A subcarrier-based target matching method

Abstract

The present invention provides a subcarrier-based target matching method. The method amplifies a received reference signal and an echo signal respectively, and sequentially performs orthogonal down-conversion and A / D sampling on the reference signal and the echo signal according to DTMB signal parameters to obtain a digital reference signal and a digital echo signal. The method utilizes the correlation between the reference signal and the echo signal on the same subcarrier to remove the PN sequence, thereby resolving the problem that a conventional range-Doppler algorithm cannot effectively suppress secondary peaks caused by PN. This method effectively suppresses the effects of the delay dimension secondary peaks of the OFDM signal ambiguity function corrected based on the PN sequence on false alarms and missed alarms during target detection. The method then improves the target accumulation gain through secondary accumulation, thereby resolving the problem that the delay dimension of the OFDM signal masks weak targets during target detection after two-dimensional range-Doppler coherent processing of the reference signal and the echo signal. This method is beneficial to target detection.

Description

Technical Field

[0001] The present invention belongs to the field of radar technology, and in particular relates to a target matching method based on OFDM signal external radiation source radar. Background Art

[0002] Passive bistatic radar (PBR) is a dual / multistatic radar with separate transmitters and receivers. It does not radiate electromagnetic signals itself, but instead passively detects targets by receiving electromagnetic signals reflected from non-cooperative sources, such as frequency modulation (FM) radio, digital terrestrial multimedia broadcasting (DTMB), global navigation satellite systems (GNSS), Wi-Fi, and long-term evolution (LTE). Compared to active radar, PBR offers advantages such as high stealth, low cost, and zero electromagnetic pollution. Currently, external-source radar technology based on civilian sources such as FM radio, analog television, digital television, and mobile communications has been widely researched. Furthermore, the appropriate deployment of illuminators enables covert surveillance of targets in an area of interest. By calculating the two-dimensional (time delay and Doppler shift) correlation between the direct-arrival signal and the echo signal reflected from the target, the target's range and velocity can be measured.

[0003] Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation method that encodes digital data on multiple orthogonal subcarriers, enabling high-speed data transmission through parallel low-speed subcarriers. It offers advantages such as high spectral efficiency, robustness to intercarrier interference (ICI) and intercarrier interference (ISI), low bit error rate, and amenability to IFFT / FFT modulation and demodulation.

[0004] In radar missions, long-range detection can be achieved by increasing transmit power, antenna gain, and signal bandwidth. However, because the overall transmitter parameters related to gain are beyond the control of passive bistatic radars, passive bistatic radars typically require a lower signal-to-noise ratio (SNR). To suppress noise and improve target detection performance, signal processing methods must be employed.

[0005] In the signal processing process, in addition to the low signal-to-noise ratio, the autocorrelation of PN also brings difficulties to signal processing. PN is a pseudo-random sequence generated by a set of shift registers, so PN has a certain correlation. Taking PN420 in the DTMB system as an example, the frame header signal PN420 consists of a pre-synchronization, a PN255 sequence and a post-synchronization, with a length of 420 symbols. Pre-synchronization and post-synchronization are defined as cyclic extensions of the PN255 sequence, where the pre-synchronization length is 82 symbols and the post-synchronization length is 83 symbols. The initial condition of the shift register determines the phase of the generated PN sequence. For DTMB signals, a superframe has 225 signal frames. The pilot part of each signal frame in each superframe uses a PN signal of different phases as a signal frame identifier. Due to the characteristics of the PN code, there are strong secondary peaks in the signal processing, which leads to the problem of weak targets being covered by strong targets. In summary, it is necessary to process the PN code according to the characteristics of the DTMB signal, and the process is as follows:

[0006] like Figure 1 As shown in the figure, an exo-radiation radar uses two receiving antennas to detect targets. One antenna receives the direct wave from a non-cooperative emitter as a reference signal to obtain transmitted signal samples; the other antenna receives the echo signal reflected by the target. The reference signal and the echo signal are then subjected to two-dimensional range-Doppler coherent processing. By searching for the peak of the mutual ambiguity function between the reference signal and the echo signal on the two-dimensional delay-Doppler plane, the target's range and Doppler information can be obtained. This shows that the range-dimension peak of the OFDM signal based on PN calibration will cause false alarms during target detection, affecting detection performance. Summary of the Invention

