The Research On Call Admission Control Policy In CDMA Mobile Communication System

The mobile communication systems based on CDMA technique are expected to support multi-traffic with different QoS requirements, such as voice, video, data, etc. The research on effective call admission control policies which can provide guaranteed QoS to as many users as possible, and maximizes resource utilization has become the hot spot in the mobile communication fields in recent years.In this paper, adaptive call admission control policies are proposed based on former research achievements.For multi-traffic with different priorities, the existing call admission control policies are built upon the concept of fixed guard channels, and can't adapt to traffic changes. So the paper proposes a dynamic multi-threshold call admission control policy which sets service threshold for each traffic based priority, and dynamically adjusts service thresholds according to system load. Simulation results show that the policy outperforms the existing fixed policies in traffic load adaptation. When the system load is lower, the policy guarantees that the call blocking rate of higher-priority traffic is below its given threshold and at the same time, decreases the call blocking rate of lower-priority traffic. When the system load is higher, the policy does its utmost to guarantee the quality of higher-priority traffic.When the traffic are non-uniformly distributed among cells, the overall call blocking rate of CDMA system is very high. To improve the system performance, the paper presents a call admission control policy based on dynamic resource reservation. It reserves some portion of the system resource in each cell for upcoming calls occurring in neighbor cells. The proportion of reserved resource can be adaptively adjusted according to the call blocking situation. Simulation results show that the policy can resolve the inter-cell unbalanced traffic problem, and it can keep better performance under changing traffic conditions than the call admission control policy based on fixed resource reservation. In addition, the paper further extends the proposed policy to intra-cell unbalanced traffic environment, and makes it more practical.