Bidirectional Worst Subchannel Avoiding Versus Best Subchannel Seeking Subcarrier-Allocation in Downlink OFDMA Systems

Abstract

In this paper, we design and investigate two subcarrier-allocation algorithms for downlink orthogonal frequency division multiple access (OFDMA) systems. One is designed to avoid assigning users as many as possible the worst subchannels, which is referred to as the bidirectional worst subchannel avoiding (BWSA) algorithm. The other one is called the best subchannel seeking (BSS) algorithm, which aims at assigning users the best possible subchannels. We study and compare the error rate, spectrum-efficiency and the complexity of the two algorithms. We also compare them with some existing subcarrier-allocation algorithms. Our studies show that both the BWSA and BSS algorithms belong to the class of low-complexity subcarrier-allocation algorithms. In general, they outperform all the other considered sub-optimal algorithms, in terms of both error performance and spectrum-efficiency. When operated in relatively large OFDMA systems, we find that both the error performance and the spectrum-efficiency attainable by the BWSA and BSS algorithms are close to that achieved by the Hungarian algorithm of high-complexity.