Research Of Key Radio Resource Management Tehcniques In Broadband Wireless Networks

With the rapid progress of mobile Internet, it becomes a big challenge to provide higher data rates and support various quality of service guarantees with limited radio resources. The mobile communication operators have the trends to deliver broadband services to their subscribers, while broadband wireless access systems begin to support high speed mobility. These targets lead to several key techniques to be adopted in broadband wireless networks, which including the Orthogonal Frequency Division Multiplexing (OFDM) or Single Carrier-Frequency Division Multiple Access (SC-FDMA), Multiple Input Multiple Output (MIMO), and various link adaptive techniques such as Adaptive Modulation and Coding (AMC).In order to achieve high system performance when adopting these techniques, radio resource management plays an important role. However, most traditional radio resource management schemes are not based on these new techniques. Improvements or some new designs of radio resource managements must be provided to meet the demands of the system performance. This dissertation focuses on the study of radio resource management of OFDM/OFDMA systems, taking the QoS guarantees as the key, gives a thorough study on two important QoS schemes, i.e. scheduling and radio resource allocation scheme, as well as call admission control scheme, and the associated technique schemes are proposed.First, the dissertation studies the characteristics of scheduling in broadband wireless networks, and gives the analysis of several key issues which have great impacts on radio resource scheduling, including QoS requirements, wireless channel, and link adaption. Based on this work, the dissertation proposes two QoS-guaranteed scheduling and resource allocation algorithms for OFDMA systems. The first algorithm determinates the scheduling priority according to the QoS requirements of each user, its signal-to-noise ratio on subchannels and their distribution characteristics to improve the system throughput. A new allocation scheme is proposed to satisfy the QoS requirements of users as much as possible first, and to maximize system throughput thereafter. The second algorithm proposes a simplified scheme than the first one. The determination of the scheduling priority is related to the QoS requirements and the subchannel qualities. In this way, the system throughput is sacrificed so as to achieve lower computational complexity of the algorithm. The simulation results show that both algorithms can satisfy the QoS requirements in mixing traffics, and the performance can be made towards a compromise between the system throughput and fairness.To get better performance of scheduling and resource allocation scheme, an efficient call admission control algorithm must be adopted to limit the number of ongoing calls in the system. The dissertation then focuses the research on the link adaptation based call admission control algorithm for broadband wireless networks. With the analysis of the characteristics of the call admission control when adopted in broadband wireless networks and the studies of the related works, the dissertation proposes a new admission control algorithm taking the user mobility and adaptive modulation and coding schemes into account. When the cell is decomposed into several concentric circles, time-frequency resources required for various traffics can be determined easily, while resources can be reserved for handoff and AMC mode-changed calls accordingly. The proposed algorithm can provide the QoS requirements for users while maintaining low blocking probability and dropping probability.The traditional performance analysis module for the call admission control does not consider the impact of the link adaptation. Therefore, the dissertation proposes a performance module based on queueing networks for the call admission control algorithm. When the modification of the users' modulation and coding schemes is treated as the jobs transmission between the nodes in the queueing networks, the impact of the adaptive modulation and coding can be introduced into the queueing networks module. Based on this performance module, the propose call admission control algorithm is analyzed to derive the blocking probability and dropping probability respectively. Finally, the results from theoretical analysis and simulation are compared to demonstrate the performance analysis module for call admission control.