CSMA/CA based networks such as those using the IEEE 802.11 DCF protocol have experienced widespread deployment due to their ease of implementation. The terminals accessing these networks are not owned or controlled by the network operators (such as in the case of cellular networks) and thus they may not abide by the protocol rules in order to gain unfair access to the network (selfish misbehavior), or simply to disturb the network operations (denial-of-service attack). Statistical signal processing can play an important role in detecting misbehaviors and DoS attacks. We first describe a method to detect selfish misbehaving terminals that may deliberately modify its backoff window to gain unfair access to the network resources. We present nonparametric batch and sequential detectors that do not require any modification on the existing CSMA/CA protocols. We then presents a robust non-parametric detection mechanism for MAC layer denial-of-service attacks that also fully complies with the existing protocols. Ns-2 simulation results show that the proposed methods have a very short detection latency and high detection accuracy.

Xiaodong Wang  received the Ph.D degree in Electrical Engineering from Princeton University. He is now on the faculty of the Department of Electrical Engineering, Columbia University. Dr. Wang's research interests fall in the general areas of computing, signal processing and communications,  and has published extensively in these areas. Among his publications is a recent book entitled "Wireless Communication Systems: Advanced Techniques for Signal Reception," published by Prentice Hall in 2003.  His current research interests include wireless communications, statistical signal processing,  and genomic signal processing. Dr. Wang received the 1999 NSF CAREER Award, and the 2001 IEEE Communications Society and Information Theory Society Joint Paper Award. He has served as an Associate Editor for the IEEE Transactions on Communications, the IEEE Transactions on Wireless Communications, the IEEE Transactions on Signal Processing, and the IEEE Transactions on Information Theory.