A method for improving the orthogonality performance of MIMO radar waveforms

Abstract

This invention discloses a method for improving the orthogonality performance of MIMO radar waveforms, as follows: After the MIMO radar antenna receives the echo signal, the echo signal of each receiving element is down-converted and converted from analog to digital, converting the analog signal into a digital signal; the digital signal of each receiving element is passed through different matched filters for matched filtering, and the output data of the matched filters are stored respectively; the output data of the m-th matched filter in the n-th receiving element is subtracted from the output data of the other matched filters in the n-th receiving element to obtain a first result; the improved data of the output data of the m-th matched filter in the n-th receiving element is calculated based on the correlation coefficient between the first result and the orthogonal waveforms output by different transmitting elements, thereby completing the improvement of the orthogonality performance of the radar waveform. This invention improves the orthogonality performance of the waveform without changing the phase information of the signal itself.

Description

Technical Field

[0001] This invention relates to the field of radar signal processing technology, and more specifically, to a method for improving the orthogonality performance of MIMO radar waveforms. Background Technology

[0002] With the continuous development of electronic information technology, the target characteristics and detection environments faced by radar are becoming increasingly complex, posing greater challenges to radar target detection performance. Traditional phased array radar systems are relatively simple, forming a narrow beam in the transmission airspace with strong directivity. They can achieve a signal power gain proportional to the square of the number of array elements in the normal direction, making them widely used in various radar equipment. However, phased array radar also has drawbacks. It is easily intercepted by enemy radar; the phased array radar beam is narrow, requiring the phased array to illuminate different angles of space separately during target detection, making it impossible to simultaneously detect the entire airspace; furthermore, phased array radar typically only utilizes the spatial degrees of freedom at the receiver, and the limitation of radar antenna array size makes it difficult for phased array radar to increase spatial degrees of freedom to improve target detection capabilities.

[0003] Multiple-input multiple-output (MIMO) radars use multiple antennas at both the transmitting and receiving ends. MIMO radars are mainly divided into distributed MIMO radars and centralized MIMO radars. This discussion focuses on centralized orthogonal MIMO radars. The array distribution of a centralized MIMO radar is basically the same as that of a traditional radar array, employing waveform diversity technology. The signal waveforms between each transmitting element or channel of the radar are mutually orthogonal. At the receiving end, each waveform signal is extracted separately using matched filters or other filters, thus obtaining the spatial degrees of freedom of the transmitting end. Therefore, the spatial degrees of freedom of MIMO radar during signal processing are much higher than those of phased array radars, resulting in higher target detection performance. Furthermore, because MIMO radar transmits orthogonal waveforms, its transmission pattern is omnidirectional, allowing it to simultaneously detect the entire airspace.

[0004] In summary, orthogonal waveforms are a necessary condition for the normal operation of centralized orthogonal MIMO radar. However, perfectly orthogonal waveforms do not exist in reality; therefore, improving the orthogonality performance of waveforms is an important research direction for orthogonal MIMO radar. Waveform performance is typically reflected in several aspects, including autocorrelation main-sidelobe ratio, orthogonality, and range resolution. Range resolution is determined by the width of the main lobe output after matched filtering; a narrower main lobe results in better range resolution. The autocorrelation main-sidelobe ratio refers to the ratio of the peak values ​​of the main lobe to the side lobes after matched filtering; a high main-sidelobe ratio can avoid the problem of weak target masking. Orthogonality refers to the cross-correlation amplitude between different transmitted signals. The orthogonality performance of the waveform directly affects the signal separation effect at the receiver, thus impacting the performance of the MIMO radar.

[0005] To improve the orthogonal performance of MIMO radar, numerous researchers both domestically and internationally have studied the design of orthogonal waveforms for MIMO radar. There are four main types of orthogonal MIMO radar waveforms: code division addressing, time division addressing, frequency division addressing, and Doppler division addressing. Based on these four waveform types, many orthogonal waveform design methods for MIMO radar have been proposed, but none of them can achieve complete orthogonality.

