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) {
214 if((freq < 40.0) || (freq > 20000.0)) // frequency out of recommended range
216 /** ITM default parameters
217 TODO: take them from tile materials (especially for sea)?
219 double eps_dielect=15.0;
220 double sgm_conductivity = 0.005;
222 double frq_mhz = freq;
224 int radio_climate = 5; // continental temperate
225 int pol= _polarization;
226 double conf = 0.90; // 90% of situations and time, take into account speed
230 int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
234 double clutter_loss = 0.0; // loss due to vegetation and urban
235 double tx_pow = _transmitter_power;
236 double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
240 double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
241 double signal_strength = tx_pow - _rx_line_losses - _tx_line_losses + ant_gain;
242 double tx_erp = dbm_to_watt(tx_pow + _tx_antenna_gain - _tx_line_losses);
245 FGScenery * scenery = globals->get_scenery();
247 double own_lat = fgGetDouble("/position/latitude-deg");
248 double own_lon = fgGetDouble("/position/longitude-deg");
249 double own_alt_ft = fgGetDouble("/position/altitude-ft");
250 double own_heading = fgGetDouble("/orientation/heading-deg");
251 double own_alt= own_alt_ft * SG_FEET_TO_METER;
256 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
257 SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
258 SGGeoc center = SGGeoc::fromGeod( max_own_pos );
259 SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
262 double sender_alt_ft,sender_alt;
263 double transmitter_height=0.0;
264 double receiver_height=0.0;
265 SGGeod sender_pos = pos;
267 sender_alt_ft = sender_pos.getElevationFt();
268 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
269 SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
270 SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
273 double point_distance= _terrain_sampling_distance;
274 double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
275 double reverse_course = SGGeodesy::courseRad(sender_pos_c, own_pos_c);
276 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
277 double probe_distance = 0.0;
278 /** If distance larger than this value (300 km), assume reception imposssible to spare CPU cycles */
279 if (distance_m > 300000)
281 /** If above 8000 meters, consider LOS mode and calculate free-space att to spare CPU cycles */
282 if (own_alt > 8000) {
283 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
284 SG_LOG(SG_GENERAL, SG_BULK,
285 "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
286 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
287 signal = link_budget - dbloss;
292 int max_points = (int)floor(distance_m / point_distance);
293 //double delta_last = fmod(distance_m, point_distance);
295 deque<double> elevations;
296 deque<string*> materials;
299 double elevation_under_pilot = 0.0;
300 if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
301 receiver_height = own_alt - elevation_under_pilot;
304 double elevation_under_sender = 0.0;
305 if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
306 transmitter_height = sender_alt - elevation_under_sender;
309 transmitter_height = sender_alt;
313 transmitter_height += _tx_antenna_height;
314 receiver_height += _rx_antenna_height;
316 //cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
317 _root_node->setDoubleValue("station[0]/rx-height", receiver_height);
318 _root_node->setDoubleValue("station[0]/tx-height", transmitter_height);
319 _root_node->setDoubleValue("station[0]/distance", distance_m / 1000);
321 unsigned int e_size = (deque<unsigned>::size_type)max_points;
323 while (elevations.size() <= e_size) {
324 probe_distance += point_distance;
325 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
326 const SGMaterial *mat = 0;
327 double elevation_m = 0.0;
329 if (scenery->get_elevation_m( probe, elevation_m, &mat )) {
330 if((transmission_type == 3) || (transmission_type == 4)) {
331 elevations.push_back(elevation_m);
