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