Signal and Communication DX Revolutionizes On-site Inspections: Enhancing Equipment Maintenance with Smartphone RTK × AR

On-site inspection and maintenance work for signal and communication equipment at railway companies is now undergoing a major turning point. Challenges that were difficult to solve with traditional methods—such as dependency on specific personnel, labor shortages, the wide geographic spread of equipment to manage, and the complexity of record-keeping—are piling up. Signal and communication equipment refers to a wide range of field devices including railway signals and points (switches), level crossing alarms and barriers, inter-station communication cables, and train radio antennas. Because these are directly linked to the safe operation of trains, reliable maintenance is required. In this situation, digital transformation (DX) is expected to be the trump card to break through on-site issues. In fact, DX of maintenance departments has become a management issue for many railway companies, and smart maintenance plans using AI and IoT are being promoted. In the field of signal and communication equipment, movements to innovate on-site operations by incorporating digital technologies are also accelerating.

In recent years, a new inspection method that combines smartphones and high-precision positioning technology (RTK-GNSS) with AR (augmented reality) has emerged and is attempting to revolutionize on-site inspections. It is expected to enable on-site equipment position measurement and inspection recording with far greater precision and efficiency, leading to improved maintenance quality. This article explains in detail the benefits and future prospects of enhancing maintenance inspections using smartphone RTK × AR as a DX initiative for railway signal and communication infrastructure.

Challenges in Maintaining and Inspecting Signal and Communication Infrastructure

The following problems have been pointed out in the traditional inspection and maintenance of signal and communication equipment:

• Task dependency and labor shortages: Maintenance of railway signal and communication equipment often concentrates in limited nighttime windows from the last train to the first train, and tends to rely on veteran employees with specialized skills and experience. As a result, techniques and know-how become dependent on specific individuals, and skill transfer during generational change becomes an issue. The workforce on site is aging, and there is concern that a large wave of retirements by veterans in the near future could lead to loss of know-how. In addition, the harshness of nighttime work makes it difficult to secure young personnel, leading to chronic labor shortages.

• Inefficiency of inspection work: Signal and communication infrastructure is spread over wide areas, and there is a limit to how many sites can be巡回ed in one night. Moreover, infrastructure built during the high economic growth period is aging, and the number of devices requiring inspection tends to increase year by year. With many devices and limited work time, the field faces an efficiency problem of having to cover a huge number of inspection targets with limited personnel. In some cases inspections fall behind, creating the risk of overlooking latent defects or delayed responses.

• Complexity of record-keeping and positional errors: Traditionally, inspection results have often been recorded on paper forms or spreadsheets, and equipment locations managed by plans or notes. Such analog methods require manually matching photos taken on site with positions on drawings, which is cumbersome and a source of errors. Furthermore, manual measurements by people have limits, and recording the installation location of equipment can result in positional errors on the order of several meters (several ft). Information tends to scatter and become person-dependent, making it difficult to share the latest status among stakeholders.

Centimeter-level Positioning with RTK-GNSS and Solo Work Enablement

To address these issues, high-precision positioning technology using RTK-GNSS (real-time kinematic GNSS) is one of the keys. RTK-GNSS uses correction information from a base station to enable positioning far more precise than ordinary GPS. Centimeter-level position measurement, which traditionally required special surveying instruments and skilled technicians, has recently become easily achievable by combining smartphones with compact RTK-compatible receivers. In Japan, the quasi-zenith satellite "Michibiki" provides a centimeter-level positioning service (CLAS), and using compatible smartphones or receivers makes it possible to measure positions with astonishing accuracy—stable to within a few centimeters (within a few inches).

For example, tasks that previously required assembling a survey team to identify equipment locations can now be done by a field engineer simply approaching a device with a smartphone in hand to obtain accurate coordinates. The need to estimate approximate positions on paper drawings or measure distances with a tape measure disappears, and a single worker can efficiently record positions for multiple devices. The dramatic improvement in positioning accuracy allows unified management of equipment ledger location information in world geodetic system coordinates, making future GIS utilization and integration with other systems easier. This advances labor-saving on-site work (enabling solo operations) and helps alleviate labor shortages.

