A rotation compensation and tracking method for missile-borne navigation receiver

Abstract

The present invention provides a method for rotation compensation and tracking of a missile-borne navigation receiver, which includes: separating the rotation Doppler from the Doppler frequency shift of the received signal; establishing a warhead rotation analysis model to determine the Doppler frequency shift of the carrier and the Doppler frequency shift of the code caused by the rotation; estimating and obtaining the warhead rotation speed; respectively initializing and tracking the space cone angle formed by the satellite signal ray and the vertical direction and the distance r from the antenna phase center to the rotation center; calculating the rotation NCO value, and then using the rotation NCO value to correct the carrier NCO value. The method can effectively improve the stability and accuracy of tracking.

Description

Technical Field

[0001] The invention belongs to the technical field of satellite navigation, and in particular relates to a rotation compensation and tracking method for a missile-borne navigation receiver. Background Art

[0002] Satellite navigation can provide users on land, sea and space with all-weather, all-time, continuous high-precision three-dimensional position, three-dimensional speed and time information. It has unparalleled advantages over other navigation methods and has been widely used in various fields of social life in recent years, especially in the military. Various types of precision-guided missiles have many technical advantages such as high precision, long range, accurate strike and reliable performance. They are the main means for military powers to ensure national security and enhance military deterrence. At the same time, countries also generally add guidance and control components to traditional conventional unguided munitions to reduce the amount of ammunition off-target, effectively improve the strike effect, and realize the upgrading and transformation of ammunition. Therefore, various advanced precision-guided weapons have become the protagonists of modern warfare.

[0003] In order to maintain flight stability, artillery shells usually rotate at high speed during flight, with a rotation speed of up to 30,000 rpm. In practice, in order to facilitate continuous reception of satellite signals during rotation, a loop antenna or a multi-antenna structure is usually used. For loop antennas, due to various reasons, the rotation center of the antenna and the phase center of the antenna will not coincide, causing the Doppler of the received satellite signal to be modulated, which will have an adverse effect on the normal reception and stable tracking of the signal, and in severe cases will cause the tracking loop to lose lock. As a result, the tracking stability and accuracy of the missile-borne navigation receiver are not high. Summary of the invention

[0004] In view of this, the present invention provides a missile-borne navigation receiver rotation compensation and tracking method to solve the deficiencies of the prior art.

[0005] In order to achieve the above object, the present invention adopts the following technical scheme:

[0006] An embodiment of the present invention provides a missile-borne navigation receiver rotation compensation and tracking method, comprising:

[0007] Separating the rotational Doppler from the Doppler shift of the received signal;

[0008] The warhead rotation analysis model is established to determine the Doppler frequency shift of the carrier and the Doppler frequency shift of the code caused by the rotation; the Doppler frequency shift of the carrier Δf=2πnr sin(2πnt-β)cosαf / c; the Doppler frequency shift of the code Δf C =2πnr sin(2πnt-β)cosαf C / c; where f is the carrier frequency, f Cis the code rate, n is the rotation speed of the warhead, r is the distance from the antenna phase center to the rotation center, α is the angle between the satellite signal ray and the projection line of the satellite signal ray on the vertical projection plane passing through the rotation axis of the projectile; β is the angle between the projection line of the satellite signal ray on the vertical projection plane passing through the rotation axis of the projectile and the vertical direction;

[0009] Estimate and obtain the warhead rotation speed;

[0010] Initialize and track the space cone angle formed by the satellite signal ray and the vertical direction and the distance r from the antenna phase center to the rotation center respectively;

[0011] The rotated NCO value is calculated and then the carrier NCO value is corrected using the rotated NCO value.

[0012] Furthermore, the warhead rotation speed is estimated by performing FFT on the product sequence of the I / Q values ​​before compensation to obtain the rotation speed value; specifically, the method includes:

[0013] Demodulate and despread the satellite signal received before compensation to obtain an I / Q integral value;

[0014] Perform dot multiplication on the integral value of I / Q to obtain a set of IQ sequences;

[0015] Perform FFT processing on the IQ sequence to obtain the spectrum sequence IQ of the IQ sequence spectrum = abs(fft(IQ,M)); where abs() means taking absolute value calculation, and M means the number of points of FFT calculation;

[0016] Find the peak of the spectrum sequence and note its unit m, and finally calculate the speed n = f s *(m-1) / M, where f s Indicates the frequency of the IQ sequence.

