Real-time Multi-user MIMO Channel Sounding and Capacity Evaluations

In multi-user multiple-input multiple-output (MU-MIMO) systems, spatial multiplexing can be employed to increase the throughput without the need for multiple antennas and expensive signal processing at the user equipments. In theory, MU-MIMO is also more immune to most of propagation limitations plaguing single-user MIMO (SU-MIMO) systems, such as channel rank loss or antenna correlation. In this paper we compare the sum rate capacity of different MU-MIMO precoding schemes such as dirty paper coding (DPC) and linear precoding to SUMIMO using real channel measurement data. The measurement data has been acquired using Eurecom’s MIMO Openair Sounder (EMOS). The EMOS can perform real-time MIMO channel measurements synchronously over multiple users. The results show that the sum rate capacity in the measured channels is worse than the one in the uncorrelated synthetic channel. However, even in the measured channels DPC increases the sum rate capacity by a factor of 3.2 compared to SU-MIMO at high SNR using four transmit and four users with one receive antenna each. Linear precoding still increases the sum rate capacity by a factor of 2.7 at high SNR but provides little gains at low SNR.