1 // radio.cxx -- implementation of FGRadio
2 // Class to manage radio propagation using the ITM model
3 // Written by Adrian Musceac YO8RZZ, 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>
32 #include <boost/scoped_array.hpp>
34 #define WITH_POINT_TO_POINT 1
38 FGRadioTransmission::FGRadioTransmission() {
41 _receiver_sensitivity = -105.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD or less
43 /** AM transmitter power in dBm.
44 * Typical output powers for ATC ground equipment, VHF-UHF:
45 * 40 dBm - 10 W (ground, clearance)
46 * 44 dBm - 20 W (tower)
47 * 47 dBm - 50 W (center, sectors)
48 * 50 dBm - 100 W (center, sectors)
49 * 53 dBm - 200 W (sectors, on directional arrays)
51 _transmitter_power = 43.0;
53 _tx_antenna_height = 2.0; // TX antenna height above ground level
55 _rx_antenna_height = 2.0; // RX antenna height above ground level
58 _rx_antenna_gain = 1.0; // maximum antenna gain expressed in dBi
59 _tx_antenna_gain = 1.0;
61 _rx_line_losses = 2.0; // to be configured for each station
62 _tx_line_losses = 2.0;
64 _polarization = 1; // default vertical
66 _propagation_model = 2;
68 _root_node = fgGetNode("sim/radio", true);
69 _terrain_sampling_distance = _root_node->getDoubleValue("sampling-distance", 90.0); // regular SRTM is 90 meters
74 FGRadioTransmission::~FGRadioTransmission()
79 double FGRadioTransmission::getFrequency(int radio) {
83 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
86 freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
89 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
96 void FGRadioTransmission::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
101 double FGRadioTransmission::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
103 // typical VOR/LOC transmitter power appears to be 100 - 200 Watt i.e 50 - 53 dBm
104 // vor/loc typical sensitivity between -107 and -101 dBm
105 // glideslope sensitivity between -85 and -81 dBm
106 if ( _propagation_model == 1) {
107 return LOS_calculate_attenuation(tx_pos, freq, 1);
109 else if ( _propagation_model == 2) {
110 return ITM_calculate_attenuation(tx_pos, freq, 1);
118 double FGRadioTransmission::receiveBeacon(SGGeod &tx_pos, double heading, double pitch) {
120 // these properties should be set by an instrument
121 _receiver_sensitivity = _root_node->getDoubleValue("station[0]/rx-sensitivity", _receiver_sensitivity);
122 _transmitter_power = watt_to_dbm(_root_node->getDoubleValue("station[0]/tx-power-watt", _transmitter_power));
123 _polarization = _root_node->getIntValue("station[0]/polarization", 1);
124 _tx_antenna_height += _root_node->getDoubleValue("station[0]/tx-antenna-height", 0);
125 _rx_antenna_height += _root_node->getDoubleValue("station[0]/rx-antenna-height", 0);
126 _tx_antenna_gain += _root_node->getDoubleValue("station[0]/tx-antenna-gain", 0);
127 _rx_antenna_gain += _root_node->getDoubleValue("station[0]/rx-antenna-gain", 0);
129 double freq = _root_node->getDoubleValue("station[0]/frequency", 144.8); // by default stay in the ham 2 meter band
131 double comm1 = getFrequency(1);
132 double comm2 = getFrequency(2);
133 if ( !(fabs(freq - comm1) <= 0.0001) && !(fabs(freq - comm2) <= 0.0001) ) {
137 double signal = ITM_calculate_attenuation(tx_pos, freq, 1);
144 void FGRadioTransmission::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
146 // adjust some default parameters in case the ATC code does not set them
147 if(ground_to_air == 1) {
148 _transmitter_power += 4.0;
149 _tx_antenna_height += 30.0;
150 _tx_antenna_gain += 2.0;
153 double comm1 = getFrequency(1);
154 double comm2 = getFrequency(2);
155 if ( !(fabs(freq - comm1) <= 0.0001) && !(fabs(freq - comm2) <= 0.0001) ) {
160 if ( _propagation_model == 0) { // skip propagation routines entirely
161 fgSetString("/sim/messages/atc", text.c_str());
163 else if ( _propagation_model == 1 ) { // Use free-space, round earth
165 double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
170 fgSetString("/sim/messages/atc", text.c_str());
173 else if ( _propagation_model == 2 ) { // Use ITM propagation model
175 double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
179 if ((signal > 0.0) && (signal < 12.0)) {
180 /** for low SNR values need a way to make the conversation
181 * hard to understand but audible
182 * in the real world, the receiver AGC fails to capture the slope
183 * and the signal, due to being amplitude modulated, decreases volume after demodulation
184 * the workaround below is more akin to what would happen on a FM transmission
185 * therefore the correct way would be to work on the volume
188 string hash_noise = " ";
189 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
190 int t_size = text.size();
191 for (int n = 1; n <= reps; ++n) {
192 int pos = rand() % (t_size -1);
193 text.replace(pos,1, hash_noise);
196 //double volume = (fabs(signal - 12.0) / 12);
197 //double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
199 //fgSetDouble("/sim/sound/voices/voice/volume", volume);
200 fgSetString("/sim/messages/atc", text.c_str());
201 //fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
204 fgSetString("/sim/messages/atc", text.c_str());
