Performance of multi-bit differential SQAM in mobile radio channel

A new multi-bit DSQAM (differential superposed quadrature amplitude modulation) for use in bandwidth and power limited digital mobile radio is proposed. A DSQAM signal is generated by a differentially encoded SQAM processor, and is detected by a multi-bit differential receiver combined with a soft decision Viterbi decoder. The simulated BER result shows that, in an AWGN channel, a 5 bit DSQAM modem achieves a 7.2 dB E_b/N₀ improvement over a conventional 1 bit differential receiver. In Rician fading channels, DSQAM demonstrates a high degree of robustness suffering only a minor loss of signal