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Re: [Discuss-gnuradio] questions about bpsk rx with different noise volt

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] questions about bpsk rx with different noise voltage
Date: Fri, 13 Apr 2012 14:45:39 -0400

On Thu, Apr 12, 2012 at 10:28 PM, Alick Zhao <address@hidden> wrote:
> On Thu, 12 Apr 2012 13:33:01 -0400, Tom Rondeau wrote:
>> Alick,
>> Why are you using 1's and 0's? Is this just for some academic exercise
>> or are you trying to do something with this kind of a constellation?
>> I'm only asking out of curiosity.
>> It also looks like you're heavily biasing the output to be all 1's and
>> very few 0's. That's going to be problematic for the recovery loops.
>> In particular, the FLL uses bandedge filters that rely on the excess
>> bandwidth. If you are never, or rarely, transitioning between symbols,
>> the excess bandwidth of the signal is going to be pretty much absent.
>> So I'd add the randomizer back in and see how that works.
>> For simulation purposes, you can probably go in and remove the FLL
>> from the receiver chain in generic_mod_demod.py.
>> Tom
> Hi Tom, thank you for pointing out the issue of my set up. I want to
> embed channel estimation function into the receiver with training
> sequences (here all 1's). In a practical configuration, I think frame
> structure with preamble containing training sequences and (randomized)
> payload should work. (Is it so?) But now I haven't looked deep into the

Yes, you should be able to use that. As long as you know the data, you
can get the channel estimation.

> packet/frame related code, and I am not sure how to find frame header
> right on constellation. (Could you give some advice?) So I just begin
> with the set up above, which is problematic for the recovery loops.
> Besides, yes I will add the scrambler back in and do some tests.
> alick

Look at the gr_framer_sink_1 (in gnuradio-core/src/lib/general). It's
a state machine that pulls apart the header info.


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