Baseband digital frequency offset mitigation techniques for the detection and frame synchronization of M-PSK signals

Abstract

In this work, various aspects of the performance degradation resulting from the frequency offset are discussed and the mitigation techniques for frequency offset are proposed. The mitigation techniques are either the frequency offset estimation technique followed by frequency offset compensation or the detection technique which is robust to frequency offset. A new baseband signal processing method for compensating frequency shift in DPSK systems is introduced which could estimate and compensate frequency offset without any known pilot symbol. This method consists of a signal processor for initial acquisition of frequency shift and a simple adaptive equalizer for tracking. The former is based on the observation that the effect of frequency shift can be eliminated by using boundary values of the received baseband signal between symbol periods. The latter is a single tap equalizer employing least mean square (LMS) adaptation algorithm. A new frame synchronization technique, which is robust to carrier frequency and phase errors, is proposed for M-ary PSK systems. This technique is derived through some modification of the procedure for obtaining the conventional maximum likelihood (ML) rule. The proposed rule is based on an operation called the double correlation which evaluates the correlation after properly multiplying the received signal with a sync pattern. The proposed frame synchronizer doesn````t require any knowledge of the received signal and it is shown through computer simulation that the proposed rule generally outperforms the existing rules when a frequency offset exists. To reduce the complexity of the proposed ML-type frame synchronizer, simplified versions of the ML-type frame synchronizer and some hybrid frame synchronizers are also proposed. A new frame synchronizer with verification is proposed employing the derived ML-type frame synchronizer. This technique is a majority decision logic combined with the correlation and the double correlation. ...