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Re: [Discuss-gnuradio] Re: One simple question

From: Johnathan Corgan
Subject: Re: [Discuss-gnuradio] Re: One simple question
Date: Tue, 12 Aug 2008 12:11:42 -0700

On Tue, Aug 12, 2008 at 11:47 AM, Jason Uher <address@hidden> wrote:

>>I will be using gold codes as the PN sequences.
>> Is it possible to purely implement in software instead of programming the
>> FPGA. As the rate is only 2Mbps isn't it possible to implement in  software
>> only  given we have a good computer to work with ?
> The 'quick and dirty' option would be to just make vectors containing
> the gold codes you want to use then put them in a repeating vector
> source.

There is a Galois form LFSR stream generator:

gr.glfsr_source_b(degree, repeat=True, mask=0, seed=1)

If the mask is not specified, it will choose one from an internal
table and generate a maximal length PRN sequence of length
2**degree-1, otherwise it will use the mask for the taps and you can
implement your own polynomial.  The degree is valid from 2-32.

The seed value is put into the LFSR as its initial value, and the
repeat parameter will cause the sequence to repeat indefinitely
instead of just once.

The _b suffix indicates that it will create samples of item size 1
(bytes).  These are unpacked; that is, the PRN sequence is transmitted
in the LSB of each byte.

Two of these wired into the inputs of gr.xor_bb will give you a Gold
code, provided you have the correct mask and seed for each of them.

Johnathan Corgan
Corgan Enterprises LLC

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