Zero Forced Precoding in Cell-Free System with Less Antennas

Cell-free system enables user equipments (UEs) to obtain higher spectral efficiency and more balanced services anywhere through cooperative services among a large number of access points (APs). However, when the number of antennas deployed by APs is smaller than the number of channels, the traditional zeros-forcing precoding (ZF) cannot eliminate the interfering signals in the direction of other UEs. To solve the above problem, we propose two scalable precoding schemes, local partial zero forcing (LPZF) precoding and local optimized zero forcing (LOZF) precoding, respectively. The number of users served by each AP is traded off with interference cancellation to maintain the good performance of ZF precoding without increasing the number of antennas deployed in each AP. Experimental simulations verify that LOZF maintains high downlink spectral efficiency while maintaining strong applicability, while LPZF has less computational complexity. To the best of our knowledge, this study presents for the first time how ZF precoding can be optimized in the above scenario.