Signal transmission system and target positioning method based on time modulation array

Abstract

The present invention discloses a signal transmission system and a target positioning method based on a time modulation array. The time modulation array signal transmission system is adopted, and the design freedom of the RF switch function parameters is fully utilized to design the time sequence of the RF switch function so that the PSK symbol is synthesized at a specific frequency and a specific direction and a beam gain is formed. When the receiving end and the transmitting end adopt a co-location deployment mode, the azimuth information of the target can be determined by the target echo BER main lobe, and the distance information is obtained according to the ToA method of sending a known symbol sequence. The present invention can simultaneously estimate the azimuth of multiple targets and solve the problem of huge computational complexity brought by traditional target estimation algorithms, such as MUSIC and BP.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal processing, and in particular relates to a signal transmission system and a target positioning method based on a time modulation array. Background Art

[0002] Radar target positioning technology has a wide range of application needs in both military and civilian fields. Traditional radar target azimuth-range estimation mostly uses the Multiple Signal Classification (MUSIC) algorithm or the Back-projection (BP) algorithm. However, whether it is MUSIC or BP or other Direction of Arrival (DoA) estimation algorithms, the full-domain search in space will bring huge computational problems.

[0003] Time modulation array is a technology that introduces radio frequency (RF) switch functions into array antenna design. By controlling the "connection" and "disconnection" time of the RF switch, the excitation time of different antenna elements can be controlled, thereby achieving the purpose of flexible array beam design. At present, the research on time modulation array technology mainly focuses on beam sidelobe suppression and harmonic beam synthesis. Making full use of the freedom of RF switch time sequence design can synthesize communication symbol information, and the application research in this area is still in a blank stage. Summary of the invention

[0004] The technical problem to be solved by the present invention is that existing DoA estimation methods for targets all require huge amounts of calculation, and a signal transmission system based on a time modulation array and a target positioning method are provided.

[0005] The technical solution adopted by the present invention is:

[0006] A signal transmission system based on a time modulation array includes N array elements arranged linearly at equal intervals, where N is a positive integer; each array element is connected to an absorptive single-pole three-throw radio frequency switch, each single-pole three-throw radio frequency switch has three states of "connection", "disconnection" and "phase reversal", and the switch state is controlled by an FPGA; at the input end, a radio frequency signal with an input carrier frequency of f0 is connected to each radio frequency switch respectively after passing through N power dividers, and the time series of the radio frequency switch function is designed by utilizing the design freedom of radio frequency switch function parameters so that it can synthesize BPSK or QPSK symbols at a specific frequency and a specific direction and form beam gain.

[0007] Furthermore, the PSO algorithm is used to solve the RF switch function parameters corresponding to the constellation point combination The solution set synthesizes information symbols at different frequencies and directions.

[0008] The target positioning method of the signal transmission system based on the time modulation array can estimate the azimuth angle of multiple targets and obtain the distance information at the same time, which specifically includes the following steps:

[0009] Step 1: The transmitter inputs an RF signal with a carrier frequency of f0, which passes through an N-power divider and is connected to each RF switch;

[0010] Step 2: Within a time modulation cycle of the RF switching function, design the RF switching function to synthesize BPSK or QPSK symbols at a specific frequency and direction and form a time series of beam gain;

[0011] Step 3: According to the designed time sequence, use FPGA to set the "connection", "disconnection" and "phase reversal" moments of each RF switch and transmit the signal;

[0012] Step 4: Receive the echo signal at the receiving end, calculate the BER in the angle space using the BER calculation module, and monitor whether the BER main lobe appears. The BER main lobe azimuth is the target space azimuth; if the BER main lobe appears, measure the distance information according to the ToA measurement method;

[0013] Step 5: If the BER main lobe does not appear, adjust the RF switch time sequence to make the beam scan between the spatial azimuth [0, π] and detect the BER main lobe. The BER main lobe azimuth corresponds to the target spatial azimuth, and the target distance R = c|Δt| / 2, where c represents the propagation speed of light in free space, and Δt represents the time difference between the received and sent symbol sequences.

