DIGITAL MODULATION MODE
3-33
Digital data mapping
The signal generator converts digital signals to the required modulation format mapped onto an
I,Q diagram. Digital data is mapped for the modulation types selected from the
Digital
Modulation Type Selection
menu (Fig. 3-22). Data mapping is defined as follows:
1. I is in phase with the carrier whereas Q is in quadrature with the carrier.
2. The Q-channel lags the I-channel by 90
°
.
3. An increase in frequency results in the rotation of a vector in a counter-clockwise direction.
PSK
For PSK the codes are mapped to specific points which are independant of the previous states. For
all the forms of PSK detailed below the vectors lie on a circle but the amplitude of the signal will
be non-constant between sampling points.
BPSK (2PSK)
The BPSK constellation is defined below and shown in Fig. 3-30.
QPSK (4PSK)
The QPSK constellation is defined below and shown in Fig. 3-31.
Q
I
P1
P0
C1079
Fig. 3-30 BPSK constellation
Data
Vector
point
0
P0
1
P1
P1
P0
P3
P2
Q
I
C1080
Fig. 3-31 QPSK constellation
Data
Vector
point
00 P0
01
P1
10
P2
11
P3