From 7d2420347293fb91efa5b6d28b549cbb504b570f Mon Sep 17 00:00:00 2001
From: Carles Fernandez <carles.fernandez@gmail.com>
Date: Fri, 8 Nov 2019 18:37:56 +0100
Subject: [PATCH 1/5] Apply new interface of dll_nc_e_minus_l_normalized

---
 .../gnuradio_blocks/dll_pll_veml_tracking.cc  | 20 +++++++++++++++++--
 .../dll_pll_veml_tracking_fpga.cc             | 15 +++++++++++++-
 ...glonass_l1_ca_dll_pll_c_aid_tracking_cc.cc |  2 +-
 ...glonass_l1_ca_dll_pll_c_aid_tracking_sc.cc |  2 +-
 .../glonass_l1_ca_dll_pll_tracking_cc.cc      |  2 +-
 ...glonass_l2_ca_dll_pll_c_aid_tracking_cc.cc |  2 +-
 ...glonass_l2_ca_dll_pll_c_aid_tracking_sc.cc |  2 +-
 .../glonass_l2_ca_dll_pll_tracking_cc.cc      |  2 +-
 .../gps_l1_ca_dll_pll_tracking_gpu_cc.cc      |  2 +-
 .../gps_l1_ca_kf_tracking_cc.cc               |  2 +-
 src/algorithms/tracking/libs/dll_pll_conf.cc  |  2 ++
 src/algorithms/tracking/libs/dll_pll_conf.h   |  2 ++
 .../tracking/libs/dll_pll_conf_fpga.cc        |  2 ++
 .../tracking/libs/dll_pll_conf_fpga.h         |  2 ++
 14 files changed, 48 insertions(+), 11 deletions(-)

diff --git a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc
index 1dabf6b84..06c4916ee 100644
--- a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc
@@ -145,6 +145,8 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     // GPS L1 C/A does not have pilot component nor secondary code
                     d_secondary = false;
                     trk_parameters.track_pilot = false;
+                    trk_parameters.slope = 1.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     // symbol integration: 20 trk symbols (20 ms) = 1 tlm bit
                     // set the preamble in the secondary code acquisition to obtain tlm symbol synchronization
                     d_secondary_code_length = static_cast<uint32_t>(GPS_CA_PREAMBLE_LENGTH_SYMBOLS);
@@ -164,6 +166,8 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     // GPS L2 does not have pilot component nor secondary code
                     d_secondary = false;
                     trk_parameters.track_pilot = false;
+                    trk_parameters.slope = 1.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                 }
             else if (signal_type == "L5")
                 {
@@ -176,6 +180,8 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     d_code_samples_per_chip = 1;
                     d_code_length_chips = static_cast<uint32_t>(GPS_L5I_CODE_LENGTH_CHIPS);
                     d_secondary = true;
+                    trk_parameters.slope = 1.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     if (trk_parameters.track_pilot)
                         {
                             // synchronize pilot secondary code
@@ -224,6 +230,8 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     d_correlation_length_ms = 4;
                     d_code_samples_per_chip = 2;  // CBOC disabled: 2 samples per chip. CBOC enabled: 12 samples per chip
                     d_veml = true;
+                    trk_parameters.slope = 3.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     if (trk_parameters.track_pilot)
                         {
                             d_secondary = true;
@@ -248,6 +256,8 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     d_code_samples_per_chip = 1;
                     d_code_length_chips = static_cast<uint32_t>(GALILEO_E5A_CODE_LENGTH_CHIPS);
                     d_secondary = true;
+                    trk_parameters.slope = 1.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     if (trk_parameters.track_pilot)
                         {
                             // synchronize pilot secondary code
@@ -294,6 +304,8 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     d_code_samples_per_chip = 1;
                     d_secondary = true;
                     trk_parameters.track_pilot = false;
+                    trk_parameters.slope = 1.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     // synchronize and remove data secondary code
                     d_secondary_code_length = static_cast<uint32_t>(BEIDOU_B1I_SECONDARY_CODE_LENGTH);
                     d_secondary_code_string = const_cast<std::string *>(&BEIDOU_B1I_SECONDARY_CODE_STR);
@@ -312,6 +324,8 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     d_code_samples_per_chip = 1;
                     d_secondary = false;
                     trk_parameters.track_pilot = false;
+                    trk_parameters.slope = 1.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     d_secondary_code_length = static_cast<uint32_t>(BEIDOU_B3I_SECONDARY_CODE_LENGTH);
                     d_secondary_code_string = const_cast<std::string *>(&BEIDOU_B3I_SECONDARY_CODE_STR);
                     d_data_secondary_code_length = static_cast<uint32_t>(BEIDOU_B3I_SECONDARY_CODE_LENGTH);
@@ -976,7 +990,7 @@ void dll_pll_veml_tracking::run_dll_pll()
         }
     else
         {
-            d_code_error_chips = dll_nc_e_minus_l_normalized(d_E_accu, d_L_accu);  // [chips/Ti]
+            d_code_error_chips = dll_nc_e_minus_l_normalized(d_E_accu, d_L_accu, trk_parameters.spc, trk_parameters.slope);  // [chips/Ti]
         }
     // Code discriminator filter
     d_code_error_filt_chips = d_code_loop_filter.apply(d_code_error_chips);  // [chips/second]
@@ -1632,7 +1646,7 @@ int dll_pll_veml_tracking::general_work(int noutput_items __attribute__((unused)
                 d_E_accu = *d_Early;
                 d_P_accu = *d_Prompt;
                 d_L_accu = *d_Late;
-
+                trk_parameters.spc = trk_parameters.early_late_space_chips;
                 // fail-safe: check if the secondary code or bit synchronization has not succeeded in a limited time period
                 if (trk_parameters.bit_synchronization_time_limit_s < (d_sample_counter - d_acq_sample_stamp) / static_cast<int>(trk_parameters.fs_in))
                     {
@@ -1733,11 +1747,13 @@ int dll_pll_veml_tracking::general_work(int noutput_items __attribute__((unused)
                                                 d_local_code_shift_chips[1] = -trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                 d_local_code_shift_chips[3] = trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                 d_local_code_shift_chips[4] = trk_parameters.very_early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
+                                                trk_parameters.spc = trk_parameters.early_late_space_narrow_chips;
                                             }
                                         else
                                             {
                                                 d_local_code_shift_chips[0] = -trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                 d_local_code_shift_chips[2] = trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
+                                                trk_parameters.spc = trk_parameters.early_late_space_narrow_chips;
                                             }
                                     }
                                 else
diff --git a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc
index 0e91a47de..350032d83 100644
--- a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc
@@ -140,6 +140,8 @@ dll_pll_veml_tracking_fpga::dll_pll_veml_tracking_fpga(const Dll_Pll_Conf_Fpga &
                     // GPS L1 C/A does not have pilot component nor secondary code
                     d_secondary = false;
                     trk_parameters.track_pilot = false;
+                    trk_parameters.slope = 1.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     // symbol integration: 20 trk symbols (20 ms) = 1 tlm bit
                     // set the preamble in the secondary code acquisition to obtain tlm symbol synchronization
                     d_secondary_code_length = static_cast<uint32_t>(GPS_CA_PREAMBLE_LENGTH_SYMBOLS);
@@ -154,6 +156,8 @@ dll_pll_veml_tracking_fpga::dll_pll_veml_tracking_fpga(const Dll_Pll_Conf_Fpga &
                     // GPS L2C has 1 trk symbol (20 ms) per tlm bit, no symbol integration required
                     d_symbols_per_bit = GPS_L2_SAMPLES_PER_SYMBOL;
                     d_correlation_length_ms = 20;
+                    trk_parameters.slope = 1.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     // GPS L2 does not have pilot component nor secondary code
                     d_secondary = false;
                     trk_parameters.track_pilot = false;
@@ -167,6 +171,8 @@ dll_pll_veml_tracking_fpga::dll_pll_veml_tracking_fpga(const Dll_Pll_Conf_Fpga &
                     d_symbols_per_bit = GPS_L5_SAMPLES_PER_SYMBOL;
                     d_correlation_length_ms = 1;
                     d_secondary = true;
+                    trk_parameters.slope = 1.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     if (d_extended_correlation_in_fpga == true)
                         {
                             if (trk_parameters.extend_correlation_symbols > 1)
@@ -218,6 +224,8 @@ dll_pll_veml_tracking_fpga::dll_pll_veml_tracking_fpga(const Dll_Pll_Conf_Fpga &
                     d_symbols_per_bit = 1;
                     d_correlation_length_ms = 4;
                     d_veml = true;
+                    trk_parameters.slope = 3.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     if (trk_parameters.track_pilot)
                         {
                             d_secondary = true;
@@ -240,6 +248,8 @@ dll_pll_veml_tracking_fpga::dll_pll_veml_tracking_fpga(const Dll_Pll_Conf_Fpga &
                     d_symbols_per_bit = 20;
                     d_correlation_length_ms = 1;
                     d_secondary = true;
+                    trk_parameters.slope = 1.0;
+                    trk_parameters.spc = trk_parameters.early_late_space_chips;
                     if (d_extended_correlation_in_fpga == true)
                         {
                             if (trk_parameters.extend_correlation_symbols > 1)
@@ -729,7 +739,7 @@ void dll_pll_veml_tracking_fpga::run_dll_pll()
         }
     else
         {
-            d_code_error_chips = dll_nc_e_minus_l_normalized(d_E_accu, d_L_accu);  // [chips/Ti]
+            d_code_error_chips = dll_nc_e_minus_l_normalized(d_E_accu, d_L_accu, trk_parameters.spc, trk_parameters.slope);  // [chips/Ti]
         }
     // Code discriminator filter
     d_code_error_filt_chips = d_code_loop_filter.apply(d_code_error_chips);  // [chips/second]
@@ -1592,6 +1602,7 @@ int dll_pll_veml_tracking_fpga::general_work(int noutput_items __attribute__((un
                         d_E_accu = *d_Early;
                         d_P_accu = *d_Prompt;
                         d_L_accu = *d_Late;
+                        trk_parameters.spc = trk_parameters.early_late_space_chips;
 
