Resource allocation in multihop OFDMA broadcast networks

This paper considers resource allocation strategies for multihop OFDMA broadcast networks consisting of a source, K destinations (users), and K dedicated decode-and-forward relays per hop. Network scenarios of practical interest have to face the availability of partial and imperfect channel state information at the transmitters (source and relays) due to fast time-varying channels, limited-rate feedback, and/or feedback delays. We address the limiting situation in which the transmitters have knowledge of the channel pathloss only and hence OFDMA is a means of implementing frequency-diversity. In this context, the computation of the optimal resource allocation maximizing a weighted sum of the users´ effective rates is not straightforward since it gives rise to a non-convex optimization problem. We analyze the two-hop case and propose a suboptimal, computationally efficient solution for which we are able to upper bound the gap from the optimum. Fortunately, the gap can be shown to be zero for some networks. For a general network with an arbitrary number of hops we propose a simplified extension of the two-hop solution.