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 = -105.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD or less
  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
  95 void FGRadioTransmission::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
  96
  97 }
  98
  99
 100 double FGRadioTransmission::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
 101
 102         // typical VOR/LOC transmitter power appears to be 100 - 200 Watt i.e 50 - 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
 117 double FGRadioTransmission::receiveBeacon(SGGeod &tx_pos, double heading, double pitch) {
 118
 119         // these properties should be set by an instrument
 120         _receiver_sensitivity = _root_node->getDoubleValue("station[0]/rx-sensitivity", _receiver_sensitivity);
 121         _transmitter_power = watt_to_dbm(_root_node->getDoubleValue("station[0]/tx-power-watt", _transmitter_power));
 122         _polarization = _root_node->getIntValue("station[0]/polarization", 1);
 123         _tx_antenna_height += _root_node->getDoubleValue("station[0]/tx-antenna-height", 0);
 124         _rx_antenna_height += _root_node->getDoubleValue("station[0]/rx-antenna-height", 0);
 125         _tx_antenna_gain += _root_node->getDoubleValue("station[0]/tx-antenna-gain", 0);
 126         _rx_antenna_gain += _root_node->getDoubleValue("station[0]/rx-antenna-gain", 0);
 127
 128         double freq = _root_node->getDoubleValue("station[0]/frequency", 144.8);        // by default stay in the ham 2 meter band
 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 -1;
 134         }
 135
 136         double signal = ITM_calculate_attenuation(tx_pos, freq, 1);
 137
 138         return signal;
 139 }
 140
 141
 142
 143 void FGRadioTransmission::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
 144
 145         // adjust some default parameters in case the ATC code does not set them
 146         if(ground_to_air == 1) {
 147                 _transmitter_power += 4.0;
 148                 _tx_antenna_height += 30.0;
 149                 _tx_antenna_gain += 2.0;
 150         }
 151
 152         double comm1 = getFrequency(1);
 153         double comm2 = getFrequency(2);
 154         if ( !(fabs(freq - comm1) <= 0.0001) &&  !(fabs(freq - comm2) <= 0.0001) ) {
 155                 return;
 156         }
 157         else {
 158
 159                 if ( _propagation_model == 0) {         // skip propagation routines entirely
 160                         fgSetString("/sim/messages/atc", text.c_str());
 161                 }
 162                 else if ( _propagation_model == 1 ) {           // Use free-space, round earth
 163
 164                         double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
 165                         if (signal <= 0.0) {
 166                                 return;
 167                         }
 168                         else {
 169                                 fgSetString("/sim/messages/atc", text.c_str());
 170                         }
 171                 }
 172                 else if ( _propagation_model == 2 ) {   // Use ITM propagation model
 173
 174                         double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 175                         if (signal <= 0.0) {
 176                                 return;
 177                         }
 178                         if ((signal > 0.0) && (signal < 12.0)) {
 179                                 /** for low SNR values need a way to make the conversation
 180                                 *       hard to understand but audible
 181                                 *       in the real world, the receiver AGC fails to capture the slope
 182                                 *       and the signal, due to being amplitude modulated, decreases volume after demodulation
 183                                 *       the workaround below is more akin to what would happen on a FM transmission
 184                                 *       therefore the correct way would be to work on the volume
 185                                 **/
 186                                 /*
 187                                 string hash_noise = " ";
 188                                 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
 189                                 int t_size = text.size();
 190                                 for (int n = 1; n <= reps; ++n) {
 191                                         int pos = rand() % (t_size -1);
 192                                         text.replace(pos,1, hash_noise);
 193                                 }
 194                                 */
 195                                 //double volume = (fabs(signal - 12.0) / 12);
 196                                 //double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
 197
 198                                 //fgSetDouble("/sim/sound/voices/voice/volume", volume);
 199                                 fgSetString("/sim/messages/atc", text.c_str());
 200                                 //fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
 201                         }
 202                         else {
 203                                 fgSetString("/sim/messages/atc", text.c_str());
