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 <simgear/scene/material/mat.hxx>
30 #include <Scenery/scenery.hxx>
32 #define WITH_POINT_TO_POINT 1
38 /** radio parameters (which should probably be set for each radio) */
40 _receiver_sensitivity = -110.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD
42 /** AM transmitter power in dBm.
43 * Note this value is calculated from the typical final transistor stage output
44 * small aircraft have portable transmitters which operate at 36 dBm output (4 Watts) others operate in the range 10-20 W
45 * later possibly store this value in aircraft description
46 * ATC comms usually operate high power equipment, thus making the link asymetrical; this is taken care of in propagation routines
47 * Typical output powers for ATC ground equipment, VHF-UHF:
48 * 40 dBm - 10 W (ground, clearance)
49 * 44 dBm - 20 W (tower)
50 * 47 dBm - 50 W (center, sectors)
51 * 50 dBm - 100 W (center, sectors)
52 * 53 dBm - 200 W (sectors, on directional arrays)
54 _transmitter_power = 43.0;
56 /** pilot plane's antenna gain + AI aircraft antenna gain
57 * real-life gain for conventional monopole/dipole antenna
60 _propagation_model = 2; // choose between models via option: realistic radio on/off
69 double FGRadio::getFrequency(int radio) {
73 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
76 freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
79 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
85 /*** TODO: receive multiplayer chat message and voice
87 void FGRadio::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
91 /*** TODO: receive navaid
93 double FGRadio::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
95 // typical VOR/LOC transmitter power appears to be 200 Watt ~ 53 dBm
96 // vor/loc typical sensitivity between -107 and -101 dBm
97 // glideslope sensitivity between -85 and -81 dBm
98 if ( _propagation_model == 1) {
99 return LOS_calculate_attenuation(tx_pos, freq, 1);
101 else if ( _propagation_model == 2) {
102 return ITM_calculate_attenuation(tx_pos, freq, 1);
109 /*** Receive ATC radio communication as text
111 void FGRadio::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
114 double comm1 = getFrequency(1);
115 double comm2 = getFrequency(2);
116 if ( !(fabs(freq - comm1) <= 0.0001) && !(fabs(freq - comm2) <= 0.0001) ) {
117 //cerr << "Frequency not tuned: " << freq << " Radio1: " << comm1 << " Radio2: " << comm2 << endl;
122 if ( _propagation_model == 0) {
123 fgSetString("/sim/messages/atc", text.c_str());
125 else if ( _propagation_model == 1 ) {
126 // TODO: free space, round earth
127 double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
129 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
130 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
134 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
135 //cerr << "Signal completely readable: " << signal << endl;
136 fgSetString("/sim/messages/atc", text.c_str());
137 /** write signal strength above threshold to the property tree
138 * to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
140 fgSetDouble("/sim/radio/comm1-signal", signal);
143 else if ( _propagation_model == 2 ) {
144 // Use ITM propagation model
145 double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
147 SG_LOG(SG_GENERAL, SG_BULK, "Signal below receiver minimum sensitivity: " << signal);
148 //cerr << "Signal below receiver minimum sensitivity: " << signal << endl;
151 if ((signal > 0.0) && (signal < 12.0)) {
152 /** for low SNR values implement a way to make the conversation
153 * hard to understand but audible
154 * in the real world, the receiver AGC fails to capture the slope
155 * and the signal, due to being amplitude modulated, decreases volume after demodulation
156 * the workaround below is more akin to what would happen on a FM transmission
157 * therefore the correct way would be to work on the volume
160 string hash_noise = " ";
161 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
162 int t_size = text.size();
163 for (int n = 1; n <= reps; ++n) {
164 int pos = rand() % (t_size -1);
165 text.replace(pos,1, hash_noise);
168 double volume = (fabs(signal - 12.0) / 12);
169 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
170 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
171 //cerr << "Usable signal at limit: " << signal << endl;
172 fgSetDouble("/sim/sound/voices/voice/volume", volume);
173 fgSetString("/sim/messages/atc", text.c_str());
174 fgSetDouble("/sim/radio/comm1-signal", signal);
175 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
178 SG_LOG(SG_GENERAL, SG_BULK, "Signal completely readable: " << signal);
179 //cerr << "Signal completely readable: " << signal << endl;
180 fgSetString("/sim/messages/atc", text.c_str());
181 /** write signal strength above threshold to the property tree
182 * to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
184 fgSetDouble("/sim/radio/comm1-signal", signal);
