CN117706503A - Residual carrier direct-expansion waveform design and capture method for measuring radar - Google Patents
Residual carrier direct-expansion waveform design and capture method for measuring radar Download PDFInfo
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- CN117706503A CN117706503A CN202311602811.4A CN202311602811A CN117706503A CN 117706503 A CN117706503 A CN 117706503A CN 202311602811 A CN202311602811 A CN 202311602811A CN 117706503 A CN117706503 A CN 117706503A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
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- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
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Abstract
The invention discloses a method for designing and capturing a residual carrier direct-spread waveform for a measuring radar, which comprises the steps that firstly, a received signal is subjected to down-conversion and fast Fourier transformation to obtain a Doppler frequency coarse estimation value; step two, taking the Doppler frequency rough estimation value as a frequency locking ring initial value, and obtaining a Doppler frequency accurate estimation value through frequency locking ring tracking; correcting the range migration caused by long-time accumulation of the received signal by using the Doppler frequency accurate estimation value and completing the phase capture of the spread spectrum pseudo code; the invention designs the direct spread spectrum sequence to ensure that the spread spectrum signal has obvious carrier components, so that the carrier Doppler frequency can be directly obtained by utilizing the fast Fourier transform while the pseudo code correlation operation is not carried out, the capturing of the pseudo code phase is further completed, the capturing time is reduced, and the occupation of operation resources is not improved.
Description
Technical Field
The invention belongs to the technical field of radar detection, and particularly relates to a residual carrier direct-spread waveform design and capture method for a measuring radar.
Background
The direct sequence spread spectrum signal has good anti-interference performance, multipath resistance, interception resistance and higher measurement accuracy, and has been widely applied in the fields of communication and radar measurement and control.
In order to improve the capturing efficiency, the conventional direct sequence spread spectrum signal capturing method needs to perform two-dimensional search of pseudo code phase and Doppler frequency, generally uses methods such as Doppler parallel capturing, pseudo code phase serial capturing, pseudo code phase parallel capturing, doppler serial capturing, segmented pseudo code correlation-fast Fourier transform (PMF-FFT) and the like, and the methods can effectively reduce the searching time of one dimension of the method, but can be at the cost of a large amount of computing resources, and are unfavorable for application to resource-limited platforms such as satellites, rockets, missiles and the like.
Aiming at the problems, in the text of 'long-period pseudo code capturing combined with spectrum correction under high dynamic environment' of the 30 th and 8 th stages of computer application in 2010, poncirus et al propose a method for improving the probability of pseudo code capturing by using a spectrum correction method, but the method has a fence effect when fast Fourier transformation is carried out, so that a larger spectrum estimation error is generated; in 2012, university of Zhejiang Yang Weijun et al, in the invention patent of an all-digital direct sequence spread spectrum communication system and a method for quickly capturing pseudo codes thereof (patent number CN 201210032239.8), a method is proposed, wherein carrier Doppler frequency is eliminated by differential multiplication, then a pseudo code phase difference is obtained by code phase parallel search, and finally the Doppler frequency is obtained by despreading the pseudo code phase difference and quick Fourier transform. The method carries out parallel capturing on the pseudo code phase and Doppler frequency, and greatly reduces the capturing time. However, due to the differential multiplication operation, multiplicative noise is introduced, so that the signal to noise ratio is rapidly deteriorated, and the method is unfavorable for being used in a low signal to noise ratio environment.
If the traditional direct sequence spread spectrum signal capturing method changes two-dimensional searching into one-dimensional searching, a large amount of computing resources are needed to be used as a cost; the methods proposed in recent years may have large frequency estimation errors or be unsuitable for achieving spread spectrum signal acquisition in low signal-to-noise environments.
Disclosure of Invention
In view of the above, the present invention provides a method for designing and capturing a residual carrier direct-spread waveform for a measurement radar, which can effectively capture a high dynamic weak signal, and solve the contradiction between computing resources and capture time.
The technical scheme for realizing the invention is as follows:
a residual carrier direct-spread waveform design and acquisition method for a survey radar, comprising the steps of:
step one, obtaining a Doppler frequency coarse estimation value by down-conversion and fast Fourier transformation of a received signal;
step two, taking the Doppler frequency rough estimation value as a frequency locking ring initial value, and obtaining a Doppler frequency accurate estimation value through frequency locking ring tracking;
and thirdly, correcting the range migration caused by long-time accumulation of the received signal by using the Doppler frequency accurate estimation value and completing the phase capture of the spread spectrum pseudo code.
In the second step, the phase discriminator of the frequency locking ring is a four-quadrant arc-tangent phase discriminator, and the frequency discrimination is realized by adopting a dot product and cross product four-quadrant arc-tangent algorithm.
In the third step, a motion compensation algorithm is adopted to correct the range migration, and according to the pseudo code phase migration item, the pseudo code capturing circuit compensates the pseudo code phase migration based on the Doppler frequency estimation result of the tracking circuit.
