Low–high SNR transition in multiuser MIMO

Multiuser multiple-input-multiple-out (MU-MIMO) plays a key role in the widely adopted 3GPP LTE standard for wireless cellular networks. Although exact and asymptotic sum-rate results are well known, the problem of obtaining intuitive analytical results for medium signal-to-noise ratios (SNRs) is still not solved. As a result of the present reported work, the bend point is proposed, which quantifies the transition between low and high SNR, i.e. the beginning of the high SNR region. The bend point is derived for MU-MIMO with zero-forcing precoding and is obtained, that it is intimately related to the intercept of the high SNR asymptote with the zero sum-rate line. Using this result, a new approximation of the sum-rate at the bend point it is shown providing a useful rule of thumb for the effect of increasing the number of antennas at medium SNR.