or combining of the signal path. These are generally referred to as ‘Trunk’ amplifiers 104.

[0009] When the signal path nears the intended subscriber group, it is advantageous for amplifying devices to not only amplify signal levels, but also to assist in the geographic distribution of these signals. Therefore, amplifiers may include signal splitting and combining devices which facilitate a tree-like signal distribution network architecture. These amplifiers split downstream signals and send them to multiple subscriber groups and combine upstream signals from multiple subscriber groups and send them to the Head End. These splitting and combing amplifiers are generally referred to as ‘Bridging Amplifiers’ 105 or colloquially as ‘Bridgers’ and typically have a 1 :2 or 1 :3 split/combine ratio. [0010] Another class of amplifying device is called a ‘Line Extender’ 106. This amplifier type is similar to a Trunk Amplifier, except it is optimised for use closer to the network customer. For example, the gain and I or signal levels produced or received by these Line Extenders may be significantly less than those conveyed by Trunk Amplifiers.

[0011 ] In the final section of a HFC network, ‘Taps’ 107 are installed on the coaxial cable as it passes a customer’s premises and a drop cable 108 is run from the tap into the customer’s premises. This connection usually terminates inside the premises at a network element such as a modem 109 which decodes network signals and provides customers with a local area network to which they can connect devices such as TVs or computers. A modem is an example of what is referred to generally as Customer’s Premises Equipment (CPE).

[0012] Taps are conventionally passive devices which couple signals from a ‘Through’ connection to a number of drop cables which allow customers to connect to the network. Conventional taps rely on ferrite-based transformers to couple signals at the appropriate levels to and from drop cables. Conventional taps do not provide amplification for any signals as they pass through the tap. The advantage of this type of network element is that they are relatively low cost and are insensitive to spectrum allocation and usage within the network bandwidth. The disadvantage is that they have limited transmission bandwidth and are excessively lossy at high frequencies which prevents the overall network being significantly upgraded.

[0013] In conventional networks, signals sent from the customer’s premises upstream to the Node traverse the same path as downstream signals, but occupy a different portion of the network spectrum.

[0014] Figure 2 shows the architecture of a conventional passive tap 200 comprising and upstream port 201 , a downstream port 202 and a plurality of N drop ports 203 coupled to drop cables 204 which lead to customer’s premises equipment 205. The N drop ports of the tap are coupled to N ports of an N-way power divider/combiner 206 which in turn is coupled to the main network cable using a directional coupler 207. N is typically 2, 4 or 8. Signals flow through the tap bi-directionally between each port. Each signal path has sufficient bandwidth to convey the entire bandwidth of upstream plus downstream channels simultaneously. [0015] Network operators are continually striving to provide increased data rates to customers. This means that networks need to be upgraded to provide wider bandwidths, either by increasing modulation complexity or by extending the upper frequency limit of the network.

[0016] One technique which can be employed to increase network bandwidth is to introduce active taps comprising amplifying circuitry which is able to overcome transmission losses at high frequencies which conventionally limit the upper operating frequency of the network. The inventor has lodged Australian Patent applications AU:2021900552 and AU:2021902022 which relate to novel network elements including active taps comprising amplifiers and mixers which extended the signal bandwidth of coaxial distribution networks. These patents describe the structure and function of active taps, but do not address issues such as deployment methods and management of these new types of network devices after they are installed.

[0017] When any type of active tap is installed into a network, a large number of taps will be coupled together in series, for example 10-20 taps. If each tap exhibits a slight, frequency-localised gain anomaly, for example a 0.5dB dip or peak, the combination of 10- 20 such devices could create an overall dip or peak of between 5 and 10dB at this frequency. Anomalous gain variation of this magnitude can significantly degrade overall network bandwidth. The inventor has therefore realised that there is a need to individually adjust each active tap to prevent accumulation of gain anomalies.

[0018] Furthermore, because gain anomalies are likely to occur in active taps, the inventor has realised that there is a need to measure localised gain characteristics within each active tap.

[0019] In addition, the inventor has realised that there is a need to communicate these measurements to a remote location where network gain adjustments can be supervised.

[0020] There is also a need to provide all of the identified functionality at minimum cost.

[0021 ] Although the concept of replacing existing high powered legacy amplifiers with active taps seems straight forward, a number of fundamental problems are likely to arise. Firstly, although the available power supplies for the network may have sufficient capacity to power the full number of active taps after they are fully installed, the power supplies may not have the capacity to power both existing high power amplifiers and a partial number of active taps simultaneously during the upgrade process. Therefore, there is a need for an improved method of upgrading a network which overcomes potential power supply capacity issues.

