kopia lustrzana https://github.com/rs1729/RS
68 wiersze
3.2 KiB
Markdown
68 wiersze
3.2 KiB
Markdown
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## Radiosonde decoders
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alternative decoders using cross-correlation for better header-synchronization
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#### Files
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* `demod_mod.c`, `demod_mod.h`, <br />
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`rs41mod.c`, `rs92mod.c`, `dfm09mod.c`, `m10mod.c`, `lms6mod.c`, `lms6Xmod.c`, `meisei100mod.c`, <br />
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`bch_ecc_mod.c`, `bch_ecc_mod.h`
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#### Compile
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`gcc -c demod_mod.c` <br />
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`gcc -c bch_ecc_mod.c` <br />
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`gcc rs41mod.c demod_mod.o bch_ecc_mod.o -lm -o rs41mod` <br />
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`gcc dfm09mod.c demod_mod.o -lm -o dfm09mod` <br />
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`gcc m10mod.c demod_mod.o -lm -o m10mod` <br />
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`gcc lms6Xmod.c demod_mod.o bch_ecc_mod.o -lm -o lms6Xmod` <br />
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`gcc meisei100mod.c demod_mod.o bch_ecc_mod.o -lm -o meisei100mod` <br />
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`gcc rs92mod.c demod_mod.o bch_ecc_mod.o -lm -o rs92mod` (needs `RS/rs92/nav_gps_vel.c`)
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#### Usage/Examples
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`./rs41mod --ecc2 -vx --ptu <audio.wav>` <br />
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`./dfm09mod --ecc -v --ptu <audio.wav>` (add `-i` for dfm06; or use `--auto`) <br />
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`./m10mod --dc -vv --ptu -c <audio.wav>` <br />
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`./lms6Xmod --vit --ecc -v <audio.wav>` <br />
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IQ data:<br />
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If the IQ data is downsampled and centered (IF band), use <br />
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`./rs41mod --iq2 <iq_data.wav>` <br />
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or with lowpass filter <br />
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`./rs41mod --iq2 --lp <iq_data.wav>` <br />
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For baseband IQ data, use
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`./rs41mod --IQ <fq> <iq_data.wav>` <br />
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where `<fq>` is the relative frequency in `-0.5 .. 0.5`;
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e.g. if the receiver is tuned to 403MHz and the (complex) sample rate is 2MHz,
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a signal at 402.5MHz would be -0.5MHz off, i.e. `<fq> = -0.5/2 = -0.25`. <br />
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For IQ data (i.e. 2 channels) it is possible to read raw data (without wav header): <br />
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`./rs41mod --IQ <fq> - <sr> <bs> <iq_data.raw>` <br />
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`<sr>`: sample rate <br />
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`<bs>=8,16,32`: bits per (real) sample (u8, s16 or f32)
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#### Remarks
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FM-demodulation is sensitive to noise at higher frequencies. A narrow low-pass filter is needed before demodulation.
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For weak signals and higher modulation indices IQ-decoding is usually better.
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<br />
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DFM:<br />
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The high modulation index has advantages in IQ-decoding. <br />
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`--ecc2` uses soft decision for 2-error words. If weak signals frequently produce errors, it is likely that
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more than 2 errors occur in a received word. Since there is no additional frame protection (e.g. CRC), the
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frames will not be decoded reliably in weak conditions. The `--dist` option has a thredshold for the number
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of errors per packet.
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<br />
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LMS6-403:<br />
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`lms6Xmod_soft.c` (testing) provides a soft viterbi decoding option `--vit2`;
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IQ-decoding is recommended for soft decoding (noisy/spikey FM-signals don't always help soft decision).
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The difference between hard and soft viterbi becomes only apparent at lower SNR. The inner convolutional
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code does most of the error correction. The concatenated outer Reed-Solomon code kicks in only at low SNR.
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soft input:<br />
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Option `--softin` expects float32 symbols as input, with `s>0` corresponding to `bit=1`.<br />
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(remark/caution: often soft bits are defined as `bit=0 -> s=+1` and `bit=1 -> s=-1` such that the identity element `0`
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for addition mod 2 corresponds to the identity element `+1` for multiplication.)
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