Design method of integrated signal of orthogonal frequency division LFM detection communication based on sidelobe QAM

Abstract

The application discloses a sidelobe QAM-based orthogonal frequency division LFM detection communication integrated signal design method, a set of transmission weight vectors is designed by establishing an optimization problem, the transmission map of the integrated signal is stable in a detection main lobe amplitude, QAM communication is realized in a sidelobe communication direction, and higher information transmission rate is realized; in a pulse repetition period, each LFM signal selects a corresponding transmission weight vector according to carried communication information, and carries the communication information in the sidelobe communication direction in a QAM modulation mode; a communication receiving end carries out matched filtering on each LFM signal, calculates the amplitude of the signal and the phase difference from the first signal, and obtains a corresponding QAM constellation point; a radar receiving end obtains target delay and Doppler information after carrying out receiving beam forming, matched filtering and complex gain compensation on the signal. The application uses the orthogonal frequency division LFM signal and the sidelobe QAM modulation method, and greatly improves the communication performance on the premise of ensuring the stability of the radar detection capability.

Description

Technical Field

[0001] This invention pertains to detection and communication technology, specifically relating to an integrated signal design method for detection and communication based on sidelobe QAM and orthogonal frequency division linear frequency modulation (LFM). Background Technology

[0002] Integrated detection and communication is a technology that integrates communication and radar detection functions into a single system. By sharing spectrum resources and hardware equipment, it simultaneously performs communication and radar detection functions, effectively reducing the hardware costs of system construction and alleviating the current shortage of wireless spectrum resources. The key to achieving integrated detection and communication lies in reasonable waveform design and reliable signal processing methods. This involves designing an integrated waveform that can satisfy both radar detection functions and stable, high-speed transmission of communication information, and designing an integrated signal processing method corresponding to this waveform to complete the extraction of radar detection information and the modulation and demodulation of communication information.

[0003] Integrated signal design in the spatial dimension typically utilizes the directivity of array antennas and assumes that radar detection targets and communication targets are at different angular positions and do not interfere with each other. Therefore, the amplitude and phase of signals in different detection and communication directions can be controlled by designing the transmit weight vector of the array antenna, thereby realizing radar detection and communication functions. One more specific approach is to use the main lobe of the beam for radar detection and transmit communication information by controlling the changes in the side lobes.The paper "J. Euziere, R. Guinvarc'h, M. Lesturgie, B. Uguen, and R. Gillard, “Dual function radar communication time-modulated array,” presented at the Int. Radar Conf., Lille, France, Oct. 2014" proposes an integrated detection and communication method that embeds information using a time-modulated array. This method controls the signal level received by the communication receiver by adjusting the phase of the transmit array between different pulses. Different signal levels represent corresponding communication symbols. However, the optimization problem based on the time-modulated array has high nonlinearity and computational complexity, making it difficult to solve and allocate energy. The paper "A. Hassanien, MG Amin, YD Zhang, F. Ahmad, Dual-function radar communications: information embedding using sidelobe control and waveform diversity, IEEE Trans. Signal Process. 64 (8) (2016)" proposes a similar method. The method 2168–2181 uses sidelobe level modulation to transmit communication information while ensuring the stability of the main lobe amplitude. Furthermore, it proposes using multiple non-interfering orthogonal waveforms to transmit different communication information, thereby increasing the communication rate and reducing the bit error rate. Its drawback is that the simple amplitude modulation method transmits communication information by controlling the sidelobe level, resulting in a low information content, and this method can only transmit the same communication information to different communication users. The paper "A. Hassanien, MG Amin, YDZhang, F. Ahmad and B. Himed, "Non-coherent PSK-based dual-function radar-communication systems," 2016 IEEE Radar Conference (RadarConf), Philadelphia, PA, USA, 2016" uses sidelobe phase modulation to transmit communication information. The receiving end obtains the communication information through coherent demodulation or non-coherent demodulation. However, this method also suffers from low information transmission rate and is limited to uniform linear arrays.

