Transmission systems for transmitting signals over power distribution networks, and transmitters for use therein
First Claim
1. A receiver for coupling to a power distribution network to receive a signal transmitted over the network and comprising at least two carrier signals having different frequencies and each modulated with a digital signal, at least a portion of the digital signal modulating each carrier signal representing the same message and the carrier frequencies being locked together, the receiver comprising:
- input circuit means for receiving the modulated carrier signals;
means for sensing which of the first and second modulated carrier signals is being most strongly received;
variable frequency oscillator means; and
phase-locked loop means responsive to the sensing means to lock the frequency of said oscillator means to whichever of the first and second modulated carrier signals is being most strongly received and to demodulate at least that carrier signal to derive the digital signal therefrom, said phase-locked loop comprising;
means for deriving first and second intermediate signals from the first and second modulated carrier signals respectively, and third and fourth intermediate signals, substantially equal in frequency to the first and second intermediate signals respectively, from said oscillator means;
a first phase detector responsive to the first modulated carrier signal and a signal derived from the first and third intermediate frequency signals to produce a first output signal having a DC component dependent on the phase difference therebetween, said first output signal also containing said digital signal;
a second phase detector responsive to the second and fourth intermediate frequency signals to produce a second output signal having a DC component dependent on the phase difference therebetween, said second output signal also containing said digital signal;
low pass filter means; and
switching means responsive to the sensing means to apply to said oscillator means, via the low pass filter means, whichever of the first and second output signals corresponds to the modulated carrier signal being most strongly received, to vary the frequency of said oscillator means in the sense which tends to reduce the phase difference producing the output signal.
1 Assignment
0 Petitions
Accused Products
Abstract
A transmission system, for transmitting signals over an electrical power distribution circuit, comprises a transmitter arranged to produce at least two carrier signals of different frequency and to modulate each of them with the same digital signal. The respective frequencies of the carrier signals are derived by frequency division from a common master oscillator, and are thus phase-coherent. The system includes a receiver for receiving the signals, comprising a respective input circuit for each modulated carrier, the input circuits each being tuned to the frequency of their respective carrier signal. A plurality of oscillator signals of different frequencies, derived from a variable frequency oscillator, are used to beat the received carrier signals to respective signals at a common frequency, which signals are summed. The summed signal at the common frequency is applied to one input of a phase detector, whose other input is connected to receive another oscillator signal, also at the common frequency, from the variable frequency oscillator. The output signal from the phase detector is applied to the variable frequency oscillator to lock its frequency to those of all the carriers and therefore to that of the master oscillator in the transmitter. The digital signal is derived from the output of the phase detector by digital correlation techniques.
41 Citations
23 Claims
-
1. A receiver for coupling to a power distribution network to receive a signal transmitted over the network and comprising at least two carrier signals having different frequencies and each modulated with a digital signal, at least a portion of the digital signal modulating each carrier signal representing the same message and the carrier frequencies being locked together, the receiver comprising:
-
input circuit means for receiving the modulated carrier signals; means for sensing which of the first and second modulated carrier signals is being most strongly received; variable frequency oscillator means; and phase-locked loop means responsive to the sensing means to lock the frequency of said oscillator means to whichever of the first and second modulated carrier signals is being most strongly received and to demodulate at least that carrier signal to derive the digital signal therefrom, said phase-locked loop comprising; means for deriving first and second intermediate signals from the first and second modulated carrier signals respectively, and third and fourth intermediate signals, substantially equal in frequency to the first and second intermediate signals respectively, from said oscillator means; a first phase detector responsive to the first modulated carrier signal and a signal derived from the first and third intermediate frequency signals to produce a first output signal having a DC component dependent on the phase difference therebetween, said first output signal also containing said digital signal; a second phase detector responsive to the second and fourth intermediate frequency signals to produce a second output signal having a DC component dependent on the phase difference therebetween, said second output signal also containing said digital signal; low pass filter means; and switching means responsive to the sensing means to apply to said oscillator means, via the low pass filter means, whichever of the first and second output signals corresponds to the modulated carrier signal being most strongly received, to vary the frequency of said oscillator means in the sense which tends to reduce the phase difference producing the output signal. - View Dependent Claims (2, 3, 4)
-
-
5. A transmission system for transmitting signals over an electrical power distribution network or a telephone network, the system comprising:
