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
  27 #include <stdlib.h>
  28 #include <deque>
  29 #include "radio.hxx"
  30 #include <simgear/scene/material/mat.hxx>
  31 #include <Scenery/scenery.hxx>
  32
  33 #define WITH_POINT_TO_POINT 1
  34 #include "itm.cpp"
  35
  36
  37 FGRadioTransmission::FGRadioTransmission() {
  38
  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         *       Typical output powers for ATC ground equipment, VHF-UHF:
  44         *       40 dBm - 10 W (ground, clearance)
  45         *       44 dBm - 20 W (tower)
  46         *       47 dBm - 50 W (center, sectors)
  47         *       50 dBm - 100 W (center, sectors)
  48         *       53 dBm - 200 W (sectors, on directional arrays)
  49         **/
  50         _transmitter_power = 43.0;
  51
  52         _tx_antenna_height = 2.0; // TX antenna height above ground level
  53
  54         _rx_antenna_height = 2.0; // RX antenna height above ground level
  55
  56
  57         _rx_antenna_gain = 1.0; // gain expressed in dBi
  58         _tx_antenna_gain = 1.0;
  59
  60         _rx_line_losses = 2.0;  // to be configured for each station
  61         _tx_line_losses = 2.0;
  62
  63         _polarization = 1; // default vertical
  64
  65         _propagation_model = 2;
  66         _terrain_sampling_distance = fgGetDouble("/sim/radio/sampling-distance", 90.0); // regular SRTM is 90 meters
  67 }
  68
  69 FGRadioTransmission::~FGRadioTransmission()
  70 {
  71 }
  72
  73
  74 double FGRadioTransmission::getFrequency(int radio) {
  75         double freq = 118.0;
  76         switch (radio) {
  77                 case 1:
  78                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  79                         break;
  80                 case 2:
  81                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  82                         break;
  83                 default:
  84                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  85
  86         }
  87         return freq;
  88 }
  89
  90 /*** TODO: receive multiplayer chat message and voice
  91 ***/
  92 void FGRadioTransmission::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
  93
  94 }
  95
  96 /*** TODO: receive navaid
  97 ***/
  98 double FGRadioTransmission::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
  99
 100         // typical VOR/LOC transmitter power appears to be 200 Watt ~ 53 dBm
 101         // vor/loc typical sensitivity between -107 and -101 dBm
 102         // glideslope sensitivity between -85 and -81 dBm
 103         if ( _propagation_model == 1) {
 104                 return LOS_calculate_attenuation(tx_pos, freq, 1);
 105         }
 106         else if ( _propagation_model == 2) {
 107                 return ITM_calculate_attenuation(tx_pos, freq, 1);
 108         }
 109
 110         return -1;
 111
 112 }
 113
 114 /*** Receive ATC radio communication as text
 115 ***/
 116 void FGRadioTransmission::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 117
 118
 119         if(ground_to_air == 1) {
 120                 _transmitter_power += 6.0;
 121                 _tx_antenna_height += 30.0;
 122                 _tx_antenna_gain += 3.0;
 123         }
 124
 125
 126         double comm1 = getFrequency(1);
 127         double comm2 = getFrequency(2);
 128         if ( !(fabs(freq - comm1) <= 0.0001) &&  !(fabs(freq - comm2) <= 0.0001) ) {
 129                 return;
 130         }
 131         else {
 132
 133                 if ( _propagation_model == 0) {
 134                         fgSetString("/sim/messages/atc", text.c_str());
 135                 }
 136                 else if ( _propagation_model == 1 ) {
 137                         // TODO: free space, round earth
 138                         double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
 139                         if (signal <= 0.0) {
 140                                 return;
 141                         }
 142                         else {
 143
 144                                 fgSetString("/sim/messages/atc", text.c_str());
 145                                 /** write signal strength above threshold to the property tree
 146                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 147                                 **/
 148                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 149                         }
 150                 }
 151                 else if ( _propagation_model == 2 ) {
 152                         // Use ITM propagation model
 153                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 154                         if (signal <= 0.0) {
 155                                 return;
 156                         }
 157                         if ((signal > 0.0) && (signal < 12.0)) {
 158                                 /** for low SNR values implement a way to make the conversation
 159                                 *       hard to understand but audible
 160                                 *       in the real world, the receiver AGC fails to capture the slope
 161                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 162                                 *       the workaround below is more akin to what would happen on a FM transmission
 163                                 *       therefore the correct way would be to work on the volume
 164                                 **/
 165                                 /*
 166                                 string hash_noise = " ";
 167                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 168                                 int t_size = text.size();
 169                                 for (int n = 1; n <= reps; ++n) {
 170                                         int pos = rand() % (t_size -1);
 171                                         text.replace(pos,1, hash_noise);
 172                                 }
 173                                 */
 174                                 double volume = (fabs(signal - 12.0) / 12);
 175                                 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 176                                 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
 177                                 //cerr << "Usable signal at limit: " << signal << endl;
 178                                 fgSetDouble("/sim/sound/voices/voice/volume", volume);