[0007] In order to solve the above problems existing in the prior art, the present invention provides a target matching method based on OFDM signal external radiation source radar. The technical problem to be solved by the present invention is achieved by the following technical solutions:

[0008] The present invention provides a subcarrier-based target matching method comprising:

[0009] Step 1: Acquire the signal received by the DTMB external emitter radar;

[0010] The signal received by the external radiation source radar of the DTMB signal includes a reference signal and an echo signal;

[0011] Step 2: Amplify the reference signal and the echo signal respectively, and perform orthogonal down-conversion and A / D sampling on the reference signal and the echo signal respectively according to DTMB signal parameters to obtain a digital reference signal and a digital echo signal;

[0012] Step 3: For the current range unit, the pilot portion of each signal segment of the digital reference signal and the digital echo signal of the range unit is removed according to the signal frame structure, and the frame body signal portion is retained to achieve segmented processing in which each signal segment is a signal frame of the DTMB signal. The DFT method is used to perform OFDM demultiplexing operations on each frame body signal of the digital reference signal and the digital echo signal to obtain multiple subcarrier domain data of the digital reference signal and multiple subcarrier domain data of the digital echo signal;

[0013] Step 4: For the current range unit, perform a matched filtering operation on the digital reference signal and the digital echo signal in the subcarrier domain data of the same sequence number of the range unit to obtain the target matching result in each subcarrier;

[0014] Step 5: Perform non-coherent accumulation on the target matching results to obtain the final target matching result of the current distance unit;

[0015] In step 6, the offset is added to the digital echo signal as a new data echo signal, and the process from step 3 to step 5 is repeated to achieve the final target matching result for each range unit.

[0016] Optionally, the external radiation source radar of the DTMB signal is provided with a reference antenna and a receiving antenna, the reference antenna points to the DTMB radiation source, the receiving antenna points to the observation area, the signal received by the reference antenna is a reference signal, and the signal received by the receiving antenna is an echo signal.

[0017] Optionally, in step 3, the reference signal is orthogonally down-converted to obtain a baseband complex envelope of the reference signal:

[0018]

[0019] Perform orthogonal down-conversion on the echo signal to obtain the baseband complex envelope of the echo signal:

[0020]

[0021] Where d(t) is a straight wave, which is a delayed copy of s(t); N C and N T are the number of discrete stationary ground scatterers and the number of targets respectively; A, C i and T m is the complex amplitude of the direct path wave, the i-th stationary ground clutter and the m-th target; and is the i-th stationary ground scatterer and the m-th Doppler shift is f dm The target delay; n(t) is the thermal noise of the monitoring channel;

[0022] The digital reference signal is expressed as:

[0023]

[0024] The digital echo signal is expressed as:

[0025]

[0026] Among them, the symbol repetition period of the OFDM signal is T s , the pilot width is T PN , symbol frame duration T f , signal bandwidth B, sampling rate f s , each OFDM symbol contains K subcarriers, and the subcarrier spacing is 1 / T f , coherent integration time T c =L*T, L is the number of OFDM symbols contained in the coherent accumulation time, t∈[0,T c ] is a fast time variable, f c is the signal carrier frequency, C k,l It represents the transmission complex symbol on carrier k in the lth subcarrier obtained by 64QAM modulation of the transmission codeword.

[0027] Optionally, before step 3, the target matching method further includes:

[0028] Determine the starting position of the first OFDM symbol through the correlation of the PN code;

[0029] The starting position of the OFDM symbol is used as the processing position of the digital reference signal and the digital echo signal in radar signal processing.