193 /*** Implement radio attenuation
194 based on the Longley-Rice propagation model
196 double FGRadio::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
200 /** ITM default parameters
201 TODO: take them from tile materials (especially for sea)?
203 double eps_dielect=15.0;
204 double sgm_conductivity = 0.005;
207 if( (freq < 118.0) || (freq > 137.0) )
208 frq_mhz = 125.0; // sane value, middle of bandplan
211 int radio_climate = 5; // continental temperate
212 int pol=1; // assuming vertical polarization although this is more complex in reality
213 double conf = 0.90; // 90% of situations and time, take into account speed
217 int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
221 double clutter_loss = 0.0; // loss due to vegetation and urban
222 double tx_pow = _transmitter_power;
223 double ant_gain = _antenna_gain;
226 if(transmission_type == 1)
227 tx_pow = _transmitter_power + 6.0;
229 if((transmission_type == 1) || (transmission_type == 3))
230 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
232 double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
234 FGScenery * scenery = globals->get_scenery();
236 double own_lat = fgGetDouble("/position/latitude-deg");
237 double own_lon = fgGetDouble("/position/longitude-deg");
238 double own_alt_ft = fgGetDouble("/position/altitude-ft");
239 double own_alt= own_alt_ft * SG_FEET_TO_METER;
242 //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
244 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
245 SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
246 SGGeoc center = SGGeoc::fromGeod( max_own_pos );
247 SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
249 /** position of sender radio antenna (HAAT)
250 sender can be aircraft or ground station
252 double ATC_HAAT = 30.0;
253 double Aircraft_HAAT = 5.0;
254 double sender_alt_ft,sender_alt;
255 double transmitter_height=0.0;
256 double receiver_height=0.0;
257 SGGeod sender_pos = pos;
259 sender_alt_ft = sender_pos.getElevationFt();
260 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
261 SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
262 SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
263 //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
265 double point_distance= 90.0; // regular SRTM is 90 meters
266 double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
267 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
268 double probe_distance = 0.0;
269 /** If distance larger than this value (300 km), assume reception imposssible */
270 if (distance_m > 300000)
272 /** If above 8000 meters, consider LOS mode and calculate free-space att */
273 if (own_alt > 8000) {
274 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
275 SG_LOG(SG_GENERAL, SG_BULK,
276 "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
277 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
278 signal = link_budget - dbloss;
283 double max_points = distance_m / point_distance;
284 deque<double> _elevations;
285 deque<string> materials;
288 double elevation_under_pilot = 0.0;
289 if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
290 receiver_height = own_alt - elevation_under_pilot + 3; //assume antenna located 3 meters above ground
293 double elevation_under_sender = 0.0;
294 if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
295 transmitter_height = sender_alt - elevation_under_sender;
298 transmitter_height = sender_alt;
301 if(transmission_type == 1)
302 transmitter_height += ATC_HAAT;
304 transmitter_height += Aircraft_HAAT;
306 SG_LOG(SG_GENERAL, SG_BULK,
307 "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
308 cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
310 unsigned int e_size = (deque<unsigned>::size_type)max_points;
312 while (_elevations.size() <= e_size) {
313 probe_distance += point_distance;
314 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
315 const SGMaterial *mat = 0;
316 double elevation_m = 0.0;
318 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
319 if((transmission_type == 3) || (transmission_type == 4)) {
320 _elevations.push_back(elevation_m);
322 const std::vector<string> mat_names = mat->get_names();
323 materials.push_back(mat_names[0]);
326 materials.push_back("None");
330 _elevations.push_front(elevation_m);
332 const std::vector<string> mat_names = mat->get_names();
333 materials.push_front(mat_names[0]);
336 materials.push_front("None");
341 if((transmission_type == 3) || (transmission_type == 4)) {
342 _elevations.push_back(0.0);
343 materials.push_back("None");
346 _elevations.push_front(0.0);
347 materials.push_front("None");
351 if((transmission_type == 3) || (transmission_type == 4)) {
352 _elevations.push_front(elevation_under_pilot);
353 _elevations.push_back(elevation_under_sender);
356 _elevations.push_back(elevation_under_pilot);
357 _elevations.push_front(elevation_under_sender);
361 double max_alt_between=0.0;
362 for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
363 if (_elevations[i] > max_alt_between) {
364 max_alt_between = _elevations[i];
368 double num_points= (double)_elevations.size();
369 //cerr << "ITM:: Max alt between: " << max_alt_between << ", num points:" << num_points << endl;
370 _elevations.push_front(point_distance);
371 _elevations.push_front(num_points -1);
372 int size = _elevations.size();
373 double itm_elev[size];
374 for(int i=0;i<size;i++) {
375 itm_elev[i]=_elevations[i];
376 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
379 if((transmission_type == 3) || (transmission_type == 4)) {
380 // the sender and receiver roles are switched
381 point_to_point(itm_elev, receiver_height, transmitter_height,
382 eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
383 pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
387 point_to_point(itm_elev, transmitter_height, receiver_height,
