FDA-MIMO radar communication integrated transmitting beam forming method

Abstract

The invention discloses an FDA-MIMO radar communication integrated transmitting beam forming method. The method comprises the following steps: constructing an FDA-MIMO radar communication integrated signal model; deducing a signal processing model of a communication receiving end; realizing communication information embedding based on beam pattern modulation through transmitting beam forming; designing a transmitting beam forming matrix to ensure the radar detection performance; establishing an FDA-MIMO radar communication integrated transmitted beam forming optimization model; and solving the optimization model by adopting a barrier function algorithm. According to the method, the beam performance of radar detection is met, multi-user communication information embedding is achieved, an eavesdropping user is prevented from intercepting the multi-user communication information at a time, the optimal transmitting beam forming matrix obtained by solving the optimization model is applied to a radar communication integrated transmitting end based on FDA-MIMO, and the transmission efficiency of the radar communication integrated transmitting end is improved. The detection and communication performance of the radar communication integrated system is effectively improved.

Description

Technical Field

[0001] The invention relates to beamforming and signal processing technology, and in particular to an FDA-MIMO radar communication integrated transmission beamforming method. Background Art

[0002] With the rapid development and widespread application of modern electronic information technology. Airborne combat platforms have put forward higher requirements for radar target detection and wireless communication performance. However, with the increasing number of various detection and communication equipment, the complexity and hardware cost of airborne systems have also increased, spectrum resources have become crowded, and the electromagnetic environment has gradually deteriorated. Dual-function radar-communication (DFRC) is regarded as a key technology to solve the above problems. The integrated design of radar and communication systems can enable radar and communication to share spectrum resources, effectively reduce electromagnetic interference between airborne radar and communication systems, and reduce the number and cost of airborne terminals. In fact, radar and communication have similarities in hardware structure and working principles, which lays the foundation for the realization of radar communication integration system.

[0003] At present, most of the existing radar communication integration design schemes are based on single antenna and phased array systems. These schemes all have the disadvantage that the radar or communication performance cannot achieve the expected results. Early single-antenna radar communication integration systems had many bottleneck problems that could not be broken through, such as high bit error rate, poor confidentiality, and low freedom of beam design. The radar communication integration system based on phased array uses the transmit beamforming of the phased array antenna. Although it has the advantages of high beam gain, strong directivity, narrow beam, and low sidelobe, the beam pointing of the transmit beam formed by the phased array antenna is constant within the duration of a single pulse. This makes it impossible for the phased array to realize the application of radar communication integration system in distance-angle two-dimensional power control, main lobe clutter interference suppression, physical layer security communication, multi-user communication, etc.

[0004] To this end, the frequency diverse array (FDA) transforms the transmission beam pattern into a multidimensional function of time, angle, and distance by introducing a stepped carrier frequency increment between each transmitting array element. In addition, by combining the frequency diverse array with the multiple-input multiple-output (MIMO) technology, a distance-angle two-dimensional point beam pattern can be obtained through frequency diversity control and orthogonal waveform transmission. Based on the unique advantages of the two-dimensional distance-angle transmission beam pattern, the radar communication integrated system can achieve a wider range of full airspace coverage, higher precision radar detection, more efficient wireless communication, lower interception radar detection and confidential wireless communication.

[0005] At present, the optimization design of transmit beamforming for radar communication integration has become a hot topic of research. However, most existing design schemes only focus on the radar and communication performance of the beam in the angle domain, and do not consider the performance of the beam in the two-dimensional range-angle region. Therefore, it is of great significance to study the design method of transmit beamforming for radar communication integration based on FDA-MIMO. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to provide an integrated transmit beamforming method for FDA-MIMO radar communication that realizes distance-angle two-dimensional point-to-point radar detection and wireless communication.

[0007] Technical solution: The FDA-MIMO radar communication integrated transmission beamforming method of the present invention comprises the following steps:

[0008] Construct an integrated signal model for FDA-MIMO radar communication based on beam pattern modulation;

[0009] The signal processing model of the communication receiving end is derived, and the closed-form expression of the weighted distance-angle two-dimensional equivalent transmission beam pattern of the receiving end is obtained;

[0010] Taking the distance-angle of the communication user as the prior information, information embedding is achieved by constraining the amplitude and phase degrees of freedom of the distance-angle equivalent transmission beam pattern at the communication user's position;

[0011] Design transmit beamforming matrix to ensure radar detection performance;

[0012] Taking communication information embedding and eavesdropping user restrictions as constraints, and minimizing the mean square error between the transmit beamforming matrix and the radar desired beam matrix as the optimization objective function, an optimization model for integrated transmit beamforming of FDA-MIMO radar communication is established.

[0013] The barrier function algorithm is used to solve the optimization model.

