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.
4 //
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.
9 //
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.
14 //
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.
18
19
20
21 #include <config.h>
22
23 #include <cmath>
24
25 #include <stdlib.h>
26 #include <deque>
27 #include "radio.hxx"
28 #include <simgear/scene/material/mat.hxx>
29 #include <Scenery/scenery.hxx>
30
31 #define WITH_POINT_TO_POINT 1
32 #include "itm.cpp"
33
34
FGRadioTransmission()35 FGRadioTransmission::FGRadioTransmission() {
36
37
38 _receiver_sensitivity = -105.0; // typical AM receiver sensitivity seems to be 0.8 microVolt at 12dB SINAD or less
39
40 /** AM transmitter power in dBm.
41 * Typical output powers for ATC ground equipment, VHF-UHF:
42 * 40 dBm - 10 W (ground, clearance)
43 * 44 dBm - 20 W (tower)
44 * 47 dBm - 50 W (center, sectors)
45 * 50 dBm - 100 W (center, sectors)
46 * 53 dBm - 200 W (sectors, on directional arrays)
47 **/
48 _transmitter_power = 43.0;
49
50 _tx_antenna_height = 2.0; // TX antenna height above ground level
51
52 _rx_antenna_height = 2.0; // RX antenna height above ground level
53
54
55 _rx_antenna_gain = 1.0; // maximum antenna gain expressed in dBi
56 _tx_antenna_gain = 1.0;
57
58 _rx_line_losses = 2.0; // to be configured for each station
59 _tx_line_losses = 2.0;
60
61 _polarization = 1; // default vertical
62
63 _propagation_model = 2;
64
65 _root_node = fgGetNode("sim/radio", true);
66 _terrain_sampling_distance = _root_node->getDoubleValue("sampling-distance", 90.0); // regular SRTM is 90 meters
67
68
69 }
70
~FGRadioTransmission()71 FGRadioTransmission::~FGRadioTransmission()
72 {
73 }
74
75
getFrequency(int radio)76 double FGRadioTransmission::getFrequency(int radio) {
77 double freq = 118.0;
78 switch (radio) {
79 case 1:
80 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
81 break;
82 case 2:
83 freq = fgGetDouble("/instrumentation/comm[1]/frequencies/selected-mhz");
84 break;
85 default:
86 freq = fgGetDouble("/instrumentation/comm[0]/frequencies/selected-mhz");
87
88 }
89 return freq;
90 }
91
92
receiveChat(SGGeod tx_pos,double freq,string text,int ground_to_air)93 void FGRadioTransmission::receiveChat(SGGeod tx_pos, double freq, string text, int ground_to_air) {
94
95 }
96
97
receiveNav(SGGeod tx_pos,double freq,int transmission_type)98 double FGRadioTransmission::receiveNav(SGGeod tx_pos, double freq, int transmission_type) {
99
100 // typical VOR/LOC transmitter power appears to be 100 - 200 Watt i.e 50 - 53 dBm
101 // vor/loc typical sensitivity between -107 and -101 dBm
102 // glideslope sensitivity between -85 and -81 dBm
103 if ( _propagation_model == 1) {
104 return LOS_calculate_attenuation(tx_pos, freq, 1);
105 }
106 else if ( _propagation_model == 2) {
107 return ITM_calculate_attenuation(tx_pos, freq, 1);
108 }
109
110 return -1;
111
112 }
113
114
receiveBeacon(SGGeod & tx_pos,double heading,double pitch)115 double FGRadioTransmission::receiveBeacon(SGGeod &tx_pos, double heading, double pitch) {
116
117 // these properties should be set by an instrument
118 _receiver_sensitivity = _root_node->getDoubleValue("station[0]/rx-sensitivity", _receiver_sensitivity);
119 _transmitter_power = watt_to_dbm(_root_node->getDoubleValue("station[0]/tx-power-watt", _transmitter_power));
