Distortion-loop analysis for full-duplex amplify-and-forward relaying in cooperative multicast scenarios

In this work we study the behavior of a full-duplex (FD) and amplify-and-forward (AF) relay where realistic limitations of FD relays in overcoming their loopback self-interference signal are taken into account. This includes the inaccuracies of the analog hardware components, as well as the limited interference estimation accuracy in the baseband (digital) domain. As it will be elaborated, due to the inter-dependency of the transmit relay power and the residual self-interference in an AF-FD relay, we observe a distortion loop that dominates the system performance when the relay dynamic range is not adequately high. The effects of this loop are then studied analytically and the optimal relay selection and power optimization is derived, assuming a setup with a single source and multiple destination nodes (multicast scenario). In order to provide further intuition, system behavior and the corresponding optimal designs are studied analytically for few extreme cases. In particular, a comparison is made with the similar relaying setup with decode-and-forward (DF) process, where the distortion loop is reduced due to decoding. Finally, the gains of the proposed design as well as the effect of different system parameters are investigated via numerical simulations.