[0014] Furthermore, an integrated signal model of FDA-MIMO radar communication based on beam pattern modulation is constructed, which specifically includes:

[0015] (A1)FDA-MIMO architecture radar communication integrated system, with M T transmit antennas, all transmit antennas simultaneously transmit M orthogonal waveforms ψ m (t),m=1,…,M,T p is the pulse duration, M orthogonal waveforms satisfy the strict orthogonality condition

[0016] (A2) Introduce the frequency increment △f of the frequency control array between different orthogonal waveforms and calculate the transmission frequency f of the mth orthogonal waveform m for:

[0017]

[0018] Among them, f c Indicates the carrier frequency of the transmitted signal;

[0019] (A3) Calculate the mth baseband transmission signal s consisting of an orthogonal waveform and a frequency increment m (t) is:

[0020]

[0021] Where, t represents the pulse time domain sampling time;

[0022] (A4) Using the transmit beamforming matrix For transmitting signal Beam pattern modulation is performed, where s1(t) is the first baseband transmission signal, s M (t) is the Mth roadbed band transmission signal; the radar communication integrated transmission signal S(t) is calculated as:

[0023] S(t)=Ws(t)

[0024] (A5) Calculate the far-field signal at a distance of R and an azimuth of θ:

[0025] s T (t-τ,θ)=a H (θ)Ws(t-τ)

[0026] Among them, s T (t-τ,θ) is the far-field signal at a distance of R and an azimuth of θ, τ = R / c is the time delay, c is the speed of light, s(t-τ) is the baseband transmission signal vector, is the launch steering vector, and its expression is:

[0027]

[0028] Where d represents the array element spacing.

[0029] Furthermore, the signal processing model of the communication receiving end is derived, and the closed-form expression of the weighted distance-angle two-dimensional equivalent transmission beam pattern of the receiving end is obtained; specifically, it includes:

[0030] (B1) has N j There are J communication users with a receiving antenna, and their distance and azimuth relative to the radar communication integrated transmitting end are R j and θ j; Calculate the received signal of the jth communication user as:

[0031] y j (t-τ j ,θ j )=β1b(θ j )s T (t-τ j ,θ j )+n j (t),j=1,…,J

[0032] Among them, yj(t-τj,θj) is the received signal of the jth communication user, τ j is the delay of the jth communication user, b(θj) is the receiving steering vector of the jth communication user, s T (t-τ j ,θ j ) is the far-field transmission signal, β1 is the loss coefficient of signal propagation, Indicates receiving noise;

[0033] (B2) Adoption After matching filtering the received signal, the output signal of the nth array element receiving the mth transmitted signal is calculated as:

[0034]

[0035] Among them, y n,m The output signal of the nth array element receiving the mth transmission signal, represents the weighted transmit beam space vector, a w,1 (θ) is the first element of the weighted transmit beam space vector, a w,2 (θ) is the second element of the weighted transmit beam space vector, aw,M(θ) is the Mth element of the weighted transmit beam space vector, and aw,m(θ) is the j ) is the mth element of the weighted transmit beam space vector;

[0036] (B3) The multi-channel matched filter output signals are superimposed into an extended vector, which is expressed as:

[0037]

[0038] in, is the extended vector formed by superimposing the output signals of multi-channel matched filters, represents the Kronecker product, is the distance-angle two-dimensional equivalent launch steering vector, and its expression is:

[0039]

[0040] Furthermore, the distance-angle of the communication user is used as prior information, and information embedding is achieved by constraining the amplitude and phase degrees of freedom of the distance-angle equivalent transmission beam pattern at the communication user position; specifically, it includes:

[0041] (C1) J communication users are located at any distance and angle gate within the coverage of the transmission beam, and the location information of each user is known a priori; during each transmission pulse, phase constellation modulation is used to represent the communication symbol; the communication information of the jth user Calculated as:

[0042]

[0043] in, Represents the original communication phase, whose value is from the set Randomly select from B Represents the number of bits of a single communication symbol, p i represents the i-th phase point in the constellation;

[0044] (C2) Using the beam pattern modulation method, the distance-angle two-dimensional equivalent transmission steering vector a is introduced into the optimization problem. r The equality constraint of (τ,θ) is expressed as:

[0045]

[0046] Among them, a r (τ j ,θ j ) is the distance-angle two-dimensional equivalent launch steering vector, ⊙ represents the Hadamard product, is the power parameter, Δ j (1) is the first power parameter, Δ j (M) is the Mth power parameter;

[0047] (C3) There are H threatening eavesdropping users in the scenario, whose distance and angle relative to the radar communication integrated transmitter are R h and θ h , h=1,…,H; the following equality constraint is introduced into the optimization problem to eliminate the phase information of the beam pattern at the eavesdropping user position:

[0048]

[0049] Among them, ar(τh,θ h ) is the distance-angle two-dimensional equivalent transmission steering vector of the hth eavesdropping user, τ h is the delay of the hth eavesdropping user, is the power coefficient of the beam pattern at the eavesdropping user, which can be set to a number close to 0 to produce a beam null at the eavesdropping user's location.

[0050] Furthermore, a transmit beamforming matrix is ​​designed to ensure radar detection performance, specifically including the following steps:

[0051] (D1) Based on the transmit steering vector of the detected target, the desired transmit beamforming matrix of the radar is designed as:

[0052]

[0053] Among them, (:,m) represents all row elements of the mth column of the matrix, W radar (:,m) are all row elements of the mth column of the radar desired transmit beamforming matrix, θ t is the azimuth of the target, a(θ t ) is the launch steering vector at the target angle;

[0054] (D2) The objective function is to minimize the mean square error between the transmit beamforming matrix and the radar's expected transmit beamforming matrix:

[0055]

[0056] Among them, W radar The desired transmit beamforming matrix for the radar.

