369 lines
16 KiB
C
369 lines
16 KiB
C
|
|
#include <unistd.h>
|
|
#include <stdbool.h>
|
|
#include <math.h>
|
|
#include <stdlib.h>
|
|
#include <assert.h>
|
|
|
|
#include <arm_math.h>
|
|
|
|
#include "freq_meas.h"
|
|
#include "sr_global.h"
|
|
#include "dsss_demod.h"
|
|
#include "simulation.h"
|
|
|
|
#include "generated/dsss_gold_code.h"
|
|
// #include "generated/dsss_butter_filter.h"
|
|
|
|
/* Generated CWT wavelet LUT */
|
|
extern const float * const dsss_cwt_wavelet_table;
|
|
|
|
//struct iir_biquad cwt_filter_bq[DSSS_FILTER_CLEN] = {DSSS_FILTER_COEFF};
|
|
|
|
void debug_print_vector(const char *name, size_t len, const float *data, size_t stride, bool index, bool debug);
|
|
static float gold_correlate_step(const size_t ncode, const float a[DSSS_CORRELATION_LENGTH], size_t offx, bool debug);
|
|
static float cwt_convolve_step(const float v[DSSS_WAVELET_LUT_SIZE], size_t offx);
|
|
//static float run_iir(const float x, const int order, const struct iir_biquad q[order], struct iir_biquad_state st[order]);
|
|
//static float run_biquad(float x, const struct iir_biquad *const q, struct iir_biquad_state *const restrict st);
|
|
static void matcher_init(struct matcher_state states[static DSSS_MATCHER_CACHE_SIZE]);
|
|
static void matcher_tick(struct matcher_state states[static DSSS_MATCHER_CACHE_SIZE],
|
|
uint64_t ts, int peak_ch, float peak_ampl);
|
|
static void group_received(struct dsss_demod_state *st);
|
|
static symbol_t decode_peak(int peak_ch, float peak_ampl);
|
|
|
|
#ifdef SIMULATION
|
|
void debug_print_vector(const char *name, size_t len, const float *data, size_t stride, bool index, bool debug) {
|
|
if (!debug)
|
|
return;
|
|
|
|
if (index) {
|
|
DEBUG_PRINTN(" %16s [", "");
|
|
for (size_t i=0; i<len; i++)
|
|
DEBUG_PRINTN("%8zu ", i);
|
|
DEBUG_PRINTN("]\n");
|
|
}
|
|
|
|
DEBUG_PRINTN(" %16s: [", name);
|
|
for (size_t i=0; i<len; i++)
|
|
DEBUG_PRINTN("%8.5f, ", data[i*stride]);
|
|
DEBUG_PRINTN("]\n");
|
|
}
|
|
#else
|
|
void debug_print_vector(unused_a const char *name, unused_a size_t len, unused_a const float *data,
|
|
unused_a size_t stride, unused_a bool index, unused_a bool debug) {}
|
|
#endif
|
|
|
|
void dsss_demod_init(struct dsss_demod_state *st) {
|
|
memset(st, 0, sizeof(*st));
|
|
matcher_init(st->matcher_cache);
|
|
}
|
|
|
|
void dsss_demod_step(struct dsss_demod_state *st, float new_value, uint64_t ts) {
|
|
//const float hole_patching_threshold = 0.01 * DSSS_CORRELATION_LENGTH;
|
|
bool log = false;
|
|
bool log_groups = false;
|
|
|
|
st->signal[st->signal_wpos] = new_value;
|
|
