src/Radio/radio.cxx

   1 // radio.cxx -- implementation of FGRadio
   2 // Class to manage radio propagation using the ITM model
   3 // Written by Adrian Musceac, started August 2011.
   4 //
   5 // This program is free software; you can redistribute it and/or
   6 // modify it under the terms of the GNU General Public License as
   7 // published by the Free Software Foundation; either version 2 of the
   8 // License, or (at your option) any later version.
   9 //
  10 // This program is distributed in the hope that it will be useful, but
  11 // WITHOUT ANY WARRANTY; without even the implied warranty of
  12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 // General Public License for more details.
  14 //
  15 // You should have received a copy of the GNU General Public License
  16 // along with this program; if not, write to the Free Software
  17 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  18
  19
  20
  21 #ifdef HAVE_CONFIG_H
  22 #  include <config.h>
  23 #endif
  24
  25 #include <math.h>
  26 #include <assert.h>
  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         /** radio parameters (which should probably be set for each radio) */
  40
  41         _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
  42
  43         /** AM transmitter power in dBm.
  44         *       Note this value is calculated from the typical final transistor stage output
  45         *       small aircraft have portable transmitters which operate at 36 dBm output (4 Watts) others operate in the range 10-20 W
  46         *       later possibly store this value in aircraft description
  47         *       ATC comms usually operate high power equipment, thus making the link asymetrical; this is taken care of in propagation routines
  48         *       Typical output powers for ATC ground equipment, VHF-UHF:
  49         *       40 dBm - 10 W (ground, clearance)
  50         *       44 dBm - 20 W (tower)
  51         *       47 dBm - 50 W (center, sectors)
  52         *       50 dBm - 100 W (center, sectors)
  53         *       53 dBm - 200 W (sectors, on directional arrays)
  54         **/
  55         _transmitter_power = 43.0;
  56
  57         _tx_antenna_height = 2.0; // TX antenna height above ground level
  58
  59         _rx_antenna_height = 2.0; // RX antenna height above ground level
  60
  61         /** pilot plane's antenna gain + AI aircraft antenna gain
  62         *       real-life gain for conventional monopole/dipole antenna
  63         **/
  64         _antenna_gain = 2.0;
  65
  66         _rx_antenna_gain = 1.0;
  67         _tx_antenna_gain = 1.0;
  68
  69         _rx_line_losses = 2.0;  // to be configured for each station
  70         _tx_line_losses = 2.0;
  71
  72         _propagation_model = 2; //  choose between models via option: realistic radio on/off
  73         _terrain_sampling_distance = fgGetDouble("/sim/radio/sampling-distance", 90.0); // regular SRTM is 90 meters
  74 }
  75
  76 FGRadioTransmission::~FGRadioTransmission()
  77 {
  78 }
  79
  80
  81 double FGRadioTransmission::getFrequency(int radio) {
  82         double freq = 118.0;
  83         switch (radio) {
  84                 case 1:
  85                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  86                         break;
  87                 case 2:
  88                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  89                         break;
  90                 default:
  91                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  92
  93         }
  94         return freq;
  95 }
  96
  97 /*** TODO: receive multiplayer chat message and voice
  98 ***/
  99 void FGRadioTransmission::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 100
 101 }
 102
 103 /*** TODO: receive navaid
 104 ***/
 105 double FGRadioTransmission::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
 106
 107         // typical VOR/LOC transmitter power appears to be 200 Watt ~ 53 dBm
 108         // vor/loc typical sensitivity between -107 and -101 dBm
 109         // glideslope sensitivity between -85 and -81 dBm
 110         if ( _propagation_model == 1) {
 111                 return LOS_calculate_attenuation(tx_pos, freq, 1);
 112         }
 113         else if ( _propagation_model == 2) {
 114                 return ITM_calculate_attenuation(tx_pos, freq, 1);
 115         }
 116
 117         return -1;
 118
 119 }
 120
 121 /*** Receive ATC radio communication as text
 122 ***/
 123 void FGRadioTransmission::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 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                 //cerr << "Frequency not tuned: " << freq << " Radio1: " << comm1 << " Radio2: " << comm2 << endl;
 130                 return;
 131         }
 132         else {
 133
 134                 if ( _propagation_model == 0) {
 135                         fgSetString("/sim/messages/atc", text.c_str());
 136                 }
 137                 else if ( _propagation_model == 1 ) {
 138                         // TODO: free space, round earth
 139                         double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
 140                         if (signal <= 0.0) {
 141                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 142                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 143                                 return;
 144                         }
 145                         else {
 146                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 147                                 //cerr << "Signal completely readable: " << signal << endl;
 148                                 fgSetString("/sim/messages/atc", text.c_str());
 149                                 /** write signal strength above threshold to the property tree
 150                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 151                                 **/
 152                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 153                         }
 154                 }
 155                 else if ( _propagation_model == 2 ) {
 156                         // Use ITM propagation model
 157                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 158                         if (signal <= 0.0) {
 159                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 160                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 161                                 return;
 162                         }
 163                         if ((signal > 0.0) && (signal < 12.0)) {
 164                                 /** for low SNR values implement a way to make the conversation
 165                                 *       hard to understand but audible
 166                                 *       in the real world, the receiver AGC fails to capture the slope
 167                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 168                                 *       the workaround below is more akin to what would happen on a FM transmission
