Enhanced signal model for instrument landing system

Abstract

This invention is related to a novel technique for generating and processing signals that benefits instrument landing systems.

Description

[0001] DESCRIPTION

[0002] Enhanced Signal Model for Instrument Landing System

[0003] Technical Field

[0004] The invention is related to a novel enhancement to conventional Instrument Landing Systems (ILS)

[0005] Prior Art

[0006] Once alternative to ILS that has been explored Microwave Landing System (MLS), which emits microwave signals in a scanning pattern, with beams that sweep back and forth to reach the aircraft. The aircraft’s onboard receiver measures the time difference between these sweeps to determine its position, offering advantages like a broader range of channels to reduce interference, better performance in adverse weather, and wider capture angles for flexible approach paths. However, MLS has significant disadvantages, such as susceptibility to environmental interference that impacts accurate beam center detection, as well as high costs and the need for additional onboard equipment. With the rise of GPS-based systems, MLS was gradually phased out, with airports adopting a combination of ILS and GPS for enhanced coverage and reliability without MLS’s high costs.

[0007] In addition, there are other techniques focused on improving the ILS system, particularly in terms of optimizing angular coverage, antenna positioning, and adjusting for runway conditions to ensure more reliable signal reception and accurate guidance. These techniques aim to enhance the robustness of the system, addressing some of the weakness inherent in traditional ILS setups. Adaptive beamforming has also been studied as a solution to reduce system complexity while maintaining functionality, and GPS-based positioning provides a global solution for navigation support. Yet, GPS remains highly vulnerable to spoofing and hacking, posing serious risks during critical landing phases.

[0008] ILS systems face additional limitations, including sensitivity to nearby terrain and obstacles that can interfere with signal transmission and reduce guidance accuracy. To counter these issues, some aircraft rely on redundant aids like VOR / DME, TACAN, or altimeters as backups in case of ILS or GPS failures; however, these systems are also susceptible to interference and spoofing. While alternatives like MLS, and GPS with ILS aim to address issues of signal interference, security, and guidance accuracy they still fall short in fully mitigating GPS hacking risks.

[0009] Additionally, advanced Al-based techniques like neural networks, fuzzy logic, and human-skill modeling have been introduced to improve adaptability and precision in landing guidance. While promising, these intelligent systems face challenges such as overfitting, high computational demands, and limited interpretability in safety-critical applications, underscoring the need for a reliable, GPS-independent solution to achieve optimal security and accuracy in modern landing operations.

[0010] As a result, all of the problems mentioned above have made it necessary to provide a novelty in the related field.

[0011] Brief Description and Objects of the Invention

[0012] The main object of the present invention is to enable the establishment of airports and landing sites virtually anywhere to enhance quality of life even in challenging environments previously deemed unsuitable due to multipath interference, such as behind mountains or in rugged terrain. By solving the issue of multipaths, the system allows for the creation of small, efficient airports or emergency landing strips in remote or hard-to-reach areas, improving access to critical services and ensuring safer travel options during emergencies. This flexibility transforms how and where aviation infrastructure can be developed, making air travel more accessible and reliable for all.

[0013] The invention provides a secure and precise aircraft (A) landing guidance system that eliminates reliance on GPS, offering robust performance even in challenging conditions. One of the key advantages is complete removal of reliance on GPS, which is redundant information in case of the GPS is spoofed or jammed. This makes the system much more secure, particularly in critical situations where reliable positioning is essential for landing aircraft.

[0014] Moreover, unlike traditional systems that depend on signal amplitude, this invention uses the delay difference between the transmitted chirps and in case of synchronization between the aircraft receiver and the airport transmitter , a locally generated chirp at the aircraft node can be used to dechirp these two chirps and extract the distance information from the airport which makes it more resilient to signal fading, environmental noise, and interference, ensuring more reliable performance in low-visibility or challenging weather conditions. In addition to these, the system can detect jamming attempts by identifying distinct signal delay patterns. This unique capability allows the system to continue operating by relaying on a different link between the airport and the aircraft where the reflected chirps from the aircraft can be used to extract the needed sensing information and transmits it back through that link to the aircraft , ensuring that the aircraft’s position is still accurately determined.

[0015] One of the most important features of the invention is its capability to detect and identify jamming signals based on unique delay patterns, enabling the system to differentiate between interference and true positioning data, and maintain accuracy despite disruptions. Additionally, it is not power-dependent, instead of relying on amplitude, multipath effects are represented as small time shifts in the signal, ensuring reliable performance even in challenging environment.

[0016] Description of the Figures of the Invention

[0017] The figures and related descriptions necessary for the subject matter of the invention to be understood better are given below.

[0018] Figure 1. A flow chart of method present invention.

