WO2007000777A1

WO2007000777A1 - Broadband hf/vhf/uhf communication on power lines

Info

Publication number: WO2007000777A1
Application number: PCT/IN2006/000223
Authority: WO
Inventors: Prasanna Gorur Narayana Srinivasa; Mayank Raj; Ritesh Kumar Kalle; Atul Pratap Singh; Srinivasa Murthy Gorur Selvapillai; Naresh Srungarakavi Venkata Samba; Reetesh Mukul; Kalluri R. Sarma
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-06-29
Filing date: 2006-06-29
Publication date: 2007-01-04
Anticipated expiration: 2007-12-29
Also published as: WO2007000777B1

Abstract

Disclosed herein is a method of transmitting a broadband signal over a set of one or more conductors which can handle transmission at VHF/UHF, exemplarily over a ubiquitous medium voltage (MV) or low voltage (LV) power line network in TV/CATV channels, wherein the transmission channel is optionally divided into a plurality of sub channels, each being separated from each other in time or in carrier frequency . It is another object of this invention to provide an apparatus for data communication at UHF/VHF over a power line network wherein a transmission channel is divided into a plurality of sub channels each being separated from each other in time or in carrier frequency, comprising: Transmission means (transmitter), Reception means (receiver), Coupling means (coupler) by using known methods, Signal Processing means (signal processing), Regeneration means and Error correction means.

Description

BROADBAND HF/VHF/UHF COMMUNICATION ON POWER LINES.

Cross-Reference to Related Applications

This application claims the benefit of the filing date of Indian Provisional application no. 822/CHE/2005, filed on June 29^th, 2005, the teachings of which are incorporated herein by reference.

BACKGROUND

FIELD OF THE INVENTION

The present invention relates to power line communications. More particularly, the invention proposes a method to transmit broadband high-frequency signals over a set of one or more conductors of a power line network, such as a ubiquitous medium voltage or low voltage network.

PRIORART

One and a half centuries after the invention of the Faraday's dynamo, the worldwide electricity grid reaches most inhabited regions of the planet. The grid distributes thousands of Giga Watts of power worldwide, through a combination of Extra High Tension (EHT 132 KV and above) main feeders, Medium voltage (MV 11KV-66KV) distribution, and Low voltage (LV - 110/220/440 V) lines to homes. Almost the entire EHT grid, most of the MV grid, and some of the LV grid is aerial, with the residual buried underground (especially MV/LV in densely populated urban areas).

The present invention is primarily but not exclusively focused on the medium voltage (MV) portion, between the main feeders and the distribution transformer to the end-users. This MV portion reaches from one or more substations, one or more end-users (homes/industries), and forms a dense grid blanketing most inhabited portions of the planet. It typically comes within a few hundred meters at most of end-users. Cables used can be aerial (in triangular/linear 3-phase configuration), or buried. Conductor thicknesses are 1 cm or more.

The MV grid is a clean and well-controlled channel compared with the LV portion, since (a) the high frequency impulse noise due to motors and other appliances is attenuated by the distribution transformers, and

(b) installation and maintenance is done by the electricity authority as opposed to end-users. Compared to EHT lines, corona and gap noise, with spectra extending into the GHz region, is relatively less at MV.

Any communication channel is characterized by its attenuation and delay, as a function of frequency. Ih the power line channel, the raw attenuation due to Ohmic loss is extremely small, due to the very thick conductors used (1 cm or more in diameter). The channel imperfections are due to losses caused by skin effect, and radiation (in aerial lines), and distortions caused by reflections (in both buried and aerial lines) caused by mismatched termination, since these lines are designed to carry 50/60Hz power.

Most prior power line work has concentrated on the in-home or in-business LV portion, typically below 30MHz. Extensive work has been carried out on characterizing in-home wiring channel. The channel is found to be highly frequency selective, with 60+dB notches, and extensive impulse noise due to light dimmers, motors, etc. OFDM (Orthogonal Frequency Division Multiplexing) has been successfully used, with 1000's of carriers yielding 45-200 Mbps throughput over 100-300 m

Work on the MV portion is limited, except for the recent work of Amirshahi and Kaverhad [1] who target lower frequencies. Amperion's system [2] is in the 1-30 MHz band, and Corridor Systems' [3] microwave e-liαe is based on surface-wave principles. In all but the last, frequencies are restricted to less than about 100 MHz or so.

