Verizon's plan to blast LTE traffic over unlicensed spectrum questioned by FCC

7 August 2015 by Steve Blum
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Can you hear me now?

Plans by mobile phone companies to use unlicensed spectrum – including that currently used by WiFi devices and wireless Internet service providers – to supplement licensed frequencies are getting a harder look from the Federal Communications Commission. The head of the FCC’s office of engineering and technology – Julius Knapp – is asking the Verizon-backed LTE-U Forum, an industry group that’s working on a standard for 4G broadband service in unlicensed bands, for more information on what, exactly, it’s up to.

Knapp’s concerns center on whether mobile carriers would “listen before talk” to determine whether someone was already using a frequency or just jump on top of a weaker signal…

Though the record reflects significant testing of [the Listen-Before-Talk technique called Carrier Sense Adaptive Transmission (CSAT)] sharing protocol with Wi-Fi, commenters did not provide information regarding the rationale behind the selection of certain key parameters for CSAT. Specifically we would like to know,what was the basis for selecting the maximum permissible transmission and minimum listening periods? Some specifications seem to suggest that these parameters are implementation-dependent and may be set by operators. Please explain the decision to have CSAT transmit on a channel even if it appears to be occupied.

The letter also raises the question of international coordination – other countries have tighter rules on use of unlicensed spectrum. Knapp is basically asking Verizon and the LTE-U Forum why it wants to implement a standard in the U.S. that wouldn’t be acceptable in most other countries. He’s wants an answer within a month.