This paper investigates the benefits of Amplify-and-Forward (AF) relaying inthe setup of multi-antenna wireless networks. The concept of Random Sequential(RS) relaying is previously introduced in the literature and showed that itachieves the maximum diversity gain in a general multi-antenna network. Here,we show that random unitary matrix multiplication at the relay nodes empowersthe RS scheme to achieve a better Diversity-Multiplexing Tradeoff (DMT) ascompared to the traditional AF relaying. First, we study the case of amulti-antenna full-duplex single-relay two-hop network, for which we show thatthe RS achieves the optimum DMT. Applying this result, we derive a newachievable DMT for the case of multi-antenna half-duplex parallel relaynetwork. Interestingly, it turns out that the DMT of the RS scheme is optimumfor the case of multi-antenna two parallel non-interfering half-duplex relays.Next, we show that random unitary matrix multiplication also improves the DMTof the Non-Orthogonal AF relaying scheme in the case of a multi-antenna singlerelay channel. Finally, we study the general case of multi-antenna full-duplexrelay networks and derive a new lower-bound on its DMT using the RS scheme.
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