Differential Relay Strategies Over Downlink Channel in Two-User Cooperative Communication System

In this paper, we propose two differential relaying strategies; Active User Strategy (AUS) and Passive Users Relaying Strategy (PURS), which could be used by the base-station to transmit data of two users over downlink channels in a two-user cooperative communication network. Differential schemes are used so the users do not require the knowledge of channel gains for decoding of their data. The performance of both schemes is evaluated for the decode-and-forward, selection relaying, and incremental relaying protocols. For the decode-and-forward protocol, the performance heavily depends upon the signal-to-noise ratio (SNR) of the link between source and relay. We propose a conditional probability of error based approach, which can be used to regulate the erroneous relaying of data. Both AUS and PURS are able to achieve performance gains as compared to the direct transmission differential scheme in the case of selection relaying and incremental relaying protocols at high SNRs. The proposed schemes perform better than their counterpart of the amplify-and-forward differential relaying proposed previously.