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 <simgear/scene/material/mat.hxx>
  30 #include <Scenery/scenery.hxx>
  31
  32 #define WITH_POINT_TO_POINT 1
  33 #include "itm.cpp"
  34
  35
  36 FGRadio::FGRadio() {
  37
  38         /** radio parameters (which should probably be set for each radio) */
  39
  40         _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
  41
  42         /** AM transmitter power in dBm.
  43         *       Note this value is calculated from the typical final transistor stage output
  44         *       small aircraft have portable transmitters which operate at 36 dBm output (4 Watts) others operate in the range 10-20 W
  45         *       later possibly store this value in aircraft description
  46         *       ATC comms usually operate high power equipment, thus making the link asymetrical; this is taken care of in propagation routines
  47         *       Typical output powers for ATC ground equipment, VHF-UHF:
  48         *       40 dBm - 10 W (ground, clearance)
  49         *       44 dBm - 20 W (tower)
  50         *       47 dBm - 50 W (center, sectors)
  51         *       50 dBm - 100 W (center, sectors)
  52         *       53 dBm - 200 W (sectors, on directional arrays)
  53         **/
  54         _transmitter_power = 43.0;
  55
  56         /** pilot plane's antenna gain + AI aircraft antenna gain
  57         *       real-life gain for conventional monopole/dipole antenna
  58         **/
  59         _antenna_gain = 2.0;
  60         _propagation_model = 2; //  choose between models via option: realistic radio on/off
  61
  62 }
  63
  64 FGRadio::~FGRadio()
  65 {
  66 }
  67
  68
  69 double FGRadio::getFrequency(int radio) {
  70         double freq = 118.0;
  71         switch (radio) {
  72                 case 1:
  73                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  74                         break;
  75                 case 2:
  76                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  77                         break;
  78                 default:
  79                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  80
  81         }
  82         return freq;
  83 }
  84
  85 /*** TODO: receive multiplayer chat message and voice
  86 ***/
  87 void FGRadio::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
  88
  89 }
  90
  91 /*** TODO: receive navaid
  92 ***/
  93 double FGRadio::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
  94
  95         // typical VOR/LOC transmitter power appears to be 200 Watt ~ 53 dBm
  96         // vor/loc typical sensitivity between -107 and -101 dBm
  97         // glideslope sensitivity between -85 and -81 dBm
  98         if ( _propagation_model == 1) {
  99                 return LOS_calculate_attenuation(tx_pos, freq, 1);
 100         }
 101         else if ( _propagation_model == 2) {
 102                 return ITM_calculate_attenuation(tx_pos, freq, 1);
 103         }
 104
 105         return -1;
 106
 107 }
 108
 109 /*** Receive ATC radio communication as text
 110 ***/
 111 void FGRadio::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 112
 113
 114         double comm1 = getFrequency(1);
 115         double comm2 = getFrequency(2);
 116         if ( !(fabs(freq - comm1) <= 0.0001) &&  !(fabs(freq - comm2) <= 0.0001) ) {
 117                 //cerr << "Frequency not tuned: " << freq << " Radio1: " << comm1 << " Radio2: " << comm2 << endl;
 118                 return;
 119         }
 120         else {
 121
 122                 if ( _propagation_model == 0) {
 123                         fgSetString("/sim/messages/atc", text.c_str());
 124                 }
 125                 else if ( _propagation_model == 1 ) {
 126                         // TODO: free space, round earth
 127                         double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
 128                         if (signal <= 0.0) {
 129                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 130                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 131                                 return;
 132                         }
 133                         else {
 134                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 135                                 //cerr << "Signal completely readable: " << signal << endl;
 136                                 fgSetString("/sim/messages/atc", text.c_str());
 137                                 /** write signal strength above threshold to the property tree
 138                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 139                                 **/
 140                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 141                         }
 142                 }
 143                 else if ( _propagation_model == 2 ) {
 144                         // Use ITM propagation model
 145                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 146                         if (signal <= 0.0) {
 147                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 148                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 149                                 return;
 150                         }
 151                         if ((signal > 0.0) && (signal < 12.0)) {
 152                                 /** for low SNR values implement a way to make the conversation
 153                                 *       hard to understand but audible
 154                                 *       in the real world, the receiver AGC fails to capture the slope
