Medium Access Control For Ad Hoc Networks Based On Nodes’ Transmission And Collision Control

With the rapid development of information technology, as well as the wide spread of wireless network and mobile communication applications, a new type of mobile computer network——wireless mobile ad hoc network came into being. Unlike traditional wireless communication networks, ad hoc networks have the characteristics:no fixed foundation supported by the base station, dynamic changes in the topology, multi-hop, bandwidth and power limited. The MAC protocol of ad hoc networks is to complete the channel access control, it is directly related to the efficiency and reliability of data transmission, which has been a research focus.Currently, IEEE802.11DCF is used most actually in ad hoc networks, which likely causes some nodes always occupying the channel, resulting in a number of unfairness problems. A large number of the studies are to solve this problem through adjusting channel access control, but most studies need exchanging information between the stations to assess the level of competition in the channel, and improved protocols with transparent topology are often at the expense of the throughput to achieving fairness.In this article, it focuses on transmission and collision control to enhance the network performance of the system throughput and fairness, which improves DCF from channel access control and data transfer. On the one hand, assessing the level of competition in the channel by setting two parameters:the ratio between nodes’transmission and collision, the number of backoff time freezed. And then, it adds an additional control after the completion of the backoff according to assessment, and controls access successive frames of the channel by adjusting the transmission probability adaptively, which helps to reducing the collision occurs, and improving the fairness; other hand, in order to avoid the degradation of throughput caused by suppression of transmission, it transmits data with no-backoff to nodes delayed, and sets the continuous transmission time dynamically according to situation delayed, and then transmits data continuously to the node meeting the conditions without competing the channel again.This article analysis the simulation through theoretical analysis and experiment on the improved protocol, results show that:the improved protocol effectively reduces the probability of collisions and node transmission delay, at the same time, improves the system fairness access to the channel and the throughput of network.