An achievable rate region for the two-way two-relay channel

We propose an achievable rate region for the two- way two-relay channel using decode-and-forward block Markovian coding. A previous attempt to obtain an achievable region for this network encountered a fundamental deadlock problem in which each relay needed to decode before the other to enable mutual assistance. In this paper, the deadlock is resolved by introducing an additional constraint that ensures some relay can decode at least one source before the other relay. The resulting achievable region is an extension of existing results for the two- way single-relay channel.