Re: [Discuss-gnuradio] Tag preemption USRP sink

[Marcus Müller]

If you're still seeing O's, but they are getting rare, this might be a
good time to play the buffer increase tricks again.


Cheers,
Marcus

On 17.12.2015 18:21, Saulo Queiroz wrote:
> thanks for the explanation ;)
>
> On 17 December 2015 at 15:10, Marcus Müller <address@hidden>
> wrote:
>
>> ha! "O"s in your output mean that the USRP source had to drop samples,
>> because your computer was slower at processing them than the USRP was at
>> producing them, filling up the buffers, until they were full to the brim
>> and nothing more would fit.
>> Of course, reducing the CPU load in this scenario, e.g. by usage of more
>> CPU-efficient filters, will reduce the number of dropped samples, and
>> hence, will reduce the FER!
>>
>>
>> On 17.12.2015 15:14, Saulo Queiroz wrote:
>>
>> Yes.
>>
>> I forgot to mention that I used QPSK 1/2 in the experiments.
>>
>>
>> On 17 December 2015 at 14:01, Marcus Müller-3 [via GnuRadio] 
>> <address@hidden> wrote:
>>
>>
>> Hm, do you see "O"s on the output?
>>
>> On 17.12.2015 15:39, Saulo Queiroz wrote:
>>
>>
>> well, I tried again and, again, FFT behaved better.
>> In case someone else wanna give a try, flowgraphs are attached.
>>
>>
>> On 17 December 2015 at 12:34, Marcus Müller <[hidden email]
>>
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=0> 
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=0>>
>>
>> wrote:
>>
>>
>> Hm, that is an interesting result.
>>
>> The point is that  the polyphase "magic" that allows decimation before
>> pushing samples through a FIR is mathematically 100% equivalent to
>>
>> doing
>>
>> the decimation after the FIR.
>> Nearly the same goes for (non-decimating) FIR vs FFT filter: whereas
>>
>> the
>>
>> FIR really just "pushes" the samples through convolution with the taps
>>
>> in
>>
>> time domain, the FFT filter just multiplies the frequency domain
>> representation of blocks of samples with the frequency domain
>>
>> equivalent to
>>
>> the taps, before transforming the result back to time domain. Should be
>> absolutely identical.
>>
>> Now, the question is: if the filters were functionally actually 100%
>> identical, what would explain the different FER? Or are we comparing
>>
>> the
>>
>> Flowgraph pre-rectructuring with the flowgraph-post-restructuring,
>>
>> where
>>
>> other things have changed, too?
>>
>> Best regards,
>> Marcus
>> On 17.12.2015 12:55, Saulo Queiroz wrote:
>>
>> Hi
>>
>> In my "through-the-air" tests with a couple of B210s the FFT filters
>> presented much lower
>> FER in comparison to the FIR filters at the Rx side. According to [1],
>>
>> the
>>
>> "FFT filters"
>> downsamples after filtering while FIR downsamples before filtering.
>>
>> cheers
>>
>> [1]
>>
>> http://www.trondeau.com/blog/2014/2/27/to-use-or-not-to-use-fft-filters.html
>>
>> On 15 December 2015 at 19:06, Saulo Queiroz <[hidden email]
>>
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=1> 
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=1>> <[hidden 
>> email]<http:///user/SendEmail.jtp?type=node&node=57342&i=2> 
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=2>> wrote:
>>
>>
>> Many thanks Bastian!
>>
>> I checked the loopback version and it seems to work very well.
>>
>> I'll check over-the-air and report here!
>>
>> On 15 December 2015 at 19:04, Bastian Bloessl <[hidden email]
>>
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=3> 
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=3>> <[hidden 
>> email]<http:///user/SendEmail.jtp?type=node&node=57342&i=4> 
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=4>>
>>
>> wrote:
>>
>>
>> Hi,
>>
>> I replaced the Frequency Xlating FFT filters with FIR filters, used the
>> Low-Pass Filter Taps block to generate taps (since I can’t get my head
>> around this notation), and removed the filter from the first
>>
>> conversion.
>>
>> Now, it seems to work. At least it receives frames. If you still have
>> problems I can send you the flow graph.
>>
>> Best,
>> Bastian
>>
>>
>>
>> On 15 Dec 2015, at 10:05, Saulo Queiroz <[hidden email]
>>
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=5> 
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=5>> <[hidden 
>> email]<http:///user/SendEmail.jtp?type=node&node=57342&i=6> 
>> <http:///user/SendEmail.jtp?type=node&node=57342&i=6>> wrote:
>>
>> Each stream has been shiffted with the xlating block.
>> The intention is to "split" a 20 MHz wide analog channel into two of 10
>>
>> MHz.
>>
>> Each 10 MHz channel transmit its own ofdm frame.
>> I attached the flowgraph for more details.
>>
>> thanks in advance.
>>
>> On 15 December 2015 at 17:42, Martin Braun-2 [via GnuRadio] <[hidden
>>
>> email]> wrote:
>>
>> tP indicates you're using corrupt tagged streams, maybe your add block
>> is overlaying them? I'm also not entirely sure what you mean by
>> 'simultaneous parallel transmissions'. Are they on different
>> frequencies? Are you mixing them together in baseband?
>>
>> Cheers,
>> Martin
>>
>>
>> On 15.12.2015 04:10, Saulo Queiroz wrote:
>>
>>
>> Hi all,
>>
>> I'm trying to Tx a same tagged stream simultaneously through two
>>
>> analog
>>
>> orthogonal channels.
>>
>> The flow path of each stream copy is: resampling, adjust tag lenght
>>
>> and
>>
>> xlating FFT filter (with shifting). After this I take the output of
>>
>> each
>>
>> filter and put into and add block then to the USRP sink. I also do the
>> reverse process at the Rx side.
>> With some packets are successfuly receive but with so many losses. At
>> the Tx side I get many "tP". Any tip on how to set simultaneous
>>
>> parallel
>>
>> transmissions without this?
>>
>> I'm using gr-ieee80211 (thanks Bastian and team :) that has worked
>> nicely with the single channel scenario.
>>
>> thanks in advance
>>
>> BR
>>
>> --
>> Saulo Jorge bq
>> - "Beware of bugs in the above code; I have only proved it correct,
>>
>> not
>>
>> tried it."
>> Donald Knuth.
>>
>>
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>>
>> --
>> Saulo Jorge bq
>> - "Beware of bugs in the above code; I have only proved it correct, not
>>
>> tried it."
>>
>> Donald Knuth.
>>
>>  wifi_tx_rx_loopback.grc (134K) Download Attachment
>>
>> View this message in context: Re: Tag preemption USRP sink
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>> --
>> Dipl.-Inform. Bastian Bloessl
>> Distributed Embedded Systems Group
>> University of Paderborn, Germanyhttp://www.ccs-labs.org/~bloessl/
>>
>>  --
>> Saulo Jorge bq
>> - "Beware of bugs in the above code; I have only proved it correct, not
>> tried it."
>> Donald Knuth.
>>
>>
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