# Fast Optimization of the Installation Position of 5G-R Antenna on the Train Roof
## 1 Introduction  
The electromagnetic interference (EMI) protection of the on-board sensitive equipment of high-speed trains is the main basis for electromagnetic compatibility (EMC) design, and also the primary requirement to ensure the safe operation of trains [1]. The wireless communication systems such as Global System for Mobile Communications for Railway (GSM-R) and Long-Term Evolution for Railway (LTE-R) bear the responsibility of information transmission for train control, ensuring the safe operation of high-speed trains. The electromagnetic environment of the high-speed rail system is complex, and the roof antenna faces many sources of EMI, and the EMI caused by the inevitability and sudden pantograph arcing is one of the most common ones. Because of the wireless communication roof antenna and pantograph arcing located above the roof, and in order to ensure the communication quality, it is difficult to use shielding technology to improve the anti-interference performance of the roof antenna [2]. Based on previous research, the main power spectrum range of pantograph arcing is from a few hundred Hz to a few GHz [3]. It interferes with antenna reception and may cause communication anomalies. Ref. [4] learned, through experiments in a reverberation chamber, that the power range of the radiation electric field strength of the pantograph arcing coupled to the GSM-R antenna port is \(-58.6\) dBm\(-\)\(-\)\(50.17\) dBm, which is greater than the minimum received signal intensity of the on-board receiver (\(-95\) dBm), which will cause EMI to the GSM-R receiverand endanger driving safety. According to the measured results, it is found that, with the increase in vehicle speed, the radiation field intensity of pantograph arcing at the same frequency will be significantly increased [5]. Therefore, with the increasing speed of high-speed trains in the future, the anti-interference research of the 5G-R antenna urgently needs to be carried out. Much research has studied the impact of pantograph arcing on wireless communication transmission systems, especially the transmission quality of the GSM-R signal. For example, reference [6], based on the self-developed experimental device, carried out an experiment on the radiated electric field intensity of a single pantograph arcing in the anechoic chamber, and determined that the pantograph arcing would cause EMI to the GSM-R communication system. Based on the statistical analysis results of a large number of measured data, reference [7] studied the radiation electric field intensity of pantograph arcing, and finally obtained the amplitude probability distribution (APD) of EMI signals. Finally, the useful signal field strength required to ensure the bit error rate (BER) required by the communication system is analyzed. Refs. [8; 9] simulated the downstream physical layer link of the LTE-R communication system by MATLAB, and concluded that the EMI caused by pantograph arcing would increase the block error ratio (BLER) of the LTE-R system (the operating frequency is 400 MHz). As a result, the number of instances of retransmission increases and the effective throughput of the system decreases by up to 21%, which seriously affects the communication quality of the system. However, with the rapid development of railway intelligence and information technology, the needs of communication services between trains and the ground are constantly increasing. As a second-generation mobile communication technology, GSM-R fails to meet the large data communication requirements of video surveillance, video conferencing, passenger service, and other high-bandwidth applications on high-speed railways [10]. However, 5G has the technical characteristics of a large bandwidth, large connection, high reliability, and low delay, which not only supports the multi-priority service quality level guarantee, but also has the high-speed adaptability of 500 km/h, which is in line with the application scenario of high-speed rail [11]. It will be a trend for 5G to replace GSM in railway applications.