On Tue, Feb 18, 2014 at 5:30 AM, Martin Braun <martin.br...@ettus.com>wrote:
> On 02/18/2014 12:28 AM, Jonathan Fox wrote: > > Dear List, > > > > I am writing a custom QPSK modulator block (demod is next) and I am > > caught up on figuring out the output. > > > > I am taking the byte data type (which I am using C++ char) and for each > > bit of the byte I would have a custom symbol per bit rate. For an > > absolute minimum in a successful PSK system, I would need about two > > symbols per bit. So the sequence of data to be passed through is growing. > > Always use uint8_t or unsigned char when handling bytes. I don't > understand the rest--minimum for PSK would be 1 bit/byte (BPSK). Are you > adaptively changing the modulation? > > > Now for where I am getting confused, when I come up with the I and Q > > data as a complex number I can only send out one sample at a time, > > right? So for each time my general_work executes it can send out only > > one sample at a time while having even more samples calculated > > representing just one value of input_items which upon modulation would > > have quite a bit output samples. At least that is how I am interpreting > > the process. > > Have you read the tutorial on how to write a block? > 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). > > > How do I get out all these samples before I get the next value of the > > input? Should I write the sample values to a buffer that the block > > should check whether it is full before processing the next char sample? > > Anyone with experience writing modulator code have any tips? Can I keep > > updating the value of out in the general_work and it will pass on to the > > flowgraph? > > OK, I really don't know what you're trying to do. Can you please make > sure you've read the tutorial on how to write blocks, and then tell us > exactly what your application is meant to do. Code snippets would also > help. > > > I have tried looking at what I believe is the PSK modulator source code, > > gr_constellation.cc but it is a pretty hard piece of code to follow. > > gr_constellation is just the mapping logic bits <-> symbols. > > > I appreciate any help and feedback. > > MB > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > 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). 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. 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. > 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()? 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. Would that change the output from a single sample to a vector of samples? 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. Again, thank you very much, you have no idea how grateful I am for this help. Jon
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