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Research On Channel Estimation And DCF Algorithm Of Wireless Internet Access For Passenger Train Application

Posted on:2011-12-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:C H PengFull Text:PDF
GTID:1102330335988999Subject:Traffic Information Engineering & Control
Abstract/Summary:PDF Full Text Request
With the rapid development of high-speed railway, the high-speed wireless Internet access service for passengers is not only essential in the demand to enhance railway service quality, but also necessary to expand the market and to promote economic development. This dissertation analyzes the wireless broadband access technologies for passenger trains.Firstly, the characteristics of high-speed railway wireless channels are analyzed and a simplified channel model in high-speed railway for IEEE802.11a is proposed. Meanwhile, the characteristics of several parameters such as Doppler shift and coherence time are discussed.To achieve accurate high-speed mobile channel estimation, A estimation method based on Kalman filter is proposed in the dissertation. The channel estimation results based on training sequences are used by the Kalman filter for recursive calculations. The obtained results are treated as observed filter values. The result of pilot estimates is used to calculate the filter parameters and track channel variations. The proposed algorithm can reflect both the variations of mobile channel in the frequency domain and time domain, Furthermore, it improves the estimation accuracy compared with the training sequences or pilot symbols estimation method. To reduce the estimation errors in time-varying channels, we also propose a midamble channel estimation scheme, which corrects the parameter of Kalman filter in real time by inserting the replicated midamble from preamble into the next data field in IEEE802.11a frame.To study the application characteristics of IEEE802.11a DCF in high-speed railways, the dissertation analyzes the relations between the throughput/media access delay and the initial value of the contention window, the order of maximum backoff, the data packet size and other parameters. A suggestion is given that the basic access mechanisms of IEEE802.11a DCF should be used in High-speed trains wireless access system.To improve the throughput of the mobile networks, A DCF improvement algorithm which increases the priority of the AP by improving the AP and STA's backoff algorithm is proposed. The improved algorithm is analyzed quantitatively by a two-dimensional discrete-time Markov model. Simulation results show that this algorithm alleviates the bottleneck issue and improves the overall throughput of the network. To further improve the network performance, we also propose an adaptive X exponent backoff algorithm. Each node does not use binary only during the backoff process, but use adaptive X exponent according to the number of nodes. The simulation results demonstrate the effectiveness of this method.
Keywords/Search Tags:Wireless broadband access, IEEE802.11a, Kalman filter, midamble, backoff algorithm, X exponent
PDF Full Text Request
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