Comtech EF Data CLO-10 - Manual (Page 33)

CLO-10 Link Optimizer Revision 1
Introduction MN/CLO-10.IOM
Because acquiring the delay and frequency offset of the interfering carrier is fundamentally a
correlation operation, anything deterministic in the interfering carrier (within the correlation
window of the algorithm) will potentially produce false correlation peaks, and result in incorrect
delays and/or frequency. Normally, this is not a problem, since energy dispersal techniques are
utilized in the vast majority of commercial and military modems; however, this is something the
user must keep in mind when troubleshooting a system that utilizes the DoubleTalk™ Carrier-in-
Carrier
® technique for signal suppression.
One possible way to mitigate false peaks is to narrow the correlation window. For example, if you
know the delay to be around 240ms, set the minimum search delay to 230ms and the maximum
search delay to 250ms.
A typical CnC system does require a 3dB increase within the band (for symmetric links). This is
usually compensated for by using a more powerful FEC like TPC or LDPC, by use of a larger
antenna, or carefully managing the link budget. Many links operate with excessive margins which
can be allocated to CnC without having to resort to changing out the equipment.
1.6.2 Application Requirements
The following conditions are necessary in order to operate Carrier-in-Carrier
®
:
• Link must be full duplex
• A CLO-10 must be used at each end of the link
• The transponder is operated as Loopback. That is, each end of the link must be able to see
a copy of its own signal in the return (downlink) path from the satellite. The looped back
signal is then subtracted which leaves the signal from the distant end of the link. CnC
cannot be used in spot beam systems.
• The transponder is “bent-pipe”, meaning no on-board processing, demodulation, or
regeneration can be employed. Demodulating/remodulating does not preserve the linear
combination of the forward and return signals and the resulting reconstituted waveform
prevents recovery of the original constituent signals.
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