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.
30 #include <simgear/scene/material/mat.hxx>
31 #include <Scenery/scenery.hxx>
33 #define WITH_POINT_TO_POINT 1
37 FGRadioTransmission::FGRadioTransmission() {
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 * Typical output powers for ATC ground equipment, VHF-UHF:
44 * 40 dBm - 10 W (ground, clearance)
45 * 44 dBm - 20 W (tower)
46 * 47 dBm - 50 W (center, sectors)
47 * 50 dBm - 100 W (center, sectors)
48 * 53 dBm - 200 W (sectors, on directional arrays)
50 _transmitter_power = 43.0;
52 _tx_antenna_height = 2.0; // TX antenna height above ground level
54 _rx_antenna_height = 2.0; // RX antenna height above ground level
57 _rx_antenna_gain = 1.0; // gain expressed in dBi
58 _tx_antenna_gain = 1.0;
60 _rx_line_losses = 2.0; // to be configured for each station
61 _tx_line_losses = 2.0;
63 _propagation_model = 2;
64 _terrain_sampling_distance = fgGetDouble("/sim/radio/sampling-distance", 90.0); // regular SRTM is 90 meters
67 FGRadioTransmission::~FGRadioTransmission()
72 double FGRadioTransmission::getFrequency(int radio) {
76 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
79 freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
82 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
88 /*** TODO: receive multiplayer chat message and voice
90 void FGRadioTransmission::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
94 /*** TODO: receive navaid
96 double FGRadioTransmission::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
98 // typical VOR/LOC transmitter power appears to be 200 Watt ~ 53 dBm
99 // vor/loc typical sensitivity between -107 and -101 dBm
100 // glideslope sensitivity between -85 and -81 dBm
101 if ( _propagation_model == 1) {
102 return LOS_calculate_attenuation(tx_pos, freq, 1);
104 else if ( _propagation_model == 2) {
105 return ITM_calculate_attenuation(tx_pos, freq, 1);
112 /*** Receive ATC radio communication as text
114 void FGRadioTransmission::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
117 if(ground_to_air == 1) {
118 _transmitter_power += 6.0;
119 _tx_antenna_height += 30.0;
120 _tx_antenna_gain += 3.0;
124 double comm1 = getFrequency(1);
125 double comm2 = getFrequency(2);
126 if ( !(fabs(freq - comm1) <= 0.0001) && !(fabs(freq - comm2) <= 0.0001) ) {
131 if ( _propagation_model == 0) {
132 fgSetString("/sim/messages/atc", text.c_str());
134 else if ( _propagation_model == 1 ) {
135 // TODO: free space, round earth
136 double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
142 fgSetString("/sim/messages/atc", text.c_str());
143 /** write signal strength above threshold to the property tree
144 * to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
146 fgSetDouble("/sim/radio/comm1-signal", signal);
149 else if ( _propagation_model == 2 ) {
150 // Use ITM propagation model
151 double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
155 if ((signal > 0.0) && (signal < 12.0)) {
156 /** for low SNR values implement a way to make the conversation
157 * hard to understand but audible
158 * in the real world, the receiver AGC fails to capture the slope
159 * and the signal, due to being amplitude modulated, decreases volume after demodulation
160 * the workaround below is more akin to what would happen on a FM transmission
161 * therefore the correct way would be to work on the volume
164 string hash_noise = " ";
165 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
166 int t_size = text.size();
167 for (int n = 1; n <= reps; ++n) {
168 int pos = rand() % (t_size -1);
169 text.replace(pos,1, hash_noise);
172 double volume = (fabs(signal - 12.0) / 12);
173 double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
174 SG_LOG(SG_GENERAL, SG_BULK, "Usable signal at limit: " << signal);
175 //cerr << "Usable signal at limit: " << signal << endl;
176 fgSetDouble("/sim/sound/voices/voice/volume", volume);
177 fgSetString("/sim/messages/atc", text.c_str());
178 fgSetDouble("/sim/radio/comm1-signal", signal);
179 fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
182 fgSetString("/sim/messages/atc", text.c_str());
183 /** write signal strength above threshold to the property tree
184 * to implement a simple S-meter just divide by 3 dB per grade (VHF norm)
186 fgSetDouble("/sim/radio/comm1-signal", signal);
