Bit loading algorithms for cooperative OFDM systems

Abstract

We investigate the resource allocation problem for an OFDM cooperative networkwith a single source-destination pair and multiple relays. Assuming knowledge of theinstantaneous channel gains for all links in the entire network, we propose several bit andpower allocation schemes aiming at minimizing the total transmission power under a target rateconstraint. First, an optimal and efficient bit loading algorithm is proposed when the relay nodeuses the same subchannel to relay the information transmitted by the source node. To furtherimprove the performance gain, subchannel permutation, in which the subchannels are reallocatedat relay nodes, is considered. An optimal subchannel permutation algorithm is first proposed andthen an efficient suboptimal algorithm is considered to achieve a better complexity-performancetradeoff. A distributed bit loading algorithm is also proposed for ad hoc networks. Simulationresults show that significant performance gains can be achieved by the proposed bit loadingalgorithms, especially when subchannel permutation is employed.