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From: cl7teckie on 7 Jul 2010 05:05

>
>yes it is often assumed that noise BW of the receiver is equal to the
>symbol rate
>
>Note the -3 dB points of an RRC (square root raised cosine) Rx filter
>are equal to the symbol rate BW so as ALPHA approaches 1 the above
>assumption gets closer and closer to true...
>
>Mark
>

Hi Mark, which assumption get closer to true, are you referring to?

I am confused, as based on my analysis, as Alpha gets bigger (towards 1),
the noise bandwidth gets larger and larger with respect to the actual
signal power. As Alpha approaches 1, the Noise Bandwidth now allows 1dB
more noise compared to the signal power.

I drew up a simulation in Excel, and integrate the total power of the noise
and that of the signal, and it agrees with my analysis. I am not just
referring to -3dB point, but integrate over the whole ideal RRC curve to
get my equivalent noise bandwidth and signal power.
From: cl7teckie on 7 Jul 2010 05:08
>On Jul 6, 6:27=A0am, "cl7teckie" <paul(a)n_o_s_p_a_m.pixelmetrix.com>
>wrote:
>
>> Any comment or disagreement are welcome.
>
>OK, I disagree.

I respect that, but please point to me, why you disagree. Like my last
post, I plot the curve of RRC (for the noise), and then RC (for the
signal), clearly they do not match/overlap perfectly. Is there something
else that i have missed?
From: dvsarwate on 7 Jul 2010 08:20
On Jul 7, 4:08 am, "cl7teckie" <paul(a)n_o_s_p_a_m.pixelmetrix.com>
wrote:
> >On Jul 6, 6:27=A0am, "cl7teckie" <paul(a)n_o_s_p_a_m.pixelmetrix.com>
> >wrote:
>
> >> Any comment or disagreement are welcome.
>
> >OK, I disagree.
>
> I respect that, but please point to me, why you disagree. Like my last
> post, I plot the curve of RRC (for the noise), and then RC (for the
> signal), clearly they do not match/overlap perfectly. Is there something
> else that i have missed?

The noise power (and hence the equivalent
noise bandwidth) is proportional to the area
under the *square* of the transfer function.
In this instance, the square of the RRC curve
is the RC curve which has the same area for
all choices of alpha in the range from 0 to 1.
Yes, the noise passes only through the RRC
filter in the receiver, but the noise power and
equivalent noise bandwidth are determined
by area under the square of the transfer function,
RC, not the transfer function RRC. This fact
was also pointed out succinctly by Vladimir
Vassilevsky earlier in this thread.

--Dilip Sarwate
From: cl7teckie on 7 Jul 2010 09:06
Hi Dilip,

I beg for your patience. I agree with you on the *square* of the transfer
function. In fact, I work out the difference [10*log(1-alpha/4)] based on
the *square* of the function. I am not purely talking about noise
equivalent bandwidth on itself, here, but comparing the noise equivalent
bandwidth to that of the signal equivalent bandwidth. The *square* of the
transfer function applies to BOTH the noise and the signal, thus again the
difference.

Paul...



>The noise power (and hence the equivalent
>noise bandwidth) is proportional to the area
>under the *square* of the transfer function.
>In this instance, the square of the RRC curve
>is the RC curve which has the same area for
>all choices of alpha in the range from 0 to 1.
>Yes, the noise passes only through the RRC
>filter in the receiver, but the noise power and
>equivalent noise bandwidth are determined
>by area under the square of the transfer function,
>RC, not the transfer function RRC. This fact
>was also pointed out succinctly by Vladimir
>Vassilevsky earlier in this thread.
>
>--Dilip Sarwate
>
From: Mark on 7 Jul 2010 10:07
On Jul 7, 5:05 am, "cl7teckie" <paul(a)n_o_s_p_a_m.pixelmetrix.com>
wrote:
> >yes it is often assumed that noise BW of the receiver is equal to the
> >symbol rate
>
> >Note the -3 dB points of an RRC (square root raised cosine) Rx filter
> >are equal to the symbol rate BW so as ALPHA approaches 1 the above
> >assumption gets closer and closer to true...
>
> >Mark
>
> Hi Mark, which assumption get closer to true, are you referring to?
>
> I am confused, as based on my analysis, as Alpha gets bigger (towards 1),
> the noise bandwidth gets larger and larger with respect to the actual
> signal power. As Alpha approaches 1, the Noise Bandwidth now allows 1dB
> more noise compared to the signal power.
>
> I drew up a simulation in Excel, and integrate the total power of the noise
> and that of the signal, and it agrees with my analysis. I am not just
> referring to -3dB point, but integrate over the whole ideal RRC curve to
> get my equivalent noise bandwidth and signal power.

Sorry, I should have said as ALPHA approaches ZERO.... (not one).. my
mistake..

When ALPHA =0 the RRC Rx filter would be rectangular with the -3 dB
BW equal to the symbol rate BW so this would also equal the noise
BW... no?

Mark


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