195 /*** Implement radio attenuation
196 based on the Longley-Rice propagation model
198 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
202 /** ITM default parameters
203 TODO: take them from tile materials (especially for sea)?
205 double eps_dielect=15.0;
206 double sgm_conductivity = 0.005;
209 if( (freq < 118.0) || (freq > 137.0) )
210 frq_mhz = 125.0; // sane value, middle of bandplan
213 int radio_climate = 5; // continental temperate
214 int pol=1; // assuming vertical polarization although this is more complex in reality
215 double conf = 0.90; // 90% of situations and time, take into account speed
219 int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
223 double clutter_loss = 0.0; // loss due to vegetation and urban
224 double tx_pow = _transmitter_power;
225 double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
229 double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
231 FGScenery * scenery = globals->get_scenery();
233 double own_lat = fgGetDouble("/position/latitude-deg");
234 double own_lon = fgGetDouble("/position/longitude-deg");
235 double own_alt_ft = fgGetDouble("/position/altitude-ft");
236 double own_alt= own_alt_ft * SG_FEET_TO_METER;
239 //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
241 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
242 SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
243 SGGeoc center = SGGeoc::fromGeod( max_own_pos );
244 SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
247 double sender_alt_ft,sender_alt;
248 double transmitter_height=0.0;
249 double receiver_height=0.0;
250 SGGeod sender_pos = pos;
252 sender_alt_ft = sender_pos.getElevationFt();
253 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
254 SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
255 SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
256 //cerr << "ITM:: sender Lat: " << parent->getLatitude() << ", Lon: " << parent->getLongitude() << ", Alt: " << sender_alt << endl;
258 double point_distance= _terrain_sampling_distance;
259 double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
260 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
261 double probe_distance = 0.0;
262 /** If distance larger than this value (300 km), assume reception imposssible */
263 if (distance_m > 300000)
265 /** If above 8000 meters, consider LOS mode and calculate free-space att */
266 if (own_alt > 8000) {
267 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
268 SG_LOG(SG_GENERAL, SG_BULK,
269 "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
270 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
271 signal = link_budget - dbloss;
276 int max_points = (int)floor(distance_m / point_distance);
277 double delta_last = fmod(distance_m, point_distance);
279 deque<double> _elevations;
280 deque<string> materials;
283 double elevation_under_pilot = 0.0;
284 if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
285 receiver_height = own_alt - elevation_under_pilot;
288 double elevation_under_sender = 0.0;
289 if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
290 transmitter_height = sender_alt - elevation_under_sender;
293 transmitter_height = sender_alt;
297 transmitter_height += _tx_antenna_height;
298 receiver_height += _rx_antenna_height;
301 SG_LOG(SG_GENERAL, SG_BULK,
302 "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters");
303 cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
305 unsigned int e_size = (deque<unsigned>::size_type)max_points;
307 while (_elevations.size() <= e_size) {
308 probe_distance += point_distance;
309 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
310 const SGMaterial *mat = 0;
311 double elevation_m = 0.0;
313 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
314 if((transmission_type == 3) || (transmission_type == 4)) {
315 _elevations.push_back(elevation_m);
317 const std::vector<string> mat_names = mat->get_names();
318 materials.push_back(mat_names[0]);
321 materials.push_back("None");
325 _elevations.push_front(elevation_m);
327 const std::vector<string> mat_names = mat->get_names();
328 materials.push_front(mat_names[0]);
331 materials.push_front("None");
336 if((transmission_type == 3) || (transmission_type == 4)) {
337 _elevations.push_back(0.0);
338 materials.push_back("None");
341 _elevations.push_front(0.0);
342 materials.push_front("None");
346 if((transmission_type == 3) || (transmission_type == 4)) {
347 _elevations.push_front(elevation_under_pilot);
348 if (delta_last > (point_distance / 2) ) // only add last point if it's farther than half point_distance
349 _elevations.push_back(elevation_under_sender);
352 _elevations.push_back(elevation_under_pilot);
353 if (delta_last > (point_distance / 2) )
354 _elevations.push_front(elevation_under_sender);
358 double max_alt_between=0.0;
359 for( deque<double>::size_type i = 0; i < _elevations.size(); i++ ) {
360 if (_elevations[i] > max_alt_between) {
361 max_alt_between = _elevations[i];
365 double num_points= (double)_elevations.size();
367 _elevations.push_front(point_distance);
368 _elevations.push_front(num_points -1);
369 int size = _elevations.size();
370 double itm_elev[size];
371 for(int i=0;i<size;i++) {
372 itm_elev[i]=_elevations[i];
373 //cerr << "ITM:: itm_elev: " << _elevations[i] << endl;
376 if((transmission_type == 3) || (transmission_type == 4)) {
377 // the sender and receiver roles are switched
378 point_to_point(itm_elev, receiver_height, transmitter_height,
379 eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
380 pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
381 if( fgGetBool( "/sim/radio/use-clutter-attenuation", false ) )
382 clutterLoss(frq_mhz, distance_m, itm_elev, materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
385 point_to_point(itm_elev, transmitter_height, receiver_height,
386 eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
387 pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
