FPGA Central

"Jon" <[email protected]> wrote in message
news:[email protected] om...
> Hello,
> I am new to DSP and digital communication as I understand for a
> given bandlimited communication channel designers use pulse shaping
> filters to shape the pulse to the bandwidth of the channel. The
> question I have has to do with the length of the pulse shaping filter
> vs. the symbol rate. After reading though some introductory digtial
> comm books I have yet to come across a good explaintion on how to
> choose the length of the filter, sample rate, and number of symbols
> that are being processed at a time in the filter. Is there any good
> reference on such topics.

Jon,

As an exercise in learning you might consider a pulse shaping filter that
takes a unit sample as its input.

Many pulse shaping filters attempt to create a good "eye" pattern. This
means that the output pulse will be zero at the tymbol interval.

So, if the sample rate is the same as the symbol rate, then a good shaping
filter for a unit sample will be a unit sample - with all other filter
coefficients zero. Otherwise the symbols would overlap.

If the sample rate is hight than the symbol rate, then a good shaping filter
for a unit sample will be a filter that is valued 1.0 at one point. Removed
from this one point will be zero values at the symbol interval. So, it
might be a good idea for the sample interval to be an integral multiple of
the symbol interval.

A filter like this will have zero value at fs/2 and possibly a multiple zero
at fs/2. Google on:
"Gibby Smith Nyquist"

Fred