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
 366     int size = _elevations.size();
 367     double itm_elev[10000];
 368
 369         for(int i=0;i<size;i++) {
 370                 itm_elev[i]=_elevations[i];
 371                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 372         }
 373
 374         if((transmission_type == 3) || (transmission_type == 4)) {
 375                 // the sender and receiver roles are switched
 376                 point_to_point(itm_elev, receiver_height, transmitter_height,
 377                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 378                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 379                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 380                         clutterLoss(frq_mhz, itm_elev, materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
 381         }
 382         else {
 383                 point_to_point(itm_elev, transmitter_height, receiver_height,
 384                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 385                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 386                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 387                         clutterLoss(frq_mhz, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 388         }
 389
 390         double pol_loss = 0.0;
 391         if (_polarization == 1) {
 392                 pol_loss = polarization_loss();
 393         }
 394         SG_LOG(SG_GENERAL, SG_BULK,
 395                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 396         //cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 397         _root_node->setDoubleValue("station[0]/link-budget", link_budget);
 398         _root_node->setDoubleValue("station[0]/terrain-attenuation", dbloss);
 399         _root_node->setStringValue("station[0]/prop-mode", strmode);
 400         _root_node->setDoubleValue("station[0]/clutter-attenuation", clutter_loss);
 401         _root_node->setDoubleValue("station[0]/polarization-attenuation", pol_loss);
 402         //cerr << "Clutter loss: " << clutter_loss << endl;
 403         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 404         //      return -1;
 405         signal = link_budget - dbloss - clutter_loss + pol_loss;
 406         double signal_strength_dbm = signal_strength - dbloss - clutter_loss + pol_loss;
 407         double field_strength_uV = dbm_to_microvolt(signal_strength_dbm);
 408         _root_node->setDoubleValue("station[0]/signal-dbm", signal_strength_dbm);
 409         _root_node->setDoubleValue("station[0]/field-strength-uV", field_strength_uV);
 410         _root_node->setDoubleValue("station[0]/signal", signal);
 411         _root_node->setDoubleValue("station[0]/tx-erp", tx_erp);
 412         return signal;
 413
 414 }
 415
 416 /*** Calculate losses due to vegetation and urban clutter (WIP)
 417 *        We are only worried about clutter loss, terrain influence
 418 *        on the first Fresnel zone is calculated in the ITM functions
 419 ***/
 420 void FGRadioTransmission::clutterLoss(double freq, double itm_elev[], deque<string> materials,
 421         double transmitter_height, double receiver_height, int p_mode,
 422         double horizons[], double &clutter_loss) {
 423
 424         double distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
 425
 426         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 427                 int mat = 0;
 428                 int j=1;
 429                 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
 430
 431                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 432                         double clutter_density = 0.0;   // percent of reflected wave
 433                         get_material_properties(materials[mat], clutter_height, clutter_density);
 434
 435                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 436                         // First Fresnel radius
 437                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 438
 439                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 440
 441                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 442                         double d1 = j * itm_elev[1];
 443                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 444                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 445                         }
 446                         double ray_height = (grad * d1) + min_elev;
 447
 448                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 449                         double intrusion = fabs(clearance);
 450
 451                         if (clearance >= 0) {
 452                                 // no losses
 453                         }
 454                         else if (clearance < 0 && (intrusion < clutter_height)) {
 455
 456                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 457                         }
 458                         else if (clearance < 0 && (intrusion > clutter_height)) {
 459                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 460                         }
 461                         else {
 462                                 // no losses
 463                         }
 464                         j++;
 465                         mat++;
 466                 }
 467
 468         }
 469         else if (p_mode == 1) {         // diffraction
 470
 471                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 472                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
 473                         int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
 474                         //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
 475                         int last = 1;
 476                         /** perform the first pass */
 477                         int mat = 0;
 478                         int j=1;
 479                         for (int k=3;k < num_points_1st + 2;k++) {
 480                                 if (num_points_1st < 1)
 481                                         break;
 482                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 483                                 double clutter_density = 0.0;   // percent of reflected wave
 484                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 485
 486                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 487                                 // First Fresnel radius
 488                                 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) );
 489
 490                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 491
 492                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 493                                 double d1 = j * itm_elev[1];
 494                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 495                                         d1 = (num_points_1st - j) * itm_elev[1];
 496                                 }
 497                                 double ray_height = (grad * d1) + min_elev;
 498
 499                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 500                                 double intrusion = fabs(clearance);
 501
 502                                 if (clearance >= 0) {
 503                                         // no losses
 504                                 }
 505                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 506
 507                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 508                                 }
 509                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 510                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 511                                 }
 512                                 else {
 513                                         // no losses
 514                                 }
 515                                 j++;
 516                                 mat++;
 517                                 last = k;
 518                         }
 519
 520                         /** and the second pass */
 521                         mat +=1;
 522                         j =1; // first point is diffraction edge, 2nd the RX elevation
 523                         for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
 524                                 if (num_points_2nd < 1)
 525                                         break;
 526                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 527                                 double clutter_density = 0.0;   // percent of reflected wave
 528                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 529
 530                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 531                                 // First Fresnel radius
 532                                 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) );
 533
 534                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 535
