Transmit outage pre-equalization for amplify-and-forward relay channels

We consider amplify-and-forward (AF) on the two-hop channel. In contrast to existing schemes, we propose to perform pre-equalization at the source, which entails a channel-independent gain at the relay and simplifies the channel estimation process. If the power constraint does not allow for pre-equalization, the source refrains from transmitting and declares a transmit outage. Channel state information (CSI) is acquired at the source and at the destination based on a single pilot transmission from the relay. The advantages of the proposed method are an extremely simple relay, a reduced pilot overhead, huge power savings at the source, and high robustness against imperfect CSI.