Equipment Visualization with Smartphone AR and Improved Inspection Quality

Using AR (augmented reality) technology on smartphones dramatically improves on-site equipment visualization and the quality of inspections. Viewing the site through a smartphone camera enables AR overlays that show the positions and routes of infrastructure not normally visible—such as buried cables and conduits or devices behind walls—right on site. For example, the underground cable routes that could previously only be understood on drawings can be visually confirmed on site, allowing accurate equipment understanding without relying on an engineer’s experience or intuition. The smartphone screen can also display pop-ups with device IDs, the date of the last inspection, and information about active lines, enabling immediate access to necessary data without flipping through paper ledgers.

AR also aids on-site guidance. Inspection points can be highlighted on the screen, and device-specific checklists can be displayed in the AR space to guide the inspector step by step. Simply pointing the smartphone will visually show the "next point to check" and the "inspection criteria," helping prevent missed tasks and inspection errors. Less experienced technicians can intuitively understand procedures and perform high-quality inspections according to standardized procedures.

Furthermore, AR enhances on-site condition recording. The "as-is" state, previously recorded by notes and photos, can be saved in three dimensions with smartphone AR. For instance, scanning the area around equipment with a smartphone to generate point cloud data, marking deteriorated areas virtually and saving them allows detailed review in the office later. Because scanned data captured on site can be used immediately for AR display without preparing special 3D models in advance, it can be integrated into routine inspections as AR accessible to anyone.

While hands-free inspection using AR-capable smart glasses is envisioned for the future, the currently most practical approach is to leverage the widely adopted smartphone. It is important to first achieve results with smartphone AR while preparing for further technological advancements.

Centralized Records with Point Cloud Data and Cloud Sharing

Point cloud data, photos, and work records acquired on site can be saved and shared on the cloud in real time. For example, 3D point clouds obtained by scanning around equipment with a smartphone, high-resolution photos taken on site, and inspection checklist results entered on a tablet are all automatically uploaded to a cloud project folder. Because data synchronization occurs in the background without site personnel needing to think about it, information sharing between field and office is realized without time lag.

Centralizing data on the cloud enables unified management of each asset’s historical information. Who performed which inspection or repair on which device and when, along with detailed conditions at that time (including photos and 3D records), can be tracked chronologically within a single system. There is no need to search through paper forms or individual spreadsheets, and stakeholders can quickly access necessary information via a web browser. Easy reference to past inspection histories supports analysis of long-term degradation trends and planning of future maintenance. In addition, office staff can quickly update drawings and prepare reports based on data acquired on site, smoothing coordination between field and office. The accumulated large datasets can be analyzed by AI to detect signs of failure early and apply to predictive maintenance.

Cloud sharing of data makes information a shared organizational asset, reducing individual-closed know-how and helping eliminate task dependency. Even if an experienced worker transfers or retires, accumulated digital records will support the next generation of technicians and back up skill transfer.

Contribution to Standardization of Work and Improvement of Maintenance Quality

The introduction of these digital technologies promotes on-site work standardization and maintenance quality improvement. By unifying inspection items and decision criteria in a system, differences among personnel are reduced and consistent, uniform results can be obtained regardless of who performs the inspection. Digital input forms and automatic judgment functions can prevent omissions in checklists and variability from subjective evaluations. Visualization of work processes allows managers to remotely grasp progress and results and give appropriate instructions as needed. Moreover, orderly digital management of inspection data and histories makes audit responses and third-party verification easier, contributing to greater reliability of maintenance operations.

DX also has a significant effect on skill transfer. Know-how cultivated over years by veteran employees can be accumulated and shared in digital form. For example, points and tips noticed on site can be left in a cloud remarks field or marked on AR screens for the next person. New employees can learn on-site work by referring to accumulated data and senior technicians’ records, and even with limited experience they can perform a certain level of work by following system guidance. Building a system that does not rely on veterans’ "intuition and experience" helps prevent quality degradation during generational handover and raises the organization’s overall maintenance level.

Inspection Workflow Scenario Using Smartphone RTK × AR

Now let’s look at an example inspection workflow that combines smartphone RTK and AR. Imagine a technician in a railway operator’s signal and communications section performing routine inspection of a level crossing device alone. The technician carries a smartphone and an RTK receiver and starts inspection using an AR app on site.

• Arrival and situation confirmation: Upon arriving at the signal installed beside the level crossing, the technician first surveys the surroundings via the smartphone screen. The underground cable burial routes obtained from past construction work are visualized on the ground in AR, allowing the cable routes and connection locations to be grasped at a glance. Basic information such as device ID and last inspection date is superimposed, enabling immediate comprehension of the inspection target.

