TTFF reduction in GPS L1 and Galileo E1

docs/CHANGELOG.md

@@ -78,6 +78,10 @@ All notable changes to GNSS-SDR will be documented in this file.
 
 ### Improvements in Reliability
 
+- Reduction of the TTFF in GPS L1 and Galileo E1 by improving the frame 
+  synchronization mechanism.
+- Bug fix in the Galileo E1/E5 telemetry decoder that produced incorrect timing 
+  information if a satellite is lost and then readquired. 
 - Check satellites' health status. If a satellite is marked as not healthy in
   its navigation message, the corresponding observables are not used for
   navigation.

src/algorithms/telemetry_decoder/gnuradio_blocks/galileo_telemetry_decoder_gs.cc

@@ -581,6 +581,11 @@ void galileo_telemetry_decoder_gs::set_satellite(const Gnss_Satellite &satellite
 void galileo_telemetry_decoder_gs::reset()
 {
     gr::thread::scoped_lock lock(d_setlock);
+    d_flag_frame_sync = false;
+    d_TOW_at_current_symbol_ms = 0;
+    d_TOW_at_Preamble_ms = 0;
+    d_fnav_nav.set_flag_TOW_set(false);
+    d_inav_nav.set_flag_TOW_set(false);
     d_last_valid_preamble = d_sample_counter;
     d_sent_tlm_failed_msg = false;
     d_stat = 0;
@@ -840,6 +845,15 @@ int galileo_telemetry_decoder_gs::general_work(int noutput_items __attribute__((
                                         d_TOW_at_current_symbol_ms = d_TOW_at_Preamble_ms + static_cast<uint32_t>(GALILEO_INAV_PAGE_PART_MS + (d_required_symbols + 1) * d_PRN_code_period_ms);
                                         d_inav_nav.set_TOW6_flag(false);
                                     }
+                                //warning: type 0 frame does not contain a valid TOW in some simulated signals, thus it is not safe to activate the following code:
+                                //                                else if (d_inav_nav.is_TOW0_set() == true)  // page 0 arrived and decoded
+                                //                                    {
+                                //                                        // TOW_0 refers to the even preamble, but when we decode it we are in the odd part, so 1 second later plus the decoding delay
+                                //                                        d_TOW_at_Preamble_ms = static_cast<uint32_t>(d_inav_nav.get_TOW0() * 1000.0);
+                                //                                        d_TOW_at_current_symbol_ms = d_TOW_at_Preamble_ms + static_cast<uint32_t>(GALILEO_INAV_PAGE_PART_MS + (d_required_symbols + 1) * d_PRN_code_period_ms);
+                                //                                        d_inav_nav.set_TOW0_flag(false);
+                                //                                        //std::cout << "FRAME 0 current tow: " << tmp_d_TOW_at_current_symbol_ms << " vs. " << d_TOW_at_current_symbol_ms + d_PRN_code_period_ms << "\n";
+                                //                                    }
                                 else
                                     {
                                         // this page has no timing information
@@ -955,6 +969,7 @@ int galileo_telemetry_decoder_gs::general_work(int noutput_items __attribute__((
 
     if (d_inav_nav.get_flag_TOW_set() == true or d_fnav_nav.get_flag_TOW_set() == true or d_cnav_nav.get_flag_CRC_test() == true)
         {
+            //std::cout << "TOW is set\n";
             current_symbol.TOW_at_current_symbol_ms = d_TOW_at_current_symbol_ms;
             // todo: Galileo to GPS time conversion should be moved to observable block.
             // current_symbol.TOW_at_current_symbol_ms -= d_delta_t;  // Galileo to GPS TOW

src/algorithms/telemetry_decoder/gnuradio_blocks/gps_l1_ca_telemetry_decoder_gs.cc

@@ -294,6 +294,24 @@ bool gps_l1_ca_telemetry_decoder_gs::decode_subframe()
 
