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; // maximum antenna 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 }
  72
  73 FGRadioTransmission::~FGRadioTransmission()
  74 {
  75 }
  76
  77
  78 double FGRadioTransmission::getFrequency(int radio) {
  79         double freq = 118.0;
  80         switch (radio) {
  81                 case 1:
  82                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  83                         break;
  84                 case 2:
  85                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  86                         break;
  87                 default:
  88                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  89
  90         }
  91         return freq;
  92 }
  93
  94 /*** TODO: receive multiplayer chat message and voice
  95 ***/
  96 void FGRadioTransmission::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
  97
  98 }
  99
 100 /*** TODO: receive navaid
 101 ***/
 102 double FGRadioTransmission::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
 103
 104         // typical VOR/LOC transmitter power appears to be 200 Watt ~ 53 dBm
 105         // vor/loc typical sensitivity between -107 and -101 dBm
 106         // glideslope sensitivity between -85 and -81 dBm
 107         if ( _propagation_model == 1) {
 108                 return LOS_calculate_attenuation(tx_pos, freq, 1);
 109         }
 110         else if ( _propagation_model == 2) {
 111                 return ITM_calculate_attenuation(tx_pos, freq, 1);
 112         }
 113
 114         return -1;
 115
 116 }
 117
 118 /*** Receive ATC radio communication as text
 119 ***/
 120 void FGRadioTransmission::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 121
 122
 123         if(ground_to_air == 1) {
 124                 _transmitter_power += 4.0;
 125                 _tx_antenna_height += 30.0;
 126                 _tx_antenna_gain += 2.0;
 127         }
 128
 129
 130         double comm1 = getFrequency(1);
 131         double comm2 = getFrequency(2);
 132         if ( !(fabs(freq - comm1) <= 0.0001) &&  !(fabs(freq - comm2) <= 0.0001) ) {
 133                 return;
 134         }
 135         else {
 136
 137                 if ( _propagation_model == 0) {
 138                         // skip propagation routines entirely
 139                         fgSetString("/sim/messages/atc", text.c_str());
 140                 }
 141                 else if ( _propagation_model == 1 ) {
 142                         // Use free-space, round earth
 143                         double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
 144                         if (signal <= 0.0) {
 145                                 return;
 146                         }
 147                         else {
 148
 149                                 fgSetString("/sim/messages/atc", text.c_str());
 150
 151                         }
 152                 }
 153                 else if ( _propagation_model == 2 ) {
 154                         // Use ITM propagation model
 155                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 156                         if (signal <= 0.0) {
 157                                 return;
 158                         }
 159                         if ((signal > 0.0) && (signal < 12.0)) {
 160                                 /** for low SNR values implement a way to make the conversation
 161                                 *       hard to understand but audible
 162                                 *       in the real world, the receiver AGC fails to capture the slope
 163                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 164                                 *       the workaround below is more akin to what would happen on a FM transmission
 165                                 *       therefore the correct way would be to work on the volume
 166                                 **/
 167                                 /*
 168                                 string hash_noise = " ";
 169                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 170                                 int t_size = text.size();
 171                                 for (int n = 1; n <= reps; ++n) {
 172                                         int pos = rand() % (t_size -1);
 173                                         text.replace(pos,1, hash_noise);
 174                                 }
 175                                 */
 176                                 double volume = (fabs(signal - 12.0) / 12);
 177                                 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 178                                 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
 179                                 //cerr << "Usable signal at limit: " << signal << endl;
 180                                 fgSetDouble("/sim/sound/voices/voice/volume", volume);
 181                                 fgSetString("/sim/messages/atc", text.c_str());
 182                                 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 183                         }
 184                         else {
 185                                 fgSetString("/sim/messages/atc", text.c_str());