388 eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
389 pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
391 SG_LOG(SG_GENERAL, SG_BULK,
392 "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
393 cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
395 clutterLoss(frq_mhz, distance_m, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
396 cerr << "Clutter loss: " << clutter_loss << endl;
397 //if (errnum == 4) // if parameters are outside sane values for lrprop, the alternative method is used
399 signal = link_budget - dbloss - clutter_loss;
404 /*** Calculate losses due to vegetation and urban clutter (WIP)
405 * We are only worried about clutter loss, terrain influence
406 * on the first Fresnel zone is calculated in the ITM functions
408 void FGRadio::clutterLoss(double freq, double distance_m, double itm_elev[], deque<string> materials,
409 double transmitter_height, double receiver_height, int p_mode,
410 double horizons[], double &clutter_loss) {
412 if (p_mode == 0) { // LOS: take each point and see how clutter height affects first Fresnel zone
414 int j=1; // first point is TX elevation, last is RX elevation
415 for (int k=3;k < (int)itm_elev[0];k++) {
417 double clutter_height = 0.0; // mean clutter height for a certain terrain type
418 double clutter_density = 0.0; // percent of reflected wave
419 get_material_properties(materials[mat], clutter_height, clutter_density);
420 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
421 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 1] + receiver_height) / distance_m;
422 // First Fresnel radius
423 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / ( distance_m * freq / 1000) );
425 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
426 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
428 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 1] + receiver_height);
429 double d1 = j * itm_elev[1];
430 if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 1] + receiver_height) ) {
431 d1 = (itm_elev[0] - j) * itm_elev[1];
433 double ray_height = (grad * d1) + min_elev;
434 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
435 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
436 double intrusion = fabs(clearance);
437 //cerr << "Clutter:: clearance: " << clearance << endl;
438 if (clearance >= 0) {
441 else if (clearance < 0 && (intrusion < clutter_height)) {
443 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
445 else if (clearance < 0 && (intrusion > clutter_height)) {
446 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
456 else if (p_mode == 1) { // diffraction
458 if (horizons[1] == 0.0) { // single horizon: same as above, except pass twice using the highest point
459 int num_points_1st = (int)floor( horizons[0] * (double)itm_elev[0] / distance_m );
460 int num_points_2nd = (int)floor( (distance_m - horizons[0]) * (double)itm_elev[0] / distance_m );
462 /** perform the first pass */
464 int j=1; // first point is TX elevation, 2nd is obstruction elevation
465 for (int k=3;k < num_points_1st ;k++) {
467 double clutter_height = 0.0; // mean clutter height for a certain terrain type
468 double clutter_density = 0.0; // percent of reflected wave
469 get_material_properties(materials[mat], clutter_height, clutter_density);
470 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
471 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 1] + clutter_height) / distance_m;
472 // First Fresnel radius
473 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (num_points_1st - j) * itm_elev[1] / 1000000) / ( num_points_1st * itm_elev[1] * freq / 1000) );
475 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
476 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
478 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 1] + clutter_height);
479 double d1 = j * itm_elev[1];
480 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 1] + clutter_height) ) {
481 d1 = (num_points_1st - j) * itm_elev[1];
483 double ray_height = (grad * d1) + min_elev;
484 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
485 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
486 double intrusion = fabs(clearance);
487 //cerr << "Clutter:: clearance: " << clearance << endl;
488 if (clearance >= 0) {
491 else if (clearance < 0 && (intrusion < clutter_height)) {
493 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
495 else if (clearance < 0 && (intrusion > clutter_height)) {
496 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
506 /** and the second pass */
508 int l =1; // first point is diffraction edge, 2nd the RX elevation
509 for (int k=last+1;k < num_points_2nd ;k++) {
511 double clutter_height = 0.0; // mean clutter height for a certain terrain type
512 double clutter_density = 0.0; // percent of reflected wave
513 get_material_properties(materials[mat], clutter_height, clutter_density);
514 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
515 double grad = fabs(itm_elev[last] + clutter_height - itm_elev[(int)itm_elev[0] + 1] + receiver_height) / distance_m;
516 // First Fresnel radius
517 double frs_rad = 548 * sqrt( (l * itm_elev[1] * (num_points_2nd - l) * itm_elev[1] / 1000000) / ( num_points_2nd * itm_elev[1] * freq / 1000) );
519 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
520 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
522 double min_elev = SGMiscd::min(itm_elev[last] + clutter_height, itm_elev[(int)itm_elev[0] + 1] + receiver_height);
523 double d1 = l * itm_elev[1];
524 if ( (itm_elev[last] + clutter_height) > (itm_elev[(int)itm_elev[0] + 1] + receiver_height) ) {
525 d1 = (num_points_2nd - l) * itm_elev[1];
527 double ray_height = (grad * d1) + min_elev;
528 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
529 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
530 double intrusion = fabs(clearance);