st->signal_wpos = (st->signal_wpos + 1) % ARRAY_LENGTH(st->signal);
|
|
|
|
/* use new, incremented wpos for gold_correlate_step as first element of old data in ring buffer */
|
|
for (size_t i=0; i<DSSS_GOLD_CODE_COUNT; i++)
|
|
st->correlation[i][st->correlation_wpos] = gold_correlate_step(i, st->signal, st->signal_wpos, false);
|
|
|
|
st->correlation_wpos = (st->correlation_wpos + 1) % ARRAY_LENGTH(st->correlation[0]);
|
|
|
|
float cwt[DSSS_GOLD_CODE_COUNT];
|
|
for (size_t i=0; i<DSSS_GOLD_CODE_COUNT; i++)
|
|
cwt[i] = cwt_convolve_step(st->correlation[i], st->correlation_wpos);
|
|
|
|
float avg = 0.0f;
|
|
for (size_t i=0; i<DSSS_GOLD_CODE_COUNT; i++)
|
|
avg += fabsf(cwt[i]);
|
|
avg /= (float)DSSS_GOLD_CODE_COUNT;
|
|
if (log) DEBUG_PRINTN("%6zu: %f ", ts, avg);
|
|
/* FIXME fix this filter */
|
|
//avg = run_iir(avg, ARRAY_LENGTH(cwt_filter_bq), cwt_filter_bq, st->cwt_filter.st);
|
|
|
|
float max_val = st->group.max;
|
|
int max_ch = st->group.max_ch;
|
|
int max_ts = st->group.max_ts;
|
|
bool found = false;
|
|
for (size_t i=0; i<DSSS_GOLD_CODE_COUNT; i++) {
|
|
float val = cwt[i] / avg;
|
|
if (log) DEBUG_PRINTN("%f ", cwt[i]);
|
|
if (log) DEBUG_PRINTN("%f ", val);
|
|
|
|
if (fabsf(val) > fabsf(max_val)) {
|
|
max_val = val;
|
|
max_ch = i;
|
|
max_ts = ts;
|
|
}
|
|
|
|
if (fabsf(val) > DSSS_THRESHOLD_FACTOR)
|
|
found = true;
|
|
}
|
|
if (log) DEBUG_PRINTN("%f %d ", max_val, found);
|
|
if (log) DEBUG_PRINTN("\n");
|
|
|
|
matcher_tick(st->matcher_cache, ts, max_ch, max_val);
|
|
|
|
if (found) {
|
|
/* Continue ongoing group */
|
|
st->group.len++;
|
|
st->group.max = max_val;
|
|
st->group.max_ch = max_ch;
|
|
st->group.max_ts = max_ts;
|
|
return;
|
|
}
|
|
|
|
if (st->group.len == 0)
|
|
/* We're between groups */
|
|
return;
|
|
|
|
if (log_groups) DEBUG_PRINTN("GROUP: %zu %d %f\n", st->group.max_ts, st->group.max_ch, st->group.max);
|
|
/* A group ended. Process result. */
|
|
group_received(st);
|
|
|
|
/* reset grouping state */
|
|
st->group.len = 0;
|
|
st->group.max_ts = 0;
|
|
st->group.max_ch = 0;
|
|
st->group.max = 0.0f;
|
|
}
|
|
|
|
/* Map a sequence match to a data symbol. This maps the sequence's index number to the 2nd to n+2nd bit of the result,
|
|
* and maps the polarity of detection to the LSb. 5-bit example:
|
|
*
|
|
* [0, S, S, S, S, S, S, P] ; S ^= symbol index (0 - 2^n+1 so we need just about n+1 bit), P ^= symbol polarity
|
|
*
|
|
* Symbol polarity is preserved from transmitter to receiver. The symbol index is n+1 bit instead of n bit since we have
|
|
* 2^n+1 symbols to express, one too many for an n-bit index.