 186                         }
 187
 188                 }
 189
 190         }
 191
 192 }
 193
 194 /***  Implement radio attenuation
 195           based on the Longley-Rice propagation model
 196 ***/
 197 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 198
 199
 200
 201         /** ITM default parameters
 202                 TODO: take them from tile materials (especially for sea)?
 203         **/
 204         double eps_dielect=15.0;
 205         double sgm_conductivity = 0.005;
 206         double eno = 301.0;
 207         double frq_mhz = freq;
 208
 209         int radio_climate = 5;          // continental temperate
 210         int pol= _polarization;
 211         double conf = 0.90;     // 90% of situations and time, take into account speed
 212         double rel = 0.90;
 213         double dbloss;
 214         char strmode[150];
 215         int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
 216         double horizons[2];
 217         int errnum;
 218
 219         double clutter_loss = 0.0;      // loss due to vegetation and urban
 220         double tx_pow = _transmitter_power;
 221         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 222         double signal = 0.0;
 223
 224
 225         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 226         double signal_strength = tx_pow - _rx_line_losses - _tx_line_losses + ant_gain;
 227         double tx_erp = dbm_to_watt(tx_pow + _tx_antenna_gain - _tx_line_losses);
 228
 229
 230         FGScenery * scenery = globals->get_scenery();
 231
 232         double own_lat = fgGetDouble("/position/latitude-deg");
 233         double own_lon = fgGetDouble("/position/longitude-deg");
 234         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 235         double own_heading = fgGetDouble("/orientation/heading-deg");
 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 reverse_course = SGGeodesy::courseRad(sender_pos_c, own_pos_c);
 261         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 262         double probe_distance = 0.0;
 263         /** If distance larger than this value (300 km), assume reception imposssible */
 264         if (distance_m > 300000)
 265                 return -1.0;
 266         /** If above 8000 meters, consider LOS mode and calculate free-space att */
 267         if (own_alt > 8000) {
 268                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 269                 SG_LOG(SG_GENERAL, SG_BULK,
 270                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 271                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 272                 signal = link_budget - dbloss;
 273                 return signal;
 274         }
 275
 276
 277         int max_points = (int)floor(distance_m / point_distance);
 278         double delta_last = fmod(distance_m, point_distance);
 279
 280         deque<double> elevations;
 281         deque<string> materials;
 282
 283
 284         double elevation_under_pilot = 0.0;
 285         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 286                 receiver_height = own_alt - elevation_under_pilot;
 287         }
 288
 289         double elevation_under_sender = 0.0;
 290         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 291                 transmitter_height = sender_alt - elevation_under_sender;
 292         }
 293         else {
 294                 transmitter_height = sender_alt;
 295         }
 296
 297
 298         transmitter_height += _tx_antenna_height;
 299         receiver_height += _rx_antenna_height;
 300
 301
 302         SG_LOG(SG_GENERAL, SG_BULK,
 303                         "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
 304         //cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 305         _root_node->setDoubleValue("station[0]/rx-height", receiver_height);
 306         _root_node->setDoubleValue("station[0]/tx-height", transmitter_height);
 307         _root_node->setDoubleValue("station[0]/distance", distance_m / 1000);
 308
 309         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 310
 311         while (elevations.size() <= e_size) {
 312                 probe_distance += point_distance;
 313                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 314                 const SGMaterial *mat = 0;
 315                 double elevation_m = 0.0;
 316
 317                 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
 318                         if((transmission_type == 3) || (transmission_type == 4)) {
 319                                 elevations.push_back(elevation_m);
 320                                 if(mat) {
 321                                         const std::vector<string> mat_names = mat->get_names();
 322                                         materials.push_back(mat_names[0]);
 323                                 }
 324                                 else {
 325                                         materials.push_back("None");
 326                                 }
 327                         }
 328                         else {
 329                                  elevations.push_front(elevation_m);
 330                                  if(mat) {
 331                                          const std::vector<string> mat_names = mat->get_names();
 332                                          materials.push_front(mat_names[0]);
 333                                 }
 334                                 else {
 335                                         materials.push_front("None");
 336                                 }
 337                         }
 338                 }
 339                 else {
 340                         if((transmission_type == 3) || (transmission_type == 4)) {
 341                                 elevations.push_back(0.0);
 342                                 materials.push_back("None");
 343                         }
 344                         else {
 345                                 elevations.push_front(0.0);
 346                                 materials.push_front("None");
 347                         }
 348                 }
 349         }
 350         if((transmission_type == 3) || (transmission_type == 4)) {
 351                 elevations.push_front(elevation_under_pilot);
 352                 if (delta_last > (point_distance / 2) )                 // only add last point if it's farther than half point_distance
 353                         elevations.push_back(elevation_under_sender);
 354         }
 355         else {
 356                 elevations.push_back(elevation_under_pilot);
 357                 if (delta_last > (point_distance / 2) )
