OFDM In-band Emissions (802.11n/ac/ax/be)

OFDM In-band Emissions provides 3 curves for measuring in-band emissions:

Average power over each subcarrier.
Limit or Unused Tone Mask over each unoccupied RU (red).
UnusedToneEVM or UnusedToneError over each RU (yellow).

The limit line and the Unused Tone EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format. are calculated according to section 36.3.19.4.4 in 802.11be/D1.1 or section 27.3.18.4.4 in 802.11ax/D4.2.

When Normalize IQ Traces in the Advanced tab is On (selected), the average power reading is normalized to average subcarrier power over occupied RU. The red curve has same value of “OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. RU Info/ Limit(dB)” over each unoccupied RU. Also, the yellow curve has the same value of “OFDM RU Info/UnusedToneEVM(dB)” and occupied RU always scales to 0 dB.

When Normalize IQ Traces in the Advanced tab is Off (deselected), the average power reading is an absolute power on that subcarrier but averaged over all symbols and PPDUs. The absolute value on the red curve and yellow curve will be scaled accordingly in order to keep their gap to subcarrier power consistent.

If a marker is inserted on subcarrier power, “Markers” trace “Upper1” corresponds to red curve and “XX carrier” / “Y delta” is narrowest location and gap between subcarrier power and “Unused Tone Mask” (limit); “Upper2” corresponds to yellow curve and “XX carrier” / “Y delta” is narrowest location and gap between subcarrier power and “Unused Tone Error”.