 169                                 *       therefore the correct way would be to work on the volume
 170                                 **/
 171                                 /*
 172                                 string hash_noise = " ";
 173                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 174                                 int t_size = text.size();
 175                                 for (int n = 1; n <= reps; ++n) {
 176                                         int pos = rand() % (t_size -1);
 177                                         text.replace(pos,1, hash_noise);
 178                                 }
 179                                 */
 180                                 double volume = (fabs(signal - 12.0) / 12);
 181                                 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 182                                 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
 183                                 //cerr << "Usable signal at limit: " << signal << endl;
 184                                 fgSetDouble("/sim/sound/voices/voice/volume", volume);
 185                                 fgSetString("/sim/messages/atc", text.c_str());
 186                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 187                                 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 188                         }
 189                         else {
 190                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 191                                 //cerr << "Signal completely readable: " << signal << endl;
 192                                 fgSetString("/sim/messages/atc", text.c_str());
 193                                 /** write signal strength above threshold to the property tree
 194                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 195                                 **/
 196                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 197                         }
 198
 199                 }
 200
 201         }
 202
 203 }
 204
 205 /***  Implement radio attenuation
 206           based on the Longley-Rice propagation model
 207 ***/
 208 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 209
 210
 211
 212         /** ITM default parameters
 213                 TODO: take them from tile materials (especially for sea)?
 214         **/
 215         double eps_dielect=15.0;
 216         double sgm_conductivity = 0.005;
 217         double eno = 301.0;
 218         double frq_mhz;
 219         if( (freq < 118.0) || (freq > 137.0) )
 220                 frq_mhz = 125.0;        // sane value, middle of bandplan
 221         else
 222                 frq_mhz = freq;
 223         int radio_climate = 5;          // continental temperate
 224         int pol=1;      // assuming vertical polarization although this is more complex in reality
 225         double conf = 0.90;     // 90% of situations and time, take into account speed
 226         double rel = 0.90;
 227         double dbloss;
 228         char strmode[150];
 229         int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
 230         double horizons[2];
 231         int errnum;
 232
 233         double clutter_loss = 0.0;      // loss due to vegetation and urban
 234         double tx_pow = _transmitter_power;
 235         double ant_gain = _antenna_gain;
 236         double signal = 0.0;
 237
 238         if(transmission_type == 1)
 239                 tx_pow = _transmitter_power + 6.0;
 240
 241         if((transmission_type == 1) || (transmission_type == 3))
 242                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 243
 244         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 245
 246         FGScenery * scenery = globals->get_scenery();
 247
 248         double own_lat = fgGetDouble("/position/latitude-deg");
 249         double own_lon = fgGetDouble("/position/longitude-deg");
 250         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 251         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 252
 253
 254         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 255
 256         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 257         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 258         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 259         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 260
 261         /**     position of sender radio antenna (HAAT)
 262                         sender can be aircraft or ground station
 263         **/
 264         double ATC_HAAT = 30.0;
 265         double Aircraft_HAAT = 5.0;
 266         double sender_alt_ft,sender_alt;
 267         double transmitter_height=0.0;
 268         double receiver_height=0.0;
 269         SGGeod sender_pos = pos;
 270
 271         sender_alt_ft = sender_pos.getElevationFt();
 272         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 273         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 274         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 275         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 276
 277         double point_distance= _terrain_sampling_distance;
 278         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 279         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 280         double probe_distance = 0.0;
 281         /** If distance larger than this value (300 km), assume reception imposssible */
 282         if (distance_m > 300000)
 283                 return -1.0;
 284         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 285         if (own_alt > 8000) {
 286                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 287                 SG_LOG(SG_GENERAL, SG_BULK,
 288                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 289                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 290                 signal = link_budget - dbloss;
 291                 return signal;
 292         }
 293
 294
 295         int max_points = (int)floor(distance_m / point_distance);
 296         double delta_last = fmod(distance_m, point_distance);
 297
 298         deque<double> _elevations;
 299         deque<string> materials;
 300
 301
 302         double elevation_under_pilot = 0.0;
 303         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 304                 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
 305         }
 306
 307         double elevation_under_sender = 0.0;
 308         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 309                 transmitter_height = sender_alt - elevation_under_sender;
 310         }
 311         else {
 312                 transmitter_height = sender_alt;
 313         }
 314
 315         if(transmission_type == 1)
 316                 transmitter_height += ATC_HAAT;
 317         else
 318                 transmitter_height += Aircraft_HAAT;
 319
