Downlink Cooperative Communication Using Differential Relaying

In this paper, we propose two differential relaying strategies; combined-transmit-relay (C-T-R) and transmit- combined-relay (T-C-R), which could be used by the base- station to transmit data of two users over downlink channels in the 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 the schemes is evaluated for decode-and-forward, selection relaying, and incremental relaying protocols. In the case of decode-and-forward protocol, the performance heavily depends upon the signal to noise ratio of the link between source and relay. We propose an exact probability of error based approach, which can be used to regulate the erroneous relaying of data. Both C-T-R and T-C-R are able to achieve performance gain as compared to the direct transmission differential scheme in the case of selection relaying and incremental relaying protocols at high SNRs. The proposed schemes also perform better than the direct transmission differential scheme.