211 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
215 /** ITM default parameters
216 TODO: take them from tile materials (especially for sea)?
218 double eps_dielect=15.0;
219 double sgm_conductivity = 0.005;
221 double frq_mhz = freq;
223 int radio_climate = 5; // continental temperate
224 int pol= _polarization;
225 double conf = 0.90; // 90% of situations and time, take into account speed
229 int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
233 double clutter_loss = 0.0; // loss due to vegetation and urban
234 double tx_pow = _transmitter_power;
235 double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
239 double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
240 double signal_strength = tx_pow - _rx_line_losses - _tx_line_losses + ant_gain;
241 double tx_erp = dbm_to_watt(tx_pow + _tx_antenna_gain - _tx_line_losses);
244 FGScenery * scenery = globals->get_scenery();
246 double own_lat = fgGetDouble("/position/latitude-deg");
247 double own_lon = fgGetDouble("/position/longitude-deg");
248 double own_alt_ft = fgGetDouble("/position/altitude-ft");
249 double own_heading = fgGetDouble("/orientation/heading-deg");
250 double own_alt= own_alt_ft * SG_FEET_TO_METER;
255 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
256 SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
257 SGGeoc center = SGGeoc::fromGeod( max_own_pos );
258 SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
261 double sender_alt_ft,sender_alt;
262 double transmitter_height=0.0;
263 double receiver_height=0.0;
264 SGGeod sender_pos = pos;
266 sender_alt_ft = sender_pos.getElevationFt();
267 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
268 SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
269 SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
272 double point_distance= _terrain_sampling_distance;
273 double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
274 double reverse_course = SGGeodesy::courseRad(sender_pos_c, own_pos_c);
275 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
276 double probe_distance = 0.0;
277 /** If distance larger than this value (300 km), assume reception imposssible to spare CPU cycles */
278 if (distance_m > 300000)
280 /** If above 8000 meters, consider LOS mode and calculate free-space att to spare CPU cycles */
281 if (own_alt > 8000) {
282 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
283 SG_LOG(SG_GENERAL, SG_BULK,
284 "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
285 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
286 signal = link_budget - dbloss;
291 int max_points = (int)floor(distance_m / point_distance);
292 double delta_last = fmod(distance_m, point_distance);
294 deque<double> elevations;
295 deque<string*> materials;
298 double elevation_under_pilot = 0.0;
299 if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
300 receiver_height = own_alt - elevation_under_pilot;
303 double elevation_under_sender = 0.0;
304 if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
305 transmitter_height = sender_alt - elevation_under_sender;
308 transmitter_height = sender_alt;
312 transmitter_height += _tx_antenna_height;
313 receiver_height += _rx_antenna_height;
315 //cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
316 _root_node->setDoubleValue("station[0]/rx-height", receiver_height);
317 _root_node->setDoubleValue("station[0]/tx-height", transmitter_height);
318 _root_node->setDoubleValue("station[0]/distance", distance_m / 1000);
320 unsigned int e_size = (deque<unsigned>::size_type)max_points;
322 while (elevations.size() <= e_size) {
323 probe_distance += point_distance;
324 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
325 const SGMaterial *mat = 0;
326 double elevation_m = 0.0;
328 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
329 if((transmission_type == 3) || (transmission_type == 4)) {
330 elevations.push_back(elevation_m);
332 const std::vector<string> mat_names = mat->get_names();
333 string* name = new string(mat_names[0]);
334 materials.push_back(name);
337 string* no_material = new string("None");
338 materials.push_back(no_material);
342 elevations.push_front(elevation_m);
344 const std::vector<string> mat_names = mat->get_names();
345 string* name = new string(mat_names[0]);
346 materials.push_front(name);
349 string* no_material = new string("None");
350 materials.push_front(no_material);
355 if((transmission_type == 3) || (transmission_type == 4)) {
356 elevations.push_back(0.0);
357 string* no_material = new string("None");
358 materials.push_back(no_material);
