Design and implementation of locomotive video monitoring system

1. Introduction

With the continuous development of my country's railway industry, locomotives are running faster and faster. Ensuring the stability and safety of locomotives has become the top priority of the railway transportation department. Helping drivers and ground management departments to monitor the locomotive operation status in real time has become a top priority. Especially after the locomotive driving was reformed from the operation of the chief and assistant drivers to the operation of a single driver, a driver must monitor the operation of the power room, auxiliary room, electrical room and other equipment rooms while operating the locomotive. In this context, it is very important to develop a locomotive video monitoring system to help the driver monitor the entire locomotive in the cab and assist the ground management department to remotely grasp the locomotive operation status in real time [2]. This article discusses the basic development plan of the locomotive video monitoring system from the aspects of network selection and system structure.

2. Wireless network selection

In order to enable the ground management department to monitor the running status of the locomotive in real time, the system must use a wireless network to transmit data. At present, in China, there are three main wireless networks that can be used for large-scale video signal transmission, namely China GPRS, China Unicom 's CDMA2000 1X, and China Netcom and China Telecom 's WLAN. These three wireless networks have their own advantages.

The following compares the advantages and disadvantages of these three wireless networks in terms of speed, stability, coverage, and tariffs, so as to select a wireless network suitable for the locomotive video surveillance system.

(1) Speed

The theoretical transmission rate of GPRS network can reach 171.2kbps, the transmission rate claimed by the operator can reach 115kbps, and the actual transmission rate is about 40kbps; the theoretical transmission rate of CDMA2000 1X network can reach 153.6kbps, and the actual transmission rate is about 70kbps; the theoretical transmission rate of WLAN network can reach 11Mbps, and the actual transmission rate can reach 8Mbps, but it is affected by the number of access users. The more access users there are, the smaller the bandwidth allocated to each user, and the slower the transmission rate.

In terms of network speed, CDMA2000 1X network is much faster than GPRS network. WLAN network is faster, but it is affected by the number of access users [3].

(2) Stability and coverage

GPRS network can be used wherever there is a network signal. Currently, GPRS network coverage is very complete and the signal is very stable. CDMA2000 1X network is the same as GPRS network. It can be used wherever there is a network signal. Although the network coverage and signal stability of CDMA2000 1X are not as good as GPRS network, they are still acceptable. The coverage of WLAN network is still very limited. It can only be used near wireless APs, and there are certain limitations in its use.

In terms of network stability, the coverage and stability of GPRS and CDMA networks are quite good, while the coverage of WLAN network is insufficient and its use is restricted.

(3) Rates

Currently, the operators of these three networks have launched many packages, including annual, monthly and data package. After a comprehensive comparison of the various tariffs of these three networks, the tariff of CDMA2000 1X network is the most advantageous.

By comparing the above three aspects, the advantages and disadvantages of the three networks are clarified. Combined with the needs of the locomotive video monitoring system for wireless networks, it was finally decided to use China Unicom's CDMA2000 1X network.

China is preparing to vigorously develop TD- SCDMA 3G network , and CDMA2000 1X belongs to the transition stage to 3G network. Selecting CDMA2000 1X network to develop locomotive video monitoring system will make it easier for developers to upgrade the product system after the implementation of 3G network standards in China, so that the locomotive video monitoring system can enjoy better network services.

3. System structure

The whole system consists of three parts: vehicle-mounted terminal, video server terminal and remote monitoring terminal. These three parts rely on CDMA2000 1X network and Internet connection. The system structure diagram is shown in Figure 1.

Figure 1 System structure diagram

3.1 In-vehicle terminal

The vehicle-mounted terminal is an important part of the locomotive video monitoring system, which will directly contact the locomotive driver. In order to facilitate development and shorten the development cycle, it is planned to use hard disk recorders and wireless video transmission modules as the core to form the vehicle-mounted terminal system.

The DVR uses Shenzhen Sunny Optical's ADR series embedded digital DVR, which uses industrial-grade dedicated digital signal processor and embedded operating system (Vxworks), which is reliable and stable. It supports 16 video inputs, and the driver can select 1 or more channels to watch through the RS485 interface in the cab . At the same time, it also supports multiple alarm inputs, and temperature and smoke sensors can be installed at key parts of the locomotive and connected to the corresponding interface of the DVR. When the temperature and smoke of the locomotive are abnormal, the DVR can sound an alarm to remind the driver to pay attention.

