Average-rate optimal PSAM transmissions over time-selective fading channels

Enabling linear minimum-mean square error (LMMSE) based estimation of random time-selective channels, pilot symbol assisted modulation (PSAM) has well documented merits as a fading countermeasure capable of improving bit error rate performance. In this paper, we establish average-rate optimality of PSAM by showing that the insertion of equi-powered and equi-spaced pilot symbols in PSAM transmissions maximizes a tight lower bound of the average channel capacity. Relying on a simple closed form expression of this bound in terms of the LMMSE channel estimator variance, we further design PSAM transmissions with optimal spacing of pilot symbols, and optimal allocation of the transmit-power budget between pilot and information symbols.