ZC sequence-based frequency-width-variable unmanned aerial vehicle suppressive interference signal generation method

Abstract

The invention provides a ZC sequence-based variable-frequency wide unmanned aerial vehicle suppressive interference signal generation method. The method comprises the following steps of S10, pre-generating ZC sequences with different lengths and root indexes; s20, unmanned aerial vehicle detection information is received, a corresponding ZC sequence is selected according to priori knowledge of unmanned aerial vehicle wireless signals in the detection information, and the ZC sequence in the frequency domain is converted into a digital baseband interference signal in the time domain through IFFT; step S30, performing low-pass filtering on the digital baseband interference signal according to the bandwidth of the digital baseband interference signal; and step S40, if the bandwidth of the signal needing to be interfered is greater than the maximum transmitting bandwidth of the radio frequency transceiver, setting the bandwidth of the signal needing to be interfered as N working bands by taking the maximum transmitting bandwidth of the radio frequency transceiver as a unit, circularly switching each working band at the frequency sweeping step interval time T, and generating a digital baseband interference signal in each working band. According to the invention, an efficient interference effect can be achieved.

Description

Technical Field

[0001] The present invention relates to the field of UAV interference suppression, and in particular to a method for generating a variable-frequency bandwidth UAV suppression interference signal based on ZC (Zadoff-Chu) sequences. Background Art

[0002] Due to the large-scale use of civilian low-cost UAVs, the accidents caused by the illegal use of such UAVs are increasing continuously. To ensure the safety of important places or major events, how to prevent and combat UAVs has become an important task. The existing anti-UAV countermeasure and combat technologies mainly adopt radio interference. Considering that narrowband power amplifiers with a working bandwidth of 100 MHz to 200 MHz have many advantages such as built-in interference sources, mature technology, low price, high power amplifier efficiency, and simple heat dissipation design, they have become the mainstream modules in the field of UAV interference.

[0003] The interference sources built in the narrowband power amplifier module usually adopt low-cost analog linear sweep signals based on a voltage-controlled oscillator (VCO). Although the working bandwidth of the narrowband power amplifier is relatively small, since the energy of the narrowband power amplifier is distributed in the entire 100 MHz to 200 MHz frequency band, the power density per unit frequency is low. The flight control and video transmission wireless signals of UAVs usually have a narrow bandwidth (generally 2M to 20 MHz), resulting in most of the energy of the transmitted interference signal being consumed in the useless frequency band, and the interference efficiency is very low.

[0004] At the same time, from the perspective of signal interference, active interference, as the main interference method, is divided into suppression interference and deception interference. The method adopted by suppression interference is that the interference device emits high-power interference signals, and the interference methods include noise interference, continuous wave interference, and pulse interference. Among them, sweep interference belongs to a type of continuous wave interference, and the interference source emits signals that change continuously in a certain manner from low frequency to high frequency or from high frequency to low frequency within a relatively wide frequency band, and the interference efficiency is low. Without knowing the modulation mode and parameter characteristics of the wireless signal to be interfered, using white noise with a uniform power spectral density in the entire working frequency band as the interference signal source is a highly efficient interference method. Usually, a pseudo-random PN (Pseudo-Random) sequence such as an m-sequence is modulated to generate a white noise signal with a specified bandwidth, and the efficiency is significantly higher than the sweep interference mode.

[0005] The ZC (Zadoff-Chu) sequence is a sequence similar to the PN sequence in terms of autocorrelation characteristics, with the characteristics of constant envelope and excellent autocorrelation characteristics still maintained after time-frequency domain transformation. It is widely used in channel reference and synchronization signals of the air interface of 4G / 5G mobile communications. The flight control and video transmission wireless signals of mainstream drones, such as the Ocusync series protocol of DJI, also use the ZC sequence for system synchronization and channel estimation, etc. Therefore, using the ZC sequence can provide a more efficient interference effect than white noise under the prior knowledge of signal modulation modes and characteristic parameters.

