A computer-implemented method and device for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise in FMCW radars

Abstract

A computer-implemented method for measuring the spectral distribution ratio between the received echo signal and the physical receiver noise, adapted for use in radars, utilising a transmitted signal (111) generated by the radar generator (5) and an echo signal (131) from the output of a low-noise antenna amplifier LNA (32), which signals are subjected to transformations in accordance with the following steps of the method: performing digitisation (201) of the transmitted signal (111) and the echo signal (131); on the basis of the digitised echo signal (132), determining (202) the echo signal power spectral density (142); on the basis of the digitised transmitted signal (112), determining (203) the transmitted signal power spectral density (122); on the basis of the digitised echo signal (132) and the digitised transmitted signal (112), determining (204) the echo signal versus transmitted signal cross-spectral density (152); on the basis of the cross-spectral density (152) as well as that of the echo (142) and transmitted signal (122), determining (205) a coherence function (162), which is a quotient of the squared modulus of the function of the echo signal versus transmitted signal cross-spectral density (152) and the product of the function of the echo signal spectral density (142) and the function of the transmitted signal spectral density (122); on the basis of the result of the calculations from the previous step, determining (206) the signal to noise ratio SNR (172), being a quotient of the coherence function (162) and the negative value of the coherence function (162) increased by one. A device for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise (1), adapted to cooperate with a radar, comprising: a transmitted signal AC converter (11), an echo signal AC converter (13), and further comprising a module for determining the transmitted signal power spectral density (12), a module for determining the echo signal power spectral density (14), a module for determining the cross-power spectral density (15), a module for determining a coherence function (16), a module for determining the signal to noise ratio SNR (17), where the functions of the modules (12, 14, 15, 16, 17) are performed using a computer system comprising at least a microprocessor, volatile memory and non-volatile memory, connected in a shared data bus, and the device is adapted to implement the method according to the invention.

Description

[0001] A computer-implemented method and device for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise in FMCW radars

[0002] Technical Field

[0003]

[0001] The object of the invention is a computer-implemented method for measuring the spectral distribution of the signal to noise ratio in systems radiolocating objects using FMCW modulation, and a measurement device implementing this method.

[0004] Description of Prior Art

[0005]

[0002] In order to measure the SNR ratio between the received echo signal and the physical receiver noise, it is necessary to perform a measurement of the power of the signal received by the radar and the noise level of one’s own receiver. At present, there are known methods for measuring the physical noise of a radar receiver after disconnecting the antenna. There are no known methods for measuring noise with the antenna connected, since there is a problem of distinguishing receiver noise received by the antenna from the simultaneously present received signal.

[0006]

[0003] Therefore, it is desirable to develop a method for measuring the SNR without the necessity to disconnect the antenna.

[0007] Summary

[0008]

[0004] The essence of the invention is a computer-implemented method for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise, adapted for use in radars, using a transmitted signal created by the radar generator and an echo signal from the output of a low-noise antenna amplifier LNA, which signals are subjected to transformations in accordance with the following consecutive steps of the method: performing digitisation of the transmitted signal and the echo signal, followed by determining the echo signal power spectral density on the basis of the digitised echo signal, and subsequently determining the transmitted signal power spectral density on the basis of the digitised transmitted signal. In the next step, the echo signal versus transmitted signal cross-spectral density is determined on the basis of the digitised echo signal and the digitised transmitted signal. Subsequently, on the basis of the cross-spectral density as well as that of the echo and transmitted signal, a coherence function is determined, which is a quotient of the squared modulus of the function of the echo signal versus transmitted signal cross-spectral density and the product of the function of the echo signal spectral density and the function of the transmitted signal spectral density (122). Afterwards, the signal to noise ratio SNR, being a quotient of the coherence function and the negative value of the coherence function increased by one, is determined on the basis of the result of the calculations from the previous step.

[0009]

[0005] The presented method solves the problem of the necessity to disconnect the antenna when measuring the signal to noise ratio, which enables its use under the conditions of actual measurement, and not solely during preliminary calibration of the devices.

[0010]

[0006] The benefit of using this method is in that the SNR can be measured in a continuous manner, without interrupting the operation of the radar in complete configuration, i.e. disconnecting the antenna from the receiver input.

