Quality based OVSF code assignment and reassignment strategies for WCDMA systems

For the downlink of 3G mobile communication system, OVSF codes are used as channelization codes to support applications with different bandwidth requirements. The code assignment and reassignment problem focuses on the subject of minimizing the number of code relocations. Previous works have been based on some unrealistic assumptions, including fixed service data rates and code-limited system capacities. In this work, we investigated this issue from a realistic perspective, by including variable service data rates and interference-limited system capacities. To achieving the best service quality, we have proposed three OVSF code assignment and reassignment strategies: sparse-first; sparse-first/rightmost; and modified sparse-first/rightmost. The simulation results, based on the evaluation of number of code reassignments, service quality and throughput, were well investigated and compared with those of other strategies. It was found that our proposed strategies outperformed others, with a significant improvement being guaranteed.