Instrument Function
R&S
®
SMBV100A
289Operating Manual 1407.6062.32 ─ 08
Example: Differential coding for QPSK modulation with K = 2 bit/symbol
Decimal display; value range for modulation symbols
Recursive coding is defined as follows: b
n
= (a
n
+ b
n-1
) modulo 4
Depending on the state of a preceding modulation symbol b
n-1
the coded modulation
symbol b
n
is obtained for example from modulation symbol a
n
= 2 as follows:
a
n
= 2 b
n-1
b
n
0 2
1 3
2 0
3 1
By means of differential coding, the assignment between modulation symbols and phase
differences shown in the following table is generated:
Modulation sym-
bol a
n
(binary,
MSB, LSB)
00 01 10 11
Phase difference 0° 90° 180° 270°
Example: Gray and differential coding for 8PSK modulation
First, a gray coding is performed according to the gray code. Afterwards, a differential
coding is performed according to the recursive coding algorithm quoted above. The
assignment between modulation symbols and phase differences shown in the following
table is generated:
"Differential coding according to VDL" can be used for modulation types with 3 bits/sym-
bol, e.g. 8PSK.
Table 5-6: Differential coding according to VDL
Modulation symbol d
n
(binary, MSB, LSB)
000 001 010 011 100 101 110 111
Phase difference 0° 45° 135° 90° 315° 270° 180° 225°
"Phase differential coding" INMARSAT and PHASE DIFF correspond to system stand-
ards Inmarsat-M and DVB according to ETS 300 429. The INMARSAT coding can gen-
erally be used for modulation types with 2 bits/symbol, such as QPSK. It uses the fol-
lowing algorithm.
Baseband Signal - Baseband Block
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