Re: [Discuss-gnuradio] correlator in gnuradio

[Nemanja Savic]

Well, I don't really know why you don't get the same n_rcvd as default benchmark. I have never seen that benchmark.
Maybe you have some silly "error" when checkin number of wrong bits. Make flowgraph with both your and default correlator and see what's going on. I would probably do that.

Nemanja

On Thu, Jun 20, 2013 at 4:13 PM, yeran <address@hidden> wrote:

Hi Nemanja,

Thanks for your kind reply!

I'm trying to design a program which will achieve the same result as the default benchmark, because I'll use the default benchmark in some part of the program too. So I use the default threshold 12. I want to make sure that is means that in the 8 Byte access code, at maximum 12 bits can be wrong for gnuradio to "find the pkt". Is this correct?

Specifically, I defined a list 'ac' which is exactly the 64-bit access code. And then compare each of the received 64-bit data with the relevant bit in ac. If they match more than 64-12=52 bits,  one packet is found.

But the test result is that using this code will always find more than the n_rcvd number of packets in default benchmark. (in benchmark, n_rcvd is the total number of packets found).

Looking forward to your further suggestions! Thanks a lot!

Best,
Ada

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Date: Thu, 20 Jun 2013 08:52:09 +0200
Subject: Re: [Discuss-gnuradio] correlator in gnuradio
From: address@hidden
To: address@hidden; address@hidden

Well, I was studying correlator, and it's pretty straight forward approach. If you specify threshold of k bits, then it will output 0x3 every time it finds pattern that differs from given preamble at max. k bits. Maybe you can provide some more information. In my designs I usually use threshold 0.

Best

Nemanja

On Wed, Jun 19, 2013 at 10:21 PM, yeran <address@hidden> wrote:

Hi everyone,

I'm trying to learning the algorithm of the correlator in generic_mod_demod.py. Then use the similar algorithm in my own block.

In the file digital_correlate_access_code_bb.cc, according to my understanding, the original algorithm is compare each bit of the 8-Byte access code with the default 8-Byte access code. If the wrong bits is less than 12 bits (the threshold), then it is decided as "access code found".

I wrote a file to detect access code, too. I compared each of the 8-Byte with the default access code. If the correct bits is more than (64bits - 12 bits), then it is decided to be found.

But when I us my program, when decoding the same data, I can always found more than the original method. For instance, when I use benchmark's original method, I can get n_rcvd=570 pkt, which means in the generic_mod_demod correlator, 570 access code are found. But my program found 577.

Has anybody been study the correlator block before? and see if there is a misunderstanding in my work?

Thanks in advance!

Ada

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Nemanja Savić

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Nemanja Savić