The Performance Analysis Of Wireless Wi-Fi DCF Access Protocol

With the rapid development and advancement of information and communicationtechnology, as a new kind of communication technology，wireless transmission which isadvancing with the times is making a big difference on people’s production and life. Andas a wireless short distance transmission technology, Wi-Fi which is widely used isincreasingly developing and maturing at a high rate of speed. But because of wirelessenvironment which is special transmission medium, Wi-Fi technology which isrepresented by IEEE 802.11 are still insufficient in many aspects, such as channelcapacity, interference resistance, energy saving, safety and so on. In this paper, theresearch and improvement is on the access protocol of Wi-Fi technology.Firstly, according to DCF protocol of IEEE 802.11 standard only provides twoaccess ways of threshold setting and does not give its optimal value. This paper comparesand analyzes two access ways of saturation throughput by Markovian mathematicalmodel and combines with the simulation results and comparisons of two access ways’time delay performance which is obtained in the OPNET Modeler simulation platform,this paper obtains the optimal switching threshold of DCF protocol in Wi-Fi technology.And according to the different scene, different method of optimal threshold setting isgiven.Secondly, based on the deeply analysis of DCF protocol binary exponential backoffalgorithm and according to this algorithm is not adaptive to congestion condition of thenetwork so that the performance of network declines rapidly with the channelcompetition intensifies, this paper designs an improved backoff algorithm. The improvedalgorithm utilizes a theoretical reference value which can be used to measure thecongestion level of network and divides the channel congestion level into three parts bytwo sliding parameters. According to every part, this paper uses an adapted backoffalgorithm so that every station can adjust itself according to the channel’s congestioncondition.Finally, this paper interprets OPNET network simulation tool in depth and analyzes working flow of node and process model of Wi-Fi in detail. This paper successfullymodifies DCF protocol in the OPNET Modeler network simulation platform and realizesthe improved algorithm. The simulation graphs prove the validity of the improvedalgorithm.