                     switch (subframe_ID)
                         {
+                        case 1:
+                            if (d_nav.satellite_validation() == true)
+                                {
+                                    // get ephemeris object for this SV (mandatory)
+                                    const std::shared_ptr<Gps_Ephemeris> tmp_obj = std::make_shared<Gps_Ephemeris>(d_nav.get_ephemeris());
+                                    this->message_port_pub(pmt::mp("telemetry"), pmt::make_any(tmp_obj));
+                                }
+
+                            break;
+                        case 2:
+                            if (d_nav.satellite_validation() == true)
+                                {
+                                    // get ephemeris object for this SV (mandatory)
+                                    const std::shared_ptr<Gps_Ephemeris> tmp_obj = std::make_shared<Gps_Ephemeris>(d_nav.get_ephemeris());
+                                    this->message_port_pub(pmt::mp("telemetry"), pmt::make_any(tmp_obj));
+                                }
+
+                            break;
                         case 3:  // we have a new set of ephemeris data for the current SV
                             if (d_nav.satellite_validation() == true)
                                 {
@@ -388,40 +406,6 @@ int gps_l1_ca_telemetry_decoder_gs::general_work(int noutput_items __attribute__
                     }
                 if (abs(corr_value) >= d_samples_per_preamble)
                     {
-                        d_preamble_index = d_sample_counter;  // record the preamble sample stamp
-                        DLOG(INFO) << "Preamble detection for GPS L1 satellite " << this->d_satellite;
-                        decode_subframe();
-                        d_stat = 1;  // enter into frame pre-detection status
-                    }
-                d_flag_TOW_set = false;
-                break;
-            }
-        case 1:  // possible preamble lock
-            {
-                // correlate with preamble
-                int32_t corr_value = 0;
-                if (d_symbol_history.size() >= GPS_CA_PREAMBLE_LENGTH_BITS)
-                    {
-                        // ******* preamble correlation ********
-                        for (int32_t i = 0; i < GPS_CA_PREAMBLE_LENGTH_BITS; i++)
-                            {
-                                if (d_symbol_history[i] < 0.0)  // symbols clipping
-                                    {
-                                        corr_value -= d_preamble_samples[i];
-                                    }
-                                else
-                                    {
-                                        corr_value += d_preamble_samples[i];
-                                    }
-                            }
-                    }
-                if (abs(corr_value) >= d_samples_per_preamble)
-                    {
-                        // check preamble separation
-                        const auto preamble_diff = static_cast<int32_t>(d_sample_counter - d_preamble_index);
-                        if (abs(preamble_diff - d_preamble_period_symbols) == 0)
-                            {
-                                DLOG(INFO) << "Preamble confirmation for SAT " << this->d_satellite;
                         d_preamble_index = d_sample_counter;  // record the preamble sample stamp
                         if (corr_value < 0)
                             {
@@ -431,21 +415,25 @@ int gps_l1_ca_telemetry_decoder_gs::general_work(int noutput_items __attribute__
                             {
                                 d_flag_PLL_180_deg_phase_locked = false;
                             }
-                                decode_subframe();
+                        DLOG(INFO) << "Preamble detection for GPS L1 satellite " << this->d_satellite;
-                                d_stat = 2;
+                        if (decode_subframe())
+                            {
+                                d_CRC_error_counter = 0;
+                                d_flag_preamble = true;  // valid preamble indicator (initialized to false every work())
+                                gr::thread::scoped_lock lock(d_setlock);
+                                d_last_valid_preamble = d_sample_counter;
+                                if (!d_flag_frame_sync)
+                                    {
+                                        d_flag_frame_sync = true;
+                                        DLOG(INFO) << " Frame sync SAT " << this->d_satellite;
+                                    }
+                                d_stat = 1;  // preamble acquired
+                            }
                     }
-                        else
-                            {
-                                if (preamble_diff > d_preamble_period_symbols)
-                                    {
-                                        d_stat = 0;  // start again
                 d_flag_TOW_set = false;
-                                    }
-                            }
-                    }
                 break;
             }
-        case 2:  // preamble acquired
+        case 1:  // preamble acquired
             {
                 if (d_sample_counter >= d_preamble_index + static_cast<uint64_t>(d_preamble_period_symbols))
                     {

src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.cc

@@ -75,6 +75,7 @@ dll_pll_veml_tracking_sptr dll_pll_veml_make_tracking(const Dll_Pll_Conf &conf_)
 dll_pll_veml_tracking::dll_pll_veml_tracking(const Dll_Pll_Conf &conf_) : gr::block("dll_pll_veml_tracking", gr::io_signature::make(1, 1, sizeof(gr_complex)),
                                                                               gr::io_signature::make(1, 1, sizeof(Gnss_Synchro)))
 {
+    //debug_action1 = false;
     // prevent telemetry symbols accumulation in output buffers
     this->set_max_noutput_items(1);
     d_trk_parameters = conf_;
@@ -1981,6 +1982,14 @@ int dll_pll_veml_tracking::general_work(int noutput_items __attribute__((unused)
                     }
             }
         }
+    //*** debug only!!
+    //force tracking loss after 120 seconds
+    //if (debug_action1 == false and (static_cast<double>(d_sample_counter) / d_trk_parameters.fs_in >= 120))
+    //    {
+    //        d_carrier_lock_fail_counter = 200000;  // force loss-of-lock condition
+    //        debug_action1 = true;
+    //    }
+    //*************
     consume_each(d_current_prn_length_samples);
     d_sample_counter += static_cast<uint64_t>(d_current_prn_length_samples);
     if (current_synchro_data.Flag_valid_symbol_output || loss_of_lock)

