Digital radioltimeter validation system
The digital radio altimeter validation system addresses the limitations of existing systems by employing phase correction and configurable delays to simulate altitudes from zero to high, supporting slope-controlled altimeters with enhanced flexibility and precision.
Patent Information
- Application Number
- FR2023008110
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2023-07-27
- Publication Date
- 2025-07-18
- Estimated Expiration
- 2043-07-27
AI Technical Summary
Existing radio altimeter validation systems are bulky, expensive, and limited in flexibility, failing to simulate both very low and very high altitudes effectively, especially for slope-controlled altimeters.
A digital radio altimeter validation system with an RF input/output interface and incompressible latency, using a linear chirp signal with quadratic phase, applies configurable delays to compensate for latency through phase correction, enabling simulation of various altitudes by converting signals into Cartesian coordinates and performing complex operations.
Enables flexible simulation of altitudes from zero to high altitudes, supporting slope-controlled altimeters with precise frequency compensation, allowing for complex dynamic scenarios and reduced sensitivity to phase noise.
Smart Images
Figure 00000010_0000 
Figure 00000011_0000
Abstract
Description
Title of the invention: Digital radio altimeter validation system
[0001] The invention relates to a digital RF card for validating a radio altimeter or radar altimeter, with frequency-modulated continuous-wave radar signals or FMCW for "Frequency-Modulated Continuous-Wave" in English.
[0002] A radio altimeter or radar altimeter is an instrument for measuring the distance of an aircraft above the ground, using the principle of Radar.
[0003] Validating a radio altimeter requires delaying the transmitted signal by very different orders of magnitude, from a few tens of >us to a few tens of ms. Physical delay lines are bulky, expensive, and limited in the possible test scenarios they offer.
[0004] Some digital systems exist and offer more flexibility, but remain quite simplistic and do not allow the simulation of very low heights for slope-controlled radio altimeters.
[0005] The prior art systems do not allow for the simulation of both very low (close to 0 feet) and very high (close to 10,000 feet) heights in a flexible manner compatible with slope-controlled radio altimeters.
[0006] Also, according to one aspect of the invention, a digital radio altimeter validation system is proposed, provided with an input / output RF interface and characterized by an incompressible latency T, configured to receive a linear chirp signal (FMCW) with linearly modulated continuous wave in frequency f (t) = at + fi and with quadratic phase s(t} = e2J^at2l^ which can also be written in complex form in Cartesian coordinates l(t) + f representing the time, and configured to retransmit it according to a configurable delay and deliver to the radio altimeter a signal + jQ'(t) exactly frequency compensated for the latency T by a linear extrapolation of its phase by calculating the difference between the current phase and the phase numerically delayed by the value to be compensated T, so that the frequency of this signal has no apparent delay.
[0007] This compensation makes it possible to simulate zero heights, and it can be extended to high heights by adding a digital delay corresponding to the associated propagation delay.
[0008] According to one embodiment, the digital radio altimeter validation system comprises: - a first converter configured to convert the signal emitted in complex form into Cartesian coordinates + into polar coordinates in p^j^tr form); - a shifter configured to perform a one-bit left shift or binary multiplication by 2 of the phase of the output signal of the first converter; - a delayer configured to apply a delay of said latency T to the phase of the output signal of the first converter; - a subtracter configured to subtract the output phase of the shifter from the output phase of the delayer; and - a second converter configured to convert the output signal of the digital system, having as module P that at the output of the first converter and as phase the output phase of the subtractor -t) - ¢)( ?-2t) into a signal in complex form in Cartesian coordinates / +jQ'(t).
[0009] A linear chirp is a signal with linear modulation of frequency f, and therefore with quadratic phase ¢, which can be expressed respectively in the form f ( t ) = Ctt + P and , z . / _ f1• , . , at2 n ■ We can express the parameters and, 6 in function of the minimum frequencies f^ and maximum fmax of the chirp and its duration T according to a _ , P = fmjn , and the initial fraction of the phase ^()) / lir
[0010] According to one embodiment, the first converter comprises a CORDIC module configured to implement a numerical calculation by rotation of coordinates for calculations of trigonometric and hyperbolic functions.
