Caltta and Chongqing Metro Launches World's First Interconnected Train-to-Ground Private Wireless Network

The TD-LTE private network for Chongqing Metro Line 10 was completed as the world's first interconnected train-to-ground TD-LTE private network, indicating that the rail transit communications has been ushered into a new era. This exemplary case facilitates Caltta’s development in wireless communications dedicated for rail transit.

Customer Demand

With a total length of about 32.15 km, Chongqing Metro Line 10 starts from the Jianxin East Road in the Jiangbei District and ends at the Wangjiazhuang Station. There are a total of 19 stations on Line 10, including 18 underground stations and 1 elevated station, with an average distance of about 1.74 km between each two stations. Line 10 adopts type-A steel-wheel monorail trainset in six-car formations operating at a maximum speed of 120 km/h.

The TD-LTE system dedicated for train-to-ground communications on Chongqing Rail Transit Line 10 should be interconnected with the system equipment installed on Line 4, Line 5, and the circle line for crossline operations.

In addition, the train-to-ground wireless communications system needed to implement automatic control and rail network coordinated dispatch for smooth and efficient crossline operation and meet the requirements for service resource sharing, such as the training, maintenance, and equipment optimization based on standardization.

In the train-to-ground wireless communication system, the CBTC signal service was carried on networks A and B, and other services are carried on network A only. Networks A and B needed QoS dispatch policies to guarantee secure transmission of train control information as well as its timeliness and reliability.

Solution

Based on advanced LTE technologies and B-TrunC standards, Caltta's solutions provided a unified dedicated wireless communication platform for interconnection with the CBTC system and a reliable QoS guarantee based on service priorities. This dedicated communications system, which was used on trains moving at a speed of up to 350 km/h, provided a variety of wireless coverage solutions in different scenarios and business models to ensure network stability and reliability.

This TD-LTE system used redundancy architecture, and therefore the A/B dual-network coverage solution as shown above was adopted. Networks A and B in the dual-network architecture were independent of each other. Each network had a set of core network and base station systems, fully covering the traffic area. The core network and base station systems of networks A and B needed be configured separately. The antenna-feeder interfaces of the base stations in the A/B dual-network architecture were connected to leaky coaxial cables or antennas through the multiplexer to provide wireless signal coverage.

The on-board TD-LTE TAU systems were deployed in the front and rear cabs of a train. The TAU antennas were installed outside driver's compartments and kept at a sight distance to the leaky coaxial cables. The TAU systems were connected to the on-board switches and signal equipment through Ethernet interfaces to exchange information. The on-board system used the Ethernet network, and the compartments were interconnected through on-board switches.

The on-board controller exchanged CBTC signals with the ground signal system through the on-board TAU system.

Customer Benefit

Chongqing Metro Line 10 achieved real interconnection as well as crossline and joint network operations in the field of rail transit.

Caltta provided the first TD-LTE system dedicated for train-to-ground communications between different equipment manufacturers in the field of rail transit. This system effectively guarantees the interconnection between CBTC information services and implementation of crossline operations. To guarantee high reliability and stability of the CBTC signal service, Caltta has fully considered the system architecture and designed a complete set of solutions.