[0014] Furthermore, the receiving end and the transmitting end are deployed in a co-located manner, and target azimuth-distance estimation is performed at the receiving end, including a bit error rate BER calculation module and a target distance estimation module; wherein, the BER is calculated by comparing the information demodulated by the communication demodulation module with the transmitted information; and the target distance estimation module implements the time of arrival ToA method estimation.

[0015] The beneficial effects produced by the present invention are:

[0016] 1. DoA estimation does not require the application of a spatial global search algorithm, which greatly saves system computing resources.

[0017] 2. The BER at the receiving end can be used as a target azimuth indicator, that is, the target azimuth is directly obtained from the spatial direction corresponding to the BER main lobe.

[0018] 3. The target azimuth angle resolution is adjustable. In the present invention, the target azimuth angle resolution is determined by the BER main lobe of the receiving end, and changing the RF switch time sequence can flexibly change the BER main lobe. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the application of a co-located radar system based on a time modulation array transceiver;

[0020] Figure 2 It is a schematic diagram of the principle of a signal transmission system based on a time modulation array;

[0021] Figure 3a is the RF switch function U n (t) the first example;

[0022] Figure 3b is the RF switch function U n (t) The second example;

[0023] Figure 3c is the RF switch function U n The third example of (t);

[0024] Figure 4a At frequency f0+f p a far-field amplitude radiation pattern of the transmitted composite information symbol;

[0025] Figure 4b At frequency f0+f p transmitting a far-field phase radiation pattern of a composite information symbol;

[0026] Figure 4c At frequency f0+2f p a far-field amplitude radiation pattern of the transmitted composite information symbol;

[0027] Figure 4d At frequency f0+2f p transmitting a far-field phase radiation pattern of a composite information symbol;

[0028] Figure 4e is at frequency f0-f p a far-field amplitude radiation pattern of the transmitted composite information symbol;

[0029] Figure 4f is at frequency f0-f p transmitting a far-field phase radiation pattern of a composite information symbol;

[0030] Figure 4g At frequency f0-2f p a far-field amplitude radiation pattern of the transmitted composite information symbol;

[0031] Figure 4h At frequency f0-2f p transmitting a far-field phase radiation pattern of a composite information symbol;

[0032] Figure 5is the average value of the far-field radiation pattern of the transmitted composite information symbol;

[0033] Figure 6 This is an example of comparing target azimuth estimation based on time modulation array and general linear array;

[0034] Figure 7 An example of target azimuth estimation based on a time-modulated array. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the accompanying drawings.

[0036] Based on time modulated array co-located radar systems, such as Figure 1 As shown in the figure, the transmitting system and the receiving system are co-located, and the transmitting end only synthesizes phase shift keying modulated PSK symbols in the spatial direction θ0. When a space target exists, the receiving end receives the target echo signal, demodulates and calculates the BER. The spatial angle corresponding to the BER main lobe is the target azimuth. The target distance information is estimated by using the ToA measurement method that sends a known synthetic symbol sequence.

[0037] Signal transmission systems based on time modulation arrays, such as Figure 2 As shown, it is composed of N array elements arranged linearly with equal spacing, where N is a positive integer. The interval between array elements is d, where d is the 1 / 2 wavelength corresponding to the input frequency f0 signal. Each array element is connected to an absorptive single-pole three-throw RF switch, and each single-pole three-throw RF switch has three states: "connect", "disconnect" and "phase reversal", and its mathematical expression is U n (t), represents the time domain periodic sequence function of the nth RF switch, U n (t) in a period T p Three examples of are shown in Figure 3, where: Figure 3a correspond Figure 3b correspond Figure 3c correspond Combining various conditions n (t) can be expressed as,

[0038]

[0039] or

[0040]

[0041] in and Indicates the positive and negative cycles (i.e., connection and disconnection) of the RF switch. The switch state is controlled by the FPGA; at the input end, the RF signal with an input carrier frequency of f0 is connected to each RF switch after passing through the N power divider.