[0011]

[0007] Continuous measurement of the SNR allows for monitoring the quality of the received echoes, and for controlling the radar range by indirectly measuring the level of the own noises of the radar.

[0012]

[0008] The object of the invention is also a device for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise, adapted to cooperate with a radar, comprising: a transmitted signal AC converter, an echo signal AC converter, and further comprising a module for determining the transmitted signal power spectral density, a module for determining the echo signal power spectral density, a module for determining the cross-power spectral density, a module for determining a coherence function, a module for determining the signal to noise ratio SNR, where the functions of the modules are performed using a computer system comprising at least a microprocessor, volatile memory and non-volatile memory, connected in a shared data bus, and the device is adapted to implement the method according to the invention.

[0009] The object of the invention is also an system comprising the device according to the invention and a radar.

[0013]

[0010] Preferably, the radar is an FMCW radar.

[0014]

[0011] Preferably, the system further comprises a first mixer, a second mixer and a heterodyne generator, configured in such a manner that they reduce the frequency of input signals delivered to the device acc. to the invention.

[0015]

[0012] The object of the invention is also a computer program comprising instructions, which following the execution of this program cause it to perform the steps of the method according to the invention, when said program is activated in a computer system.

[0016]

[0013] The object of the invention is also a computer-readable data storage medium comprising instructions, which once executed by a computer system cause the computer system to perform the steps of the method according to the invention.

[0017] Description of the Drawings

[0018]

[0014] The object of the invention is shown in embodiments in the drawing, in which:

[0015] Fig. 1 . presents a block diagram of the device for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise;

[0019]

[0016] Fig. 2. presents an system using the device for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise and an FMCW ground-penetrating radar;

[0020]

[0017] Fig. 3. presents an system for direct incorporation of the device for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise in the transmitter and receiver circuits of an FMCW ground-penetrating radar;

[0021]

[0018] Fig. 4. presents the system of a ground-penetrating radar using the device for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise by means of systems mixing the frequencies of the transmitted and echo signal in order to lower the frequency of signals directed to an SNR meter;

[0019] Fig. 5. presents an system using the device for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise and an FMCW ground-penetrating radar operating in a homodyne configuration;

[0022]

[0020] Fig 6. presents a flowchart of the computer-implemented method for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise.

[0023] Notation and nomenclature

[0024]

[0021] Certain parts of the detailed description which is provided below are presented as part of procedures, data processing steps or other representations of symbolic operations on bit data, which can be performed in computer memory. Therefore, the logical steps are performed by the computer, which requires physical manipulation of physical quantities. Usually, these quantities take on the form of electrical or magnetic signals, suitable for storage, transmission, connection, comparison, or for other ways of manipulating data in a computer system. Due to their widespread use, these data are referred to as signals, time series, bits, packages, messages, values, elements, symbols, signs, expressions, numbers and the like. In addition, all of these terms or those similar to them should be identified with their corresponding physical quantities, and they are merely convenient terms for these physical quantities. Terms such as “processing” or “creating” or “transmitting” or “executing” or “determining” or “detecting” or “receiving” or “selecting” or “calculating” or “generating” or the like refer to the actions and processes of a computer system which manipulates and converts the data represented as physical (electronic) quantities in computer registers and memories into different data, similarly represented as physical quantities in memories or registers or other information storages. A computer-readable medium (memory), as defined in the present document, can usually be non-volatile and / or comprise a nonvolatile device. In this context, a non-volatile memory storage medium may comprise a device which can be material, which means that the device has a specific physical form, although this device may change its physical state. Therefore, for example, the term non-volatile refers to a device which remains material, although it changes its state.

[0025] Embodiment 1 — a computer-implemented method for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise.

[0026]

[0022] The computer-implemented method for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise is implemented using a device 1 , for simplicity called an SNR meter 1 , illustrated in Fig. 1 . The method is illustrated using the example of measuring the signal to noise ratio of an FMCW radar echo.

