Research Of Doppler Effect, Handoff, Dropped Call And Vehicle Analysis System In GSM-R

Recently,high-speed railway develops rapidly in our country and its operating length will reach eighteen thousand kilometer by2015. In such large scale of high speed railway line, network communication technique becomes an important part to ensure the safety and stability of high speed railway system. GSM-R network which is based on mature GSM network is applied to transmit wireless data in high speed railway nowadays, with dispatching communication function, train dispatching and et al. added to meet the specific dispatching communicating requirement and it is an important communication platform to modern high-speed train operation control. So, real-time monitoring of the status of wireless network in high-speed railway is one of the key techniques in the supervision of high-speed train operation in every country and it is paid great attention in the industry. It is needed to design a system that can detect the real-time wireless network status with rapid development of high-speed railway in China.According to requirement of the Project of national science and technology plan, the paper de-signs a system that can do data collection of GSM-R network, layer two and layer three signalling parsing, operation data statistics, operation parameter association analysis, fault analysis and basic early warning in the basis of deep analysis of communication mechanism including Doppler effect, frequent handoff, bit error, dropped-call probability and et at., combining with engineering appli-cation. After the measurement in some high-speed railway lines, the system has met the design requirement exactly. Aiming at the great importance of continuous communication in high-speed railway wireless network, the paper studies fast effective handoff algorithm and related parameter optimization and discusses some related problems that the wireless network will evolve into LTE-R in the future. The main contributions of the dissertation are summarized as follows:1、Aiming at the demand of the security operations in high-speed railway and the require-ment of the Project of national science and technology plan, the paper designs a system that can do data collection, data analysis and basic early warning to GSM-R network. By means of deeply parsing the layer two and layer three signalling which is composed of binary code generated by wireless module and creating database, the paper implements a wireless network parameter query system which meets train operation control service. The system not only has the function of real-time data collection and data storing, but al-so the intelligent analysis function of parameter association and provides aided decision basement for fault analysis and basic early warning of wireless network. The system provides application background for the follow-up communication mechanism studies including Doppler effect, handoff algorithm, dropped-call probability et at. in this paper.2、The bit error rate produced by Doppler effect in the data transmitting process is studied in the high speed wireless network. By means of analysing the Doppler frequency shift from single base station and multiple base stations in the straight to curve, we deduced the formula of Doppler frequency shift and obtained the evolution of frequency shift when the train is running. That can be applied in the correction of Doppler Frequency shift in wireless communication. In addition, taking no count of other factors such as weather and geography, we build a simulating model of data-transmitting error rate of GSM-R wireless network to simulate the variation of bit error rate of data-transmitting. By using the simulink tool-box belonging to matlab, we discover that the Doppler frequency is decreasing gradually and the bit error rate is decreasing shakingly when the train is becoming closer and closer to the base station. The trend is supported by practical data of some high-speed railway.By comparing the different distance between the base station and the rail, we know that the longer the distance, the bigger the low bit error rate area is. That will be benefit for the site selection of base station. Previous studies on bit error rate are not combined with practical data, so the research can fills in the gaps and is helpful to build voice analysis subsystem in vehicle analysis system.3、The handoff algorithm in high speed wireless network is studied and a proposed handoff algorithm based on Doppler effect and RSSI measurement is evaluated. The algorithm performs handoff when the Doppler frequency shift value is negative and the measured signal strength of the adjacent base station exceeds that of the serving base station by a hysteresis level. The hysteresis level varies with different Doppler shift values. The average number of handoffs, average delay of handoffs, and average dropped calls are adopted as criteria for performance. Numerical results are presented to demonstrate the feasibility of the Doppler-effect-based algorithm. The proposed algorithm is compared with two other handoff algorithms. One is based on absolute and relative signal strength measurements; the other on hysteresis variable. It is found that the proposed handoff al-gorithm performs better than the other two handoff algorithms and can avoid ping-pong effect and decrease the handoff delay and dropped calls in log-normal fading environ-ments. Previous studies on handoff algorithm can not avoid ping-pong effect, but ping-pong effect is very important phenomenon in high-speed environment, so the research is helpful to build handoff analysis subsystem in vehicle analysis system.4, Without considering the impact of Doppler effect on dropped-call probability, the paper analyzes the dropped-call probability caused by handoff in high speed network environ-ment. Starting from the study of handoff in high speed network, the paper deduces the handoff probability in different positions and then gains the dropped-call probability in different positions to propose a model of dropped-call probability analysis. On the basis of theoretical analysis, the paper simulates the dropped-call probability in GSM-R and LTE-R and finds that the average dropped-call probability in LTE-R is about29.23%lower than GSM-R. The paper simulates the dropped-call probability with different train through loss and finds that the larger the train through loss, the higher the dropped-call probability, the average dropped-call probability can rise to0.8%when train through loss is24dB. The paper simulates the dropped-call probability with different train speed and finds that the faster the train speed is, the higher the dropped-call probability is, the average dropped-call probability with the speed of540km/h is151.56%higher than the speed of60km/h. The paper simulates the dropped-call probability with fault base station and finds that the average dropped-call probability with normal base station is just36.3%of the condition with a fault base station. Previous studies on dropped-call probability are lack of analysis model, so the research is of great importance in vehicle analysis, network optimization and follow-up study of LTE-R.