Performance of a medium-data-rate 16-ary DE-QAM modem in a nonlinear Rician channel

A new structure for a medium bit rate (2 Mb/s) differentially encoded quadrature amplitude modulation (16-DEQAM) demodulator operating over a nonlinear land mobile satellite channel, is proposed and its performance is evaluated. The synchronization and detection digital techniques employed in this system are described. The hardware speed limitations have been overcome effectively with extensive use of look-up tables and concurrent digital signal processing on polar signal representation. The modulator uses a look-up table technique which incorporates a spectral shaped filter and a baseband predistortion circuit capable of compensating for the AM-AM and AM-PM distortions introduced by a high power amplifier (HPA). The system performance is evaluated by computer simulation over a non-linear additive white gaussian noise (AWGN) and Rician fading channel