The Half-Duplex Gaussian Two-Way Relay Channel with Direct Links

We study the half-duplex Gaussian two-way relay channel with direct user-to-user links. In this setup, two users exchange data via a relay and via direct user-to-user links. Due to the half-duplex constraint, the channel can be in one of eight different states at any time (two of which are useless: no node transmitting and no node listening). Restricting to only four states, we propose a scheme that utilizes lattice codes to improve upon existing four-state schemes. Using all six states, we propose another scheme that utilizes lattice codes and coherent combining, and show that it can outperform existing schemes.