• Identifying inspection points with high-precision positioning: Next, the RTK-GNSS receiver attached to the smartphone acquires correction signals and the technician’s current position is determined with centimeter-level accuracy (inch-level accuracy). The technician taps the foundation of the signal or the adjacent control box on the app to measure and record the exact coordinates on site. Distance measurements that were previously done with tape measures or visual estimation are automatically recorded accurately, eliminating the need to later convert them into drawings.

• Inspection and recording with AR: An inspection checklist is displayed on the smartphone, and the technician follows prompts to sequentially check the signal lamp status, loose wiring and terminal corrosion, and the operation of the level crossing barrier. If an anomaly is found, the technician photographs the location with the smartphone camera. For example, if rust is found at the base of the signal pole, the technician marks that area in AR and saves a note like “rust progression observed.” Work notes for each inspection item can also be entered by voice on the smartphone, ensuring reliable recording even when both hands are occupied.

• Detailed recording via point cloud scanning: If more detailed recording is required, the technician uses the smartphone’s LiDAR scanner to scan around the equipment and obtain 3D point cloud data. The marked rust area and the exact geometry of the signal base are digitally preserved with high accuracy. This makes it possible to analyze deterioration precisely in the office later and compare changes at the next inspection.

• Data sharing and follow-up: When the inspection is complete, all collected data are automatically uploaded to the cloud. Supervisors and colleagues in the office can view inspection results in real time and send additional instructions to the field as needed. By the time the technician leaves the site, a draft of the report has already been generated in the cloud and only requires manager review. The accumulated inspection data are integrated into a historical database, and the recorded rust information is reflected in future repair planning.

From this scenario, it is clear that using smartphone RTK × AR enables a single technician to perform highly accurate inspections and recordings in a short time, greatly improving work efficiency and quality compared to traditional methods. Completing tasks efficiently within the limited nighttime work window after the last train is a major advantage of DX adoption. Data-driven inspections that do not rely on personal intuition or experience are likely to become the mainstream of future maintenance work. Specific solutions to the issues raised at the beginning—such as eliminating person-dependency and simplifying record management—are becoming visible.

Effects of Introducing the Integrated Smartphone RTK × AR Tool "LRTK"

As a solution that allows easy use of these advanced technologies on site, an integrated tool called "LRTK" has emerged, combining a smartphone-mounted RTK-GNSS receiver with point cloud measurement and AR functions. Simply attaching a dedicated receiver to a smartphone enables anyone to intuitively perform centimeter-level surveying and 3D scanning, and the acquired data can be used directly for AR display and cloud sharing. LRTK dramatically streamlines measurement and recording work that previously required specialized equipment or advanced skills. Because it leverages the user’s existing smartphone without requiring the purchase of expensive laser scanners or dedicated AR devices, it is also cost-effective. There have been reports that it can be used on site with no prior training, and its intuitive operation lowers the barrier to DX adoption. The expected benefits of introducing LRTK include, for example, the following points.

• Enables simple centimeter-level surveying: With just a smartphone and a compact receiver, accurate positioning is possible, allowing on-site personnel to perform tasks that previously required the surveying department. Measuring required points while touring the site alone will immediately produce plotted results on a map, enabling creation of ledgers without positional errors.

• Realizes AR inspections with a smartphone: Measured point cloud data and existing drawing information can be overlaid and displayed as AR on the smartphone. Workers can visualize buried objects in situ, highlight inspection points, and be guided, supporting intuitive inspection tasks. Even workers without specialized knowledge can immediately grasp necessary information via AR, helping prevent inspection oversights and reducing work time.

• Cloud recording and sharing of data: Measurement and inspection data are automatically uploaded to the cloud, and report-ready information is consolidated as soon as the site work finishes. This eliminates the need to re-enter paper forms later and allows one-click reporting to the office. Data stored in the cloud are shared among all stakeholders, reducing communication errors and enabling decisions based on the latest information.

Tools like LRTK, which promote on-site DX in an accessible form through smartphone RTK × AR, achieve both labor saving and enhancement in railway infrastructure maintenance management. Going forward, on-site DX initiatives are expected to accelerate further across railway companies. Introducing digital technologies into the maintenance domain will be a key to sustaining safe and stable transport services into the future. By moving away from person-dependent work and establishing data-driven smart maintenance, it will be possible to maintain equipment safely and reliably while reducing the risk of mistakes and accidents even with limited human resources. With DX as tailwind, the maintenance sites for signal and communication equipment are expected to undergo major transformation. Indeed, on-site DX is poised to shape the future of railway maintenance.