 155                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 156                                 *       the workaround below is more akin to what would happen on a FM transmission
 157                                 *       therefore the correct way would be to work on the volume
 158                                 **/
 159                                 /*
 160                                 string hash_noise = " ";
 161                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 162                                 int t_size = text.size();
 163                                 for (int n = 1; n <= reps; ++n) {
 164                                         int pos = rand() % (t_size -1);
 165                                         text.replace(pos,1, hash_noise);
 166                                 }
 167                                 */
 168                                 double volume = (fabs(signal - 12.0) / 12);
 169                                 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 170                                 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
 171                                 //cerr << "Usable signal at limit: " << signal << endl;
 172                                 fgSetDouble("/sim/sound/voices/voice/volume", volume);
 173                                 fgSetString("/sim/messages/atc", text.c_str());
 174                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 175                                 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 176                         }
 177                         else {
 178                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 179                                 //cerr << "Signal completely readable: " << signal << endl;
 180                                 fgSetString("/sim/messages/atc", text.c_str());
 181                                 /** write signal strength above threshold to the property tree
 182                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 183                                 **/
 184                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 185                         }
 186
 187                 }
 188
 189         }
 190
 191 }
 192
 193 /***  Implement radio attenuation
 194           based on the Longley-Rice propagation model
 195 ***/
 196 double FGRadio::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 197
 198
 199
 200         /** ITM default parameters
 201                 TODO: take them from tile materials (especially for sea)?
 202         **/
 203         double eps_dielect=15.0;
 204         double sgm_conductivity = 0.005;
 205         double eno = 301.0;
 206         double frq_mhz;
 207         if( (freq < 118.0) || (freq > 137.0) )
 208                 frq_mhz = 125.0;        // sane value, middle of bandplan
 209         else
 210                 frq_mhz = freq;
 211         int radio_climate = 5;          // continental temperate
 212         int pol=1;      // assuming vertical polarization although this is more complex in reality
 213         double conf = 0.90;     // 90% of situations and time, take into account speed
 214         double rel = 0.90;
 215         double dbloss;
 216         char strmode[150];
 217         int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
 218         double horizons[2];
 219         int errnum;
 220
 221         double clutter_loss;    // loss due to vegetation and urban
 222         double tx_pow = _transmitter_power;
 223         double ant_gain = _antenna_gain;
 224         double signal = 0.0;
 225
 226         if(transmission_type == 1)
 227                 tx_pow = _transmitter_power + 6.0;
 228
 229         if((transmission_type == 1) || (transmission_type == 3))
 230                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 231
 232         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 233
 234         FGScenery * scenery = globals->get_scenery();
 235
 236         double own_lat = fgGetDouble("/position/latitude-deg");
 237         double own_lon = fgGetDouble("/position/longitude-deg");
 238         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 239         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 240
 241
 242         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 243
 244         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 245         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 246         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 247         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 248
 249         /**     position of sender radio antenna (HAAT)
 250                         sender can be aircraft or ground station
 251         **/
 252         double ATC_HAAT = 30.0;
 253         double Aircraft_HAAT = 5.0;
 254         double sender_alt_ft,sender_alt;
 255         double transmitter_height=0.0;
 256         double receiver_height=0.0;
 257         SGGeod sender_pos = pos;
 258
 259         sender_alt_ft = sender_pos.getElevationFt();
 260         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 261         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 262         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 263         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 264
 265         double point_distance= 90.0; // regular SRTM is 90 meters
 266         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 267         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 268         double probe_distance = 0.0;
