OFDM synaesthesia integrated system and method based on four-dimensional antenna array combined with space-time modulation

Abstract

The present invention discloses an OFDM-synaesthesia integration system based on a four-dimensional antenna array combined with space-time modulation. The system includes an OFDM modulator, a baseband signal modulator, a digital-to-analog converter, an upconverter, a local oscillator signal generator, a power amplifier (PA), a duplexer, a power splitter / combiner, a four-dimensional wave control module, a four-dimensional transceiver assembly, an antenna unit, a low-noise amplifier, a downconverter, an analog-to-digital converter, a digital signal processor, a radar analyzer, and optical fibers and cables connecting the various parts. The four-dimensional transceiver assembly mainly consists of a high-speed radio frequency switch, a phase shifter, an amplifier, etc. The present invention also discloses an OFDM-synaesthesia integration method based on a four-dimensional antenna array combined with space-time modulation. The method can maximize the use of the entire space-time degree of freedom, reduce the energy loss caused by the high peak-to-average power ratio, effectively improve the working efficiency of the radio frequency system, and realize target detection under non-scanning operation by using the higher side lobes formed by time modulation, thereby reducing the complexity of the synaesthesia integration system.

Description

Technical Field

[0001] The present invention belongs to the field of antenna engineering technology, and relates to wireless communication technology and array signal processing. Specifically, it utilizes a four-dimensional antenna array to modulate the amplitude, and jointly integrates and utilizes the space-time degrees of freedom of the four-dimensional antenna system to improve the working efficiency of the radio frequency system. It also utilizes the higher side lobes formed by the modulation function to achieve high-precision perception, and can be used in a synaesthesia integrated system based on multi-carrier modulation. Background Art

[0002] With the rapid development of electronic information technology, research in radar and communication technologies has made tremendous progress, and the concept of synaesthesia integration has been proposed. Synaesthesia integration achieves radar perception and communication transmission through a common set of hardware devices. Compared to traditional single radar or communication equipment, it achieves a high degree of hardware integration and efficient spectrum utilization. As a new type of array antenna with strong design flexibility, four-dimensional antennas have a very large application space and potential advantages in the field of synaesthesia integration technology. Currently, there are literature reports on the application of four-dimensional antenna arrays in dynamic directional modulation, secure communications, two-dimensional direction finding, etc. Time-modulated antenna arrays are a type of four-dimensional antenna array.

[0003] In the patent with publication number CN113922827A, a beam control system and method for radar communication integration is proposed. The system makes full use of the ultra-low sidelobe and multi-harmonic characteristics of the time-modulated array to achieve a high-gain radar scanning beam while generating two freely scanning communication beams, realizing radar communication integration in the RF part. This technology focuses on beam control in radar communication integration and does not involve specific signal design. When the radar angle is consistent with the communication angle, the radar signal at the center frequency and the communication signal in the sideband will inevitably interfere with each other, causing damage to the radar and communication indicators. In addition, in a multi-channel and multi-functional scenario, if the total energy of the system remains unchanged, the energy of each channel will inevitably decrease, that is, this technology achieves integration at the expense of both communication and perception performance.

[0004] In the paper "A Secure Dual-Function Radar Communication System via Time-Modulated Arrays," Z. Xu et al. propose a low-complexity target estimation method for OFDM-based interaural communication signals. OFDM, as a communications technology, is currently widely used in 4G LTE and 5G, and has enormous potential for application in 5G Advanced and 6G. Extending OFDM technology to interaural communication systems makes communication information vulnerable to eavesdropping by potential targets. However, time-modulated arrays enable secure communication through beamforming. This process also disrupts signals from all directions other than the intended user, making it difficult to estimate the parameters of the perceived target.

[0005] As a multi-carrier modulation technology, OFDM's high peak-to-average power ratio (PAPR) cannot be ignored. High baseband signals can severely impact the efficiency of power amplifiers. For example, Tagore Technology's TA9110K GaN power amplifier maintains a stable 15dB gain at an output power of 18-25dBm at a 2000MHz frequency. This corresponds to an input power of 3-10dBm. Therefore, the instantaneous input power of the signal should be between 3-10dBm. Assuming two signals with average power of 10dBm, with gains of 7dB and 3dB, respectively, their peak values ​​can be inferred to be 17dBm and 13dBm, respectively. The input power of the former requires a 7dB backoff, while the latter only requires a 3dB backoff. Ultimately, the output powers are 18dBm and 22dBm, respectively, a difference of 4dB. Therefore, PAPR is a crucial factor in the design of OFDM radio systems. So far, research on the peak-to-average power ratio of OFDM synaesthesia integrated signals has yet to be carried out.