 179                                 fgSetString("/sim/messages/atc", text.c_str());
 180                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 181                                 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 182                         }
 183                         else {
 184                                 fgSetString("/sim/messages/atc", text.c_str());
 185                                 /** write signal strength above threshold to the property tree
 186                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 187                                 **/
 188                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 189                         }
 190
 191                 }
 192
 193         }
 194
 195 }
 196
 197 /***  Implement radio attenuation
 198           based on the Longley-Rice propagation model
 199 ***/
 200 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 201
 202
 203
 204         /** ITM default parameters
 205                 TODO: take them from tile materials (especially for sea)?
 206         **/
 207         double eps_dielect=15.0;
 208         double sgm_conductivity = 0.005;
 209         double eno = 301.0;
 210         double frq_mhz;
 211         if( (freq < 118.0) || (freq > 137.0) )
 212                 frq_mhz = 125.0;        // sane value, middle of bandplan
 213         else
 214                 frq_mhz = freq;
 215         int radio_climate = 5;          // continental temperate
 216         int pol= _polarization;
 217         double conf = 0.90;     // 90% of situations and time, take into account speed
 218         double rel = 0.90;
 219         double dbloss;
 220         char strmode[150];
 221         int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
 222         double horizons[2];
 223         int errnum;
 224
 225         double clutter_loss = 0.0;      // loss due to vegetation and urban
 226         double tx_pow = _transmitter_power;
 227         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 228         double signal = 0.0;
 229
 230
 231         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 232
 233         FGScenery * scenery = globals->get_scenery();
 234
 235         double own_lat = fgGetDouble("/position/latitude-deg");
 236         double own_lon = fgGetDouble("/position/longitude-deg");
 237         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 238         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 239
 240
 241         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 242
 243         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 244         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 245         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 246         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 247
 248
 249         double sender_alt_ft,sender_alt;
 250         double transmitter_height=0.0;
 251         double receiver_height=0.0;
 252         SGGeod sender_pos = pos;
 253
 254         sender_alt_ft = sender_pos.getElevationFt();
 255         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 256         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 257         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 258         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 259
 260         double point_distance= _terrain_sampling_distance;
 261         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 262         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 263         double probe_distance = 0.0;
 264         /** If distance larger than this value (300 km), assume reception imposssible */
 265         if (distance_m > 300000)
 266                 return -1.0;
 267         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 268         if (own_alt > 8000) {
 269                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 270                 SG_LOG(SG_GENERAL, SG_BULK,
 271                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 272                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 273                 signal = link_budget - dbloss;
 274                 return signal;
 275         }
 276
 277
 278         int max_points = (int)floor(distance_m / point_distance);
 279         double delta_last = fmod(distance_m, point_distance);
 280
 281         deque<double> _elevations;
 282         deque<string> materials;
 283
 284
 285         double elevation_under_pilot = 0.0;
 286         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 287                 receiver_height = own_alt - elevation_under_pilot;
 288         }
 289
 290         double elevation_under_sender = 0.0;
 291         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 292                 transmitter_height = sender_alt - elevation_under_sender;
 293         }
 294         else {
 295                 transmitter_height = sender_alt;
 296         }
 297
 298
 299         transmitter_height += _tx_antenna_height;
 300         receiver_height += _rx_antenna_height;
 301
 302
 303         SG_LOG(SG_GENERAL, SG_BULK,
 304                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 305         cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 306
 307         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 308
 309         while (_elevations.size() <= e_size) {
 310                 probe_distance += point_distance;
 311                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 312                 const SGMaterial *mat = 0;
 313                 double elevation_m = 0.0;
 314
 315                 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
 316                         if((transmission_type == 3) || (transmission_type == 4)) {
 317                                 _elevations.push_back(elevation_m);
 318                                 if(mat) {
 319                                         const std::vector<string> mat_names = mat->get_names();
 320                                         materials.push_back(mat_names[0]);
 321                                 }
 322                                 else {
 323                                         materials.push_back("None");
 324                                 }
 325                         }
 326                         else {
 327                                  _elevations.push_front(elevation_m);
 328                                  if(mat) {
