A drone over a disaster zone is useful only if the information it sees can get back to the people making decisions. In mountains, forests or damaged communities, that communications link can be harder to maintain than the flight itself.
A research group led by Professor Hiroshi Harada at Kyoto University’s Graduate School of Informatics has demonstrated live HD video transmission from a flying drone using a narrowband VHF system based on the Wi-SUN FAN international wireless specification. Kyoto University announced the result on September 28.[1]
Using only 400 kHz of occupied bandwidth at 220 MHz, the system achieved 600 kbit/s and transmitted 1,280×720 video at 10 frames per second for more than ten minutes while the drone was flying. A 1,200 kHz configuration at 170 MHz reached 2,400 kbit/s.[2]
One qualification is essential: the moving-drone test covered about 50 meters, not kilometers. Kyoto’s VHF-IoT platform is intended for much longer links, and the group previously demonstrated roughly 34 km of VHF video transmission between fixed locations. Combining long range, airborne mobility and stable live HD video remains the next stage of the work.[3]
Why move down to VHF?
Drones commonly communicate through Wi-Fi or cellular networks. Those systems offer far more bandwidth than the new VHF link, but they have limitations in exactly the places where emergency and infrastructure drones can be most valuable.
Wi-Fi generally operates in gigahertz bands and can be strongly affected by terrain, vegetation and obstacles. Cellular systems provide wide-area coverage where infrastructure exists, but a mountain valley may be outside the service area, and a severe disaster can damage base stations, backhaul or power supplies.
The Kyoto system uses VHF bands around 170 MHz and 220 MHz. Lower-frequency radio waves generally diffract around terrain and obstacles more effectively than gigahertz signals under comparable conditions. The tradeoff is bandwidth: there is far less spectrum available for moving data.[1]
Japan created a regulatory path for VHF-IoT in 2025
The research sits behind a recent change in Japanese spectrum policy. In December 2025, Japan’s Information and Communications Council issued a partial report on technical conditions for narrowband IoT systems using parts of the V-High spectrum and guard bands around public broadband systems.
Kyoto University’s technical material identifies lower-band operation at 170.0–177.5 MHz and upper-band operation at 217.5–222.0 MHz, with regulatory conditions including power limits designed for public- and public-interest self-operated networks. The system is intended for use on land and in the air, including communications where ordinary mobile coverage is unavailable.[4]
The group had already sent video about 34 km
In May 2026, Harada’s group demonstrated video transmission over approximately 34 km using the 220 MHz VHF-IoT band and only 400 kHz of channel bandwidth. That earlier system relied primarily on a point-to-point link using FSK modulation at 150 kbit/s.[3]
The September experiment solves a different problem. A drone does not sit at a fixed radio site. Its distance, altitude, orientation and surrounding terrain change continuously. The researchers therefore moved from the earlier FSK link to Wi-SUN FAN using OFDM, while also introducing network formation and video-delivery techniques designed for a moving radio environment.[2]
The research sequence is important: first show that narrowband VHF can carry video a very long distance, then show that a moving aircraft can maintain a networked link capable of live HD video.
From 150 kbit/s to 600 kbit/s in the same 400 kHz bandwidth
The new system uses orthogonal frequency-division multiplexing, or OFDM. Rather than sending the entire data stream on one carrier, OFDM divides information among multiple orthogonal subcarriers. It is a familiar principle in technologies such as Wi-Fi and LTE, but here it is being applied to a much narrower VHF IoT channel.
At 220 MHz, the prototype used 1 watt of transmit power and 400 kHz of occupied bandwidth to reach 600 kbit/s. At 170 MHz, a 1,200 kHz channel with 250 mW reached 2,400 kbit/s, the maximum data rate specified in the applicable Wi-SUN FAN mode.[2]
Those rates are tiny beside modern 5G. That comparison misses the purpose. The target is not dense urban broadband; it is useful communications where ordinary broadband may not exist.
Compressing HD video into a constrained radio link
Increasing the radio rate alone was not enough. The group also redesigned how video crosses the link.
