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 #define NDEBUG
  27 #include <assert.h>
  28 #include <stdlib.h>
  29 #include <deque>
  30 #include "radio.hxx"
  31 #include <simgear/scene/material/mat.hxx>
  32 #include <Scenery/scenery.hxx>
  33
  34 #define WITH_POINT_TO_POINT 1
  35 #include "itm.cpp"
  36
  37
  38 FGRadioTransmission::FGRadioTransmission() {
  39
  40         /** radio parameters (which should probably be set for each radio) */
  41
  42         _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
  43
  44         /** AM transmitter power in dBm.
  45         *       Note this value is calculated from the typical final transistor stage output
  46         *       small aircraft have portable transmitters which operate at 36 dBm output (4 Watts) others operate in the range 10-20 W
  47         *       later possibly store this value in aircraft description
  48         *       ATC comms usually operate high power equipment, thus making the link asymetrical; this is taken care of in propagation routines
  49         *       Typical output powers for ATC ground equipment, VHF-UHF:
  50         *       40 dBm - 10 W (ground, clearance)
  51         *       44 dBm - 20 W (tower)
  52         *       47 dBm - 50 W (center, sectors)
  53         *       50 dBm - 100 W (center, sectors)
  54         *       53 dBm - 200 W (sectors, on directional arrays)
  55         **/
  56         _transmitter_power = 43.0;
  57
  58         _tx_antenna_height = 2.0; // TX antenna height above ground level
  59
  60         _rx_antenna_height = 2.0; // RX antenna height above ground level
  61
  62         /** pilot plane's antenna gain + AI aircraft antenna gain
  63         *       real-life gain for conventional monopole/dipole antenna
  64         **/
  65         _antenna_gain = 2.0;
  66
  67         _rx_antenna_gain = 1.0;
  68         _tx_antenna_gain = 1.0;
  69
  70         _rx_line_losses = 2.0;  // to be configured for each station
  71         _tx_line_losses = 2.0;
  72
  73         _propagation_model = 2; //  choose between models via option: realistic radio on/off
  74         _terrain_sampling_distance = fgGetDouble("/sim/radio/sampling-distance", 90.0); // regular SRTM is 90 meters
  75 }
  76
  77 FGRadioTransmission::~FGRadioTransmission()
  78 {
  79 }
  80
  81
  82 double FGRadioTransmission::getFrequency(int radio) {
  83         double freq = 118.0;
  84         switch (radio) {
  85                 case 1:
  86                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  87                         break;
  88                 case 2:
  89                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  90                         break;
  91                 default:
  92                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  93
  94         }
  95         return freq;
  96 }
  97
  98 /*** TODO: receive multiplayer chat message and voice
  99 ***/
 100 void FGRadioTransmission::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 101
 102 }
 103
 104 /*** TODO: receive navaid
 105 ***/
 106 double FGRadioTransmission::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
 107
 108         // typical VOR/LOC transmitter power appears to be 200 Watt ~ 53 dBm
 109         // vor/loc typical sensitivity between -107 and -101 dBm
 110         // glideslope sensitivity between -85 and -81 dBm
 111         if ( _propagation_model == 1) {
 112                 return LOS_calculate_attenuation(tx_pos, freq, 1);
 113         }
 114         else if ( _propagation_model == 2) {
 115                 return ITM_calculate_attenuation(tx_pos, freq, 1);
 116         }
 117
 118         return -1;
 119
 120 }
 121
 122 /*** Receive ATC radio communication as text
 123 ***/
 124 void FGRadioTransmission::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 125
 126
 127         double comm1 = getFrequency(1);
 128         double comm2 = getFrequency(2);
 129         if ( !(fabs(freq - comm1) <= 0.0001) &&  !(fabs(freq - comm2) <= 0.0001) ) {
 130                 //cerr << "Frequency not tuned: " << freq << " Radio1: " << comm1 << " Radio2: " << comm2 << endl;
 131                 return;
 132         }
 133         else {
 134
 135                 if ( _propagation_model == 0) {
 136                         fgSetString("/sim/messages/atc", text.c_str());
 137                 }
 138                 else if ( _propagation_model == 1 ) {
 139                         // TODO: free space, round earth
 140                         double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
 141                         if (signal <= 0.0) {
 142                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 143                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 144                                 return;
 145                         }
 146                         else {
 147                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 148                                 //cerr << "Signal completely readable: " << signal << endl;
 149                                 fgSetString("/sim/messages/atc", text.c_str());
 150                                 /** write signal strength above threshold to the property tree
 151                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 152                                 **/
 153                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 154                         }
 155                 }
 156                 else if ( _propagation_model == 2 ) {
 157                         // Use ITM propagation model
 158                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 159                         if (signal <= 0.0) {
 160                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 161                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 162                                 return;
 163                         }
 164                         if ((signal > 0.0) && (signal < 12.0)) {
 165                                 /** for low SNR values implement a way to make the conversation
 166                                 *       hard to understand but audible
 167                                 *       in the real world, the receiver AGC fails to capture the slope
 168                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 169                                 *       the workaround below is more akin to what would happen on a FM transmission
 170                                 *       therefore the correct way would be to work on the volume
 171                                 **/
 172                                 /*
 173                                 string hash_noise = " ";
 174                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 175                                 int t_size = text.size();
 176                                 for (int n = 1; n <= reps; ++n) {