388 if( fgGetBool( "/sim/radio/use-clutter-attenuation", false ) )
389 clutterLoss(frq_mhz, distance_m, itm_elev, materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
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 cerr << "Clutter loss: " << clutter_loss << endl;
396 //if (errnum == 4) // if parameters are outside sane values for lrprop, the alternative method is used
398 signal = link_budget - dbloss - clutter_loss;
403 /*** Calculate losses due to vegetation and urban clutter (WIP)
404 * We are only worried about clutter loss, terrain influence
405 * on the first Fresnel zone is calculated in the ITM functions
407 void FGRadioTransmission::clutterLoss(double freq, double distance_m, double itm_elev[], deque<string> materials,
408 double transmitter_height, double receiver_height, int p_mode,
409 double horizons[], double &clutter_loss) {
411 distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
413 if (p_mode == 0) { // LOS: take each point and see how clutter height affects first Fresnel zone
416 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
418 double clutter_height = 0.0; // mean clutter height for a certain terrain type
419 double clutter_density = 0.0; // percent of reflected wave
420 get_material_properties(materials[mat], clutter_height, clutter_density);
422 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
423 // First Fresnel radius
424 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / ( distance_m * freq / 1000) );
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] + 2] + receiver_height);
429 double d1 = j * itm_elev[1];
430 if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
431 d1 = (itm_elev[0] - j) * itm_elev[1];
433 double ray_height = (grad * d1) + min_elev;
435 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
436 double intrusion = fabs(clearance);
438 if (clearance >= 0) {
441 else if (clearance < 0 && (intrusion < clutter_height)) {
443 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
445 else if (clearance < 0 && (intrusion > clutter_height)) {
446 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/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] * itm_elev[0]/ distance_m );
460 int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
461 //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
463 /** perform the first pass */
466 for (int k=3;k < num_points_1st + 2;k++) {
467 if (num_points_1st < 1)
469 double clutter_height = 0.0; // mean clutter height for a certain terrain type
470 double clutter_density = 0.0; // percent of reflected wave
471 get_material_properties(materials[mat], clutter_height, clutter_density);
473 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
474 // First Fresnel radius
475 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) );
477 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
479 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
480 double d1 = j * itm_elev[1];
481 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
482 d1 = (num_points_1st - j) * itm_elev[1];
484 double ray_height = (grad * d1) + min_elev;
486 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
487 double intrusion = fabs(clearance);
489 if (clearance >= 0) {
492 else if (clearance < 0 && (intrusion < clutter_height)) {
494 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
496 else if (clearance < 0 && (intrusion > clutter_height)) {
497 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
507 /** and the second pass */
509 j =1; // first point is diffraction edge, 2nd the RX elevation
510 for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
511 if (num_points_2nd < 1)
513 double clutter_height = 0.0; // mean clutter height for a certain terrain type
514 double clutter_density = 0.0; // percent of reflected wave
515 get_material_properties(materials[mat], clutter_height, clutter_density);
517 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
518 // First Fresnel radius
519 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (num_points_2nd - j) * itm_elev[1] / 1000000) / ( num_points_2nd * itm_elev[1] * freq / 1000) );
521 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
523 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
524 double d1 = j * itm_elev[1];
525 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
526 d1 = (num_points_2nd - j) * itm_elev[1];
528 double ray_height = (grad * d1) + min_elev;
530 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
531 double intrusion = fabs(clearance);
533 if (clearance >= 0) {
536 else if (clearance < 0 && (intrusion < clutter_height)) {
538 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
540 else if (clearance < 0 && (intrusion > clutter_height)) {
541 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
551 else { // double horizon: same as single horizon, except there are 3 segments
553 int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
554 int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
555 int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
556 //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
557 //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
559 /** perform the first pass */
561 int j=1; // first point is TX elevation, 2nd is obstruction elevation
562 for (int k=3;k < num_points_1st +2;k++) {
563 if (num_points_1st < 1)
565 double clutter_height = 0.0; // mean clutter height for a certain terrain type
566 double clutter_density = 0.0; // percent of reflected wave
567 get_material_properties(materials[mat], clutter_height, clutter_density);
569 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
570 // First Fresnel radius
571 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) );
573 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
575 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
576 double d1 = j * itm_elev[1];
577 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
