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 += 4.0;
 123                 _tx_antenna_height += 30.0;
 124                 _tx_antenna_gain += 2.0;
 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
 149                         }
 150                 }
 151                 else if ( _propagation_model == 2 ) {
 152                         // Use ITM propagation model
 153                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 154                         if (signal <= 0.0) {
 155                                 return;
 156                         }
 157                         if ((signal > 0.0) && (signal < 12.0)) {
 158                                 /** for low SNR values implement a way to make the conversation
 159                                 *       hard to understand but audible
 160                                 *       in the real world, the receiver AGC fails to capture the slope
 161                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 162                                 *       the workaround below is more akin to what would happen on a FM transmission
 163                                 *       therefore the correct way would be to work on the volume
 164                                 **/
 165                                 /*
 166                                 string hash_noise = " ";
 167                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 168                                 int t_size = text.size();
 169                                 for (int n = 1; n <= reps; ++n) {
 170                                         int pos = rand() % (t_size -1);
 171                                         text.replace(pos,1, hash_noise);
 172                                 }
 173                                 */
 174                                 double volume = (fabs(signal - 12.0) / 12);
 175                                 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 176                                 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
 177                                 //cerr << "Usable signal at limit: " << signal << endl;
 178                                 fgSetDouble("/sim/sound/voices/voice/volume", volume);
 179                                 fgSetString("/sim/messages/atc", text.c_str());
 180                                 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 181                         }
 182                         else {
 183                                 fgSetString("/sim/messages/atc", text.c_str());
 184                         }
 185
 186                 }
 187
 188         }
 189
 190 }
 191
 192 /***  Implement radio attenuation
 193           based on the Longley-Rice propagation model
 194 ***/
 195 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 196
 197
 198
 199         /** ITM default parameters
 200                 TODO: take them from tile materials (especially for sea)?
 201         **/
 202         double eps_dielect=15.0;
 203         double sgm_conductivity = 0.005;
 204         double eno = 301.0;
 205         double frq_mhz;
 206         if( (freq < 118.0) || (freq > 137.0) )
 207                 frq_mhz = 125.0;        // sane value, middle of bandplan
 208         else
 209                 frq_mhz = freq;
 210         int radio_climate = 5;          // continental temperate
 211         int pol= _polarization;
 212         double conf = 0.90;     // 90% of situations and time, take into account speed
 213         double rel = 0.90;
 214         double dbloss;
 215         char strmode[150];
 216         int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
 217         double horizons[2];
 218         int errnum;
 219
 220         double clutter_loss = 0.0;      // loss due to vegetation and urban
 221         double tx_pow = _transmitter_power;
 222         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 223         double signal = 0.0;
 224
 225
 226         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 227         double signal_strength = tx_pow - _rx_line_losses - _tx_line_losses + ant_gain;
 228         double tx_erp = dbm_to_watt(tx_pow + _tx_antenna_gain - _tx_line_losses);
 229
 230
 231         FGScenery * scenery = globals->get_scenery();
 232
 233         double own_lat = fgGetDouble("/position/latitude-deg");
 234         double own_lon = fgGetDouble("/position/longitude-deg");
 235         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 236         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 237
 238
 239         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 240
 241         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 242         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 243         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 244         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 245
 246
 247         double sender_alt_ft,sender_alt;
 248         double transmitter_height=0.0;
 249         double receiver_height=0.0;
 250         SGGeod sender_pos = pos;
 251
 252         sender_alt_ft = sender_pos.getElevationFt();
 253         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 254         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 255         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 256         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 257
 258         double point_distance= _terrain_sampling_distance;
 259         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 260         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 261         double probe_distance = 0.0;
 262         /** If distance larger than this value (300 km), assume reception imposssible */
 263         if (distance_m > 300000)
 264                 return -1.0;
 265         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 266         if (own_alt > 8000) {
 267                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 268                 SG_LOG(SG_GENERAL, SG_BULK,
 269                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 270                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 271                 signal = link_budget - dbloss;
 272                 return signal;
 273         }
 274
 275
 276         int max_points = (int)floor(distance_m / point_distance);
 277         double delta_last = fmod(distance_m, point_distance);
 278
 279         deque<double> _elevations;
 280         deque<string> materials;
 281
 282
 283         double elevation_under_pilot = 0.0;
 284         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 285                 receiver_height = own_alt - elevation_under_pilot;
 286         }
 287
 288         double elevation_under_sender = 0.0;
 289         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 290                 transmitter_height = sender_alt - elevation_under_sender;
 291         }
 292         else {
 293                 transmitter_height = sender_alt;
 294         }
 295
 296
 297         transmitter_height += _tx_antenna_height;
 298         receiver_height += _rx_antenna_height;