[0022] Furthermore, the upgrade process needs to consider co-existence of active taps with legacy network equipment such as high power amplifiers during the upgrade. The high output levels of these amplifiers can overload sensitive active tap amplifiers until these amplifiers are removed from service. Therefore, there is a need to identify device structures and methods which overcome network equipment incompatibility during the upgrade process.

[0023] Although the inventor’s accompanying patent AU: 2021902022 identifies functionality which can be beneficially included in active tap designs to facilitate the upgrade process, an optimal upgrade method and device design has not been identified.

[0024] Accordingly, the inventor has realised that there is a need for optimised devices and methods which facilitate deployment of active taps into an existing coaxial distribution network.

[0025] From a different perspective, when active taps are introduced into a network, the reliability of the overall network can be substantially reduced because the network is dependent on a large number of active devices (taps) connected in series, each having a finite mean time before failure (MTBF). Therefore, the inventor has identified that there is a need for an improved active tap device design and usage method which reduces the impact of individual active tap failure on the network.

[0026] The discussion throughout this specification comes about due to the realisation of the inventor and/or the identification of certain prior art problems by the inventor and, moreover, any discussion of documents, devices, acts or knowledge in this specification is included to explain the context of the invention. It should not be taken as an admission that any of the material forms a part of the prior art base or the common general knowledge in the relevant art in Australia or elsewhere on or before the priority date of the disclosure and claims herein.

[0027] Furthermore, the preceding discussion of background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

SUMMARY OF INVENTION

[0028] It is an object of the present invention to provide a method and apparatus, which alleviates at least one disadvantage associated with related art arrangements as discussed herein.

[0029] In general, and from a number of different aspects, the present invention provides:

• An active tap comprising one or more electronically adjustable de-bump filters and means of controlling said filters which prevents the accumulation of coincident gain anomalies in a network and provides improved overall network gain characteristics,

• An active tap comprising a means of measuring signal amplitudes received by the tap, or transmitted by the tap, or both, in a frequency band comprising at least a portion of the signal frequency range coupled through the tap,

• An active tap comprising a means of receiving and transmitting telemetry signals from and to a remote site for the purpose of remotely monitoring and controlling the state and function of the active tap,

• A method of deploying active taps into a legacy network comprising the connection of an auxiliary power supply to the network during the upgrade process

• A method of deploying active taps into a legacy network by commencing installation of the taps at the most remote locations of the network first and progressing upstream toward legacy amplifiers, thereby gradually providing sufficient distributed gain to allow removal of these legacy amplifiers without disrupting network traffic.

• An active tap device and method for monitoring and controlling signal flow through the tap comprising a passive bypass signal path which is selected using latching switches and which couples signals through the tap without passing through any active circuitry.

[0030] It is therefore an object of the preferred embodiments described herein to overcome or alleviate at least one of the above noted drawbacks of conventional systems or to at least provide a useful alternative to conventional systems. [0031 ] These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. Accordingly, further scope of applicability of embodiments of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure herein will become apparent to those skilled in the art from this detailed description.

[0032] Other aspects and preferred forms are disclosed in the specification and/or defined in the appended claims, forming a part of the description of the invention.

[0033] Further scope of applicability of embodiments of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the disclosure herein will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Further disclosure, objects, advantages and aspects of preferred and other embodiments of the present invention may be better understood by those skilled in the relevant art by reference to the following description of embodiments taken in conjunction with the accompanying drawings, which are given by way of illustration only, and thus are not limitative of the disclosure herein, and in which:

Figure 1 shows a simplified symbolic representation of a conventional HFC coaxial distribution network.

Figure 2 shows a simplified symbolic representation of a prior art passive tap.

Figures 3a and 3b show a simplified circuit diagram and performance characteristics of a single stage de-bumping filter according to a first aspect of the present invention in accordance with preferred embodiments. Figures 4a and 4b show a simplified circuit diagram and performance characteristics of a two stage de-bumping filter according to another aspect of the present invention in accordance with preferred embodiments.

Figure 5 shows a simplified circuit diagram of a de-bumping filter employing PIN diodes according to a preferred embodiment of an additional aspect of the present invention in accordance with preferred embodiments.

Figures 6a, 6b and 6c show a simplified block diagram of gain monitoring circuitry according to additional preferred embodiments of the present invention.

