src/Radio/radio.cxx

   1 // radio.cxx -- implementation of FGRadio
   2 // Class to manage radio propagation using the ITM model
   3 // Written by Adrian Musceac, started August 2011.
   4 //
   5 // This program is free software; you can redistribute it and/or
   6 // modify it under the terms of the GNU General Public License as
   7 // published by the Free Software Foundation; either version 2 of the
   8 // License, or (at your option) any later version.
   9 //
  10 // This program is distributed in the hope that it will be useful, but
  11 // WITHOUT ANY WARRANTY; without even the implied warranty of
  12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 // General Public License for more details.
  14 //
  15 // You should have received a copy of the GNU General Public License
  16 // along with this program; if not, write to the Free Software
  17 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  18
  19
  20
  21 #ifdef HAVE_CONFIG_H
  22 #  include <config.h>
  23 #endif
  24
  25 #include <math.h>
  26 #include <stdlib.h>
  27 #include <deque>
  28 #include "radio.hxx"
  29 #include <simgear/scene/material/mat.hxx>
  30 #include <Scenery/scenery.hxx>
  31
  32 #define WITH_POINT_TO_POINT 1
  33 #include "itm.cpp"
  34
  35
  36 FGRadioTransmission::FGRadioTransmission() {
  37
  38         /** radio parameters (which should probably be set for each radio) */
  39
  40         _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
  41
  42         /** AM transmitter power in dBm.
  43         *       Note this value is calculated from the typical final transistor stage output
  44         *       small aircraft have portable transmitters which operate at 36 dBm output (4 Watts) others operate in the range 10-20 W
  45         *       later possibly store this value in aircraft description
  46         *       ATC comms usually operate high power equipment, thus making the link asymetrical; this is taken care of in propagation routines
  47         *       Typical output powers for ATC ground equipment, VHF-UHF:
  48         *       40 dBm - 10 W (ground, clearance)
  49         *       44 dBm - 20 W (tower)
  50         *       47 dBm - 50 W (center, sectors)
  51         *       50 dBm - 100 W (center, sectors)
  52         *       53 dBm - 200 W (sectors, on directional arrays)
  53         **/
  54         _transmitter_power = 43.0;
  55
  56         _tx_antenna_height = 2.0; // TX antenna height above ground level
  57
  58         _rx_antenna_height = 2.0; // RX antenna height above ground level
  59
  60         /** pilot plane's antenna gain + AI aircraft antenna gain
  61         *       real-life gain for conventional monopole/dipole antenna
  62         **/
  63         _antenna_gain = 2.0;
  64         _propagation_model = 2; //  choose between models via option: realistic radio on/off
  65
  66 }
  67
  68 FGRadioTransmission::~FGRadioTransmission()
  69 {
  70 }
  71
  72
  73 double FGRadioTransmission::getFrequency(int radio) {
  74         double freq = 118.0;
  75         switch (radio) {
  76                 case 1:
  77                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  78                         break;
  79                 case 2:
  80                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  81                         break;
  82                 default:
  83                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  84
  85         }
  86         return freq;
  87 }
  88
  89 /*** TODO: receive multiplayer chat message and voice
  90 ***/
  91 void FGRadioTransmission::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
  92
  93 }
  94
  95 /*** TODO: receive navaid
  96 ***/
  97 double FGRadioTransmission::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
  98
  99         // typical VOR/LOC transmitter power appears to be 200 Watt ~ 53 dBm
 100         // vor/loc typical sensitivity between -107 and -101 dBm
 101         // glideslope sensitivity between -85 and -81 dBm
 102         if ( _propagation_model == 1) {
 103                 return LOS_calculate_attenuation(tx_pos, freq, 1);
 104         }
 105         else if ( _propagation_model == 2) {
 106                 return ITM_calculate_attenuation(tx_pos, freq, 1);
 107         }
 108
 109         return -1;
 110
 111 }
 112
 113 /*** Receive ATC radio communication as text
 114 ***/
 115 void FGRadioTransmission::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 116
 117
 118         double comm1 = getFrequency(1);
 119         double comm2 = getFrequency(2);
 120         if ( !(fabs(freq - comm1) <= 0.0001) &&  !(fabs(freq - comm2) <= 0.0001) ) {
 121                 //cerr << "Frequency not tuned: " << freq << " Radio1: " << comm1 << " Radio2: " << comm2 << endl;
 122                 return;
 123         }
 124         else {
 125
 126                 if ( _propagation_model == 0) {
 127                         fgSetString("/sim/messages/atc", text.c_str());
 128                 }
 129                 else if ( _propagation_model == 1 ) {
 130                         // TODO: free space, round earth
 131                         double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
 132                         if (signal <= 0.0) {
 133                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 134                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 135                                 return;
 136                         }
 137                         else {
 138                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 139                                 //cerr << "Signal completely readable: " << signal << endl;
 140                                 fgSetString("/sim/messages/atc", text.c_str());
 141                                 /** write signal strength above threshold to the property tree