361 string* no_material = new string("None");
362 elevations.push_front(0.0);
363 materials.push_front(no_material);
367 if((transmission_type == 3) || (transmission_type == 4)) {
368 elevations.push_front(elevation_under_pilot);
369 //if (delta_last > (point_distance / 2) ) // only add last point if it's farther than half point_distance
370 elevations.push_back(elevation_under_sender);
373 elevations.push_back(elevation_under_pilot);
374 //if (delta_last > (point_distance / 2) )
375 elevations.push_front(elevation_under_sender);
379 double num_points= (double)elevations.size();
382 elevations.push_front(point_distance);
383 elevations.push_front(num_points -1);
385 int size = elevations.size();
386 boost::scoped_array<double> itm_elev( new double[size] );
388 for(int i=0;i<size;i++) {
389 itm_elev[i]=elevations[i];
392 if((transmission_type == 3) || (transmission_type == 4)) {
393 // the sender and receiver roles are switched
394 ITM::point_to_point(itm_elev.get(), receiver_height, transmitter_height,
395 eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
396 pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
397 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
398 calculate_clutter_loss(frq_mhz, itm_elev.get(), materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
401 ITM::point_to_point(itm_elev.get(), transmitter_height, receiver_height,
402 eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
403 pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
404 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
405 calculate_clutter_loss(frq_mhz, itm_elev.get(), materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
408 double pol_loss = 0.0;
409 // TODO: remove this check after we check a bit the axis calculations in this function
410 if (_polarization == 1) {
411 pol_loss = polarization_loss();
413 //SG_LOG(SG_GENERAL, SG_BULK,
414 // "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
415 //cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
416 _root_node->setDoubleValue("station[0]/link-budget", link_budget);
417 _root_node->setDoubleValue("station[0]/terrain-attenuation", dbloss);
418 _root_node->setStringValue("station[0]/prop-mode", strmode);
419 _root_node->setDoubleValue("station[0]/clutter-attenuation", clutter_loss);
420 _root_node->setDoubleValue("station[0]/polarization-attenuation", pol_loss);
421 //if (errnum == 4) // if parameters are outside sane values for lrprop, bail out fast
424 // temporary, keep this antenna radiation pattern code here
425 double tx_pattern_gain = 0.0;
426 double rx_pattern_gain = 0.0;
427 double sender_heading = 270.0; // due West
428 double tx_antenna_bearing = sender_heading - reverse_course * SGD_RADIANS_TO_DEGREES;
429 double rx_antenna_bearing = own_heading - course * SGD_RADIANS_TO_DEGREES;
430 double rx_elev_angle = atan((itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m) * SGD_RADIANS_TO_DEGREES;
431 double tx_elev_angle = 0.0 - rx_elev_angle;
432 if (_root_node->getBoolValue("use-tx-antenna-pattern", false)) {
433 FGRadioAntenna* TX_antenna;
434 TX_antenna = new FGRadioAntenna("Plot2");
435 TX_antenna->set_heading(sender_heading);
436 TX_antenna->set_elevation_angle(0);
437 tx_pattern_gain = TX_antenna->calculate_gain(tx_antenna_bearing, tx_elev_angle);
440 if (_root_node->getBoolValue("use-rx-antenna-pattern", false)) {
441 FGRadioAntenna* RX_antenna;
442 RX_antenna = new FGRadioAntenna("Plot2");
443 RX_antenna->set_heading(own_heading);
444 RX_antenna->set_elevation_angle(fgGetDouble("/orientation/pitch-deg"));
445 rx_pattern_gain = RX_antenna->calculate_gain(rx_antenna_bearing, rx_elev_angle);
449 signal = link_budget - dbloss - clutter_loss + pol_loss + rx_pattern_gain + tx_pattern_gain;
450 double signal_strength_dbm = signal_strength - dbloss - clutter_loss + pol_loss + rx_pattern_gain + tx_pattern_gain;
451 double field_strength_uV = dbm_to_microvolt(signal_strength_dbm);
452 _root_node->setDoubleValue("station[0]/signal-dbm", signal_strength_dbm);
453 _root_node->setDoubleValue("station[0]/field-strength-uV", field_strength_uV);
454 _root_node->setDoubleValue("station[0]/signal", signal);
455 _root_node->setDoubleValue("station[0]/tx-erp", tx_erp);
457 //_root_node->setDoubleValue("station[0]/tx-pattern-gain", tx_pattern_gain);
458 //_root_node->setDoubleValue("station[0]/rx-pattern-gain", rx_pattern_gain);
460 for (unsigned i =0; i < materials.size(); i++) {
469 void FGRadioTransmission::calculate_clutter_loss(double freq, double itm_elev[], deque<string*> &materials,
470 double transmitter_height, double receiver_height, int p_mode,
