In-kernel passive measurement of the performance impact of hidden terminals in 802.11 wireless networks

The negative performance impact of the presence of hidden terminals in wireless networks has been well know for decades. Despite much research in the area, many deployed networks continue to suffer a performance penalty because of hidden terminals. Ad hoc wireless networks are particularly susceptible to hidden terminal collisions because there are fewer opportunities to plan the network in a way that avoids or reduces the number of hidden terminals. Measuring the presence of hidden terminals and the impact they are having on performance is difficult, especially in a network of many nodes. Without such measurements, the users and operators of wireless networks can not tell if performance problems are caused by hidden terminals or some other problem. We introduce new methodology that can detect the presence of hidden terminals and estimate the performance impact they are causing. The methodology requires no additional hardware and is suitable for wide scale deployment and long term operation. The approach is based on in-kernel instrumentation of the wireless network stack. The design, implementation, and testing of the approach are covered. Results from in-lab testing and the measurement of a live commercial 802.11 network are also presented, including a case study where performance was significantly improved