An Efficient Assignment of Transmission Opportunity in QoS Guaranteed Wireless LAN

IEEE802.11e standard adopts several important techniques to guarantee the quality of service (QoS) of multimedia communications in wireless LAN. A key technique introduced in the standard is an efficient media access control based on hybrid coordination function (HCF), in which each flow is assigned an appropriate transmission opportunity (TXOP) to satisfy several requirements on the flow such as the delay bound and the communication bandwidth. Although it could provide an efficient tool to guarantee the QoS in wireless LAN, HCF has a serious drawback such that a useless bandwidth assignment frequently occurs, which is primarily due to the limitation of the scheme such that all flows share the same service interval (SI). In this paper, we propose a new scheduling scheme that associates each flow with its own SI according to the hardness of the delay bound. The effect of the scheme is experimentally evaluated by simulation. The result of simulations indicates that the number of admitted flows and the data transmission rate certainly increase by the proposed scheme