System Overview
R&S
®
CMW500
70
User Manual 1173.9463.02 ─ 02
4.3.7 TX Measurements
The purpose of a TX measurement is to assess the performance of an RF transmitter.
Despite the differences in detail, TX measurements for different network standards have
many properties in common.
4.3.7.1
Power Results
Power measurements are essential, e.g. for checking whether the transmitter output
power complies with the power class of the device under test, or testing various power
control mechanisms. The R&S CMW500 provides two different types of power results:
●
Most of the power results are averaged over an appropriate time/frequency interval
(e.g. a WiMAX burst). Average powers are used to check whether a transmitter pro-
duces the correct output power.
●
Traces for the power versus time show a series of consecutive power steps or give
detailed insight into the transmitted power, including the structure of power ramps
and possible effects of the modulation.
For details refer to the description of the measurement firmware applications.
4.3.7.2
Modulation Accuracy
Modulation accuracy is the ability of the UE transmitter to generate an ideally modulated
signal. Modulation accuracy is assessed by a number of quantities which are analogous
for all digital phase modulation schemes.
The modulation parameters are acquired in a single measurement process. The calcu-
lation is based on the comparison of the actual output signal Z of the transmitter under
test with a reference signal R that is generated by the R&S CMW500 and represents an
ideal error-free received signal.
An example for the process (WCDMA signals) is described in specification 3GPP TS
24.121, Annex B.
For a detailed description for WIMAX signals refer to the description of the "WiMAX Mea-
surement" firmware application.
Timing and Frequency Error
The R&S CMW500 must establish time synchronization with the input RF signal and
estimate its timing, carrier frequency and power. The frequency error is the offset of the
measured carrier frequency from the nominal RF frequency of the measured radio chan-
nel.
The calculated reference signal R is modified using the estimated timing, frequency error
and power. The resulting corrected reference signal R' is used to determine the error
vector magnitude, magnitude error and phase error.
The timing error is the deviation of the measured signal timing from the expected timing,
which is generally derived from a trigger event.
Measurements
