Hi Gilad, You are correct about getting zeros when using history and I am using history. But, I am accounting for that by using the offset:
const gr_complex *current = (const gr_complex *)&((const gr_complex *)input_items[0])[(history() -1)]; Also, if that is the case, shouldn't the behaviour be consistent across unit-tests and flowgraph usage? Regarding getting 0s from the device, I went through the discussion. I agree to it. So, I'll have to account for the zero values. Any ideas on how to do that? The reason why I don't want to use an 'if' block is simply because the situation of 0 values is expected to share a very small fraction of the entire run and to handle that small case, the regular cases will also necessarily have to go through that additional 'if' check. I wanted to avoid that. Regards, Anshul On 31 March 2018 at 10:37, Gilad Beeri (ApolloShield) < [email protected]> wrote: > Disclosure: I haven't looked at your code. > > 0 values can be presented in GNU Radio when you use history, because if > your history is N, the first N-1 items are going to be zeros. > > Anyway, regarding your comment "it is not expected that a device/stream > would ever spit out zero values.", > I did have 0 values from a USRP device, see discussion in > http://lists.ettus.com/pipermail/usrp-users_lists. > ettus.com/2017-October/026851.html. > > > > On Sat, Mar 31, 2018 at 6:52 AM Anshul Thakur <[email protected]> > wrote: > >> Michael, Marcus, >> >> Right now, the code is a work in progress so I haven't made a git >> repository out of it. However, I have it on dropbox. Here's the link to the >> source folder(p1_detector_impl.cc is the source in question): >> >> *https://www.dropbox.com/sh/blfmxsaidrkh28t/AAArp8IHavzCGFlJs6E6-Hrca?dl=0 >> <https://www.dropbox.com/sh/blfmxsaidrkh28t/AAArp8IHavzCGFlJs6E6-Hrca?dl=0>* >> >> As for Marcus's question regarding why use a circular buffer? >> >> It isn't exactly a circular buffer now, but more of a shift register. The >> reasons are as follows: >> 1. I needed running sums for correlations in B-Branch and C-Branch >> correlators, and Power Sums (for average power) to normalize them. Then, I >> also needed a finite delay buffer to delay the C-Branch before it gets >> multiplied with the B-Branch. >> 2. It kind of carried over from the last implementation attempt: >> >> Assertion: If a peak is detected after the multiplication, the signal >> boundary is 1024 samples behind that index. >> >> Once the correlations crossed a threshold (the code entered state=1), >> *instead >> of looking back, I then needed to look forward to see if it were a false >> alarm or not*. So, I compute the correlations across all available >> current inputs and try to find a peak. If a peak is found, enter state=3 >> where we do a correlation with the carrier distribution sequence after FFT >> of all signals of interest. So, here, I not only needed just the single >> value (the running sum), but the entire state of the delay register and the >> B-Branch correlator. >> >> I hope I am able to convey the reason for implementing one myself. >> >> In the current implementation, I make an assumption that the threshold is >> so high that only the desired signals would cross it (100-150 times the >> average). So I skip the state=1 logic and directly go into state=2 logic of >> aggressively doing a FFT and correlation with the CDS. >> >> However, I don't think this has a binding on the incoming values. Use of >> buffers is internal to the implementation, I am just printing out the >> current values as they arrive. >> >> For example, when I use the test file in 'make test', the values fed in >> are non-zero from t=1. However, when using gnuradio-companion, t=56 line is >> where the file source starts yielding proper inputs to my block. The stdout >> prints of the initial values in both GRC and make tests are attached. The >> gnuradio-companion version has my first 55 samples zeroed and the 56th >> input onward is then same for both. >> >> >> P.S.: The source stream is a 1.2 Gigs file, so haven't uploaded it. If >> you'd like I can do that too. It was generated by using a DVB-T2 Tx block >> and writing the output into a file sink. >> >> Warm regards, >> Anshul Thakur >> >> On 31 March 2018 at 02:27, Müller, Marcus (CEL) <[email protected]> wrote: >> >>> Hi Anshul, >>> >>> you shouldn't have to have your own buffer for a running sum – can you >>> explain why you're doing that? >>> A running sum can trivially be implemented with the IIR filter block >>> with Feed-Forward taps (1,) and Feed-back taps (1,0)! >>> Where does in a running sum does a division take place? >>> >>> > (a) Why am I getting the initial zero samples from the file block in >>> > gnuradio_companion and non-zero values when using a vector_source in >>> > unit tests? >>> >>> If these zeros are not in the file you're reading, your block has a >>> bug! >>> >>> >>> > (b) What can I do about it (here specifically as a fix to the >>> > situation, and a general guideline to always remember)? >>> >>> good question, but we'd need to know your code, your motivation for a >>> circular buffer, and why you're implementing a running sum yourself! >>> >>> Best regards, >>> Marcus >>> >>> On Fri, 2018-03-30 at 23:19 +0530, Anshul Thakur wrote: >>> > Hi, >>> > >>> > I used a circular buffer of finite size to keep the past 'N' power >>> > values of the sample stream in my block as a part of creating a >>> > running sum. This buffer is initialized to 0 in the constructor. >>> > The running sum of powers is used to compute the average power used >>> > in computing signal correlation. >>> > >>> > I have a capture stream (cfile) to test the operation of the block. >>> > The test case uses a vector_source_c block to read the contents of >>> > the file into memory. The unit tests pass without error. >>> > >>> > However, when I use the block in a flowgraph in that reads the same >>> > file from a file source block gnuradio_companion, I am getting the >>> > first few sample values as 0 which cause a divide by zero >>> > problem. This messes up the rest of the running sum. I don't want to >>> > put an 'if' block that checks for the zero condition as it is not >>> > expected that a device/stream would ever spit out zero values. >>> > >>> > (a) Why am I getting the initial zero samples from the file block in >>> > gnuradio_companion and non-zero values when using a vector_source in >>> > unit tests? >>> > >>> > (b) What can I do about it (here specifically as a fix to the >>> > situation, and a general guideline to always remember)? >>> > >>> > I am using GNURadio version 3.7.12. >>> > >>> > Regards, >>> > Anshul >>> > _______________________________________________ >>> > Discuss-gnuradio mailing list >>> > [email protected] >>> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> [email protected] >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >
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