File burst_demod_core.h¶

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Feedforward BPSK DSSS frame demodulator. More...

• #include "clib_common.h"
• #include "jm_perf.h"
• #include "ppe/ppe_core.h"
• #include "fft/fft_core.h"
• #include "spectral/spectral_core.h"
• #include <complex.h>

Classes¶

Public Functions¶

Detailed Description¶

The whole post-acquisition payload chain, in C, with no tracking loops: * preamble estimate — segment-despread the unmodulated, repeated acq preamble into partial correlations and feed them to ppe, giving a coarse (frequency, chirp-rate); * sample-rate dechirp by (f0, rate) — removes Doppler AND Doppler rate; * despread the data section with the (short) data code -> soft BPSK symbols; * frame sync — correlate the symbols against the known sync word; the complex peak gives the frame offset and the residual phase (derotated); * slice the payload to bits; verify the CRC-16 trailer -> frame_valid.

Seed from acquisition with set_prior(coarse Doppler, preamble start), set_preamble(acq code, reps) and set_sync(sync word), then demod(burst). One max_rate knob spans near-static Doppler (0) to severe LEO chirp. One-shot per burst. Composes ppe (which composes fft + spectral).

burst_demod_state_t *d = burst_demod_create(dcode, 50, 4, 1e6, 0, 0, 256, 10);
burst_demod_set_preamble(d, acode, 500, 5);
burst_demod_set_sync(d, sync, 31);
burst_demod_set_prior(d, f0_coarse, preamble_start);
size_t nbits = burst_demod_demod(d, x, n, bits, 256);   // d->frame_valid ...

Public Functions Documentation¶

function burst_demod_create¶

Create a burst demodulator.

burst_demod_state_t * burst_demod_create (
    const uint8_t * data_code,
    size_t data_code_len,
    size_t spc,
    double chip_rate,
    double carrier_hz,
    double max_rate,
    size_t payload_len,
    size_t est_segments
) 

Parameters:

• data_code Data spreading code (0/1); copied.
• data_code_len Data spreading factor (chips/symbol).
• spc Samples per chip.
• chip_rate Chip rate (Hz).
• carrier_hz RF carrier (Hz) for code-Doppler scaling; 0 = ignore.
• max_rate Chirp-rate search half-span (cycles/sample^2 at the input rate); 0 = Doppler only (no rate search).
• payload_len Number of payload data symbols (bits) in a frame.
• est_segments Partial correlations per acq period (segmentation for the feedforward estimate; larger tolerates more rate).

Returns:

Heap state, or NULL on bad args / allocation failure.

function burst_demod_demod¶

Demodulate a burst; write the payload bits to out .

size_t burst_demod_demod (
    burst_demod_state_t * state,
    const float complex * x,
    size_t x_len,
    uint8_t * out,
    size_t max_out
) 

Returns:

Number of bits written (0 on failure / too-short burst). The read-back fields (frame_valid, est_*, frame_offset) are updated.

function burst_demod_demod_max_out¶

Max output bits = payload_len (caller sizes the buffer).

size_t burst_demod_demod_max_out (
    burst_demod_state_t * state
) 

function burst_demod_destroy¶

Destroy a demodulator.

void burst_demod_destroy (
    burst_demod_state_t * state
) 

Parameters:

• state May be NULL.

function burst_demod_reset¶

Clear the read-backs (config is preserved).

void burst_demod_reset (
    burst_demod_state_t * state
) 

function burst_demod_set_preamble¶

Set the unmodulated acq preamble code + repetition count.

void burst_demod_set_preamble (
    burst_demod_state_t * state,
    const uint8_t * acq_code,
    size_t acq_code_len,
    size_t reps
) 

function burst_demod_set_prior¶

Seed from acquisition: coarse Doppler + preamble start sample.

void burst_demod_set_prior (
    burst_demod_state_t * state,
    double f0_coarse,
    size_t start
) 

function burst_demod_set_sync¶

Set the known frame-sync word (0/1 symbols).

void burst_demod_set_sync (
    burst_demod_state_t * state,
    const uint8_t * sync,
    size_t sync_len
) 

The documentation for this class was generated from the following file native/inc/burst_demod/burst_demod_core.h