Quantum and Evolution Series Installation and Operating Handbook
8-26
The
Data Rate
is normally the frequency of the clock used on the terrestrial port however if
Drop/Insert is active the Data Rate is 64kbps times the number of timeslots
dropped/Inserted.
As the modem uses PSK (Phase Shift Keying) the
Symbol Rate
is the rate of
phase
changes
on the carrier. Each phase change represents a new symbol to the demodulator,
and depending on the modulation scheme that symbol may convey one (BPSK), two
(QPSK), three (8PSK), or four (16QAM) bits of information.
The diagram below shows how the symbol rate is built up from the data rate.
Relationship Between Data Rate and Symbol Rate
You will see that with 1/2 rate FEC and QPSK (a common combination), the Symbol Rate is
the same as the Data Rate (assuming no Framing or Reed-Solomon). This is a useful
combination to check on any data sheet, as this will give you the Symbol Rate limits of the
modem, from which the Data Rate limits in all other modes and combinations can normally
be derived.
1.30 Determining Maximum ESC Baud Rates
Should you wish to determine the exact maximum ESC Baud rates, in order to change the
overhead allocation to achieve specific ESC rates with specific overheads, then the
following sections may be useful.
1.30.1 IBS
For Standard IBS the
exact
maximum continuous rate is: