Throughput Optimization of non-real-time flows with delay guarantee of real-time flows in WLANs

Due to the rapid growth of real-time applications in wireless local area networks (WLANs), quality-of-service (QoS) guarantee becomes one of the key issues for IEEE 802.11e enhanced distributed channel access (EDCA) networks. In contrast to most existing studies which only focus on providing delay guarantee to real-time flows, in this paper we study the open question of how to adaptively tune system parameters to maximize the aggregate throughput of non-real-time flows with a certain mean access delay constraint on real-time flows for saturated IEEE 802.11e EDCA networks. Explicit expressions of the maximum aggregate throughput of non-real-time flows and the optimal initial backoff window sizes are obtained, and verified by simulation results. The analysis shows that for a given mean access delay constraint, the maximum aggregate throughput of non-real-time flows declines as the number of real-time nodes grows. It drops to zero when the number of realtime nodes exceeds a critical threshold, indicating that the delay requirement cannot be satisfied. An admission control scheme is further proposed, where the maximum number of real-time nodes that can be enrolled is derived as a linearly increasing function of the mean access delay constraint.