[0030] Optionally, step 3 includes:

[0031] Step 31: Taking the processing position as a starting point, remove the pilot portion of each signal segment according to the length of the OFDM symbol, retain the frame body signal portion to achieve segmented processing of each signal segment as a signal frame of the DTMB signal, the first segment signal of the reference signal, and the second segment signal of the echo signal;

[0032] Step 32: According to the characteristics of the OFDM signal, perform demultiplexing operations on the first segment signal and the second segment signal respectively to obtain subcarrier domain data of the reference signal and subcarrier domain data of the echo signal.

[0033] Optionally, the information on carrier k can be expressed as:

[0034]

[0035] According to the form of OFDM signal, the digital echo signal is expressed as:

[0036]

[0037] The target matching result is expressed as:

[0038]

[0039] Where n = τf s Represents the subcarrier domain distance delay unit, d = Lf d / f s Represents a Doppler unit, the sampling length of the digital reference signal and the digital echo signal is N, there are L OFDM symbols in total, and the total number of subcarriers for each OFDM symbol is K, N = L (N pn +N b ), where N pn is the duration of the pilot PN, N b is the duration of the frame, S echo,k represents the subcarrier domain sampling of carrier k; H k =[h k,1 …h k,l …h k,L ] T , H is the transmission channel response of carrier k, h k,l is a complex coefficient, representing the transmission channel response of OFDM symbol l on carrier k; Q k =[C k,1 …C k,l …C k,L ] T is the symbol transmitted by carrier k, C k,l Indicates the transmission information C of OFDM symbol l on carrier k k,l The reference signal S ref Perform OFDM demodulation to obtain; Represents the corresponding element product of matrices of the same dimension; N k is the contribution of noise on carrier k, and the channel transfer function is H(f).

[0040] Optionally, the final matching result of the current distance unit is expressed as:

[0041]

[0042] Optionally, step 6 includes:

[0043] Add the offset to the digital echo signal as a new data echo signal, and repeat steps 3 to 5 to obtain the final target matching result for each range unit;

[0044] According to the final target matching result, a peak is detected on the range-Doppler plane, thereby determining the target detection corresponding to the peak.

[0045] The present invention provides a subcarrier-based target matching method that utilizes the correlation between a reference signal and an echo signal on the same subcarrier, removes the PN sequence, and performs secondary accumulation on the target. This method can address the problem that conventional range-Doppler algorithms cannot effectively suppress secondary peaks caused by PN. This method can effectively suppress the effects of the delay-dimension secondary peaks of the OFDM signal ambiguity function, which is corrected based on the PN sequence, on false alarms and missed alarms during target detection. The method then improves the target accumulation gain through secondary accumulation. This method solves the problem that the delay dimension of the OFDM signal obscures weak targets during target detection after two-dimensional range-Doppler coherent processing of the reference signal and the echo signal, thereby facilitating target detection.

[0046] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 A schematic diagram of a bistatic configuration of a Link16 signal external emitter radar according to an embodiment of the present invention;

[0048] Figure 2 A schematic flow chart of a subcarrier-based target matching method provided in an embodiment of the present invention;

[0049] Figure 3 A schematic diagram of the distance dimension results when the offset is 10 distance units in a simulation experiment of the subcarrier-based target matching method provided by an embodiment of the present invention;

[0050] Figure 4 A schematic diagram of the distance dimension results when the offset is 15 distance units in a simulation experiment of the subcarrier-based target matching method provided by an embodiment of the present invention;

[0051] Figure 5 A schematic diagram of distance dimension results in a simulation experiment of a conventional MTD method provided in an embodiment of the present invention;

[0052] Figure 6 A schematic diagram of Doppler dimension results when the offset is 10 range units in a simulation experiment of a subcarrier-based target matching method provided by an embodiment of the present invention;

[0053] Figure 7 A schematic diagram of Doppler dimension results when the offset is 15 range units in a simulation experiment of a subcarrier-based target matching method provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0054] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0055] like Figure 2 As shown, the present invention provides a subcarrier-based target matching method comprising:

[0056] Step 1: Acquire the signal received by the DTMB external emitter radar;

[0057] Among them, the signal received by the external radiation source radar of the DTMB signal includes a reference signal and an echo signal; the external radiation source radar of the DTMB signal is equipped with a reference antenna and a receiving antenna, the reference antenna points to the DTMB radiation source, and the receiving antenna points to the observation area. The signal received by the reference antenna is the reference signal, and the signal received by the receiving antenna is the echo signal.

