SU/MU-MIMO in IEEE 802.11ac: PHY+MAC performance comparison for single antenna stations

Most of studies dealing with single user multiple input multiple output (SU-MIMO) and multiple user MIMO (MU-MIMO) rely on physical (PHY) layer only or medium access control (MAC) layer only simulations. In the first case, the apparent considerable performance gains enabled by space division multiple access (SDMA) in downlink transmissions are often obtained without taking into account sounding and channel access induced overhead. In the second case, crosstalk interference (CTI) between stations served by the SDMA transmission is not always accounted for. Consequently, in order to take into account all the parameters and characteristics of these two transmission schemes, precise PHY+MAC modeling is needed. A realistic and fair comparison can thus be performed. The new approach presented in this paper is based on a multi-user simulation platform containing an all inclusive PHY layer combined with an elaborated MAC layer working in a symbiotic manner. In order to discriminate the characteristics of each transmission scheme, the SU/MU comparison is done for single antenna stations, channel inversion being used as the precoding scheme. In addition, the influence of CTI in SDMA transmissions is also studied so as to compare the real gains of MU-MIMO with the generally accepted gains.