Opportunistic Cooperation Strategies for Multiple Access Relay Channels with Compute-and-Forward

TL;DR

This paper introduces two opportunistic cooperation strategies for multiple access relay channels using compute-and-forward, significantly improving throughput and diversity gain while reducing outage probability.

Contribution

It proposes novel cooperation strategies that adaptively activate only when beneficial, achieving double the throughput and higher diversity gain compared to existing methods.

Findings

Both strategies double network throughput at high SNR.

The strategies reduce outage probability regardless of relay placement.

The first strategy nearly achieves diversity gain of two, the second exactly achieves it.

Abstract

This paper studies the application of compute-and-forward to multiple access relay channels (MARC). Despite its promising advantage of improving network throughput, it is not straightforward to apply compute-and-forward to the MARC. This paper proposes two efficient cooperation strategies for the MARC with compute-and-forward. Both proposed strategies are opportunistic in the sense that the cooperation between the relay and the destination are performed only when it is needed for the sake of high transmission efficiency. In the first strategy, the relay helps the destination by sending its local optimal integer coefficient vector without taking into account that the resulting integer coefficient matrix at the destination is full rank. In contrast, in the second strategy, the relay forwards its ``best'' coefficient vector that always ensures a full rank coefficient matrix at the destination. Both of the proposed strategies achieve twice the network throughput of the existing strategies at high signal-to-noise power ratio (SNR). They also have lower outage probability, independent of relay placement. Furthermore, the first strategy nearly achieves diversity gain of order two, and the second one achieves exactly the diversity gain of order two, which cannot be achieved by the existing strategies.