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Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work

From: Kevin Reid
Subject: Re: [Discuss-gnuradio] simple mod-demod combinations doesn't work
Date: Tue, 25 Oct 2016 15:26:23 -0700

On Tue, Oct 25, 2016 at 2:21 PM, Fons Adriaensen <address@hidden> wrote:
Between the two incoherent domains there is a buffer and a resampler. The resampler is adjusted so that the average number of samples 'in the pipeline' is constant. The problem is finding a reliable and noise-free estimate of that number. At both ends we don't have a clean continuous stream, but samples are written and read in blocks, and the timing of those write and read operations can be irregular. The solution is to have a delay-locked-loop (DLL) at either side to remove measured timing jitter. This provides a continuous mapping of time to the number of samples written and read. The difference between the two is average number of samples in the buffer, which is compared to a target value. The filtered difference then controls the resampling ratio.

For what it's worth, if there were a GNU Radio block which implements this algorithm it would be useful to me.

I develop ShinySDR which is a multipurpose receiver application which can use an arbitrary number of RF sources and software demodulators, and combine the audio outputs where applicable. That in itself presents a clock domain problem, but there are also a variety of other problematic cases (related to live reconfiguration and squelch) which could be addressed with the same solution.

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