Some history on unlicensed spectrum

In 1985, the FCC issued the nearly forgotten “Spread Spectrum Order” (should be called the Mike Marcus Order) making 234.5 Mhz of radio frequency spectrum available in three bands to any device certified by the FCC to conform to rules about the strength of the signal it transmitted. This order was slightly revised in 1990 after manufacturers raised questions about implementation details.

In 1997, the FCC added 200 MHz of spectrum from 5.15 to 5.35 GHz to the 125 MHz allocated in 5 GHz in the 1985 order and took back 25 MHz. Hence, it assigned 300 GHz in three 5 GHz U-NII sub-bands.

In 2003, the Commission added 255 MHz to the unlicensed pool, from 5.47-5.725 GHz, increasing the 5 GHz allocation to 555 MHz.

In 2014 the FCC added back the 25Ghz starting at 5.825 GHz that had been in the 1985 order,

In 2020, it added 45 MHz of unlicensed close to the upper edge of 5 GHz. It added another 1,200 MHz raging from the high end of 5 GHz to the lower end of 7 GHz (and everything in between) in its infamous 6 GHz order also in 2020.

Summing it up

Today, 700 MHz of spectrum in the 5 GHz band is unlicensed, as well as 1125 in the 6-7 GHz band. All in all, 2084.5 MHz has been assigned in the sub-millimeter wave bands; on average every nine years the FCC adds 400 MHz to the unlicensed pool. This is contrary to wild claims that you may have read.

In a few years, none of this is likely to matter much. The largest pool of contiguous unlicensed spectrum is the 7,000 MHz allocated in the 2013 Wi-Gig order. This band was first addressed by the FCC in a 1995 Report and Order, Docket 94-124. It hasn’t been heavily used because of technical limitations, but it may well be the future of Wi-Fi.

This spectrum is used in outdoor networks as backhaul for public Wi-Fi and other networks. Cambium Networks sells a 7.6 GBps device that does just this.

Millimeter wave Wi-Fi

The big hang-up for indoor use has been the belief that signals in this band can’t penetrate walls, but Airvine says it has solved this problem. They point out that interior walls are generally made of sheetrock, a material that is transparent to 60 GHz signals:

Common building materials include sheetrock (aka drywall), wood, glass, brick, stone, metal, and concrete.  Sheetrock is found in all modern office buildings, but the others will also be present in many cases.  A sheetrock wall is fairly transparent to 60 GHz signals and usually consists of two 5/8 inch pieces of gypsum separated by an air gap of about 4 inches.  That gap is often filled with soundproofing material, but these substances are not dense and are easily penetrated.  Places where you might run into metal include elevator shafts that are usually in the center of the building.  Glass can be divided into interior single-pane glass that is easily penetrated and exterior dual-pane glass with a metallic coating that is almost totally impenetrable to 60 GHz signals.  The latter is actually a good thing as it prevents interior RF from escaping the work area, and exterior RF from entering the work area.

Hence, 60 GHz solves two problems: it passes through walls but is stopped by exterior windows, limiting interference with neighbors. If Wi-Fi will kindly shift to 60 GHz indoors we won’t need to rob 5G and 6G of the spectrum they need for high-speed, outdoor mobile coverage.

Two ways to solve every spectrum problem

There are always at least two ways to solve every wireless congestion problem: we can throw more spectrum at it or we can do better engineering. Airvine appears to have taken the latter course.

We often say we have to use spectrum intelligently because they aren’t making more of it. But there is never a shortage of clever engineers who can figure out how to make use of available spectrum resources.

The FCC has done the heavy lifting by making a jaw-dropping band of 60 GHz available to the wireless industry for unlicensed use. All the industry has to do is seize the opportunity.

The 3 GHz band is uniquely good for mobile networks. It’s a shame to see it wasted on generic applications such as CBRS and in-home Wi-Fi when much more appropriate bands are available.