 269         /** If distance larger than this value (300 km), assume reception imposssible */
 270         if (distance_m > 300000)
 271                 return -1.0;
 272         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 273         if (own_alt > 8000) {
 274                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 275                 SG_LOG(SG_GENERAL, SG_BULK,
 276                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 277                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 278                 signal = link_budget - dbloss;
 279                 return signal;
 280         }
 281
 282
 283         double max_points = distance_m / point_distance;
 284         deque<double> _elevations;
 285         deque<string> materials;
 286
 287
 288         double elevation_under_pilot = 0.0;
 289         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 290                 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
 291         }
 292
 293         double elevation_under_sender = 0.0;
 294         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 295                 transmitter_height = sender_alt - elevation_under_sender;
 296         }
 297         else {
 298                 transmitter_height = sender_alt;
 299         }
 300
 301         if(transmission_type == 1)
 302                 transmitter_height += ATC_HAAT;
 303         else
 304                 transmitter_height += Aircraft_HAAT;
 305
 306         SG_LOG(SG_GENERAL, SG_BULK,
 307                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 308         //cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 309
 310         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 311
 312         while (_elevations.size() <= e_size) {
 313                 probe_distance += point_distance;
 314                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 315                 const SGMaterial *mat = 0;
 316                 double elevation_m = 0.0;
 317
 318                 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
 319                         if((transmission_type == 3) || (transmission_type == 4)) {
 320                                 _elevations.push_back(elevation_m);
 321                                 if(mat) {
 322                                         const std::vector<string> mat_names = mat->get_names();
 323                                         materials.push_back(mat_names[0]);
 324                                 }
 325                                 else {
 326                                         materials.push_back("None");
 327                                 }
 328                         }
 329                         else {
 330                                  _elevations.push_front(elevation_m);
 331                                  if(mat) {
 332                                          const std::vector<string> mat_names = mat->get_names();
 333                                          materials.push_front(mat_names[0]);
 334                                 }
 335                                 else {
 336                                         materials.push_front("None");
 337                                 }
 338                         }
 339                 }
 340                 else {
 341                         if((transmission_type == 3) || (transmission_type == 4)) {
 342                                 _elevations.push_back(0.0);
 343                                 materials.push_back("None");
 344                         }
 345                         else {
 346                                 _elevations.push_front(0.0);
 347                                 materials.push_front("None");
 348                         }
 349                 }
 350         }
 351         if((transmission_type == 3) || (transmission_type == 4)) {
 352                 _elevations.push_front(elevation_under_pilot);
 353                 _elevations.push_back(elevation_under_sender);
 354         }
 355         else {
 356                 _elevations.push_back(elevation_under_pilot);
 357                 _elevations.push_front(elevation_under_sender);
 358         }
 359
 360
 361         double max_alt_between=0.0;
 362         for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
 363                 if (_elevations[i] > max_alt_between) {
 364                         max_alt_between = _elevations[i];
 365                 }
 366         }
 367
 368         double num_points= (double)_elevations.size();
 369         //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
 370         _elevations.push_front(point_distance);
 371         _elevations.push_front(num_points -1);
 372         int size = _elevations.size();
 373         double itm_elev[size];
 374         for(int i=0;i<size;i++) {
 375                 itm_elev[i]=_elevations[i];
 376                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 377         }
 378
 379
 380         /** first Fresnel zone radius
 381                 frequency in the middle of the bandplan, more accuracy is not necessary
 382         */
 383         double fz_clr= 8.657 * sqrt(distance_m / 0.125);
 384
 385         // TODO: If we clear the first Fresnel zone, we are into line of sight territory
 386
 387         // else we need to calculate point to point link loss
 388         if((transmission_type == 3) || (transmission_type == 4)) {
 389                 // the sender and receiver roles are switched
