A New Achievable Rate Region for the Gaussian Two-Way Relay Channel via Hybrid Broadcast Protocol

In this letter, we study the Gaussian two-way relay channel (GTWRC) with a direct link in which two nodes want to exchange information with each other with the help of a relay node in the presence of a direct link between two nodes. Specially, we focus on a protocol with four phases, which is called the hybrid broadcast (HBC) protocol. In the HBC protocol, sequential transmissions from both users are followed by a transmission from the relay. Using nested lattice codes, we obtain a new achievable rate region for this protocol. In fact, utilizing a four-stage lattice partition chain, we introduce an intermediate lattice in our lattice-based coding scheme, and by using it, we split the codebook of each node judiciously into two parts. This enables us to decode a linear combination of lattice codewords partially at the relay. Using our proposed strategy, we show that the achievable rate region is superior to the obtained achievable rate region by Kim, Mitran, and Tarokh.