CN109194415B - Broadband OFDM signal angle measurement method and system in unmanned aerial vehicle data chain - Google Patents

Broadband OFDM signal angle measurement method and system in unmanned aerial vehicle data chain Download PDF

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CN109194415B
CN109194415B CN201811007955.4A CN201811007955A CN109194415B CN 109194415 B CN109194415 B CN 109194415B CN 201811007955 A CN201811007955 A CN 201811007955A CN 109194415 B CN109194415 B CN 109194415B
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azimuth
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付林罡
闫朝星
罗翔
孙亚男
李辉
李响
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Beijing Research Institute of Telemetry
Aerospace Long March Launch Vehicle Technology Co Ltd
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Aerospace Long March Launch Vehicle Technology Co Ltd
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    • H04—ELECTRIC COMMUNICATION TECHNIQUE
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Abstract

The invention relates to a broadband OFDM signal angle measurement method and an angle measurement system in an unmanned aerial vehicle data chain, wherein the method carries out secondary moment detection based on a sum-difference synthesis signal, firstly obtains the secondary moment of the synthesis signal and the expected value of the secondary moment, further obtains an azimuth detection signal and a pitching detection signal, and further calculates to obtain an angle measurement estimated value based on the normalization of the secondary moment, thereby remarkably improving the angle measurement precision of the OFDM data chain compared with the traditional method; in addition, the broadband OFDM signal angle measurement method in the data chain of the unmanned aerial vehicle is designed aiming at the broadband OFDM signal, is suitable for a single radio frequency channel receiver, does not need other PCM/FM, CDMA or BPSK/QPSK and other signal auxiliary angle tracking, can realize the three-in-one of the telemetering and remote control data chain, has the anti-multipath performance, simplifies the system architecture and saves the signal frequency band resource.

Description

Broadband OFDM signal angle measurement method and system in unmanned aerial vehicle data chain
Technical Field
The invention relates to the technical field of digital wireless communication transmission, in particular to a broadband OFDM signal angle measurement method and an angle measurement system in an unmanned aerial vehicle data chain.
Background
In an unmanned aerial vehicle data link system, a ground control station needs to accurately point to an airborne communication terminal, an angle tracking system mainly comprises three modes of manual tracking, program tracking and self-tracking, the self-tracking is the mainstream angle tracking mode at present, and the tracking precision, robustness and reaction speed are obviously superior to the two modes. The self-tracking is mainly divided into five modes of stepping tracking, conical scanning tracking, monopulse tracking, phased array scanning tracking, multi-beam tracking and the like according to the principle. A single-pulse tracking system with a fast tracking speed is often adopted to compare received signals from two or more antenna beams, and angular deviation information between the antenna and a target is extracted to determine the position of the target. The single pulse technique is divided into two basic types of amplitude comparison and phase comparison. The phase consistency of the receiving channel is higher than that of a single pulse. The phase consistency requirement of the amplitude-comparison single pulse on a receiving channel is lower.
Under the single-pulse tracking system, the single-pulse tracking system can be divided into the following parts according to the number of radio frequency channels: three-channel single pulse, two-channel single pulse and single-channel single pulse angle tracking systems. Compared with a multi-channel single-pulse angle tracking system, the single-channel single-pulse angle tracking system has the advantages of simple structure and low complexity, and particularly relates to the problem of channel backup in practical engineering application, and a single-pulse single channel is undoubtedly the best solution. The traditional single pulse angle tracking mostly adopts waveforms with constant envelope forms, such as PCM-FM pulse modulation, BPSK, QPSK or CDMA spread spectrum signals and the like. The essence of the baseband signal processing of the single-channel angle tracking receiver is to demodulate amplitude modulation signals and separate azimuth and pitch angle error signals according to corresponding time sequence relation. The common methods for amplitude-modulated signal demodulation include envelope detection and synchronous detection, and the envelope detection is relatively simple to realize.
In the patent "zhou sai wen yaxiang, a goniometric method for unmanned aerial vehicles. CN 102156275B, 2012 "designed an array antenna with a tracking accuracy of 0.11 °, and satisfied the requirement that the measurement and control accuracy of the unmanned aerial vehicle is generally less than 0.2 °. In the document "wangsan. single channel angle tracking receiver baseband signal processing technique. the synchronous demodulation method is adopted in the university of sienna electronics technology 2012" to demodulate the angle error signal with low signal-to-noise ratio. In the literature, "sonningshuai" monopulse spread spectrum angle tracking system research and FPGA design realization, Chongqing: in the university of Chongqing, 2014 ", in order to eliminate the influence of the signal amplitude, a carrier signal amplitude influence factor V is adopted to perform normalization processing on the error signal. The literature, "Liujiaxing", wideband signal angle tracking and four-channel single-pulse scheme [ J ]. aircraft measurement and control science, 2011,30(5):20-25. "angle acquisition is performed at low carrier-to-noise ratio, and a four-channel single-pulse scheme is designed for FM modulation and PSK signals according to a sum-path signal and a difference-path normalized signal. The patent of the fifty-fourth department of electronic science and technology in china entitled "li qiang, minjie" method for detecting phase difference and relative amplitude of input signals by using single channel, patent no: ZL 200610102076.0, 2006 "," lieqiang et al. ZL 200610102075.6, 2006 "," Zhang Ximing et al. CN 101707578B, 2009 "designs a method for receiving, demodulating and modulating signal sources, respectively.
