A Low Complexity User Grouping Based Multiuser MISO Downlink Precoder

Abstract

We consider low complexity precoding for the Multiple Input Single Output (MISO)Gaussian Broadcast channel with $N_t$ antennas at the base station and $N_u$ singleantenna users in the downlink. Theoretical studies have suggested high throughputcommunication with increasing spatial dimensions i.e., $\\min(N_t,N_u)$.Nevertheless, most modern communication standards are unable to exploitthe spatial dimension fully, since they are restricted to orthogonal communicationtechniques like TDMA/FDMA (Time/Frequency Division Multiplexed Access) which areknown to be sub-optimal.This restriction is mostly due to the prohibitive complexity of optimal/near-optimalprecoding schemes.On the other hand low complexity techniques like Zero Forcing (ZF) and MMSE have poor sum rate performance.In this paper, we propose a novel low-complexity user grouping based precoding scheme whichschedules all users on the same time-frequency resource (i.e., optimal utilization of resources).The proposed precoder is analytically shown to achieve a sum rate performance significantly better than the ZF precoderat similar complexity.Through simulations, it is also observed to achieve a significant fractionof the sum rate achieved by the optimal schemes.