Abstract: Congestion control is an important factor for the performance of IEEE 802. 11 in Ad hoc wireless network. When congestion occurs, the packet rate is controlled, and researching what time congestion exists is a primary task. This paper performed researches on multi-hop Ad hoc network by modeling the packet sending process of individual node. Considering packet maximum retry time and packet buffer queue, and on the basis of 802. 11 DCF basic access mechanisms, the paper proposed an infinite state quasi birth-and-death model. 13y solving the model, the research on how to prevent saturated network under flooding mechanism was performed and corresponding formula which involves the packet arrival rate on MAC layer was obtained. The impact of packet arrival rate on stability was pointed out. This is fundamentally different from earlier work,which usually focuses on the DCF mechanisms itself,while we from the net- work layer view proposed a new model which accurately describes the actual packet transmission process and formulari- zes the mathematical relationship between the stability and packet arrival rate, which provides a mathematical tool for congestion control research.

Key words: Quasi-birth-and-death, 802. 11 DCF, Ad hoc, Packet arrival rate, Flooding, Congestion