International Journal of Computer Science Issues

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Abstract—Adaptive orthogonal frequency division multiple Access (OFDMA) has recently been recognized as a promising Technique for providing high spectral efficiency in future broadband Wireless systems. The research over the last decade on Adaptive OFDMA systems has focused on adapting the allocation Of radio resources, such as sub carriers and power, to the instantaneous Channel conditions of all users. However, such “fast” adaptation requires high computational complexity and excessive signalling overhead. This hinders the deployment of adaptive OFDMA systems worldwide. This paper proposes a slow adaptive OFDMA scheme, in which the sub carrier allocation is updated on a much slower timescale than that of the fluctuation of instantaneous channel conditions. Meanwhile, the data rate requirements of individual users are accommodated on the fast timescale with high probability, thereby meeting the requirements except occasional outage. Such an objective has a natural chance constrained programming formulation, which is known to be intractable. To circumvent this difficulty, we formulate safe tractable constraints or the problem based on recent advances in chance constrained programming. We then develop a polynomial-time algorithm for computing an optimal solution to the reformulated problem. Our results show that the proposed slow adaptation scheme drastically reduces both computational cost and control signalling overhead when compared with the conventional fast adaptive OFDMA.