Carrier synchronization for 16-ary DEQAM transmission

The authors describe a carrier recovery loop for coherent demodulation of a 16-ary differentially encoded quadrature-amplitude-modulation (DEQAM) signal. The loop uses a decision-feedback technique. The bit-error rate (BER) performance of the modem in the presence of noisy carrier reference signals provided by the loop and the transient response of the loop in the absence and presence of additive white Gaussian noise are investigated by means of computer simulation. Results indicate that the performance of the loop is dependent on the error rate. At BER=10^-4 and in the presence of frequency offset, the loop achieves lock within 75 symbol intervals, and the signal-to-noise ratio degradation is 1.5 dB