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

[Fisheep]

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 :)
>> --
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>>
>>
>>
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