[0006] In summary, since the current MIMO radar waveforms are non-orthogonal, which can negatively impact the performance of orthogonal MIMO radar, a method is needed to improve the orthogonality of the waveforms. Summary of the Invention

[0007] In order to improve the orthogonality performance of existing MIMO radar waveforms and thus reduce the impact of non-orthogonal waveforms on the target detection performance of MIMO radar, this invention provides a method for improving the orthogonality performance of MIMO radar waveforms.

[0008] To achieve the above-mentioned objectives of this invention, the technical solution adopted is as follows:

[0009] A method for improving the orthogonality performance of MIMO radar waveforms, the method comprising the following steps:

[0010] After the MIMO radar antenna receives the echo signal, it performs down-conversion and digital-to-analog conversion on the echo signal of each receiving array element to convert the analog signal into a digital signal.

[0011] The digital signal of each receiving array element is subjected to matched filtering through different matched filters, and the output data of the matched filters are stored separately.

[0012] The first result is obtained by subtracting the output data of the m-th matched filter in the n-th receiving array element from the output data of the m-th matched filter in the n-th receiving array element.

[0013] Based on the correlation coefficient between the first result and the orthogonal waveforms output by different transmitting array elements, the improved data of the output data of the m-th matched filter in the n-th receiving array element is calculated, thereby completing the improvement of the radar waveform orthogonality performance.

[0014] Preferably, if the goal is to extract the m'-th waveform signal, the matched filtering process is as follows:

[0015]

[0016] In the formula, y n,m' (t) represents the output data of the matched filter, x n (t) represents the received signal of the nth receiving element, h m'(t) represents the matched filter for the m′-th phase-coded waveform, * denotes convolution, ξ represents the power of the echo signal, and s m' (t) The waveform emitted by the m′-th transmitting element. Let represent the steering vector of the nth receiving element and the m′th transmitting element, m represent the mth orthogonal waveform, t represent fast time, M represent the total number of orthogonal MIMO radar transmitting elements, and r represent the steering vector of the nth receiving element and the m′th transmitting element. m，m' s represents the correlation coefficient between the m-th orthogonal waveform and the m′-th orthogonal waveform in a zero-delay period. m (t) represents the waveform emitted by the m-th transmitting element. This represents the steering vector of the nth receiving element and the mth transmitting element.

[0017] Furthermore, the formula for calculating the received signal of the nth receiving array element is as follows:

[0018]

[0019] Furthermore, the formula for calculating the matched filter of the m-th phase-coded waveform is as follows:

[0020] h m (t)=s m * (-t)

[0021] in,(·) * Indicates taking the conjugate; s m * (-t) represents the waveform s m The conjugate of (t) is used to simultaneously reverse the entire signal.

[0022] Furthermore, the formula for calculating the first result is as follows:

[0023] v n,m,m' (t)=y n,m (t)-y n,m' (t)

[0024] In the formula, y n,m (t) represents the output data of the m-th matched filter in the n-th receiving element, y n,m' (t) represents the output data of the m′-th matched filter in the n-th receiver element.

[0025] Furthermore, the improved data for calculating the output data of the m-th matched filter in the n-th receiving element based on the correlation coefficient between the first result and the orthogonal waveforms output by different transmitting array elements is calculated using the following formula:

[0026]

[0027] In the formula, Indicates improved data, This indicates taking the real part.

[0028] Furthermore, the method also includes:

[0029] Also to Normalization is performed as follows:

[0030]

[0031] In this context, |·| is the modulo symbol.

[0032] Furthermore, the digital signal of each receiving array element is subjected to matched filtering through different matched filters, and the output data of the matched filters are stored separately, denoted as .

[0033]

[0034] After each element in Y is processed to obtain preliminary improved data, it undergoes normalization. The processed data is denoted as...

