Abstract: In a frequency division multiplexed (FDM) telecommunications system, data is encoded on carriers stepped in frequency within each of a sequence of symbols. The carriers may be arranged in groups between which there are frequency bands in which interference may be expected. The symbols are of predetermined length and are transmitted at a predetermined frequency, and synchronisation to the symbols is needed at a receiver in order to decode the received symbols. During a synchronisation time, a sequence of synchronisation symbols carrying predetermined data is transmitted. The receiver performs unsynchronised Fast Fourier Transforms (FFTs) on the received symbols, starting successive FFTs at about the predetermined symbol frequency. The output of each FFT is evaluated by removing the predetermined data coding from the detected carriers and summing the detected phase differences between the carriers.

Abstract: An apparatus for coupling signals to a transmission line, such as a power line (120). The apparatus comprises an input for receiving a wanted signal; a first coupler for coupling the wanted signal (Vmain) onto the line at a first position (Y); a cancelling means (WB, WR, WY), coupled to the input, for deriving a cancelling signal (Vaux) from the wanted signal; a second coupler for coupling the cancelling signal onto the line at a second position (X), spaced from the first position; wherein the wanted signal and the cancelling signal destructively combine in a single direction of propagation along the line while enabling the wanted signal to propagate in the other direction along the line. The apparatus can be used to minimise radiation from an unshielded part of an electricity distribution network, such as substation (100), or to allow re-use of a frequency band on other power lines.

Abstract: Speech-band signals such as voice telephony and facsimile are trasnmitted over a power line communications system. The method comprises: receiving speech-band signals at the communications station from speech-band communications equipment; digitising the speech-band signals; encoding the digitised signals into data packets; and transmitting the data packets to/from a station over a part of the line which is external to the premises, using a packet data communications protocol. Equipment can selectively route the speech-band signals via the power line or the PSTN.

Abstract: An Apparatus for extracting communications signals from power lines, which lines are arranged such that leakage of signals occurs between them. The apparatus receives a signal from each of at least two of lines (blue, red, yellow) and combines the received signals so as to increase the ratio of wanted signal to interference plus noise S/(1+N). Preferably the combining is achieved by weights WB, WR, WY and a summer. The weights phase shift and scale the received signals in amplitude. The apparatus can also be used for transmitting in the downstream direction.

Abstract: A power line communications system has a power line having a plurality of conductors which carry communications signals. A set of communications signals are coupled to a set of the plurality of conductors, each signal being coupled to a respective one of the set of conductors and the phasor relationship of the set of communications signals is chosen such that radiation of communications signals from the power line is minimised. The phasor relationship may be achieved by phase shifting one or more of the signals. This method allows communications signals to be transmitted at higher power levels, thereby extending range of transmission, while minimizing radiation from the line.

Abstract: Digital control of analogue beamformers utilising PIN diodes in a shunt circuit bi-phase attenuator arrangement is difficult because of the diodes extremely non-linear control response. There is disclosed a PIN diode circuit arrangement comprising a digital to analogue converter (DAC) with a reference voltage controller arranged to vary the DACs response to digital input signals to compensate for the PIN diode's non-linear response making this look substantially linear in the digital domain. The circuit preferably incorporates a feedback arrangement from the output of the DAC to its reference voltage input.

Abstract: This invention relates to telecommunications systems. In a subscriber loop carrying high speed data signals, noise cancellation is achieved by a data signal demodulator having first and second inputs 81,82, arranged to receive differential data signal and local field RFI input signals respectively. A feedback signal of the demodulator is sampled, processed, vector modulated and then combined with the local field RFI input signal of the demodulator. The combined signal is summed with the differential input signal to thereby reduce interference coupled with the first input.

Abstract: Communications signals are transmitted over a power distribution network. A plurality of communications stations which are coupled to the power lines are served by a base station. Communications signals are coupled between the base station and the distribution network, and the flow of the communications signals is controlled according to the station that it is desired to communicate with by preferentially transmitting along or receiving from a power line to which the desired communications station is coupled. The base station can be coupled to each of the power lines or to the busbars at a distribution station.

Abstract: A power line communications system has at least one power line upon which noise level varies with time. The system determines quiet periods when noise upon the line is at a reduced level and transmits one or more data packets within the quiet periods, so as to increase data throughput in the system.

Abstract: A method and apparatus of reducing interference in a broadband radio frequency link is disclosed. Different signals are received by two antenna elements, in a first case the signals comprise differently polarized signals at the same or an offset frequency; in a second case the signals comprise a wanted signal and an interference signal, wherein the interfering signal is treated as an independent channel. The method comprises the steps of receiving radio frequency signals on two independent paths, selecting a portion of the radio frequency signal in each receive path or the desired signal path after demodulation where a predetermined frequency or band of frequencies is known to be absent; measuring the signal power; determining weights in a feedback path; and applying the feedback control signals to an algorithm which determines the weight(s) applied to the wanted signal such that the signal power in the summed signal(s) due to the interfering signal is reduced or cancelled.

Abstract: A repeater for use with Time Division Duplex (TDD) communications such as CT2 delivered over mains electricity cables. The repeater is coupled to a mains cable via a branch (the cable is not broken) and in alternate TDD phases converts signals from f.sub.1 .fwdarw.f.sub.2 or f.sub.2 .fwdarw.f.sub.1 and amplifies them. A clock signal to control timing of the conversion step is derived from a dedicated channel, a tone, or a call in progress. A regenerator function may be combined with the repeater.