Coherent phase shift keyed demodulator for power line communication systems

• US 4,379,284 A
• Filed: 07/17/1981
• Issued: 04/05/1983
• Est. Priority Date: 09/21/1979
• Status: Expired due to Fees

• Current Assignee: ABB Power T&D Co Inc (ABB Limited)
• Original Assignee: Westinghouse Electric Corporation (Paramount Global (f/k/a ViacomCBS Inc.))
• Inventors: Boykin, John R.
• Primary Examiner(s): Yusko, Donald J.
• Application Number:
  US06/284,261
• Time in Patent Office: 627 Days
• Field of Search: 340/310 R, 340/825.7, 375/82, 375/83, 375/52, 375/39
• US Class Current: 375/329
• CPC Class Codes: H04L 27/2337 using digital techniques to measure the time between zero-crossings
• CPC Class Codes: H04L 7/0331 with a digital phase-locked loop [PLL] processing binary samples, e.g. add/subtract logic for correction of receiver clock H04L7/0337 takes precedence
• CPC Class Codes: H04L 7/046 using a dotting sequence

Abstract

An apparatus and method for coherent phase demodulation of a binary phase shift keyed carrier includes sequentially processing plus and minus polarity samples of plural carrier segments occurring within each carrier data symbol. The samples for each segment provide a binary coded signal for producing corresponding first and second relative phase angle vector signals. The second vector signals are summed over several data symbols to generate reference phase angle signal vector signals. Correlation signals are produced from phase comparison of each of the first vectors with the reference vector signals. The correlation signals are summed in a synchronized relationship for the carrier segments included in each data symbol. The sums of the correlation signals represent either positive or negative correlations with the one and zero data bits of the carrier data symbols.

Claims

1. A power line carrier communication system for transmitting coherent phase shift keyed (CPSK) carrier data transmissions, comprising:

power line coupler means for being mounting in signal communication with power line conductors transmitting a carrier having binary phase modulated data;

receiver means for receiving carrier signals from said power line coupler and including high pass filter means for attenuating electric power frequencies conducted on said power line conductors along with said carrier, said receiver further including band filter means having a center frequency substantially equal to a predetermined frequency of said carrier and still further including signal clipping and amplifying means for producing hard limited signals varying between two levels in response to said carrier; and

a coherent phase demodulator for receiving said hard limited signals and including a source of sampling pulses having a predetermined sampling frequency wherein the ratio of said carrier frequency and said sampling frequency is not equal to an integer, polarity sampling means for producing polarity sample bit signals having binary values responsive to the two levels of said hard limited signals and occurring at the frequency of said sampling pulses, said sample bit signals having reoccurring predetermined groups thereof with an integer number of said groups occurring during each one of equal data symbol times in said carrier, whereby said groups define plural carrier segments within each data symbol time, said demodulator further including means producing first vector signals representing a relative phase angle corresponding to the binary coded values of each of said groups of sample bits and still further including means producing reference vector signals representing a phase angle responsive to weighted sum averages of phase angle representations corresponding to binary coded values of each of a predetermined integer number of said groups of sample bits occurring an integer number of said data symbols, said demodulator still further including phase detector means responsive to said first vector signals and said reference vector signals for producing correlation signals representing relative measures of positive and negative correlation of the phase angles of said first and reference vector signals, said demodulator still further including summing means for algebraically adding said correlation signals derived from each of said first vector signals produced during said plural carrier segments and within each data symbol and correspondingly producing correlation sum signals having positive and negative values representing opposite binary conditions of the carrier data symbols, and said demodulator still further including data bit output means having means for continuously relating the positive and negative values of said correlation sum signals to one and the other of said opposite binary conditions of said data symbols, respectively, for producing data bit output signals having the same binary logic states during the received carrier data symbols of a single carrier data transmission.

2. The power line carrier communication system as claimed in claim 1 wherein said carrier has a frequency within a range of about 9 kHz to 15 kHz.

3. The power line carrier communication system as claimed in claim 2 wherein said receiver means and said coherent phase demodulator means are both included in large numbers of communication terminals located at remote electric power customer locations for producing automated monitoring and control of electric loads at the remote customer locations.

4. The power line carrier communication system as claimed in claim 1 wherein said carrier data transmissions include a message format having data information immediately preceding a preamble format having plural synchronizing data bit symbols and plurality of polarity indicator data bit symbols.

5. The power line carrier communication system as claimed in claim 4 wherein said coherent phase demodulator includes data bit synchronization means responsive to said correlation signals produced during the occurrence of said plural synchronizing data bits so as to produce consecutively occurring correlations sum signals at said summing means and being further responsive to consecutively occurring sums of absolute values of said correlation sum signals, and said synchronization means including selectively resettable counter means for cyclically controlling said summing means so as to algebraically sum predetermined groups of said correlation signals with said resettable counter having an initial reset condition in response to a maximum one of said sums of absolute values of said correlation sum signals.

6. The power line carrier communication system of claim 5 wherein said coherent phase demodulator includes a data bit correlator means responsive to consecutively occurring correlation sum signals having common ones of either of said positive and negative values thereof produced in response to said plural polarity indicator data bits and temporary storage means for storing a binary logic state identifying the common ones of either of said positive and negative values for effecting said continuously relating of the positive and negative values of said correlation sum signals to said data symbols.

7. The power line carrier communication system of claim 6 wherein said data bit correlator means includes counter means responsive to the common ones of either of said positive and negative values of the correlation sum signals being produced to indicate the end of said preamble format and the beginning of said message format.