 177                                         int pos = rand() % (t_size -1);
 178                                         text.replace(pos,1, hash_noise);
 179                                 }
 180                                 */
 181                                 double volume = (fabs(signal - 12.0) / 12);
 182                                 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 183                                 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
 184                                 //cerr << "Usable signal at limit: " << signal << endl;
 185                                 fgSetDouble("/sim/sound/voices/voice/volume", volume);
 186                                 fgSetString("/sim/messages/atc", text.c_str());
 187                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 188                                 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 189                         }
 190                         else {
 191                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 192                                 //cerr << "Signal completely readable: " << signal << endl;
 193                                 fgSetString("/sim/messages/atc", text.c_str());
 194                                 /** write signal strength above threshold to the property tree
 195                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 196                                 **/
 197                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 198                         }
 199
 200                 }
 201
 202         }
 203
 204 }
 205
 206 /***  Implement radio attenuation
 207           based on the Longley-Rice propagation model
 208 ***/
 209 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 210
 211
 212
 213         /** ITM default parameters
 214                 TODO: take them from tile materials (especially for sea)?
 215         **/
 216         double eps_dielect=15.0;
 217         double sgm_conductivity = 0.005;
 218         double eno = 301.0;
 219         double frq_mhz;
 220         if( (freq < 118.0) || (freq > 137.0) )
 221                 frq_mhz = 125.0;        // sane value, middle of bandplan
 222         else
 223                 frq_mhz = freq;
 224         int radio_climate = 5;          // continental temperate
 225         int pol=1;      // assuming vertical polarization although this is more complex in reality
 226         double conf = 0.90;     // 90% of situations and time, take into account speed
 227         double rel = 0.90;
 228         double dbloss;
 229         char strmode[150];
 230         int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
 231         double horizons[2];
 232         int errnum;
 233
 234         double clutter_loss = 0.0;      // loss due to vegetation and urban
 235         double tx_pow = _transmitter_power;
 236         double ant_gain = _antenna_gain;
 237         double signal = 0.0;
 238
 239         if(transmission_type == 1)
 240                 tx_pow = _transmitter_power + 6.0;
 241
 242         if((transmission_type == 1) || (transmission_type == 3))
 243                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 244
 245         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 246
 247         FGScenery * scenery = globals->get_scenery();
 248
 249         double own_lat = fgGetDouble("/position/latitude-deg");
 250         double own_lon = fgGetDouble("/position/longitude-deg");
 251         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 252         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 253
 254
 255         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 256
 257         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 258         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 259         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 260         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 261
 262         /**     position of sender radio antenna (HAAT)
 263                         sender can be aircraft or ground station
 264         **/
 265         double ATC_HAAT = 30.0;
 266         double Aircraft_HAAT = 5.0;
 267         double sender_alt_ft,sender_alt;
 268         double transmitter_height=0.0;
 269         double receiver_height=0.0;
 270         SGGeod sender_pos = pos;
 271
 272         sender_alt_ft = sender_pos.getElevationFt();
 273         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 274         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 275         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 276         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 277
 278         double point_distance= _terrain_sampling_distance;
 279         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 280         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 281         double probe_distance = 0.0;
 282         /** If distance larger than this value (300 km), assume reception imposssible */
 283         if (distance_m > 300000)
 284                 return -1.0;
 285         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 286         if (own_alt > 8000) {
 287                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 288                 SG_LOG(SG_GENERAL, SG_BULK,
 289                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 290                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 291                 signal = link_budget - dbloss;
 292                 return signal;
 293         }
 294
 295
 296         int max_points = (int)floor(distance_m / point_distance);
 297         double delta_last = fmod(distance_m, point_distance);
 298
 299         deque<double> _elevations;
 300         deque<string> materials;
 301
 302
 303         double elevation_under_pilot = 0.0;
 304         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 305                 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
 306         }
 307
 308         double elevation_under_sender = 0.0;
 309         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 310                 transmitter_height = sender_alt - elevation_under_sender;
 311         }
 312         else {
 313                 transmitter_height = sender_alt;
 314         }
 315
 316         if(transmission_type == 1)
 317                 transmitter_height += ATC_HAAT;
 318         else
 319                 transmitter_height += Aircraft_HAAT;
 320
 321         SG_LOG(SG_GENERAL, SG_BULK,
 322                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 323         cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 324
 325         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 326
 327         while (_elevations.size() <= e_size) {
 328                 probe_distance += point_distance;
 329                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 330                 const SGMaterial *mat = 0;
