Service manual

WLAN TX Measurements
R&S
®
FSV-K91/91n/91ac/91p
32Operating Manual 1176.7649.02 ─ 04
Knowing the normalized power and undisturbed reference signal, the transmitter base-
band filter is estimated by minimizing the cost function of a maximum-likelihood-based
estimator:
(17) (3 - 9)
where:
r(v): the oversampled measurement signal
ŝ: the normalized oversampled power
n
(v): the undisturbed reference signal
N: the observation length
L: the filter length
: the variation parameters of the frequency offset
: the variation parameters of the phase offset
, : the variation parameters of the IQ-offset
: the coefficients of the transmitter filter
The frequency-, the phase- and the IQ-offset are estimated jointly with the coefficients
of the transmitter filter to increase the estimation quality.
Once the transmitter filter is known, all other unknown signal parameters are estimated
with a maximum-likelihood-based estimation, which minimizes the cost function:





1
0
2
~
~
2
2
~~
)(
~
)(
~
)(
~
)
~
(
N
QIQQQQII
jfj
ojosgsgjsgeerL



(18) (3 - 10)
where:
, : the variation parameters of the gain used in the I/Q-branch
: the crosstalk factor of the Q-branch into the I-branch
s
I
(v), s
Q
(v): the filtered reference signal of the I/Q-branch.
The unknown signal parameters are estimated in a joint estimation process to increase
the accuracy of the estimates.
The accurate estimates of the frequency offset, the IQ-imbalance, the quadrature-mis-
match and the normalized IQ-offset are displayed by the measurement software. The
IQ-imbalance is the quotient of the estimates of the gain factor of the Q-branch, the
crosstalk factor and the gain factor of the I-branch:
Signal Processing of the IEEE 802.11b Application