The IEEE 802.11e EDCA (Enhanced Distributed Channel Access) mecha-nism has been proposed to improve QoS (Quality of Service) of various services in WLAN (Wireless Local Area Network). By dierentiating the channel ac-
cess delay depending on ACs (Access Categories), this mechanism can provide the relative service dierentiation among ACs. In this paper, we consider that WLAN is deployed in medical environments to transfer medical trac and we reveal that the quality of the medical trac (especially, ECG signal) is sig- nicantly deteriorated even with the service dierentiation by IEEE 802.11e.
Also, we analyze the reason of performance degradation and show that IEEE 802.11e EDCA is hard to assure absolute transmission opportunity of high-priority trac against low-priority trac.
In order to improve QoS of WLAN in medical environment, we rstly es-tablish the service priority of medical trac based on their medical urgency, and then we propose three eective channel access mechanisms, which dier-
entiate either AIFS (Arbitrary Inter-Frame Space) or CW (Contention Win-dow). The rst scheme, referred to as dierentiated AIFS (DIFF-AIFS), sets the value of AIFS in a dierentiated way to provide high-priority trac with
the absolute access channel opportunity. Although this scheme can avoid QoS degradation of high-priority trac, it incurs unnecessary channel access de-lay to low-priority trac, reducing the overall network utilization. The second
scheme, named as DIFF-CW1, is proposed to compensate for this problem; by modifying the size of CW properly, it can enhance relative QoS dierentiation without degrading overall utilization. The third scheme DIFF-CW2 modies
the backo process of the second scheme to further improve utilization while assuring strict QoS of high-priority trac. We compare the performance of three proposed schemes via simulations.