Current developments in Wi-Fi spectrum

The price of continuing Wi-Fi activity is eternal vigilance

Current developments in Wi-Fi spectrum
Credit: Christiaan Colen

The allocation of radio spectrum is a fiercely contested matter. Government regulators—the FCC in the U.S., OFCOM in the U.K., and others—manage spectrum as a national resource. They seek to balance the needs of various groups, including cellular operators, government users, scientific and amateur radio groups. And, of course, they represent the public both directly and via their political masters.

Industries that depend on access to spectrum must work hard to ensure continuing access, and they must head off proposals for new services that might cause interference. As established users of the 2.4 GHz and 5 GHz bands, here are some of the areas where the Wi-Fi industry is active today, working with regulators.

The main concern in 2.4 GHz is with some spectrum allocated to Globalstar, a U.S. company. This is at the edge of the current band in what would be channel 14. Over recent years, Globalstar has repeatedly sought to build out commercial service. Its latest proposal would use this spectrum, originally intended for satellite downlinks to mobile phones, for terrestrial LTE networks. The main concern in the Wi-Fi industry is that any new service should not interfere with adjacent, existing Wi-Fi communications at the top end of the band.

Threats and opportunities for Wi-Fi

In the 5 GHz band, there are several opportunities and threats for Wi-Fi. We talk of 5 GHz as a whole, but of course it is made up of a number of sub-bands.

At the low end of the band, 5150-5350 MHz (UNII-1, UNII-2A), recent developments are encouraging. The rules in the U.S. are stable, and other regulators, including Canada and the U.K., are looking to loosen indoor-only and transmit power restrictions to allow broader Wi-Fi applications.

But the middle part of the band, 5350-5470 MHz (UNII-2B), where we had hoped to fill in a gap between existing Wi-Fi channels, now appears to be closed to Wi-Fi. A number of other users—earth observation satellites, government radars and drone communications—have made strong claims for this band. This is a pity because if Wi-Fi gained access to the channels between 64 and 100, more of the wider 40 and 80 MHz Wi-Fi channels could be used.

From 5470-5725 MHz (UNII-2C), Wi-Fi is allowed in most countries subject to Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC), with some exceptions around 5600-5650 MHz for Doppler weather radars. DFS is a spectrum-sharing technique where a Wi-Fi transmitter, on detecting a radar, is required to leave the channel to avoid interference. It works well, but some early Wi-Fi equipment could be misconfigured by the installer to use DFS channels without enabling DFS, and there have been documented cases of interference under these circumstances.

Strong direction from the Wi-Fi Alliance and recent actions by the FCC and ETSI mean this misconfiguration should no longer be possible. Nevertheless, meteorological radar operators continue to report that they suffer from interference in this band—for which they blame Wi-Fi—and to press regulators for actions to restrict its use.

The high end of the band, from 5725-5850 MHz (UNII-3) is allowed in the U.S. There are signs that other regulators may open up this band: OFCOM in the U.K. is moving in this direction. The incumbents are satellite fixed links.

And at the end of the 5 GHz band, from 5850-5925 MHz, there are opportunities for more Wi-Fi usage. This spectrum was reserved 10-20 years ago by U.S. and European regulators for vehicle-to-vehicle and road tolling communications. Since there are safety and economic aspects to these uses, it was made a dedicated band and protocols were developed under IEEE 802.11 for Dedicated Short-Range Communications (DSRC) as a variant of Wi-Fi. But the auto manufacturers have been very slow to roll out equipment, so the broad Wi-Fi industry has gone back to the regulator to see if there are opportunities to share this band and use it for Wi-Fi in places where DSRC is not active. It is early in the process, but we may see some sharing opportunities here.

The future of the Wi-Fi spectrum

The overall picture for existing Wi-Fi spectrum is stable. Challengers would like to restrict usage in some bands, but regulators are mindful of the great amount of data carried by Wi-Fi and are unlikely to take back what has already been allocated.

However, there is little room for growth in the existing spectrum regime. Many point to the congestion already seen in the 2.4 GHz band and suggest we will soon see similar issues at 5 GHz, as usage intensifies. The Wi-Fi Alliance sees the need for an extra 500 MHz to 1 GHz of spectrum by 2020, and possibly 1.3 to 1.8 GHz by 2025, to keep up with demands for unlicensed communications. Industry participants are already working with regulators to identify expansion spectrum and avoid this coming crunch.

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