[0057] Furthermore, with the constraints of communication information embedding and eavesdropping user restrictions, and minimizing the mean square error between the transmit beamforming matrix and the radar expected beam matrix as the optimization goal, an optimization design model for integrated transmit beamforming of FDA-MIMO radar communication is established: specifically:

[0058]

[0059] Among them, the first constraint represents the phase embedding and power control of the communication user; the second constraint represents the phase constraint and power limit of the eavesdropping user; the objective function represents the radar transmit beamforming matrix that achieves the minimum mean square error under the premise of communication symbol embedding.

[0060] Furthermore, the barrier function algorithm is used to solve the optimization model, including:

[0061] (E1) The feasible domain is recorded as:

[0062] (E2) Define the barrier function:

[0063] in, B(W) is a continuous function whose independent variable is the transmit beamforming matrix W. When the independent variable W approaches the boundary of the feasible region, B(W)→+∞. Its expression is selected from the following two forms:

[0064]

[0065] (E3) Initialization: Given an initial interior point W( 0 )∈S, error threshold ε>0, initial parameters of the algorithm Shrinkage factor β∈(0,1), maximum number of iterations K max , set the current iteration step k = 1;

[0066] (E4)If k≤K max , perform calculation; otherwise, stop the calculation and jump to step E7;

[0067] (E5) The transmit beamforming matrix W calculated for the k-1th time ( k-1 ) is the initial point, and the following unconstrained optimization problem is solved to obtain the minimum value W( k ):

[0068]

[0069] (E6) Convergence judgment: If r( k )B(W( k ))<ε, stop calculation and jump to step E7; otherwise, r(k+1)=βr ( k), k=k+1, return to step E4; wherein r( k+1 ) and r( k ) are the algorithm parameters for the k-1th and kth calculations respectively;

[0070] (E7) Output W opt =W( k ), where W opt is the optimal transmit beamforming matrix.

[0071] The system corresponding to the above method includes:

[0072] A signal model building unit, used to build an integrated signal model of FDA-MIMO radar communication based on beam pattern modulation;

[0073] A communication signal processing unit, used to derive a signal processing model of a communication receiving end and obtain a closed-form expression of a weighted distance-angle two-dimensional equivalent transmission beam pattern of the receiving end;

[0074] A communication information embedding unit, used to embed information by constraining the amplitude and phase degrees of freedom of the distance-angle equivalent transmission beam pattern at the communication user position, taking the distance-angle of the communication user as prior information;

[0075] A transmit beamforming matrix design unit, used to design a transmit beamforming matrix to ensure radar detection performance;

[0076] The optimization model building unit is used to meet the constraints of communication information embedding and eavesdropping user restrictions, and to minimize the mean square error between the transmit beamforming matrix and the radar expected beam matrix as the optimization objective function, so as to establish the FDA-MIMO radar communication integrated transmit beamforming optimization model;

[0077] The optimization model solving unit is used to solve the optimization model by using a barrier function algorithm.

[0078] A control device for storing and processing the above method, including a processor, a communication interface, a memory and a communication bus;

[0079] Wherein, the processor, the communication interface, and the memory communicate with each other via the communication bus;

[0080] The memory is used to store computer programs;

[0081] The processor is used to implement the steps of the FDA-MIMO radar communication integrated transmission beamforming method when executing the program stored in the memory.

[0082] A storage medium for storing and executing the method, wherein a computer program is stored on the storage medium, and when the computer program is executed by at least one processor, the steps of the FDA-MIMO radar communication integrated transmit beamforming method are implemented.

[0083] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: (1) By optimizing the design of the transmit beamforming matrix of FDA-MIMO, phase modulation of communication information is adopted and embedded into the beam diagram for transmission. The communication information is embedded in the weighted distance-angle two-dimensional equivalent transmit beam diagram by using an equality constraint. Under the constraints of communication information embedding and eavesdropping user restriction, the mean square error between the transmit beamforming matrix and the radar expected beam matrix is ​​minimized as the optimization objective function, and an FDA-MIMO radar communication integrated transmit beamforming optimization model is established. The convex optimization algorithm is used to obtain the optimal transmit beamforming matrix, so that the distance-angle beam diagram of FDA-MIMO is used to realize two-dimensional point-to-point radar target detection and secure wireless communication, thereby improving radar detection performance and communication reliability; (2) Not only does it meet the beam performance of radar detection, but it also realizes the embedding of communication information of multiple users, preventing eavesdropping users from intercepting the communication information of multiple users at one time. Moreover, the optimal transmit beamforming matrix obtained by solving the proposed optimization model is applied to the radar communication integrated transmitting end based on FDA-MIMO, effectively improving the detection and communication performance of the radar communication integrated system. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1 A flow chart of an integrated transmit beamforming method for FDA-MIMO radar communication;

[0085] Figure 2 Design scenario for integrated transmit beamforming for FDA-MIMO radar communication;

[0086] Figure 3 is the transmit beam pattern in the angle dimension;

[0087] Figure 4 It is the range-angle transmit-receive beam pattern at the radar target;

[0088] Figure 5 The distance-angle transmission-reception beam pattern at the communication user;

[0089] Figure 6 is the distance-angle two-dimensional bit error rate;

[0090] Figure 7 is the bit error rate in angle dimension;

[0091] Figure 8 is the distance dimension bit error rate. DETAILED DESCRIPTION

[0092] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0093] Starting from the actual scenarios of radar detection and wireless communication, the present invention proposes an FDA-MIMO radar communication integrated transmit beamforming method, system, device and storage medium, which minimizes the mean square error between the transmit beamforming matrix and the radar expected beam matrix under the communication information embedding constraint condition of beam pattern modulation, thereby realizing distance-angle two-dimensional point-to-point radar detection and wireless communication.

