Call departure reassignment and performance enhancement of OVSF codes in downlink of CDMA based networks

Abstract

The use of orthogonal variable spreading factor (OVSF) codes give an additional advantage of addressing variable rate requirement of CDMA networks. However, these codes suffer from code blocking problem which further increases due to random nature of call arrival and departure. When a call departs the vacant capacity of the call creates fragmentation in the sub tree where it belongs. The proposed assignment schemes in this paper, in order to reduce fragmentation assigns fragmented vacant capacity of this sub tree to other sub tree(s) and vice versa using reassignment. The proposed schemes guarantees reduced blocking of future high rate calls. It also leads to good system throughput and fairness. Through simulations, it has been demonstrated that the proposed scheme(s) not only adequately reduces code blocking probability but also requires significantly lesser number of code searches as reassignment process is activated in offline mode and online mode is used to locate a vacant code for assignment, which makes it suitable for the real time calls.