Efficient Utilization of Orthogonal Variable Spreading Factor Trees Using Two levels Of Hierarchies and Adaptive Rate Control Mechanism

A novel code assignment and re-assignment mechanism is proposed to accommodate users with different data rate requirements in WCDMA systems employing OVSF codes. The new mechanism overcomes the drawbacks of several static and dynamic algorithms for code assignment. Specifically, it reduces significantly code blocking probability due to the fragmentation of the OVSF code tree and allows dynamic rate control mechanism. Our proposed mechanism minimizes the code blocking and code reassignment process to new calls using code residual crowded partitioning algorithm. This has the advantage of providing heterogeneous data rates to mobile users and fully utilizes the system capacity. Moreover, the unreserved bandwidth of the network can be shared fairly among competing mobile users. Extensive simulations were made to validate the proposed mechanism and results have proven the superiority of our algorithm with respect to existing algorithms.