Improving the Spectral Efficiency of a Downlink 5G Heterogeneous Massive MIMO System Using Beamforming Technique

To meet the demand for an improved quality of experience for user equipment (UE) and improved spectral efficiency offered by mobile network operators, 5G Networks have been designed to employ advanced technologies such as beamforming, Massive MIMO, etc. However, the major issue facing 5G systems is interference due to the implementation of universal frequency reuse for all cells in the 5G Network. This work proposes a coordinated beamforming technique for a two-tier downlink 5G massive MIMO system to tackle inter-cell interference and consequently improve the system spectral efficiency of the 5G system. The choice of coordinated beamforming vectors that optimized the weighted sum spectral efficiency of the system while satisfying the constraints was formulated as a non-convex, non-polynomial hard (NP-Hard) optimization problem and reformulated to a convex problem by fixing the signal-to-interference-and--noise ratio (SINR) to a threshold and solved using CVX. The results showed that the proposed method attained at least the theoretical minimum achievable spectral efficiency for a 5G system which is 30 bit/s/Hz, outperforming other methods based on same parameters: Kr = 9, N = 20, SNR = 30dB, (where Kr and N are the total number of UEs in the system and the total number of transmit antenna at the base stations). The results also showed that with an increase in Kr and N, spectral efficiency is improved.