src/Radio/radio.cxx

   1 // commradio.cxx -- implementation of FGCommRadio
   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 #include <stdlib.h>
  27 #include <deque>
  28
  29 #include <Scenery/scenery.hxx>
  30
  31 #define WITH_POINT_TO_POINT 1
  32 #include "itm.cpp"
  33
  34
  35 FGRadio::FGRadio() {
  36
  37         /////////// radio parameters ///////////
  38         _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
  39         // AM transmitter power in dBm.
  40         // Note this value is calculated from the typical final transistor stage output
  41         // !!! small aircraft have portable transmitters which operate at 36 dBm output (4 Watts)
  42         // later store this value in aircraft description
  43         // ATC comms usually operate high power equipment, thus making the link asymetrical; this is ignored for now
  44         _transmitter_power = 43.0;
  45         //pilot plane's antenna gain + AI aircraft antenna gain
  46         //real-life gain for conventional monopole/dipole antenna
  47         _antenna_gain = 2.0;
  48         _propagation_model = 2; //  choose between models via option: realistic radio on/off
  49
  50 }
  51
  52 FGRadio::~FGRadio()
  53 {
  54 }
  55
  56
  57 double FGCommRadio::getFrequency(int radio) {
  58         double freq = 118.0;
  59         switch (radio) {
  60                 case 1:
  61                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  62                         break;
  63                 case 2:
  64                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  65                         break;
  66                 default:
  67                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  68
  69         }
  70         return freq;
  71 }
  72
  73
  74
  75
  76 void FGRadio::receiveText(SGGeod tx_pos, double freq, string text,
  77         int ground_to_air) {
  78
  79         double comm1 = getFrequency(1);
  80         double comm2 = getFrequency(2);
  81         if ( (freq != comm1) &&  (freq != comm2) ) {
  82                 return;
  83         }
  84         else {
  85                 double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
  86                 if (signal <= 0)
  87                         return;
  88                 if ((signal > 0) && (signal < 12)) {
  89                         //for low SNR values implement a way to make the conversation
  90                         //hard to understand but audible
  91                         //how this works in the real world, is the receiver AGC fails to capture the slope
  92                         //and the signal, due to being amplitude modulated, decreases volume after demodulation
  93                         //the implementation below is more akin to what would happen on a FM transmission
  94                         //therefore the correct way would be to work on the volume
  95                         /*
  96                         string hash_noise = " ";
  97                         int reps = fabs((int)signal - 11);
  98                         int t_size = text.size();
  99                         for (int n=1;n<=reps * 2;n++) {
 100                                 int pos = rand() % t_size -1;
 101                                 text.replace(pos,1, hash_noise);
 102                         }
 103                         */
 104
 105                 }
 106                 fgSetString("/sim/messages/atc", text.c_str());
 107         }
 108
 109 }
 110
 111 double FGRadio::ITM_calculate_attenuation(SGGeod pos, double freq,
 112                                int transmission_type) {
 113
 114         ///  Implement radio attenuation
 115         ///  based on the Longley-Rice propagation model
 116
 117         ////////////// ITM default parameters //////////////
 118         // in the future perhaps take them from tile materials?
