Service manual

WLAN TX Measurements
R&S
®
FSV-K91/91n/91ac/91p
33Operating Manual 1176.7649.02 ─ 04
(19) (3 - 11)
The quadrature-mismatch is a measure for the crosstalk of the Q-branch into the I-
branch:
(20) (3 - 12)
The normalized IQ-offset is defined as the magnitude of the IQ-offset normalized by
the magnitude of the reference signal:
2
22
22
ˆˆ
ˆˆ
2
1









gg
oo
QI
QI
OffsetIQ
(21) (3 - 13)
At this point of the signal processing all unknown signal parameters such as timing-,
frequency-, phase-, IQ-offset and IQ-imbalance have been evaluated and the mea-
surement signal can be corrected accordingly.
Using the corrected measurement signal r(v) and the estimated reference signal ŝ(v),
the modulation quality parameters can be calculated. The mean error vector magnitude
(EVM) is the quotient of the root-mean-square values of the error signal power and the
reference signal power:








1
0
2
1
0
2
)(
ˆ
)(
ˆ
)(
N
v
N
v
vs
vsvr
EVM
(22) (3 - 14)
Whereas the instant error vector magnitude is the momentary error signal magnitude
normalized by the root mean square value of the reference signal power:





1
0
2
)(
ˆ
)(
ˆ
)(
)(
N
v
vs
vsvr
vEVM
(23) (3 - 15)
In [2] a different algorithm is proposed to calculate the error vector magnitude. In a first
step the IQ-offset in the I-branch and the IQ-offset of the Q-branch are estimated sepa-
rately:
Signal Processing of the IEEE 802.11b Application