[0006] In the patent with publication number CN113114321B, a joint space-time modulation (JSTM) secure communication system based on a four-dimensional antenna array is proposed. This transmission scheme uses the space-time freedom of the four-dimensional antenna system through joint integration to improve the transmission efficiency of the physical layer secure communication of the four-dimensional antenna array. The invention uses a single-carrier modulation signal of 16-QAM (Quadrature Amplitude Modulation) to modulate the phase information in the baseband and the amplitude information in the time function. However, the information transmission rate of the single-carrier modulation signal is low, and it is prone to inter-code interference and increase the bit error rate. In addition, the focus of the invention is on confidential communication rather than using JSTM to improve communication indicators. So far, there have been no reports on the application of using joint space-time modulation signal transmission scheme to improve communication efficiency.

[0007] In response to the above application requirements, the present invention proposes an OFDM synaesthesia integration system and method based on a four-dimensional antenna array combined with space-time modulation. The four-dimensional antenna array is used to modulate the amplitude, and the space-time degrees of freedom of the four-dimensional antenna system are used in a combined and integrated manner to improve the working efficiency of the radio frequency system. The higher side lobes formed by the modulation function are used to achieve high-precision perception, which can be used in a synaesthesia integration system based on multi-carrier modulation. Summary of the Invention

[0008] The present invention proposes an OFDM-synaesthesia integrated system based on a four-dimensional antenna array combined with space-time modulation. The system includes an OFDM modulator, a baseband signal modulator, a digital-to-analog converter, an upconverter, a local oscillator signal generator, a power amplifier (PA), a duplexer, a power splitter / combiner, a four-dimensional beam control module, a four-dimensional transceiver assembly, an antenna unit, a low-noise amplifier, a downconverter, an analog-to-digital converter, a digital signal processor, a radar analyzer, and optical fibers and cables connecting the various components. The four-dimensional beam control module implements time modulation of the high-speed radio frequency switch in the four-dimensional transceiver assembly.

[0009] The present invention also proposes an OFDM synaesthesia integration method based on a four-dimensional antenna array combined with space-time modulation. This method maximizes the utilization of all space-time degrees of freedom, reduces output back-off in the power amplifier due to high peak-to-average power ratio, and effectively improves the transmission efficiency of the communication system. Furthermore, the higher sidelobes formed by time modulation enable target detection in non-scanning conditions, reducing system complexity.

[0010] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions. Consider an N t The linear arrangement of the four-dimensional antenna array with equal spacing d, the excitation phase of the kth antenna element is φ kEach antenna unit is connected to a high-speed RF switch at the back end, and the time modulation function in the kth antenna link is expressed as U k (t). If the center frequency of the antenna is f0, the baseband signal is s b (t), then the far-field formula of the four-dimensional antenna array radiation field carrying the baseband signal is

[0011]

[0012] Where θ is the angle between the signal transmission direction and the axial direction of the antenna array, e is a natural constant, and β is the free space wave number.

[0013] Assume that the target communication direction is θ0. According to the superposition of the directional patterns of the phased array, φ k =-kβdcosθ0, then the transmission signal of the four-dimensional antenna array at θ0 can be simplified to

[0014]

[0015] It can be observed that the time modulation effect of the signal in the desired direction θ0 is linear superposition, while the signal in other directions is nonlinear superposition, which will distort the signal in the undesired direction. In addition, the transmission signal of the overall system is composed of the baseband signal s b (t) and time function The target signal to be transmitted can be mapped to the baseband modulation signal and the time modulation function respectively, and the space-time degrees of freedom can be further jointly integrated.

[0016] The target signal is considered to be a subcarrier with N number of subcarriers s , the center frequency is f c , the subcarrier spacing is f s , the number of symbols is N p Assume that the symbol carried by the sth subcarrier of the μth OFDM symbol is d(s,μ). Then the mathematical expression of the signal model is as follows

[0017]

[0018] Among them, rect(t / T p ) represents a rectangular pulse wave whose period satisfies T p =1 / f s .