 299
 300
 301         SG_LOG(SG_GENERAL, SG_BULK,
 302                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 303         //cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 304         _root_node->setDoubleValue("station[0]/rx-height", receiver_height);
 305         _root_node->setDoubleValue("station[0]/tx-height", transmitter_height);
 306         _root_node->setDoubleValue("station[0]/distance", distance_m / 1000);
 307
 308         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 309
 310         while (_elevations.size() <= e_size) {
 311                 probe_distance += point_distance;
 312                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 313                 const SGMaterial *mat = 0;
 314                 double elevation_m = 0.0;
 315
 316                 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
 317                         if((transmission_type == 3) || (transmission_type == 4)) {
 318                                 _elevations.push_back(elevation_m);
 319                                 if(mat) {
 320                                         const std::vector<string> mat_names = mat->get_names();
 321                                         materials.push_back(mat_names[0]);
 322                                 }
 323                                 else {
 324                                         materials.push_back("None");
 325                                 }
 326                         }
 327                         else {
 328                                  _elevations.push_front(elevation_m);
 329                                  if(mat) {
 330                                          const std::vector<string> mat_names = mat->get_names();
 331                                          materials.push_front(mat_names[0]);
 332                                 }
 333                                 else {
 334                                         materials.push_front("None");
 335                                 }
 336                         }
 337                 }
 338                 else {
 339                         if((transmission_type == 3) || (transmission_type == 4)) {
 340                                 _elevations.push_back(0.0);
 341                                 materials.push_back("None");
 342                         }
 343                         else {
 344                                 _elevations.push_front(0.0);
 345                                 materials.push_front("None");
 346                         }
 347                 }
 348         }
 349         if((transmission_type == 3) || (transmission_type == 4)) {
 350                 _elevations.push_front(elevation_under_pilot);
 351                 if (delta_last > (point_distance / 2) )                 // only add last point if it's farther than half point_distance
 352                         _elevations.push_back(elevation_under_sender);
 353         }
 354         else {
 355                 _elevations.push_back(elevation_under_pilot);
 356                 if (delta_last > (point_distance / 2) )
 357                         _elevations.push_front(elevation_under_sender);
 358         }
 359
 360
 361         double num_points= (double)_elevations.size();
 362
 363         _elevations.push_front(point_distance);
 364         _elevations.push_front(num_points -1);
 365         int size = _elevations.size();
 366         double itm_elev[size];
 367         for(int i=0;i<size;i++) {
 368                 itm_elev[i]=_elevations[i];
 369                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 370         }
 371
 372         if((transmission_type == 3) || (transmission_type == 4)) {
 373                 // the sender and receiver roles are switched
 374                 point_to_point(itm_elev, receiver_height, transmitter_height,
 375                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 376                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 377                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 378                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
 379         }
 380         else {
 381                 point_to_point(itm_elev, transmitter_height, receiver_height,
 382                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 383                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 384                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 385                         clutterLoss(frq_mhz, distance_m, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 386         }
 387
 388         double pol_loss = 0.0;
 389         if (_polarization == 1) {
 390                 pol_loss = polarization_loss();
 391         }
 392         SG_LOG(SG_GENERAL, SG_BULK,
 393                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 394         //cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 395         _root_node->setDoubleValue("station[0]/link-budget", link_budget);
 396         _root_node->setDoubleValue("station[0]/terrain-attenuation", dbloss);
 397         _root_node->setStringValue("station[0]/prop-mode", strmode);
 398         _root_node->setDoubleValue("station[0]/clutter-attenuation", clutter_loss);
 399         _root_node->setDoubleValue("station[0]/polarization-attenuation", pol_loss);
 400         //cerr << "Clutter loss: " << clutter_loss << endl;
 401         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 402         //      return -1;
 403         signal = link_budget - dbloss - clutter_loss + pol_loss;
 404         double signal_strength_dbm = signal_strength - dbloss - clutter_loss + pol_loss;
 405         double field_strength_uV = dbm_to_microvolt(signal_strength_dbm);
 406         _root_node->setDoubleValue("station[0]/signal-dbm", signal_strength_dbm);
 407         _root_node->setDoubleValue("station[0]/field-strength-uV", field_strength_uV);
 408         _root_node->setDoubleValue("station[0]/signal", signal);
 409         _root_node->setDoubleValue("station[0]/tx-erp", tx_erp);
 410         return signal;
 411
 412 }
 413
 414 /*** Calculate losses due to vegetation and urban clutter (WIP)
 415 *        We are only worried about clutter loss, terrain influence
 416 *        on the first Fresnel zone is calculated in the ITM functions
 417 ***/
 418 void FGRadioTransmission::clutterLoss(double freq, double distance_m, double itm_elev[], deque<string> materials,
 419         double transmitter_height, double receiver_height, int p_mode,
 420         double horizons[], double &clutter_loss) {
 421
 422         distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
 423
 424         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 425                 int mat = 0;
 426                 int j=1;
 427                 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
 428
 429                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 430                         double clutter_density = 0.0;   // percent of reflected wave
 431                         get_material_properties(materials[mat], clutter_height, clutter_density);
