A frequency-stepped distributed coherent radar transmitting and receiving coherent fusion method

Abstract

This invention relates to a frequency-stepped distributed coherent radar transceiver coherent fusion method. Addressing the low resolution problem of conventional distributed coherent radars, it achieves high-precision, high-resolution detection performance. The specific steps include: S1 transmitting orthogonal frequency-stepped signal waveforms; S2 processing orthogonal echo signals; S3 estimating coherent parameters and Doppler frequencies; S4 receiving coherent fusion; S5 determining whether the parameter estimation accuracy meets requirements; S6 transmitting coherent frequency-stepped signal waveforms; S7 broadband synthesis of pulse group signals; and S8 transceiver coherent fusion. This invention achieves high range resolution by transmitting frequency-stepped signal waveforms, simultaneously realizing multi-station distributed radar signal transceiver coherent fusion and broadband synthesis.

Description

Technical Field

[0001] This invention relates to the field of distributed coherent radar technology. Background Technology

[0002] To improve target detection power and accuracy, and to meet the demands of flexible operations, Lincoln Laboratory proposed the Distributed Coherent Radar (DCAR) concept in 2003. This involves distributing multiple radars or arrays and performing signal-level fusion processing on multiple small-aperture radars to effectively form a large-aperture radar. DCAR offers a series of advantages, including high flexibility, good mobility, ease of maintenance, and high cost-effectiveness, overcoming the inherent shortcomings of large-aperture radar and providing a new approach to improving the signal-to-noise ratio at the receiver and enhancing target detection performance. Currently, DCAR has attracted widespread attention in the radar field both domestically and internationally, possessing significant research and application value.

[0003] Signal-level coherent fusion of distributed radar can improve the signal-to-noise ratio of target echoes, thereby enhancing detection capability and parameter estimation accuracy. Existing research on distributed coherent radar is mainly based on narrowband signal models, resulting in low resolution and a lack of high-resolution target detection capabilities. High-range target resolution can be achieved by increasing the signal waveform bandwidth; however, achieving instantaneous high bandwidth places high technical demands on both transmission and reception.

[0004] To achieve high range resolution under instantaneous narrowband transmission and reception conditions, the theory of frequency-stepped radar signals has been proposed in existing technologies. Initially applied to radar imaging, frequency-stepped radar signal waveforms have been applied to various radar systems and applications as the theory has matured. Research institutions such as Beijing Institute of Technology and the 23rd Research Institute of the Second Academy of Aerospace Science and Technology have conducted verification experiments on the theory and are gradually applying it to engineering fields. Applying the theory of frequency-stepped radar signals to the field of distributed coherent radar can solve the problem of low resolution in distributed coherent radar and achieve broadband distributed transmit-receive coherent fusion. Summary of the Invention

[0005] To overcome the low resolution of conventional narrowband distributed coherent radar, this invention proposes a frequency-stepping distributed coherent radar transmit-receive coherent fusion method.

[0006] To achieve the above objectives, the technical solution proposed by this invention includes the following steps:

[0007] S1 transmits orthogonal frequency step signal waveforms: The conventional transmitting unit transmits mutually orthogonal frequency step multi-pulse signal waveforms, which are separated by matched filtering for coherent parameter estimation; the auxiliary transmitting unit transmits fixed frequency multi-pulse signal waveforms that are orthogonal to the conventional transmitting unit, which are processed by pulse Doppler for Doppler frequency estimation.

[0008] S2 Quadrature Echo Signal Processing: The conventional receiving unit performs matched filtering on the quadrature frequency step echo signal transmitted by the conventional transmitting unit, and the auxiliary receiving unit performs matched filtering and pulse Doppler processing on the fixed frequency echo signal transmitted by the auxiliary transmitting unit.