[0011] In one embodiment, the delayer comprises a FIFO queue.
[0012] According to one embodiment, the second converter comprises a module CORDIC configured to implement numerical calculation by coordinate rotation for calculations of trigonometric and hyperbolic functions.
[0013] Alternatively, the second converter comprises a piecewise polynomial approximation module of the complex exponential.
[0014] According to another embodiment, the digital RF radio altimeter validation card comprises: - a delayer (Ret2) configured to apply a delay of said latency T to the signal received / ( / ) , Q{t) from the radio altimeter by the RF card having already undergone an incompressible latency Q(t - t ), and output the signal received from the radio altimeter delayed by 2t, I(C2t), ; - a complex multiplier (MultComplexe) configured to apply complex multiplications to the signal received I(t) , Q(t) from the radio altimeter by the RF card having already undergone an incompressible latency T , / (fT) , Q(tT) , and output the signals j2(7-T)-Q2(jT) ,27( / -t) Q(tT) , and / 2(fT) =p2(?-t); - a conjugate multiplier (MultConj) configured to apply complex multiplications to the output signals of the delay (Ret2) and the output signals / 2( / -r)-g2( / -T) and 2 / ( t - T ) Q(tr) of the complex multiplier (MultComp) to output the signals / 3 = ct 03 = and - a divider (Div) configured to apply divisions to the output signals of the conjugate multiplier (MultConj) by the output / 2 (t - t ) + g2 (t - T ) = p2 (Ji) of the complex multiplier (MultComplexe), and output the signal J(t) + jQ(t) =
[0015] The invention will be better understood by studying some embodiments described as non-limiting examples and illustrated by the appended drawings in which: - [Fig.l] schematically illustrates a digital RF card for validating a radio altimeter, according to one aspect of the invention; and - [Fig.2] schematically illustrates a digital RF card for validating a radio altimeter, according to another aspect of the invention.
[0016] The present invention relates to a digital radio altimeter validation system, provided with an RF input / output interface and characterized by an incompressible latency T, configured to receive a linear chirp FMCW signal with a continuous wave linearly modulated in frequency f (t) = at + P and with a quadratic phase s(t) = ¢2M« / 2 / 2 + / *+}■), which can also be written in complex form in Cartesian coordinates l(t) + f representing time. The digital radio altimeter validation system is also configured to retransmit the signal $(t) according to a configurable delay and deliver to the radio altimeter a signal + jQ'(t) exactly compensated in frequency for the latency T by a linear extrapolation of its phase by calculating the difference between the current phase and the phase digitally delayed by the value to be compensated T.
[0017] [Fig.l] schematically represents a digital RF card for radio altimeter validation, according to an embodiment of the invention.
[0018] The digital system is also configured to deliver to the radio altimeter a corrected signal with a delay of 2t in complex form in Cartesian coordinates + jQ'(i) corresponding to the signal reflected at a predetermined height, in which the received signal is compensated by a linear extrapolation of its phase, from the current phase and the phase digitally delayed by the value to be compensated T.
[0019] The digital radio altimeter validation system includes: - a first converter Convl configured to convert the signal emitted in complex form into Cartesian coordinates l(t -t) + jQ^t -t) into polar coordinates in the form; - a Dec shifter configured to perform a one-bit left shift or binary multiplication by 2 of the phase of the output signal of the first converter Convl; - a delayer Ret configured to apply a delay of said latency T to the phase of the output signal of the first converter Convl; - a subtracter Sub configured to subtract the output phase of the shifter Dec from the output phase of the delayer Ret; and - a second converter Conv2 configured to convert the output signal of the digital system, having as module P that at the output of the first converter Convl and as phase the output phase of the subtractor Sous 2¢(fT)-¢(^-2T), into a signal in complex form in Cartesian coordinates J '( / ) + jQ '( / ).