120 _polarization = _root_node->getIntValue("station[0]/polarization", 1);
121 _tx_antenna_height += _root_node->getDoubleValue("station[0]/tx-antenna-height", 0);
122 _rx_antenna_height += _root_node->getDoubleValue("station[0]/rx-antenna-height", 0);
123 _tx_antenna_gain += _root_node->getDoubleValue("station[0]/tx-antenna-gain", 0);
124 _rx_antenna_gain += _root_node->getDoubleValue("station[0]/rx-antenna-gain", 0);
125
126 double freq = _root_node->getDoubleValue("station[0]/frequency", 144.8); // by default stay in the ham 2 meter band
127
128 double comm1 = getFrequency(1);
129 double comm2 = getFrequency(2);
130 if ( !(fabs(freq - comm1) <= 0.0001) && !(fabs(freq - comm2) <= 0.0001) ) {
131 return -1;
132 }
133
134 double signal = ITM_calculate_attenuation(tx_pos, freq, 1);
135
136 return signal;
137 }
138
139
140
receiveATC(SGGeod tx_pos,double freq,string text,int ground_to_air)141 void FGRadioTransmission::receiveATC(SGGeod tx_pos, double freq, string text, int ground_to_air) {
142
143 // adjust some default parameters in case the ATC code does not set them
144 if(ground_to_air == 1) {
145 _transmitter_power += 4.0;
146 _tx_antenna_height += 30.0;
147 _tx_antenna_gain += 2.0;
148 }
149
150 double comm1 = getFrequency(1);
151 double comm2 = getFrequency(2);
152 if ( !(fabs(freq - comm1) <= 0.0001) && !(fabs(freq - comm2) <= 0.0001) ) {
153 return;
154 }
155 else {
156
157 if ( _propagation_model == 0) { // skip propagation routines entirely
158 fgSetString("/sim/messages/atc", text.c_str());
159 }
160 else if ( _propagation_model == 1 ) { // Use free-space, round earth
161
162 double signal = LOS_calculate_attenuation(tx_pos, freq, ground_to_air);
163 if (signal <= 0.0) {
164 return;
165 }
166 else {
167 fgSetString("/sim/messages/atc", text.c_str());
168 }
169 }
170 else if ( _propagation_model == 2 ) { // Use ITM propagation model
171
172 double signal = ITM_calculate_attenuation(tx_pos, freq, ground_to_air);
173 if (signal <= 0.0) {
174 return;
175 }
176 if ((signal > 0.0) && (signal < 12.0)) {
177 /** for low SNR values need a way to make the conversation
178 * hard to understand but audible
179 * in the real world, the receiver AGC fails to capture the slope
180 * and the signal, due to being amplitude modulated, decreases volume after demodulation
181 * the workaround below is more akin to what would happen on a FM transmission
182 * therefore the correct way would be to work on the volume
183 **/
184 /*
185 string hash_noise = " ";
186 int reps = (int) (fabs(floor(signal - 11.0)) * 2);
187 int t_size = text.size();
188 for (int n = 1; n <= reps; ++n) {
189 int pos = rand() % (t_size -1);
190 text.replace(pos,1, hash_noise);
191 }
192 */
193 //double volume = (fabs(signal - 12.0) / 12);
194 //double old_volume = fgGetDouble("/sim/sound/voices/voice/volume");
195
196 //fgSetDouble("/sim/sound/voices/voice/volume", volume);
197 fgSetString("/sim/messages/atc", text.c_str());
198 //fgSetDouble("/sim/sound/voices/voice/volume", old_volume);
199 }
200 else {
201 fgSetString("/sim/messages/atc", text.c_str());
202 }
203 }
204 }
205 }
206
207
ITM_calculate_attenuation(SGGeod pos,double freq,int transmission_type)208 double FGRadioTransmission::ITM_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
209
210
211 if((freq < 40.0) || (freq > 20000.0)) // frequency out of recommended range
212 return -1;
