White-Space Wi-Fi

 By: Christopher C. Davis

On September 23, the FCC officially published its guidelines to allow the use of “white-space” in the television radio spectrum for wireless communication. Publications such as the New York Times and PC World have been quick to point out the advantages of range and speed that such white-space devices could bring over traditional Wi-Fi. Such signals will penetrate walls far more easily than traditional Wi-Fi and will have a significantly longer range. The real question, of course, is what might this technology mean for the future? My powers as an oracle are very limited and I am not a wireless engineer, but I started speculating as to the business opportunities inherent in the FCC’s decision and I am pretty excited. One quick caveat: this technology is not yet available and no one knows exactly how it will operate. Based on published reports, however, I am assuming that white-space wi-fi has a range of three miles. If that number turns out to be lower, then my map will have to be re-drawn. No one doubts, however, that the range is far greater than traditional wi-fi. Obviously, the issue of range has less to do with the transmission towers and more to do with the transmission strength of the user’s router or laptop. Since we do not yet know the strength of the upcoming devices, what I discuss now is speculation.

The traditional problem with downtown “hotspots” in cities is that it takes so many transmitters to cover a significant area and the signal is easily degraded by walls or other obstructions. White-space Wi-Fi solves both of those problems. The lower frequency signals are unhindered by normal walls and will cover a wide swath of area. Based on the three-mile estimate, I put together a quick map of the coverage needed for the city of Madison, Wisconsin. I wanted to provide double-coverage for the downtown area and some of the more densely populated locations. It looks like it will take approximately five transmitters to comfortably cover the entire city:

This looks like a great opportunity for a burgeoning networking company. The immediate advantages to both provider and user are obvious when compared to land-line service: 1) Not having to maintain physical wires; 2) Limited points of possible failure; and 3) Consistent high-quality service across the metro area. Those are major advantages as the country becomes more and more dependant on network connectivity.

There are certainly technology hurdles as well, however. No one yet knows how much bandwidth these white-space bands will carry. While there is significantly more white-space with which to work in a city like Madison, New York, with far denser population and less free white-space may simply run out of wireless bandwidth. iPhone users in San Francisco already face this problem. On the other hand, since these protocols are just now being hammered out and there are no legacy devices to support, engineers may be able to avoid this problem. Finally, since the available white-space will vary based on location, the transmitters and receivers will need to be relatively sophisticated in order to find and redirect to the correct channels.

For now, though, we can dream of a near future world where wireless bandwidth is widely available and unhindered by walls. Hopefully, white-space Wi-Fi can deliver that dream.


One thought on “White-Space Wi-Fi

  1. I strongly supported opening the white space to ISM use, but I think some of the claims of increased range are overstated. Going from 2450MHz to 550MHz buys you 13dB improvement in free-space path loss(FSPL). On one hand, that means you can do the same coverage with 1/20th of the power. OTOH, usually there’s some obstacle between the transmitter and receiver whose influence predominates over FSPL. Sometimes obstacles attenuate lower frequency less, yes, BUT sometimes higher frequencies are better b/c the smaller wavelengths can squeeze between obstacles. I agree w/ you that time will tell how much benefit the lower frequencies are when it comes to practical range.

    The biggest benefit to this IMHO is reducing congestion. 2.4GHz is jam packed. You can easily do 3 miles line of sight on 2.4GHz, but it can be hard to get decent throughput in a city b/c the band’s congested. 5GHz is much freer, but it’s a higher frequency with 7dB more FSPL than 2.4GHz. Uncongested VHF/UHF spectrum is very welcome.

    I don’t see any startup opportunities, though, b/c I believe people who make current Wi-Fi cards will simply make cards w/ the same chipsets but with downconverters to the newly-approved bands. OTOH, I hope someone will think up something disruptive that I haven’t even dreamed of.

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