Coherent phase shift keyed demodulator for power line communication systems

Claim 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.