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                         // skip propagation routines entirely
 137                         fgSetString("/sim/messages/atc", text.c_str());
 138                 }
 139                 else if ( _propagation_model == 1 ) {
 140                         // Use free-space, round earth
 141                         double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
 142                         if (signal <= 0.0) {
 143                                 return;
 144                         }
 145                         else {
 146
 147                                 fgSetString("/sim/messages/atc", text.c_str());
 148                                 /** write signal strength above threshold to the property tree
 149                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 150                                 **/
 151                                 _root_node->setDoubleValue("station[0]/signal", signal);
 152                         }
 153                 }
 154                 else if ( _propagation_model == 2 ) {
 155                         // Use ITM propagation model
 156                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 157                         if (signal <= 0.0) {
 158                                 return;
 159                         }
 160                         if ((signal > 0.0) && (signal < 12.0)) {
 161                                 /** for low SNR values implement a way to make the conversation
 162                                 *       hard to understand but audible
 163                                 *       in the real world, the receiver AGC fails to capture the slope
 164                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 165                                 *       the workaround below is more akin to what would happen on a FM transmission
 166                                 *       therefore the correct way would be to work on the volume
 167                                 **/
 168                                 /*
 169                                 string hash_noise = " ";
 170                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 171                                 int t_size = text.size();
 172                                 for (int n = 1; n <= reps; ++n) {
 173                                         int pos = rand() % (t_size -1);
 174                                         text.replace(pos,1, hash_noise);
 175                                 }
 176                                 */
 177                                 double volume = (fabs(signal - 12.0) / 12);
 178                                 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 179                                 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
 180                                 //cerr << "Usable signal at limit: " << signal << endl;
 181                                 fgSetDouble("/sim/sound/voices/voice/volume", volume);
 182                                 fgSetString("/sim/messages/atc", text.c_str());
 183                                 _root_node->setDoubleValue("station[0]/signal", signal);
 184                                 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 185                         }
 186                         else {
 187                                 fgSetString("/sim/messages/atc", text.c_str());
 188                                 /** write signal strength above threshold to the property tree
 189                                 *       to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
 190                                 **/
 191                                 _root_node->setDoubleValue("station[0]/signal", signal);
 192                         }
 193
 194                 }
 195
 196         }
 197
 198 }
 199
 200 /***  Implement radio attenuation
 201           based on the Longley-Rice propagation model
 202 ***/
 203 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 204
 205
 206
 207         /** ITM default parameters
 208                 TODO: take them from tile materials (especially for sea)?
 209         **/
 210         double eps_dielect=15.0;
 211         double sgm_conductivity = 0.005;
 212         double eno = 301.0;
 213         double frq_mhz;
 214         if( (freq < 118.0) || (freq > 137.0) )
 215                 frq_mhz = 125.0;        // sane value, middle of bandplan
 216         else
 217                 frq_mhz = freq;
 218         int radio_climate = 5;          // continental temperate
 219         int pol= _polarization;
 220         double conf = 0.90;     // 90% of situations and time, take into account speed
 221         double rel = 0.90;
 222         double dbloss;
 223         char strmode[150];
 224         int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
 225         double horizons[2];
 226         int errnum;
 227
 228         double clutter_loss = 0.0;      // loss due to vegetation and urban
 229         double tx_pow = _transmitter_power;
 230         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 231         double signal = 0.0;
 232
 233
 234         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 235         double signal_strength = tx_pow - _rx_line_losses - _tx_line_losses + ant_gain;
 236
 237         FGScenery * scenery = globals->get_scenery();
 238
 239         double own_lat = fgGetDouble("/position/latitude-deg");
 240         double own_lon = fgGetDouble("/position/longitude-deg");
 241         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 242         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 243
 244
 245         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 246
 247         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 248         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 249         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 250         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 251
 252
 253         double sender_alt_ft,sender_alt;
 254         double transmitter_height=0.0;
 255         double receiver_height=0.0;
 256         SGGeod sender_pos = pos;
 257
 258         sender_alt_ft = sender_pos.getElevationFt();
 259         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 260         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 261         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 262         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 263
 264         double point_distance= _terrain_sampling_distance;
 265         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 266         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 267         double probe_distance = 0.0;
 268         /** If distance larger than this value (300 km), assume reception imposssible */
 269         if (distance_m > 300000)
 270                 return -1.0;
 271         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 272         if (own_alt > 8000) {
