Hybrid beam-forming techniques for multi-cell massive MIMO

Abstract

Various hybrid beam-forming research works are currently underway, as the cost and power consumption of fully digital beam-forming limit its applicability in fifth generation (5G) massive multiple input multiple output (MIMO). A majority of studies assumed that the channel state information (CSI) is perfect, the hardware is ideal and the network is represented as a single-cell scenario. As a result, studies incorporating Kalman-based precoders with existing beamformers for multi-cell systems under non-ideal conditions warrant further investigation. This study aimed to achieve the performance analysis of Kalman hybrid beam-forming technique for multi-cell massive MIMO under hardware impairment and imperfect CSI. The spectral efficiency (SE) of the multi-cell based Kalman hybrid beam-forming technique has been analysed along with zero forcing, minimum mean square error (MMSE), and mean square error (MSE) precoders. It can be seen from the MATLAB simulation that the SE of fully digital MSE, Kalman, MMSE, and zero forcing precoders at signal to noise ratio (SNR) of 20 dB and number of transmitting antennas of 128 under nonideal conditions is 8 bps/Hz, 7 bps/Hz, 5.2 bps/Hz, and 6 bps/Hz respectively. The SE of fully digital, Kalman, MMSE, and zero forcing precoders at SNR of 20 dB for 128 transmitting antennas under ideal conditions is 11 bps/Hz, 9.6 bps/Hz, 7.2 bps/Hz, 8.1 bps/Hz respectively. Additionally, the simulation shows that when the number of transmitting antennas rises and the number of users falls, the SE of beam-formers increases. Increasing the number of transmitting antennas and decreasing the number of users mitigate the effect of hardware impairments and imperfect CSI in a multi-cell based linear beam-formers. Imperfect hardware and CSI, in general, degrade the SE of multi-cell multi-user based linear beamformers.