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Research On Wireless Channel Characteristics And System Optimization In The High-Speed Railway Scenario

Posted on:2016-07-02Degree:DoctorType:Dissertation
Country:ChinaCandidate:J H QiuFull Text:PDF
GTID:1222330470955952Subject:Communication and Information System
Abstract/Summary:PDF Full Text Request
The rapid and extensive growth of the high-speed railway (HSR) in China has spurred a multitude of development in related industries, such as telecommunications, machinery, power and so forth. As China has entered the4G eras, the wideband communication has become an indispensable part of the HSR services. Passengers now expect access to various mobile communication services such as voice, video, as well as high-speed data uploading and downloading. The paper focuses on the wideband wireless access on the HSR, and explores the channel characteristics and the method of system optimization on the HSR.The paper focused on the methods of the channel measurement and analysis. Based on the measurement theory, the channel measurement methods were summarized, and three usual measurement campuses were compared. The feasibilities of the channel measurements based on the WCDMA and PropSound were identified, including the laboratory calibration and the actual measurement experiences, and the basic channel parameters were analyzed. In the method of data extraction, the noise-floor decision was introduced, and three methods of how to search the multipath were proposed, including the partial maximum method, the threshold decision method and the clustering method. For the channel modeling, the tap delay line (TDL) model, cluster delay line (CDL) and the Markov based TDL under non-stationary condition were discussed.The channel propagation characteristics under the high-speed condition were investigated in this paper, based on the channel measurement at2.35GHz with the bandwidth of50MHz on the Zhengxi Line. According the the variation of the multipaths during the process that the train passed through the transmitter, the measurement process was divided into four sub-regions, referred to RA (Remote Area), TA (Toward Area), CA (Close Area) and AA (Arrival Area), respectively. Through the analysis of the actual measurement data, it was concluded that the multipath properties on the HSR were affected by two remarkable factors:the periodically moving scattering from the pylons and the random scattering from the other hybrid time-varying surroundings. In terms of these two types of scatters, a hybrid CDL channel model combing the theoretical and statistical propagation features was established. At the same time, the cluster number, average cluster gain, average MPC number and MPC decay in each cluster for different regions were analyzed. The comparison of the measurement results and the other measurements showed that there some similar properties among them. To evaluate the accuracy of the proposed channel model, the simulated data were compared with the measurement data, and they were consistent both in the statistical model and the theoretical model.As the downlink modulation scheme of the long term evolution (LTE), OFMD is sensitive to the frequency offset. The Doppler shift caused by the high mobility will destroy the orthogonality of subcarriers and result in the inter-carrier interference (ICI). We considered the dynamic resource allocation for the OFDMA system under the two-hop communication architecture on the HSR, in which the mobile base station (MBS) on the top of the moving train transported the signal from the base station (BS) on the ground to the user equipments (UE) in the train. The joint optimization problem was decomposed into three sub-optimal problems, and the iteration optimization for the power allocation between the BS and MBS was employed to solve the non-convex problem due to the complicated expression of the ICI. Moreover, to reduce the overhead and complexity of the signal-subcarrier-based assignment, the chunk-based allocation was proposed when considering the correlation between adjacent subcarriers in the MBS-UE link. Simulation results showed that the iteration algorithm could converge well, and the total capacity was increased evidently in the high-speed environment.At last, the channel characteristics in the high-speed environment were analyzed in this paper. The Doppler caused by the high-speed movement leaded to the fast channel fading. Based on the time-varying properties of the channel, the interference of the OFDM was calculated, and the frequency channel matrix was obtained. The simulation showed that the large Doppler could lead to the serious ICI for the OFDM system. The paper proposed the associated channel estimation in the time domain, and set up the matrix of the time-varying channel impulse response (CIR). Then the matrix of the time-varying channel impulse response was transformed into the channel frequency response matrix. Using a serial interference cancellation algorithm, the subcarrier was demodulated one by one according to the signal to interference ratio (SIR). At the same time, the interferences of this subcarrier to the other subcarriers were then cancelled. Compared with the parallel interference cancellation algorithm, the system performance could be further improved by using the serial interference cancellation algorithm...
Keywords/Search Tags:HSR, Channel measurement and modeling, LTE, Resource allocation, Doppler shift, Interference cancellation
PDF Full Text Request
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