Another LTE-M Breakthrough: Caltta Helps Establish the First Subway Line with CBTC Interoperability in Chongqin

Introduction: Chongqing Metro Line 10 is an express line to Jiangbei International Airport. Costing a total of 21 billion yuan, its first phase is 34 km in length. Construction started in 2014, and the track went into trial operation on December 28, 2017. As a national demo project showcasing interoperable subways, Line 10 uses Caltta’swireless train-to-ground communication system. It adopts 1.8GHz-based LTE technology and CBTC, the most advanced technology for carrying metro signals. Its interoperability tests have been completed under the guidance of the China Urban Rail Transit Association, and corresponding national standards have been formed.

Caltta provided an E2E wireless communication solution, equipment, and delivery services for Line 10, covering five core LTE networks, 135 LTE base stations, and 26 train-mounted terminals.

Caltta PMR Radios-Disrupting the industry with optimal transit reliability

WLAN previously used to carry signal services for wireless communications in rail transit. However, considering security, reliability and stability, WLAN technology is increasingly unsuitable for bearing signals.

China Urban Rail Transit Association released the Urban Rail Transit Equipment Technical Specifications. As a key member of the rail cross-strait association, Caltta is also a major contributor to the preparation of LTE-M standards. Standards that have been issued so far include LTE-M System Requirements Specifications, LTE-M System Overall Architecture and Function Specifications, LTE-M System Air Interface Specifications, LTE-M System Core Network Data Interface Specifications, LTE-M System Equipment Technical Specifications, LTE-M Terminal Equipment Technical Specifications, and LTE-M System Borne CBTC Service and Interface Specifications.

The interoperability test for CBTC services borne by LTE on Chongqing Subway Line 10 has laid a solid foundation for China’s rail transit industry to establish interoperability benchmarks.

The formal trial operation of Line 10 confirms the feasibility of using LTE technology to build a highly reliable rail transit communications network.  As well as Chongqing Subway Line 10, numerous other cities, including Hangzhou, Harbin, Nanchang, Honghe Prefecture, and Yunnan, have deployed Caltta's rail transit Zi-LTE solution to construct wireless communication networks based on LTE. Services carried by these networks include PIS, CCTV, CBTC, and trunking calls.

Caltta PMR Radios-Creating a new starting point for rail transit

Line 10 uses steel wheels and a steel rail system, with each train comprising six compartments. The train runs from 07:30 to 20:30 at minimum intervals of 8 minutes. A total of 14 trains are running at any one time, and a one-way end-to-end journey is 52 minutes. It takes only 30 minutes to travel from Liyuchi station to Jiangbei Airport T3 Terminal.

The highlight of Line 10 lies in its innovation status as a national metro interoperability demo project in Chongqing that deploys Caltta's 1.8GHz-based LTE solution to carry CBTC services. It combines advanced control, computing, network, and communications technologies to provide digital, network-based and intelligent services. It has also achieved trans-line interoperability and trans-line operations for the first time.

Caltta PMR Radios-Building a reliable private network

Line 10’s wireless train-to-ground communications system is a TD-LTE private network that supports trans-line interoperability and operations. It needs to be interoperable with signal suppliers’ system equipment on Line 4, Line 5, and the Ring Line. It must also meet the requirements for smooth and efficient scheduling of automated, coordinated, and unified trans-line train operations, as well as the requirements for sharing resources for standardized training, maintenance, and equipment optimization.

Caltta’s wireless train-to-ground communication system solution is based on advanced LTE technology and B-TrunC standards, and provides a dedicated wireless communication platform to support CBTC interoperability. It offers A and B dual-network bearers, with both networks A and B supporting QoS policies that prioritize the safe transmission of train control messages. Messages for other services are independently carried over the A network. This meets requirements for real-time, reliability, and security for train control message transmission. The dedicated communications system can support speeds of up to 350 km/h. It includes a variety of wireless coverage solutions for different scenarios and service modes to ensure network stability and reliability.

Line 10 will realize real interoperability in the rail transit field, enabling trains to travel on different lines and achieve trans-line, cross-line, and co-line network operations. It will provide rich experience for replicating the solution on rail transit in the future, using LTE technology to carry more services.