Mocomtech CDM-QX - Manual (Page 87)

CDM-Qx/QxL Multi-Channel Satellite Modem with DoubleTalk™ Carrier-in-Carrier® Revision 7
Front Panel Operation MN/CDMQX.IOM
5–21
5.4.3 CONFIG: Rx (Receive)
Rx: FEC Demod Code Data Freq
Acq Descram Buf Inv Misc CnC
Select FEC, Demod, Code, Data, Freq, Acq, Descram, Buf, Inv, Misc, or CnC using the ◄ ►
arrow keys, then press
ENTER
. The user will then be taken to a further submenu. Each selection is
described briefly as follows:
FEC
(Forward Error Correction) This submenu permits the user to select the method of FEC
used for reception (Viterbi, TPC, etc). FEC type takes the highest configuration priority.
Demod
(Demodulation) This submenu permits the user to select the modulation type used for
reception (BPSK, QPSK, 8-PSK, etc.). The available choice of modulation will depend on
the FEC type chosen.
Code
(FEC Code Rate) This submenu permits the user to select the FEC Code Rate used for
reception (Rate 1/2, Rate 3/4, etc). The available choice of Code Rate will depend on both
the FEC type and Demodulation type selected.
Data
(Data Rate) This submenu permits the user to select the receive data rate, in steps of 1
bps. The choice of data rate will depend on the FEC type, Demodulation type, and Code
Rate selected.
Freq
(Frequency) This submenu permits the user to select the receive frequency, from 950 MHz
to 1950 MHz, in steps of 100Hz for L-Band units, or from 50 MHz to 90 MHz and from 100
MHz to 180 MHz for 70/140MHz units.
Acq
(Acquisition) This submenu permits the user to determine the amount of frequency uncertainty the
demodulator will search over in order to find and lock to an incoming carrier.
Descram
(Descrambler) This submenu permits the user to select whether or not data descrambling
is used.
Buf
(Buffer) This submenu permits the user to select whether or not the Plesiochronous/
Doppler buffer is used, and if so, the size of that buffer.
Inv
(Inversion) This submenu permits the user to invert the sense of the received spectrum, or
to invert the sense of the received baseband data.
Misc
(Miscellaneous) This submenu will allow the user to select Eb/No Alarm Threshold (EbNo)
and Rx roll-off (alpha) factor Rx α.
CnC (Carrier-in-Carrier
®
) This submenu allows the user to set-up the CnC parameters.
The FEC type takes the highest configuration priority, and the selection here
depends on what, if any, optional plug-in Codecs are installed. The choice of
FEC type then determines what demodulation types, code rates, and data
rates are available. The order of hierarchy is therefore:
FEC type ► Demodulation type ► Code Rate ► Data Rate
(Highest) (Lowest)
If the user changes a parameter within this hierarchy, the other parameters may become invalid.
In this case, the software will change those other parameters, in order to maintain a valid
configuration at all times.
Example: Suppose the user has selected Viterbi + Reed Solomon, QPSK, Rate 1/2. Now, the
user changes the demodulation type from QPSK to 16-QAM. In this case, Rate 1/2 is no longer a
valid code rate, and so it will be automatically changed to the nearest valid code rate (Rate 3/4).
Detailed descriptions for each of the Rx configuration submenus follow.
IMPORTANT