The most surprising aspect of a recent story relating to Television Broadcast Whitespace (Television Broadcasting Incumbents Launch Pre-emptive Advertising Strike Against Portable Whitespace Devices) was that Television Broadcasters appear to be supportive of license-exempt Whitespace communications:
We also believe that there are ways to utilize spectrum through fixed systems that can offer the advantages of broadband to rural consumers without threatening viewers who rely on over-the-air television. - Excerpt from a letter by National Association of Broadcasters (NAB) and Association For Maximum Service Television (MSTV) to FCC Chairman Martin.
At most, I expected grudging acceptance by television broadcasters of the concept of License-exempt Television Broadcast Whitespace communications, with minimal cooperation. But, from the posting below, that actually isn't the case. But I was still hardpressed to believe "active" cooperation regarding Television Broadcast Whitespace until I had seen television broadcast organizations state that they "embrace" such a concept, in documents that are on official record. So, the posting below assumes new relevance, and explains that, with 802.22, not just why television broadcasters "aren't afraid" of License-exempt Television Broadcast Whitespace communications... but perhaps more importantly, how such communications will work and not interfere with continuing television broadcasting.
(Click below to continue the story.)
Carl R. Stevenson is President and Chief Technical Officer (CTO) of WK3C Wireless LLC, a consulting firm specializing in a variety of wireless communications related services. I've known of Carl for several years by reputation as a well-respected Amateur Radio Operator - WK3C and a key technical resource for Agere / Lucent Technologies (WLAN products since acquired / consolidated into Proxim) during the formative years of Wireless Local Area Networks (WLANs) leading to the successful standardization of WLANs into 802.11, and eventual codification of 802.11 interoperability into Wi-Fi.
Stevenson is the Chair of the Institute of Electrical and Electronic Engineers (IEEE) 802.22 (Wikipedia).
which is developing standards for "Wireless Regional Area Networks
(WRANs). Specifically 802.22 is developing standards for making use of
Television Broadcast Whitespace (unused television broadcast channels)
for Broadband Wireless Internet Access.
On July 29, 2007, Stevenson wrote an illuminating note to a private mailing list which I monitor, providing an illuminating "behind the scenes" look at the progress being made with 802.22, but also some surprising context about the (surprisingly positive) "politics" of dealing with incumbent television broadcasters, whose "spectrum" 802.22 is designed to use. Stevenson's note, and some followup comments from a private email conversation are reproduced below, in whole, by permission. No content editing was done - only formatting changes.
Stevenson wanted me to emphasize that in this note, he is "speaking in this instance as an individual, not in an official capacity".
(Stevenson's note to the mailing list begins.)
From: "Carl R. Stevenson" <wk3c@wk3c.com>
Date: July 29, 2007 7:32:02 AM PDT
IEEE 802.11 (a.k.a. Wi-Fi) was designed and intended as a LOCAL Area Network. The fact that it is being "stretched" beyond that in an effort to provide longer range communications is evidence of the need for more appropriate spectrum (below 1 GHz) for longer range broadband access. Of that, I don't think there is any doubt.
And, I agree that a suitable amount of unlicensed (or at least non-exclusive, very "light licensed") spectrum below 1 GHz would enable broadband access in more rural areas, where the population density is too low for a viable business case for wired solutions, where NLOS [Non/Near Line Of Sight] propagation is more the rule than the exception, where foliage penetration is an issue, etc.
WISPs are trying valiantly to provide broadband access in many such areas using IEEE 802.11, but to cover the same area at 2.4 GHz as at, say 450-700 MHz, will generally require 6-8x as many (or more) base stations and their associated backhauls.
