RADIO ALTIMETRY SYSTEM SUITABLE FOR INSTALLATION ON AN AIRCRAFT
A dual-radar system with FMCW and UWB technologies enhances radio altimetry resilience against diverse interferences, ensuring accurate altitude measurements and operational safety during critical flight phases.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- AIRBUS OPERATIONS (SAS)
- Filing Date
- 2024-03-19
- Publication Date
- 2026-04-24
AI Technical Summary
Existing radio altimeters, particularly those using FMCW radar technology, are susceptible to interference from both low-power interference over a wide frequency band and high-power interference localized to specific frequencies, which can lead to operational restrictions and make single-pilot operations difficult, especially during critical flight phases like landing and take-off.
A radio altimetry system combining FMCW and UWB radar technologies, with an electronic consolidation circuit to provide a consolidated altitude value, enhancing resilience against various interferences by leveraging the strengths of both systems, including FMCW's resistance to low-power interference and UWB's resistance to high-power interference.
The system provides robust altitude measurements by filtering out unreliable data, ensuring accurate and reliable altitude information even in challenging conditions, thereby improving operational safety and integrity during critical flight phases.
Abstract
Description
Title of the invention: RADIO ALTIMETRY SYSTEM SUITABLE FOR USE ON BOARD AN AIRCRAFT technical field
[0001] The field of the invention is that of altimeters.
[0002] More specifically, the present invention relates to a radio altimetry system suitable for being carried in an aircraft and for providing an altitude of said aircraft above the ground.
[0003] The altitude above the ground is also called "ALG altitude" (for "Above Ground Level"). It is generally measured in feet (one foot, whose symbol is "ft", for "foot" or "feet" in English, is equal to 0.3048 meters). STATE OF PRIOR ART
[0004] Radio altimetry systems, also called "radio altimeters" or "radar altimeters", are used in the field of civil or military aeronautics.
[0005] They are used in particular during automatic flight phases or critical flight phases, such as approach, landing (including flare and roll-out operations) and take-off. In particular, the flare operation depends entirely on the radio altimeter.
[0006] The altitude measurement above ground (AGL altitude) provided by a radio altimeter can be used for various functions implemented in an aircraft:
[0007] - aircraft control, particularly for landing operations (automatic or manual) and takeoff;
[0008] - protection against impacts without loss of control (or CFIT, for "Controlled Flight Into Terrain (in English);
[0009] - pilot awareness via the cockpit screen;
[0010] - the activation, for example below 2300 ft (i.e., 701.04 m), of a wind shear surveillance system;
[0011] - the inhibition of dangerous maneuvers close to the ground;
[0012] - the generation of alerts and warnings in the cockpit;
[0013] etc.
[0014] In the prior art, different types of radio altimeters are known, the general principle of such instruments being to measure height by measuring the propagation time of radio signals emitted and received after reflection on the ground.
[0015] In particular, the majority of civil aircraft use a radio altimeter based on frequency-modulated continuous wave radar technology, known as FMCW radar technology (for "Frequency Modulated Continuous Wave"). In the following section According to the description, such a radio altimeter is called an "FMCW radio altimeter". To ensure safety and proper operation, it is common to carry two or three FMCW radio altimeters on the aircraft.
[0016] The FMCW radio altimeter uses the [4.2 GHz; 4.4 GHz] frequency band, which is itself within the C-band. The C-band is very useful for telecommunications, but as a result, it is very congested and prone to interference. Consequently, the frequency bands adjacent to the one used by the FMCW radio altimeter are increasingly susceptible to interference. For this reason, the FMCW radio altimeter is potentially subject to external common-mode failures due to interference, leading to operational restrictions (for example, for low-visibility operations) and making single-pilot operation (SPO) difficult.
[0017] The FMCW radio altimeter has the advantage of operating at relatively high power, which offers a good level of resistance to interference, particularly low-power interference generated over a wide frequency band. However, it operates on a single band and is therefore susceptible to high-power interference localized to specific frequencies.
[0018] It is therefore desirable to provide a solution (radio altimetry system) offering resilience to various interferences, i.e. both to low power interference, generated in a wide frequency band, and to high power interference, localized on particular frequencies.
