  In this paper, a Gaussian two-way relay channel, where two source nodes
exchange messages with each other through a relay, is considered. We assume
that all nodes operate in full-duplex mode and there is no direct channel
between the source nodes. We propose an achievable scheme composed of nested
lattice codes for the uplink and structured binning for the downlink. We show
that the scheme achieves within 1/2 bit from the cut-set bound for all channel
parameters and becomes asymptotically optimal as the signal to noise ratios
increase.
