Capacity Analysis for the Gaussian Two-Pair Two-Way Relay Channel

Abstract

This paper studies the transceiver design of the Gaussian two-pair two-way relay channel (TWRC), where two pairs of users exchange information through a common relay in a pairwise manner. Our main contribution is to show that our scheme can achieve the capacity of the two-pair TWRC to within 1/2 bit per user. In the proof, we develop a hybrid coding scheme involving Gaussian random coding, nested lattice coding, superposition coding, and network-coded decoding. Further, we present a message-reassembling strategy to decouple the coding design for the user-to-relay and relay-to-user links, so as to provide more flexibility to fully exploit the channel randomness. We also show that judicious power allocation among the superimposed codeword components at the relay is needed to approach the channel capacity.