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