 119         double eps_dielect=15.0;
 120         double sgm_conductivity = 0.005;
 121         double eno = 301.0;
 122         double frq_mhz;
 123         if( (freq < 118.0) || (freq > 137.0) )
 124                 frq_mhz = 125.0;        // sane value, middle of bandplan
 125         else
 126                 frq_mhz = freq;
 127         int radio_climate = 5;          // continental temperate
 128         int pol=1;      // assuming vertical polarization although this is more complex in reality
 129         double conf = 0.90;     // 90% of situations and time, take into account speed
 130         double rel = 0.90;
 131         double dbloss;
 132         char strmode[150];
 133         int errnum;
 134
 135         double tx_pow,ant_gain;
 136         double signal = 0.0;
 137
 138         if(transmission_type == 1)
 139                 tx_pow = _transmitter_power + 6.0;
 140
 141         if((transmission_type == 1) || (transmission_type == 3))
 142                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 143
 144         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 145
 146         FGScenery * scenery = globals->get_scenery();
 147
 148         double own_lat = fgGetDouble("/position/latitude-deg");
 149         double own_lon = fgGetDouble("/position/longitude-deg");
 150         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 151         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 152
 153
 154         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 155
 156         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 157         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 158         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 159         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 160
 161         // position of sender radio antenna (HAAT)
 162         // sender can be aircraft or ground station
 163         double ATC_HAAT = 30.0;
 164         double Aircraft_HAAT = 5.0;
 165         double sender_alt_ft,sender_alt;
 166         double transmitter_height=0.0;
 167         double receiver_height=0.0;
 168         SGGeod sender_pos = pos;
 169
 170         sender_alt_ft = sender_pos.getElevationFt();
 171         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 172         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 173         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 174         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 175
 176         double point_distance= 90.0; // regular SRTM is 90 meters
 177         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 178         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 179         double probe_distance = 0.0;
 180         // If distance larger than this value (300 km), assume reception imposssible to preserve resources
 181         if (distance_m > 300000)
 182                 return -1.0;
 183         // If above 9000, consider LOS mode and calculate free-space att
 184         if (own_alt > 9000) {
 185                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 186                 signal = link_budget - dbloss;
 187                 return signal;
 188         }
 189
 190
 191         double max_points = distance_m / point_distance;
 192         deque<double> _elevations;
 193
 194         double elevation_under_pilot = 0.0;
 195         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 196                 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
 197         }
 198
 199         double elevation_under_sender = 0.0;
 200         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 201                 transmitter_height = sender_alt - elevation_under_sender;
 202         }
 203         else {
 204                 transmitter_height = sender_alt;
 205         }
 206
 207         if(transmission_type == 1)
 208                 transmitter_height += ATC_HAAT;
 209         else
 210                 transmitter_height += Aircraft_HAAT;
 211
 212         cerr << "ITM:: RX-height: " << receiver_height << ", TX-height: " << transmitter_height << ", Distance: " << distance_m << endl;
 213
 214         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 215
 216         while (_elevations.size() <= e_size) {
 217                 probe_distance += point_distance;
 218                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 219
 220                 double elevation_m = 0.0;
 221
 222                 if (scenery->get_elevation_m( probe, elevation_m, NULL )) {
 223                         if((transmission_type == 3) || (transmission_type == 4)) {
 224                                 _elevations.push_back(elevation_m);
 225                         }
 226                         else {
 227                                  _elevations.push_front(elevation_m);
 228                         }
 229                 }
 230                 else {
 231                         if((transmission_type == 3) || (transmission_type == 4)) {
 232                                 _elevations.push_back(elevation_m);
 233                         }
 234                         else {
 235                         _elevations.push_front(0.0);
 236                         }
 237                 }
 238         }
 239         if((transmission_type == 3) || (transmission_type == 4)) {
 240                 _elevations.push_front(elevation_under_pilot);
 241                 _elevations.push_back(elevation_under_sender);
 242         }
 243         else {
 244                 _elevations.push_back(elevation_under_pilot);
 245                 _elevations.push_front(elevation_under_sender);
 246         }
 247
 248
 249         double max_alt_between=0.0;
 250         for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
 251                 if (_elevations[i] > max_alt_between) {
 252                         max_alt_between = _elevations[i];
 253                 }
 254         }
 255
 256         double num_points= (double)_elevations.size();
 257         //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
 258         _elevations.push_front(point_distance);
 259         _elevations.push_front(num_points -1);
 260         int size = _elevations.size();
 261         double itm_elev[size];
 262         for(int i=0;i<size;i++) {
 263                 itm_elev[i]=_elevations[i];
 264                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 265         }
 266
 267
 268         // first Fresnel zone radius
 269         // frequency in the middle of the bandplan, more accuracy is not necessary
 270         double fz_clr= 8.657 * sqrt(distance_m / 0.125);
 271
 272         // TODO: If we clear the first Fresnel zone, we are into line of sight teritory
 273
 274         // else we need to calculate point to point link loss
 275         if((transmission_type == 3) || (transmission_type == 4)) {
 276                 // the sender and receiver roles are switched
 277                 point_to_point(itm_elev, receiver_height, transmitter_height,
 278                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 279                         pol, conf, rel, dbloss, strmode, errnum);
 280
 281         }
 282         else {
 283
 284                 point_to_point(itm_elev, transmitter_height, receiver_height,
 285                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 286                         pol, conf, rel, dbloss, strmode, errnum);
 287         }
 288
 289         cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 290
 291         //if (errnum == 4)
 292         //      return -1;
 293         signal = link_budget - dbloss;
 294         return signal;
 295
 296 }