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ROI-S04488
Table 2-2 Typical Operation of Differential Encoding Circuit
TIME SLOT
NATURAL-
Data 1
BINARY-
Data 2
CODED
DATA
Quaternary
ENCODED
Quaternary
DATA
Data 1
Data 2
2.3.2
4-Phase Shift Keying Modulation
Table 2-2 shows typical operation of the differential encoding circuit.
Phases in the natural-binary-coded pulse streams are accumulated in
quaternary notation at every time slot. The data streams thus encoded are
reconverted into pulse streams in gray code and then sent to a driver.
0*
1
2
3
0
1
1
1
1
0
1
3
2
+
+
+
0
1
0
2
0
0
0
1
0
1
0
0
Note: * Operating process given above assumes that the initial time slot
is 0.
To permit 4-phase shift keying modulation, the encoded data streams are
converted into two separate two-level baseband signals for the P and Q
channels by the digital-to-analog converter (D-A CONV) on the MOD
section according to the logical status (see Fig. 2-3). To limit the
associated transmitter output power spectrum, the voltage spectrum of the
two-level baseband signal is shaped by each low-pass filter. The filtered
signals are applied to a 4-phase modulator (4PH MOD).
To obtain an 850 MHz IF carriers for 4PH MOD, an 850 MHz carrier is
generated by the 850 MHz voltage controlled oscillator (VCO), and is split
into two for the P and Q channels. The 850 MHz carrier for the Q channel
is phase-shifted by π /2 from the P channel.
The MOD modulates each of the 850 MHz carriers with a related two-
level baseband signal, and combines the modulated 850 MHz signals on
the P and Q channels to arrange a four-phase assignment as shown in Fig.
2-2.
The obtained 850 MHz IF signal is filtered by a LPF for eliminating the
out-of-band components, amplified up to the required level by an
automatic gain control (AGC) amplifier and sent to the ODU. Then, it is
combined with 450 kHz amplitude-modulated engineering orderwire
(EOW) signal and 10 MHz amplitude shift keying (ASK)-modulated
control signal.
FUNCTIONAL OPERATION
4
5
6
7
8
9
1
0
1
0
1
0
0
0
0
1
1
0
2
0
2
1
3
0
' ' ' ' ' ' ' ' ' ' ' ' ' ' '
0
0
2
3
2
2
0
0
1
1
1
1
0
0
0
1
0
0
10
11 ...
1
0 ...
1
1 ...
3
1 ...
+
+
1
2 ...
0
1 ...
1
0 ...
2-19
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