Thanks a lot Albert:
I am multiplying my file source with GLFSR source and then giving the product
to modulation blocks in transmitting flowgraph. In the receiving flowgraph
after demodulating the signal I am passing the demodulated signal through PN
Correlator block having same values of degree, mask and seed parameters and
then save the file into sink source. I am not able to receive the same data(it
only works when I use degree=1, mask and seed =0 for both GLFSR and PN
Correlator i.e. making GLFSR a constant source of magnitude 1). Do I have to
use the PN Correlator block in some other manner? Or I should use some other
blocks after PN Correlator block to retrieve the original data?
Regards.
Ahmed.
________________________________
From: Albert Chun-Chieh Huang <alberthuang...@gmail.com>
To: Ahmed Zaheer <ghumman1...@yahoo.com>
Cc: "discuss-gnuradio@gnu.org" <discuss-gnuradio@gnu.org>
Sent: Saturday, December 1, 2012 7:46 AM
Subject: Re: [Discuss-gnuradio] Direct Sequence Spread Spectrum Question.
Ahmed Zaheer <ghumman1...@yahoo.com> writes:
> I was trying to implement Direct Sequence Spread Spectrum in gnuradio. In the
> transmitting flowgraph I am using GLFSR source to multiply it with the file
> which I am transmitting. At the receiver end I am able to receive it by
> multiplying it with same GLFSR source with the same values. But there is no
> acquisition being done. I am seeing a block named PN Correlator. But I don't
> know what this block does and where should I use this block in the flowgraph.
> My question is does anybody know what the PN Correlator block does and is it
> performing the acquisition or not.
>
> Any help/comments would be greatly appreciated.
>
> Regards.
Ahmed,
After taking a look at digital_pn_correlator_cc.cc, I think it's a
serial code acquisition block as described in its header. The output
will be cross-correlation of PN sequence and input samples. Input sample
pointer is advanced by noutput_items samples for each call, and the
output value is derived from multiplying input samples by PN sequence,
both are length of whole PN sequence. If you think noutput_items to be
one, then it will be easier to understand this code. So, yes, it's
serial search code acquisition to my understanding. If you monitor the
output of digital_pn_correlator, you should see a spike when the
acquisition is achieved, and the interval between two spikes will be
roughly the length of PN sequence due to noise effect. I think its input
is time domain samples from your front-end.
This is my understanding of this block. Hope it helps.
Best Regards,
Albert
--
Albert Chun-Chieh Huang(黃俊傑)
Blog: Random Notes, http://alberthuang314.blogspot.com/
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