Railway emergency system plays an important role in emergency rescue work. When an emergency happens, the railway emergency system should have basic wireless communication capabilities. At present, the access equipment adopts Wi-Fi and wireless PBX technology, which can meet the most basic requirements of emergency system. This paper analyzes the characteristics of Wi-Fi and wireless PBX technology, compares their advantages and disadvantages, and summarizes their applications in emergency systems.
Railway emergency system; Wireless communication technology; App application
introduce
With the increasing scale of railway construction in China, the speed and density of trains have been greatly improved, and the requirements for transportation safety and emergency communication support capacity have become more and more strict. Once a traffic accident or serious natural disaster occurs, the railway emergency communication system must respond immediately and send the on-site information to the emergency command center, so that the higher authorities can truly understand the actual situation on the spot, take countermeasures, and convey the instructions to the on-site emergency rescue personnel in time.
1 Overview of Railway Emergency System
1. 1 Communication equipment of railway emergency center
The communication equipment of the emergency center is the core part of the railway emergency system. Its main function is to effectively connect the accident site with the emergency center and realize the real-time interaction of voice, video and data information, so that the emergency command center can adopt corresponding solutions. The main equipment communicates with the automatic telephone network and the dispatching communication network through the external interface, which completes the access of the integrated video system on the one hand and the image information of the still image system on the other hand, and provides real and reliable information data for the image display system.
1.2 railway emergency communication access equipment
In the railway emergency system, emergency communication access equipment is an indispensable part. Through various communication technologies, the voice, data and video information of the accident scene are connected to emergency rescue command centers at all levels through transmission networks. Usually, emergency communication access equipment mainly includes: field terminal equipment, emergency access equipment of GSM-R base station and access points of stations or sections adjacent to the accident site. Among them, emergency site terminal equipment is divided into three types, namely mobile audio-visual acquisition equipment, data terminal equipment and voice terminal.
2 principles of railway emergency system construction
(1) advanced. In the construction of emergency system, the network realizes transmission function through wireless, optical fiber and data network.
(2) convenience. The on-site deployment of emergency system should be convenient and simple, and the access mode should be flexible, so as to ensure the opening of business in a short time.
(3) Economic practicability. Make full use of existing data network and optical fiber resources.
(4) integration. Connect optical fiber and data network through interfaces such as optical fiber, AV, Z, etc. to realize the access of devices such as images and telephones, and the system devices should be compatible.
(5) Scalability. Through wireless communication technology, voice, image and other services are extended to the interval, and interconnected with existing automatic telephone, dispatching telephone network and dynamic and static diagrams. Between China's railway emergency system station and emergency center, the existing optical fiber and data network can be optimized and integrated to improve transmission stability, solve the problem of narrow transmission bandwidth and reduce construction investment. Emergency calls, static and dynamic maps and other services are carried by wireless platforms, which can access railway inter-section communication services in various forms.
3 access scheme
At the scene of disaster relief, wireless voice access should be solved first. Under normal circumstances, the emergency site shall be equipped with at least 4 dedicated mobile phones, the site base station equipment can be easily moved, and the wireless network shall be set up quickly. Although the universal 3G/4G system and GSM-R mobile phone can realize voice access, the mobile communication network in the accident area may not be able to cover it. In railway accidents caused by earthquakes, floods and other natural disasters, the general network often cannot play its role, so it is necessary to introduce special wireless networks and special mobile phones. Private wireless network, if you choose GSM or CDMA, involves many devices and complicated networking. Although some manufacturers have integrated important equipment such as mobile switching center and base station controller, their weight and volume are difficult to meet the needs of fast and convenient emergency communication, and the cost is extremely high. In order to meet the demand of wireless voice communication in railway emergency scene, the best technical scheme at present is: ①Wi-Fi mobile phone; ② Wireless PBX mobile phone scheme. These two technologies have good advantages, which are not only suitable for the work of railway emergency site in terms of volume and weight, but also convenient to carry, less in cost and not difficult to realize.
