Low-complexity ZF precoding method for downlink of massive MIMO system

In massive multiple-input-multiple-output (MIMO) systems, the downlink zero-forcing (ZF) precoding method needs to compute the pseudoinverse of large matrices, which introduces high computational complexity, especially when the number of antennas is large or infinite. Although, based on Neumann series expansion, several approximation algorithms could reduce the complexity, calculating the optimisation coefficients would cost large amounts of resources and produce large delay. A novel method, also based on Neumann series expansion, is proposed. In this method, the multiplication of full matrices is transformed into multiplication of diagonal matrices by hollow matrices, effectively reducing computational complexity. Meanwhile, consideration of a simple expression of optimisation coefficients so as to avoid large delay is very useful in high-mobility scenarios. Analysis and simulation results show the effectiveness of the proposed method.