                         // fail-safe: check if the secondary code or bit synchronization has not succeeded in a limited time period
                         if (trk_parameters.bit_synchronization_time_limit_s < (d_sample_counter - d_acq_sample_stamp) / static_cast<int>(trk_parameters.fs_in))
@@ -1734,11 +1745,13 @@ int dll_pll_veml_tracking_fpga::general_work(int noutput_items __attribute__((un
                                                         d_local_code_shift_chips[1] = -trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                         d_local_code_shift_chips[3] = trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                         d_local_code_shift_chips[4] = trk_parameters.very_early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
+                                                        trk_parameters.spc = trk_parameters.early_late_space_narrow_chips;
                                                     }
                                                 else
                                                     {
                                                         d_local_code_shift_chips[0] = -trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                         d_local_code_shift_chips[2] = trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
+                                                        trk_parameters.spc = trk_parameters.early_late_space_narrow_chips;
                                                     }
                                             }
                                         else
diff --git a/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_c_aid_tracking_cc.cc b/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_c_aid_tracking_cc.cc
index e87e15d23..54bf7188d 100644
--- a/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_c_aid_tracking_cc.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_c_aid_tracking_cc.cc
@@ -708,7 +708,7 @@ int glonass_l1_ca_dll_pll_c_aid_tracking_cc::general_work(int noutput_items __at
 
                     // ################## DLL ##########################################################
                     // DLL discriminator
-                    d_code_error_chips_Ti = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2]);  // [chips/Ti] //early and late
+                    d_code_error_chips_Ti = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2], d_early_late_spc_chips, 1.0);  // [chips/Ti] //early and late
                     // Code discriminator filter
                     d_code_error_filt_chips_s = d_code_loop_filter.get_code_nco(d_code_error_chips_Ti);  // input [chips/Ti] -> output [chips/second]
                     d_code_error_filt_chips_Ti = d_code_error_filt_chips_s * CURRENT_INTEGRATION_TIME_S;
diff --git a/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_c_aid_tracking_sc.cc b/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_c_aid_tracking_sc.cc
index cd712c5b6..390f93c7c 100644
--- a/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_c_aid_tracking_sc.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_c_aid_tracking_sc.cc
@@ -705,7 +705,7 @@ int glonass_l1_ca_dll_pll_c_aid_tracking_sc::general_work(int noutput_items __at
 
                     // ################## DLL ##########################################################
                     // DLL discriminator
-                    d_code_error_chips_Ti = dll_nc_e_minus_l_normalized(std::complex<float>(d_correlator_outs_16sc[0].real(), d_correlator_outs_16sc[0].imag()), std::complex<float>(d_correlator_outs_16sc[2].real(), d_correlator_outs_16sc[2].imag()));  // [chips/Ti] //early and late
+                    d_code_error_chips_Ti = dll_nc_e_minus_l_normalized(std::complex<float>(d_correlator_outs_16sc[0].real(), d_correlator_outs_16sc[0].imag()), std::complex<float>(d_correlator_outs_16sc[2].real(), d_correlator_outs_16sc[2].imag()), d_early_late_spc_chips, 1.0);  // [chips/Ti] //early and late
                     // Code discriminator filter
                     d_code_error_filt_chips_s = d_code_loop_filter.get_code_nco(d_code_error_chips_Ti);  // input [chips/Ti] -> output [chips/second]
                     d_code_error_filt_chips_Ti = d_code_error_filt_chips_s * CURRENT_INTEGRATION_TIME_S;
diff --git a/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_tracking_cc.cc b/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_tracking_cc.cc
index ac1ad9a91..fd235c659 100644
--- a/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_tracking_cc.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/glonass_l1_ca_dll_pll_tracking_cc.cc
@@ -567,7 +567,7 @@ int Glonass_L1_Ca_Dll_Pll_Tracking_cc::general_work(int noutput_items __attribut
 
             // ################## DLL ##########################################################
             // DLL discriminator
-            code_error_chips = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2]);  // [chips/Ti] //early and late
+            code_error_chips = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2], d_early_late_spc_chips, 1.0);  // [chips/Ti] //early and late
             // Code discriminator filter
             code_error_filt_chips = d_code_loop_filter.get_code_nco(code_error_chips);  // [chips/second]
             double T_chip_seconds = 1.0 / static_cast<double>(d_code_freq_chips);
diff --git a/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_c_aid_tracking_cc.cc b/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_c_aid_tracking_cc.cc
index 1e8445b73..818f2da78 100644
--- a/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_c_aid_tracking_cc.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_c_aid_tracking_cc.cc
@@ -704,7 +704,7 @@ int glonass_l2_ca_dll_pll_c_aid_tracking_cc::general_work(int noutput_items __at
 
                     // ################## DLL ##########################################################
                     // DLL discriminator
-                    d_code_error_chips_Ti = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2]);  // [chips/Ti] //early and late
+                    d_code_error_chips_Ti = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2], d_early_late_spc_chips, 1.0);  // [chips/Ti] //early and late
                     // Code discriminator filter
                     d_code_error_filt_chips_s = d_code_loop_filter.get_code_nco(d_code_error_chips_Ti);  // input [chips/Ti] -> output [chips/second]
                     d_code_error_filt_chips_Ti = d_code_error_filt_chips_s * CURRENT_INTEGRATION_TIME_S;
diff --git a/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_c_aid_tracking_sc.cc b/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_c_aid_tracking_sc.cc
index 4a8609aa5..47cbbae5b 100644
--- a/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_c_aid_tracking_sc.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_c_aid_tracking_sc.cc
@@ -703,7 +703,7 @@ int glonass_l2_ca_dll_pll_c_aid_tracking_sc::general_work(int noutput_items __at
 