531 //cerr << "Clutter:: clearance: " << clearance << endl;
532 if (clearance >= 0) {
535 else if (clearance < 0 && (intrusion < clutter_height)) {
537 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
539 else if (clearance < 0 && (intrusion > clutter_height)) {
540 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
551 else { // double horizon: same as single horizon, except there are 3 segments
553 int num_points_1st = (int)floor( horizons[0] * (double)itm_elev[0] / distance_m );
554 int num_points_2nd = (int)floor( (horizons[1] - horizons[0]) * (double)itm_elev[0] / distance_m );
555 int num_points_3rd = (int)floor( (distance_m - horizons[1]) * (double)itm_elev[0] / distance_m );
557 /** perform the first pass */
559 int j=1; // first point is TX elevation, 2nd is obstruction elevation
560 for (int k=3;k < num_points_1st ;k++) {
562 double clutter_height = 0.0; // mean clutter height for a certain terrain type
563 double clutter_density = 0.0; // percent of reflected wave
564 get_material_properties(materials[mat], clutter_height, clutter_density);
565 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
566 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 1] + clutter_height) / distance_m;
567 // First Fresnel radius
568 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (num_points_1st - j) * itm_elev[1] / 1000000) / ( num_points_1st * itm_elev[1] * freq / 1000) );
570 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
571 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
573 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 1] + clutter_height);
574 double d1 = j * itm_elev[1];
575 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 1] + clutter_height) ) {
576 d1 = (num_points_1st - j) * itm_elev[1];
578 double ray_height = (grad * d1) + min_elev;
579 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
580 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
581 double intrusion = fabs(clearance);
582 //cerr << "Clutter:: clearance: " << clearance << endl;
583 if (clearance >= 0) {
586 else if (clearance < 0 && (intrusion < clutter_height)) {
588 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
590 else if (clearance < 0 && (intrusion > clutter_height)) {
591 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
600 /** and the second pass */
602 int l =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
603 for (int k=last;k < num_points_2nd ;k++) {
605 double clutter_height = 0.0; // mean clutter height for a certain terrain type
606 double clutter_density = 0.0; // percent of reflected wave
607 get_material_properties(materials[mat], clutter_height, clutter_density);
608 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
609 double grad = fabs(itm_elev[last] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 1] + clutter_height) / distance_m;
610 // First Fresnel radius
611 double frs_rad = 548 * sqrt( (l * itm_elev[1] * (num_points_2nd - j) * itm_elev[1] / 1000000) / ( num_points_2nd * itm_elev[1] * freq / 1000) );
613 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
614 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
616 double min_elev = SGMiscd::min(itm_elev[last] + clutter_height, itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height);
617 double d1 = l * itm_elev[1];
618 if ( (itm_elev[last] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 1] + clutter_height) ) {
619 d1 = (num_points_2nd - l) * itm_elev[1];
621 double ray_height = (grad * d1) + min_elev;
622 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
623 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
624 double intrusion = fabs(clearance);
625 //cerr << "Clutter:: clearance: " << clearance << endl;
626 if (clearance >= 0) {
629 else if (clearance < 0 && (intrusion < clutter_height)) {
631 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
633 else if (clearance < 0 && (intrusion > clutter_height)) {
634 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
645 /** third and final pass */
647 int m =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
648 for (int k=last;k < num_points_3rd ;k++) {
650 double clutter_height = 0.0; // mean clutter height for a certain terrain type
651 double clutter_density = 0.0; // percent of reflected wave
652 get_material_properties(materials[mat], clutter_height, clutter_density);
653 //cerr << "Clutter:: material: " << materials[mat] << " height: " << clutter_height << ", density: " << clutter_density << endl;
654 double grad = fabs(itm_elev[last] + clutter_height - itm_elev[(int)itm_elev[0] + 1] + receiver_height) / distance_m;
655 // First Fresnel radius
656 double frs_rad = 548 * sqrt( (m * itm_elev[1] * (num_points_3rd - m) * itm_elev[1] / 1000000) / ( num_points_3rd * itm_elev[1] * freq / 1000) );
658 //cerr << "Clutter:: fresnel radius: " << frs_rad << endl;
659 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
661 double min_elev = SGMiscd::min(itm_elev[last] + clutter_height, itm_elev[(int)itm_elev[0] + 1] + receiver_height);
662 double d1 = m * itm_elev[1];
663 if ( (itm_elev[last] + clutter_height) > (itm_elev[(int)itm_elev[0] + 1] + receiver_height) ) {
664 d1 = (num_points_3rd - m) * itm_elev[1];
666 double ray_height = (grad * d1) + min_elev;
667 //cerr << "Clutter:: ray height: " << ray_height << " ground height:" << itm_elev[k] << endl;
668 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
669 double intrusion = fabs(clearance);
670 //cerr << "Clutter:: clearance: " << clearance << endl;
671 if (clearance >= 0) {
674 else if (clearance < 0 && (intrusion < clutter_height)) {
676 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * freq/100;
678 else if (clearance < 0 && (intrusion > clutter_height)) {
679 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * freq/100;
692 else if (p_mode == 2) { // troposcatter: ignore ground clutter for now...