[0094] The present invention considers a radar communication integration scenario, in which the integrated system transmits information to multiple communication users while detecting the target. The transmitting end of the integrated system adopts the FDA-MIMO architecture, that is, the transmitted signal is an orthogonal waveform group with stepped frequency diversity, and a digital transmit beamformer is used to weight the orthogonal waveform. First, a signal model based on the integration of FDA-MIMO radar communication is constructed, and a communication signal processing method for the integration of FDA-MIMO radar communication is derived to obtain a closed-form expression of the distance-angle two-dimensional equivalent transmission steering vector after weighting at the receiving end. Secondly, taking the distance-angle of the communication user as the prior information, the communication information embedding based on beam pattern modulation is realized through transmit beamforming, and the optimization objective function is to minimize the mean square error between the transmit beamforming matrix and the radar expected beam matrix, and establish an optimization model for the integrated transmit beamforming of FDA-MIMO radar communication. Finally, the barrier function algorithm is used to solve the established optimization problem.

[0095] Symbols in the present invention: Bold lowercase letter a represents a vector, bold uppercase letter A represents a matrix, (·) T , (·) * , (·) H represent transpose, conjugate and conjugate transpose operations respectively, |·| represents absolute value operation, ||·||2 and ||·|| F represents the 2-norm and Frobenius norm, and represent complex numbers, real numbers, and positive integer sets, respectively, I N and 1 N They represent the N×N unit matrix and the N-dimensional all-1 vector respectively.

[0096] like Figure 1 As shown, the method of the present invention comprises the following steps:

[0097] First, build the FDA-MIMO radar communication integrated system design scenario:

[0098] The transmitting end of the radar communication integrated system is an FDA-MIMO architecture, and the array configuration is a one-dimensional uniform linear array with M TThere are transmitting antennas with an array element spacing of d. All transmitting antennas simultaneously transmit M orthogonal waveforms that meet the strict orthogonal conditions, and perform stepped frequency diversity modulation of the frequency-controlled array on the orthogonal waveforms of different channels. There is a radar detection target and J communication users in the space, such as Figure 2 shown.

[0099] S1. Constructing the integrated transmission signal model of FDA-MIMO radar communication, including the following steps:

[0100] A1: All transmitting antennas simultaneously transmit M orthogonal waveforms ψ m (t),m=1,…,M,T p is the pulse duration, M orthogonal waveforms satisfy the strict orthogonality condition

[0101] A2: Introduce the frequency increment △f of the frequency control array between different orthogonal waveforms and calculate the transmission frequency f of the mth orthogonal waveform m for:

[0102]

[0103] Among them, f c Indicates the carrier frequency of the transmitted signal.

[0104] A3: Calculate the mth baseband transmission signal s consisting of orthogonal waveforms and frequency increments m (t) is:

[0105]

[0106] Where t represents the pulse time domain sampling time.

[0107] A4: In order to control the transmission pattern and embed communication information, a transmit beamforming matrix is ​​used For transmitting signal Beam pattern modulation is performed, where s1(t) is the first baseband transmission signal, s M (t) is the Mth roadbed band transmission signal. The radar communication integrated transmission signal S(t) is calculated as:

[0108] S(t)=Ws(t) (3)

[0109] A5: Under the assumption of narrowband signal, the far-field signal at a distance of R and an azimuth of θ is calculated as:

[0110] s T (t-τ,θ)=a H (θ)Ws(t-τ) (4)

[0111] Among them, s T(t-τ,θ) is the far-field signal at a distance of R and an azimuth of θ, τ = R / c is the time delay, c is the speed of light, s(t-τ) is the baseband transmission signal vector, is the launch steering vector, and its expression is:

[0112]

[0113] Where d represents the array element spacing.

[0114] S2. Derive a communication signal processing method for FDA-MIMO radar communication integration, which specifically includes the following steps:

[0115] B1: Consider N j There are J communication users with a receiving antenna, and their distance and azimuth relative to the radar communication integrated transmitting end are R j and θ j . The received signal of the jth communication user is calculated as:

[0116] y j (t-τ j ,θ j )=β1b(θ j )s T (t-τ j ,θ j )+n j (t), j=1,…,J (6)

[0117] Among them, yj(t-τj,θj) is the received signal of the jth communication user, τ j is the delay of the jth communication user, b(θj) is the receiving steering vector of the jth communication user, s T (t-τ j ,θ j ) is the far-field transmission signal, β1 is the loss coefficient of signal propagation, Indicates receiving noise.

[0118] B2: Adoption After matching filtering is performed on the received signal of equation (7), the output signal of the nth array element receiving the mth transmitted signal is calculated as:

[0119]

[0120] Among them, y n,m The output signal of the nth array element receiving the mth transmission signal, represents the weighted transmit beam space vector, a w (θ) is the weighted transmit beam space vector, a w,1(θ) is the first element of the weighted transmit beam space vector, a w,2 (θ) is the second element of the weighted transmit beam space vector, a w,M (θ) is the Mth element of the weighted transmit beam space vector, a w,m (θ j ) is the mth element of the weighted transmit beam space vector.

