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Cutting-Edge Tech: The Driving Force Behind China’s Rapid Urban Rail Development Huawei’s TDD 1.8 GHz LTE-M Solution Builds a Reliable, Converged, and Simplified Private Wireless Network for Train-to-Ground Communications
Huawei’s world-leading wireless solutions may be best known for the benefits they provide for carrier public networks, but they also have a huge impact for urban rail transit customers in terms of private networks.
Indeed, ninety metro lines in China have already deployed Huawei’s Time Division Duplex (TDD) 1.8 GHz Long Term Evolution Machine-Type Communication (LTE-M) private network solution to build a more secure and reliable train-to-ground communications private wireless network. The network efficiently carries Communications-Based Train Control (CBTC), trunking, the Passenger Information System (PIS), and Closed-Circuit Television (CCTV) services — enabling China’s urban rail industry and fostering its rapid development.
The urban rail multi-line network scale in China ranks first in the world. By the end of 2018, 5761.4 km of urban rail lines (22% of the global total) were put into operation in the Chinese mainland, and transported 21.07 billion passengers. Under such circumstances, the CBTC, voice dispatching, PIS, and CCTV applications support the secure, reliable, and proper operations of urban rail networks where the wireless communications platform implements the key function — data connection.
A traditional wireless communications solution uses four networks in two modes to carry related services. Three Wi-Fi networks are used to carry CBTC, PIS, and CCTV services over public frequency bands, but are vulnerable to interference, which may even cause unexpected train stoppages. Meanwhile, limited Wi-Fi coverage distance means that multiple devices are required, complicating maintenance, while poor overall network performance during high-speed train movement makes it difficult to speed up the network, holding back transport innovation. Furthermore, a narrowband Terrestrial Trunked Radio (TETRA) network, which bears trunking services, can’t support the functions of smart urban rail and intelligent devices, including video calls, task dispatching, and multimedia services.
To address the pain points of traditional wireless communications solutions, China officially released the LTE-M standard in 2016, strictly defining the capability requirements for carrying CBTC, trunking, PIS, and CCTV services. LTE-M technology offers three significant advantages:
1. Reliability: dedicated frequency bands avoid interference from public signals; dual-network redundancy backup.
2. Convergence: unified bearing of multiple services; 9-level Quality of Service (QoS) mechanism that ensures CBTC is the highest priority.
3. Simplification: up to 1.2 km coverage radius of a single base station with easy deployment and maintenance, requiring no devices between two urban rail stations.
By the end of 2019, more than 130 urban rail lines in 40 cities across China had chosen to build LTE-M networks to carry CBTC, trunking, PIS, and CCTV services. Among them, Huawei has helped urban rail customers in 36 cities build LTE-M private networks for 90 lines with its world-leading LTE solution.
According to the 3GPP, frequencies from 1710 MHz to 1785 MHz, and from 1805 Mhz to 1880 MHz are used for LTE FDD Band 3. The frequency band from 1785 MHz to 1805 MHz serves as a guard bandwidth and is not used by any carriers.
Long-term theoretical analysis and definitive verification carried out in China, show that the TDD 1.8 GHz frequency band can be applied in various industries. It will not interfere with the frequency bands of neighboring carriers when frequency isolation (2 MHz) or space isolation is ensured.
Zhengzhou Metro Line 1 commenced operations in 2013. This line adopted LTE-M to carry PIS and CCTV services for the first time, achieving a stable train-to-ground wireless transmission of 8 Mbit/s in the downlink and 6 Mbit/s in the uplink. This marked the first adoption of real-time HD PIS in the urban rail sector. In the opinion of customers, compared with other technologies, LTE has advanced capabilities in network capacity, coverage, anti-interference, and high mobility. Such capabilities help enhance customer confidence in deploying Huawei's LTE-M solution for metro construction in the future.
Chongqing Metro Line 5 (opened in 2017) and Loop Line (opened in 2018) use LTE-M that features interference-free licensed frequency band, dual-network 1+1 backup, highly reliable seamless switchover, multi-service QoS, and other technologies, to provide the highest quality assurance for CBTC services, enabling agile operations across these two major metro lines. At the same time, Beijing Subway Yanfang Line and Nanjing Metro Line S9 began operations by deploying LTE-M to carry CBTC services.
The Branch Line of Guangzhou Metro Line 14 began operations in 2017. Here, an LTE-M wireless network carries voice trunking, video backhaul, train status monitoring, ICT application platforms, and other communications services required for metro operations and management. The network provides multiple dispatching modes, including point-to-point calls, group calls, and Public Address (PA).
The industry chain of TDD 1.8 GHz LTE-M is developing rapidly, guided by clear spectrum specifications and industry standards. In just five years, approximately ten vendors are now able to provide the TDD 1.8 GHz LTE-M solution, working alongside dozens of on-board terminal and trunking terminal vendors. Huawei’s solution has completed Interoperability Tests (IOTs) with mainstream CBTC, PIS, and CCTV vendors. As these tests suggest, the solution can be successfully applied in customer train-to-ground communications.
In 2020, Huawei will launch the visualized IPH solution for metro lines, adopting unattended driving and the enhanced Machine Type Communication (eMTC) Internet of Things (IoT) solution that does not require manual inspection based on the TDD 1.8 GHz LTE-M standard.
In the international market, the development of broadband urban rail train-to-ground communications is accelerating. Huawei’s TDD 1.8 GHz LTE-M solution has been replicated worldwide: it has been commercialized by urban rail in Australia, and by light rail in Ethiopia and Angola. Construction in the Southern Pacific, Central Asia, and Africa is ongoing. Huawei will continue to innovate its TDD 1.8 GHz LTE-M solution for urban rail to enable ubiquitous connectivity and facilitate the rapid development of the urban rail industry worldwide.