 142                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 143                                 **/
 144                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 145                         }
 146                 }
 147                 else if ( _propagation_model == 2 ) {
 148                         // Use ITM propagation model
 149                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 150                         if (signal <= 0.0) {
 151                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
 152                                 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
 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                                 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
 183                                 //cerr << "Signal completely readable: " << signal << endl;
 184                                 fgSetString("/sim/messages/atc", text.c_str());
 185                                 /** write signal strength above threshold to the property tree
 186                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 187                                 **/
 188                                 fgSetDouble("/sim/radio/comm1-signal", signal);
 189                         }
 190
 191                 }
 192
 193         }
 194
 195 }
 196
 197 /***  Implement radio attenuation
 198           based on the Longley-Rice propagation model
 199 ***/
 200 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 201
 202
 203
 204         /** ITM default parameters
 205                 TODO: take them from tile materials (especially for sea)?
 206         **/
 207         double eps_dielect=15.0;
 208         double sgm_conductivity = 0.005;
 209         double eno = 301.0;
 210         double frq_mhz;
 211         if( (freq < 118.0) || (freq > 137.0) )
 212                 frq_mhz = 125.0;        // sane value, middle of bandplan
 213         else
 214                 frq_mhz = freq;
 215         int radio_climate = 5;          // continental temperate
 216         int pol=1;      // assuming vertical polarization although this is more complex in reality
 217         double conf = 0.90;     // 90% of situations and time, take into account speed
 218         double rel = 0.90;
 219         double dbloss;
 220         char strmode[150];
 221         int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
 222         double horizons[2];
 223         int errnum;
 224
 225         double clutter_loss = 0.0;      // loss due to vegetation and urban
 226         double tx_pow = _transmitter_power;
 227         double ant_gain = _antenna_gain;
 228         double signal = 0.0;
 229
 230         if(transmission_type == 1)
 231                 tx_pow = _transmitter_power + 6.0;
 232
 233         if((transmission_type == 1) || (transmission_type == 3))
 234                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 235
 236         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 237
 238         FGScenery * scenery = globals->get_scenery();
 239
 240         double own_lat = fgGetDouble("/position/latitude-deg");
 241         double own_lon = fgGetDouble("/position/longitude-deg");
 242         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 243         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 244
 245
 246         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 247
 248         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 249         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 250         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 251         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 252
 253         /**     position of sender radio antenna (HAAT)
 254                         sender can be aircraft or ground station
 255         **/
 256         double ATC_HAAT = 30.0;
 257         double Aircraft_HAAT = 5.0;
 258         double sender_alt_ft,sender_alt;
 259         double transmitter_height=0.0;
 260         double receiver_height=0.0;
 261         SGGeod sender_pos = pos;
 262
 263         sender_alt_ft = sender_pos.getElevationFt();
 264         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 265         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 266         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 267         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 268
 269         double point_distance= 90.0; // regular SRTM is 90 meters
 270         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 271         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 272         double probe_distance = 0.0;
 273         /** If distance larger than this value (300 km), assume reception imposssible */
 274         if (distance_m > 300000)
 275                 return -1.0;
 276         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 277         if (own_alt > 8000) {
 278                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 279                 SG_LOG(SG_GENERAL, SG_BULK,
 280                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 281                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 282                 signal = link_budget - dbloss;
 283                 return signal;
 284         }
 285
 286
 287         double max_points = distance_m / point_distance;
 288         deque<double> _elevations;
 289         deque<string> materials;
 290
 291
 292         double elevation_under_pilot = 0.0;
 293         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 294                 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
 295         }
 296
 297         double elevation_under_sender = 0.0;
 298         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 299                 transmitter_height = sender_alt - elevation_under_sender;
 300         }
 301         else {
