An Efficient Multicode Design for Real Time QoS Support in OVSF Based CDMA Networks

Orthogonal variable spreading factor (OVSF) codes are used for CDMA based networks to handle multimedia rates. While waiting time (or call establishment delay) is a significant QoS parameter for real time calls, its impact on non-real time calls is negligible. Traditionally, the call handling in OVSF based CDMA system has been accomplished with multi code approach, where the arriving call is divided into many quantized fractions and each fraction is handled by different code. These designs are very efficient for non-real time calls, but the code search corresponding to each fraction needs significant time that makes existing multi code approaches unsuitable for real time calls. This paper describes a novel multi code design, in which the waiting time for real time call is zero. The design initially assigns the incoming call to the vacant code with the capacity equal to call capacity, and subsequently looks for the vacant codes for each quantized fraction after code assignment. Once the vacant codes with capacities equal to the capacity of all rate fractions are available, the call is shifted to these codes. The information of this code assignment for every fraction needs to be sent to the receiver like existing schemes. Therefore, there is no additional hardware requirement for the proposed design. Simulation results show significant dominance of our scheme as compared to the existing multi code schemes.