Outage performance of relay-assisted co-existing MIMO downlinks that exploit interference

We investigate the outage performance of relay assisted transmissions of coexisting radio systems. Employing simple linear precoding designs, we explore the potential of utilising the cross-interference between the two coexisting systems to mutually improve performance. While conventionally the aim of the relay is to isolate the two concurrent transmissions by completely removing the interference between them, we make use of interference energy when the interference between the two systems is mutually constructive. In this direction two adaptive linear precoding techniques are proposed for the relay and compared to conventional precoding. We use the cognitive radio paradigm to illustrate the associated benefits. It is shown by theoretical analysis and simulation that the constructive interference provides a source of additional green signal energy that benefits the outage performance of both communication links.