 536                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 537                                 double d1 = j * itm_elev[1];
 538                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 539                                         d1 = (num_points_2nd - j) * itm_elev[1];
 540                                 }
 541                                 double ray_height = (grad * d1) + min_elev;
 542
 543                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 544                                 double intrusion = fabs(clearance);
 545
 546                                 if (clearance >= 0) {
 547                                         // no losses
 548                                 }
 549                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 550
 551                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 552                                 }
 553                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 554                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 555                                 }
 556                                 else {
 557                                         // no losses
 558                                 }
 559                                 j++;
 560                                 mat++;
 561                         }
 562
 563                 }
 564                 else {  // double horizon: same as single horizon, except there are 3 segments
 565
 566                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
 567                         int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
 568                         int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
 569                         //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
 570                         //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
 571                         int last = 1;
 572                         /** perform the first pass */
 573                         int mat = 0;
 574                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 575                         for (int k=3;k < num_points_1st +2;k++) {
 576                                 if (num_points_1st < 1)
 577                                         break;
 578                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 579                                 double clutter_density = 0.0;   // percent of reflected wave
 580                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 581
 582                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 583                                 // First Fresnel radius
 584                                 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) );
 585
 586                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 587
 588                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 589                                 double d1 = j * itm_elev[1];
 590                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 591                                         d1 = (num_points_1st - j) * itm_elev[1];
 592                                 }
 593                                 double ray_height = (grad * d1) + min_elev;
 594
 595                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 596                                 double intrusion = fabs(clearance);
 597
 598                                 if (clearance >= 0) {
 599                                         // no losses
 600                                 }
 601                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 602
 603                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 604                                 }
 605                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 606                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 607                                 }
 608                                 else {
 609                                         // no losses
 610                                 }
 611                                 j++;
 612                                 last = k;
 613                         }
 614                         mat +=1;
 615                         /** and the second pass */
 616                         int last2=1;
 617                         j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 618                         for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
 619                                 if (num_points_2nd < 1)
 620                                         break;
 621                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 622                                 double clutter_density = 0.0;   // percent of reflected wave
 623                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 624
 625                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
 626                                 // First Fresnel radius
 627                                 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) );
 628
 629                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 630
 631                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
 632                                 double d1 = j * itm_elev[1];
 633                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
 634                                         d1 = (num_points_2nd - j) * itm_elev[1];
 635                                 }
 636                                 double ray_height = (grad * d1) + min_elev;
 637
 638                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 639                                 double intrusion = fabs(clearance);
 640
 641                                 if (clearance >= 0) {
 642                                         // no losses
 643                                 }
 644                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 645
 646                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 647                                 }
 648                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 649                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 650                                 }
 651                                 else {
 652                                         // no losses
 653                                 }
 654                                 j++;
 655                                 mat++;
 656                                 last2 = k;
 657                         }
 658
 659                         /** third and final pass */
 660                         mat +=1;
 661                         j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 662                         for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
 663                                 if (num_points_3rd < 1)
 664                                         break;
 665                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 666                                 double clutter_density = 0.0;   // percent of reflected wave
 667                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 668
 669                                 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 670                                 // First Fresnel radius
 671                                 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) );
 672
 673
 674                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 675
 676                                 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 677                                 double d1 = j * itm_elev[1];
 678                                 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 679                                         d1 = (num_points_3rd - j) * itm_elev[1];
 680                                 }
 681                                 double ray_height = (grad * d1) + min_elev;
 682
 683                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 684                                 double intrusion = fabs(clearance);
 685
 686                                 if (clearance >= 0) {
 687                                         // no losses
 688                                 }
 689                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 690
 691                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 692                                 }
 693                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 694                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 695                                 }
 696                                 else {
 697                                         // no losses
 698                                 }
 699                                 j++;
 700                                 mat++;
 701
 702                         }
 703
 704                 }
 705         }
 706         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now...
