Vacant Code Searching and Selection of Optimum Code Assignment Scheme in WCDMA Wireless Networks

Most of 3G and beyond WCDMA networks use orthogonal variable spreading factor (OVSF) code tree for channelization codes. The codes in the code tree are limited and the performance of wireless network depends upon the code assignment to new calls. The paper aims to provide mathematical description for number of codes searched prior to assigning one (or more) suitable vacant code(s) to new call. To the best of Author's knowledge no such description is given in the past. The number of codes searched decides the speed of the code assignment scheme and can be very significant QoS factor for delay prone services like voice transmission, video conferencing etc. Also the code assignment schemes are compared for code blocking which leads to loss in spectral efficiency of the system.