From: Albert Chun-Chieh Huang <address@hidden>
To: Ahmed Zaheer <address@hidden>
Cc: "address@hidden" <address@hidden>
Sent: Saturday, December 1, 2012 7:46 AM
Subject: Re: [Discuss-gnuradio] Direct Sequence Spread Spectrum Question.
Ahmed Zaheer <
address@hidden> 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/