An Error Propagation Free Decode and Forward Scheme for Channel-Unaware Two-Way Relay Networks

This paper considers channel-unaware two-way relay networks (TWRNs) with a single-antenna decode-and-forward (DF) relay. These networks typically rely on differential signalling which results in error propagation and error floors. To overcome this drawback, we develop a novel differential signalling scheme, which, in contrast with existing ones, does not cause detection errors to propagate from one block to the next. We obtain a union bound on the block error rate (BLER), which shows that the proposed differential method exhibits superior performance to existing schemes, eliminates error floors and results in a BLER that decays as the inverse of the signal-to-noise ratio. Furthermore, the proposed scheme removes the unitarity restriction on the transmitted symbols in conventional differential signalling. Therefore, non-unitary symbols can be used in the differential signalling which provides more degrees of design freedom and better performance. Our numerical results confirm our analytical findings.