ITU adopts new standard for free-space optical links in mobile networks
A new ITU recommendation sets technical specifications for terrestrial free-space optical systems designed to support short-range mobile backhaul infrastructure.
The International Telecommunication Union (ITU) approved Recommendation ITU-T G.641 on 29 November 2025, establishing technical specifications for terrestrial free-space optical (FSO) communication systems used in mobile backhaul networks. The recommendation was published on 5 March 2026, as part of the ITU-T standards series on transmission systems and digital networks.
The document defines optical interface specifications for short-range free-space optical links that connect network infrastructure without the need for physical fibre cables. These systems use light beams transmitted through the air to carry high-speed data between network nodes, offering an alternative solution where fibre deployment is difficult or costly.
The standard focuses on point-to-point terrestrial FSO systems designed for mobile backhaul, which connects base stations to the core telecommunications network. The recommendation specifies interface parameters for both the free-space optical link and the fibre interfaces that connect network equipment to the optical transmission system.
The specification uses a so-called ‘black link’ model, where two networking elements convert signals between fibre and free-space transmission. In this architecture, optical signals travel from a fibre interface, pass through a free-space optical path, and are then converted back into fibre signals at the receiving end.
The recommendation also defines a range of technical parameters required for reliable optical communication, including transmitter power, beam divergence, alignment tolerance, signal attenuation and latency. Performance indicators such as bit-error ratios and optical signal-to-noise ratios are included to ensure stable data transmission.
Environmental factors affecting free-space optical communication are also addressed. The document highlights how atmospheric conditions such as fog, rain, snow and turbulence can influence signal quality and link reliability, and provides models for estimating attenuation caused by these effects.
By setting common technical specifications, ITU recommendation aims to support interoperable and reliable deployment of free-space optical links, which are increasingly used to expand high-capacity connectivity in mobile and broadband networks.