 320         SG_LOG(SG_GENERAL, SG_BULK,
 321                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 322         cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 323
 324         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 325
 326         while (_elevations.size() <= e_size) {
 327                 probe_distance += point_distance;
 328                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 329                 const SGMaterial *mat = 0;
 330                 double elevation_m = 0.0;
 331
 332                 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
 333                         if((transmission_type == 3) || (transmission_type == 4)) {
 334                                 _elevations.push_back(elevation_m);
 335                                 if(mat) {
 336                                         const std::vector<string> mat_names = mat->get_names();
 337                                         materials.push_back(mat_names[0]);
 338                                 }
 339                                 else {
 340                                         materials.push_back("None");
 341                                 }
 342                         }
 343                         else {
 344                                  _elevations.push_front(elevation_m);
 345                                  if(mat) {
 346                                          const std::vector<string> mat_names = mat->get_names();
 347                                          materials.push_front(mat_names[0]);
 348                                 }
 349                                 else {
 350                                         materials.push_front("None");
 351                                 }
 352                         }
 353                 }
 354                 else {
 355                         if((transmission_type == 3) || (transmission_type == 4)) {
 356                                 _elevations.push_back(0.0);
 357                                 materials.push_back("None");
 358                         }
 359                         else {
 360                                 _elevations.push_front(0.0);
 361                                 materials.push_front("None");
 362                         }
 363                 }
 364         }
 365         if((transmission_type == 3) || (transmission_type == 4)) {
 366                 _elevations.push_front(elevation_under_pilot);
 367                 if (delta_last > (point_distance / 2) )                 // only add last point if it's farther than half point_distance
 368                         _elevations.push_back(elevation_under_sender);
 369         }
 370         else {
 371                 _elevations.push_back(elevation_under_pilot);
 372                 if (delta_last > (point_distance / 2) )
 373                         _elevations.push_front(elevation_under_sender);
 374         }
 375
 376
 377         double max_alt_between=0.0;
 378         for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
 379                 if (_elevations[i] > max_alt_between) {
 380                         max_alt_between = _elevations[i];
 381                 }
 382         }
 383
 384         double num_points= (double)_elevations.size();
 385         //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
 386         _elevations.push_front(point_distance);
 387         _elevations.push_front(num_points -1);
 388         int size = _elevations.size();
 389         double itm_elev[size];
 390         for(int i=0;i<size;i++) {
 391                 itm_elev[i]=_elevations[i];
 392                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 393         }
 394
 395         if((transmission_type == 3) || (transmission_type == 4)) {
 396                 // the sender and receiver roles are switched
 397                 point_to_point(itm_elev, receiver_height, transmitter_height,
 398                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 399                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 400                 if( fgGetBool( "/sim/radio/use-clutter-attenuation", false ) )
 401                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
 402         }
 403         else {
 404                 point_to_point(itm_elev, transmitter_height, receiver_height,
 405                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 406                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 407                 if( fgGetBool( "/sim/radio/use-clutter-attenuation", false ) )
 408                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 409         }
 410         SG_LOG(SG_GENERAL, SG_BULK,
 411                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 412         cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 413
 414         cerr << "Clutter loss: " << clutter_loss << endl;
 415         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 416         //      return -1;
 417         signal = link_budget - dbloss - clutter_loss;
 418         return signal;
 419
 420 }
 421
 422 /*** Calculate losses due to vegetation and urban clutter (WIP)
 423 *        We are only worried about clutter loss, terrain influence
 424 *        on the first Fresnel zone is calculated in the ITM functions
 425 ***/
 426 void FGRadioTransmission::clutterLoss(double freq, double distance_m, double itm_elev[], deque<string> materials,
 427         double transmitter_height, double receiver_height, int p_mode,
 428         double horizons[], double &clutter_loss) {
 429
 430         distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
 431
 432         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 433                 int mat = 0;
 434                 int j=1;
 435                 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
 436
 437                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 438                         double clutter_density = 0.0;   // percent of reflected wave
 439                         get_material_properties(materials[mat], clutter_height, clutter_density);
 440
 441                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 442                         // First Fresnel radius
 443                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 444                         assert(frs_rad > 0);
 445
 446                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 447
 448                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 449                         double d1 = j * itm_elev[1];
 450                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 451                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 452                         }
 453                         double ray_height = (grad * d1) + min_elev;
 454
 455                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 456                         double intrusion = fabs(clearance);
 457
 458                         if (clearance >= 0) {
