Satellite Communications/Satellite Modulation

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Question
Hi,

In VSAT ,what is meant by CCM which is mentioned on Receive chain/Forward Carrier and CPM on Transmit Chain/Return Carrier?

Also Can we minimize the effect of Rain on KU Band while using the above mention Modulation techniques?

Answer
Hi Yousuf,

Apologies for the delay, I was on a short holiday.

CCM is used in DVB-S2 and stands for Constant Coding and Modulation.
This is where the used modcod (modulation like QPSK/8PSK/... and FEC) remain constant and don't change.
It is in contrast with ACM (Adaptive Coding and Modulation) where the used modcod can be changed dynamically depending on the receive conditions. By using ACM, one can use higher efficiency modcods when there is no fading which avoids the need for an additional rain-fade margin.

CPM for return channels is Constant Phase Modulation, this allows for the usage of low power BUCs that are always fully driven into saturation (so not wasting power in needed output back-off).

Typically ACM will be used to minimize the effect of rainfading and increase the overall efficieny in the DVB-S2 outbound. For CPM return channles ARL is used (Adaptive Return Link) which used different (fixed coding) carrier slots depending on the receive conditions.

I hope this answers your questions,

Best regards, Dave

Satellite Communications

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Dave Suffys

Expertise

Questions related to design of satellite communication links.

Experience

Satellite communication, link budgets, DVB-S2, ACM

Organizations
Newtec

Education/Credentials
Telecommunications engineer, Sales Support Manager at Newtec

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