Downlink resource allocation for orthogonal frequency division multiple access systems.

Abstract

Wireless spectral efficiency is increasingly important due to the rapid growth of demand for high data rate wideband wireless services. The design of a multi-carrier system,such as an orthogonal frequency division multiple access (OFDMA) system, enables high system capacity suited for these wideband wireless services. This system capacity can be further optimised with a resource allocation scheme by exploiting the characteristics of the wireless fading channels. The fundamental idea of a resource allocation scheme is to efficiently distribute the available wireless resources, such as the sub-carriers and transmission power, among all admitted users in the system. In this thesis, we present the findings of the investigation into the impact of several resource allocation schemes in an OFDMA environment. We show that in an OFDMA environment without the consideration of sub-carrier assignment, the sub-optimal power allocation closed-form solution can be derived via a constrained optimisation with the duality theorem. With a perfect feedback of channel condition, the proposed low-complexity algorithm that utilises the closed-form solution can maximise the sum capacity to approach near-optimal capacity. We derive the sub-optimal sub-carrier and power allocation closed-form solution via a similar constrained optimisation process. With an imperfect or outdated feedback of channel condition, the adaptive sub-carrier and power allocation scheme not only fails to improve but also further deteriorates the system throughput. We present and discuss the formation of the finite-state Markov channel. We show that by using the dynamics of the Markov channel, the channel quality can be reliably predicted in advance. We analyse via simulation the spectral efficiency achieved by this channel prediction scheme on an OFDMA system. We address the importance of fairness in resource allocation from a game-theoretic perspective. With different utility and preference functions that best describe the gain in users’ throughput as more sub-carriers are allocated to the individual user, we formulate the resource allocation problem into cooperative and non-cooperative games. We study via simulation the effectiveness and fairness of the cooperative and non-cooperative resource allocation schemes on an OFDMA system. Finally, we draw conclusions on our research work and outline the future research topics in connection with our current studies.