With the increase of the high-speed data transmission code rate in order of magnitude, the problem of angle tracking of broadband signals is more and more concerned, and particularly, an unmanned aerial vehicle data chain needs to adopt an OFDM (orthogonal frequency division multiplexing) system capable of resisting multipath interference in a low-elevation environment, and the higher peak-to-average ratio characteristic of the broadband signal provides a challenge for angle measurement of the unmanned aerial vehicle data chain system adopting OFDM. The method in the above document cannot be directly used for angle measurement of high peak-to-average ratio OFDM signals on one hand, and on the other hand, the normalization processing method using factors or four channels is not suitable for single-channel single-pulse angle measurement.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a broadband OFDM signal angle measurement method in an unmanned aerial vehicle data chain.
Another object of the present invention is to provide a broadband OFDM signal angle measurement system in a data chain of an unmanned aerial vehicle.
The above purpose of the invention is realized by the following technical scheme:
the broadband OFDM signal angle measurement method in the data chain of the unmanned aerial vehicle comprises the following steps:
calculating a second moment of a synthesized signal and an expected value of the second moment according to an OFDM signal sent by the unmanned aerial vehicle and a sum path signal and a difference path signal obtained by performing sum difference processing on a radio frequency signal received by a receiving antenna;
detecting the second moment of the synthesized signal by using a low-frequency square wave, and integrating in a period of the low-frequency square wave to obtain an azimuth detection signal and a pitching detection signal;
and calculating to obtain a measured angle estimation value based on second moment normalization according to the expected value of the second moment of the synthesized signal, the azimuth detection signal and the pitch detection signal.
In the above method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data link, a specific method for calculating a second moment of a synthesized signal and an expected value of the second moment according to an OFDM signal sent by an unmanned aerial vehicle and a sum signal and a difference signal obtained by performing sum and difference processing on a radio frequency signal received by a receiving antenna is as follows:
(1.1) receiving signals sent by the unmanned aerial vehicle and represented as a plurality of radio frequency signals by the receiving antenna, and obtaining a sum path signal, an azimuth difference path signal and a pitching difference path signal after sum difference processing according to OFDM signals sent by the unmanned aerial vehicle;
(1.2) multiplying and modulating the azimuth difference path signal and the pitch difference path signal through a low-frequency square wave, then carrying out amplitude modulation on the sum path signal, and then coupling to obtain a synthetic signal;
(1.3) calculating a second moment of the synthesized signal from the synthesized signal;
and (1.4) obtaining the expected value of the second moment of the synthesized signal according to the second moment of the synthesized signal.
In the above method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data chain, in step (1.1), a digital expression of the OFDM signal transmitted by the unmanned aerial vehicle via a wireless channel is as follows:
Figure BDA0001784393290000031
wherein: n is an integer of 0 to Ns-1，NsThe FFT size adopted by OFDM modulation is represented as a positive integer; x (k) is a time domain signal, H (k) is a frequency domain response of a transmitted signal through a channel, EsFor transmit signal power, z (n) is the signal time domain noise.
In the above method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data link, the specific method in which the receiving antenna in step (1.1) receives signals sent by the unmanned aerial vehicle and indicates the signals as a plurality of radio frequency signals, and according to the OFDM signals sent by the unmanned aerial vehicle, sum and difference processing is performed to obtain a sum path signal, a azimuth difference path signal, and a pitch difference path signal is as follows:
the receiving terminal antenna multi-horn or multi-mode feed source receives the signal U (t) sent by the unmanned aerial vehicle, and the signal U (t) is represented as 4 radio frequency signals U1(t)、U2(t)、U3(t)、U4(t) obtaining a sum signal U after sum and difference processing∑(t) azimuth difference path signal UΔA(t) pitching differential signal UΔE(t) are respectively:
Figure BDA0001784393290000041
Figure BDA0001784393290000042
Figure BDA0001784393290000043
wherein: s (t) is an analog waveform of signal s (n), AmMu is the slope of the antenna differential signal pattern, omega is the carrier frequency, d is the antenna spacing, lambda is the wavelength, A is the angle of the target from the electrical axis in azimuth and E is the angle of the target from the electrical axis in elevation,
Figure BDA0001784393290000044
is the signal phase, t is the time variable.
In the above method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data chain, in the step (1.2), the azimuth difference path signal and the pitch difference path signal are modulated by multiplying a low-frequency square wave, and then the sum path signal is subjected to amplitude modulation, and then a specific method for obtaining a synthetic signal by coupling is as follows:
the azimuth difference circuit signalUΔA(t) and Pitch Difference Signal UΔE(t) passing a low frequency square wave g1(t)、g2(t) multiplying modulation, and summing the signals U∑(t) amplitude modulating, and then coupling to obtain a composite signal U∑Δ(t)：
Figure BDA0001784393290000045
Wherein: s (t) is the analog waveform of signal s (n), G is amplitude modulation parameter, and low-frequency square wave G1(t)、g2(t) is represented as follows:
Figure BDA0001784393290000051
wherein: t is the low frequency square wave period.
In the above method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data chain, the specific method for calculating a second moment of a synthesized signal according to the synthesized signal in step (1.3) is as follows:
Figure BDA0001784393290000052
wherein: m2The second moment of the resultant signal.
In the above method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data chain, the specific method for obtaining the expected value of the second moment of the synthesized signal according to the second moment of the synthesized signal in step (1.4) is as follows:
due to A2+E2＝θ2Where θ is the target off-antenna electrical axis angle, the expectation of a and E is set to 0, the expectation of θ is set to 0, and the expected value of the second moment of the resulting composite signal is:
Figure BDA0001784393290000053
wherein: c { M }2The expected value of the second moment of the synthesized signal is obtained; c { | s: (t)|2Is right to | s (t)2And calculating an expected value.