 432
 433                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 434                         // First Fresnel radius
 435                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 436
 437                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 438
 439                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 440                         double d1 = j * itm_elev[1];
 441                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 442                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 443                         }
 444                         double ray_height = (grad * d1) + min_elev;
 445
 446                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 447                         double intrusion = fabs(clearance);
 448
 449                         if (clearance >= 0) {
 450                                 // no losses
 451                         }
 452                         else if (clearance < 0 && (intrusion < clutter_height)) {
 453
 454                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 455                         }
 456                         else if (clearance < 0 && (intrusion > clutter_height)) {
 457                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 458                         }
 459                         else {
 460                                 // no losses
 461                         }
 462                         j++;
 463                         mat++;
 464                 }
 465
 466         }
 467         else if (p_mode == 1) {         // diffraction
 468
 469                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 470                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
 471                         int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
 472                         //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
 473                         int last = 1;
 474                         /** perform the first pass */
 475                         int mat = 0;
 476                         int j=1;
 477                         for (int k=3;k < num_points_1st + 2;k++) {
 478                                 if (num_points_1st < 1)
 479                                         break;
 480                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 481                                 double clutter_density = 0.0;   // percent of reflected wave
 482                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 483
 484                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 485                                 // First Fresnel radius
 486                                 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) );
 487
 488                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 489
 490                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 491                                 double d1 = j * itm_elev[1];
 492                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 493                                         d1 = (num_points_1st - j) * itm_elev[1];
 494                                 }
 495                                 double ray_height = (grad * d1) + min_elev;
 496
 497                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 498                                 double intrusion = fabs(clearance);
 499
 500                                 if (clearance >= 0) {
 501                                         // no losses
 502                                 }
 503                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 504
 505                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 506                                 }
 507                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 508                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 509                                 }
 510                                 else {
 511                                         // no losses
 512                                 }
 513                                 j++;
 514                                 mat++;
 515                                 last = k;
 516                         }
 517
 518                         /** and the second pass */
 519                         mat +=1;
 520                         j =1; // first point is diffraction edge, 2nd the RX elevation
 521                         for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
 522                                 if (num_points_2nd < 1)
 523                                         break;
 524                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 525                                 double clutter_density = 0.0;   // percent of reflected wave
 526                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 527
 528                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 529                                 // First Fresnel radius
 530                                 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) );
 531
 532                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 533
 534                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 535                                 double d1 = j * itm_elev[1];
 536                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 537                                         d1 = (num_points_2nd - j) * itm_elev[1];
 538                                 }
 539                                 double ray_height = (grad * d1) + min_elev;
 540
 541                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 542                                 double intrusion = fabs(clearance);
 543
 544                                 if (clearance >= 0) {
 545                                         // no losses
 546                                 }
 547                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 548
 549                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 550                                 }
 551                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 552                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 553                                 }
 554                                 else {
 555                                         // no losses
 556                                 }
 557                                 j++;
 558                                 mat++;
 559                         }
 560
 561                 }
 562                 else {  // double horizon: same as single horizon, except there are 3 segments
 563
 564                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
 565                         int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
 566                         int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
 567                         //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
 568                         //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
 569                         int last = 1;