                     // ################## DLL ##########################################################
                     // DLL discriminator
-                    d_code_error_chips_Ti = dll_nc_e_minus_l_normalized(std::complex<float>(d_correlator_outs_16sc[0].real(), d_correlator_outs_16sc[0].imag()), std::complex<float>(d_correlator_outs_16sc[2].real(), d_correlator_outs_16sc[2].imag()));  // [chips/Ti] //early and late
+                    d_code_error_chips_Ti = dll_nc_e_minus_l_normalized(std::complex<float>(d_correlator_outs_16sc[0].real(), d_correlator_outs_16sc[0].imag()), std::complex<float>(d_correlator_outs_16sc[2].real(), d_correlator_outs_16sc[2].imag()), d_early_late_spc_chips, 1.0);  // [chips/Ti] //early and late
                     // Code discriminator filter
                     d_code_error_filt_chips_s = d_code_loop_filter.get_code_nco(d_code_error_chips_Ti);  // input [chips/Ti] -> output [chips/second]
                     d_code_error_filt_chips_Ti = d_code_error_filt_chips_s * CURRENT_INTEGRATION_TIME_S;
diff --git a/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_tracking_cc.cc b/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_tracking_cc.cc
index 53d6a2d81..a2f5b8caa 100644
--- a/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_tracking_cc.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/glonass_l2_ca_dll_pll_tracking_cc.cc
@@ -567,7 +567,7 @@ int Glonass_L2_Ca_Dll_Pll_Tracking_cc::general_work(int noutput_items __attribut
 
             // ################## DLL ##########################################################
             // DLL discriminator
-            code_error_chips = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2]);  // [chips/Ti] //early and late
+            code_error_chips = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2], d_early_late_spc_chips, 1.0);  // [chips/Ti] //early and late
             // Code discriminator filter
             code_error_filt_chips = d_code_loop_filter.get_code_nco(code_error_chips);  // [chips/second]
             double T_chip_seconds = 1.0 / static_cast<double>(d_code_freq_chips);
diff --git a/src/algorithms/tracking/gnuradio_blocks/gps_l1_ca_dll_pll_tracking_gpu_cc.cc b/src/algorithms/tracking/gnuradio_blocks/gps_l1_ca_dll_pll_tracking_gpu_cc.cc
index 09e7c4f0b..45f20c898 100644
--- a/src/algorithms/tracking/gnuradio_blocks/gps_l1_ca_dll_pll_tracking_gpu_cc.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/gps_l1_ca_dll_pll_tracking_gpu_cc.cc
@@ -384,7 +384,7 @@ int Gps_L1_Ca_Dll_Pll_Tracking_GPU_cc::general_work(int noutput_items __attribut
 
             // ################## DLL ##########################################################
             // DLL discriminator
-            code_error_chips_Ti = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2]);  // [chips/Ti]  // early and late
+            code_error_chips_Ti = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2], d_early_late_spc_chips, 1.0);  // [chips/Ti]  // early and late
             // Code discriminator filter
             code_error_filt_chips = d_code_loop_filter.get_code_nco(code_error_chips_Ti);                      // input [chips/Ti] -> output [chips/second]
             code_error_filt_secs_Ti = code_error_filt_chips * CURRENT_INTEGRATION_TIME_S / d_code_freq_chips;  // [s/Ti]
diff --git a/src/algorithms/tracking/gnuradio_blocks/gps_l1_ca_kf_tracking_cc.cc b/src/algorithms/tracking/gnuradio_blocks/gps_l1_ca_kf_tracking_cc.cc
index c0ab52ddc..62ec9644b 100644
--- a/src/algorithms/tracking/gnuradio_blocks/gps_l1_ca_kf_tracking_cc.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/gps_l1_ca_kf_tracking_cc.cc
@@ -748,7 +748,7 @@ int Gps_L1_Ca_Kf_Tracking_cc::general_work(int noutput_items __attribute__((unus
             // New code Doppler frequency estimation based on carrier frequency estimation
             d_code_freq_chips = GPS_L1_CA_CODE_RATE_CPS + ((d_carrier_doppler_hz * GPS_L1_CA_CODE_RATE_CPS) / GPS_L1_FREQ_HZ);
             // DLL discriminator
-            code_error_chips = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2]);  // [chips/Ti] early and late
+            code_error_chips = dll_nc_e_minus_l_normalized(d_correlator_outs[0], d_correlator_outs[2], d_early_late_spc_chips, 1.0);  // [chips/Ti] early and late
             // Code discriminator filter
             code_error_filt_chips = d_code_loop_filter.get_code_nco(code_error_chips);  // [chips/second]
             double T_chip_seconds = 1.0 / static_cast<double>(d_code_freq_chips);
diff --git a/src/algorithms/tracking/libs/dll_pll_conf.cc b/src/algorithms/tracking/libs/dll_pll_conf.cc
index 1cf6569ca..7027bb522 100644
--- a/src/algorithms/tracking/libs/dll_pll_conf.cc
+++ b/src/algorithms/tracking/libs/dll_pll_conf.cc
@@ -61,6 +61,8 @@ Dll_Pll_Conf::Dll_Pll_Conf()
     very_early_late_space_chips = 0.5;
     early_late_space_narrow_chips = 0.1;
     very_early_late_space_narrow_chips = 0.1;
+    slope = 1.0;
+    spc = 0.5;
     extend_correlation_symbols = 5;
     cn0_samples = FLAGS_cn0_samples;
     cn0_smoother_samples = 200;
diff --git a/src/algorithms/tracking/libs/dll_pll_conf.h b/src/algorithms/tracking/libs/dll_pll_conf.h
index 9b2b6a773..b36efda26 100644
--- a/src/algorithms/tracking/libs/dll_pll_conf.h
+++ b/src/algorithms/tracking/libs/dll_pll_conf.h
@@ -63,6 +63,8 @@ public:
     float very_early_late_space_chips;
     float early_late_space_narrow_chips;
     float very_early_late_space_narrow_chips;
+    float slope;
+    float spc;
     int32_t extend_correlation_symbols;
     bool high_dyn;
     int32_t cn0_samples;
diff --git a/src/algorithms/tracking/libs/dll_pll_conf_fpga.cc b/src/algorithms/tracking/libs/dll_pll_conf_fpga.cc
index 7d1361a4e..36682e927 100644
--- a/src/algorithms/tracking/libs/dll_pll_conf_fpga.cc
+++ b/src/algorithms/tracking/libs/dll_pll_conf_fpga.cc
@@ -63,6 +63,8 @@ Dll_Pll_Conf_Fpga::Dll_Pll_Conf_Fpga()
     very_early_late_space_chips = 0.5;
     early_late_space_narrow_chips = 0.1;
     very_early_late_space_narrow_chips = 0.1;
+    slope = 1.0;
+    spc = 0.5;
     extend_correlation_symbols = 5;
     cn0_samples = FLAGS_cn0_samples;
     cn0_smoother_samples = 200;
diff --git a/src/algorithms/tracking/libs/dll_pll_conf_fpga.h b/src/algorithms/tracking/libs/dll_pll_conf_fpga.h
index dcc3f9847..545e82c36 100644
--- a/src/algorithms/tracking/libs/dll_pll_conf_fpga.h
+++ b/src/algorithms/tracking/libs/dll_pll_conf_fpga.h
@@ -67,6 +67,8 @@ public:
     float very_early_late_space_chips;
     float early_late_space_narrow_chips;
     float very_early_late_space_narrow_chips;
+    float slope;
+    float spc;
     int32_t extend_correlation_symbols;
     bool high_dyn;
     int32_t cn0_samples;

