Analog Source Exchange with the Help of a Relay

The problem of bidirectionally transmitting two analog sources over a fading channel with the help of a relay is studied. In the regime of high signal-to-noise ratios, upper and lower bounds on the exponent of the end-to-end expected distortion are derived. It is shown that simple two-way relaying protocols based on the separation of source and channel coding can provide significant improvements in the distortion exponent over their one-way counterparts. In particular, in the regime of low channel bandwidth to source bandwidth ratios, an amplify-and-forward scheme is shown to achieve good distortion performance, albeit at the cost of large feedback overhead. In the regime of high bandwidth ratio, even better performance is achieved by a novel adaptive decode-and-forward scheme that successfully exploits low-rate feedback from the relay to the source nodes.