[0019] As a multi-carrier modulation method, OFDM's Peak to Average Power Ratio (PAPR) is one of the indicators that cannot be ignored in the design process. The Complementary Cumulative Distribution Function (CCDF) is usually used to intuitively represent the probability of PAPR exceeding a certain threshold value PAPR0 in a multi-carrier transmission system. s The OFDM signal is expressed as follows

[0020]

[0021] Assume that the sampling frequency of the OFDM signal is f sp is the maximum subcarrier frequency N s f s J times, that is, f sp =JN s f s In order to make the sampled digital signal retain the information in the original signal completely and avoid aliasing, according to the Nyquist sampling theorem, J ≥ 2 must be satisfied. In addition, in order to make the PAPR of the discrete-time OFDM signal consistent with that of the continuous-time OFDM signal, J ≥ 4 must be satisfied. In summary, the discretized OFDM signal can be expressed as

[0022]

[0023] The four-dimensional antenna array transmitter architecture proposed in this patent is a joint space-time modulation, and the modulation is achieved by a high-speed RF switch, so the time modulation function U of the nth target signal sampling period is k (t) can be written as

[0024] U k (t)=0 or 1,(n-1)T sp <t≤nT sp (6)

[0025] Among them, the switching modulation period is consistent with the sampling period of the discretized OFDM signal, that is, T sp =1 / f sp .

[0026] The main idea of ​​this method is to split the OFMD signal into two parts, mapping them to baseband modulation and switching modulation, respectively, and further integrate them to utilize the space-time degrees of freedom. The following scheme is adopted here, carrying most of the amplitude information in the time function and most of the phase information in the baseband modulation. The specific expressions are Equations (7) and (8).

[0027] The OFDM-based synaesthesia integrated signal is converted into sMAX As the threshold value, the peak limit processing is performed initially. Here, the CCDF of the OFDM signal is 10 -2 The peak value corresponding to the threshold value is regarded as s MAX , get the modulated signal s c (t).

[0028] Assume U sum (t) represents the number of conducting units at the same time, then

[0029]

[0030] Among them, ceil{·} represents the rounding up operation, here through U k (t) Random combination realization at time t.

[0031] Under the above modulation method, combined with formula (2), the joint space-time modulation signal s JSTM (t) is expressed as follows

[0032]

[0033] However, the above method will cause large out-of-band radiation, which will not only induce in-band distortion but also increase the hardware requirements. Therefore, the joint space-time modulation signal needs to pass through a cutoff frequency of f pass After the low-pass filter, the baseband signal s that actually enters the power amplifier is obtained. b (t).

[0034] In general, the technical solution of the present invention is to load a four-dimensional transceiver component including a radio frequency switch at the rear end of each antenna unit, and use the conduction state change of the antenna unit to modulate most of the amplitude information on the time function and modulate most of the phase information on the baseband signal, thereby reducing the peak-to-average power ratio of the baseband signal.

[0035] The innovation of this invention lies in the proposed OFDM synaesthesia integrated system and method based on a four-dimensional antenna array combined with space-time modulation, demonstrating the potential of combining a four-dimensional antenna array with space-time modulation with a multi-carrier modulation system. The beneficial effects of this invention include improving the efficiency of the RF system by shifting most of the signal power pressure from the baseband to the time function, and achieving high-precision perception by utilizing the higher sidelobes generated by time function modulation. This method can be used in a synaesthesia integrated system based on multi-carrier modulation. Furthermore, the antenna backend structure is simple, making it easy to design and implement.

[0036] This invention can simultaneously realize single-channel secure communication and all-round high-precision perception in the integration of synaesthesia functions. Compared with traditional synaesthesia integration systems, an OFDM synaesthesia integration system based on a four-dimensional antenna array combined with space-time modulation has an additional perception function on the basis of a certain gain in communication effect. Compared with general OFDM-based phased array communication systems, the four-dimensional antenna array system with space-time modulation has greater radiation power in the main lobe direction and realizes secure communication by utilizing the randomness of the time function; compared with traditional phased array radars, the four-dimensional antenna array synaesthesia integration system with space-time modulation does not require scanning to achieve all-round perception. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a structural diagram of the OFDM synaesthesia integrated system based on four-dimensional antenna array and space-time modulation.

[0038] Figure 2 This is a flow chart of the OFDM synaesthesia integration method based on four-dimensional antenna array combined with space-time modulation.

[0039] Figure 3 It is the time modulation function of the four-dimensional antenna array when it is working under the OFDM synaesthesia integrated architecture based on the four-dimensional antenna array combined with space-time modulation. The switching frequency is the same as the sampling frequency of the OFDM signal.

[0040] Figure 4 This is the baseband signal spectrum diagram under the OFDM synaesthesia integrated architecture based on four-dimensional antenna array and space-time modulation.

[0041] Figure 5 It is the radiation power pattern when the communication angle is 90 degrees under the OFDM synaesthesia integrated architecture based on four-dimensional antenna array and space-time modulation.

