Investigation spectral efficiency of massive MIMO

Abstract

The radio spectrum being a limited resource, increase in the number of mobile subscribers in the future places a demand on the available radio spectrum and need to utilize it more efficiently in order to provide quality of service (higher data rates with low latency) to the subscribers. Due to this need to use the spectrum more efficiently, we introduce and study massive MIMO also known as “very large MIMO” which deploys a very large number of antennas at the base station (hundreds of antennas). We mainly place our focus on the downlink transmission in presence of the different linear pre-coding schemes. Namely zero forcing (ZF), maximum ratio transmission (MRT) and minimum mean square error (MMSE) that the base station uses to serve many users over a Rayleigh channel, considering perfect channel state information, number of base station antennas being one hundred and sixty active users in a single cell. We determine and compare the spectral efficiency of massive MIMO using two of these pre-coding schemes (ZF and MRT) and make plots of the spectral efficiency against the number of antennas and the number of users. The results obtained show that a better spectral efficiency is obtained when using zero forcing (approximately twice that of MRT) compared to maximum ratio transmission. We also make graphical comparison between the different antenna deployment systems (SISO and MIMO) with massive MIMO. It is seen that massive MIMO gives a higher spectral efficiency compared to SISO and MIMO. Approximately three times better spectral efficiency compared to SISO.