src/Radio/radio.cxx

   1 // radio.cxx -- implementation of FGRadio
   2 // Class to manage radio propagation using the ITM model
   3 // Written by Adrian Musceac, started August 2011.
   4 //
   5 // This program is free software; you can redistribute it and/or
   6 // modify it under the terms of the GNU General Public License as
   7 // published by the Free Software Foundation; either version 2 of the
   8 // License, or (at your option) any later version.
   9 //
  10 // This program is distributed in the hope that it will be useful, but
  11 // WITHOUT ANY WARRANTY; without even the implied warranty of
  12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 // General Public License for more details.
  14 //
  15 // You should have received a copy of the GNU General Public License
  16 // along with this program; if not, write to the Free Software
  17 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  18
  19
  20
  21 #ifdef HAVE_CONFIG_H
  22 #  include <config.h>
  23 #endif
  24
  25 #include <math.h>
  26
  27 #include <stdlib.h>
  28 #include <deque>
  29 #include "radio.hxx"
  30 #include <simgear/scene/material/mat.hxx>
  31 #include <Scenery/scenery.hxx>
  32
  33 #define WITH_POINT_TO_POINT 1
  34 #include "itm.cpp"
  35
  36
  37 FGRadioTransmission::FGRadioTransmission() {
  38
  39
  40         _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
  41
  42         /** AM transmitter power in dBm.
  43         *       Typical output powers for ATC ground equipment, VHF-UHF:
  44         *       40 dBm - 10 W (ground, clearance)
  45         *       44 dBm - 20 W (tower)
  46         *       47 dBm - 50 W (center, sectors)
  47         *       50 dBm - 100 W (center, sectors)
  48         *       53 dBm - 200 W (sectors, on directional arrays)
  49         **/
  50         _transmitter_power = 43.0;
  51
  52         _tx_antenna_height = 2.0; // TX antenna height above ground level
  53
  54         _rx_antenna_height = 2.0; // RX antenna height above ground level
  55
  56
  57         _rx_antenna_gain = 1.0; // gain expressed in dBi
  58         _tx_antenna_gain = 1.0;
  59
  60         _rx_line_losses = 2.0;  // to be configured for each station
  61         _tx_line_losses = 2.0;
  62
  63         _polarization = 1; // default vertical
  64
  65         _propagation_model = 2;
  66
  67         _root_node = fgGetNode("sim/radio", true);
  68         _terrain_sampling_distance = _root_node->getDoubleValue("sampling-distance", 90.0); // regular SRTM is 90 meters
  69 }
  70
  71 FGRadioTransmission::~FGRadioTransmission()
  72 {
  73 }
  74
  75
  76 double FGRadioTransmission::getFrequency(int radio) {
  77         double freq = 118.0;
  78         switch (radio) {
  79                 case 1:
  80                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  81                         break;
  82                 case 2:
  83                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  84                         break;
  85                 default:
  86                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  87
  88         }
  89         return freq;
  90 }
  91
  92 /*** TODO: receive multiplayer chat message and voice
  93 ***/
  94 void FGRadioTransmission::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
  95
  96 }
  97
  98 /*** TODO: receive navaid
  99 ***/
 100 double FGRadioTransmission::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
 101
 102         // typical VOR/LOC transmitter power appears to be 200 Watt ~ 53 dBm
 103         // vor/loc typical sensitivity between -107 and -101 dBm
 104         // glideslope sensitivity between -85 and -81 dBm
 105         if ( _propagation_model == 1) {
 106                 return LOS_calculate_attenuation(tx_pos, freq, 1);
 107         }
 108         else if ( _propagation_model == 2) {
 109                 return ITM_calculate_attenuation(tx_pos, freq, 1);
 110         }
 111
 112         return -1;
 113
 114 }
 115
 116 /*** Receive ATC radio communication as text
 117 ***/
 118 void FGRadioTransmission::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 119
 120
 121         if(ground_to_air == 1) {
 122                 _transmitter_power += 6.0;
 123                 _tx_antenna_height += 30.0;
 124                 _tx_antenna_gain += 3.0;
 125         }
 126
 127
 128         double comm1 = getFrequency(1);
 129         double comm2 = getFrequency(2);
 130         if ( !(fabs(freq - comm1) <= 0.0001) &&  !(fabs(freq - comm2) <= 0.0001) ) {
 131                 return;
 132         }
 133         else {
 134
 135                 if ( _propagation_model == 0) {
 136                         fgSetString("/sim/messages/atc", text.c_str());
 137                 }
 138                 else if ( _propagation_model == 1 ) {
 139                         // TODO: free space, round earth
 140                         double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
 141                         if (signal <= 0.0) {
 142                                 return;
 143                         }
 144                         else {
 145
 146                                 fgSetString("/sim/messages/atc", text.c_str());
 147                                 /** write signal strength above threshold to the property tree
 148                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 149                                 **/
 150                                 _root_node->setDoubleValue("station[0]/signal", signal);
 151                         }
 152                 }
 153                 else if ( _propagation_model == 2 ) {
 154                         // Use ITM propagation model
 155                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 156                         if (signal <= 0.0) {
 157                                 return;
 158                         }
 159                         if ((signal > 0.0) && (signal < 12.0)) {
 160                                 /** for low SNR values implement a way to make the conversation
 161                                 *       hard to understand but audible
 162                                 *       in the real world, the receiver AGC fails to capture the slope
 163                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 164                                 *       the workaround below is more akin to what would happen on a FM transmission
 165                                 *       therefore the correct way would be to work on the volume
 166                                 **/
 167                                 /*
 168                                 string hash_noise = " ";
 169                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 170                                 int t_size = text.size();