Corridor Systems propose a microwave e-line, which uses surface-wave technologies Corridor's solution, is based on the world's first distributed antenna system (DAS) to use the existing medium- voltage electric grid. The PowerCorridor^ta MOBILE system provides extremely cost effective hole filling and coverage extension with greatly simplified permitting and installation - all at CAPEX (Capital Expenditure) costs that are a fraction of alternative solutions. The system supports all wireless systems including 2G, 3G and WiFi. The present invention differs from Corridor Systems, in that it does not use surface wave propagation techniques, and is based on the propagation of TEM/TE/TM modes themselves. US Patent 3,728,632, US Patent 7,027,483 and US Patent 6,031,862 refer to Ultra Wideband technology. The present invention uses standard TV/CATV technology. UWB uses a large bandwidth to reduce peak power while the present invention uses the VHF/UHF FM/TV/CATV band, and stays within the channel structure

SUMMARY OF THE INVENTION

It is an object of this invention to provide a method of transmitting a broadband signal over a set of one or more conductors which can handle transmission at VHF/UHF, exemplarily over a ubiquitous medium voltage (MV) or low voltage (LV) power line network in TV/CATV channels, wherein the transmission channel is optionally divided into a plurality of sub channels, each being separated from each other in time, carrier frequency or in access method. It is another object of this invention to provide an apparatus for data communication at UHF/VHF over a power line network wherein a transmission channel is divided into a plurality of sub channels each being separated from each other in time, carrier frequency or in access method, comprising: Transmission means (transmitter), Reception means (receiver), Coupling means (coupler) by using known methods, Signal Processing means (signal processing), Regeneration means and Error correction means.

Based on theoretical and experimental tests carried out over Medium voltage power lines, the present invention proposes a communication system, which is amongst the world's fastest, in the area of its application. As a consequence of the loss of this line being very low, with the bandwidth potentially extending to GHz, including the VHF/FM/UHF bands, these lines are ideal conduits for high-frequency communication. Shannon capacities of the MV grid i.e. transfer rate of the channel, are shown to extend from 100's of Mbps to several of Gbps (over a Km or more), testifying to its potential as an excellent intermediary between the limited fiber infrastructure, and the ubiquitous but relatively low bandwidth wireless channel. Even higher capacities are available using multiple- input multiple-output (MIMO) techniques, by exciting multiple conductors, with optimized amplitude and phase. The power line technology described in this application can be applied in both wired and wireless settings.

As opposed to other systems utilizing OFDM and similar narrowband technologies the present invention exploits the fact that in India and many developing countries, the Terrestrial FM and TV band is by and large unused beyond a few FM/VHF channels. Consequentially, hundreds' of MHz of bandwidth is available which can be utilized for high-speed communication. Since these channels are earmarked for broadcast purposes, but unused, the entire 6-8 MHz of channel is available for alternative purposes, without extensive spectral shaping/notching to avoid electromagnetic interference. As such, simpler modulation techniques instead of OFDM can be used, and higher spectral density can be achieved. The present invention is not limited to developing nations, since reuse of the VHF/UHF band is being discussed in the IEEE 802.22 workgroup worldwide.

The present invention, in an embodiment, describes a new way of high-speed communication on power lines, using primarily transverse-electric magnetic modes, cable television (CATV) bands and hardware, and MEMO concepts. System capacities are in several Gigabits using portions of the VHF/UHF band. In this embodiment, the system works by transmitting VHF/UHF signals on MWLV power lines and using CATV hardware with a few auxiliary pieces of equipment.

This embodiment exploits the fact that, the loss of the MV aerial lines is low enough for the use of Cable Modem technology (DOCSIS 2.0 [4] and its variants), achieving extensive economies of scale. This technology can be used by equalizing the complex power line channel to resemble a Coax channel. In addition, the use of higher frequencies than the current state-of-art (in the FM/VHF/UHF region) reduces the amount of coupled power line noise, improving SNR.

In addition to cable modem technology, modulation schemes of analog and digital broadcasting can be employed on the line, thus retaining compatibility with the spectral allocation plan, while utilizing the power line channel.

The main ideas in the invention are:

• Using a quasi-TEM analysis, it can be shown that radiation from the huge MV grid is not significantly more than that from small antennas few wavelengths long. The essence of the argument is that for straight sections, radiation increases very slowly with length - the amortized radiation resistance per unit length is quite small. Only in irregular sections (sharp bends, taps, etc) does radiation significantly increase. Since skin effect and dielectric losses are small, and characteristic impedances are in the 100's of ohms, the attenuation per unit length is small leading to huge channel capacities (Gbits/s in the VHF/UHF band). • Since the attenuation is low in the VHF/UHF band, a system can be cost-effectively designed using CATV infrastructure (transmitter, receiver, amplifiers etc), or Gigabit Ethernet infrastructure (GBE).

• By a proper amplitude and phasing of currents injected into two more conductors, radiation can be reduced reducing channel attenuation

• By choosing appropriate amplitude and phasing of currents injected into three or more conductors, amortized radiation per conductor can be reduced relative to two conductors, improving channel performance relative to using two conductors. Thus the use of multiple- input multiple-output techniques can offer great benefit and can almost triple the capacity with fifty percent more infrastructure.

• By an appropriate amplitude and phasing of currents injected into two or more conductors - radiation can be increased, offering more coverage by the wireless mode of transmission. Figure 6 shows an exemplary embodiment wherein the signal is coupled using a wireless link from the ground to the transmitter on the line unit (AT900 on the ground and AT800 on the power line), and reception is done by wireless detection of the radiated field (using antennas ATlOOO and receiver RX600) at the destination. Antennas ATlOOO and receiver RX600 can be located far away from the MV line, depending on the received signal to noise ratio.