578 d1 = (num_points_1st - j) * itm_elev[1];
580 double ray_height = (grad * d1) + min_elev;
582 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
583 double intrusion = fabs(clearance);
585 if (clearance >= 0) {
588 else if (clearance < 0 && (intrusion < clutter_height)) {
590 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
592 else if (clearance < 0 && (intrusion > clutter_height)) {
593 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
602 /** and the second pass */
604 j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
605 for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
606 if (num_points_2nd < 1)
608 double clutter_height = 0.0; // mean clutter height for a certain terrain type
609 double clutter_density = 0.0; // percent of reflected wave
610 get_material_properties(materials[mat], clutter_height, clutter_density);
612 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
613 // First Fresnel radius
614 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (num_points_2nd - j) * itm_elev[1] / 1000000) / ( num_points_2nd * itm_elev[1] * freq / 1000) );
616 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
618 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
619 double d1 = j * itm_elev[1];
620 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
621 d1 = (num_points_2nd - j) * itm_elev[1];
623 double ray_height = (grad * d1) + min_elev;
625 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
626 double intrusion = fabs(clearance);
628 if (clearance >= 0) {
631 else if (clearance < 0 && (intrusion < clutter_height)) {
633 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
635 else if (clearance < 0 && (intrusion > clutter_height)) {
636 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
646 /** third and final pass */
648 j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
649 for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
650 if (num_points_3rd < 1)
652 double clutter_height = 0.0; // mean clutter height for a certain terrain type
653 double clutter_density = 0.0; // percent of reflected wave
654 get_material_properties(materials[mat], clutter_height, clutter_density);
656 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
657 // First Fresnel radius
658 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (num_points_3rd - j) * itm_elev[1] / 1000000) / ( num_points_3rd * itm_elev[1] * freq / 1000) );
661 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
663 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
664 double d1 = j * itm_elev[1];
665 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
666 d1 = (num_points_3rd - j) * itm_elev[1];
668 double ray_height = (grad * d1) + min_elev;
670 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
671 double intrusion = fabs(clearance);
673 if (clearance >= 0) {
676 else if (clearance < 0 && (intrusion < clutter_height)) {
678 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
680 else if (clearance < 0 && (intrusion > clutter_height)) {
681 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
693 else if (p_mode == 2) { // troposcatter: ignore ground clutter for now...
699 /*** Temporary material properties database
700 * height: median clutter height
701 * density: radiowave attenuation factor
703 void FGRadioTransmission::get_material_properties(string mat_name, double &height, double &density) {
705 if(mat_name == "Landmass") {
710 else if(mat_name == "SomeSort") {
715 else if(mat_name == "Island") {
719 else if(mat_name == "Default") {
723 else if(mat_name == "EvergreenBroadCover") {
727 else if(mat_name == "EvergreenForest") {
731 else if(mat_name == "DeciduousBroadCover") {
735 else if(mat_name == "DeciduousForest") {
739 else if(mat_name == "MixedForestCover") {
743 else if(mat_name == "MixedForest") {
747 else if(mat_name == "RainForest") {
751 else if(mat_name == "EvergreenNeedleCover") {
755 else if(mat_name == "WoodedTundraCover") {
759 else if(mat_name == "DeciduousNeedleCover") {
763 else if(mat_name == "ScrubCover") {
767 else if(mat_name == "BuiltUpCover") {
771 else if(mat_name == "Urban") {
775 else if(mat_name == "Construction") {
779 else if(mat_name == "Industrial") {
783 else if(mat_name == "Port") {
787 else if(mat_name == "Town") {
791 else if(mat_name == "SubUrban") {
795 else if(mat_name == "CropWoodCover") {
799 else if(mat_name == "CropWood") {
803 else if(mat_name == "AgroForest") {
814 /*** implement simple LOS propagation model (WIP)
816 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
818 if( (freq < 118.0) || (freq > 137.0) )
819 frq_mhz = 125.0; // sane value, middle of bandplan
823 double tx_pow = _transmitter_power;
824 double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
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;
836 double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
838 //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
840 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
842 SGGeod sender_pos = pos;
844 sender_alt_ft = sender_pos.getElevationFt();
845 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
847 receiver_height = own_alt;
848 transmitter_height = sender_alt;
850 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
853 transmitter_height += _tx_antenna_height;
854 receiver_height += _rx_antenna_height;
857 /** radio horizon calculation with wave bending k=4/3 */
858 double receiver_horizon = 4.12 * sqrt(receiver_height);
859 double transmitter_horizon = 4.12 * sqrt(transmitter_height);
860 double total_horizon = receiver_horizon + transmitter_horizon;
862 if (distance_m > total_horizon) {
866 // free-space loss (distance calculation should be changed)
867 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
868 signal = link_budget - dbloss;
869 SG_LOG(SG_GENERAL, SG_BULK,
870 "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm ");
871 //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;