[0006] In addition, currently, the transmit bandwidth of medium- and low-cost RF transceiver chips such as ADI's AD9363 / 9361 is generally only 20MHz - 50MHz, which is much lower than the 100MHz - 200MHz operating bandwidth of narrowband power amplifiers. When multiple UAV wireless signals that appear simultaneously are distributed in the range of 100MHz - 200MHz, a single digital interference source based on these RF transceiver chips cannot achieve simultaneous suppression interference on multiple UAVs like a narrowband power amplifier. Summary of the Invention

[0007] To solve at least one technical problem in the prior art, an embodiment of the present invention provides a method for generating a variable-frequency bandwidth UAV suppression interference signal based on the ZC sequence, which can achieve an efficient interference effect, reduce the requirement for the linearity of the power amplifier, and improve the amplification efficiency of the power amplifier; at the same time, it realizes interference suppression on multiple UAVs. To achieve the above technical objectives, the technical solution adopted in the embodiment of the present invention is:

[0008] An embodiment of the present invention provides a method for generating a variable-frequency bandwidth UAV suppression interference signal based on the ZC sequence, including the following steps:

[0009] Step S10, pre-generate ZC sequences with different lengths and root indexes and load them into the memory of the interference device;

[0010] Step S20, receive UAV detection information, select the corresponding ZC sequence according to the prior knowledge of the UAV wireless signal in the detection information, and convert the ZC sequence in the frequency domain into a digital baseband interference signal in the time domain through IFFT transformation;

[0011] Step S30, perform low-pass filtering on the digital baseband interference signal according to its bandwidth;

[0012] Step S40, if the bandwidth of the signal to be interfered with is greater than the maximum transmit bandwidth of the RF transceiver, then take the maximum transmit bandwidth of the RF transceiver as a unit, set the bandwidth of the signal to be interfered with into N working frequency bands, perform cyclic switching of each working frequency band at a frequency sweep step interval time T, and generate a digital baseband interference signal based on Step S20 and Step S30 in each working frequency band.

[0013] Further, in step S10, the ZC sequence is as shown in formula (1):

[0014]

[0015] where i represents the i-th complex symbol in the ZC sequence, r represents the root index of the ZC sequence, and L is the length of the ZC sequence; different root indices r correspond to different ZC sequences;

[0016] According to different prior knowledge, for the UAV wireless signal;

[0017] If the subcarrier spacing, ZC sequence length, and root index are known, a first type of ZC sequence with the same subcarrier spacing as the UAV wireless signal, and the same length and root index is pre-generated;

[0018] If only the UAV wireless signal bandwidth is known, the subcarrier spacing is pre-specified, a second type of ZC sequence with a prime length is pre-generated, and the root index is a randomly generated value less than the ZC sequence length.

[0019] Further, the pre-specified subcarrier spacing is 50 KHz.

[0020] Further, step S20 specifically includes:

[0021] Step S201, if the UAV wireless signal with the ZC sequence length, root index, and subcarrier spacing is known in advance, then a first type of ZC sequence with the same subcarrier spacing as the known UAV wireless signal, and the same length and root index is selected for IFFT transformation; the number of points of the IFFT is set to the power of 2 that is greater than the ZC sequence length and closest to the length, and the ZC sequence is extended to the same length as the IFFT points by padding zeros before and after the ZC sequence;

[0022] Step S202, if only the UAV wireless signal bandwidth is known, then a second type of ZC sequence with a length matching the UAV wireless signal bandwidth is selected for IFFT transformation; the number of points of the IFFT transformation is set to the power of 2 that is greater than the ZC sequence length and closest to the length, and the ZC sequence is extended to the same length as the IFFT points by padding zeros before and after the ZC sequence;

[0023] Step S203: If the UAV operates in a frequency hopping mode, according to the known frequency hopping points and signal bandwidths at the frequency hopping points in the pre-known UAV frequency hopping spectrum, load the second type of ZC sequence with a length of 53 for filling at each frequency hopping point, then perform zero-padding in the frequency domain in the frequency bands without interference, and then perform IFFT transformation. The setting method of the number of IFFT points is as follows: Divide the maximum transmission bandwidth of the radio frequency transceiver by the pre-specified subcarrier spacing and round up to obtain n; set the number of IFFT points to the power of 2 that is greater than or equal to n and closest to n.

[0024] Further, in step S203, when the subcarrier spacing is 50KHz, the corresponding number of IFFT points is 1024.

[0025] Further, in step S30, perform raised cosine roll-off shaping low-pass filtering on the digital interference baseband signal, and select the raised cosine roll-off factor as 0.2.

[0026] Further, in step S40, the value of N is not greater than 4.