 707                 clutter_loss = 0.0;
 708         }
 709
 710 }
 711
 712 /***    Temporary material properties database
 713 *               height: median clutter height
 714 *               density: radiowave attenuation factor
 715 ***/
 716 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 717
 718         if(mat_name == "Landmass") {
 719                 height = 15.0;
 720                 density = 0.2;
 721         }
 722
 723         else if(mat_name == "SomeSort") {
 724                 height = 15.0;
 725                 density = 0.2;
 726         }
 727
 728         else if(mat_name == "Island") {
 729                 height = 15.0;
 730                 density = 0.2;
 731         }
 732         else if(mat_name == "Default") {
 733                 height = 15.0;
 734                 density = 0.2;
 735         }
 736         else if(mat_name == "EvergreenBroadCover") {
 737                 height = 20.0;
 738                 density = 0.2;
 739         }
 740         else if(mat_name == "EvergreenForest") {
 741                 height = 20.0;
 742                 density = 0.2;
 743         }
 744         else if(mat_name == "DeciduousBroadCover") {
 745                 height = 15.0;
 746                 density = 0.3;
 747         }
 748         else if(mat_name == "DeciduousForest") {
 749                 height = 15.0;
 750                 density = 0.3;
 751         }
 752         else if(mat_name == "MixedForestCover") {
 753                 height = 20.0;
 754                 density = 0.25;
 755         }
 756         else if(mat_name == "MixedForest") {
 757                 height = 15.0;
 758                 density = 0.25;
 759         }
 760         else if(mat_name == "RainForest") {
 761                 height = 25.0;
 762                 density = 0.55;
 763         }
 764         else if(mat_name == "EvergreenNeedleCover") {
 765                 height = 15.0;
 766                 density = 0.2;
 767         }
 768         else if(mat_name == "WoodedTundraCover") {
 769                 height = 5.0;
 770                 density = 0.15;
 771         }
 772         else if(mat_name == "DeciduousNeedleCover") {
 773                 height = 5.0;
 774                 density = 0.2;
 775         }
 776         else if(mat_name == "ScrubCover") {
 777                 height = 3.0;
 778                 density = 0.15;
 779         }
 780         else if(mat_name == "BuiltUpCover") {
 781                 height = 30.0;
 782                 density = 0.7;
 783         }
 784         else if(mat_name == "Urban") {
 785                 height = 30.0;
 786                 density = 0.7;
 787         }
 788         else if(mat_name == "Construction") {
 789                 height = 30.0;
 790                 density = 0.7;
 791         }
 792         else if(mat_name == "Industrial") {
 793                 height = 30.0;
 794                 density = 0.7;
 795         }
 796         else if(mat_name == "Port") {
 797                 height = 30.0;
 798                 density = 0.7;
 799         }
 800         else if(mat_name == "Town") {
 801                 height = 10.0;
 802                 density = 0.5;
 803         }
 804         else if(mat_name == "SubUrban") {
 805                 height = 10.0;
 806                 density = 0.5;
 807         }
 808         else if(mat_name == "CropWoodCover") {
 809                 height = 10.0;
 810                 density = 0.1;
 811         }
 812         else if(mat_name == "CropWood") {
 813                 height = 10.0;
 814                 density = 0.1;
 815         }
 816         else if(mat_name == "AgroForest") {
 817                 height = 10.0;
 818                 density = 0.1;
 819         }
 820         else {
 821                 height = 0.0;
 822                 density = 0.0;
 823         }
 824
 825 }
 826
 827 /*** implement simple LOS propagation model (WIP)
 828 ***/
 829 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 830         double frq_mhz;
 831         if( (freq < 118.0) || (freq > 137.0) )