698 /*** Temporary material properties database
699 * height: median clutter height
700 * density: radiowave attenuation factor
702 void FGRadio::get_material_properties(string mat_name, double &height, double &density) {
704 if(mat_name == "Landmass") {
709 else if(mat_name == "SomeSort") {
714 else if(mat_name == "Island") {
718 else if(mat_name == "Default") {
722 else if(mat_name == "EvergreenBroadCover") {
726 else if(mat_name == "EvergreenForest") {
730 else if(mat_name == "DeciduousBroadCover") {
734 else if(mat_name == "DeciduousForest") {
738 else if(mat_name == "MixedForestCover") {
742 else if(mat_name == "MixedForest") {
746 else if(mat_name == "RainForest") {
750 else if(mat_name == "EvergreenNeedleCover") {
754 else if(mat_name == "WoodedTundraCover") {
758 else if(mat_name == "DeciduousNeedleCover") {
762 else if(mat_name == "ScrubCover") {
766 else if(mat_name == "BuiltUpCover") {
770 else if(mat_name == "Urban") {
774 else if(mat_name == "Construction") {
778 else if(mat_name == "Industrial") {
782 else if(mat_name == "Port") {
786 else if(mat_name == "Town") {
790 else if(mat_name == "SubUrban") {
794 else if(mat_name == "CropWoodCover") {
798 else if(mat_name == "CropWood") {
802 else if(mat_name == "AgroForest") {
813 /*** implement simple LOS propagation model (WIP)
815 double FGRadio::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
817 if( (freq < 118.0) || (freq > 137.0) )
818 frq_mhz = 125.0; // sane value, middle of bandplan
822 double tx_pow = _transmitter_power;
823 double ant_gain = _antenna_gain;
825 double ATC_HAAT = 30.0;
826 double Aircraft_HAAT = 5.0;
827 double sender_alt_ft,sender_alt;
828 double transmitter_height=0.0;
829 double receiver_height=0.0;
830 double own_lat = fgGetDouble("/position/latitude-deg");
831 double own_lon = fgGetDouble("/position/longitude-deg");
832 double own_alt_ft = fgGetDouble("/position/altitude-ft");
833 double own_alt= own_alt_ft * SG_FEET_TO_METER;
835 if(transmission_type == 1)
836 tx_pow = _transmitter_power + 6.0;
838 if((transmission_type == 1) || (transmission_type == 3))
839 ant_gain = _antenna_gain + 3.0; //pilot plane's antenna gain + ground station antenna gain
841 double link_budget = tx_pow - _receiver_sensitivity + ant_gain;
843 //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
845 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
847 SGGeod sender_pos = pos;
849 sender_alt_ft = sender_pos.getElevationFt();
850 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
852 receiver_height = own_alt;
853 transmitter_height = sender_alt;
855 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
857 if(transmission_type == 1)
858 transmitter_height += ATC_HAAT;
860 transmitter_height += Aircraft_HAAT;
862 /** radio horizon calculation with wave bending k=4/3 */
863 double receiver_horizon = 4.12 * sqrt(receiver_height);
864 double transmitter_horizon = 4.12 * sqrt(transmitter_height);
865 double total_horizon = receiver_horizon + transmitter_horizon;
867 if (distance_m > total_horizon) {
871 // free-space loss (distance calculation should be changed)
872 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
873 signal = link_budget - dbloss;
874 SG_LOG(SG_GENERAL, SG_BULK,
875 "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
876 //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
881 /*** Material properties database
883 void FGRadio::set_material_properties() {