Re: [Discuss-gnuradio] Need of delay=58 in the PSK Symbol Recovery Guided Tutorial

[Francisco Albani]

Thanks, Nathan.

I tried what you suggested:

Blocks:
VS) Vector source: value=range(256), repeat=no.
D) Delay=50.
TS) 2-input Time Sink.

Connections:
VS-->TS(0)
VS-->D-->TS(1)

with this result:

* Pairs fed to the Time Sink:
(0, 0)
(1, 0)
(2, 0)
[...]
(49, 0)
(50, 0)
(51, 1)
(52, 2)
etc.

I expected this result and I have no trouble understanding it.

I'm afraid I wasn't able to express myself correctly.

I'm not ignoring how the delay block works; I'm asking about the 58
initial bits that come out of the receiver (which are paired to the
zeros added by the delay!)

Let me explain it with a diagram:

r: bit from the receiver.
s: bit from the source.

Pairs fed to the Time Sink:

(r0, 0)
(r1, 0)
[...]
(r57, 0)
(r58, s0)  <--- this is the first that matches nicely!
(r59, s1)
etc.

I want to know where the r's come from. Are they just transient values?

Thanks for your patience!

Francisco.

2015-05-23 11:42 GMT-03:00 West, Nathan <address@hidden>:
> Perhaps an experiment will clear this up.
>
> Make a vector source and a two input qt time sink. Make one time sink input
> a direct connection to the vector source. Make the other go to a delay block
> which is then connected to the vector source.
>
> Set the vector source to not repeat and you should see what happens in the
> delay block. Make the vector long enough that you can see something useful
> on the plot (maybe range(256)).
>
> On Saturday, May 23, 2015, Francisco Albani <address@hidden>
> wrote:
>>
>> 2015-05-22 22:46 GMT-03:00 Martin Braun <address@hidden>:
>> > On 22.05.2015 18:13, Francisco Albani wrote:
>> >> Hi Martin and thanks for your answer.
>> >>
>> >> What those zeros added to the original stream align to in the received
>> >> one?
>>
>> Excuse me for my bad English. This is what I wanted to write:
>>
>> {To} what {are} those zeros (added to the original stream) aligned in
>> the received one?
>>
>> >
>> > When you init a delay block with a positive value, it creates a
>> > 'history' (this is actually also the correct GNU Radio term). This is,
>> > by default, a bunch of zeros.
>>
>> I can imagine that, but my point is: that bunch of zeros is going to
>> be consumed, by the 2-input sink, together with 58 samples coming out
>> of the demodulator/decoder.
>>
>> That represents 7 bytes and 2 bits or 29 psk symbols, which actually
>> are upsampled by a factor of 4, resulting in 116 complex samples.
>>
>> I don't understand where are they coming from.
>>
>> > Read our docs w.r.t. history to find out more.
>>
>> I couldn't find them. Can you point them?
>>
>> >
>> > Cheers,
>> > M
>>
>> Many thanks!, Martin.
>>
>> Bye
>>
>> >>
>> >> In other words, where are those 58 "spurious" bits at the beginning of
>> >> the received stream coming from?
>> >>
>> >> Are they just the result of transient behavior inside the sync blocks?
>> >>
>> >> 2015-05-22 21:51 GMT-03:00 Martin Braun <address@hidden>:
>> >>> On 22.05.2015 17:38, Francisco Albani wrote:
>> >>>> Hi, I managed to successfully replicate the results of this tutorial:
>> >>>>
>> >>>>
>> >>>> https://gnuradio.org/redmine/projects/gnuradio/wiki/Guided_Tutorial_PSK_Demodulation
>> >>>>
>> >>>> and, of course I understand the reason for a delay between the bits
>> >>>> of
>> >>>> the source and the receiver.
>> >>>>
>> >>>> But then I was struck by this: considering that the 2-input QT GUI
>> >>>> Time Sink consumes one sample of each at the same time and waits
>> >>>> otherwise, wouldn't this act as an "involuntary" synchronizer for the
>> >>>> bit streams?
>> >>>
>> >>> The time sink will consume input streams synchronously, that's
>> >>> correct,
>> >>> but in this example, we also want to make sure the actual content is
>> >>> sync'd as well. So the delay block will insert some zeros before the
>> >>> signal starts, shifting signal in time such that they become aligned
>> >>> in
>> >>> the time sink.
>> >>>
>> >>> M
>> >>>
>> >>>
>> >>> _______________________________________________
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>> >
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