 459                                 // no losses
 460                         }
 461                         else if (clearance < 0 && (intrusion < clutter_height)) {
 462
 463                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 464                         }
 465                         else if (clearance < 0 && (intrusion > clutter_height)) {
 466                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 467                         }
 468                         else {
 469                                 // no losses
 470                         }
 471                         j++;
 472                         mat++;
 473                 }
 474
 475         }
 476         else if (p_mode == 1) {         // diffraction
 477
 478                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 479                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
 480                         int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
 481                         cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
 482                         int last = 1;
 483                         /** perform the first pass */
 484                         int mat = 0;
 485                         int j=1;
 486                         for (int k=3;k < num_points_1st + 2;k++) {
 487                                 if (num_points_1st < 1)
 488                                         break;
 489                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 490                                 double clutter_density = 0.0;   // percent of reflected wave
 491                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 492
 493                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 494                                 // First Fresnel radius
 495                                 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) );
 496                                 assert(frs_rad > 0);
 497
 498                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 499
 500                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 501                                 double d1 = j * itm_elev[1];
 502                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 503                                         d1 = (num_points_1st - j) * itm_elev[1];
 504                                 }
 505                                 double ray_height = (grad * d1) + min_elev;
 506
 507                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 508                                 double intrusion = fabs(clearance);
 509
 510                                 if (clearance >= 0) {
 511                                         // no losses
 512                                 }
 513                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 514
 515                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 516                                 }
 517                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 518                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 519                                 }
 520                                 else {
 521                                         // no losses
 522                                 }
 523                                 j++;
 524                                 mat++;
 525                                 last = k;
 526                         }
 527
 528                         /** and the second pass */
 529                         mat +=1;
 530                         j =1; // first point is diffraction edge, 2nd the RX elevation
 531                         for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
 532                                 if (num_points_2nd < 1)
 533                                         break;
 534                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 535                                 double clutter_density = 0.0;   // percent of reflected wave
 536                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 537
 538                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 539                                 // First Fresnel radius
 540                                 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) );
 541                                 assert(frs_rad > 0);
 542
 543                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 544
 545                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 546                                 double d1 = j * itm_elev[1];
 547                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 548                                         d1 = (num_points_2nd - j) * itm_elev[1];
 549                                 }
 550                                 double ray_height = (grad * d1) + min_elev;
 551
 552                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 553                                 double intrusion = fabs(clearance);
 554
 555                                 if (clearance >= 0) {
 556                                         // no losses
 557                                 }
 558                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 559
 560                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 561                                 }
 562                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 563                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 564                                 }
 565                                 else {
 566                                         // no losses
 567                                 }
 568                                 j++;
 569                                 mat++;
 570                         }
 571
 572                 }
 573                 else {  // double horizon: same as single horizon, except there are 3 segments
 574
 575                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
 576                         int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
 577                         int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
 578                         cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
 579                         cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
 580                         int last = 1;
 581                         /** perform the first pass */
 582                         int mat = 0;
 583                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 584                         for (int k=3;k < num_points_1st +2;k++) {
 585                                 if (num_points_1st < 1)
 586                                         break;
 587                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 588                                 double clutter_density = 0.0;   // percent of reflected wave
 589                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 590
