Free-space optical Ethernet communications error-correction technology


Free-space optical Ethernet communications error-correction technology developed by Sony Computer Science Laboratories, Inc. (Sony CSL) has been documented as an Experimental Specification (Orange Book) of the Consultative Committee for Space Data Systems (CCSDS).


This technology was proposed by the Sony CSL SOL project in the Optical Communications Working Group (SLS-OPT) of the Consultative Committee for Space Data Systems (CCSDS), an international standards organization, as part of Common Technical Document Working Group Committee Activities of the Japan Aerospace Exploration Agency (JAXA).


This technology documented as an Experimental Specification improves the error-correction mechanism of the Small Optical Link for International Space Station (SOLISS). It has the following features.

  • Supports Ethernet-frame full-duplex communication

Ordinary Ethernet can be used as a Data Link Layer protocol by encapsulating the inner payload using Generic Framing Procedure (GFP) (ITU-T G.7041/Y.1303). As space development by private companies expands, the use of technology that is widely used on the ground instead of developing original protocols is beneficial from the viewpoint of improving compatibility and reducing development costs.

  • Deals with degradation in communication quality caused by atmospheric fluctuations

In contrast to communication systems that use optical fiber as transmission paths, the degradation of communication quality due to atmospheric fluctuations must be considered in free-space optical communications between satellites and ground stations. Here, the received level of the signal light fluctuates causing burst errors to occur, but this technology achieved burst-error resistance by arranging Reed-Solomon code, which is robust to burst error by itself, in product code form and interchanging the order of sending and receiving signals by block interleaving. In addition, further improvement in correction performance can be expected by iterative correction using the product code structure and by erasure correction. Reed-Solomon product code also excels in efficient use of power in error correction making it a scheme applicable to mounting on small satellites. 

Fluctuations in the received level of signal light can also affect the synchronization of received data. This technology is equipped with a synchronization protection mechanism based on SYNC markers designed so that synchronization can be stabilized even under such fluctuating conditions. It also enables the frequency components of the atmospheric fluctuations and communication signal to be separated by removing the low-frequency components of the communication signal. For low-speed communication signals, low-frequency components can be sufficiently removed using 8b10b code, and for high-speed signals, both low-frequency removal and code rate can be achieved by means of a frame synchronous scrambler.

  • Optimization for communication channel characteristics

Burst error length fluctuates according to atmospheric conditions between satellites and ground stations. The number of interleaved blocks is variable length in this technology, so sufficient protection can be provided even under conditions in which long burst errors can occur. On the other hand, given that the communication channel between satellites can be treated as a vacuum, decreasing the number of interleaved blocks can reduce error-correction latency. In addition to the communication signal itself, this technology is equipped with a transmission area for meta-information called sub-data. This area can also be used for dynamically adjusting the number of interleaved blocks according to communication channel characteristics.


Irving S. Reed and Gustave Solomon of Massachusetts Institute of Technology’s Lincoln Laboratory developed Reed-Solomon code in 1960. It was first used as an actual communication system in the Voyager project in 1977 and subsequently became the standard coding system for NASA satellites and probes. In the 1980s, Sony and Philips adopted Reed-Solomon code in the compact disk (CD) standard for music playback, and it continues to be used in DVD and Blu-Ray Disk products.

Sony CSL focuses on the similarity between errors in optical discs caused by fingerprints, dust, scratches, etc. and errors in optical communications between satellites and ground stations caused by atmospheric fluctuations. It develops optical communication terminals that apply error-correction technologies researched and developed by the Sony Group. With this Experimental Specification, we expect this technology to be publically released as a standard through the CCSDS documentation process and not as a proprietary standard and to thereby improve interoperability in space optical communication. Looking to the future, Sony CSL will continue its research and development efforts toward the implementation of high-quality space communication systems.



The Consultative Committee for Space Data Systems (CCSDS)


CCSDS 142.10-O-1


Generic Framing Procedure