Unlicensed National Information Infrastructure (U-NII) devices operating in the 5.25-5.35 GHz and 5.47-5.725 GHz band are required to protect federal government radar systems and Earth Exploration-Satellite Service (EESS) and the Space Research Service (SRS) operations. Protecting the radar systems requires using Dynamic Frequency Selection (DFS) while protecting the satellite/space systems requires using transmitter power control (TPC) to ensure transmitter power does not exceed that necessary to maintain communications.
In response to requests for clarification or reconsideration of these rules and test procedures used to demonstrate compliance with them filed by the Wi-Fi Alliance, Globespan Virata and Extreme Networks Inc., the FCC issued a Memorandum Opinion and Order (FCC 06-96), granting requests to clarify TPC requirements (Section 15.407(h)(1)), but dismissing requests to clarify the channel availability check time requirement (Section 15.407(h)(2)(ii)), to revise the rules to state that U-NII devices are not required to detect and avoid frequency-hopping radar signals and to modify the definition of a U-NII central controller that must include DFS capability. The commission's memorandum also includes a revised measurement procedure for certifying U-NII devices comply with DFS requirements in these bands.
The FCC said that there is no need to require TPC for systems operating with an effective isotropic radiated power (EIRP) of less than 500 mW, although a the first sentence of Section 15.407(h)(1) states all U-NII devices must employ a TPC mechanism. The memorandum, however, indicates that the TPC requirement does apply to each U-NII device, since a U-NII device's transmission output power has to be combined with antenna gain to determine the overall EIRP. Refer to the MO&O for a discussion of the DFS requirement for U-NII devices.
The discussion of DFS and the measurement procedures is too complex to cover in this summary -- see the Memorandum Opinion and Order (FCC 06-96) for details.
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