On 02/19/2014 12:23 AM, Jonathan Fox wrote: > Thank you for the response, I apologize, I wasn't very clear at all in > explaining my problem and I can see that I came across confusing. Let me > quickly re-explain. > > I am creating a QPSK modulator. I have a variable duration/sample rate > (stretching out the bit sequence, incase my terminology is incorrect).
Is your sampling rate variable, or the symbol rate? Where in the modulation process should it vary? > The minimum of it should be about two samples per input bit. I am also > having a minimum two samples/symbol (just like the stock PSK > modulator). I am taking the bit sequence of the input char and I am > using unsigned char datatype like the one block example from the > tutorial unpack_k_bits_bb. Now I am modulating the bit sequence into a > waveform that has a set number of samples as a result of the duration > that is specified. So in the end I have N number of samples generated > for every byte that is received from the input buffer. OK, but how is N calculated? At runtime, or at initialization? > My confusion is the output_buffer. I look at the squarer code from the > tutorial and see general_work() and think of one input sample comes in, > one output sample comes out for each execution of the routine. Lets just > say after processing 1 byte from the input, I have 800 samples of I and > Q data that make up the modulated waveform. Those 800 samples need get > out to the flow graph before the next input comes in. Still don't know how you'd get 800 samples from 1 byte, but let's say that is correct: In this case, you consume() 1 item (byte) and produce() 800 items (samples). >> I don't understand what you're writing. In any block, you can output as >> much items as is space in the output buffer (and should). > > So I can write to the output buffer as much as I need to do, does it > involve set_output_multiple()? You can write to the output buffer equal to or less than noutput_items items. > Do I make sure noutput_items is equal to number of samples I wish to > output? I always though nouput_items equals 1 for non-vector data, and > d_vlen for any vectors whose size is d_vlen. You only read from noutput_items, it's how the scheduler tells you much space there is in the buffer. > Would that change the output from a single sample to a vector of samples? The i/o signature. > I am going to feed directly to the USRP sink, so a vector output is not > what I want, just a continuous stream of samples. > > Also, where can I see the source code for the PSK modulator block? When > I type "PSK" in Nautilus' search function, the only C++ code I see the > receiver, snr estimator. I see python scripts for it qpsk and dpsk, that > have calls for constellation. If that is it, I apologize for my > ignorance, I thought it would be a normal C++ block. We don't need a PSK modulator as such. Open the grc-examples for PSK, and you will see we connect a "chunks to symbols" block to the pulse shaping filter. M _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