[0019] Furthermore, since the flare operation is triggered and carried out below 100 ft AGL (i.e. 30.48 m above ground level), it is also desirable that the solution provided (radio altimetry system) allows for strengthening the measurement at low altitude (for example below 100 ft AGL). Description of the invention
[0020] A radio altimetry system suitable for installation on an aircraft and for providing the aircraft's altitude above the ground is proposed herein, comprising:
[0021] - a first subsystem based on modulated continuous wave radar technology in frequency, known as FMCW radar technology, providing an initial altitude value for the aircraft above the ground;
[0022] - a second subsystem based on ultra-wideband radar technology, known as UWB radar technology, providing a second altitude value for the aircraft above the ground; and
[0023] - an electronic circuit, referred to as a consolidation circuit, configured for:
[0024] - compare the second altitude value to a predetermined altitude threshold above from the ground;
[0025] - if the second altitude value is less than or equal to the predetermined threshold altitude above ground, determine a consolidated value for the aircraft's altitude above ground, based on the first and second altitude values; and
[0026] - if the second altitude value is greater than the predetermined altitude threshold at- above ground, determine a consolidated value of aircraft altitude above ground, based on the first altitude value and without taking into account the second altitude value.
[0027] Thus, the proposed radio altimetry system comprises two subsystems based on distinct but complementary radar technologies in terms of robustness against interference, namely a first subsystem (hereinafter referred to as the "FMCW subsystem") based on FMCW radar technology and a second subsystem (hereinafter referred to as the "UWB subsystem") based on UWB (Ultra WideBand) radar technology. Furthermore, the proposed radio altimetry system includes electronic consolidation circuitry that provides a consolidated ground altitude value from the first and second ground altitude values provided respectively by the FMCW and UWB subsystems.
[0028] In this way, the proposed radio altimetry system offers resilience to various types of interference: low-power interference generated over a wide frequency band, and high-power interference localized to specific frequencies. Indeed, as mentioned above, the FMCW subsystem has the advantage of operating with relatively high power and over a limited frequency band, thus providing a good level of resistance to low-power interference generated over an ultra-wide frequency band. Complementarily, the UWB subsystem has the advantage of operating over an ultra-wide frequency band and with relatively low power, thus providing a good level of resistance to high-power interference localized to specific frequencies.
[0029] Furthermore, the UWB subsystem uses UWB pulses which introduce dissimilarity. They are very short (e.g. 2ns) with a large bandwidth (e.g. 500MHz), so that they provide a level of accuracy similar to that of an FMCW subsystem and are therefore compatible with the flare operation.
[0030] The UWB frequency band used by the UWB subsystem is below 10 GHz, so it remains unaffected by heavy rain and attenuation due to fog. This is an important point for critical operations carried out in low visibility conditions (heavy rain, fog).
[0031] Furthermore, the consolidation electronic circuitry ensures that the second altitude value, provided by the UWB subsystem, is only taken into account if it is less than or equal to a predetermined altitude threshold above ground level. Thus, the proposed radio altimetry system makes it possible to enhance the measurement at low altitudes, i.e., below the predetermined altitude threshold above ground level.
[0032] It should be noted that the UWB subsystem is very low power (for example, limited to a maximum of -41.3 dBm / MHz), so that the range is limited to a few tens of meters. However, this is sufficient for the flare operation, which begins between approximately 35 ft and 80 ft (50 ft on average), as well as for the roll-out and take-off operations.
[0033] According to a particular embodiment, the first subsystem is configured to use a first frequency band, and the second subsystem is configured to use at least a second frequency band distinct from the first frequency band.
[0034] According to a particular embodiment, the first frequency band is the [4.2 GHz; 4.4 GHz] band and the second frequency band is within the [3.1 GHz; 10.6 GHz] band.
[0035] According to a particular embodiment, the second subsystem is configured to perform frequency jumps between at least two distinct frequency bands of the first frequency band.
[0036] According to a particular embodiment, the second subsystem is configured to use at least one pulse pattern that is distinct from a waveform used by the first subsystem.
[0037] According to a particular embodiment, the first and second subsystems share at least one element belonging to the group comprising an antenna and a coaxial cable.
[0038] According to a particular embodiment, the electronic consolidation circuitry is further configured to, in the event of a difference between the first and second altitude values exceeding a predetermined altitude difference threshold, select one of the first and second altitude values according to at least one selection parameter, to form the consolidated value.
[0039] According to a particular embodiment, at least one selection parameter belongs to the group comprising:
[0040] - a barometric altitude provided by a barometric altimeter;
[0041] - an inertial altitude provided by an inertial measurement unit; and
[0042] - a memorized altitude resulting from the memorization of a previous value consolidated.
[0043] According to a particular embodiment, selecting one of the first and second altitude values depending on at least one selection parameter includes:
[0044] - determine a reference altitude as a function of at least one parameter of selection; and
[0045] - select, from the first and second altitude values, the altitude value the closest to the reference altitude.
