Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2009, Article ID 462396, 14 pages doi:10.1155/2009/462396 Research Article Busy Bursts for Trading off Throughput and Fairness in Cellular OFDMA-TDD Birendra Ghimire, 1 Gunther Auer, 2 and Harald Haas 1, 3 1 Institute for Digital Communications, Joint Research Institute for Signal and Image Processing, The University of Edinburgh, EH9 3JL, UK 2 DOCOMO Euro-Labs, Landsberger Straße 312, 80687 Munich, Germany 3 School of Engineering and Science, Jacobs University Bremen, 28759 Bremen, Germany Correspondence should be addressed to Harald Haas, h.haas@ed.ac.uk Received 1 July 2008; Accepted 8 December 2008 Recommended by Mohamed Hossam Ahmed Decentralised interference management for orthogonal frequency division multiple access (OFDMA) operating in time division duplex (TDD) cellular systems is addressed. Interference aware allocation of time-frequency slots is accomplished by letting receivers transmit a busy burst (BB) in a time-multiplexed minislot, upon successful reception of data. Exploiting TDD channel reciprocity, an exclusion region around a victim receiver is established, whose size is determined by a threshold parameter, known at the entire network. By adjusting this threshold parameter, the amount of cochannel interference (CCI) caused to active receivers in neighbouring cells is dynamically controlled. It is demonstrated that by tuning the interference threshold parameter, system throughput can be traded off for improving user throughput at the cell boundary, which in turn enhances fairness. Moreover, a variable BB power is proposed that allows an individual link to signal the maximum CCI it can tolerate whilst satisfying a certain quality-of-service constraint. The variable BB power variant not only alleviates the need to optimise the interference threshold parameter, but also achieves a favourable tradeoff between system throughput and fairness. Finally, link adaptation conveyed by BB signalling is proposed, where the transmission format is matched to the instantaneous channel conditions. Copyright © 2009 Birendra Ghimire et al. 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. 1. Introduction Orthogonal frequency division multiplexing (OFDM) has been selected as a radio access technology for a number of wireless communication systems, for instance, the wireless local area network (WLAN) standard IEEE 802.11 [1], the European terrestrial video broadcasting standard DVB-T [2], and for beyond 3rd generation (B3G) mobile communica- tion systems [3]. In OFDMA, the available resources are partitioned into time-frequency slots, also referred to as chunks, which can be flexibly distributed among a number of users who share the wireless medium. Provided that channel knowledge is available at the transmitter, resources can be assigned to users with favourable channel conditions, giving rise to multiuser diversity [4]. Interference management is one of the major challenges for cellular wireless systems, as transmissions in a given cell cause cochannel interference (CCI) to the neighbouring cells. Full-frequency reuse where the transmitters are allowed an unrestricted access to all resources causes high CCI, which particularly impacts the cell-edge users [5–7]. Although CCI can be mitigated by traditional frequency planning, this potentially results in a loss in bandwidth efficiency due to insufficient spatial reuse of radio resources. Fractional fre- quency reuse (FFR) [4–6, 8] addresses this issue by realising that in the cellular networks CCI predominantly affects users near the cell boundary. FFR typically involves a subband with full-frequency reuse that is exempt from any slot assignment restrictions. The allocation of the remaining subbands is coordinated among neighbouring cells, in a way that the users in the given cell are denied access to subbands assigned to the cell-edge users in the adjacent cells. To this end, in [5] a user is classified as a cell-edge user based on the path loss to the desired base station (BS). This approach ignores the fact that the channel attenuation of the desired and the interfering signals is uncorrelated, and therefore fails to