Satellite Communications/Roll off factor
Would you please explain to me whatís exactly Roll off factor mean plus itís effect in the Eb/No
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.
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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
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.