3. 1Wi-Fi technology
Wi-Fi phones connected to WLAN can realize wireless voice communication through direct access and relay. In the emergency system, the registration server of Wi-Fi mobile phone is generally provided by the accident site or emergency command center, which is connected with AP access point, and Wi-Fi mobile phone uses AP to register with the server, so as to realize calls between mobile phones and between mobile phones and fixed telephones. At present, the 2.4GHz frequency band used by global Wi-Fi is a free frequency band, and users can make or receive calls at will within the coverage area of Wi-Fi, regardless of time and place. Broadband data applications based on WLAN can be used with Wi-Fi. Wi-Fi transmission speed is fast, and the effective distance is more than 300m·m m. If AP equipment is added in a suitable place, it can meet the voice call function of railway emergency system. The frequency used by Wi-Fi belongs to the free frequency band, and the AP module can realize the compatibility of voice and data communication. Wi-Fi mobile phone is a universal product with less investment. However, the power of AP and Wi-Fi phones is not high, generally within 400MW. If we want to meet the 500m distance stipulated by the railway emergency system, we need to add relay equipment at appropriate positions. In addition, the wavelength of the frequency band used by Wi-Fi is 12.5cm, and the diffraction ability is not high, so it is difficult to guarantee the call quality in the complicated environment such as tunnels and mountains.
3.2PBX technology
The component of wireless PBX equipment is the host, and each host can be equipped with 1~90 mobile phones. Using frequency hopping technology, it hops 100 times per second in 100 channels in a pseudo-random way. In addition, the addressing of wireless PBX technology adopts code division multiple access, and each mobile phone and host has a separate code, with a large coding capacity of more than 60 thousand, which has good security and confidentiality. The whole wireless PBX system covers a large area, which can exceed 1000m in open areas. Cell phones can be grouped, and you can talk without the host. At the same time, it has single call, group call and group call functions. Using the effective connection with the main communication equipment of the railway emergency command center, the secondary dispatching communication function and teleconference function between the center and the accident site are realized through the emergency command console. Technical advantages of wireless PBX: ①NLOS communication coverage reaches more than 1000m; ② The frequency band used in wireless PBX mode is 900MHz, with long wavelength and strong diffraction ability; ③ Full duplex bidirectional communication and half duplex multi-channel communication can be realized; ④ group calling function can be realized; ⑤ The mobile phone has good dustproof and rainproof functions. Disadvantages of wireless PBX technology: ① wireless PBX technology does not belong to free frequency band, and it needs to be filed with relevant state departments when it is used; (2) Hosts and mobile phones are not commonly used devices, and the purchase route has certain particularity, so the input cost is high.
4 conclusion
In the railway emergency communication system, both Wi-Fi and wireless PBX technologies can meet the needs of the railway emergency communication system. However, in the specific use of Wi-Fi mode, it is necessary to add relay equipment. According to the investigation on the use of railway emergency site, from the aspects of professionalism, convenience, wireless coverage and diffraction ability, the special mobile phone of wireless PBX has obvious advantages and has been well popularized and applied in railway emergency system. For Wi-Fi, its main advantage is that it can give full play to the role of IP technology, closely combine various data and video services based on IP technology, and realize wireless communication function without occupying the voice channel of emergency rescue site access equipment. On the whole, the implementation of Wi-Fi is centralized and compact, and the investment cost is not high. Wi-Fi technology has certain application value when the environmental factors at the accident site are not too complicated and there is no requirement for diffraction ability and distance. In the future, the application of Wi-Fi technology will be more convenient because of the reserved IP interface after China Railway realizes the main scheme of optical communication. On the other hand, due to the limited number of analog users reserved in the optical communication train, it is impossible to directly connect with wireless PBX equipment, and VoIP analog gateway is needed for transfer, so the application of wireless PBX in railway communication system in the future will be limited.
refer to
Li Weihua. Application of Wi-Fi and wireless PBX technology in railway emergency communication [J]. Railway Technical Supervision, 20 14 (12).
Zhang Jianhua, Liu Jiawei. Development and Application of Wi-Fi Technology in Wireless Communication [J]. Television Technology, 20 13 (06).
[3] Gao. Discussion on Wireless PBX Scheme and Mobile Collaborative Development [C]. Annual Meeting of China Communication Information and Communication Network Technology Society in 2009.
Li Bin. Research and Implementation of Wireless Image Transmission System for Railway Emergency Communication [J]. Railway Communication Signal, 20 14 (08).
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