This is why we started the IEEE 802.22 WG on Wireless Regional Area Networks (see http://www.ieee802.org/22), which is developing a Standard for wireless broadband access, targeting the "white space" that exists (and will exist after the DTV [Digital Television] transition is completed) in spectrum allocated to the TV Broadcast Service, using cognitive radio techniques (sensing, geolocation, and "intelligence") to allow the deployment of fixed point-multipoint broadband access service on a non-interfering basis to licensed service, using geographically unused TV channels. (In the US, this will be in the range of TV channels 2-51 ... Channels above 51 have already been re-allocated, with some to go to public safety communications needs and the remainder to be auctioned - per law. In other countries the transition to DTV will vary, but from presentations I've made at various ITU-R and IEEE symposiums and workshops, there is considerable interest in what 802.22 is doing, with many regulators readily seeing how it could be of great benefit to their constitutents.)
*Congress* mandated that spectrum in the "recovered" channels 52-69 go, in part to public safety, with the remainder being auctioned off, with the proceeds of the auction intended to fund, at least in part, the "coupon" program for DTV settop boxes.
However, the FCC has proposed that the "white space" in the remaining TV band (2-51) be made available for unlicensed devices.
There are generally two views on how this "white space" could/ought_to be used:
1) IEEE 802.22's PAR (Project Authorization Request) limits the scope of the Standard to a fixed, point-multipoint, cognitive radio based solution to provide wireless broadband access (aimed at areas that don't have broadband and aren't likely to get it any time soon). Think "wireless DSL" or "wireless cable modem" type of service. No, it won't be 100 Mbps because the channels are only 6 MHz wide (like the laws of physics relating to propagation, Shannon's law hasn't been repealed), but it will be WAY better than the crappy dial-up service that people in these areas are generally limited to and it will be economically deployable, since a single base station will be able to cover a much larger area than could be covered from the same site at higher frequencies (nominal 30-40 km cell radius in average terrain with good site selection, YMMV [Your Mileage May Vary] depending on terrain, more if the BS [Base Station] were allowed more than 4W EIRP - and the MAC will handle round trip delays to 100 km for those cases where the site is exceptionally good and/or more than 4 W EIRP BS power is allowed).
This approach and scope was selected by the Study Group that crafted the PAR because the participants overwhelmingly believed that this would be the "best and highest" (and most appropriate in fitting the characteristics of the spectrum to an application) use of this spectrum.
People in urbanized areas generally have multiple options for broadband access and the wireless ones at higher frequencies are economically viable - in fact, in dense environments, you don't want signals that propagate TOO far because you need to achieve total system capacity through frequency reuse.
People from the (far) outer 'burbs out to as far into the "boondocks" as you wish to go don't - and can't be economically served with wireline solutions or wireless at higher frequencies - therefore, they are unlikely to get broadband "any time soon now" by those means.
And, I am happy to report that the broadcast community is supportive of what we're doing in 802.22 and they have, from the very beginning, been actively participating in the development of the Standard in a most cooperative and constructive way (in the form of active representatives from NAB [National Association of Broadcasters], MSTV [Association For Maximum Service Television], NABA [North American Broadcasters Association], Fox, and CBS). They have NOT been AT ALL "obstructionist" in ANY way. Yes, they have a vested interest to help make sure that we "get it right" and that our use of the spectrum will not cause widespread interference to TV reception, but that is perfectly reasonable. They have also on many occasions made valuable suggestions aimed at enhancing the success of the Standard.
2) On the other hand, some big corporations (Intel, Microsoft, and a few others) are pushing for "personal portable" use of the "white space," where devices like laptops and PDAs (ostensibly) would use the spectrum for "more Wi-Fi". (I am convinced that what they REALLY want to do is to use this spectrum to stream multiple HD streams from receivers, DVD players, etc. to multiple monitors around the home ...)
The other aspect is that, even with lower powers, the potential for interference posed by such devices, which will move around in an uncontrolled manner, will likely be indoors and close to victim TV sets, and will be essentially totally untraceable (how do you find them / identify the operator in an effort to resolve interference problems?) (On the other hand in the IEEE 802.22 system, all CPEs will be slaves to the BS and all BS's will be registered in a registration database to faciliate the identification and resolution of a source of interference should something malfunction.)
While they support 802.22 as a sharing partner, not surprisingly the broadcasters are opposed to the totally uncontrolled situation that such "personal portable" devices would present. (Remember, they are supporting - and actively, constructively participating in - the development of 802.22.)
