Channel-Aware Subchannel Renumbering and Downlink Burst Allocation for IEEE 802.16 OFDMA Systems

This paper investigates the downlink burst allocation problem in IEEE 802.16 OFDMA system. In order to increase the subchannel utilization and to improve the network throughput, a channel-aware renumbering (CSR) scheme and a channel-aware downlink burst allocation (CDBA) scheme are proposed in this paper. CSR considers the difference among subchannel qualities of MSs and logically renumbers the subchannels so that each MS can have a group of subchannels supported the same and more efficient modulation and coding (MC) scheme. CDBA is to decide the size, shape and the position of each burst. Because of the rectangular burst allocation constraint, some slots in or among rectangular bursts will be wasted. These two kinds of slot wastage problems are defined as internal and external fragmentation problems in the paper. Therefore, in order to comply with the rectangular burst allocation constraint, to overcome the fragmentation problems and to increase the network throughput, CDBA is to determine the size and the position of each MS's burst based on the subchannel qualities of MSs and the bandwidth requirements. The simulation results show that CDBA with CSR outperforms other related approaches with or without CSR in terms of the throughput, the service ratio, the subchannel utilization and the DL-MAP overhead.