[0017] Furthermore, the initialization and tracking of the space cone angle formed by the satellite signal ray and the vertical direction specifically include:

[0018] Three sets of local codes and local carriers are generated at three angles of β+θ, β, and β-θ, respectively, where β is the spatial cone angle and θ is the convergence step size; then the compensation amount is calculated according to the Doppler frequency shift of the carrier and the Doppler frequency shift of the code, and the rotation compensation amount is obtained and then applied to the rotating NCO;

[0019] Three groups of local codes and local carriers are used for demodulation and despreading respectively to obtain three groups of I / Q values. The angle corresponding to the best group of I / Q values ​​is selected as a new reference, and the NCO is updated.

[0020] Further, initializing and tracking the distance r from the antenna phase center to the rotation center specifically includes:

[0021] A step value is added and subtracted from the current r, and then the rotation compensation is calculated, and then demodulated and despread to obtain three groups of I / Q values. The optimal group of I / Q values ​​corresponding to r is selected as the current compensation amount.

[0022] Further, calculating the rotated NCO value and then using the rotated NCO value to correct the carrier NCO value specifically includes:

[0023] When the navigation signal is the GPS L1 signal, the carrier NCO accumulator bit width is 32 bits and the signal sampling rate is f s , the signal intermediate frequency is f i , the satellite Doppler is f d , the code rate is f ca , the rotation speed is n rpm, then the step values ​​of the carrier NCO without rotation compensation, the code NCO without rotation compensation, and the rotation NCO are:

[0024] f carrystep =(f i +f d )*2 32 / f s

[0025] f castep =(f ca +f d / 1540)*2 32 / f s

[0026] f rotatestep =n*2 32 / f s

[0027] After obtaining the phase value of the rotated NCO, perform the rotation phase difference to obtain Δθ rotate , and then the rotation phase difference Δθ rotate Adding it to the carrier NCO and code NCO can effectively compensate for the rotation phase;

[0028] f carrystep =(f i +f d )*2 32 / f s +Δθ rotate

[0029] f castep =(f ca +f d / 1540)*2 32 / f s +Δθ rotate / 1540.

[0030] The invention provides a missile-borne navigation receiver rotation compensation and tracking method, which can effectively improve the tracking stability and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0032] Figure 1 is a flow chart of a missile-borne navigation receiver rotation compensation and tracking method provided by an embodiment of the present invention;

[0033] Figure 2 is the missile-borne receiver coordinate system;

[0034] Figure 3 It is the I / Q output without rotation compensation;

[0035] Figure 4 is the Doppler output without rotation compensation;

[0036] Figure 5 is the I / Q output after rotation compensation;

[0037] Figure 6 is the Doppler output after rotation compensation. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] Figure 1 The figure is a flow chart of a method for rotation compensation and tracking of a missile-borne navigation receiver provided by an embodiment of the present invention. The method comprises the following steps:

[0040] S101. Separate the rotational Doppler from the Doppler frequency shift of the received signal.

[0041] The Doppler of the received signal consists of two parts: translational Doppler and rotational Doppler, and the translational Doppler and rotational Doppler are separable, which creates conditions for effectively compensating the influence of the projectile rotation on the navigation receiver.

[0042] S102, establishing a warhead rotation analysis model to determine the Doppler frequency shift of the carrier and the Doppler frequency shift of the code caused by the rotation.

[0043] Establish a model of bullet rotation. The main steps are as follows:

[0044] Figure 2 The missile-borne receiver coordinate system is given, the deviation between the antenna phase center and the antenna rotation center is r(OP), O is the antenna rotation center, P is the antenna phase center, the shell rotates around the Y axis, S is the satellite position, α is the angle between OS and OE, and β is the angle between OE and OD. α is the angle between the satellite signal ray OS and the projection line OE of the satellite signal ray on the vertical projection plane passing through the shell rotation axis; β is the angle between the projection line OE of the satellite signal ray on the vertical projection plane passing through the shell rotation axis and the vertical direction OD. Among them, cosαcosβ=cos∠DOS.