From bb8416402c6ed728d7e71dd8d42c3e30aa65c595 Mon Sep 17 00:00:00 2001
From: Carles Fernandez <carles.fernandez@gmail.com>
Date: Fri, 7 Feb 2020 10:58:33 +0100
Subject: [PATCH 2/5] Fix normalization in dll_nc_e_minus_l_normalized
 discriminator (see #333)

---
 .../gnuradio_blocks/dll_pll_veml_tracking.cc  |  21 +-
 .../dll_pll_veml_tracking_fpga.cc             |  16 +-
 src/algorithms/tracking/libs/dll_pll_conf.cc  |   1 +
 src/algorithms/tracking/libs/dll_pll_conf.h   |   1 +
 .../tracking/libs/dll_pll_conf_fpga.cc        |   1 +
 .../tracking/libs/dll_pll_conf_fpga.h         |   1 +
 .../tracking/libs/tracking_discriminators.cc  |   5 +-
 .../tracking/libs/tracking_discriminators.h   |  90 ++++++++-
 src/tests/test_main.cc                        |   4 +-
 .../tracking/discriminator_test.cc            | 189 ++++++++++++++++++
 10 files changed, 320 insertions(+), 9 deletions(-)
 create mode 100644 src/tests/unit-tests/signal-processing-blocks/tracking/discriminator_test.cc

diff --git a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc
index 06c4916ee..8f2506c50 100644
--- a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc
@@ -147,6 +147,7 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     trk_parameters.track_pilot = false;
                     trk_parameters.slope = 1.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.y_intercept = 1.0;
                     // symbol integration: 20 trk symbols (20 ms) = 1 tlm bit
                     // set the preamble in the secondary code acquisition to obtain tlm symbol synchronization
                     d_secondary_code_length = static_cast<uint32_t>(GPS_CA_PREAMBLE_LENGTH_SYMBOLS);
@@ -168,6 +169,7 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     trk_parameters.track_pilot = false;
                     trk_parameters.slope = 1.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.y_intercept = 1.0;
                 }
             else if (signal_type == "L5")
                 {
@@ -182,6 +184,7 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     d_secondary = true;
                     trk_parameters.slope = 1.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.y_intercept = 1.0;
                     if (trk_parameters.track_pilot)
                         {
                             // synchronize pilot secondary code
@@ -230,8 +233,9 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     d_correlation_length_ms = 4;
                     d_code_samples_per_chip = 2;  // CBOC disabled: 2 samples per chip. CBOC enabled: 12 samples per chip
                     d_veml = true;
-                    trk_parameters.slope = 3.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                    trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
                     if (trk_parameters.track_pilot)
                         {
                             d_secondary = true;
@@ -258,6 +262,7 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     d_secondary = true;
                     trk_parameters.slope = 1.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.y_intercept = 1.0;
                     if (trk_parameters.track_pilot)
                         {
                             // synchronize pilot secondary code
@@ -306,6 +311,7 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     trk_parameters.track_pilot = false;
                     trk_parameters.slope = 1.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.y_intercept = 1.0;
                     // synchronize and remove data secondary code
                     d_secondary_code_length = static_cast<uint32_t>(BEIDOU_B1I_SECONDARY_CODE_LENGTH);
                     d_secondary_code_string = const_cast<std::string *>(&BEIDOU_B1I_SECONDARY_CODE_STR);
@@ -326,6 +332,7 @@ dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::bl
                     trk_parameters.track_pilot = false;
                     trk_parameters.slope = 1.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.y_intercept = 1.0;
                     d_secondary_code_length = static_cast<uint32_t>(BEIDOU_B3I_SECONDARY_CODE_LENGTH);
                     d_secondary_code_string = const_cast<std::string *>(&BEIDOU_B3I_SECONDARY_CODE_STR);
                     d_data_secondary_code_length = static_cast<uint32_t>(BEIDOU_B3I_SECONDARY_CODE_LENGTH);
@@ -990,7 +997,7 @@ void dll_pll_veml_tracking::run_dll_pll()
         }
     else
         {
-            d_code_error_chips = dll_nc_e_minus_l_normalized(d_E_accu, d_L_accu, trk_parameters.spc, trk_parameters.slope);  // [chips/Ti]
+            d_code_error_chips = dll_nc_e_minus_l_normalized(d_E_accu, d_L_accu, trk_parameters.spc, trk_parameters.slope, trk_parameters.y_intercept);  // [chips/Ti]
         }
     // Code discriminator filter
     d_code_error_filt_chips = d_code_loop_filter.apply(d_code_error_chips);  // [chips/second]
@@ -1647,6 +1654,11 @@ int dll_pll_veml_tracking::general_work(int noutput_items __attribute__((unused)
                 d_P_accu = *d_Prompt;
                 d_L_accu = *d_Late;
                 trk_parameters.spc = trk_parameters.early_late_space_chips;
+                if (std::string(trk_parameters.signal) == "E1")
+                    {
+                        trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                        trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                    }
                 // fail-safe: check if the secondary code or bit synchronization has not succeeded in a limited time period
                 if (trk_parameters.bit_synchronization_time_limit_s < (d_sample_counter - d_acq_sample_stamp) / static_cast<int>(trk_parameters.fs_in))
                     {
@@ -1748,6 +1760,11 @@ int dll_pll_veml_tracking::general_work(int noutput_items __attribute__((unused)
                                                 d_local_code_shift_chips[3] = trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                 d_local_code_shift_chips[4] = trk_parameters.very_early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                 trk_parameters.spc = trk_parameters.early_late_space_narrow_chips;
+                                                if (std::string(trk_parameters.signal) == "E1")
+                                                    {
+                                                        trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                                                        trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                                                    }
                                             }
                                         else
                                             {
diff --git a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc
index 350032d83..4ba8a1a17 100644
--- a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc
@@ -142,6 +142,7 @@ dll_pll_veml_tracking_fpga::dll_pll_veml_tracking_fpga(const Dll_Pll_Conf_Fpga &
                     trk_parameters.track_pilot = false;
                     trk_parameters.slope = 1.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.y_intercept = 1.0;
                     // symbol integration: 20 trk symbols (20 ms) = 1 tlm bit
                     // set the preamble in the secondary code acquisition to obtain tlm symbol synchronization
                     d_secondary_code_length = static_cast<uint32_t>(GPS_CA_PREAMBLE_LENGTH_SYMBOLS);
@@ -158,6 +159,7 @@ dll_pll_veml_tracking_fpga::dll_pll_veml_tracking_fpga(const Dll_Pll_Conf_Fpga &
                     d_correlation_length_ms = 20;
                     trk_parameters.slope = 1.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.y_intercept = 1.0;
                     // GPS L2 does not have pilot component nor secondary code
                     d_secondary = false;
                     trk_parameters.track_pilot = false;
@@ -173,6 +175,7 @@ dll_pll_veml_tracking_fpga::dll_pll_veml_tracking_fpga(const Dll_Pll_Conf_Fpga &
                     d_secondary = true;
                     trk_parameters.slope = 1.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.y_intercept = 1.0;
                     if (d_extended_correlation_in_fpga == true)
                         {
                             if (trk_parameters.extend_correlation_symbols > 1)
@@ -224,8 +227,9 @@ dll_pll_veml_tracking_fpga::dll_pll_veml_tracking_fpga(const Dll_Pll_Conf_Fpga &
                     d_symbols_per_bit = 1;
                     d_correlation_length_ms = 4;
                     d_veml = true;
-                    trk_parameters.slope = 3.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                    trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
                     if (trk_parameters.track_pilot)
                         {
                             d_secondary = true;
@@ -250,6 +254,7 @@ dll_pll_veml_tracking_fpga::dll_pll_veml_tracking_fpga(const Dll_Pll_Conf_Fpga &
                     d_secondary = true;
                     trk_parameters.slope = 1.0;
                     trk_parameters.spc = trk_parameters.early_late_space_chips;
+                    trk_parameters.y_intercept = 1.0;
                     if (d_extended_correlation_in_fpga == true)
                         {
                             if (trk_parameters.extend_correlation_symbols > 1)
@@ -739,7 +744,7 @@ void dll_pll_veml_tracking_fpga::run_dll_pll()
         }
     else
         {
-            d_code_error_chips = dll_nc_e_minus_l_normalized(d_E_accu, d_L_accu, trk_parameters.spc, trk_parameters.slope);  // [chips/Ti]
+            d_code_error_chips = dll_nc_e_minus_l_normalized(d_E_accu, d_L_accu, trk_parameters.spc, trk_parameters.slope, trk_parameters.y_intercept);  // [chips/Ti]
         }
     // Code discriminator filter
     d_code_error_filt_chips = d_code_loop_filter.apply(d_code_error_chips);  // [chips/second]
@@ -1603,6 +1608,11 @@ int dll_pll_veml_tracking_fpga::general_work(int noutput_items __attribute__((un
                         d_P_accu = *d_Prompt;
                         d_L_accu = *d_Late;
                         trk_parameters.spc = trk_parameters.early_late_space_chips;
+                        if (std::string(trk_parameters.signal) == "E1")
+                            {
+                                trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                                trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                            }
 
