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How to Block WLAN Interference
To provide additional unlicensed spectrum for high-speed data services, the FCC recently allocated 300 MHz of spectrum under the U-NII (Unlicensed National Information Infrastructure) label, which traverses frequencies from 5.15 to 5.35 GHz and 5.725 to 5.825 GHz.
Devices that use unlicensed spectrum range from garage door openers and cordless phones to WLAN equipment. For businesses, WLAN devices let enterprises provide mobility for their workers and increase productivity. But there's a price to pay with this wireless freedom: Because these devices use the same spectrum, they can interfere with one another.
Most radio devices, such as cordless phones and other analog devices, communicate over narrowband transmission, using little bandwidth and a high-power concentration. But narrowband transmission is susceptible to jamming and interference because the frequency it uses is static. Just as a jet airplane taking off can drown out a conversation, a higher-power device, such as an MRI machine, an RF (radio frequency) lighting system or even a garage door opener, can drown out a cordless phone if both are operating on the same frequency.
That's why WLANs instead use spread-spectrum technology--it maximizes bandwidth usage and minimizes interference with other devices. In contrast to narrowband, spread spectrum uses a wider frequency range than is needed to send data and uses less power. It's more difficult for other devices to intercept the signal because spread spectrum is spread out and looks like meaningless noise to narrowband devices. Wi-Fi, digital cordless phones and Bluetooth devices all use spread spectrum.
But even with spread spectrum, Bluetooth can still interfere with WLANs, because both use the same RF area. Bluetooth, the popular standard for wireless personal-area networks, uses a form of spread spectrum called FHSS (frequency-hopping spread spectrum), which eliminates the concept of channels and uses the entire 2.4-GHz spectrum (see "Bluetooth Spreads Out" chart). Instead of transmitting inside a specific frequency range, it "hops" around to different frequencies approximately 1,600 times a second. FHSS use eliminates interference because even if some of the spectrum is used by another device, the signal can be transmitted again on the next frequency selected with minimal performance reduction.
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