Service manual

WLAN TX Measurements
R&S
®
FSV-K91/91n/91ac/91p
48Operating Manual 1176.7649.02 ─ 04
3.8.2 EVM Measurement
The R&S FSV-K91 option provides two different types of EVM calculation.
Peak EVM (IEEE)
Peak EVM (IEEE) evaluates the EVM as defined in section 18.4.7.8 "Transmit modula-
tion accuracy" of the IEEE 802.11b standard. The measurement signal is corrected in
respect of frequency error and clock deviation before EVM calculation. Additionally the
specified calculation removes the dc offset of the measurement signal.
The standard does not specify a normalization factor for the error vector magnitude. To
get a level independent EVM value, the R&S FSV-K91 normalizes the EVM values, so
that an EVM of 100% indicates that the error power on the I- or Q-channels equals the
mean power on the I- or Q-channels respectively.
The Peak EVM is the maximum EVM over all chips of one burst. If more than one burst
is evaluated (several analyzed bursts in the capture buffer or with the help of Overall
Burst Count), the Min / Mean / Max columns show the minimum, mean or maximum
Peak EVM of all analyzed bursts.
The IEEE 802.11b standard allows a Peak EVM of less than 35%. In contrary to the
specification, the R&S FSV-K91 does not limit the measurement to 1000 chips length,
but searches the maximum over the whole burst.
Measurement Result Types