The applications of this technology in a wired and a wireless setting, include: 1. Connecting countrywide fiber backbone to the end subscribers (e.g. villages) over the MV power line. MV power line functions as an excellent 2^nd tier distribution network, accessible within 2 Km of most areas of India and other parts of the world. 2. Functioning as a distributed antenna backbone for improving wireless reception in poorly served areas. 3. Expanding the reach of Information Technology to the vast populace underserved by the current infrastructure. In particular, the employment in the IT and ITES sector can be expanded to rural areas, thus adding to India's IT/TIES workforce

The Basic Characteristics of Signal Transmission on the MV Grid can be found in [5] and [6]. While attenuation per km does increase as frequency increases, both the theory and experiments described there substantiate the contention that transmission at VHF/UHF in the MV band is indeed possible. Ih addition it is demonstrated therein that CATV infrastructure can be employed for communication as per the invention. BRIEF DESCRIPTION OF DRAWINGS:

Figure 1 shows a Generic Power line Communication System; Figure 2 shows a Generic transmitter;

Figure 3 shows a generic receiver with an equalizer;

Figure 4 shows three methods of Signal Regeneration Method; Rl — Regenerator is an amplifier. R2 - Regenerator is an amplifier followed by an exemplary threshold detector. R3 - Regenerator Consists of a Receiver followed by Transmitter. Figure 5 shows Excitation on three phases;

Figure 6 shows reception using wireless pickup of the radiated field from the line; Figure 7 shows Radiated energy with respect to number of radiators, array factor only;

Figure 8 shows Antenna Array of radiators in the Z-direction driven from a possibly fictitious ground; Figure 9 shows Gain from Optimal Excitation (3-conductors);

Figure 10 shows Gain from Optimal Excitation (6-conductors); Figure 11 shows a regeneration section with two stages of amplification; Figure 12 shows the response of the channel derived from experimental data; Figure 13 shows the Post Equalizer for the channel; and

Figure 14 shows the equivalent response of the channel filter and Equalizer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 1 shows a Generic Bidirectional Power Line Communication System on a 3-phase (ubiquitous) MV line MVlO. The transmitter sends the waveform, possibly with some spectral pre- shaping over the line MVlO. Ih general, the line is heavily mismatched, with branches, transformers, etc. For left to right transmission, the transmitter TxIOO (or Tx500 in the other direction) encodes and modulates the signal and sends it to the coupler. The coupler Co200 (or Co400 in the other direction) is a device used to link data terminals to the network. - The Regenerator R300 is a device that is used to restore the signal. Regeneration can be a just an amplification Rl, an amplification followed by thresholding R2, or complete reception and retransmission R3. At the receiver end the coupler Co400 (or Co200 in the other direction) links the received signal to the receiver Rx600 (or Rx700 in the other direction). The receiver demodulates the signal and checks it for errors and performs the necessary action. The transmitter, regenerator, and line unit can be placed completely on the MV line itself, or partially on the ground also, with means of communication between the ground and the coupler unit provided. The coupling between transmitter and/or receiver and the line requires sufficient isolation. For this, state-of-art couplers can be used. As mentioned before, the transceiver signal processors can be located in either the line unit or at the ground. If located in the line unit, the entire signal processing takes places on the line unit. Else an analog signal can be transmitted between the ground unit and the line, with the signal processing done in the ground unit (which can be a vanilla cable modem, with a built in equalizer).

Figure 2 shows a generic transmitter block diagram. Any type of error detecting and correcting code ElOO can be used, like Read Solomon Codes (RS Codes) The Interleaver 1200 is used for spreading the data sequence to nullify burst errors. The signal is then modulated by modulator M300 and Pre-Equalized PEQ400 and then transmitted through the Transmit filter TF500. . Exemplarily, the modulator M300 can be a cable modem, in which case the modulation scheme would correspond to a cable modem modulation scheme.

Figure 3 shows a generic receiver block diagram. The signal is received through the received filter RFlOO. It is then passed through the channel equalizer EQ200 to nullify the non-linear phase characteristics of the channel. The signal is demodulated in DM300 and then de-interleaved DI400 and checked for any errors in the Error Detection and Correction EDC500 block, which checks it for any errors and corrects them if they exist.

The system shown in Figure 1 can be constructed using CATV (Community Antenna Television) system, using its standard equipment like modulators, demodulators, amplifiers, equalizers etc. This provides a cost-effective way of constructing the hardware for the above purpose.

The power line communication channel has varying degrees of frequency selectivity, due to the large number of reflections, as well as radiative resonances and anti-resonances. As such, an optimal receiver shown in Figure 3 in general involves a channel inversion, followed by possibly Viterbi detection. The channel can be inverted using specially structured equalizers EQ200, for high-speed computation. Specifically, a low cost receiver can use a CATV or GBE or similar card, together with a front-end channel shaper (equalizers).

When CATV technology is used for this channel, the resulting frequency shaped signal is received, pre-equalized to resemble the coax line, and detected. A vanilla cable modem can be used at the receiver, provided

1. The channel is adequately equalized by the combination of the transmitter Txl00/Tx500 (Figure 1) and receiver Rx600/Rx700 (Figure 1) (possibly together with additional transmit spectral shaping, and a front-end equalizer).

