Power line communication systems

• US 5,952,914 A
• Filed: 09/10/1997
• Issued: 09/14/1999
• Est. Priority Date: 09/10/1997
• Status: Expired due to Term

• Current Assignee: Rakuten, Inc. (Rakuten Group, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Wynn, Woodson Dale
• Primary Examiner(s): Hofsass, Jeffery
• Assistant Examiner(s): PHAM, TOAN NGOC
• Application Number:
  US08/926,609
• Time in Patent Office: 734 Days
• Field of Search: 340/310.01, 340/310.02, 340/310.03, 340/310.05, 340/310.06, 340/310.07, 340/310.2, 375/259, 455/3.3
• US Class Current: 370/290
• CPC Class Codes: H04B 3/23 using a replica of transmitted signal in the time domain, e.g. echo cancellers
• CPC Class Codes: H04B 3/34 by systematic interconnection of lengths of cable during laying; by addition of balancing components to cable during laying

Abstract

Two duplex channels are provided using only three lines, two power lines and one neutral line. The transmitter/receiver of each duplex channel includes adaptive filters to cancel cross-coupling introduced by the common neutral line. Each channel is coupled to a power line using a hybrid line driver/receiver device. The hybrid line driver/receiver device includes an echo canceller and a bridge circuit to allow transmitting and receiving signals to and from a single power line with minimized echoing effects. The signal-to-noise ratios of each duplex channel is significantly increased so that two duplex channels may be implemented using only three wire connections. Thus, the communication capacity of power line communication systems is greatly increased compared to that for a single 2-wire channel.

Claims

1. A power line communications system, comprising:

a first power line and a second power line;

a neutral line;

a transmitter/receiver coupled to the neutral line and the first and the second power lines, the transmitter/receiver transmitting and receiving information using the first power line and the neutral line as a first channel and the second power line and the neutral line as a second channel, wherein the first channel is independent of the second channel.

2. The system of claim 1, wherein the transmitter/receiver comprises:

a first receiver coupled to the first power line and the neutral line, the first receiver generating a first output;

a second receiver coupled to the second power line and the neutral line, the second receiver generating a second output; and

an equalizing device coupled to the first and the second receivers, the equalizing device receiving the first and the second outputs and generating a first channel output and a second channel output.

3. The system of claim 2, wherein the equalizing device comprises:

a first equalizer receiving the first output of the first receiver and generating a first equalizer output;

a second equalizer receiving the second output of the second receiver and generating a second equalizer output;

a first summer subtracting the second equalizer output from the first equalizer output to generate the first channel output;

a third equalizer receiving the first output of the first receiver and generating a third equalizer output;

a fourth equalizer receiving the second output of the second receiver and generating a fourth equalizer output; and

a second summer subtracting the third equalizer output from the fourth equalizer output to generate the second channel output.

4. The system of claim 3, wherein each of the first, the second, the third and the fourth equalizers is selected from any one of an adaptive filter, a linear feedback equalizer, a decision feedback equalizer and an echo canceller.

5. The system of claim 2, wherein the equalizer device comprises:

a first equalizer receiving the second output of the second receiver and generating a first equalizer output;

a first summer subtracting the first equalizer output from the first output of the first receiver to generate a first summer output;

a second equalizer receiving the first summer output and generating the first channel output;

a third equalizer receiving the first output of the first receiver and generating a third equalizer output;

a second summer subtracting the third equalizer output from the second output of the second receiver to generate a second summer output; and

a fourth equalizer receiving the second summer output and generating the second channel output.

6. The system of claim 5, wherein each of the first, the second, the third and the fourth equalizers is selected from any one of an adaptive filter, a linear feedback equalizer, a decision feedback equalizer and an echo canceller.

7. The system of claim 1, wherein the transmitter/receiver comprises:

a transmitter;

a receiver;

a hybrid circuit coupled to the transmitter, the receiver and one of the first and the second channels as a data channel, the hybrid circuit transmitting data to and receiving the data from the data channel.

8. The system of claim 7, wherein the hybrid circuit comprises:

a first resistor having a first terminal and a second terminal, the first terminal being connected to a first terminal of the hybrid circuit and the second terminal being connected to a fourth terminal of the hybrid circuit which is coupled to a power line of the data channel;

a second resistor having a first terminal and a second terminal, the first terminal of the hybrid circuit being connected to the first terminal of the hybrid circuit and the second terminal of the second resistor being connected to a third terminal of the hybrid circuit; and

an impedance device connected between the third terminal of the hybrid circuit and a second terminal of the hybrid circuit which is a neutral line of the data channel, the impedance device having an impedance value substantially equal to a channel impedance of the data channel.

