MPSK spread spectrum communications receiver with carrier recovery and tracking using weighted correlation techniques

Abstract

A multiple phase shift keying (MPSK) spread spectrum communications receiver uses weighted correlation techniques for carrier recovery and tracking. The receiver includes three subsystems: a synchronization system, a carrier tracking system, and a data demodulation system. To demodulate the received signal, the receiver requires a carrier frequency that matches the frequency of an associated transmitter as well as the sampling (or chip) and symbol clocks that are synchronized with those of the transmitter. In the disclosed receiver, the carrier tracking subsystem continually tracks the carrier frequency of the received signal using a tracking scheme that uses weighted correlation techniques. The weighted correlation technique combines signals from two correlator modules, an R-correlator module and a W-correlator module, to generate the correlation output.; The R-correlator is similar to conventional correlators. The W-correlator, however, is unlike conventional correlators. Each product term of the correlation is weighted by a sampling index within a symbol period and then summed to obtain a weighted correlation value. The receiver has a tracking range that is twice the symbol rate and the tracking range is independent of the number of keying phases M.