Capacity analysis and performance evaluation of call admission control for multimedia packet transmission in UMTS WCDMA system

摘要

Packet transmission combined with WCDMA (Wideband Code Division Multiple Access) access technique defined in the Universal Mobile Telecommunication System (UMTS) provides high flexibility in resource allocation in order to integrate multimedia services with different requirements. However, this flexibility requires to design an efficient call admission control (CAC) able to control the number of active users in a system where capacity varies according with the level of interference. Taking into account the stochastic nature of multimedia traffic and the changes in the available capacity in the CDMA system, an effective capacity request is derived and used to characterize the resources required by each mobile user in order to meet its respective quality of service requirements. These requirements are expressed in terms of rate and delay constraints in addition to the signal to interference ratio. After setting an effective capacity threshold for the system, a linear approximation is used to find the total amount of resources required by all the mobile users already admitted in the system and the new connection request. Packet transmission is considered for both real time and non real time services while a centralized demand assignment algorithm has been implemented in order to provide QoS in the packet level. Performance in a multicell scenario and in time variant wireless channel conditions has been evaluated considering channel-stated scheduling algorithms. Computer simulation results are given to demonstrate the performance of the proposed method.