[0027] The beneficial effects brought by the technical solution provided by the embodiment of the present invention are as follows:

[0028] 1) For some UAVs with cracked or known wireless communication protocols, make full use of prior knowledge to generate ZC sequences with known lengths and root indexes, and seriously deteriorate the synchronization and channel estimation performance of UAVs by centrally interfering with the time-domain reference signals of UAV wireless signals, achieving an efficient interference effect.

[0029] 2) For UAVs with known signal bandwidths or frequency hopping modes, pre-generate ZC sequences with lengths matching the signal bandwidths, and based on IFFT transformation, realize interference signals with variable bandwidths and arbitrary comb-shaped spectra, concentrate the power of the interference signals on the frequency points where the UAV wireless signals are located, significantly improve the power spectral density of the interference signals, and use the constant envelope characteristic of the ZC sequences to reduce the requirements for the linearity of the power amplifier and improve the amplification efficiency of the power amplifier.

[0030] 3) Aiming at the problem that the maximum transmission bandwidth of existing radio frequency transceiver chips is limited, resulting in that a single digital interference source cannot effectively interfere with multiple UAVs, use the fast frequency locking function of existing radio frequency transceiver chips to divide the signal bandwidth to be interfered into multiple working frequency bands with fixed bandwidths, and realize the block frequency hopping mode through cyclic switching of the working frequency bands, expand the bandwidth of the interference signals, and achieve simultaneous interference suppression of multiple UAVs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a flowchart of a method for generating a suppressor interference signal for a variable-bandwidth UAV based on a ZC sequence in an embodiment of the present invention.

[0032] Figure 2Schematic diagram of generating a suppressing interference signal for a frequency-hopping mode UAV in an embodiment of the present invention. Detailed implementation manners

[0033] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0035] In the description of the embodiments of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and can also be the communication inside two elements. It can be a wireless connection or a wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0036] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] As Figure 1 shown, an embodiment of the present invention proposes a method for generating a suppressing interference signal for a UAV with variable frequency bandwidth based on ZC sequences, including the following steps:

[0038] Step S10, pre-generate ZC sequences with different lengths and root indices, and load them into the memory of the interference device;

[0039] The ZC sequence is shown in formula (1):

[0040]

[0041] where i represents the i-th complex symbol in the ZC sequence, r represents the root index of the ZC sequence, and L is the length of the ZC sequence; different root indices r correspond to different ZC sequences;

[0042] For the UAV wireless signal, according to different prior knowledge;

[0043] If the subcarrier spacing, ZC sequence length, and root index are known, a first type of ZC sequence with the same subcarrier spacing as the UAV wireless signal, and the same length and root index is pre-generated; for example, if the subcarrier spacing of the UAV wireless signal of a certain type of UAV is 15KHz, the length is 601, and the root index is 600, then a ZC sequence with a subcarrier spacing of 15KHz, a length of 601, and a root index of 600 is generated;

[0044] If only the UAV wireless signal bandwidth is known, the subcarrier spacing is pre-specified, and a second type of ZC sequence with a prime length is pre-generated, and the root index is a randomly generated value less than the ZC sequence length;

[0045] In this embodiment, considering that the UAV wireless signal bandwidth is generally in the range of 2M to 20MHz, when only the UAV wireless signal bandwidth is known, the pre-specified subcarrier spacing is 50KHz, and the ZC sequence lengths are default selected as 53, 149, 239, 337, 443, 653, 857, and 1009, etc.; by pre-specifying the subcarrier spacing and generating ZC sequences of different lengths, the dynamic adjustment of the interference signal bandwidth is realized.

[0046] Step S20, receive the UAV detection information, select the corresponding ZC sequence according to the prior knowledge of the UAV wireless signal in the detection information, and convert the ZC sequence in the frequency domain into a digital baseband interference signal in the time domain through IFFT transformation;

[0047] Due to the constant envelope characteristic of the ZC sequence, the peak-to-average ratio of the signal after IFFT transformation still remains at a relatively low level; in this embodiment, the number of IFFT points refers to the number of sampling points used in the inverse Fourier transform;

[0048] Specifically, it includes:

[0049] Step S201, if the UAV wireless signal with the ZC sequence length, root index, and subcarrier spacing is known in advance, select the first type of ZC sequence with the same subcarrier spacing as the known UAV wireless signal, and the same length and root index for IFFT transformation; the number of IFFT points is set to the power of 2 that is greater than the ZC sequence length and closest to the length, and the ZC sequence is extended to the same length as the number of IFFT points by padding zeros before and after the ZC sequence;

