1 // radio.cxx -- implementation of FGRadio
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 (which should probably be set for each radio) */
39 _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
41 /** AM transmitter power in dBm.
42 * Note this value is calculated from the typical final transistor stage output
43 * small aircraft have portable transmitters which operate at 36 dBm output (4 Watts) others operate in the range 10-20 W
44 * later possibly store this value in aircraft description
45 * ATC comms usually operate high power equipment, thus making the link asymetrical; this is taken care of in propagation routines
46 * Typical output powers for ATC ground equipment, VHF-UHF:
47 * 40 dBm - 10 W (ground, clearance)
48 * 44 dBm - 20 W (tower)
49 * 47 dBm - 50 W (center, sectors)
50 * 50 dBm - 100 W (center, sectors)
51 * 53 dBm - 200 W (sectors, on directional arrays)
53 _transmitter_power = 43.0;
55 /** pilot plane's antenna gain + AI aircraft antenna gain
56 * real-life gain for conventional monopole/dipole antenna
59 _propagation_model = 2; // choose between models via option: realistic radio on/off
68 double FGRadio::getFrequency(int radio) {
72 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
75 freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
78 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
84 /*** TODO: receive multiplayer chat message and voice
86 void FGRadio::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
90 /*** TODO: receive navaid
92 double FGRadio::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
94 // typical VOR/LOC transmitter power appears to be 200 Watt ~ 53 dBm
95 // vor/loc typical sensitivity between -107 and -101 dBm
96 // glideslope sensitivity between -85 and -81 dBm
97 if ( _propagation_model == 1) {
98 return LOS_calculate_attenuation(tx_pos, freq, 1);
100 else if ( _propagation_model == 2) {
101 return ITM_calculate_attenuation(tx_pos, freq, 1);
108 /*** Receive ATC radio communication as text
110 void FGRadio::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
113 double comm1 = getFrequency(1);
114 double comm2 = getFrequency(2);
115 if ( !(fabs(freq - comm1) <= 0.0001) && !(fabs(freq - comm2) <= 0.0001) ) {
116 //cerr << "Frequency not tuned: " << freq << " Radio1: " << comm1 << " Radio2: " << comm2 << endl;
121 if ( _propagation_model == 0) {
122 fgSetString("/sim/messages/atc", text.c_str());
124 else if ( _propagation_model == 1 ) {
125 // TODO: free space, round earth
126 double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
128 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
129 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
133 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
134 //cerr << "Signal completely readable: " << signal << endl;
135 fgSetString("/sim/messages/atc", text.c_str());
136 /** write signal strength above threshold to the property tree
137 * to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
139 fgSetDouble("/sim/radio/comm1-signal", signal);
142 else if ( _propagation_model == 2 ) {
143 // Use ITM propagation model
144 double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
146 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
147 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
150 if ((signal > 0.0) && (signal < 12.0)) {
151 /** for low SNR values implement a way to make the conversation
152 * hard to understand but audible
153 * in the real world, the receiver AGC fails to capture the slope
154 * and the signal, due to being amplitude modulated, decreases volume after demodulation
155 * the workaround below is more akin to what would happen on a FM transmission
156 * therefore the correct way would be to work on the volume
159 string hash_noise = " ";
160 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
161 int t_size = text.size();
162 for (int n = 1; n <= reps; ++n) {
163 int pos = rand() % (t_size -1);
164 text.replace(pos,1, hash_noise);
167 double volume = (fabs(signal - 12.0) / 12);
168 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
169 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
170 //cerr << "Usable signal at limit: " << signal << endl;
171 fgSetDouble("/sim/sound/voices/voice/volume", volume);
172 fgSetString("/sim/messages/atc", text.c_str());
173 fgSetDouble("/sim/radio/comm1-signal", signal);
174 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
177 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
178 //cerr << "Signal completely readable: " << signal << endl;
179 fgSetString("/sim/messages/atc", text.c_str());
180 /** write signal strength above threshold to the property tree
181 * to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
183 fgSetDouble("/sim/radio/comm1-signal", signal);
