地鐵環(huán)境下車地可靠無線通信機制的設(shè)計與實現(xiàn).pdf

1、南京航空航天大學(xué)碩士學(xué)位論文地鐵環(huán)境下車地可靠無線通信機制的設(shè)計與實現(xiàn)姓名：林威儀申請學(xué)位級別：碩士專業(yè)：計算機科學(xué)與技術(shù)指導(dǎo)教師：陳兵2010-12地鐵環(huán)境下車地可靠無線通信機制的設(shè)計與實現(xiàn) ii ABSTRACT Wireless LAN has been widely used in various industry, which is applied to the subway communication system. How

2、ever, there are many technical problems that are still unsolved. Recently, the Wireless LAN can support the low rate movement of mobile nodes , but it is not enough for the movements of a high-speed within a large-scale,

3、 and the train control information system demands high reliability. Therefore, the key issues of the subway communication system are the handoff between station(STA) and access point(AP) and the reliability of “train-to-

4、earth” communication. The project named “Research on generalization of IEEE 802.11a/b/g radio station” is a subitem of a transformation of scientific and technological achievements in Jiangsu Province. The reliable “trai

5、n-to-earth” communication is the core ingredient. Firstly, the wireless network in subway communication system was particularly analyzed, and contrasted with current WLAN. The problems that were pointed out from the rese

6、arch were thoroughly studied. Consequently, a dual-link collaborative handoff algorithm and a dual-sta collaborative communication scheme were proposed to deal with these problems. Finally, detailed implementation and te

7、sts have been given in this paper. Solutions to these problems such as high delay, high packet loss rate, low stability and reliability exist in current handoff schemes. Every STA was disposed two communication links, a

8、dual-link collaborative handoff algorithm and a dual-link selection and data transmission algorithm is presented in this paper. This is necessary to acquire accurate signal quality by smooth processing and control the ha

9、ndoff between two communication links at the appropriate time by threshold of difference value and packet forwarding using dual-thread. This was then implemented under linux and tested by Ixchariot. The result suggests t

10、hat dual-link scheme does not have delayed pulse in comparison with single link scheme. Additionally, the packet loss rate is close to zero and the average throughout is increased by 20% in dual-link scheme. Moreover, to

11、 enhance the stability and reliability of the subway wireless communication system, two gateways and two STAs was disposed and a dual-sta collaborative communication scheme was proposed. Implementation between two gatewa

12、ys and two STAs were required to design a state testing scheme. Therefore, this can be used to improve system reliability as it can detect system malfunctions. There are three kinds of work modes that were proposed: hot-

13、backup mode, load balance mode and hot standby mode. Each mode has been designed to solve the problems stated previously. The result shows that this scheme can reach the expected requirements, thus achieving reliable and