[0004] ASK transmits information by controlling the amplitude of the signal, while PSK transmits information by controlling the phase of the signal. QAM modulation combines ASK and PSK methods, modulating the signal in both amplitude and phase dimensions to include richer communication information. For linear frequency modulation (LFM) signals, by adjusting the frequency range and modulation slope of each signal to ensure their spectra do not overlap, orthogonality between signals can be maintained, generating a set of orthogonally frequency-divided LFM signals as the carrier of an integrated signal. Summary of the Invention

[0005] The problem this invention aims to solve is to select a suitable sidelobe modulation method and integrated waveform in scenarios where the radar detection target and the communication target are not in the same direction, so as to enable the sidelobe communication end to have faster and more stable performance while ensuring that the radar detection function is not affected.

[0006] The technical solution adopted by this invention to solve the above-mentioned technical problems is an integrated signal design method for detection and communication based on sidelobe QAM, comprising the following steps:

[0007] Within a single transmission cycle, a set of orthogonal frequency division multiplexing (OFDM) LFM signals is used to simultaneously perform detection and communication functions. Each LFM signal adjusts its corresponding transmit antenna weight vector according to the QAM communication information it carries, achieving QAM modulation in the communication direction of the sidelobe while ensuring stable signal amplitude in the detection main lobe direction. This set of OFDM LFM signals with selected transmit weight vectors is then superimposed and transmitted as an integrated signal. The communication receiver first down-converts the received signal to obtain a baseband signal, then separates it into individual orthogonal signals through matched filtering. Amplitude and phase decisions are made on each separated orthogonal signal to demodulate the QAM communication symbol information it carries. The radar receiver beamforms the signals received in the receiving array, then performs matched filtering to separate the individual orthogonal linear frequency modulated (LFM) signals. After complex gain compensation, the individual LFM signals are superimposed to extract the target's time delay and Doppler information.

[0008] This invention combines orthogonal frequency division multiplexing (LFM) with sidelobe-controlled integrated detection and communication signals, and provides corresponding signal processing methods. It utilizes a set of orthogonal frequency division multiplexing (LFM) signals to achieve high-speed and stable transmission of communication symbols, while ensuring the reliability of radar detection functions, thus achieving a balance between radar detection performance and communication performance.

[0009] The beneficial effects of this invention are: using multiple orthogonal frequency division LFM signals to transmit information and adopting QAM modulation significantly improves the communication rate; the orthogonal frequency division LFM signals are in different frequency ranges, which can maintain the non-interference between different signal carriers and ensure the stability of communication performance; the radar detection and communication are at different angular positions, and the transmission weight vector design ensures the stability of the radar main lobe amplitude, thus maintaining the radar detection performance unaffected by the communication function. Attached Figure Description

[0010] Figure 1 This is a flowchart illustrating the method of the present invention;

[0011] Figure 2 It is a graph showing the relationship between the normalized transmit power and the angle of the generated weight vector;

[0012] Figure 3 This is a comparison chart of the bit error rates of communication functions;

[0013] Figure 4 This is a comparison chart showing the impact of the number of orthogonal signals on the communication receiver; Figure 4 In the example, (a) represents a single frequency division LFM signal, and (b) represents 100 frequency division LFM signals.

[0014] Figure 5 This is a graph showing the accuracy of radar angle measurement. Detailed Implementation

[0015] An integrated radar-communication method based on spatial sidelobe QAM, such as... Figure 1 As shown, it includes the following steps:

[0016] Step 1: Design a set of transmit weight vectors so that after selecting the appropriate weight vectors, the orthogonal LFM signals can maintain stable signal amplitude in the direction of the main lobe and obtain the desired QAM communication symbols in the specific sidelobe communication direction. The communication information is determined by the amplitude and phase of the sidelobe signals.

