src/Radio/radio.cxx

   1 // radio.cxx -- implementation of FGRadio
   2 // Class to manage radio propagation using the ITM model
   3 // Written by Adrian Musceac, started August 2011.
   4 //
   5 // This program is free software; you can redistribute it and/or
   6 // modify it under the terms of the GNU General Public License as
   7 // published by the Free Software Foundation; either version 2 of the
   8 // License, or (at your option) any later version.
   9 //
  10 // This program is distributed in the hope that it will be useful, but
  11 // WITHOUT ANY WARRANTY; without even the implied warranty of
  12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13 // General Public License for more details.
  14 //
  15 // You should have received a copy of the GNU General Public License
  16 // along with this program; if not, write to the Free Software
  17 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
  18
  19
  20
  21 #ifdef HAVE_CONFIG_H
  22 #  include <config.h>
  23 #endif
  24
  25 #include <math.h>
  26
  27 #include <stdlib.h>
  28 #include <deque>
  29 #include "radio.hxx"
  30 #include <simgear/scene/material/mat.hxx>
  31 #include <Scenery/scenery.hxx>
  32
  33 #define WITH_POINT_TO_POINT 1
  34 #include "itm.cpp"
  35
  36
  37 FGRadioTransmission::FGRadioTransmission() {
  38
  39
  40         _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
  41
  42         /** AM transmitter power in dBm.
  43         *       Typical output powers for ATC ground equipment, VHF-UHF:
  44         *       40 dBm - 10 W (ground, clearance)
  45         *       44 dBm - 20 W (tower)
  46         *       47 dBm - 50 W (center, sectors)
  47         *       50 dBm - 100 W (center, sectors)
  48         *       53 dBm - 200 W (sectors, on directional arrays)
  49         **/
  50         _transmitter_power = 43.0;
  51
  52         _tx_antenna_height = 2.0; // TX antenna height above ground level
  53
  54         _rx_antenna_height = 2.0; // RX antenna height above ground level
  55
  56
  57         _rx_antenna_gain = 1.0; // gain expressed in dBi
  58         _tx_antenna_gain = 1.0;
  59
  60         _rx_line_losses = 2.0;  // to be configured for each station
  61         _tx_line_losses = 2.0;
  62
  63         _polarization = 1; // default vertical
  64
  65         _propagation_model = 2;
  66
  67         _root_node = fgGetNode("sim/radio", true);
  68         _terrain_sampling_distance = _root_node->getDoubleValue("sampling-distance", 90.0); // regular SRTM is 90 meters
  69
  70
  71 }
  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                         clutterLoss(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                         clutterLoss(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         //cerr << "Clutter loss: " << clutter_loss << endl;
 402         //if (errnum == 4)      // if parameters are outside sane values for lrprop, the alternative method is used
 403         //      return -1;
 404         double sender_heading = 270.0; // due West
 405         double tx_antenna_bearing = sender_heading - reverse_course;
 406         double rx_antenna_bearing = own_heading - course;
 407         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;
 408         double tx_elev_angle = 0.0 - rx_elev_angle;
 409         _TX_antenna = new FGRadioAntenna("Plot2");
 410         _TX_antenna->set_heading(sender_heading);
 411         _TX_antenna->set_elevation_angle(0);
 412         double tx_pattern_gain = _TX_antenna->calculate_gain(tx_antenna_bearing, tx_elev_angle);
 413         _RX_antenna = new FGRadioAntenna("Plot2");
 414         _RX_antenna->set_heading(own_heading);
 415         _RX_antenna->set_elevation_angle(fgGetDouble("/orientation/pitch-deg"));
 416         double rx_pattern_gain = _RX_antenna->calculate_gain(rx_antenna_bearing, rx_elev_angle);
 417
 418         delete _TX_antenna;
 419         delete _RX_antenna;
 420         signal = link_budget - dbloss - clutter_loss + pol_loss;
 421         double signal_strength_dbm = signal_strength - dbloss - clutter_loss + pol_loss;
 422         double field_strength_uV = dbm_to_microvolt(signal_strength_dbm);
 423         _root_node->setDoubleValue("station[0]/signal-dbm", signal_strength_dbm);
 424         _root_node->setDoubleValue("station[0]/field-strength-uV", field_strength_uV);
 425         _root_node->setDoubleValue("station[0]/signal", signal);
 426         _root_node->setDoubleValue("station[0]/tx-erp", tx_erp);
 427         _root_node->setDoubleValue("station[0]/tx-pattern-gain", tx_pattern_gain);
 428         _root_node->setDoubleValue("station[0]/rx-pattern-gain", rx_pattern_gain);
 429         return signal;
 430
 431 }
 432
 433 /*** Calculate losses due to vegetation and urban clutter (WIP)
 434 *        We are only worried about clutter loss, terrain influence
 435 *        on the first Fresnel zone is calculated in the ITM functions
 436 ***/
 437 void FGRadioTransmission::clutterLoss(double freq, double itm_elev[], deque<string> materials,
 438         double transmitter_height, double receiver_height, int p_mode,
 439         double horizons[], double &clutter_loss) {
 440
 441         double distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
 442
 443         if (p_mode == 0) {      // LOS: take each point and see how clutter height affects first Fresnel zone
 444                 int mat = 0;
 445                 int j=1;
 446                 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
 447
 448                         double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 449                         double clutter_density = 0.0;   // percent of reflected wave
 450                         get_material_properties(materials[mat], clutter_height, clutter_density);
 451
 452                         double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 453                         // First Fresnel radius
 454                         double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / (  distance_m * freq / 1000) );
 455
 456                         //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 457
 458                         double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 459                         double d1 = j * itm_elev[1];
 460                         if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 461                                 d1 = (itm_elev[0] - j) * itm_elev[1];
 462                         }
 463                         double ray_height = (grad * d1) + min_elev;
 464
 465                         double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 466                         double intrusion = fabs(clearance);
 467
 468                         if (clearance >= 0) {
 469                                 // no losses
 470                         }
 471                         else if (clearance < 0 && (intrusion < clutter_height)) {
