Flexible Code Allocation to Improve System Utilization Using Nonblocking OVSF Codes in WCDMA

In next generation wireless networks, system resources such as transmission power and channelization codes should be allocated efficiently and fairly to individual transmissions. Efficient assignment of channelization codes such as orthogonal variable spreading factor (OVSF) codes in WCDMA-based cellular networks is crucial in supporting the delay and rate guarantees of real-time flows. However, OVSF codes support data rates that are powers of two and do not support many intermediate data rates. This reduces some flexibility in the allocation of code resources, and under poor channel conditions it may result in over-provisioning a real-time flow as well as under-provisioning a non-real-time flow. Nonblocking OVSF (NOVSF) codes can, however, support many intermediate data rates. This paper proposes an NOVSF code/time-slot allocation algorithm to achieve better system utilization and better flexibility in code allocation. Simulation results show that when compared to OVSF codes, the use of NOVSF codes reduces the call blocking probability of real-time flows and provides better overall throughput for non-real-time flows.