In the method for measuring the angle of the broadband OFDM signal in the data chain of the unmanned aerial vehicle, the second moment of the synthesized signal is detected by using a low-frequency square wave, and the second moment is integrated in the period of the low-frequency square wave to obtain the azimuth detection signal and the pitch detection signal, and the specific method comprises the following steps:
Figure BDA0001784393290000054
Figure BDA0001784393290000055
wherein g is1(t)、g2(T) is a low frequency square wave, T is the period of the low frequency square wave, gAFor the azimuth detection signal, gEIs a pitch detection signal.
In the above method for measuring angles of broadband OFDM signals in an unmanned aerial vehicle data link, a specific method for obtaining an angle measurement estimation value based on second-order moment normalization by calculation based on an expected value of a second-order moment of the synthesized signal, the azimuth detection signal and the pitch detection signal is as follows:
Figure BDA0001784393290000061
Figure BDA0001784393290000062
wherein: a is an azimuth angle measurement estimated value, E is a pitch angle measurement estimated value, gAFor the azimuth detection signal, gEIs a pitch detection signal.
In the broadband OFDM signal angle measurement method in the data chain of the unmanned aerial vehicle, the angle measurement method sets the low-frequency square wave g according to the stages of takeoff, cruise and return to different tasks of the unmanned aerial vehicle1(t)、g2(T) the period T is two shifts, respectively f1＝1/T1、f2＝1/T2And is andf1＜f2；
setting a threshold T according to the size of an AGC signal when the distance between a ground station and a target unmanned aerial vehicle changesaIf the received AGC signal exceeds the threshold TaThen f is selected1Obtaining a fast tracking speed at a short distance; if the received AGC signal does not exceed the threshold TaThen f is selected2And high angle measurement precision is obtained at a long distance.
In the above method for measuring angle of broadband OFDM signal in data chain of unmanned aerial vehicle, f is1＝1/T1＝1kHz、f2＝1/T2＝100Hz。
Broadband OFDM signal angle measurement system in unmanned aerial vehicle data link, including second moment expectation acquisition module, detection signal acquisition module and angle measurement estimated value acquisition module, wherein:
a second moment expected value acquisition module: according to an OFDM signal sent by an unmanned aerial vehicle and a sum-path signal and a difference-path signal obtained after sum-difference processing is carried out on a radio-frequency signal received by a receiving antenna, calculating a second moment of a synthesized signal and an expected value of the second moment, sending the second moment of the synthesized signal to a detection signal acquisition module, and sending the expected value of the second moment of the synthesized signal to an angle measurement estimated value acquisition module;
a detection signal acquisition module: receiving a second moment of a synthesized signal sent by a second moment expected value acquisition module, detecting the second moment of the synthesized signal by using a low-frequency square wave, integrating in a low-frequency square wave period to obtain an azimuth detection signal and a pitch detection signal, and sending the azimuth detection signal and the pitch detection signal to an angle measurement estimated value acquisition module;
an angle measurement estimation value acquisition module: receiving an azimuth detection signal and a pitch detection signal sent by a detection signal acquisition module, receiving an expected value of a second moment of a synthesized signal sent by a second moment expected value acquisition module, and calculating to obtain an angle measurement estimated value based on second moment normalization according to the expected value of the second moment of the synthesized signal, the azimuth detection signal and the pitch detection signal.
In the broadband OFDM signal angle measurement system in the data link of the unmanned aerial vehicle, the specific method for calculating the expected values of the second moment and the second moment of the synthesized signal by the second moment expected value acquisition module according to the sum and difference signals obtained by sum and difference processing of the OFDM signal transmitted by the unmanned aerial vehicle and the radio frequency signal received by the receiving antenna is as follows:
(1.1) receiving signals sent by the unmanned aerial vehicle and represented as a plurality of radio frequency signals by the receiving antenna, and obtaining a sum path signal, an azimuth difference path signal and a pitching difference path signal after sum difference processing according to OFDM signals sent by the unmanned aerial vehicle;
(1.2) multiplying and modulating the azimuth difference path signal and the pitch difference path signal through a low-frequency square wave, then carrying out amplitude modulation on the sum path signal, and then coupling to obtain a synthetic signal;
(1.3) calculating a second moment of the synthesized signal from the synthesized signal;
and (1.4) obtaining the expected value of the second moment of the synthesized signal according to the second moment of the synthesized signal.
In the above broadband OFDM signal angle measurement system in the data chain of the drone, the digital expression of the OFDM signal sent by the drone in step (1.1) passing through the wireless channel is as follows:
Figure BDA0001784393290000071
wherein: n is an integer of 0 to Ns-1，NsThe FFT size adopted by OFDM modulation is represented as a positive integer; x (k) is a time domain signal, H (k) is a frequency domain response of a transmitted signal through a channel, EsFor transmit signal power, z (n) is the signal time domain noise.