 472
 473                                 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 474                         }
 475                         else if (clearance < 0 && (intrusion > clutter_height)) {
 476                                 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 477                         }
 478                         else {
 479                                 // no losses
 480                         }
 481                         j++;
 482                         mat++;
 483                 }
 484
 485         }
 486         else if (p_mode == 1) {         // diffraction
 487
 488                 if (horizons[1] == 0.0) {       //      single horizon: same as above, except pass twice using the highest point
 489                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
 490                         int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
 491                         //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
 492                         int last = 1;
 493                         /** perform the first pass */
 494                         int mat = 0;
 495                         int j=1;
 496                         for (int k=3;k < num_points_1st + 2;k++) {
 497                                 if (num_points_1st < 1)
 498                                         break;
 499                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 500                                 double clutter_density = 0.0;   // percent of reflected wave
 501                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 502
 503                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 504                                 // First Fresnel radius
 505                                 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) );
 506
 507                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 508
 509                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 510                                 double d1 = j * itm_elev[1];
 511                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 512                                         d1 = (num_points_1st - j) * itm_elev[1];
 513                                 }
 514                                 double ray_height = (grad * d1) + min_elev;
 515
 516                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 517                                 double intrusion = fabs(clearance);
 518
 519                                 if (clearance >= 0) {
 520                                         // no losses
 521                                 }
 522                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 523
 524                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 525                                 }
 526                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 527                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 528                                 }
 529                                 else {
 530                                         // no losses
 531                                 }
 532                                 j++;
 533                                 mat++;
 534                                 last = k;
 535                         }
 536
 537                         /** and the second pass */
 538                         mat +=1;
 539                         j =1; // first point is diffraction edge, 2nd the RX elevation
 540                         for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
 541                                 if (num_points_2nd < 1)
 542                                         break;
 543                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 544                                 double clutter_density = 0.0;   // percent of reflected wave
 545                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 546
 547                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 548                                 // First Fresnel radius
 549                                 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) );
 550
 551                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 552
 553                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 554                                 double d1 = j * itm_elev[1];
 555                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 556                                         d1 = (num_points_2nd - j) * itm_elev[1];
 557                                 }
 558                                 double ray_height = (grad * d1) + min_elev;
 559
 560                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 561                                 double intrusion = fabs(clearance);
 562
 563                                 if (clearance >= 0) {
 564                                         // no losses
 565                                 }
 566                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 567
 568                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 569                                 }
 570                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 571                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 572                                 }
 573                                 else {
 574                                         // no losses
 575                                 }
 576                                 j++;
 577                                 mat++;
 578                         }
 579
 580                 }
 581                 else {  // double horizon: same as single horizon, except there are 3 segments
 582
 583                         int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
 584                         int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
 585                         int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
 586                         //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
 587                         //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
 588                         int last = 1;
 589                         /** perform the first pass */
 590                         int mat = 0;
 591                         int j=1; // first point is TX elevation, 2nd is obstruction elevation
 592                         for (int k=3;k < num_points_1st +2;k++) {
 593                                 if (num_points_1st < 1)
 594                                         break;
 595                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 596                                 double clutter_density = 0.0;   // percent of reflected wave
 597                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 598