[0042] Figure 6 It is the constellation diagram of signals transmitted in several typical directions under the OFDM synaesthesia integrated architecture based on four-dimensional antenna array and space-time modulation when the communication angle is always 90 degrees.

[0043] Figure 7 It is a bit error rate pattern with a signal-to-noise ratio of 14dB under the OFDM synaesthesia integrated architecture based on a four-dimensional antenna array and space-time modulation when the communication angle is always 90 degrees.

[0044] Figure 8 It is the angle-angle ambiguity function of the transmitted signal under the OFDM synaesthesia integrated architecture based on four-dimensional antenna array and space-time modulation when the communication angle is always 90 degrees.

[0045] Figure 9It is the speed-distance ambiguity function of the signal transmitted in several typical directions under the OFDM synaesthesia integrated architecture based on four-dimensional antenna array and space-time modulation when the communication angle is always 90 degrees. Specific implementation plan

[0046] Figure 1 A flow chart of a specific embodiment of the synaesthesia integration system based on a four-dimensional antenna array is given.

[0047] Figure 2 An OFDM interaceptive integrated system based on four-dimensional antenna array combined with space-time modulation is presented, including an OFDM modulator (1), a baseband signal modulator (2), a digital-to-analog converter (3), an upconverter (4), a local oscillator signal generator (5), a power amplifier (6), a duplexer (7), a power splitter / combiner (8), a four-dimensional wave control module (9), a four-dimensional transceiver component (10), an antenna unit (11), a low noise amplifier (12), a downconverter (13), an analog-to-digital converter (14), a digital signal processor (15), a radar analyzer (16), and optical fibers and cables connecting the various parts. The four-dimensional wave control module is used to implement time modulation of the high-speed radio frequency switch in the four-dimensional transceiver component. The antenna is shared by the transmitter and receiver, including N t = 16 evenly spaced elements, with a spacing of half a wavelength. Each element is connected to an RF switch, which periodically switches on and off to apply time modulation to the antenna array.

[0048] The original signal uses an OFDM synaesthesia integrated signal with 1024 subcarriers, a subcarrier spacing of 30kHz, and a symbol number of 1000. The bandwidth is 30*1024=30.72MHz. During the antenna transmission phase, the array is modulated using a joint space-time modulation function. Figure 3 The specific form of this time modulation function is given. In the process of modulating the baseband signal, the peak limiting operation specifically adopts the clipping algorithm, which is expressed as follows:

[0049]

[0050] Figure 4 The spectrum of the modulated baseband signal is given. The cutoff frequency of the low-pass filter is 40MHz. After power amplification, it is radiated by the transmitting antenna. During transmission, the loading of the baseband signal and the time modulation function is realized through a field programmable logic device (FPGA), so that clock synchronization can be achieved.

[0051] Assume that the communication angle is 90 degrees in azimuth. Since the peak-to-average power ratio of the baseband signal is about 3dB, and the peak-to-average power ratio of the target OFDM signal is about 11dB, in the calculation of the normalized radiation power pattern, the output power of the power amplifier in the four-dimensional antenna array system will be 8dB higher than that in the phased array system. However, the four-dimensional antenna array system introduces an additional set of 0 / 1 switches compared to the phased array system, resulting in a switch insertion loss of about 2dB. Taking these two points into consideration, as shown in the figure, Figure 5 , the transmit beamforming method proposed in the present invention can still achieve higher radiation power in the communication direction.

[0052] Figure 6-Figure 7 The results shown in the figure confirm that the OFDM interawareness integration method based on four-dimensional antenna array combined with space-time modulation proposed in the present invention can realize single-channel secure communication. Figure 6 Assume the signal-to-noise ratio is 14dB.

[0053] Figure 8-Figure 9 The results shown confirm that the OFDM synaesthesia integration method based on four-dimensional antenna array combined with space-time modulation proposed in the present invention can achieve all-round high-precision perception in a non-scanning state.

[0054] A specific embodiment of the present invention has been described above. It should be understood that this is only presented in an illustrative form and is not restrictive. Therefore, various changes in form and details can be made without departing from the spirit and scope of the present invention, which is obvious to those skilled in the art without the need for creative work. All of the above should be regarded as the scope of the present invention. A specific embodiment of the present invention has been described above. It should be understood that this is only presented in an illustrative form and is not restrictive. Therefore, various changes in form and details can be made without departing from the spirit and scope of the present invention, which is obvious to those skilled in the art without the need for creative work. All of the above should be regarded as the scope of the present invention.

