Performance analysis and mode selection of SU-MIMO and MU-MIMO in 802.11ac

IEEE 802.11ac, also known as gigabit Wi-Fi is the latest and emerging wireless local area network (WLAN) standard. The Very High Throughput (VHT) of the order of Gbps can be achieved primarily with two important modifications when compared with the previous 802.11n standard. The first one is the increased number of spatial streams (8 as compared to 4 in 11n standard) and the second one is the support for multi user - multiple input multiple output (MU-MIMO). This paper places key discussions and simulation results pertaining to these two objectives. It also compares the performance of MU-MIMO and single user - multiple input multiple output (SU-MIMO) precoding techniques assuming perfect Channel State Information at the Transmitter (CSIT) for both high and low correlation channels. The paper also introduces a novel algorithm that optimizes the various precoding algorithms by reducing the computational calculations with the mathematical background for the capacity calculations. By analyzing the performances of various precoding schemes used for SU-MIMO and MU-MIMO, the mode switching SNR can be found out. This quantitative measure of SNR is certainly a powerful measure to choose between SU and MU-MIMO and also to serve all the users to the best possible extent. Also, estimation of the mode selection with very less computational effort highlights the advantages of the algorithm over the existing algorithms.