Adaptive coding for pilot symbol assisted modulation without feedback

We show that pilot symbol assisted modulation (PSAM) schemes can be improved by adapting the coded modulation strategy at the sender to the quality of the channel measurement at the receiver, without requiring any channel feedback from the receiver. The transmitter employs interleaved codes, with data symbols coded according to their distance from the nearest pilot symbols. The performance benefits from this approach are quantified in the context of binary signaling over time-varying Rayleigh fading channels described by a Gauss-Markov model. The spacing of the pilot symbols is optimized to maximize the mutual information between input and output in the preceding setting. Causal and non-causal channel estimators of varying complexity and delay are considered. It is shown that, by appropriate optimization for the spacing between consecutive pilot symbols, the adaptive coding techniques proposed can yield up to 30% improvement in achievable rate, without any feedback from the receiver to the sender.