 599                                 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
 600                                 // First Fresnel radius
 601                                 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) );
 602
 603                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 604
 605                                 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
 606                                 double d1 = j * itm_elev[1];
 607                                 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
 608                                         d1 = (num_points_1st - j) * itm_elev[1];
 609                                 }
 610                                 double ray_height = (grad * d1) + min_elev;
 611
 612                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 613                                 double intrusion = fabs(clearance);
 614
 615                                 if (clearance >= 0) {
 616                                         // no losses
 617                                 }
 618                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 619
 620                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 621                                 }
 622                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 623                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 624                                 }
 625                                 else {
 626                                         // no losses
 627                                 }
 628                                 j++;
 629                                 last = k;
 630                         }
 631                         mat +=1;
 632                         /** and the second pass */
 633                         int last2=1;
 634                         j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
 635                         for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
 636                                 if (num_points_2nd < 1)
 637                                         break;
 638                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 639                                 double clutter_density = 0.0;   // percent of reflected wave
 640                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 641
 642                                 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
 643                                 // First Fresnel radius
 644                                 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) );
 645
 646                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 647
 648                                 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
 649                                 double d1 = j * itm_elev[1];
 650                                 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
 651                                         d1 = (num_points_2nd - j) * itm_elev[1];
 652                                 }
 653                                 double ray_height = (grad * d1) + min_elev;
 654
 655                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 656                                 double intrusion = fabs(clearance);
 657
 658                                 if (clearance >= 0) {
 659                                         // no losses
 660                                 }
 661                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 662
 663                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 664                                 }
 665                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 666                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 667                                 }
 668                                 else {
 669                                         // no losses
 670                                 }
 671                                 j++;
 672                                 mat++;
 673                                 last2 = k;
 674                         }
 675
 676                         /** third and final pass */
 677                         mat +=1;
 678                         j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
 679                         for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
 680                                 if (num_points_3rd < 1)
 681                                         break;
 682                                 double clutter_height = 0.0;    // mean clutter height for a certain terrain type
 683                                 double clutter_density = 0.0;   // percent of reflected wave
 684                                 get_material_properties(materials[mat], clutter_height, clutter_density);
 685
 686                                 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
 687                                 // First Fresnel radius
 688                                 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) );
 689
 690
 691                                 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 );    // K=4/3
 692
 693                                 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
 694                                 double d1 = j * itm_elev[1];
 695                                 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
 696                                         d1 = (num_points_3rd - j) * itm_elev[1];
 697                                 }
 698                                 double ray_height = (grad * d1) + min_elev;
 699
 700                                 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
 701                                 double intrusion = fabs(clearance);
 702
 703                                 if (clearance >= 0) {
 704                                         // no losses
 705                                 }
 706                                 else if (clearance < 0 && (intrusion < clutter_height)) {
 707
 708                                         clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
 709                                 }
 710                                 else if (clearance < 0 && (intrusion > clutter_height)) {
 711                                         clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
 712                                 }
 713                                 else {
 714                                         // no losses
 715                                 }
 716                                 j++;
 717                                 mat++;
 718
 719                         }
 720
 721                 }
 722         }
 723         else if (p_mode == 2) {         //      troposcatter: ignore ground clutter for now...
