[USRP-users] Fwd: LFSR SEQUENCE GNURADIO_USRP2

Dan CaJacob dan at spacequest.com
Fri Jun 1 01:00:32 EDT 2012


It's a compact form representing the LFSR taps represented by the polynomial x^4 + x^3 + x^0.  Where x = 2, the polynomial becomes 2^4 + 2^3 + 2^0 = 16 + 8 + 1 = 25.  The hexadecimal representation of decimal 25 is 0x19.

If you google LFSR (linear feedback shift register), you can learn more.  Basically, they are used as pseudo random bit sequence generators, like the Gold codes used in GPS.  Certain taps settings will generate certain lengths of codesbefore the sequence repeats.


On May 31, 2012, at 2:45 PM, Nazmul Islam <mnislam at winlab.rutgers.edu> wrote:

> Click at the GLFSR source and select the type "byte". The byte mode produces 1 & 0 whereas the the float mode produces 1 & -1, etc.
> 
> You can control the sample rate of the GLFSR source by using a throttle. You can find it in the 'Misc' block. You need to put the throttle between the GLFSR source and the USRP sink. I guess that the sampling rate defined in the throttle & the USRP block should be equal.
> 
> As Josh said, the output is simply the connection of the dots. That's why, it is giving triangular shape.
> 
> <<one more thing how to get the desired output ie for x^4 + x^3 + x^0 = 0x19  but where this 0x19 came from?>>
> 
> Not sure about this. Will let you know if I find out.
> 
> Best,
> 
> Nazmul
> 
> On Thu, May 31, 2012 at 2:18 PM, Josh Blum <josh at ettus.com> wrote:
> 
> 
> On 05/31/2012 01:56 AM, JAY PRAKASH wrote:
> > Sir, Actually I have to measure channel impulse response.I am using
> > gnuradio for the purpose. As per the theory I can do so by sending the BPSK
> > modulated PN sequence.But like your doubt I need to know the rate of PN
> > sequence transmission and control it too.But the big doubt is the output of
> > GLFSR.It should be  1 and 0 sequence but here it appears to be 1 and -1
> > and the edges are not sharp too.The output is triangular in cases.I have
> > attached the image of my output.
> > one more thing how to get the desired output ie for x^4 + x^3 + x^0 = 0x19
> > but where this 0x19 came from? I am not able to get it.
> >
> >
> 
> I suspect that the author of the block had a specific use case in mind
> for the -1, 1 But, someone on the gnuradio mailing list may have more
> insight.
> 
> As far as the plot goes, the output looks correct. I recommend changing
> from line mode to dot mode, the output may make more sense then.
> 
> -josh
> 
> > Please help me out in the concerned doubts. I shall be obliged for your
> > support.
> >
> > Thanks
> >
> >
> > Actually
> > Jay Prakash
> > B.Tech Part III
> > Electronics Engineering
> > IIT BHU
> > VARANASI
> >
> >
> >
> >
> > _______________________________________________
> > USRP-users mailing list
> > USRP-users at lists.ettus.com
> > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com
> 
> _______________________________________________
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> 
> 
> -- 
> Muhammad Nazmul Islam
> 
> Graduate Student
> Electrical & Computer Engineering
> Wireless Information & Networking Laboratory
> Rutgers, USA.
> 
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