2. The frequency selective MV line does not cause deep notches to appear in the spectrum. If required, attenuators can be placed on the line to reduce the strength of unwanted reflections.

3. Intermediate regeneration is used if required to restore signal levels R300 in Figure 1. As shown in Figure 4, this regeneration can be just amplification Rl, an amplification followed by thresholding R2, or complete reception and retransmission R3.

Alternatively, if there are too many spectral notches, transmission of the notched out information can be carried out at other frequencies, and frequency shifting can be used to create a "virtual TV channel" for the cable modem. Other techniques can also be used for creating a "virtual TV channel" from the large amount of channel bandwidth, and diversity in the form of 3 -phases and/or 6-phases available.

The medium voltage grid is a branching structure, with potentially large mismatches at branching points. This branching structure can be partitioned into subsections by receiving and re-transmitting the signal at regenerators, as shown in Figure 4. The subsections can operate independently. However, the residual radiation from the subsections impinges on the adjacent subsections, thus reducing SIR (signal to interference ratio).

Ih principle, frequency diversity can be used in different sections to reduce SII. However, the interference pattern is not circular, due to the varying route of the MV line (unlike a circular wireless cell). The set of reusable frequencies has to be determined based on determining the exact radiation pattern of the MV section taking into account its geometry. Note that the pickup is strongest at the sending end (i.e. the transmitter) - this is a form of near-end-cross-talk (NEXT). NEXT cancellation techniques can be applied at the sending end, and at transceivers close to it. Of course, code diversity can be used instead of frequency diversity. Code reuse factor depends on interference pattern, analogous to above.

Medium voltage power lines (11 KV, 33KV) are generally 3-phase (either delta or Y-connected), and sometimes double circuit with 2 3-phase circuits. These multiple phases offer (partially) independent channels, which can be exploited to improve capacity, diversity, reduce power, etc. as per well-known MIMO (multiple-input-multiple-output) principles, and this is discussed further below.

The benefits, which can be obtained using MIMO principles, are first discussed. Then, some of the ways in which MMO can be optimally used to improve performance are outlined. Finally - some of the underlying theoretical basis is discussed.

Single circuit lines offer two independent channels, between the source and destination. Double circuit lines offer at least four. This facilitates one or more of the following

1. Doubling or quadrupling channel capacity for single/double circuit lines.

2. Improving SNR/BER performance using the channel diversity. Conductors in the three phases encounter differing amounts of coupling to each other, to metallic posts, and other objects, and encounter different degrees of mismatches enroute. In addition, the conductors of the three circuits follow slightly different paths along the route of the 3-phase circuit. Hence the behaviour of channels offered by these conductors is different - both amplitude and phase response - resulting in diversity among the signals received along the three phases. 3. Provided the amplitude and phase of the excitation is chosen correctly, the radiation of an array of N conductors scales less than linearly with respect to the number of conductors N (it is approximately logarithmic in N - please see the discussion below). Thus the received output power by launching power of the same frequency, (with an appropriate phase and amplitude) in 3-phases has less relative radiation loss compared to launching power on only two. Similarly, a joint signal launched on all six phases has much less relative radiation loss compared to launching it on two. This can be used for reducing the attenuation of the channel. 4. With an appropriate phase and amplitude, the radiation can be also increased. This causes the radiated energy to increase, and hence increases the coverage by wireless mode of transmission.

5. Different frequencies, codes, polarizations, etc can be used on the two channels of a 3- _^ phase circuit.

Optimal excitation (magnitude and phase of the transmitted signal) of multiple conductors (three conductors are shown in Figure 5) allows further control of radiation/attenuation. In Figure 5, the amplitude of the signal on each of the phases can be controlled by variable gain blocks G700, G800 and G900, while the phases can be controlled by variable time delays PHlOOO, PHIlOO, and PH1200. The controller CT1300 is used to set the gain and time delay blocks appropriately. A proper choice of excitation can reduce radiation from a set of multiple conductors, to even below the radiation from fewer conductors, reducing channel attenuation. This can be implemented easily using state-of-art DSP technology, even at the high frequencies being used in the invention. A proper choice of excitation can also increase radiation from a set of multiple conductors, thereby increasing coverage of the wireless mode of transmission. In both cases, the excitation has to be adaptively determined, due to the random irregular nature of the MV grid.

A theoretical basis for determining the optimal excitation is outlined below. First, a 3-phase line, only two phases of which are excited, nevertheless conveys coupled energy through the third conductor, with low loss. Hence, classical MIMO techniques can be used to get more information about the transmitted signal, by tapping into the 3^rd nominally unexcited conductor. Indeed at

VHF/UHF, the MV grid radiates in addition to conveying energy. This radiated energy can itself be picked up by a suitable number of antennae placed near the line. Thus a dual excitation multi output system (some on the conductors, some on antennas near it) is created.