 358                         elevations.push_front(elevation_under_sender);
 359         }
 360
 361
 362         double num_points= (double)elevations.size();
 363
 364         elevations.push_front(point_distance);
 365         elevations.push_front(num_points -1);
 366         int size = elevations.size();
 367         double itm_elev[size];
 368         for(int i=0;i<size;i++) {
 369                 itm_elev[i]=elevations[i];
 370                 //cerr << "ITM:: itm_elev: " << elevations[i] << endl;
 371         }
 372
 373         if((transmission_type == 3) || (transmission_type == 4)) {
 374                 // the sender and receiver roles are switched
 375                 point_to_point(itm_elev, receiver_height, transmitter_height,
 376                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 377                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 378                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 379                         calculate_clutter_loss(frq_mhz, itm_elev, materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
 380         }
 381         else {
 382                 point_to_point(itm_elev, transmitter_height, receiver_height,
 383                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 384                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 385                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 386                         calculate_clutter_loss(frq_mhz, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 387         }
 388
 389         double pol_loss = 0.0;
 390         if (_polarization == 1) {
 391                 pol_loss = polarization_loss();
 392         }
 393         SG_LOG(SG_GENERAL, SG_BULK,
 394                         "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 395         //cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 396         _root_node->setDoubleValue("station[0]/link-budget", link_budget);
 397         _root_node->setDoubleValue("station[0]/terrain-attenuation", dbloss);
 398         _root_node->setStringValue("station[0]/prop-mode", strmode);
 399         _root_node->setDoubleValue("station[0]/clutter-attenuation", clutter_loss);
 400         _root_node->setDoubleValue("station[0]/polarization-attenuation", pol_loss);
 401         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 402         //      return -1;
 403         double tx_pattern_gain = 0.0;
 404         double rx_pattern_gain = 0.0;
 405         if (_root_node->getBoolValue("use-antenna-pattern", false)) {
 406                 double sender_heading = 270.0; // due West
 407                 double tx_antenna_bearing = sender_heading - reverse_course * SGD_RADIANS_TO_DEGREES;
 408                 double rx_antenna_bearing = own_heading - course * SGD_RADIANS_TO_DEGREES;
 409                 double rx_elev_angle = atan((itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m) * SGD_RADIANS_TO_DEGREES;
 410                 double tx_elev_angle = 0.0 - rx_elev_angle;
 411                 FGRadioAntenna* TX_antenna;
 412                 FGRadioAntenna* RX_antenna;
 413                 TX_antenna = new FGRadioAntenna("Plot2");
 414                 TX_antenna->set_heading(sender_heading);
 415                 TX_antenna->set_elevation_angle(0);
 416                 tx_pattern_gain = TX_antenna->calculate_gain(tx_antenna_bearing, tx_elev_angle);
 417                 RX_antenna = new FGRadioAntenna("Plot2");
 418                 RX_antenna->set_heading(own_heading);
 419                 RX_antenna->set_elevation_angle(fgGetDouble("/orientation/pitch-deg"));
 420                 rx_pattern_gain = RX_antenna->calculate_gain(rx_antenna_bearing, rx_elev_angle);
 421
 422                 delete TX_antenna;
 423                 delete RX_antenna;
 424         }
 425
 426         signal = link_budget - dbloss - clutter_loss + pol_loss + rx_pattern_gain + tx_pattern_gain;
 427         double signal_strength_dbm = signal_strength - dbloss - clutter_loss + pol_loss + rx_pattern_gain + tx_pattern_gain;
 428         double field_strength_uV = dbm_to_microvolt(signal_strength_dbm);
 429         _root_node->setDoubleValue("station[0]/signal-dbm", signal_strength_dbm);
 430         _root_node->setDoubleValue("station[0]/field-strength-uV", field_strength_uV);
 431         _root_node->setDoubleValue("station[0]/signal", signal);
 432         _root_node->setDoubleValue("station[0]/tx-erp", tx_erp);
 433         //_root_node->setDoubleValue("station[0]/tx-pattern-gain", tx_pattern_gain);
 434         //_root_node->setDoubleValue("station[0]/rx-pattern-gain", rx_pattern_gain);
 435         return signal;
 436
 437 }
 438
 439 /*** Calculate losses due to vegetation and urban clutter (WIP)
 440 *        We are only worried about clutter loss, terrain influence
 441 *        on the first Fresnel zone is calculated in the ITM functions
 442 ***/
 443 void FGRadioTransmission::calculate_clutter_loss(double freq, double itm_elev[], deque<string> &materials,
 444         double transmitter_height, double receiver_height, int p_mode,
 445         double horizons[], double &clutter_loss) {
 446
 447         double distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
 448
 449         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 450                 int mat = 0;
 451                 int j=1;
 452                 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
 453
 454                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 455                         double clutter_density = 0.0;   // percent of reflected wave
 456                         get_material_properties(materials[mat], clutter_height, clutter_density);
 457
 458                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 459                         // First Fresnel radius
 460                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 461
 462                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 463
 464                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 465                         double d1 = j * itm_elev[1];
 466                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 467                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 468                         }
 469                         double ray_height = (grad * d1) + min_elev;
 470
 471                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 472                         double intrusion = fabs(clearance);
 473
 474                         if (clearance >= 0) {
 475                                 // no losses
 476                         }
