Optical Spectrum (> 3 THz) - WRC-12 to consider procedures for free-space optical links (by Fabio Leite, Deputy Director, BR)

ITU-R to deal with the next big step in data transmission through 'optical spectrum' in the greater than 3 THz (above 3000 GHz) bandwidth.

Delivery of broadband services
through optical wireless.

Activities in ITU-R (ITU Radiocommunication Sector)

The World Radiocommunication Conference (WRC) process is once again called upon in its consensus building capacity to address regulatory procedures in frequencies above 3000 GHz, including revision of the relevant parts of the ITU Radio Regulations.

The ITU Plenipotentiary Conference decided (see Resolution 118 (Marrakesh, 2002)) that world radiocommunication conferences (WRCs) can include in their agendas 'items relevant to spectrum regulation of frequencies above 3000 GHz and take any appropriate measures, including revision of the relevant parts of the Radio Regulations'.

WRC-07 adopted Resolution 955, which resolved that possible procedures for free-space optical links should be considered by WRC-12, taking into account the results of ITU-R studies covering at least sharing aspects with other services, a clear definition of the band limits and the measures to be considered if allocations to various services in the Radio Regulations above 3000 GHz are considered feasible.

WRC-12 1.6 will therefore address possible procedures for free-space optical links, taking into account the results of ITU-R studies, in accordance with Resolution 955 (WRC-07).

ITU-R Study Group 1 (Spectrum management) has been the responsible group carrying out the preparatory studies on free-space optical links.

Because emitters used in near-infrared, free-space links have extremely narrow beam-width, and terrestrial emitters can only cause interference over very short distances, cases of terrestrial interference will be very rare and easily resolved on a local basis. Moreover, interference between inter-satellite links would also be rare due to directed and narrow beam-widths, and the vast geometry of space.

In summary, no evidence has been provided that interference between free-space optical systems is a concern. Existing ITU-R Recommendations and Reports, e.g. Report ITU-R F.2106 - 'Fixed service applications using free-space optical links' sufficiently address free-space optical links.

Implementation aspects

Industry is deploying free-space optical systems for different applications. They provide high security, low cost, low power, and high transmitting rates. Optical links are suitable for 1–2 Gbits/s rates over distances in the range of 1–5 km.

Some applications use single high-brightness LED with a cheap loupe lens which creates a bright narrow beam that can stream DVD-quality video over neighbourhoods.





Photocredits: Wikipedia

Optical signal propagation in free space is affected by atmospheric turbulence and pointing errors, which fade the signal at the receiver and deteriorate the link performance.

Free-space optical communication between satellites networked together can permit high data rates between different places on Earth. The use of optical radiation as a carrier between the satellites permits very narrow beam divergence. Due to the narrow divergence and the large distance between the satellites, pointing from one satellite to another is difficult. The pointing task is further complicated by vibration of the pointing system caused by tracking noise and mechanical impacts.

In the future, broadband wireless access systems, free-space optical links will be a promising system to provide point-to-point line-of-sight networks.


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