Capacity Analysis Based on Channel Measurements of Massive MU-MIMO System at 3.5 GHz

Massive multiple-input multiple-output (MIMO) is considered as one of the promising fifth Generation (5G) technologies, one of its key properties is the favorable propagation condition which describes mutual orthogonality among channels to different users. In this paper, we investigate to what extent the favorable condition can be realized by increasing the number of transmitting antennas (Tx) to 256 in a practical Urban Macro (UMa) scenario based on channel measurements at 3.5 GHz. Multi-user MIMO (MU-MIMO) capacity based on the zero forcing block diagonalized (ZFBD) scheme is evaluated, and the results are compared to the independent identically distributed (i.i.d.) channel. The performance improvements are found to decelerate at 64 Tx and certain gap from i.i.d. channel remains for all cases. The eigenvalue distributions of the composed two users' channel matrix are then checked, and very limited decorrelation of the users' sub-channels is observed. Finally, we consider number growths of receiving antennas (Rx) and numerical results indicate that the capacity gain is dependent on the scenario conditions and the antenna configurations at both Rx and Tx sides, although sustained growths are observed. Therefore, the full gain of favorable propagation is not entirely achieved in our measured practical channel environment.