[0121] B3: The multi-channel matched filter output signals of equation (7) are superimposed into an extended vector, which is expressed as:

[0122]

[0123] in, is the extended vector formed by superimposing the output signals of multi-channel matched filters, represents the Kronecker product, is the distance-angle two-dimensional equivalent launch steering vector, and its expression is:

[0124]

[0125] S3, implementing communication information embedding based on beam pattern modulation through transmit beamforming, specifically comprising the following steps:

[0126] C1: Assume that J communication users are located at any distance and angle gate within the coverage of the transmission beam, and the location information of each user is known a priori. During each transmission pulse, phase constellation modulation is used to represent the communication symbol. The communication information of the jth user It can be calculated as:

[0127]

[0128] in, Represents the original communication phase, whose value is from the set Randomly select from B Represents the number of bits of a single communication symbol, p i represents the i-th phase point in the constellation.

[0129] C2: Using the beam pattern modulation method, the distance-angle two-dimensional equivalent transmission steering vector a is introduced into the optimization problem r The equality constraint of (τ,θ) can be expressed as:

[0130]

[0131] Among them, a r (τ j ,θ j) is the distance-angle two-dimensional equivalent launch steering vector, ⊙ represents the Hadamard product, is the power parameter, Δ j (1) is the first power parameter, Δ j (M) is the Mth power parameter.

[0132] C3: Consider that there are H threatening eavesdropping users in the scenario, whose distance and angle relative to the radar communication integrated transmitter are R h and θ h , h=1,…,H. In order to prevent eavesdropping users from intercepting communication information, the following equality constraint is introduced into the optimization problem to eliminate the phase information of the beam pattern at the eavesdropping user's position:

[0133]

[0134] Among them, a r (τ h ,θ h ) is the distance-angle two-dimensional equivalent transmission steering vector of the h-th eavesdropping user, τh is the time delay of the h-th eavesdropping user, is the power coefficient of the beam pattern at the eavesdropping user, which can be set to a number close to 0 to produce a beam null at the eavesdropping user's location.

[0135] S4. Designing a transmit beamforming matrix to ensure radar detection performance includes the following steps:

[0136] D1: In order to achieve a higher radar detection signal-to-noise ratio, the radar's desired transmit beamforming matrix is ​​designed based on the transmit steering vector of the detection target's azimuth angle:

[0137]

[0138] Among them, (:,m) represents all row elements of the mth column of the matrix, W radar (:,m) are all row elements of the mth column of the radar desired transmit beamforming matrix, θ t is the azimuth of the target, a(θ t ) is the launch steering vector at the target angle.

[0139] D2: The objective function is to minimize the mean square error between the transmit beamforming matrix and the radar's expected transmit beamforming matrix:

[0140]

[0141] Among them, W radar The desired transmit beamforming matrix for the radar.

[0142] S5. Taking the communication information embedding and eavesdropping user restrictions as constraints and minimizing the mean square error between the transmit beamforming matrix and the radar desired beam matrix as the optimization goal, an optimization design model for integrated transmit beamforming of FDA-MIMO radar communication is established:

[0143]

[0144] In formula (15), the first constraint represents the phase embedding and power control of the communication user; the second constraint represents the phase constraint and power limit of the eavesdropping user; the objective function represents the radar transmit beamforming matrix that achieves the minimum mean square error under the premise of communication symbol embedding.

[0145] S6. The barrier function algorithm is used to solve the optimization design problem of the integrated transmit beamforming of the constructed FDA-MIMO radar communication, which specifically includes the following steps:

[0146] E1: The feasible domain is recorded as:

[0147] E2: Define the barrier function:

[0148] in, B(W) is a continuous function whose independent variable is the transmit beamforming matrix W. When the independent variable W approaches the boundary of the feasible region, B(W)→+∞. Its expression is selected from the following two forms:

[0149]

[0150] E3: Initialization: Given an initial interior point W( 0 )∈S, error threshold ε>0, initial parameters of the algorithm Shrinkage factor β∈(0,1), maximum number of iterations K max , set the current iteration step k=1.

[0151] E4: If k≤K max , perform calculation; otherwise, stop calculation and jump to step E7.

[0152] E5: The transmit beamforming matrix W calculated for the k-1th time ( k-1 ) is the initial point, and the following unconstrained optimization problem is solved to obtain the minimum value W( k ):

[0153]

[0154] E6: Convergence judgment: If r(k)B(W(k))<ε, stop the calculation and jump to step E7; otherwise, r (k+1)=βr (k) , k=k+1, return to step E4; wherein, r (k+1) and r (k) are the algorithm parameters for the k-1th and kth calculations respectively.

[0155] E7: Output W opt =W( k ), where W opt is the optimal transmit beamforming matrix.

[0156] The system corresponding to the above method includes:

[0157] A signal model building unit, used to build an integrated signal model of FDA-MIMO radar communication based on beam pattern modulation;

[0158] A communication signal processing unit, used to derive a signal processing model of a communication receiving end and obtain a closed-form expression of a weighted distance-angle two-dimensional equivalent transmission beam pattern of the receiving end;

[0159] A communication information embedding unit, used to embed information by constraining the amplitude and phase degrees of freedom of the distance-angle equivalent transmission beam pattern at the communication user position, taking the distance-angle of the communication user as prior information;

[0160] A transmit beamforming matrix design unit, used to design a transmit beamforming matrix to ensure radar detection performance;

[0161] The optimization model building unit is used to meet the constraints of communication information embedding and eavesdropping user restrictions, and to minimize the mean square error between the transmit beamforming matrix and the radar expected beam matrix as the optimization objective function, so as to establish the FDA-MIMO radar communication integrated transmit beamforming optimization model;

[0162] The optimization model solving unit is used to solve the optimization model by using a barrier function algorithm.

