src/Instrumentation/commradio.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 FGCommRadio::FGCommRadio(SGPropertyNode *node) {
  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 FGCommRadio::~FGCommRadio()
  53 {
  54 }
  55
  56 void FGCommRadio::init ()
  57 {
  58 }
  59
  60
  61 void FGCommRadio::bind ()
  62 {
  63 }
  64
  65
  66 void FGCommRadio::update ()
  67 {
  68         if (dt <= 0.0) {
  69                 return; // paused
  70     }
  71 }
  72
  73 double FGCommRadio::getFrequency(int radio) {
  74         double freq = 118.0;
  75         switch (radio) {
  76                 case 1:
  77                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  78                         break;
  79                 case 2:
  80                         freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
  81                         break;
  82                 default:
  83                         freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
  84
  85         }
  86         return freq;
  87 }
  88
  89
  90
  91
  92 void FGCommRadio::receiveText(SGGeod tx_pos, double freq, string text,
  93         int ground_to_air) {
  94
  95         comm1 = getFrequency(1);
  96         comm2 = getFrequency(2);
  97         if ( (freq != comm1) &&  (freq != comm2) ) {
  98                 return;
  99         }
 100         else {
 101                 double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
 102                 if (signal <= 0)
 103                         return;
 104                 if ((signal > 0) && (signal < 12)) {
 105                         //for low SNR values implement a way to make the conversation
 106                         //hard to understand but audible
 107                         //how this works in the real world, is the receiver AGC fails to capture the slope
 108                         //and the signal, due to being amplitude modulated, decreases volume after demodulation
 109                         //the implementation below is more akin to what would happen on a FM transmission
 110                         //therefore the correct way would be to work on the volume
 111                         /*
 112                         string hash_noise = " ";
 113                         int reps = fabs((int)signal - 11);
 114                         int t_size = text.size();
 115                         for (int n=1;n<=reps * 2;n++) {
 116                                 int pos = rand() % t_size -1;
 117                                 text.replace(pos,1, hash_noise);
 118                         }
 119                         */
 120
 121                 }
 122                 fgSetString("/sim/messages/atc", text.c_str());
 123         }
 124
 125 }
 126
 127 double FGCommRadio::ITM_calculate_attenuation(SGGeod pos, double freq,
 128                                int transmission_type) {
 129
 130         ///  Implement radio attenuation
 131         ///  based on the Longley-Rice propagation model
 132
 133         ////////////// ITM default parameters //////////////
 134         // in the future perhaps take them from tile materials?
 135         double eps_dielect=15.0;
 136         double sgm_conductivity = 0.005;
 137         double eno = 301.0;
 138         double frq_mhz;
 139         if( (freq < 118.0) || (freq > 137.0) )
 140                 frq_mhz = 125.0;        // sane value, middle of bandplan
 141         else
 142                 frq_mhz = freq;
 143         int radio_climate = 5;          // continental temperate
 144         int pol=1;      // assuming vertical polarization although this is more complex in reality
 145         double conf = 0.90;     // 90% of situations and time, take into account speed
 146         double rel = 0.90;      // ^^
 147         double dbloss;
 148         char strmode[150];
 149         int errnum;
 150
 151         double tx_pow,ant_gain;
 152         double signal = 0.0;
 153
 154         if(transmission_type == 1)
 155                 tx_pow = _transmitter_power + 6.0;
 156
 157         if((transmission_type == 1) || (transmission_type == 3))
 158                 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
 159
 160         double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
 161
 162         FGScenery * scenery = globals->get_scenery();
 163
 164         double own_lat = fgGetDouble("/position/latitude-deg");
 165         double own_lon = fgGetDouble("/position/longitude-deg");
 166         double own_alt_ft = fgGetDouble("/position/altitude-ft");
 167         double own_alt= own_alt_ft * SG_FEET_TO_METER;
 168
 169
 170         //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
 171
 172         SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
 173         SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
 174         SGGeoc center = SGGeoc::fromGeod( max_own_pos );
 175         SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
 176
 177         // position of sender radio antenna (HAAT)
 178         // sender can be aircraft or ground station
 179         double ATC_HAAT = 30.0;
 180         double Aircraft_HAAT = 5.0;
 181         double sender_alt_ft,sender_alt;
 182         double transmitter_height=0.0;
 183         double receiver_height=0.0;
 184         SGGeod sender_pos = pos;
 185
 186         sender_alt_ft = sender_pos.getElevationFt();
 187         sender_alt = sender_alt_ft * SG_FEET_TO_METER;
