Generalized Buffer-State-Based Relay Selection with Collaborative Beamforming

In this paper, we propose a generalized buffer-state-based relaying protocol in the context of finite buffer-aided cooperative systems. The proposed relaying scheme relies on two concepts: the simultaneous activation of multiple source-to-relay links and buffer-state-based relay selection for packet transmission and reception. In order to avoid buffer overflow, as well as an empty buffer at the relay nodes, we introduce a novel thresholding scheme that gives priority to link selection. The proposed scheme is capable of achieving a lower outage probability and a lower end-to-end packet delay than existing buffer-aided relaying protocols. Moreover, the concept of collaborative beamforming is invoked for the proposed buffer-aided relaying scheme, in order to improve the received signal-to-noise ratio at the destination node. We also derive analytical bounds of the outage probability and the average packet delay of the proposed scheme with the aid of Markov-chain analysis. Our simulation results demonstrate the clear performance advantages of the proposed scheme over conventional schemes, which are especially explicit for scenarios with a high number of relay nodes.