The wireless video transmission module uses the Beijing Baimu Company's Jimu 728M-CDMA wireless video transmitter, which can be easily developed through the SDK provided by the manufacturer. The functional structure of the module is shown in Figure 2.

Figure 2 Structure diagram of JIMU 728M

JIMU 728M uses the H.264-based active video compression algorithm , which has the characteristics of high compression efficiency and low system power consumption. Due to the special processing on chroma compression, it can achieve high compression efficiency while also ensuring good clarity and color reproduction quality, with a maximum resolution of 704x576. The module has built-in CDMA communication control protocol and TCP/IP protocol, supports dynamic or fixed IP address mode, domain name resolution, multiple trigger start modes, and has 2 bidirectional auxiliary serial ports, which can be connected to serial user equipment and support bidirectional measurement and control data multiplexing. The transmission rate is: color 320x240/CDMA2000 1X - average 5 frames/second, maximum 15 frames/second; color 640x480/CDMA2000 1X - average 0.5 frames/second, maximum 2 frames/second.

The NTSC or PAL video signal output by the camera is connected to this module and sent to the DSP chip after being decoded by the decoder.

DSP adopts the video compression algorithm based on H.264, and uses the latest video compression technologies such as multi-mode multi-size motion estimation and 4x4 integer lossless transformation, with the advantages of high coding efficiency and good image quality. DSP sends the compressed video data to the CDMA module and sends the video data to the video server through the wireless network, thus realizing the wireless transmission of video signals.

In addition, the operation recording unit on the locomotive is an important device to ensure the safe operation of the locomotive. It records various data during the operation of the locomotive. On the vehicle side, a small single-chip system can be used to read these operation data from the locomotive TAX box in real time and send them to the RS232 interface of the Jimu 728M module. These data are wirelessly transmitted to the server, so that ground monitoring personnel can also understand the locomotive operation data in real time.

3.2 Video Server

The video server is a key part of the entire locomotive video monitoring system. It is the hub of communication between the vehicle-mounted terminal and the ground remote monitoring terminal. The vehicle-mounted terminal sends data to the server through the wireless network, and the remote monitoring terminal browses these important data in real time through the video server. Because a large amount of video data needs to be processed, the video server requires a hardware platform with good performance and stable operation. In addition, it is necessary to apply for an independent fixed IP address so that each ground remote monitoring terminal can access the video server. The video server software is developed on the SDK provided by Baimu Company and matched with Jimu 728M, which is simple and convenient. The server software workflow is as follows:

(1) The server starts and sends a short message containing local address information to the vehicle-mounted terminal. At this time, the vehicle-mounted terminal is offline; (2) After receiving the short message, the vehicle-mounted terminal automatically goes online and then connects to the server. At this time, the vehicle-mounted terminal is in a dormant state; (3) The server sends an activation command to the vehicle-mounted terminal. When the vehicle-mounted terminal is activated, the server can control the transmitter to transmit video images and perform other remote operations. At this time, the vehicle-mounted terminal is in an activated state; (4) After the server operation is completed, the connection with the transmitter is disconnected, and then the server is shut down. At this time, the site is offline.

3.3 Remote Monitoring Terminal

The remote monitoring terminal is a platform for ground management personnel to monitor the operation status of locomotives and the driving conditions of drivers in real time. It only needs to install a set of client software on an ordinary PC with Internet access. The video server first assigns user names and passwords to each ground monitoring terminal. The remote monitoring terminal uses the user name and password to log in to the video server through the client software. Users of different levels can obtain different permissions to browse or control each vehicle terminal. The workflow of the remote monitoring client software is as follows:

(1) Set network parameters, including server address/port, local address/port, user name/password; (2) Connect to the video server, determine whether the connection is successful or failed, and generate corresponding events; (3) After connecting to the video server, a list of vehicle terminals will appear. Select the name of the vehicle terminal to be browsed and start video browsing; (4) After starting video browsing, you can set video parameters and select different screen browsing of the vehicle terminal; (5) After finishing video browsing, you can exit from the video server and disconnect.

4. Conclusion

It is very necessary to develop a locomotive video monitoring system, which can help drivers drive locomotives better, reduce drivers' work pressure, reduce drivers' work intensity, and improve the safety of locomotive driving. In addition, the system can also help ground management departments implement remote real-time monitoring for easy management.

This development solution is based on DVR and video transmission modules, with a short development cycle and a simple and feasible process.