Three-phase differential transmission for two-way relay networks with direct link

Differential transmission can be applied to wireless relay networks to mitigate the difficulties involved in estimating channel state information at the transceiver and the relay node. In this paper, we investigate relaying protocol design for two-way relay networks (TWRNs) with direct link. We propose several simple yet effective threshold-based three-phase differential transmission schemes for TWRNs to exploit the direct link, including separate differential decode-and-forward, joint differential decode-and-forward, and differential multiply-and-forward. In these schemes, the relay re-encode and forward the received signal only when the received signal-to-noise ratios (SNRs) of the two source-relay links are above a predefined threshold. Numerical results show that the proposed three-phase protocols outperform the conventional two-phase protocol significantly in the high signal-to-noise ratio region.