1 // commradio.cxx -- implementation of FGCommRadio
2 // Class to manage radio propagation using the ITM model
3 // Written by Adrian Musceac, started August 2011.
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.
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.
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.
29 #include <Scenery/scenery.hxx>
31 #define WITH_POINT_TO_POINT 1
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
48 _propagation_model = 2; // choose between models via option: realistic radio on/off
57 double FGRadio::getFrequency(int radio) {
61 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
64 freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
67 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
76 void FGRadio::receiveText(SGGeod tx_pos, double freq, string text,
79 double comm1 = getFrequency(1);
80 double comm2 = getFrequency(2);
81 if ( (freq != comm1) && (freq != comm2) ) {
85 double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
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
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);
106 fgSetString("/sim/messages/atc", text.c_str());
111 double FGRadio::ITM_calculate_attenuation(SGGeod pos, double freq,
112 int transmission_type) {
114 /// Implement radio attenuation
115 /// based on the Longley-Rice propagation model
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;
123 if( (freq < 118.0) || (freq > 137.0) )
124 frq_mhz = 125.0; // sane value, middle of bandplan
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
135 double tx_pow,ant_gain;
138 if(transmission_type == 1)
139 tx_pow = _transmitter_power + 6.0;
141 if((transmission_type == 1) || (transmission_type == 3))
142 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
144 double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
146 FGScenery * scenery = globals->get_scenery();
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;
154 //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
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 );
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;
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;
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
181 if (distance_m > 300000)
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;
191 double max_points = distance_m / point_distance;
192 deque<double> _elevations;
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
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;
204 transmitter_height = sender_alt;
207 if(transmission_type == 1)
208 transmitter_height += ATC_HAAT;
210 transmitter_height += Aircraft_HAAT;
212 cerr << "ITM:: RX-height: " << receiver_height << ", TX-height: " << transmitter_height << ", Distance: " << distance_m << endl;
214 unsigned int e_size = (deque<unsigned>::size_type)max_points;
216 while (_elevations.size() <= e_size) {
217 probe_distance += point_distance;
218 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
220 double elevation_m = 0.0;
222 if (scenery->get_elevation_m( probe, elevation_m, NULL )) {
223 if((transmission_type == 3) || (transmission_type == 4)) {
224 _elevations.push_back(elevation_m);
227 _elevations.push_front(elevation_m);
231 if((transmission_type == 3) || (transmission_type == 4)) {
232 _elevations.push_back(elevation_m);
235 _elevations.push_front(0.0);
239 if((transmission_type == 3) || (transmission_type == 4)) {
240 _elevations.push_front(elevation_under_pilot);
241 _elevations.push_back(elevation_under_sender);
244 _elevations.push_back(elevation_under_pilot);
245 _elevations.push_front(elevation_under_sender);
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];
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;
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);
272 // TODO: If we clear the first Fresnel zone, we are into line of sight teritory
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);
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);
289 cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
293 signal = link_budget - dbloss;