RADIO ALTIMETRY SYSTEM SUITABLE FOR AIRCRAFT INSTALLATION

Abstract

The invention relates to a radio altimetry system (101) suitable for being carried on board an aircraft and for providing an altitude of the aircraft above the ground, comprising: a first subsystem (201) based on FMCW technology and providing a first altitude value (V1); a second subsystem (202) based on UWB technology and providing a second altitude value (V2); and electronic consolidation circuitry (203) (configured to: compare the second value to a predetermined threshold; if the second value is less than or equal to the threshold, determine a consolidated value (VC) based on the first and second values; and if the second value is greater than the threshold, determine a consolidated value (VC) based on the first value and without taking into account the second value). In this way, the proposed radio altimetry system provides resilience to various interferences. Figure to be published with the abstract: Fig. 2

Description

Title of the invention: RADIO ALTIMETRY SYSTEM SUITABLE FOR INSTALLATION IN 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 capable of being mounted on an aircraft and of providing an altitude of said aircraft above the ground.

[0003] Altitude above ground level is also called "AGL altitude" (for "Above Ground Level" in English). 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 "altimetric radar", are used in the field of civil or military aeronautics.

[0005] They are in particular used during automatic flight phases or critical flight phases, such as approach, landing (with in particular flare and roll out operations) and takeoff. In particular, the flare operation depends entirely on the radio altimeter.

[0006] The altitude measurement above ground level (AGL altitude) provided by a radio altimeter can be used for various functions implemented in an aircraft:

[0007] - control of the aircraft, in particular for landing operations (automatic or manual) and take-off;

[0008] - Controlled Impact Fit (CFIT) protection 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] - inhibition of dangerous maneuvers near the ground;

[0012] - the generation of alerts and warnings in the cockpit;

[0013] etc.

[0014] In the state of the art, different types of radio altimeters are known, the general principle of such instruments being to measure the height by measuring the propagation time of radio signals transmitted 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 English). In the following In 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 frequency band [4.2 GHz; 4.4 GHz] which is itself included in the C frequency band. The C band is very interesting for telecommunications, but as a result it is very congested and subject to interference. Consequently, the frequency bands adjacent to the frequency band used by the FMCW radio altimeter are increasingly subject to interference. For this reason, the FMCW radio altimeter is potentially subject to external common mode failures, due to interference and leading to operational restrictions (e.g. for low visibility operations) and making the technique of flying with a single pilot (SPO, for "Single Pilot in Operation" in English) difficult to achieve.

[0017] The FMCW radio altimeter has the advantage of operating with relatively high power, which provides a good level of resistance to interference, particularly low-power interference generated in a wide frequency band. But it operates on a single band and is therefore sensitive to high-power interference, located on particular frequencies.

[0018] It is therefore desirable to provide a solution (radio altimetry system) offering resilience to various interferences, i.e. both to low power interferences, generated in a wide frequency band, and to high power interferences, located on particular frequencies.

[0019] Furthermore, since the flare operation is triggered and carried out below 100 ft AGL (i.e. 30.48 m above the ground), it is also desirable that the solution provided (radio altimetry system) allows the measurement to be reinforced at low altitude (for example below 100 ft AGL). Statement of the invention

[0020] A radio altimetry system is proposed herein capable of being carried on board an aircraft and of providing an altitude of said aircraft above the ground, comprising:

[0021] - a first subsystem based on modulated continuous wave radar technology in frequency, called FMCW radar technology, providing an initial altitude value of the aircraft above the ground;

[0022] - a second subsystem based on ultra-wideband radar technology, called UWB radar technology, providing a second altitude value of the aircraft above the ground; and

[0023] - an electronic circuit, called consolidation, 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, determining a consolidated altitude value of the aircraft above ground, based on the first and second altitude values; and

[0026] - if the second altitude value is greater than the predetermined altitude threshold au- above the ground, determine a consolidated altitude value of the aircraft above the ground, based on the first altitude value and ignoring 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 called "FMCW subsystem") based on FMCW radar technology and a second subsystem (hereinafter called "UWB subsystem") based on UWB radar technology (for "Ultra WideBand" in English). Furthermore, the proposed radio altimetry system comprises electronic consolidation circuitry which makes it possible to provide a consolidated value of altitude above the ground from the first and second values ​​of altitude above the ground provided respectively by the FMCW subsystem and the UWB subsystem.

[0028] In this way, the proposed radio altimetry system offers resilience to various interferences: low power interferences, generated in a wide frequency band, and high power interferences, localized on particular frequencies. Indeed, as already mentioned above, the FMCW subsystem has the advantage of operating with relatively high power and on a limited frequency band, thus making it possible to offer a good level of resistance to low power interferences generated in an ultra wide frequency band. In a complementary manner, the UWB subsystem has the advantage of operating on an ultra wide frequency band and with relatively low power, thus making it possible to offer a good level of resistance to high power interferences localized on particular frequencies.