333 const std::vector<string> mat_names = mat->get_names();
334 string* name = new string(mat_names[0]);
335 materials.push_back(name);
338 string* no_material = new string("None");
339 materials.push_back(no_material);
343 elevations.push_front(elevation_m);
345 const std::vector<string> mat_names = mat->get_names();
346 string* name = new string(mat_names[0]);
347 materials.push_front(name);
350 string* no_material = new string("None");
351 materials.push_front(no_material);
356 if((transmission_type == 3) || (transmission_type == 4)) {
357 elevations.push_back(0.0);
358 string* no_material = new string("None");
359 materials.push_back(no_material);
362 string* no_material = new string("None");
363 elevations.push_front(0.0);
364 materials.push_front(no_material);
368 if((transmission_type == 3) || (transmission_type == 4)) {
369 elevations.push_front(elevation_under_pilot);
370 //if (delta_last > (point_distance / 2) ) // only add last point if it's farther than half point_distance
371 elevations.push_back(elevation_under_sender);
374 elevations.push_back(elevation_under_pilot);
375 //if (delta_last > (point_distance / 2) )
376 elevations.push_front(elevation_under_sender);
380 double num_points= (double)elevations.size();
383 elevations.push_front(point_distance);
384 elevations.push_front(num_points -1);
386 int size = elevations.size();
387 boost::scoped_array<double> itm_elev( new double[size] );
389 for(int i=0;i<size;i++) {
390 itm_elev[i]=elevations[i];
393 if((transmission_type == 3) || (transmission_type == 4)) {
394 // the sender and receiver roles are switched
395 ITM::point_to_point(itm_elev.get(), receiver_height, transmitter_height,
396 eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
397 pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
398 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
399 calculate_clutter_loss(frq_mhz, itm_elev.get(), materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
402 ITM::point_to_point(itm_elev.get(), transmitter_height, receiver_height,
403 eps_dielect, sgm_conductivity, eno, frq_mhz, radio_climate,
404 pol, conf, rel, dbloss, strmode, p_mode, horizons, errnum);
405 if( _root_node->getBoolValue( "use-clutter-attenuation", false ) )
406 calculate_clutter_loss(frq_mhz, itm_elev.get(), materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
409 double pol_loss = 0.0;
410 // TODO: remove this check after we check a bit the axis calculations in this function
411 if (_polarization == 1) {
412 pol_loss = polarization_loss();
414 //SG_LOG(SG_GENERAL, SG_BULK,
415 // "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum);
416 //cerr << "ITM:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, " << strmode << ", Error: " << errnum << endl;
417 _root_node->setDoubleValue("station[0]/link-budget", link_budget);
418 _root_node->setDoubleValue("station[0]/terrain-attenuation", dbloss);
419 _root_node->setStringValue("station[0]/prop-mode", strmode);
420 _root_node->setDoubleValue("station[0]/clutter-attenuation", clutter_loss);
421 _root_node->setDoubleValue("station[0]/polarization-attenuation", pol_loss);
422 //if (errnum == 4) // if parameters are outside sane values for lrprop, bail out fast
425 // temporary, keep this antenna radiation pattern code here
426 double tx_pattern_gain = 0.0;
427 double rx_pattern_gain = 0.0;
428 double sender_heading = 270.0; // due West
429 double tx_antenna_bearing = sender_heading - reverse_course * SGD_RADIANS_TO_DEGREES;
430 double rx_antenna_bearing = own_heading - course * SGD_RADIANS_TO_DEGREES;
431 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;
432 double tx_elev_angle = 0.0 - rx_elev_angle;
433 if (_root_node->getBoolValue("use-tx-antenna-pattern", false)) {
434 FGRadioAntenna* TX_antenna;
435 TX_antenna = new FGRadioAntenna("Plot2");
436 TX_antenna->set_heading(sender_heading);
437 TX_antenna->set_elevation_angle(0);
438 tx_pattern_gain = TX_antenna->calculate_gain(tx_antenna_bearing, tx_elev_angle);
441 if (_root_node->getBoolValue("use-rx-antenna-pattern", false)) {