Figures 7 shows a simplified block diagram of combined gain monitoring and telemetry receiving circuitry according to another preferred embodiment of the present invention.

Figure 8 shows an example of a network which can be upgraded according to a preferred method of another aspect of the present invention in accordance with preferred embodiments.

Figures 9a and 9b show flow charts summarising preferred network upgrade methods according to another aspect of the present invention in accordance with preferred embodiments.

Figure 10 shows a simplified block diagram of failure mode bypass circuitry according to another preferred embodiment of the present invention.

Figure 1 1 shows an example of a network comprising multiple power supply regions which can be upgraded according to another preferred method of the present invention.

Figure 12 is a flow chart summarising a preferred network upgrade method according to another aspect of the present invention in accordance with preferred embodiments.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT SOF THE INVENTION

[0035] Preferred embodiments of the present invention will now be described in relation to the drawings. Where possible, equivalent numbers have been used to identify the same element in each drawing or sub-drawing. Terms such as “top” and “bottom” are intended to aid description of the drawings as shown and are not meant to restrict the scope of the invention. [0036] The term “coaxial distribution network” or “coaxial network” refers to a telecommunication network where information is conveyed to and from customer’s premises using electrical signals carried on coaxial cables.

[0037] The term Hybrid Fibre Coax, abbreviated as HFC, refers to one type of coaxial distribution network coupled to an optical fibre Node where subscribers access the network using electrical signals which are conveyed through the coaxial network to and from the Node.

[0038] The term “HFC Node” or “Node” refers to network equipment in an HFC network which converts signals between an optical format and an electrical format which is coupled to a coaxial distribution network.

[0039] The term “CPE” is used to refer to Customer’s Premises Equipment located within a customer’s premises and connected to the coaxial network. A “modem”, which is used to transmit and receive signals to and from the coaxial network, is an example of one type of CPE.

[0040] The terms “modem” or “customer modem” refer to any device located within a customer’s premises which converts signals carried by the coaxial network into a different electrical signal format.

[0041 ] The terms “upstream” and “downstream” refer to a signal propagation direction toward, and away from, a Node, respectively.

[0042] The term “Port” refers to a signal interface provided by means of a coaxial connector.

[0043] The terms “upstream-facing port” and “upstream port” each mean a signal port for exchanging signals with the network node.

[0044] The term “downstream-facing port”, and “downstream port”, each mean a signal port for exchanging signals with equipment which is most distant from the network node.

[0045] The term “tap” refers to an HFC network device used to connect a group of 1 or more customers to the network and which comprises an upstream port, a downstream port, and a plurality of ‘drop’ ports which are used to connect CPE to the network. [0046] The term “through” when referencing a signal path in a tap refers to signals coupled between the tap’s upstream and downstream ports.

[0047] The term “mixer” means a nonlinear device which accepts 2 or more signals at frequencies F1 , F2 etc and produces signals at frequencies which are sums and differences of multiples of F1 and F2 etc, e.g., F1 +F2, 3*F1 -2*F2 etc.

[0048] The term “passband” of a device, circuit element or signal path means the frequency range in which signals pass through the device, circuit element or signal path, and outside of which signals passing through the device, circuit element or signal path are substantially attenuated.

[0049] The term “branching network element” or “BNE” refers to a passive or active device which splits a single downstream signal path into multiple downstream signal paths (branches) and which combines multiple upstream signal paths (branches) into a single upstream signal path. Taps are not included in this BNE definition.

[0050] The term “legacy network element” or “LNE” refers to either passive or active devices installed in an existing network prior to network upgrade. Taps, splitters, couplers and amplifiers are examples of LNEs.

[0051 ] The term “upgraded network element” or “UNE” refers to either passive or active devices which increase network performance when installed in place of an LNE in an existing network. Active taps, active splitters and active couplers are examples of UNEs which may provide improved performance compared to passive LNE equivalents.

[0052] The term “transceiver” refers to an interface device which can both receive and transmit signals either sequentially or simultaneously.

[0053] The term “passband” of a device, circuit element or signal path refers to the frequency range in which signals pass through the device, circuit element or signal path, and outside of which signals passing through the device, circuit element or signal path are substantially attenuated.

[0054] The term “hard-line” refers generally to coaxial cables, typically having a semirigid form, which pass customer’s premises and allow customers to connect to the network through taps coupled to the hard-line. [0055] The term “telemetry” refers to signals which are exchanged between network elements and central sites for the purpose of controlling or monitoring the network elements.