[0058] Step 2: Amplify the reference signal and the echo signal respectively, and perform orthogonal down-conversion and A / D sampling on the reference signal and the echo signal respectively according to the DTMB signal parameters to obtain a digital reference signal and a digital echo signal;

[0059] Set the symbol repetition period T of the OFDM signal s , the pilot width is T PN , symbol frame duration T f , signal bandwidth B, sampling rate f s , each OFDM symbol contains K subcarriers, and the subcarrier spacing is 1 / T f . Coherent integration time T c =L*T, where L is the number of OFDM symbols contained in the coherent integration time. The transmitted signal is:

[0060]

[0061] where t∈[0,T c ] is a fast time variable, f c is the signal carrier frequency, C k,l represents the transmission complex symbol on carrier k in the lth subcarrier, which is modulated by 64QAM by the transmission code element. The received reference signal is down-converted, and the baseband complex envelope of the reference signal is obtained as:

[0062]

[0063] Similar to the reference signal, the baseband complex envelope of the obtained echo signal is:

[0064]

[0065] Where d(t) is the straight wave, which is the delayed copy of s(t); N C and N T are the number of discrete stationary ground scatterers and the number of targets respectively; A, C i and T mis the complex amplitude of the direct path wave, the i-th stationary ground clutter and the m-th target; and is the i-th stationary ground scatterer and the m-th Doppler shift is f dm is the time delay of the target (relative to the direct path wave); n(t) is the thermal noise of the monitoring channel.

[0066] After A / D sampling of the reference signal, the digital reference signal is expressed as:

[0067]

[0068] After A / D sampling of the echo signal, the digital echo signal is expressed as:

[0069]

[0070] Among them, the symbol repetition period of the OFDM signal is T s , the pilot width is T PN , symbol frame duration T f , signal bandwidth B, sampling rate f s , each OFDM symbol contains K subcarriers, and the subcarrier spacing is 1 / T f , coherent integration time T c =L*T, L is the number of OFDM symbols contained in the coherent accumulation time, t∈[0,T c ] is a fast time variable, f c is the signal carrier frequency, C k,l It represents the transmission complex symbol on carrier k in the lth subcarrier obtained by 64QAM modulation of the transmission codeword.

[0071] Step 3: For the current range unit, the pilot portion of each signal segment of the digital reference signal and the digital echo signal of the range unit is removed according to the signal frame structure, and the frame body signal portion is retained to achieve segmented processing in which each signal segment is a signal frame of the DTMB signal. The DFT method is used to perform OFDM demultiplexing operations on each frame body signal of the digital reference signal and the digital echo signal to obtain multiple subcarrier domain data of the digital reference signal and multiple subcarrier domain data of the digital echo signal;

[0072] Before performing segmentation processing in this step, it is necessary to determine the starting position of the first OFDM symbol through the correlation of the PN code; the starting position of the OFDM symbol is used as the processing position of the digital reference signal and the digital echo signal in radar signal processing.

[0073] It's worth noting that before performing the same PN slicing and FFT operations, the starting position of the OFDM symbol must be determined. In communication signal processing, the traditional method is to determine the starting position through the correlation of the PN code. Demodulation can then yield the reference signal data in the subcarrier domain.

[0074] In a specific optional implementation process, step 3 includes:

[0075] Step 31: Starting from the processing position, remove the pilot portion of each signal segment according to the length of the OFDM symbol, retain the frame body signal portion to achieve segmented processing of each signal segment as a signal frame of the DTMB signal, the first segment signal of the reference signal, and the second segment signal of the echo signal;

[0076] Step 32: According to the characteristics of the OFDM signal, perform demultiplexing operations on the first segment signal and the second segment signal respectively to obtain subcarrier domain data of the reference signal and subcarrier domain data of the echo signal.

