| The IEEE 802.11 standard has been proposed since the nineties of the last century. These standard series develop rapidly for their high reliability, anti-jamming, flexible mobility, high secrecy, simple arrangement and maintenance. They are widely used in the environments which are not easy to arrange wires and frequently changing, and by the workers who have no fixed office location or home office users who need to get information service. That brings people much convenience.However, IEEE802.11 wireless LAN as a new technology is not very mature and perfect. It has unfair problems caused by performance anomaly .It is short of service differentiation functions .And it has the problems that the entire throughput will decrease when the number of nodes is increasing .Owing to the technology generally used, simple schemes are more popular in practice. Considering this factor, we propose a simple and feasible scheme to solve the problem based on the IEEE802.11 protocol. Our main work and innovations are as follow:(1) We make a deep analysis for IEEE802.11 protocol mechanism and present a model different from the Markov which is only appropriate for integrally analyzing and studying the network. This just has macroscopical sense .While the model presented here is effective for network performance parameters of each node. Hence, it has microcosmic sense for us to deeply discuss the problem. Meanwhile it has macroscopical sense after adding all the performances of each node.(2) The network performances will be seriously dropping because of the performance anomaly caused under the multi-rate nodes circumstances. We aim at this problem carrying out the research as follows: (a)we analyze the performance anomaly in detail caused by the existing multi-rate nodes .(b)we put forward a transmission rate packet size adjustment strategy(TRPSA).It can effectively settle the fairness in the multi-rate and multi-node case.(c)we provide strict theory proof and simulation. We verify that TRPSA can realize the fairness in the multi-rate and multi-node case and availably enhance the network performances. The physical realization of TRPSA is easy and simple. It can be achieved by writing the driver but not changing any hardware. These merits make TRPSA be apt to spread in real network.(3) QoS is quite critical for the wireless LAN. When we analyze the QoS limitations for IEEE 802.11 MAC,this paper introduces the strategy of QoS with Service differentiation proposed for the present IEEE802.11 wireless LAN and propose two solutions:one is that service differentiation strategy based on slot adaptive adjustment,which has the function to undraw the throughput of each priority node. On that basis,we further put forward service differentiation strategy based on the packet length adaptive adjustment which can implement throughput divisional function. And the tactics is easy to control and implement.(4) In IEEE 802.11 wireless LAN,because when the number of node increases, collision will accordingly increase,the utilization rate of the channels will drop and the total throughput won't increase but lower.These can lead to the system performance decline. This paper designs a Dynamic Slot Time Based on Number of Nodes (DSTBNN). Then, through in-depth theoretical analysis, we verify that the method can effectively improve the system throughput and the network performances.Finally,we adopt NS2 simulation software and have carried on the simulation many times in various scenarios. Based on the analysis of experimental results we show that this method is simple and effective.It can optimize the network performances based on the changeable number of nodes.It can significantly improve the system throughput and network performances. |
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