[0042] The target positioning method of the signal transmission system based on the time modulation array comprises the following steps:

[0043] Step 1: The transmitter inputs a radio frequency signal with a carrier frequency of f0, passes through an N-power divider, and is connected to each radio frequency switch. The expression of the transmitted signal in free space is:

[0044]

[0045] Among them, θ represents the spatial direction about the vertical viewing axis, such as Figure 2 As shown, θ∈[–π / 2,π / 2]; definition

[0046]

[0047] Will U n (t) Fourier expansion can be expressed as

[0048]

[0049] Among them, f p =1 / T p , B qn The qth Fourier coefficient representing the time series function of the nth RF switch can be expressed as

[0050]

[0051] definition

[0052]

[0053] It is known that sinc(x)=sin(πx) / (πx), so F(θ) can be expressed as

[0054]

[0055] Step 2: within a time modulation cycle of the RF switch function, design the RF switch function to synthesize binary phase shift keying modulation BPSK or quadrature phase shift keying modulation QPSK symbols at a specific frequency and direction and form a time series of beam gain; according to the expression F(θ) in step 1, at the frequency f0+qf p , spatial direction θ q The transmitted signal of the synthetic PSK symbol can be expressed as

[0056]

[0057] In order to q Directional composite information symbol, F q (θ q ) requires synthesizing all possible constellation point combinations in the in-phase-quadrature space. For example, when q = 1, at frequency f0 + f p , the spatial direction θ1 synthesizes the BPSK symbol, then the following equation needs to be solved:

[0058]

[0059] in, and for The two sets of solutions can generate two opposite constellation point signs, namely C1 and –C1, where C1 is any complex number that makes the above equation have a solution. Since the above equation has no closed expression for the solution, the particle swarm optimization algorithm PSO in engineering can be used to solve it. Similarly, if you want to p and f0+2f p , spatial directions θ1 and θ2, respectively, synthesize BPSK symbols, then it is necessary to find four groups of solutions to synthesize four possible constellation point combinations, namely (C1, C2), (C1, –C2), (- –C1, C2), (–C1, –C2), where C2 is any complex number corresponding to the frequency f0+2f p By using this method to design the RF switch function, PSK symbols can be synthesized at a specific frequency and direction, while there is no symbol information in other spatial directions. Therefore, the azimuth angle corresponding to the BER main lobe of the target echo can be used as an indicator of the target azimuth angle. q (θ q ) and F –q (–θ q ) is a conjugate relationship, so when the frequency f0+qf p There is a solution to synthesize PSK symbols at frequency f0–qf p The PSK symbol is automatically synthesized, and its azimuth is symmetrical about the vertical axis. For better explanation, an example of PSK symbol synthesis is given. p and f0+2f p , corresponding to the spatial directions θ1 = 20° and θ2 = 45°, respectively, to synthesize QPSK symbols. p and f0+2f p At the same time, QPSK symbols are synthesized, so 16 possible constellation point combinations need to be synthesized. Set the parameters N = 12, ρ = 0, and use the PSO algorithm to obtain a possible set of solutions for the 16 constellation point combinations, as shown in Table 1.

[0060] Table 1 At frequency f0+f p and f0+2fp , corresponding to the spatial direction θ1=20°,θ2=45°, the RF switch function parameters of the synthesized QPSK symbol

[0061]

[0062]

[0063] Step 3: According to the time sequence designed in step 2, use FPGA to set each RF switch "connection", "disconnection" and "phase reversal" time and transmit the signal. According to Table 1, use FPGA to set the RF switch function parameters, and the far-field radiation diagram of the transmitted signal is shown in Figure 4. Figure 4a and Figure 4b It can be found that at the frequency f0+f p , only in the spatial direction θ1 = 20°, the QPSK symbol is synthesized and the beam gain is formed, while in other spatial directions, the phase information is destroyed, indicating that the QPSK symbol information cannot be demodulated in other directions. Similarly, at the frequency f0+2f p , the QPSK symbol is synthesized only in the spatial direction θ2 = 45°, and the beam gain is formed, such as Figure 4c and Figure 4d Because F q (θ q ) and F –q (–θ q ) is a conjugate relationship, so at the frequency f0–f p With f0–2f p The QPSK symbols are automatically synthesized, and their directions are respectively f0+f p 、f0+2f p Symmetric about the vertical axis, such as Figure 4e to Figure 4h Because the radiation pattern varies slightly when different QPSK symbols are transmitted, one way to observe it is to take the average value. Figure 5 The average values ​​of the radiation patterns for transmitting different QPSK symbols are shown.

