Bandwidth Compressive 16-State SQAM Modems Through Saturated Amplifiers

The performance of new bandwidth compressive 16 SQAM (Superposed-QAM) modems, operating in a highly power-efficient saturation mode, is analyzed. Nonlinearly amplified 16 SQAM retains the out-of-band energy much lower than 4-level rectangular (i.e., 16 QAM) or sinusoidal shaped (i.e., MAMSK) QAM, and operates within 0.7 dB of theoretical (i.e., 16 QAM in Nyquist linear channel) performance at
P(e) = 10^{-6}
using simple 4th-order Butterworth LPF's. Effects of baseband pulse shaping, receive filter BT
s
, power level variations and propagation time difference (or static phase shift) of transmit HPA's are analyzed in terms of BER.