[0017] While ensuring the stability of the main lobe and limiting the sidelobes, a weight vector is designed to precisely control the amplitude and phase of the signal in a specified communication direction, making it correspond to QAM constellation points, thereby achieving the embedding of sidelobe communication information. Specifically, the design concept of the weight vector is as follows:

[0018] Assuming the radar operates in a certain spatial sector... That is, the detection range of the main lobe is In order to maintain the stability of the signal amplitude in the direction of the main lobe, the objective function is set to minimize the difference between the desired transmit beam pattern and the actual transmit beam pattern. In the sidelobe region, to avoid interfering with the normal function of the radar, the voltage level in the sidelobe region is constrained to be below a preset threshold. That is, the maximum level of the sidelobe; in the communication direction The level and phase of the constrained integrated signal are equal to a specific value, representing a specific QAM communication symbol. Indexed by the direction of the main lobe. The total number of directions in the direction of the main lobe. For side lobe direction indexing The total number of directions in the direction of the side lobes For communication direction index, This represents the total number of communication directions.

[0019] The weight vector design problem is modeled as follows:

[0020] ;

[0021] in, Indicates that under given constraints Below, by adjusting the beamforming weight vector Minimize the direction of the main lobe of the detector The maximum deviation between the actual and expected radiation patterns in the image. Let k be the weight vector for the k-th transmitted beamforming. This represents the desired transmit beam pattern, where the superscript j represents the imaginary unit. For direction The launch steering vector, The set maximum sidelobe level, It is the direction of communication. phase, It is the k-th waveform in the communication direction The sidelobe level set above (i.e., the amplitude component of the QAM symbol). This indicates the conjugate transpose.

[0022] The optimization problem described above is a convex optimization problem, and solving it yields a set of emission weight vectors.

[0023] Step 2: Select a set of orthogonal frequency division multiplexing (OFDM) signals as the integrated signal, and select the corresponding weight vector according to the QAM communication symbol carried by each signal, so that the signal can simultaneously perform radar detection and communication functions. Each orthogonal OFDM waveform... Each beam corresponds to an independent transmit beam, which is composed of transmit weight vectors. It is determined that different waveforms can be configured with different weight vectors, thereby carrying different QAM communication symbols on different waveforms.

[0024] Specifically, select an appropriate modulation slope. and frequency interval A set of baseband orthogonal frequency division LFM signals was obtained. The k-th LFM waveform Waveform Index ,Right now:

[0025] ;

[0026] in, The starting frequency, For continuous time, It is the modulation slope. , It is the bandwidth of the subband. It is the pulse width. This represents the number of waveforms in a set of orthogonal waveforms. Let... =0, the sending end selects the weight vector based on the communication information. It acts on a specific LFM signal, thereby embedding communication information into the radar signal and transmitting the signal. It can be represented as:

[0027] ;

[0028] in, Total transmission power, This indicates taking the conjugate.

[0029] Theoretically, the more orthogonal waveforms there are, the higher the communication rate. However, this will increase the signal bandwidth. Furthermore, since the weighted waveforms are not absolutely orthogonal, there is mutual influence between the signals, which will lead to an increase in the bit error rate. Therefore, a balance needs to be struck between the communication rate and the bit error rate.

[0030] This invention employs incoherent modulation, requiring the design of an additional reference signal. This reference signal is orthogonal to all other signals. A separate set of weight vectors is used to beamform the reference signal waveform. This invention... As a phase reference signal.

[0031] Step 3: The communication receiver performs analog-to-digital conversion (A / D) and down-conversion on the received integrated detection and communication signal to obtain the baseband signal. Then, it performs matched filtering on the baseband signal to obtain the communication symbol carried by each LFM waveform and obtain the transmission data.