 204                         }
 205                 }
 206         }
 207 }
 208
 209
 210 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 211
 212
 213
 214         /** ITM default parameters
 215                 TODO: take them from tile materials (especially for sea)?
 216         **/
 217         double eps_dielect=15.0;
 218         double sgm_conductivity = 0.005;
 219         double eno = 301.0;
 220         double frq_mhz = freq;
 221
 222         int radio_climate = 5;          // continental temperate
 223         int pol= _polarization;
 224         double conf = 0.90;     // 90% of situations and time, take into account speed
 225         double rel = 0.90;
 226         double dbloss;
 227         char strmode[150];
 228         int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
 229         double horizons[2];
 230         int errnum;
 231
 232         double clutter_loss = 0.0;      // loss due to vegetation and urban
 233         double tx_pow = _transmitter_power;
 234         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 235         double signal = 0.0;
 236
 237
 238         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 239         double signal_strength = tx_pow - _rx_line_losses - _tx_line_losses + ant_gain;
 240         double tx_erp = dbm_to_watt(tx_pow + _tx_antenna_gain - _tx_line_losses);
 241
 242
 243         FGScenery * scenery = globals->get_scenery();
 244
 245         double own_lat = fgGetDouble("/position/latitude-deg");
 246         double own_lon = fgGetDouble("/position/longitude-deg");
 247         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 248         double own_heading = fgGetDouble("/orientation/heading-deg");
 249         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 250
 251
 252
 253
 254         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 255         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 256         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 257         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 258
 259
 260         double sender_alt_ft,sender_alt;
 261         double transmitter_height=0.0;
 262         double receiver_height=0.0;
 263         SGGeod sender_pos = pos;
 264
 265         sender_alt_ft = sender_pos.getElevationFt();
 266         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 267         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 268         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 269
 270
 271         double point_distance= _terrain_sampling_distance;
 272         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 273         double reverse_course = SGGeodesy::courseRad(sender_pos_c, own_pos_c);
 274         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 275         double probe_distance = 0.0;
 276         /** If distance larger than this value (300 km), assume reception imposssible to spare CPU cycles */
 277         if (distance_m > 300000)
 278                 return -1.0;
 279         /** If above 8000 meters, consider LOS mode and calculate free-space att to spare CPU cycles */
 280         if (own_alt > 8000) {
 281                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 282                 SG_LOG(SG_GENERAL, SG_BULK,
 283                         "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
 284                 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
 285                 signal = link_budget - dbloss;
 286                 return signal;
 287         }
 288
 289
 290         int max_points = (int)floor(distance_m / point_distance);
 291         double delta_last = fmod(distance_m, point_distance);
 292
 293         deque<double> elevations;
 294         deque<string> materials;
 295
 296
 297         double elevation_under_pilot = 0.0;
 298         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 299                 receiver_height = own_alt - elevation_under_pilot;
 300         }
 301
 302         double elevation_under_sender = 0.0;
 303         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 304                 transmitter_height = sender_alt - elevation_under_sender;
 305         }
 306         else {
 307                 transmitter_height = sender_alt;
 308         }
 309
 310
 311         transmitter_height += _tx_antenna_height;
 312         receiver_height += _rx_antenna_height;
 313
 314         //cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
 315         _root_node->setDoubleValue("station[0]/rx-height", receiver_height);
 316         _root_node->setDoubleValue("station[0]/tx-height", transmitter_height);
 317         _root_node->setDoubleValue("station[0]/distance", distance_m / 1000);
 318
 319         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 320
 321         while (elevations.size() <= e_size) {
 322                 probe_distance += point_distance;
 323                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 324                 const SGMaterial *mat = 0;
 325                 double elevation_m = 0.0;
 326
 327                 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
 328                         if((transmission_type == 3) || (transmission_type == 4)) {
 329                                 elevations.push_back(elevation_m);
 330                                 if(mat) {
 331                                         const std::vector<string> mat_names = mat->get_names();
 332                                         materials.push_back(mat_names[0]);
 333                                 }
 334                                 else {
 335                                         materials.push_back("None");
 336                                 }
 337                         }
 338                         else {
 339                                  elevations.push_front(elevation_m);
