Re: [Discuss-gnuradio] Tag preemption USRP sink

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 <ssaulojorge@gmail.com> 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 <bloessl@ccs-labs.org>  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 <ssaulojorge@gmail.com> 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.      _______________________________________________  Discuss-gnuradio mailing list  [hidden email]  https://lists.gnu.org/mailman/listinfo/discuss-gnuradio    

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To start a new topic under GnuRadio, email [hidden email]  To unsubscribe from GnuRadio, click here.  NAML        --  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  Sent from the GnuRadio mailing list archive at Nabble.com.  _______________________________________________  Discuss-gnuradio mailing list  Discuss-gnuradio@gnu.org  https://lists.gnu.org/mailman/listinfo/discuss-gnuradio  

  --  Dipl.-Inform. Bastian Bloessl  Distributed Embedded Systems Group  University of Paderborn, Germany  http://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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