The specific method for obtaining the sum path signal, the azimuth difference path signal and the elevation difference path signal after the sum difference processing according to the OFDM signal sent by the unmanned aerial vehicle is as follows:
the receiving terminal antenna multi-horn or multi-mode feed source receives the signal U (t) sent by the unmanned aerial vehicle, and the signal U (t) is represented as 4 radio frequency signals U1(t)、U2(t)、U3(t)、U4(t) obtaining a sum signal U after sum and difference processing∑(t) Azimuth difference circuit signal UΔA(t) pitching differential signal UΔE(t) are respectively:
Figure BDA0001784393290000081
Figure BDA0001784393290000082
Figure BDA0001784393290000083
wherein: s (t) is an analog waveform of signal s (n), AmMu is the slope of the antenna differential signal pattern, omega is the carrier frequency, d is the antenna spacing, lambda is the wavelength, A is the angle of the target from the electrical axis in azimuth and E is the angle of the target from the electrical axis in elevation,
Figure BDA0001784393290000085
is the signal phase, t is the time variable.
In the above broadband OFDM signal angle measurement system in the data chain of the unmanned aerial vehicle, in the step (1.2), the azimuth difference path signal and the pitch difference path signal are modulated by multiplying a low-frequency square wave, and then the sum path signal is subjected to amplitude modulation, and then a specific method for obtaining a synthetic signal by coupling is as follows:
the azimuth difference circuit signal UΔA(t) and Pitch Difference Signal UΔE(t) passing a low frequency square wave g1(t)、g2(t) multiplying modulation, and summing the signals U∑(t) amplitude modulating, and then coupling to obtain a composite signal U∑Δ(t)：
Figure BDA0001784393290000084
Wherein: s (t) is the analog waveform of signal s (n), G is amplitude modulation parameter, and low-frequency square wave G1(t)、g2(t) representsThe following were used:
Figure BDA0001784393290000091
wherein: t is a low-frequency square wave period;
the specific method for calculating the second moment of the synthesized signal according to the synthesized signal in the step (1.3) is as follows:
Figure BDA0001784393290000092
wherein: m2Second moment of the synthesized signal;
the specific method for obtaining the expected value of the second moment of the synthesized signal according to the second moment of the synthesized signal in the step (1.4) is as follows:
due to A2+E2＝θ2Where θ is the target off-antenna electrical axis angle, the expectation of a and E is set to 0, the expectation of θ is set to 0, and the expected value of the second moment of the resulting composite signal is:
Figure BDA0001784393290000093
wherein: c { M }2The expected value of the second moment of the synthesized signal is obtained; c { | s (t) & gtdoes not dust2Is right to | s (t)2And calculating an expected value.
In the above system for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data link, the specific method in which the detection signal acquisition module detects the second moment of the synthesized signal with a low-frequency square wave and integrates within a period of the low-frequency square wave to obtain an azimuth detection signal and a pitch detection signal includes:
Figure BDA0001784393290000094
Figure BDA0001784393290000095
wherein g is1(t)、g2(T) is a low frequency square wave, T is the period of the low frequency square wave, gAFor the azimuth detection signal, gEIs a pitch detection signal;
the specific method for obtaining the angle measurement estimation value based on the second moment normalization by the angle measurement estimation value acquisition module according to the expected value of the second moment of the synthesized signal, the azimuth detection signal and the pitch detection signal through calculation comprises the following steps:
Figure BDA0001784393290000101
Figure BDA0001784393290000102
wherein: a is an azimuth angle measurement estimated value, E is a pitch angle measurement estimated value, gAFor the azimuth detection signal, gEIs a pitch detection signal.
Compared with the prior art, the invention has the following beneficial effects:
(1) according to the broadband OFDM signal angle measurement method in the data chain of the unmanned aerial vehicle, the second moment detection is carried out on the basis of the sum and difference synthesis signal, and the direction and pitch angle measurement estimated values based on the second moment normalization are obtained, so that the angle measurement precision of the OFDM data chain is improved compared with that of the traditional method;
(2) the angle measuring method of the broadband OFDM signal in the data link of the unmanned aerial vehicle is designed aiming at the broadband OFDM signal, is suitable for a single radio frequency channel receiver, does not need other PCM/FM, CDMA or BPSK/QPSK and other signal auxiliary angle tracking, can realize the three-in-one of the remote measuring and remote control data link, has the anti-multipath performance, simplifies the system architecture and saves the signal frequency band resource;
(3) the broadband OFDM signal angle measurement method in the data chain of the unmanned aerial vehicle can work at two-gear low-frequency square wave according to the stages of takeoff, cruising and returning to different tasks of the unmanned aerial vehicle, judge according to the threshold value, give out a reasonable threshold value, obtain fast tracking speed in a short distance, obtain high angle measurement precision in a long distance, obtain different tracking speed and angle measurement precision, and have strong adaptability;
(4) according to the broadband OFDM signal angle measurement method and the broadband OFDM signal angle measurement system in the unmanned aerial vehicle data chain, the second moment detection is carried out based on the sum-difference synthesis signal, the second moment of the synthesis signal and the expected value of the second moment are obtained firstly, the azimuth detection signal and the pitching detection signal are further obtained, and the angle measurement estimated value based on the second moment normalization is obtained through calculation.
(5) Tests show that compared with a square rate method, the normalization angle measurement estimation method is not influenced by a signal-to-noise ratio in the low signal-to-noise ratio performance of 0dB to 10dB, meanwhile, the normalization angle measurement estimation method is not influenced by signal amplitude change, accurate automatic gain control is not needed, standard deviation performance of the normalization angle measurement estimation method is basically lower than 0.2 degree in 0dB to 20dB, and the requirement of unmanned angle tracking precision is met.