442 FGRadioAntenna* RX_antenna;
443 RX_antenna = new FGRadioAntenna("Plot2");
444 RX_antenna->set_heading(own_heading);
445 RX_antenna->set_elevation_angle(fgGetDouble("/orientation/pitch-deg"));
446 rx_pattern_gain = RX_antenna->calculate_gain(rx_antenna_bearing, rx_elev_angle);
450 signal = link_budget - dbloss - clutter_loss + pol_loss + rx_pattern_gain + tx_pattern_gain;
451 double signal_strength_dbm = signal_strength - dbloss - clutter_loss + pol_loss + rx_pattern_gain + tx_pattern_gain;
452 double field_strength_uV = dbm_to_microvolt(signal_strength_dbm);
453 _root_node->setDoubleValue("station[0]/signal-dbm", signal_strength_dbm);
454 _root_node->setDoubleValue("station[0]/field-strength-uV", field_strength_uV);
455 _root_node->setDoubleValue("station[0]/signal", signal);
456 _root_node->setDoubleValue("station[0]/tx-erp", tx_erp);
458 //_root_node->setDoubleValue("station[0]/tx-pattern-gain", tx_pattern_gain);
459 //_root_node->setDoubleValue("station[0]/rx-pattern-gain", rx_pattern_gain);
461 for (unsigned i =0; i < materials.size(); i++) {
470 void FGRadioTransmission::calculate_clutter_loss(double freq, double itm_elev[], deque<string*> &materials,
471 double transmitter_height, double receiver_height, int p_mode,
472 double horizons[], double &clutter_loss) {
474 double distance_m = itm_elev[0] * itm_elev[1]; // only consider elevation points
475 unsigned mat_size = materials.size();
476 if (p_mode == 0) { // LOS: take each point and see how clutter height affects first Fresnel zone
479 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
481 double clutter_height = 0.0; // mean clutter height for a certain terrain type
482 double clutter_density = 0.0; // percent of reflected wave
483 if((unsigned)mat >= mat_size) { //this tends to happen when the model interferes with the antenna (obstructs)
484 //cerr << "Array index out of bounds 0-0: " << mat << " size: " << mat_size << endl;
487 get_material_properties(materials[mat], clutter_height, clutter_density);
489 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
490 // First Fresnel radius
491 double frs_rad = 548 * sqrt( (j * itm_elev[1] * (itm_elev[0] - j) * itm_elev[1] / 1000000) / ( distance_m * freq / 1000) );
492 if (frs_rad <= 0.0) { //this tends to happen when the model interferes with the antenna (obstructs)
493 //cerr << "Frs rad 0-0: " << frs_rad << endl;
496 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
498 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
499 double d1 = j * itm_elev[1];
500 if ((itm_elev[2] + transmitter_height) > ( itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
501 d1 = (itm_elev[0] - j) * itm_elev[1];
503 double ray_height = (grad * d1) + min_elev;
505 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
506 double intrusion = fabs(clearance);
508 if (clearance >= 0) {
511 else if (clearance < 0 && (intrusion < clutter_height)) {
513 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
515 else if (clearance < 0 && (intrusion > clutter_height)) {
516 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
526 else if (p_mode == 1) { // diffraction
528 if (horizons[1] == 0.0) { // single horizon: same as above, except pass twice using the highest point
529 int num_points_1st = (int)floor( horizons[0] * itm_elev[0]/ distance_m );
530 int num_points_2nd = (int)ceil( (distance_m - horizons[0]) * itm_elev[0] / distance_m );
531 //cerr << "Diffraction 1 horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << endl;
533 /** perform the first pass */
536 for (int k=3;k < num_points_1st + 2;k++) {
537 if (num_points_1st < 1)
539 double clutter_height = 0.0; // mean clutter height for a certain terrain type
540 double clutter_density = 0.0; // percent of reflected wave
542 if((unsigned)mat >= mat_size) {
543 //cerr << "Array index out of bounds 1-1: " << mat << " size: " << mat_size << endl;
546 get_material_properties(materials[mat], clutter_height, clutter_density);
548 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