[0050] Step S202, if only the UAV wireless signal bandwidth is known, select the second type of ZC sequence with a length matching the UAV wireless signal bandwidth for IFFT transformation; the number of points for IFFT transformation is set to the power of 2 that is greater than and closest to the length of the ZC sequence. By padding zeros before and after the ZC sequence, the ZC sequence is extended to the same length as the IFFT number of points;

[0051] The following table takes the maximum transmit bandwidth of the RF transceiver as 51.2 MHz and the subcarrier spacing as 50 KHz as an example, and gives the ZC sequence length corresponding to different UAV wireless signal bandwidths and the actual bandwidth of the digital baseband interference signal;

[0052] UAV wireless signal bandwidth ZC sequence length IFFT point number Actual bandwidth of interference signal 0 - 6 MHz 149 256 7.45 MHz 6 MHz - 10 MHz 239 256 11.95 MHz 10 MHz - 15 MHz 337 512 16.85 MHz 15 MHz - 20 MHz 443 512 22.15 MHz 25 MHz - 30 MHz 653 1024 32.65 MHz. 30 MHz - 40 MHz 857 1024 42.85 MHz 40 MHz - 50 MHz 1009 1024 50.45 MHz

[0053] Considering the Doppler frequency shift generated by the rapid flight of the UAV and the possible clock frequency drift caused by the temperature change of the RF devices of the interference device itself, the bandwidth of the generated digital baseband interference signal is usually 1 - 3 MHz larger than the UAV wireless signal bandwidth;

[0054] Step S203, if the UAV operates in the frequency hopping mode, according to the known hopping frequency points and the signal bandwidth at each hopping frequency point in the UAV frequency hopping map, load the second type of ZC sequence with a length of 53 at each hopping frequency point for filling, then perform zero-padding in the frequency domain in the frequency bands without interference, and then perform IFFT transformation; the setting method of the number of points for IFFT is: divide the maximum transmit bandwidth of the RF transceiver by the pre-specified subcarrier spacing and round up to get n; the number of points for IFFT is set to the power of 2 that is greater than or equal to n and closest to n; as Figure 2 shown;

[0055] When the subcarrier spacing is 50 KHz, the interference bandwidth corresponding to each hopping frequency point is 2.65 MHz. Since the signal bandwidth at each hopping frequency point in the frequency hopping system generally does not exceed 2 MHz, a protection bandwidth of about 1 MHz is reserved to cope with the Doppler frequency shift of the UAV; considering the limitations of the digital source devices of the RF transceiver (the maximum transmit bandwidth is 51.2 MHz), the bandwidth span of the digital baseband interference signal in the frequency hopping mode is limited to 51.2 MHz, and the corresponding IFFT number of points is 1024 when the subcarrier spacing is 50 KHz;

[0056] Step S30, perform low-pass filtering on the digital baseband interference signal according to its bandwidth;

[0057] In this embodiment, perform raised cosine roll-off shaping low-pass filtering on the digital interference baseband signal, and the raised cosine roll-off factor is selected as 0.2 to eliminate inter-symbol interference in the time domain;

[0058] Step S40: If the bandwidth of the signal to be jammed is greater than the maximum transmission bandwidth of the RF transceiver, then, taking the maximum transmission bandwidth of the RF transceiver as a unit, set the bandwidth of the signal to be jammed into N operating frequency bands, and perform cyclic switching of each operating frequency band at a frequency-sweeping step interval time T. Generate a digital baseband jamming signal for each operating frequency band based on Step S20 and Step S30.

[0059] The RF transceiver chip has a fast frequency locking mode. Taking AD9361 as an example, the switching delay for a frequency interval exceeding 100 MHz can be controlled within 20 us, and the fastest switching can be completed in 5 us.

[0060] When the bandwidth of the signal to be jammed is greater than the maximum transmission bandwidth of the RF transceiver, by setting N operating frequency bands (numbered 0, 1,..., N - 1), the bandwidth of each operating frequency band is set to the maximum bandwidth of the RF transceiver chip, such as 50 MHz. Starting from frequency band 0, every T time (frequency-sweeping step interval time), switch from one operating frequency band to another. If the currently resident operating frequency band is N - 1, then cycle back to frequency band 0; generate a digital baseband jamming signal for each operating frequency band based on Step S20 and Step S30.

[0061] Considering the jamming efficiency, generally N is not greater than 4. When the operating frequency band is 50 MHz, a jamming signal with a maximum bandwidth of 200 MHz can be generated.