 591                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 592                                 // First Fresnel radius
 593                                 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) );
 594                                 assert(frs_rad > 0);
 595
 596                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 597
 598                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 599                                 double d1 = j * itm_elev[1];
 600                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 601                                         d1 = (num_points_1st - j) * itm_elev[1];
 602                                 }
 603                                 double ray_height = (grad * d1) + min_elev;
 604
 605                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 606                                 double intrusion = fabs(clearance);
 607
 608                                 if (clearance >= 0) {
 609                                         // no losses
 610                                 }
 611                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 612
 613                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 614                                 }
 615                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 616                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 617                                 }
 618                                 else {
 619                                         // no losses
 620                                 }
 621                                 j++;
 622                                 last = k;
 623                         }
 624                         mat +=1;
 625                         /** and the second pass */
 626                         int last2=1;
 627                         j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 628                         for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
 629                                 if (num_points_2nd < 1)
 630                                         break;
 631                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 632                                 double clutter_density = 0.0;   // percent of reflected wave
 633                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 634
 635                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
 636                                 // First Fresnel radius
 637                                 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) );
 638                                 //cerr << "Double horizon second pass:: fresnel radius: " << frs_rad << " points2: " << num_points_2nd << " j: " << j << endl;
 639                                 assert(frs_rad > 0);
 640                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 641
 642                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
 643                                 double d1 = j * itm_elev[1];
 644                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
 645                                         d1 = (num_points_2nd - j) * itm_elev[1];
 646                                 }
 647                                 double ray_height = (grad * d1) + min_elev;
 648
 649                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 650                                 double intrusion = fabs(clearance);
 651
 652                                 if (clearance >= 0) {
 653                                         // no losses
 654                                 }
 655                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 656
 657                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 658                                 }
 659                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 660                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 661                                 }
 662                                 else {
 663                                         // no losses
 664                                 }
 665                                 j++;
 666                                 mat++;
 667                                 last2 = k;
 668                         }
 669
 670                         /** third and final pass */
 671                         mat +=1;
 672                         j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 673                         for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
 674                                 if (num_points_3rd < 1)
 675                                         break;
 676                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 677                                 double clutter_density = 0.0;   // percent of reflected wave
 678                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 679
 680                                 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 681                                 // First Fresnel radius
 682                                 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) );
 683                                 //cerr << "Double horizon third pass:: fresnel radius: " << frs_rad << " points3: " << num_points_3rd << " j: " << j << endl;
 684                                 assert(frs_rad > 0);
 685
 686                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 687
 688                                 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 689                                 double d1 = j * itm_elev[1];
 690                                 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 691                                         d1 = (num_points_3rd - j) * itm_elev[1];
 692                                 }
 693                                 double ray_height = (grad * d1) + min_elev;
 694
 695                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 696                                 double intrusion = fabs(clearance);
 697
 698                                 if (clearance >= 0) {
 699                                         // no losses
 700                                 }
 701                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 702
 703                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 704                                 }
 705                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 706                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 707                                 }
 708                                 else {
 709                                         // no losses
 710                                 }
 711                                 j++;
 712                                 mat++;
 713
 714                         }
 715
 716                 }
 717         }
 718         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now...
