Rohde & Schwarz R&S CMW-KM300, User Manual, Page: 331 / 388

NB-IoT NPRACH Measurement
R&S
®
CMW-KM300/-KS300
331 User Manual 1178.5689.02 ─ 06
length" W. The minimum test requirement 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.
Time
...
Cyclic prefix Preamble sequence
EVM window
W
 EVM
l
 EVM
h
Figure 4-1: 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, section F.5.F).
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, for example, due to the
effects of time domain windowing of FIR pulse shaping.
FFT processing window
Figure 4-2: Cyclic prefix
EVM window settings
Use the settings in the section "Config... > Measurement Control > Modulation > EVM
Window Length" to adjust the length of the EVM window (see
"EVM Window Length"
on page 345). The minimum value of one FFT symbol means that EVM
h
equals EVM
l
.
Use the setting "Config... > Measurement Control > Modulation > EVM Window Posi-
tion" to select whether the result diagrams (traces) are calculated for low or high EVM
window position, see
"EVM Window Position" on page 345. Statistical tables provide
results for both window positions.
4.2.6 NB-IoT Preamble Structure
In the time domain, a single preamble consists of four symbol groups. And a symbol
group consists of one cyclic prefix (CP) and five symbols.
General Description
深圳德标仪器
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