|
|
*/
|
|
symbol_t decode_peak(int peak_ch, float peak_ampl) {
|
|
return (peak_ch<<1) | (peak_ampl > 0);
|
|
}
|
|
|
|
void matcher_init(struct matcher_state states[static DSSS_MATCHER_CACHE_SIZE]) {
|
|
for (size_t i=0; i<DSSS_MATCHER_CACHE_SIZE; i++)
|
|
states[i].last_phase = -1; /* mark as inactive */
|
|
}
|
|
|
|
/* TODO make these constants configurable from Makefile */
|
|
const int group_phase_tolerance = (int)(DSSS_CORRELATION_LENGTH * 0.10);
|
|
|
|
void matcher_tick(struct matcher_state states[static DSSS_MATCHER_CACHE_SIZE], uint64_t ts, int peak_ch, float peak_ampl) {
|
|
/* TODO make these constants configurable from Makefile */
|
|
const float skip_sampling_depreciation = 0.2f; /* 0.0 -> no depreciation, 1.0 -> complete disregard */
|
|
const float score_depreciation = 0.1f; /* 0.0 -> no depreciation, 1.0 -> complete disregard */
|
|
const int current_phase = ts % DSSS_CORRELATION_LENGTH;
|
|
const int max_skips = TRANSMISSION_SYMBOLS/4*3;
|
|
bool debug = false;
|
|
|
|
bool header_printed = false;
|
|
for (size_t i=0; i<DSSS_MATCHER_CACHE_SIZE; i++) {
|
|
if (states[i].last_phase == -1)
|
|
continue; /* Inactive entry */
|
|
|
|
if (current_phase == states[i].last_phase) {
|
|
/* Skip sampling */
|
|
float score = fabsf(peak_ampl) * (1.0f - skip_sampling_depreciation);
|
|
if (score > states[i].candidate_score) {
|
|
if (debug && !header_printed) {
|
|
header_printed = true;
|
|
DEBUG_PRINTN("windows %zu\n", ts);
|
|
}
|
|
if (debug) DEBUG_PRINTN(" skip %zd old=%f new=%f\n", i, states[i].candidate_score, score);
|
|
/* We win, update candidate */
|
|
assert(i < DSSS_MATCHER_CACHE_SIZE);
|
|
states[i].candidate_score = score;
|
|
states[i].candidate_phase = current_phase;
|
|
states[i].candidate_data = decode_peak(peak_ch, peak_ampl);
|
|
states[i].candidate_skips = 1;
|
|
}
|
|
}
|
|
|
|
/* Note of caution on group_phase_tolerance: Group detection has some latency since a group is only considered
|
|
* "detected" after signal levels have fallen back below the detection threshold. This means we only get to
|
|
* process a group a couple ticks after its peak. We have to make sure the window is still open at this point.
|
|
* This means we have to match against group_phase_tolerance should a little bit loosely.
|
|
*/
|
|
int phase_delta = current_phase - states[i].last_phase;
|
|
if (phase_delta < 0)
|
|
phase_delta += DSSS_CORRELATION_LENGTH;
|
|
if (phase_delta == group_phase_tolerance + DSSS_DECIMATION) {
|
|
if (debug && !header_printed) {
|
|
header_printed = true;
|
|
DEBUG_PRINTN("windows %zu\n", ts);
|
|
}
|
|
if (debug) DEBUG_PRINTN(" %zd ", i);
|
|
/* Process window results */
|
|
assert(i < DSSS_MATCHER_CACHE_SIZE);
|
|
assert(0 <= states[i].data_pos && states[i].data_pos < TRANSMISSION_SYMBOLS);
|
|
states[i].data[ states[i].data_pos ] = states[i].candidate_data;
|
|
states[i].data_pos = states[i].data_pos + 1;
|
|
states[i].last_score = score_depreciation * states[i].last_score +
|
|
(1.0f - score_depreciation) * states[i].candidate_score;
|
|
if (debug) DEBUG_PRINTN("commit pos=%d val=%d score=%f ", states[i].data_pos, states[i].candidate_data, states[i].last_score);
|
|
states[i].candidate_score = 0.0f;
|
|
states[i].last_skips += states[i].candidate_skips;
|
|
|
|
if (states[i].last_skips > max_skips) {
|
|
if (debug) DEBUG_PRINTN("expire ");
|
|
states[i].last_phase = -1; /* invalidate entry */
|
|
|
|
