| In this research, 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-FSP (Fixed Code Assignment with Fixed Set Partitioning) and DCA-CAC (Dynamic Code Assignment with Call Admission Control) with an objective to maximize the average data throughput of the system. The FCA-FSP partitions a set of OVSF codes into multiple groups, each of which consists of codes with the same spreading factor and supports only the corresponding class of calls. We optimize the partitioning so that the average throughput is maximized. An optimal DCA-CAC policy is derived through the linear programming technique under the framework of the Markov Decision Process.; Second, computationally-efficient dynamic code assignment (DCA) with call admission control for OVSF-CDMA systems is examined. The objective is to generate an average data throughput close to that of the optimal scheme while demanding much lower design and implementation complexity. Along this direction, we proceed with two different approaches. The first one is to develop a hybrid code assignment scheme that integrates FCA and DCA. The second one is to adopt the one-stage-lookahead suboptimal code assignment scheme, which does not require a complex MDP solution process yet provides nearly-optimal performance.; Finally, on-line dynamic OVSF code assignment and call admission schemes that are adaptive to non-stationary incoming traffic conditions are studied. The proposed schemes consist of two steps: (i) on-line estimation of parameters of varying traffics and (ii) design of a dynamic OVSF code assignment and call admission control schemes adaptive to the estimated traffic. In the first step, traffic parameters are estimated using a bootstrap principle. In the second step, two alternative schemes, i. e. the dynamic partitioning scheme with fixed code assignment (FCA) and the short-stage look-ahead call admission control (CAC) for dynamic code assignment (DCA), are proposed to maximize the throughput with respect to estimated traffic parameters. |