 171                                 for (int n = 1; n <= reps; ++n) {
 172                                         int pos = rand() % (t_size -1);
 173                                         text.replace(pos,1, hash_noise);
 174                                 }
 175                                 */
 176                                 double volume = (fabs(signal - 12.0) / 12);
 177                                 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 178                                 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
 179                                 //cerr << "Usable signal at limit: " << signal << endl;
 180                                 fgSetDouble("/sim/sound/voices/voice/volume", volume);
 181                                 fgSetString("/sim/messages/atc", text.c_str());
 182                                 _root_node->setDoubleValue("station[0]/signal", signal);
 183                                 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 184                         }
 185                         else {
 186                                 fgSetString("/sim/messages/atc", text.c_str());
 187                                 /** write signal strength above threshold to the property tree
 188                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 189                                 **/
 190                                 _root_node->setDoubleValue("station[0]/signal", signal);
 191                         }
 192
 193                 }
 194
 195         }
 196
 197 }
 198
 199 /***  Implement radio attenuation
 200           based on the Longley-Rice propagation model
 201 ***/
 202 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 203
 204
 205
 206         /** ITM default parameters
 207                 TODO: take them from tile materials (especially for sea)?
 208         **/
 209         double eps_dielect=15.0;
 210         double sgm_conductivity = 0.005;
 211         double eno = 301.0;
 212         double frq_mhz;
 213         if( (freq < 118.0) || (freq > 137.0) )
 214                 frq_mhz = 125.0;        // sane value, middle of bandplan
 215         else
 216                 frq_mhz = freq;
 217         int radio_climate = 5;          // continental temperate
 218         int pol= _polarization;
 219         double conf = 0.90;     // 90% of situations and time, take into account speed
 220         double rel = 0.90;
 221         double dbloss;
 222         char strmode[150];
 223         int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
 224         double horizons[2];
 225         int errnum;
 226
 227         double clutter_loss = 0.0;      // loss due to vegetation and urban
 228         double tx_pow = _transmitter_power;
 229         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 230         double signal = 0.0;
 231
 232
 233         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 234
 235         FGScenery * scenery = globals->get_scenery();
 236
 237         double own_lat = fgGetDouble("/position/latitude-deg");
 238         double own_lon = fgGetDouble("/position/longitude-deg");
 239         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 240         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 241
 242
 243         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 244
 245         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 246         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 247         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 248         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 249
 250
 251         double sender_alt_ft,sender_alt;
 252         double transmitter_height=0.0;
 253         double receiver_height=0.0;
 254         SGGeod sender_pos = pos;
 255
 256         sender_alt_ft = sender_pos.getElevationFt();
 257         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 258         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 259         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 260         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 261
 262         double point_distance= _terrain_sampling_distance;
 263         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 264         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 265         double probe_distance = 0.0;
 266         /** If distance larger than this value (300 km), assume reception imposssible */
 267         if (distance_m > 300000)
 268                 return -1.0;
 269         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 270         if (own_alt > 8000) {
 271                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 272                 SG_LOG(SG_GENERAL, SG_BULK,
 273                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 274                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 275                 signal = link_budget - dbloss;
 276                 return signal;
 277         }
 278
 279
 280         int max_points = (int)floor(distance_m / point_distance);
 281         double delta_last = fmod(distance_m, point_distance);
 282
 283         deque<double> _elevations;
 284         deque<string> materials;
 285
 286
 287         double elevation_under_pilot = 0.0;
 288         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 289                 receiver_height = own_alt - elevation_under_pilot;
 290         }
 291
 292         double elevation_under_sender = 0.0;
 293         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 294                 transmitter_height = sender_alt - elevation_under_sender;
 295         }
 296         else {
 297                 transmitter_height = sender_alt;
 298         }
 299
 300
 301         transmitter_height += _tx_antenna_height;
 302         receiver_height += _rx_antenna_height;
 303
 304
 305         SG_LOG(SG_GENERAL, SG_BULK,
 306                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 307         //cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 308         _root_node->setDoubleValue("station[0]/rx-height", receiver_height);
 309         _root_node->setDoubleValue("station[0]/tx-height", transmitter_height);
 310         _root_node->setDoubleValue("station[0]/distance", distance_m);
 311
 312         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 313
 314         while (_elevations.size() <= e_size) {
 315                 probe_distance += point_distance;
 316                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 317                 const SGMaterial *mat = 0;
 318                 double elevation_m = 0.0;
 319
 320                 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
 321                         if((transmission_type == 3) || (transmission_type == 4)) {
 322                                 _elevations.push_back(elevation_m);