-
at least one transmitter adapted to be coupled to the network, the or each transmitter comprising a first radio receiver for receiving broadcast control signals and for deriving timing signals therefrom, means for generating at least one network carrier signal, and means responsive to said timing signals for modulating the or each network carrier signal with a digital signal representing a message to be transmitted over the network and for applying the or each modulated network carrier signal to the network, at instants determined by said timing signals, for transmission thereover; and at least one receiver adapted to be coupled to the network, the or each receiver comprising input circuit means for receiving the or each modulated network carrier signal from the network, means for demodulating the or each modulated network carrier signal received by the input circuit means, a second radio receiver for receiving said broadcast control signals and for deriving said timing signals therefrom, and means responsive to the timing signals derived from the second radio receiver for deriving the digital signal from the, or at least one of the, demodulated signals. - View Dependent Claims (6, 7, 8, 9, 10)
-
-
11. A receiver for coupling to a power distribution network to receive a signal transmitted over the network and comprising at least first and second carrier signals having different frequencies and each modulated with the same digital signal, the carrier frequencies being locked together, the receiver comprising:
-
input circuit means for receiving the modulated carrier signals; variable frequency oscillator means; means for deriving from said oscillator means first and second oscillator signals whose frequency different equals the frequency difference between said first and second carrier signals, and a third oscillator signal whose frequency is equal to said frequency difference; first mixer means responsive to the first carrier signal and the first oscillator signal to produce a first intermediate signal whose frequency is equal to said frequency difference; second mixer means responsive to the second carrier signal and the second oscillator signal to produce a second intermediate signal whose frequency is equal to said frequency difference; and phase-locked loop means responsive to the intermediate signals and the third oscillator signal to lock the frequency of said oscillator means to whichever of the first and second carrier signals is being most strongly received and to demodulate at least the intermediate signal obtained from that carrier signal to derive the digital signal therefrom.
-
-
12. A transmission system for transmitting carrier-borne digital signals of predetermined bit rate over an electrical power distribution network whose transmission characteristics can vary at a rate comparable with said bit rate, the system comprising:
-
at least one transmitter adapted to be coupled to the network, the or each transmitter comprising means for producing at least two coherent carrier signals having different frequencies, means for simultaneously modulating each of the carrier signals with a digital signal, at least a portion of the digital signal modulating each carrier signal representing the same message, and means for simultaneously applying the modulated carrier signals to the network for transmission thereover; and a least one receiver adapted to be coupled to the network, the or each receiver comprising input circuit means for receiving the modulated carrier signals from the network, means for sensing which of the modulated carrier signals is being most strongly received, variable frequency oscillator means, and phase-locked loop means responsive to the sensing means to lock the frequency of said oscillator means to whichever of the modulated carrier signals is being mostly strongly received and to demodulate at least that carrier signal to derive the digital signal therefrom. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19)
-
-
20. A transmission system for transmitting carrier-borne digital signals of predetermined bit rate over an electrical power distribution network whose transmission characteristics can vary at a rate comparable with said bit rate, the system comprising:
-
at least one transmitter adapted to be coupled to the network, the or each transmitter comprising means for producing at least two coherent carrier signals having different frequencies, means for simultaneously modulating each of the carrier signals with a digital signal, at least a portion of the digital signal modulating each carrier signal representing the same message, and means for simultaneously applying the modulated carrier signals to the network for transmission thereover; and at least one receiver adapted to be coupled to the network, the or each receiver comprising input circuit means for receiving the modulated carrier signals, variable frequency oscillator means, means for deriving from said oscillator means first and second oscillator signals whose frequency difference equals the frequency difference between said at least two carrier signals and third oscillator signal whose frequency is equal to said frequency difference, first mixer means responsive to one of said at least two carrier signals and the first oscillator signal to produce a first intermediate signal whose frequency is equal to said frequency difference, second mixer means responsive to the other of said at least two carrier signals and the second oscillator signal to produce a second intermediate signal whose frequency is equal to said frequency difference, and phase-locked loop means responsive to the intermediate signals and the third oscillator signal to lock the frequency of said oscillator means to whichever of said at least two carrier signals is being most strongly received and to demodulate at least the intermediate signal obtained from that carrier signal to derive the digital signal therefrom. - View Dependent Claims (21, 22, 23)
-
Specification