Glenn Fleishman posts a great
commentary on the recent discussion about the “tragedy of the commons”
of the 2.4 GHz space. Given some comments on the matter by Dewayne
Hendricks, member of the FCC Technology Adisory Council and chairman of the FCC’s Spectrum Management Working Group. Definitely worth a read – Glenn points out the real issues involved, the technology limitations, and the industry standards coming out designed to promote shared use of the spectrum.
This is an interesting thought experiment – will the success of the
2.4GHz spectrum (and any other unlicensed spectrum) fail due to its own
success? Will illegal amplifiers turn the spectrum into another
Citizen’s Band? Even without illegal amps, is it doomed to failure
because the density of devices will increase too quickly?
I don’t think so. But it does remain an open question – how much is
enough? In other words, as 802.11h and other standards that help to
reduce interference become more popular, at what density of spectrum do
even those methods fail? Surely there is a transmission power and
density for which the specrtum becomes unusable. The question is, can
technological advances outpace the bandwidth needs of the public? As
more bandwidth is available over the airwaves, whether by spectrum
allocation, frequency increases, or new standards for interoperable
devices, at what point will the spectrum be rendered effectively
unusable? To what extent is legislation or regulation needed here?
Maybe the answer lies in the fact that the unlicensed spectrum (2.4GHz,
used by 802.11b and others, and 5.3GHz, used by 802.11a), while
unlincensed, IS NOT UNREGULATED. Among other things, all devices have
to follow FCC Part 15 rules, which means that they must be approved by
the FCC before the manufacturers can offer them for sale. Perhaps the
key to saving the commons is to ensure that these devices are
interoperable and, well, for the lack of a better term, polite to other
users of the spectrum.
Of course, this would be an extension to the FCC’s regulatory capacity -
essentially asking it to endorse certain protocols at a layer above the
radio. However, I think that by focusing on protocols rather than
products, it (a) does not act anti-competitively, and (b) promotes
the public good (remember, WE own the airwaves!) by enabling more
functionality and usability of the spectrum we use. And if we are
smart, we can agree to a level of interference protection that all
higher level radio protocols can use, allowing for even greater
flexibility.
Think of it as a new layer, sitting between layers 1 and 2 of the
network stack – the new layer would provide for interference detection,
channel switching, and possibly even automated changes in the spread
spectrum algorithms to make sure that different devices, running
different higher-level protocols, would automatically detect each other
and not interfere with each other.
Related posts:
It sounds as if you’re proposing the “spectrum etiquette,” in the 1910-1920, 1920-1930, and 2390-2400 MHz bands for unlicensed Part 15 devices. It already exists, enshrined in the FCC rules. I proposed it in 1991. It may not be perfect, but it is an alternative approach. It permits devices of unlike manufacture to intelligently share the spectrum without having to exchange information. No manufacturers of unlicensed data communications products ever used it. That’s right — two of the three bands are unused for unlicensed data communications. 802.11b captured their investment. The FCC has now proposed to re-allocate these three bands, and likely to auction them. One of these bands (1920-1930 MHz) is used for enterprise-level cordless phone systems. Virtually all of the proponents of this etiquette were members of IEEE 802.11, by the way. Eventually we turned our attention to what is now 802.11a at 5 GHz.
“[1]Presentation to the Technical Advisory Council ([2]TAC) of the [3]FCC by [4]Vanu [5]Bose “[6]Software Radio: Enabling Dynamic Spectrum Management” and [7]David Reed “[8]How wireless networks scale: the illusion of spectrum scarcity.””
“Counterintuitive results from multiuser information theory, network architectures, and physics:
* Multipath increases capacity
* Repeating increases capacity
* Motion increases capacity
* Repeating reduces energy (safety)
* Distributed computation increases battery life
* Channel sharing decreases latency and jitter”
Highly recommended presentation suggesting that the cost of spectrum management by “exclusive property rights” mandated by the State outweighs the advantages we could obtain from a new model that acknowledges physics and the 70 years of receiver development since the regulatory model was adopted at the time of the sinking of the Titanic.
Also suggests that tragedy of the commons, desirable as it is as justification for those with a bleak view of human self-interest, is more counter-intuitive and less inevitable in WLAN than we might expect.
Hamish.
References
1. http://www.fcc.gov/realaudio/mt042602.ram
2. http://ftp.fcc.gov/cgb/dro/tac.html
3. http://www.fcc.gov/
4. http://www.vanu.com/
5. http://www.sds.lcs.mit.edu/~vanu/home.html
6. http://www.seas.gwu.edu/~cjackson/TAC/vanuinc-tac.pdf
7. http://www.reed.com/dprframeweb/dprframe.asp
8. http://www.seas.gwu.edu/~cjackson/TAC/Spectrum%20capacity%20myth%20FCC%20TAC.pdf