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内容記述 |
Broadband Wireless Access (BWA) networks are becoming an infrastructure for broadband connectivity for residential and mobile users with various type of applications including data, voice, and video transfer. As wiring is not required, BWA networks are expected to provide low pricing for high-speed last mile connectivity. Beside that, BWA networks are also to bring the access to the areas where the access has been economically unavailable. Hence, these networks can extend the community and bring connectivity to the larger number of people.<br /> This PhD dissertation is about resource allocation scheme for BWA network. The resource allocation scheme plays an important role in supporting the network to achieve the aforementioned goals, ie. to provide Quality of Service (QoS) for applications with various characteristics. In addition, according to the nature of wireless link, channel condition may fluctuate and some users may face low signal-to-interference-noise ratio, which results in low transmission capability. Hence, the resource allocation scheme must take channel condition into account and ensure that all users’ applications are allocated enough network resource in a fair manner.<br /> We compare the performance of various resource allocation schemes for the BWA network that is based on Orthogonal Frequency Division Multiplexing (OFDM) in Time Division Duplex (TDD) mode which serves the fixed and nomadic subscribers. In this case, channel condition is presumably stable because the subscriber stations have no mobility, and hence, transmission rate is fixed. We propose a novel resource allocation and packet scheduling scheme in order to serve several classes of traffic with various requirements in this fixed-rate case. The scheme is based on deficit counters, which can provide fairness and flexibility at the same time.<br /> Our study also covers the case where users move with various patterns of mobility. In this case, the Orthogonal Frequency Division Multiple Access (OFDMA) technique is recommended. OFDMA allows an Adaptive Modulation and Coding(AMC) technique so that users with inferior channel condition can change the modulation and coding scheme to the more reliable one. This technique ensures connectivity and increases reliability. Furthermore, OFDMA enhances the network capacity by dividing data in the multiple streams and sending via multiple subchannels with low transmission rate in parallel. OFDMA with AMC provides multiuser multichannel diversity, which should be exploited by the resource allocation scheme.<br /> Thus, in this dissertation, we present our research work for fair resource allocation with the consideration of users’mobility and variation of wireless channel condition. We employ a matrix to model multiuser multichannel diversity. In addition, we propose three novel resource allocation schemes with the objective of providing QoS and maintaining fairness while trying to maximize the total system throughput, All three schemes are based on Proportional Fairness(PF) utility. function because this function is the balance trade between throughput and fairness. The first scheme focuses on fair resource allocation while maximizing total system throughput. In the second scheme, we analyze PF utility function for a multicarrier system, and derive a novel PF-based utility function that takes users’ data rate requirement into consideration. The third scheme focuses on providing service to multiple classes of users. The scheme tries to guarantee QoS for the guaranteed class, while serves the non-guaranteed class as much as possible.<br /> Moreover, this dissertation contains the evaluation of the schemes’ performance in various ways with the realistic assumption that users’ queue are finitely backlogged and can be empty from time to time. In summary, our schemes provide the completely solutions for resource allocation and packet scheduling in various case of a BWA system ranging from the case where users are nomadic or have no mobility to the case where users have full mobility with various speed.The schemes cover many dilemma issues that are introduced by BWA networks such as the maximization of network utilization, fairness, classes of users with different requirements, and traffic with individual data rate requirement. In addition, our work also considers reducing the number of iterative computation to reduce the computation complexity in order to provide the feasible implementation in the realistic systems. |
要旨・審査要旨 (287.2 kB)
