Coherent versus noncoherent massive SIMO systems: Which has better performance?

We consider one single-antenna transmitter communicating over a block-fading channel with a receiver that has a large number of antennas. We analyze coherent schemes with training overhead and noncoherent schemes with no training overhead. The latter systems only know the large scale fading statistics and the additive Gaussian noise power. In contrast to prior work on capacity characterizations of such systems, our approach is based on comparing error exponents with an increasing number of receive antennas. We provide an analytical lower bound on the error exponent for both coherent and noncoherent systems, and describe it explicitly for the case of a communication system with PSK constellations. Based on these analytic expressions, we show that noncoherent schemes can significantly outperform coherent schemes in channels with a strong line of sight component, low SNR or a short coherence time. We present numerical comparisons of our analytical BER performance bounds with Monte Carlo simulations for typical PSK constellations, system sizes and fading/noise statistics.