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Signal sets employing amplitude and phase keying (APK) with large alphabets conserve bandwidth and do not require as high a signal-to-noise ratio (SNR) as phase-shift keying (PSK). Twenty-nine empirically generated APK sets with M -ary alphabet sizes from 4 to 128 are investigated to determine optimum designs. Selected sets are compared on the basis of a symbol-error-probability bound for both average and peak SNR. Results are presented in the form of symbol error curves. The degradation caused by nonlinearities in a typical TWT amplifier is examined. The effects of AM-AM and AM-PM distortion on APK are presented as a function of power backoff for single-carrier operation (when APK is at the greatest disadvantage compared with PSK). Modem implementation methods, including carrier phase reconstruction techniques, are discussed for basic APK designs.
Thomas et al. (Fri,) studied this question.
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