Performance Modeling of a Bottleneck Node in an IEEE 802.11 Ad-hoc Network

The IEEE 802.11 MAC protocol, often used in ad-hoc networks, has the tendency to share the capacity equally amongst the active nodes, irrespective of their loads. An inherent drawback of this fair-sharing policy is that a node that serves as a relay-node for multiple flows is likely to become a bottleneck. This paper proposes a flow-level performance model of such a bottleneck node using fluid flow analysis. Assuming Poisson initiations of new flow transfers at the bottleneck node, we obtain useful insightful, robust and explicit expressions for characteristics related to the overall flow transfer time, the buffer occupancy, and the packet delay at the bottleneck node. The analysis is enabled by a translation of the behavior of the bottleneck node and the source nodes in terms of an M/G/1 queueing model. We conclude the paper by an assessment of the impact of alternative capacity sharing amongst source nodes and the bottleneck in order to improve the performance of the bottleneck