Add work on noncoherent acquisition

src/algorithms/acquisition/gnuradio_blocks/pcps_acquisition.cc

@@ -97,7 +97,7 @@ pcps_acquisition::pcps_acquisition(const Acq_Conf& conf_) : gr::block("pcps_acqu
     if (acq_parameters.bit_transition_flag)
         {
             d_fft_size *= 2;
-            acq_parameters.max_dwells = 1;  //Activation of acq_parameters.bit_transition_flag invalidates the value of acq_parameters.max_dwells
+            acq_parameters.max_dwells = 1;  // Activation of acq_parameters.bit_transition_flag invalidates the value of acq_parameters.max_dwells
         }
 
     d_fft_codes = static_cast<gr_complex*>(volk_gnsssdr_malloc(d_fft_size * sizeof(gr_complex), volk_gnsssdr_get_alignment()));
@@ -128,6 +128,15 @@ pcps_acquisition::pcps_acquisition(const Acq_Conf& conf_) : gr::block("pcps_acqu
     d_dump_number = 0;
     d_dump_channel = acq_parameters.dump_channel;
     samplesPerChip = acq_parameters.samples_per_chip;
+    // todo: CFAR statistic not available for non-coherent integration
+    if (acq_parameters.max_dwells == 1)
+        {
+            d_use_CFAR_algorithm_flag = acq_parameters.use_CFAR_algorithm_flag;
+        }
+    else
+        {
+            d_use_CFAR_algorithm_flag = false;
+        }
 }
 
 
@@ -427,17 +436,49 @@ void pcps_acquisition::dump_results(int effective_fft_size)
         }
 }
 
-float pcps_acquisition::first_vs_second_peak_statistics(uint32_t& indext, int& doppler)
+
+float pcps_acquisition::max_to_input_power_statistic(uint32_t& indext, int& doppler, float input_power)
 {
-    float firstPeak = 0.0;
+    float grid_maximum = 0.0;
     int index_doppler = 0;
     uint32_t tmp_intex_t = 0;
     uint32_t index_time = 0;
+    float fft_normalization_factor = static_cast<float>(d_fft_size) * static_cast<float>(d_fft_size);
 
     // Look for correlation peaks in the results ==============================
     // Find the highest peak and compare it to the second highest peak
     // The second peak is chosen not closer than 1 chip to the highest peak
     //--- Find the correlation peak and the carrier frequency --------------
+    for (int i = 0; i < d_num_doppler_bins; i++)
+        {
+            volk_gnsssdr_32f_index_max_32u(&tmp_intex_t, d_magnitude_grid[i], d_fft_size);
+            if (d_magnitude_grid[i][tmp_intex_t] > grid_maximum)
+                {
+                    grid_maximum = d_magnitude_grid[i][tmp_intex_t];
+                    index_doppler = i;
+                    index_time = tmp_intex_t;
+                }
+        }
+    indext = index_time;
+    doppler = -static_cast<int>(acq_parameters.doppler_max) + d_doppler_step * index_doppler;
+
+    float magt = grid_maximum / (fft_normalization_factor * fft_normalization_factor);
+    return magt / input_power;
+}
+
+
+float pcps_acquisition::first_vs_second_peak_statistic(uint32_t& indext, int& doppler)
+{
+    // Look for correlation peaks in the results
+    // Find the highest peak and compare it to the second highest peak
+    // The second peak is chosen not closer than 1 chip to the highest peak
+
+    float firstPeak = 0.0;
+    int index_doppler = 0;
+    uint32_t tmp_intex_t = 0;
+    uint32_t index_time = 0;
+
+    // Find the correlation peak and the carrier frequency
     for (int i = 0; i < d_num_doppler_bins; i++)
         {
             volk_gnsssdr_32f_index_max_32u(&tmp_intex_t, d_magnitude_grid[i], d_fft_size);
@@ -451,12 +492,11 @@ float pcps_acquisition::first_vs_second_peak_statistics(uint32_t& indext, int& d
     indext = index_time;
     doppler = -static_cast<int>(acq_parameters.doppler_max) + d_doppler_step * index_doppler;
 
-    // -- - Find 1 chip wide code phase exclude range around the peak
+    // Find 1 chip wide code phase exclude range around the peak
-    //uint32_t samplesPerChip = ceil(GPS_L1_CA_CHIP_PERIOD * static_cast<float>(this->d_fs_in));
     int32_t excludeRangeIndex1 = index_time - samplesPerChip;
     int32_t excludeRangeIndex2 = index_time + samplesPerChip;
 
-    // -- - Correct code phase exclude range if the range includes array boundaries
+    // Correct code phase exclude range if the range includes array boundaries
     if (excludeRangeIndex1 < 0)
         {
             excludeRangeIndex1 = d_fft_size + excludeRangeIndex1;
@@ -476,11 +516,11 @@ float pcps_acquisition::first_vs_second_peak_statistics(uint32_t& indext, int& d
         }
     while (idx != excludeRangeIndex2);
 
-    //--- Find the second highest correlation peak in the same freq. bin ---
+    // Find the second highest correlation peak in the same freq. bin ---
     volk_gnsssdr_32f_index_max_32u(&tmp_intex_t, d_tmp_buffer, d_fft_size);
     float secondPeak = d_tmp_buffer[tmp_intex_t];
 
-    // 5- Compute the test statistics and compare to the threshold
+    // Compute the test statistics and compare to the threshold
     return firstPeak / secondPeak;
 }
 