[0020] It is proposed to use a digital system to simulate the propagation channel, in particular by introducing a delay using a FIFO queue to simulate a height. It is thus possible to carry out all the desired tests.
[0021] Unfortunately the RF interface at the input / output of the digital system has an incompressible latency T due to the propagation times, which prevents the simulation of heights lower than hmin — Ct / 2; c corresponding to the propagation speed of the wave in its medium (generally assimilated to the speed of light in a vacuum).
[0022] However, being digital makes it possible to compensate for this delay by applying a signal with a negative phase slope (non-causal). In other words, it is possible to use complex operators to compensate the phase by the amount by which it has varied over the duration T.
[0023] For example, the received continuous frequency modulated background can be of the form €2jn(at2l2+pt+y\ and the chirp principle can be linear with variable slope of frequency f(t) -at + ft.
[0024] The phase correction is compatible with zero propagation time for testing an FMCW radio altimeter.
[0025] It is possible to write the frequency of a linear chirp according to t ( t ) = at + (3, and therefore the associated chirp can be written s(t) = = pe 2 j^o au+ i Wu+ Y) = pe 2 .!^® 2 / 2 +ri+v)-
[0026] The received signal r then essentially corresponds to the transmitted signal s, with a delay T and an attenuation A. By mixing the two, we obtain a pure beat frequency: BF(t) = s(t) xr^t) = s(t) x A s*(It); BF^tj = Ap2 x *+y) xe = Ap2 x
[0027] The frequency of this signal is t ri = «t, and the height of the carrier can be deduced as h _ çxt _ . n“ 2 “ 2a
[0028] It is possible to fix the value of a at transmission and seek to determine the iron value at reception, or to vary the value of a so as to obtain a known Ibf frequency. This latter principle, less complex to implement, is that of slope-controlled radio altimeters.
[0029] By studying the phase shifts of the emitted signal, it appears that <[>( tt) - ([>( t-2x) =(|>(t) -(|)(tT) -27TCCT2, i.e. ( t ) = 2(|> ( t - T ) - (|) ( t -2t ) + 2îTaT2. For a linear chirp, “ is constant and therefore 2tï«t2 also: by mixing the received signal delayed by T with the signal delayed by 2t, we obtain a frequency-compensated signal.
[0030] The first converter Convl may comprise a CORDIC module configured to implement a numerical calculation by coordinate rotation for calculations of trigonometric and hyperbolic functions.
[0031] The Ret delayer may comprise a first-in, first-out FIFO type queue.
[0032] The second converter Conv2 may comprise a CORDIC module configured to implement a numerical calculation by coordinate rotation for calculations of trigonometric and hyperbolic functions.
[0033] Alternatively, the second converter Conv2 may comprise a piecewise polynomial approximation module of the complex exponential.
[0034] According to another embodiment, as illustrated in [Fig.2], the digital radio altimeter validation system comprises: - a delayer (Ret2) configured to apply a delay of said latency T to the signal received Z(O , Q(t) from the radio altimeter by the RF card having already undergone an incompressible latency T , Z ( / - t ) , Q( t - J and output the signal received from the radio altimeter delayed by 2t , Z (L2t ) , Q( t-2i ) ; - a complex multiplier (MultComplexe) configured to apply complex multiplications to the signal received Z(f), QU) from the radio altimeter by the RF card having already undergone an incompressible latency T, Z(f - t), Q(tt) , and output the signals I2(tT)QAt-'t) , and / 2(Ct) +ô2(zt) = p2; - a conjugate multiplier (MultConj) configured to apply complex multiplications to the output signals of the delay (Ret2) and the output signals Z2(^-t)-ô2(Zt) and 2 / ( ï - T ) of the multiplier complex (MultComp) to output the signals / 3 = I 1^2 + and ^-^and - a divider (Div) configured to apply divisions to the output signals of the conjugate multiplier (MultConj) by the output +Q2(tT:') =p2 of the complex multiplier (MultComplexe), and output the signal j(^) + jQ(t) =
[0035] Having a digital architecture allows for complex dynamic scenarios with a wide variety of possible heights.
