The Diversity-Multiplexing Tradeoff of the Dynamic Decode-and-Forward Protocol on a MIMO Half-Duplex Relay Channel

TL;DR

This paper characterizes the diversity-multiplexing tradeoff of the dynamic decode-and-forward protocol in half-duplex MIMO relay channels, providing closed-form solutions for specific channel classes and comparing its performance to other protocols.

Contribution

It offers a convex optimization framework to analyze the tradeoff, derives closed-form solutions for special cases, and compares the dynamic decode-and-forward protocol with static and full-duplex protocols.

Findings

Tradeoff curves match full-duplex decode-and-forward for certain channels.

Dynamic decode-and-forward outperforms static compress-and-forward at low multiplexing gains.

Performance of dynamic decode-and-forward is close to full-duplex decode-and-forward.

Abstract

The diversity-multiplexing tradeoff of the dynamic decode-and-forward protocol is characterized for the half-duplex three-terminal (m,k,n)-relay channel where the source, relay and the destination terminals have m, k and n antennas, respectively. It is obtained as a solution to a simple, two-variable, convex optimization problem and this problem is solved in closed form for special classes of relay channels, namely, the (1,k,1) relay channel, the (n,1,n) relay channel and the (2,k,2) relay channel. Moreover, the tradeoff curves for a certain class of relay channels, such as the (m,k,n>k) channels, are identical to those for the decode-and-forward protocol for the full duplex channel while for other classes of channels they are marginally lower at high multiplexing gains. Our results also show that for some classes of relay channels and at low multiplexing gains the diversity orders of the dynamic decode-and-forward protocol protocol are greater than those of the static compress-and-forward protocol which in turn is known to be tradeoff optimal over all {\em static} half duplex protocols. In general, the dynamic decode-and-forward protocol has a performance that is comparable to that of the static compress-and-forward protocol which, unlike the dynamic decode-and-forward protocol, requires global channel state information at the relay node. Its performance is also close to that of the decode-and-forward protocol over the full-duplex relay channel thereby indicating that the half-duplex constraint can be compensated for by the dynamic operation of the relay wherein the relay switches from the receive to the transmit mode based on the source-relay channel quality.