[0056] The term “microcontroller” refers to a computing device containing a central processing unit, data and program memory and peripheral interface circuitry.

[0057] According to a first aspect, the present invention provides an active tap comprising one or more amplifiers and at least one de-bumping filter wherein:

• said filter comprises at least two parallel signal paths,

• said parallel signal paths comprise impedances of substantially the same value

• said impedances can be represented at any frequency as predominantly an inductor and capacitor connected in series at a mid-point

• said predominant capacitive element of one signal path is connected to said predominant inductive element of another signal path,

• a resistive element is connected between the mid-points of said predominant inductive and capacitances elements of the at least two signal paths, and

• the transmission characteristic of said filter is controlled by varying the resistance of said resistive element by means of an applied voltage or current.

[0058] Figures 3a and 3b show a circuit schematic and simulation response of one preferred embodiment of the present invention. Filter 300 comprises two series resonant circuits formed by C1 / L1 and C2 / L2 which are connected in parallel. According to the present invention the capacitor of one series resonant circuit is connected to the inductor of the other series resonant circuit. In this example C1 is connected to L2 and L2 is connected to C1 . A resistor R1 is connected between the mid points of the series resonant circuits. The frequency response of the filter is controlled by adjusting the value of R1 . The component values shown in Figure 3a are only one example of an embodiment of the present invention.

[0059] The operating principle of the filter can be revealed by considering two extreme cases:

• When resistor R1 is an open circuit, the filter is reduced to two series resonant circuits arranged in parallel (L1/C1 in parallel with L2/C2). The net effect is that signal transmission through the filter is maximised at the series resonant frequency of L1/C1 (and L2/C2), • When resistor R1 is a short circuit, two parallel resonant circuits are formed (L2/C1 and L1/C2) which are connected in series. In this case, these parallel resonant circuits are open circuit at the resonant frequency of L2/C1 (and L1/C2) and signal transmission is minimised at this frequency. Note this is the same frequency as the previous case because preferably L1 =L2 and C1 =C2.

[0060] Therefore, by adjusting the value of R1 , the filter response can be altered to provide either increased or decreased transmission at the resonant frequency. Preferably the inductance of L1 and L2 and the capacitance of C1 and C2 are substantially equal,

[0061 ] The filter structure is designed by first selecting the centre frequency of the band where transmission characteristics are to be altered. This determines the LC product for the filter reactances. Then the Q of the resonant circuit is determined, meaning the narrowness of the equalisation characteristic in the frequency domain. The Q of the filter is influenced by the magnitude of the inductive and capacitive impedances and the resistive impedance presented at the filter input and output ports, which is typically 75 ohms. Finally, the resistance of controlling resistor R1 is determined according to the filter adjustment range. Preferably the filter provides a flat transmission characteristic when the resistance of R1 is comparable to the filter port impedances, i.e., 75 ohms.

[0062] In order to optimise the filter characteristics, a circuit simulation program such as SPICE is iteratively used to adjust component values while monitoring overall transmission characteristics and control range.

[0063] Filter 300 is shown connected between a signal source V1 having output impedance Rs, and a load resistor RL. Figure 3b shows the response of the filter for signals passing from the signal source to the load, resulting in voltage Vout. Curve 301 shows a flat filter response which occurs when R1 is 31 .5 ohms. The resistance which gives a flat response may depend on the choice of other filter components and the source and load impedances connected to the filter. Curves 302 and 303 correspond to R1 values of 27.5 and 23.5 ohms respectively. Curves 304 and 305 correspond to R1 values of 35.5 and 39.5 ohms respectively.

[0064] Given the example component values indicated in Figure 3a, the insertion loss of the filter can be varied by approximately +/- 0.4dB by adjusting the resistance of R1 by +/- 25%. This allows the filter to provide localised gain correction near the resonant frequency of the filter’s reactances, which is approximately 5MHz in this example. This localised correction is referred to as ‘de-bumping’.

[0065] In order to provide gain correction over a wider frequency band, multiple filter stages can be used and are preferably cascaded together. Figure 4a shows an example of combination of two de-bumping filters 410 and 41 1 according to an alternative embodiment of the present invention. Figure 4b shows the simulated response of this two stage de-bumping filter for all possible combinations of resistors R1 and R2 chosen from the set of values: [23.5, 27.5, 31 .5, 35.5, 39.5] ohms. It is evident from these curves that many possible equalisation responses can be provided by adjusting R1 and R2.