[0077] Assume that the sampling length of the digital reference signal and the digital echo signal is N, they both contain L OFDM symbols and the total number of subcarriers per OFDM symbol is K. According to the characteristics of OFDM signals, N=L(N pn +N b ), where N pn is the duration of the pilot PN, N b is the duration of the frame body. The information on carrier k can be expressed as

[0078]

[0079] Among them, S echo,k represents the subcarrier domain sampling of carrier k; H k =[h k,1 …h k,l …h k,L ] T , H is the transmission channel response of carrier k, h k,l is a complex coefficient, representing the transmission channel response of OFDM symbol l on carrier k; Q k =[C k,1 …C k,l …C k,L ] T is the symbol transmitted by carrier k, C k,l Indicates the transmission information C of OFDM symbol l on carrier k k,l The reference signal S ref Perform OFDM demodulation to obtain; Represents the corresponding element product of matrices of the same dimension; N k is the contribution of noise on carrier k.

[0080] The channel transfer function can be represented by H(f). For multipath clutter, the transmission channel can be considered as a time-invariant channel during the entire processing and analysis process. However, since the target echo contains the target Doppler frequency shift, the target echo has a different propagation channel response for each symbol on the same carrier, and the propagation channel response of the lth OFDM symbol on the same carrier has a phase shift relative to the first OFDM symbol. Therefore, the target echo can be expressed as

[0081]

[0082] in,

[0083]

[0084]

[0085] The four terms on the right side of the target echo formula represent the direct wave, multipath clutter, target echo, and noise respectively. According to the formula, the channel responses of the direct wave and multipath clutter are H(f k )and For ease of analysis, since multipath clutter is a delayed copy of the direct wave, the two terms representing the direct wave and multipath clutter can be combined into one term. echo,k Can be simplified to

[0086]

[0087] in,

[0088]

[0089]

[0090] Combine the direct wave and multipath clutter in the same carrier k into one with Q k The completely correlated terms, in which the direct wave and multipath clutter contained can be eliminated by the algorithm based on the correlation between the direct wave and multipath clutter. After the elimination operation, S echo,k Only the target echo and noise contributions are included. Note that U k,m and Q k The phase difference between them is caused by the Doppler shift of the target. Although the target echo term and the reference signal have the same form in the carrier domain as in the time domain, the impact of the channel transfer function change caused by the target phase shift needs further analysis.

[0091] In order to clearly analyze the impact of the change in the transfer function, it is necessary to consider the form of a certain OFDM symbol in carrier k. According to the form of the OFDM signal, the echo signal is expressed as:

[0092]

[0093] Step 4: For the current range unit, perform a matched filtering operation on the digital reference signal and the digital echo signal in the subcarrier domain data of the same sequence number of the range unit to obtain the target matching result in each subcarrier;

[0094] The target matching result is expressed as:

[0095]

[0096] Where n = τf s Represents the subcarrier domain distance delay unit, d = Lf d / f s Represents a Doppler unit, the sampling length of the digital reference signal and the digital echo signal is N, there are L OFDM symbols in total, and the total number of subcarriers for each OFDM symbol is K, N = L (N pn +N b ), where N pn is the duration of the pilot PN, N b is the duration of the frame, S echo,k represents the subcarrier domain sampling of carrier k; H k =[h k,1 …h k,l …h k,L ] T , H is the transmission channel response of carrier k, h k,l is a complex coefficient, representing the transmission channel response of OFDM symbol l on carrier k; Q k =[C k,1 …C k,l …C k,L ] T is the symbol transmitted by carrier k, C k,l Indicates the transmission information C of OFDM symbol l on carrier k k,l The reference signal S ref Perform OFDM demodulation to obtain; Represents the corresponding element product of matrices of the same dimension; N k is the contribution of noise on carrier k, and the channel transfer function is H(f).