src/algorithms/tracking/gnuradio_blocks/dll_pll_veml_tracking.h

@@ -198,6 +198,8 @@ private:
     bool d_dump_mat;
     bool d_acc_carrier_phase_initialized;
     bool d_enable_extended_integration;
+    //debug only
+    //bool debug_action1;
 };
 
 

src/algorithms/tracking/libs/dll_pll_conf.cc

@@ -34,7 +34,7 @@ Dll_Pll_Conf::Dll_Pll_Conf()
     enable_fll_pull_in = false;
     enable_fll_steady_state = false;
     pull_in_time_s = 10;
-    bit_synchronization_time_limit_s = pull_in_time_s + 60;
+    bit_synchronization_time_limit_s = pull_in_time_s + 10;
     fll_filter_order = 1;
     pll_filter_order = 3;
     dll_filter_order = 2;
@@ -138,7 +138,7 @@ void Dll_Pll_Conf::SetFromConfiguration(const ConfigurationInterface *configurat
     enable_fll_steady_state = configuration->property(role + ".enable_fll_steady_state", enable_fll_steady_state);
     fll_bw_hz = configuration->property(role + ".fll_bw_hz", fll_bw_hz);
     pull_in_time_s = configuration->property(role + ".pull_in_time_s", pull_in_time_s);
-    bit_synchronization_time_limit_s = pull_in_time_s + 60;
+    bit_synchronization_time_limit_s = configuration->property(role + ".bit_synchronization_time_limit_s", bit_synchronization_time_limit_s);
     early_late_space_chips = configuration->property(role + ".early_late_space_chips", early_late_space_chips);
     early_late_space_narrow_chips = configuration->property(role + ".early_late_space_narrow_chips", early_late_space_narrow_chips);
     very_early_late_space_chips = configuration->property(role + ".very_early_late_space_chips", very_early_late_space_chips);

src/core/system_parameters/galileo_inav_message.cc

@@ -1337,6 +1337,8 @@ int32_t Galileo_Inav_Message::page_jk_decoder(const char* data_jk)
                     WN_0 = static_cast<int32_t>(read_navigation_unsigned(data_jk_bits, WN_0_BIT));
                     DLOG(INFO) << "WN_0= " << WN_0;
                     TOW_0 = static_cast<int32_t>(read_navigation_unsigned(data_jk_bits, TOW_0_BIT));
+                    flag_TOW_set = true;  // set to false externally
+                    flag_TOW_0 = true;    // set to false externally
                     DLOG(INFO) << "TOW_0= " << TOW_0;
                     DLOG(INFO) << "flag_tow_set" << flag_TOW_set;
                 }

src/core/system_parameters/galileo_inav_message.h

@@ -164,6 +164,21 @@ public:
         flag_TOW_6 = flag_tow6;
     }
 
+    inline int32_t get_TOW0() const
+    {
+        return TOW_0;
+    }
+
+    inline bool is_TOW0_set() const
+    {
+        return flag_TOW_0;
+    }
+
+    inline void set_TOW0_flag(bool flag_tow0)
+    {
+        flag_TOW_0 = flag_tow0;
+    }
+
     inline bool get_flag_GGTO() const
     {
         return (flag_GGTO_1 == true and flag_GGTO_2 == true and flag_GGTO_3 == true and flag_GGTO_4 == true);
@@ -395,6 +410,7 @@ private:
     bool flag_iono_and_GST{};  // Flag indicating that ionospheric and GST parameters (word 5) have been received
     bool flag_TOW_5{};
     bool flag_TOW_6{};
+    bool flag_TOW_0{};
     bool flag_TOW_set{};    // it is true when page 5 or page 6 arrives
     bool flag_utc_model{};  // Flag indicating that utc model parameters (word 6) have been received