[0066] From another perspective the present invention provides an adjustable de-bump filter. Figure 5 shows a two stage de-bumping filter comprising a first stage 510 and second stage 51 1 . Instead of resistors R1 and R2 as shown in Figure 4a, PIN diodes D1 and D2 are included in the circuit. The resistance of these diodes is controlled independently by adjusting the ‘DC’ bias current flowing through them, as represented symbolically by current sources 11 and I2. In this context the term ‘DC’ includes time varying bias currents which, for example, might adjust for temperature drifts or other quantities which change slowly with time.

[0067] Components such as inductors or RF chokes L5 and L6 are preferably included to provide a ‘DC’ return path for diode bias currents. The impedance of these components at the operating frequency of the filters is chosen to be high enough that they do not cause the RF signal path to be significantly affected. Inductor or RF chokes may also be included in series with the bias current sources. Although current sources are shown in Figure 5, the present invention is not restricted to this type of bias current source and any source of bias current can be used within the scope of the invention.

[0068] Preferably, PIN diode bias current is controlled using a device such as a microcontroller which is co-located with the filters and coupled to the diodes. Preferably, this controller communicates with a centralised location in order to determine the gain adjustment required to optimise the overall network and hence the gain setting for each filter stage. On receiving commands from the centralised site, the controller applies appropriate bias currents to each diode. The controller may also be programmed to make certain types of adjustment autonomously without communication with a centralised site. [0069] From an additional perspective the present invention provides an active tap comprising:

• an upstream signal port and a downstream signal port,

• one or more signal monitors coupled to said upstream port, or said downstream signal port, or to each port,

• a signal amplitude measuring device coupled to each attenuator

• a microcontroller coupled to said signal amplitude measuring device, wherein:

• said signal amplitude measuring device comprises an oscillator, mixer and bandpass filter,

• said microcontroller sweeps the frequency of said oscillator across a spectrum of interest within the bandwidth of signals propagating through said tap, and

• said microcontroller stores a digital code in its memory which represents the amplitude of said upstream or downstream signals within a specified frequency range.

[0070] Figures 6a-c show simplified symbolic representations of various preferred embodiments of the present invention. In each figure active tap 620 comprises upstream 621 and downstream 622 signal ports. Signals passing through the taps are amplified by downstream amplifiers 630 and upstream amplifiers 631 . Imperfections in these amplifiers or surrounding circuitry can cause the gain to differ from expected values and cause ‘bumps’ in the gain vs frequency characteristics of the tap. In order to correct for these gain anomalies, it is necessary to measure the gain characteristics of the amplifier. This can be achieved by sampling the signal as it passes through the tap.

[0071 ] According to one embodiment of the present invention, Figure 6a shows signal monitor 623a coupled to the upstream port 621 of active tap 620. This signal monitor may comprise an inductive element such as a transformer or directional coupler, or a resistive divider, or a capacitive divider. For example, this signal monitor would produce a version of the signal present at the tap upstream port attenuated by 20dB. The primary reason for using an attenuating signal monitor is to allow access to the signal on the upstream port with minimal impact to the amplitude of the signal. Of course, the signal present at the upstream port of tap 621 can have components of both upstream and downstream signals. [0072] The output of signal monitor 623a is coupled to a frequency translating device such as a mixer 624 which is coupled to an oscillator 625 and filter 626. Oscillator 625 is coupled to a microcontroller 627 which programs oscillator 625 to change its output to specific frequencies. This allows the oscillator frequency to be swept across a band of frequencies in succession. As the frequency of oscillator 625 is changed, the signal present at the output of mixer 624 appears as a frequency translated version of the signal present at the tap upstream port 621 . The output of mixer 624 is coupled to bandpass filter 626 which selects a band of frequencies. This filter is preferably a narrow band device such as a simple series tuned circuit, or a complex filter such as a bulk acoustic wave (BAW) device. The output of filter 626 is coupled to detector 628 which produces a voltage which is proportional to either the RMS amplitude or power of the frequency translated signal which falls within the passband of filter 626. The output of detector 628 is coupled to microcontroller 627 which converts this voltage to a digital code and either acts autonomously to correct amplitude anomalies or passes the digital code through a telemetry channel to a remote site for analysis and further action. In this manner, the present invention is able to measure the amplitude vs frequency characteristics of the signals present at the upstream, port of tap 621 .

