Optimized Decision-Directed Carrier Recovery Loop for 16-QAM Constellations

In many communication systems, fast and unambiguous carrier phase synchronization is required. When the synchronizer uses a periodic phase detector, it is currently the subject of ambiguous locking. Generally, for fast acquisition systems, the phase ambiguity is removed by the use of differential encoding. However, this results in degraded bit error probability performance. In this paper we introduce and describe an optimized phase detector suited to 16-QAM receivers which prevents ambiguous locking and performs relatively rapid acquisition. Based on a new decision scheme, the proposed phase detector outperforms a classical decision directed phase detector over a Gaussian channel, notably in the presence of frequency offset and even for low signal-to-noise ratios. An analytical analysis of the S-curve of the proposed phase detector is also carried out.