More U-NII Channels Could Mean More Interference
Nov 19, 2003
Good news for companies that work in the unlicensed-spectrum bands. The FCC just
released an additional 255 megahertz in the 5.470 GHz-5.725 GHz band for
unlicensed devices. Those who can take advantage of this development include
carriers and service providers that support unlicensed National Information
Infrastructure (U-NII) devices, including radio LANs operating under Part 15 of
the FCC's rules. The new spectrum also should help promote broadband usage in
rural and underserved areas via wireless ISPs that are using unlicensed spectrum
as their transmission mode.
A downside to making more spectrum available is the increased possibility of
interference between a growing number of users. The FCC now will requires U-NII
devices operating in the 5.250 GHz-5.350 GHz and the 5.470 GHz-5.725 GHz bands
to use "dynamic frequency selection," which the agency calls a
"listen-before-talk mechanism," and transmit power control to provide federal
users of unlicensed spectrum and services with additional interference
protection.
The agency also adopted a notice of inquiry and notice of proposed rulemaking to
gather comment on what it believes could be a new way to quantify and manage
interference among different services, including unlicensed ones. Calling it
"interference temperature," this proposed model for addressing interference
takes into account the actual cumulative RF energy from transmissions of
spectrum-based devices, and it would set a maximum cap on the aggregate of these
transmissions, the FCC says. In contrast, the current approach for managing
interference focuses on specifying and limiting the transmit powers of
individual spectrum-based devices as the chief way to prevent interference.
The NPRM seeks comment on various technical rules that would establish
procedures and use the interference temperature model on a limited basis in the
6,525 MHz-6700 MHz band and portions of the 12.75 GHz-13.25 GHz band. While
these band are used predominantly by satellite and fixed microwave services,
there could be a tie-in with increased usage in the unlicensed bands.
One Current Interference Buster
As any company that has spent at least thousands to sniff out the source of
interference to its wireless LAN will tell you, you can do it inexpensively, you
can do it easily, you can do it right or any combination of two. However, a new,
intelligent spectrum-management tool developed by Waltham, Mass.-based Cognio,
which deals in cognitive radio technologies for unlicensed-band wireless
solutions, may be changing that thought.
"The challenges in the unlicensed band have been in getting a grip on the
complete list of participants on the band, those things that disrupt and how to
overcome them," says Naresh Balinga, vice president of marketing. "This is the
ever-growing problem in the 2 GHz-to-5-GHz bands. As you see more deployment,
you'll see more congestion."
First hinted about in June, Cognio's product - now in prototype -- looks at the
physical RF layer, sees who is using it and then pinpoints them, which enables
the IT department to tweak its channels and to lock down the wireless LAN from
intruders. It is based on Cognio's SAGE spectrum-analysis engine coupled with
its ASTRA platform. It will be tested with an unnamed group of early partners,
and it could go commercial next summer.
Because one unlicensed WLAN user cannot force an interfering WLAN user from
stopping operations, the only think it can do is tweak the parameters of its own
network. "[Using our product], the carrier gets the data (from the network user)
about problems within the WLAN environment, and it then decides how to mitigate
the problem, such as changing the channels an end user uses," Balinga says.
"This is akin to watering the lawn with the right sprinklers."
>>Naresh Balinga, [EMAIL PROTECTED]<<
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