[0046] According to a particular embodiment, the predetermined altitude threshold above ground is between 25 and 35 meters, and in a particular implementation it is equal to 100 ft (i.e. 30.48 m).
[0047] An aircraft comprising the radio altimetry system shown above is also proposed here, in any of its embodiments. Brief description of the drawings
[0048] The features of the invention mentioned above, as well as others, will become clearer upon reading the following description of at least one exemplary embodiment, said description being made in relation to the accompanying drawings, among which:
[0049] [Fig-1] schematically illustrates, in side view, an aircraft equipped with a system of radio altimetry;
[0050] [Fig.2] schematically illustrates the radio altimetry system, in one embodiment;
[0051] [Fig.3] schematically illustrates an example of the hardware architecture of the electronic consolidation circuit included in the radio altimetry system, in one embodiment; and
[0052] [Fig.4] schematically illustrates an example of a consolidation algorithm, executed by the electronic consolidation circuitry, in one embodiment.
[0053] DETAILED DESCRIPTION OF IMPROVEMENTS
[0054] Fig. 1 schematically illustrates, in side view, an aircraft 100 equipped with a radio altimetry system 101.
[0055] The radio altimeter system 101 is an onboard electronic device. For example, it is part of an electronic circuitry of the aircraft avionics 100. Its location in the aircraft may vary depending on the aircraft model.
[0056] The radio altimetry system 101 is schematically illustrated in [Fig.2], in an embodiment in which it comprises a first radio altimetry subsystem 201, a second radio altimetry subsystem 202 and an electronic consolidation circuitry 203.
[0057] The first subsystem 201, also referred to hereafter as the "FMCW subsystem" (and noted as "RA FMCW" in [Fig. 2]), is based on continuous wave radar technology Frequency modulated, or FMCW (Frequency Modulated Continuous Wave) radar technology, provides an initial altitude value (V1) of the aircraft 100 meters above ground level. The FMCW 201 subsystem is configured to use a first frequency band, which provides a first communication channel. In one embodiment, this is the [4.2 GHz; 4.4 GHz] band.
[0058] The second subsystem 202, also referred to hereafter as the "UWB subsystem" (and denoted "RA UWB" in [Fig. 2]), is based on ultra-wideband radar technology, known as UWB radar technology (for "Ultra WideBand"). It provides a second V2 value for the aircraft's altitude 100 meters above the ground. The UWB 202 subsystem is configured to use at least one second frequency band distinct from the first frequency band. In one embodiment, the UWB 202 subsystem is configured to perform frequency hopping between at least two frequency bands (each offering a different communication channel), distinct from the first frequency band. In one embodiment, the frequency bands between which the frequency hopping is performed are within the [3.1 GHz; 10.6 GHz] band and each have a bandwidth of 500 MHz.For example, the UWB 202 subsystem monitors the interference received in these frequency bands and chooses the one with the least interference. In another example, the UWB 202 subsystem itself determines a suitable 500 MHz frequency band (in terms of interference) within a range of permitted frequencies (e.g., [3.1 GHz; 10.6 GHz]).
[0059] Thus, the FMCW 201 and UWB 202 subsystems use different frequency bands, and therefore complementary communication channels, which provides an appropriate level of robustness against all RF (radio frequency) threats. This complementarity improves the availability and integrity of the data (altitude values) provided by the radio altimetry system. Indeed, as detailed below, if one of the first and second altitude values VI and V2 is lost, the other can still be used, thus increasing availability. If the two are inconsistent, an alert can be triggered, which increases integrity.
[0060] In one embodiment, the UWB 202 subsystem is configured to use at least one pulse pattern that is distinct from a waveform used by the FMCW 201 subsystem. The introduced dissimilarity (e.g. frequency hopping and / or code and / or timing) allows for better resilience of the radio altimetry system 101 against threats to data security and against multipath attacks.
[0061] In one embodiment, the FMCW 201 subsystem and the UWB 202 subsystem share an antenna (for example, a passive C-band microstrip patch antenna) and / or a coaxial cable. This reduces the implementation costs of the radio altimetry system 101.
[0062] The electronic consolidation circuitry 203 receives the first and second altitude values VI and V2 and generates, based on these and one or more selection parameters PI, P2 and P3 (see below the description of [Fig.4]), a consolidated altitude value VC above ground.
[0063] Figure 4 schematically illustrates an example of a consolidation algorithm, executed by the electronic consolidation circuitry 203, in an embodiment of the invention.
