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) */
  38
  39         _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
  40
  41         /** AM transmitter power in dBm.
  42         *       Note this value is calculated from the typical final transistor stage output
  43         *       small aircraft have portable transmitters which operate at 36 dBm output (4 Watts)
  44         *       later possibly store this value in aircraft description
  45         *       ATC comms usually operate high power equipment, thus making the link asymetrical; this is taken care of in propagation routines
  46         **/
  47         _transmitter_power = 43.0;
  48
  49         /** pilot plane's antenna gain + AI aircraft antenna gain
  50         *       real-life gain for conventional monopole/dipole antenna
  51         **/
  52         _antenna_gain = 2.0;
  53         _propagation_model = 2; //  choose between models via option: realistic radio on/off
  54
  55 }
  56
  57 FGRadio::~FGRadio()
  58 {
  59 }
  60
  61
  62 double FGRadio::getFrequency(int radio) {
  63         double freq = 118.0;
  64         switch (radio) {
  65                 case 1:
  66                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  67                         break;
  68                 case 2:
  69                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  70                         break;
  71                 default:
  72                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  73
  74         }
  75         return freq;
  76 }
  77
  78 /*** TODO: receive multiplayer chat message and voice
  79 ***/
  80 void FGRadio::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
  81
  82 }
  83
  84 /*** TODO: receive navaid
  85 ***/
  86 double FGRadio::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
  87
  88         // need to implement transmitter power
  89         if ( _propagation_model == 1) {
  90                 return LOS_calculate_attenuation(tx_pos, freq, 1);
  91         }
  92         else if ( _propagation_model == 2) {
  93                 return ITM_calculate_attenuation(tx_pos, freq, 1);
  94         }
  95
  96         return -1;
  97
  98 }
  99
 100 /*** Receive ATC radio communication as text
 101 ***/
 102 void FGRadio::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 103
 104
 105         double comm1 = getFrequency(1);
 106         double comm2 = getFrequency(2);
 107         if ( !(fabs(freq - comm1) <= 0.0001) &&  !(fabs(freq - comm2) <= 0.0001) ) {
 108                 //cerr << "Frequency not tuned: " << freq << " Radio1: " << comm1 << " Radio2: " << comm2 << endl;
 109                 return;
 110         }
 111         else {
 112
 113                 if ( _propagation_model == 0) {
 114                         fgSetString("/sim/messages/atc", text.c_str());
 115                 }
 116                 else if ( _propagation_model == 1 ) {
 117                         // TODO: free space, round earth
 118                         double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
 119                         if (signal <= 0.0) {
 120                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 121                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 122                                 return;
 123                         }
 124                         else {
 125                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 126                                 //cerr << "Signal completely readable: " << signal << endl;
 127                                 fgSetString("/sim/messages/atc", text.c_str());
 128                                 /** write signal strength above threshold to the property tree
 129                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 130                                 **/
 131                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 132                         }
 133                 }
 134                 else if ( _propagation_model == 2 ) {
 135                         // Use ITM propagation model
 136                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 137                         if (signal <= 0.0) {
 138                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 139                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 140                                 return;
 141                         }
 142                         if ((signal > 0.0) && (signal < 12.0)) {
 143                                 /** for low SNR values implement a way to make the conversation
 144                                 *       hard to understand but audible
 145                                 *       in the real world, the receiver AGC fails to capture the slope
 146                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 147                                 *       the workaround below is more akin to what would happen on a FM transmission
 148                                 *       therefore the correct way would be to work on the volume
 149                                 **/
 150                                 /*
 151                                 string hash_noise = " ";
 152                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 153                                 int t_size = text.size();
 154                                 for (int n = 1; n <= reps; ++n) {
 155                                         int pos = rand() % (t_size -1);
 156                                         text.replace(pos,1, hash_noise);
 157                                 }
 158                                 */
 159                                 double volume = (fabs(signal - 12.0) / 12);
 160                                 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 161                                 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
 162                                 //cerr << "Usable signal at limit: " << signal << endl;
 163                                 fgSetDouble("/sim/sound/voices/voice/volume", volume);
 164                                 fgSetString("/sim/messages/atc", text.c_str());
 165                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 166                                 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 167                         }
 168                         else {
 169                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 170                                 //cerr << "Signal completely readable: " << signal << endl;
 171                                 fgSetString("/sim/messages/atc", text.c_str());
 172                                 /** write signal strength above threshold to the property tree
 173                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 174                                 **/
 175                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 176                         }