Claims

1. An OFDM synaesthesia integration method based on a four-dimensional antenna array combined with space-time modulation is characterized by: The invention adopts an OFDM interawareness integrated system based on a four-dimensional antenna array combined with space-time modulation, wherein the system comprises an OFDM modulator (1), a baseband signal modulator (2), a digital-to-analog converter (3), an up-converter (4), a local oscillator signal generator (5), a power amplifier (6), a duplexer (7), a power splitter / combiner (8), a four-dimensional wave control module (9), a four-dimensional transceiver component (10), an antenna unit (11), a low noise amplifier (12), a down-converter (13), an analog-to-digital converter (14), a digital signal processor (15), a radar analyzer (16), and optical fibers and cables connecting the various parts; after the bit data to be transmitted enters the OFDM modulator, it is respectively connected to the four-dimensional wave control module and the baseband signal modulator; the digital signal generated by the OFDM modulator is respectively sent to the four-dimensional wave control module and the baseband signal modulator; the four-dimensional wave control module is respectively connected to the OFDM modulator and each four-dimensional transceiver component; the four-dimensional transceiver component comprises a plurality of optical fibers and cables that can be realized. The high-speed RF switch, phase shifter and amplifier of the present time modulation are connected to and controlled by the four-dimensional wave control module, and are also connected to the power splitter and combiner and the antenna unit; the baseband signal modulator is connected to the OFDM modulator and the digital-to-analog converter to convert the digital signal into an analog signal and enter the RF end; the digital-to-analog converter is connected to the baseband signal modulator and the up-converter; in addition to being connected to the local oscillator signal generator and the digital baseband modulator, the up-converter is also connected to the power splitter and combiner through a duplexer; the power splitter and combiner are connected to the four-dimensional transceiver components of each unit, and each four-dimensional transceiver component is then connected to its corresponding antenna unit; in addition, the duplexer is also connected to the low-noise amplifier, the low-noise amplifier is connected to the down-converter, one end of the down-converter is connected to the local oscillator signal generator, and the other end is connected to the analog-to-digital converter, and the analog-to-digital converter is connected to the digital signal processor; the signal after digital signal processing enters the radar analyzer for analysis to obtain radar indicators; the method includes the following steps: S1, the bit data generated by the bit data generator is transmitted to the OFDM modulator to generate a synaesthesia integrated signal; S2. Mapping the above-mentioned synaesthesia integrated signal to the four-dimensional wave control module and the baseband signal modulator, respectively, and collaboratively designing the baseband phase modulation and the antenna amplitude modulation to obtain a modulated synaesthesia integrated signal; The method of mapping the synaesthesia integrated signal to the digital baseband modulator in step S2 is specifically as follows: S201, the OFDM-based synaesthesia integrated signal is converted into s MAX As the threshold value, the peak limit processing is performed initially. Here, the complementary cumulative distribution function CCDF of the OFDM signal is set to 10 -2 The peak value corresponding to the threshold value is regarded as s MAX , get the modulated signal s c (t); S202: Perform joint space-time modulation on the peak-limited signal to obtain a joint space-time modulation signal s JSTM (t) is expressed as follows: Among them, U sum (t) is the number of conducting cells at time t; S203, the joint space-time modulation signal s JSTM (t) passes through a cutoff frequency f pass The low-pass filter is used to obtain the final baseband signal s b (t); The method of mapping the synaesthesia integrated signal to the four-dimensional wave control module in step S2 is as follows, so that the time modulation function of each unit satisfies the following expression: Among them, ceil{·} represents the rounding up operation, U k (t) represents the temporal modulation function of the kth unit, N t represents the total number of antenna elements in the array; S3, amplifying the modulated low-PAPR synaesthesia integrated signal in a power amplifier with less input power back-off, and then radiating and transmitting the signal through a transmitting antenna; S4a, the radiated signal is received by a receiving antenna located in the communication angle direction to form a communication signal, and is converted into a digital communication signal; S5a, performing digital signal processing on the digital communication signal, and obtaining transmitted bit data through OFDM demodulation; S4b, the radiation signal is reflected by the detection target to form a radar echo signal, which is received by the receiving antenna and converted into a digital echo signal; S4b, performing digital signal processing on the digital echo signal, and obtaining radar information of the detected target through a radar perception algorithm.

2. The OFDM synaesthesia integration method based on four-dimensional antenna array combined with space-time modulation according to claim 1 is further characterized by The randomness of the four-dimensional antenna array in time modulation is fully utilized to form higher side lobes in space, and the OFDM synaesthesia integrated signal is used to realize target detection in non-scanning conditions, reducing the complexity of the synaesthesia integrated system.

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