Modeling and resource management in wireless multimedia wcdma systems

The focus of this thesis is on modeling and optimal resource management in wireless multimedia wideband code-division multiple access (WCDMA) systems. Resource management in CDMA systems has two major roles: to increase spectral efficiency by controlling cochannel interference, and to accommodate multimedia services by proper adjustment of the allocated resources. In this thesis, the system model supports a new class of services with limited delay tolerance in addition to real time and delay insensitive services which have been already considered in the literature. The basic control variables in CDMA resource management are transmit powers, data rates, and base station assignments (handoff decision). Previous works have included a subset of these variables in their resource management algorithms. In this thesis, these control variables are combined in a mathematical programming problem which maximizes the profit gained by a wireless multimedia service provider subject to satisfying the service and quality of service (QoS) requirement for each user. The profit is obtained as the difference between the network revenue and cost. A pricing scheme has been developed to map the network throughput onto the network revenue and the handoff switching overhead onto a certain cost. In this pricing scheme, every user pays proportionally to its instantaneous data rate and quality of service. The mathematical programming problem is analyzed, restructured, and solved for single- and multi-cell systems. The single-cell. solution has the advantage of low complexity and global convergence in comparison with the previous work. Maximum achievable throughput (capacity) of a single cell is mathematically evaluated and has been used as the benchmark for performance measure of single- and multi-cell systems. For multi-cell systems, different solution approaches lead to different results. The best result is generated by the improved mixed-integer nonlinear programming (I-MINLP) algorithm which achieves up to 94% of the capacity in a network with 9 base stations, equivalent to a reuse efficiency of 0.94. The sensitivity of the resource management solution to erroneous input data (path gains) is examined. It has been shown that the higher the capacity utilization, the higher the vulnerability to estimation error. As a practical issue, resource management at different operation levels (centralized, partially decentralized, decentralized, and fully decentralized) is discussed. To facilitate the centralized implementation, a more practical version for the I-MINLP algorithm has been developed. The centralized and partially decentralized schemes are preferred for their high performance and flexibility. Then contribution of this thesis is confined to the reverse link of WCDMA systems. We have assumed that necessary mechanisms to perform handoff procedures, when a user is assigned to a new base station, exist and have not addressed soft handoff. A resource management algorithm that combines the result of this research with the well known closed-loop power control is suggested to enhance reverse-link FDD-mode resource management in IMT-2000, the global standard for third-generation wireless systems. A part of this research has been reported in [1, 2].