[0073] Preferably oscillator 625 and mixer 624 translate the signal present at port 621 upwards in frequency. This up-conversion overcomes issues associated with image frequencies which would be translated into the passband of bandpass filter 626 if a down conversion was used. These image frequency signal components would lead to incorrect interpretation of signal amplitudes and must be avoided.

[0074] In certain applications it may be preferable to sense signal amplitudes at the downstream port of the tap instead of the upstream port. Accordingly, Figure 6b shows an alternative embodiment of the present invention which operates in the same manner as the circuit of Figure 6a, except that signal monitor 623b is coupled to the downstream port 622 of tap 620.

[0075] It may also be preferably to sense the difference in signal amplitudes as they arrive at, and leave, the tap. Accordingly, Figure 6c shows an alternative embodiment of the present invention where two signal monitors 623c and 623d are coupled to each port of tap 620 and to switch 629 which is able to select one signal or the other to be coupled to mixer 624. In this way, the present invention is able to measure the differential gain characteristics of active tap 620 and to adjust the tap characteristics to remove gain anomalies.

[0076] From another perspective, the present invention provides a telemetry receiver for an active tap comprising:

• One or more signal monitors coupled to one or more signal ports of the tap,

• A frequency translating circuit comprising an oscillator coupled to said one or more signal monitors,

• A filter coupled to said frequency translating circuit,

• A demodulating telemetry receiver and a signal amplitude detector coupled to said filter, and

• A microcontroller coupled to said telemetry receiver and said signal amplitude detector, wherein:

• Said oscillator is adjusted to the frequency of a telemetry channel which passes through the tap, and

• Said microcontroller adjusts the frequency of said oscillator and receives data carried in said telemetry channel.

[0077] According to a preferred embodiment of the present invention, the same circuit used to measure gain anomalies across the broad spectrum of signal traffic passing through the tap and is also used to couple narrow band telemetry signals to the tap’s microcontroller for processing.

[0078] Figure 7 shows a symbolic diagram of a preferred embodiment of the present invention. Reference numbers 7xx in this diagram correspond to equivalent components labelled 6xx in Figures 6a-c. To implement this embodiment of the present invention, additional filter 732 and RF receiver 733 are added.

[0079] For example, telemetry may be conveyed on a narrow out-of-band (OOB) carrier at 5MHz. This frequency may be chosen for telemetry because this low frequency portion of the signal spectrum is unsuitable for QAM encoded signal traffic, but may be acceptable for low data rate telemetry. Because 5MHz is not a common radio transmission frequency, a custom 5MHz signal receiver would need to be included in the active tap to receive these signals, which adds complexity and cost. Instead, a significant implementation and cost benefit can be obtained if an industry standard, highly integrated receiver can be used instead, for example one suited to the 300-348 MHz frequency band.

[0080] Unfortunately, RF spectral bands such as 300-348 MHz are likely to be allocated to customer traffic in the network and cannot be used for telemetry. However, the present invention overcomes this incompatibility by using the frequency translating ability of circuitry included in the active tap for the purpose of measuring gain characteristics.

[0081 ] In the above example, 5MHz telemetry traffic arriving at an active tap is converted up to a frequency between 300 - 348 MHz by the available signal level monitoring circuitry and an industry standard, low cost highly integrated receiver is used to demodulate the telemetry content. The advantage of this approach is that a high degree of sophistication can be obtained (including packet handling, error correction encryption etc) with a very low incremental cost increase. The gain measuring circuitry of the active tap is in fact preferably dedicated by default to telemetry processing, except during relatively infrequent gain monitoring tasks.

[0082] Because upstream transmission of telemetry signals can be achieved very simply using baseband hardware, particularly at OOB frequencies such as 5MHz, the present invention comprises generation of upstream telemetry signals using the microcontroller itself, or using simple dedicated peripheral circuitry without the need for frequency translation.

[0083] From another perspective, the present invention provides a method of upgrading the capacity of a signal path in existing coaxial distribution network by replacing legacy network elements (LNE) with upgraded network elements (UNE), comprising the steps of:

• Replacing LNEs in said signal path with UNEs starting with LNEs which are furthermost from the optical node feeding the network, and progressing sequentially toward the node

• Stopping when a branching network element (BNE) or the Node itself is encountered,

• Replacing LNE’s with UNEs on any other signal paths flowing through said BNE in the same manner, starting from the LNE which is furthermost from the node,

• Replacing the BNE with a UNE, and

• Replacing any other LNE in said signal path in the same manner. [0084] The advantage of installing active tap UNEs into a network is that gain is distributed throughout the network and can more effectively overcome losses, thereby increasing the transmission capacity of the network. The difficulty in achieving this outcome lies in transitioning from a localised, high power legacy amplifier topology to a distributed amplifier topology, while maintaining network services for customers at all times during the upgrade. The present invention comprises a method of installing UNE which eliminates dependence of the network on localised high power amplifiers.

