Optimized rate-adaptive PSAM for MIMO MRC systems with transmit and receive CSI imperfections

Abstract

The impact of imperfect channel state information (CSI) on the performance of transmit-beamforming (TB) over multiple-input multiple-output (MIMO) Rayleigh fading channels when using constant-power rate-adaptive pilot symbol assisted modulation (PSAM) is investigated. Specifically, imperfect CSI is accounted for with respect to both estimation and prediction errors, thereby allowing to quantify the performance degradation of the adaptive PSAM-based TB system due to both channel estimation and prediction errors. Such errors entail a mismatch between the optimal transmit/receive beamforming weights and the transmission rate implied by the true CSI on the one hand, and the actual values of these quantities as determined based on the estimated and predicted CSI, on the other hand. The compound effect of both estimation and prediction errors on the overall system performance is assessed in terms of the achievable average spectral efficiency, average bit error probability and outage probability, for which approximate closed-form expressions are derived for arbitrary numbers of transmit and receive antennas. Furthermore, the latter metrics are used to optimize the PSAM parameters, namely the power allocation between data and pilot symbols as well as the pilot spacing in order to maximize the achievable average spectral efficiency while adhering to a fixed target bit error probability.