[0062] In the jamming device, the digital baseband jamming signal is then mixed to obtain an RF jamming signal for transmission.

[0063] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for generating a suppressor interference signal of a variable-frequency bandwidth unmanned aerial vehicle based on ZC sequences, characterized in that Including the following steps: Step S10: Pre-generate ZC sequences with different lengths and root indices, and load them into the memory of the interference device; Step S20: Receive the UAV detection information, select the corresponding ZC sequence according to the prior knowledge of the UAV wireless signal in the detection information, and convert the ZC sequence in the frequency domain into a digital baseband interference signal in the time domain through IFFT transformation; Step S30: Perform low-pass filtering on the digital baseband interference signal according to its bandwidth; Step S40: If the bandwidth of the signal to be interfered with is greater than the maximum transmission bandwidth of the radio frequency transceiver, then take the maximum transmission bandwidth of the radio frequency transceiver as a unit, set the bandwidth of the signal to be interfered with into N working frequency bands, perform cyclic switching of each working frequency band at a sweep frequency step interval time T, and generate a digital baseband interference signal based on Step S20 and Step S30 in each working frequency band.

2. The method for generating a variable-frequency bandwidth UAV suppression interference signal based on ZC sequences according to claim 1, wherein In Step S10, the ZC sequence is as shown in formula (1): where i represents the i-th complex symbol in the ZC sequence, r represents the root index of the ZC sequence, and L is the length of the ZC sequence; different root indices r correspond to different ZC sequences; According to different prior knowledge, for UAV wireless signals; If the subcarrier spacing, ZC sequence length, and root index are known, pre-generate the first type of ZC sequence with the same subcarrier spacing as the UAV wireless signal, and the same length and root index; If only the UAV wireless signal bandwidth is known, then pre-specify the subcarrier spacing, pre-generate the second type of ZC sequence with a prime number length, and the root index is a randomly generated value less than the ZC sequence length.

3. The method for generating a variable-frequency bandwidth UAV suppression interference signal based on ZC sequences according to claim 2, wherein The pre-specified subcarrier spacing is 50KHz.

4. The method for generating a variable-frequency bandwidth UAV suppression interference signal based on ZC sequences according to claim 2, wherein Step S20 specifically includes: Step S201: If the UAV wireless signal with the ZC sequence length, root index, and subcarrier spacing is known in advance, then select the first type of ZC sequence with the same subcarrier spacing as the known UAV wireless signal, and the same length and root index for IFFT transformation; the number of IFFT points is set to the power of 2 greater than and closest to the ZC sequence length, and the ZC sequence is extended to the same length as the IFFT points by padding zeros before and after the ZC sequence; Step S202: If only the UAV wireless signal bandwidth is known, then select the second type of ZC sequence with a length matching the UAV wireless signal bandwidth for IFFT transformation; the number of IFFT transformation points is set to the power of 2 greater than and closest to the ZC sequence length, and the ZC sequence is extended to the same length as the IFFT points by padding zeros before and after the ZC sequence; Step S203: If the UAV operates in the frequency hopping mode, according to the known frequency hopping points and signal bandwidths at the frequency hopping points in the UAV frequency hopping spectrum, load the second type of ZC sequence with a length of 53 at each frequency hopping point for filling, then perform zero-padding operation in the frequency domain in the non-interference frequency band, and then perform IFFT transformation; the setting method of the number of IFFT points is as follows: divide the maximum transmission bandwidth of the radio frequency transceiver by the pre-specified subcarrier spacing and round up to get n; the number of IFFT points is set to the power of 2 that is greater than or equal to n and closest to n.

5. The method for generating a variable-frequency bandwidth UAV suppression interference signal based on the ZC sequence according to claim 4, characterized in that In step S203, when the subcarrier spacing is 50 KHz, the corresponding number of IFFT points is 1024 points.

6. The method for generating a variable-frequency bandwidth UAV suppression interference signal based on the ZC sequence according to any one of claims 1 to 5, characterized in that In step S30, perform raised cosine roll-off shaping low-pass filtering on the digital interference baseband signal, and the raised cosine roll-off factor is selected to be 0.

2.

7. The method for generating a variable-frequency bandwidth UAV suppression interference signal based on the ZC sequence according to any one of claims 1 to 5, characterized in that In step S40, the value of N is not greater than 4.

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