Re: [Discuss-gnuradio] Selecting the precise sampling point from many samples

[CEL]

Hi Carlo,

not quite sure I get what you mean with "bandlimiting"? What with
"transposing"? 

Regarding "padding": do you mean interpolation? Again, you'd use a
resampler, and in your case, the rational resampler with decimation=1,
interpolation = 48 would do the trick.

Best regards,
Marcus

On Mon, 2018-06-04 at 22:09 +1000, Carlo Manfredini wrote:
> Thank you for your detailed reply.
> I've taken a look at those links and for now are having some success
> using the Clock Recovery MM block with default settings (and 24
> samples/symbol) to capture the data at 2kbps...followed by a Bit
> Slicer.
> 
> After I modulate this 2kbps bit stream to 4-QAM I have a complex 
> 1kSymbol/s stream...as a data stream...with bandlimiting from the QAM
> block.
> 
> Can you suggest how I can pad this out so that I can output it from
> my 48kSps DAC device  such that it is output at a real rate of
> 1kSymbol/sec ?
> 
> Ive tried out "repeat" blocks but without any significant progress.
> 
> What is the best approach for this situation of having to transpose a
> data  stream to a specific output rate ?
> 
> Regards.
> 
> 
> 
> 
> 
> On 1 June 2018 at 22:25, Andy Walls <address@hidden>
> wrote:
> > > From:         Carlo Manfredini
> > > Date:         Fri, 1 Jun 2018 21:24:26 +1000
> > > Hello,
> > > I have a 2kbps bipolar data stream (in hardware) which I will
> > sample
> > > at 48kSps and bring into GR.
> > > Once in GR, I wish to be able to sample only once per bit...so I
> > use
> > > the "Keep 1 in N" block (where N=24) and this reduces my rate to
> > > 2kSps...with 1 sample per original data bit.
> > > 
> > > However, I wish to be able to control exactly at which point in
> > the
> > > 48kSps stream that I sample down to 2kSps.
> > > 
> > > This is equivalent in hardware terms to being able to select at
> > which
> > > point in each bit period that I sample once per bit.ie: selecting
> > the
> > > decision point in an eye pattern).
> > > 
> > > The reason for this process is that I simply wish to read in the
> > > original 2kbps bit stream so that I can use this data to do some
> > PSK
> > > modulation in GR etc...but my inputting device only runs at
> > 48kSps.
> > > 
> > > Is there some way with existing GR blocks that I can tell where
> > > abouts in the 48kSps stream that I have actually sampled ? so
> > that I
> > > can manually set this sampling point.
> > 
> > This is precisely the function of the Symbol Synchronization
> > blocks.
> > 
> > https://www.gnuradio.org/wp-content/uploads/2017/12/Andy-Walls-Samp
> > les-to-Digital-Symbols.pdf
> > 
> > You should play with the example here:
> > 
> > https://github.com/gnuradio/gnuradio/blob/master/gr-digital/example
> > s/demod/symbol_sync_test_float.grc
> > https://github.com/gnuradio/gnuradio/blob/master/gr-digital/example
> > s/demod/symbol_sync_test_float_ted_gain.m
> > 
> > 
> > You'll probably want to do something like:
> > 
> >  -> Decimating FIR filter -> FIR Filter -> Symbol Sync -> Binary
> > Slicer -> 
> > 
> > The first decimating FIR filter would anti-alias filter and
> > downsample
> > by, let's say, 2 or 4, to bring the stream down to either 12 or 6
> > samples per symbol.
> > 
> > The second FIR filter would be a pulse matched filter, to get rid
> > of
> > noise and peak the symbol centers.  (You can merge this filter into
> > the
> > previous filter, if you want.)
> > 
> > The Symbol Sync block estimates the exact symbol centers, and
> > downsamples to just those sample points.
> > 
> > The binary slicer just thresholds its input samples to give you 1
> > or 0
> > valued samples on output.
> > 
> > > Perhaps a simpler question is : how do I know where the "Keep 1
> > in N"
> > > block is sampling ?
> > 
> > You don't.
> > 
> > Regards,
> > Andy
> > 
> > > Thanks for any hints...hopefully I have explained this
> > adequately.
> > 
> 
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

smime.p7s
Description: S/MIME cryptographic signature