 302                 transmitter_height = sender_alt;
 303         }
 304
 305         if(transmission_type == 1)
 306                 transmitter_height += ATC_HAAT;
 307         else
 308                 transmitter_height += Aircraft_HAAT;
 309
 310         SG_LOG(SG_GENERAL, SG_BULK,
 311                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 312         cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 313
 314         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 315
 316         while (_elevations.size() <= e_size) {
 317                 probe_distance += point_distance;
 318                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 319                 const SGMaterial *mat = 0;
 320                 double elevation_m = 0.0;
 321
 322                 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
 323                         if((transmission_type == 3) || (transmission_type == 4)) {
 324                                 _elevations.push_back(elevation_m);
 325                                 if(mat) {
 326                                         const std::vector<string> mat_names = mat->get_names();
 327                                         materials.push_back(mat_names[0]);
 328                                 }
 329                                 else {
 330                                         materials.push_back("None");
 331                                 }
 332                         }
 333                         else {
 334                                  _elevations.push_front(elevation_m);
 335                                  if(mat) {
 336                                          const std::vector<string> mat_names = mat->get_names();
 337                                          materials.push_front(mat_names[0]);
 338                                 }
 339                                 else {
 340                                         materials.push_front("None");
 341                                 }
 342                         }
 343                 }
 344                 else {
 345                         if((transmission_type == 3) || (transmission_type == 4)) {
 346                                 _elevations.push_back(0.0);
 347                                 materials.push_back("None");
 348                         }
 349                         else {
 350                                 _elevations.push_front(0.0);
 351                                 materials.push_front("None");
 352                         }
 353                 }
 354         }
 355         if((transmission_type == 3) || (transmission_type == 4)) {
 356                 _elevations.push_front(elevation_under_pilot);
 357                 _elevations.push_back(elevation_under_sender);
 358         }
 359         else {
 360                 _elevations.push_back(elevation_under_pilot);
 361                 _elevations.push_front(elevation_under_sender);
 362         }
 363
 364
 365         double max_alt_between=0.0;
 366         for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
 367                 if (_elevations[i] > max_alt_between) {
 368                         max_alt_between = _elevations[i];
 369                 }
 370         }
 371
 372         double num_points= (double)_elevations.size();
 373         //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
 374         _elevations.push_front(point_distance);
 375         _elevations.push_front(num_points -1);
 376         int size = _elevations.size();
 377         double itm_elev[size];
 378         for(int i=0;i<size;i++) {
 379                 itm_elev[i]=_elevations[i];
 380                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 381         }
 382
 383         if((transmission_type == 3) || (transmission_type == 4)) {
 384                 // the sender and receiver roles are switched
 385                 point_to_point(itm_elev, receiver_height, transmitter_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, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
 390         }
 391         else {
 392                 point_to_point(itm_elev, transmitter_height, receiver_height,
 393                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 394                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 395                 if( fgGetBool( "/sim/radio/use-clutter-attenuation", false ) )
 396                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 397         }
 398         SG_LOG(SG_GENERAL, SG_BULK,
 399                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 400         cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 401
 402         cerr << "Clutter loss: " << clutter_loss << endl;
 403         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 404         //      return -1;
 405         signal = link_budget - dbloss - clutter_loss;
 406         return signal;
 407
 408 }
 409
 410 /*** Calculate losses due to vegetation and urban clutter (WIP)
 411 *        We are only worried about clutter loss, terrain influence
 412 *        on the first Fresnel zone is calculated in the ITM functions
 413 ***/
 414 void FGRadioTransmission::clutterLoss(double freq, double distance_m, double itm_elev[], deque<string> materials,
 415         double transmitter_height, double receiver_height, int p_mode,
 416         double horizons[], double &clutter_loss) {
 417
 418         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 419                 int mat = 0;
 420                 int j=1; // first point is TX elevation, last is RX elevation
 421                 for (int k=3;k < (int)itm_elev[0];k++) {
 422
 423                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 424                         double clutter_density = 0.0;   // percent of reflected wave
 425                         get_material_properties(materials[mat], clutter_height, clutter_density);