Drawings
FIG. 1 is a schematic block diagram of a method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data chain according to the present invention;
FIG. 2 is a performance diagram of an average value of angle measurement estimation of a broadband OFDM signal angle measurement method in an unmanned aerial vehicle data chain according to an embodiment of the present invention;
fig. 3 is a standard deviation performance diagram of angle measurement estimation under different frequency square waves of the method for measuring the angle of the broadband OFDM signal in the data chain of the unmanned aerial vehicle according to the embodiment of the present invention.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific examples:
as shown in fig. 1, a schematic block diagram of a method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data chain according to the present invention is shown, and the method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data chain specifically includes the following steps:
step one, calculating a second moment of the synthesized signal and an expected value of the second moment
The digital expression that the unmanned aerial vehicle sends OFDM signals through a wireless channel is
Figure BDA0001784393290000111
Wherein: n is an integer of 0 to Ns-1，NsThe FFT size adopted by OFDM modulation is represented as a positive integer; x (k) is a time domain signal, H (k) is a frequency domain response of a transmitted signal through a channel, EsFor transmit signal power, z (n) is the signal time domain noise.
The receiving terminal antenna multi-horn or multi-mode feed source receives the signal U (t) sent by the unmanned aerial vehicle, and the signal U (t) is represented as 4 radio frequency signals U1(t)、U2(t)、U3(t)、U4(t) obtaining a sum signal U after sum and difference processing∑(t) azimuth difference path signal UΔA(t) pitching differential signal UΔE(t) are respectively:
Figure BDA0001784393290000112
Figure BDA0001784393290000121
Figure BDA0001784393290000122
wherein: s (t) is an analog waveform of signal s (n), AmMu is the antenna differential signal pattern slope (difference slope), omega is the carrier frequency, d is the antenna spacing, lambda is the wavelength, A is the angle of the target in azimuth off the electrical axis, E is the angle of the target in elevation off the electrical axis,
Figure BDA0001784393290000123
is the signal phase, t is the time variable.
Will azimuth difference circuit signal UΔA(t) pitching differential signal UΔE(t) passing a low frequency square wave g1(t)、g2(t) multiplying the modulated sum signal U∑(t) amplitude modulated and thereafter passed through a coupler to form a composite signal U∑Δ(t)，
Figure BDA0001784393290000124
Wherein: s (t) is the analog waveform of signal s (n), G is the amplitude modulation parameter, which takes the value of 1/4 in this embodiment, and G is the low frequency square wave1(t)、g2(T) with T as the period:
Figure BDA0001784393290000125
wherein:
Figure BDA0001784393290000126
the synthetic signal is down-converted and filtered to be used as an input signal of a digital receiver, and a second moment M of the synthetic signal is calculated firstly2And its expected value C { M2}：
Figure BDA0001784393290000127
Due to A2+E2＝θ2Since theta is the target off-axis angle of the antenna, when the azimuth angle error A and the pitch angle error E are small, the expectation of A and E is 0 and the expectation of theta is 0, the expected secondary moment value C { M }2The method is as follows:
Figure BDA0001784393290000131
wherein: c { M }2The expected value of the second moment of the synthesized signal is obtained; c { | s (t) & gtdoes not dust2Is right to | s (t)2And calculating an expected value.
Step two, using the second moment of the received composite signal obtained in step one as low frequency square wave g1(t)、g2(T) detecting, and integrating in a low-frequency square wave period T to obtain an azimuth detection signal gAPitch detection signal gE：
Figure BDA0001784393290000132
Figure BDA0001784393290000133
Step (III) of obtaining the second moment M in the step (I)2The azimuth detection signal g obtained in the step (II)APitch detection signal gESetting a G value 1/4, and calculating to obtain a goniometric estimated value based on second moment normalization:
Figure BDA0001784393290000134
Figure BDA0001784393290000135
wherein: a is an azimuth angle measurement estimated value, E is a pitch angle measurement estimated value, gAFor the azimuth detection signal, gEIs a pitch detection signal.
Setting the low-frequency square wave g by the angle measuring method from the step (one) to the step (three) according to the stages of takeoff, cruise and return to different tasks of the unmanned aerial vehicle1(t)、g2(T) the period T is two shifts, respectively f1＝1/T1、f2＝1/T2And f is1＜f2. Specifically, the embodiment of the invention is provided with two-gear low-frequency square wave g1(t)、g2(T) periods T are each f1＝1/T1＝1kHz、f2＝1/T2Setting a threshold value T according to the size of an AGC signal when the distance between a ground station and a target unmanned aerial vehicle changes under the condition of 100HzaAnd designing angle measurement to work in two low-frequency square wave detection modes respectively according to whether the angle measurement exceeds a threshold value, so that a fast tracking speed is obtained at a short distance, and high angle measurement precision is obtained at a long distance.
If the received AGC signal exceedsThreshold TaThen f is selected1＝1/T11kHz, obtaining fast tracking speed at a close distance; if the received AGC signal does not exceed the threshold TaThen f is selected2＝1/T2At 100Hz, high angular accuracy is obtained at long distances.
Specifically, the threshold T in the embodiment of the present inventionaThe value is determined according to an AGC algorithm or module, for example, when an AD9361 chip is used as a channel module, the AGC value is 100.
Example 1
The performance simulation result of the broadband OFDM single-channel single-pulse angle measurement method is analyzed.
As shown in fig. 1, a schematic block diagram of a method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data chain according to the present invention is shown, a feed source of an antenna A, B, C, D generates a sum-path signal, an azimuth and elevation difference-path signal, and a single-channel signal is synthesized based on a low-frequency square wave, a channel unit obtains an AGC signal by using an AD9361, and after a second-order moment signal is detected by the low-frequency square wave in a digital receiver, azimuth and elevation error signals are calculated by normalization, and then self-tracking of a flying target by the antenna is realized by an antenna controller.