 724                 clutter_loss = 0.0;
 725         }
 726
 727 }
 728
 729 /***    Temporary material properties database
 730 *               height: median clutter height
 731 *               density: radiowave attenuation factor
 732 ***/
 733 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
 734
 735         if(mat_name == "Landmass") {
 736                 height = 15.0;
 737                 density = 0.2;
 738         }
 739
 740         else if(mat_name == "SomeSort") {
 741                 height = 15.0;
 742                 density = 0.2;
 743         }
 744
 745         else if(mat_name == "Island") {
 746                 height = 15.0;
 747                 density = 0.2;
 748         }
 749         else if(mat_name == "Default") {
 750                 height = 15.0;
 751                 density = 0.2;
 752         }
 753         else if(mat_name == "EvergreenBroadCover") {
 754                 height = 20.0;
 755                 density = 0.2;
 756         }
 757         else if(mat_name == "EvergreenForest") {
 758                 height = 20.0;
 759                 density = 0.2;
 760         }
 761         else if(mat_name == "DeciduousBroadCover") {
 762                 height = 15.0;
 763                 density = 0.3;
 764         }
 765         else if(mat_name == "DeciduousForest") {
 766                 height = 15.0;
 767                 density = 0.3;
 768         }
 769         else if(mat_name == "MixedForestCover") {
 770                 height = 20.0;
 771                 density = 0.25;
 772         }
 773         else if(mat_name == "MixedForest") {
 774                 height = 15.0;
 775                 density = 0.25;
 776         }
 777         else if(mat_name == "RainForest") {
 778                 height = 25.0;
 779                 density = 0.55;
 780         }
 781         else if(mat_name == "EvergreenNeedleCover") {
 782                 height = 15.0;
 783                 density = 0.2;
 784         }
 785         else if(mat_name == "WoodedTundraCover") {
 786                 height = 5.0;
 787                 density = 0.15;
 788         }
 789         else if(mat_name == "DeciduousNeedleCover") {
 790                 height = 5.0;
 791                 density = 0.2;
 792         }
 793         else if(mat_name == "ScrubCover") {
 794                 height = 3.0;
 795                 density = 0.15;
 796         }
 797         else if(mat_name == "BuiltUpCover") {
 798                 height = 30.0;
 799                 density = 0.7;
 800         }
 801         else if(mat_name == "Urban") {
 802                 height = 30.0;
 803                 density = 0.7;
 804         }
 805         else if(mat_name == "Construction") {
 806                 height = 30.0;
 807                 density = 0.7;
 808         }
 809         else if(mat_name == "Industrial") {
 810                 height = 30.0;
 811                 density = 0.7;
 812         }
 813         else if(mat_name == "Port") {
 814                 height = 30.0;
 815                 density = 0.7;
 816         }
 817         else if(mat_name == "Town") {
 818                 height = 10.0;
 819                 density = 0.5;
 820         }
 821         else if(mat_name == "SubUrban") {
 822                 height = 10.0;
 823                 density = 0.5;
 824         }
 825         else if(mat_name == "CropWoodCover") {
 826                 height = 10.0;
 827                 density = 0.1;
 828         }
 829         else if(mat_name == "CropWood") {
 830                 height = 10.0;
 831                 density = 0.1;
 832         }
 833         else if(mat_name == "AgroForest") {
 834                 height = 10.0;
 835                 density = 0.1;
 836         }
 837         else {
 838                 height = 0.0;
 839                 density = 0.0;
 840         }
 841
 842 }
 843
 844 /*** implement simple LOS propagation model (WIP)
 845 ***/
 846 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
 847         double frq_mhz;
 848         if( (freq < 118.0) || (freq > 137.0) )
