Quality of service guarantee for real-time VBR traffic flows with different delay bound and loss probability requirements in WLANs

The medium access control of IEEE 802.11e defines a novel coordination function, namely hybrid coordination function (HCF), which allocates transmission opportunity (TXOP) to stations taking their quality of service (QoS) requirements into account. However, the reference TXOP allocation scheme of HCF controlled channel access, a contention-free channel access function of HCF, is only suitable for constant bit rate traffic. For variable bit rate (VBR) traffic, serious packet loss may occur. In this article, we generalize the reference design with an efficient TXOP allocation algorithm, a multiplexing mechanism, and an associated admission control unit to guarantee QoS for VBR flows with different delay bound and packet loss probability requirements. We define equivalent flows and aggregate packet loss probability to take advantage of both intra-flow and inter-flow multiplexing gains so that high bandwidth efficiency can be achieved. Moreover, the concept of weighted-loss fair service scheduling is adopted to allocate the aggregate TXOP to individual flows. From numerical results obtained by computer simulations, we found that our proposed scheme meets QoS requirements and results in much higher bandwidth efficiency than previous algorithms.