Capacity of the two-way relay channel within a constant gap

We study the capacity of the full-duplex bidirectional (or two-way) relay channel with two nodes and one relay. The channels in the forward direction are assumed to be different (in general) than the channels in the backward direction, i.e. channel reciprocity is not assumed. We use the recently proposed deterministic approach to capture the essence of the problem and to determine a good transmission and relay strategy for the Gaussian channel. Depending on the ratio of the individual channel gains, we propose to use either a simple amplify-and-forward or a particular superposition coding strategy at the relay. We analyse the achievable rate region and show that the scheme achieves to within 3 bits the cut-set bound for all values of channel gains. Copyright (C) 2010 John Wiley & Sons, Ltd.