 329                                          const std::vector<string> mat_names = mat->get_names();
 330                                          materials.push_front(mat_names[0]);
 331                                 }
 332                                 else {
 333                                         materials.push_front("None");
 334                                 }
 335                         }
 336                 }
 337                 else {
 338                         if((transmission_type == 3) || (transmission_type == 4)) {
 339                                 _elevations.push_back(0.0);
 340                                 materials.push_back("None");
 341                         }
 342                         else {
 343                                 _elevations.push_front(0.0);
 344                                 materials.push_front("None");
 345                         }
 346                 }
 347         }
 348         if((transmission_type == 3) || (transmission_type == 4)) {
 349                 _elevations.push_front(elevation_under_pilot);
 350                 if (delta_last > (point_distance / 2) )                 // only add last point if it's farther than half point_distance
 351                         _elevations.push_back(elevation_under_sender);
 352         }
 353         else {
 354                 _elevations.push_back(elevation_under_pilot);
 355                 if (delta_last > (point_distance / 2) )
 356                         _elevations.push_front(elevation_under_sender);
 357         }
 358
 359
 360         double num_points= (double)_elevations.size();
 361
 362         _elevations.push_front(point_distance);
 363         _elevations.push_front(num_points -1);
 364         int size = _elevations.size();
 365         double itm_elev[size];
 366         for(int i=0;i<size;i++) {
 367                 itm_elev[i]=_elevations[i];
 368                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 369         }
 370
 371         if((transmission_type == 3) || (transmission_type == 4)) {
 372                 // the sender and receiver roles are switched
 373                 point_to_point(itm_elev, receiver_height, transmitter_height,
 374                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 375                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 376                 if( fgGetBool( "/sim/radio/use-clutter-attenuation", false ) )
 377                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
 378         }
 379         else {
 380                 point_to_point(itm_elev, transmitter_height, receiver_height,
 381                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 382                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 383                 if( fgGetBool( "/sim/radio/use-clutter-attenuation", false ) )
 384                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 385         }
 386         SG_LOG(SG_GENERAL, SG_BULK,
 387                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 388         cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 389
 390         cerr << "Clutter loss: " << clutter_loss << endl;
 391         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 392         //      return -1;
 393         signal = link_budget - dbloss - clutter_loss;
 394         return signal;
 395
 396 }
 397
 398 /*** Calculate losses due to vegetation and urban clutter (WIP)
 399 *        We are only worried about clutter loss, terrain influence
 400 *        on the first Fresnel zone is calculated in the ITM functions
 401 ***/
 402 void FGRadioTransmission::clutterLoss(double freq, double distance_m, double itm_elev[], deque<string> materials,
 403         double transmitter_height, double receiver_height, int p_mode,
 404         double horizons[], double &clutter_loss) {
 405
 406         distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
 407
 408         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 409                 int mat = 0;
 410                 int j=1;
 411                 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
 412
 413                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 414                         double clutter_density = 0.0;   // percent of reflected wave
 415                         get_material_properties(materials[mat], clutter_height, clutter_density);
 416
 417                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 418                         // First Fresnel radius
 419                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 420
 421                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 422
 423                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 424                         double d1 = j * itm_elev[1];
 425                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 426                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 427                         }
 428                         double ray_height = (grad * d1) + min_elev;
 429
 430                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 431                         double intrusion = fabs(clearance);
 432
 433                         if (clearance >= 0) {
 434                                 // no losses
 435                         }
 436                         else if (clearance < 0 && (intrusion < clutter_height)) {
 437
 438                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 439                         }
 440                         else if (clearance < 0 && (intrusion > clutter_height)) {
 441                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 442                         }
 443                         else {
 444                                 // no losses
 445                         }
 446                         j++;
 447                         mat++;
 448                 }
 449
 450         }
 451         else if (p_mode == 1) {         // diffraction
 452
 453                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 454                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
 455                         int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
 456                         //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
 457                         int last = 1;
 458                         /** perform the first pass */