 426                         //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
 427                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 1] + receiver_height) / distance_m;
 428                         // First Fresnel radius
 429                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 430
 431                         //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
 432                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 433
 434                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 1] + receiver_height);
 435                         double d1 = j * itm_elev[1];
 436                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 1] + receiver_height) ) {
 437                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 438                         }
 439                         double ray_height = (grad * d1) + min_elev;
 440                         //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
 441                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 442                         double intrusion = fabs(clearance);
 443                         //cerr << "Clutter:: clearance: " << clearance << endl;
 444                         if (clearance >= 0) {
 445                                 // no losses
 446                         }
 447                         else if (clearance < 0 && (intrusion < clutter_height)) {
 448
 449                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
 450                         }
 451                         else if (clearance < 0 && (intrusion > clutter_height)) {
 452                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
 453                         }
 454                         else {
 455                                 // no losses
 456                         }
 457                         j++;
 458                         mat++;
 459                 }
 460
 461         }
 462         else if (p_mode == 1) {         // diffraction
 463
 464                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 465                         int num_points_1st = (int)floor( horizons[0] * (double)itm_elev[0] / distance_m );
 466                         int num_points_2nd = (int)floor( (distance_m - horizons[0]) * (double)itm_elev[0] / distance_m );
 467                         int last = 1;
 468                         /** perform the first pass */
 469                         int mat = 0;
 470                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 471                         for (int k=3;k < num_points_1st ;k++) {
 472
 473                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 474                                 double clutter_density = 0.0;   // percent of reflected wave
 475                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 476                                 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
 477                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 1] + clutter_height) / distance_m;
 478                                 // First Fresnel radius
 479                                 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) );
 480
 481                                 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
 482                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 483
 484                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 1] + clutter_height);
 485                                 double d1 = j * itm_elev[1];
 486                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 1] + clutter_height) ) {
 487                                         d1 = (num_points_1st - j) * itm_elev[1];
 488                                 }
 489                                 double ray_height = (grad * d1) + min_elev;
 490                                 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
 491                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 492                                 double intrusion = fabs(clearance);
 493                                 //cerr << "Clutter:: clearance: " << clearance << endl;
 494                                 if (clearance >= 0) {
 495                                         // no losses
 496                                 }
 497                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 498
 499                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
 500                                 }
 501                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 502                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
 503                                 }
 504                                 else {
 505                                         // no losses
 506                                 }
 507                                 j++;
 508                                 mat++;
 509                                 last = k;
 510                         }
 511
 512                         /** and the second pass */
 513
 514                         int l =1; // first point is diffraction edge, 2nd the RX elevation
 515                         for (int k=last+1;k < num_points_2nd ;k++) {
 516
 517                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 518                                 double clutter_density = 0.0;   // percent of reflected wave
 519                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 520                                 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
 521                                 double grad = fabs(itm_elev[last] + clutter_height - itm_elev[(int)itm_elev[0] + 1] + receiver_height) / distance_m;
 522                                 // First Fresnel radius