[0064] In a step 401, the consolidation electronic circuitry 203 obtains the first and second altitude values VI and V2 generated by the FMCW subsystem 201 and the UWB subsystem 202 respectively.
[0065] In step 402, the consolidation electronic circuitry 203 compares the second altitude value V2 to a first predetermined threshold SI of altitude above ground level. For example, step 402 consists of performing the following test: "V2 < SI?". In one embodiment, the first predetermined threshold SI is between 25 and 35 meters. In a particular implementation, it is equal to 100 ft (i.e., 30.48 m).
[0066] If the second altitude value V2 is greater than the first predetermined threshold SI (a "no" response to the test in step 402), the consolidation electronic circuitry 203 executes step 404, in which it determines the consolidated altitude value VC based on the first altitude value VI and without considering the second altitude value V2 (VC = f(VI)). In a particular implementation of step 404, the consolidated altitude value VC is equal to the first altitude value VL. In other words, the second altitude value V2 is filtered out when its value is greater than the first threshold SI (for example, 100 ft). This is because UWB technology is considered to involve only low-energy signal pulses, which do not allow the measurement of altitudes greater than this first threshold.If the UWB 2002 subsystem nevertheless provides a second altitude value V2 that is higher than the first SI threshold, it is assumed that this V2 value is probably unreliable.
[0067] If the second altitude value V2 is less than or equal to the first predetermined threshold SI (response "yes" to the test in step 402), the consolidation electronic circuitry 203 performs step 403 in which it determines the consolidated altitude value VC as a function of the first and second altitude values VI and V2 (VC = f (VI, V2)).
[0068] At the end of step 403 or 404, the consolidation electronic circuitry 203 executes step 405 in which it stores the consolidated altitude value VC, for possible use in the next iteration of the consolidation algorithm just described (return to step 401; for example, the consolidation electronic circuitry 203 obtains the first and second altitude values VI and V2 every 50 ms).
[0069] In a particular implementation, illustrated in [Fig.4], step 403 itself comprises steps 403a to 403f.
[0070] In step 403a, the consolidation electronic circuitry 203 compares a difference between the first and second altitude values VI and V2 to a second predetermined altitude difference threshold S2. For example, step 403a consists of performing the following test: “| VI - V2 | < S2 ?”.
[0071] If the difference between the first and second altitude values VI and V2 is less than or equal to the second predetermined threshold S2 (a "yes" response to the test in step 403a, meaning there is no significant difference between VI and V2), the consolidation electronic circuitry 203 performs step 403b, in which it determines the consolidated altitude value VC as a combination of the first and second altitude values VI and V2. For example, VC is the average of VI and V2. In one variant, VC is equal to VI. In another variant, VC is equal to V2.
[0072] If the difference between the first and second altitude values VI and V2 is greater than the second predetermined threshold S2 (response "no" to the test in step 403a, meaning that there is a significant difference between VI and V2), the consolidation electronic circuitry 203 performs step 403c in which it obtains a reference altitude Aref as a function of one or more selection parameters, for example: - a barometric altitude (parameter PI on the [Fig.2]) provided by a barometric altimeter; - an inertial altitude (parameter P2 on [Fig.2]) provided by an inertial measurement unit; and - a memorized altitude (parameter P3 on the [Fig.2]) resulting from a memorization of a previous consolidated value VC.
[0073] In one implementation, the stored altitude (P3) is used simply to initialize the inertial altitude (P2) and the barometric altitude (PI), which are relative altitudes and must therefore start from a reference based on a true altitude (relative to the ground). This true altitude corresponds, for example, to the last time when there was no significant difference between the two altitude values VI and V2, that is to say, to the stored altitude (P3).
[0074] Following step 403c, the consolidation electronic circuitry 203 executes step 403d and one of steps 403e and 403f, thereby selecting (to form the consolidated value VC) the first and second altitude values VI and V2 that are closest to the reference altitude Aref. In this way, the use of one or more of the parameters PI, P2, and P3 helps with discrimination and thus improves the continuity of the radio altimetry system 101.
[0075] More specifically, in step 403d the electronic circuitry of consolidation 203 performs the following test: "| VI-Aref | < |V2-Aref| ?".
[0076] If the first altitude value V1 is closest to the reference altitude Aref (answer "yes" to the test in step 403d), the consolidation electronic circuitry 203 chooses, in step 403e, the first altitude value VI as the consolidated value VC (VC = VI).
[0077] If the second altitude value V2 is closest to the reference altitude Aref (response "no" to the test in step 403d), the consolidation electronic circuitry 203 chooses, in step 403f, the second altitude value V2 as the consolidated value VC (VC = V2).