Fig. 2 is a performance diagram of an average value of angle measurement estimation of the method for measuring an angle of a broadband OFDM signal in an unmanned aerial vehicle data chain according to the embodiment of the present invention; setting the angle deviation to be 1 DEG and 2 DEG, setting the low-frequency square wave 1/T to be 1kHz, and setting the FFT length of the OFDM signal to be N under the condition that the signal-to-noise ratio is 0dB to 20dBs1024, the effective carrier Nu512, the subcarrier is 10kHz, and the simulation result analysis shows that compared with the square rate method, the normalized angle measurement estimation method is not influenced by the signal-to-noise ratio in the performance of 0dB-10dB with low signal-to-noise ratio. Meanwhile, the method of the invention is not influenced by signal amplitude change and does not need accurate automatic gain control.
As shown in fig. 3, a standard deviation performance diagram of angle measurement estimation under different frequency square waves of the broadband OFDM signal angle measurement method in the data chain of the unmanned aerial vehicle in the embodiment of the present invention is shown, and it can be known from simulation result analysis that the square rate method has poor performance at low signal-to-noise ratio of 0dB to 10dB, and the standard deviation performance of the normalized angle measurement estimation method of the present invention is basically lower than 0.2 ° within 0dB to 20dB, so that the requirement of general unmanned angle tracking accuracy is satisfied.
The above description is only for the best mode of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Those skilled in the art will appreciate that the invention may be practiced without these specific details.

Claims (15)

1. A broadband OFDM signal angle measurement method in an unmanned aerial vehicle data chain is characterized in that: the method comprises the following steps:
calculating a second moment of a synthesized signal and an expected value of the second moment according to an OFDM signal sent by the unmanned aerial vehicle and a sum path signal and a difference path signal obtained by performing sum difference processing on a radio frequency signal received by a receiving antenna;
detecting the second moment of the synthesized signal by using a low-frequency square wave, and integrating in a period of the low-frequency square wave to obtain an azimuth detection signal and a pitching detection signal;
according to the expected value of the second moment of the synthesized signal, the azimuth detection signal and the pitch detection signal, the angle measurement estimated value based on the second moment normalization is obtained through calculation, and the specific method comprises the following steps:
Figure FDA0002988752220000011
Figure FDA0002988752220000012
wherein: a is an azimuth angle measurement estimated value, E is a pitch angle measurement estimated value, gAFor the azimuth detection signal, gEFor pitch detection signals, C { M }2The expected value of the second moment of the composite signal, d the antenna spacing and λ the wavelength.
2. The method of claim 1, wherein the method comprises: the specific method for calculating the second moment of the synthesized signal and the expected value of the second moment according to the OFDM signal sent by the unmanned aerial vehicle and the sum-difference signal and the difference signal obtained by the sum-difference processing of the radio frequency signal received by the receiving antenna is as follows:
(1.1) receiving signals sent by the unmanned aerial vehicle and represented as a plurality of radio frequency signals by the receiving antenna, and obtaining a sum path signal, an azimuth difference path signal and a pitching difference path signal after sum difference processing according to OFDM signals sent by the unmanned aerial vehicle;
(1.2) multiplying and modulating the azimuth difference path signal and the pitch difference path signal through a low-frequency square wave, then carrying out amplitude modulation on the sum path signal, and then coupling to obtain a synthetic signal;
(1.3) calculating a second moment of the synthesized signal from the synthesized signal;
and (1.4) obtaining the expected value of the second moment of the synthesized signal according to the second moment of the synthesized signal.
3. The method of claim 2, wherein the method comprises: in the step (1.1), the digital expression of the OFDM signal transmitted by the drone through the wireless channel is as follows:
Figure FDA0002988752220000021
wherein: n is an integer of 0 to Ns-1，NsThe FFT size adopted by OFDM modulation is represented as a positive integer; x (k) is a time domain signal, H (k) is a frequency domain response of a transmitted signal through a channel, EsFor transmit signal power, z (n) is the signal time domain noise.
4. The method of claim 3, wherein the method comprises: the specific method for obtaining the sum path signal, the azimuth difference path signal and the elevation difference path signal after the sum difference processing according to the OFDM signal sent by the unmanned aerial vehicle is as follows:
the receiving terminal antenna multi-horn or multi-mode feed source receives the signal U (t) sent by the unmanned aerial vehicle, and the signal U (t) is represented as 4 radio frequency signals U1(t)、U2(t)、U3(t)、U4(t) obtaining a sum signal U after sum and difference processing∑(t) azimuth difference path signal UΔA(t) pitching differential signal UΔE(t) are respectively:
Figure FDA0002988752220000022
Figure FDA0002988752220000023
Figure FDA0002988752220000024
wherein: s (t) is an analog waveform of signal s (n), AmMu is the slope of the antenna differential signal pattern, omega is the carrier frequency, d is the antenna spacing, lambda is the wavelength, A is the angle of the target from the electrical axis in azimuth and E is the angle of the target from the electrical axis in elevation,
Figure FDA0002988752220000025
is the signal phase, t is the time variable.
