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Suboptimal dynamic code assignment and call admission control for OVSF-CDMA communication systems

In this work, we consider the problem of assigning OVSF (Orthogonal Variable Spreading Factor) codes to arriving calls for multi-rate code-division multiple access systems, and propose a sequence of algorithms to solve this problem from different angles. First, we introduce two new policies, called FCA (Fixed Code Assignment) with fixed set partitioning and DCA (Dynamic Code Assignment) with call admission control under an objective to maximize the average data throughput of the system. Numerical simulation confirms that optimized FCA and DCA perform better than DCA with a greedy policy as the traffic load increases and high-rate calls become dominant. Second, a suboptimal DCA with call admission control is examined. The objective is to generate an average data throughput of the system close to that of the optimal scheme while demanding much lower design and implementation complexity than the optimal scheme. By means of capacity or class partitioning and partial resource sharing, we can significantly reduce the computational complexity, thus achieving good design and implementation scalability. Numerical evaluation shows the superior performance of the proposed schemes with low complexity.