 570                         /** perform the first pass */
 571                         int mat = 0;
 572                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 573                         for (int k=3;k < num_points_1st +2;k++) {
 574                                 if (num_points_1st < 1)
 575                                         break;
 576                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 577                                 double clutter_density = 0.0;   // percent of reflected wave
 578                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 579
 580                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 581                                 // First Fresnel radius
 582                                 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) );
 583
 584                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 585
 586                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 587                                 double d1 = j * itm_elev[1];
 588                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 589                                         d1 = (num_points_1st - j) * itm_elev[1];
 590                                 }
 591                                 double ray_height = (grad * d1) + min_elev;
 592
 593                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 594                                 double intrusion = fabs(clearance);
 595
 596                                 if (clearance >= 0) {
 597                                         // no losses
 598                                 }
 599                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 600
 601                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 602                                 }
 603                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 604                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 605                                 }
 606                                 else {
 607                                         // no losses
 608                                 }
 609                                 j++;
 610                                 last = k;
 611                         }
 612                         mat +=1;
 613                         /** and the second pass */
 614                         int last2=1;
 615                         j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 616                         for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
 617                                 if (num_points_2nd < 1)
 618                                         break;
 619                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 620                                 double clutter_density = 0.0;   // percent of reflected wave
 621                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 622
 623                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
 624                                 // First Fresnel radius
 625                                 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) );
 626
 627                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 628
 629                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
 630                                 double d1 = j * itm_elev[1];
 631                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
 632                                         d1 = (num_points_2nd - j) * itm_elev[1];
 633                                 }
 634                                 double ray_height = (grad * d1) + min_elev;
 635
 636                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 637                                 double intrusion = fabs(clearance);
 638
 639                                 if (clearance >= 0) {
 640                                         // no losses
 641                                 }
 642                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 643
 644                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 645                                 }
 646                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 647                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 648                                 }
 649                                 else {
 650                                         // no losses
 651                                 }
 652                                 j++;
 653                                 mat++;
 654                                 last2 = k;
 655                         }
 656
 657                         /** third and final pass */
 658                         mat +=1;
 659                         j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 660                         for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
 661                                 if (num_points_3rd < 1)
 662                                         break;
 663                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 664                                 double clutter_density = 0.0;   // percent of reflected wave
 665                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 666
 667                                 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 668                                 // First Fresnel radius
 669                                 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) );
 670
 671
 672                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 673
 674                                 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 675                                 double d1 = j * itm_elev[1];
 676                                 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 677                                         d1 = (num_points_3rd - j) * itm_elev[1];
 678                                 }
 679                                 double ray_height = (grad * d1) + min_elev;
 680
 681                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 682                                 double intrusion = fabs(clearance);
 683
 684                                 if (clearance >= 0) {
 685                                         // no losses
 686                                 }
 687                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 688
 689                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 690                                 }
 691                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 692                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 693                                 }
 694                                 else {
 695                                         // no losses
 696                                 }
 697                                 j++;
 698                                 mat++;
 699
 700                         }
 701
 702                 }
 703         }
 704         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now...