 523                                 double frs_rad = 548 * sqrt( (l * itm_elev[1] * (num_points_2nd - l) * itm_elev[1] / 1000000) / (  num_points_2nd * itm_elev[1] * freq / 1000) );
 524
 525                                 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
 526                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 527
 528                                 double min_elev = SGMiscd::min(itm_elev[last] + clutter_height, itm_elev[(int)itm_elev[0] + 1] + receiver_height);
 529                                 double d1 = l * itm_elev[1];
 530                                 if ( (itm_elev[last] + clutter_height) > (itm_elev[(int)itm_elev[0] + 1] + receiver_height) ) {
 531                                         d1 = (num_points_2nd - l) * itm_elev[1];
 532                                 }
 533                                 double ray_height = (grad * d1) + min_elev;
 534                                 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
 535                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 536                                 double intrusion = fabs(clearance);
 537                                 //cerr << "Clutter:: clearance: " << clearance << endl;
 538                                 if (clearance >= 0) {
 539                                         // no losses
 540                                 }
 541                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 542
 543                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
 544                                 }
 545                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 546                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
 547                                 }
 548                                 else {
 549                                         // no losses
 550                                 }
 551                                 j++;
 552                                 l++;
 553                                 mat++;
 554                         }
 555
 556                 }
 557                 else {  // double horizon: same as single horizon, except there are 3 segments
 558
 559                         int num_points_1st = (int)floor( horizons[0] * (double)itm_elev[0] / distance_m );
 560                         int num_points_2nd = (int)floor( (horizons[1] - horizons[0]) * (double)itm_elev[0] / distance_m );
 561                         int num_points_3rd = (int)floor( (distance_m - horizons[1]) * (double)itm_elev[0] / distance_m );
 562                         int last = 1;
 563                         /** perform the first pass */
 564                         int mat = 0;
 565                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 566                         for (int k=3;k < num_points_1st ;k++) {
 567
 568                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 569                                 double clutter_density = 0.0;   // percent of reflected wave
 570                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 571                                 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
 572                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 1] + clutter_height) / distance_m;
 573                                 // First Fresnel radius
 574                                 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) );
 575
 576                                 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
 577                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 578
 579                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 1] + clutter_height);
 580                                 double d1 = j * itm_elev[1];
 581                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 1] + clutter_height) ) {
 582                                         d1 = (num_points_1st - j) * itm_elev[1];
 583                                 }
 584                                 double ray_height = (grad * d1) + min_elev;
 585                                 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
 586                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 587                                 double intrusion = fabs(clearance);
 588                                 //cerr << "Clutter:: clearance: " << clearance << endl;
 589                                 if (clearance >= 0) {
 590                                         // no losses
 591                                 }
 592                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 593
 594                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
 595                                 }
 596                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 597                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
 598                                 }
 599                                 else {
 600                                         // no losses
 601                                 }
 602                                 j++;
 603                                 last = k;
 604                         }
 605
 606                         /** and the second pass */
 607
 608                         int l =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 609                         for (int k=last;k < num_points_2nd ;k++) {
 610
 611                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 612                                 double clutter_density = 0.0;   // percent of reflected wave
 613                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 614                                 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
 615                                 double grad = fabs(itm_elev[last] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 1] + clutter_height) / distance_m;
