Submitted to IEEE Transactions on Vehicular Technology, Aug 30th. 2008.
In this paper we derive power loading strategies for single-user and multicast OFDM wireless links in the presence of a non-regenerative relay node. Our approach is based on the minimization of vector error-rate at the destination subject to individual power constraints at the source and at the relay. For the single-user case, we propose a joint max-min power loading strategy that is optimal at large signal-tonoise ratios and in doing so we show how the original problem may be recast into an effective (no-relay) OFDM power loading problem with a previously known solution. Using bounds on effective signal-tonoise ratios, we propose disjoint power loading strategies that require channel state information either at the source, or at the relay, but not at both. For the multicast scenario we propose a max-min equalizing solution that yields a minimum effective signal-to-noise ratio at each user terminal. We also formulate several linear solutions based on prioritizing the users in the network. Our single-user simulations show considerable error-rate performance gains for the proposed joint max-min solution and also gives hints as to where disjoint power loading is best effective. Our multicast simulations show that the max-min equalizing solution is best suited for networks with random user locations, while the linear prioritizing solutions work best for networks with fixed user locations.
Preprint available upon request.