Line 4 of the Hangzhou Metro was opened for experimental operation in February 2015. Different from its previous counterparts, Caltta's train-to-ground wireless system dedicated for communications incorporated PIS, CCTV, and other services into the LTE network. This was the world's first commercial case of LTE technologies in rail transit industry, indicating that Caltta has achieved a leading position in the LTE technologies for rail transit.
In addition to common voice services and trunking dispatch services, the wireless communications system for metro provides various data services, such as video streaming, video surveillance, and online advertisements. However, the existing wireless system hardly met the increasing requirements for high-speed data services. Many problems appeared out of the WLAN in high-speed scenarios, such as low security, poor coverage, frequent handover, low bandwidth, and various sources of interference. Based on the features of metro, the TD-LTE train-to-ground multi-service transmission system was tailored to meet the requirements of metro lines in terms of good coverage, mobility management, and security.
As shown in the following figure, the train-to-ground wireless communications system consists of the core network in the control center subsystem, base stations (distributed base stations containing the BBU+RRU) in the station subsystem, and TAUs and antennas in the on-board subsystem.
Except for the transmission and power grounding systems in the TD-LTE network architecture, the entire application system is divided into the following three subsystems based on their locations:
Control center subsystem
Caltta's train-to-ground wireless solution based on LTE technologies provides ground-to-train communications, including on-board terminals, base stations, core networks, and other end-to-end solutions. Using the leading distributed (BBU+RRU) base station architecture and leaky coaxial cables, this solution effectively improves the coverage in line corners, underground tunnels, and other areas with poor coverage. The system provides CBTC, voice and video trunking dispatch, and other integrated services. The LTE system realizes nine QoS Class Identifiers (QCIs), based on where the resources are allocated and dispatched to meet the requirements in multi-service scenarios. The solution integrating multiple networks saves customer investment to the maximum degree.
Caltta is one of the first equipment manufacturers engaged in the research on 4G private network application technologies and is the first to propose integrated 4G communication solutions for rail transit. Featuring a high transmission rate, high spectral efficiency, and low latency, LTE is preferred in private network systems, and its performance has been widely verified in the global market. Caltta's rail transit solution provides carrier-class reliability and stability of the operation equipment security system. Thanks to the adaptability to high-speed scenarios and efficient switching performance of LTE equipment, this solution provides good signal coverage, and significantly reduces the devices deployed alongside the railways as well as the difficulty and cost of wireless network operation and maintenance for the customer.
The application of LTE technologies for constructing the world's first commercial LTE train-to-ground network is of great significance for the Hangzhou Metro. It indicates that the wireless communications system for metro has also entered the 4G era and will improve the operational efficiency and service quality of the Hangzhou Metro and provide a better travel experience for passengers.