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01-0868-401B 12/02
QPSK Demodulator Application Notes
Information
Rate/Symbol
Rate/Channel
Spacing
This section provides rate definitions and relationships as well as information on
channel spacing.
Definitions
Information Rate (Bits/Sec)
Information rate is the rate of data leaving the demodulator measured in bits per
second. For Tiernan systems, the information rate is generally equal to the
aggregate transport stream rate.
Channel Rate (Bits/Sec)
Channel rate is the rate of data in the demodulator, before the FEC decoding. The
channel rate equals the information rate plus the FEC encoding overhead,
measured in bits per second.
Symbol Rate (Symbols/Sec)
Symbol rate is the rate of symbols being transmitted through the channel
measured in bits per second. For QPSK modulation, there are 2 bits per symbol.
The formula for converting the data rate to the symbol rate is provided in the
chapter on using the front panel.
Aggregate Rate (Bits/Sec)
Aggregate rate is the data rate of the encoder output
transport stream. The transport stream can be either a single transport stream or
several multiplexed transports streams. The aggregate rate is generally the
information rate going into the modulator or coming out of the demodulator.
Relationships
Information Rate = Aggregate Rate
where the code_rate can be 1/2, 2/3, 3/4, 5/6, 7/8
The minimum required E
b
/N
0
level varies depending on the selected code rate.
For a table showing the relationship between E
b
/N
0
levels and code rates, refer to
the chapter on troubleshooting.
Maximum Rates
Symbol Rates
The minimum and maximum symbol rates are:
■
Minimum = 1 Mbaud
■
Maximum = 30 Mbaud
Information Rates
The minimum and maximum information rates are provided in the following
table.
Minimum and Maximum Information Rates
Code Rate
1/2
2/3
3/4
5/6
7/8
Minimum Information Rate (Mbps)
0.92
1.23
1.38
1.54
1.61
Maximum Information Rate (Mbps)
27.6
36.8
41.5
46.1
48.4
Symbol Rate
1
2
⁄
* 204
188
⁄
(
)
* 1
Code Rate
⁄
(
)
*Information Rate
=
