EURASIP Journal on Wireless Communications and Networking
Volume 2008 (2008), Article ID 160307, 10 pages
doi:10.1155/2008/160307
Research Article
Practical Approaches to Adaptive Resource Allocation in OFDM Systems
Department of Electrical and Communications Engineering, Helsinki University of Technology, P.O. Box 3000, TKK 02015, Finland
Received 30 April 2007; Revised 6 September 2007; Accepted 28 September 2007
Academic Editor: Luc Vandendorpe
Copyright © 2008 N. Y. Ermolova and B. Makarevitch. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Whenever a communication system operates in a time-frequency
dispersive radio channel, the link adaptation provides a benefit
in 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 subcarrier
allocations. While the well-known water-filling principle provides
the optimal solution for both margin-maximization and
rate-maximization problems, implementation complexity often makes
difficult its application in practical systems. This paper
presents a few suboptimal (low-complexity) adaptive loading
algorithms for both single- and multiuser OFDM systems. We show
that the single-user system performance can be improved by
suitable power loading and an algorithm based on the incomplete
channel state information is derived. At the same time, the power
loading in a multiuser system only slightly affects performance
while the initial subcarrier allocation has a rather big impact. A
number of subcarrier allocation algorithms are discussed and the
best one is derived on the basis of the order statistics theory.