Cable Technology Feature Article
White Spaces: Super WiFi, or Not?
By Barlow Keener, Attorney
Brough had some great observations about the limits for white spaces, both in terms of 1) the power and 2) the height limitations imposed by the FCC order and the physical limitations of the lower 56-806Mhz spectrum.
What are white spaces? White spaces are those white, fuzzy channels on TV between the channels you watch. With digital TV, the white spaces became available either for a) auction or b) “open commons” use, as some in the Internet world may think of the final decision. The FCC chose to open, somewhat, with a lot of restrictions, the use of white spaces to the public similar to how 2.4Ghz is open for use by WiFi (News - Alert) devices and microwave ovens or 900Mhz open for use by cordless telephones and baby monitors. The power rand height restrictions were hotly contested by those wanting to build devices and use the spectrum. Fred Goldstein, of Ionary Consulting, for example, suggested that the FCC height restriction of 75m over “average” terrain would prohibit those in mountain towns or other areas from receiving service.
Super WiFi. Many, including the FCC, call white spaces “Super WiFi.” Chairman Genachowski explained that Super WiFi is “WiFi, but with longer range, faster speeds, and more reliable connections.”
The reason the FCC coined the term “Super WiFi “ is because everyone has the image of TV channels 2-69 (54Mhz-806Mhz) going many miles and going through brick walls. The idea or image that TV white space signals that operate similar to 2.4Ghz WiFi will be able to go miles and miles and go through walls, unlike 2.4Ghz Wi-Fi which is blocked by walls, gets folks excited.
But we need to stop, and think. TV antennas are often around 1,000 feet tall, sometimes taller. The typical analog TV channel can blast 1350 kilowatts (that is “kilo” or 1,350,000 watts). Even digital TV channels blast at 300kw. An example: the power of a TV signal in Boston is from the FCC.gov DTV section:
The white spaces devices are a fraction of this TV power and are limited to 100 feet in height, for fixed radios. White space signals will not go through building walls as many imagine.
Did TV signals blast through brick walls? Recall that in the days of old (1960-2000), TV signals did not “blast” through brick walls like Superman. Every home in the country had the ubiquitous, huge TV antenna on the roof well above the walls. Why was the antenna a) on the roof and b) huge? The TV antenna was on the roof because the lower frequencies 50-806Mhz could not penetrate blocks, masonry, and other objects. The VHF (Channels 2-13) TV antenna was big because the lower frequencies on which VHF operated -- 50-216Mhz -- have bigger wavelengths than 2.4Ghz and thus require larger antenna elements of the type that has virtually disappeared from our home roof.
For white spaces, under the Sept. 23, 2010 order, WISPs can use up to 4watts EIRP for a fixed radio (not the power used by TV stations to blast through walls which is 1,000kw or 1,000,000w) and for the portable device that we are going to carry around, the power limit is 40mw (milliwatts = 1,000th of a watt, so 40mw = .04w) adjacent and 100mw (=.1w) when not adjacent to another to a protected TV channel. This power restriction is only slightly more than the typical 250,000,000 WiFi access points now typically generating 20 mw each with an average range of 300 sf.
The FCC Sept. 23, 2010 order limits fixed white spaces antennas to a maximum height of 100 feet (30 meters) above ground level, not the 1000 feet height typically occupied by TV station antennas.
The big question. The limitations of height, power and low spectrum will, if we are lucky, be equal to the delivery of service you now experience with Wi-Fi. But it will not be better, it could be worse. The requirement for larger antennas needed for 50Mhz-700Mhz in the personal devices may be tricky.
I am not a technologist, but an attorney, so I am sure we will see some amazing innovation in this area. The white spaces order is a great step forward to making efficient use of a public property, spectrum. It is a great experiment toward determining if a new type of shared spectrum radio will work where the radio contacts a data base to determine if a channel is not occupied by another provider.
The real question, however, is: if the lower spectrum 50Mhz to 700Mhz spectrum imitations (described above) combined with the FCC’s white spaces order restrictions on antenna height and radio power, will there be something far less than “Super WiFi?”
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Edited by Tammy Wolf