[0032] Specifically, assuming the communication receiver has a single antenna, the baseband signal received by the communication receiver of the j-th user is... Represented as:

[0033] ;

[0034] in, The channel coefficient represents the received signal, and it is determined by the characteristics of the propagation environment between the transmitting array and the communication receiver. Indicates transpose. This represents the signal delay for the j-th user. This represents zero-mean additive white Gaussian noise. (The remaining text appears to be incomplete and fragmented, possibly due to OCR errors. A more accurate translation would require the full context.) One transmitted signal Matched filtering can separate K orthogonal LFM signals to obtain the j-th user receiver. The received signal is then compared with the j-th LFM signal. One transmitted waveform The result after matched filtering :

[0035] ;

[0036] in, The received waveforms are respectively With transmitted waveform The result after matched filtering, in time The maximum value is generated at a certain point, and its maximum value is related to the energy of the signal. This is the result of matching and filtering other signals and noise with the transmitted waveform. Because it is incoherent communication and the first LFM waveform is used as the reference waveform, the calculation is as follows:

[0037] ;

[0038] in, Indicates the angular direction of the communication user. In direction Above, the first The ratio of the matched filtering result of the individual waveform to that of the reference waveform is used to demodulate the QAM symbols. and Indicates the first The transmitted LFM signal is located at an angle of... The amplitude and phase of the QAM communication symbols carried by the communication receiver. According to amplitude and phase The amplitude and phase of the result are compared with a preset threshold value and mapped to the nearest constellation point to determine the corresponding communication symbol and recover the transmission data.

[0039] Step 4: The radar receiver performs analog-to-digital conversion (A / D) and down-conversion on the integrated signals received by different antennas to obtain the baseband signal. The baseband signal is then beamformed, and different LFM echo signals are separated by matched filtering. Each LFM echo signal is then superimposed after complex gain compensation. Finally, the target echo delay is determined based on the peak position of the superimposed signal. Then, MTD processing technology is used to perform FFT operations between different pulses to obtain the target Doppler frequency information.

[0040] Specifically, the baseband signal received by the radar receiving antenna Represented as:

[0041] ;

[0042] in, This indicates the total number of targets detected by the radar. For the target index, For the first One goal The direction in which it is located. Indicates the first The reflection coefficient of the target; and They are N×1 dimensional and M×1 dimensional in the direction respectively. The transmit and receive steering vectors are given, where N and M represent the number of antenna elements in the transmit and receive arrays, respectively. This indicates a baseband signal that takes Doppler frequency into account. This represents the dot product. It is the first The Doppler frequency of the target For the first The echo delay of each target; The signal received by the antenna sidelobe is represented by an M×1 dimensional vector. This represents zero-mean additive white Gaussian noise.

[0043] exist The direction is used to perform receive beamforming on the baseband signal, resulting in:

[0044] ;

[0045] in, This indicates the beamforming direction of the radar receiver, i.e., the angle at which the radar receiver points. This is the received beam vector. The received beamformed signal is compared with the first... One transmitted waveform The output of a single waveform after matched filtering is as follows:

[0046] ;

[0047] in, This is the transmitted beam pattern. For receiving beam pattern; To receive waveforms With the kth transmitted waveform The result after matched filtering, in time The maximum value is generated at that point. It is the result of matching filtering other signals and noise with the transmitted waveform.

[0048] because It is relatively small, therefore The term can be ignored. After complex gain compensation of the signal, the results of all matched filtering are superimposed to obtain the final radar detection result after all vector compensation. :

[0049] ;

[0050] in, For coefficient terms, ; This represents the sum of other signals and noise after all waveforms have been matched and filtered. Each waveform After matched filtering, the true time delay of the target echo will be within the range. A peak value is generated at this point. When the outputs of these waveforms are superimposed, the peak value remains at [location missing]. Furthermore, due to energy accumulation, the peak value is more prominent and easier to detect. Therefore... All in The maximum value is generated at that point, and the maximum amplitude still exists after superposition. Therefore, the target echo delay can be determined based on the location of the peak value. After the above operations, the output signal differs in phase between different pulses. This phase difference is mainly caused by the Doppler effect caused by the target's motion. In order to further extract the target's Doppler frequency information, the system adopts MTD processing technology to perform FFT operation between different pulses, compensate for the phase difference, realize the coherent accumulation of the signal, and obtain the target's Doppler frequency information in the phase. The target's distance and radial velocity can be calculated by using the target echo delay and the target's Doppler frequency information.

