[femto]

I don't know the answer to why the 2.4GHz ISM band is at 2.4GHz, but I do know the answer as to why the 2.4GHz band was chosen over others. (I also know why the 61.5 GHZ ISM bad was chosen to be 61.5GHz.)

The choice of the 2.4GHz band needs to be seen in the context of 1995, when the first WLAN prototypes were built.

The lower limit was set by the desire to have the smallest antennas possible, to allow WLAN equipped devices to be portable. The higher the frequency, the smaller the wavelength, the smaller the antenna.

The upper limit was set by what was technically possible in 1995. The desire was to use cheap CMOS technology to build WLANs. In 1995, it was just possible to build a 2.4GHz radio in CMOS and research was in progress to build a 5GHz radio.

Consequently the first WLANs came out at 2.4GHz. Since then, WLANs have remained at that frequency for compatibility reasons (Metcalfe's law). 802.11a was defined to be 5GHz, because 802.11a came out after 802.11b and by then a 5GHz radio was possible in CMOS. Due to the dominance of 2.4GHz, 802.11g was later defined to be 802.11a at 2.4GHz, to take advantage of readily available 2.4GHz RF components, and allow 802.11a rates without having to have a dual-band radio.

61.5GHz was chosen for ISM because it is heavily attenuated by oxygen the atmosphere. This makes it unsuitable for long-range communications, but great for short range, since the high attenuation provides a degree of isolation between networks.

[gonzo]

Your post is full of errors.

CMOS radio didn't exist in 1995.

802.11a didn't come out 'after' 802.11b. 802.11a and 802.11b were ratified on the SAME DAY.

802.11g is a bit more than "802.11a in 2.4GHz".

[femto]

I'm looking at this from the point of view of the technology, rather than the standards, as that's where I was involved. From a technology point of view, 802.11b (particularly its 1 and 2Mbps modes) was developed before 802.11a, and so is "older". I know this, because I had the design for the world's first 802.11a modem on my computer's screen, and one of the professors had earlier bought an instance of a DSSS WLAN (essentially 802.11b) to see how it performed.

Granted the early "802.11b" radios might not have been CMOS. Their frequency was limited by what was technically possible in a consumer product though. I can't remember exactly what was in that "802.11b" WLAN. The 802.11a band was definitely set by what was possible in CMOS. The CMOS radio itself might not have existed in 1995, but planning was in progress and we had a pretty good idea of what was possible.

[gonzo]

802.11b was CCK modulation (and to a lessor extent PBCC, but that didn't take-off).

DSSS wasn't 802.11b, it was 802.11 (or half of it, the other PHY at that point was FHSS). 802.11b's 1Mbps and 2Mbps modes were DSSS, and pre-existed 802.11b. These (and the FHSS PHY) were all part of the 1997 standard. 802.11b and 802.11a came along in September of 1999.

Who is 'we'? Because you don't seem to know what you're talking about.

[femto]

"we" = the authors of this paper:

http://www.sss-mag.com/pdf/97_mmlan.pdf

Percival is an inventor on one of the fundamental WLAN patents (recently in the news):

http://www.google.com/patents/US5487069

Skellern and Weste were the founders of Radiata Communications, which was first to market with 802.11a, before being bought by Cisco.

http://www.computerworld.com.au/article/75649/cisco_acquires...

I'm one of the other authors. Maybe I'm wrong, in that the written history tells it differently, but I'm recalling what was said around the meeting table and across the office partition. I might be a bit loose with the terminology, but to me it's not packaged up neatly into standards, as it was a non-linear development process when I was dealing with it. --- Edit: fix URL + name

[coob]

Is there any need to be so uncivilly acerbic?

[andrewcooke]

after a little googling i can find references to papers pblished in 1994 and 1995 that refer to GHz CMOS components (eg A. Rofougaran et al., A 1 GHz CMOS RF Front-end IC with Wide Dynamic Range, ESSCIR, 1995, pp. 250-253; J. Carols and M. S. J. Steyaert, A 1.5 GHz Highly Linear CMOS Down Conversion Mixer, IEEE Journal of Solid-State Circuits, Vol. 30, 1995, pp. 736-742.)

i know nothing about this, so perhaps they are irrelevant, but on face value it seems like a 2.5GHz system could have existed in labs at that date, or at least was clearly going to be possible.

[gonzo]

many people were chasing the dream of CMOS radio in the mid-90s.

You could even make it work in the lab, but holding a design in production wasn't possible then.