} else if (states[i].data_pos == TRANSMISSION_SYMBOLS) {
|
|
if (debug) DEBUG_PRINTN("match ");
|
|
/* Frame received completely */
|
|
handle_dsss_received(states[i].data);
|
|
states[i].last_phase = -1; /* invalidate entry */
|
|
}
|
|
if (debug) DEBUG_PRINTN("\n");
|
|
}
|
|
}
|
|
}
|
|
|
|
static float gaussian(float a, float b, float c, float x) {
|
|
float n = x-b;
|
|
return a*expf(-n*n / (2.0f* c*c));
|
|
}
|
|
|
|
|
|
static float score_group(const struct group *g, int phase_delta) {
|
|
/* TODO make these constants configurable from Makefile */
|
|
const float distance_func_phase_tolerance = 10.0f;
|
|
return fabsf(g->max) * gaussian(1.0f, 0.0f, distance_func_phase_tolerance, phase_delta);
|
|
}
|
|
|
|
void group_received(struct dsss_demod_state *st) {
|
|
bool debug = false;
|
|
const int group_phase = st->group.max_ts % DSSS_CORRELATION_LENGTH;
|
|
/* This is the score of a decoding starting at this group (with no context) */
|
|
float base_score = score_group(&st->group, 0);
|
|
|
|
float min_score = INFINITY;
|
|
ssize_t min_idx = -1;
|
|
ssize_t empty_idx = -1;
|
|
for (size_t i=0; i<DSSS_MATCHER_CACHE_SIZE; i++) {
|
|
|
|
/* Search for empty entries */
|
|
if (st->matcher_cache[i].last_phase == -1) {
|
|
empty_idx = i;
|
|
continue;
|
|
}
|
|
|
|
/* Search for entries with matching phase */
|
|
/* This is the score of this group given the cached decoding at [i] */
|
|
int phase_delta = st->matcher_cache[i].last_phase - group_phase;
|
|
if (abs(phase_delta) <= group_phase_tolerance) {
|
|
|
|
float group_score = score_group(&st->group, phase_delta);
|
|
if (st->matcher_cache[i].candidate_score < group_score) {
|
|
assert(i < DSSS_MATCHER_CACHE_SIZE);
|
|
if (debug) DEBUG_PRINTN(" appending %zu %d score=%f pd=%d\n", i, decode_peak(st->group.max_ch, st->group.max), group_score, phase_delta);
|
|
/* Append to entry */
|
|
st->matcher_cache[i].candidate_score = group_score;
|
|
st->matcher_cache[i].candidate_phase = group_phase;
|
|
st->matcher_cache[i].candidate_data = decode_peak(st->group.max_ch, st->group.max);
|
|
st->matcher_cache[i].candidate_skips = 0;
|
|
}
|
|
}
|
|
|
|
/* Search for weakest entry */
|
|
/* TODO figure out this fitness function */
|
|
float score = st->matcher_cache[i].last_score * (1.5f + 0.1 * st->matcher_cache[i].data_pos);
|
|
if (debug) DEBUG_PRINTN(" score %zd %f %f %d", i, score, st->matcher_cache[i].last_score, st->matcher_cache[i].data_pos);
|
|
if (score < min_score) {
|
|
min_idx = i;
|
|
min_score = score;
|
|
}
|
|
}
|
|
|
|
/* If we found empty entries, replace one by a new decoding starting at this group */
|
|
if (empty_idx >= 0) {
|
|
if (debug) DEBUG_PRINTN(" empty %zd %d\n", empty_idx, decode_peak(st->group.max_ch, st->group.max));
|
|
assert(0 <= empty_idx && empty_idx < DSSS_MATCHER_CACHE_SIZE);
|
|
st->matcher_cache[empty_idx].last_phase = group_phase;
|
|
st->matcher_cache[empty_idx].candidate_score = base_score;
|
|
st->matcher_cache[empty_idx].last_score = base_score;
|
|
st->matcher_cache[empty_idx].candidate_phase = group_phase;
|
|
st->matcher_cache[empty_idx].candidate_data = decode_peak(st->group.max_ch, st->group.max);
|
|
st->matcher_cache[empty_idx].data_pos = 0;
|
|
st->matcher_cache[empty_idx].candidate_skips = 0;
|
|
st->matcher_cache[empty_idx].last_skips = 0;
|
|
|
|
/* If the weakest decoding in cache is weaker than a new decoding starting here, replace it */
|
|