[0163] The control device of the above method comprises a processor, a communication interface, a memory and a communication bus;

[0164] Wherein, the processor, the communication interface, and the memory communicate with each other via the communication bus;

[0165] The memory is used to store computer programs;

[0166] The processor is used to implement the steps of the FDA-MIMO radar communication integrated transmission beamforming method when executing the program stored in the memory.

[0167] The storage medium of the above method stores a computer program, and when the computer program is executed by at least one processor, the steps of the FDA-MIMO radar communication integrated transmit beamforming method are implemented.

[0168] Simulation results:

[0169] In order to verify the feasibility and superiority of the proposed method, the following simulation scenario is designed: Assuming that a range gate is 10m, the monitoring range is 150 range gates, and there is a target located at R t =0.75km,θ t =0°, there are three communication users located at R1 = 0.4km, θ1 = -50°, R2 = 1.3km, θ1 = -30° and R3 = 1.0km, θ3 = 40°, that is, J = 3. The radar communication integrated system performs radar target detection and communication information transmission at the same time.

[0170] The specific experimental process is:

[0171] Step 1: Radar detection and communication scenario modeling

[0172] The array configuration of the radar communication integrated system is a one-dimensional uniform linear array, the array element spacing is half wavelength d = λ / 2, and the number of transmitting antennas and receiving antennas is M. T =M R =21. The carrier frequency of the transmitted signal is f c =3GHz, the step frequency increment of the frequency control array is △f=200kHz, and the signal bandwidth is B=100MHz. The number of orthogonal waveforms M=5, and the Oppermann sequence is used as the orthogonal waveform. The parameters of the Oppermann sequence are set to q=1, n=3, and p=1. Assume that a range gate is 10m, the monitoring range is 150 range gates, and there is a target located at R t =0.75km,θ t = 0°, there are three communication users located at R1 = 0.4 km, θ1 = -50°, R2 = 1.3 km, θ1 = -30° and R3 = 1.0 km, θ3 = 40°, i.e. J = 3. The receiving array of each communication user has antennas, the power of embedded communication information is set to A total of 1000 Monte Carlo experiments were performed, with 10 7 The communication channel coefficients are modeled as random variables with unit size and uniformly distributed phases.

[0173] Step 2: Optimize the transmit beamforming matrix

[0174] The convex optimization algorithm is used to iteratively solve the optimization model of transmit beamforming, obtain the transmit beamforming matrix, and further model the transmit signal. The specific solution method can be obtained with the help of various convex optimization algorithm toolboxes, such as the CVX toolbox in MATLAB.

[0175] Step 3: Beam Pattern Simulation

[0176] Figure 3 The figure shows the transmit beam diagram, where the green dotted lines represent the azimuths of the three communication users and the pink dotted lines represent the azimuths of the radar target. Without considering the delay, the transmit beam diagram of the FDA-MIMO proposed in the present invention maintains high-gain azimuth directivity through the transmit beamforming technology, and forms high gain at each preset desired angle. Figure 4 and Figure 5 The transmit-receive two-way beam diagram at the radar target and the communication user, red represents the high gain area, and blue represents the low gain area. The normalized non-adaptive weight vector is used here To achieve receive beamforming, where u TR (τ′,θ′) is the receive beamforming weight vector, b(θ′) is the angle-dimensional receive beamforming weight vector, a r (τ′,θ′) is the distance-angle two-dimensional receive beamforming weight vector, τ′ is the distance of beamforming, and θ′ is the angle of beamforming. Obviously, after matched filtering, channel separation, and receive beamforming, the distance-angle degree of freedom of two-dimensional coupling in the FDA-MIMO transmit signal can be successfully separated. The transmit-receive two-way pattern only produces high-gain areas at the locations of the radar target and the three preset communication users, which can achieve point-to-point two-dimensional detection and transmission.

[0177] Step 4: Communication demodulation processing and bit error rate simulation

[0178] The received signal-to-noise ratio is fixed to SNR = 11dB, and the bit error rates of the three communication users are calculated at all distance and angle gates. In order to clearly show the two-dimensional relationship between the bit error rate and the distance-angle, the value of the bit error rate is logarithmically normalized, that is, P ee =-log10(BER) / max(-log10(BER)), where P ee is the bit error rate after logarithmic normalization, BER is the bit error rate, P ee The larger the value, the lower the bit error rate. Figure 6 A distance-angle two-dimensional bit error rate simulation diagram is given. It can be seen that in the scenario, only three preset communication users can realize communication information demodulation, and the non-preset sidelobe area and radar target have high bit error rates, indicating that the method proposed in the present invention can achieve low interception characteristics in the distance-angle two-dimensional. Further, Figure 7and Figure 8 The bit error rate profiles of the angle dimension and the distance dimension are given. It can be seen that the communication information of the three users can only be demodulated and recovered at their corresponding positions, indicating that the method proposed in the present invention can achieve single-pulse multi-user communication capability.

