Microwave Radio Communications SCM4000, Техническое справочное руководство

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C
Symbol Rate Calculations C-1 SCM4000 Technical Reference Manual
Symbol Rate Calculations
C.1 Appendix Overview
This Appendix is provided as a guide to determine the symbol
rate required for your SCM4000 based on your particular Data
Channel interface configurations.
In digital communications, the symbol rate is the total bit rate
divided by the number of bits transmitted in each symbol.
Symbol rate is particularly relevant to digital modulation where
the number of symbols allowed in the modulation scheme is a
key factor in determining how many bits-per-second the radio
system can transmit. Symbol rate is measured in symbols-per-
second.
The total bit rate is the sum of the bit rates of all active Data
Channel interfaces (ASI, DS3/E3, T1/E1, SMPTE, Ethernet, and
RS-232/RS-485). The total bit rate must not exceed symbol rate
calculation values for the modulation type selected.
Table C-1 , Table C-2 , and Table C-3 are provided as examples
illustrating determination of symbol rates. Table C-2 and Table
C-3 illustrate symbol rates determined using different total bit
rates. The examples will be described in the following
paragraphs. Your actual symbol rate will be determined using
Table C-4 and Table C-5 .
Table C-1 illustrates typical standard Data Channel interfaces
and standard fixed or variable bit rates associated with each of
the Data Channel interface examples.
Table C-2 illustrates Valid symbol rates for QPSK , 16QAM ,
32QAM , and 64QAM modulation for the typical bit rate examples
shown in Table C-1 .
Table C-3 illustrates Invalid and Valid symbol rates for QPSK ,
16QAM
,
32QAM
, and
64QAM
modulation based on a higher
Total bit rate than is shown in Table C-1 .
Table C-4 is provided to determine the suggested symbol rate
and the suggested modulation type based on the total bit rate
and the RF channel bandwidth.
Table C-5 is a blank worksheet used to calculate your total bit
rate and to determine your suggested symbol rate. Copies of
Table C-5 are to be reproduced locally, as required.
C.2 Bit Rates and Symbol Rates
Bit rates are determined based on your particular SCM4000
Data Channel interface settings, as configured at the factory.
In the example shown in Table C-1 , Data Channel T1/E1 1 , T1/
E1 2 , ASI 2 , and SMPTE 3 interfaces were selected as a typical
configuration. The fixed values for T1/E1 1 , T1/E1 2 , and
SMPTE 3 and a variable value for ASI 2 were entered into the
Table, the values were copied into the Summary Rates column,
the rates were added, and the sum was entered into the Total
block.
The Total was then located in the Table C-4 Summary Rate
Total column and the corresponding symbol rate values for
QPSK , 16QAM , 32QAM , and 64QAM were recorded. When
locating the Summary Rate Total value in Table C-4 , the rate
should be rounded upward .
In the example shown in Table C-2 , the Total bit rate and the
associated symbol rates for QPSK , 16QAM , 32QAM , and
64QAM were entered into the Table. Symbol rates for each of
the four modulation types are listed in Table C-4 for the Total bit
rate example of 32.9847 and are therefore Valid symbol rates
for each modulation type.