Amended FCC rules will help wireless LANs, alliance says

Amended FCC rules will help wireless LANs, alliance says
By John Walko, CommsDesign.com
May 22, 2002 (9:26 p.m. EST)
URL: http://www.eetimes.com/story/OEG20020522S0018

The head of the Wireless Ethernet Compatibility Alliance has endorsed the amendment of rules made last week by the Federal Communications Commission, saying they will allow better use of spectrum by wireless LAN technologies.

“This is a very solid ruling by the FCC,” said WECA chief Dennis Eaton. “It appropriately allows better use of the valuable spectrum while allowing innovative technologies to improve performance. The FCC is to be commended for each element of this decision.”

The amendment will permit new wireless LAN technologies to operate in the 916-MHz, 2.4-GHz and 5.7-GHz frequencies under the existing rules for spread-spectrum systems.

The ruling makes three changes that improve usage of the spectrum: it allows new digital transmission technologies; reduces the number of required channels for frequency hopping spread-spectrum radios; and eliminates the processing gain requirement for direct sequence spread-spectrum (DSSS) systems .

The amendments allow digital transmission technologies like OFDM (orthogonal division multiplexing) in the 2.4-GHz (2,400-to-2,483.5-MHz) band, the technique that will be used by the next generation of Wi-Fi technology with data rates of up to 54 Mbits per second.

The changes in adaptive hopping will now allow a frequency hopping technology, like Bluetooth, to temporarily spread its energy across a reduced number of channels, allowing it to avoid operating in the same part of the band as a nearby Wi-Fi signal. The number of hopping channels can be decreased from 75 to as few as 15 on a temporary basis for frequency hopping technologies like Bluetooth.

By eliminating the processing gain requirement for DSSS systems, which had limted the types of modulation techniques manufacturers could use in their equipment, the amended rules give hardware vendors more flexibility and opens a path to higher data rates.

The new rules will allow the use of as few as 15 hopping channels for frequency hoppin g spread-spectrum systems (FHSS) in the 2.4-GHz band. These systems will be able to use channel bandwidth up to 5-MHz wide, but will need to reduce their output power to 125 mW if fewer than 75 hopping channels are employed.

This will allow new FHSS systems to avoid occupied channels and in this way avoid the interference that mars current generation systems.