Use new frequency+phase estimation method for preamble
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8060137c1d
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@ -3,6 +3,8 @@
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#include <malloc.h>
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#include <math.h>
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#include "freq_est.h"
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#include "correlator.h"
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bool correlator_init(correlator_ctx_t *ctx, const float complex *search_seq, size_t nsymbols)
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@ -114,13 +116,13 @@ const float complex* correlator_get_conj_search_sequence(correlator_ctx_t *ctx)
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}
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float correlator_get_mean_phase_deviation(correlator_ctx_t *ctx)
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float correlator_get_mean_phase_deviation(correlator_ctx_t *ctx, size_t L)
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{
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float complex mean_unrotated_symbol = 0;
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size_t n = (ctx->history_ptr - ctx->search_sequence_len + 1) & ctx->buffer_size_mask;
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for(size_t m = 0; m < ctx->search_sequence_len; m++) {
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for(size_t m = ctx->search_sequence_len - L; m < ctx->search_sequence_len; m++) {
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size_t nm = (n + m) & ctx->buffer_size_mask;
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mean_unrotated_symbol += ctx->search_sequence[m] * ctx->input_history[nm];
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}
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@ -130,30 +132,32 @@ float correlator_get_mean_phase_deviation(correlator_ctx_t *ctx)
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}
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/* Louise & Regiannini frequency estimator */
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float correlator_get_mean_frequency_deviation(correlator_ctx_t *ctx)
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float correlator_get_mean_frequency_deviation(correlator_ctx_t *ctx, size_t L, float *phase_offset)
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{
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float complex z[ctx->search_sequence_len];
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float complex z[L];
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size_t n = (ctx->history_ptr - ctx->search_sequence_len + 1) & ctx->buffer_size_mask;
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// remove the influence of the data from the received symbols
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for(size_t m = 0; m < ctx->search_sequence_len; m++) {
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size_t m0 = ctx->search_sequence_len - L;
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for(size_t m = m0; m < ctx->search_sequence_len; m++) {
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size_t nm = (n + m) & ctx->buffer_size_mask;
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z[m] = ctx->search_sequence[m] * ctx->input_history[nm];
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z[m - m0] = ctx->search_sequence[m] * ctx->input_history[nm];
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printf("%+.6f%+.6fj - %+.6f%+.6fj\n", crealf(ctx->search_sequence[m]), cimagf(ctx->search_sequence[m]), crealf(ctx->input_history[nm]), cimagf(ctx->input_history[nm]));
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}
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/* Louise & Regiannini frequency estimator */
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/*
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// Calculate averaged phase increments for <N> sub-sequences
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size_t N = ctx->search_sequence_len/2;
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size_t N = L/2;
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float complex R_kappa[N];
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for(size_t kappa = 0; kappa < N; kappa++) {
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for(size_t k = 0; k < ctx->search_sequence_len - kappa; k++) {
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for(size_t k = 0; k < L - kappa; k++) {
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R_kappa[kappa] += z[k + kappa] * conj(z[k]);
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}
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R_kappa[kappa] /= ctx->search_sequence_len - kappa;
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R_kappa[kappa] /= L - kappa;
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}
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// Calculate phase estimate (in radians/sample)
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@ -165,5 +169,8 @@ float correlator_get_mean_frequency_deviation(correlator_ctx_t *ctx)
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float arg = cargf(sum_R_kappa);
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return arg / ((float)M_PI * (1 + N));
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return arg / (1 + N);
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*/
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return freq_est_data_free(z, L, phase_offset);
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}
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@ -120,9 +120,10 @@ const float complex* correlator_get_conj_search_sequence(correlator_ctx_t *ctx);
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* found.
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*
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* \param ctx The correlator context to use.
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* \param L Number of symbols to use (at the end of the sequence)
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* \returns The mean phase deviation in radians.
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*/
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float correlator_get_mean_phase_deviation(correlator_ctx_t *ctx);
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float correlator_get_mean_phase_deviation(correlator_ctx_t *ctx, size_t L);
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/*!
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* \brief Calculate mean frequency deviation between current input and search sequence.
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@ -135,9 +136,12 @@ float correlator_get_mean_phase_deviation(correlator_ctx_t *ctx);
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* symbol sequences.
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*
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* \param ctx The correlator context to use.
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* \param L Number of symbols to use (at the end of the sequence)
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* \param phase_offset The phase offset of the symbol *following* the preamble.
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* May be NULL if not needed.
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* \returns The mean frequency deviation in radians/symbol.
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*/
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float correlator_get_mean_frequency_deviation(correlator_ctx_t *ctx);
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float correlator_get_mean_frequency_deviation(correlator_ctx_t *ctx, size_t L, float *phase_offset);
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#endif // CORRELATOR_H
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@ -22,8 +22,7 @@ static void linear_regression(size_t nx, const float *y, float *m, float *t)
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}
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*m = numerator / denominator;
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//*t = mean_y - (*m) * mean_x;
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*t = y[0]; // This should work because x always starts at 0.
