Power line communication system

• US 5,844,949 A
• Filed: 10/09/1996
• Issued: 12/01/1998
• Est. Priority Date: 10/09/1996
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Hershey, John Erik, Welles, Kenneth Brakeley II, Gaus, Richard Charles Jr., Korkosz, Richard August, Saulnier, Gary Jude
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): PARK, ALBERT C
• Application Number:
  US08/728,020
• Time in Patent Office: 783 Days
• Field of Search: 340/310.02, 340/310.03, 340/310.01, 375/260, 375/200, 375/205, 375/296, 375/295, 375/259, 385/27
• US Class Current: 375/346
• CPC Class Codes: H04B 2203/5416 by adding signals to the wave form of the power source
• CPC Class Codes: H04B 2203/5495 having measurements and testing channel
• CPC Class Codes: H04B 3/54 Systems for transmission via power distribution lines
• CPC Class Codes: H04L 1/04 using frequency diversity
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26

Abstract

A system for communicating digital information over wires having a great deal of harmonic distortion, such as a power line, employs a transmitter which transmitter which creates a carrier wave for each of a plurality of signals to be sent. This carrier wave has frequency lobes positioned between the frequency lobes of the harmonic distortion. Each of the lobes of a single carrier signal is encoded with the same bit value during a given bit period. This signal is then mixed with any existing signal on the wire. At a remote receiver coupled to the wires, the signal is sensed, filtered, and Fourier transformed into coefficients. The signal-to-noise (S/N) ratio of each Fourier coefficient is determined by a novel S/N estimation technique. The coefficients are weighted based upon the S/N ratio estimation, and decoded, preferably by an inner product of the weighted Fourier coefficients. Additionally, the S/N ratio estimates could be time averaged before being used in the weighting and bit decoding.

Claims

1. A system for communicating digital information over a wire having a harmonic interference frequency lobes comprising:

a) a transmitter for transmitting message bits of a signal s₁ having;

i. a carrier wave synthesis device for creating a carrier wave having a plurality of frequency lobes between interference lobes described by;

##EQU4## where t is time, f_ik are frequencies between said harmonic interference lobes, M is the number of signal frequency lobes desired, α

_k, β

_k, are predetermined signal amplitudes, and φ

k,θ

k are predetermined phase offsets;

ii. a bit encoder coupled to a timing device, the synthesis device, and said wire, which inverts a carrier waveform for a single bit period for one bit value of said message bit, and leaves the carrier wave unchanged for a second message bit value to create an encoded message;

iii. a summation device coupled to the bit encoder and said wire, for summing the encoded message with existing signals on said wire;

b) a receiver coupled to said wire which decodes the encoded message into message bits.

2. The system for communicating digital information over a wire of claim 1 wherein the carrier wave synthesis device comprises:

a) a timing device to determine bit periods, and bit rate timing;

b) a storage device having a prestored carrier waveform;

c) a playback device coupled to the timing device and the storage device for playing back the prestored waveform according to bit rate timing.

3. The system for communicating digital information over a wire of claim 1 wherein the receiver comprises:

a) a sampler which converts a continuous signal into a series of discrete time samples;

b) a quantizer coupled to the sampler which reduces the precision of the discrete time samples;

c) a Fourier Transform device which performs a Fourier transform on the samples obtained at time t to result in Fourier coefficients X_k (t);

d) a decoder which performs an inner product of the Fourier coefficients X_k (t), and determine if the inner product is above or below a predetermined threshold to produce decoded message bits.

4. The system for communicating digital information over a wire of claim 3 further comprising:

a) a signal-to-noise (S/N) estimation device which estimates S/N based upon a reliability indication estimate |δ

_k | for each of the Fourier coefficients;

b) a combiner which weights each of the Fourier coefficients X_k (t) according to |δ

_k | to result in weighted Fourier coefficients X_k (t) passed to the decoder used in place of X_k (t) in determining bit decisions.

5. The system for communicating digital information over a wire of claim 3, further comprising:

a) a signal-to-noise (S/N) estimation device which estimates |δ

_k | from Fourier coefficients acquired at times t and t-1, X_k (t), X_k (t-1), respectively according to the equation;

##EQU5## where X_k (t-1)=x₁ +jy₁ and X_k (t)=X₂ +jy₂ for each of the Fourier coefficients;

b) a combiner which weights each of the Fourier coefficients X_k (t) according to |δ

_k | to result in weighted Fourier coefficients X_k (t) passed to the decoder used in place of X_k (t) in determining bit decisions.

6. The system for communicating digital information over a wire of claim 4 further comprising:

an averager coupled between S/N estimation device and the combiner for receiving a plurality of |δ

_k | estimates for Fourier coefficients X_k (t) over time, and performing an average of |δ

_k | to result in an |δ

_k | for each lobe, provided to the combiner, and used in place of |δ

_k | to result in the modified Fourier coefficients X_k (t).

7. The system for communicating digital information over a wire of claim 1 further comprising a plurality of transmitters each transmitting digital signals s_i, where i ≠

1 at frequencies between harmonic interference lobes, but at frequencies different than those of other transmitters of the system.