A Low Complexity User Grouping Based Multiuser MISO Downlink Precoder

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 single antenna users in the downlink. Theoretical studies have suggested high throughput communication with increasing spatial dimensions i.e., min(N_t,N_u). Nevertheless, most modern communication standards are unable to exploit the spatial dimension fully, since they are restricted to orthogonal communication techniques like TDMA/FDMA (Time/Frequency Division Multiplexed Access) which are known to be sub-optimal. This restriction is mostly due to the prohibitive complexity of optimal/near-optimal precoding 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 which schedules 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 precoder at similar complexity. Through simulations, it is also observed to achieve a significant fraction of the sum rate achieved by the optimal schemes.