Instrument Functions for Vector Signal Analysis
R&S
®
FSV-K70
172
Operating Manual 1176.7578.02 ─ 09
Unlike QPSK modulation, the Q component of Offset QPSK modulation is delayed by
half a symbol period against the I component in the time domain. The symbol time
instants of the I and the Q component therefore do not coincide.
The offset EVM controls the calculation of all results that are based on the error vector.
It affects the EVM, Real/Imag and Vector I/Q result displays as well as the EVM results
in the Result Summary (EVM and MER).
You can select the way the R&S
FSVA/FSV calculates the error vector results.
If "Offset EVM" is inactive, the R&S
FSVA/FSV substracts the measured signal from
the reference signal to calculate the error vector. This method results in the fact that
the error vector contains two symbol instants per symbol period: one that corresponds
to the I component and one that corresponds to the Q component.
If "Offset EVM" is active however, the R&S
FSVA/FSV compensates the delay of the Q
component with respect to the I component in the measurement signal as well as the
reference signal
before
calculating the error vector. That means that the error vector
contains only one symbol instant per symbol period.
Remote command:
Estimation Points/Sym
The estimation points per symbol affect and control synchronization of the signal. You
can set the estimation points manually or let the R&S
FSVA/FSV decide which estima-
tion points to use.
If you define the estimation points manually, you can set the estimation points to 1 or 2
per symbol or the value of the
per symbol. Setting the estima-
tion points to "1" means that the estimation algorithm takes only the symbol time
instants into account, while setting the estimation points to "Capture Oversampling"
means that all sample time instants are weighted equally.
If you select the automatic routine, the R&S
FSVA/FSV uses 2 estimation points per
symbol for Offset QPSK modulation and 1 estimation point per symbol for other PSK
and QAM modulated signals. For MSK and FSK modulated signals the estimation
points correspond to the capture oversampling.
Remote command:
Coarse Synchronization
It is not only possible to check whether the pattern is part of the signal, but also to use
the pattern for synchronization, in order to obtain the correct reference signal. Depend-
ing on the signal, making use of the pattern for synchronization speeds up your mea-
surement considerably and makes it more robust against high carrier frequency off-
sets. However, in case the parameter is set to "Pattern", you should make sure that the
pattern is suitable for synchronization, e.g. a pattern that was made for synchronization
purposes like in GSM. In case the pattern is short or the pattern does not have good
synchronization properties, e.g. a pattern that consists of only one symbol that is
repeated, this parameter should be set to "Data".
Configuring VSA Measurements
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