Optimal Two-Way Buffer-Aided Relaying: Achieving the Best Outage and Delay Performance With Small Buffer Sizes

Abstract

In this paper, we consider two-way relaying where two users exchange information through a decode-and-forward (DF) buffer-aided (BA) relay. We formulate a generic BA relaying protocol that is based on both the channel and buffer states and that can be parameterized by two parameters. Through a Markov chain analysis, we show how these parameters can be selected for the sake of minimizing the outage probability (OP) and average packet delay (APD) for asymptotic values of the signal-to-noise ratio. The performed optimization sheds more light on the impact of the buffer sizes on the triad of diversity order, coding gain and APD that can be contemplated. In particular, we prove that equipping the relay with two buffers of size three each is sufficient for extracting the full capabilities of two-way BA relaying. Depending on the network setup, one or both buffer sizes can be further reduced to two at the expense of a reduced coding gain without affecting the diversity order and asymptotic APD. Simulations under the generalized $\kappa -\mu $ fading demonstrate the appropriateness of the performed optimization of the relaying parameters and buffer sizes.