May 12, 2002

The "tragedy" of the radio spectrum commons?

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. Posted by dsifry at May 12, 2002 2:50 PM | View blog reactions

Comments

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.

Posted by: Bennett Kobb at May 13, 2002 5:45 PM

“[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

Posted by: Hamish MacEwan at May 13, 2002 10:04 PM