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Spectrum Reality

January 16th, 2012 by | 3 Comments »

Now that a detente of sorts has been reached with Congressional efforts to muzzle some of the most egregious criminal sites on the Internet, attention came resume on some of the other pressing tech policy issues.The spectrum crunch was at the top of the agenda before the anti-crime discussion began in earnest in December (why is December always the time for monster tech policy issues?) and with all sides in agreement that Protect IP and SOPA can move forward without DNS filtering, it seems that attention will once again shift back to spectrum.

The mobile network providers and the House Energy and Commerce Committee are on one side of the current spectrum auctions issue, arguing that the FCC needs guidance from Congress about incentive auction parameters, while the Senate and the FCC say that the Commission should have a free hand in designing the auction. An additional issue concerns the extent of the FCC’s power to force broadcasters to different frequencies that will make more spectrum available for auction (the “repacking” issue.) A third issue concerns the forced sharing of channels by broadcasters, most of whom don’t require the full allocation they were given in the DTV transition. A number of broadcasters transmit 4 or 5 separate programs at a time, and all but the first tend to be low quality programs with limited appeal.

There’s plenty of spectrum available for current needs in rural areas, so the crunch is an urban phenomenon. Broadcasters have two reasons for holding out from the incentive auctions:

  1. They recognize that spectrum is becoming more valuable, so the longer they can hold onto their (free) assignment, the more money they can get; and
  2. Some broadcasters are interested in developing new services that target mobile devices such as mobile TV and even broadband.

In addition to the broadcasters, the incentive auctions are opposed by tech companies who want to reserve some spectrum for unlicensed use; this system is often called “Super Wi-Fi” or “Wi-Fi on Steroids” but  it doesn’t actually have much similarity with Wi-Fi.

Wi-Fi and its close cousin, Bluetooth, rely on sensing the air for traffic before transmitting. This is known as “Carrier Sensing” and it’s a very old and well established system that packet radio networks have employed since Aloha NET in the 1960s. Wi-Fi supplements CS with a two additional tweaks: A collision detection system and a collision avoidance system. (“Collisions” are what happens when two or more computers transmit packets at the same time in the same area on the same channel.) So the full name of the Wi-Fi technology is CSMA-CA, for “Carrier Sensing Multiple Access with Collision Avoidance.

CSMA-CA only works over short spans of time; when transmitters are separated from each other by more than 100 microseconds or so, it ceases to provide effective control and collisions become very frequent, which reduces the ability of the network to provide good, predictable service. This is the reason that cellular networks don’t use CSMA-CA. In its place, they use scheduling systems on exclusively licensed spectrum and systems of clever bit coding like the CDMA (Code Division Multiple Access) invented by Qualcomm and pervasively borrowed by 3G mobile broadband standards world-wide.

Unlicensed use of spectrum over large areas is a different problem than the one that Wi-Fi and Bluetooth solve, and it’s not a problem that we currently have a good solution for. This may be moot in many cases, provided that unlicensed spectrum deployment continues to follow the Wi-Fi model of small networks with limited power. There is spectrum available above 3 GHz that can be used for this purpose, and some Wi-Fi aficionados (Brough Turner for one) propose to add it to the unlicensed inventory.

White Spaces advocates maintain that the 700 MHz spectrum used for TV has unique benefits that the 3GHz+ freqencies don’t provide. We’ll examine those arguments in the next post.

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Reader Comments

  1. My sense is that there is less opposition from the average broadcaster to the concept of incentive auctions than auction proponents think. What they don’t like is the prospect of their coverage, perhaps, being cut in half in any channel repacking. I think some language in legislation on replicating current coverage would speed this up. Coverage would not have to be the same, as towers might move, but maybe something such as the same number of people being covered.

    Anticipating the next post, on 700 MHz I’d say that it does have unique characteristics — as does all spectrum — but those characteristics don’t make it that suitable for urban white-space use. Coverage is better, as the proponents say, but the downside is that interference travels further too. (That’s an issue with cellular frequencies, too.) The lack of white-space channels in urban areas compounds that use case.

    I’ve looked at white space as mostly a long-distance rural service. It will propagate better than 2.4 GHz but the narrower bandwidth means data rates somewhere between dial-up and 2.4 GHz, until channel aggregation becomes practical. For some very long paths it may be the only practical solution, but Wi-Fi won’t go away.

    I’m optimistic on it as a business, but I don’t think it will be a bigger business than Wi-Fi, as the FCC Chairman said in a recent speech. The whole Wi-Fi on steroids, or Super Wi-Fi stuff I have never gotten. Chuck Jackson has a good piece on here about that.

  2. I am a LPTV operator, one of the broadcast groups that, according to the new spectrum bill, have very few rights going forward, even failing to gain status as a broadcast licensee, though that is exactly what I am. I don’t think many Full Power broadcasters will be interested in an incentive auction, especially when you consider that it is the major markets that are desired. When you take out markets along the eastern seaboard, and those that require coordination with Canada and Mexico an auction is rendered toothless. The smart thing to do business-wise would be to cut a deal with any LPTV operator willing to part with spectrum–it wouldn’t even have to be from auction proceeds, make a monetary offer and get LPTV out of the way. This would go a long way towards realizing the needed spectrum.

    Another thing is that until the architecture is adjusted to allow for a broadcast overlay component, congestion will always pop up…so the FCC can either allow broadcasters to take care of video congestion via a broadcast overlay or take forever trying to clear the band.

    You’re the smart engineers, help me out on this.
    bbandeveywheuh@gmail.com

  3. One other thing I need to address is the “free” label put on broadcasters.

    This from your article; “They recognize that spectrum is becoming more valuable, so the longer they can hold onto their (free) assignment, the more money they can get;”

    See material taken from Wikipedia: When the FCC held a lottery for cellular licenses in the early 1980s, many ordinary Americans got rich by winning the right to establish cellular systems in cities across America.

    So how many times have you said that the early wireless carriers received “free” licenses?

    I converted analog TV stations and the new digital equipment wasn’t free, nothing is “free”. As anyone that has ever been in the TV biz knows, there was a competing standard to 8-VSB that was more along the lines of OFDM–if the TV industry had adopted this standard we wouldn’t even be having this banal discussion. I received my early CP’s via a lottery and anyone else could have done the same. It seems a little trite to continue using the “free” term. If I give you a “free” CP are you going to go build a TV station?