[0029] In addition, the UWB subsystem uses UWB pulses that introduce dissimilarity. They are very short (e.g. 2ns) with a large bandwidth (e.g. 500MHz), so they provide a similar level of accuracy as 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 that it remains insensitive to heavy rain and fog attenuation. This is an important point for critical operations that take place 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 threshold of altitude above the ground. Thus, the proposed radio altimetry system makes it possible to reinforce the measurement at low altitude, i.e. below the predetermined threshold of altitude above the ground.

[0032] It will 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 starts 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 band [4.2 GHz; 4.4 GHz] and the second frequency band is included in the band [3.1 GHz; 10.6 GHz],

[0035] According to a particular embodiment, the second subsystem is configured to perform frequency hops between at least two frequency bands distinct from the first frequency band.

[0036] According to a particular embodiment, the second subsystem is configured to use at least one pulse pattern which 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 ​​greater than a predetermined altitude difference threshold, select one of the first and second altitude values ​​as a function of at least one selection parameter, to form the consolidated value.

[0039] According to a particular embodiment, the 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 unit; and

[0042] - a stored altitude resulting from a storage of a previous value consolidated.

[0043] According to a particular embodiment, the fact of 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 among the first and second altitude values, the altitude value closest to the reference altitude.

[0046] According to a particular embodiment, the predetermined threshold of altitude above the ground is between 25 and 35 meters, and in a particular implementation it is equal to 100 ft (i.e. 30.48 m).

[0047] Also provided herein is an aircraft comprising the radio altimetry system presented above, in any of its embodiments. Brief description of the drawings

[0048] The characteristics of the invention mentioned above, as well as others, will appear more clearly on reading the following description of at least one exemplary embodiment, said description being made in relation to the attached 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 hardware architecture of the electronic consolidation circuitry 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 EMBODIMENTS

[0054] [Fig.l] schematically illustrates, in side view, an aircraft 100 equipped with a radio altimetry system 101.

[0055] The radio altimetry system 101 is an on-board electronic equipment. For example, it is part of an electronic circuitry of the avionics of the aircraft 100. Its location in the aircraft may vary depending on the aircraft models.

[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 consolidation electronic circuitry 203.

[0057] The first subsystem 201, also called hereinafter “FMCW subsystem” (and noted “RA FMCW” in [Fig.2]), is based on continuous wave radar technology frequency modulated, called FMCW radar technology (for “Frequency Modulated Continuous Wave” in English). It provides a first value V1 of altitude of the aircraft 100 above the ground. The FMCW subsystem 201 is configured to use a first frequency band, which offers a first communication channel. In one embodiment, this is the band [4.2 GHz; 4.4 GHz].

[0058] The second subsystem 202, also called hereinafter “UWB subsystem” (and noted “UWB RA” in [Fig. 2]), is based on an ultra-wideband radar technology, called UWB radar technology (for “Ultra WideBand” in English). It provides a second altitude value V2 of the aircraft 100 above the ground. The UWB subsystem 202 is configured to use at least one second frequency band distinct from the first frequency band. In one embodiment, the UWB subsystem 202 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 included in the band [3.1 GHz; 10.6 GHz] and each have a width equal to 500 MHz.For example, the UWB subsystem 202 monitors interference received in these frequency bands and chooses the one with the least interference. In another example, the UWB subsystem 202 itself determines a suitable (in terms of interference) 500 MHz frequency band within an authorized frequency range (e.g. [3.1 GHz; 10.6 GHz]).

[0059] Thus, the FMCW subsystem 201 and the UWB subsystem 202 use different frequency bands, and therefore complementary communication channels, which makes it possible to obtain 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, which increases availability. If the two are inconsistent, an alert can be triggered, which increases integrity.

[0060] In one embodiment, the UWB subsystem 202 is configured to use at least one pulse pattern that is distinct from a waveform used by the FMCW subsystem 201. The introduced dissimilarity (e.g., frequency hopping and / or code and / or timing) allows for improved resilience of the radio altimetry system 101 against threats to data security and against multipath.

[0061] In one embodiment, the FMCW subsystem 201 and the UWB subsystem 202 share an antenna (e.g., 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, as a function of these and of one or more selection parameters PI, P2 and P3 (see below the description of [Fig.4]), a consolidated value VC of altitude above the ground.

[0063] [Fig.4] schematically illustrates an example of a consolidation algorithm, executed by the electronic consolidation circuitry 203, in one embodiment of the invention.

[0064] In a step 401, the electronic consolidation 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 a step 402, the electronic consolidation circuitry 203 compares the second altitude value V2 to a first predetermined threshold SI of altitude above the ground. For example, step 402 consists of carrying out 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 (response “no” to the test of step 402), the electronic consolidation circuitry 203 executes step 404 in which it determines the consolidated altitude value VC as a function of the first altitude value VI and without taking into account 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 when its value is greater than the first threshold SI (for example 100 ft). Indeed, it is considered that UWB technology only involves low-energy signal pulses, which do not allow altitudes greater than this first threshold to be measured.If the UWB 2002 subsystem nevertheless provides a second altitude value V2 higher than the first SI threshold, it is assumed that this V2 value is probably not reliable.