 719                 clutter_loss = 0.0;
 720         }
 721
 722 }
 723
 724 /***    Temporary material properties database
 725 *               height: median clutter height
 726 *               density: radiowave attenuation factor
 727 ***/
 728 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 729
 730         if(mat_name == "Landmass") {
 731                 height = 15.0;
 732                 density = 0.2;
 733         }
 734
 735         else if(mat_name == "SomeSort") {
 736                 height = 15.0;
 737                 density = 0.2;
 738         }
 739
 740         else if(mat_name == "Island") {
 741                 height = 15.0;
 742                 density = 0.2;
 743         }
 744         else if(mat_name == "Default") {
 745                 height = 15.0;
 746                 density = 0.2;
 747         }
 748         else if(mat_name == "EvergreenBroadCover") {
 749                 height = 20.0;
 750                 density = 0.2;
 751         }
 752         else if(mat_name == "EvergreenForest") {
 753                 height = 20.0;
 754                 density = 0.2;
 755         }
 756         else if(mat_name == "DeciduousBroadCover") {
 757                 height = 15.0;
 758                 density = 0.3;
 759         }
 760         else if(mat_name == "DeciduousForest") {
 761                 height = 15.0;
 762                 density = 0.3;
 763         }
 764         else if(mat_name == "MixedForestCover") {
 765                 height = 20.0;
 766                 density = 0.25;
 767         }
 768         else if(mat_name == "MixedForest") {
 769                 height = 15.0;
 770                 density = 0.25;
 771         }
 772         else if(mat_name == "RainForest") {
 773                 height = 25.0;
 774                 density = 0.55;
 775         }
 776         else if(mat_name == "EvergreenNeedleCover") {
 777                 height = 15.0;
 778                 density = 0.2;
 779         }
 780         else if(mat_name == "WoodedTundraCover") {
 781                 height = 5.0;
 782                 density = 0.15;
 783         }
 784         else if(mat_name == "DeciduousNeedleCover") {
 785                 height = 5.0;
 786                 density = 0.2;
 787         }
 788         else if(mat_name == "ScrubCover") {
 789                 height = 3.0;
 790                 density = 0.15;
 791         }
 792         else if(mat_name == "BuiltUpCover") {
 793                 height = 30.0;
 794                 density = 0.7;
 795         }
 796         else if(mat_name == "Urban") {
 797                 height = 30.0;
 798                 density = 0.7;
 799         }
 800         else if(mat_name == "Construction") {
 801                 height = 30.0;
 802                 density = 0.7;
 803         }
 804         else if(mat_name == "Industrial") {
 805                 height = 30.0;
 806                 density = 0.7;
 807         }
 808         else if(mat_name == "Port") {
 809                 height = 30.0;
 810                 density = 0.7;
 811         }
 812         else if(mat_name == "Town") {
 813                 height = 10.0;
 814                 density = 0.5;
 815         }
 816         else if(mat_name == "SubUrban") {
 817                 height = 10.0;
 818                 density = 0.5;
 819         }
 820         else if(mat_name == "CropWoodCover") {
 821                 height = 10.0;
 822                 density = 0.1;
 823         }
 824         else if(mat_name == "CropWood") {
 825                 height = 10.0;
 826                 density = 0.1;
 827         }
 828         else if(mat_name == "AgroForest") {
 829                 height = 10.0;
 830                 density = 0.1;
 831         }
 832         else {
 833                 height = 0.0;
 834                 density = 0.0;
 835         }
 836
 837 }
 838
 839 /*** implement simple LOS propagation model (WIP)
 840 ***/
 841 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 842         double frq_mhz;
 843         if( (freq < 118.0) || (freq > 137.0) )
 844                 frq_mhz = 125.0;        // sane value, middle of bandplan
 845         else
 846                 frq_mhz = freq;
 847         double dbloss;
 848         double tx_pow = _transmitter_power;
 849         double ant_gain = _antenna_gain;
 850         double signal = 0.0;
 851         double ATC_HAAT = 30.0;
 852         double Aircraft_HAAT = 5.0;
 853         double sender_alt_ft,sender_alt;
 854         double transmitter_height=0.0;
 855         double receiver_height=0.0;
 856         double own_lat = fgGetDouble("/position/latitude-deg");
 857         double own_lon = fgGetDouble("/position/longitude-deg");
 858         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 859         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 860
 861         if(transmission_type == 1)
 862                 tx_pow = _transmitter_power + 6.0;
 863
 864         if((transmission_type == 1) || (transmission_type == 3))
 865                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 866
 867         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 868
 869         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 870
 871         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 872
 873         SGGeod sender_pos = pos;
 874
 875         sender_alt_ft = sender_pos.getElevationFt();
 876         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 877
 878         receiver_height = own_alt;
 879         transmitter_height = sender_alt;
 880
 881         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 882
 883         if(transmission_type == 1)
 884                 transmitter_height += ATC_HAAT;
 885         else
 886                 transmitter_height += Aircraft_HAAT;
 887
 888         /** radio horizon calculation with wave bending k=4/3 */
 889         double receiver_horizon = 4.12 * sqrt(receiver_height);
 890         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 891         double total_horizon = receiver_horizon + transmitter_horizon;
 892
 893         if (distance_m > total_horizon) {
 894                 return -1;
 895         }
 896
 897         // free-space loss (distance calculation should be changed)
 898         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 899         signal = link_budget - dbloss;
 900         SG_LOG(SG_GENERAL, SG_BULK,
 901                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 902         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 903         return signal;
 904
 905 }
 906
 907