471 double horizons[], double &clutter_loss) {
473 double distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
474 unsigned mat_size = materials.size();
475 if (p_mode == 0) { // LOS: take each point and see how clutter height affects first Fresnel zone
478 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
480 double clutter_height = 0.0; // mean clutter height for a certain terrain type
481 double clutter_density = 0.0; // percent of reflected wave
482 if((unsigned)mat >= mat_size) { //this tends to happen when the model interferes with the antenna (obstructs)
483 //cerr << "Array index out of bounds 0-0: " << mat << " size: " << mat_size << endl;
486 get_material_properties(materials[mat], clutter_height, clutter_density);
488 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
489 // First Fresnel radius
490 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / ( distance_m * freq / 1000) );
491 if (frs_rad <= 0.0) { //this tends to happen when the model interferes with the antenna (obstructs)
492 //cerr << "Frs rad 0-0: " << frs_rad << endl;
495 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
497 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
498 double d1 = j * itm_elev[1];
499 if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
500 d1 = (itm_elev[0] - j) * itm_elev[1];
502 double ray_height = (grad * d1) + min_elev;
504 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
505 double intrusion = fabs(clearance);
507 if (clearance >= 0) {
510 else if (clearance < 0 && (intrusion < clutter_height)) {
512 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
514 else if (clearance < 0 && (intrusion > clutter_height)) {
515 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
525 else if (p_mode == 1) { // diffraction
527 if (horizons[1] == 0.0) { // single horizon: same as above, except pass twice using the highest point
528 int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
529 int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
530 //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
532 /** perform the first pass */
535 for (int k=3;k < num_points_1st + 2;k++) {
536 if (num_points_1st < 1)
538 double clutter_height = 0.0; // mean clutter height for a certain terrain type
539 double clutter_density = 0.0; // percent of reflected wave
541 if((unsigned)mat >= mat_size) {
542 //cerr << "Array index out of bounds 1-1: " << mat << " size: " << mat_size << endl;
545 get_material_properties(materials[mat], clutter_height, clutter_density);
547 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
548 // First Fresnel radius
549 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) );
550 if (frs_rad <= 0.0) {
551 //cerr << "Frs rad 1-1: " << frs_rad << endl;
554 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
556 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
557 double d1 = j * itm_elev[1];
558 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
559 d1 = (num_points_1st - j) * itm_elev[1];
561 double ray_height = (grad * d1) + min_elev;
563 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
564 double intrusion = fabs(clearance);
566 if (clearance >= 0) {
569 else if (clearance < 0 && (intrusion < clutter_height)) {
571 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
573 else if (clearance < 0 && (intrusion > clutter_height)) {
574 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
584 /** and the second pass */
586 j =1; // first point is diffraction edge, 2nd the RX elevation
587 for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
588 if (num_points_2nd < 1)
590 double clutter_height = 0.0; // mean clutter height for a certain terrain type
591 double clutter_density = 0.0; // percent of reflected wave
593 if((unsigned)mat >= mat_size) {
594 //cerr << "Array index out of bounds 1-2: " << mat << " size: " << mat_size << endl;
597 get_material_properties(materials[mat], clutter_height, clutter_density);
599 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
600 // First Fresnel radius
601 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) );
602 if (frs_rad <= 0.0) {
603 //cerr << "Frs rad 1-2: " << frs_rad << " numpoints2 " << num_points_2nd << " j: " << j << endl;
606 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
608 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
609 double d1 = j * itm_elev[1];
610 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
611 d1 = (num_points_2nd - j) * itm_elev[1];
613 double ray_height = (grad * d1) + min_elev;
615 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
