Abstract: This paper focuses on the issue of available bandwidth estimation in wireless ad hoc networks and takes the overall QoS provision as the standard in estimation. The analytical model for IEEE 802.11-based networks in nonsaturated heterogeneous conditions is presented which maps the QoS metrics of the flows into the network parameters, based on which we then propose an available bandwidth estimation algorithm for QoS provision. The major feature and thus the advantage of the estimation algorithm over existing algorithms is that it takes the flow's QoS demands on delay, packet loss ratio and throughput as the constraints in available bandwidth estimation, and thus overcomes the drawbacks of the existing schemes that only take the maximum achievable throughput as the available bandwidth while the flow’s other QoS demands may be affected. This makes the estimation results more reasonable and accurate. Both the proposed model and the estimation algorithm are validated through extensive simulations.