[0027]

[0023] It is assumed that an FMCW radar, illustrated schematically in Fig. 2, comprises a frequency-modulated generator 5, a transmitting antenna 2, a receiving antenna 3 and an echo signal input LNA amplifier 32. The relationship between the signals 1 1 1 and 31 1 at the terminals of the antennas is described by a radar channel transmittance function h(f) 4. Noises in the radar arrangement are defined by a serial backup noise source defined by the function n(f) 31 , referring to the input of the radar receiver system.

[0028]

[0024] The measurement of the ratio between the echo signal and the own noise of the receiver system is performed by means of the SNR meter 1. The transmitted signal 1 1 1 generated by the generator 5 and the echo signal 131 recorded at the output of the receiver circuit LNA amplifier 32 are introduced into the meter 1.

[0029]

[0025] The signal 1 1 1 from the arrangement of the FMCW generator 5 is introduced at the input of a transmitted signal AC converter 1 1 . The signal 1 1 1 is converted by the converter 1 1 into a digital form. The signal 131 from the output of the receiver circuit input LNA amplifier 32 is introduced at the input of a received signal AC converter 13. Similarly, the signal 131 is converted by the converter 13 into a digital form.

[0030]

[0026] All the modules and blocks performing the calculations listed in the present and the following embodiments are implemented by means of a computer system comprising at least a microprocessor, volatile memory and non-volatile memory, connected in a shared data bus.

[0031]

[0027] The digital form of the FMCW generator signal 112 is directed to a transmitted signal power spectrum module 12, which calculates the transmitted signal power spectrum 122. The digital form of the echo signal 132 is directed to a received signal power spectrum module 14, which calculates the echo signal power spectrum 142. The signals 1 12 and 132 are simultaneously directed to a cross-power spectrum module 15, which calculates the echo signal versus transmitted signal cross-power spectrum 152. Afterwards, the signals 122, 152 and 142 are directed to a coherence function module 16, which calculates the coherence function of the signals 122 and 142. The signal of the coherence function 162 is directed to an SNR module 17, which calculates the signal to noise ratio SNR 172.

[0032]

[0028] In order to perform the calculations, the coherence function is established between the transmitted signal 1 11 directed to the transmitting antenna 2 and the received signal 131 acquired from the output of the input LNA amplifier 32 of the receiver circuit, connected to the receiving antenl na 3. The signal path between the nodes of the signals 11 1 and 131 is as follows: the signal 1 1 1 enters the transmitting antenna 2, the antenna radiates a wave towards the target, the wave reflects from the target and returns to the receiving antenna 3, the antenna generates a signal 31 1 which is directed to the input LNA amplifier 32.

[0033]

[0029] It is assumed that the passage of the signal from the node of the signal 1 1 1 to the node of the signal 31 1 is defined by a transmittance function h(f) 4, which describes the transmission properties of the radar channel. The input noise of the receiver system is represented by an equivalent noise source 31 , incorporated between the nodes of the signals 31 1 and 312.

[0034]

[0030] The signal 131 at the output of the receiver system 32 equals

[0035] *131( / ) = h( / ) in( / ) + / ), (1 )

[0036]

[0031] where n(f) is a Fourier transform of the time series of noise n(t), a source incorporated between the nodes of the signals 31 1 and 312. The signal 131 is directed to the SNR meter 1 , where after digitisation in the arrangement 13 it is directed to the arrangement 14, which calculates the spectral density 142 of the signal 132. where are the power spectrum of the transmitted signal 111 and the power spectrum of the noise n(t), respectively.

[0037]

[0032] Following the digitisation of the signal 111 in the module 11 , the transmitted signal 112 is directed to the module 12, in which the power spectrum is calculated

[0038] S122 (f) = S111 (f) (4)

[0039]

[0033] Furthermore, the signals 112 and 132 are introduced into the module 15, where the cross-spectral density 152 of these signals is calculated

[0040]

[0034] Assuming that the noise n(t) of the receiver system is coloured Gaussian noise, not correlated with the transmitted signal 112, the result is as follows

[0041]

[0035] The signals 122, 152 and 142 are directed to the module 16, in which the coherence function of the signals 112 and 132 is calculated

[0042] The relationship (7) indicates that the value of the coherence function in the presence of noise is lower than 1 .