 390                 point_to_point(itm_elev, receiver_height, transmitter_height,
 391                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 392                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 393
 394         }
 395         else {
 396                 point_to_point(itm_elev, transmitter_height, receiver_height,
 397                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 398                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 399         }
 400         SG_LOG(SG_GENERAL, SG_BULK,
 401                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 402         cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 403
 404         clutterLoss(frq_mhz, distance_m, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 405         cerr << "Clutter loss: " << clutter_loss << endl;
 406         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 407         //      return -1;
 408         signal = link_budget - dbloss - clutter_loss;
 409         return signal;
 410
 411 }
 412
 413 /*** Calculate losses due to vegetation and urban clutter (WIP)
 414 *        We are only worried about clutter loss, terrain influence
 415 *        on the first Fresnel zone is calculated in the ITM functions
 416 ***/
 417 void FGRadio::clutterLoss(double freq, double distance_m, double itm_elev[], deque<string> materials,
 418         double transmitter_height, double receiver_height, int p_mode,
 419         double horizons[], double &clutter_loss) {
 420
 421         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 422                 int j=1; // first point is TX elevation, last is RX elevation
 423                 for (int k=3;k < (int)itm_elev[0];k++) {
 424
 425                         double clutter_height = 0.0;    // clutter height hard-coded to 15 for now
 426                         double clutter_density = 0.0;   // percent of reflected wave
 427                         get_material_properties(materials[j-1], clutter_height, clutter_density);
 428                         //cerr << "Clutter:: material: " << materials[j-1] << " height: " << clutter_height << ", density: " << clutter_density << endl;
 429                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 430                         // First Fresnel radius
 431                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 432                         //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
 433                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 434
 435                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 436                         double d1 = j * itm_elev[1];
 437                         if (fabs(min_elev - itm_elev[2]) <= 0.0001)
 438                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 439                         double ray_height = (grad * d1) + min_elev;
 440                         //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
 441                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad;
 442                         double intrusion = fabs(clearance);
 443                         //cerr << "Clutter:: clearance: " << clearance << endl;
 444                         if (clearance >= 0) {
 445                                 clutter_loss +=0.0;
 446                         }
 447                         else if (clearance < 0 && (intrusion < clutter_height)) {
 448
 449                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
 450                         }
 451                         else if (clearance < 0 && (intrusion > clutter_height)) {
 452                                 clutter_loss += clutter_density * (clutter_height / (frs_rad *2 ) ) * freq/100;
 453                         }
 454                         else {
 455                                 clutter_loss += 0.0;
 456                         }
 457                         j++;
 458                 }
 459
 460         }
 461         else if (p_mode == 1) {         // diffraction
 462
 463                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 464
 465                 }
 466                 else {  // double horizon: same as single horizon, except there are 3 segments
 467
 468                 }
 469         }
 470         else if (p_mode == 2) {         //      troposcatter: use the first smooth earth horizon as mid point
 471
 472         }
 473
 474 }
 475
 476 /***    Material properties database
 477 *               height: median clutter height
 478 *               density: radiowave attenuation factor
 479 ***/
 480 void FGRadio::get_material_properties(string mat_name, double &height, double &density) {
 481
 482         if(mat_name == "Landmass") {
 483                 height = 15.0;
 484                 density = 0.2;
 485         }
 486
 487         else if(mat_name == "SomeSort") {
 488                 height = 15.0;
 489                 density = 0.2;
 490         }
 491
 492         else if(mat_name == "Island") {
 493                 height = 15.0;
 494                 density = 0.2;
 495         }
 496         else if(mat_name == "Default") {
 497                 height = 15.0;
 498                 density = 0.2;
 499         }
 500         else if(mat_name == "EvergreenBroadCover") {
 501                 height = 20.0;
 502                 density = 0.2;
 503         }
 504         else if(mat_name == "EvergreenForest") {
 505                 height = 20.0;
 506                 density = 0.2;
 507         }