5. The method of claim 2, wherein the method comprises: in the step (1.2), the sum signal is subjected to amplitude modulation after the azimuth difference signal and the pitch difference signal are multiplied and modulated by a low-frequency square wave, and then a specific method for obtaining a synthetic signal through coupling is as follows:
the azimuth difference circuit signal UΔA(t) and Pitch Difference Signal UΔE(t) passing a low frequency square wave g1(t)、g2(t) multiplying modulation, and summing the signals U∑(t) amplitude modulating, and then coupling to obtain a composite signal U∑Δ(t)：
Figure FDA0002988752220000031
Wherein: s (t) is the analog waveform of signal s (n), G is amplitude modulation parameter, and low-frequency square wave G1(t)、g2(t) is represented as follows:
Figure FDA0002988752220000032
wherein: t is the period of the low-frequency square wave, AmMu is the slope of the antenna differential signal pattern, omega is the carrier frequency, d is the antenna spacing, lambda is the wavelength, A is the angle of the target from the electrical axis in azimuth and E is the angle of the target from the electrical axis in elevation,
Figure FDA0002988752220000033
is the phase of the signal, t is a time variable
6. The method of claim 2, wherein the method comprises: the specific method for calculating the second moment of the synthesized signal according to the synthesized signal in the step (1.3) is as follows:
Figure FDA0002988752220000034
wherein: m2Second moment of the resultant signal, s (t) being an analog waveform of the signal s (n), AmMu is the slope of the antenna differential signal pattern, omega is the carrier frequency, d is the antenna spacing, lambda is the wavelength, A is the angle of the target from the electrical axis in azimuth and E is the angle of the target from the electrical axis in elevation,
Figure FDA0002988752220000041
is the signal phase, t is the time variable, and G is the amplitude modulation parameter.
7. The method of claim 6, wherein the method comprises: the specific method for obtaining the expected value of the second moment of the synthesized signal according to the second moment of the synthesized signal in the step (1.4) is as follows:
due to A2+E2＝θ2Where θ is the target off-antenna electrical axis angle, the expectation of a and E is set to 0, the expectation of θ is set to 0, and the expected value of the second moment of the resulting composite signal is:
Figure FDA0002988752220000042
wherein: c { M }2The expected value of the second moment of the synthesized signal is obtained; c { | s (t) & gtdoes not dust2Is right to | s (t)2And calculating an expected value.
8. The method of claim 1, wherein the method comprises: the specific method for detecting the second moment of the synthesized signal by using the low-frequency square wave and obtaining the azimuth detection signal and the pitch detection signal by integrating in the period of the low-frequency square wave comprises the following steps:
Figure FDA0002988752220000043
Figure FDA0002988752220000044
wherein g is1(t)、g2(T) is a low frequency square wave, T is the period of the low frequency square wave, gAFor the azimuth detection signal, gEFor pitch detection signals, AmIs the signal amplitude, mu is the antenna differential signal pattern slope,g is the amplitude modulation parameter, s (t) is the analog waveform of the signal s (n), d is the antenna spacing, λ is the wavelength, A is the angle of the target from the electrical axis in azimuth, E is the angle of the target from the electrical axis in elevation, M is the amplitude of the target from the electrical axis in elevation, and2the second moment of the resultant signal.
9. The method for measuring the angle of the broadband OFDM signal in the data chain of the unmanned aerial vehicle according to any one of claims 1 to 8, wherein: the angle measurement method sets the low-frequency square wave g according to the stages of takeoff, cruise and return to different tasks of the unmanned aerial vehicle1(t)、g2(T) the period T is two shifts, respectively f1＝1/T1、f2＝1/T2And f is1＜f2；
Setting a threshold T according to the size of an AGC signal when the distance between a ground station and a target unmanned aerial vehicle changesaIf the received AGC signal exceeds the threshold TaThen f is selected1Obtaining a fast tracking speed at a short distance; if the received AGC signal does not exceed the threshold TaThen f is selected2And high angle measurement precision is obtained at a long distance.
10. The method of claim 9, wherein the method comprises: f is1＝1/T1＝1kHz、f2＝1/T2＝100Hz。
11. Broadband OFDM signal angle measurement system in unmanned aerial vehicle data link, its characterized in that: the device comprises a second moment expected value acquisition module, a detection signal acquisition module and an angle measurement estimated value acquisition module, wherein:
a second moment expected value acquisition module: according to an OFDM signal sent by an unmanned aerial vehicle and a sum-path signal and a difference-path signal obtained after sum-difference processing is carried out on a radio-frequency signal received by a receiving antenna, calculating a second moment of a synthesized signal and an expected value of the second moment, sending the second moment of the synthesized signal to a detection signal acquisition module, and sending the expected value of the second moment of the synthesized signal to an angle measurement estimated value acquisition module;
a detection signal acquisition module: receiving a second moment of a synthesized signal sent by a second moment expected value acquisition module, detecting the second moment of the synthesized signal by using a low-frequency square wave, integrating in a low-frequency square wave period to obtain an azimuth detection signal and a pitch detection signal, and sending the azimuth detection signal and the pitch detection signal to an angle measurement estimated value acquisition module;
an angle measurement estimation value acquisition module: receiving an azimuth detection signal and a pitch detection signal sent by a detection signal acquisition module, receiving an expected value of a second moment of a synthesized signal sent by a second moment expected value acquisition module, calculating to obtain an angle measurement estimated value based on second moment normalization according to the expected value of the second moment of the synthesized signal, the azimuth detection signal and the pitch detection signal,
wherein: according to the expected value of the second moment of the synthesized signal, the azimuth detection signal and the pitch detection signal, the angle measurement estimated value based on the second moment normalization is obtained through calculation, and the specific method comprises the following steps:
Figure FDA0002988752220000051
Figure FDA0002988752220000052
wherein: a is an azimuth angle measurement estimated value, E is a pitch angle measurement estimated value, gAFor the azimuth detection signal, gEFor pitch detection signals, C { M }2The expected value of the second moment of the composite signal, d the antenna spacing and λ the wavelength.
