114 Keysight WLAN Measurement Guide
Concepts
WLAN Measurement Concepts
Spectral Flatness Measurement Concepts
Purpose
Variation in carrier flatness of OFDM signals in IEEE 802.11a/g/n/ac will
reduce demodulation margins and degrade link performance. This
measurement applies to test carrier flatness of OFDM signals in IEEE
802.11a/g/n/ac.
Measurement Method
For 802.11a and 802.11g (ERP-OFDM/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 (defined as Section 1) 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 (defined as Section 2) 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… –1 and +1… +16 (defined as Section 1) 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… –17 and +17…
+28 (defined as Section 2) shall deviate no more than +2/–4 dB from the
average energy of subcarriers with indices –16… –1 and +1… +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… –2 and +2… +42 (defined as Section 1) shall
deviate no more than ± 2 dB from their average energy. The average energy of
the constellations in each of the subcarriers with indices –58… –43 and +43…
+58 (defined as Section 2) shall deviate no more than +2/–4 dB from the
average energy of subcarriers with indices –42… –2 and +2… +42.
In MCS 32 format and non-HT duplicate format, the average energy of the
constellations in each of the subcarriers with indices –42… –33, –31… –6 and
+6… +31, +33… +42 (defined as Section 1) shall deviate no more than ± 2 dB
from their average energy. The average energy of the constellations in each of
the subcarriers with indices –58… –43 and +43… +58 (defined as Section 2)
shall deviate no more than +2/–4 dB from the average energy of subcarriers
with indices –42… –33, –31… –6 and +6… +31, +33… +42.