 340                                  if(mat) {
 341                                          const std::vector<string> mat_names = mat->get_names();
 342                                          materials.push_front(mat_names[0]);
 343                                 }
 344                                 else {
 345                                         materials.push_front("None");
 346                                 }
 347                         }
 348                 }
 349                 else {
 350                         if((transmission_type == 3) || (transmission_type == 4)) {
 351                                 elevations.push_back(0.0);
 352                                 materials.push_back("None");
 353                         }
 354                         else {
 355                                 elevations.push_front(0.0);
 356                                 materials.push_front("None");
 357                         }
 358                 }
 359         }
 360         if((transmission_type == 3) || (transmission_type == 4)) {
 361                 elevations.push_front(elevation_under_pilot);
 362                 if (delta_last > (point_distance / 2) )                 // only add last point if it's farther than half point_distance
 363                         elevations.push_back(elevation_under_sender);
 364         }
 365         else {
 366                 elevations.push_back(elevation_under_pilot);
 367                 if (delta_last > (point_distance / 2) )
 368                         elevations.push_front(elevation_under_sender);
 369         }
 370
 371
 372         double num_points= (double)elevations.size();
 373
 374
 375         elevations.push_front(point_distance);
 376         elevations.push_front(num_points -1);
 377
 378         int size = elevations.size();
 379         double *itm_elev;
 380         itm_elev = new double[size];
 381
 382         for(int i=0;i<size;i++) {
 383                 itm_elev[i]=elevations[i];
 384         }
 385
 386         if((transmission_type == 3) || (transmission_type == 4)) {
 387                 // the sender and receiver roles are switched
 388                 point_to_point(itm_elev, receiver_height, transmitter_height,
 389                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 390                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 391                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 392                         calculate_clutter_loss(frq_mhz, itm_elev, materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
 393         }
 394         else {
 395                 point_to_point(itm_elev, transmitter_height, receiver_height,
 396                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 397                         pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
 398                 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
 399                         calculate_clutter_loss(frq_mhz, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
 400         }
 401
 402         double pol_loss = 0.0;
 403         // TODO: remove this check after we check a bit the axis calculations in this function
 404         if (_polarization == 1) {
 405                 pol_loss = polarization_loss();
 406         }
 407         //SG_LOG(SG_GENERAL, SG_BULK,
 408         //              "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
 409         //cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 410         _root_node->setDoubleValue("station[0]/link-budget", link_budget);
 411         _root_node->setDoubleValue("station[0]/terrain-attenuation", dbloss);
 412         _root_node->setStringValue("station[0]/prop-mode", strmode);
 413         _root_node->setDoubleValue("station[0]/clutter-attenuation", clutter_loss);
 414         _root_node->setDoubleValue("station[0]/polarization-attenuation", pol_loss);
 415         //if (errnum == 4)      // if parameters are outside sane values for lrprop, bail out fast
 416         //      return -1;
 417
 418         // temporary, keep this antenna radiation pattern code here
 419         double tx_pattern_gain = 0.0;
 420         double rx_pattern_gain = 0.0;
 421         double sender_heading = 270.0; // due West
 422         double tx_antenna_bearing = sender_heading - reverse_course * SGD_RADIANS_TO_DEGREES;
 423         double rx_antenna_bearing = own_heading - course * SGD_RADIANS_TO_DEGREES;
 424         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;
 425         double tx_elev_angle = 0.0 - rx_elev_angle;
 426         if (_root_node->getBoolValue("use-tx-antenna-pattern", false)) {
 427                 FGRadioAntenna* TX_antenna;
 428                 TX_antenna = new FGRadioAntenna("Plot2");
 429                 TX_antenna->set_heading(sender_heading);
 430                 TX_antenna->set_elevation_angle(0);
 431                 tx_pattern_gain = TX_antenna->calculate_gain(tx_antenna_bearing, tx_elev_angle);
 432                 delete TX_antenna;
 433         }
 434         if (_root_node->getBoolValue("use-rx-antenna-pattern", false)) {
 435                 FGRadioAntenna* RX_antenna;
 436                 RX_antenna = new FGRadioAntenna("Plot2");
 437                 RX_antenna->set_heading(own_heading);
 438                 RX_antenna->set_elevation_angle(fgGetDouble("/orientation/pitch-deg"));
 439                 rx_pattern_gain = RX_antenna->calculate_gain(rx_antenna_bearing, rx_elev_angle);
 440                 delete RX_antenna;
 441         }
 442
 443         signal = link_budget - dbloss - clutter_loss + pol_loss + rx_pattern_gain + tx_pattern_gain;
 444         double signal_strength_dbm = signal_strength - dbloss - clutter_loss + pol_loss + rx_pattern_gain + tx_pattern_gain;