 177
 178                 }
 179
 180         }
 181
 182 }
 183
 184 /***  Implement radio attenuation
 185           based on the Longley-Rice propagation model
 186 ***/
 187 double FGRadio::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 188
 189
 190
 191         /** ITM default parameters
 192                 TODO: take them from tile materials (especially for sea)?
 193         **/
 194         double eps_dielect=15.0;
 195         double sgm_conductivity = 0.005;
 196         double eno = 301.0;
 197         double frq_mhz;
 198         if( (freq < 118.0) || (freq > 137.0) )
 199                 frq_mhz = 125.0;        // sane value, middle of bandplan
 200         else
 201                 frq_mhz = freq;
 202         int radio_climate = 5;          // continental temperate
 203         int pol=1;      // assuming vertical polarization although this is more complex in reality
 204         double conf = 0.90;     // 90% of situations and time, take into account speed
 205         double rel = 0.90;
 206         double dbloss;
 207         char strmode[150];
 208         int errnum;
 209
 210         double tx_pow = _transmitter_power;
 211         double ant_gain = _antenna_gain;
 212         double signal = 0.0;
 213
 214         if(transmission_type == 1)
 215                 tx_pow = _transmitter_power + 6.0;
 216
 217         if((transmission_type == 1) || (transmission_type == 3))
 218                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 219
 220         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 221
 222         FGScenery * scenery = globals->get_scenery();
 223
 224         double own_lat = fgGetDouble("/position/latitude-deg");
 225         double own_lon = fgGetDouble("/position/longitude-deg");
 226         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 227         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 228
 229
 230         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 231
 232         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 233         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 234         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 235         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 236
 237         /**     position of sender radio antenna (HAAT)
 238                         sender can be aircraft or ground station
 239         **/
 240         double ATC_HAAT = 30.0;
 241         double Aircraft_HAAT = 5.0;
 242         double sender_alt_ft,sender_alt;
 243         double transmitter_height=0.0;
 244         double receiver_height=0.0;
 245         SGGeod sender_pos = pos;
 246
 247         sender_alt_ft = sender_pos.getElevationFt();
 248         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 249         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 250         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 251         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 252
 253         double point_distance= 90.0; // regular SRTM is 90 meters
 254         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 255         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 256         double probe_distance = 0.0;
 257         /** If distance larger than this value (300 km), assume reception imposssible */
 258         if (distance_m > 300000)
 259                 return -1.0;
 260         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 261         if (own_alt > 8000) {
 262                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 263                 SG_LOG(SG_GENERAL, SG_BULK,
 264                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 265                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 266                 signal = link_budget - dbloss;
 267                 return signal;
 268         }
 269
 270
 271         double max_points = distance_m / point_distance;
 272         deque<double> _elevations;
 273
 274         double elevation_under_pilot = 0.0;
 275         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 276                 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
 277         }
 278
 279         double elevation_under_sender = 0.0;
 280         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 281                 transmitter_height = sender_alt - elevation_under_sender;
 282         }
 283         else {
 284                 transmitter_height = sender_alt;
 285         }
 286
 287         if(transmission_type == 1)
 288                 transmitter_height += ATC_HAAT;
 289         else
 290                 transmitter_height += Aircraft_HAAT;
 291
 292         SG_LOG(SG_GENERAL, SG_BULK,
 293                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 294         cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 295
 296         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 297
 298         while (_elevations.size() <= e_size) {
 299                 probe_distance += point_distance;
 300                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 301
 302                 double elevation_m = 0.0;
 303
 304                 if (scenery->get_elevation_m( probe, elevation_m, NULL )) {
 305                         if((transmission_type == 3) || (transmission_type == 4)) {
 306                                 _elevations.push_back(elevation_m);
 307                         }
 308                         else {
 309                                  _elevations.push_front(elevation_m);
 310                         }
 311                 }
 312                 else {
