Threshold extension block phase estimator for quasi-coherent communications systems

The phase-locked loop (PLL) has for many years been the technique-of-choice for estimating received carrier phase in coherent m-ary phase-shift keyed (MPSK) communications systems. With advances in technology and the proliferation of burst communications systems, block phase estimators (BPE), began to be used to avoid "hang-up" problems encountered during PLL signal acquisition. The BPE for higher order modulations must be preceded by a nonlinearity to remove the effects of modulation, and is followed by a "sector tracking" algorithm to maintain the full range of the output phase estimate. This configuration is susceptible to "sector slips" just as a PLL experiences "cycle slips". The invention relates to a threshold extension block phase estimator (TEBPE) which estimates phase in the presence of noise. Threshold and sector slips are controlled by an iterative calculation. This can be of crucial advantage in coded systems. Another attribute of the TEBPE is it can be configured as a hybrid feedback loop incorporating characteristics of both the BPE and the PLL. This gives a high degree of flexibility with very fast acquisition times at high signal-to-noise ratio (SNR), and improved threshold performance at low SNR.