Abstract
In this paper, we deal with the problem of assuring medical-grade quality of service (QoS) for real-time medical applications in wireless healthcare systems based on IEEE 802.11e. Firstly, we show that the differentiated channel access of IEEE 802.11e cannot effectively assure medical-grade QoS because of priority inversion. To resolve this problem, we propose an efficient channel access algorithm. The proposed algorithm adjusts arbitrary inter-frame space (AIFS) in the IEEE 802.11e protocol depending on the QoS measurement of medical traffic, to provide differentiated near-absolute priority for medical traffic. In addition, based on rigorous capacity analysis, we propose an admission control scheme that can avoid performance degradation due to network overload. Via extensive simulations, we show that the proposed mechanism strictly assures the medical-grade QoS and improves the throughput of low-priority traffic by more than several times compared to the conventional IEEE 802.11e.
Highlights
Wireless communication technologies have given rise to a paradigm shift in the communication area
An enhanced distributed channel access (EDCA) mechanism of the IEEE 802.11e media access control (MAC) protocol defines four access categories (ACs), each of which represents a relative level of service priority, and provides differentiated channel access depending on the ACs, i.e., a frame belonging to a high-priority AC is preferentially transmitted compared to a frame belonging to a low-priority AC
The residual backoff counter (RBC) of nodeL becomes smaller than the initial backoff counters (IBCs) of nodeH, and the first frame of nodeL can be transmitted sooner than the third frame of nodeH. This example confirms that even larger values of AIFSN and contention window (CW) in the low-priority AC eventually lead to a priority inversion, which originates from the property of freezing/releasing the backoff counter and is unavoidable in the contention-based channel access
Summary
Wireless communication technologies have given rise to a paradigm shift in the communication area. An enhanced distributed channel access (EDCA) mechanism of the IEEE 802.11e media access control (MAC) protocol defines four access categories (ACs), each of which represents a relative level of service priority, and provides differentiated channel access depending on the ACs, i.e., a frame belonging to a high-priority AC is preferentially transmitted compared to a frame belonging to a low-priority AC This conventional EDCA only provides relative service differentiation, but it neither quantitatively assures the QoS requirements in terms of delay, loss, or throughput, nor provides their absolute guarantee. The proposed admission control can maintain acceptable QoS for ongoing connections by preventing network overload It contributes to decreasing collisions of ECG traffic owing to delayed admission. We propose an algorithm, called adaptive AIFS, which controls the channel access probability of low-priority traffic in order to guarantee the required medical-grade QoS and to improve the overall network performance.
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