Performance of a circular signal set in a regenerative satellite system employing TWTA or SSPA

Abstract

This paper presents the results of a computer-simulation study of a (4,12) circular signal set for use over regenerative satellite links. The signal has a 16-ary symbol alphabet. The satellite transponders and each of the earth-stations use either travelling-wave-tube amplifers (TWTAs) or solid-state power amplifiers (SSPAs) for high-power amplification. Several different earth-stations are assumed to have simultaneous access to a given regenerative satellite, in an arrangement of frequency division multiple access (FDMA). Thus, adjacent-Channel-Interference (ACI) can be introduced into the wanted signal by the immediately adjacent channels. The performances of the signal are compared to those of a 16-ary differentially encoded-quadrature-amplitude-modulated (16-ary DEQAM) signal with a rectangular signal set and the results are used to determine to preferred signal set for spectrally efficient transmission over satellite links. It has been shown that, with TWTAs used for high-power amplification and in the absence of ACI, the circular signal set has an advantage of about 3 dB over the rectangular signal set, at the error rate of 10-4. While in the presence of the ACI, the advantage is 2 dB. With SSPAs, the respective advantages becomes 0.7 and 0.5 dB.