616 double intrusion = fabs(clearance);
618 if (clearance >= 0) {
621 else if (clearance < 0 && (intrusion < clutter_height)) {
623 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
625 else if (clearance < 0 && (intrusion > clutter_height)) {
626 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
636 else { // double horizon: same as single horizon, except there are 3 segments
638 int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
639 int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
640 int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
641 //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
642 //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
644 /** perform the first pass */
646 int j=1; // first point is TX elevation, 2nd is obstruction elevation
647 for (int k=3;k < num_points_1st +2;k++) {
648 if (num_points_1st < 1)
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 if((unsigned)mat >= mat_size) {
653 //cerr << "Array index out of bounds 2-1: " << mat << " size: " << mat_size << endl;
656 get_material_properties(materials[mat], clutter_height, clutter_density);
658 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
659 // First Fresnel radius
660 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) );
661 if (frs_rad <= 0.0) {
662 //cerr << "Frs rad 2-1: " << frs_rad << " numpoints1 " << num_points_1st << " j: " << j << endl;
665 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
667 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
668 double d1 = j * itm_elev[1];
669 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
670 d1 = (num_points_1st - j) * itm_elev[1];
672 double ray_height = (grad * d1) + min_elev;
674 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
675 double intrusion = fabs(clearance);
677 if (clearance >= 0) {
680 else if (clearance < 0 && (intrusion < clutter_height)) {
682 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
684 else if (clearance < 0 && (intrusion > clutter_height)) {
685 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
695 /** and the second pass */
697 j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
698 for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
699 if (num_points_2nd < 1)
701 double clutter_height = 0.0; // mean clutter height for a certain terrain type
702 double clutter_density = 0.0; // percent of reflected wave
703 if((unsigned)mat >= mat_size) {
704 //cerr << "Array index out of bounds 2-2: " << mat << " size: " << mat_size << endl;
707 get_material_properties(materials[mat], clutter_height, clutter_density);
709 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
710 // First Fresnel radius
711 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) );
712 if (frs_rad <= 0.0) {
713 //cerr << "Frs rad 2-2: " << frs_rad << " numpoints2 " << num_points_2nd << " j: " << j << endl;
716 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
718 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
719 double d1 = j * itm_elev[1];
720 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
721 d1 = (num_points_2nd - j) * itm_elev[1];
723 double ray_height = (grad * d1) + min_elev;
725 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
726 double intrusion = fabs(clearance);
728 if (clearance >= 0) {
731 else if (clearance < 0 && (intrusion < clutter_height)) {
733 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
735 else if (clearance < 0 && (intrusion > clutter_height)) {
736 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
746 /** third and final pass */
748 j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
749 for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
750 if (num_points_3rd < 1)
752 double clutter_height = 0.0; // mean clutter height for a certain terrain type
753 double clutter_density = 0.0; // percent of reflected wave
754 if((unsigned)mat >= mat_size) {
755 //cerr << "Array index out of bounds 2-3: " << mat << " size: " << mat_size << endl;
758 get_material_properties(materials[mat], clutter_height, clutter_density);
760 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
761 // First Fresnel radius
762 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) );
763 if (frs_rad <= 0.0) {
764 //cerr << "Frs rad 2-3: " << frs_rad << " numpoints3 " << num_points_3rd << " j: " << j << endl;
768 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
770 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
771 double d1 = j * itm_elev[1];
772 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
773 d1 = (num_points_3rd - j) * itm_elev[1];
