Transmit Power Control (TPC)

Transmit Power Control (TPC) dynamically adjusts a device’s transmit power to the level needed for reliable communication. Whether TPC is required, and which power limits apply, depends on the market and the relevant frequency range.

Scope and Regulatory Requirements

• European Union: ETSI EN 301 893 V2.2.1 specifies TPC requirements for 5 GHz RLAN equipment within its scope.

• United States: 47 CFR §15.407 defines the applicable power-control and operating requirements for U-NII devices.

• Canada: ISED RSS-247 contains the Canadian requirements for licence-exempt RLAN devices.

U-NII is terminology used in the United States and Canada. European requirements are identified by frequency range and ETSI sub-band.

Technical Requirements under EN 301 893

The effect of TPC is sub-band-specific:

• Sub-band 1: The same power limits apply with or without TPC; there is no general 3 dB reduction for equipment without TPC.

• Sub-bands 2 and 3 and Annex B sub-band 4: Equipment without TPC is subject to power limits 3 dB below the corresponding limits for equipment using TPC.

• TPC range: Where TPC is implemented, the lowest available power level must be at least 6 dB below the maximum power level.

Testing and Compliance

Testing must use the requirements applicable to the target market, frequency range and equipment configuration. It typically verifies power-control behaviour, maximum EIRP and the available TPC range. TPC also complements Dynamic Frequency Selection (DFS) where both functions apply.