NTT, NTT-ME, and NTT e-Drone Technology Demonstrate a Method to Reduce Delay Variation in Wireless Segments and Stabilize Video Quality for Remote Drone Operation
Enabling real-time remote inspections, contributing to enhanced safety and labor savings

News Highlights:

Background

In Japan, labor shortages are becoming increasingly severe, creating challenges in securing personnel for infrastructure and equipment inspection tasks. As a result, expectations for remote inspections using drones are rising, as a means to conduct inspections without on-site dispatch.

Autonomous flight is suitable for inspections in fixed locations and relatively large areas. In contrast, in cases such as construction sites and factory inspections, where inspection points vary daily or where operations take place in relatively confined spaces, precise, safe, and real-time remote drone operation is required. This requires not only uninterrupted communication but also stable video transmission without distortion.

A key challenge has been that fluctuations in packet delay cause video distortion, leading to reduced operational precision. In wireless segments, such fluctuations occur because uplink and downlink communications share the same frequency band and because retransmission control is triggered when wireless quality deteriorates. To address these challenges, a technology was demonstrated that reduces delay variation in wireless segments and stabilizes video quality, with the aim of enabling operators to control drones remotely with confidence.

Results

In this demonstration, a remote drone operation environment was established in which an operator controlled a drone while viewing camera footage transmitted over a network. The system was configured with a drone deployed at the Robot Test Field in Minamisoma City, Fukushima Prefecture, and operated from Koriyama City, Fukushima Prefecture. Two sites located approximately 60 km apart in a straight line were connected via FLET'S VPN, with Local 5G used in the wireless segment. Under this environment, successful remote operation of the drone was confirmed.

In addition, a function to compensate for delay variation occurring in the wireless segment was implemented in the system. When high-load video transmission was conducted, video distortion was observed for 12% of the total transmission time. By applying this technology, the duration of video distortion was reduced to 5%. Furthermore, as significant video distortion can cause operators to interrupt control and increase the time required to reach a destination, travel time was also evaluated. A movement that required an average of 35 seconds under visual line-of-sight operation in Minamisoma was completed in an average of 32 seconds through remote operation from Koriyama without interruption. This confirmed that the system achieves video quality sufficient for stable and uninterrupted operation.

Figure 1. Configuration of the remote drone operation demonstration

Technical Highlights

In wireless segments, delay variation caused by retransmission control and other factors leads to fluctuations in video frame timing, resulting in video distortion. This technology analyzes the video rate using traffic information collected from the wireless base station and corrects frame intervals in an optical network device according to the analyzed video rate. As a result, delay variation generated in the wireless segment can be reduced (Figure 2). While a wireless base station alone cannot adequately address delay variation in the wireless segment, coordinated control across both wireless and optical segments enables reduction of delay variation and stabilization of video quality.

The technology consists of the following three steps:

Figure 2. Optical-wireless coordinated control technology for mitigating delay variation

Video quality is considered more stable when the distribution of video frame intervals is closer to the ideal value. Before applying this technology, delay variation in the wireless segment caused significant variability in frame intervals, resulting in video distortion (Figure 3). By applying this technology, delay variation is reduced and frame intervals are brought closer to the ideal value, thereby eliminating video distortion.

Figure 3. Video frame intervals and video distortion

Roles and Contributions

Future Outlook

This technology enables stable delivery of high-quality video to remote operators. Beyond drones, broader application to the operation of unmanned aerial vehicles and robots is anticipated, and efforts will be made to advance its commercialization.

The technology can also be applied to remote operations beyond inspection tasks. Its adoption across a wide range of fields will be promoted to support remote operational workflows and help address labor shortages.

[Glossary]

¹Local 5G　URL: https://business.ntt-east.co.jp/solution/local5g/ (Japanese)

²FLET'S VPN　URL: https://business.ntt-east.co.jp/service/vpnprio/ (Japanese)

³Tsukuba Forum 2026　URL: https://www.rd.ntt/e/as/tforum/

About NTT

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