src/Radio/radio.cxx

   1 // radio.cxx -- implementation of FGRadio
   2 // Class to manage radio propagation using the ITM model
   3 // Written by Adrian Musceac, started August 2011.
   4 //
   5 // This program is free software; you can redistribute it and/or
   6 // modify it under the terms of the GNU General Public License as
   7 // published by the Free Software Foundation; either version 2 of the
   8 // License, or (at your option) any later version.
   9 //
  10 // This program is distributed in the hope that it will be useful, but
  11 // WITHOUT ANY WARRANTY; without even the implied warranty of
  12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 // General Public License for more details.
  14 //
  15 // You should have received a copy of the GNU General Public License
  16 // along with this program; if not, write to the Free Software
  17 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  18
  19
  20
  21 #ifdef HAVE_CONFIG_H
  22 #  include <config.h>
  23 #endif
  24
  25 #include <math.h>
  26 #include <stdlib.h>
  27 #include <deque>
  28 #include "radio.hxx"
  29 #include <Scenery/scenery.hxx>
  30
  31 #define WITH_POINT_TO_POINT 1
  32 #include "itm.cpp"
  33
  34
  35 FGRadio::FGRadio() {
  36
  37         /** radio parameters (which should probably be set for each radio via constructor) */
  38         _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
  39
  40         /** AM transmitter power in dBm.
  41         *       Note this value is calculated from the typical final transistor stage output
  42         *       small aircraft have portable transmitters which operate at 36 dBm output (4 Watts)
  43         *       later store this value in aircraft description
  44         *       ATC comms usually operate high power equipment, thus making the link asymetrical; this is ignored for now
  45         **/
  46         _transmitter_power = 43.0;
  47
  48         /** pilot plane's antenna gain + AI aircraft antenna gain
  49         *       real-life gain for conventional monopole/dipole antenna
  50         **/
  51         _antenna_gain = 2.0;
  52         _propagation_model = 2; //  choose between models via option: realistic radio on/off
  53
  54 }
  55
  56 FGRadio::~FGRadio()
  57 {
  58 }
  59
  60
  61 double FGRadio::getFrequency(int radio) {
  62         double freq = 118.0;
  63         switch (radio) {
  64                 case 1:
  65                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  66                         break;
  67                 case 2:
  68                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  69                         break;
  70                 default:
  71                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  72
  73         }
  74         return freq;
  75 }
  76
  77
  78
  79
  80 void FGRadio::receiveText(SGGeod tx_pos, double freq, string text,
  81         int ground_to_air) {
  82
  83         /*
  84         double comm1 = getFrequency(1);
  85         double comm2 = getFrequency(2);
  86         if ( (freq != comm1) &&  (freq != comm2) ) {
  87                 cerr << "Frequency not tuned: " << freq << " Radio1: " << comm1 << " Radio2: " << comm2 << endl;
  88                 return;
  89         }
  90         else {
  91         */
  92                 if ( _propagation_model == 0) {
  93                         fgSetString("/sim/messages/atc", text.c_str());
  94                 }
  95                 else if ( _propagation_model == 1 ) {
  96                         // free space, round earth
  97                 }
  98                 else if ( _propagation_model == 2 ) {
  99                         // Use ITM propagation model
 100                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 101                         if (signal <= 0.0) {
 102                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 103                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 104                                 return;
 105                         }
 106                         if ((signal > 0.0) && (signal < 12.0)) {
 107                                 /** for low SNR values implement a way to make the conversation
 108                                 *       hard to understand but audible
 109                                 *       in the real world, the receiver AGC fails to capture the slope
 110                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 111                                 *       the workaround below is more akin to what would happen on a FM transmission
 112                                 *       therefore the correct way would be to work on the volume
 113                                 **/
 114                                 /*
 115                                 string hash_noise = " ";
 116                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 117                                 int t_size = text.size();
 118                                 for (int n = 1; n <= reps; ++n) {
 119                                         int pos = rand() % (t_size -1);
 120                                         text.replace(pos,1, hash_noise);
 121                                 }
 122                                 */
 123                                 double volume = (fabs(signal - 12.0) / 12);
 124                                 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 125                                 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
 126                                 //cerr << "Usable signal at limit: " << signal << endl;
 127                                 fgSetDouble("/sim/sound/voices/voice/volume", volume);
 128                                 fgSetString("/sim/messages/atc", text.c_str());
 129                                 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 130                         }
 131                         else {
 132                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 133                                 //cerr << "Signal completely readable: " << signal << endl;
 134                                 fgSetString("/sim/messages/atc", text.c_str());