[0019] Figure 2. A schematic view of circuit of signal processing at the receiver of algorithm.

[0020] Figure 3. A representative view of system for lateral detection.

[0021] Figure 4. A representative view of system for vertical detection.

[0022] Reference Numbers

[0023] The parts and components that are given in the figures are referenced for the subject matter of the invention to be understood better.

[0024] A. Aircraft

[0025] G. Ground unit

[0026] L. Localizer

[0027] G. Glide-slope

[0028] LC1. Lateral carrier 1

[0029] LC2. Lateral carrier 2

[0030] LB1. Lateral beam 1 LB2. Lateral beam 2

[0031] GC1. Vertical carrier 1

[0032] GC2. Vertical carrier 2

[0033] GB1. Vertical beam 1

[0034] GB2. Vertical beam 2

[0035] TS. Transmitted Signal

[0036] LNA. Linear Noise Amplifier

[0037] F. IF Filter

[0038] IF A. IF Amplifier

[0039] M. Mixer

[0040] DC. DC Block

[0041] DSP. Digital Signal Processing

[0042] Detailed Description of the Invention

[0043] The invention is related to an enhancement technique signal model for instrument landing system.

[0044] Referring to Fig. 1; The first step of the present invention is generating chirp signal and transmitting in two separate beams for both the localizer (L) system and the glide slope (G) system which are part ground unit, using different carrier frequencies for each transmit beam. The localizer (L) uses two beams, one on each side of the runway centerline (CL), to provide lateral guidance. These beams are oriented along the centerline (CL) of the landing runway to ensure the aircraft (A) is aligned correctly for a safe approach. The glide slope (G) also uses two beams, one directed slightly above and one directed slightly below the ideal descent path, to provide vertical guidance. By transmitting chirp signals in these beams and using distinct carrier frequencies for each, the system ensures independent processing of signals.

[0045] In the next step, the transmitted chirp signals are received and processed at the aircraft’s (A) receiver. First the signals are passing through the passband filters to extract only the band of the transmitted signal, then dechirped. The dechirping process involves using one received chirp from one beam to process the other received signal from the second beam, taking it to the time domain by FFT allowing the system to handle multipath effects such as reflections from buildings or the ground. By aligning the multipath-affected signals, this method effectively compensates for environmental interference. Unlike conventional systems that rely on amplitude modulation where multipath effects lead to signal degradation and distortion due to fading, this method focuses on the shift in the chirp signals rather than amplitude. By dechirping the two received chirps with each other, challenges caused by multipath and fading are effectively eliminated. Since both signals travel through the same channel, the effects of the channel are canceled out during the dechirping process.

[0046] If a jammer attempts to disrupt the signal, the interference will manifest as an additional shift in signal. At this point, the system automatically identifies the jammer by detection of the additional shift and stops relying on the guidance provided by the localizer signals. The aircraft is alerted based on mentioned detection. In this case, assistance may be requested from the airport for alternative navigation or manual intervention. Thus, this method allows the system to continue operating by relaying on a different link between the airport and the airplane where the reflected chirps from the airplane can be used to extract the needed sensing information and transmits it back through that link to the airplane, ensuring that the aircraft’s position is still accurately determined.

[0047] The reflected signal from the aircraft (A) will travel back to the airport, where the same dechirping process occurs. This allows for real-time, accurate positioning data to be obtained at both the aircraft (A) and the ground unit. By processing the signals in this manner, the system ensures reliable performance, unaffected by the environmental factors that limit conventional airport navigation systems.

[0048] Referring to Fig 3 and 4; the airport utilizes both the localizer system (L) and glide slope (G) systems for aircraft (A) navigation. The localizer (L) transmits two separate chirps called SLi(t) and SL2<t) at two different frequencies and different beams. The transmitted localizer (L) signal in the air at any point from the center line (L) can be given as Si(ri) is form of the lateral guidance signal, A is amplitude of the lateral guidance signal, is carrier frequency of the first lateral guidance signal, f2is carrier frequency of the second lateral guidance signal.

[0049] Similarly, the glide slope transmits a chirp at two different frequencies, f3and f4, in two beams that offers vertical positioning data. wherein sg(ri) is form of the vertical guidance signal, A is amplitude of the vertical guidance signal, f3is frequency of the first vertical guidance signal, f4is frequency of the second vertical guidance signal.

[0050] In Fig. 3, the lateral guidance signals are represented by lateral carrier 1 (LC1), lateral beam 1 (LB1) and lateral carrier 2 (LC2), lateral beam 2 (LB2). The vertical guidance signals are represented by vertical carrier 1 (GC1), vertical beam 1 (GB1) and vertical carrier 2 (GC2), vertical beam 2 (GB1).