 459                         int mat = 0;
 460                         int j=1;
 461                         for (int k=3;k < num_points_1st + 2;k++) {
 462                                 if (num_points_1st < 1)
 463                                         break;
 464                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 465                                 double clutter_density = 0.0;   // percent of reflected wave
 466                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 467
 468                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 469                                 // First Fresnel radius
 470                                 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) );
 471
 472                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 473
 474                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 475                                 double d1 = j * itm_elev[1];
 476                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 477                                         d1 = (num_points_1st - j) * itm_elev[1];
 478                                 }
 479                                 double ray_height = (grad * d1) + min_elev;
 480
 481                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 482                                 double intrusion = fabs(clearance);
 483
 484                                 if (clearance >= 0) {
 485                                         // no losses
 486                                 }
 487                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 488
 489                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 490                                 }
 491                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 492                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 493                                 }
 494                                 else {
 495                                         // no losses
 496                                 }
 497                                 j++;
 498                                 mat++;
 499                                 last = k;
 500                         }
 501
 502                         /** and the second pass */
 503                         mat +=1;
 504                         j =1; // first point is diffraction edge, 2nd the RX elevation
 505                         for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
 506                                 if (num_points_2nd < 1)
 507                                         break;
 508                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 509                                 double clutter_density = 0.0;   // percent of reflected wave
 510                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 511
 512                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 513                                 // First Fresnel radius
 514                                 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) );
 515
 516                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 517
 518                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 519                                 double d1 = j * itm_elev[1];
 520                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 521                                         d1 = (num_points_2nd - j) * itm_elev[1];
 522                                 }
 523                                 double ray_height = (grad * d1) + min_elev;
 524
 525                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 526                                 double intrusion = fabs(clearance);
 527
 528                                 if (clearance >= 0) {
 529                                         // no losses
 530                                 }
 531                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 532
 533                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 534                                 }
 535                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 536                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 537                                 }
 538                                 else {
 539                                         // no losses
 540                                 }
 541                                 j++;
 542                                 mat++;
 543                         }
 544
 545                 }
 546                 else {  // double horizon: same as single horizon, except there are 3 segments
 547
 548                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
 549                         int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
 550                         int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
 551                         //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
 552                         //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
 553                         int last = 1;
 554                         /** perform the first pass */
 555                         int mat = 0;
 556                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 557                         for (int k=3;k < num_points_1st +2;k++) {
 558                                 if (num_points_1st < 1)
 559                                         break;
 560                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 561                                 double clutter_density = 0.0;   // percent of reflected wave
 562                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 563
 564                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 565                                 // First Fresnel radius
 566                                 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) );
 567
 568                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 569
 570                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 571                                 double d1 = j * itm_elev[1];
 572                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 573                                         d1 = (num_points_1st - j) * itm_elev[1];
 574                                 }
 575                                 double ray_height = (grad * d1) + min_elev;
