Capacity of multi-user MIMO systems with MMSE and ZF precoding

Spatial multiplexing can be deployed to achieve higher throughput in multi-user multiple-input multiple-output (MU-MIMO) systems. Many linear precoding techniques require each antenna to transmit its own data. The precoding techniques such as zero forcing (ZF) and minimum mean square error (MMSE) have presented for optimal capacity in the system. In this paper, we compare the channel capacity with ZF and MMSE when the relationship between the number of transmitting antennas and the number of receiving antenna changes. We apply the two types of precoding to multiple antennas in MU-MIMO downlink transmissions. We find that their impact on capacity is different, and which one provides higher capacity is dependent on the antenna numbers. The simulation results show the impact on capacity with different combinations of transmitting and receiving antennas. Finally, the simulation results demonstrate that the proposed structure can achieve the capacity-approaching performance of the precoding in different antenna environments.