 273                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 274                 SG_LOG(SG_GENERAL, SG_BULK,
 275                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 276                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 277                 signal = link_budget - dbloss;
 278                 return signal;
 279         }
 280
 281
 282         int max_points = (int)floor(distance_m / point_distance);
 283         double delta_last = fmod(distance_m, point_distance);
 284
 285         deque<double> _elevations;
 286         deque<string> materials;
 287
 288
 289         double elevation_under_pilot = 0.0;
 290         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 291                 receiver_height = own_alt - elevation_under_pilot;
 292         }
 293
 294         double elevation_under_sender = 0.0;
 295         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 296                 transmitter_height = sender_alt - elevation_under_sender;
 297         }
 298         else {
 299                 transmitter_height = sender_alt;
 300         }
 301
 302
 303         transmitter_height += _tx_antenna_height;
 304         receiver_height += _rx_antenna_height;
 305
 306
 307         SG_LOG(SG_GENERAL, SG_BULK,
 308                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 309         //cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 310         _root_node->setDoubleValue("station[0]/rx-height", receiver_height);
 311         _root_node->setDoubleValue("station[0]/tx-height", transmitter_height);
 312         _root_node->setDoubleValue("station[0]/distance", distance_m);
 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                 if (delta_last > (point_distance / 2) )                 // only add last point if it's farther than half point_distance
 358                         _elevations.push_back(elevation_under_sender);
 359         }
 360         else {
 361                 _elevations.push_back(elevation_under_pilot);
 362                 if (delta_last > (point_distance / 2) )
 363                         _elevations.push_front(elevation_under_sender);
 364         }
 365
 366
 367         double num_points= (double)_elevations.size();
 368
 369         _elevations.push_front(point_distance);
 370         _elevations.push_front(num_points -1);
 371         int size = _elevations.size();
 372         double itm_elev[size];
 373         for(int i=0;i<size;i++) {
 374                 itm_elev[i]=_elevations[i];
 375                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 376         }
 377
 378         if((transmission_type == 3) || (transmission_type == 4)) {
 379                 // the sender and receiver roles are switched
 380                 point_to_point(itm_elev, receiver_height, transmitter_height,
 381                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 382                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 383                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 384                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
 385         }
 386         else {
 387                 point_to_point(itm_elev, transmitter_height, receiver_height,
 388                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 389                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 390                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 391                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 392         }
 393
 394         double pol_loss = 0.0;
 395         if (_polarization == 1) {
 396                 pol_loss = polarization_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         _root_node->setDoubleValue("station[0]/link-budget", link_budget);
 402         _root_node->setDoubleValue("station[0]/terrain-attenuation", dbloss);
 403         _root_node->setStringValue("station[0]/prop-mode", strmode);
 404         _root_node->setDoubleValue("station[0]/clutter-attenuation", clutter_loss);
 405         _root_node->setDoubleValue("station[0]/polarization-attenuation", pol_loss);
 406         //cerr << "Clutter loss: " << clutter_loss << endl;
 407         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 408         //      return -1;
 409         signal = link_budget - dbloss - clutter_loss + pol_loss;
 410         double signal_strength_dbm = signal_strength - dbloss - clutter_loss + pol_loss;
 411         double field_strength_uV = dbm_to_microvolt(signal_strength_dbm);
 412         _root_node->setDoubleValue("station[0]/signal-dbm", signal_strength_dbm);
 413         _root_node->setDoubleValue("station[0]/field-strength-uV", field_strength_uV);
 414         return signal;
 415
 416 }
 417
 418 /*** Calculate losses due to vegetation and urban clutter (WIP)
 419 *        We are only worried about clutter loss, terrain influence
 420 *        on the first Fresnel zone is calculated in the ITM functions
 421 ***/
 422 void FGRadioTransmission::clutterLoss(double freq, double distance_m, double itm_elev[], deque<string> materials,
 423         double transmitter_height, double receiver_height, int p_mode,
 424         double horizons[], double &clutter_loss) {
 425
 426         distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
 427
 428         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 429                 int mat = 0;
 430                 int j=1;
 431                 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
 432
 433                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 434                         double clutter_density = 0.0;   // percent of reflected wave
 435                         get_material_properties(materials[mat], clutter_height, clutter_density);
 436
 437                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 438                         // First Fresnel radius
 439                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 440
 441                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 442
 443                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 444                         double d1 = j * itm_elev[1];
 445                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 446                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 447                         }
 448                         double ray_height = (grad * d1) + min_elev;
 449
 450                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 451                         double intrusion = fabs(clearance);
 452
 453                         if (clearance >= 0) {
 454                                 // no losses
 455                         }
 456                         else if (clearance < 0 && (intrusion < clutter_height)) {
 457
 458                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 459                         }
 460                         else if (clearance < 0 && (intrusion > clutter_height)) {
