AF two-path half duplex relaying with inter-relay self interference cancellation: diversity analysis and its improvement

In this paper, we consider a network consisting of one source, one destination and two relays, under a half duplex constraint. We analyze an amplify-and-forward (AF) two-path relaying scheme where one of the relays additionally performs inter-relay interference cancellation. With this inter-relay self interference cancellation, we show that degradation in performance can be significantly reduced when inter-relay channel gain increases. By treating the AF two-path relaying as an equivalent MIMO space time code, we derive an upper bound for the pairwise error probability (PEP) of this system. Previous works indicate that only a diversity order of two can be achieved even though physically there are three possibly independent spatial paths to the destination. From our analysis of the PEP, we analytically prove and identify the reason to the limited diversity order of two. We then propose a simple but novel precoding scheme which allows the system to achieve a full diversity order of three while maintaining the spectral efficiency gain of the two-path relaying protocol. A robust precoding design to achieve full diversity order with high coding gain is also proposed.