[0009] S3 Coherent Parameter and Doppler Frequency Estimation: Extract the processed echo signals from the conventional receiving unit and the auxiliary receiving unit, and estimate the coherent parameters and Doppler frequency using the peak method respectively;

[0010] S4 receive coherent fusion: Perform coherent parameter and Doppler frequency compensation on the multi-echo signals of each cycle, and superimpose the compensated multi-echo signals to achieve receive coherent fusion;

[0011] S5 determines whether the parameter estimation accuracy meets the requirements: calculate the signal-to-noise ratio gain after coherent fusion of the echo signals in each cycle, and compare it with the coherent performance threshold. When the signal-to-noise ratio gain of the fused signal in each cycle is greater than or equal to the threshold, proceed to step S6; when the signal-to-noise ratio gain of the fused signal in any cycle is less than the threshold, proceed to S1, retransmit the quadrature frequency step signal, and perform parameter estimation.

[0012] S6 transmits coherent frequency step signal waveform: Each conventional transmitting unit transmits the same frequency step signal waveform, and the transmitted signal waveform of each transmitting unit is compensated for in time and phase using coherent parameters;

[0013] S7 pulse group signal broadband synthesis: Matched filtering and Doppler frequency compensation processing are performed on multiple received signals, and then broadband synthesis is achieved by frequency shifting and superposition of the processed multi-pulse frequency domain signals;

[0014] S8 transmit / receive coherent fusion: The broadband synthesized signal is compensated for in time and phase using coherent parameters, and the compensated signal is superimposed to achieve transmit / receive coherent fusion.

[0015] The beneficial effects of this invention are as follows: By stepping the signal waveform at the transmission frequency, this invention adds auxiliary transmitting and receiving units to estimate the Doppler frequency and coherent parameters, thereby achieving broadband distributed transceiver coherent fusion. This solves the problem of low resolution in narrowband distributed coherent radar and can simultaneously realize spatial transceiver coherent fusion and broadband synthesis of multi-station distributed radar signals, improving target detection accuracy and resolution. Attached Figure Description

[0016] Figure 1 Schematic diagram of the general structure of distributed phased coherent radar.

[0017] Figure 2 Flowchart of frequency-stepped distributed coherent radar transceiver coherent fusion information processing. Detailed Implementation

[0018] This invention proposes a frequency-stepped distributed coherent radar transceiver coherent fusion method. By transmitting frequency-stepped signal waveforms, auxiliary transmitting and receiving units are added to estimate and compensate for Doppler frequency and coherent parameters, thereby achieving broadband distributed transceiver coherent fusion.

[0019] Preferred implementation process and information processing of the present invention are as follows: Figure 2 As shown, the specific process is described as follows:

[0020] The general structure of a distributed phased coherent radar system is illustrated in the following diagram. Figure 1 As shown, the system consists of K+1 transmitting units, L+1 receiving units, and a central control system. The K+1 transmitting units include K conventional transmitting units and 1 auxiliary transmitting unit, while the L+1 receiving units include L conventional receiving units and 1 auxiliary receiving unit. For ease of distinction, the conventional transmitting units are numbered 1 to K, the auxiliary transmitting units are numbered K+1, the conventional receiving units are numbered 1 to L, and the auxiliary transmitting units are numbered L+1. All transceiver units are deployed with a short baseline, exhibiting identical electromagnetic scattering characteristics towards the target.

[0021] S1 transmits orthogonal frequency step signal waveforms: K conventionally transmitted mutually orthogonal frequency step signal waveforms, the pulse signal of the nth (1≤n≤N) cycle transmitted by transmitting unit k (1≤k≤K) can be expressed as:

[0022]

[0023] In the formula, t represents the fast time variable, n represents the slow time variable (number of pulse cycles), f0 represents the initial local oscillator frequency, Δf represents the frequency step value during a single pulse cycle, and u k (t) represents the baseband signal modulation waveform of transmitting unit k, with bandwidth B = Δf. This represents the initial phase of the local oscillator k in the transmitting unit.

[0024] The auxiliary transmitting unit transmits fixed-frequency multi-pulse signal waveforms that are orthogonal to those of the conventional transmitting unit. The pulse signal of the nth (1≤n≤N) period transmitted by the auxiliary transmitting unit K+1 can be expressed as:

[0025]

[0026] In the formula, u K+1 (t) represents the baseband signal modulation waveform of transmitting unit K+1, with a bandwidth of Δf. This represents the initial phase of the local oscillator in the transmitting unit K+1.

