Preemptive Admission Control Mechanism for Strict QoS Guarantee to Life-Saving Emergency Traffic in Wireless LANs
The increasing usage of distributed emergency services (e.g. natural disaster or disaster caused by humans) in wireless local area networks requires the support of immediate channel access with strict quality of service (QoS) guarantee from a medium access control (MAC) protocol. The IEEE 802.11e/enhanced distributed channel access (EDCA) standard is the MAC enhancement for QoS. Unfortunately, 802.11e (EDCA) neither supports emergency traffic nor provides a strict QoS guarantee especially for a large number of users who report an emergency. To address this problem of achieving a strict QoS guarantee for emergency traffic, we previously developed and reported a multi-preemptive EDCA (MP-EDCA) protocol suitable for operating under low to medium traffic loads. However, MP-EDCA does not provide a strict QoS guarantee to life-saving emergency traffic (e.g. ambulance calls) in highly loaded networks. In this paper, we provide a solution to the problem of achieving a strict QoS guarantee to life-saving emergency traffic under high traffic loads. To this end, we propose a preemptive admission control (PAC) mechanism for MP-EDCA called PAC-MP-EDCA. The proposed PAC-MP-EDCA protects ongoing life-saving emergency traffic flows by giving high priority; thus, assures a QoS guarantee (in terms of lower packet delays) to life-saving emergency traffic when a high number of nodes require immediate channel access during emergency time. The priorities are set by carefully adjusting the short inter-frame space and slot-time in the emergency frames. The performance of PAC-MP-EDCA is evaluated by Riverbed Modeler simulation. Results obtained show that the proposed PAC-MP-EDCA achieved up to 98% lower MAC delays for life-saving emergency nodes and about 15% higher throughput than MP-EDCA under high traffic loads.