 313                         if((transmission_type == 3) || (transmission_type == 4)) {
 314                                 _elevations.push_back(elevation_m);
 315                         }
 316                         else {
 317                         _elevations.push_front(0.0);
 318                         }
 319                 }
 320         }
 321         if((transmission_type == 3) || (transmission_type == 4)) {
 322                 _elevations.push_front(elevation_under_pilot);
 323                 _elevations.push_back(elevation_under_sender);
 324         }
 325         else {
 326                 _elevations.push_back(elevation_under_pilot);
 327                 _elevations.push_front(elevation_under_sender);
 328         }
 329
 330
 331         double max_alt_between=0.0;
 332         for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
 333                 if (_elevations[i] > max_alt_between) {
 334                         max_alt_between = _elevations[i];
 335                 }
 336         }
 337
 338         double num_points= (double)_elevations.size();
 339         //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
 340         _elevations.push_front(point_distance);
 341         _elevations.push_front(num_points -1);
 342         int size = _elevations.size();
 343         double itm_elev[size];
 344         for(int i=0;i<size;i++) {
 345                 itm_elev[i]=_elevations[i];
 346                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 347         }
 348
 349
 350         /** first Fresnel zone radius
 351                 frequency in the middle of the bandplan, more accuracy is not necessary
 352         */
 353         double fz_clr= 8.657 * sqrt(distance_m / 0.125);
 354
 355         // TODO: If we clear the first Fresnel zone, we are into line of sight territory
 356
 357         // else we need to calculate point to point link loss
 358         if((transmission_type == 3) || (transmission_type == 4)) {
 359                 // the sender and receiver roles are switched
 360                 point_to_point(itm_elev, receiver_height, transmitter_height,
 361                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 362                         pol, conf, rel, dbloss, strmode, errnum);
 363
 364         }
 365         else {
 366
 367                 point_to_point(itm_elev, transmitter_height, receiver_height,
 368                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 369                         pol, conf, rel, dbloss, strmode, errnum);
 370         }
 371         SG_LOG(SG_GENERAL, SG_BULK,
 372                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 373         cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 374
 375         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 376         //      return -1;
 377         signal = link_budget - dbloss;
 378         return signal;
 379
 380 }
 381
 382 /*** implement simple LOS propagation model (WIP)
 383 ***/
 384 double FGRadio::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 385         double frq_mhz;
 386         if( (freq < 118.0) || (freq > 137.0) )
 387                 frq_mhz = 125.0;        // sane value, middle of bandplan
 388         else
 389                 frq_mhz = freq;
 390         double dbloss;
 391         double tx_pow = _transmitter_power;
 392         double ant_gain = _antenna_gain;
 393         double signal = 0.0;
 394         double ATC_HAAT = 30.0;
 395         double Aircraft_HAAT = 5.0;
 396         double sender_alt_ft,sender_alt;
 397         double transmitter_height=0.0;
 398         double receiver_height=0.0;
 399         double own_lat = fgGetDouble("/position/latitude-deg");
 400         double own_lon = fgGetDouble("/position/longitude-deg");
 401         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 402         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 403
 404         if(transmission_type == 1)
 405                 tx_pow = _transmitter_power + 6.0;
 406
 407         if((transmission_type == 1) || (transmission_type == 3))
 408                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 409
 410         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 411
 412         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 413
 414         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 415
 416         SGGeod sender_pos = pos;
 417
 418         sender_alt_ft = sender_pos.getElevationFt();
 419         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 420
 421         receiver_height = own_alt;
 422         transmitter_height = sender_alt;
 423
 424         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 425
 426         if(transmission_type == 1)
 427                 transmitter_height += ATC_HAAT;
 428         else
 429                 transmitter_height += Aircraft_HAAT;
 430
 431         /** radio horizon calculation with wave bending k=4/3 */
 432         double receiver_horizon = 4.12 * sqrt(receiver_height);
 433         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 434         double total_horizon = receiver_horizon + transmitter_horizon;
 435
 436         if (distance_m > total_horizon) {
 437                 return -1;
 438         }
 439
 440         // free-space loss (distance calculation should be changed)
 441         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 442         signal = link_budget - dbloss;
 443         SG_LOG(SG_GENERAL, SG_BULK,
 444                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 445         cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 446         return signal;
 447
 448 }