 331                 double elevation_m = 0.0;
 332
 333                 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
 334                         if((transmission_type == 3) || (transmission_type == 4)) {
 335                                 _elevations.push_back(elevation_m);
 336                                 if(mat) {
 337                                         const std::vector<string> mat_names = mat->get_names();
 338                                         materials.push_back(mat_names[0]);
 339                                 }
 340                                 else {
 341                                         materials.push_back("None");
 342                                 }
 343                         }
 344                         else {
 345                                  _elevations.push_front(elevation_m);
 346                                  if(mat) {
 347                                          const std::vector<string> mat_names = mat->get_names();
 348                                          materials.push_front(mat_names[0]);
 349                                 }
 350                                 else {
 351                                         materials.push_front("None");
 352                                 }
 353                         }
 354                 }
 355                 else {
 356                         if((transmission_type == 3) || (transmission_type == 4)) {
 357                                 _elevations.push_back(0.0);
 358                                 materials.push_back("None");
 359                         }
 360                         else {
 361                                 _elevations.push_front(0.0);
 362                                 materials.push_front("None");
 363                         }
 364                 }
 365         }
 366         if((transmission_type == 3) || (transmission_type == 4)) {
 367                 _elevations.push_front(elevation_under_pilot);
 368                 if (delta_last > (point_distance / 2) )                 // only add last point if it's farther than half point_distance
 369                         _elevations.push_back(elevation_under_sender);
 370         }
 371         else {
 372                 _elevations.push_back(elevation_under_pilot);
 373                 if (delta_last > (point_distance / 2) )
 374                         _elevations.push_front(elevation_under_sender);
 375         }
 376
 377
 378         double max_alt_between=0.0;
 379         for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
 380                 if (_elevations[i] > max_alt_between) {
 381                         max_alt_between = _elevations[i];
 382                 }
 383         }
 384
 385         double num_points= (double)_elevations.size();
 386         //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
 387         _elevations.push_front(point_distance);
 388         _elevations.push_front(num_points -1);
 389         int size = _elevations.size();
 390         double itm_elev[size];
 391         for(int i=0;i<size;i++) {
 392                 itm_elev[i]=_elevations[i];
 393                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 394         }
 395
 396         if((transmission_type == 3) || (transmission_type == 4)) {
 397                 // the sender and receiver roles are switched
 398                 point_to_point(itm_elev, receiver_height, transmitter_height,
 399                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 400                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 401                 if( fgGetBool( "/sim/radio/use-clutter-attenuation", false ) )
 402                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
 403         }
 404         else {
 405                 point_to_point(itm_elev, transmitter_height, receiver_height,
 406                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 407                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 408                 if( fgGetBool( "/sim/radio/use-clutter-attenuation", false ) )
 409                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 410         }
 411         SG_LOG(SG_GENERAL, SG_BULK,
 412                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 413         cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 414
 415         cerr << "Clutter loss: " << clutter_loss << endl;
 416         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 417         //      return -1;
 418         signal = link_budget - dbloss - clutter_loss;
 419         return signal;
 420
 421 }
 422
 423 /*** Calculate losses due to vegetation and urban clutter (WIP)
 424 *        We are only worried about clutter loss, terrain influence
 425 *        on the first Fresnel zone is calculated in the ITM functions
 426 ***/
 427 void FGRadioTransmission::clutterLoss(double freq, double distance_m, double itm_elev[], deque<string> materials,
 428         double transmitter_height, double receiver_height, int p_mode,
 429         double horizons[], double &clutter_loss) {
 430
 431         distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
 432
 433         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 434                 int mat = 0;
 435                 int j=1;
 436                 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
 437
 438                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 439                         double clutter_density = 0.0;   // percent of reflected wave
 440                         get_material_properties(materials[mat], clutter_height, clutter_density);
 441
 442                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 443                         // First Fresnel radius
 444                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 445                         assert(frs_rad > 0);
 446
 447                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 448
 449                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 450                         double d1 = j * itm_elev[1];
 451                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 452                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 453                         }
 454                         double ray_height = (grad * d1) + min_elev;
 455
 456                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 457                         double intrusion = fabs(clearance);
 458
 459                         if (clearance >= 0) {
 460                                 // no losses
 461                         }
 462                         else if (clearance < 0 && (intrusion < clutter_height)) {
 463
 464                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 465                         }