 461                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 462                         }
 463                         else {
 464                                 // no losses
 465                         }
 466                         j++;
 467                         mat++;
 468                 }
 469
 470         }
 471         else if (p_mode == 1) {         // diffraction
 472
 473                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 474                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
 475                         int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
 476                         //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
 477                         int last = 1;
 478                         /** perform the first pass */
 479                         int mat = 0;
 480                         int j=1;
 481                         for (int k=3;k < num_points_1st + 2;k++) {
 482                                 if (num_points_1st < 1)
 483                                         break;
 484                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 485                                 double clutter_density = 0.0;   // percent of reflected wave
 486                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 487
 488                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 489                                 // First Fresnel radius
 490                                 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) );
 491
 492                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 493
 494                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 495                                 double d1 = j * itm_elev[1];
 496                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 497                                         d1 = (num_points_1st - j) * itm_elev[1];
 498                                 }
 499                                 double ray_height = (grad * d1) + min_elev;
 500
 501                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 502                                 double intrusion = fabs(clearance);
 503
 504                                 if (clearance >= 0) {
 505                                         // no losses
 506                                 }
 507                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 508
 509                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 510                                 }
 511                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 512                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 513                                 }
 514                                 else {
 515                                         // no losses
 516                                 }
 517                                 j++;
 518                                 mat++;
 519                                 last = k;
 520                         }
 521
 522                         /** and the second pass */
 523                         mat +=1;
 524                         j =1; // first point is diffraction edge, 2nd the RX elevation
 525                         for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
 526                                 if (num_points_2nd < 1)
 527                                         break;
 528                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 529                                 double clutter_density = 0.0;   // percent of reflected wave
 530                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 531
 532                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 533                                 // First Fresnel radius
 534                                 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) );
 535
 536                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 537
 538                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 539                                 double d1 = j * itm_elev[1];
 540                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 541                                         d1 = (num_points_2nd - j) * itm_elev[1];
 542                                 }
 543                                 double ray_height = (grad * d1) + min_elev;
 544
 545                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 546                                 double intrusion = fabs(clearance);
 547
 548                                 if (clearance >= 0) {
 549                                         // no losses
 550                                 }
 551                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 552
 553                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 554                                 }
 555                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 556                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 557                                 }
 558                                 else {
 559                                         // no losses
 560                                 }
 561                                 j++;
 562                                 mat++;
 563                         }
 564
 565                 }
 566                 else {  // double horizon: same as single horizon, except there are 3 segments
 567
 568                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
 569                         int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
 570                         int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
 571                         //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
 572                         //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
 573                         int last = 1;
 574                         /** perform the first pass */
 575                         int mat = 0;
 576                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 577                         for (int k=3;k < num_points_1st +2;k++) {
 578                                 if (num_points_1st < 1)
 579                                         break;
 580                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 581                                 double clutter_density = 0.0;   // percent of reflected wave
 582                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 583
 584                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 585                                 // First Fresnel radius
 586                                 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) );
 587
 588                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 589
 590                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 591                                 double d1 = j * itm_elev[1];
