A Strict Quality of Service MAC Framework for Emergency Traffic in Wireless LANs
The increasing usage of wireless local area networks (WLANs) in distributed emergency services (e.g., for natural or manmade disasters, telemedicine, and health care) and other time-critical applications requires an efficient medium access control (MAC) protocol. This MAC protocol would support emergency traffic and provide a strict quality of service (QoS) guarantee in saturated emergency applications where a high number of nodes report an emergency. The IEEE 802.11e working group enhanced the 802.11 MAC protocol to support QoS. However, recent studies have shown that the 802.11e standard has limitations since it neither supports emergency traffic nor provides a QoS guarantee under medium-to-high traffic loads. In this thesis, a strict QoS MAC framework for emergency traffic in distributed WLANs under medium-to-high traffic loads is investigated. This framework is based on novel MAC protocols supporting emergency traffic in WLANs. This research first proposes a multiple preemptive MAC protocol (termed as multi-preemptive enhanced distributed channel access [MP-EDCA]), which was developed by modifying an enhanced 802.11e standard (EDCA) in which high priority emergency traffic is given the privilege to preempt the low priority traffic in accessing the medium. A significant network performance gain with respect to lower delays for lifesaving emergency traffic is obtained with MP-EDCA under medium-to-high traffic loads. The improved performance is achieved by modifying the slot time and short inter-frame space in the frame header. One of the most crucial mechanisms for providing a strict QoS guarantee in WLANs is admission Control. The admission control estimates the state of the network’s resources and thereby decide the emergency traffic flow that can be admitted without promising more resources than are available and therefore violating a previously made guarantee. Thus, a preemptive admission control MAC protocol is developed and reported in this thesis to support a strict QoS guarantee for emergency traffic in WLANs. To serve more emergency nodes in WLANs, it is useful to be able to redesign frame aggregation and BlockAck method of MP-EDCA protocol mentioned earlier. The frame aggregation with a simple 2-bit BlockAck scheme (called FASBA) for MP-EDCA is investigated in this thesis. FASBA enhances the capabilities of MP-EDCA, provides assurance of service delivery and offers higher throughput performance by reducing MAC transmission overheads.