 576
 577                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 578                                 double intrusion = fabs(clearance);
 579
 580                                 if (clearance >= 0) {
 581                                         // no losses
 582                                 }
 583                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 584
 585                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 586                                 }
 587                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 588                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 589                                 }
 590                                 else {
 591                                         // no losses
 592                                 }
 593                                 j++;
 594                                 last = k;
 595                         }
 596                         mat +=1;
 597                         /** and the second pass */
 598                         int last2=1;
 599                         j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 600                         for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
 601                                 if (num_points_2nd < 1)
 602                                         break;
 603                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 604                                 double clutter_density = 0.0;   // percent of reflected wave
 605                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 606
 607                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
 608                                 // First Fresnel radius
 609                                 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) );
 610
 611                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 612
 613                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
 614                                 double d1 = j * itm_elev[1];
 615                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
 616                                         d1 = (num_points_2nd - j) * itm_elev[1];
 617                                 }
 618                                 double ray_height = (grad * d1) + min_elev;
 619
 620                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 621                                 double intrusion = fabs(clearance);
 622
 623                                 if (clearance >= 0) {
 624                                         // no losses
 625                                 }
 626                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 627
 628                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 629                                 }
 630                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 631                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 632                                 }
 633                                 else {
 634                                         // no losses
 635                                 }
 636                                 j++;
 637                                 mat++;
 638                                 last2 = k;
 639                         }
 640
 641                         /** third and final pass */
 642                         mat +=1;
 643                         j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 644                         for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
 645                                 if (num_points_3rd < 1)
 646                                         break;
 647                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 648                                 double clutter_density = 0.0;   // percent of reflected wave
 649                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 650
 651                                 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 652                                 // First Fresnel radius
 653                                 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) );
 654
 655
 656                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 657
 658                                 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 659                                 double d1 = j * itm_elev[1];
 660                                 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 661                                         d1 = (num_points_3rd - j) * itm_elev[1];
 662                                 }
 663                                 double ray_height = (grad * d1) + min_elev;
 664
 665                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 666                                 double intrusion = fabs(clearance);
 667
 668                                 if (clearance >= 0) {
 669                                         // no losses
 670                                 }
 671                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 672
 673                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 674                                 }
 675                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 676                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 677                                 }
 678                                 else {
 679                                         // no losses
 680                                 }
 681                                 j++;
 682                                 mat++;
 683
 684                         }
 685
 686                 }
 687         }
 688         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now...
 689                 clutter_loss = 0.0;
 690         }
 691
 692 }
 693
 694 /***    Temporary material properties database
 695 *               height: median clutter height
 696 *               density: radiowave attenuation factor
 697 ***/
 698 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 699
 700         if(mat_name == "Landmass") {
 701                 height = 15.0;
 702                 density = 0.2;
 703         }
 704
 705         else if(mat_name == "SomeSort") {
 706                 height = 15.0;
 707                 density = 0.2;
 708         }
 709
 710         else if(mat_name == "Island") {
 711                 height = 15.0;