 466                         else if (clearance < 0 && (intrusion > clutter_height)) {
 467                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 468                         }
 469                         else {
 470                                 // no losses
 471                         }
 472                         j++;
 473                         mat++;
 474                 }
 475
 476         }
 477         else if (p_mode == 1) {         // diffraction
 478
 479                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 480                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
 481                         int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
 482                         //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
 483                         int last = 1;
 484                         /** perform the first pass */
 485                         int mat = 0;
 486                         int j=1;
 487                         for (int k=3;k < num_points_1st + 2;k++) {
 488                                 if (num_points_1st < 1)
 489                                         break;
 490                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 491                                 double clutter_density = 0.0;   // percent of reflected wave
 492                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 493
 494                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 495                                 // First Fresnel radius
 496                                 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (num_points_1st - j) * itm_elev[1] / 1000000) / ( num_points_1st * itm_elev[1] * freq / 1000) );
 497                                 assert(frs_rad > 0);
 498
 499                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 500
 501                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 502                                 double d1 = j * itm_elev[1];
 503                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 504                                         d1 = (num_points_1st - j) * itm_elev[1];
 505                                 }
 506                                 double ray_height = (grad * d1) + min_elev;
 507
 508                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 509                                 double intrusion = fabs(clearance);
 510
 511                                 if (clearance >= 0) {
 512                                         // no losses
 513                                 }
 514                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 515
 516                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 517                                 }
 518                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 519                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 520                                 }
 521                                 else {
 522                                         // no losses
 523                                 }
 524                                 j++;
 525                                 mat++;
 526                                 last = k;
 527                         }
 528
 529                         /** and the second pass */
 530                         mat +=1;
 531                         j =1; // first point is diffraction edge, 2nd the RX elevation
 532                         for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
 533                                 if (num_points_2nd < 1)
 534                                         break;
 535                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 536                                 double clutter_density = 0.0;   // percent of reflected wave
 537                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 538
 539                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 540                                 // First Fresnel radius
 541                                 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (num_points_2nd - j) * itm_elev[1] / 1000000) / (  num_points_2nd * itm_elev[1] * freq / 1000) );
 542                                 assert(frs_rad > 0);
 543
 544                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 545
 546                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 547                                 double d1 = j * itm_elev[1];
 548                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 549                                         d1 = (num_points_2nd - j) * itm_elev[1];
 550                                 }
 551                                 double ray_height = (grad * d1) + min_elev;
 552
 553                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 554                                 double intrusion = fabs(clearance);
 555
 556                                 if (clearance >= 0) {
 557                                         // no losses
 558                                 }
 559                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 560
 561                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 562                                 }
 563                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 564                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 565                                 }
 566                                 else {
 567                                         // no losses
 568                                 }
 569                                 j++;
 570                                 mat++;
 571                         }
 572
 573                 }
 574                 else {  // double horizon: same as single horizon, except there are 3 segments
 575
 576                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
 577                         int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
 578                         int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
 579                         //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
 580                         //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
 581                         int last = 1;
 582                         /** perform the first pass */
 583                         int mat = 0;
 584                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 585                         for (int k=3;k < num_points_1st +2;k++) {
 586                                 if (num_points_1st < 1)
 587                                         break;
 588                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 589                                 double clutter_density = 0.0;   // percent of reflected wave
 590                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 591
