MDP-based OVSF code assignment scheme and call admission control for Wideband-CDMA communications

Since the orthogonal characteristic of the Orthogonal Variable Spreading Factor (OVSF) code tree in Wideband CDMA (WCDMA) systems, code blocking increases as traffic load or required rate increases. This causes inefficient utilization of channelization codes. Hence, how to efficiently manage the resource of channelization codes of OVSF code tree in WCDMA is an important issue and has been studied extensively. Therefore, in this paper we focus on how to assign channelization code efficiently. Additionally, most researches did not consider the analysis of tree state with dynamic traffic load and lack of systematic call admission control (CAC) mechanism. Therefore, in this paper, we first propose the Markov decision process (MDP) based analysis to assign channelization codes efficiently. Next, we extend the MDP-based approach as the call admission control mechanism to maximize system revenue while reducing blocking. Numerical results indicate that the proposed MDP approach yields the best fractional reward loss and code blocking reward loss as compare to that of others, including the random, left most, and crowded first schemes, and the MDP-based CAC outperforms the capacity-based CAC significantly.