 477                         else if (clearance < 0 && (intrusion < clutter_height)) {
 478
 479                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 480                         }
 481                         else if (clearance < 0 && (intrusion > clutter_height)) {
 482                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 483                         }
 484                         else {
 485                                 // no losses
 486                         }
 487                         j++;
 488                         mat++;
 489                 }
 490
 491         }
 492         else if (p_mode == 1) {         // diffraction
 493
 494                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 495                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
 496                         int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
 497                         //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
 498                         int last = 1;
 499                         /** perform the first pass */
 500                         int mat = 0;
 501                         int j=1;
 502                         for (int k=3;k < num_points_1st + 2;k++) {
 503                                 if (num_points_1st < 1)
 504                                         break;
 505                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 506                                 double clutter_density = 0.0;   // percent of reflected wave
 507                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 508
 509                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 510                                 // First Fresnel radius
 511                                 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) );
 512
 513                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 514
 515                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 516                                 double d1 = j * itm_elev[1];
 517                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 518                                         d1 = (num_points_1st - j) * itm_elev[1];
 519                                 }
 520                                 double ray_height = (grad * d1) + min_elev;
 521
 522                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 523                                 double intrusion = fabs(clearance);
 524
 525                                 if (clearance >= 0) {
 526                                         // no losses
 527                                 }
 528                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 529
 530                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 531                                 }
 532                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 533                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 534                                 }
 535                                 else {
 536                                         // no losses
 537                                 }
 538                                 j++;
 539                                 mat++;
 540                                 last = k;
 541                         }
 542
 543                         /** and the second pass */
 544                         mat +=1;
 545                         j =1; // first point is diffraction edge, 2nd the RX elevation
 546                         for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
 547                                 if (num_points_2nd < 1)
 548                                         break;
 549                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 550                                 double clutter_density = 0.0;   // percent of reflected wave
 551                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 552
 553                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 554                                 // First Fresnel radius
 555                                 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) );
 556
 557                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 558
 559                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 560                                 double d1 = j * itm_elev[1];
 561                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 562                                         d1 = (num_points_2nd - j) * itm_elev[1];
 563                                 }
 564                                 double ray_height = (grad * d1) + min_elev;
 565
 566                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 567                                 double intrusion = fabs(clearance);
 568
 569                                 if (clearance >= 0) {
 570                                         // no losses
 571                                 }
 572                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 573
 574                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 575                                 }
 576                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 577                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 578                                 }
 579                                 else {
 580                                         // no losses
 581                                 }
 582                                 j++;
 583                                 mat++;
 584                         }
 585
 586                 }
 587                 else {  // double horizon: same as single horizon, except there are 3 segments
 588
 589                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
 590                         int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
 591                         int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
 592                         //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
 593                         //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
 594                         int last = 1;
 595                         /** perform the first pass */
 596                         int mat = 0;
 597                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 598                         for (int k=3;k < num_points_1st +2;k++) {
 599                                 if (num_points_1st < 1)
 600                                         break;
 601                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 602                                 double clutter_density = 0.0;   // percent of reflected wave