[0097] Step 5: Perform non-coherent accumulation on the target matching results to obtain the final target matching result of the current distance unit;

[0098] Among them, the final matching result of the current distance unit is expressed as:

[0099]

[0100] In step 6, the offset is added to the digital echo signal as a new data echo signal, and the process from step 3 to step 5 is repeated to achieve the final target matching result for each range unit.

[0101] In a specific optional implementation process: Step 6 includes:

[0102] Add the offset to the digital echo signal as a new data echo signal, and repeat steps 3 to 5 to obtain the final target matching result for each range unit;

[0103] According to the final target matching result, a peak is detected on the range-Doppler plane, thereby determining the target detection corresponding to the peak.

[0104] For the convenience of analysis, the clutter cancellation algorithm can eliminate the influence of direct waves and multipath, so only the form of the target reflected echo is considered, and the noise itself has no correlation with the reference signal. Obviously, although the reference signal can be obtained through demodulation, it is unrealistic to find the frame header position of the target echo through the PN code because the signal-to-noise ratio of the target echo is not ideal. Therefore, it is necessary to add an offset to the target echo. All distance units are detected in this process. At the same time, since each OFDM code element requires PN cutting and FFT operation, no matter what the detection distance is, the upper limit of the offset will not exceed the length of an OFDM code element, that is, an offset of the length of an OFDM symbol will directly realize the detection of all distance units. Adding an offset to the target echo is equivalent to adding an offset to the delay τ m Therefore, the target echo can be expressed as

[0105]

[0106] After adding different offsets, the echoes need to be de-OFDMed again, and steps 3 through 5 are repeated to obtain the accumulated results for different range bins. The final transformation results show that |ψ(r, d, k)| will peak at the target location on the range-Doppler plane, thus completing target detection.

[0107] As can be seen from the specific embodiments of the present invention, the specific concept of the present invention is as follows: due to the strong correlation between PN sequences, the delay dimension of the reference signal and the echo signal undergoes two-dimensional range-Doppler coherent processing, resulting in a secondary peak in the time dimension. Furthermore, due to the frame structure of the DTMB signal, the Doppler dimension of the reference signal and the echo signal undergoes two-dimensional range-Doppler coherent processing, resulting in a secondary peak at the signal frame period. These secondary peaks in the two-dimensional delay-Doppler plane seriously affect target detection performance. Therefore, the PN sequence is first removed and the signal is transformed into the carrier domain. Then, two-dimensional range-Doppler coherent processing is performed on the different subcarrier signals. Finally, non-coherent accumulation is performed on the different subcarrier signals to suppress the range secondary peak and improve the target detection signal-to-noise ratio.

[0108] The present invention provides a subcarrier-based target matching method that utilizes the correlation between a reference signal and an echo signal on the same subcarrier, removes the PN sequence, and performs secondary accumulation on the target. This method can address the problem that conventional range-Doppler algorithms cannot effectively suppress secondary peaks caused by PN. This method can effectively suppress the effects of the delay-dimension secondary peaks of the OFDM signal ambiguity function, which is corrected based on the PN sequence, on false alarms and missed alarms during target detection. The method then improves the target accumulation gain through secondary accumulation. This method solves the problem that the delay dimension of the OFDM signal obscures weak targets during target detection after two-dimensional range-Doppler coherent processing of the reference signal and the echo signal, thereby facilitating target detection.

[0109] The performance of the subcarrier-based target matching method provided by the present invention is verified through simulation experiments below.

[0110] 1. Simulation conditions of the embodiment of the present invention:

[0111] In the experiment of the present invention, the symbol repetition period of the OFDM signal is set to T = 555.6 μs, and the pilot width is T PN =55.6μs, symbol frame duration T f =500μs, signal bandwidth B = 7.56MHz sampling rate f s =7.56 MHz, each OFDM symbol contains 3780 subcarriers, and the subcarrier spacing is 2 kHz. The coherent integration time T = 0.125 s, which means that the coherent processing time includes 225 OFDM symbols. The digital signal obtained by downsampling the reference signal and echo signal is a complex signal of length N = 850500.