 323                                 if(mat) {
 324                                         const std::vector<string> mat_names = mat->get_names();
 325                                         materials.push_back(mat_names[0]);
 326                                 }
 327                                 else {
 328                                         materials.push_back("None");
 329                                 }
 330                         }
 331                         else {
 332                                  _elevations.push_front(elevation_m);
 333                                  if(mat) {
 334                                          const std::vector<string> mat_names = mat->get_names();
 335                                          materials.push_front(mat_names[0]);
 336                                 }
 337                                 else {
 338                                         materials.push_front("None");
 339                                 }
 340                         }
 341                 }
 342                 else {
 343                         if((transmission_type == 3) || (transmission_type == 4)) {
 344                                 _elevations.push_back(0.0);
 345                                 materials.push_back("None");
 346                         }
 347                         else {
 348                                 _elevations.push_front(0.0);
 349                                 materials.push_front("None");
 350                         }
 351                 }
 352         }
 353         if((transmission_type == 3) || (transmission_type == 4)) {
 354                 _elevations.push_front(elevation_under_pilot);
 355                 if (delta_last > (point_distance / 2) )                 // only add last point if it's farther than half point_distance
 356                         _elevations.push_back(elevation_under_sender);
 357         }
 358         else {
 359                 _elevations.push_back(elevation_under_pilot);
 360                 if (delta_last > (point_distance / 2) )
 361                         _elevations.push_front(elevation_under_sender);
 362         }
 363
 364
 365         double num_points= (double)_elevations.size();
 366
 367         _elevations.push_front(point_distance);
 368         _elevations.push_front(num_points -1);
 369         int size = _elevations.size();
 370         double itm_elev[size];
 371         for(int i=0;i<size;i++) {
 372                 itm_elev[i]=_elevations[i];
 373                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 374         }
 375
 376         if((transmission_type == 3) || (transmission_type == 4)) {
 377                 // the sender and receiver roles are switched
 378                 point_to_point(itm_elev, receiver_height, transmitter_height,
 379                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 380                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 381                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 382                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
 383         }
 384         else {
 385                 point_to_point(itm_elev, transmitter_height, receiver_height,
 386                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 387                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 388                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 389                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 390         }
 391
 392         double pol_loss = 0.0;
 393         if (_polarization == 1) {
 394                 pol_loss = polarization_loss();
 395         }
 396         SG_LOG(SG_GENERAL, SG_BULK,
 397                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 398         //cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 399         _root_node->setDoubleValue("station[0]/link-budget", link_budget);
 400         _root_node->setDoubleValue("station[0]/terrain-attenuation", dbloss);
 401         _root_node->setStringValue("station[0]/prop-mode", strmode);
 402         _root_node->setDoubleValue("station[0]/clutter-attenuation", clutter_loss);
 403         _root_node->setDoubleValue("station[0]/polarization-attenuation", pol_loss);
 404         //cerr << "Clutter loss: " << clutter_loss << endl;
 405         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 406         //      return -1;
 407         signal = link_budget - dbloss - clutter_loss + pol_loss;
 408         return signal;
 409
 410 }
 411
 412 /*** Calculate losses due to vegetation and urban clutter (WIP)
 413 *        We are only worried about clutter loss, terrain influence
 414 *        on the first Fresnel zone is calculated in the ITM functions
 415 ***/
 416 void FGRadioTransmission::clutterLoss(double freq, double distance_m, double itm_elev[], deque<string> materials,
 417         double transmitter_height, double receiver_height, int p_mode,
 418         double horizons[], double &clutter_loss) {
 419
 420         distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
 421
 422         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 423                 int mat = 0;
 424                 int j=1;
 425                 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
 426
 427                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 428                         double clutter_density = 0.0;   // percent of reflected wave
 429                         get_material_properties(materials[mat], clutter_height, clutter_density);
 430
 431                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 432                         // First Fresnel radius
 433                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 434
 435                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 436
 437                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 438                         double d1 = j * itm_elev[1];
 439                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 440                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 441                         }
 442                         double ray_height = (grad * d1) + min_elev;
 443
 444                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 445                         double intrusion = fabs(clearance);
 446
 447                         if (clearance >= 0) {
 448                                 // no losses
 449                         }
 450                         else if (clearance < 0 && (intrusion < clutter_height)) {
 451
 452                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 453                         }
 454                         else if (clearance < 0 && (intrusion > clutter_height)) {
