1 Introduction GSM-R is a comprehensive special digital mobile communication system designed for railway communication. It is an element that adds dispatch communication function and is suitable for high-speed environment on the basis of GSM cellular system. It can meet the railway special dispatch communication requirements proposed by the International Railway Union. In the design of the GSM-R network, the application of the GSM-R theory improves the reliability of the railway communication system, solves the problems of high channel congestion rate and low call success rate, and reduces network construction costs. 2 GSM-R network GSM-R network mainly includes wireless network, switching network and wired transmission network, among which wireless network includes checking base station parameters, planning frequency, dividing location area, determining traffic load, blocking rate, base station antenna angle, transmission power and other parameters, and reducing the same Frequency interference and non-co-frequency interference, etc .; and the switching network includes determining the base station frequency, cell parameters (CDD) and handover parameters. The GSM-R core network adopts a secondary network structure, that is, the establishment of a regional convergence center (TMSC) for mobile services and a local service end office (MSC), and the mesh connection between the convergence centers. The general setting of the cell is to install a directional antenna along the rail to form an oval cell along the rail; in the marshalling station with large traffic but low train speed, fan-shaped cell coverage can be used; and the low-speed road section with low population density and the track are interwoven At the same time, omnidirectional cell coverage is used. Each cell has one or several base transceiver stations, the number of which is determined by the amount of traffic. When the train speed exceeds 140 km / h, the use of GSM signals can reduce the communication quality and increase the bit error rate. The increase in bit error rate will reduce the voice quality, even when the quality of service reaches the minimum threshold, especially the data related to ERTMS (European Railway Transport Management System) and ETCS (European Railway Control System) will be interrupted, resulting in train failure Necessary parking or deceleration, so a dual-network coverage system is needed to improve the reliability of the system. 2.1 Wireless network part (1) Field strength coverage of wireless networks Field strength coverage is often related to the specific geographical location distribution, and is adjusted according to the specific geographical environment and the actual situation of the base station. Improve the downlink signal coverage by increasing the base station's transmit power, increasing the antenna height, adjusting the antenna's horizontal or vertical angle, and installing repeaters. Generally speaking, along the railway or highway, mainly consider the strip coverage distribution along the line, you can use a dual-sector base station, each zone 180 °; the antenna uses a single polarization 3 dB lobe width of 90 ° high gain directional antenna , The two antennas are placed opposite each other, and the maximum radiation direction is consistent with the direction of the expressway. If the traffic volume in the direction of the road is very low, considering the equipment cost, a bidirectional antenna with an omnidirectional antenna deformation is adopted. The bidirectional 3 dB lobe width is 70 ° and the maximum gain is 14 dB. (2) Wireless parameter setting In the GSM-R network, the parameters related to wireless devices and interfaces can most affect the service performance of the network, including cell selection, control channel, wireless measurement, power control, handover control and other parameters. These parameters It has an important impact on cell coverage, signaling traffic distribution, and network service performance. The basic principle of adjusting wireless parameters is to comprehensively consider the actual wireless channel characteristics, traffic characteristics and signaling traffic carrying conditions, make full use of existing wireless resources, and use the traffic sharing method to evenly distribute the traffic and signaling traffic of the entire network. (3) The purpose of traffic setting is to balance the traffic of the mobile communication network as much as possible in advance. Make the entire network service load even. Especially in some densely populated commercial areas, attention should be paid to switch congestion when optimizing traffic. (4) Division of overlapping area The Qinghai-Tibet line section is designed with the size of the overlapping area according to the actual geographical environment to avoid weak field areas. The overlapping area can obtain the C / I value of the mobile station according to the frequency reuse scheme. The width a of the overlapping area is: two-cell multiplexing:
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