                         // fail-safe: check if the secondary code or bit synchronization has not succeeded in a limited time period
                         if (trk_parameters.bit_synchronization_time_limit_s < (d_sample_counter - d_acq_sample_stamp) / static_cast<int>(trk_parameters.fs_in))
@@ -1746,6 +1756,8 @@ int dll_pll_veml_tracking_fpga::general_work(int noutput_items __attribute__((un
                                                         d_local_code_shift_chips[3] = trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                         d_local_code_shift_chips[4] = trk_parameters.very_early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                         trk_parameters.spc = trk_parameters.early_late_space_narrow_chips;
+                                                        trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                                                        trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
                                                     }
                                                 else
                                                     {
diff --git a/src/algorithms/tracking/libs/dll_pll_conf.cc b/src/algorithms/tracking/libs/dll_pll_conf.cc
index 7027bb522..dcc0194d7 100644
--- a/src/algorithms/tracking/libs/dll_pll_conf.cc
+++ b/src/algorithms/tracking/libs/dll_pll_conf.cc
@@ -63,6 +63,7 @@ Dll_Pll_Conf::Dll_Pll_Conf()
     very_early_late_space_narrow_chips = 0.1;
     slope = 1.0;
     spc = 0.5;
+    y_intercept = 1.0;
     extend_correlation_symbols = 5;
     cn0_samples = FLAGS_cn0_samples;
     cn0_smoother_samples = 200;
diff --git a/src/algorithms/tracking/libs/dll_pll_conf.h b/src/algorithms/tracking/libs/dll_pll_conf.h
index b36efda26..ef9eb8495 100644
--- a/src/algorithms/tracking/libs/dll_pll_conf.h
+++ b/src/algorithms/tracking/libs/dll_pll_conf.h
@@ -65,6 +65,7 @@ public:
     float very_early_late_space_narrow_chips;
     float slope;
     float spc;
+    float y_intercept;
     int32_t extend_correlation_symbols;
     bool high_dyn;
     int32_t cn0_samples;
diff --git a/src/algorithms/tracking/libs/dll_pll_conf_fpga.cc b/src/algorithms/tracking/libs/dll_pll_conf_fpga.cc
index 36682e927..f806332d7 100644
--- a/src/algorithms/tracking/libs/dll_pll_conf_fpga.cc
+++ b/src/algorithms/tracking/libs/dll_pll_conf_fpga.cc
@@ -65,6 +65,7 @@ Dll_Pll_Conf_Fpga::Dll_Pll_Conf_Fpga()
     very_early_late_space_narrow_chips = 0.1;
     slope = 1.0;
     spc = 0.5;
+    y_intercept = 1.0;
     extend_correlation_symbols = 5;
     cn0_samples = FLAGS_cn0_samples;
     cn0_smoother_samples = 200;
diff --git a/src/algorithms/tracking/libs/dll_pll_conf_fpga.h b/src/algorithms/tracking/libs/dll_pll_conf_fpga.h
index 545e82c36..8097a6c71 100644
--- a/src/algorithms/tracking/libs/dll_pll_conf_fpga.h
+++ b/src/algorithms/tracking/libs/dll_pll_conf_fpga.h
@@ -69,6 +69,7 @@ public:
     float very_early_late_space_narrow_chips;
     float slope;
     float spc;
+    float y_intercept;
     int32_t extend_correlation_symbols;
     bool high_dyn;
     int32_t cn0_samples;
diff --git a/src/algorithms/tracking/libs/tracking_discriminators.cc b/src/algorithms/tracking/libs/tracking_discriminators.cc
index 6c5e9dbb5..718216713 100644
--- a/src/algorithms/tracking/libs/tracking_discriminators.cc
+++ b/src/algorithms/tracking/libs/tracking_discriminators.cc
@@ -34,7 +34,6 @@
 
 #include "tracking_discriminators.h"
 #include "MATH_CONSTANTS.h"
-#include <cmath>
 
 //  All the outputs are in RADIANS
 
@@ -130,7 +129,7 @@ double pll_cloop_two_quadrant_atan(gr_complex prompt_s1)
  * where \f$E=\sqrt{I_{ES}^2+Q_{ES}^2}\f$ is the Early correlator output absolute value and
  * \f$L=\sqrt{I_{LS}^2+Q_{LS}^2}\f$ is the Late correlator output absolute value. The output is in [chips].
  */
-double dll_nc_e_minus_l_normalized(gr_complex early_s1, gr_complex late_s1)
+double dll_nc_e_minus_l_normalized(gr_complex early_s1, gr_complex late_s1, float spc, float slope, float y_intercept)
 {
     double P_early = std::abs(early_s1);
     double P_late = std::abs(late_s1);
@@ -139,7 +138,7 @@ double dll_nc_e_minus_l_normalized(gr_complex early_s1, gr_complex late_s1)
         {
             return 0.0;
         }
-    return 0.5 * (P_early - P_late) / E_plus_L;
+    return ((y_intercept - slope * spc) / slope) * (P_early - P_late) / E_plus_L;
 }
 
 
diff --git a/src/algorithms/tracking/libs/tracking_discriminators.h b/src/algorithms/tracking/libs/tracking_discriminators.h
index 350d31fd6..0d0a82274 100644
--- a/src/algorithms/tracking/libs/tracking_discriminators.h
+++ b/src/algorithms/tracking/libs/tracking_discriminators.h
@@ -39,6 +39,7 @@
 #define GNSS_SDR_TRACKING_DISCRIMINATORS_H_
 
