Vacant codes grouping and fast OVSF code assignment scheme for WCDMA networks

Abstract

Channelization codes used in WCDMA are Orthogonal Variable Spreading Factor (OVSF) codes. These codes suffer from code blocking limitation. Many designs are proposed to avoid this limitation but most of them do not consider number of codes searched, which affects call establishment delay prior to handling a call. We propose a fast OVSF code assignment design which aims to reduce number of codes searched with optimal/suboptimal code blocking. The code assignment scheme aims to use those vacant codes whose parents are already blocked. This leads to occurrence of more vacant codes in groups, which ultimately leads to less code blocking for higher rate calls. The number of codes searched increases linearly in our design compare to most of other novel proposed single code methods like crowded first assignment, where it increases exponentially with increase in user rates. Also the calculation of vacant codes at one layer will be sufficient to identify the vacant code adjacency for all the layers which reduces complexity. Simulation results are presented to verify the superiority of the design.