The beneficial effects are that:
1. aiming at the problem of high dynamic weak signals, the invention designs the direct spread spectrum sequence to have obvious carrier components, the waveform design mode is simple, the coarse estimation of the carrier Doppler frequency can be directly obtained by utilizing the fast Fourier transform, the two-dimensional search of the Doppler frequency and the pseudo code phase is changed into the one-dimensional search of the pseudo code phase, the capturing time is reduced, and the contradiction between the computing resource and the capturing time is effectively solved.
2. After the Doppler frequency coarse estimation value is placed in the frequency locking ring, the pseudo code phase migration compensation can be performed by utilizing the Doppler frequency fine estimation value obtained by tracking, the signal energy is effectively accumulated in a low signal-to-noise ratio environment, and the rapid capture of the high-dynamic weak signal is realized.
3. The waveform design method provided by the invention is simple and effective, the capturing mode does not need Doppler frequency and pseudo code phase two-dimensional search, the contradiction between operation resources and capturing time is effectively solved, and the method can be well applied to a light and small resource limited platform, and the quick capturing of weak maneuvering targets is realized.
Drawings
Fig. 1 is a diagram showing the waveform comparison of unbalanced pseudocode and original pseudocode after every 2 points.
Fig. 2 is a general flow chart of the method of the present invention.
Detailed Description
The invention will now be described in detail by way of example with reference to the accompanying drawings.
The invention provides a direct sequence spread spectrum signal waveform design and rapid capturing method containing residual carrier waves, which overcomes the influence of code phase migration caused by high dynamic state under the condition of lower resource utilization rate and realizes rapid capturing of weak maneuvering targets.
In order to construct a received signal with residual carriers, the direct spreading sequence is designed as follows: every N for m-sequences in the transmitted signal inter Point insertion of a 1 (N) inter Set value) because the number of sequences 0,1 after construction is unequal, a pseudo code sequence with direct flow is obtained, as shown in fig. 1.
The radar receives the carrier signal containing the residual, and after digital down-conversion, low-pass filtering, extraction and fast Fourier transformation, the carrier signal is passed through a square detector and N nc And accumulating the secondary non-phase parameters, and finally detecting a peak-to-average ratio threshold and selecting M in N to judge so as to obtain a Doppler frequency coarse estimation value. The Doppler frequency coarse estimation value is used as an initial value to be provided to a frequency locking loop circuit, and the frequency locking loop circuitThe stable tracking result of (2) is the accurate Doppler estimated value. And finishing migration correction by using the Doppler accurate estimated value, and realizing quick capture of pseudo codes. The implementation flow of the invention is shown in figure 2, and the specific implementation steps are as follows:
step 1: the received signal is subjected to down-conversion and fast fourier transformation to obtain a coarse estimate of the doppler frequency.
The radar received signal may be expressed as the sum of the pseudo-code modulation term and the residual carrier term, i.e
Wherein t is k ＝k·t s ，t s For sampling time interval, A 1 Modulating the signal amplitude of the term for pseudo code, A 2 For residual carrier term signal amplitude, PN (t k +τ) is pseudo code with a delay amount τ, ω I Is of intermediate frequency, omega d As the carrier doppler frequency is the frequency of the carrier wave,to receive the carrier phase, n (t k ) To receive noise.
The pseudo code modulation term is spread to have spectrum similar to narrow band Gaussian noise, and the fast Fourier transform process can not accumulate energy, and the influence of the pseudo code modulation term can be ignored when the signal to noise ratio of the residual carrier is fixed, so the signal after quadrature down conversion can be expressed as
Wherein n' (t) k ) Is the noise after quadrature down-conversion.
The high frequency component is filtered out after low pass filtering, and the time domain form of the residual carrier wave in the received signal is
Wherein n "(t) k ) Is noise after low pass filtering.
After fast Fourier transformation, T is completed ca Taking N as the phase-coherent accumulation of ms nc Adding the modular squares of the secondary phase parameter accumulation results to obtain a non-phase parameter accumulation result, then carrying out peak-to-average ratio threshold detection and M-selecting judgment in N, and leading the signal frequency domain result F (k) to be in omega d At which peaks occur, whereby a rough estimate of the doppler frequency is obtained.
Step 2: and taking the Doppler frequency rough estimation value as a frequency locking ring initial value, and obtaining a Doppler frequency accurate estimation value through frequency locking ring tracking.
The purpose of the frequency-locked loop is to keep the frequencies consistent between the local carrier and the receive carrier, but does not require that the phases be consistent. Because Doppler frequency shift introduced by relative movement of a transmitter and a receiver generally changes randomly, a frequency-locking loop firstly detects the frequency difference between a local carrier wave and a received carrier wave through a frequency discriminator, then the frequency of the local carrier wave generated by a carrier wave numerical control oscillator is regulated by using the frequency discrimination result after filtering treatment, and after multiple feedback regulation, the locally regenerated carrier wave frequency is consistent with the received carrier wave frequency.
The phase discriminator of the frequency-locked loop adopts a four-quadrant arc-tangent phase discriminator, adopts a dot product and cross product four-quadrant arc-tangent algorithm to realize frequency discrimination, and adopts the frequency discrimination algorithm
In Deltaf d For Doppler frequency estimation error, T s For sampling time interval, N is the number of sampling points cleared by integration, NT s The time interval for which the integral clears.