[0078] Figure 3 schematically illustrates an example of the hardware architecture of the cir electronic consolidation circuitry 203 included in the radio altimetry system 101. In this example, the electronic consolidation circuitry 203 then includes, connected by a communication bus 310: a processor or CPU (Central Processing Unit) 301; a RAM (Random Access Memory) 302; a ROM (Read Only Memory) 303, for example a Flash memory; a data storage device, such as a HDD (Hard Disk Drive), or a storage media reader, such as an SD (Secure Digital) card reader 304; at least one communication interface 305 allowing the electronic consolidation circuitry 203 to interact in the avionics of the aircraft 100.
[0079] The processor 301 is capable of executing instructions loaded into RAM 302 from ROM 303, external memory (not shown), a storage medium such as an SD card, or a communication network (not shown). When the consolidation electronic circuitry 203 is powered on, the processor 301 is able to read instructions from RAM 302 and execute them. These instructions form a computer program causing the processor 301 to implement the behaviors, steps, and algorithms described herein.
[0080] All or part of the behaviors, steps, and algorithms described herein can thus be implemented in software form by executing a set of instructions by a programmable machine, such as a DSP (Digital Signal Processor) or a microcontroller, or be implemented in hardware form by a dedicated machine or component (chip) or a dedicated set of components (chipset), such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specific Integrated Circuit). Generally speaking, the consolidation electronic circuitry 203 is arranged and configured to implement the behaviors, steps, and algorithms described herein.
Claims
Demands
1. A radio altimetry system (101) suitable for installation in an aircraft (100) and for providing an altitude of said aircraft above the ground, comprising: - a first subsystem (201) based on frequency-modulated continuous wave radar technology, known as FMCW radar technology, providing a first altitude value (VI) of the aircraft above the ground; - a second subsystem (202) based on ultra-wideband radar technology, known as UWB radar technology, providing a second altitude value (V2) of the aircraft above the ground; and - electronic circuitry (203), known as consolidation circuitry, configured to: - compare the second altitude value to a predetermined altitude threshold above the ground; - if the second altitude value is less than or equal to the predetermined altitude threshold above ground, determine a consolidated altitude value (VC) of the aircraft above ground, based on the first and second altitude values;and - if the second altitude value is greater than the predetermined altitude threshold above ground, determine a consolidated altitude value (VC) of the aircraft above ground, based on the first altitude value and without taking into account the second altitude value.;
2. Radio altimetry system according to claim 1, wherein the first subsystem (201) is configured to use a first frequency band, and wherein the second subsystem (202) is configured to use at least a second frequency band distinct from the first frequency band.
3. Radio altimetry system according to claim 2, wherein the first frequency band is the [4.2 GHz; 4.4 GHz] band and wherein the second frequency band is within the [3.1 GHz; 10.6 GHz] band.
4. Radio altimetry system according to any one of claims 2 and 3, wherein the second subsystem (202) is configured to perform frequency hopping between at least two distinct frequency bands of the first frequency band.
5. Radio altimetry system (101) according to any one of the claims indications 1 to 4, wherein the second subsystem (202) is configured to use at least one pulse pattern that is distinct from a waveform used by the first subsystem (201).
6. Radio altimetry system (101) according to any one of claims 1 to 5, wherein the first and second radio subsystems (201, 202) share at least one element belonging to the group comprising an antenna and a coaxial cable.
7. Radio altimetry system (101) according to any one of claims 1 to 6, wherein the consolidation electronic circuitry (203) is further configured to, in the event of a difference between the first and second altitude values exceeding a predetermined altitude difference threshold, select one of the first and second altitude values according to at least one selection parameter, to form the consolidated value.
8. Radio altimetry system (101) according to claim 7, wherein at least one selection parameter belongs to the group comprising: - a barometric altitude provided by a barometric altimeter; - an inertial altitude provided by an inertial measurement unit; and - a stored altitude resulting from the storage of a previous consolidated value.
9. Radio altimetry system (101) according to any one of claims 7 and 8, wherein selecting one of the first and second altitude values as a function of at least one selection parameter comprises: - determining a reference altitude as a function of at least one selection parameter; and - selecting, among the first and second altitude values, the altitude value closest to the reference altitude.
10. Radio altimetry system (101) according to any one of claims 1 to 9, wherein the predetermined altitude threshold above ground is between 25 and 35 meters.
11. Aircraft (100) comprising the radio altimetry system (101) according to any one of claims 1 to 10.