Performance of a rate-3/4 coded signal, incorporated with a circular signal set for regenerative satellite transmissions

The author describes a digital modem that transmits a rate-3/4 convolutionally encoded 16-ary amplitude and phase modulated (CE16APM) signal, over a regenerative satellite link. The signal uses a (4,12) circular signal constellation set and has a coding gain of about 4 dB at a bit error rate of 10 ^-4, over an encoded eight-phase-shift keyed (8PSK) signal. The high-power amplifier (HPA) at each of the earth-station transmitters or on board the satellite transmitter may introduce nonlinear AM-AM and AM-PM conversion effects into the CE16APM signal. Results of a series of computer-simulation tests are presented. These evaluate the effects of bandlimiting, nonlinear distortion and ACI (adjacent-channel interference) on the performance of the modem. The HPA are tested with different values of output backoff (OBO). The performances of the preferred system arrangements are compared with those of a rate-3/4 convolutionally encoded 16-ary quadrature-amplitude-modulated (CE16QAM) signal, using a rectangular signal constellation set, and of an uncoded 8PSK signal.<>