BeamRaster: A Practical Fast Massive MU-MIMO System With Pre-Computed Precoders

Abstract

In order to achieve more dramatic spatial multiplexing gains, both industry and academia have pushed towards the massive Multi-User Multi-Input and Multi-Output (MU-MIMO) systems. However, traditional linear precoding techniques do not scale up well with the number of antennas, i.e., they either have high implementation difficulties (zero-forcing) or sacrifice wireless capacity as a price (conjugate or codebook-based precoding). In this paper, we present a novel precoding scheme, BeamRaster, which is a fast and high efficient scheme for massive MU-MIMO system. Inspired from the codebook-based precoding, BeamRaster pre-computes a set of angle-domain beam filters that divide the channel into directional subspaces. Unlike previous work, BeamRaster carefully manages the cross-interference using (1) a grating table to track the correlation among beams in real-time, (2) an interference-aware user-beam selection, and (3) a pre-distortion method to cancel the residual interference because of side-lobes. We implement and evaluate the BeamRaster using FPGA and software defined radio platform. On one hand, BeamRaster is easy to implement in hardware, i.e., it can realize the precoding for a 64-antenna MU-MIMO system in real time with a single Altera Stratix V FPGA. On the other hand, both the experiments with medium-scale antennas and simulations with large-scale antennas show that BeamRaster can achieve high capacity gain.