Research And Application Of LTE Special Network Coverage For High Speed Railway

China's "four vertical and four horizontal" high-speed railway network,the end of 2017 total mileage of nearly 30,000 kilometers of nearly 4 million passengers a day to transport more than 4 million between the various towns and cities.The Fuxing train has reached a speed of 350 km per hour,which has been contributed to a bunch of disadvantages,such as frequent switch,high rate of call drop,call disconnection and so on.In terms of data services,the low data transmission speed may cause the difficulty of downloading video and browsing web page.Above all,the coverage of High-speed railway LTE network is in an emergency.high Doppler frequency shift and frequent switching due to fast speed,high penetration loss and complex and changeable scenes along the way,all of which hinder the high quality coverage of wireless networks.aiming at the difficulties above in wireless network construction,This paper mainly focuses in the key technologies and solutions to the construction difficulties.The main contents and results are as follows:1.The wireless network structure of LTE is studied.The orthogonal frequency division multiplexing(OFDM)and multi-input multi-output(MIMO)technologies are analyzed.The negative influence of Doppler frequency shift is reduced by adopting automatic frequency control technology and setting base station speed mode.Combined with data analysis and engineering experience,the following conclusions could be analyzed: the grazing angle must be greater than 10 degrees,and distance between base station and rail must be controlled within 300 meters,and the antenna height should be between 15 and 25 meters relative to the rail surface.It is suggested that the location of base station should be cross-distributed on both sides of the railway as far as possible,and the base station at the bend should be located on the inside of the bend.When the gauge of the station is less than 100 meters,the high gain antenna with narrow lobe should be adopted.By adopting the engineering suggested values above,the impact of penetration loss is reduced.A cell merging technique for 8~12 RF remote units is proposed,whichshows that the overlap distance of a single switch should not over 200 meters.By adopting the technical means above the frequency of handover is reduced,which ensures the smooth handover and enhancement of the user's perception.2.The principle and method of LTE network planning for high speed railway are studied.The received power of reference signal is not less than-110 dBm,the ratio of reference signal to interference noise is not less than-3 dB,and the coverage rate is 90%.Taking the Beijing section of Beijing-Guangzhou high-speed railway as a case study,due to the 1.8G confusion of public network,the frequent switching and the serious interference of the same frequency,and the high utilization ratio of physical resource block in some cells,it is suggested to use 2.1G hetero-frequency network.Referring to the high-speed rail speed of 300 km per hour,according to the calculation of 30 s per switching,the effect of staying in the same cell within 2500 meters should be ensured.4~6 base stations cells are needed to merge into a supercell to ensure user awareness,which contributes to putting forward a 2.1G SFN networking strategy.Finally,the whole coverage scheme of Beijing-Guangzhou high-speed railway in Beijing section is simulated by Huawei U-NET software.Through the comparison and analysis of the simulation results,it is found that the overall coverage scheme can meet the needs of the construction target,wichvalidates the feasibility of this high-speed rail network coverage.