213 /** ITM default parameters
214 TODO: take them from tile materials (especially for sea)?
215 **/
216 double eps_dielect=15.0;
217 double sgm_conductivity = 0.005;
218 double eno = 301.0;
219 double frq_mhz = freq;
220
221 int radio_climate = 5; // continental temperate
222 int pol= _polarization;
223 double conf = 0.90; // 90% of situations and time, take into account speed
224 double rel = 0.90;
225 double dbloss;
226 char strmode[150];
227 int p_mode = 0; // propgation mode selector: 0 LOS, 1 diffraction dominant, 2 troposcatter
228 double horizons[2];
229 int errnum;
230
231 double clutter_loss = 0.0; // loss due to vegetation and urban
232 double tx_pow = _transmitter_power;
233 double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
234 double signal = 0.0;
235
236
237 double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
238 double signal_strength = tx_pow - _rx_line_losses - _tx_line_losses + ant_gain;
239 double tx_erp = dbm_to_watt(tx_pow + _tx_antenna_gain - _tx_line_losses);
240
241
242 FGScenery * scenery = globals->get_scenery();
243
244 double own_lat = fgGetDouble("/position/latitude-deg");
245 double own_lon = fgGetDouble("/position/longitude-deg");
246 double own_alt_ft = fgGetDouble("/position/altitude-ft");
247 double own_heading = fgGetDouble("/orientation/heading-deg");
248 double own_alt= own_alt_ft * SG_FEET_TO_METER;
249
250
251
252
253 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
254 SGGeod max_own_pos = SGGeod::fromDegM( own_lon, own_lat, SG_MAX_ELEVATION_M );
255 SGGeoc center = SGGeoc::fromGeod( max_own_pos );
256 SGGeoc own_pos_c = SGGeoc::fromGeod( own_pos );
257
258
259 double sender_alt_ft,sender_alt;
260 double transmitter_height=0.0;
261 double receiver_height=0.0;
262 SGGeod sender_pos = pos;
263
264 sender_alt_ft = sender_pos.getElevationFt();
265 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
266 SGGeod max_sender_pos = SGGeod::fromGeodM( pos, SG_MAX_ELEVATION_M );
267 SGGeoc sender_pos_c = SGGeoc::fromGeod( sender_pos );
268
269
270 double point_distance= _terrain_sampling_distance;
271 double course = SGGeodesy::courseRad(own_pos_c, sender_pos_c);
272 double reverse_course = SGGeodesy::courseRad(sender_pos_c, own_pos_c);
273 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
274 double probe_distance = 0.0;
275 /** If distance larger than this value (300 km), assume reception imposssible to spare CPU cycles */
276 if (distance_m > 300000)
277 return -1.0;
278 /** If above 8000 meters, consider LOS mode and calculate free-space att to spare CPU cycles */
279 if (own_alt > 8000) {
280 dbloss = 20 * log10(distance_m) +20 * log10(frq_mhz) -27.55;
281 SG_LOG(SG_GENERAL, SG_BULK,
282 "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation");
283 //cerr << "ITM Free-space mode:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm, free-space attenuation" << endl;
284 signal = link_budget - dbloss;
285 return signal;
286 }
287
288
289 int max_points = (int)floor(distance_m / point_distance);
290 //double delta_last = fmod(distance_m, point_distance);
291
292 deque<double> elevations;
293 deque<string*> materials;
294
295
296 double elevation_under_pilot = 0.0;
297 if (scenery->get_elevation_m( max_own_pos, elevation_under_pilot, NULL )) {
298 receiver_height = own_alt - elevation_under_pilot;
299 }
300
301 double elevation_under_sender = 0.0;
302 if (scenery->get_elevation_m( max_sender_pos, elevation_under_sender, NULL )) {
303 transmitter_height = sender_alt - elevation_under_sender;
304 }
305 else {
306 transmitter_height = sender_alt;
307 }
308
309
310 transmitter_height += _tx_antenna_height;
311 receiver_height += _rx_antenna_height;
312
313 //cerr << "ITM:: RX-height: " << receiver_height << " meters, TX-height: " << transmitter_height << " meters, Distance: " << distance_m << " meters" << endl;
314 _root_node->setDoubleValue("station[0]/rx-height", receiver_height);
