Efficient Joint Unicast/Multicast Transmission over IEEE 802.11e WLANs

Multimedia communications over WLAN is widely acknowledged as one of the key, emerging applications for wireless LANs. As with any multiservice network, there is the need to provision the WLANs with the QoS mechanisms capable of guaranteeing the requirements of various services. The IEEE 802.11e (EDCA) standard defines the required QoS mechanisms into the protocol architecture of IEEE 802.11 WLANs. However, recent studies have shown that EDCA performs poorly when the medium is highly loaded due to the high collision rate. Numerous proposals have been reported in the literature aiming to overcome this main drawback. However, EDCA and the proposed mechanisms continue to have a serious problem with a specific type of application: the multicast traffic. In EDCA (as in DCF) the multicast service is defined as an unreliable service, i.e., it does not include the use of ACK frames. Furthermore, different to the unicast service, the multicast service makes use of a single rate out of the various rates included in the Basic Service Set (BSS) defined by the IEEE 802.11 standard. This situation has led many researchers to design techniques aiming to improve the multicast transmission such as Auto Rate Selection mechanism for Multicast (ARMS) and Hierarchical-ARSM (H-ARSM). In this paper we present a comparative performance evaluation when supporting different services, such as, voice, video, best-effort, background and in presence of multicast traffic. Our simulation results show the benefits present in multimedia applications when the unicast and multicast traffic are sent efficiently.