 #include <gnuradio/gr_complex.h>
+#include <cmath>
 
 /*! brief FLL four quadrant arctan discriminator
  *
@@ -99,7 +100,7 @@ double pll_cloop_two_quadrant_atan(gr_complex prompt_s1);
  * where \f$E=\sqrt{I_{ES}^2+Q_{ES}^2}\f$ is the Early correlator output absolute value and
  * \f$L=\sqrt{I_{LS}^2+Q_{LS}^2}\f$ is the Late correlator output absolute value. The output is in [chips].
  */
-double dll_nc_e_minus_l_normalized(gr_complex early_s1, gr_complex late_s1);
+double dll_nc_e_minus_l_normalized(gr_complex early_s1, gr_complex late_s1, float spc = 0.5, float slope = 1.0, float y_intercept = 1.0);
 
 
 /*! \brief DLL Noncoherent Very Early Minus Late Power (VEMLP) normalized discriminator
@@ -115,4 +116,91 @@ double dll_nc_e_minus_l_normalized(gr_complex early_s1, gr_complex late_s1);
 double dll_nc_vemlp_normalized(gr_complex very_early_s1, gr_complex early_s1, gr_complex late_s1, gr_complex very_late_s1);
 
 
+template <typename Fun>
+double CalculateSlope(Fun &&f, double x)
+{
+    static constexpr double dx = 1e-6;
+
+    return (f(x + dx / 2.0) - f(x - dx / 2.0)) / dx;
+}
+
+template <typename Fun>
+double CalculateSlopeAbs(Fun &&f, double x)
+{
+    static constexpr double dx = 1e-6;
+
+    return (std::abs(f(x + dx / 2.0)) - std::abs(f(x - dx / 2.0))) / dx;
+}
+
+template <typename Fun>
+double GetYIntercept(Fun &&f, double x)
+{
+    double slope = CalculateSlope(f, x);
+    double y1 = f(x);
+
+    return y1 - slope * x;
+}
+
+template <typename Fun>
+double GetYInterceptAbs(Fun &&f, double x)
+{
+    double slope = CalculateSlopeAbs(f, x);
+    double y1 = std::abs(f(x));
+    return y1 - slope * x;
+}
+
+// SinBocCorrelationFunction and CosBocCorrelationFunction from
+// Sousa, F. and Nunes, F., "New Expressions for the Autocorrelation
+// Function of BOC GNSS Signals", NAVIGATION - Journal of the Institute
+// of Navigation, March 2013.
+//
+template <int M = 1, int N = M>
+double SinBocCorrelationFunction(double offset_in_chips)
+{
+    static constexpr int TWO_P = 2 * M / N;
+
+    double abs_tau = std::abs(offset_in_chips);
+
+    if (abs_tau > 1.0)
+        {
+            return 0.0;
+        }
+
+    int k = static_cast<int>(std::ceil(TWO_P * abs_tau));
+
+    double sgn = ((k & 0x01) == 0 ? 1.0 : -1.0);  // (-1)^k
+
+    return sgn * (2.0 * (k * k - k * TWO_P - k) / TWO_P + 1.0 +
+                     (2 * TWO_P - 2 * k + 1) * abs_tau);
+}
+
+
+template <int M = 1, int N = M>
+double CosBocCorrelationFunction(double offset_in_chips)
+{
+    static constexpr int TWO_P = 2 * M / N;
+
+    double abs_tau = std::abs(offset_in_chips);
+
+    if (abs_tau > 1.0)
+        {
+            return 0.0;
+        }
+
+    int k = static_cast<int>(std::floor(2.0 * TWO_P * abs_tau));
+
+    if ((k & 0x01) == 0)  // k is even
+        {
+            double sgn = ((k >> 1) & 0x01 ? -1.0 : 1.0);  // (-1)^(k/2)
+
+            return sgn * ((2 * k * TWO_P + 2 * TWO_P - k * k) / (2.0 * TWO_P) + (-2 * TWO_P + k - 1) * abs_tau);
+        }
+    else
+        {
+            double sgn = (((k + 1) >> 1) & 0x01 ? -1.0 : 1.0);  // (-1)^((k+1)/2)
+
+            return sgn * ((k * k + 2 * k - 2 * k * TWO_P + 1) / (2.0 * TWO_P) + (2 * TWO_P - k - 2) * abs_tau);
+        }
+}
+
 #endif
diff --git a/src/tests/test_main.cc b/src/tests/test_main.cc
index 64acede83..693750cc2 100644
--- a/src/tests/test_main.cc
+++ b/src/tests/test_main.cc
@@ -105,19 +105,21 @@ DECLARE_string(log_dir);
 #endif
 #include "unit-tests/signal-processing-blocks/tracking/cpu_multicorrelator_real_codes_test.cc"
 #include "unit-tests/signal-processing-blocks/tracking/cpu_multicorrelator_test.cc"
+#include "unit-tests/signal-processing-blocks/tracking/discriminator_test.cc"
 #include "unit-tests/signal-processing-blocks/tracking/galileo_e1_dll_pll_veml_tracking_test.cc"
 #include "unit-tests/signal-processing-blocks/tracking/galileo_e5a_tracking_test.cc"
 #include "unit-tests/signal-processing-blocks/tracking/glonass_l1_ca_dll_pll_c_aid_tracking_test.cc"
 #include "unit-tests/signal-processing-blocks/tracking/glonass_l1_ca_dll_pll_tracking_test.cc"
 #include "unit-tests/signal-processing-blocks/tracking/tracking_loop_filter_test.cc"
 
+
 #if CUDA_BLOCKS_TEST
 #include "unit-tests/signal-processing-blocks/tracking/gpu_multicorrelator_test.cc"
 #endif
 
 #if FPGA_BLOCKS_TEST
-#include "unit-tests/signal-processing-blocks/acquisition/gps_l1_ca_pcps_acquisition_test_fpga.cc"
 #include "unit-tests/signal-processing-blocks/acquisition/galileo_e1_pcps_ambiguous_acquisition_test_fpga.cc"
+#include "unit-tests/signal-processing-blocks/acquisition/gps_l1_ca_pcps_acquisition_test_fpga.cc"
 #include "unit-tests/signal-processing-blocks/tracking/gps_l1_ca_dll_pll_tracking_test_fpga.cc"
 #endif
 
