Factors and Trade-offs in Bandwidth Efficient Modulation and Coding Schemes Design

This paper explores the factors and trade-offs involved in the design of bandwidth efficient modulation and coding schemes for application in high data rate digital transmission systems such as a satellite communication downlink operating under constraints of limited bandwidth and power. The interplay of symbol correlation, carrier-to-noise ratio, available bandwidth, filter roll-off factor and forward error correction in meeting desired transmission quality target is presented. Some of the ideas developed are then applied to develop new 16APSK and 32APSK modulation constellations. It is shown that, compared with the well-known DVB-S2 constellations, the new arrangements produce lower bit error rates and hence some saving in signal power when operated in additive white Gaussian noise (AWGN) channels. Although not yet tested, it is expected that the observed advantage of the new constellations will be maintained in the presence of amplifier-induced non-linearity in satellite transmission channels since the new constellations are constructed on the same number of amplitude rings as in the DVB-S2 schemes.