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Re: [Discuss-gnuradio] Selecting the precise sampling point from many sa
From: |
CEL |
Subject: |
Re: [Discuss-gnuradio] Selecting the precise sampling point from many samples |
Date: |
Mon, 4 Jun 2018 12:59:19 +0000 |
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.
> >
>
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