Spectral Efficiency of MU-Massive MIMO System for Perfect and Imperfect CSI Condition

Multi User Massive MIMO (MU-Massive MIMO) is a form of multi-user large-scale antennas technology, in which hundreds number of antennas serve a significantly smaller number of users. This system is assumed operates over a frequency-selective and uses Orthogonal Frequency Division Multiplexing (OFDM). The system performance is observed in two conditions, the first condition is that the BS is assumed to know the channel information perfectly (perfect CSI condition), the second condition is that the BS performs the channel estimation process at a certain coherence interval (imperfect CSI condition). The BS estimates channel information from the pilot sent by user using Minimum Mean Square Error (MMSE) estimator. Several precoding techniques are used to overcome Multiuser Interference (MUI) at the receiver, namely Maximum Ratio (MRT), Zero Forcing (ZF) and MMSE. The observed parameter are Bit Error Rate (BER) and Spectral Efficiency (SE). From the simulation results, it can be seen that the use of a large number of array antennas can significantly increase the spectral efficiency. ZF and MMSE precoding work better than MRT precoding in minimizing MUI. Spectral efficiency is also affected by the channel model, where the spectral efficiency on the UR-LOS channel is higher than Rayleigh channel. In the imperfect CSI condition, the channel estimation error is getting bigger, so that the spectral efficiency will decrease and become lower than the perfect CSI condition.