Call admission control and resource utilization in WCDMA networks

摘要

Unlike FDMA or TDMA systems, CDMA is interference limited and has a soft capcity that changes depending on the interference felt at the base station at a given time. Admitting a new call and user movement increases the interference level in the system. Therefore a robust Call Admission and Power Control Mechanism is needed. This thesis discusses the main approaches mentioned in the literature on Call Admission Control and Power Control and analyses two modern solutions, namely the QoS aware Power Control and Handoff Prioritization scheme introduced by [T. Rachidi, A. Y. Elbatji, M. Sebbane, and H. Bouzekri 2004] and the Received Power based simulation model discussed in [A. Capone and S. Redana 2001], in greater detail. Then we proceed to recommend improvements that are then tested in a MATLAB simulation environment. The recommended changes improve the overall dropping and handoff loss probabilities. The impact of the NRT overload mechanism discussed in [T. Rachidi, A. Y. Elbatji, M. Sebbane, and H. Bouzekri 2004] is also investigated. The investigations determined the optimum solution achievable with the NRT overload parameter settings. As the final task, a discrete time dynamic feedback control system that aims to keep the dropping and handoff loss rates for RT services below a target value regardless of the traffic dynamics or the bandwidth requirements is designed. A simple Integral Feedback controller is chosen for this task because a controller that is capable of reducing steady state error is required. The controller is used for the NRT overload mechanism while the NRT error rate is left as best effort. The controller parameters are tuned using simulations and the final result is benchmarked against two algorithms that have fixed NRT overload parameters by simulating in environments under various Poisson call arrival rates and traffic loads. The NRT overload mechanism with our controller performed best by holding the RT error rate at the required target value while producing comparatively lower NRT error rates.