[0179] The working principle and working process of the invention are as follows:

[0180] Consider a radar communication integration scenario. The integrated system sends downlink symbol information to multiple communication users while detecting the target. The transmitter of the integrated system adopts the FDA-MIMO architecture, that is, the transmitted signal is an orthogonal waveform group with stepped frequency diversity, and the digital transmit beamformer is used to weight the orthogonal waveform to realize beam pattern modulation. First, the FDA-MIMO radar communication integrated signal model based on beam pattern modulation is constructed, the signal processing model of the communication receiving end is derived, and the closed-form expression of the weighted distance-angle two-dimensional equivalent transmit beam pattern of the receiving end is obtained. Secondly, the distance-angle of the communication user is used as the prior information, and the information is embedded by constraining the amplitude and phase degrees of freedom of the distance-angle equivalent transmit beam pattern at the communication user position. Under the constraints of communication information embedding and eavesdropping user restrictions, the optimization model of FDA-MIMO radar communication integrated transmit beamforming is established with the minimum mean square error between the transmit beamforming matrix and the radar expected beam matrix as the optimization objective function. Finally, the convex optimization algorithm is used to solve the established optimization problem.

Claims

1. A FDA-MIMO radar communication integrated transmit beamforming method, characterized in that: The following steps are involved: Construct an integrated signal model for FDA-MIMO radar communication based on beam pattern modulation; The signal processing model of the communication receiving end is derived, and the closed-form expression of the weighted distance-angle two-dimensional equivalent transmission beam pattern of the receiving end is obtained; Taking the distance-angle of the communication user as the prior information, information embedding is achieved by constraining the amplitude and phase degrees of freedom of the distance-angle equivalent transmission beam pattern at the communication user's position; Design transmit beamforming matrix to ensure radar detection performance; Taking communication information embedding and eavesdropping user restrictions as constraints, and minimizing the mean square error between the transmit beamforming matrix and the radar desired beam matrix as the optimization objective function, an optimization model for integrated transmit beamforming of FDA-MIMO radar communication is established. The barrier function algorithm is used to solve the optimization model.

2. The FDA-MIMO radar communication integrated transmit beamforming method according to claim 1, characterized in that: Construct an integrated signal model for FDA-MIMO radar communication based on beam pattern modulation, including: (A1)FDA-MIMO architecture radar communication integrated system, with M T transmit antennas, all transmit antennas simultaneously transmit M orthogonal waveforms ψ m (t),m=1,…,M,T p is the pulse duration, M orthogonal waveforms satisfy the strict orthogonality condition (A2) Introduce the frequency increment △f of the frequency control array between different orthogonal waveforms and calculate the transmission frequency f of the mth orthogonal waveform m for: Among them, f c Indicates the carrier frequency of the transmitted signal; (A3) Calculate the mth baseband transmission signal s consisting of an orthogonal waveform and a frequency increment m (t) is: Where, t represents the pulse time domain sampling time; (A4) Using the transmit beamforming matrix For transmitting signal Beam pattern modulation is performed, where s1(t) is the first baseband transmission signal, s M (t) is the Mth roadbed band transmission signal; the radar communication integrated transmission signal S(t) is calculated as: S(t)=Ws(t) (A5) Calculate the far-field signal at a distance of R and an azimuth of θ: s T (t-τ,θ)=a H (θ)Ws(t-τ) Among them, s T (t-τ,θ) is the far-field signal at a distance of R and an azimuth of θ, τ = R / c is the time delay, c is the speed of light, s(t-τ) is the baseband transmission signal vector, is the launch steering vector, and its expression is: Where d represents the array element spacing.

3. The FDA-MIMO radar communication integrated transmit beamforming method according to claim 1, characterized in that: The signal processing model of the communication receiving end is derived, and the closed-form expression of the weighted distance-angle two-dimensional equivalent transmission beam pattern of the receiving end is obtained; specifically, it includes: (B1) has N j There are J communication users with a receiving antenna, and their distance and azimuth relative to the radar communication integrated transmitting end are R j and θ j ; Calculate the received signal of the jth communication user as: y j (t-t j ,i j )=β1b(θ j )s T (t-t j ,i j )+n j (t),j=1,…,J Among them, y j (t-τ j ,θ j ) is the received signal of the jth communication user, τ j is the delay of the jth communication user, b(θ j ) is the receiving steering vector of the jth communication user, s T (t-τ j ,θ j ) is the far-field transmission signal, β1 is the loss coefficient of signal propagation, Indicates receiving noise; (B2) Adoption After matching filtering the received signal, the output signal of the nth array element receiving the mth transmitted signal is calculated as: Among them, y n,m The output signal of the nth array element receiving the mth transmission signal, represents the weighted transmit beam space vector, a w,1 (θ) is the first element of the weighted transmit beam space vector, a w,2 (θ) is the second element of the weighted transmit beam space vector, a w,M (θ) is the Mth element of the weighted transmit beam space vector, a w,m (θ j ) is the mth element of the weighted transmit beam space vector; (B3) The multi-channel matched filter output signals are superimposed into an extended vector, which is expressed as: in, is the extended vector formed by superimposing the output signals of multi-channel matched filters, represents the Kronecker product, is the distance-angle two-dimensional equivalent launch steering vector, and its expression is:

4. The FDA-MIMO radar communication integrated transmit beamforming method according to claim 1, characterized in that: Taking the distance-angle of the communication user as the prior information, information embedding is achieved by constraining the amplitude and phase degrees of freedom of the distance-angle equivalent transmission beam pattern at the communication user's position; specifically, it includes: (C1) J communication users are located at any distance and angle gate within the coverage of the transmission beam, and the location information of each user is known a priori; during each transmission pulse, phase constellation modulation is used to represent the communication symbol; the communication information of the jth user Calculated as: in, Represents the original communication phase, whose value is from the set Randomly select from B Represents the number of bits of a single communication symbol, p i represents the i-th phase point in the constellation; (C2) Using the beam pattern modulation method, the distance-angle two-dimensional equivalent transmission steering vector a is introduced into the optimization problem. r The equality constraint of (τ,θ) is expressed as: Among them, a r (τ j ,θ j ) is the distance-angle two-dimensional equivalent launch steering vector, ⊙ represents the Hadamard product, is the power parameter, Δ j (1) is the first power parameter, Δ j (M) is the Mth power parameter; (C3) There are H threatening eavesdropping users in the scenario, whose distance and angle relative to the radar communication integrated transmitter are R h and θ h , h=1,…,H; the following equality constraint is introduced into the optimization problem to eliminate the phase information of the beam pattern at the eavesdropping user position: Among them, a r (τ h ,θ h ) is the distance-angle two-dimensional equivalent transmission steering vector of the hth eavesdropping user, τ h is the delay of the h-th eavesdropping user, is the power coefficient of the beam pattern at the eavesdropping user, which can be set to a number close to 0 to produce a beam null at the eavesdropping user's location.

5. The FDA-MIMO radar communication integrated transmit beamforming method according to claim 1, characterized in that: Designing the transmit beamforming matrix to ensure radar detection performance includes the following steps: (D1) Based on the transmit steering vector of the detected target, the desired transmit beamforming matrix of the radar is designed as: Among them, (:,m) represents all row elements of the mth column of the matrix, W radar (:,m) are all row elements of the mth column of the radar desired transmit beamforming matrix, θ t is the azimuth of the target, a(θ t ) is the launch steering vector at the target angle; (D2) The objective function is to minimize the mean square error between the transmit beamforming matrix and the radar's expected transmit beamforming matrix: Among them, W radar The desired transmit beamforming matrix for the radar.

6. The FDA-MIMO radar communication integrated transmit beamforming method according to claim 1, characterized in that: Taking communication information embedding and eavesdropping user restrictions as constraints, and minimizing the mean square error between the transmit beamforming matrix and the radar desired beam matrix as the optimization goal, an FDA-MIMO radar communication integrated transmit beamforming optimization design model is established: specifically: Among them, the first constraint represents the phase embedding and power control of the communication user; the second constraint represents the phase constraint and power limit of the eavesdropping user; the objective function represents the radar transmit beamforming matrix that achieves the minimum mean square error under the premise of communication symbol embedding.

7. The FDA-MIMO radar communication integrated transmit beamforming method according to claim 1, characterized in that: The barrier function algorithm is used to solve the optimization model, including: (E1) The feasible domain is recorded as: (E2) Define the barrier function: in, B(W) is a continuous function whose independent variable is the transmit beamforming matrix W. When the independent variable W approaches the boundary of the feasible region, B(W)→+∞. Its expression is selected from the following two forms: (E3) Initialization: Given an initial interior point W (0) ∈S, error threshold ε>0, initial parameters of the algorithm Shrinkage factor β∈(0,1), maximum number of iterations K max , set the current iteration step k = 1; (E4)If k≤K max , perform calculation; otherwise, stop the calculation and jump to step E7; (E5) The transmit beamforming matrix W calculated for the k-1th time ( k-1 ) is the initial point, and the following unconstrained optimization problem is solved to obtain the minimum value W( k ): (E6) Convergence judgment: If r (k) B(W (k) )<ε, stop the calculation and jump to step E7; otherwise, r (k+1) =βr (k) , k=k+1, return to step E4; wherein r( k+1 ) and r( k ) are the algorithm parameters for the k-1th and kth calculations respectively; (E7) Output W opt =W (k) , where W opt is the optimal transmit beamforming matrix.

8. An FDA-MIMO radar communication integrated transmit beamforming system, characterized in that: include: A signal model building unit, used to build an integrated signal model of FDA-MIMO radar communication based on beam pattern modulation; A communication signal processing unit, used to derive a signal processing model of a communication receiving end and obtain a closed-form expression of a weighted distance-angle two-dimensional equivalent transmission beam pattern of the receiving end; A communication information embedding unit, used to embed information by constraining the amplitude and phase degrees of freedom of the distance-angle equivalent transmission beam pattern at the communication user position, taking the distance-angle of the communication user as prior information; A transmit beamforming matrix design unit, used to design a transmit beamforming matrix to ensure radar detection performance; The optimization model building unit is used to meet the constraints of communication information embedding and eavesdropping user restrictions, and to minimize the mean square error between the transmit beamforming matrix and the radar expected beam matrix as the optimization objective function, so as to establish the FDA-MIMO radar communication integrated transmit beamforming optimization model; The optimization model solving unit is used to solve the optimization model by using a barrier function algorithm.

9. A control device, characterized in that: including a processor, a communication interface, a memory and a communication bus; Wherein, the processor, the communication interface, and the memory communicate with each other via the communication bus; The memory is used to store computer programs; The processor is used to implement the steps of the FDA-MIMO radar communication integrated transmit beamforming method described in any one of claims 1 to 7 when executing the program stored in the memory.

10. A storage medium, characterized in that: The storage medium stores a computer program, which, when executed by at least one processor, implements the steps of the FDA-MIMO radar communication integrated transmit beamforming method as described in any one of claims 1 to 7.

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