[0112] The PN sequence forms the frame header and is generated according to the DTMB standard. The transport bit stream in the frame body is randomly generated, modulated using 64QAM, and finally transmitted to each subcarrier via IFFT.

[0113] The reference signal contains only the transmitted signal and noise components. The multipath clutter in the echo signal is eliminated using the ECA algorithm, and the noise is modeled as complex Gaussian white noise.

[0114] The first simulation experiment was designed to verify the effectiveness of this method in suppressing the secondary peaks of the PN pilot. Based on the above settings, the target echo contained information from two targets: one in the 15th range bin with a Doppler shift of 10Hz and a signal-to-noise ratio of 0dB, and the other in the 10th range bin with a Doppler shift of 9Hz and a signal-to-noise ratio of -40dB.

[0115] 2. Analysis of simulation results of the experiment of the present invention:

[0116] Figure 3 It is the result range unit of the method of the present invention when offset=10, corresponding to the 10th range unit. Figure 4 That’s right. Figure 5 This is the range of cells for MTD test results. Figure 2 、 Figure 4 and Figure 5 It can be seen that in traditional methods, due to the influence of PN, the secondary peaks of stronger targets will cover the weaker targets. This makes the weaker targets almost impossible to detect. In the method proposed in this invention, since different range bins are processed separately, targets in different range bins are detected separately. Despite this, the target in the 10th range bin is still clearly visible. Therefore, it can be concluded that the method proposed in this invention can effectively improve the problem of target masking caused by secondary peak noise caused by PN.

[0117] The second simulation experiment verified the robustness of this method to noise. The signal format was identical to the first simulation experiment. The difference was that in the second simulation, only one target echo was present in the 10th range bin, with a Doppler shift of 5 Hz and a signal-to-noise ratio as low as -40 dB.

[0118] Figure 6 The Doppler dimension results of the proposed method when the offset is 10. Figure 7 The MTD results are shown in Doppler. Figure 6 and Figure 7 It is clear that the traditional MTD method is unable to detect the target. When the target echo signal-to-noise ratio is low, the noise energy overwhelms the target echo. However, after processing with the method of the present invention, the target echo energy remains approximately 5dB above the noise floor. Therefore, it can be concluded that compared with the traditional method, the proposed method is more robust to noise.

[0119] Although the present application is described herein in conjunction with various embodiments, in the process of implementing the claimed application, those skilled in the art can understand and implement other changes to the disclosed embodiments by reviewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude multiple situations. A single processor or other unit can implement several functions listed in the claims. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0120] The above is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should be considered to fall within the scope of protection of the present invention.

Claims

1. A subcarrier-based target matching method, characterized in that: include: Step 1: Acquire the signal received by the DTMB external emitter radar; The signal received by the external radiation source radar of the DTMB signal includes a reference signal and an echo signal; Step 2: Amplify the reference signal and the echo signal respectively, and perform orthogonal down-conversion and A / D sampling on the reference signal and the echo signal respectively according to DTMB signal parameters to obtain a digital reference signal and a digital echo signal; Step 3: For the current range unit, the pilot portion of each signal segment of the digital reference signal and the digital echo signal of the range unit is removed according to the signal frame structure, and the frame body signal portion is retained to achieve segmented processing in which each signal segment is a signal frame of the DTMB signal. The DFT method is used to perform OFDM demultiplexing operations on each frame body signal of the digital reference signal and the digital echo signal to obtain multiple subcarrier domain data of the digital reference signal and multiple subcarrier domain data of the digital echo signal; Step 4: For the current range unit, perform a matched filtering operation on the digital reference signal and the digital echo signal of the range unit in the subcarrier domain data of the same sequence number to obtain the target matching result in each subcarrier; Step 5: Perform non-coherent accumulation on the target matching results to obtain the final target matching result of the current distance unit; Step 6: Add the offset to the digital echo signal as a new data echo signal, and repeat the process from step 3 to step 5 to achieve the final target matching result for each range cell; The step 3 comprises: Step 31: Taking the processing position as a starting point, remove the pilot portion of each signal segment according to the length of the OFDM symbol, retain the frame body signal portion to achieve segmented processing of each signal segment as a signal frame of the DTMB signal, the first segment signal of the reference signal, and the second segment signal of the echo signal; Step 32: According to the characteristics of the OFDM signal, perform demultiplexing operations on the first segment signal and the second segment signal respectively to obtain subcarrier domain data of the reference signal and subcarrier domain data of the echo signal.