315 _root_node->setDoubleValue("station[0]/tx-height", transmitter_height);
316 _root_node->setDoubleValue("station[0]/distance", distance_m / 1000);
317
318 unsigned int e_size = (deque<unsigned>::size_type)max_points;
319
320 while (elevations.size() <= e_size) {
321 probe_distance += point_distance;
322 SGGeod probe = SGGeod::fromGeoc(center.advanceRadM( course, probe_distance ));
323 const simgear::BVHMaterial *material = 0;
324 double elevation_m = 0.0;
325
326 if (scenery->get_elevation_m( probe, elevation_m, &material )) {
327 const SGMaterial *mat;
328 mat = dynamic_cast<const SGMaterial*>(material);
329 if((transmission_type == 3) || (transmission_type == 4)) {
330 elevations.push_back(elevation_m);
331 if(mat) {
332 const std::vector<string> mat_names = mat->get_names();
333 string* name = new string(mat_names[0]);
334 materials.push_back(name);
335 }
336 else {
337 string* no_material = new string("None");
338 materials.push_back(no_material);
339 }
340 }
341 else {
342 elevations.push_front(elevation_m);
343 if(mat) {
344 const std::vector<string> mat_names = mat->get_names();
345 string* name = new string(mat_names[0]);
346 materials.push_front(name);
347 }
348 else {
349 string* no_material = new string("None");
350 materials.push_front(no_material);
351 }
352 }
353 }
354 else {
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);
359 }
360 else {
361 string* no_material = new string("None");
362 elevations.push_front(0.0);
363 materials.push_front(no_material);
364 }
365 }
366 }
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);
371 }
372 else {
373 elevations.push_back(elevation_under_pilot);
374 //if (delta_last > (point_distance / 2) )
375 elevations.push_front(elevation_under_sender);
376 }
377
378
379 double num_points= (double)elevations.size();
380
381
382 elevations.push_front(point_distance);
383 elevations.push_front(num_points -1);
384
385 int size = elevations.size();
386 std::vector<double> itm_elev(size);
387
388 for(int i=0;i<size;i++) {
389 itm_elev[i]=elevations[i];
390 }
391
392 if((transmission_type == 3) || (transmission_type == 4)) {
393 // the sender and receiver roles are switched
394 ITM::point_to_point(itm_elev.data(), 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.data(), materials, receiver_height, transmitter_height, p_mode, horizons, clutter_loss);
399 }
400 else {
401 ITM::point_to_point(itm_elev.data(), 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.data(), materials, transmitter_height, receiver_height, p_mode, horizons, clutter_loss);
406 }
407
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();
412 }
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
422 // return -1;
423
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);
438 delete TX_antenna;
439 }
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);
446 delete RX_antenna;
447 }
448
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);
456
457 //_root_node->setDoubleValue("station[0]/tx-pattern-gain", tx_pattern_gain);
458 //_root_node->setDoubleValue("station[0]/rx-pattern-gain", rx_pattern_gain);
459
460 for (unsigned i =0; i < materials.size(); i++) {
461 delete materials[i];
462 }
463
464 return signal;
465
466 }
467
468
calculate_clutter_loss(double freq,double itm_elev[],deque<string * > & materials,double transmitter_height,double receiver_height,int p_mode,double horizons[],double & clutter_loss)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) {
472
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
476 int mat = 0;
477 int j=1;
478 for (int k=3;k < (int)(itm_elev[0]) + 2;k++) {
479
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;
484 break;
485 }
486 get_material_properties(materials[mat], clutter_height, clutter_density);
487
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;
493 continue;
494 }
495 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
496
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];
501 }
502 double ray_height = (grad * d1) + min_elev;