[0051] The signals passes through an L tap channel defined as follows

[0052] Where L is the maximum number of paths in the environment and hi and n are ithchannel gain and ithdelay form of ithpath respectively. Here the Doppler is neglected since it can be estimated and compensated.

[0053] After passing through the channel, the received signals can be separated to received localizer signals and rj2(t) and glide slope signals rgl(t) and rp2(t) after passing through two different Rx Filter, which extract the specific frequency bands of the transmitted signals, removing unwanted out-of-band signal. The filtered signals are then amplified by linear noise amplifiers (LNA), ensuring the signals are strengthened without distortion.

[0054] The localizer received baseband signals for jthbaseband can be written as:

[0055] If the aircraft (A) is not aligned with the centerline (CL) of localizer (L), the signals rzi(n) and r;2(n) will bereceived with a delay relative to one another. Consequently, one signal will arrive later than the other. By dechirping one signal with the other, the resulting beat frequency fbcan be determined, which depends on the delay between the two signals. The dechirping process, involving the conjugate of one of the chirps, can be expressed as: wherein d(ri) is discrete dechirped signal, A is amplitude, L is number of channel taps, H is channel, N is total number of samples, T is time delay of the aircraft from where the information is extracted and Tj is time delay caused by the multipaths where n is the time samples.

[0056] Referring to Fig. 2; A DC block (DC) is applied to remove any low-frequency components or DC offsets introduced during dechirping. The transmitted signal (TS) then passes through an IF filter (F) to eliminate intermediate frequencies, followed by an IF amplifier (IF A) to boost the signal strength for further processing and peak detection. Then we perform the FFT of d(n) to reveal peaks at the beat frequencies fb, which encode the delay difference and thus the positional information.

[0057] The FFT of d(n) is defined as wherein m is frequency samples, d(m) is discrete dechirped signal in the frequency domain, d(n) is discrete dechirped signal, A is amplitude, L is number of channel taps, h is channel, N is total number of samples, T is time delay of the aircraft from where the information is extracted and Ti j is time delay caused by the multipaths where n is the time samples.

[0058] The exponential term represents the phases and represents shifts induced by multipaths.

[0059] It is important to note that each delay tap introduced by the channel will result in a shift distinct from the shift caused by the aircraft’s (A) position. These channel -induced taps will appear separately from the desired location information. Additionally, since these taps are associated with smaller channel gains the primary shifts between the chirps, corresponding to the aircraft’s (A) position, will have a higher power.

[0060] If a jammer introduces an additional signal q(n) the total received signal at the receiver is expressed as:

[0061] The jammer signal can be modeled as: wherein Jjy is multipath delay of the jammer signal.

[0062] If a jammer is present, after performing the dechirping process and taking the FFT of the dechirped signal, three peaks higher than the threshold will appear instead of one in the delay domain.

[0063] Normally, the FFT of the dechirped signal produces a single peak corresponding to the legitimate beat frequency fb, which encodes the aircraft’s (A) positional information. However, a jammer introduces an additional delay T , resulting in two other peaks at a different frequency fj- The presence of these three peaks is a clear indication of jamming. At this point, the system automatically identifies the interference and stops relying on the guidance provided by the vertical and horizontal signals. The aircraft (A) crew is alerted to the issue, and assistance is requested from the airport for alternative navigation or manual intervention. This immediate detection and fallback protocol ensure safety by preventing reliance on corrupted positional information.

[0064] The transmitted signal reflects of the aircraft’s (A) body and returns to the airport from multiple directions, carrying lateral and vertical information. At the airport (ground unit), a similar processing method can be applied to determine the aircraft’s (A) location. Additionally, by dechirping the received signal with the transmitted chirp, the distance between the aircraft (A) and the airport can be calculated, providing an added functionality for the airport.

[0065] The distance between the aircraft (A) and the airport can be estimated by dechirping each reflected signal by its transmitted version. The jthreflected signal can be given as wherein m is frequency samples, rr7(n) is the reflected received signal, A is amplitude, L is number of channel taps, h is channel, N is total number of samples, TrdJ- is time delay of the aircraft from where the information is extracted and Trl J- is time delay caused by the multipaths where n is the time samples.

[0066] To extracted the distance information, without loss to generality any of the reflected chirps can be used. The dechirping process can be given as:

[0067] After performing the FFT : wherein

[0068] Tdis the round-trip time.

[0069] (—rl— Tdm)n = 0

[0070] The distance can be extracted from the shift introduced to the longest peak.

[0071] References:

[0072] [1] Sanders, L. and Fritch, V., 1973. Instrument landing systems. IEEE Transactions on Communications, 21(5), pp.435-454.

