Accurate and energy-efficient congestion level measurement in ad hoc networks

Congestion in ad hoc networks not only degrades throughput, but also wastes the scarce energy due to a large number of retransmissions and packet drops. For efficient congestion control, an accurate and timely estimation of resource demands by measuring the network congestion level is necessary. Unlike the wired networks, congestion level measurement in ad hoc networks is more difficult due to time-variant channel capacity, contention among neighboring nodes, and non-deterministic node scheduling. In this paper, we propose a new congestion detection mechanism that quantifies the congestion level accurately and energy-efficiently at both a node-level (implemented at the MAC layer) and a flow-level (implemented at the routing layer) in ad hoc networks. For accurate congestion measurement, a set of metrics that decouple the measurement from various MAC protocol characteristics is defined. For energy-efficient congestion measurement, an asynchronous channel loading measurement scheme called Lazy Measurement, which emulates synchronous measurement by using virtual channel sampling, is incorporated into the proposed scheme. Simulation results show the proposed mechanism significantly cut down the energy needed to accurately measure congestion while maintaining high level of accuracy needed for timely congestion control.