Wireless MIMO relay networks have received significant interests in recent years. However, most MIMO relay techniques require high complexity equalizers and error free forwarding at the relay to collect diversity. In this paper, we propose high-rate and low-complexity decode-and-forward (DF) MIMO relay designs that achieve cooperative diversity, receive diversity or joint diversity. We introduce a power-scaling strategy for MIMO relays to enable cooperative diversity. Zero-forcing equalizers are employed at both relay and destination to maintain low-complexity. We also develop a channel-controlled ARQ scheme to collect receive diversity. Through mathematical analysis, we prove the diversity order achieved by each proposed design and numerical simulations confirm the theoretical claims.

Wireless relay networks have caught a lot of attention recently due to their potential to enhance performance by combating fading effects. Numerous strategies have been proposed in the literature to enable cooperative diversity. Among them, decode-and-forward protocol has been well adopted because of its low implementation complexity. However, most decode-and-forward based schemes assume that the relay node has perfect error detection or has feedback information from the destination. In this paper, we design power profiles at the relay which enable diversity at the destination without any feedback or coding assumptions at the relay and source. Furthermore, the diversity orders enabled by any general power profile are quantified. We then summarize necessary and sufficient conditions on the power profiles to guarantee full diversity at the destination. The theoretical analysis is corroborated with numerical simulations.