 592                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 593                                 // First Fresnel radius
 594                                 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (num_points_1st - j) * itm_elev[1] / 1000000) / (  num_points_1st * itm_elev[1] * freq / 1000) );
 595                                 assert(frs_rad > 0);
 596
 597                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 598
 599                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 600                                 double d1 = j * itm_elev[1];
 601                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 602                                         d1 = (num_points_1st - j) * itm_elev[1];
 603                                 }
 604                                 double ray_height = (grad * d1) + min_elev;
 605
 606                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 607                                 double intrusion = fabs(clearance);
 608
 609                                 if (clearance >= 0) {
 610                                         // no losses
 611                                 }
 612                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 613
 614                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 615                                 }
 616                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 617                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 618                                 }
 619                                 else {
 620                                         // no losses
 621                                 }
 622                                 j++;
 623                                 last = k;
 624                         }
 625                         mat +=1;
 626                         /** and the second pass */
 627                         int last2=1;
 628                         j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 629                         for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
 630                                 if (num_points_2nd < 1)
 631                                         break;
 632                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 633                                 double clutter_density = 0.0;   // percent of reflected wave
 634                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 635
 636                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
 637                                 // First Fresnel radius
 638                                 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (num_points_2nd - j) * itm_elev[1] / 1000000) / (  num_points_2nd * itm_elev[1] * freq / 1000) );
 639
 640                                 assert(frs_rad > 0);
 641                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 642
 643                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
 644                                 double d1 = j * itm_elev[1];
 645                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
 646                                         d1 = (num_points_2nd - j) * itm_elev[1];
 647                                 }
 648                                 double ray_height = (grad * d1) + min_elev;
 649
 650                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 651                                 double intrusion = fabs(clearance);
 652
 653                                 if (clearance >= 0) {
 654                                         // no losses
 655                                 }
 656                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 657
 658                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 659                                 }
 660                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 661                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 662                                 }
 663                                 else {
 664                                         // no losses
 665                                 }
 666                                 j++;
 667                                 mat++;
 668                                 last2 = k;
 669                         }
 670
 671                         /** third and final pass */
 672                         mat +=1;
 673                         j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 674                         for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
 675                                 if (num_points_3rd < 1)
 676                                         break;
 677                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 678                                 double clutter_density = 0.0;   // percent of reflected wave
 679                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 680
 681                                 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 682                                 // First Fresnel radius
 683                                 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (num_points_3rd - j) * itm_elev[1] / 1000000) / (  num_points_3rd * itm_elev[1] * freq / 1000) );
 684
 685                                 assert(frs_rad > 0);
 686
 687                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 688
 689                                 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 690                                 double d1 = j * itm_elev[1];
 691                                 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 692                                         d1 = (num_points_3rd - j) * itm_elev[1];
 693                                 }
 694                                 double ray_height = (grad * d1) + min_elev;
 695
 696                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 697                                 double intrusion = fabs(clearance);
 698
 699                                 if (clearance >= 0) {
 700                                         // no losses
 701                                 }
 702                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 703
 704                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 705                                 }
 706                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 707                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 708                                 }
 709                                 else {
 710                                         // no losses
 711                                 }
 712                                 j++;
 713                                 mat++;
 714
 715                         }
 716
 717                 }
 718         }
 719         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now...
