Immediate neighbor assignment and reduction in code blocking for OVSF-WCDMA

Code blocking is a major problem in Orthogonal Variable Spreading factor (OVSF) codes. Low rates are scattered in code tree which leads to more code blocking for high rate users. The paper proposes an immediate neighbor busy code design which leads to less code blocking to different user rates, utilizing full capacity of parent codes. For a new call, the vacant code is optimum if the most of the capacity under the parent of the vacant code is already utilized. Subsequently the code is picked from the crowded part of the code tree. This ultimately creates lot of vacant portion in the code tree for higher rate calls. Our system architecture and code assignment strategy provides significant improvement in number of code searches (call processing delay) and complexity. Simulation results are demonstrated to show the superiority of the proposed design as compared to other existing schemes.