Abstract:
Cost effectiveness and easiness in deployment make IEEE 802.11 Wireless Local Area Network (WLAN) one of the most widely deployed wireless technologies now-a-days. To cope up with the thriving necessity of Quality of Service (QoS) required by modern multimedia applications, IEEE 802.11 Working Group proposes an enhanced version of the 802.11, also known as 802.11e. The access mechanism of 802.11e, referred to as Enhanced Distributed Channel Access (EDCA), assigns different types of data traffic with different priorities based on the QoS requirements of the traffic. For each priority, it uses a different set of medium access parameters to introduce QoS support. Differentiating channel access probability based on only traffic priority can ensure QoS statistically in enhanced distributed channel access (EDCA) of IEEE 802.11e. However, it may seriously affect the overall performance in the presence of degraded channel conditions, specially for the distant stations far away from the access point (AP). To overcome this limitation, cooperative communication is getting very popular in wireless communication where sender station transmits data via a helper node to alleviate the adverse effect of low data rate due to bad channel condition. Most of the cooperative MAC protocols are based on DCF mode and concentrate on finding an optimal helper on the basis of data rate only. In this research work, an effective channel access scheme is proposed which exploits the benefit of cooperative communication in order to mitigate the adverse effect of bad channel condition while maintaining deterministically prioritized channel access for high priority traffic. Unlike EDCA, the proposed scheme chooses a prospective helper to assist the sender in transmission whenever a distant station with degraded channel condition wins the channel contention. The major difference with the state of the art cooperative MAC protocols is that it selects an optimal helper node which has data of equal or higher as well as supports significantly high data rate for cooperative transmission. Analytical results show that proposed protocol outperforms the existing protocols in terms of throughput and delay performance.
