MDP-based analysis for multicode assignment in 3G WCDMA networks

3G WCDMA networks adopt the orthogonal variable spreading factor (OVSF) code tree as code management to assign single channelization code for achieving variable rate for real-time multimedia communication. Based on the orthogonal characteristic of the OVSF codes, an allocated code will block the channelization codes, which are at the descendant branches of the allocated code and the ancestral codes of it. Several pieces of research have extensively studied ways to overcome such a problem. In addition, the data rate of traffic classes should be powers of two of the basic rate, which is impractical and results in wasting system bandwidth. One good solution is to assign the multiple codes for an accepted connection. Nevertheless, it brings two drawbacks: high complexity of handling multiple codes and increasing cost of using more Rake combiners at both the base stations and mobile nodes. Consequently, there is a trade-off between the waste rate and complexity of handling multiple code assignment. 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 the waste rate. Numerical results indicate that the proposed MDP approach yields the fewest reassignments and least number of codes per connection while reducing waste rate as compare to other approaches.