Further improvements can be made by exciting all 3-phases or 6-phases simultaneously. The radiated energy depends on the antenna array pattern resulting from the excitation. The notation CL\

— |θj|trΦj, is used for the excitation on the ith conductor. It can be shown that the antenna array pattern A(φ) and radiation resistance R_raa satisfy the following equations:

Rrad = -^V-Jl) which is again logarithmic in the effective length

α (no subscript) is the attenuation constant for the mode in question, β is the propagation constant/? = 2^/ where λ is the wavelength, η is the impedance of free space:

A(φ) = \ + Y_ja_ie^m'^c∞(φ-^δ'⁾ (0.1)

<=2

Where di is the inter-conductor spacing, and φ the angle from the horizontal [7]. This exhibits maxima and minima as a function of frequency, and also amplitude and phase.

Figure 7 shows the relative radiated energy of an equally excited (all a; = 1) array with 1 meter element spacing with 2, 3, and 6 radiators, considering only the antenna pattern A(φ). All elements were excited equally in this example.

Clearly at several frequencies, the radiated energy of 3/6 radiators is less than 3/6 times (a minimum of 1.6/2.8 times) that of a single radiator. Hence the radiated loss considerably reduces due to the mutual coupling between the radiators. Alternatively, the set of conductors behaves more and more like an ideal waveguide. As such, as long as at these frequencies, the characteristic impedance is not too low, the relative radiation and hence attenuation is reduced compared to the 2- wire case.

Figure 7 also shows that an appropriate selection of frequency can lead to increased radiation (at the maxima), implying increased coverage by wireless reception of the same radiation. For a given frequency, the radiated energy can be minimized or maximized by choosing an optimal excitation. From Equation (0.1) above,

- ^{1 +}Σ i-2 h V^{v> 3*M cwt}^ ^{J +}Σ 2-2 h K^{w e"J}^ ^cwϊsM ' ^+κ ⁺Σ Σ k I \^a ■ U^'^"*' V^{W co}* ^{M Ml C05(}^' ^M i-2 /-2

F(β), or equivalently the radiated energy is minimizing/maximiizing the integral:

This is a quadratic in the unknown excitations a_t —

and can be optimized by standard conjugate gradient and similar techniques.

Based on all this, the attenuation α of an N-conductor system at a certain frequency, amplitude and phase excitation can be obtained from energy balance. Basically, the energy input into each conductor is the current times the characteristic impedance Z₀ ^N of the conductor with respect to a possibly fictitious ground. Figure 8 shows the case for 6-conductors AAlOO, AA200, AA300, AA400, AA500, AA600 with respect to fictitious ground G700. Each conductor has Ohmic losses R_0Im, and the entire system radiates as a whole. It can be shown from energy balance, that the attenuation α satisfies the equation: IaNZ" =

This equation implies that a N-conductor system behaves like a 2-conductor system, provided the

characteristic impedance Zo^N and ohmic loss R^ohm are scaled by the , the change of

the radiation of the N conductor system relative to N independent radiating conductors. An appropriate choice of frequency and/or amplitude and/or phase of excitation (at each of the N conductors), enables this relative radiation to be changed, changing the balance between the radiated and transmitted energy, and offering control of both wire line attenuation and wireless coverage.

Figure 9 shows the gain (considering only Antenna factor A(φ)) from optimally phased excitation, for a 3-conductor MV line in triangular configuration, and Figure 10 shows the same for a 6- conductor line (double circuit), with the conductors in a 3 horizontal rows of 2 conductors each.

In Figure 9, 2-opt/2-Eq is the relative radiation (as a function of frequency in MHz) from an excitation of 2-conductors chosen to maximally reduce radiation, relative to 2-conductors equally excited. 3-Eq/2-Eq is the relative radiation from an equally excited 3-conductor array to an equally excited 2-conductor array. 3-Opt/2-Eq is the relative radiation from an excitation of 3-conductors chosen to maximally reduce radiation, relative to 2-conductors equally excited. 3-Opt/2-Opt is the relative radiation from an excitation of 3-conductors chosen to maximally reduce radiation, relative to 2-conductors optimally excited. Similarly for Figure 10, 2O/2E, 3O/3E, 4O/4E, 5O/5E, and

6O/6E refer to the cases of 2,3,4,5 and 6 conductors optimally excited relative to 2 conductors equally excited.

Consider the 3-conductor case first. Here, for exciting two conductors with an optimal phasing, the radiated energy can reduce by up to a factor of 2 relative to equal excitation (around 300 MHz). It is even less below 100 MHz, but the system of the present invention is predominantly in the higher VHF/UHF bands. If all 3-conductors are excited with the same amplitude and phase, the radiated energy varies from a low of 50% (equal excitation is optimal here) to a high of 180% relative to 2- conductors equally excited. If all 3-conductors are optimally excited, field cancellation reduces the radiation from a low of 50% to a high of 150% relative to 2-conductors equally excited. On an average, the radiation is about 6% more than the 2-conductor equally excited case. Relative to the 2-conductor optimally excited case, the field is about 35% more. Since the mutual impedances are small,(this can be shown by a detailed electromagnetic analysis) the energy absorbed is roughly twice the energy of the 2-conductor system. Hence, as more conductors are excited, the energy absorbed increases more than the radiation, leading to a substantial decrease in signal attenuation. The 3-conductor system offers better wave guiding than the 2-conductor system. The wave guiding properties can be modulated by choosing the excitation to result in the optimal value of attenuation - low attenuation for wire line transmission and high attenuation (large radiation) for wireless coverage.