 508         else if(mat_name == "DeciduousBroadCover") {
 509                 height = 15.0;
 510                 density = 0.3;
 511         }
 512         else if(mat_name == "DeciduousForest") {
 513                 height = 15.0;
 514                 density = 0.3;
 515         }
 516         else if(mat_name == "MixedForestCover") {
 517                 height = 20.0;
 518                 density = 0.25;
 519         }
 520         else if(mat_name == "MixedForest") {
 521                 height = 15.0;
 522                 density = 0.25;
 523         }
 524         else if(mat_name == "RainForest") {
 525                 height = 25.0;
 526                 density = 0.55;
 527         }
 528         else if(mat_name == "EvergreenNeedleCover") {
 529                 height = 15.0;
 530                 density = 0.2;
 531         }
 532         else if(mat_name == "WoodedTundraCover") {
 533                 height = 5.0;
 534                 density = 0.15;
 535         }
 536         else if(mat_name == "DeciduousNeedleCover") {
 537                 height = 5.0;
 538                 density = 0.2;
 539         }
 540         else if(mat_name == "ScrubCover") {
 541                 height = 3.0;
 542                 density = 0.15;
 543         }
 544         else if(mat_name == "BuiltUpCover") {
 545                 height = 30.0;
 546                 density = 0.7;
 547         }
 548         else if(mat_name == "Urban") {
 549                 height = 30.0;
 550                 density = 0.7;
 551         }
 552         else if(mat_name == "Construction") {
 553                 height = 30.0;
 554                 density = 0.7;
 555         }
 556         else if(mat_name == "Industrial") {
 557                 height = 30.0;
 558                 density = 0.7;
 559         }
 560         else if(mat_name == "Port") {
 561                 height = 30.0;
 562                 density = 0.7;
 563         }
 564         else if(mat_name == "Town") {
 565                 height = 10.0;
 566                 density = 0.5;
 567         }
 568         else if(mat_name == "SubUrban") {
 569                 height = 10.0;
 570                 density = 0.5;
 571         }
 572         else if(mat_name == "CropWoodCover") {
 573                 height = 10.0;
 574                 density = 0.1;
 575         }
 576         else if(mat_name == "CropWood") {
 577                 height = 10.0;
 578                 density = 0.1;
 579         }
 580         else if(mat_name == "AgroForest") {
 581                 height = 10.0;
 582                 density = 0.1;
 583         }
 584         else {
 585                 height = 0.0;
 586                 density = 0.0;
 587         }
 588
 589 }
 590
 591 /*** implement simple LOS propagation model (WIP)
 592 ***/
 593 double FGRadio::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 594         double frq_mhz;
 595         if( (freq < 118.0) || (freq > 137.0) )
 596                 frq_mhz = 125.0;        // sane value, middle of bandplan
 597         else
 598                 frq_mhz = freq;
 599         double dbloss;
 600         double tx_pow = _transmitter_power;
 601         double ant_gain = _antenna_gain;
 602         double signal = 0.0;
 603         double ATC_HAAT = 30.0;
 604         double Aircraft_HAAT = 5.0;
 605         double sender_alt_ft,sender_alt;
 606         double transmitter_height=0.0;
 607         double receiver_height=0.0;
 608         double own_lat = fgGetDouble("/position/latitude-deg");
 609         double own_lon = fgGetDouble("/position/longitude-deg");
 610         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 611         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 612
 613         if(transmission_type == 1)
 614                 tx_pow = _transmitter_power + 6.0;
 615
 616         if((transmission_type == 1) || (transmission_type == 3))
 617                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 618
 619         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 620
 621         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 622
 623         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 624
 625         SGGeod sender_pos = pos;
 626
 627         sender_alt_ft = sender_pos.getElevationFt();
 628         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 629
 630         receiver_height = own_alt;
 631         transmitter_height = sender_alt;
 632
 633         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 634
 635         if(transmission_type == 1)
 636                 transmitter_height += ATC_HAAT;
 637         else
 638                 transmitter_height += Aircraft_HAAT;
 639
 640         /** radio horizon calculation with wave bending k=4/3 */
 641         double receiver_horizon = 4.12 * sqrt(receiver_height);
 642         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 643         double total_horizon = receiver_horizon + transmitter_horizon;
 644
 645         if (distance_m > total_horizon) {
 646                 return -1;
 647         }
 648
 649         // free-space loss (distance calculation should be changed)
 650         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 651         signal = link_budget - dbloss;
 652         SG_LOG(SG_GENERAL, SG_BULK,
 653                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 654         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 655         return signal;
 656
 657 }
 658
 659 /*** Material properties database
 660 ***/
 661 void FGRadio::set_material_properties() {
 662
 663
 664 }