Rohde & Schwarz SMM100A, Руководство пользователя

Страница: 141 / 1088

Configuring the internal baseband source
R&S
®
SMM100A
141 User Manual 1179.1341.02 ─ 05
Example: Differential coding for QPSK modulation with K = 2 bit/symbol
Decimal display; the value range for modulation symbols is a
n
= {0, 1, 2, 3}
According to Table 4-8 and for k = 2 , the recursive coding is defined as b
n
= (a
n
+ b
–1
)
modulo 4
Depending on the state of a preceding modulation symbol b
–1
, the coded modulation
symbol b
n
is obtained, for example, from modulation symbol a
n
= 2 as follows:
b
–1
0 1 2 3
b
n
2 3 0 1
With differential coding, the assignment of modulation symbols a
n
(binary indication:
MSB, LSB) to the phase differences shown in the following table is generated:
Table 4-9: Phase difference for QPSK
Modulation symbol a
n
00 01 10 11
Phase difference 0° 90° 180° 270°
Example: Differential coding for modulation type pi/4DQPSK
With differential coding switched on at the same time, the obtained constellation dia-
gram for pi/4DQPSK is similar to that of 8PSK. Phase shifts are however assigned to
the individual modulation symbols. The
Table 4-10 shows the assignment of modula-
tion symbols a
n
(binary indication: MSB, LSB) to phase shifts of the I/Q vector in rela-
tion to the selected coding.
Table 4-10: Phase shifts for pi/4DQPSK
Modulation symbol a
n
00 01 10 11
"Coding = Off" + 45° + 135° - 135° - 45°
"Coding = NADC, PDC, PHS, TETRA, or APCO25
(PSK)" + 45° + 135° - 45° - 135°
"Coding = TFTS" - 135° + 135° - 45° + 45°
Example: Gray and differential coding for 8PSK modulation
When this coding scheme is used, the gray coding according to the gray code is per-
formed before the differential coding. The later uses the recursive coding algorithm
quoted above (see
Table 4-8 ). The assignment of modulation symbols a
n
(binary indi-
cation: MSB, LSB) to the phase differences shown in the following table is generated:
Table 4-11: Differential coding according to VDL 1)
Modulation symbol d
n
000 001 010 011 100 101 110 111
Phase difference 0° 45° 135° 90° 270° 315° 225° 180°
1)
"Differential coding according to VDL" can be used for modulation types with 3 bits/
symbol, e.g. 8PSK.
Generating custom digital modulated signals