Research On The Radio Wave Coverage And The Handover Performance Of LTE-M

In recent years, Communication-Based Train Control (CBTC) system is developing fast in our country. As the basis of CBTC system, Train-ground communication is being used for data transmission between the train and the ground, which is also updating quickly. Up to now, Wireless Local Area Network (WLAN) based CBTC system is widely used in urban rail transit. With continuous expansion of urban rail transit services, WLAN is being unable to meet the needs of urban rail transit. With the rapid development of wireless communication technology, LTE-M, which is based on the LTE technology, is becoming the candidate technology to bear the urban rail transit services instead of WLAN.LTE-M based CBTC system will be used in Beijing subway line Yanfang. To improve the anti-interference ability of the signal and reduce the transmission loss, the leaky coaxial cable is used as signal transmission medium between the train and ground. The transmission channel of the leaky coaxial cable is different from that in free space, and it’s the first time for LTE technology being used in urban rail transit. The lack of experience of the channel models makes it difficult to do network planning, which makes the determination of the transmission channel model becomes more important. The building of the channel models helps to provide guidance on network planning and improve the communication performance.The research in the thesis includes:(1) Introduce the characteristics of the LTE signal, study the requirements of field strength test in high speed railway environment, and develop a set of field strength test system for LTE-M.(2) With the test data from the leaky coaxial cable, by using the Lee’s law[22]and the polynomial fitting we build a mathematical model for the path loss of the leaky coaxial cable. Then, we use the AIC (AICc) judgement to choose a suitable small-scale fading distribution model for the test data. Finally, a complete transmission channel model of leakage coaxial cable is established.(3) Based on the transmission channel model, a handover decision method based on channel model predicting is put forward. Compared with traditional methods, the decision helps more to reduce the impact of multipath fading and improve the handover performances.The results show that the transmission loss of the leaky coaxial cable increases linearly when the transmission distance grows, and the coefficient of the transmission loss is about 0.0426 dBm/m. The small scale fading distribution model for the leaky coaxial cable is the lognormal distribution. Lastly, the handover method proposed in this paper was proved to be useful in improving handover performances.