[0036] The phase compensation carried out makes it possible to restore the value of the frequency.
[0037] The present invention is simple to implement, and not very sensitive to phase noise.
Claims
Claims
1. Digital radio altimeter validation system, provided with an RF input / output interface and characterized by an incompressible latency T, configured to receive a linear chirp (FMCW) signal s(t) with linearly modulated continuous wave frequency f(t) = at + fi and quadratic phase s(t) — + / W), which can also be written in complex form in Cartesian coordinates f representing time, and configured to retransmit it according to a configurable delay and deliver to the radio altimeter a signal jQ'(t) exactly frequency compensated for the latency T by a linear extrapolation of its phase by calculating the difference between the current phase and the phase digitally delayed by the value to be compensated T.
2. Digital radio altimeter validation system, according to claim 1, comprising: - a first converter (Convl) configured to convert the signal transmitted in complex form into Cartesian coordinates l(t) + into polar coordinates in the form; - a shifter (Dec) configured to perform a left shift of one bit or binary multiplication by 2 of the phase of the output signal of the first converter (Convl); - a delayer (Ret) configured to apply a delay of said latency T to the phase of the output signal of the first converter (Convl); - a subtracter (Sous) configured to subtract the output phase of the shifter (Dec) from the delayer output phase (Ret);and - a second converter (Conv2) configured to convert the output signal of the digital system, having as module f that at the output of the first converter (Convl) and as phase the output phase of the subtractor (Sous) 2(|)(£-t) -¢(C2t), into a signal in complex form in Cartesian coordinates I\t) + jQ'Çt)-;
3. A digital radio altimeter validation system, according to claim 2, wherein the first converter (Convl) includes a CORDIC module configured to implement numerical computation by coordinate rotation for calculations of trigonometric and hyperbolic functions.
4. A digital radio altimeter validation system according to claim 2 or 3, wherein the delayer (Ret) comprises a FIFO queue.
5. Digital radio altimeter validation system, according to one of claims 2 to 4, in which the second converter (Conv2) comprises a CORDIC module configured to implement a digital calculation by rotation of coordinates for calculations of trigonometric and hyperbolic functions.
6. Digital radio altimeter validation system, according to one of claims 2 to 4, in which the second converter (Conv2) comprises a piecewise polynomial approximation module of the exponential.
7. Digital radio altimeter validation system, according to claim 1, comprising: - a delayer (Ret2) configured to apply a delay of said latency T to the signal received Z ( f , Q(t) from the radio altimeter by the RF card having already undergone an incompressible latency T,Z(?- T) , Q(t - T ), and output the signal received from the radio altimeter delayed by 2t , Z(C2t) , Ô(C2t); - a complex multiplier (MultComplexe) configured to apply complex multiplications to the signal received I{t) , Q(t) from the radio altimeter by the RF card having already undergone an incompressible latency T , Z ( / - T ) , Q(ti) , and output the signals I2(ti) -Q2(tr) , 21(1-1) QU-1) ,andI2(ti)+Q2(ti) =p2(tT);- a conjugate multiplier (MultConj) configured to apply complex multiplications to the output signals of the delay (Ret2) and the output signals I2(t-1)-Q2(ti) and 2Z(fT) QU-i) of the complex multiplier (MultComp) to output the signals Z3 = Z]Z2 + Q^ and Q3 = UQ^ - Q^û and - a divider (Div) configured to apply divisions to the output signals of the conjugate multiplier; (MultConj) by the output + Q2(7-t) = ^2( / ^) of the complex multiplier (MultComplex), and output the signal + jQ(j) -^2^-^(-2^