Switch-and-Stay Transmit Diversity for Cooperative Decode-and-Forward Systems

We consider the application of switch-and-stay transmit diversity (SSTD) to a three-node cooperative diversity system with decode-and-forward relaying. The basic idea of SSTD generally is to use a certain transmit antenna as long as the induced signal quality satisfies a given requirement while the transmitter switches to another antenna element if this is no longer the case. Applying this principle to the source node of a cooperative diversity system is significantly more complex than for conventional single-hop systems since the selected antenna element generally affects both the source-to-relay and the source-to-destination link. In this regard, we consider three different approaches, namely relay-driven, destination-driven, as well as jointly-driven optimal switching, always targeting at minimizing the outage probability between source and destination. For all cases, we determine exact analytical closed-form expressions for the resulting outage probability assuming Rayleigh-fading on all hops as well as asymptotic expressions, based on which it is possible to directly quantify the achievable diversity order.