I personally understand, and agree with, their concerns with, and opposition to, "personal portable" operation. I see it as a recipe for disaster in terms of interference (and if that genie gets out of the bottle I don't see how you can push him back in ...).
The white space in the TV bands is NOT "your father's Part 15 unlicensed band". There are licensed incumbents there who have a right to protection from harmful interference. To mix unlicensed and licensed operations in the same band requires considerably more order than the "may the best man win, food fight" regulatory environment that exists in the 900 MHz, 2.4 GHz, and 5 GHz unlicensed bands. The IEEE 802.22 Standard is being designed to meet the following (summary) requirements:
1) To operate on a non-interfering basis to the licensed services with which it will share spectrum.
2) To include coexistence mechanisms to promote equitable sharing between neighboring (or co-located) 802.22 systems and to maximize the effective use of the spectrum.
3) To provide a valuable, useful service, optimized to the spectrum and propagation conditions (where "value" is best quantified in terms of benefit to society and benefit to the economy)
I would argue that there are already multiple solutions operating in the higher frequency for low power, short range communications (802.11x, UWB, etc.) that can do this job. How many solutions (in different bands) do we REALLY need?
The TV band "white space" is "special" in terms of its propagation characteristics and should be used for the "best fit" application. Should we devalue the utility and societal benefit of the TV band "white space" and risk disastrous interference to the licensed services by allowing "personal portable" use and creating another "food fight" situation? I think not.
(Dave, I have "soap-boxed" more than just a bit in the interest of elaborating on this important subject, but I hope I also gave you an understandable answer to your original question ...)
Regards,
Carl R. Stevenson
President and CTO, WK3C Wireless LLC
(Chair of the IEEE 802.22 WG, but speaking in this instance as an individual, not in an official capacity)
(Stevenson's note to the mailing list ends.)
When I contacted Stevenson for permission to reprint his mailing list posting here in BWIA UHF, he offered some additional points:
Also, please note that NAB, MSTV, NABA, Fox, CBS (i.e., "the broadcasters") are long-time participants in the 802.22 Working Group. Their participation has, from the very beginning been cooperative, constructive, and beneficial... In NO way "obstructionist." They support our fixed use sharing, because
they can see how our architecture (point-multipoint, with CPEs being slaves to the BS), cognitive radio capabilities (both sensing and geolocation), etc. can successfully operate on (appropriate sets of) geographically unused TV channels without causing them harm.
Portable devices, on the other hand, as stated below are a totally different situation because of the inability to control the deployment, the problems with sensing and geolocation indoors, the increased interference potential when such devices operate indoors in proximity to TV receivers, cable boxes, etc., and the inability to "put the genie back in the bottle when it's found that he doesn't behave himself."
In summary, fixed use is doable and manageable as a sharing partner for TV broadcasting, portable/mobile use is a recipe for disaster.
Finally, please make it clear that my views/comments are my own and not an official statement by / on behalf of the WG.
My thoughts:
Given how incredibly jealously that television broadcasters have "guarded" "their" spectrum in previous decades, but having been forced to "surrender" large portions of it to cellular, commercial land mobile radio, and public safety (channels 70-83), public safety in some metropolitan areas (channels 14-20), and in 2009, commercial and public safety 700 MHz bands (channels 52-69), one could conclude that cooperating with the development of 802.22 is the lesser of two evils. While License-exempt Television Broadcast Whitespace communications "presumes" non-interference with continued television broadcasting... one can see why television broadcasters would strongly prefer a system like 802.22 that features centralized control with a single point of contact and more of a "professional" systems approach instead of "ad hoc" devices proposed by the "White Spaces Coalition".
The development of 802.22, and especially the cooperation of the television broadcasters in 802.22, bodes well for a new, and potentially highly effective and cost-effective option for Broadband Wireless Internet Access in rural areas.
By Steve Stroh
This article is Copyright © 2007 by Steve Stroh except for large portions of (indicated) content from Carl Stevenson. Excerpts and links are expressly permitted (and encouraged).
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