 603                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 604
 605                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 606                                 // First Fresnel radius
 607                                 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) );
 608
 609                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 610
 611                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 612                                 double d1 = j * itm_elev[1];
 613                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 614                                         d1 = (num_points_1st - j) * itm_elev[1];
 615                                 }
 616                                 double ray_height = (grad * d1) + min_elev;
 617
 618                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 619                                 double intrusion = fabs(clearance);
 620
 621                                 if (clearance >= 0) {
 622                                         // no losses
 623                                 }
 624                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 625
 626                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 627                                 }
 628                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 629                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 630                                 }
 631                                 else {
 632                                         // no losses
 633                                 }
 634                                 j++;
 635                                 last = k;
 636                         }
 637                         mat +=1;
 638                         /** and the second pass */
 639                         int last2=1;
 640                         j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 641                         for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
 642                                 if (num_points_2nd < 1)
 643                                         break;
 644                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 645                                 double clutter_density = 0.0;   // percent of reflected wave
 646                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 647
 648                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
 649                                 // First Fresnel radius
 650                                 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) );
 651
 652                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 653
 654                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
 655                                 double d1 = j * itm_elev[1];
 656                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
 657                                         d1 = (num_points_2nd - j) * itm_elev[1];
 658                                 }
 659                                 double ray_height = (grad * d1) + min_elev;
 660
 661                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 662                                 double intrusion = fabs(clearance);
 663
 664                                 if (clearance >= 0) {
 665                                         // no losses
 666                                 }
 667                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 668
 669                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 670                                 }
 671                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 672                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 673                                 }
 674                                 else {
 675                                         // no losses
 676                                 }
 677                                 j++;
 678                                 mat++;
 679                                 last2 = k;
 680                         }
 681
 682                         /** third and final pass */
 683                         mat +=1;
 684                         j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 685                         for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
 686                                 if (num_points_3rd < 1)
 687                                         break;
 688                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 689                                 double clutter_density = 0.0;   // percent of reflected wave
 690                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 691
 692                                 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 693                                 // First Fresnel radius
 694                                 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) );
 695
 696
 697                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 698
 699                                 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 700                                 double d1 = j * itm_elev[1];
 701                                 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 702                                         d1 = (num_points_3rd - j) * itm_elev[1];
 703                                 }
 704                                 double ray_height = (grad * d1) + min_elev;
 705
 706                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 707                                 double intrusion = fabs(clearance);
 708
 709                                 if (clearance >= 0) {
 710                                         // no losses
 711                                 }
 712                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 713
 714                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 715                                 }
 716                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 717                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 718                                 }
 719                                 else {
 720                                         // no losses
 721                                 }
 722                                 j++;
 723                                 mat++;
 724
 725                         }
 726
 727                 }
 728         }
 729         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now...
