Wireless MIMO Switching with Network Coding

TL;DR

This paper introduces a wireless MIMO switching framework using beamforming and network coding to optimize traffic routing among multiple stations, demonstrating that a small subset of switch matrices suffices for high throughput.

Contribution

It proposes a novel MIMO switch architecture with efficient scheduling strategies and shows that a limited set of permutation matrices can achieve near-optimal throughput.

Findings

For N=4 and 5, only N-1 switch matrices are needed for good throughput.

Physical-layer network coding significantly improves throughput.

The scheduling problem remains manageable for large N under the proposed approach.

Abstract

In a generic switching problem, a switching pattern consists of a one-to-one mapping from a set of inputs to a set of outputs (i.e., a permutation). We propose and investigate a wireless switching framework in which a multi-antenna relay is responsible for switching traffic among a set of $N$ stations. We refer to such a relay as a MIMO switch. With beamforming and linear detection, the MIMO switch controls which stations are connected to which other stations. Each beamforming matrix realizes a permutation pattern among the stations. We refer to the corresponding permutation matrix as a switch matrix. By scheduling a set of different switch matrices, full connectivity among the stations can be established. In this paper, we focus on "fair switching" in which equal amounts of traffic are to be delivered for all $N(N-1)$ ordered pairs of stations. In particular, we investigate how the system throughput can be maximized. In general, for large $N$ the number of possible switch matrices (i.e., permutations) is huge, making the scheduling problem combinatorially challenging. We show that for the cases of N=4 and 5, only a subset of $N-1$ switch matrices need to be considered in the scheduling problem to achieve good throughput. We conjecture that this will be the case for large $N$ as well. This conjecture, if valid, implies that for practical purposes, fair-switching scheduling is not an intractable problem. We also investigate MIMO switching with physical-layer network coding in this paper. We find that it can improve throughput appreciably.