Satellite Communications/Roll off factor

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Question
QUESTION: Hi,
Would you please explain to me whatís exactly Roll off factor mean plus itís effect in the Eb/No

ANSWER: Hi,

The roll-off factor determines how steep the filter is at the output of a modulator.
A digitally modulated signal would have an infinite bandwidth if it was not filtered. The filter at the output of the modulator has a certain slope at the edge. You see this at http://en.wikipedia.org/wiki/File:Raised-cosine_filter.svg

Changin the roll-off has no effect on the Eb/No.

Dave

---------- FOLLOW-UP ----------

QUESTION: Hi Dave,
 as you explained Changing the roll-off has no effect on the Eb/No. is it correct even if Iam using DVB-S2 ? beacuse I heard somewhere it has an effect in Eb/No calculation

Answer
Hi,

The Es/No and Eb/No are independent of the used roll-off.
If you would use the CNR (defined as carrier power over the noise in the total occupied bandwidth) then the CNR is indeed dependent of the roll-off.
For a higher roll-off, more noise will be taken into account over the same symbolrate.
Hence the required CNR will increase when the roll-off increases.

I hope this answers your question.

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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