[0085] Figure 8 shows a simplified example of a coaxial distribution network comprising a Head End 840 and Node 841 which convey signal traffic to and from the network along signal path 859. This example network also comprises a plurality of LNEs including Taps 842, Splitter 843, Line Extender amplifier 844 and Bridging Amplifiers 845 and 855.

[0086] As an example of a preferred method of the present invention, LNE tap 846, being furthermost from the node along signal path 859, is upgraded first. Then LNE taps 847 and 848 are upgraded, until BNE splitter 843 is reached. Then, LNE tap 849 is replaced, then LNE taps 850 and 851 . Finally, LNE Splitter 843 is replaced, followed by LNE taps 852 - 854 and then the remainder of the network.

[0087] Although the above example describes a process of completely upgrading one branch of BNE Splitter 843 (Taps 846-848), then the second branch (Taps 849-851 ), upgrading both of these branches simultaneously is also within the scope of the invention.

[0088] Accordingly, the general principle of this aspect of the present invention is that LNEs are replaced starting with those most distant from the Node. Therefore, the exact order of replacement of each LNE within the network, or actual distance from an LNE to the Node, is not intended to limit the scope of the invention. For example, upgrading LNEs in Figure 8 in the following order falls within the scope of the invention: 846, 849, 847, 850, 848, 851 , 843.

[0089] Figures 9a and 9b provide flow chart representations of two preferred methods according to the present invention.

[0090] From another perspective the present invention provides an active tap comprising:

• A microcontroller device and

• One or more switching devices having a first state and a second state, wherein:

• Said microcontroller exchanges telemetry signals with a remote location

• Said microcontroller monitors local circuit parameters within the active tap

• Said microcontroller is coupled to said one or more switching devices.

• Said switching devices cause network traffic signals within the tap to either pass through a signal path comprising amplifiers when in said first state or to pass through a signal path comprising only passive circuit elements when in said second state, and

• Said switching devices comprise a latching mechanism which maintains either said first state or said second state in the absence of power.

[0091 ] Because networks employing active taps have large numbers of active devices in series, the overall reliability and MTBF of the network is lower than in conventional passive networks. To address this issue, the present invention provides a passive ‘bypass’ signal path which can be selected in the event of active tap failure.

[0092] A symbolic circuit of the present invention is provided in Figure 10. Active tap 1020 comprises upstream oriented port 1021 and downstream oriented port 1022. Preferably two switching elements 1060a and 1060b work in unison to select either amplified signal path 1062 or passive signal path 1063. These switching elements are preferably electro-mechanical devices which are either physically separate or combined in a single module. These switching elements preferably comprise latching mechanisms which maintain their configuration (state) after they are forced into that state. For example, this latching mechanism may employ permanent magnets which hold electro-mechanical contacts in place until the device is forced into a different state by application of electric current or voltage. Latching relays are an example of one type of switching element.

[0093] Preferably switching elements 1060a and 1060b are coupled to and controlled by a microcontroller device 1027. This device is preferably coupled to either the upstream oriented port 1021 or downstream oriented port 1022 of the tap and communicates over a telemetry channel to a remote location. Microcontroller 1027 also monitors tap functionality and is programmed to identify failure modes of the tap, for example an internal power supply voltage which falls outside of a specified range. In the event of a significant failure, microcontroller 1027 controls the state of switching elements 1060a and 1060b so that passive bypass signal path 1061 is selected and the impact of the tap failure on the network is minimised. Although the gain provided by a failed tap would no longer be available to the network, the distributed gain available from adjacent active taps will be able to make up for the gain shortfall.

[0094] According to a preferred embodiment of the present invention, if microcontroller 1027 itself fails, preferably switching elements 1060a and 1060b are forced into the state which selects passive bypass signal path 1061 by autonomous tap circuitry. For example, this behaviour can be controlled by watch-dog circuitry associated with the microcontroller.

