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To: Raymond Duray who wrote (8344)	9/5/2000 1:36:38 AM
From: axial	Respond to of 12823

Hi, Ray - Well, my take on it was the old good news/bad news scenario. Though some investors will have visions of sugarplums dancing in their heads, the 2.4 GHz playground just got a lot more crowded. While there is a business opportunity for many companies, the FCC decision will have the effect of degrading the efficacy of the spectrum for any user: IEEE 802.11a, 802.11b, Bluetooth, HomeRF, and any number of unlicensed walkie-talkie devices by any number of manufacturers. Frank posted a question, a while back, on the likelihood of interference in the 2.4 GHz spectrum, when using an in-building enterprise LAN. In the short dialogue that ensued, I made reference to the Master's thesis of Timothy Shephard at MIT: his paper(s) can be accessed here, for anyone who wants a head-spinning dive into the mathematical basis of the probabilities of interference: citeseer.nj.nec.com But his references were to interference in managed networks; the low probability of interference that he assigns is subject to revision in an unmanaged LAN/MAN environment. A while back, I read an article, which you later referenced, Ray, which stated (I'm recalling this from memory, so I may be wrong, here) that data transmission rates in 802.11a would drop by around 30% when a collision necessitates a retransmission. I would expect approximately the same result in 802.11b, and HOME RF, unless a standard permits the transmission of damaged data. Reading the minutes of some IEEE meetings lately, the possibility of just such a mechanism has been discussed, but it brings with it its own set of problems. My point is, in the 2.4 GHz spectrum, I would be leery of accepting promised throughput rates in areas with busy spectrum. OTOH, present users of the 'net run into delayed or lost packets frequently: this whole argument may be a distinction without a practical difference. The decision of the FCC (and they certainly appear to have researched the matter thoroughly) may turn out to be the right one. Whether it's IEEE, ITU, Bluetooth, whatever, you run into references by engineers who are worrying about interference at 2.4 GHz. Will it turn out to be, like Y2K, a non-event? I don't know. I'm just now doing some research on Home RF: to what extent transmission will be affected by a packet-header collision, is unclear. In a larger sense, this turnaround by the FCC reflects the business, and investment uncertainties introduced by unmanaged spectrum allocation, in comparison to say, Europe. "Let the market decide" is a fine rallying call, but I wonder how the business community, and the investment community (never mind the end user) will feel if the FCC continues to re-draw the yardlines, and move the goalposts, in spectrum allocation. FWIW ;-) Regards, Jim

To: Raymond Duray who wrote (8344)	9/5/2000 3:17:31 AM
From: axial	Read Replies (1) \| Respond to of 12823

Ray - A quick comparison of the various short-range 2.4 GHz standards before the FCC decision... zdnet.com The article is of interest, too. Regards, Jim

To: Raymond Duray who wrote (8344)	9/7/2000 11:27:57 AM
From: axial	Respond to of 12823

Re: Interference @ 2.4 GHz: one last article... Coexistence Issues in the 2.4 GHz IDSM Band Sep 06, 2000 Rich Ditch, Motorola As more devices are introduced in the unregulated 2.4 GHz band, more people are expressing concern that devices built on different standards or industry specifications will degrade the performance of other devices or experience reduced performance themselves. This is an unfortunate reality of an unregulated band, and there can be no advance guarantees for any device operating in the 2.4 GHz ISM band. At least two groups are trying to address the concerns of Coexistence: IEEE 802.15.2 Coexistence, and Bluetooth 2 Coexistence Group. Under the IEEE 802.15 PAN group, a Task Group (802.15.2) has been formed with an objective of creating Recommended Practices for the Coexistence of wireless devices operating in the 2.4 GHz ISM band. TG2 is modeling MAC and PHY layers of Bluetooth, 802.15.1 (i.e., Bluetooth 1.0), and 802.11 standards and will perform analyses of the amount of degradation to be expected between logical pairs of potential interferers. In a parallel effort, actual physical tests of prototype or commercial products will be conducted to verify modeling results. TG2 meets as part of the bimonthly 802 process, plus TG2 has regular biweekly conference calls to move the work forward. All 802.15.2 sessions are open to anyone attending the 802 sessions, and their results are made public on the IEEE 802.15 web site. Follow links for TG2 for current documents, leaders, Call for Proposals, upcoming meetings, etc. The Bluetooth Coexistence Group is a similar activity being driven by Bluetooth promoter company concerns for a viable product. The focus of this group is to determine what degradation Bluetooth devices may encounter in real world use where other 2.4 GHz devices are operating. The group is also modeling the MAC and PHY layers of Bluetooth, 802.11, HomeRF, and other 2.4 GHz standards. Time and frequency interference studies are being generated, based on numerous assumptions for traffic models, loss, and operating environments. The Bluetooth group has closed participation as determined by the Bluetooth SIG. It is expected that results will influence designs of Bluetooth devices to make them more robust. Results will also be generalized and made available in time on the public side of the Bluetooth web site: www.bluetooth.com. anywhereyougo.com