Practical approaches to adaptive resource allocation in OFDM systems

Abstract

Whenever a communication system operates in a time-frequencydispersive radio channel, the link adaptation provides a benefitin terms of any system performance metric by employing time,frequency, and, in case of multiple users, multiuser diversities.With respect to an orthogonal frequency division multiplexing(OFDM) system, link adaptation includes bit, power, and subcarrierallocations. While the well-known water-filling principle providesthe optimal solution for both margin-maximization andrate-maximization problems, implementation complexity often makesdifficult its application in practical systems. This paperpresents a few suboptimal (low-complexity) adaptive loadingalgorithms for both single- and multiuser OFDM systems. We showthat the single-user system performance can be improved bysuitable power loading and an algorithm based on the incompletechannel state information is derived. At the same time, the powerloading in a multiuser system only slightly affects performancewhile the initial subcarrier allocation has a rather big impact. Anumber of subcarrier allocation algorithms are discussed and thebest one is derived on the basis of the order statistics theory.