An assignment scheme for downlink OVSF codes based on analyzing the two-dimensional state of codes

In downlink of WCDMA, Orthogonal Variable spreading factor (OVSF) codes are used to support variable bit rate services. So the assignment scheme and allocation arithmetic of OVSF codes determine the utilization of downlink bandwidth and affect the performance of the whole network. In this paper, we analyze the disadvantages of DCA scheme and propose a new multi-code reassignment scheme which can increase the utilization of downlink bandwidth and decrease the code fragments on the OVSF code tree. The simulation results show that this scheme can reduce the impact of reassignment process to system efficiently and maintain low call blocking ratio at the same time.