Performance of MRC and EGC M-QAM with imperfect channel estimation

We study the effect of imperfect channel estimation (ICE) on the error probability performance of M-level quadrature amplitude modulation (M-QAM) with maximum ratio combining (MRC) and equal gain combining (EGC) diversity formats in Nakagami fading channels. We provide a novel formulation of the bit error rate (BER) of M-QAM with ICE in terms of the signal constellation-dependent effective signal-to-noise ratios (SNRs) or amplitudes, which allows us to derive the general, accurate, and easy-to-evaluate BER formulas for square and rectangular diversity M-QAM with channel estimation errors. Our result shows that the performance loss caused by ICE may be manifested by the signal decision space distortion and a scaling of the effective SNR. Furthermore, we evaluate the performance of M-QAM with pilot-symbol assisted modulation (PSAM) and present some insightful findings