[0043]

[0036] The power ratio between the signal S106(f) observed at the output 311 of the radar channel and the power of the local noise N(f) generated by the backup source 31 equals

[0037] After substituting the relationship (8) into (7), it can be seen that the coherence function between the transmitted signal and the echo signal equals (9)

[0044]

[0038] When there is no noise at the input of the receiving arrangement, the signal to noise ratio is defined by the formula (8): SNR ( / ) = oo, hence the coherence function (9) is: = 1- Thisisdue to the fact that the linear arrangement of a radar channel with the transmittance function h(f) links the input signal 1 12 with the output signal 132 in a deterministic manner, ensuring coherence of the amplitudes and phases of the echo signals in the entire examined frequency interval.

[0045]

[0039] In the second extreme case of very small values of the SNR(f) « 1 , the coherence function is: r noOT » NR(f) « o (10)

[0046]

[0040] In the module 17, on the basis of the signal 162 generated in the coherence function calculation block 16, the signal 172 is calculated according to the formula (9):

[0047]

[0041] The signal 172 unambiguously determines the ratio between the echo signal and the receiver noise at the input of the radar receiver system. The input noise may be interpreted more broadly, e.g. as noise generated by the receiver system, having the following components: the noise of the input LNA amplifier + the noise of the antenna system + thermal noises generated by the surroundings. The signal 172 may be calculated in real time, which allows for immediate quality assessment of the echo signal as a function of frequency.

[0048] Systems comprising device according to the invention

[0049] Embodiment 2

[0050]

[0042] Fig. 3 presents a system comprising a device for radiolocating objects in space (a radar or a ground-penetrating radar) using an SNR meter 1. The radar part of the system comprises a frequency-modulated FMCW generator 5, generating a transmitted signal 1 1 1 . A transmitting antenna 2 is connected to the generator

[0051] 5. A signal 131 generated in a receiving antenna 3 is directed to a receiving arrangement 33, where it is converted into information about the object reflecting the waves. The transmitted signal 1 1 1 and the received signal 131 are simultaneously directed to the SNR meter 1 . At the output, the SNR meter

[0052] 1 generates a spectrum of the signal to echo noise ratio 172 within the scope of retuning the FMCW signal.

[0053]

[0043] The typical technical parameters of an SNR meter 1 incorporated in the arrangement of a typical FMCW ground-penetrating radar (SGPR-H) are as follows:

[0054] Modulation type: Linear triangular FM

[0055] Generator power 100 mW

[0056] FM retuning range 300 MHz to 1600 MHz

[0057] Retuning range in percent 137%

[0058] FM retuning rate 100 us

[0059] Differential echo frequency range 0 to 5 MHz

[0060] Resolving power per depth 5 cm

[0061] The range of detecting a metal item with a surface area of 1 mA2 in dry sand 40 m.

[0062] Embodiment 3

[0063]

[0044] The system presented in Fig. 4 is similar to the system presented in Fig. 3, except a first mixer 6 and a second mixer 7 operated by a shared heterodyne signal generator 8 are used in order to lower the frequency of the transmitted signal 1 11 and the received echo signal 131. Due to the use of down-mixing, the signals 1 1 1 A and 131 A carrying information about the spectral characteristics of the transmitted and received signal may be analysed more easily using the system of an SNR meter 1 , considering that signals with lower bands require lower computing power. Embodiment 4

[0064]

[0045] It refers to the system illustrated in Fig. 5, which uses an SNR meter 1 and a ground-penetrating radar with a receiving homodyne system.

[0065]

[0046] A transmitting FMCW generator 5 is connected via a transmitting antenna delay line 21 to a transmitting antenna 2 and the input of a second mixer 7 serving the function of a homodyne mixer. A receiving antenna 3 is connected via a receiving antenna delay line 24 to the second input of the second mixer 7. The differential signal generated by the second mixer is fed to a receiving part low- pass filter 25. An output filter signal 131 L representing the echo signal is connected to one of the inputs of the SNR meter 1 system. A second transmitted reference signal 1 11 L being an FMCW signal after the transformations of a homodyne system is fed to the SNR meter 1 and generated by means of a first mixer 6. The first input of the mixer 6 is directly connected to the output of the signal 1 1 1 generator. After passing through a signal generator delay line 22, the signal from the first input is directed to the second input of the mixer 6. The output of the first mixer 6 is incorporated into the SNR meter 1 via a transmitting part low-pass filter 23.