192 /*** Implement radio attenuation
193 based on the Longley-Rice propagation model
195 double FGRadio::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
199 /** ITM default parameters
200 TODO: take them from tile materials (especially for sea)?
202 double eps_dielect=15.0;
203 double sgm_conductivity = 0.005;
206 if( (freq < 118.0) || (freq > 137.0) )
207 frq_mhz = 125.0; // sane value, middle of bandplan
210 int radio_climate = 5; // continental temperate
211 int pol=1; // assuming vertical polarization although this is more complex in reality
212 double conf = 0.90; // 90% of situations and time, take into account speed
218 double tx_pow = _transmitter_power;
219 double ant_gain = _antenna_gain;
222 if(transmission_type == 1)
223 tx_pow = _transmitter_power + 6.0;
225 if((transmission_type == 1) || (transmission_type == 3))
226 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
228 double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
230 FGScenery * scenery = globals->get_scenery();
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_alt= own_alt_ft * SG_FEET_TO_METER;
238 //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
240 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
241 SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
242 SGGeoc center = SGGeoc::fromGeod( max_own_pos );
243 SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
245 /** position of sender radio antenna (HAAT)
246 sender can be aircraft or ground station
248 double ATC_HAAT = 30.0;
249 double Aircraft_HAAT = 5.0;
250 double sender_alt_ft,sender_alt;
251 double transmitter_height=0.0;
252 double receiver_height=0.0;
253 SGGeod sender_pos = pos;
255 sender_alt_ft = sender_pos.getElevationFt();
256 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
257 SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
258 SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
259 //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
261 double point_distance= 90.0; // regular SRTM is 90 meters
262 double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
263 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
264 double probe_distance = 0.0;
265 /** If distance larger than this value (300 km), assume reception imposssible */
266 if (distance_m > 300000)
268 /** If above 8000 meters, consider LOS mode and calculate free-space att */
269 if (own_alt > 8000) {
270 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
271 SG_LOG(SG_GENERAL, SG_BULK,
272 "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
273 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
274 signal = link_budget - dbloss;
279 double max_points = distance_m / point_distance;
280 deque<double> _elevations;
282 double elevation_under_pilot = 0.0;
283 if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
284 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
287 double elevation_under_sender = 0.0;
288 if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
289 transmitter_height = sender_alt - elevation_under_sender;
292 transmitter_height = sender_alt;
295 if(transmission_type == 1)
296 transmitter_height += ATC_HAAT;
298 transmitter_height += Aircraft_HAAT;
300 SG_LOG(SG_GENERAL, SG_BULK,
301 "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
302 //cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
304 unsigned int e_size = (deque<unsigned>::size_type)max_points;
306 while (_elevations.size() <= e_size) {
307 probe_distance += point_distance;
308 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
310 double elevation_m = 0.0;
312 if (scenery->get_elevation_m( probe, elevation_m, NULL )) {
313 if((transmission_type == 3) || (transmission_type == 4)) {
314 _elevations.push_back(elevation_m);
317 _elevations.push_front(elevation_m);
321 if((transmission_type == 3) || (transmission_type == 4)) {
322 _elevations.push_back(elevation_m);
325 _elevations.push_front(0.0);
329 if((transmission_type == 3) || (transmission_type == 4)) {
330 _elevations.push_front(elevation_under_pilot);
331 _elevations.push_back(elevation_under_sender);
334 _elevations.push_back(elevation_under_pilot);
335 _elevations.push_front(elevation_under_sender);
339 double max_alt_between=0.0;
340 for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
341 if (_elevations[i] > max_alt_between) {
342 max_alt_between = _elevations[i];
346 double num_points= (double)_elevations.size();
347 //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
348 _elevations.push_front(point_distance);
349 _elevations.push_front(num_points -1);
350 int size = _elevations.size();
351 double itm_elev[size];
352 for(int i=0;i<size;i++) {
353 itm_elev[i]=_elevations[i];
354 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
358 /** first Fresnel zone radius
359 frequency in the middle of the bandplan, more accuracy is not necessary
361 double fz_clr= 8.657 * sqrt(distance_m / 0.125);
363 // TODO: If we clear the first Fresnel zone, we are into line of sight territory
365 // else we need to calculate point to point link loss
366 if((transmission_type == 3) || (transmission_type == 4)) {
367 // the sender and receiver roles are switched
368 point_to_point(itm_elev, receiver_height, transmitter_height,
369 eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
370 pol, conf, rel, dbloss, strmode, errnum);
374 point_to_point(itm_elev, transmitter_height, receiver_height,
375 eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
376 pol, conf, rel, dbloss, strmode, errnum);
378 SG_LOG(SG_GENERAL, SG_BULK,
379 "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
380 cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
382 //if (errnum == 4) // if parameters are outside sane values for lrprop, the alternative method is used
384 signal = link_budget - dbloss;
389 /*** implement simple LOS propagation model (WIP)
391 double FGRadio::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
393 if( (freq < 118.0) || (freq > 137.0) )
394 frq_mhz = 125.0; // sane value, middle of bandplan
398 double tx_pow = _transmitter_power;
399 double ant_gain = _antenna_gain;
401 double ATC_HAAT = 30.0;
402 double Aircraft_HAAT = 5.0;
403 double sender_alt_ft,sender_alt;
404 double transmitter_height=0.0;
405 double receiver_height=0.0;
406 double own_lat = fgGetDouble("/position/latitude-deg");
407 double own_lon = fgGetDouble("/position/longitude-deg");
408 double own_alt_ft = fgGetDouble("/position/altitude-ft");
409 double own_alt= own_alt_ft * SG_FEET_TO_METER;
411 if(transmission_type == 1)
412 tx_pow = _transmitter_power + 6.0;
414 if((transmission_type == 1) || (transmission_type == 3))
415 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
417 double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
419 //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
421 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
423 SGGeod sender_pos = pos;
425 sender_alt_ft = sender_pos.getElevationFt();
426 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
428 receiver_height = own_alt;
429 transmitter_height = sender_alt;
431 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
433 if(transmission_type == 1)
434 transmitter_height += ATC_HAAT;
436 transmitter_height += Aircraft_HAAT;
438 /** radio horizon calculation with wave bending k=4/3 */
439 double receiver_horizon = 4.12 * sqrt(receiver_height);
440 double transmitter_horizon = 4.12 * sqrt(transmitter_height);
441 double total_horizon = receiver_horizon + transmitter_horizon;
443 if (distance_m > total_horizon) {
447 // free-space loss (distance calculation should be changed)
448 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
449 signal = link_budget - dbloss;
450 SG_LOG(SG_GENERAL, SG_BULK,
451 "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
452 //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;