The wire line attenuation gains for ideally straight 3-conductor configurations are easily 15 dB/Km. For the 6-conductor case, the gains are even more, with the radiation from 6-conductors limited to about 2.5 to 3 times that for a 2-conductor pair, and the energy input being about 5 times that for a 2 conductor pair.

The optimal amplitude/phase of the excitation on each conductor has to be determined adaptively, due to the random MV grid geometry. The adaptation can be based on a gradient descent algorithm in the amplitude/phase, given an excitation at any conductor, composed of a single amplitude/phase at a single frequency, or alternatively, the signal power can be allocated amongst the multiple

• amplitudes/phases, and the power then packed into the best amplitude/phase by perturbing the powers of the different amplitude/phases, and examining the received power. The different phases can be examined in TDM order, etc. Signal power can be spread (possibly according to water filling) amongst the different amplitude/phase combinations, for diversity in face of changes in the MV grid due to wind, faults, etc. In essence the multi-conductor MV grid is being controlled like a phased-array-radar, but the control is to reduce emissions to reduce wire line attenuation, not to steer the beam. The control can be set to increase emissions also. In such a case, the signal can be picked up wirelessly using far away antennas also, provided the signal strength is adequate.

Use of Signal Regeneration:

A communication system built on this channel in general uses various degrees of amplification and/or regeneration. This regeneration can be simple amplification, thresholding, or more sophisticated detection. In general, a number of amplification stages are followed by a complete detection algorithm. If there are M amplification spans, each compensating for a span loss L, with a noise figure F each before detection, the SNR at the detector for a launch power of Pi is

SNR( M"¹ span in dB) = P; - L - 10*logl0(M) - KT₃B - F

It is assumed that the noise input at each stage is independently additive, and can be modeled by an antenna noise temperature T_a . K is Boltzmannn's Constant 1.38*10^'23 Joules per Kelvin, and B is the total bandwidth. For an input power of 10 dBM for each 8 MHz channel, with a span loss of up to 80 dB, and an antenna noise temperature of less than 1000 K at a few hundred MHz, and a noise figure F of 6 dB, the SNR becomes

SNR( M"¹ span in dB) = -20 - 80 - 10*logl0(M) - 10*loglO(1.38*10-²³ * 1000 * 8*10⁶) - F

SNR(M* span in dB) = -100 - 10*logl0(M) -10*logl0(l.38*10-") - 6 = -100 - 101ogl0(M) + 129.6 - 6 = 23.6 - 101ogl0(M)

For a system carrying approximately 3 B/Hz, about 10 dB SNR as per Shannon theory, is needed. Thus about 10 stages of amplification can be used, before complete signal regeneration is required. This corresponds to a regenerator spacing of between 5 to 7 Km, at an amplifier spacing of about 750 meters.

Figure 11 shows a regenerated section with two stages of amplification AlOO and A200, followed by signal regeneration R300. The intermediate signal amplifiers AlOO and A200 boost the signal level well beyond the noise (thermal and/or power line harmonics). Signal regeneration is required at the end of the third span; else the SNR will drop below the minimum allowable for the system BER. M-MO techniques as outlined previously can be used to increase repeater and/or regenerator spacing.

Figs. 12 to 14 illustrate some examples of the channel and equilizer derived during experiments*.

Figure 12 shows the response of the channel derived from experimental data. Using the experimental data of the attenuation in the channel for various frequencies measured from 48.2 MHz to 583.2 MHz. They are normalized to 1 GHz and modeled the response of the channel as an Infinite Impulse Response (IIR) Filter of type Direct Form π Transposed. The filter order was found to be 13 with an impulse response of length 2518. The filter was found to be stable with 13 zeros and 13 poles.

Figure 13 illustrates the Post Equalizer for the channel. Using the transfer function of the filter (representing the response of the channel described above) the transfer function was inverted, thus forming a zero-forcing filter with a response just opposite to that of the channel filter. The equalizer was designed as an Infinite Impulse Response (WC) Filter of the form Direct-Form II Transposed filter. The filter was optimized to be of the order of 10 and with an impulse response of length 651. The filter was found to be stable with 10 poles and 10 zeros.

Figure 14 illustrates the equivalent response of the channel filter and Equalizer.

Various forms of coding can be used in this communication system. Reed Solomon codes with heavy interleaving are useful to eliminate errors caused by bursty power line faults. Turbo codes can buy additional SNR to reduce power and hence radiated emissions if required. However, - due to the operation of this system in broadcast bands, emissions are less of an issue compared to the 1-

30 MHz region, assuming one or more channels in the broadcast VHFAJHF band is allocated for wire line transmission. If the wireless mode of coverage is desired, then power grid will act as a large distributed antenna fed with signals in the band under consideration.