[0051] Simulation Experiment

[0052] The effectiveness of this invention is verified below with reference to the accompanying drawings and simulation experiments. The order of QAM is set to 16, meaning each communication symbol represents 4 bits of information. The channel coefficients are modeled as random variables with constant magnitude and uniformly distributed random phase. The radar signal carrier frequency is 5GHz, and the total bandwidth B is 50MHz. The total bandwidth is divided into 100 sub-bands, generating a set of frequency division orthogonal LFM signals with a bandwidth of 0.5MHz and a pulse width of 50 microseconds. The reference signal is used for phase reference, and the phase... =0, sidelobe level =0.1, and the bandwidth is also 0.5MHz. The PRF is set to 5kHz, and each quadrature signal can transmit 20kbit of communication data within one pulse, so the total communication rate is 2M bit / s.

[0053] Consider a communication user at an angle of -30°, with the maximum communication sidelobe level set to 0.1, the number of transmitting antenna array elements being 16, and a uniform linear array being used. The targets are located at spatial angles of 25° and 27° respectively. It is assumed that the target reflection coefficient is constant during each radar pulse, but varies with the pulse and follows a uniform distribution. The radar beam points at 30°, and the pulse accumulation number is 256.

[0054] Figure 2 This is a graph showing the relationship between the normalized transmit power and angle of the generated weight vectors. All weight vectors have almost identical radiation patterns within the main beam, but there are differences in the amplitude and phase of the radiation patterns in the communication direction, which correspond one-to-one with the amplitude and phase on the constellation diagram.

[0055] Figure 3 It is randomly generated. The bit error rate (BER) graph was obtained by testing the communication function using 1 symbol. Compared with sidelobe QAM without orthogonal signals, this method has a slightly higher BER at the same signal-to-noise ratio, but the communication rate is improved.

[0056] Figure 4 This chart compares the impact of an excessive number of orthogonal signals on the communication receiver. Because the signals are not perfectly orthogonal, as the number of frequency-division LFM signals increases, the interference between them intensifies, affecting the matched filtering result. This leads to distortion of the output waveform and a shift in the signal's peak value. Therefore, it is necessary to select an appropriate number of orthogonal signals to ensure a balance between communication performance stability and high efficiency.

[0057] Figure 5 This is a graph showing the radar angle measurement accuracy results. 200 experiments were conducted for different signal-to-noise ratios, demonstrating that the radar detection RMSE decreases as the signal-to-noise ratio increases, and it maintains good performance.

[0058] Table 1 records the range and velocity detection results for five radar-simulated targets. The targets were located at spatial angles of 25° to 35°, with the radar beam pointing at 30° and a signal-to-noise ratio of 0dB. The actual range and velocity of the targets are shown in the table. Compared with the test results from pure radar, the accuracy of radar velocity and range measurement errors obtained from the integrated waveform showed almost no decrease, maintaining good detection capabilities.

[0059] Actual distance (km) Distance measurement (km) Distance error (km) Actual speed (m / s) Velocity measurement (m / s) Velocity error (m / s) 10 10.001 0.001 100 100.781 0.781 25 25.002 0.002 120 120.703 0.703 15 15.001 0.001 110 110.742 0.742 25 25.002 0.002 100 100.781 0.781 20 20.001 0.001 80 80.859 0.859

[0060] The above simulation experiments have verified the effectiveness and reliability of the present invention.

[0061] In summary, the integrated detection and communication signal design method based on sidelobe QAM uses QAM modulation and orthogonal frequency division LFM signals to carry communication information, which greatly improves the communication rate while ensuring the stability of radar detection function and achieving a balance between detection and communication performance.

