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Re: [Discuss-gnuradio] bpsk lost some packet when transmit data discont


From: Michael Berman
Subject: Re: [Discuss-gnuradio] bpsk lost some packet when transmit data discontinuously
Date: Wed, 10 Mar 2010 14:22:36 -0800

I am not sure why you would be losing packets with one modulator, and not with another.  I unfortunately am not overly familiar with these blocks, and I was not the one who made these modifications for our project.  It could be that the dbpsk modulator is properly padding for the packet size, while the bpsk is not.  This is only a guess on my part.  Either way, it takes a lot of digging to get to the bottom of these problems.

As for the other modifications made to the packetizer.py with the preamble; this was done to give a better chance for the receiver to lock onto the signal before the actual data is sent.

Sorry I could not be more help than this.

-Michael Berman

On Tue, Mar 9, 2010 at 6:08 AM, Fisheep <address@hidden> wrote:

Thanks for your reply.

I thought that the problem can not get enough data to fill up a packet could
happen on any modulator.

But why we could receive every packet properly when using dbpsk and lost
packets when using bpsk?
(Under transmitting each packet with a time interval.)

And I went through the packetizer.py quickly and found that it seems that
different modulations have different packet preambles.
i.e.
preamble = conv_packed_binary_string_to_1_0_string('\xA4\xF2')
preamble_bpsk = conv_packed_binary_string_to_1_0_string('\x55\x55\x55')
preamble_qpsk =
conv_packed_binary_string_to_1_0_string('\x1E\x1E\x1E\x1E\x1E\x1E')
...
Does this different cause the bpsk can not receive data properly?


Again, Thanks for your reply. It really helps me a lot.
I am deeply appreciative.

                           Fisheep :)



Michael Berman-2 wrote:
>
> The problem does not lie with the bpsk modulator, the problem is in the
> packetizer.  The packetizer waits until it gets enough data to completely
> fill up a packet, generally resulting in the loss of the last packet as
> there is not enough data to fill it perfectly.
>
> There is a modified copy of the packetizer.py that you could use that has
> been set up to handle this specific async digital communication scenario
> at
> http://code.google.com/p/softwaredefinedradio .  If you look at
> .../trunk/src/Data_Path, there is a modified Python file for
> packetizer.py.
> You may also want to look at the dpsk.py file in this directory, as it
> shows
> how to set up the top level design to use a message queue for the
> asynchronous sending of packets.  The last (useful) file in this director
> is
> the txrx_controller.py, which establishes a custom rudimentary protocol to
> ensure packet retrieval went well, and all information is received
> properly.  There is some documentation for this in the Docs folder.
>
>
> -Michael Berman
>
> On Tue, Mar 9, 2010 at 12:03 AM, Fisheep <address@hidden> wrote:
>
>>
>> Hi:
>>
>> I have some problem about dbpsk and bpsk using benchmark_tx/rx.py with
>> some
>> modification.
>>
>> My experiment set up was that the transmitter waits for a time delay (0.5
>> s)
>> after sending a packet.
>> It means that we transmit data discontinuously.
>>
>> If we using dbpsk modulation, we can successfully receive every packet.
>> But if we removed the differential encoder/decoder (equals to bpsk
>> modulation), we uaually
>> lost some packet (almost half of the data lost).
>>
>> However, when we transmit data continuously,the bpsk modulation seems
>> work
>> fine and we can successfully receive every packet.
>>
>> My problem is that what reason causing the bpsk modulation can not
>> successfully receive packet when
>> transmit data discontinuously.
>>
>> Could anyone have any idea about it, please let me know.
>> I am deeply appreciative.
>>
>>                             Fisheep :)
>> --
>> View this message in context:
>> http://old.nabble.com/bpsk-lost-some-packet-when-transmit-data-discontinuously-tp27832481p27832481.html
>> Sent from the GnuRadio mailing list archive at Nabble.com.
>>
>>
>>
>> _______________________________________________
>> Discuss-gnuradio mailing list
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>>
>
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>

--
View this message in context: http://old.nabble.com/bpsk-lost-some-packet-when-transmit-data-discontinuously-tp27832481p27836131.html
Sent from the GnuRadio mailing list archive at Nabble.com.



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