R&S FSV-K70, Руководство пользователя

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Brief Description of Vector Signal Analysis
R&S
®
FSV-K70
49 Operating Manual 1176.7578.02 ─ 09
2.4.4 Pattern Symbol Check
This stage performs a bit-by-bit comparison between the selected pattern and the
demodulated bits. It is important to note that this comparison is only performed at posi-
tions that have been identified by the IQ pattern search as possible pattern positions.
The algorithm and a simple example are illustrated in
Figure 2-46 .
First, the pattern candidate bits are extracted from the whole bitstream calculated by
the "Demodulation & Symbol Decisions" stage. This means that the symbol stream is
cut at the position that has been detected by the
I/Q Pattern Search as the start of the
pattern. The extracted sequence is then compared to the selected pattern.
If the demodulation has been ambiguous with respect to the absolute phase position,
the extracted sequence needs to be compared to all possible rotated versions of the
selected pattern. For example, in the case of QPSK modulation, the rotational symme-
try has the order four, i.e. there are four pattern hypotheses. If the extracted sequence
coincides with one of the hypotheses, the pattern is declared as "found" and the abso-
lute phase corresponding to the appropriate hypothesis is passed on. Both the symbol
decisions and the IQ measurement signal are then rotated with this pattern phase (for
the whole result range), thus resolving the phase ambiguity.
For more information refer to:
●
Chapter 2.4.3, "Demodulation and Symbol Decisions" , on page 47
●
Chapter 2.4.2, "I/Q Pattern Search" , on page 46
Demodulation Overview