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Theory of Operation
The puncture patterns for the 3/4 and 7/8 rate encoders are as follows:
Code Rate
Notes:
When using 5/6 rate 8PSK operation, 3/4 rate puncturing is used for every five input bits
to the encoder. No puncturing is done for 2/3 rate 8PSK. The 16QAM operation is
similar to QPSK, except that twice as much information is sent per symbol time as in
QPSK.
At the outputs of the encoders, the data is grouped and split into the following number of
separate data streams:
Modulation Type
This data is fed into a look-up table for a Digital-to-Analog (D/A) converter to perform
amplitude equalization of the rectangular pulses. The amplitude-equalized data is passed
to the analog Nyquist filters for spectral shaping, as well as delay equalization.
The pulse-shaped I and Q baseband data is applied to the RF modulator, which performs
translation to the desired IF frequency. The RF synthesizer is a hybrid DDS-PLL design,
which accommodates a 2.5 kHz step size with low phase noise, using a single loop. The
RF section has a stability of
to provide
control the output from -20 to +5 dBm, in 0.1 dB steps. An AGC circuit maintains the
output level to
5–8
Puncture Pattern
C0
3/4
101
110
7/8
1000101
1111010
1. 1 = code bits to be transmitted
2. 0 = deleted code bits
No. of Data Streams
QPSK
8PSK
16QAM
±
10 PPM. An optional high stability TCXO can be installed
±
0.2 PPM stability. The IF strip provides gain and amplitude stabilization to
±
0.5 dB over frequency and temperature.
C1
2
3
4
SDM-9000 Satellite Modem
Rev. 4
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