 445         double field_strength_uV = dbm_to_microvolt(signal_strength_dbm);
 446         _root_node->setDoubleValue("station[0]/signal-dbm", signal_strength_dbm);
 447         _root_node->setDoubleValue("station[0]/field-strength-uV", field_strength_uV);
 448         _root_node->setDoubleValue("station[0]/signal", signal);
 449         _root_node->setDoubleValue("station[0]/tx-erp", tx_erp);
 450
 451         //_root_node->setDoubleValue("station[0]/tx-pattern-gain", tx_pattern_gain);
 452         //_root_node->setDoubleValue("station[0]/rx-pattern-gain", rx_pattern_gain);
 453
 454         delete[] itm_elev;
 455
 456         return signal;
 457
 458 }
 459
 460
 461 void FGRadioTransmission::calculate_clutter_loss(double freq, double itm_elev[], deque<string> &materials,
 462         double transmitter_height, double receiver_height, int p_mode,
 463         double horizons[], double &clutter_loss) {
 464
 465         double distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
 466
 467         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 468                 int mat = 0;
 469                 int j=1;
 470                 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
 471
 472                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 473                         double clutter_density = 0.0;   // percent of reflected wave
 474                         get_material_properties(materials[mat], clutter_height, clutter_density);
 475
 476                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 477                         // First Fresnel radius
 478                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 479
 480                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 481
 482                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 483                         double d1 = j * itm_elev[1];
 484                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 485                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 486                         }
 487                         double ray_height = (grad * d1) + min_elev;
 488
 489                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 490                         double intrusion = fabs(clearance);
 491
 492                         if (clearance >= 0) {
 493                                 // no losses
 494                         }
 495                         else if (clearance < 0 && (intrusion < clutter_height)) {
 496
 497                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 498                         }
 499                         else if (clearance < 0 && (intrusion > clutter_height)) {
 500                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 501                         }
 502                         else {
 503                                 // no losses
 504                         }
 505                         j++;
 506                         mat++;
 507                 }
 508
 509         }
 510         else if (p_mode == 1) {         // diffraction
 511
 512                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 513                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
 514                         int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
 515                         //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
 516                         int last = 1;
 517                         /** perform the first pass */
 518                         int mat = 0;
 519                         int j=1;
 520                         for (int k=3;k < num_points_1st + 2;k++) {
 521                                 if (num_points_1st < 1)
 522                                         break;
 523                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 524                                 double clutter_density = 0.0;   // percent of reflected wave
 525                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 526
 527                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 528                                 // First Fresnel radius
 529                                 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) );
 530
 531                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 532
 533                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 534                                 double d1 = j * itm_elev[1];
 535                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 536                                         d1 = (num_points_1st - j) * itm_elev[1];
 537                                 }
 538                                 double ray_height = (grad * d1) + min_elev;
 539
 540                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 541                                 double intrusion = fabs(clearance);
 542
 543                                 if (clearance >= 0) {
 544                                         // no losses
 545                                 }
 546                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 547
 548                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 549                                 }
 550                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 551                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 552                                 }
 553                                 else {
 554                                         // no losses
 555                                 }
 556                                 j++;
 557                                 mat++;
 558                                 last = k;
 559                         }
 560
 561                         /** and the second pass */
 562                         mat +=1;