[0035] In the formula, This represents the data after the waveform orthogonality has been improved.

[0036] A MIMO radar waveform orthogonality improvement system includes:

[0037] The processing module is used to perform down-conversion and digital-to-analog conversion on the echo signal of each receiving element after the MIMO radar antenna receives the echo signal, converting the analog signal into a digital signal; it is used to subtract the output data of other matched filters in the nth receiving element from the output data of the mth matched filter in the nth receiving element to obtain a first result; it is used to calculate the improved data of the output data of the mth matched filter in the nth receiving element based on the correlation coefficient between the first result and the orthogonal waveforms output by different transmitting elements, thereby improving the orthogonality performance of the radar waveform;

[0038] The matched filtering module is used to perform matched filtering on the digital signal of each receiving array element through different matched filters.

[0039] The storage module is used to store the output data of the matched filter separately.

[0040] A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, it performs the steps of the method described above.

[0041] The beneficial effects of this invention are as follows:

[0042] This invention performs matched filtering on the digital signal of each receiving array element through different matched filters. Since the signal processing of each matched filter is independent and needs to be performed separately, and each signal processing requires the use of the output data of other matched filters, this method is suitable for processing at the digital signal end.

[0043] This invention subtracts the output data of other matched filters in the nth receiving array element from the output data of the mth matched filter in the nth receiving array element to obtain a first result, and calculates the improved data of the output data of the mth matched filter in the nth receiving array element based on the correlation coefficient, thereby improving the orthogonality performance of the waveform.

[0044] This invention can improve the orthogonality of waveforms without altering the phase information of the signal itself. This invention can be applied to various waveform signals and is not limited by the type of waveform transmitted by the radar. Attached Figure Description

[0045] Figure 1 This is a flowchart of the steps in the MIMO radar waveform orthogonality improvement method described in this invention.

[0046] Figure 2 This is a block diagram illustrating the principle of the MIMO radar waveform orthogonality improvement system described in this invention. Detailed Implementation

[0047] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0048] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0049] Example 1

[0050] This embodiment of the MIMO radar uses an antenna array. Different transmitting elements transmit mutually orthogonal waveform signals. Here, it is assumed that the transmitted waveforms are phase-coded waveforms. Let the number of transmitting elements in the orthogonal MIMO radar be M, the corresponding number of orthogonal waveforms be M, and the number of receiving elements be N. Since the transmitted waveforms are known, their correlation coefficients can be calculated in advance, and the correlation coefficients of each waveform in zero delay are recorded for subsequent signal processing. The correlation coefficient between the m-th and m'-th waveforms in zero delay is denoted as r. m,m' When m = m', r m,m' This is the autocorrelation coefficient. Generally, the autocorrelation coefficient is 1.

[0051] like Figure 1 As shown, a method for improving the orthogonality performance of MIMO radar waveforms includes the following steps:

[0052] After the MIMO radar antenna receives the echo signal, it performs down-conversion and digital-to-analog conversion on the echo signal of each receiving array element to convert the analog signal into a digital signal.

[0053] The digital signal of each receiving array element is subjected to matched filtering through different matched filters, and the output data of the matched filters are stored separately.

[0054] The first result is obtained by subtracting the output data of the m-th matched filter in the n-th receiving array element from the output data of the m-th matched filter in the n-th receiving array element.

[0055] Based on the correlation coefficient between the first result and the orthogonal waveforms output by different transmitting array elements, the improved data of the output data of the m-th matched filter in the n-th receiving array element is calculated, thereby completing the improvement of the radar waveform orthogonality performance.

[0056] This invention performs matched filtering on the digital signal of each receiving array element through different matched filters. Since the signal processing of each matched filter is independent and needs to be performed separately, and each signal processing requires the use of the output data of other matched filters, this method is suitable for processing at the digital signal end.