 135                         }
 136
 137                 }
 138
 139         //}
 140
 141 }
 142
 143 /***  Implement radio attenuation
 144           based on the Longley-Rice propagation model
 145 ***/
 146 double FGRadio::ITM_calculate_attenuation(SGGeod pos, double freq,
 147                                int transmission_type) {
 148
 149
 150
 151         /** ITM default parameters
 152                 TODO: take them from tile materials (especially for sea)?
 153         **/
 154         double eps_dielect=15.0;
 155         double sgm_conductivity = 0.005;
 156         double eno = 301.0;
 157         double frq_mhz;
 158         if( (freq < 118.0) || (freq > 137.0) )
 159                 frq_mhz = 125.0;        // sane value, middle of bandplan
 160         else
 161                 frq_mhz = freq;
 162         int radio_climate = 5;          // continental temperate
 163         int pol=1;      // assuming vertical polarization although this is more complex in reality
 164         double conf = 0.90;     // 90% of situations and time, take into account speed
 165         double rel = 0.90;
 166         double dbloss;
 167         char strmode[150];
 168         int errnum;
 169
 170         double tx_pow = _transmitter_power;
 171         double ant_gain = _antenna_gain;
 172         double signal = 0.0;
 173
 174         if(transmission_type == 1)
 175                 tx_pow = _transmitter_power + 6.0;
 176
 177         if((transmission_type == 1) || (transmission_type == 3))
 178                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 179
 180         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 181
 182         FGScenery * scenery = globals->get_scenery();
 183
 184         double own_lat = fgGetDouble("/position/latitude-deg");
 185         double own_lon = fgGetDouble("/position/longitude-deg");
 186         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 187         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 188
 189
 190         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 191
 192         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 193         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 194         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 195         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 196
 197         /**     position of sender radio antenna (HAAT)
 198                         sender can be aircraft or ground station
 199         **/
 200         double ATC_HAAT = 30.0;
 201         double Aircraft_HAAT = 5.0;
 202         double sender_alt_ft,sender_alt;
 203         double transmitter_height=0.0;
 204         double receiver_height=0.0;
 205         SGGeod sender_pos = pos;
 206
 207         sender_alt_ft = sender_pos.getElevationFt();
 208         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 209         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 210         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 211         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 212
 213         double point_distance= 90.0; // regular SRTM is 90 meters
 214         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 215         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 216         double probe_distance = 0.0;
 217         /** If distance larger than this value (300 km), assume reception imposssible */
 218         if (distance_m > 300000)
 219                 return -1.0;
 220         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 221         if (own_alt > 8000) {
 222                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 223                 SG_LOG(SG_GENERAL, SG_BULK,
 224                         "LOS-mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 225                 //cerr << "LOS-mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 226                 signal = link_budget - dbloss;
 227                 return signal;
 228         }
 229
 230
 231         double max_points = distance_m / point_distance;
 232         deque<double> _elevations;
 233
 234         double elevation_under_pilot = 0.0;
 235         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 236                 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
 237         }
 238
 239         double elevation_under_sender = 0.0;
 240         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 241                 transmitter_height = sender_alt - elevation_under_sender;
 242         }
 243         else {
 244                 transmitter_height = sender_alt;
 245         }
 246
 247         if(transmission_type == 1)
 248                 transmitter_height += ATC_HAAT;
 249         else
 250                 transmitter_height += Aircraft_HAAT;
 251
 252         SG_LOG(SG_GENERAL, SG_BULK,
 253                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 254         cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 255
 256         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 257
 258         while (_elevations.size() <= e_size) {
 259                 probe_distance += point_distance;
 260                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 261
 262                 double elevation_m = 0.0;
 263
 264                 if (scenery->get_elevation_m( probe, elevation_m, NULL )) {
 265                         if((transmission_type == 3) || (transmission_type == 4)) {
 266                                 _elevations.push_back(elevation_m);
 267                         }
 268                         else {
 269                                  _elevations.push_front(elevation_m);
 270                         }
 271                 }
 272                 else {
 273                         if((transmission_type == 3) || (transmission_type == 4)) {
 274                                 _elevations.push_back(elevation_m);
 275                         }
 276                         else {
 277                         _elevations.push_front(0.0);
 278                         }
 279                 }
 280         }
 281         if((transmission_type == 3) || (transmission_type == 4)) {
 282                 _elevations.push_front(elevation_under_pilot);
 283                 _elevations.push_back(elevation_under_sender);
 284         }
 285         else {
 286                 _elevations.push_back(elevation_under_pilot);
 287                 _elevations.push_front(elevation_under_sender);
 288         }
 289
 290
 291         double max_alt_between=0.0;
 292         for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
 293                 if (_elevations[i] > max_alt_between) {
 294                         max_alt_between = _elevations[i];
 295                 }
 296         }
 297
 298         double num_points= (double)_elevations.size();
 299         //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
 300         _elevations.push_front(point_distance);
 301         _elevations.push_front(num_points -1);
 302         int size = _elevations.size();
 303         double itm_elev[size];
 304         for(int i=0;i<size;i++) {
 305                 itm_elev[i]=_elevations[i];
 306                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 307         }
 308
 309
 310         /** first Fresnel zone radius
 311                 frequency in the middle of the bandplan, more accuracy is not necessary
 312         */
 313         double fz_clr= 8.657 * sqrt(distance_m / 0.125);
 314
 315         // TODO: If we clear the first Fresnel zone, we are into line of sight territory
 316
 317         // else we need to calculate point to point link loss
 318         if((transmission_type == 3) || (transmission_type == 4)) {
 319                 // the sender and receiver roles are switched
 320                 point_to_point(itm_elev, receiver_height, transmitter_height,
 321                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 322                         pol, conf, rel, dbloss, strmode, errnum);
 323
 324         }
 325         else {
 326
 327                 point_to_point(itm_elev, transmitter_height, receiver_height,
 328                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 329                         pol, conf, rel, dbloss, strmode, errnum);
 330         }
 331         SG_LOG(SG_GENERAL, SG_BULK,
 332                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 333         cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 334
 335         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 336         //      return -1;
 337         signal = link_budget - dbloss;
 338         return signal;
 339
 340 }