The future of railways depends on reliable and critical mobile broadband connections, which are supported by innovative 5G network solutions to enable faster, safer and more environmentally friendly travel. Let's look at how railway communications depend on excellent network design.

Director of Network Design and Optimization

Director of Network Design and Optimization

Director of Network Design and Optimization

The railway transportation sector is exploring digitization to enhance customer experience, improve day-to-day operational efficiency, and maintain network security and data integrity.

From improved on-board monitoring systems to trains equipped with IoT connected sensors, etc., the next few years will usher in a new era of highly interconnected trains and railways. For railway operators, this means better management of the daily services that passengers rely on in order to always reach their destinations on time.

To achieve this, network-level infrastructure changes are required. GSM-R is a traditional communication technology for railways and will be replaced by 5G. A new framework called the Future Railway Mobile Communication System (FRMCS) is planned to be deployed on approximately 200,000 kilometers of arterial railways. This 5G-based framework will modernize train services and help railway operators maintain business success. 5G can also help meet the increasing demands and expectations of passengers, enabling them to work online and have a perfect communication experience on the train.

Figure 1: Future railway mobile communications.

FRMCS is based on the railway dedicated 5G frequency band. However, the amount of spectrum dedicated to FRMCS is not enough to meet the needs of railways. However, 5G also provides passengers with Gigabit train connections based on CSP. This will enable CSPs to provide the required strict and heterogeneous SLAs through network slicing, and supplement the capacity required by railways for their applications. This will change the rules of the railway game, because the same technology can satisfy FRMCS applications as well as the needs of advanced consumers, such as video streaming, video calls or games-all of which are 500 kilometers while traveling on a train. Hour.

Have you noticed that the pitch of the ambulance is higher when it is approaching you and lower when it is away? This is called the Doppler effect, and it also affects radio waves, making communication with high-speed trains particularly complicated.

Figure 2 summarizes the SLAs for consumer applications and specific railway-related SLAs to support various voice, video, and data services applicable to railway communication scenarios:

Figure 2: Example performance requirements for railway scenarios, based on 3GPP TS 22.289. Consumer application requirements based on Ericsson smartphone laboratory research. The size of the bubble illustrates the required reliability.

Network design is the process of obtaining the best infrastructure layout for your network while meeting the service level requirements of all use cases. Reliable coverage and sufficient capacity are the basis for a high-performance, high-availability and future-oriented mobile network covering railway tracks.

In order to meet the strict service level requirements of FRMCS and ensure the high performance of passenger communication in the train, careful network design is essential, and several aspects need to be considered:

The first step in the network design process is the "determining the size" stage, in which service level requirements, traffic models, radio technology, and frequency spectrum will produce signal strength and signal-to-noise ratio targets. In this step, the number of stations required can already be estimated, and the scale and required investment can be indicated.

In order to plan the network deployment, it is necessary to model the characteristics of the radio environment along the railway and inside the carriages. To do this, use radio planning simulation tools that need to be set up and properly calibrated.

The use of simulation tools for reliable railway planning includes three pillars: propagation prediction models, accurate geographic data, and railway-specific radio aspects.

The propagation model is the core of the community planning tool. It estimates how the wave propagates in a specific environment, so that the best site location can be proposed to meet the required service level requirements. Since the propagation mode of radio waves depends on its frequency and landscape, the propagation model should be adjusted according to field measurements in typical railway environments (such as dikes, soundproof walls, bridges, roads on railway bridges, and urban and rural areas) to ensure They present the given reality in the most accurate way.

Figure 3: Sample data for propagation model adjustment.

The propagation model tuning/calibration procedure follows a standard procedure in which continuous wave measurements are used to adjust the coefficients of the selected propagation model. Usually, a large number of measurement samples are required to calibrate the model, and a subset of samples are used to validate the experience propagation model.

Measurement collection can be a time-consuming task, requiring precise telecommunications engineering expertise to adjust the model.

Figure 4: Model adjustment steps: filtering (left) and statistics (right).

In the field of telecommunications, as part of the network design process, the precise 3D map used in the cell planning tool is called geographic data. High-quality geographic data simulates building heights, building materials, terrain types (called clutter), and even vegetation-basically anything with different radio waves.

Map errors, incorrect clutter heights, and incorrect clutter types can all jeopardize this process. In terms of railway network design, it is important to obtain extremely accurate geographic data with high resolution along the railway track itself.

Aerial photos can automatically detect any radio technology obstacles and incorporate them into geographic data. In the automatic process, clutter type, clutter height, 3D buildings and vegetation are generated. Manual control is required to make corrections and ensure that the results are based on real-world scenarios.

Figure 5: 3D propagation prediction along railway tracks.

For GSM-R and FRMCS, the train can install a receiver antenna on the roof, so the outdoor planning threshold is sufficient to ensure a seamless layer for critical communications. Defensive, conservative planning is suitable to ensure that a high-quality network is combined with a reliable redundancy solution.

There are different ways to provide broadband networks for public customers in the car. One method is to use the receiver antenna on the roof of the car and distribute the mobile signal through the repeater antenna in the train, as shown in Figure 6. The solution has been proven, but requires a lot of maintenance, and due to frequency dependence, it is neither flexible nor future-proof.

Recently, train companies have been testing and installing so-called "RF windows". These RF windows have been optimally laser processed for commonly used frequencies and have lower attenuation compared to conventional train windows. In this case, the installation of a repeater can be prevented.

In order to guarantee the service level requirements inside the train with RF window, the solution needs to be modeled correctly. For example, the angle of incidence between the antenna position and the train position must be considered. As shown in Figure 7, according to the angle at which the signal hits the train window, the corresponding attenuation should be considered in the planning tool.

Reliable network design is the foundation for meeting the stringent performance requirements associated with mission-critical railway communications and meeting consumer expectations, whether at home or on a train traveling at 500 km/h, these expectations remain the same.

The network design may determine the best site location and provide the target performance with the best TCO, but its complexity cannot be ignored. Despite the existence of community planning tools, it is not easy to operate them in order to obtain the correct results. Highly skilled experts associated with a global knowledge base are required to keep up with the latest industry developments and realize the potential of 5G-based FRMCS.

Learn more about network design and optimization.

Read our blog to learn how network operations can make 5G systems more resilient.

This is why 5G networks need new methods of operation.

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