[0057] This invention subtracts the output data of other matched filters in the nth receiving array element from the output data of the mth matched filter in the nth receiving array element to obtain a first result, and calculates the improved data of the output data of the mth matched filter in the nth receiving array element based on the correlation coefficient, thereby improving the orthogonality performance of the waveform.

[0058] This invention can improve the orthogonality of waveforms without altering the phase information of the signal itself. This invention can be applied to various waveform signals and is not limited by the type of waveform transmitted by the radar.

[0059] In a specific embodiment, the waveform transmitted by the m-th transmitting element is denoted as s. m (t), where t represents fast time. At the receiving end, after the MIMO radar antenna receives the echo signal, the echo signal of each receiving array element is down-converted and converted from analog to digital, converting the analog signal into a digital signal. The down-conversion, or frequency reduction, can be achieved through a low-pass filter; the digital-to-analog conversion can be directly implemented using a digital-to-analog converter chip.

[0060] At this point, the received signal of the nth receiving element can be expressed as:

[0061]

[0062] Where ζ is the power of the echo signal, This refers to the phase information of the signal.

[0063] Since the transmitted waveform is a phase-coded waveform, the signal of each receiving element must be extracted using a different matched filter. The matched filter h for the m-th phase-coded waveform... m (t) is shown below:

[0064] h m (t)=s m * (-t)

[0065] In one specific embodiment, the digital signal of each receiving array element is subjected to matched filtering through different matched filters, and the output data of the matched filters are stored separately. Since the waveforms are non-orthogonal, the output of each matched filter contains signals of other waveforms besides the target signal; these are called redundant signals. After matched filtering, each waveform signal is extracted and stored separately. Therefore, the signal data dimension of each receiving array element at a certain sampling point is 1×M. Let y be the output data of the nth receiving array element after matched filtering. n =[y n,1 ,y n,2 ,...,y n,M ], where y n,m This represents the output data of the m-th matched filter.

[0066] Since the transmitted waveform is a phase-coded waveform, the signal of each receiving element must be extracted using a different matched filter. The matched filter h for the m-th phase-coded waveform... m (t) is shown below:

[0067] h m (t)=s m *(-t)

[0068] in,(·) * Indicates taking the conjugate, s m * (-t) represents the waveform s m The conjugate of (t) is used to simultaneously reverse the entire signal.

[0069] Preferably, if the goal is to extract the m'-th waveform signal, the matched filtering process is as follows:

[0070]

[0071] In the formula, y n,m' (t) represents the output data of the matched filter, x n (t) represents the received signal of the nth receiving element, h m' (t) represents the matched filter for the m′-th phase-coded waveform, * denotes convolution, ξ represents the power of the echo signal, and s m' (t) The waveform emitted by the m′-th transmitting element. Let represent the steering vector of the nth receiving element and the m′th transmitting element, m represent the mth orthogonal waveform, t represent fast time, M represent the total number of orthogonal MIMO radar transmitting elements, and r represent the steering vector of the nth receiving element and the m′th transmitting element. m，m' s represents the correlation coefficient between the m-th orthogonal waveform and the m′-th orthogonal waveform in a zero-delay period. m (t) represents the waveform emitted by the m-th transmitting element. This represents the steering vector of the nth receiving element and the mth transmitting element.

[0072] As can be seen from the formula above, the output of the matched filter contains a small amount of redundant signal in addition to the target signal. The power of the redundant signal is determined by the correlation coefficient r. m,m' Decision. Store the output of the received signal from each receiver element after passing through the matched filter, denoted as .

[0073]

[0074] In one specific embodiment, the output data of the m-th matched filter in the n-th receiving array element is subtracted from the output data of the other matched filters in the n-th receiving array element to obtain a first result; wherein the calculation formula for the first result is as follows:

[0075] δ n,m,m' (t)=y n,m (t)-y n,m' (t)

[0076] In the formula, y n,m (t) represents the output data of the m-th matched filter in the n-th receiving element, yn,m' (t) represents the output data of the m′-th matched filter in the n-th receiver element.