2. The subcarrier-based target matching method according to claim 1, characterized in that: The external radiation source radar of the DTMB signal is provided with a reference antenna and a receiving antenna. The reference antenna points to the DTMB radiation source, and the receiving antenna points to the observation area. The signal received by the reference antenna is a reference signal, and the signal received by the receiving antenna is an echo signal.

3. The subcarrier-based target matching method according to claim 1, wherein: In step 3, the reference signal is orthogonally down-converted to obtain the baseband complex envelope of the reference signal: Perform orthogonal down-conversion on the echo signal to obtain the baseband complex envelope of the echo signal: Where d(t) is a straight wave, which is a delayed copy of s(t); N C and N T are the number of discrete stationary ground scatterers and the number of targets respectively; A, C i and T m is the complex amplitude of the direct path wave, the i-th stationary ground clutter and the m-th target; and is the i-th stationary ground scatterer and the m-th Doppler shift is f dm The target delay; n(t) is the thermal noise of the monitoring channel; The digital reference signal is expressed as: The digital echo signal is expressed as: Among them, the symbol repetition period of the OFDM signal is T s , the pilot width is T PN , symbol frame duration T f , signal bandwidth B, sampling rate f s , each OFDM symbol contains K subcarriers, and the subcarrier spacing is 1 / T f , coherent integration time T c =L*T, L is the number of OFDM symbols contained in the coherent accumulation time, t∈[0,T c ] is a fast time variable, f c is the signal carrier frequency, C k,l It represents the transmission complex symbol on carrier k in the lth subcarrier obtained by 64QAM modulation of the transmission codeword.

4. The subcarrier-based target matching method according to claim 1, characterized in that: Before step 3, the target matching method further includes: Determine the starting position of the first OFDM symbol through the correlation of the PN code; The starting position of the OFDM symbol is used as the processing position of the digital reference signal and the digital echo signal in radar signal processing.

5. The subcarrier-based target matching method according to claim 1, wherein: The information on carrier k can be expressed as: According to the form of OFDM signal, the digital echo signal is expressed as: The target matching result is expressed as: Where n = τf s Represents the subcarrier domain distance delay unit, d = Lf d / f s Represents a Doppler unit, the sampling length of the digital reference signal and the digital echo signal is N, there are L OFDM symbols in total, and the total number of subcarriers for each OFDM symbol is K, N = L (N pn +N b ), where N pn is the duration of the pilot PN, N b is the duration of the frame, S echo,k represents the subcarrier domain sampling of carrier k; H k =[h k,1 …h k,l …h k,L ] T , H is the transmission channel response of carrier k, h k,l is a complex coefficient, representing the transmission channel response of OFDM symbol l on carrier k; Q k =[C k,1 …C k,l …C k,L ] T is the symbol transmitted by carrier k, C k,l Indicates the transmission information C of OFDM symbol l on carrier k k,l The reference signal S ref Perform OFDM demodulation to obtain; Represents the corresponding element product of matrices of the same dimension; N k is the contribution of noise on carrier k, and the channel transfer function is H(f).

6. The subcarrier-based target matching method according to claim 5, characterized in that: The final matching result of the current distance unit is expressed as:

7. The subcarrier-based target matching method according to claim 6, characterized in that: The step 6 comprises: Add the offset to the digital echo signal as a new data echo signal, and repeat steps 3 to 5 to obtain the final target matching result for each range unit; According to the final target matching result, a peak is detected on the range-Doppler plane, thereby determining the target detection corresponding to the peak.

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