[0073] [2] Evans, T.E., 1986. Microwave Landing System. IEEE Aerospace and Electronic Systems Magazine, 7(5), pp.6-9.

[0074] [3] Li, Y., Yang, B., Yang, L., He, Z., Niu, K. and Wu, W., 2006, June. Adaptive instrument landing system in future air traffic control. In 2006 6th International Conference on ITS Telecommunications (pp. 931-934). IEEE.

[0075] [4] Jeong, M.S., Bae, J., Jun, H.S. and Lee, Y.J., 2016. Flight test evaluation of ILS and GBAS performance at Gimpo International Airport. GPS solutions, 20, pp.473-483.

[0076] [5] Winick, A.B. and Brandewie, D.M., 1970. VOR / DME system improvements. Proceedings of the IEEE, 58(3), pp.430-437.

[0077] [6] Videmsek, A., de Haag, M.U. and Bleakley, T., 2019, September. Evaluation of RADAR altimeter-aided GPS for precision approach using flight test data. In 2019 IEEE / AIAA 38th Digital Avionics Systems Conference (DASC) (pp. 1-10). IEEE.

[0078] [7] liguni, Y., Akiyoshi, H. and Adachi, N., 1998. An intelligent landing system based on a human skill model. IEEE Transactions on Aerospace and Electronic Systems, 34(3), pp.877- 882.

[0079] [8] Ionita, S. and Sofron, E., 2002, January. The fuzzy model for aircraft (A) landing control. In AFSS International Conference on Fuzzy Systems (pp. 47-54). Berlin, Heidelberg: Springer Berlin Heidelberg. [9] Thain, A., Estienne, J.P., Peres, G., Spitz, B. and Evain, L., 2010, April. A rigorous simulator of ILS perturbations. In Proceedings of the Fourth European Conference on Antennas and Propagation (pp. 1-5). IEEE.

[0080]

[0010] Sathaye, H., Schepers, D., Ranganathan, A. and Noubir, G., 2019, May. Wireless attacks on aircraft (A) landing systems. In Proceedings of the 12th Conference on Security and Privacy in Wireless and Mobile Networks (pp. 295-297).

Claims

CLAIMS1. A method for determining aircraft (A) position for Instrument Landing Systems (ILS), comprising:• generating and transmitting, via a ground unit, chirp signals in separate beams for lateral and vertical guidance signals, wherein: o the lateral guidance signals are transmitted, by a localizer (L) system, in two beams oriented along a runway centerline (CL) using distinct carrier frequencies, and o the vertical guidance signals are transmitted, by a glide-slope (G) system in two beams along an ideal descent path using distinct carrier frequencies;• receiving the transmitted chirp signals at a receiver associated with an aircraft (A);• filtering the signals to extract frequency-specific components for each guidance signal,• dechirping the signals by combining one chirp signal with another to extract positional information,• applying a fast Fourier transform (FFT) to resolve multipath-affected signals and align them to compensate for environmental interference and to reveals peaks at the beat frequencies, which encode the delay difference and thus the positional information,• determining lateral and vertical positional data of the aircraft based on the processed signals.

2. A method according to Claim 1 , wherein the lateral guidance signals transmitted via two beams, one to the left and one to the right of the runway centerline (L) and vertical guidance signals transmitted via two beams, one above and one below the ideal descent path of the aircraft (A).

3. A method according to Claim 1, characterized by further comprising step of applying DC block (DC) or DC offsets to remove any low-frequency components during dechirping.

4. A method according to Claim 1 or 3, characterized by further comprises boosting the signal strength by IF amplifier (IF A).

5. A method according to any of preceding claims, wherein separated lateral guidance signal that are transmitted through beam have in form ofSi(n) is form of the lateral guidance signal, A is amplitude of the lateral guidance signal, / j is carrier frequency of the first lateral guidance signal, f2is carrier frequency of the second lateral guidance signal and separated vertical guidance signal that are transmitted through beams have in form ofsg(n) is form of the vertical guidance signal, A is amplitude of the vertical guidance signal, f3is carrier frequency of the first vertical guidance signal, f4is carrier frequency of the second vertical guidance signal.

6. A method according to any of preceding claims, wherein determining lateral and vertical position based on delay of signals relative to one another.

7. A method according to any of preceding claims, further comprises steps of identifying jamming interference by detecting additional peaks exceeding a predefined power threshold in the FFT.

8. A method according to Claim 7, wherein identifying j amming interference by detecting distinct signal delay patterns which occurs as additional peaks in the processed signal.

9. A system comprising means for carrying out the steps of the method of Claim 1 to 8.

10. A computer program comprising instructions which, when the program is executed by the system of claim 9, cause the computer to carry out the method of claim 1 to 8.

11. A computer-readable data carrier having stored thereon the computer program of claim

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