549 // First Fresnel radius
550 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) );
551 if (frs_rad <= 0.0) {
552 //cerr << "Frs rad 1-1: " << frs_rad << endl;
555 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
557 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
558 double d1 = j * itm_elev[1];
559 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
560 d1 = (num_points_1st - j) * itm_elev[1];
562 double ray_height = (grad * d1) + min_elev;
564 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
565 double intrusion = fabs(clearance);
567 if (clearance >= 0) {
570 else if (clearance < 0 && (intrusion < clutter_height)) {
572 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
574 else if (clearance < 0 && (intrusion > clutter_height)) {
575 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
585 /** and the second pass */
587 j =1; // first point is diffraction edge, 2nd the RX elevation
588 for (int k=last+2;k < (int)(itm_elev[0]) + 2;k++) {
589 if (num_points_2nd < 1)
591 double clutter_height = 0.0; // mean clutter height for a certain terrain type
592 double clutter_density = 0.0; // percent of reflected wave
594 if((unsigned)mat >= mat_size) {
595 //cerr << "Array index out of bounds 1-2: " << mat << " size: " << mat_size << endl;
598 get_material_properties(materials[mat], clutter_height, clutter_density);
600 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
601 // First Fresnel radius
602 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) );
603 if (frs_rad <= 0.0) {
604 //cerr << "Frs rad 1-2: " << frs_rad << " numpoints2 " << num_points_2nd << " j: " << j << endl;
607 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
609 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
610 double d1 = j * itm_elev[1];
611 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
612 d1 = (num_points_2nd - j) * itm_elev[1];
614 double ray_height = (grad * d1) + min_elev;
616 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
617 double intrusion = fabs(clearance);
619 if (clearance >= 0) {
622 else if (clearance < 0 && (intrusion < clutter_height)) {
624 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
626 else if (clearance < 0 && (intrusion > clutter_height)) {
627 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
637 else { // double horizon: same as single horizon, except there are 3 segments
639 int num_points_1st = (int)floor( horizons[0] * itm_elev[0] / distance_m );
640 int num_points_2nd = (int)floor(horizons[1] * itm_elev[0] / distance_m );
641 int num_points_3rd = (int)itm_elev[0] - num_points_1st - num_points_2nd;
642 //cerr << "Double horizon:: horizon1: " << horizons[0] << " horizon2: " << horizons[1] << " distance: " << distance_m << endl;
643 //cerr << "Double horizon:: points1: " << num_points_1st << " points2: " << num_points_2nd << " points3: " << num_points_3rd << endl;
645 /** perform the first pass */
647 int j=1; // first point is TX elevation, 2nd is obstruction elevation
648 for (int k=3;k < num_points_1st +2;k++) {
649 if (num_points_1st < 1)
651 double clutter_height = 0.0; // mean clutter height for a certain terrain type
652 double clutter_density = 0.0; // percent of reflected wave
653 if((unsigned)mat >= mat_size) {
654 //cerr << "Array index out of bounds 2-1: " << mat << " size: " << mat_size << endl;
657 get_material_properties(materials[mat], clutter_height, clutter_density);
659 double grad = fabs(itm_elev[2] + transmitter_height - itm_elev[num_points_1st + 2] + clutter_height) / distance_m;
660 // First Fresnel radius
661 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) );
662 if (frs_rad <= 0.0) {
663 //cerr << "Frs rad 2-1: " << frs_rad << " numpoints1 " << num_points_1st << " j: " << j << endl;
666 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
668 double min_elev = SGMiscd::min(itm_elev[2] + transmitter_height, itm_elev[num_points_1st + 2] + clutter_height);
669 double d1 = j * itm_elev[1];