[0067] If the second altitude value V2 is less than or equal to the first predetermined threshold SI (response “yes” to the test of step 402), the electronic consolidation circuit 203 executes 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 electronic consolidation circuitry 203 executes step 405 in which it stores the consolidated altitude value VC, with a view to its possible use in the following iteration of the consolidation algorithm which has just been described (return to step 401; for example, the electronic consolidation 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 electronic consolidation 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 carrying out 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 (response “yes” to the test of step 403a, meaning that there is no significant difference between VI and V2), the electronic consolidation circuitry 203 executes 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 of step 403a, meaning that there is a significant difference between VI and V2), the electronic consolidation circuitry 203 executes 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 in [Fig.2]) provided by a barometric altimeter; - an inertial altitude (parameter P2 in [Fig.2]) provided by an inertial unit; and - a stored altitude (parameter P3 in [Fig.2]) resulting from the storage of a previous consolidated value VC.

[0073] In one implementation, the stored altitude (P3) is used just to initiate 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, i.e. to the stored altitude (P3).

[0074] At the end of step 403c, the electronic consolidation circuitry 203 executes step 403d and one of steps 403e and 403f, thus making it possible to select (to form the consolidated value VC), that of the first and second altitude values ​​VI and V2 which is closest to the reference altitude Aref. In this way, the use of one or more of the parameters PI, P2 and P3 makes it possible to assist in discrimination and therefore to improve the continuity of the radio altimetry system 101.

[0075] More precisely, in step 403d the electronic consolidation circuitry 203 performs the following test: “| VI-Aref | < |V2-Aref| ?”.

[0076] If the first altitude value V1 is closest to the reference altitude Aref (response “yes” to the test of step 403d), the electronic consolidation circuit 203 chooses, in step 403e, the first altitude value VI as consolidated value VC (VC = VI).

[0077] If the second altitude value V2 is closest to the reference altitude Aref (response “no” to the test of step 403d), the electronic consolidation circuit 203 chooses, in step 403f, the second altitude value V2 as consolidated value VC (VC = V2).

[0078] [Fig.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 comprises, connected by a communication bus 310: a processor or CPU (“Central Processing Unit” in English) 301; a RAM (“Random Access Memory” in English) 302; a ROM (“Read Only Memory” in English) 303, for example a Flash memory; a data storage device, such as a hard disk drive HDD (“Hard Disk Drive” in English), or a storage media reader, such as an SD (“Secure Digital” in English) 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 the RAM 302 from the ROM 303, an external memory (not shown), a storage medium, such as an SD card, or a communications network (not shown). When the consolidation electronic circuitry 203 is powered on, the processor 301 is capable of reading instructions from the RAM 302 and executing 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 may 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 machine or a dedicated component (chip) or a set of components (chipset), such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application-Specified Integrated Circuit). Generally speaking, the electronic consolidation circuitry 203 is arranged and configured to implement the behaviors, steps and algorithms described herein.

Claims

Claims

1. Radio altimetry system (101) capable of being embarked in an aircraft (100) and of providing an altitude of said aircraft above the ground, comprising: - a first subsystem (201) based on a frequency modulated continuous wave radar technology, called FMCW radar technology, providing a first altitude value (VI) of the aircraft above the ground; - a second subsystem (202) based on an ultra-wideband radar technology, called UWB radar technology, providing a second altitude value (V2) of the aircraft above the ground; and - electronic circuitry (203), called 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 threshold of altitude above the ground, determining a consolidated value (VC) of altitude of the aircraft above the ground, based on the first and second altitude values;and - if the second altitude value is greater than the predetermined threshold altitude above ground, determining a consolidated value (VC) of altitude of the aircraft above ground, based on the first altitude value and without taking into account the second altitude value.;

2. The radio altimetry system of 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 one second frequency band distinct from the first frequency band.

3. A radio altimetry system according to claim 2, wherein the first frequency band is the band [4.2 GHz; 4.4 GHz] and wherein the second frequency band is included in the band [3.1 GHz; 10.6 GHz],

4. A 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. A 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. A 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. A 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 ​​greater than a predetermined altitude difference threshold, select one of the first and second altitude values ​​as a function of at least one selection parameter, to form the consolidated value.

8. Radio altimetry system (101) according to claim 7, wherein the 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 unit; and - a stored altitude resulting from a storage of a previous consolidated value.

9. A 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 the at least one selection parameter comprises: - determining a reference altitude as a function of the at least one selection parameter; and - selecting, from among the first and second altitude values, the altitude value closest to the reference altitude.

10. A radio altimetry system (101) according to any one of claims 1 to 9, wherein the predetermined threshold of altitude above ground is between 25 and 35 meters.

11. An aircraft (100) comprising the radio altimetry system (101) according to any one of claims 1 to 10.

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