Performance of 8SQAM in a nonlinearly amplified multichannel interference environment

A new modem technique - 8-state superposed QAM (8SQAM) - for use in power and bandwidth limited digital communication system is proposed. 8SQAM generates output signals which have a smooth and continuous phase transition and a reduced envelope fluctuation by keeping correlation between amplitudes and phases of two subsequent symbols. 8SQAM signal is free of inter-symbol interference (ISI), and has a compact power spectrum. Accordingly, 8SQAM, as compared with a conventional 8PSK, is influenced a little by ISI and adjacent channel interference (ACI) caused by nonlinear distortions. In this paper, the performance of 8SQAM, in a nonlinearly amplified multichannel environment impaired by AWGN, ISI, and ACI, is analyzed via computer simulation. The simulation result shows that 8SQAM outperforms 8PSK by 2.3dB in CNR to maintain BER=1×10^-4 when input back-off (IBO) of HPA is 1dB and channel spacing, ΔF is 0.417f_b.