 563                         j =1; // first point is diffraction edge, 2nd the RX elevation
 564                         for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
 565                                 if (num_points_2nd < 1)
 566                                         break;
 567                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 568                                 double clutter_density = 0.0;   // percent of reflected wave
 569                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 570
 571                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 572                                 // First Fresnel radius
 573                                 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) );
 574
 575                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 576
 577                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 578                                 double d1 = j * itm_elev[1];
 579                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 580                                         d1 = (num_points_2nd - j) * itm_elev[1];
 581                                 }
 582                                 double ray_height = (grad * d1) + min_elev;
 583
 584                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 585                                 double intrusion = fabs(clearance);
 586
 587                                 if (clearance >= 0) {
 588                                         // no losses
 589                                 }
 590                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 591
 592                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 593                                 }
 594                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 595                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 596                                 }
 597                                 else {
 598                                         // no losses
 599                                 }
 600                                 j++;
 601                                 mat++;
 602                         }
 603
 604                 }
 605                 else {  // double horizon: same as single horizon, except there are 3 segments
 606
 607                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
 608                         int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
 609                         int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
 610                         //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
 611                         //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
 612                         int last = 1;
 613                         /** perform the first pass */
 614                         int mat = 0;
 615                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 616                         for (int k=3;k < num_points_1st +2;k++) {
 617                                 if (num_points_1st < 1)
 618                                         break;
 619                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 620                                 double clutter_density = 0.0;   // percent of reflected wave
 621                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 622
 623                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 624                                 // First Fresnel radius
 625                                 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) );
 626
 627                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 628
 629                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 630                                 double d1 = j * itm_elev[1];
 631                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 632                                         d1 = (num_points_1st - j) * itm_elev[1];
 633                                 }
 634                                 double ray_height = (grad * d1) + min_elev;
 635
 636                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 637                                 double intrusion = fabs(clearance);
 638
 639                                 if (clearance >= 0) {
 640                                         // no losses
 641                                 }
 642                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 643
 644                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 645                                 }
 646                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 647                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 648                                 }
 649                                 else {
 650                                         // no losses
 651                                 }
 652                                 j++;
 653                                 last = k;
 654                         }
 655                         mat +=1;
 656                         /** and the second pass */
 657                         int last2=1;
 658                         j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 659                         for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
 660                                 if (num_points_2nd < 1)
 661                                         break;
 662                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 663                                 double clutter_density = 0.0;   // percent of reflected wave
 664                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 665
 666                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
 667                                 // First Fresnel radius
