In this paper a new 16-ary Differentially Encoded Quadrature Amplitude (16-DEQAM) demodulator for medium and high bit rate (from 2 MBit/s to 100 MBit/s) Land Mobile Satellite Communications 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 acquisition and Bit Error Rate(BER) performances are evaluated by computer simulation over Additive White Gaussian Noise (AWGN) and Rician fading channel.