 730                 clutter_loss = 0.0;
 731         }
 732
 733 }
 734
 735 /***    Temporary material properties database
 736 *               height: median clutter height
 737 *               density: radiowave attenuation factor
 738 ***/
 739 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 740
 741         if(mat_name == "Landmass") {
 742                 height = 15.0;
 743                 density = 0.2;
 744         }
 745
 746         else if(mat_name == "SomeSort") {
 747                 height = 15.0;
 748                 density = 0.2;
 749         }
 750
 751         else if(mat_name == "Island") {
 752                 height = 15.0;
 753                 density = 0.2;
 754         }
 755         else if(mat_name == "Default") {
 756                 height = 15.0;
 757                 density = 0.2;
 758         }
 759         else if(mat_name == "EvergreenBroadCover") {
 760                 height = 20.0;
 761                 density = 0.2;
 762         }
 763         else if(mat_name == "EvergreenForest") {
 764                 height = 20.0;
 765                 density = 0.2;
 766         }
 767         else if(mat_name == "DeciduousBroadCover") {
 768                 height = 15.0;
 769                 density = 0.3;
 770         }
 771         else if(mat_name == "DeciduousForest") {
 772                 height = 15.0;
 773                 density = 0.3;
 774         }
 775         else if(mat_name == "MixedForestCover") {
 776                 height = 20.0;
 777                 density = 0.25;
 778         }
 779         else if(mat_name == "MixedForest") {
 780                 height = 15.0;
 781                 density = 0.25;
 782         }
 783         else if(mat_name == "RainForest") {
 784                 height = 25.0;
 785                 density = 0.55;
 786         }
 787         else if(mat_name == "EvergreenNeedleCover") {
 788                 height = 15.0;
 789                 density = 0.2;
 790         }
 791         else if(mat_name == "WoodedTundraCover") {
 792                 height = 5.0;
 793                 density = 0.15;
 794         }
 795         else if(mat_name == "DeciduousNeedleCover") {
 796                 height = 5.0;
 797                 density = 0.2;
 798         }
 799         else if(mat_name == "ScrubCover") {
 800                 height = 3.0;
 801                 density = 0.15;
 802         }
 803         else if(mat_name == "BuiltUpCover") {
 804                 height = 30.0;
 805                 density = 0.7;
 806         }
 807         else if(mat_name == "Urban") {
 808                 height = 30.0;
 809                 density = 0.7;
 810         }
 811         else if(mat_name == "Construction") {
 812                 height = 30.0;
 813                 density = 0.7;
 814         }
 815         else if(mat_name == "Industrial") {
 816                 height = 30.0;
 817                 density = 0.7;
 818         }
 819         else if(mat_name == "Port") {
 820                 height = 30.0;
 821                 density = 0.7;
 822         }
 823         else if(mat_name == "Town") {
 824                 height = 10.0;
 825                 density = 0.5;
 826         }
 827         else if(mat_name == "SubUrban") {
 828                 height = 10.0;
 829                 density = 0.5;
 830         }
 831         else if(mat_name == "CropWoodCover") {
 832                 height = 10.0;
 833                 density = 0.1;
 834         }
 835         else if(mat_name == "CropWood") {
 836                 height = 10.0;
 837                 density = 0.1;
 838         }
 839         else if(mat_name == "AgroForest") {
 840                 height = 10.0;
 841                 density = 0.1;
 842         }
 843         else {
 844                 height = 0.0;
 845                 density = 0.0;
 846         }
 847
 848 }
 849
 850 /*** implement simple LOS propagation model (WIP)
 851 ***/
 852 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 853         double frq_mhz;
 854         if( (freq < 118.0) || (freq > 137.0) )
