To support the varying Quality-of-Service (QoS) requirements of emerging applications such as those involving continuous media, a new standard IEEE 802.11e has been specified [1]. This standard aims to support QoS by providing differentiated classes of service at the medium access control (MAC) layer to enhance the ability of physical layers to deliver time-critical traffic in the presence of traditional data packets. The 802.11e standard defines four access categories (ACs). These four ACs have different transmission priorities. The transmission priority is the probability of successfully earning the chance to transmit when individual ACs are competing to access the wireless channel the higher the transmission priority, the better is the opportunity to transmit.123-To support the varying Quality-of-Service (QoS) requirements of emerging applications such as those involving continuous media, a new standard IEEE 802.11e has been specified [1]. This standard aims to support QoS by providing differentiated classes of service at the medium access control (MAC) layer to enhance the ability of physical layers to deliver time-critical traffic in the presence of traditional data packets. The 802.11e standard defines four access categories (ACs). These four ACs have different transmission priorities. The transmission priority is the probability of successfully earning the chance to transmit when individual ACs are competing to access the wireless channel　the higher the transmission priority, the better is the opportunity to transmit.123