Research Studies Project Report (M.Eng.) - Asian Institute of Technology, 2002

A research study submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Advanced Technologies

Emerging Third Generation (3G) wireless standards promise to support the relative higher and variable data rate services with various QoS considerations. Wideband Code Division Multiple Access (W-CDMA) scheme has been proposed by the Universal Mobile Telecommunications System (UMTS) for fulfilling these requirements. MCCDMA and OVSF-CDMA are some of the CDMA schemes for implementation under 3G systems. OVSF-CDMA is better suited than MC-CDMA for its hardware simplicity, but suffers from code blocking. To eliminate the code blocking is an important issue in OVSF-CDMA. This research work is mainly concerned with the elimination of code blocking with a suitable dynamic code assignment (DCA) scheme. The DCA guarantees the admission of a new call if the remaining capacity of the system can support it regardless of the orthogonality constraint that can arise in the system. This is done by reassigning the calls in descendant codes to other unused codes to satisfy the orthogonality constraint. An optimum algorithm which uses minimum number of reassignment is proposed. The work is then extended to investigate the performance of the system in terms of code utilization, overall blocking and Individual blackings. The work is further extended to study the performance of the system with traffics of various QoS classes (Conversational, Streaming, Interactive and Background) introduced by UMTS for Third Generation Partnership Project (3GPP). Based on the simulation results, the DCA can improve the performance of the system by improving the code utilization and decreasing the blocking of higher rate calls. The guard capacity concept with delay is utilized to the low priority calls which can be further helpful to reduce the blocking of higher rate and higher priority calls. It is observed that a proper choice of the guard capacity is important to get the desirable performance of the system.