503
504 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
505 double intrusion = fabs(clearance);
506
507 if (clearance >= 0) {
508 // no losses
509 }
510 else if (clearance < 0 && (intrusion < clutter_height)) {
511
512 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
513 }
514 else if (clearance < 0 && (intrusion > clutter_height)) {
515 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
516 }
517 else {
518 // no losses
519 }
520 j++;
521 mat++;
522 }
523
524 }
525 else if (p_mode == 1) { // diffraction
526
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;
531 int last = 1;
532 /** perform the first pass */
533 int mat = 0;
534 int j=1;
535 for (int k=3;k < num_points_1st + 2;k++) {
536 if (num_points_1st < 1)
537 break;
538 double clutter_height = 0.0; // mean clutter height for a certain terrain type
539 double clutter_density = 0.0; // percent of reflected wave
540
541 if((unsigned)mat >= mat_size) {
542 //cerr << "Array index out of bounds 1-1: " << mat << " size: " << mat_size << endl;
543 break;
544 }
545 get_material_properties(materials[mat], clutter_height, clutter_density);
546
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;
552 continue;
553 }
554 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
555
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];
560 }
561 double ray_height = (grad * d1) + min_elev;
562
563 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
564 double intrusion = fabs(clearance);
565
566 if (clearance >= 0) {
567 // no losses
568 }
569 else if (clearance < 0 && (intrusion < clutter_height)) {
570
571 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
572 }
573 else if (clearance < 0 && (intrusion > clutter_height)) {
574 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
575 }
576 else {
577 // no losses
578 }
579 j++;
580 mat++;
581 last = k;
582 }
583
584 /** and the second pass */
585 mat +=1;
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)
589 break;
590 double clutter_height = 0.0; // mean clutter height for a certain terrain type
591 double clutter_density = 0.0; // percent of reflected wave
592
593 if((unsigned)mat >= mat_size) {
594 //cerr << "Array index out of bounds 1-2: " << mat << " size: " << mat_size << endl;
595 break;
596 }
597 get_material_properties(materials[mat], clutter_height, clutter_density);
598
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;
604 continue;
605 }
606 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
607
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];
612 }
613 double ray_height = (grad * d1) + min_elev;
614
615 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
616 double intrusion = fabs(clearance);
617
618 if (clearance >= 0) {
619 // no losses
620 }
621 else if (clearance < 0 && (intrusion < clutter_height)) {
622
623 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
624 }
625 else if (clearance < 0 && (intrusion > clutter_height)) {
626 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
627 }
628 else {
629 // no losses
630 }
631 j++;
632 mat++;
633 }
634
635 }
636 else { // double horizon: same as single horizon, except there are 3 segments
637
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;
643 int last = 1;
644 /** perform the first pass */
645 int mat = 0;
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)
649 break;
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;
654 break;
655 }
656 get_material_properties(materials[mat], clutter_height, clutter_density);
657
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;
663 continue;
664 }
665 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
666
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];
671 }
672 double ray_height = (grad * d1) + min_elev;
673
674 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
675 double intrusion = fabs(clearance);
676
677 if (clearance >= 0) {
678 // no losses
679 }
