On uplink call level QoS in DS-CDMA networks

摘要

Quality of service (QoS) in direct sequence code division multiple access networks with multiple traffic types can be described with a number of measures. One such measure is the handoff QoS deterioration probability, defined as the probability that the handoff into a new cell or sector of the network will cause violation of the signal to interference and noise ratio requirements for other users (the outage condition). In order to prevent outage events upon handoff for various traffic types, we propose a two tier admission policy. In the first tier, network capacity is calculated on the basis of a given bound on outage probability. Since this may not suffice to reduce the handoff QoS deterioration probability, in the second tier we reserve extra bandwidth for handoff calls below the threshold determined by tier 1 admission. The modified, two tier admission control algorithm is executed only when a call is admitted into the network, so that the admitted calls can freely execute handoffs using the reserved bandwidth. Three different tier 2 policies that differ in complexity and performance have been investigated through analytical modeling. The first policy reserves a fixed number of guard channels out of the soft capacity of the network. In the second policy, the number of reserved channels is proportional to the estimated handoff call arrival rate. In the third policy, the number of reserved channels is obtained through a convex function of the estimated handoff call arrival rate; an additional tuning parameter controls the level of handoff deterioration probability at a given new call arrival rate. The third policy has been found to offer the best performance under increasing traffic load. Analytical results for this tier 2 policy have been verified through simulation for voice traffic only, and mixed voice and data traffic.