Contribution of multiplexing and diversity to ergodic capacity of spatial multiplexing MIMO channels at finite SNR

We show that while the multiplexing effect of the spatial multiplexing MIMO channel has the greatest influence on ergodic capacity at infinite SNR, the contribution of diversity to enhancing ergodic capacity at finite SNR is comparable to or greater than that of multiplexing as the number of antennas increases to a moderate level. For instance, we show that the contribution of diversity to ergodic capacity surpasses that of multiplexing for an equal number of transmit and receive antennas of eight and SNR < 13dB, a possible practical scenario for the upcoming 4G standards such as LTE-Advanced. This result leads us to conclude that the use of spatial multiplexing detection algorithms that extract the full diversity, such as the Maximum Likelihood (ML) algorithm, becomes more crucial when the number of antennas grows to a moderate level.