@@ -510,36 +550,37 @@ void pcps_acquisition::acquisition_core(unsigned long int samp_count)
                << " ,sample stamp: " << samp_count << ", threshold: "
                << d_threshold << ", doppler_max: " << acq_parameters.doppler_max
                << ", doppler_step: " << d_doppler_step
-               << ", use_CFAR_algorithm_flag: " << (acq_parameters.use_CFAR_algorithm_flag ? "true" : "false");
+               << ", use_CFAR_algorithm_flag: " << (d_use_CFAR_algorithm_flag ? "true" : "false");
 
     lk.unlock();
-    if (acq_parameters.use_CFAR_algorithm_flag)
+
+    if (d_use_CFAR_algorithm_flag)
         {
-            // 1- (optional) Compute the input signal power estimation
+            // Compute the input signal power estimation
             volk_32fc_magnitude_squared_32f(d_magnitude, in, d_fft_size);
             volk_32f_accumulator_s32f(&d_input_power, d_magnitude, d_fft_size);
             d_input_power /= static_cast<float>(d_fft_size);
         }
-    // 2- Doppler frequency search loop
+
+    // Doppler frequency grid loop
     if (!d_step_two)
         {
             for (unsigned int doppler_index = 0; doppler_index < d_num_doppler_bins; doppler_index++)
                 {
-                    // Remove doppler
+                    // Remove Doppler
                     volk_32fc_x2_multiply_32fc(d_fft_if->get_inbuf(), in, d_grid_doppler_wipeoffs[doppler_index], d_fft_size);
 
-                    // 3- Perform the FFT-based convolution  (parallel time search)
+                    // Perform the FFT-based convolution  (parallel time search)
                     // Compute the FFT of the carrier wiped--off incoming signal
                     d_fft_if->execute();
 
-                    // Multiply carrier wiped--off, Fourier transformed incoming signal
+                    // Multiply carrier wiped--off, Fourier transformed incoming signal with the local FFT'd code reference
-                    // with the local FFT'd code reference using SIMD operations with VOLK library
                     volk_32fc_x2_multiply_32fc(d_ifft->get_inbuf(), d_fft_if->get_outbuf(), d_fft_codes, d_fft_size);
 
-                    // compute the inverse FFT
+                    // Compute the inverse FFT
                     d_ifft->execute();
 
-                    // compute squared magnitude (and accumulate in case of non-coherent integration)
+                    // Compute squared magnitude (and accumulate in case of non-coherent integration)
                     size_t offset = (acq_parameters.bit_transition_flag ? effective_fft_size : 0);
                     if (d_num_noncoherent_integrations_counter == 1)
                         {
@@ -556,15 +597,19 @@ void pcps_acquisition::acquisition_core(unsigned long int samp_count)
                             memcpy(grid_.colptr(doppler_index), d_magnitude_grid[doppler_index], sizeof(float) * effective_fft_size);
                         }
                 }
-            // 5- Compute the test statistics and compare to the threshold
+
-            float computed_statistic = first_vs_second_peak_statistics(indext, doppler);
+            // Compute the test statistic
-            if (d_test_statistics < computed_statistic or !acq_parameters.bit_transition_flag)
+            if (d_use_CFAR_algorithm_flag)
                 {
+                    d_test_statistics = max_to_input_power_statistic(indext, doppler, d_input_power);
+                }
+            else
+                {
+                    d_test_statistics = first_vs_second_peak_statistic(indext, doppler);
+                }
             d_gnss_synchro->Acq_delay_samples = static_cast<double>(indext % acq_parameters.samples_per_code);
             d_gnss_synchro->Acq_doppler_hz = static_cast<double>(doppler);
             d_gnss_synchro->Acq_samplestamp_samples = samp_count;
-                    d_test_statistics = computed_statistic;
-                }
         }
     else
         {
@@ -592,7 +637,7 @@ void pcps_acquisition::acquisition_core(unsigned long int samp_count)
                     volk_gnsssdr_32f_index_max_32u(&indext, d_magnitude, effective_fft_size);
                     magt = d_magnitude[indext];
 
-                    if (acq_parameters.use_CFAR_algorithm_flag)
+                    if (d_use_CFAR_algorithm_flag)
                         {
                             // Normalize the maximum value to correct the scale factor introduced by FFTW
                             magt = d_magnitude[indext] / (fft_normalization_factor * fft_normalization_factor);
@@ -602,7 +647,7 @@ void pcps_acquisition::acquisition_core(unsigned long int samp_count)
                         {
                             d_mag = magt;
 
-                            if (!acq_parameters.use_CFAR_algorithm_flag)
+                            if (!d_use_CFAR_algorithm_flag)
                                 {
                                     // Search grid noise floor approximation for this doppler line
                                     volk_32f_accumulator_s32f(&d_input_power, d_magnitude, effective_fft_size);
@@ -635,6 +680,7 @@ void pcps_acquisition::acquisition_core(unsigned long int samp_count)
                         }
                 }
         }
+
     lk.lock();
     if (!acq_parameters.bit_transition_flag)
         {

src/algorithms/acquisition/gnuradio_blocks/pcps_acquisition.h

@@ -95,13 +95,15 @@ private:
 
     void dump_results(int effective_fft_size);
 
-    float first_vs_second_peak_statistics(uint32_t& indext, int& doppler);
+    float first_vs_second_peak_statistic(uint32_t& indext, int& doppler);
+    float max_to_input_power_statistic(uint32_t& indext, int& doppler, float input_power);
 
     Acq_Conf acq_parameters;
     bool d_active;
     bool d_worker_active;
     bool d_cshort;
     bool d_step_two;
+    bool d_use_CFAR_algorithm_flag;
     int d_positive_acq;
     float d_threshold;
     float d_mag;