[0064] Step 4: Receive the echo signal at the receiving end, use the BER calculation module to calculate the BER in the angle space, monitor whether the BER main lobe appears, and the BER main lobe azimuth is the target space azimuth; if the BER main lobe appears, measure the distance information according to the ToA measurement method. Since the synthesized QPSK symbol only forms beam gain at a specific frequency and direction, when the beam is aimed at the target, an obvious BER main lobe can be obtained by demodulating the target echo. Therefore, the BER main lobe at the receiving end can be used as a target azimuth indicator. Assuming the target azimuth is +20°, the signal-to-noise ratio SNR = 17dB, Figure 6A comparison of the target echo BER based on the time modulation array and the general linear array is given. By transmitting the signal synthesized by the time modulation array, when the beam is aimed at the target, the BER main lobe is formed only in the target direction, so the target echo BER main lobe can be used as a target azimuth indicator; while the general linear array will form a high BER side lobe, so the target azimuth information cannot be determined. Figure 7 In order to use the RF switch function parameters in Table 1, an example of target azimuth estimation based on the time modulation array synthetic signal is transmitted. Assuming that the four targets are located at ±20° and ±45° respectively, SNR = 17dB, and the target echo is demodulated, it can be found that the BER main lobe is formed in the target direction, so the target azimuth can be determined using the BER main lobe. After determining the target azimuth, a known symbol sequence can be sent, and the target distance R can be calculated using the time difference between the received and sent symbol sequences, namely the ToA detection method, with the formula R = c|Δt| / 2, where c represents the propagation speed of light in free space, and Δt represents the time difference between the received and sent symbol sequences.

[0065] Step 5: If the BER main lobe does not appear, adjust the RF switch time sequence to make the beam scan between the spatial azimuth [0, π] and detect the BER main lobe. The BER main lobe azimuth corresponds to the target spatial azimuth, and the target distance R = c|Δt| / 2. If the transmitted signal beam is not aimed at the target, the BER presents a characteristic of an approximate horizontal line in the angle space, indicating that there is no target at this azimuth.

Claims

1. A target positioning method for a signal transmission system based on a time modulation array, characterized in that: The system consists of N The array is composed of array elements arranged linearly with equal spacing, N is a positive integer; each array element is connected to an absorptive single-pole three-throw RF switch, each single-pole three-throw RF switch has three states: connected, disconnected and phase inversion, and the switch state is controlled by FPGA; at the input end, the input carrier frequency is f 0 RF signal passes through N The power divider is connected to each RF switch. By utilizing the design freedom of RF switch function parameters, the time series of RF switch function is designed to synthesize BPSK or QPSK symbols at a specific frequency and direction and form beam gain. The PSO algorithm is used to solve the RF switch function parameters corresponding to the constellation point combination ( ) solution set, synthesizing information symbols at different frequencies and directions; The target positioning method comprises the following steps: Step 1: The transmitter inputs the carrier frequency f 0 RF signal, after N Power divider, connected to each RF switch; Step 2: within a time modulation cycle of the RF switch function, design the RF switch function to synthesize BPSK or QPSK symbols at a specific frequency and a specific direction and form a time series of beam gain; Step 3: According to the designed time sequence, use FPGA to set the "connect", "disconnect" and "phase reversal" moments of each RF switch and transmit the signal; Step 4: Receive the echo signal at the receiving end, use the BER calculation module to calculate the BER in the angle space, and monitor whether the BER main lobe appears. The azimuth of the BER main lobe is the azimuth of the target space; If the BER main lobe appears, the distance information is measured according to the ToA measurement method; Step 5: If the BER main lobe does not appear, adjust the RF switch time sequence to make the beam scan between the spatial azimuth [0, π] and detect the BER main lobe. The BER main lobe azimuth corresponds to the target spatial azimuth, and the target distance R = c |Δ t | / 2, where, c represents the speed of light in free space, Δ t represents the time difference between the received and transmitted symbol sequence, The receiving end and the transmitting end are deployed in a co-located manner, and the target azimuth-distance estimation is performed at the receiving end, including a BER calculation module and a target distance estimation module; wherein the BER calculation is obtained by comparing the information demodulated by the communication demodulation module with the transmitted information; The target distance estimation module implements the ToA method estimation.

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