LTE-U vs. WiFi fight gets closer to a settlement

Broadcom brief the FCC on the last sticking point slowing spectrum-sharing agreement

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FCC filings by Broadcom reveal the chip-maker is still feeling bullish about the controversial LTE-U (LTE-Unlicensed) push.

In a world of squeezed spectrum, US carriers are keenly watching the development of LTE-U, because it would let them borrow Wi-Fi frequencies if they're not being used.

That idea is controversial because of fears that LTE-U might degrade Wi-Fi performance. The technology has therefore been opposed by Google, cable TV companies, and the Electronic Frontier Foundation.

Last year, the Wi-Fi Alliance took the role of peacemaker, proposing a coexistence plan, and Broadcom last week briefed the FCC on how it thinks things are going.

The company's technical director Matthew Fischer and product director Christopher Szymanski last week told FCC legal advisors Edward Smith and Johanna Thomas the LTE-U/WiFi Coexistence Test Plan is progressing more quickly than typical WiFi Alliance processes.

The chief area of disagreement within the alliance is how to define “quiet”.

To comply with 802.11, WiFi devices are allowed to consider a channel available if there's no other signals at -82 dBm, but Fischer and Szymanski told the FCC chip vendors typically over-engineer their devices to detect other transmissions down as far as -90 dBm.

Although the signal threshold is the sticking point, the industry agrees that WiFi users should suffer no more impact from LTE-U than if they were in the presence of another WiFi network. ®

Bootnote: For those unfamiliar with signal measurements, dBm means “decibels referenced to one milliwatt”. The minimum signal that can be received under 802.11 is -100 dBm, or 0.1 picowatt; -82 dBm, which triggers collision detection in a WiFi transceiver, is a little under 10 pW. ®


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