Asymmetric Two-Way Relay with Doubly Nested Lattice Codes

Two-way relaying can significantly improve the spectrum efficiency of bi-directional information transmission between two nodes with the help of half-duplex relays. However, in the general case of asymmetric channel gains, the achievable rates of both directions are restricted by the link with the worse channel quality. In this paper, we propose a new three-phase cooperative transmission protocol, which exploits the direct link and the time resource of a two-way relay system more efficiently. We derive the rate region outer bound of this protocol, and propose a practical transmission scheme based on doubly nested lattice codes, which can achieve this outer bound within 0.5 bit. Numerical results show the superiority of this protocol over two other classical protocols in asymmetric channels.