Claims

1. A method for integrated signal design of orthogonal frequency division LFM detection and communication based on sidelobe QAM, characterized in that, include: Within a transmission cycle, a set of orthogonal frequency division linear frequency modulation (LFM) signals, which maintain orthogonality by setting different frequency offsets to prevent spectrum overlap, are used as an integrated signal carrier. Each LFM signal selects the corresponding transmit antenna weight vector according to the orthogonal amplitude modulation (QAM) communication information it carries, completes orthogonal amplitude modulation in the sidelobe communication direction, and maintains stable signal amplitude in the main lobe detection direction. The integrated signal is transmitted by superimposing the individual orthogonal frequency division LFM signals after selecting the transmission weight vector; The communication receiver down-converts the received signal to obtain the baseband signal, separates each quadrature signal through matched filtering, performs amplitude and phase determination on each separated quadrature signal, and demodulates the quadrature amplitude modulation communication symbol information carried by it. The radar receiver performs beamforming on the signals received from the receiving array, then performs matched filtering to separate the orthogonal LFM signals. After complex gain compensation, the LFM signals are superimposed to extract the target's time delay and Doppler information.

2. The method as described in claim 1, wherein the k-th LFM waveform selects the transmission weight vector based on the QAM communication information it carries. It is superimposed with other waveforms to form an integrated baseband transmission signal. : ； in, Total transmission power, For continuous time, Indicates taking the conjugate. The waveform index represents the number of waveforms in a set of orthogonal waveforms. , Let k be the weight vector for the k-th transmitted beamforming. This is the k-th LFM waveform.

3. The method as described in claim 2, characterized in that, Orthogonal Frequency Division Multiplexing (LFM) signals prevent overlap in the frequency domain by setting different frequency offsets. The k-th LFM waveform... Represented as: ; in, The starting frequency, It is the modulation slope. , It is the bandwidth of the subband. It is the pulse width, and the superscript j is the imaginary unit.

4. The method as described in claim 1, characterized in that, The radar receiver performs beamforming in the direction of target detection and uses orthogonal LFM waveforms. The output signal after matching filtering of each waveform is obtained by performing matched filtering separately. Waveform Index , This indicates the number of waveforms in a set of orthogonal waveforms.

5. The method as described in claim 4, characterized in that, For output signal Complex gain compensation is performed, and the results of all matched filters are superimposed to obtain the final radar detection result after all vector compensation and superposition. : ； in, For beamforming direction, For direction The launch steering vector, This indicates the conjugate transpose.

6. The method as described in claim 5, characterized in that, The output signal after matched filtering contains the time delay information of the detected target. This time delay information is manifested as a peak value generated at the target echo time delay after the received waveform and the transmitted waveform are matched and filtered. After the matched and filtered outputs of all waveforms are superimposed, the peak value still exists at the same time delay position. The target echo delay can be determined based on the position of the peak value.

7. The method as described in claim 6, characterized in that, After determining the target echo delay, the phase difference between different pulses is used to extract Doppler frequency information, thereby obtaining the target's relative velocity.

8. The method as described in claim 1, characterized in that, The communication employs incoherent modulation, with an additional reference signal designed that is orthogonal to all other signals. A separate set of weight vectors is used to beamform the reference signal waveform; here, the first LFM waveform of an orthogonal frequency division multiplexing (OFDM) waveform is employed. As a phase reference signal; in the angular direction where the communication user is located Above, the first The ratio of the matched filtering results of the LFM waveform to the reference waveform : ； in, Indicates the first The received signal of the first communication user terminal is the same as that of the second. One transmitted LFM signal The result after matched filtering.

9. The method as described in claim 1, characterized in that, The transmit antenna weight vector is obtained by solving the following optimization problem: ； in, Let k be the weight vector for the k-th transmitted beamforming. To detect the range of the main lobe, It is the side lobe region. Indexed by the direction of the main lobe. The total number of directions in the direction of the main lobe. For side lobe direction indexing The total number of directions in the direction of the side lobes For communication direction index, This represents the total number of communication directions. Indicates that under given constraints Below, by adjusting the beamforming weight vector Minimize the direction of the main lobe of the detector The maximum deviation between the actual and expected radiation patterns in the system; This represents the desired transmit beam pattern, where the superscript j represents the imaginary unit. For direction The launch steering vector, The set maximum sidelobe level, It is the direction of communication. phase, It is the first The LFM waveform in the communication direction The sidelobe level set above, This indicates the conjugate transpose.

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