Analysis of pilot symbol assisted modulation (PSAM) systems with power control and diversity

Abstract

Pilot symbol assisted modulation schemes are used on fading channels to enable coherent demodulation at the receiver. Furthermore, diversity receivers (such as RAKE receivers) are used to combat the effects of fading. Higher orders of diversity result in greater protection against fading but, for the same total received energy, lower the quality of the channel estimates. This tradeoff in diversity order for pilot symbol-based schemes is captured analytically in the bit-error probability expressions derived in this paper. The higher the signal-to-noise ratio, the larger is the optimum diversity order. Results are then extended to the case with power control. Power control works to mitigate the fading and the tradeoff tilts in favor of using lower orders of diversity. The optimum diversity order depends strongly on the extent of averaging used to obtain the channel estimates and the proportion of the total energy assigned to the pilot symbols.