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*t = mean_y - (*m) * mean_x;
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}
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@ -52,12 +51,23 @@ float freq_est_unknown_bpsk(const float complex *recv, size_t n, float *final_ph
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float freq_est_known_symbols(const float complex *recv, const float complex *ref, size_t n, float *final_phase)
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{
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float complex symbols[n];
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// remove the data influence from the symbols
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for(size_t i = 0; i < n; i++) {
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symbols[i] = conjf(ref[i]) * recv[i];
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}
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return freq_est_data_free(symbols, n, final_phase);
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}
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float freq_est_data_free(const float complex *symbols, size_t n, float *final_phase)
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{
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float phases[n];
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// square the symbols and calculate phase
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for(size_t i = 0; i < n; i++) {
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phases[i] = cargf(conjf(ref[i]) * recv[i]);
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phases[i] = cargf(symbols[i]);
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}
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liquid_unwrap_phase(phases, n);
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@ -23,8 +23,8 @@ float freq_est_unknown_bpsk(const float complex *recv, size_t n, float *final_ph
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* \brief Estimate the frequency of known symbols.
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*
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* This function removes the data influence by calculating
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* recv[k]*conj(ref[k]), calculates the phase values and then performs linear
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* regression on those to determine the frequency.
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* recv[k]*conj(ref[k]), and then calls \ref freq_est_data_free() with the
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* result.
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*
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* \param recv Pointer to the array of received symbols.
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* \param ref Pointer to the array of reference symbols (e.g. a preamble).
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@ -35,4 +35,18 @@ float freq_est_unknown_bpsk(const float complex *recv, size_t n, float *final_ph
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*/
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float freq_est_known_symbols(const float complex *recv, const float complex *ref, size_t n, float *final_phase);
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/*!
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* \brief Estimate the frequency from data-free symbols.
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*
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* This function calculates the phase values from the given symbols and then
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* performs linear regression on those to determine the frequency.
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*
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* \param symbols Pointer to the array of received symbols.
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* \param n Number of symbols given.
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* \param final_phase Pointer to a float where the phase correction value is
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* stored. May be NULL if that value is not required.
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* \returns The estimated frequency in radians per sample.
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*/
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float freq_est_data_free(const float complex *symbols, size_t n, float *final_phase);
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#endif // FREQ_EST_H
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@ -141,15 +141,15 @@ int main(void)
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// Preamble found!
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printf("Preamble found at symbol %u: %.3f > %.3f\n", i/RRC_SPS, cabsf(corr_out), 0.5f * preamble_get_symbol_count());
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float mean_phase_error = correlator_get_mean_phase_deviation(&preamble_correlator);
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float mean_frequency_error = correlator_get_mean_frequency_deviation(&preamble_correlator);
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float phase_offset;
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float mean_frequency_error = correlator_get_mean_frequency_deviation(&preamble_correlator, FREQ_EST_L, &phase_offset);
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printf("Preamble phase deviation: %.6f rad\n", mean_phase_error);
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printf("Phase offset: %.6f rad\n", phase_offset);
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printf("Preamble frequency deviation: %.6f rad/symbol\n", mean_frequency_error);
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// adjust the frequency and phase of the NCO with the estimations from the preamble
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nco_crcf_adjust_frequency(carrier_nco, -mean_frequency_error / RRC_SPS);
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nco_crcf_adjust_phase(carrier_nco, mean_phase_error);
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nco_crcf_adjust_frequency(carrier_nco, mean_frequency_error / RRC_SPS * 0.5f);
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nco_crcf_adjust_phase(carrier_nco, phase_offset);
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printf("New estimated carrier frequency: %.6f\n", nco_crcf_get_frequency(carrier_nco));
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@ -160,7 +160,7 @@ int main(void)
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printf("import matplotlib.pyplot as pp\n");
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print_complex_array("pre", preamble_get_symbols(), preamble_get_symbol_count());
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print_complex_array("recv", input_history, preamble_get_symbol_count());
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printf("pp.plot(recv * pre.conj())\n");
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printf("pp.plot(np.angle(recv * pre.conj()))\n");
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printf("pp.show()\n");
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// receive and decode the header
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@ -174,7 +174,7 @@ int main(void)
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if(((i/RRC_SPS) % FREQ_EST_L) == 0) {
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float freq_est = freq_est_unknown_bpsk(symsync_out + symsync_out_len - FREQ_EST_L, FREQ_EST_L, NULL);
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float freq_adjustment = (freq_est / RRC_SPS) * 0.5f;
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float freq_adjustment = (freq_est / RRC_SPS) * 0.3f;
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nco_crcf_adjust_frequency(carrier_nco, freq_adjustment);
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printf("Frequency adjustment: %.6f - carrier frequency: %.6f\n", freq_adjustment, nco_crcf_get_frequency(carrier_nco));
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@ -2,10 +2,13 @@ add_executable(
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test_correlator
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../src/correlator.c
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../src/correlator.h
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../src/freq_est.c
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../src/freq_est.h
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test_correlator.c
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)
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target_link_libraries(
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test_correlator
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m
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liquid
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)
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