 592                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 593                                         d1 = (num_points_1st - j) * itm_elev[1];
 594                                 }
 595                                 double ray_height = (grad * d1) + min_elev;
 596
 597                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 598                                 double intrusion = fabs(clearance);
 599
 600                                 if (clearance >= 0) {
 601                                         // no losses
 602                                 }
 603                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 604
 605                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 606                                 }
 607                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 608                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 609                                 }
 610                                 else {
 611                                         // no losses
 612                                 }
 613                                 j++;
 614                                 last = k;
 615                         }
 616                         mat +=1;
 617                         /** and the second pass */
 618                         int last2=1;
 619                         j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 620                         for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
 621                                 if (num_points_2nd < 1)
 622                                         break;
 623                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 624                                 double clutter_density = 0.0;   // percent of reflected wave
 625                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 626
 627                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
 628                                 // First Fresnel radius
 629                                 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) );
 630
 631                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 632
 633                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
 634                                 double d1 = j * itm_elev[1];
 635                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
 636                                         d1 = (num_points_2nd - j) * itm_elev[1];
 637                                 }
 638                                 double ray_height = (grad * d1) + min_elev;
 639
 640                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 641                                 double intrusion = fabs(clearance);
 642
 643                                 if (clearance >= 0) {
 644                                         // no losses
 645                                 }
 646                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 647
 648                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 649                                 }
 650                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 651                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 652                                 }
 653                                 else {
 654                                         // no losses
 655                                 }
 656                                 j++;
 657                                 mat++;
 658                                 last2 = k;
 659                         }
 660
 661                         /** third and final pass */
 662                         mat +=1;
 663                         j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 664                         for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
 665                                 if (num_points_3rd < 1)
 666                                         break;
 667                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 668                                 double clutter_density = 0.0;   // percent of reflected wave
 669                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 670
 671                                 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 672                                 // First Fresnel radius
 673                                 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) );
 674
 675
 676                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 677
 678                                 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 679                                 double d1 = j * itm_elev[1];
 680                                 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 681                                         d1 = (num_points_3rd - j) * itm_elev[1];
 682                                 }
 683                                 double ray_height = (grad * d1) + min_elev;
 684
 685                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 686                                 double intrusion = fabs(clearance);
 687
 688                                 if (clearance >= 0) {
 689                                         // no losses
 690                                 }
 691                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 692
 693                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 694                                 }
 695                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 696                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 697                                 }
 698                                 else {
 699                                         // no losses
 700                                 }
 701                                 j++;
 702                                 mat++;
 703
 704                         }
 705
 706                 }
 707         }
 708         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now...
 709                 clutter_loss = 0.0;
 710         }
 711
 712 }
 713
 714 /***    Temporary material properties database
 715 *               height: median clutter height
 716 *               density: radiowave attenuation factor
 717 ***/
 718 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 719
 720         if(mat_name == "Landmass") {
 721                 height = 15.0;
 722                 density = 0.2;
 723         }
 724
 725         else if(mat_name == "SomeSort") {
 726                 height = 15.0;
 727                 density = 0.2;
 728         }
 729
 730         else if(mat_name == "Island") {
 731                 height = 15.0;
 732                 density = 0.2;
 733         }
 734         else if(mat_name == "Default") {
 735                 height = 15.0;
 736                 density = 0.2;
 737         }
 738         else if(mat_name == "EvergreenBroadCover") {
 739                 height = 20.0;
 740                 density = 0.2;
 741         }
 742         else if(mat_name == "EvergreenForest") {
