Research on using PIDS vehicle-to-ground wireless channel for vehicle information uploading

1. Introduction

At present, each control center of Guangzhou Metro can realize basic functions such as video monitoring inside vehicles and issuing information to trains. According to the original design, the upload of various vehicle information of running trains must be aggregated to the dedicated wireless trunking master station equipment of the control center through a dedicated wireless data vehicle-mounted station, and then transferred to the main control system through the data transmission console and the agreed interface for use by vehicle-related maintenance personnel.

However, due to the large amount of vehicle information data and the transmission channel bandwidth limitation of the dedicated wireless data vehicle-mounted station, some important information of the running vehicles cannot be uploaded in real time, such as vehicle status information, passenger-related facility operation information, train fault information, etc. On the one hand, this information helps dispatchers understand the vehicle status, organize train operation, organize passenger flow at stations, etc., and on the other hand, it can also provide certain help and guidance for vehicle maintenance.

This paper will do the following research, which is to upload the vehicle information to the control center through the wireless channel between the passenger information display system (PIDS, hereinafter referred to as PIDS) and the vehicle.

2. Current methods for uploading vehicle information

1. Vehicle information

Vehicle information mainly refers to data that can reflect various states, performance, faults, etc. during the operation of the train. Since the train is mobile, the data can be uploaded to the control center through a designated wireless channel for use by relevant monitoring and maintenance personnel.

Vehicle information is mainly divided into three types: Class I, Class II, and Class III. Class I and Class II are mainly train status information with a small amount of data.

As an extension and supplement to the first and second types of information, the third type of vehicle information contains a large amount of information, mainly including fault records, monitoring data and environmental data, which can provide support and help for the maintenance personnel of the vehicle depot to timely identify fault characteristics and discover potential faults, so that the maintenance personnel can plan maintenance activities, decide the parking location of the return train and decide the personnel involved in handling the fault. If only the first and second types of fault information with less data are used for rough judgment, the accuracy and timeliness of fault analysis will be affected.

The realization of uploading the three types of information can improve the accuracy of fault judgment on the main line and the efficiency of maintenance management, and needs to be transmitted back to the control center in real time for fault data analysis. Therefore, it belongs to the important type of vehicle information.

2. Current vehicle information upload method

According to the original design, Guangzhou Metro currently uses a dedicated wireless trunking communication transmission channel to transparently transmit various vehicle information of running trains. The principle diagram is shown in Figure 1.

As can be seen from Figure 1, the vehicle information is sent to the data vehicle radio through the RS422 serial port by the vehicle system. The data vehicle radio then uploads the data to the control center master station equipment through a dedicated wireless cluster base station through wireless communication. Finally, it is transferred to the main control system through the data transmission console and the agreed interface and displayed for use by relevant monitoring and maintenance personnel.

At the same time, it can be seen that all the equipment between the train and the main control system is only a transparent transmission channel, and no modification is made to the content of the vehicle information. The bandwidth of the transmission channel directly affects the efficiency of the vehicle uploading information to the control center.

3. Problems at the current stage

1. Large amount of vehicle information data

Under normal operation, the vehicle generally generates Class I and Class II information, and the data volume of this type of information is relatively small. Once a train fails (door, coupler, bogie, traction, power supply, air supply, brake, auxiliary inverter, air conditioning, etc.), a large amount of Class III fault alarm information will be generated, and the data volume of this type of information is basically measured in MB.

2. The transmission channel bandwidth is too narrow

The data buffer of the onboard radio is only 1KB, and the maximum transmission rate of the RS422 serial port is 19.2kbps.

During the actual implementation process, it was found that the first and second category alarm information can be uploaded in real time through a dedicated wireless transmission channel because the data volume is not large.

For the three types of information calculated at MB level, due to the large amount of information, the data vehicle radio can only provide 1K bytes of transmission bandwidth, and there is a big bottleneck in information transmission and data restoration.

3. Occupy dedicated wireless trunking communication channel resources

The base station equipment of Guangzhou Metro's dedicated wireless trunking system is generally equipped with 2 transceiver channel machines, each of which is equipped with 4 channels, for a total of 8 channels. The first channel is the control channel, and the remaining 7 channels can be assigned as voice channels or data channels as needed. An important application of the dedicated wireless trunking communication system is to provide a set of reliable and real-time voice dispatching and command auxiliary equipment for the safe dispatching of trains within the subway network. Therefore, in order to ensure normal train operation and dispatching and commanding, the demand for voice channels must be fully guaranteed.

When transparently uploading vehicle information through the channel of the dedicated wireless trunking system, the wireless base station must allocate a channel resource for data communication, which will reduce the channels available for voice communication. This may result in insufficient wireless channels being allocated to wireless users who need to use voice calls (especially voice calls between drivers and dispatchers), resulting in the inability to use voice calls.

4. The control center cannot obtain vehicle fault information in real time

In the case of a train failure, since a large amount of fault information is not transmitted to the control center in a timely and effective manner, the vehicle maintenance technicians are unable to obtain the on-site fault situation in time to help guide the on-site fault handlers to carry out corresponding emergency treatment. This may affect passenger transportation due to untimely handling of train faults, and have a significant negative impact on operations and the company's image. 4. Use PIDS train-to-ground wireless channel for vehicle information

Upload 1. Train-to-ground wireless communication channel

In the urban rail transit industry, the train-to-ground wireless communication channels can be roughly divided into the following types: dedicated cluster dispatching system train-to-ground wireless channels, civil communication train-to-ground wireless channels, PIDS train-to-ground wireless channels and signal system train-to-ground wireless channels.

Civilian communication vehicle-ground wireless channels are under the jurisdiction of operators and require additional high fees when used. Signal system vehicle-ground wireless channels are dedicated to signal system equipment and are not suitable for other uses. Most PIDS vehicle-ground wireless channels are established and maintained by subways.

2.PIDS vehicle-to-ground wireless channel

The PIDS vehicle-to-ground wireless channel uses WIFI to access the AP device. According to the relevant technical indicators, the effective average bandwidth should not be less than 10Mbps. The principle is shown in Figure 2.

As can be seen from Figure 2, the PIDS train-to-ground wireless channel also provides a transparent transmission channel that can connect the train and the control center. Simply by adding interfaces between the PIDS and the vehicle and the main control system, the PIDS train-to-ground wireless channel can be used instead.

5. Add interfaces between PIDS, vehicle and main control system (see Table 1)

6. Comparison of the two methods

The vehicle information is uploaded to the control center via the dedicated wireless vehicle-to-ground channel and the PIDS wireless vehicle-to-ground channel. The comparison can be mainly carried out from the items shown in Table 2.

From the comparison in Table 2, it can be clearly seen that uploading vehicle information via the PIDS vehicle-to-ground wireless channel is more practical and can solve the current problems of excessive vehicle information data volume and narrow transmission channel bandwidth.

VII. Conclusion

The dedicated wireless trunking communication system is an important system for subway train dispatching and command, mainly providing guarantee for the voice communication of train dispatchers and drivers. Vehicle information is a concentrated reflection of various real-time status and fault conditions of the train, and provides important auxiliary judgment information for relevant monitoring and maintenance technicians in the control center to participate in train fault handling. However, since the dedicated wireless train-to-ground channel cannot meet the demand, after research and comparison, it is found that the use of PIDS train-to-ground wireless channel can not only replace the dedicated wireless train-to-ground channel to realize the function of uploading vehicle information to the control center, but also is better than the dedicated wireless train-to-ground channel.