diff --git a/src/tests/unit-tests/signal-processing-blocks/tracking/discriminator_test.cc b/src/tests/unit-tests/signal-processing-blocks/tracking/discriminator_test.cc
new file mode 100644
index 000000000..d4c1086d4
--- /dev/null
+++ b/src/tests/unit-tests/signal-processing-blocks/tracking/discriminator_test.cc
@@ -0,0 +1,189 @@
+/*!
+ * \file discriminator_test.cc
+ * \brief  This file implements tests for the tracking discriminators
+ * \author Cillian O'Driscoll, 2019. cillian.odriscoll(at)gmail.com
+ *
+ *
+ * -------------------------------------------------------------------------
+ *
+ * Copyright (C) 2010-2019  (see AUTHORS file for a list of contributors)
+ *
+ * GNSS-SDR is a software defined Global Navigation
+ *          Satellite Systems receiver
+ *
+ * This file is part of GNSS-SDR.
+ *
+ * GNSS-SDR is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * GNSS-SDR is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with GNSS-SDR. If not, see <https://www.gnu.org/licenses/>.
+ *
+ * -------------------------------------------------------------------------
+ */
+
+#include "tracking_discriminators.h"
+#include <gtest/gtest.h>
+#include <cmath>
+//#include <cstddef>
+#include <vector>
+
+double BpskCorrelationFunction(double offset_in_chips)
+{
+    double abs_tau = std::abs(offset_in_chips);
+
+    if (abs_tau > 1.0)
+        {
+            return 0.0;
+        }
+    return 1.0 - abs_tau;
+}
+
+
+TEST(DllNcEMinusLNormalizedTest, Bpsk)
+{
+    std::vector<gr_complex> complex_amplitude_vector = {{1.0, 0.0}, {-1.0, 0.0}, {0.0, 1.0}, {1.0, 1.0}};
+    std::vector<double> spacing_vector = {0.5, 0.25, 0.1, 0.01};
+    std::vector<double> error_vector = {0.0, 0.01, 0.1, 0.25, -0.25, -0.1, -0.01};
+
+    for (auto A : complex_amplitude_vector)
+        {
+            for (auto spacing : spacing_vector)
+                {
+                    for (auto err : error_vector)
+                        {
+                            gr_complex E = A * static_cast<float>(BpskCorrelationFunction(err - spacing));
+                            gr_complex L = A * static_cast<float>(BpskCorrelationFunction(err + spacing));
+
+                            double disc_out = dll_nc_e_minus_l_normalized(E, L, spacing);
+
+                            if (std::abs(err) < 2.0 * spacing)
+                                {
+                                    EXPECT_NEAR(disc_out, err, 1e-4) << " Spacing: " << spacing;
+                                }
+                            else
+                                {
+                                    EXPECT_TRUE(err * disc_out >= 0.0);
+                                }
+
+                            if (spacing != 0.5 and err != 0.0)
+                                {
+                                    double disc_out_old = dll_nc_e_minus_l_normalized(E, L);
+
+                                    EXPECT_NE(disc_out_old, err);
+                                }
+                        }
+                }
+        }
+}
+
+
+TEST(DllNcEMinusLNormalizedTest, SinBoc11)
+{
+    std::vector<gr_complex> complex_amplitude_vector = {{1.0, 0.0}, {-1.0, 0.0}, {0.0, 1.0}, {1.0, 1.0}};
+    std::vector<double> spacing_vector = {0.75, 0.6666, 5.0 / 12.0, 0.25, 1.0 / 6.0, 0.01};
+    std::vector<double> error_vector = {0.0, 0.01, 0.1, 0.25, -0.25, -0.1, -0.01};
+
+    for (auto A : complex_amplitude_vector)
+        {
+            for (auto spacing : spacing_vector)
+                {
+                    double corr_slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, spacing);
+                    double y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, spacing);
+
+                    for (auto err : error_vector)
+                        {
+                            gr_complex E = A * static_cast<float>(SinBocCorrelationFunction<1, 1>(err - spacing));
+                            gr_complex L = A * static_cast<float>(SinBocCorrelationFunction<1, 1>(err + spacing));
+
+                            double disc_out = dll_nc_e_minus_l_normalized(E, L, spacing, corr_slope, y_intercept);
+                            double corr_slope_at_err = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, spacing + err);
+                            double corr_slope_at_neg_err = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, spacing - err);
+
+                            bool in_linear_region = (std::abs(err) < spacing) and (std::abs(corr_slope_at_err - corr_slope_at_neg_err) < 0.01);
+                            double norm_factor = (y_intercept - corr_slope * spacing) / spacing;
+
+                            if (in_linear_region)
+                                {
+                                    EXPECT_NEAR(disc_out, err, 1e-4) << " Spacing: " << spacing << ", slope : " << corr_slope << ", y_intercept: " << y_intercept << ", norm: " << norm_factor << " E: " << E << ", L: " << L;
+                                    if (norm_factor != 0.5 and err != 0.0)
+                                        {
+                                            double disc_out_old = dll_nc_e_minus_l_normalized(E, L);
+                                            EXPECT_NE(disc_out_old, err) << " Spacing: " << spacing << ", slope : " << corr_slope << ", y_intercept: " << y_intercept << ", norm: " << norm_factor << " E: " << E << ", L: " << L;
+                                        }
+                                }
+                        }
+                }
+        }
+}
+
+
+TEST(CosBocCorrelationFunction, FixedPoints)
+{
+    double res = CosBocCorrelationFunction<1, 1>(0.0);
+    EXPECT_NEAR(res, 1.0, 1e-4);
+    res = CosBocCorrelationFunction<1, 1>(0.2);
+    EXPECT_NEAR(res, 0.0, 1e-4);
+    res = CosBocCorrelationFunction<1, 1>(0.25);
+    EXPECT_NEAR(res, -0.25, 1e-4);
+    res = CosBocCorrelationFunction<1, 1>(0.5);
+    EXPECT_NEAR(res, -0.5, 1e-4);
+    res = CosBocCorrelationFunction<1, 1>(0.75);
+    EXPECT_NEAR(res, 0.25, 1e-4);
+    res = CosBocCorrelationFunction<1, 1>(1.0);
+    EXPECT_NEAR(res, 0.0, 1e-4);
+    res = CosBocCorrelationFunction<1, 1>(-0.2);
+    EXPECT_NEAR(res, 0.0, 1e-4);
+    res = CosBocCorrelationFunction<1, 1>(-0.5);
+    EXPECT_NEAR(res, -0.5, 1e-4);
+    res = CosBocCorrelationFunction<1, 1>(-0.75);
+    EXPECT_NEAR(res, 0.25, 1e-4);
+    res = CosBocCorrelationFunction<1, 1>(-1.0);
+    EXPECT_NEAR(res, 0.0, 1e-4);
+}
+
+
+TEST(DllNcEMinusLNormalizedTest, CosBoc11)
+{
+    std::vector<gr_complex> complex_amplitude_vector = {{1.0, 0.0}, {-1.0, 0.0}, {0.0, 1.0}, {1.0, 1.0}};
+    std::vector<double> spacing_vector = {0.875, 0.588, 0.1, 0.01};
+    std::vector<double> error_vector = {0.0, 0.01, 0.1, 0.25, -0.25, -0.1, -0.01};
+
+    for (auto A : complex_amplitude_vector)
+        {
+            for (auto spacing : spacing_vector)
+                {
+                    double corr_slope = -CalculateSlopeAbs(&CosBocCorrelationFunction<1, 1>, spacing);
+                    double y_intercept = GetYInterceptAbs(&CosBocCorrelationFunction<1, 1>, spacing);
+                    for (auto err : error_vector)
+                        {
+                            gr_complex E = A * static_cast<float>(CosBocCorrelationFunction<1, 1>(err - spacing));
+                            gr_complex L = A * static_cast<float>(CosBocCorrelationFunction<1, 1>(err + spacing));
+
+                            double disc_out = dll_nc_e_minus_l_normalized(E, L, spacing, corr_slope, y_intercept);
+                            double corr_slope_at_err = -CalculateSlopeAbs(&CosBocCorrelationFunction<1, 1>, spacing + err);
+                            double corr_slope_at_neg_err = -CalculateSlopeAbs(&CosBocCorrelationFunction<1, 1>, spacing - err);
+
+                            bool in_linear_region = (std::abs(err) < spacing) and (std::abs(corr_slope_at_err - corr_slope_at_neg_err) < 0.01);
+                            double norm_factor = (y_intercept - corr_slope * spacing) / spacing;
+
+                            if (in_linear_region)
+                                {
+                                    EXPECT_NEAR(disc_out, err, 1e-4) << " Spacing: " << spacing << ", slope : " << corr_slope << ", y_intercept: " << y_intercept << ", norm: " << norm_factor << " E: " << E << ", L: " << L;
+                                    if (norm_factor != 0.5 and err != 0.0)
+                                        {
+                                            double disc_out_old = dll_nc_e_minus_l_normalized(E, L);
+                                            EXPECT_NE(disc_out_old, err) << " Spacing: " << spacing << ", slope : " << corr_slope << ", y_intercept: " << y_intercept << ", norm: " << norm_factor << " E: " << E << ", L: " << L;
+                                        }
+                                }
+                        }
+                }
+        }
+}

From bdc8c71e315d228c208cc715035deb6691ba12b0 Mon Sep 17 00:00:00 2001
From: Carles Fernandez <carles.fernandez@gmail.com>
Date: Sat, 8 Feb 2020 18:39:21 +0100
Subject: [PATCH 3/5] Add SPDX license id in header