} else if (min_score < base_score && min_idx >= 0) {
|
|
if (debug) DEBUG_PRINTN(" min %zd %d\n", min_idx, decode_peak(st->group.max_ch, st->group.max));
|
|
assert(0 <= min_idx && min_idx < DSSS_MATCHER_CACHE_SIZE);
|
|
st->matcher_cache[min_idx].last_phase = group_phase;
|
|
st->matcher_cache[min_idx].candidate_score = base_score;
|
|
st->matcher_cache[min_idx].last_score = base_score;
|
|
st->matcher_cache[min_idx].candidate_phase = group_phase;
|
|
st->matcher_cache[min_idx].candidate_data = decode_peak(st->group.max_ch, st->group.max);
|
|
st->matcher_cache[min_idx].data_pos = 0;
|
|
st->matcher_cache[min_idx].candidate_skips = 0;
|
|
st->matcher_cache[min_idx].last_skips = 0;
|
|
}
|
|
}
|
|
|
|
#if 0
|
|
float run_iir(const float x, const int order, const struct iir_biquad q[order], struct iir_biquad_state st[order]) {
|
|
float intermediate = x;
|
|
for (int i=0; i<(order+1)/2; i++)
|
|
intermediate = run_biquad(intermediate, &q[i], &st[i]);
|
|
return intermediate;
|
|
}
|
|
|
|
float run_biquad(float x, const struct iir_biquad *const q, struct iir_biquad_state *const restrict st) {
|
|
/* direct form 2, see https://en.wikipedia.org/wiki/Digital_biquad_filter */
|
|
float intermediate = x + st->reg[0] * -q->a[0] + st->reg[1] * -q->a[1];
|
|
float out = intermediate * q->b[0] + st->reg[0] * q->b[1] + st->reg[1] * q->b[2];
|
|
st->reg[1] = st->reg[0];
|
|
st->reg[0] = intermediate;
|
|
return out;
|
|
}
|
|
#endif
|
|
|
|
float cwt_convolve_step(const float v[DSSS_WAVELET_LUT_SIZE], size_t offx) {
|
|
float sum = 0.0f;
|
|
for (ssize_t j=0; j<DSSS_WAVELET_LUT_SIZE; j++) {
|
|
/* Our wavelet is symmetric so convolution and correlation are identical. Use correlation here for ease of
|
|
* implementation */
|
|
sum += v[(offx + j) % DSSS_WAVELET_LUT_SIZE] * dsss_cwt_wavelet_table[j];
|
|
//DEBUG_PRINT(" j=%d v=%f w=%f", j, v[(offx + j) % DSSS_WAVELET_LUT_SIZE], dsss_cwt_wavelet_table[j]);
|
|
}
|
|
return sum;
|
|
}
|
|
|
|
/* Compute last element of correlation for input [a] and hard-coded gold sequences.
|
|
*
|
|
* This is intened to be used once for each new incoming sample in [a]. It expects [a] to be of length
|
|
* [dsss_correlation_length] and produces the one sample where both the reference sequence and the input fully overlap.
|
|
* This is equivalent to "valid" mode in numpy's terminology[0].
|
|
*
|
|
* [0] https://docs.scipy.org/doc/numpy/reference/generated/numpy.correlate.html
|
|
*/
|
|
float gold_correlate_step(const size_t ncode, const float a[DSSS_CORRELATION_LENGTH], size_t offx, bool debug) {
|
|
|
|
float acc_outer = 0.0f;
|
|
uint8_t table_byte = 0;
|
|
if (debug) DEBUG_PRINTN("Correlate n=%zd: ", ncode);
|
|
for (size_t i=0; i<DSSS_GOLD_CODE_LENGTH; i++) {
|
|
|
|
if ((i&7) == 0) {
|
|
table_byte = dsss_gold_code_table[ncode][i>>3]; /* Fetch sequence table item */
|
|
if (debug) DEBUG_PRINTN("|");
|
|
}
|
|
int bv = table_byte & (0x80>>(i&7)); /* Extract bit */
|
|
bv = !!bv*2 - 1; /* Map 0, 1 -> -1, 1 */
|
|
if (debug) DEBUG_PRINTN("%s%d\033[0m", bv == 1 ? "\033[92m" : "\033[91m", (bv+1)/2);
|
|
|
|
float acc_inner = 0.0f;
|
|
for (size_t j=0; j<DSSS_DECIMATION; j++)
|
|
acc_inner += a[(offx + i*DSSS_DECIMATION + j) % DSSS_CORRELATION_LENGTH]; /* Multiply item */
|
|
//if (debug) DEBUG_PRINTN("%.2f ", acc_inner);
|
|
acc_outer += acc_inner * bv;
|
|
}
|
|
if (debug) DEBUG_PRINTN("\n");
|
|
return acc_outer / DSSS_CORRELATION_LENGTH;
|
|
}
|