 712                 density = 0.2;
 713         }
 714         else if(mat_name == "Default") {
 715                 height = 15.0;
 716                 density = 0.2;
 717         }
 718         else if(mat_name == "EvergreenBroadCover") {
 719                 height = 20.0;
 720                 density = 0.2;
 721         }
 722         else if(mat_name == "EvergreenForest") {
 723                 height = 20.0;
 724                 density = 0.2;
 725         }
 726         else if(mat_name == "DeciduousBroadCover") {
 727                 height = 15.0;
 728                 density = 0.3;
 729         }
 730         else if(mat_name == "DeciduousForest") {
 731                 height = 15.0;
 732                 density = 0.3;
 733         }
 734         else if(mat_name == "MixedForestCover") {
 735                 height = 20.0;
 736                 density = 0.25;
 737         }
 738         else if(mat_name == "MixedForest") {
 739                 height = 15.0;
 740                 density = 0.25;
 741         }
 742         else if(mat_name == "RainForest") {
 743                 height = 25.0;
 744                 density = 0.55;
 745         }
 746         else if(mat_name == "EvergreenNeedleCover") {
 747                 height = 15.0;
 748                 density = 0.2;
 749         }
 750         else if(mat_name == "WoodedTundraCover") {
 751                 height = 5.0;
 752                 density = 0.15;
 753         }
 754         else if(mat_name == "DeciduousNeedleCover") {
 755                 height = 5.0;
 756                 density = 0.2;
 757         }
 758         else if(mat_name == "ScrubCover") {
 759                 height = 3.0;
 760                 density = 0.15;
 761         }
 762         else if(mat_name == "BuiltUpCover") {
 763                 height = 30.0;
 764                 density = 0.7;
 765         }
 766         else if(mat_name == "Urban") {
 767                 height = 30.0;
 768                 density = 0.7;
 769         }
 770         else if(mat_name == "Construction") {
 771                 height = 30.0;
 772                 density = 0.7;
 773         }
 774         else if(mat_name == "Industrial") {
 775                 height = 30.0;
 776                 density = 0.7;
 777         }
 778         else if(mat_name == "Port") {
 779                 height = 30.0;
 780                 density = 0.7;
 781         }
 782         else if(mat_name == "Town") {
 783                 height = 10.0;
 784                 density = 0.5;
 785         }
 786         else if(mat_name == "SubUrban") {
 787                 height = 10.0;
 788                 density = 0.5;
 789         }
 790         else if(mat_name == "CropWoodCover") {
 791                 height = 10.0;
 792                 density = 0.1;
 793         }
 794         else if(mat_name == "CropWood") {
 795                 height = 10.0;
 796                 density = 0.1;
 797         }
 798         else if(mat_name == "AgroForest") {
 799                 height = 10.0;
 800                 density = 0.1;
 801         }
 802         else {
 803                 height = 0.0;
 804                 density = 0.0;
 805         }
 806
 807 }
 808
 809 /*** implement simple LOS propagation model (WIP)
 810 ***/
 811 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 812         double frq_mhz;
 813         if( (freq < 118.0) || (freq > 137.0) )
 814                 frq_mhz = 125.0;        // sane value, middle of bandplan
 815         else
 816                 frq_mhz = freq;
 817         double dbloss;
 818         double tx_pow = _transmitter_power;
 819         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 820         double signal = 0.0;
 821
 822         double sender_alt_ft,sender_alt;
 823         double transmitter_height=0.0;
 824         double receiver_height=0.0;
 825         double own_lat = fgGetDouble("/position/latitude-deg");
 826         double own_lon = fgGetDouble("/position/longitude-deg");
 827         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 828         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 829
 830
 831         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 832
 833         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 834
 835         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 836
 837         SGGeod sender_pos = pos;
 838
 839         sender_alt_ft = sender_pos.getElevationFt();
 840         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 841
 842         receiver_height = own_alt;
 843         transmitter_height = sender_alt;
 844
 845         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 846
 847
 848         transmitter_height += _tx_antenna_height;
 849         receiver_height += _rx_antenna_height;
 850
 851
 852         /** radio horizon calculation with wave bending k=4/3 */
 853         double receiver_horizon = 4.12 * sqrt(receiver_height);
 854         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 855         double total_horizon = receiver_horizon + transmitter_horizon;
 856
 857         if (distance_m > total_horizon) {
 858                 return -1;
 859         }
 860
 861         // free-space loss (distance calculation should be changed)
 862         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 863         signal = link_budget - dbloss;
 864         SG_LOG(SG_GENERAL, SG_BULK,
 865                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 866         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 867         return signal;
 868
 869 }
 870
 871 /*** calculate loss due to polarization mismatch
 872 *       this function is only reliable for vertical polarization
 873 *       due to the V-shape of horizontally polarized antennas
 874 ***/
 875 double FGRadioTransmission::polarization_loss() {
 876
 877         double theta_deg;
 878         double roll = fgGetDouble("/orientation/roll-deg");
 879         double pitch = fgGetDouble("/orientation/pitch-deg");
 880         double theta = acos( sqrt( cos(roll) * cos(roll) + cos(pitch) * cos(pitch) ));
 881         if (_polarization == 1)
 882                 theta_deg = 90.0 - theta;
 883         else
 884                 theta_deg = theta;
 885         if (fabs(theta_deg) > 85.0)     // we don't want to converge into infinity
 886                 theta_deg = 85.0;
 887         return 10 * log10(cos(theta_deg) * cos(theta_deg));
 888 }
 889
 890