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Successful Ground-to-Satellite Laser Communications Applying Next-Generation Error Correction Codes, Mitigating Atmospheric Turbulence

October 22, 2025

National Institute of Information and Communications Technology
Nagoya Institute of Technology

Abstract

The National Institute of Information and Communications Technology (NICT, President: TOKUDA Hideyuki Ph.D.) and the Nagoya Institute of Technology (NITech, President: OBATA Makoto), collaborated with the Japan Aerospace Exploration Agency (JAXA), have achieved the world’s first successful demonstration of next-generation error correction codes, mitigating the impact of atmospheric turbulence on ground-to-satellite laser communications.
Atmospheric turbulence in ground-to-satellite laser links is known to cause fading, resulting in burst data errors. Error correction codes are one of the key technologies to mitigate such effects. In this experiment, we transmitted next-generation error correction codes with high correction capability (5G NR LDPC and DVB-S2) and successfully corrected burst data errors caused by atmospheric turbulence in the laser link. This result confirmed that both codes can significantly improve communication quality compared to conventional schemes.
This achievement is expected to contribute to the practical implementation of ground-to-satellite laser communications by applying these codes.

Achievements

Figure1 Experimental Setup of Data Transmission with Next-Generation Error Correction Codes
NICT has been conducting research and development to implement practical ground-to-satellite laser communications. NICT recognizes overcoming atmospheric turbulence as one of technical challenges for the practical implementation. To address this challenge, NICT has carried out ground-to-geostationary (GEO) satellite laser communication experiments using NICT’s 1-meter optical ground station and JAXA’s Laser Utilizing Communication System (LUCAS) onboard the optical data relay satellite, in order to investigate the impact of atmospheric turbulence on communication quality.
This investigation revealed that atmospheric turbulence causes fading lasting from several milliseconds to several tens of milliseconds, which generates burst data errors. These errors lead to degraded and unstable communication quality. Currently, two approaches are available to overcome these effects: optical compensation schemes and error correction codes. Focusing on the advantage of eliminating control systems of optics, NICT adopted error correction codes. We have been working on a plan to demonstrate error correction using next-generation codes with higher correction capability than conventional Reed-Solomon codes, including 5G NR LDPC for 5G applications and DVB-S2 for satellite broadcasting.
In this experiment, NICT, in collaboration with NITech, conducted data transmission with next-generation error correction codes, including 5G NR LDPC and DVB-S2, using a 60 Mbps downlink on the ground-to-GEO satellite laser communication link between NICT’s 1-meter optical ground station and LUCAS. Utilizing NICT’s experiences acquiring atmospheric turbulence, the parameters involved with interleaving method and error correction code were optimized to address burst errors caused by fading.
Analyzing this experimental data successfully demonstrated the correction of burst data errors caused by atmospheric turbulence-induced fading, marking that the world’s first confirmation that 5G NR LDPC and DVB-S2 can significantly improve communication quality compared to conventional codes. These advanced codes not only offer high error correction capability but also are expected to assist practical application in ground-to-satellite laser communications due to achieving easily implementable hardware and potential interoperability with future 5G communication systems.

Future Prospects

This achievement leads to the improvement of communication quality for ground-to-satellite laser links and accelerates their practical implementation. It also enables applying existing terrestrial 5G communication protocols and satellite broadcasting standards to space communication network system. In the future, this technology is expected to play a key role in ground-to-satellite laser communication systems.
This work will be presented on October 28, 2025 (Tuesday), in the International Conference on Space Optical Systems and Applications (ICSOS) 2025, a leading international conference on space optical communication systems.

Appendix

Error correction codes
Data errors may occur due to the influence of the communication channel or equipment in data transmission phase. Error correction codes are additional codes appended to the original communication data to correct such errors. In the area of communications, forward error correction (FEC) is commonly used to detect and correct data errors. One of key parameter for error correction codes is the coding rate (*), which was adjusted in this experiment to enhance error correction capability.
(*) Coding rate = (Amount of original data) / (Total amount of original data plus error correction code data).
Atmospheric turbulence and fading
A phenomenon in which the optical wavefront becomes distorted due to factors such as temperature changes, variations in the atmospheric refractive index, and convection and turbulence caused by wind. In ground-to-satellite laser communications, atmospheric turbulence causes received optical power fluctuations, leading to degradation of communication quality and even signal outages. The phenomenon is known as fading. Since the atmospheric refractive index is constantly changing due to random wind variations, predicting atmospheric turbulence is extremely difficult.
5G NR LDPC
In the fifth-generation mobile communication system (5G New Radio: 5G NR), LDPC (Low-Density Parity-Check) codes have been adopted as error correction codes to achieve high-speed and highly reliable communication. LDPC codes offer error correction capability to approach the theoretical limit known as the Shannon limit. Furthermore, LDPC decoding algorithms are well-suited for parallel processing, making them ideal for meeting the low-latency and high-throughput requirements of the 5G physical layer.
DVB-S2
DVB-S2 (Digital Video Broadcasting - Satellite, Second Generation) is the second-generation digital transmission standard developed for satellite broadcasting. It adopts a powerful error correction scheme called concatenated coding to improve transmission efficiency and error correction capability. Furthermore, it supports adaptive modulation and coding, allowing the modulation scheme and code rate to change dynamically according to the conditions of the satellite broadcasting radio propagation channel. As a result, DVB-S2 achieves up to approximately 50% improvement in spectral efficiency compared to the first-generation DVB-S standard.
NICT’s optical ground stations
Optical ground stations, equipped with a reflective-type 1 meter aperture telescope. These optical ground stations are installed at three NICT locations: Headquarters, the Kashima Space Technology Center, and the Okinawa Electromagnetic Technology Center. These stations are capable of tracking moving objects such as Low Earth Orbit (LEO) satellites and HAPS (High-Altitude Platform Stations). In this experiment, the 1-meter optical ground station at NICT’s Okinawa Electromagnetic Technology Center was used to conduct a ground-to-satellite optical communication experiment with LUCAS, an inter-satellite laser communication system onboard a geostationary satellite.
Laser Utilizing Communication System （LUCAS）
The Laser Utilizing Communication System (LUCAS) is an inter-satellite laser communication system onboard GEO satellite (at an altitude of 36,000 km) to relay communications between earth observation satellites in LEO orbit (at altitudes of 200-1,000 km) and ground stations. This greatly expands the real-time communication coverage between earth observation satellites and ground stations. Furthermore, by replacing conventional radio-based inter-satellite relay links with laser links, LUCAS enables a significant increase in communication capacity, supporting the advancement and higher resolution of earth observation satellites.
Interleaving method
An interleaving method is a digital processing component that rearranges the order of transmission data according to a predefined rule on the transmitter side. This process disperses burst data errors into a pattern closer to random errors, thereby improving the error correction capability of error correction codes. When applied to ground-to-satellite laser communications, interleaving can randomize burst errors caused by atmospheric turbulence, offering significant mitigation effects. The interleaving method has a parameter named as depth. Increasing the depth extends the correction period for fading. In this experiment, the depth of interleaving method was optimized based on the anticipated duration of fading caused by atmospheric turbulence.

Technical Contact

KOTAKE Hideaki
Space Communication Systems Laboratory
Wireless Networks Research Center
Network Research Institute
National Institute of Information and Communications Technology

OKAMOTO Eiji
Professor
Electrical and Mechanical Engineering Group
Nagoya Institute of Technology

Media Contact

Press Office
Public Relations Department
National Institute of Information and Communications Technology

Planning & Public Relations Division
Nagoya Institute of Technology