Air Navigation - Satellite Based Augmentation System (TCAS Low cost)

This project I send to ESNC (European Satellite Navigation Competition) in 2010, but the other projects were very good and I was not selected to follow the project.

However I think that this project is interesting and therefore I publish this post.

Description.

AN-SBAS works similarly at DME (Distance MeasurementEquipment) or SSR (Secondary Surveillance RADAR). , and the signal flight time, (t), provide to us the distance:

where c is the signal speed. (≈light speed).

The frequency in SSR, that use the systems such as TCAS, IFF, Transponder, is the 1030MHz for interrogation and 1090MHz answer signal. The systems interrogator send a "question" signal in 1030MHZ and the aircraft reply with any code, depend of the question emitted in the first signal.

If we have a GNSS coordinates with a 100m error, the time error is error/c.

into the aircraft we can readjust the internal clock time with the GNSS time and we have over  3e-5 seconds of error, (plus the system error).

If we synchronize the time UTC with satellite (GNSS) with the t transponder we can emit the signal synchronize in all airplanes, and we can see the distant between aircraft with the delay between the emit signal and the receive signal with a error is the equal to sum of DOPs of both aircrafts, and if we have 100m, the system show 200m of error. (This distance is very close)

Air augmentation (Transponder Update)

The range of this signal normally in aeronautical system is  250NM, the signal reach this range in 0.16 seconds, therefore we can emit and refresh the signal each 0.16 + between pulse.

For example 0.04 seconds of pulse, therefore 0.2 seconds, the system emit 5 times per second, and we allow that the each pulse no interference with previous pulse. Into the terminal area, the system can low the signal power, or it could to use another frequency to increase the refresh and the times per second.

The precision is increasing with the proximity, due to the atmospheric disturbances decrease, (inversely proportional), therefore the error decreases

t1< t2 the signal travels in the atmosphere minus time in t1 and therefore it has minus exposition to disturbances.

The idea of the system is create a volume of security, where if aircraft receives a signal in t lower of t previously selected, the system show a signal of the proximity traffic, and aircraft has directional antennas as TCAS antennas, it can know the emission radial such us a RADAR.

Ground update 

(DME)

Other advantage of the system is the coordination of the emissions, all planes send the signal in the same time, therefore rationing the electromagnetic spectrum  and this is one of problems with DME. the question have a poor regulation for it don't receive several questions in the same time, and each answer only one aircraft. If this system update DME,  it doesn't need questions and the answer provides information to all users of system.

The system is compatible  with the all system because if the DME could send the answer and one signal coordinate with the UTC, and without error due to the GNSS receiver of DME is static. The aircraft with the new DME system no question because recieve the answer UTC and clears electromagnetic spectrum for others airplanes with old DME system.

(TMA)

In airports and terminal areas with directional antenna, such as the VDF system, could mark distance with the AN-SBAS and direction with the arrays 

All airplanes sends the signal with synchronise with the GNSS time, the signal reach the VDF in the sequence  red, black, green and blue airplane. With the directional antenna, de VDF could know the direction of the signal, and read the position respect to him

The problem with the signal is the signal between airplanes very closes, could appear as one airplane, but the signal is with a pulse determinate, the VDF could recognize this error, or compare the other signal transponder with information with SSR. Also if we put other VDF in other points of the airport, they compare measures between them, and they could resolve this problem.

The airplanes could mark the relative position between theirs, with the antennas such as ADF antenna, or other directional antennas. This signal if we use PSK codification or digital FM, we can use de Doppler effect for more information, with this signal we can use the signal no only to know the distant, with Doppler, we can know the speed respect us. The speed between aircraft could measure with several pulses, but the Doppler provide more precision, because 10m/s cause increase o decrease the signal about 3.4KHz.

If the case in which use standard words with X bits, for example 12 bits, (SSR standard), if the system repeat 5 times this signal, we can through Doppler if the signal is 0.04s the signal time read for other airplane, change the time reception

And if we know the time emission and we can detect changes of the 1e-9 seconds the can read speed Doppler, of the 7.5m/s

The improves with the Doppler system, is the best relative speed measure, and this parameter is important due to if the relative speed is constant, if we maintain the path and the speed, when we will cross the paths we will crash between us. This system provides TCAS operation.

Into the terminal area where we have a increase of the airplanes density, the controller we have a better control with this system if use VDF system, this system provides direction of the airplanes and the time provides distance.

In a future DGBAS provide integrity between ground segment, and air segment, due to the DGBAS could read the position the airplane while it is landing.

Adventages of AN-SBAS.

The system is based in the time GNSS, however, the system send a message, and this message could send GNSS localization data, and this system can create a other airplane based augmentation system between them.

In Terminal area, if the AN-SBAS send the signal, and in ground use VDF, (VHF Direction Finder), (direction detector signal but in our case will be L band (LBDF)), this system with 2 VDFs could detect deviations in signal GNSS and provide to each airplane our correction or zone correction such as GBAS (Ground Based Augmentation System).

The correction for each aircraft would be to provide in landing stage, more focus and eliminate radiofrequency contamination in other areas, and it provide high accuracy, reliability of the other air navigation systems

Respect to integrity and availability, in terminal areas  we could be ground system o fixed or mobile, (Car, UAS, balloon fit in ground), for check the system, and into de AN-SBAS. The system can have satellite’s emulator based in ground, such as NAV aids, for example the atomic time send the signal in HF, MF and LF (long range), and this signal we can to use for integrity of the system, because is in static coordinates, and can provide Integrity signal for GNSS signal, (if I know my coordinates an the coordinates of the other transmiter I know the time of flight the signal,  and if this doesn't fulfill the system have any error)

The availability, with GNSS and the atomic time are global, therefore the system has availability with integrity global.

Electromagnetic spectrum are a problem today, therefore we need new systems that improve our spectrum with a reasonable prices and technologies. Today we use the same concept navigation systems since 1950, and for reason of the reliable and available, we still use this system. The problem of this system, although manufacture technology has changed, is the concept. Today all navigation systems can operate same with GNSS, and reach new capabilities.

The AN-SBAS, is complementary for navigation system, and simplifies and augment TCAS system, for more uses, such as instrument landing, navigation, SSR control. The difference is use the time satellite to synchronizes the pulse that transponder send, therefore it provides us distance measure.

This system update several navigation concepts, and this new system is cheaper to manufacture and calibrate and monitored, due to the other systems of navigation, this need expensive calibration. For example VOR, that the calibration needs to deploy test airplanes. This system only needs the onmidirectional antenna cheaper with more MBTF that other special antenna, such as VOR or ILS antenna.

This system are smaller than substituted systems and it can use others part of others system, for example GNSS antenna in ARINC 429 or NMEA. This is translating in less weight and therefore less consumption fuel, (in air's segment).