Application of Information Combining to Relay Networks

Relay networks have attracted great attention in recent years due to their ability to extend the coverage of cellular systems. Their capacity is often analyzed by the max-flow min- cut theorem which provides an upper bound on the true capacity. However, the exact capacity is generally still unknown. This paper applies information combining to determine the achievable rate of a simple relay network. Presupposing an ideal code of appropriate rate and optimum symbol-by-symbol soft-output decoding at the relay, this semi-analytical approach delivers upper and lower bounds on the achievable mutual information of the network. The obtained results identify three different regions concerning the optimum rate of the code. Simulations of a nearly capacity achieving half-rate repeat accumulate code confirm the semi-analytic results.