Brief Description of Vector Signal Analysis
R&S
®
FSV-K70
25
Operating Manual 1176.7578.02 ─ 09
2.3.2 Rotating PSK
A rotating PSK modulation is basically a PSK modulation in which additional phase
shifts occur. These phase shifts depend on the symbol number, e.g. for a
π
/4-QPSK,
the third symbol has an additional phase offset of (3-1)*
π
/4. This offset has the same
effect as a rotation of the basic system of coordinates by the offset angle after each
symbol.
The method is highly important in practical applications because it prevents signal tran-
sitions through the zeros in the I/Q plane. This reduces the dynamic range of the
modulated signal and the linearity requirements for the amplifier.
In practice, the method is used for 3
π
/8-8PSK, for example, and (in conjunction with
phase-differential coding) for
π
/4-DQPSK.
Symbol mapping
The logical constellation diagram for 3
π
/8-8PSK comprises 8 points that correspond to
). A counter-clockwise offset (rotation) of 3
π
/8 is
inserted after each symbol transition.
0
1
2
3
4
5
6
7
Figure 2-15: Constellation diagram for 3
π
/8 8PSK before rotation including the symbol mapping for
EDGE
Symbol Mapping
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