 855                 frq_mhz = 125.0;        // sane value, middle of bandplan
 856         else
 857                 frq_mhz = freq;
 858         double dbloss;
 859         double tx_pow = _transmitter_power;
 860         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 861         double signal = 0.0;
 862
 863         double sender_alt_ft,sender_alt;
 864         double transmitter_height=0.0;
 865         double receiver_height=0.0;
 866         double own_lat = fgGetDouble("/position/latitude-deg");
 867         double own_lon = fgGetDouble("/position/longitude-deg");
 868         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 869         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 870
 871
 872         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 873
 874         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 875
 876         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 877
 878         SGGeod sender_pos = pos;
 879
 880         sender_alt_ft = sender_pos.getElevationFt();
 881         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 882
 883         receiver_height = own_alt;
 884         transmitter_height = sender_alt;
 885
 886         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 887
 888
 889         transmitter_height += _tx_antenna_height;
 890         receiver_height += _rx_antenna_height;
 891
 892
 893         /** radio horizon calculation with wave bending k=4/3 */
 894         double receiver_horizon = 4.12 * sqrt(receiver_height);
 895         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 896         double total_horizon = receiver_horizon + transmitter_horizon;
 897
 898         if (distance_m > total_horizon) {
 899                 return -1;
 900         }
 901         double pol_loss = 0.0;
 902         if (_polarization == 1) {
 903                 pol_loss = polarization_loss();
 904         }
 905         // free-space loss (distance calculation should be changed)
 906         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 907         signal = link_budget - dbloss + pol_loss;
 908         SG_LOG(SG_GENERAL, SG_BULK,
 909                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 910         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 911         return signal;
 912
 913 }
 914
 915 /*** calculate loss due to polarization mismatch
 916 *       this function is only reliable for vertical polarization
 917 *       due to the V-shape of horizontally polarized antennas
 918 ***/
 919 double FGRadioTransmission::polarization_loss() {
 920
 921         double theta_deg;
 922         double roll = fgGetDouble("/orientation/roll-deg");
 923         if (fabs(roll) > 85.0)
 924                 roll = 85.0;
 925         double pitch = fgGetDouble("/orientation/pitch-deg");
 926         if (fabs(pitch) > 85.0)
 927                 pitch = 85.0;
 928         double theta = fabs( atan( sqrt(
 929                 pow(tan(roll * SGD_DEGREES_TO_RADIANS), 2) +
 930                 pow(tan(pitch * SGD_DEGREES_TO_RADIANS), 2) )) * SGD_RADIANS_TO_DEGREES);
 931
 932         if (_polarization == 0)
 933                 theta_deg = 90.0 - theta;
 934         else
 935                 theta_deg = theta;
 936         if (theta_deg > 85.0)   // we don't want to converge into infinity
 937                 theta_deg = 85.0;
 938
 939         double loss = 10 * log10( pow(cos(theta_deg * SGD_DEGREES_TO_RADIANS), 2) );
 940         //cerr << "Polarization loss: " << loss << " dBm " << endl;
 941         return loss;
 942 }
 943
 944
 945 double FGRadioTransmission::watt_to_dbm(double power_watt) {
 946         return 10 * log10(1000 * power_watt);   // returns dbm
 947 }
 948
 949 double FGRadioTransmission::dbm_to_watt(double dbm) {
 950         return exp( (dbm-30) * log(10) / 10);   // returns Watts
 951 }
 952
 953 double FGRadioTransmission::dbm_to_microvolt(double dbm) {
 954         return sqrt(dbm_to_watt(dbm) * 50) * 1000000;   // returns microvolts
 955 }
 956
 957