 455                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 456                         }
 457                         else {
 458                                 // no losses
 459                         }
 460                         j++;
 461                         mat++;
 462                 }
 463
 464         }
 465         else if (p_mode == 1) {         // diffraction
 466
 467                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 468                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
 469                         int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
 470                         //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
 471                         int last = 1;
 472                         /** perform the first pass */
 473                         int mat = 0;
 474                         int j=1;
 475                         for (int k=3;k < num_points_1st + 2;k++) {
 476                                 if (num_points_1st < 1)
 477                                         break;
 478                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 479                                 double clutter_density = 0.0;   // percent of reflected wave
 480                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 481
 482                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 483                                 // First Fresnel radius
 484                                 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) );
 485
 486                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 487
 488                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 489                                 double d1 = j * itm_elev[1];
 490                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 491                                         d1 = (num_points_1st - j) * itm_elev[1];
 492                                 }
 493                                 double ray_height = (grad * d1) + min_elev;
 494
 495                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 496                                 double intrusion = fabs(clearance);
 497
 498                                 if (clearance >= 0) {
 499                                         // no losses
 500                                 }
 501                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 502
 503                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 504                                 }
 505                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 506                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 507                                 }
 508                                 else {
 509                                         // no losses
 510                                 }
 511                                 j++;
 512                                 mat++;
 513                                 last = k;
 514                         }
 515
 516                         /** and the second pass */
 517                         mat +=1;
 518                         j =1; // first point is diffraction edge, 2nd the RX elevation
 519                         for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
 520                                 if (num_points_2nd < 1)
 521                                         break;
 522                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 523                                 double clutter_density = 0.0;   // percent of reflected wave
 524                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 525
 526                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 527                                 // First Fresnel radius
 528                                 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) );
 529
 530                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 531
 532                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 533                                 double d1 = j * itm_elev[1];
 534                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 535                                         d1 = (num_points_2nd - j) * itm_elev[1];
 536                                 }
 537                                 double ray_height = (grad * d1) + min_elev;
 538
 539                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 540                                 double intrusion = fabs(clearance);
 541
 542                                 if (clearance >= 0) {
 543                                         // no losses
 544                                 }
 545                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 546
 547                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 548                                 }
 549                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 550                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 551                                 }
 552                                 else {
 553                                         // no losses
 554                                 }
 555                                 j++;
 556                                 mat++;
 557                         }
 558
 559                 }
 560                 else {  // double horizon: same as single horizon, except there are 3 segments
 561
 562                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
 563                         int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
 564                         int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
 565                         //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
 566                         //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
 567                         int last = 1;
 568                         /** perform the first pass */
 569                         int mat = 0;
 570                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 571                         for (int k=3;k < num_points_1st +2;k++) {
 572                                 if (num_points_1st < 1)
 573                                         break;
 574                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 575                                 double clutter_density = 0.0;   // percent of reflected wave
 576                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 577
 578                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 579                                 // First Fresnel radius
 580                                 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) );
 581
 582                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 583