 616                                 // First Fresnel radius
 617                                 double frs_rad = 548 * sqrt( (l * itm_elev[1] * (num_points_2nd - j) * itm_elev[1] / 1000000) / (  num_points_2nd * itm_elev[1] * freq / 1000) );
 618
 619                                 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
 620                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 621
 622                                 double min_elev = SGMiscd::min(itm_elev[last] + clutter_height, itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height);
 623                                 double d1 = l * itm_elev[1];
 624                                 if ( (itm_elev[last] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 1] + clutter_height) ) {
 625                                         d1 = (num_points_2nd - l) * itm_elev[1];
 626                                 }
 627                                 double ray_height = (grad * d1) + min_elev;
 628                                 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
 629                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 630                                 double intrusion = fabs(clearance);
 631                                 //cerr << "Clutter:: clearance: " << clearance << endl;
 632                                 if (clearance >= 0) {
 633                                         // no losses
 634                                 }
 635                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 636
 637                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
 638                                 }
 639                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 640                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
 641                                 }
 642                                 else {
 643                                         // no losses
 644                                 }
 645                                 j++;
 646                                 l++;
 647                                 mat++;
 648                                 last = k;
 649                         }
 650
 651                         /** third and final pass */
 652
 653                         int m =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 654                         for (int k=last;k < num_points_3rd ;k++) {
 655
 656                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 657                                 double clutter_density = 0.0;   // percent of reflected wave
 658                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 659                                 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
 660                                 double grad = fabs(itm_elev[last] + clutter_height - itm_elev[(int)itm_elev[0] + 1] + receiver_height) / distance_m;
 661                                 // First Fresnel radius
 662                                 double frs_rad = 548 * sqrt( (m * itm_elev[1] * (num_points_3rd - m) * itm_elev[1] / 1000000) / (  num_points_3rd * itm_elev[1] * freq / 1000) );
 663
 664                                 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
 665                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 666
 667                                 double min_elev = SGMiscd::min(itm_elev[last] + clutter_height, itm_elev[(int)itm_elev[0] + 1] + receiver_height);
 668                                 double d1 = m * itm_elev[1];
 669                                 if ( (itm_elev[last] + clutter_height) > (itm_elev[(int)itm_elev[0] + 1] + receiver_height) ) {
 670                                         d1 = (num_points_3rd - m) * itm_elev[1];
 671                                 }
 672                                 double ray_height = (grad * d1) + min_elev;
 673                                 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
 674                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 675                                 double intrusion = fabs(clearance);
 676                                 //cerr << "Clutter:: clearance: " << clearance << endl;
 677                                 if (clearance >= 0) {
 678                                         // no losses
 679                                 }
 680                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 681
 682                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
 683                                 }
 684                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 685                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
 686                                 }
 687                                 else {
 688                                         // no losses
 689                                 }
 690                                 j++;
 691                                 m++;
 692                                 mat++;
 693                                 last = k+1;
 694                         }
 695
 696                 }
 697         }
 698         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now...
 699                 clutter_loss = 0.0;
 700         }
 701
 702 }
 703
 704 /***    Temporary material properties database
 705 *               height: median clutter height
 706 *               density: radiowave attenuation factor
 707 ***/
 708 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 709
 710         if(mat_name == "Landmass") {
 711                 height = 15.0;
 712                 density = 0.2;
 713         }
 714
 715         else if(mat_name == "SomeSort") {
 716                 height = 15.0;
 717                 density = 0.2;
 718         }
 719
 720         else if(mat_name == "Island") {
 721                 height = 15.0;
 722                 density = 0.2;