 849                 frq_mhz = 125.0;        // sane value, middle of bandplan
 850         else
 851                 frq_mhz = freq;
 852         double dbloss;
 853         double tx_pow = _transmitter_power;
 854         double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
 855         double signal = 0.0;
 856
 857         double sender_alt_ft,sender_alt;
 858         double transmitter_height=0.0;
 859         double receiver_height=0.0;
 860         double own_lat = fgGetDouble("/position/latitude-deg");
 861         double own_lon = fgGetDouble("/position/longitude-deg");
 862         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 863         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 864
 865
 866         double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
 867
 868         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 869
 870         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 871
 872         SGGeod sender_pos = pos;
 873
 874         sender_alt_ft = sender_pos.getElevationFt();
 875         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 876
 877         receiver_height = own_alt;
 878         transmitter_height = sender_alt;
 879
 880         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 881
 882
 883         transmitter_height += _tx_antenna_height;
 884         receiver_height += _rx_antenna_height;
 885
 886
 887         /** radio horizon calculation with wave bending k=4/3 */
 888         double receiver_horizon = 4.12 * sqrt(receiver_height);
 889         double transmitter_horizon = 4.12 * sqrt(transmitter_height);
 890         double total_horizon = receiver_horizon + transmitter_horizon;
 891
 892         if (distance_m > total_horizon) {
 893                 return -1;
 894         }
 895         double pol_loss = 0.0;
 896         if (_polarization == 1) {
 897                 pol_loss = polarization_loss();
 898         }
 899         // free-space loss (distance calculation should be changed)
 900         dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 901         signal = link_budget - dbloss + pol_loss;
 902         SG_LOG(SG_GENERAL, SG_BULK,
 903                         "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
 904         //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
 905         return signal;
 906
 907 }
 908
 909 /*** calculate loss due to polarization mismatch
 910 *       this function is only reliable for vertical polarization
 911 *       due to the V-shape of horizontally polarized antennas
 912 ***/
 913 double FGRadioTransmission::polarization_loss() {
 914
 915         double theta_deg;
 916         double roll = fgGetDouble("/orientation/roll-deg");
 917         if (fabs(roll) > 85.0)
 918                 roll = 85.0;
 919         double pitch = fgGetDouble("/orientation/pitch-deg");
 920         if (fabs(pitch) > 85.0)
 921                 pitch = 85.0;
 922         double theta = fabs( atan( sqrt(
 923                 pow(tan(roll * SGD_DEGREES_TO_RADIANS), 2) +
 924                 pow(tan(pitch * SGD_DEGREES_TO_RADIANS), 2) )) * SGD_RADIANS_TO_DEGREES);
 925
 926         if (_polarization == 0)
 927                 theta_deg = 90.0 - theta;
 928         else
 929                 theta_deg = theta;
 930         if (theta_deg > 85.0)   // we don't want to converge into infinity
 931                 theta_deg = 85.0;
 932
 933         double loss = 10 * log10( pow(cos(theta_deg * SGD_DEGREES_TO_RADIANS), 2) );
 934         //cerr << "Polarization loss: " << loss << " dBm " << endl;
 935         return loss;
 936 }
 937
 938
 939 double FGRadioTransmission::watt_to_dbm(double power_watt) {
 940         return 10 * log10(1000 * power_watt);   // returns dbm
 941 }
 942
 943 double FGRadioTransmission::dbm_to_watt(double dbm) {
 944         return exp( (dbm-30) * log(10) / 10);   // returns Watts
 945 }
 946
 947 double FGRadioTransmission::dbm_to_microvolt(double dbm) {
 948         return sqrt(dbm_to_watt(dbm) * 50) * 1000000;   // returns microvolts
 949 }
 950
 951