680 else if (clearance < 0 && (intrusion < clutter_height)) {
681
682 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
683 }
684 else if (clearance < 0 && (intrusion > clutter_height)) {
685 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
686 }
687 else {
688 // no losses
689 }
690 j++;
691 mat++;
692 last = k;
693 }
694 mat +=1;
695 /** and the second pass */
696 int last2=1;
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)
700 break;
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;
705 break;
706 }
707 get_material_properties(materials[mat], clutter_height, clutter_density);
708
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;
714 continue;
715 }
716 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
717
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];
722 }
723 double ray_height = (grad * d1) + min_elev;
724
725 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
726 double intrusion = fabs(clearance);
727
728 if (clearance >= 0) {
729 // no losses
730 }
731 else if (clearance < 0 && (intrusion < clutter_height)) {
732
733 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
734 }
735 else if (clearance < 0 && (intrusion > clutter_height)) {
736 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
737 }
738 else {
739 // no losses
740 }
741 j++;
742 mat++;
743 last2 = k;
744 }
745
746 /** third and final pass */
747 mat +=1;
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)
751 break;
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;
756 break;
757 }
758 get_material_properties(materials[mat], clutter_height, clutter_density);
759
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;
765 continue;
766 }
767
768 //double earth_h = distance_m * (distance_m - j * itm_elev[1]) / ( 1000000 * 12.75 * 1.33 ); // K=4/3
769
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];
774 }
775 double ray_height = (grad * d1) + min_elev;
776
777 double clearance = ray_height - (itm_elev[k] + clutter_height) - frs_rad * 8/10;
778 double intrusion = fabs(clearance);
779
780 if (clearance >= 0) {
781 // no losses
782 }
783 else if (clearance < 0 && (intrusion < clutter_height)) {
784
785 clutter_loss += clutter_density * (intrusion / (frs_rad * 2) ) * (freq/100) * (itm_elev[1]/100);
786 }
787 else if (clearance < 0 && (intrusion > clutter_height)) {
788 clutter_loss += clutter_density * (clutter_height / (frs_rad * 2 ) ) * (freq/100) * (itm_elev[1]/100);
789 }
790 else {
791 // no losses
792 }
793 j++;
794 mat++;
795
796 }
797
798 }
799 }
800 else if (p_mode == 2) { // troposcatter: ignore ground clutter for now... maybe do something with weather
801 clutter_loss = 0.0;
802 }
803
804 }
805
806
get_material_properties(string * mat_name,double & height,double & density)807 void FGRadioTransmission::get_material_properties(string* mat_name, double &height, double &density) {
808
809 if(!mat_name)
810 return;
811
812 if(*mat_name == "Landmass") {
813 height = 15.0;
814 density = 0.2;
815 }
816
817 else if(*mat_name == "SomeSort") {
818 height = 15.0;
819 density = 0.2;
820 }
821
822 else if(*mat_name == "Island") {
823 height = 15.0;
824 density = 0.2;
825 }
826 else if(*mat_name == "Default") {
827 height = 15.0;
828 density = 0.2;
829 }
830 else if(*mat_name == "EvergreenBroadCover") {
831 height = 20.0;
832 density = 0.2;
833 }
834 else if(*mat_name == "EvergreenForest") {
835 height = 20.0;
836 density = 0.2;
837 }
838 else if(*mat_name == "DeciduousBroadCover") {
839 height = 15.0;
840 density = 0.3;
841 }
842 else if(*mat_name == "DeciduousForest") {
843 height = 15.0;
844 density = 0.3;
845 }
846 else if(*mat_name == "MixedForestCover") {
847 height = 20.0;
848 density = 0.25;
849 }
850 else if(*mat_name == "MixedForest") {
851 height = 15.0;
852 density = 0.25;
853 }
854 else if(*mat_name == "RainForest") {
855 height = 25.0;
856 density = 0.55;
857 }
858 else if(*mat_name == "EvergreenNeedleCover") {
859 height = 15.0;
860 density = 0.2;
861 }
