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 #include "radio.hxx"
  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 FGRadio::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 = _transmitter_power;
 136         double ant_gain = _antenna_gain;
 137         double signal = 0.0;
 138
 139         if(transmission_type == 1)
 140                 tx_pow = _transmitter_power + 6.0;
 141
 142         if((transmission_type == 1) || (transmission_type == 3))
 143                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 144
 145         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 146
 147         FGScenery * scenery = globals->get_scenery();
 148
 149         double own_lat = fgGetDouble("/position/latitude-deg");
 150         double own_lon = fgGetDouble("/position/longitude-deg");
 151         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 152         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 153
 154
 155         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 156
 157         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 158         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 159         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 160         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 161
 162         // position of sender radio antenna (HAAT)
 163         // sender can be aircraft or ground station
 164         double ATC_HAAT = 30.0;
 165         double Aircraft_HAAT = 5.0;
 166         double sender_alt_ft,sender_alt;
 167         double transmitter_height=0.0;
 168         double receiver_height=0.0;
 169         SGGeod sender_pos = pos;
 170
 171         sender_alt_ft = sender_pos.getElevationFt();
 172         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 173         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 174         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 175         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 176
 177         double point_distance= 90.0; // regular SRTM is 90 meters
 178         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 179         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 180         double probe_distance = 0.0;
 181         // If distance larger than this value (300 km), assume reception imposssible
 182         if (distance_m > 300000)
 183                 return -1.0;
 184         // If above 9000, consider LOS mode and calculate free-space att
 185         if (own_alt > 9000) {
 186                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 187                 signal = link_budget - dbloss;
 188                 return signal;
 189         }
 190
 191
 192         double max_points = distance_m / point_distance;
 193         deque<double> _elevations;
 194
 195         double elevation_under_pilot = 0.0;
 196         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 197                 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
 198         }
 199
 200         double elevation_under_sender = 0.0;
 201         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 202                 transmitter_height = sender_alt - elevation_under_sender;
 203         }
 204         else {
 205                 transmitter_height = sender_alt;
 206         }
 207
 208         if(transmission_type == 1)
 209                 transmitter_height += ATC_HAAT;
 210         else
 211                 transmitter_height += Aircraft_HAAT;
 212
 213         cerr << "ITM:: RX-height: " << receiver_height << ", TX-height: " << transmitter_height << ", Distance: " << distance_m << endl;
 214
 215         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 216
 217         while (_elevations.size() <= e_size) {
 218                 probe_distance += point_distance;
 219                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 220
 221                 double elevation_m = 0.0;
 222
 223                 if (scenery->get_elevation_m( probe, elevation_m, NULL )) {
 224                         if((transmission_type == 3) || (transmission_type == 4)) {
 225                                 _elevations.push_back(elevation_m);
 226                         }
 227                         else {
 228                                  _elevations.push_front(elevation_m);
 229                         }
 230                 }
 231                 else {
 232                         if((transmission_type == 3) || (transmission_type == 4)) {
 233                                 _elevations.push_back(elevation_m);
 234                         }
 235                         else {
 236                         _elevations.push_front(0.0);
 237                         }
 238                 }
 239         }
 240         if((transmission_type == 3) || (transmission_type == 4)) {
 241                 _elevations.push_front(elevation_under_pilot);
 242                 _elevations.push_back(elevation_under_sender);
 243         }
 244         else {
 245                 _elevations.push_back(elevation_under_pilot);
 246                 _elevations.push_front(elevation_under_sender);
 247         }
 248
 249
 250         double max_alt_between=0.0;
 251         for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
 252                 if (_elevations[i] > max_alt_between) {
 253                         max_alt_between = _elevations[i];
 254                 }
 255         }
 256
 257         double num_points= (double)_elevations.size();
 258         //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
 259         _elevations.push_front(point_distance);
 260         _elevations.push_front(num_points -1);
 261         int size = _elevations.size();
 262         double itm_elev[size];
 263         for(int i=0;i<size;i++) {
 264                 itm_elev[i]=_elevations[i];
 265                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 266         }
 267
 268
 269         // first Fresnel zone radius
 270         // frequency in the middle of the bandplan, more accuracy is not necessary
 271         double fz_clr= 8.657 * sqrt(distance_m / 0.125);
 272
 273         // TODO: If we clear the first Fresnel zone, we are into line of sight territory
 274
 275         // else we need to calculate point to point link loss
 276         if((transmission_type == 3) || (transmission_type == 4)) {
 277                 // the sender and receiver roles are switched
 278                 point_to_point(itm_elev, receiver_height, transmitter_height,
 279                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 280                         pol, conf, rel, dbloss, strmode, errnum);
 281
 282         }
 283         else {
 284
 285                 point_to_point(itm_elev, transmitter_height, receiver_height,
 286                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 287                         pol, conf, rel, dbloss, strmode, errnum);
 288         }
 289
 290         cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 291
 292         //if (errnum == 4)
 293         //      return -1;
 294         signal = link_budget - dbloss;
 295         return signal;
 296
 297 }