Multi-Antenna Cooperative Wireless Systems: A Diversity-Multiplexing Tradeoff Perspective

TL;DR

This paper analyzes the diversity-multiplexing tradeoff in multi-antenna relay networks, comparing protocols and configurations, and establishing bounds and optimal strategies for different relay capabilities and network geometries.

Contribution

It provides a comprehensive DMT analysis for various multi-antenna relay scenarios, identifying optimal protocols and highlighting limitations in mimicking MIMO performance.

Findings

Decode-and-forward is DMT optimal with single-antenna nodes.

Compress-and-forward remains optimal even with increased direct link degrees of freedom.

Half-duplex relays exhibit different DMT behavior, with CF still optimal.

Abstract

We consider a general multiple antenna network with multiple sources, multiple destinations and multiple relays in terms of the diversity-multiplexing tradeoff (DMT). We examine several subcases of this most general problem taking into account the processing capability of the relays (half-duplex or full-duplex), and the network geometry (clustered or non-clustered). We first study the multiple antenna relay channel with a full-duplex relay to understand the effect of increased degrees of freedom in the direct link. We find DMT upper bounds and investigate the achievable performance of decode-and-forward (DF), and compress-and-forward (CF) protocols. Our results suggest that while DF is DMT optimal when all terminals have one antenna each, it may not maintain its good performance when the degrees of freedom in the direct link is increased, whereas CF continues to perform optimally. We also study the multiple antenna relay channel with a half-duplex relay. We show that the half-duplex DMT behavior can significantly be different from the full-duplex case. We find that CF is DMT optimal for half-duplex relaying as well, and is the first protocol known to achieve the half-duplex relay DMT. We next study the multiple-access relay channel (MARC) DMT. Finally, we investigate a system with a single source-destination pair and multiple relays, each node with a single antenna, and show that even under the idealistic assumption of full-duplex relays and a clustered network, this virtual multi-input multi-output (MIMO) system can never fully mimic a real MIMO DMT. For cooperative systems with multiple sources and multiple destinations the same limitation remains to be in effect.