[0027] For all uk (t)(1≤k≤K+1), all satisfy the mutual orthogonality relation, that is:

[0028]

[0029] In the formula, k1, k2∈[1,K+1], This indicates the relevant operations.

[0030] The transmitted signal waveform of a distributed coherent system in one processing cycle is represented as:

[0031]

[0032] S2 Orthogonal Signal Echo Processing: Assuming the target contains only a single scattering point, and due to the short baseline deployment, the complex scattering coefficients of electromagnetic wave signals along different paths are equal, denoted as... The signal received by each receiving unit is a mixed echo after scattering from each signal. The down-converted echo signal of the l-th (1≤l≤L)-th (1≤n≤N)-th cycle of the conventional receiving unit is represented as:

[0033]

[0034] In the formula, This represents the time delay from the transmitting unit k to the receiving unit l after being scattered by the target (assuming that the delay of the echo signal of different periods is the same). n represents the local oscillator phase introduced by the down-conversion of receiving unit l. l (t,n) represents the additional noise signal, f d,n The additional Doppler frequency of the echo signal in the nth period is represented as:

[0035] f d,n =[f0+(n-1)△f](v) t +v r ) / c (6)

[0036] In the formula, v t and v r These represent the radial velocities of the target relative to the transmitting and receiving units, respectively.

[0037] The matched filtering process performed on the single-cycle echo signal after down-conversion by receiving unit l is expressed as follows:

[0038]

[0039] In the formula, n lk (t,n) represents the noise signal output by the matched filter. The above processing is performed on the echo signals of all periods of all receiving units.

[0040] Similarly, the above processing is applied to the signal received by the auxiliary receiving unit L+1, as follows:

[0041]

[0042] The received signals of auxiliary receiving unit L+1 for N periods are processed using a slow-time FFT method to achieve pulse Doppler processing, as follows:

[0043]

[0044] S3 coherent parameters and Doppler frequency estimation: Assuming all received signals use the propagation path from the first transmitting unit, scattered by the target, to the first receiving unit as the reference standard, let:

[0045]

[0046]

[0047]

[0048]

[0049]

[0050]

[0051]

[0052] Then equation (7) can be expressed as

[0053]

[0054] These are collectively referred to as the coherent parameters of the nth transmission cycle. The peak values ​​of the matched filter output signals for each path are extracted, and the coherent parameters are estimated using the peak value method, expressed as:

[0055]

[0056] In the formula, The value of t represents the maximum value of "·", max(·) represents the maximum value of "·", and phase(·) represents the phase value of "·".

[0057] The coherent parameters for N periods are estimated in the manner described above.

[0058] According to equation (9), extract |Y L+1K+1 (t,f)|peak value, using the peak value method to estimate the Doppler frequency value, therefore the estimated Doppler frequency value is expressed as:

[0059]

[0060] This represents the value of f corresponding to the maximum value of the "·". Therefore, the estimated Doppler frequencies for echoes of different periods are:

[0061]

[0062] S4 receive coherent fusion: for each processed signal y lk The following results were obtained by performing coherent parameter and Doppler frequency compensation on (t,n):

[0063]

[0064] In the formula, n l " k (t,n) represents the compensated noise signal. After parameter compensation of all multi-channel echoes in each period, they are superimposed to achieve coherent fusion of the received signals. The coherent fusion result is expressed as follows:

[0065]

[0066] S5 determines whether the parameter estimation accuracy meets the requirements: calculate the signal-to-noise ratio (SNR) gain for all coherently fused y(t,n) (1≤n≤N). gain and the coherent performance threshold Th gain For comparison, when the coherent fused signal y(t,n) of each cycle satisfies the SNR gain ≥Th gain If the parameter estimation accuracy meets the requirements, proceed to step S6; if there exists an SNR of y(t,n) gain <Th gain If the parameter estimation accuracy does not meet the requirements, switch to S1 and retransmit the quadrature frequency step signal to perform parameter estimation.

[0067] S6 transmits coherent frequency-stepped waveforms: K conventional transmitting units transmit the same frequency-stepped signal waveforms, and time and phase transmission compensation is performed using coherent parameters. The pulse signal of the nth (1≤n≤N) cycle transmitted by transmitting unit k (1≤k≤K) can be expressed as:

[0068]

[0069] In the formula, u(t) represents the waveform of the transmitted baseband signal, and its bandwidth is Δf.