12. The broadband OFDM signal goniometry system for data link of drone of claim 11, wherein: the specific method for calculating the second moment of the synthesized signal and the expected value of the second moment by the second moment expected value acquisition module according to the OFDM signal sent by the unmanned aerial vehicle and the sum signal and the difference signal obtained by sum and difference processing of the radio frequency signal received by the receiving antenna is as follows:
(1.1) receiving signals sent by the unmanned aerial vehicle and represented as a plurality of radio frequency signals by the receiving antenna, and obtaining a sum path signal, an azimuth difference path signal and a pitching difference path signal after sum difference processing according to OFDM signals sent by the unmanned aerial vehicle;
(1.2) multiplying and modulating the azimuth difference path signal and the pitch difference path signal through a low-frequency square wave, then carrying out amplitude modulation on the sum path signal, and then coupling to obtain a synthetic signal;
(1.3) calculating a second moment of the synthesized signal from the synthesized signal;
and (1.4) obtaining the expected value of the second moment of the synthesized signal according to the second moment of the synthesized signal.
13. The broadband OFDM signal goniometry system for data link of drone of claim 12, wherein: in the step (1.1), the digital expression of the OFDM signal transmitted by the drone through the wireless channel is as follows:
Figure FDA0002988752220000061
wherein: n is an integer of 0 to Ns-1，NsThe FFT size adopted by OFDM modulation is represented as a positive integer; x (k) is a time domain signal, H (k) is a frequency domain response of a transmitted signal through a channel, EsFor transmit signal power, z (n) is the signal time domain noise.
The specific method for obtaining the sum path signal, the azimuth difference path signal and the elevation difference path signal after the sum difference processing according to the OFDM signal sent by the unmanned aerial vehicle is as follows:
the receiving terminal antenna multi-horn or multi-mode feed source receives the signal U (t) sent by the unmanned aerial vehicle, and the signal U (t) is represented as 4 radio frequency signals U1(t)、U2(t)、U3(t)、U4(t) obtaining a sum signal U after sum and difference processing∑(t) azimuth difference path signal UΔA(t) pitching differential signal UΔE(t) are respectively:
Figure FDA0002988752220000071
Figure FDA0002988752220000072
Figure FDA0002988752220000073
wherein: s (t) is an analog waveform of signal s (n), AmMu is the slope of the antenna differential signal pattern, omega is the carrier frequency, d is the antenna spacing, lambda is the wavelength, A is the angle of the target from the electrical axis in azimuth and E is the angle of the target from the electrical axis in elevation,
Figure FDA0002988752220000076
is the signal phase, t is the time variable.
14. The broadband OFDM signal goniometry system for data link of drone of claim 12, wherein: in the step (1.2), the sum signal is subjected to amplitude modulation after the azimuth difference signal and the pitch difference signal are multiplied and modulated by a low-frequency square wave, and then a specific method for obtaining a synthetic signal through coupling is as follows:
the azimuth difference circuit signal UΔA(t) and Pitch Difference Signal UΔE(t) passing a low frequency square wave g1(t)、g2(t) multiplying modulation, and summing the signals U∑(t) amplitude modulating, and then coupling to obtain a composite signal U∑Δ(t)：
Figure FDA0002988752220000074
Wherein: s (t) is the analog waveform of signal s (n), G is amplitude modulation parameter, and low-frequency square wave G1(t)、g2(t) is represented as follows:
Figure FDA0002988752220000075
wherein: t is a low-frequency square wave period;
the specific method for calculating the second moment of the synthesized signal according to the synthesized signal in the step (1.3) is as follows:
Figure FDA0002988752220000081
wherein: m2Second moment of the synthesized signal;
the specific method for obtaining the expected value of the second moment of the synthesized signal according to the second moment of the synthesized signal in the step (1.4) is as follows:
due to A2+E2＝θ2Where θ is the target off-antenna electrical axis angle, the expectation of a and E is set to 0, the expectation of θ is set to 0, and the expected value of the second moment of the resulting composite signal is:
Figure FDA0002988752220000082
wherein: c { | s (t) & gtdoes not dust2Is right to | s (t)2Obtaining an expected value, s (t) being an analog waveform of the signal s (n), AmIs the signal amplitude, mu is the antenna differential signal pattern slope, omega is the carrier frequency,
Figure FDA0002988752220000085
is the signal phase, t is the time variable.
15. The broadband OFDM signal goniometry system for data link of drone of claim 11, wherein: the specific method that the detection signal acquisition module detects the second moment of the synthesized signal by using a low-frequency square wave and integrates in a low-frequency square wave period to obtain the azimuth detection signal and the pitch detection signal comprises the following steps:
Figure FDA0002988752220000083
Figure FDA0002988752220000084
wherein g is1(t)、g2(T) is a low frequency square wave, T is the period of the low frequency square wave, gAFor the azimuth detection signal, gEIs a pitch detection signal;
wherein: a is an azimuth angle measurement estimated value, E is a pitch angle measurement estimated value, gAFor the azimuth detection signal, gEFor pitch detection signals, C { M }2The expected value of the second moment of the resultant signal, s (t) an analog waveform of the signal s (n), AmMu is the slope of the antenna differential signal pattern, d is the antenna spacing, lambda is the wavelength, t is the time variable, M2G is the second moment of the composite signal and is the amplitude modulation parameter.
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