 584                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 585                                 double d1 = j * itm_elev[1];
 586                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 587                                         d1 = (num_points_1st - j) * itm_elev[1];
 588                                 }
 589                                 double ray_height = (grad * d1) + min_elev;
 590
 591                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 592                                 double intrusion = fabs(clearance);
 593
 594                                 if (clearance >= 0) {
 595                                         // no losses
 596                                 }
 597                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 598
 599                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 600                                 }
 601                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 602                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 603                                 }
 604                                 else {
 605                                         // no losses
 606                                 }
 607                                 j++;
 608                                 last = k;
 609                         }
 610                         mat +=1;
 611                         /** and the second pass */
 612                         int last2=1;
 613                         j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 614                         for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
 615                                 if (num_points_2nd < 1)
 616                                         break;
 617                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 618                                 double clutter_density = 0.0;   // percent of reflected wave
 619                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 620
 621                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
 622                                 // First Fresnel radius
 623                                 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) );
 624
 625                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 626
 627                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
 628                                 double d1 = j * itm_elev[1];
 629                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
 630                                         d1 = (num_points_2nd - j) * itm_elev[1];
 631                                 }
 632                                 double ray_height = (grad * d1) + min_elev;
 633
 634                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 635                                 double intrusion = fabs(clearance);
 636
 637                                 if (clearance >= 0) {
 638                                         // no losses
 639                                 }
 640                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 641
 642                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 643                                 }
 644                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 645                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 646                                 }
 647                                 else {
 648                                         // no losses
 649                                 }
 650                                 j++;
 651                                 mat++;
 652                                 last2 = k;
 653                         }
 654
 655                         /** third and final pass */
 656                         mat +=1;
 657                         j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 658                         for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
 659                                 if (num_points_3rd < 1)
 660                                         break;
 661                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 662                                 double clutter_density = 0.0;   // percent of reflected wave
 663                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 664
 665                                 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 666                                 // First Fresnel radius
 667                                 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) );
 668
 669
 670                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 671
 672                                 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 673                                 double d1 = j * itm_elev[1];
 674                                 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 675                                         d1 = (num_points_3rd - j) * itm_elev[1];
 676                                 }
 677                                 double ray_height = (grad * d1) + min_elev;
 678
 679                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 680                                 double intrusion = fabs(clearance);
 681
 682                                 if (clearance >= 0) {
 683                                         // no losses
 684                                 }
 685                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 686
 687                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 688                                 }
 689                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 690                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 691                                 }
 692                                 else {
 693                                         // no losses
 694                                 }
 695                                 j++;
 696                                 mat++;
 697
 698                         }
 699
 700                 }
 701         }
 702         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now...
 703                 clutter_loss = 0.0;
 704         }
 705
 706 }
 707
 708 /***    Temporary material properties database
 709 *               height: median clutter height
 710 *               density: radiowave attenuation factor
 711 ***/
 712 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 713
 714         if(mat_name == "Landmass") {
 715                 height = 15.0;
 716                 density = 0.2;
 717         }
 718
 719         else if(mat_name == "SomeSort") {
 720                 height = 15.0;
 721                 density = 0.2;
 722         }
 723
 724         else if(mat_name == "Island") {