 705                 clutter_loss = 0.0;
 706         }
 707
 708 }
 709
 710 /***    Temporary material properties database
 711 *               height: median clutter height
 712 *               density: radiowave attenuation factor
 713 ***/
 714 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 715
 716         if(mat_name == "Landmass") {
 717                 height = 15.0;
 718                 density = 0.2;
 719         }
 720
 721         else if(mat_name == "SomeSort") {
 722                 height = 15.0;
 723                 density = 0.2;
 724         }
 725
 726         else if(mat_name == "Island") {
 727                 height = 15.0;
 728                 density = 0.2;
 729         }
 730         else if(mat_name == "Default") {
 731                 height = 15.0;
 732                 density = 0.2;
 733         }
 734         else if(mat_name == "EvergreenBroadCover") {
 735                 height = 20.0;
 736                 density = 0.2;
 737         }
 738         else if(mat_name == "EvergreenForest") {
 739                 height = 20.0;
 740                 density = 0.2;
 741         }
 742         else if(mat_name == "DeciduousBroadCover") {
 743                 height = 15.0;
 744                 density = 0.3;
 745         }
 746         else if(mat_name == "DeciduousForest") {
 747                 height = 15.0;
 748                 density = 0.3;
 749         }
 750         else if(mat_name == "MixedForestCover") {
 751                 height = 20.0;
 752                 density = 0.25;
 753         }
 754         else if(mat_name == "MixedForest") {
 755                 height = 15.0;
 756                 density = 0.25;
 757         }
 758         else if(mat_name == "RainForest") {
 759                 height = 25.0;
 760                 density = 0.55;
 761         }
 762         else if(mat_name == "EvergreenNeedleCover") {
 763                 height = 15.0;
 764                 density = 0.2;
 765         }
 766         else if(mat_name == "WoodedTundraCover") {
 767                 height = 5.0;
 768                 density = 0.15;
 769         }
 770         else if(mat_name == "DeciduousNeedleCover") {
 771                 height = 5.0;
 772                 density = 0.2;
 773         }
 774         else if(mat_name == "ScrubCover") {
 775                 height = 3.0;
 776                 density = 0.15;
 777         }
 778         else if(mat_name == "BuiltUpCover") {
 779                 height = 30.0;
 780                 density = 0.7;
 781         }
 782         else if(mat_name == "Urban") {
 783                 height = 30.0;
 784                 density = 0.7;
 785         }
 786         else if(mat_name == "Construction") {
 787                 height = 30.0;
 788                 density = 0.7;
 789         }
 790         else if(mat_name == "Industrial") {
 791                 height = 30.0;
 792                 density = 0.7;
 793         }
 794         else if(mat_name == "Port") {
 795                 height = 30.0;
 796                 density = 0.7;
 797         }
 798         else if(mat_name == "Town") {
 799                 height = 10.0;
 800                 density = 0.5;
 801         }
 802         else if(mat_name == "SubUrban") {
 803                 height = 10.0;
 804                 density = 0.5;
 805         }
 806         else if(mat_name == "CropWoodCover") {
 807                 height = 10.0;
 808                 density = 0.1;
 809         }
 810         else if(mat_name == "CropWood") {
 811                 height = 10.0;
 812                 density = 0.1;
 813         }
 814         else if(mat_name == "AgroForest") {
 815                 height = 10.0;
 816                 density = 0.1;
 817         }
 818         else {
 819                 height = 0.0;
 820                 density = 0.0;
 821         }
 822
 823 }
 824
 825 /*** implement simple LOS propagation model (WIP)
 826 ***/
 827 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 828         double frq_mhz;
 829         if( (freq < 118.0) || (freq > 137.0) )
