Research On Channel Contention In Wireless Ad Hoc Networks

The wireless Ad Hoc network is a communication network which is composed of several wireless terminals equipped with wireless transmitters and receivers. The wireless Ad Hoc network is distributed managed, and terminals do not rely on infrastructure, communicating with each other through multi-hop communication. The wireless Ad Hoc network is very useful in temporary arrangement of communications and no fixed communication infrastructure environments, such as military communications, emergency search and rescue, temporary meeting, sensor networks, because the network has the characteristics of easy arrangement.In this dissertation, we focus on the contention problem while nodes share channel in wireless Ad Hoc network. We try to improve the TCP (Transport Control Protocol) and MAC (Medium Access Control) protocol to ease the network contention and improve the network performance. The congestion control mechanism in TCP adjusts the amount of data sent to the network. So accurate congestion control could reduce the amount of data of the networks, thereby reduce contention. The MAC protocol is used to control the access of media. Through the reasonable mechanism, on the one hand we can make sure that each node could access wireless channel successful, on the other hand we can reduce the collision and interference. The main achievements are as follows:(1) We introduce a rate control algorithm based on channel utilization and contention ratio, which is added to congestion control mechanism of TCP. In this algorithm, an accurate measure of real-time network status of the link layer is introduced. TCP adjusts the cwnd (congestion window) based on the real-time network status, which alleviates the greed of TCP congestion control and reduces the contention.(2) Based on the analysis of the shortcomings of the IEEE 802.11 MAC, We design a interference avoidance algorithm which is added to the IEEE 802.11 DCF mechanism. The algorithm considers the signal attenuation and the difference between the transmission range and the interference range, and proposed an algorithm named extended network allocation vector mechanism (ENAV). The simulation results show that the contention is reduced and the network performance is improved.