 668                                 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) );
 669
 670                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 671
 672                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
 673                                 double d1 = j * itm_elev[1];
 674                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
 675                                         d1 = (num_points_2nd - j) * itm_elev[1];
 676                                 }
 677                                 double ray_height = (grad * d1) + min_elev;
 678
 679                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 680                                 double intrusion = fabs(clearance);
 681
 682                                 if (clearance >= 0) {
 683                                         // no losses
 684                                 }
 685                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 686
 687                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 688                                 }
 689                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 690                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 691                                 }
 692                                 else {
 693                                         // no losses
 694                                 }
 695                                 j++;
 696                                 mat++;
 697                                 last2 = k;
 698                         }
 699
 700                         /** third and final pass */
 701                         mat +=1;
 702                         j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 703                         for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
 704                                 if (num_points_3rd < 1)
 705                                         break;
 706                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 707                                 double clutter_density = 0.0;   // percent of reflected wave
 708                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 709
 710                                 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 711                                 // First Fresnel radius
 712                                 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) );
 713
 714
 715                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 716
 717                                 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 718                                 double d1 = j * itm_elev[1];
 719                                 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 720                                         d1 = (num_points_3rd - j) * itm_elev[1];
 721                                 }
 722                                 double ray_height = (grad * d1) + min_elev;
 723
 724                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 725                                 double intrusion = fabs(clearance);
 726
 727                                 if (clearance >= 0) {
 728                                         // no losses
 729                                 }
 730                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 731
 732                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 733                                 }
 734                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 735                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 736                                 }
 737                                 else {
 738                                         // no losses
 739                                 }
 740                                 j++;
 741                                 mat++;
 742
 743                         }
 744
 745                 }
 746         }
 747         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now... maybe do something with weather
 748                 clutter_loss = 0.0;
 749         }
 750
 751 }
 752
 753
 754 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 755
 756         if(mat_name == "Landmass") {
 757                 height = 15.0;
 758                 density = 0.2;
 759         }
 760
 761         else if(mat_name == "SomeSort") {
 762                 height = 15.0;
 763                 density = 0.2;
 764         }
 765
 766         else if(mat_name == "Island") {
 767                 height = 15.0;
 768                 density = 0.2;
 769         }
 770         else if(mat_name == "Default") {
 771                 height = 15.0;
 772                 density = 0.2;
 773         }
 774         else if(mat_name == "EvergreenBroadCover") {
 775                 height = 20.0;
 776                 density = 0.2;
 777         }
 778         else if(mat_name == "EvergreenForest") {
 779                 height = 20.0;
 780                 density = 0.2;
 781         }
 782         else if(mat_name == "DeciduousBroadCover") {
 783                 height = 15.0;
 784                 density = 0.3;
 785         }
 786         else if(mat_name == "DeciduousForest") {
 787                 height = 15.0;
 788                 density = 0.3;
 789         }
 790         else if(mat_name == "MixedForestCover") {
 791                 height = 20.0;
 792                 density = 0.25;
 793         }
 794         else if(mat_name == "MixedForest") {
 795                 height = 15.0;
 796                 density = 0.25;
 797         }
 798         else if(mat_name == "RainForest") {
 799                 height = 25.0;
 800                 density = 0.55;
 801         }
 802         else if(mat_name == "EvergreenNeedleCover") {
 803                 height = 15.0;
