3 WLAN Mode
3.9 Spectral Flatness Measurement
3.9 Spectral Flatness Measurement
Variation in carrier flatness of OFDM signals in IEEE 802.11a/g/n/ac/ah/ax will
reduce demodulation margins and degrade link performance.
The spectral flatness measurement applies to test carrier flatness of OFDM signals
in IEEE Std 802.11a-1999(R2003),IEEE Std 802.11g-2003,IEEE Std 802.11n-
2009,IEEE P802.11ac™/D1.1,IEEE P802.11ah™/D0.2, IEEE Std 802.11ax D1.0, IEEE
Std 802.11be D0.2.
Measurement Algorithm
For 802.11a and 802.11g-ERP-OFDM and 802.11g-DSSS-OFDM: The spectrum
flatness measurement measures energy flatness of sub-carriers in OFDM system.
The average energy of the constellations in each of the spectral lines –16… –1 and
+1… +16 will deviate no more than ± 2 dB from their average energy. The average
energy of the constellations in each of the spectral lines –26… –17 and +17… +26
will deviate no more than +2/–4 dB from the average energy of spectral lines –16… –
1 and +1… +16. The average energy can be computed by averaging energy on the
sub-carriers from –16 to 16. Please note, zero sub-carrier is not included in this
computation phase.
For 802.11n in a 20 MHz channel and in corresponding 20 MHz transmission in a 40
MHz channel, the average energy of the constellations in each of the subcarriers
with indices –16 to –1 and +1 to +16 shall deviate no more than ± 2 dB from their
average energy. The average energy of the constellations in each of the subcarriers
with indices –28 to –17 and +17 to +28 shall deviate no more than +2/–4 dB from
the average energy of subcarriers with indices –16 to –1 and +1 to +16.
In a 40 MHz transmission (excluding PPDUs in MCS 32 format and non-HT duplicate
format) the average
energy of the constellations in each of the subcarriers with indices –42 to –2 and +2
to +42 shall deviate no
more than ± 2 dB from their average energy. The average energy of the
constellations in each of the subcarriers with indices –43 to –58 and +43 to +58 shall
deviate no more than +2/–4 dB from the average energy of subcarriers with indices
–42 to –2 and +2 to +42.
In MCS 32 format and non-HT duplicate format the average energy of the
constellations in each of the subcarriers with indices -42 to -33, -31 to -6, +6 to +31,
and +33 to +42 shall deviate no more than ± 2 dB from
their average energy. The average energy of the constellations in each of the
subcarriers with indices –43 to
1409 WLAN Mode User's &Programmer's Reference
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