 188         SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
 189         SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
 190         //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
 191
 192         double point_distance= 90.0; // regular SRTM is 90 meters
 193         double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
 194         double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
 195         double probe_distance = 0.0;
 196         // If distance larger than this value (300 km), assume reception imposssible to preserve resources
 197         if (distance_m > 300000)
 198                 return -1.0;
 199         // If above 9000, consider LOS mode and calculate free-space att
 200         if (own_alt > 9000) {
 201                 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
 202                 signal = link_budget - dbloss;
 203                 return signal;
 204         }
 205
 206
 207         double max_points = distance_m / point_distance;
 208         deque<double> _elevations;
 209
 210         double elevation_under_pilot = 0.0;
 211         if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
 212                 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
 213         }
 214
 215         double elevation_under_sender = 0.0;
 216         if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
 217                 transmitter_height = sender_alt - elevation_under_sender;
 218         }
 219         else {
 220                 transmitter_height = sender_alt;
 221         }
 222
 223         if(transmission_type == 1)
 224                 transmitter_height += ATC_HAAT;
 225         else
 226                 transmitter_height += Aircraft_HAAT;
 227
 228         cerr << "ITM:: RX-height: " << receiver_height << ", TX-height: " << transmitter_height << ", Distance: " << distance_m << endl;
 229
 230         unsigned int e_size = (deque<unsigned>::size_type)max_points;
 231
 232         while (_elevations.size() <= e_size) {
 233                 probe_distance += point_distance;
 234                 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
 235
 236                 double elevation_m = 0.0;
 237
 238                 if (scenery->get_elevation_m( probe, elevation_m, NULL )) {
 239                         if((transmission_type == 3) || (transmission_type == 4)) {
 240                                 _elevations.push_back(elevation_m);
 241                         }
 242                         else {
 243                                  _elevations.push_front(elevation_m);
 244                         }
 245                 }
 246                 else {
 247                         if((transmission_type == 3) || (transmission_type == 4)) {
 248                                 _elevations.push_back(elevation_m);
 249                         }
 250                         else {
 251                         _elevations.push_front(0.0);
 252                         }
 253                 }
 254         }
 255         if((transmission_type == 3) || (transmission_type == 4)) {
 256                 _elevations.push_front(elevation_under_pilot);
 257                 _elevations.push_back(elevation_under_sender);
 258         }
 259         else {
 260                 _elevations.push_back(elevation_under_pilot);
 261                 _elevations.push_front(elevation_under_sender);
 262         }
 263
 264
 265         double max_alt_between=0.0;
 266         for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
 267                 if (_elevations[i] > max_alt_between) {
 268                         max_alt_between = _elevations[i];
 269                 }
 270         }
 271
 272         double num_points= (double)_elevations.size();
 273         //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
 274         _elevations.push_front(point_distance);
 275         _elevations.push_front(num_points -1);
 276         int size = _elevations.size();
 277         double itm_elev[size];
 278         for(int i=0;i<size;i++) {
 279                 itm_elev[i]=_elevations[i];
 280                 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
 281         }
 282
 283
 284         // first Fresnel zone radius
 285         // frequency in the middle of the bandplan, more accuracy is not necessary
 286         double fz_clr= 8.657 * sqrt(distance_m / 0.125);
 287
 288         // TODO: If we clear the first Fresnel zone, we are into line of sight teritory
 289
 290         // else we need to calculate point to point link loss
 291         if((transmission_type == 3) || (transmission_type == 4)) {
 292                 // the sender and receiver roles are switched
 293                 point_to_point(itm_elev, receiver_height, transmitter_height,
 294                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 295                         pol, conf, rel, dbloss, strmode, errnum);
 296
 297         }
 298         else {
 299
 300                 point_to_point(itm_elev, transmitter_height, receiver_height,
 301                         eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
 302                         pol, conf, rel, dbloss, strmode, errnum);
 303         }
 304
 305         cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
 306
 307         //if (errnum == 4)
 308         //      return -1;
 309         signal = link_budget - dbloss;
 310         return signal;
 311
 312 }