 723         }
 724         else if(mat_name == "Default") {
 725                 height = 15.0;
 726                 density = 0.2;
 727         }
 728         else if(mat_name == "EvergreenBroadCover") {
 729                 height = 20.0;
 730                 density = 0.2;
 731         }
 732         else if(mat_name == "EvergreenForest") {
 733                 height = 20.0;
 734                 density = 0.2;
 735         }
 736         else if(mat_name == "DeciduousBroadCover") {
 737                 height = 15.0;
 738                 density = 0.3;
 739         }
 740         else if(mat_name == "DeciduousForest") {
 741                 height = 15.0;
 742                 density = 0.3;
 743         }
 744         else if(mat_name == "MixedForestCover") {
 745                 height = 20.0;
 746                 density = 0.25;
 747         }
 748         else if(mat_name == "MixedForest") {
 749                 height = 15.0;
 750                 density = 0.25;
 751         }
 752         else if(mat_name == "RainForest") {
 753                 height = 25.0;
 754                 density = 0.55;
 755         }
 756         else if(mat_name == "EvergreenNeedleCover") {
 757                 height = 15.0;
 758                 density = 0.2;
 759         }
 760         else if(mat_name == "WoodedTundraCover") {
 761                 height = 5.0;
 762                 density = 0.15;
 763         }
 764         else if(mat_name == "DeciduousNeedleCover") {
 765                 height = 5.0;
 766                 density = 0.2;
 767         }
 768         else if(mat_name == "ScrubCover") {
 769                 height = 3.0;
 770                 density = 0.15;
 771         }
 772         else if(mat_name == "BuiltUpCover") {
 773                 height = 30.0;
 774                 density = 0.7;
 775         }
 776         else if(mat_name == "Urban") {
 777                 height = 30.0;
 778                 density = 0.7;
 779         }
 780         else if(mat_name == "Construction") {
 781                 height = 30.0;
 782                 density = 0.7;
 783         }
 784         else if(mat_name == "Industrial") {
 785                 height = 30.0;
 786                 density = 0.7;
 787         }
 788         else if(mat_name == "Port") {
 789                 height = 30.0;
 790                 density = 0.7;
 791         }
 792         else if(mat_name == "Town") {
 793                 height = 10.0;
 794                 density = 0.5;
 795         }
 796         else if(mat_name == "SubUrban") {
 797                 height = 10.0;
 798                 density = 0.5;
 799         }
 800         else if(mat_name == "CropWoodCover") {
 801                 height = 10.0;
 802                 density = 0.1;
 803         }
 804         else if(mat_name == "CropWood") {
 805                 height = 10.0;
 806                 density = 0.1;
 807         }
 808         else if(mat_name == "AgroForest") {
 809                 height = 10.0;
 810                 density = 0.1;
 811         }
 812         else {
 813                 height = 0.0;
 814                 density = 0.0;
 815         }
 816
 817 }
 818
 819 /*** implement simple LOS propagation model (WIP)
 820 ***/
 821 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 822         double frq_mhz;
 823         if( (freq < 118.0) || (freq > 137.0) )
 824                 frq_mhz = 125.0;        // sane value, middle of bandplan
 825         else
 826                 frq_mhz = freq;
 827         double dbloss;
 828         double tx_pow = _transmitter_power;
 829         double ant_gain = _antenna_gain;
 830         double signal = 0.0;
 831         double ATC_HAAT = 30.0;
 832         double Aircraft_HAAT = 5.0;
 833         double sender_alt_ft,sender_alt;
 834         double transmitter_height=0.0;
 835         double receiver_height=0.0;
 836         double own_lat = fgGetDouble("/position/latitude-deg");
 837         double own_lon = fgGetDouble("/position/longitude-deg");
 838         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 839         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 840
 841         if(transmission_type == 1)
 842                 tx_pow = _transmitter_power + 6.0;
 843
 844         if((transmission_type == 1) || (transmission_type == 3))
 845                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 846
 847         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 848
 849         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 850
 851         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 852
 853         SGGeod sender_pos = pos;
 854
 855         sender_alt_ft = sender_pos.getElevationFt();
 856         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 857
 858         receiver_height = own_alt;
 859         transmitter_height = sender_alt;
 860
 861         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 862
 863         if(transmission_type == 1)
 864                 transmitter_height += ATC_HAAT;
 865         else
 866                 transmitter_height += Aircraft_HAAT;
 867
 868         /** radio horizon calculation with wave bending k=4/3 */
 869         double receiver_horizon = 4.12 * sqrt(receiver_height);
 870         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 871         double total_horizon = receiver_horizon + transmitter_horizon;
 872
 873         if (distance_m > total_horizon) {
 874                 return -1;
 875         }
 876
 877         // free-space loss (distance calculation should be changed)
 878         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 879         signal = link_budget - dbloss;
 880         SG_LOG(SG_GENERAL, SG_BULK,
 881                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 882         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 883         return signal;
 884
 885 }
 886
 887