One technique is packet aggregation: combining multiple video packets so that less of the limited airtime is consumed by repeated protocol overhead. The system also controls transmission according to the importance of individual video frames, giving more protection and transmission priority to frames that are especially important for reconstructing the stream.[1]
Compressed video is structurally uneven. Losing one reference frame can damage the usefulness of many subsequent frames that depend on it. On a constrained and changing wireless link, treating every packet identically can therefore waste bandwidth. Prioritizing the information that matters most helps preserve a view that remains usable even when capacity is tight.
The drone flew at 25 and 50 meters
The test aircraft carried a VHF-band Wi-SUN FAN router, a camera and the video-transmission unit. Researchers flew it at altitudes of 25 and 50 meters. On the ground, a Wi-SUN FAN border router received the data and a receiver decoded, displayed and recorded the video in real time.[2]
The team reports stable HD 1,280×720 video at 10 fps for more than ten minutes in the 400 kHz configuration. It also demonstrated video transmission in the wider 1,200 kHz, 2,400 kbit/s mode.
Ten frames per second is not cinematic video. For search, reconnaissance and infrastructure inspection, however, the relevant comparison is often not streaming entertainment but whether responders can continuously see motion and changes instead of waiting for occasional still images.
Wi-SUN grew out of smart-grid networking
Wi-SUN—Wireless Smart Ubiquitous Network—grew from standards including IEEE 802.15.4g, standardized in 2012 for smart-utility networks. It was designed for low-power, long-range packet communications among devices such as smart meters, sensors and monitors.[5]
Wi-SUN FAN, or Field Area Network, extends that idea to large outdoor IPv6 mesh networks. Nodes can relay traffic for one another rather than requiring every device to reach a central base station directly. Kyoto University says the technology can support more than 20 relay hops in a multi-hop network.[2]
In July 2026, the Wi-SUN FAN specification was adopted as ISO/IEC/IEEE 32857:2026. For utilities and public infrastructure operators, that international-standard status matters because equipment is expected to interoperate across vendors rather than locking a network to one proprietary radio system.[6]
A drone can become a network node, not just a flying camera
That mesh capability is what makes the project more interesting than a point-to-point video link. A drone can behave as a network node, establish an IP connection automatically and potentially pass data through another drone or ground station when a direct path is unavailable.
Kyoto’s next-stage plan is to test multiple ground stations and drones forming a wider communications area through multi-hop links, with an eye toward a drone-delivery management network. In mountainous terrain, a vehicle hidden behind a ridge might eventually reach an operator through another node rather than needing a direct line back to one base station.[2]
Disaster communications are not a speed contest
In a major disaster, commercial communications can be weakened by power loss, broken fiber links, damaged sites or congestion. The requirement then changes. The goal is not to outperform normal urban broadband. It is to maintain enough independent communications capacity to deliver location, aircraft status, sensor readings and situational video.
Japan’s VHF-IoT framework has been developed with public and public-interest networks in mind. Its value proposition is therefore complementary: long propagation, self-operated infrastructure and resilience in places where cellular or Wi-Fi systems may be unavailable or fragile.
The kilometer-scale flying test has not happened yet
The most important limitation should remain visible. Kyoto says the VHF system is expected to support links beyond 10 km and has already demonstrated roughly 34 km of fixed-site video transmission. But the September moving-drone test itself covered about 50 meters.[3]
The next test is to combine the achievements: kilometer-scale distance, a moving aircraft, terrain and obstacles, autonomous network formation and stable real-time video—all at once.
The team says it will vary altitude, distance, terrain and obstructions in future field trials, while also working toward higher frame rates and more efficient video control. Potential applications include disaster assessment and search and rescue, infrastructure inspection in mountainous areas, remote logistics and drone operations outside cellular coverage.[2]
The 50-meter demonstration is therefore not the destination. It is the point at which three previously separate ideas—long-range VHF propagation, Wi-SUN mesh networking and bandwidth-conscious live video—have been put onto an aircraft and made to work together.