 804                 density = 0.2;
 805         }
 806         else if(mat_name == "WoodedTundraCover") {
 807                 height = 5.0;
 808                 density = 0.15;
 809         }
 810         else if(mat_name == "DeciduousNeedleCover") {
 811                 height = 5.0;
 812                 density = 0.2;
 813         }
 814         else if(mat_name == "ScrubCover") {
 815                 height = 3.0;
 816                 density = 0.15;
 817         }
 818         else if(mat_name == "BuiltUpCover") {
 819                 height = 30.0;
 820                 density = 0.7;
 821         }
 822         else if(mat_name == "Urban") {
 823                 height = 30.0;
 824                 density = 0.7;
 825         }
 826         else if(mat_name == "Construction") {
 827                 height = 30.0;
 828                 density = 0.7;
 829         }
 830         else if(mat_name == "Industrial") {
 831                 height = 30.0;
 832                 density = 0.7;
 833         }
 834         else if(mat_name == "Port") {
 835                 height = 30.0;
 836                 density = 0.7;
 837         }
 838         else if(mat_name == "Town") {
 839                 height = 10.0;
 840                 density = 0.5;
 841         }
 842         else if(mat_name == "SubUrban") {
 843                 height = 10.0;
 844                 density = 0.5;
 845         }
 846         else if(mat_name == "CropWoodCover") {
 847                 height = 10.0;
 848                 density = 0.1;
 849         }
 850         else if(mat_name == "CropWood") {
 851                 height = 10.0;
 852                 density = 0.1;
 853         }
 854         else if(mat_name == "AgroForest") {
 855                 height = 10.0;
 856                 density = 0.1;
 857         }
 858         else {
 859                 height = 0.0;
 860                 density = 0.0;
 861         }
 862
 863 }
 864
 865
 866 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 867
 868         double frq_mhz = freq;
 869         double dbloss;
 870         double tx_pow = _transmitter_power;
 871         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 872         double signal = 0.0;
 873
 874         double sender_alt_ft,sender_alt;
 875         double transmitter_height=0.0;
 876         double receiver_height=0.0;
 877         double own_lat = fgGetDouble("/position/latitude-deg");
 878         double own_lon = fgGetDouble("/position/longitude-deg");
 879         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 880         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 881
 882
 883         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 884
 885         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 886
 887         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 888
 889         SGGeod sender_pos = pos;
 890
 891         sender_alt_ft = sender_pos.getElevationFt();
 892         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 893
 894         receiver_height = own_alt;
 895         transmitter_height = sender_alt;
 896
 897         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 898
 899
 900         transmitter_height += _tx_antenna_height;
 901         receiver_height += _rx_antenna_height;
 902
 903
 904         /** radio horizon calculation with wave bending k=4/3 */
 905         double receiver_horizon = 4.12 * sqrt(receiver_height);
 906         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 907         double total_horizon = receiver_horizon + transmitter_horizon;
 908
 909         if (distance_m > total_horizon) {
 910                 return -1;
 911         }
 912         double pol_loss = 0.0;
 913         if (_polarization == 1) {
 914                 pol_loss = polarization_loss();
 915         }
 916         // free-space loss (distance calculation should be changed)
 917         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 918         signal = link_budget - dbloss + pol_loss;
 919
 920         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 921         return signal;
 922
 923 }
 924
 925 /*** calculate loss due to polarization mismatch
 926 *       this function is only reliable for vertical polarization
 927 *       due to the V-shape of horizontally polarized antennas
 928 ***/
 929 double FGRadioTransmission::polarization_loss() {
 930
 931         double theta_deg;
 932         double roll = fgGetDouble("/orientation/roll-deg");
 933         if (fabs(roll) > 85.0)
 934                 roll = 85.0;
 935         double pitch = fgGetDouble("/orientation/pitch-deg");
 936         if (fabs(pitch) > 85.0)
 937                 pitch = 85.0;
 938         double theta = fabs( atan( sqrt(
 939                 pow(tan(roll * SGD_DEGREES_TO_RADIANS), 2) +
 940                 pow(tan(pitch * SGD_DEGREES_TO_RADIANS), 2) )) * SGD_RADIANS_TO_DEGREES);
 941
 942         if (_polarization == 0)
 943                 theta_deg = 90.0 - theta;
 944         else
 945                 theta_deg = theta;
 946         if (theta_deg > 85.0)   // we don't want to converge into infinity
 947                 theta_deg = 85.0;
 948
 949         double loss = 10 * log10( pow(cos(theta_deg * SGD_DEGREES_TO_RADIANS), 2) );
 950         //cerr << "Polarization loss: " << loss << " dBm " << endl;
 951         return loss;
 952 }
 953
 954
 955 double FGRadioTransmission::watt_to_dbm(double power_watt) {
 956         return 10 * log10(1000 * power_watt);   // returns dbm
 957 }
 958
 959 double FGRadioTransmission::dbm_to_watt(double dbm) {
 960         return exp( (dbm-30) * log(10.0) / 10.0);       // returns Watts
 961 }
 962
 963 double FGRadioTransmission::dbm_to_microvolt(double dbm) {
 964         return sqrt(dbm_to_watt(dbm) * 50) * 1000000;   // returns microvolts
 965 }
 966
 967