670 if ( (itm_elev[2] + transmitter_height) > (itm_elev[num_points_1st + 2] + clutter_height) ) {
671 d1 = (num_points_1st - j) * itm_elev[1];
673 double ray_height = (grad * d1) + min_elev;
675 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
676 double intrusion = fabs(clearance);
678 if (clearance >= 0) {
681 else if (clearance < 0 && (intrusion < clutter_height)) {
683 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
685 else if (clearance < 0 && (intrusion > clutter_height)) {
686 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
696 /** and the second pass */
698 j =1; // first point is 1st obstruction elevation, 2nd is 2nd obstruction elevation
699 for (int k=last+2;k < num_points_1st + num_points_2nd +2;k++) {
700 if (num_points_2nd < 1)
702 double clutter_height = 0.0; // mean clutter height for a certain terrain type
703 double clutter_density = 0.0; // percent of reflected wave
704 if((unsigned)mat >= mat_size) {
705 //cerr << "Array index out of bounds 2-2: " << mat << " size: " << mat_size << endl;
708 get_material_properties(materials[mat], clutter_height, clutter_density);
710 double grad = fabs(itm_elev[last+1] + clutter_height - itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) / distance_m;
711 // First Fresnel radius
712 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) );
713 if (frs_rad <= 0.0) {
714 //cerr << "Frs rad 2-2: " << frs_rad << " numpoints2 " << num_points_2nd << " j: " << j << endl;
717 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
719 double min_elev = SGMiscd::min(itm_elev[last+1] + clutter_height, itm_elev[num_points_1st + num_points_2nd +2] + clutter_height);
720 double d1 = j * itm_elev[1];
721 if ( (itm_elev[last+1] + clutter_height) > (itm_elev[num_points_1st + num_points_2nd + 2] + clutter_height) ) {
722 d1 = (num_points_2nd - j) * itm_elev[1];
724 double ray_height = (grad * d1) + min_elev;
726 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
727 double intrusion = fabs(clearance);
729 if (clearance >= 0) {
732 else if (clearance < 0 && (intrusion < clutter_height)) {
734 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
736 else if (clearance < 0 && (intrusion > clutter_height)) {
737 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
747 /** third and final pass */
749 j =1; // first point is 2nd obstruction elevation, 3rd is RX elevation
750 for (int k=last2+2;k < (int)itm_elev[0] + 2;k++) {
751 if (num_points_3rd < 1)
753 double clutter_height = 0.0; // mean clutter height for a certain terrain type
754 double clutter_density = 0.0; // percent of reflected wave
755 if((unsigned)mat >= mat_size) {
756 //cerr << "Array index out of bounds 2-3: " << mat << " size: " << mat_size << endl;
759 get_material_properties(materials[mat], clutter_height, clutter_density);
761 double grad = fabs(itm_elev[last2+1] + clutter_height - itm_elev[(int)itm_elev[0] + 2] + receiver_height) / distance_m;
762 // First Fresnel radius
763 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) );
764 if (frs_rad <= 0.0) {
765 //cerr << "Frs rad 2-3: " << frs_rad << " numpoints3 " << num_points_3rd << " j: " << j << endl;
769 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
771 double min_elev = SGMiscd::min(itm_elev[last2+1] + clutter_height, itm_elev[(int)itm_elev[0] + 2] + receiver_height);
772 double d1 = j * itm_elev[1];
773 if ( (itm_elev[last2+1] + clutter_height) > (itm_elev[(int)itm_elev[0] + 2] + receiver_height) ) {
774 d1 = (num_points_3rd - j) * itm_elev[1];
776 double ray_height = (grad * d1) + min_elev;
778 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
779 double intrusion = fabs(clearance);
781 if (clearance >= 0) {
784 else if (clearance < 0 && (intrusion < clutter_height)) {
786 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
788 else if (clearance < 0 && (intrusion > clutter_height)) {
789 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
801 else if (p_mode == 2) { // troposcatter: ignore ground clutter for now... maybe do something with weather