[0095] From another perspective the present invention provides a method of upgrading a coaxial distribution network comprising the steps of:

• Identifying existing power sources which supply each individual network region

• Calculating whether said existing power sources can supply peak interim power load required during the upgrade

• Identifying vulnerable network regions where said existing power sources are unable to supply said peak interim power load during the upgrade,

• Connecting a temporary auxiliary power supply to a vulnerable network region,

• Upgrading said vulnerable network region,

• Removing legacy amplifiers not needed after the upgrade, and

• Disconnecting said temporary auxiliary power supply, wherein:

• Said auxiliary power supply matches the voltage characteristics of said existing power source and increases the current available for the network.

• Said peak interim power load (Ppk) is defined as the power load of the existing network before upgrade (Pexisting) plus the load of any additional devices installed into the network at the completing of the upgrade (Padd): Ppk = Pexisting + Padd

[0096] In order to maintain network services during a network upgrade, legacy amplifiers need to remain in service until the upgraded network is ready to continue operation without them. These legacy amplifiers generally limit network performance, have poor power efficiencies and consume significant amounts of power. Therefore, it is advantageous to remove them in a network upgrade, particularly if a distributed gain architecture (as for example provided by active taps) is adopted and can provide the necessary amplification without them. However high powered legacy amplifiers are required until all passive legacy network equipment is removed from service. Although the power requirements of individual distributed gain elements such as active taps are much lower than high power legacy amplifiers, many of these gain elements are required in an equivalent distributed gain network. With careful planning, the total power requirements of the distributed gain network can fall within the supply capacity of existing network power sources. This means that there is no need to upgrade the network power sources which saves significant cost. However, at the final stage of the upgrade, when both the existing legacy amplifiers and almost the full complement of distributed gain devices are installed, the total load placed on the existing network power supplies may significantly exceed their capacity. The present invention addresses this problem by determining which network segments are at risk of power supply overload and temporarily fitting auxiliary power supplies to support the interim peak power requirement. When the network is fully upgraded and legacy amplifiers have been removed, the auxiliary power supplies are removed.

[0097] Figure 1 1 provides an example of a coaxial distribution network comprising Node 1 141 , high power legacy amplifiers 1 144, 1145 and 1155. The network is divided into two separate regions 1 170 and 1171 which are powered by legacy power sources 1 172 and 1 173. For example, these power sources may provide 50 volts AC at 25 amps. In this example, this power is required to supply legacy amplifiers 1 144, 1 145 and 1155 prior to the upgrade. Regions 1 170 and 1 171 are separated by power blocking devices 1 176 which allow the passage of RF signals but block the flow of power from one region to another. This means that each region is powered independently.

[0098] According to a preferred method of the present invention, vulnerable network regions are identified and auxiliary power supplies 1 174 and 1 175 are fitted to boost the power available to the network during the upgrade. These auxiliary power supplies are preferably situated close to the legacy power supply locations e.g., 1 174, but may also be located at convenient locations anywhere in the network. For example, it may be advantageous to power the network from a remote location e.g., 1 175 in Figure 1 1 to minimise voltage drop along network cables.

[0099] Preferably auxiliary power supplies maintain the legacy network operating voltage close to its operating value, but increase the available current.

[00100] Figure 12 provides a flow chart summary of the preferred method of the present invention. [00101 ] As noted above, while this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification(s). This application is intended to cover any variations, uses or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth.

[00102] “Comprises/comprising” when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. Thus, unless the context clearly requires otherwise, throughout the description and the claims, the words ‘comprise’, ‘comprising’, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

[00103] “Coupled” when used in this specification is taken to specify the presence an electrical connection between two or more circuit elements either by direct connection or by indirect connection through intermediate elements.

[00104] While this invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modification(s). This application is intended to cover any variations uses or adaptations of the invention following in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth.

[00105] As the present invention may be embodied in several forms without departing from the spirit of the essential characteristics of the invention, it should be understood that the above described embodiments are not to limit the present invention unless otherwise specified, but rather should be construed broadly within the spirit and scope of the invention as defined in the appended claims. The described embodiments are to be considered in all respects as illustrative only and not restrictive.

[00106] Various modifications and equivalent arrangements are intended to be included within the spirit and scope of the invention and appended claims. Therefore, the specific embodiments are to be understood to be illustrative of the many ways in which the principles of the present invention may be practiced. In the following claims, any means- plus-function clauses are intended to cover structures as performing the defined function and not only structural equivalents, but also equivalent structures. For example, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface to secure wooden parts together, in the environment of fastening wooden parts, a nail and a screw are equivalent structures.