*Experimental results.

REFERENCES

[1] Amirshahi, P., and M. Kaverhad, Transmission Channel Model and Capacity of Overhead Multi-Conductor Medium-Voltage Power-Lines for Broadband Communications, Proceedings of

IEEE Consumer Communications and Networking Conference, January 2005.

[2] Amperion Web Page, http://www.amperion.com

[3] Corridor Systems Home Page, http://www.corridor.biz

[4] http://www3.ietf.org/proceedings/01 dec/slides/ipcdn-3/ [5] S.Prasanna. Aerial MV lines at VHF/UHF: Quasi-TEM Analysis and Experimental

Results, ISPLC 2006 International Symposium on Power Line Communications, March 26-

29, 2006 Orlando, Florida, USA.

[6] G. N. Srinivasa Prasanna, The MV Aerial Power Grid at VHF/UHF Rivals Fiber in

Capacity, Optical Fiber Conference, March 5-10, 2006 Anaheim, California, USA [7] Jordan, E.G., and Balmain, K.C., Electromagnetic Waves and Radiating Systems, Prentice-Hall,

India, 2^nd Ed, 1968

Claims

CLAIMS:

1. A method for transmitting a broadband signal over a set of one or more conductors of a power line network, such as a ubiquitous medium voltage (MV) or low voltage network, transmission occurring at UHF/VHF wherein a transmission channel is divided into a plurality of sub channels each being separated from the other in time, or in carrier frequency, comprising the steps of: a. Allocating unused sub channels which result in using those channels for transmission as per the invention, which aforesaid channels have not been earmarked for broadcast communication using electromagnetic radio wave propagation; b. Generating and Transmitting a waveform over two or more conductors in free space; c. Receiving a waveform with a loss less than free space loss, over two or more conductors and/or one or more antennas. d. Coupling a low power signal to a high power transmission, MV or LV line; e. Signal Processing; f. Regeneration; and g. Error Correction.

2. A method as claimed in claim 1, wherein the step of allocating unused sub channels includes a step of: a. Spectral shaping to preferentially occupy spectral notches in the spectrum of said broadcast, said spectral notches exemplarily caused by horizontal or vertical flyback in the case of TV broadcast, b. Transmission at a power level non-interfering to said broadcast communication.

3. The method as claimed in claim 1, wherein the step of transmission uses a modulation scheme used by TV or CATV transmission.

4. The method as claimed in claim 1, wherein the step of signal generation, processing, or reception includes the step of using standard TV, CATV and/or FM equipment, exemplarily modulators, amplifiers, and modems.

5. The method as claimed in claim 4, wherein the system uses an agile (i.e. frequency variable) or fixed frequency CATV modulator for signal generation and transmission.

6. The method as claimed in claim 4, wherein the system uses a CATV receiver for reception.

7. The method as claimed in claim 4, wherein the system uses a CATV transceiver for both transmission and reception.

8. The method as claimed in claim 4, wherein the system uses a CATV amplifier for boosting the signal at a point in between transmission and reception.

9. The method as claimed in claim 8, wherein the system uses a CATV amplifier followed by a signal processor, to boost the signal level, and sharpen the transitions for an appropriate modulation scheme.

10. The method as claimed in claim 4, wherein the system uses a CATV transceiver with a pre and post equalizer either separately attached or integral with it, for both transmission and reception, to have the channel seen by the said CATV transceiver resemble CATV.

11. The method as claimed in claim 1, wherein the step of transmission includes the step of two or more conductors being excited simultaneously, with an appropriate choice of relative phase and/or amplitude for reducing radiation, and hence reducing channel attenuation.

12. The method as claimed in claim 1, wherein the step of transmission includes the step of two or more conductors being excited simultaneously, with an appropriate choice of relative phase and/or amplitude for increasing radiation, and hence increasing coverage by the wireless mode of transmission.

13. The method as claimed in claim 1, wherein the step of reception further includes signal detection on multiple conductors, and/or antennas located possibly close to the two or more conductors.

14. The method as claimed in claim 11, wherein the step of transmission further comprises the step of adaptive amplitude modulation (power control) and/or phasing of currents injected at multiple conductors, to reduce radiation, and attenuation, the adaptation being done by co-operative signaling between the steps of transmission and reception.

15. The method as claimed in claim 11, wherein the step of transmission further comprises the step of signaling and/or data channel spread over multiple amplitude/phase/frequency excitations at each conductor, for diversity gain.

16. The method as claimed in claim 1, wherein the step of transmission further comprises the step of using multiple frequency channels and/or multiple timeslots for multiple accesses on the MV line.

17. The method as claimed in claim 1, wherein the step of transmission further comprises the step of using the MV backbone for backhauling (i.e. connecting a point with switching infrastructure to the antennas) cellular wireless and/or wire line signals.

18. The method as claimed in claim 17, wherein the MV backbone is used for implementation of 4+G systems, using possibly small antennas located close to each other (micro-cells).

19. The method as claimed in claim 1, wherein the step of signal processing uses Reed- Solomon and/or Turbo coding for improving SNR or reducing emissions.