[0066] Other embodiments of systems with the devices acc. to the invention

[0047] In each of the embodiments from 2 to 4, the transmitting 2 and receiving antenna 3 can be replaced with a single antenna, to which the transmitted 1 1 1 and received signal 31 1 are connected via a circulator I directional coupler.

[0067]

[0048] List of references

[0068] 1 — SNR meter

[0069] 2 — transmitting antenna

[0070] 3 — receiving antenna

[0071] 4 — radar system transmittance

[0072] 5 — FMCW generator

[0073] 6 — first mixer

[0074] 7 — second mixer

[0075] 8 — heterodyne signal generator — transmitted signal AC converter — transmitted signal power spectral density module — received signal AC converter — echo signal power spectral density module — cross-power density module — coherence module — SNR module — transmitting antenna delay line — generator signal delay line — transmitting part low-pass filter — receiving antenna delay line — receiving part low-pass filter — backup noise source — receiver circuit low-noise amplifier (LNA) 1 — FMCW generator signal 1 — received signal 1 A — FMCW generator signal transferred to a lower frequency band 1 L — FMCW signal after transformations of the homodyne system 2 — digital form of the FMCW generator signal 2 — transmitted signal power spectrum 1 — echo signal 1 A — received signal transferred to a lower frequency band 1 L — received signal after transformations of the homodyne system2 — digital form of the echo signal 2 — echo signal power spectrum 2 — echo signal versus transmitted signal cross-power spectrum2 — coherence function 2 — SNR output signal 1 — receiving antenna output signal 2 — receiving antenna output signal comprising noise 2 — FMCW ground-penetrating radar output signal

Claims

CLAIMS1. A computer-implemented method for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise, adapted for use in radars, utilising a transmitted signal (111 ) generated by the radar generator (5) and an echo signal (131 ) from the output of a low-noise antenna amplifier LNA (32), which signals are subjected to transformations in accordance with the following consecutive steps of the method:— performing digitisation (201 ) of the transmitted signal (111 ) and the echo signal (131 );— on the basis of the digitised echo signal (132), determining (202) the echo signal power spectral density (142);— on the basis of the digitised transmitted signal (112), determining (203) the transmitted signal power spectral density (122);— on the basis of the digitised echo signal (132) and the digitised transmitted signal (112), determining (204) the echo signal versus transmitted signal cross-spectral density (152);— on the basis of the cross-spectral density (152) as well as that of the echo (142) and transmitted signal (122), determining (205) a coherence function (162), which is a quotient of the squared modulus of the function of the echo signal versus transmitted signal cross-spectral density (152) and the product of the function of the echo signal spectral density (142) and the function of the transmitted signal spectral density (122);— on the basis of the result of the calculations from the previous step, determining (206) the signal to noise ratio SNR (172), being a quotient of the coherence function (162) and the negative value of the coherence function (162) increased by one.

2. A device for measuring the spectral distribution of the ratio between the received echo signal and the physical receiver noise (1 ), suitable for cooperating with a radar, comprising:— a transmitted signal AC converter (11 ),— an echo signal AC converter (13),and further comprising:— a module for determining the transmitted signal power spectral density (12),— a module for determining the echo signal power spectral density (14),— a module for determining the cross-power spectral density (15),— a module for determining the coherence function (16),— a module for determining the signal to noise ratio SNR (17) where the functions of the modules (12,14,15,16,17) are performed with the use of a computer system comprising at least a microprocessor, volatile memory and non-volatile memory, connected in a shared data bus and the device is suitable for implementing the method according to claim 1 .

3. An system comprising:— the device (1 ) according to claim 2,— a radar.

4. The system according to claim 3, where the radar is an FMCW radar.

5. The system according to claim 4, further comprising:— a first mixer (7),— a second mixer (8),— and a heterodyne generator (9), configured such that they lower the frequency of the input signals delivered to the device (1 ).

6. A computer program comprising instructions, which following the execution of this program cause it to perform the steps of the method according to the claims from 1 , when said program is activated in a computer system.

7. A computer-readable data storage medium comprising instructions, which once executed by a computer system cause the computer system to perform the steps of the method according to claim 1 .

Images