IP: fcvc rule mods 802.11

[David Farber <dfarber () earthlink net>]

-----Original Message-----
From: Charles Brownstein <cbrownst () cnri reston va us>
Date: Thu, 23 May 2002 12:01:34 
To: farber () cis upenn edu
Subject: fyi

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 May 23, 2002 05:22 AM
 
 FCC modifies rules governing 2.4GHz spectrum
 By Ephraim Schwartz
 
 IN RECOGNITION OF the growing significance of the unlicensed wireless band used by 802.11x and Bluetooth, among 
others, the FCC this week modified the rules that govern the 2.4GHz spectrum. The most significant result of the rule 
changes to FCC rule Part 15.247 will allow for the co-existence of wireless LAN devices with devices using Bluetooth.
 The changes will also mean that developers using the 2.4GHz band will not be limited to 11Mbps data rates and thus 
gives 802.11g, the recently adopted IEEE standard for these devices that perform at 54Mbps while being backward 
compatibility with the older 11MBps devices, the FCC seal of approval.
 The chairman of the Wireless Ethernet Compatibility Alliance (Wi-Fi), Dennis Eaton, praised the changes and said it 
will ultimately result in products with higher data rates and lower interference.
 The FCC has been extremely responsive to the industry and consumers. It recognizes how precious the spectrum is, said 
Eaton, in Mountain View, Calif.
 Under the previous rules, data rates were capped at 11Mbps in the 2400MHz-to-2483.5MHz (2.4GHz) band, while under the 
new rules there is no effective data rate limit. The ruling allows new digital transmission technologies such as OFDM 
(orthogonal division multiplexing), which have the higher data rates, to be used in the 2.4GHZ spectrum. Previous to 
the rules changes, OFDM could only be used in the 5.1GHz band.
 OFDM decreases what is called in the industry multipath fade. A phenomenon that is caused, especially indoors, as a 
single signal bounces off various barriers. By sending the same signal over multiple paths the signal power is less 
likely to fade or weaken.
 Meanwhile, the 2.4GHZ band has an inherently stronger signal with a longer range and can travel through walls better 
than the 5.1GHz band used by IEEE 802.11a. However, the 5GHz band allows more users to be on the same channel 
simultaneously. In the 2.4GHz band there is a maximum of three non-overlapping megahertz channels while in the 5GHz 
band there are 12 non-overlapping channels. This means more users can be co-located in the same spot not interfering 
with each other all using the same band, according to Eaton.
 Eaton also believes the FCC rulings will result in dual-band devices.
 The technology is headed toward dual-band chip sets in as soon as six months that support operation in both, like a 
dual-band chip set in a cell phone. By allowing the use of OFDM in both, it also allows for a lot of technology reuse, 
Eaton said.
 Reducing the number of hopping channels from a minimum of 75 to as little as 15 under the second rule change on 
adaptive hopping allows a Bluetooth radio signal to hop around when it is in the presence of Wi-Fi signal, Eaton said.
 The co-existence issue goes away, Eaton said.
 Laptop manufacturers can also be expected to more easily deploy notebooks with both Wi-Fi and Bluetooth built in.
 
 
 InfoWorld Editor at Large
 
 
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