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Why 2.4GHz? Chasing wireless history

indiegogo.com

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Re: Why 2.4GHz? Chasing wireless history

#21

Post by wwwtyro »

cmsmith wrote: post #18
jaytaylor wrote: post #12

Given that the FCC is funded by the taxpayers I find it frustrating that the FCC document archive is sitting behind a paywall-esque system. Is there a good reason for this? With all the money it costs to physically store and maintain the documents, I would imagine that they could instead scan and index them, and then put them up online and make them available to taxpayers for free, since we (the taxpayers) have effec…

It's the same reason that federally funded scientific research is only available in for-profit journals. Someone has to pay for the costs associated with publishing things, and the scientists/FCC don't want it coming out of their budget. Of course, the money being paid to access papers in for-profit journals is also coming from the government, just in a less efficient way.

The cost of publishing - especially written documents - has dropped to essentially free in the last two decades, though. I hear your argument from time to time, but it's a really hard sell these days.

Re: Why 2.4GHz? Chasing wireless history

#22

Post by 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.

Re: Why 2.4GHz? Chasing wireless history

#25

Post by hosay123 »

My (anecdotal) understanding was that it is due to the technologies available around the time the oven was introduced. In particular, the size of the horn was directly proportional to the wavelength employed. For purely practical reasons, the wavelength was naturally restricted to the range for which an efficient and practically sized horn could be produced: i.e. something a typical person could carry and install in their home, with a low enough draw that it didn't require three-phase power.

Re: Why 2.4GHz? Chasing wireless history

#26

Post by gonzo »

femto wrote: post #22

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…

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".

Re: Why 2.4GHz? Chasing wireless history

#27

Post by tingletech »

jaytaylor wrote: post #12

Given that the FCC is funded by the taxpayers I find it frustrating that the FCC document archive is sitting behind a paywall-esque system. Is there a good reason for this? With all the money it costs to physically store and maintain the documents, I would imagine that they could instead scan and index them, and then put them up online and make them available to taxpayers for free, since we (the taxpayers) have effec…

Their material seems to be in the national archives.

http://www.archives.gov/research/guide-fed-records/groups/17...

BCPI seems like some sort of copy service / a service for people who do not want to fly in and physically visit the archives.

Re: Why 2.4GHz? Chasing wireless history

#28

Post by femto »

gonzo wrote: post #26
femto wrote: post #22

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…

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".

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.

Re: Why 2.4GHz? Chasing wireless history

#29

Post by maaku »

rtkwe wrote: post #6

I always assumed those were set aside as unlicensed spectrum and that was why so many things existed along those bands. Probably also some propagation characteristics?

I think the Indiegogo is to find out why 2.4ghz was chosen over other possible bands.
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