9. The system of claim 8, wherein the transmitter comprises a driver having a single input and two outputs, the driver driving the first and the second terminals of the hybrid circuit with the two outputs.

10. The system of claim 9, wherein the driver comprises:

a first buffer having a first positive input terminal, a first negative terminal and a first output terminal;

a second buffer having a second positive input terminal, a second negative terminal and a second output terminal;

a third resistor having a first terminal connected to the first output terminal of the first buffer, and a second terminal connected to the first negative input terminal of the first buffer;

a fourth resistor having a first terminal connected to the second output terminal of the second buffer, and a second terminal connected to the second negative input terminal of the second buffer; and

a fifth resistor having a first terminal connected to the second terminal of the third resistor, and a second terminal connected the second terminal of the fourth resistor, the first output terminal of the first buffer being connected to the first terminal of the hybrid circuit and the second output terminal of the second buffer being connected to the second terminal of the hybrid circuit.

11. The system of claim 9, wherein the receiver comprises:

a differential receiver coupled to the third and the fourth terminals of the hybrid circuit;

a summer having a positive input connected to an output terminal of the differential receiver;

a receiver buffer having an input terminal connected to an output terminal of the summer; and

an echo canceller connected between the single input of the driver and a negative input of the summer, the echo canceller being connected to the output terminal of the summer to receive a error signal for updating weights of the echo canceller.

12. The system of claim 11, wherein the echo canceller is an adaptive filter.

13. The system of claim 1, wherein the transmitter/receiver comprises:

a transmitter;

a receiver; and

an echo canceller coupled to the transmitter and the receiver, wherein the echo canceller cancels signals transmitted by the transmitter from signals received by the receiver.

14. The system of claim 13, wherein the echo canceller is an adaptive filter.

15. The system of claim 1, further comprising a plurality of decoupling devices, a first portion of the decoupling devices being connected in-line to the first power line and a second portion of the decoupling devices being connected in-line to the second power line, the transmitter/receiver being coupled to the first and the second power lines between two of the decoupling devices.

16. The system of claim 1, wherein the transmitter/receiver is coupled to the first and the second power lines through capacitors.

17. The system of claim 1, wherein the first and the second channels are duplex channels.

18. A method for operating a power line communications system, comprising:

transmitting first information through a first power line and a neutral line;

transmitting second information through a second power line and the neutral line;

receiving third information through the first power line and the neutral line; and

receiving fourth information through the second power line and the neutral line, wherein the first power line and the neutral line forms a first channel, and the second power line and the neutral line forms a second channel, the first channel being independent of the second channel.

19. The method of claim 18, further comprising:

generating a first output from the first channel;

generating a second output from the second channel; and

equalizing the first and the second outputs to generate a first channel output and a second channel output.

20. The method of claim 19, wherein the equalizing step comprises:

equalizing the first output to generate a first equalized output;

equalizing the second output to generate a second equalized output;

subtracting the second equalized output from the first equalized to generate the first channel output;

equalizing the first output to generate a third equalized output;

equalizing the second output to generate a fourth equalized output; and

subtracting the third equalized output from the fourth equalized to generate the second channel output.

21. The method of claim 20, wherein each of the first, the second, the third and the fourth equalized outputs is generated by any one of an adaptive filter, a linear feedback equalizer, a decision feedback equalizer and an echo canceller.

22. The method of claim 19, wherein the equalizing step comprises:

equalizing the second output to generate a first equalized output;

subtracting the first equalized output from the first output to generate a first summer output;

equalizing the first summer output to generate the first channel output;

equalizing the first output to generate a third equalized output;

subtracting the third equalized output from the second output to generate a second summer output; and

equalizing the second summer output to generate the second channel output.

23. The method of claim 22, wherein each of the first, the second, the third and the fourth equalized outputs is generated by any one of an adaptive filter, a linear feedback equalizer, a decision feedback equalizer and an echo canceller.

24. The method of claim 18, wherein the first and third information are transmitted and received over the first channel through a first hybrid circuit, and the second and fourth information are transmitted and received over the second channel through a second hybrid circuit.

25. The method of claim 18, further comprising:

echo cancelling the first information from the third information; and

echo cancelling the second information from the fourth information.

26. The method of claim 18, further comprising decoupling the first and second power lines by placing decoupling devices in-line to the first and the second power lines, wherein the first and the second information are transmitted and the third and fourth information are received from the first and the second power lines between the decoupling devices.