[0077] This completes the signal preprocessing, and we call the first result the difference data.

[0078] In a specific embodiment, the improved data for the output data of the m-th matched filter in the n-th receiving element is calculated based on the correlation coefficient between the first result and the orthogonal waveforms output by different transmitting array elements. The calculation formula is as follows:

[0079]

[0080] In the formula, Indicates improved data, This indicates taking the real part.

[0081] In this embodiment, the output data of the m-th matched filter is supplemented with the difference data, thus improving the orthogonality of the signal. Through this process, the redundant signal components in the output data of the m-th matched filter can be significantly reduced without changing the phase of the signal itself, thereby improving the orthogonality of the waveform.

[0082] The improved data for the output of the m-th matched filter in the n-th receiving element can be obtained using the above formula. The component ratio of the redundant signal in the middle is y n,m (t) is greatly reduced.

[0083] Finally, each Normalization is also required, and the method further includes:

[0084] Also to Normalization is performed as follows:

[0085]

[0086] In this context, |·| is the modulo symbol.

[0087] In this embodiment, each element in Y is processed through the above steps (after obtaining preliminary improved data, normalization is performed), and the processed data is denoted as... In the formula, This represents the data after the waveform orthogonality has been improved.

[0088] This completes the signal processing of all data, thereby improving the orthogonality of all array element signals.

[0089] Example 2

[0090] Based on the MIMO radar waveform orthogonality performance improvement method described in Example 1, this example also provides a MIMO radar waveform orthogonality performance improvement system, including:

[0091] include:

[0092] The processing module is used to perform down-conversion and digital-to-analog conversion on the echo signal of each receiving element after the MIMO radar antenna receives the echo signal, converting the analog signal into a digital signal; it is used to subtract the output data of other matched filters in the nth receiving element from the output data of the mth matched filter in the nth receiving element to obtain a first result; it is used to calculate the improved data of the output data of the mth matched filter in the nth receiving element based on the correlation coefficient between the first result and the orthogonal waveforms output by different transmitting elements, thereby improving the orthogonality performance of the radar waveform;

[0093] The matched filtering module is used to perform matched filtering on the digital signal of each receiving array element through different matched filters.

[0094] The storage module is used to store the output data of the matched filter separately.

[0095] Example 3

[0096] This embodiment also provides a computer device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the steps of the MIMO radar waveform orthogonality improvement method as described in Embodiment 1.

[0097] The memory and processor are connected via a bus, which can include any number of interconnecting buses and bridges, connecting various circuits of one or more processors and memories. The bus can also connect various other circuits, such as peripheral devices, voltage regulators, and power management circuits, which are well known in the art and will not be described further herein. The bus interface provides an interface between the bus and the transceiver. The transceiver can be a single element or multiple elements, such as multiple receivers and transmitters, providing a unit for communicating with various other devices over a transmission medium. Data processed by the processor is transmitted over the wireless medium via an antenna, which further receives data and transmits it to the processor.

[0098] This embodiment also provides a computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the steps of the MIMO radar waveform orthogonality improvement method as described in Embodiment 1.

[0099] That is, those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a device (which may be a microcontroller, chip, etc.) or processor to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0100] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for improving the orthogonality performance of MIMO radar waveforms, characterized in that: The method includes the following steps: After the MIMO radar antenna receives the echo signal, it performs down-conversion and digital-to-analog conversion on the echo signal of each receiving array element to convert the analog signal into a digital signal. The digital signal of each receiving array element is subjected to matched filtering through different matched filters, and the output data of the matched filters are stored separately. The first result is obtained by subtracting the output data of the m-th matched filter in the n-th receiving array element from the output data of the m-th matched filter in the n-th receiving array element. Based on the correlation coefficient between the first result and the orthogonal waveforms output by different transmitting array elements, the improved data of the output data of the m-th matched filter in the n-th receiving array element is calculated, thereby completing the improvement of the radar waveform orthogonality performance; The formula for calculating the first result is as follows: δ n,m,m' (t)=y n,m (t)-y n,m' (t) In the formula, y n,m (t) represents the output data of the m-th matched filter in the n-th receiving element, y n,m' (t) represents the output data of the m′-th matched filter in the n-th receiver element.