20. The method as claimed in claim 1, wherein the step of transmission further comprises the step of using multi-conductor and/or multi-antenna excitation and/or reception, possibly with optimal amplitude and/or phase, to improve SNR and/or bit rate and/or reduce emissions and/or other performance metrics.

21. The method as claimed in claim 1, wherein the step of regeneration further comprises the step of placing repeaters and/or regenerators periodically, with a repeater or regenerator handling one or more channels, said repeaters being exemplary amplifiers, and regenerators being exemplary decoders that completely decode the signal, and/or sharpen the transitions.

22. The method as claimed in claim 1, wherein the step of allocating unused sub channels includes the step of frequency planning and/or allocation, to niinirnize interference between adjacent systems carrying possibly different data. This step exemplarily allocates sub channels whose geographic coverage follows the contours of the MV grid, and which said coverage need not be approximately circular.

23. A method as claimed in claim 1, wherein the step of allocating unused sub channels includes the step of matching the frequency spectrum of the modulation chosen to the audio, chrominance and luminance signals of a TV broadcast system (including frequency notches and tilt).

24. A method as claimed in claim 1, where both wireless and wire line modes are used, exemplarily with both wire line transceivers and wireless transceivers.

25. A method as claimed in claim 16 being used as a multi-access channel connecting all transceivers on the same power line.

26. A method as claimed in claim 25 being used as a multi-access channel, with lower frequencies allocated to further away transceiver pairs, possibly to improve SNR, reduce power and or increase bit rate

27. An apparatus for data communication at UHF/VHF over a power line network wherein a transmission channel is divided into a plurality of sub channels each being separated from each other in time or in carrier frequency, comprising: a. Transmission means (transmitter); b. Reception means (receiver); c. Coupling means (coupler) by using known methods; d. Signal Processing means (signal processing); e. Regeneration means; and f. Error correction means.

28. The apparatus as claimed in claim 27, wherein the signal processing means comprises standard CATV and/or FM modulators and modems.

29. The apparatus as claimed in claim 27, wherein the transmission means performs auxiliary filtering by means of pre-shaping.

30. The apparatus as claimed in claim 27, wherein the reception means performs auxiliary filtering by means of post-shaping.

31. The apparatus as claimed in claim 27, wherein the transmission means comprises means for multiple conductors being excited simultaneously for reducing relative radiation, and hence reducing channel attenuation.

32. The apparatus as claimed in claim 27, wherein the transmission means comprises means for multiple excitations being replaced by signal detection on multiple conductors, and/or antennas located possibly close to the MV line.

33. The apparatus as claimed in claim 27, wherein the transmission means comprises fixed or adaptive amplitude modulation (power control) and/or phasing of currents injected at multiple conductors, to reduce radiation, and attenuation, the adaptation being done by co- operative signaling between the steps of transmission and reception.

34. The apparatus as claimed in claim 27, wherein the transmission means comprises signaling and/or data channel spread over multiple amplitude/phase excitations at each conductor, for diversity gain.

35. The apparatus as claimed in claim 27, wherein the transmission means comprises using multiple frequency channels and/or multiple timeslots for multiple access on the MV line.

36. The apparatus as claimed in claim 27, wherein the transmission means comprises using the MV backbone for backhauling wireless and/or wire line signals.

37. The apparatus as claimed in claim 27, wherein the transmission means comprises the MV backbone being used for implementation of 4+G systems, using possibly small antennas located close to each other (micro-cells).

38. The apparatus as claimed in claim 27, wherein the signal processing means comprises using Reed-Solomon and/or Turbo coding used for improving SNR or reducing emissions.

39. The apparatus as claimed in claim 27, wherein the transmission means comprises using multi-conductor and/or multi-antenna excitation and/or reception, possibly with optimal amplitude and/or phase, to improve SNR and/or bit rate and/or reduce emissions and/or other performance metrics.

40. The apparatus as claimed in claim 27, wherein the regeneration means comprises placing repeaters and/or regenerators periodically, with a repeater or regenerator handling one or more channels, said repeaters being exemplary amplifiers, and regenerators being exemplary decoders that completely decode the signal, and/or sharpen the transitions.

41. The apparatus as claimed in claim 27, wherein the transmission means comprises frequency planning and/or allocation, to minimize interference between adjacent systems carrying possibly different data.

42. The apparatus as claimed in claim 27, wherein the transmission means comprises matching the frequency spectrum of the modulation chosen to the audio, chrominance and luminance signals of a TV broadcast system (including frequency notches and tilt).

43. The apparatus as claimed in claim 27, wherein the transmission means comprises choosing the frequency spectrum of the modulation such that it occupies the spectral notches of a vanilla TV signal, and possibly at a level transparent to TV sets.

44. The apparatus as claimed in claim 27, being used in both wireless and wire line modes.

45. The apparatus as claimed in claim 27, being used as a multi-access channel connecting all transceivers on the same power bus.

46. The apparatus as claimed in claim 27, being used as a multi-access channel, with lower frequencies allocated to further away transceiver pairs, possibly to improve SNR, reduce power and or increase bit rate.