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LTE PRACH Measurement
R&S
®
CMW-KM5xx/-KS5xx
744
User Manual 1173.9628.02 ─ 16
chapter 4.3.2.5, "Trigger Settings"
4.2.6 Calculation of Modulation Results
Modulation results are based on a comparison between the measured signal, correc-
ted by the average frequency and timing offset for each measured subframe, and an
ideal reference waveform.
See also: "Modulation Accuracy" in the R&S
CMW user manual, chapter "System
Overview"
3GPP TS 36.101, Annex F, specifies the following additional conditions:
●
The I/Q origin offset shall be removed from the evaluated signal before calculating
the EVM.
●
The EVM calculation shall be based on two different FFT processing windows in
time domain, separated by the "EVM window length" W. The minimum test require-
ment applies to the larger of the two obtained EVM values.
The definition of the EVM window and the two FFT processing windows is shown
below.
Fig. 4-2: EVM window definition
The EVM window is centered on the cyclic prefix (CP) at the beginning of the pream-
ble. Its length is specified in the standard, depending on the preamble format (see
3GPP TS 36.101, table F.5.5-1).
The CP is a cyclic extension of the preamble sequence. As a consequence the EVM
for a signal with good modulation accuracy is expected to be largely independent of the
EVM window size. Differences between EVM
h
and EVM
l
arise e.g. due to the effects of
time domain windowing of FIR pulse shaping.
Fig. 4-3: Cyclic prefix
General Description
深圳德标仪器
135-1095-0799