An improved PSK scheme for fading channels

The performance of uncoded phase-shift-keying (PSK) schemes over fading channels is only inversely proportional to the signal-to-noise ratio, which is not very reliable for digital communication applications. Improving their performance has been approached by means of coded modulation schemes, where code redundancy combined with interleaving introduces some degree of diversity that depends on the complexity of the code. This paper proposes an alternative way in improving the performance of PSK schemes over fading channels by looking at the reference scheme first. It is shown that by using interleaving combined with a proper signal constellations and still using symbol-by-symbol detection, a higher diversity is obtained and the performance of uncoded PSK schemes over fading channels is considerably improved. With this simple modification, the obtained performance is comparable to that of the best four-state trellis-coded-modulation (TCM) 8PSK schemes reported in the literature. By optimizing the reference scheme first, it is shown that this technique optimizes the performance of Ungerboeck's trellis-coded 8PSK schemes over fading channels. In fact, without altering their performance over the additive white Gaussian noise (AWGN) channel, significant coding gain over fading channels is achieved.