Channel capacity characteristics of multi-user MIMO systems in urban area

Multiple-Input Multiple-Output (MIMO) and Multi-User MIMO (MU-MIMO) systems have been expected to improve the channel capacity over a limited bandwidth of existing networks [1], [2]. The effects on channel capacity of Single-User MIMO (SU-MIMO) systems in urban scenarios have been previously studied [3]. It has been clarified that the larger number of antennas cannot contribute the improvement on the channel capacity in urban SU-MIMO scenarios due to very high spatial correlation. In this paper, we focus on the MU-MIMO transmission because it can discriminate multiple users by the difference of Angle of Arrival (AoA). We compare the Multi Access Channel (MAC) capacity in uplink with the channel capacity in SU-MIMO by setting the total numbers of transmitting and receiving antennas of SU-MIMO and MU-MIMO to be the same. When the same numbers of antenna elements are used, the better performance is obtained with MU-MIMO in urban scenarios, unlike identical independent distributed (i.i.d.) channels which are generally assumed in MIMO transmission. We also clarify an interesting relationship between the channel capacity improvement of MU-MIMO compared with SU-MIMO and a path visibility.