The frequency-locked loop has better dynamic stress than the phase-locked loop. The frequency locking loop is realized by a first-order filter and a second-order loop. The optimal filter used is:
wherein omega n Is characteristic frequency, ζ is damping coefficient, K 0 Is the loop gain.
The mapping relation of the digital rectangular integral can be known:where T represents the output period of the loop filter.
The discrete transfer function expression is:
step 3: and correcting the range migration caused by long-time accumulation of the received signal by using the Doppler frequency accurate estimation value and completing the phase capture of the spread spectrum pseudo code.
The received pseudo code signal rate may be expressed as
Wherein R is cr To receive pseudo code rate, R c To transmit pseudo code rate, f up Is a radio frequency, f d Is Doppler frequency offset and can be expressed as
The received pseudo code rate may be expressed as
Under the high dynamic condition, the radar and the transponder have larger speed and acceleration, so that the receiving pseudo code rate changes, the rate deviation causes pseudo code phase migration, the phase migration increases with time, the code phases of different periods in the coherent accumulation time are not aligned, and the accumulation loss is caused. The received signal is
Wherein t is k ＝k·t s (k＝0,1,…,K-1)，t s For sampling time interval, K is total sampling point number, P s For receiving signal power, d (t k ) In order to modulate the data in such a way,for the presence of delay τ and phase migration term +.>Pseudo code omega of (2) I Is of intermediate frequency, omega d For the carrier Doppler frequency, n (t k ) Is noise.
The invention corrects the range migration by adopting a motion compensation algorithm, and the pseudo code capturing circuit compensates the pseudo code phase migration based on the Doppler frequency estimation result of the tracking circuit according to the specific pseudo code phase migration item in the above.
When the acquisition circuit generates the local pseudo code, the local pseudo code frequency word is compensated according to the Doppler frequency estimated by the tracking circuit, so that the pseudo code rate containing code Doppler is obtained:
wherein R is c For pseudo code rate, f d Presetting Doppler frequency for tracking circuit, f up Is a radio frequency. Wherein the code Doppler frequency item to be compensated is
Because the Doppler frequency is an accurate estimated value given by the tracking circuit, compensation can be well completed, and effective accumulation of weak signal energy is realized.
After compensation, digital quadrature down-conversion is carried out on the intermediate frequency signals, L points are integrated and removed, and N points I, Q are obtained through circumferential correlation, wherein the two paths of signals are as follows:
in the method, in the process of the invention,for local pseudo code delay,/->To estimate the doppler frequency, L is the integral clearing point number, i (i=0, 1, …, N-1) is the intermediate accumulation sequence number in the correlation process, N is the circumferential correlation result sequence number, N is the total number of circumferential correlation results, and n=k/L.
Combining I (n) and Q (n) into complex form
Wherein omega is d In order to receive the doppler frequency,for estimated received Doppler frequency, < >>For integrating the cleared signal, +.>Pseudo code after integral clearing, t L ＝L·t s Is the integral clearing time.
The known circumference correlation theorem is
Wherein X (K) and Y (K) are Fourier transform results of X (i) and Y (i), respectively, and represent conjugate operation. By comparing the formula (15) with the formula (16)Is regarded as +.>PN (it) L ) Is related to the circumference of the (c).
To the quadrature down-conversion result if the influence of the modulated data d (k) and the noise n (k) is not countedFFT is performed together with the local pseudo code PN (it) L ) Conjugate multiplying FFT of (1), and performing IFFT to obtain fast circumferential correlation result>At->And->Is traversed in the search space of (1), when +.>And->When (I)>The modulus of (2) can take the maximum value, (·) N A cyclic operation with a period of N is shown. Thus, by detecting->After the peak value of (1) is detected and judged by a logic, pseudo code phase estimation is obtained
Wherein n is max Is thatThe subscript n corresponding to the peak value.
In summary, the above embodiments are only preferred embodiments of the present invention, and are not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (3)
1. A residual carrier direct-spread waveform design and acquisition method for a survey radar, comprising the steps of:
step one, obtaining a Doppler frequency coarse estimation value by down-conversion and fast Fourier transformation of a received signal;
step two, taking the Doppler frequency rough estimation value as a frequency locking ring initial value, and obtaining a Doppler frequency accurate estimation value through frequency locking ring tracking;
and thirdly, correcting the range migration caused by long-time accumulation of the received signal by using the Doppler frequency accurate estimation value and completing the phase capture of the spread spectrum pseudo code.
2. The method for designing and capturing a residual carrier direct-spread waveform for a measuring radar according to claim 1, wherein in the second step, the phase detector of the frequency-locked loop is a four-quadrant arctangent phase detector, and a dot product and cross product four-quadrant arctangent algorithm is adopted to realize frequency identification.
3. The method for designing and capturing the direct spread waveform of the residual carrier wave for the measuring radar according to claim 1, wherein in the third step, a motion compensation algorithm is adopted to correct the range migration, and according to the pseudo code phase migration term, the pseudo code capturing circuit compensates the pseudo code phase migration based on the Doppler frequency estimation result of the tracking circuit.
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