Downlink SINR Study in Multiuser Large Scale Antenna Systems

In this paper, the downlink signal-to-interference-plus-noise ratio (SINR) performance in multiuser large scale antenna systems with matched filter (MF) and regularized zero-forcing (RZF) precoding is investigated. The probability density function (PDF) for MF is derived and the distribution in high signal-to-noise ratio (SNR) regime is studied. Results indicate that the PDF of downlink SINR for MF converges to \(\mathcal F\) distribution when the interference is dominant over noise. For MF, the asymptotic SINR is just the reciprocal of the ratio of the number of users \(U\) to the number of transmit antennas \(N\) , and is irrelevant to the average transmit power when \(N\) and \(U\) grow with fixed ratio. However, when \(U\) is a large constant, the transmit power could be proportional to \(\ln N \big /N \) to maintain a specified quality of service, as a result of the large scale antenna system effect. In addition, the closed form of asymptotic SINR for RZF is derived by solving two mathematical expectations related to eigenvalues of large dimensional random matrices. Simulation results validate the derived PDF and analytical results.