Is there possible to have item drops?

GNU Radio
1

Hi all,

It seems this is a ridiculous question, however, I didn’t find any
solution
for my problem.

I have already a bunch of custom blocks connected to each other which
play
role as a transmitter (tx). I want to connect tx to a fir filter by
using
fir_filter_ccc block. I set the filter taps with specific ones. I also
have
this filter in Matlab. The output of the filter is connected to a sink
file.

When I see the output (tx) and filtering it by Matlab and comparing it
with
the output of the gnuradio filter, I see both of the following:

  1. Both matlab and gnuradio filtered output, have little difference in a
    range of 0.01. (I’m using gr_complex data).

  2. After a while, Matlab output and GNURadio’s output will differ as
    high
    as 1000 in magnitude!!

I guess, there is item drops in this filtering. I know, the probability
of
this event is so weak, anyway, item drop even can happen in GNURadio?

Where is my problem?

Best,
Mostafa

2

Hello Mostafa,

filtering is a inherently lossy operation: it’s an operation that
involves multiplication and addition of floating point numbers.
Matlab internally uses double (float64) values, whereas GNU Radio,
usually, uses single precision (float32) numbers for performance
reasons.
Now, without knowing what kind of signal you are filtering with what
kind of taps you are using with what kind of GNU Radio filters and what
Matlab functions, there’s nothing to guess on how these differences
occur.
What I can say though is that I’ve never seen an item drop in GNU
Radio’s runtime, and we have strong tests against that. Now, it’s
entirely possible that any of our filter implementations might have
bugs, but I kind of doubt that. It’s most probably simply numeric
accuracy that kills your samples.

Greetings,
Marcus

3

Discuss-gnuradio mailing list
[email protected]
https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

4

I’m a bit confused. Your diagram

TX->FIR->…
->Filesink

Indicates that TX is a source, whereas TX usually is an information sink
in DSP. Maybe you want to fill us in about the type of block TX is?

Greetings,
Marcus

5

Tx is an abbreviation of tx blocks! :slight_smile:

I finally found the problem! I used heap memory but I never release it
in
different blocks! So during the runtime, the memory allocation get the
error: “std::bad_alloc” after somewhile. Now this is fine.

Thank you too much,
Best,
Mostafa

On Thu, Oct 16, 2014 at 4:16 PM, Marcus M. [email protected]
wrote:

something

Best,

multiplication and addition of floating point numbers.
entirely

role as a transmitter (tx). I want to connect tx to a fir filter by

  1. Both matlab and gnuradio filtered output, have little difference in a
    Where is my problem?

–

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6

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On 16.10.2014 22:02, Mostafa A. wrote:

Tx is an abbreviation of tx blocks! :slight_smile:
That still doesn’t make sense! :slight_smile:
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