Optimal number of RAKE combiners for multiple codes assignment with fast handoff in UMTS mobile networks

To achieve high data rate transmission in personal multimedia communications, 3G wideband CDMA systems (WCDMA) adopt the orthogonal variable spreading factor (OVSF) code tree for channelization codes management. However, it can waste system capacity. One good solution causes two drawbacks, long handoff delay and new call setup delay, which can degrade significantly the performance of 3G cellular systems. Therefore, we propose an adaptive efficient partition algorithm with the Markov decision process (MDP) analysis approach to provide fast handoff while reducing the waste rate significantly. There are two primary motivations for the proposed MDP approach. First, based on the current state of the OVSF code tree, an adaptive partition algorithm is proposed to determine multiple codes for new connections. After determining these codes, we adopt the MDP analysis to assign least-cost codes for them, which results in reducing a large number of reassignments. Second, to support fast handoff processing, the MDP approach assigns a single channelization code for each handoff connection. Thus, the dropping rate and grade of service (GOS) can be reduced. Numerical results show that the proposed approach yields several advantages, including the lowest GOS, the least waste rate, and the least number of reassignments. Finally, the optimal number of RAKE combiners is deduced.