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