---
 .../tracking/discriminator_test.cc                 | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/src/tests/unit-tests/signal-processing-blocks/tracking/discriminator_test.cc b/src/tests/unit-tests/signal-processing-blocks/tracking/discriminator_test.cc
index d4c1086d4..efdc5a220 100644
--- a/src/tests/unit-tests/signal-processing-blocks/tracking/discriminator_test.cc
+++ b/src/tests/unit-tests/signal-processing-blocks/tracking/discriminator_test.cc
@@ -13,18 +13,7 @@
  *
  * This file is part of GNSS-SDR.
  *
- * GNSS-SDR is free software: you can redistribute it and/or modify
- * it under the terms of the GNU General Public License as published by
- * the Free Software Foundation, either version 3 of the License, or
- * (at your option) any later version.
- *
- * GNSS-SDR is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
- * You should have received a copy of the GNU General Public License
- * along with GNSS-SDR. If not, see <https://www.gnu.org/licenses/>.
+ * SPDX-License-Identifier: GPL-3.0-or-later
  *
  * -------------------------------------------------------------------------
  */
@@ -32,7 +21,6 @@
 #include "tracking_discriminators.h"
 #include <gtest/gtest.h>
 #include <cmath>
-//#include <cstddef>
 #include <vector>
 
 double BpskCorrelationFunction(double offset_in_chips)

From 52b9dfb8c058f85d3ca6d7e84f7f9010357323ec Mon Sep 17 00:00:00 2001
From: Carles Fernandez <carles.fernandez@gmail.com>
Date: Thu, 13 Feb 2020 18:45:57 +0100
Subject: [PATCH 4/5] Do not add extra work for nothing

---
 .../gnuradio_blocks/dll_pll_veml_tracking.cc  | 21 ++++++++++---------
 .../dll_pll_veml_tracking_fpga.cc             | 14 ++++++-------
 2 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc
index bd16fe9d3..3d159fd69 100644
--- a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc
@@ -1643,11 +1643,12 @@ int dll_pll_veml_tracking::general_work(int noutput_items __attribute__((unused)
                 d_P_accu = *d_Prompt;
                 d_L_accu = *d_Late;
                 trk_parameters.spc = trk_parameters.early_late_space_chips;
-                if (std::string(trk_parameters.signal) == "E1")
-                    {
-                        trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
-                        trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
-                    }
+                // if (std::string(trk_parameters.signal) == "E1")
+                //    {
+                //        trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                //        trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                //    }
+
                 // fail-safe: check if the secondary code or bit synchronization has not succeeded in a limited time period
                 if (trk_parameters.bit_synchronization_time_limit_s < (d_sample_counter - d_acq_sample_stamp) / static_cast<int>(trk_parameters.fs_in))
                     {
@@ -1749,11 +1750,11 @@ int dll_pll_veml_tracking::general_work(int noutput_items __attribute__((unused)
                                                 d_local_code_shift_chips[3] = trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                 d_local_code_shift_chips[4] = trk_parameters.very_early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                 trk_parameters.spc = trk_parameters.early_late_space_narrow_chips;
-                                                if (std::string(trk_parameters.signal) == "E1")
-                                                    {
-                                                        trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
-                                                        trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
-                                                    }
+                                                // if (std::string(trk_parameters.signal) == "E1")
+                                                //    {
+                                                //        trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                                                //        trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                                                //    }
                                             }
                                         else
                                             {
diff --git a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc
index d2682bf10..c7f341d6f 100644
--- a/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc
+++ b/src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking_fpga.cc
@@ -1597,11 +1597,11 @@ int dll_pll_veml_tracking_fpga::general_work(int noutput_items __attribute__((un
                         d_P_accu = *d_Prompt;
                         d_L_accu = *d_Late;
                         trk_parameters.spc = trk_parameters.early_late_space_chips;
-                        if (std::string(trk_parameters.signal) == "E1")
-                            {
-                                trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
-                                trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
-                            }
+                        // if (std::string(trk_parameters.signal) == "E1")
+                        //    {
+                        //        trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                        //        trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                        //    }
 
                         // fail-safe: check if the secondary code or bit synchronization has not succeeded in a limited time period
                         if (trk_parameters.bit_synchronization_time_limit_s < (d_sample_counter - d_acq_sample_stamp) / static_cast<int>(trk_parameters.fs_in))
@@ -1745,8 +1745,8 @@ int dll_pll_veml_tracking_fpga::general_work(int noutput_items __attribute__((un
                                                         d_local_code_shift_chips[3] = trk_parameters.early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                         d_local_code_shift_chips[4] = trk_parameters.very_early_late_space_narrow_chips * static_cast<float>(d_code_samples_per_chip);
                                                         trk_parameters.spc = trk_parameters.early_late_space_narrow_chips;
-                                                        trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
-                                                        trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                                                        // trk_parameters.slope = -CalculateSlopeAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
+                                                        // trk_parameters.y_intercept = GetYInterceptAbs(&SinBocCorrelationFunction<1, 1>, trk_parameters.spc);
                                                     }
                                                 else
                                                     {

From d477c8ee280cdf724e76568ad3cdc91279cff36d Mon Sep 17 00:00:00 2001
From: Carles Fernandez <carles.fernandez@gmail.com>
Date: Fri, 14 Feb 2020 19:00:42 +0100
Subject: [PATCH 5/5] Document change in discriminator implementation

---
 src/algorithms/tracking/libs/tracking_discriminators.cc | 2 +-
 src/algorithms/tracking/libs/tracking_discriminators.h  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/algorithms/tracking/libs/tracking_discriminators.cc b/src/algorithms/tracking/libs/tracking_discriminators.cc
index ca54bd5b0..448e7713f 100644
--- a/src/algorithms/tracking/libs/tracking_discriminators.cc
+++ b/src/algorithms/tracking/libs/tracking_discriminators.cc
@@ -113,7 +113,7 @@ double pll_cloop_two_quadrant_atan(gr_complex prompt_s1)
 /*
  * DLL Noncoherent Early minus Late envelope normalized discriminator:
  * \f{equation}
- *     error=\frac{1}{2}\frac{E-L}{E+L},
+ *     error = \frac{y_{intercept} - \text{slope} * \epsilon}{\text{slope}} \frac{E-L}{E+L},
  * \f}
  * where \f$E=\sqrt{I_{ES}^2+Q_{ES}^2}\f$ is the Early correlator output absolute value and
  * \f$L=\sqrt{I_{LS}^2+Q_{LS}^2}\f$ is the Late correlator output absolute value. The output is in [chips].
diff --git a/src/algorithms/tracking/libs/tracking_discriminators.h b/src/algorithms/tracking/libs/tracking_discriminators.h
index a797ff863..fcba833b8 100644
--- a/src/algorithms/tracking/libs/tracking_discriminators.h
+++ b/src/algorithms/tracking/libs/tracking_discriminators.h
@@ -84,7 +84,7 @@ double pll_cloop_two_quadrant_atan(gr_complex prompt_s1);
  *
  * DLL Noncoherent Early minus Late envelope normalized discriminator:
  * \f{equation}
- *     error=\frac{E-L}{E+L},
+ *     error = \frac{y_{intercept} - \text{slope} * \epsilon}{\text{slope}} \frac{E-L}{E+L},
  * \f}
  * where \f$E=\sqrt{I_{ES}^2+Q_{ES}^2}\f$ is the Early correlator output absolute value and
  * \f$L=\sqrt{I_{LS}^2+Q_{LS}^2}\f$ is the Late correlator output absolute value. The output is in [chips].