 743                 height = 20.0;
 744                 density = 0.2;
 745         }
 746         else if(mat_name == "DeciduousBroadCover") {
 747                 height = 15.0;
 748                 density = 0.3;
 749         }
 750         else if(mat_name == "DeciduousForest") {
 751                 height = 15.0;
 752                 density = 0.3;
 753         }
 754         else if(mat_name == "MixedForestCover") {
 755                 height = 20.0;
 756                 density = 0.25;
 757         }
 758         else if(mat_name == "MixedForest") {
 759                 height = 15.0;
 760                 density = 0.25;
 761         }
 762         else if(mat_name == "RainForest") {
 763                 height = 25.0;
 764                 density = 0.55;
 765         }
 766         else if(mat_name == "EvergreenNeedleCover") {
 767                 height = 15.0;
 768                 density = 0.2;
 769         }
 770         else if(mat_name == "WoodedTundraCover") {
 771                 height = 5.0;
 772                 density = 0.15;
 773         }
 774         else if(mat_name == "DeciduousNeedleCover") {
 775                 height = 5.0;
 776                 density = 0.2;
 777         }
 778         else if(mat_name == "ScrubCover") {
 779                 height = 3.0;
 780                 density = 0.15;
 781         }
 782         else if(mat_name == "BuiltUpCover") {
 783                 height = 30.0;
 784                 density = 0.7;
 785         }
 786         else if(mat_name == "Urban") {
 787                 height = 30.0;
 788                 density = 0.7;
 789         }
 790         else if(mat_name == "Construction") {
 791                 height = 30.0;
 792                 density = 0.7;
 793         }
 794         else if(mat_name == "Industrial") {
 795                 height = 30.0;
 796                 density = 0.7;
 797         }
 798         else if(mat_name == "Port") {
 799                 height = 30.0;
 800                 density = 0.7;
 801         }
 802         else if(mat_name == "Town") {
 803                 height = 10.0;
 804                 density = 0.5;
 805         }
 806         else if(mat_name == "SubUrban") {
 807                 height = 10.0;
 808                 density = 0.5;
 809         }
 810         else if(mat_name == "CropWoodCover") {
 811                 height = 10.0;
 812                 density = 0.1;
 813         }
 814         else if(mat_name == "CropWood") {
 815                 height = 10.0;
 816                 density = 0.1;
 817         }
 818         else if(mat_name == "AgroForest") {
 819                 height = 10.0;
 820                 density = 0.1;
 821         }
 822         else {
 823                 height = 0.0;
 824                 density = 0.0;
 825         }
 826
 827 }
 828
 829 /*** implement simple LOS propagation model (WIP)
 830 ***/
 831 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 832         double frq_mhz;
 833         if( (freq < 118.0) || (freq > 137.0) )
 834                 frq_mhz = 125.0;        // sane value, middle of bandplan
 835         else
 836                 frq_mhz = freq;
 837         double dbloss;
 838         double tx_pow = _transmitter_power;
 839         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 840         double signal = 0.0;
 841
 842         double sender_alt_ft,sender_alt;
 843         double transmitter_height=0.0;
 844         double receiver_height=0.0;
 845         double own_lat = fgGetDouble("/position/latitude-deg");
 846         double own_lon = fgGetDouble("/position/longitude-deg");
 847         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 848         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 849
 850
 851         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 852
 853         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 854
 855         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 856
 857         SGGeod sender_pos = pos;
 858
 859         sender_alt_ft = sender_pos.getElevationFt();
 860         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 861
 862         receiver_height = own_alt;
 863         transmitter_height = sender_alt;
 864
 865         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 866
 867
 868         transmitter_height += _tx_antenna_height;
 869         receiver_height += _rx_antenna_height;
 870
 871
 872         /** radio horizon calculation with wave bending k=4/3 */
 873         double receiver_horizon = 4.12 * sqrt(receiver_height);
 874         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 875         double total_horizon = receiver_horizon + transmitter_horizon;
 876
 877         if (distance_m > total_horizon) {
 878                 return -1;
 879         }
 880         double pol_loss = 0.0;
 881         if (_polarization == 1) {
 882                 pol_loss = polarization_loss();
 883         }
 884         // free-space loss (distance calculation should be changed)
 885         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 886         signal = link_budget - dbloss + pol_loss;
 887         SG_LOG(SG_GENERAL, SG_BULK,
 888                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 889         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 890         return signal;
 891
 892 }
 893
 894 /*** calculate loss due to polarization mismatch
 895 *       this function is only reliable for vertical polarization
 896 *       due to the V-shape of horizontally polarized antennas
 897 ***/
 898 double FGRadioTransmission::polarization_loss() {
 899
 900         double theta_deg;
 901         double roll = fgGetDouble("/orientation/roll-deg");
 902         if (fabs(roll) > 85.0)
 903                 roll = 85.0;
 904         double pitch = fgGetDouble("/orientation/pitch-deg");
 905         if (fabs(pitch) > 85.0)
 906                 pitch = 85.0;
 907         double theta = fabs( atan( sqrt(
 908                 pow(tan(roll * SGD_DEGREES_TO_RADIANS), 2) +
 909                 pow(tan(pitch * SGD_DEGREES_TO_RADIANS), 2) )) * SGD_RADIANS_TO_DEGREES);
 910
 911         if (_polarization == 0)
 912                 theta_deg = 90.0 - theta;
 913         else
 914                 theta_deg = theta;
 915         if (theta_deg > 85.0)   // we don't want to converge into infinity
 916                 theta_deg = 85.0;
 917
 918         double loss = 10 * log10( pow(cos(theta_deg * SGD_DEGREES_TO_RADIANS), 2) );
 919         //cerr << "Polarization loss: " << loss << " dBm " << endl;
 920         return loss;
 921 }
 922
 923
 924 double FGRadioTransmission::power_to_dbm(double power_watt) {
 925         return 10 * log10(1000 * power_watt);   // returns dbm
 926 }
 927
 928 double FGRadioTransmission::dbm_to_power(double dbm) {
 929         return exp( (dbm-30) * log(10) / 10);   // returns Watts
 930 }
 931
 932 double FGRadioTransmission::dbm_to_microvolt(double dbm) {
 933         return sqrt(dbm_to_power(dbm) * 50) * 1000000;  // returns microvolts
 934 }
 935
 936