Research And Implementation Of CSMA/CA Protocol In WLAN

In recent years, with the rapid development of wireless networks, wireless LAN applications throughout various fields, in people's lives everywhere. Now there are lots of places, such as cafes, cinemas, hotels, shopping malls are able to provide people with free use of wireless Internet service, people can access the wireless local area network for data communication and network communication anytime, anywhere, as brought great convenience to people's life.As wired LAN, the site in WLAN is by sharing channel resources to achieve the communication, there are cases where contention channel. In the IEEE 802.11 LAN, the channel how to share resources, the time of site sends and receives data by the MAC layer protocol coordination function determined. The MAC layer protocol is one of very important protocol in the 802.11 series standard, and the distributed coordination function is the main function of the MAC layer protocol. Distributed Coordination Function for channel resources allocation does not provide a centralized control, but in each site, using the algorithm of carrier sense multiple access of distributed access, namely CSMA / CA protocol backoff algorithm. In this way, each site only to obtain channel resources and the right to communicate by performing backoff algorithm.DCF protocol using CSMA / CA protocol to minimize the probability of collision in each site. Because once the collision, the channel resources would be wasted in the data frame transmission time, so the protocol performance has a direct impact on the network throughput. Although the backoff algorithm in this agreement can according to the current channel state and the traffic status of the data frame to adjust the backoff time for each site, effectively reduce the probability of conflict, but the back-off time adjustment way too single, can not be combined with the current channel intensity of competition for adaptive adjustment, especially for heavy-duty network adaptability is not enough, when the network is busy, there is a phenomenon of unfair. So how based on the current network load adaptive selection of a suitable back-off time, improve the adaptability of heavy load network, further reduce the probability of collisions, realize the rational utilization of channel resources, to achieve higher throughput is an important direction of current research for WLAN.This paper focuses on CSMA/CA protocol and its backoff algorithm, and to improve the CSMA/CA backoff algorithm deficiencies. In order to facilitate understanding of the links between the CSMA / CA protocol and network performance from theory, the article cites a widely used CSMA/CA protocols theory analytical method at present: a two-dimensional Markov model analysis method put forward by Bianchi. In this model, the site status and metastasis relational expression is derived for each network saturation throughput and network parameters, and then to the results of this analysis do in-depth analysis. The results show that the CSMA/CA backoff algorithm initial backoff window CW_min value is directly related to network throughput and delay, so setting CW_min value to be taken into account.Reference conclusions are obtained by Markov model analysis, and some other backoff algorithm, this paper proposes a new improved algorithm. New algorithm does not change the competitive maximum and minimum values, the window is still [CW_min, CW_max], but within this limit the addition of a defined parameter CW_basic, use it as a reference for network load weight. If the value of contention window of the site is greater than the CW_basic, it considers the current network load is heavy, not easy to use contention channel; otherwise, that the network load is light, the competition is not very intense. New algorithm for the two different network conditions, to take a different backoff window setting mechanism, so that the site at any network loads are able to get proper contention window value, and retreated further reduce the waiting time of collision and retreat, thereby improve the network throughput.Finally, the new algorithm using MATLAB platform for network simulation test, and to analyze the test results. The simulation results showed that: compared with the original algorithm, the new algorithm on the throughput is better, average delay and packet retransmission rate is lower than the original algorithm.