808 void FGRadioTransmission::get_material_properties(string* mat_name, double &height, double &density) {
813 if(*mat_name == "Landmass") {
818 else if(*mat_name == "SomeSort") {
823 else if(*mat_name == "Island") {
827 else if(*mat_name == "Default") {
831 else if(*mat_name == "EvergreenBroadCover") {
835 else if(*mat_name == "EvergreenForest") {
839 else if(*mat_name == "DeciduousBroadCover") {
843 else if(*mat_name == "DeciduousForest") {
847 else if(*mat_name == "MixedForestCover") {
851 else if(*mat_name == "MixedForest") {
855 else if(*mat_name == "RainForest") {
859 else if(*mat_name == "EvergreenNeedleCover") {
863 else if(*mat_name == "WoodedTundraCover") {
867 else if(*mat_name == "DeciduousNeedleCover") {
871 else if(*mat_name == "ScrubCover") {
875 else if(*mat_name == "BuiltUpCover") {
879 else if(*mat_name == "Urban") {
883 else if(*mat_name == "Construction") {
887 else if(*mat_name == "Industrial") {
891 else if(*mat_name == "Port") {
895 else if(*mat_name == "Town") {
899 else if(*mat_name == "SubUrban") {
903 else if(*mat_name == "CropWoodCover") {
907 else if(*mat_name == "CropWood") {
911 else if(*mat_name == "AgroForest") {
923 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
925 double frq_mhz = freq;
927 double tx_pow = _transmitter_power;
928 double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
931 double sender_alt_ft,sender_alt;
932 double transmitter_height=0.0;
933 double receiver_height=0.0;
934 double own_lat = fgGetDouble("/position/latitude-deg");
935 double own_lon = fgGetDouble("/position/longitude-deg");
936 double own_alt_ft = fgGetDouble("/position/altitude-ft");
937 double own_alt= own_alt_ft * SG_FEET_TO_METER;
940 double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
942 //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
944 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
946 SGGeod sender_pos = pos;
948 sender_alt_ft = sender_pos.getElevationFt();
949 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
951 receiver_height = own_alt;
952 transmitter_height = sender_alt;
954 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
957 transmitter_height += _tx_antenna_height;
958 receiver_height += _rx_antenna_height;
961 /** radio horizon calculation with wave bending k=4/3 */
962 double receiver_horizon = 4.12 * sqrt(receiver_height);
963 double transmitter_horizon = 4.12 * sqrt(transmitter_height);
964 double total_horizon = receiver_horizon + transmitter_horizon;
966 if (distance_m > total_horizon) {
969 double pol_loss = 0.0;
970 if (_polarization == 1) {
971 pol_loss = polarization_loss();
973 // free-space loss (distance calculation should be changed)
974 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
975 signal = link_budget - dbloss + pol_loss;
977 //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
982 /*** calculate loss due to polarization mismatch
983 * this function is only reliable for vertical polarization
984 * due to the V-shape of horizontally polarized antennas
986 double FGRadioTransmission::polarization_loss() {
989 double roll = fgGetDouble("/orientation/roll-deg");
990 if (fabs(roll) > 85.0)
992 double pitch = fgGetDouble("/orientation/pitch-deg");
993 if (fabs(pitch) > 85.0)
995 double theta = fabs( atan( sqrt(
996 pow(tan(roll * SGD_DEGREES_TO_RADIANS), 2) +
997 pow(tan(pitch * SGD_DEGREES_TO_RADIANS), 2) )) * SGD_RADIANS_TO_DEGREES);
999 if (_polarization == 0)
1000 theta_deg = 90.0 - theta;
1003 if (theta_deg > 85.0) // we don't want to converge into infinity
1006 double loss = 10 * log10( pow(cos(theta_deg * SGD_DEGREES_TO_RADIANS), 2) );
1007 //cerr << "Polarization loss: " << loss << " dBm " << endl;
1012 double FGRadioTransmission::watt_to_dbm(double power_watt) {
1013 return 10 * log10(1000 * power_watt); // returns dbm
1016 double FGRadioTransmission::dbm_to_watt(double dbm) {
1017 return exp( (dbm-30) * log(10.0) / 10.0); // returns Watts
1020 double FGRadioTransmission::dbm_to_microvolt(double dbm) {
1021 return sqrt(dbm_to_watt(dbm) * 50) * 1000000; // returns microvolts