 832                 frq_mhz = 125.0;        // sane value, middle of bandplan
 833         else
 834                 frq_mhz = freq;
 835         double dbloss;
 836         double tx_pow = _transmitter_power;
 837         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 838         double signal = 0.0;
 839
 840         double sender_alt_ft,sender_alt;
 841         double transmitter_height=0.0;
 842         double receiver_height=0.0;
 843         double own_lat = fgGetDouble("/position/latitude-deg");
 844         double own_lon = fgGetDouble("/position/longitude-deg");
 845         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 846         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 847
 848
 849         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 850
 851         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 852
 853         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 854
 855         SGGeod sender_pos = pos;
 856
 857         sender_alt_ft = sender_pos.getElevationFt();
 858         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 859
 860         receiver_height = own_alt;
 861         transmitter_height = sender_alt;
 862
 863         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 864
 865
 866         transmitter_height += _tx_antenna_height;
 867         receiver_height += _rx_antenna_height;
 868
 869
 870         /** radio horizon calculation with wave bending k=4/3 */
 871         double receiver_horizon = 4.12 * sqrt(receiver_height);
 872         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 873         double total_horizon = receiver_horizon + transmitter_horizon;
 874
 875         if (distance_m > total_horizon) {
 876                 return -1;
 877         }
 878         double pol_loss = 0.0;
 879         if (_polarization == 1) {
 880                 pol_loss = polarization_loss();
 881         }
 882         // free-space loss (distance calculation should be changed)
 883         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 884         signal = link_budget - dbloss + pol_loss;
 885         SG_LOG(SG_GENERAL, SG_BULK,
 886                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 887         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 888         return signal;
 889
 890 }
 891
 892 /*** calculate loss due to polarization mismatch
 893 *       this function is only reliable for vertical polarization
 894 *       due to the V-shape of horizontally polarized antennas
 895 ***/
 896 double FGRadioTransmission::polarization_loss() {
 897
 898         double theta_deg;
 899         double roll = fgGetDouble("/orientation/roll-deg");
 900         if (fabs(roll) > 85.0)
 901                 roll = 85.0;
 902         double pitch = fgGetDouble("/orientation/pitch-deg");
 903         if (fabs(pitch) > 85.0)
 904                 pitch = 85.0;
 905         double theta = fabs( atan( sqrt(
 906                 pow(tan(roll * SGD_DEGREES_TO_RADIANS), 2) +
 907                 pow(tan(pitch * SGD_DEGREES_TO_RADIANS), 2) )) * SGD_RADIANS_TO_DEGREES);
 908
 909         if (_polarization == 0)
 910                 theta_deg = 90.0 - theta;
 911         else
 912                 theta_deg = theta;
 913         if (theta_deg > 85.0)   // we don't want to converge into infinity
 914                 theta_deg = 85.0;
 915
 916         double loss = 10 * log10( pow(cos(theta_deg * SGD_DEGREES_TO_RADIANS), 2) );
 917         //cerr << "Polarization loss: " << loss << " dBm " << endl;
 918         return loss;
 919 }
 920
 921
 922 double FGRadioTransmission::watt_to_dbm(double power_watt) {
 923         return 10 * log10(1000 * power_watt);   // returns dbm
 924 }
 925
 926 double FGRadioTransmission::dbm_to_watt(double dbm) {
 927         return exp( (dbm-30) * log(10.0) / 10.0);       // returns Watts
 928 }
 929
 930 double FGRadioTransmission::dbm_to_microvolt(double dbm) {
 931         return sqrt(dbm_to_watt(dbm) * 50) * 1000000;   // returns microvolts
 932 }
 933
 934