mmWave Empowers High-Speed Rail with Intelligent Data Dumps

In China, high-speed rail has become the preferred mode of long-distance travel, with about 50 million people using the continuously expanding high-speed rail network every year. During train operations, a large amount of data is generated, including information on train scheduling, composition, and the status of locomotives and carriages. This data needs to be synchronized in real-time with the operation control center and railway locomotive maintenance facilities. The amount of data that each train needs to dump can reach several hundred gigabytes, or even up to terabytes. In the past, manual hard disk copy was the only option, which was inefficient and prone to data loss or leakage, posing security risks.

With the widespread use of high-definition cameras, the amount of inspection data is increasing, making the bottleneck in train-to-ground data dumping increasingly prominent. Millimeter wave (mmWave) technology, characterized by large bandwidth, low latency, and strong anti-interference, can reach speeds of up to 10 Gbps with a single CPE. By using 5G mmWave transmission equipment, high-speed wireless data transfer between the train and the ground can be achieved. This not only enables the automatic and efficient transfer of train data but also ensures the integrity and security of onboard data.

Based on a deep understanding of railway communication requirements and rich experience in millimeter wave technology, ZTE has proposed a high-bandwidth automatic data dump solution based on mmWave transmission as shown in Fig. 1.

The automatic dumping system based on mmWave transmission consists of a train-mounted data monitoring subsystem, a train-to-ground data transmission subsystem, and a ground data processing center.

The train-mounted data monitoring subsystem completes data collection, processing, recording, transmission, and dumping. It communicates with the locomotive network control systems, train operation control recording devices, and locomotive onboard safety protection systems using Ethernet data acquisition.

The wireless network of the train-to-ground data transmission subsystem uses mmWave to complete data transmission from the vehicle to the ground. The wired network utilizes the existing comprehensive railway IT network to complete data transmission within the three-level network framework of the railway corporation, railway bureau, and locomotive/maintenance depot.

The main function of the ground data processing center is to process, store, manage, and diagnose real-time locomotive operational status and fault information forwarded by the train-to-ground transmission subsystem. It also performs big data analysis and statistical evaluations based on locomotive service data and provides data interfaces for other information systems.

The following focuses on the train-to-ground data transmission subsystem, which mainly includes a train-mounted router, a train-mounted CPE (TAU), a ground mmWave base station (mmW gNB), a relay gateway, and an intelligent computing unit NE (NodeEngine).

• Train-mounted router: The train-mounted router connects monitoring cameras, storage, and other onboard devices. It establishes a VPN tunnel with the relay gateway. Video surveillance data and other data collected onboard are sent to the mmW CPE, mmW gNB and relay gateway through the aggregation router, and then forwarded to the railway’s comprehensive IT network via a newly built UPF. The processing of downlink stream data follows a similar process, but in the opposite direction.  
• Train-mounted CPE (TAU): The TAU is installed on the roof of the train and is mainly responsible for automatically establishing a connection with the ground mmW gNB and uploading data from the train-mounted router at high speed.
• mmW gNB: The mmW AAU is a radio unit installed on the walls of the high-speed train station or on both sides of the platform. It establishes a wireless connection with the train-mounted CPE through large-scale antenna array beamforming and transmits the baseband digital signal to the mmW BBU in the central computer room via optical fiber. The mmW BBU is a baseband processing unit connected to the relay gateway in the data center via optical fiber or Ethernet cables.   
• Relay gateway: The relay gateway module receives data sent by the onboard TAU and forwards it to the corresponding network element, such as a storage server or monitoring data analysis platform.
• Intelligent computing unit NE: On the one hand, the intelligent computing board supports authentication technologies such as whitelisting for the air interface, addressing security issues. On the other hand, it supports service recognition, service perception, and service guarantee strategies based on artificial intelligence algorithms, ensuring the efficiency and security of the vehicle-to-ground transmission system.

ZTE’s mmWave products support the 26 GHz and 28 GHz frequency bands, with a maximum working bandwidth of 1600 MHz. They utilize large-scale antenna arrays and analog beamforming, providing a maximum coverage distance of over 10 km. The products also support dynamic frame structures, allowing for dynamic adjustments of uplink and downlink frame ratios to meet the bandwidth requirements of different services. With the DDDSU frame structure, the maximum downlink speed can reach 25 Gbps, while with the DSUUU frame structure, the uplink speed can reach 16 Gbps. They support various networking modes, such as NSA, NR-DC, NR-CA, FR2 Only, accommodating different networking scenarios.

Compared to the traditional sub-6G frequency band, mmWave offers a greater bandwidth advantage. Unlike Wi-Fi, it operates in licensed frequency bands, providing less interference and more reliable transmission performance. Compared to microwave, it supports not only point-to-multi-point transmission but also CPE mobility, making it more suitable for scenarios where multiple trains transmit data simultaneously. Additionally, compared to wired transmission, it has lower construction costs and is easier to deploy.

At present, the mmWave-based automatic train-to-ground data dump solution has been successfully implemented in Shanghai Shentong Metro, achieving a transmission rate of over 7 Gbps. This solution features simplified deployment, one-key dump, one-key detection, and automatic backup. It enables automatic docking, rapid storage and processing of data from each subsystem of the railway locomotives and vehicles. At the same time, it provides strong edge data computing capabilities, including video image analysis, and is expected to become the primary solution for data dump in future railway systems.