 725                 height = 15.0;
 726                 density = 0.2;
 727         }
 728         else if(mat_name == "Default") {
 729                 height = 15.0;
 730                 density = 0.2;
 731         }
 732         else if(mat_name == "EvergreenBroadCover") {
 733                 height = 20.0;
 734                 density = 0.2;
 735         }
 736         else if(mat_name == "EvergreenForest") {
 737                 height = 20.0;
 738                 density = 0.2;
 739         }
 740         else if(mat_name == "DeciduousBroadCover") {
 741                 height = 15.0;
 742                 density = 0.3;
 743         }
 744         else if(mat_name == "DeciduousForest") {
 745                 height = 15.0;
 746                 density = 0.3;
 747         }
 748         else if(mat_name == "MixedForestCover") {
 749                 height = 20.0;
 750                 density = 0.25;
 751         }
 752         else if(mat_name == "MixedForest") {
 753                 height = 15.0;
 754                 density = 0.25;
 755         }
 756         else if(mat_name == "RainForest") {
 757                 height = 25.0;
 758                 density = 0.55;
 759         }
 760         else if(mat_name == "EvergreenNeedleCover") {
 761                 height = 15.0;
 762                 density = 0.2;
 763         }
 764         else if(mat_name == "WoodedTundraCover") {
 765                 height = 5.0;
 766                 density = 0.15;
 767         }
 768         else if(mat_name == "DeciduousNeedleCover") {
 769                 height = 5.0;
 770                 density = 0.2;
 771         }
 772         else if(mat_name == "ScrubCover") {
 773                 height = 3.0;
 774                 density = 0.15;
 775         }
 776         else if(mat_name == "BuiltUpCover") {
 777                 height = 30.0;
 778                 density = 0.7;
 779         }
 780         else if(mat_name == "Urban") {
 781                 height = 30.0;
 782                 density = 0.7;
 783         }
 784         else if(mat_name == "Construction") {
 785                 height = 30.0;
 786                 density = 0.7;
 787         }
 788         else if(mat_name == "Industrial") {
 789                 height = 30.0;
 790                 density = 0.7;
 791         }
 792         else if(mat_name == "Port") {
 793                 height = 30.0;
 794                 density = 0.7;
 795         }
 796         else if(mat_name == "Town") {
 797                 height = 10.0;
 798                 density = 0.5;
 799         }
 800         else if(mat_name == "SubUrban") {
 801                 height = 10.0;
 802                 density = 0.5;
 803         }
 804         else if(mat_name == "CropWoodCover") {
 805                 height = 10.0;
 806                 density = 0.1;
 807         }
 808         else if(mat_name == "CropWood") {
 809                 height = 10.0;
 810                 density = 0.1;
 811         }
 812         else if(mat_name == "AgroForest") {
 813                 height = 10.0;
 814                 density = 0.1;
 815         }
 816         else {
 817                 height = 0.0;
 818                 density = 0.0;
 819         }
 820
 821 }
 822
 823 /*** implement simple LOS propagation model (WIP)
 824 ***/
 825 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 826         double frq_mhz;
 827         if( (freq < 118.0) || (freq > 137.0) )
 828                 frq_mhz = 125.0;        // sane value, middle of bandplan
 829         else
 830                 frq_mhz = freq;
 831         double dbloss;
 832         double tx_pow = _transmitter_power;
 833         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 834         double signal = 0.0;
 835
 836         double sender_alt_ft,sender_alt;
 837         double transmitter_height=0.0;
 838         double receiver_height=0.0;
 839         double own_lat = fgGetDouble("/position/latitude-deg");
 840         double own_lon = fgGetDouble("/position/longitude-deg");
 841         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 842         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 843
 844
 845         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 846
 847         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 848
 849         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 850
 851         SGGeod sender_pos = pos;
 852
 853         sender_alt_ft = sender_pos.getElevationFt();
 854         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 855
 856         receiver_height = own_alt;
 857         transmitter_height = sender_alt;
 858
 859         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 860
 861
 862         transmitter_height += _tx_antenna_height;
 863         receiver_height += _rx_antenna_height;
 864
 865
 866         /** radio horizon calculation with wave bending k=4/3 */
 867         double receiver_horizon = 4.12 * sqrt(receiver_height);
 868         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 869         double total_horizon = receiver_horizon + transmitter_horizon;
 870
 871         if (distance_m > total_horizon) {
 872                 return -1;
 873         }
 874
 875         // free-space loss (distance calculation should be changed)
 876         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 877         signal = link_budget - dbloss;
 878         SG_LOG(SG_GENERAL, SG_BULK,
 879                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 880         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 881         return signal;
 882
 883 }
 884
 885 /*** calculate loss due to polarization mismatch
 886 *       this function is only reliable for vertical polarization
 887 *       due to the V-shape of horizontally polarized antennas
 888 ***/
 889 double FGRadioTransmission::polarization_loss() {
 890
 891         double theta_deg;
 892         double roll = fgGetDouble("/orientation/roll-deg");
 893         if (fabs(roll) > 85.0)
 894                 roll = 85.0;
 895         double pitch = fgGetDouble("/orientation/pitch-deg");
 896         if (fabs(pitch) > 85.0)
 897                 pitch = 85.0;
 898         double theta = fabs( atan( sqrt(
 899                 pow(tan(roll * SGD_DEGREES_TO_RADIANS), 2) +
 900                 pow(tan(pitch * SGD_DEGREES_TO_RADIANS), 2) )) * SGD_RADIANS_TO_DEGREES);
 901
 902         if (_polarization == 0)
 903                 theta_deg = 90.0 - theta;
 904         else
 905                 theta_deg = theta;
 906         if (theta_deg > 85.0)   // we don't want to converge into infinity
 907                 theta_deg = 85.0;
 908
 909         double loss = 10 * log10( pow(cos(theta_deg * SGD_DEGREES_TO_RADIANS), 2) );
 910         //cerr << "Polarization loss: " << loss << " dBm " << endl;
 911         return loss;
 912 }
 913
 914