correlator: added functions for phase and frequency estimation

This commit is contained in:
Thomas Kolb 2022-02-03 22:17:37 +01:00
parent c17c7e060f
commit 423f1d6416
2 changed files with 83 additions and 0 deletions

View file

@ -1,6 +1,7 @@
#include <stdio.h> #include <stdio.h>
#include <string.h> #include <string.h>
#include <malloc.h> #include <malloc.h>
#include <math.h>
#include "correlator.h" #include "correlator.h"
@ -111,3 +112,58 @@ const float complex* correlator_get_conj_search_sequence(correlator_ctx_t *ctx)
{ {
return ctx->search_sequence; return ctx->search_sequence;
} }
float correlator_get_mean_phase_deviation(correlator_ctx_t *ctx)
{
float complex mean_unrotated_symbol = 0;
size_t n = (ctx->history_ptr - ctx->search_sequence_len + 1) & ctx->buffer_size_mask;
for(size_t m = 0; m < ctx->search_sequence_len; m++) {
size_t nm = (n + m) & ctx->buffer_size_mask;
mean_unrotated_symbol += ctx->search_sequence[m] * ctx->input_history[nm];
}
// no need to divide by ctx->search_sequence_len because division does not change the angle
return cargf(mean_unrotated_symbol);
}
/* Louise & Regiannini frequency estimator */
float correlator_get_mean_frequency_deviation(correlator_ctx_t *ctx)
{
float complex z[ctx->search_sequence_len];
size_t n = (ctx->history_ptr - ctx->search_sequence_len + 1) & ctx->buffer_size_mask;
// remove the influence of the data from the received symbols
for(size_t m = 0; m < ctx->search_sequence_len; m++) {
size_t nm = (n + m) & ctx->buffer_size_mask;
z[m] = ctx->search_sequence[m] * ctx->input_history[nm];
}
// Calculate averaged phase increments for <N> sub-sequences
size_t N = ctx->search_sequence_len/2;
float complex R_kappa[N];
for(size_t kappa = 0; kappa < N; kappa++) {
for(size_t k = 0; k < ctx->search_sequence_len - kappa; k++) {
R_kappa[kappa] += z[k + kappa] * conj(z[k]);
}
R_kappa[kappa] /= ctx->search_sequence_len - kappa;
}
// Calculate phase estimate (in radians/sample)
float complex sum_R_kappa = 0;
for(size_t kappa = 0; kappa < N; kappa++) {
sum_R_kappa += R_kappa[kappa];
}
float arg = cargf(sum_R_kappa);
return arg / ((float)M_PI * (1 + N));
}

View file

@ -112,5 +112,32 @@ void correlator_get_input_history(correlator_ctx_t *ctx, float complex *history)
*/ */
const float complex* correlator_get_conj_search_sequence(correlator_ctx_t *ctx); const float complex* correlator_get_conj_search_sequence(correlator_ctx_t *ctx);
/*!
* \brief Calculate mean phase deviation between current input and search sequence.
*
* \details
* Calling this probably only makes sense directly after a correlation peak was
* found.
*
* \param ctx The correlator context to use.
* \returns The mean phase deviation in radians.
*/
float correlator_get_mean_phase_deviation(correlator_ctx_t *ctx);
/*!
* \brief Calculate mean frequency deviation between current input and search sequence.
*
* \details
* Calling this probably only makes sense directly after a correlation peak was
* found.
*
* This uses the Louise & Regiannini frequency estimation algorithm for known
* symbol sequences.
*
* \param ctx The correlator context to use.
* \returns The mean frequency deviation in radians/symbol.
*/
float correlator_get_mean_frequency_deviation(correlator_ctx_t *ctx);
#endif // CORRELATOR_H #endif // CORRELATOR_H