862 else if(*mat_name == "WoodedTundraCover") {
863 height = 5.0;
864 density = 0.15;
865 }
866 else if(*mat_name == "DeciduousNeedleCover") {
867 height = 5.0;
868 density = 0.2;
869 }
870 else if(*mat_name == "ScrubCover") {
871 height = 3.0;
872 density = 0.15;
873 }
874 else if(*mat_name == "BuiltUpCover") {
875 height = 30.0;
876 density = 0.7;
877 }
878 else if(*mat_name == "Urban") {
879 height = 30.0;
880 density = 0.7;
881 }
882 else if(*mat_name == "Construction") {
883 height = 30.0;
884 density = 0.7;
885 }
886 else if(*mat_name == "Industrial") {
887 height = 30.0;
888 density = 0.7;
889 }
890 else if(*mat_name == "Port") {
891 height = 30.0;
892 density = 0.7;
893 }
894 else if(*mat_name == "Town") {
895 height = 10.0;
896 density = 0.5;
897 }
898 else if(*mat_name == "SubUrban") {
899 height = 10.0;
900 density = 0.5;
901 }
902 else if(*mat_name == "CropWoodCover") {
903 height = 10.0;
904 density = 0.1;
905 }
906 else if(*mat_name == "CropWood") {
907 height = 10.0;
908 density = 0.1;
909 }
910 else if(*mat_name == "AgroForest") {
911 height = 10.0;
912 density = 0.1;
913 }
914 else {
915 height = 0.0;
916 density = 0.0;
917 }
918
919 }
920
921
LOS_calculate_attenuation(SGGeod pos,double freq,int transmission_type)922 double FGRadioTransmission::LOS_calculate_attenuation(SGGeod pos, double freq, int transmission_type) {
923
924 double frq_mhz = freq;
925 double dbloss;
926 double tx_pow = _transmitter_power;
927 double ant_gain = _rx_antenna_gain + _tx_antenna_gain;
928 double signal = 0.0;
929
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;
937
938
939 double link_budget = tx_pow - _receiver_sensitivity - _rx_line_losses - _tx_line_losses + ant_gain;
940
941 //cerr << "ITM:: pilot Lat: " << own_lat << ", Lon: " << own_lon << ", Alt: " << own_alt << endl;
942
943 SGGeod own_pos = SGGeod::fromDegM( own_lon, own_lat, own_alt );
944
945 SGGeod sender_pos = pos;
946
947 sender_alt_ft = sender_pos.getElevationFt();
948 sender_alt = sender_alt_ft * SG_FEET_TO_METER;
949
950 receiver_height = own_alt;
951 transmitter_height = sender_alt;
952
953 double distance_m = SGGeodesy::distanceM(own_pos, sender_pos);
954
955
956 transmitter_height += _tx_antenna_height;
957 receiver_height += _rx_antenna_height;
958
959
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;
964
965 if (distance_m > total_horizon) {
966 return -1;
967 }
968 double pol_loss = 0.0;
969 if (_polarization == 1) {
970 pol_loss = polarization_loss();
971 }
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;
975
976 //cerr << "LOS:: Link budget: " << link_budget << ", Attenuation: " << dbloss << " dBm " << endl;
977 return signal;
978
979 }
980
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
984 ***/
polarization_loss()985 double FGRadioTransmission::polarization_loss() {
986
987 double theta_deg;
988 double roll = fgGetDouble("/orientation/roll-deg");
989 if (fabs(roll) > 85.0)
990 roll = 85.0;
991 double pitch = fgGetDouble("/orientation/pitch-deg");
992 if (fabs(pitch) > 85.0)
993 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);
997
998 if (_polarization == 0)
999 theta_deg = 90.0 - theta;
1000 else
1001 theta_deg = theta;
1002 if (theta_deg > 85.0) // we don't want to converge into infinity
1003 theta_deg = 85.0;
1004
1005 double loss = 10 * log10( pow(cos(theta_deg * SGD_DEGREES_TO_RADIANS), 2) );
1006 //cerr << "Polarization loss: " << loss << " dBm " << endl;
1007 return loss;
1008 }
1009
1010
watt_to_dbm(double power_watt)1011 double FGRadioTransmission::watt_to_dbm(double power_watt) {
1012 return 10 * log10(1000 * power_watt); // returns dbm
1013 }
1014
dbm_to_watt(double dbm)1015 double FGRadioTransmission::dbm_to_watt(double dbm) {
1016 return exp( (dbm-30) * log(10.0) / 10.0); // returns Watts
1017 }
1018
dbm_to_microvolt(double dbm)1019 double FGRadioTransmission::dbm_to_microvolt(double dbm) {
1020 return sqrt(dbm_to_watt(dbm) * 50) * 1000000; // returns microvolts
1021 }
1022
1023
1024