2. The method for improving the orthogonality performance of MIMO radar waveforms according to claim 1, characterized in that: Suppose we want to extract the m'-th waveform signal, then the matched filtering process is as follows: In the formula, y n,m' (t) represents the output data of the matched filter, x n (t) represents the received signal of the nth receiving element, h m' (t) represents the matched filter for the m′-th phase-coded waveform, * denotes convolution, ξ represents the power of the echo signal, and s m' (t) The waveform emitted by the m′-th transmitting element. Let represent the steering vector of the nth receiving element and the m′th transmitting element, m represent the mth orthogonal waveform, t represent fast time, M represent the total number of orthogonal MIMO radar transmitting elements, and r represent the steering vector of the nth receiving element and the m′th transmitting element. m，m' This indicates that the m-th orthogonal waveform and the m′-th orthogonal waveform are extended from 0. The correlation coefficient in time, s m (t) represents the waveform emitted by the m-th transmitting element. This represents the steering vector of the nth receiving element and the mth transmitting element.

3. The method for improving the orthogonality performance of MIMO radar waveforms according to claim 2, characterized in that: The formula for calculating the received signal of the nth receiving array element is as follows:

4. The method for improving the orthogonality performance of MIMO radar waveforms according to claim 2, characterized in that: The formula for calculating the matched filter of the m-th phase-coded waveform is as follows: h m (t)=s m * (-t) in,(·) * Indicates taking the conjugate; s m * (-t) represents the waveform s m The conjugate of (t) is used to simultaneously reverse the entire signal.

5. The method for improving the orthogonality performance of MIMO radar waveforms according to claim 1, characterized in that: The improved data for the output data of the m-th matched filter in the n-th receiving element is calculated based on the correlation coefficient between the first result and the orthogonal waveforms output by different transmitting array elements. The calculation formula is as follows: In the formula, Indicates improved data, This indicates taking the real part.

6. The method for improving the orthogonality performance of MIMO radar waveforms according to claim 5, characterized in that: The method further includes: Also to Normalization is performed as follows: In this context, |·| is the modulo symbol.

7. The method for improving the orthogonality performance of MIMO radar waveforms according to claim 6, characterized in that: The digital signal of each receiving array element is subjected to matched filtering through different matched filters, and the output data of the matched filters are stored separately, denoted as . After each element in Y is processed to obtain preliminary improved data, it undergoes normalization. The processed data is denoted as... In the formula, This represents the data after the waveform orthogonality has been improved.

8. A MIMO radar waveform orthogonality improvement system, characterized in that: include: The processing module is used to perform down-conversion and digital-to-analog conversion on the echo signal of each receiving element after the MIMO radar antenna receives the echo signal, converting the analog signal into a digital signal; it is used to subtract the output data of other matched filters in the nth receiving element from the output data of the mth matched filter in the nth receiving element to obtain a first result; it is used to calculate the improved data of the output data of the mth matched filter in the nth receiving element based on the correlation coefficient between the first result and the orthogonal waveforms output by different transmitting elements, thereby improving the orthogonality performance of the radar waveform; The matched filtering module is used to perform matched filtering on the digital signal of each receiving array element through different matched filters. The storage module is used to store the output data of the matched filter separately. The formula for calculating the first result is as follows: δ n,m,m' (t)=y n,m (t)-y n,m' (t) In the formula, y n,m (t) represents the output data of the m-th matched filter in the n-th receiving element, y n,m' (t) represents the output data of the m′-th matched filter in the n-th receiver element.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, it implements the steps of the method as described in any one of claims 1 to 7.

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