 830                 frq_mhz = 125.0;        // sane value, middle of bandplan
 831         else
 832                 frq_mhz = freq;
 833         double dbloss;
 834         double tx_pow = _transmitter_power;
 835         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 836         double signal = 0.0;
 837
 838         double sender_alt_ft,sender_alt;
 839         double transmitter_height=0.0;
 840         double receiver_height=0.0;
 841         double own_lat = fgGetDouble("/position/latitude-deg");
 842         double own_lon = fgGetDouble("/position/longitude-deg");
 843         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 844         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 845
 846
 847         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 848
 849         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 850
 851         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 852
 853         SGGeod sender_pos = pos;
 854
 855         sender_alt_ft = sender_pos.getElevationFt();
 856         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 857
 858         receiver_height = own_alt;
 859         transmitter_height = sender_alt;
 860
 861         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 862
 863
 864         transmitter_height += _tx_antenna_height;
 865         receiver_height += _rx_antenna_height;
 866
 867
 868         /** radio horizon calculation with wave bending k=4/3 */
 869         double receiver_horizon = 4.12 * sqrt(receiver_height);
 870         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 871         double total_horizon = receiver_horizon + transmitter_horizon;
 872
 873         if (distance_m > total_horizon) {
 874                 return -1;
 875         }
 876         double pol_loss = 0.0;
 877         if (_polarization == 1) {
 878                 pol_loss = polarization_loss();
 879         }
 880         // free-space loss (distance calculation should be changed)
 881         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 882         signal = link_budget - dbloss + pol_loss;
 883         SG_LOG(SG_GENERAL, SG_BULK,
 884                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 885         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 886         return signal;
 887
 888 }
 889
 890 /*** calculate loss due to polarization mismatch
 891 *       this function is only reliable for vertical polarization
 892 *       due to the V-shape of horizontally polarized antennas
 893 ***/
 894 double FGRadioTransmission::polarization_loss() {
 895
 896         double theta_deg;
 897         double roll = fgGetDouble("/orientation/roll-deg");
 898         if (fabs(roll) > 85.0)
 899                 roll = 85.0;
 900         double pitch = fgGetDouble("/orientation/pitch-deg");
 901         if (fabs(pitch) > 85.0)
 902                 pitch = 85.0;
 903         double theta = fabs( atan( sqrt(
 904                 pow(tan(roll * SGD_DEGREES_TO_RADIANS), 2) +
 905                 pow(tan(pitch * SGD_DEGREES_TO_RADIANS), 2) )) * SGD_RADIANS_TO_DEGREES);
 906
 907         if (_polarization == 0)
 908                 theta_deg = 90.0 - theta;
 909         else
 910                 theta_deg = theta;
 911         if (theta_deg > 85.0)   // we don't want to converge into infinity
 912                 theta_deg = 85.0;
 913
 914         double loss = 10 * log10( pow(cos(theta_deg * SGD_DEGREES_TO_RADIANS), 2) );
 915         //cerr << "Polarization loss: " << loss << " dBm " << endl;
 916         return loss;
 917 }
 918
 919
 920 double FGRadioTransmission::watt_to_dbm(double power_watt) {
 921         return 10 * log10(1000 * power_watt);   // returns dbm
 922 }
 923
 924 double FGRadioTransmission::dbm_to_watt(double dbm) {
 925         return exp( (dbm-30) * log(10) / 10);   // returns Watts
 926 }
 927
 928 double FGRadioTransmission::dbm_to_microvolt(double dbm) {
 929         return sqrt(dbm_to_watt(dbm) * 50) * 1000000;   // returns microvolts
 930 }
 931
 932