Markov Decision Process Based Multiple Codes Assignment in UMTS WCDMA Mobile Networks |
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Authors: | Ben-Jye Chang |
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Affiliation: | (1) Department of Computer Science & Information Engineering, Chaoyang University of Technology, Taichung, Taiwan, R.O.C |
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Abstract: | For achieving high transmission rate in mobile multimedia communications, 3G WCDMA systems adopt the Orthogonal Variable Spreading
Factor (OVSF) code tree to assign a single channelization code for each accepted connection. Based on the orthogonal characteristic
of an OVSF code tree, an allocated code blocks the channelization codes that are on the descendant branches and the ancestral
codes of the allocated code. Several researches have been proposed to overcome the code-blocking problem for maximizing system
utilization. By using both the code assignment and reassignment mechanisms, the system utilization and code blocking can be
improved. Nevertheless, the data rate of traffic classes in such single code assignment system should be powers of two of
the basic rate, which is impractical and wastes the system capacity when the required rate is not powers of two of the basic
rate. A good solution is to assign multiple codes to a new connection, but causes two drawbacks: high complexity of handling
multiple codes and high cost from using more number of rake combiners. Consequently, there is a trade-off between waste rate
and complexity of handling multiple codes assignments. In previous researches, high computation complexity of assigning multiple
codes for a connection and large number of reassignment codes suppressed the advantage of reducing waste rate. Therefore,
we propose an adaptive efficient partition algorithm with the Markov Decision Process (MDP) analysis approach to reduce the
large number of reassignment codes while improving waste rate. There are two main motivations in the proposed approach. First,
we propose an adaptive efficient partition algorithm to determine multiple codes based on the current state of the OVSF code
tree for the new incoming connection. Second, after determining the multiple codes, we adopt the MDP analysis to assign the
least-cost code for each determined code. Numerical results demonstrate that the proposed MDP approach yields the least number
of reassignments and the least number of codes per connection while reducing waste rate significantly, as compared to other
approaches. |
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Keywords: | multicode assignment MDP WCDMA networks reassignment waste rate |
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