775 double ray_height = (grad * d1) + min_elev;
777 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
778 double intrusion = fabs(clearance);
780 if (clearance >= 0) {
783 else if (clearance < 0 && (intrusion < clutter_height)) {
785 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
787 else if (clearance < 0 && (intrusion > clutter_height)) {
788 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
800 else if (p_mode == 2) { // troposcatter: ignore ground clutter for now... maybe do something with weather
807 void FGRadioTransmission::get_material_properties(string* mat_name, double &height, double &density) {
812 if(*mat_name == "Landmass") {
817 else if(*mat_name == "SomeSort") {
822 else if(*mat_name == "Island") {
826 else if(*mat_name == "Default") {
830 else if(*mat_name == "EvergreenBroadCover") {
834 else if(*mat_name == "EvergreenForest") {
838 else if(*mat_name == "DeciduousBroadCover") {
842 else if(*mat_name == "DeciduousForest") {
846 else if(*mat_name == "MixedForestCover") {
850 else if(*mat_name == "MixedForest") {
854 else if(*mat_name == "RainForest") {
858 else if(*mat_name == "EvergreenNeedleCover") {
862 else if(*mat_name == "WoodedTundraCover") {
866 else if(*mat_name == "DeciduousNeedleCover") {
870 else if(*mat_name == "ScrubCover") {
874 else if(*mat_name == "BuiltUpCover") {
878 else if(*mat_name == "Urban") {
882 else if(*mat_name == "Construction") {
886 else if(*mat_name == "Industrial") {
890 else if(*mat_name == "Port") {
894 else if(*mat_name == "Town") {
898 else if(*mat_name == "SubUrban") {
902 else if(*mat_name == "CropWoodCover") {
906 else if(*mat_name == "CropWood") {
910 else if(*mat_name == "AgroForest") {
922 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
924 double frq_mhz = freq;
926 double tx_pow = _transmitter_power;
927 double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
930 double sender_alt_ft,sender_alt;
931 double transmitter_height=0.0;
932 double receiver_height=0.0;
933 double own_lat = fgGetDouble("/position/latitude-deg");
934 double own_lon = fgGetDouble("/position/longitude-deg");
935 double own_alt_ft = fgGetDouble("/position/altitude-ft");
936 double own_alt= own_alt_ft * SG_FEET_TO_METER;
939 double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
941 //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
943 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
945 SGGeod sender_pos = pos;
947 sender_alt_ft = sender_pos.getElevationFt();
948 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
950 receiver_height = own_alt;
951 transmitter_height = sender_alt;
953 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
956 transmitter_height += _tx_antenna_height;
957 receiver_height += _rx_antenna_height;
960 /** radio horizon calculation with wave bending k=4/3 */
961 double receiver_horizon = 4.12 * sqrt(receiver_height);
962 double transmitter_horizon = 4.12 * sqrt(transmitter_height);
963 double total_horizon = receiver_horizon + transmitter_horizon;
965 if (distance_m > total_horizon) {
968 double pol_loss = 0.0;
969 if (_polarization == 1) {
970 pol_loss = polarization_loss();
972 // free-space loss (distance calculation should be changed)
973 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
974 signal = link_budget - dbloss + pol_loss;
976 //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
981 /*** calculate loss due to polarization mismatch
982 * this function is only reliable for vertical polarization
983 * due to the V-shape of horizontally polarized antennas
985 double FGRadioTransmission::polarization_loss() {
988 double roll = fgGetDouble("/orientation/roll-deg");
989 if (fabs(roll) > 85.0)
991 double pitch = fgGetDouble("/orientation/pitch-deg");
992 if (fabs(pitch) > 85.0)
994 double theta = fabs( atan( sqrt(
995 pow(tan(roll * SGD_DEGREES_TO_RADIANS), 2) +
996 pow(tan(pitch * SGD_DEGREES_TO_RADIANS), 2) )) * SGD_RADIANS_TO_DEGREES);
998 if (_polarization == 0)
999 theta_deg = 90.0 - theta;
1002 if (theta_deg > 85.0) // we don't want to converge into infinity
1005 double loss = 10 * log10( pow(cos(theta_deg * SGD_DEGREES_TO_RADIANS), 2) );
1006 //cerr << "Polarization loss: " << loss << " dBm " << endl;
1011 double FGRadioTransmission::watt_to_dbm(double power_watt) {
1012 return 10 * log10(1000 * power_watt); // returns dbm
1015 double FGRadioTransmission::dbm_to_watt(double dbm) {
1016 return exp( (dbm-30) * log(10.0) / 10.0); // returns Watts
1019 double FGRadioTransmission::dbm_to_microvolt(double dbm) {
1020 return sqrt(dbm_to_watt(dbm) * 50) * 1000000; // returns microvolts