[0070] S7 pulse group signal broadband synthesis: The down-converted echo signal of the l-th (1≤l≤L) conventional receiving unit in the n-th (1≤n≤N) cycle is represented as:

[0071]

[0072] Since the parameter estimation accuracy meets the requirements, therefore Then r l (t,n) can be represented as:

[0073]

[0074] For r l The (t,n) is processed by matched filtering with h(t) = u(t), and the output result is as follows:

[0075]

[0076] In the formula This represents the output result of the matched filter, for y l Doppler frequency compensation was performed on (t,n), and the results are as follows:

[0077]

[0078] Next, bandwidth synthesis of the signal is achieved by frequency shifting and superposition of multi-pulse frequency domain signals. (y′) l Transforming (t,n) into the fast time-frequency domain yields:

[0079]

[0080] In the formula, A f (f) represents the frequency domain result of A(t), for the obtained Y l (f,n) is frequency shifted, Y l The frequency shift (f,n) is:

[0081]

[0082] The result after frequency shift is:

[0083]

[0084] All Y′ l The signals (f, n) are superimposed to obtain the broadband synthesized frequency domain signal, as shown below:

[0085]

[0086] Y l (f) Perform IFFT transformation to the time domain to obtain the time domain signal after bandwidth synthesis, as follows:

[0087]

[0088] In the formula Z(t-τ) l1 )express Time-domain transformation results.

[0089] S8 transmit / receive coherent fusion: for all y l (t)(1≤l≤L) is compensated for in terms of receiving time and phase using coherent parameters to obtain

[0090]

[0091] The compensated signals are coherently superimposed to achieve coherent fusion of transmit and receive signals. The result is shown below:

[0092]

Claims

1. A frequency-stepped distributed coherent radar transceiver coherent fusion method, characterized in that: S1: Transmit orthogonal frequency step signal waveforms: The conventional transmitting unit transmits mutually orthogonal frequency step multi-pulse signal waveforms, which are separated by matched filtering for coherent parameter estimation; the auxiliary transmitting unit transmits fixed frequency multi-pulse signal waveforms that are orthogonal to the conventional transmitting unit, which are processed by pulse Doppler for Doppler frequency estimation. S2: Quadrature echo signal processing: The conventional receiving unit performs matched filtering on the quadrature frequency step echo signal transmitted by the conventional transmitting unit, and the auxiliary receiving unit performs matched filtering and pulse Doppler processing on the fixed frequency echo signal transmitted by the auxiliary transmitting unit. S3: Coherent parameter and Doppler frequency estimation: Extract the processed echo signals from the conventional receiving unit and the auxiliary receiving unit, and use the peak method to estimate the coherent parameters and Doppler frequency respectively; S4: Receive coherent fusion: Perform coherent parameter and Doppler frequency compensation on the multi-echo signals of each cycle, and superimpose the compensated multi-echo signals to achieve receive coherent fusion; S5: Determine if the parameter estimation accuracy meets the requirements: Calculate the signal-to-noise ratio gain after coherent fusion of the echo signals in each cycle and compare it with the coherent performance threshold. When the signal-to-noise ratio gain of the fused signal in each cycle is greater than or equal to the threshold, proceed to step S6; when the signal-to-noise ratio gain of the fused signal in any cycle is less than the threshold, proceed to S1, retransmit the quadrature frequency step signal, and perform parameter estimation. S6: Transmit coherent frequency step signal waveform: Each conventional transmitting unit transmits the same frequency step signal waveform, and the transmitted signal waveform of each transmitting unit is compensated for in time and phase using coherent parameters; S7: Wideband synthesis of pulse group signals: Matched filtering and Doppler frequency compensation are performed on multiple received signals, and then the processed multi-pulse frequency domain signals are synthesized by frequency shifting and superposition. S8: Transceiver Coherent Fusion: The broadband synthesized signal is compensated for in time and phase using coherent parameters, and the compensated signals are superimposed to achieve transmit-receive coherent fusion.

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