 720                 clutter_loss = 0.0;
 721         }
 722
 723 }
 724
 725 /***    Temporary material properties database
 726 *               height: median clutter height
 727 *               density: radiowave attenuation factor
 728 ***/
 729 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 730
 731         if(mat_name == "Landmass") {
 732                 height = 15.0;
 733                 density = 0.2;
 734         }
 735
 736         else if(mat_name == "SomeSort") {
 737                 height = 15.0;
 738                 density = 0.2;
 739         }
 740
 741         else if(mat_name == "Island") {
 742                 height = 15.0;
 743                 density = 0.2;
 744         }
 745         else if(mat_name == "Default") {
 746                 height = 15.0;
 747                 density = 0.2;
 748         }
 749         else if(mat_name == "EvergreenBroadCover") {
 750                 height = 20.0;
 751                 density = 0.2;
 752         }
 753         else if(mat_name == "EvergreenForest") {
 754                 height = 20.0;
 755                 density = 0.2;
 756         }
 757         else if(mat_name == "DeciduousBroadCover") {
 758                 height = 15.0;
 759                 density = 0.3;
 760         }
 761         else if(mat_name == "DeciduousForest") {
 762                 height = 15.0;
 763                 density = 0.3;
 764         }
 765         else if(mat_name == "MixedForestCover") {
 766                 height = 20.0;
 767                 density = 0.25;
 768         }
 769         else if(mat_name == "MixedForest") {
 770                 height = 15.0;
 771                 density = 0.25;
 772         }
 773         else if(mat_name == "RainForest") {
 774                 height = 25.0;
 775                 density = 0.55;
 776         }
 777         else if(mat_name == "EvergreenNeedleCover") {
 778                 height = 15.0;
 779                 density = 0.2;
 780         }
 781         else if(mat_name == "WoodedTundraCover") {
 782                 height = 5.0;
 783                 density = 0.15;
 784         }
 785         else if(mat_name == "DeciduousNeedleCover") {
 786                 height = 5.0;
 787                 density = 0.2;
 788         }
 789         else if(mat_name == "ScrubCover") {
 790                 height = 3.0;
 791                 density = 0.15;
 792         }
 793         else if(mat_name == "BuiltUpCover") {
 794                 height = 30.0;
 795                 density = 0.7;
 796         }
 797         else if(mat_name == "Urban") {
 798                 height = 30.0;
 799                 density = 0.7;
 800         }
 801         else if(mat_name == "Construction") {
 802                 height = 30.0;
 803                 density = 0.7;
 804         }
 805         else if(mat_name == "Industrial") {
 806                 height = 30.0;
 807                 density = 0.7;
 808         }
 809         else if(mat_name == "Port") {
 810                 height = 30.0;
 811                 density = 0.7;
 812         }
 813         else if(mat_name == "Town") {
 814                 height = 10.0;
 815                 density = 0.5;
 816         }
 817         else if(mat_name == "SubUrban") {
 818                 height = 10.0;
 819                 density = 0.5;
 820         }
 821         else if(mat_name == "CropWoodCover") {
 822                 height = 10.0;
 823                 density = 0.1;
 824         }
 825         else if(mat_name == "CropWood") {
 826                 height = 10.0;
 827                 density = 0.1;
 828         }
 829         else if(mat_name == "AgroForest") {
 830                 height = 10.0;
 831                 density = 0.1;
 832         }
 833         else {
 834                 height = 0.0;
 835                 density = 0.0;
 836         }
 837
 838 }
 839
 840 /*** implement simple LOS propagation model (WIP)
 841 ***/
 842 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 843         double frq_mhz;
 844         if( (freq < 118.0) || (freq > 137.0) )
 845                 frq_mhz = 125.0;        // sane value, middle of bandplan
 846         else
 847                 frq_mhz = freq;
 848         double dbloss;
 849         double tx_pow = _transmitter_power;
 850         double ant_gain = _antenna_gain;
 851         double signal = 0.0;
 852         double ATC_HAAT = 30.0;
 853         double Aircraft_HAAT = 5.0;
 854         double sender_alt_ft,sender_alt;
 855         double transmitter_height=0.0;
 856         double receiver_height=0.0;
 857         double own_lat = fgGetDouble("/position/latitude-deg");
 858         double own_lon = fgGetDouble("/position/longitude-deg");
 859         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 860         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 861
 862         if(transmission_type == 1)
 863                 tx_pow = _transmitter_power + 6.0;
 864
 865         if((transmission_type == 1) || (transmission_type == 3))
 866                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 867
 868         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 869
 870         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 871
 872         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 873
 874         SGGeod sender_pos = pos;
 875
 876         sender_alt_ft = sender_pos.getElevationFt();
 877         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 878
 879         receiver_height = own_alt;
 880         transmitter_height = sender_alt;
 881
 882         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 883
 884         if(transmission_type == 1)
 885                 transmitter_height += ATC_HAAT;
 886         else
 887                 transmitter_height += Aircraft_HAAT;
 888
 889         /** radio horizon calculation with wave bending k=4/3 */
 890         double receiver_horizon = 4.12 * sqrt(receiver_height);
 891         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 892         double total_horizon = receiver_horizon + transmitter_horizon;
 893
 894         if (distance_m > total_horizon) {
 895                 return -1;
 896         }
 897
 898         // free-space loss (distance calculation should be changed)
 899         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 900         signal = link_budget - dbloss;
 901         SG_LOG(SG_GENERAL, SG_BULK,
 902                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 903         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 904         return signal;
 905
 906 }
 907
 908