[0045] The calculation formula of satellite Doppler frequency shift is:

[0046] Δf=v r f / c (1)

[0047] Where Δf is the Doppler frequency shift, v r is the relative speed between the receiver and the satellite, f is the frequency of the transmitted signal, and c is the speed of light.

[0048] like Figure 1 As shown, let v τ is the tangential velocity of the receiver antenna phase center with the antenna rotation center, then the component of this velocity in the OS direction can be expressed as:

[0049] v r =v τ sin(2πnt-β)cosα (2)

[0050] Where n is the antenna speed, due to v τ =2πnr (n is the rotation speed of the warhead, r is the distance between the antenna phase center and the rotation center), therefore, the Doppler frequency shift of the carrier and code caused by rotation can be expressed as:

[0051] Δf=2πnr sin(2πnt-β)cosαf / c (3)

[0052] Δf C =2πnr sin(2πnt-β)cosαf C / c (4)

[0053] Since the code rate is much lower than the carrier frequency, the rotation mainly affects the carrier tracking but has little effect on the code tracking. Only carrier compensation is considered below.

[0054] In principle, as long as the rotation speed n, radius r and angles α and β are known, the corresponding local carrier and local code can be generated to demodulate the Doppler modulation caused by the rotation.

[0055] S103, estimating and obtaining the bullet rotation speed.

[0056] The rotation speed value can be obtained by performing fast Fourier transform (FFT) on the product sequence of the I / Q values ​​before compensation.

[0057] If the estimated period of the warhead rotation speed is 1 second, the received satellite signal before compensation is demodulated and demultiplexed to obtain the I / Q integral value. Assuming the integration time is 1 millisecond, 1000 sets of I / Q integral values ​​can be obtained in 1 second, recorded as I and Q. Then, the I / Q integral values ​​are multiplied to obtain a set of sequences:

[0058] IQ(k)=I(k)*Q(k) (k=1,2,…,1000)

[0059] Then, the spectrum sequence of the IQ sequence can be obtained by performing FFT processing on the IQ sequence:

[0060] IQ spectrum = abs(fft(IQ,M))

[0061] Where abs() means taking the absolute value for calculation, and M means the number of points for FFT calculation. Then find the peak of the spectrum sequence and note its unit m, and finally calculate the rotation speed:

[0062] n=f s *(m-1) / M. Among them, f s represents the frequency of the IQ sequence. For an integration time of 1 millisecond, f s Then it is 1000.

[0063] S104, respectively initializing and tracking the space cone angle formed by the satellite signal ray and the vertical direction and the distance r from the antenna phase center to the rotation center.

[0064] Initialization and tracking of the space cone angle ∠DOS formed by the satellite signal ray OS and the vertical direction OZ.

[0065] In practice, the position of the satellite is unknown to the navigation receiver. Figure 1 The spatial cone angle ∠DOS is unknown, so the spatial cone angle ∠DOS is initialized to 0°.

[0066] In order to ensure the convergence of the space cone angle, and to take into account the convergence speed and tracking accuracy of the space cone angle tracking, the initial convergence step size is set to θ = 90°, which will ensure that the satellite can converge in the entire airspace. The space cone angle tracking process is adaptively adjusted, and the step size is set to θ = 10° for the final stable tracking.

[0067] Assume that the angle ∠DOS is β at a certain moment. Similar to code loop tracking, three sets of local codes and local carriers are generated with three ∠DOS angles of β+θ, β, and β-θ respectively. Then, the compensation amount is calculated according to equations (3) and (4). After the rotation compensation amount is obtained, the rotation compensation amount is applied to the rotating NCO.

[0068] Demodulate and despread the three groups of local codes and local carriers respectively to obtain three groups of I / Q values. Select the angle ∠DOS corresponding to the best group of I / Q values ​​as the new reference and update the NCO.

[0069] Initialize and track the distance r from the antenna phase center to the rotation center.

[0070] The distance r can be set to an initial value according to the product characteristics.

[0071] The tracking of distance r is similar to the spatial cone angle. A step value is added and subtracted on the basis of the current radius r, and then the rotation compensation amount is calculated. Then, demodulation and despreading are performed respectively to obtain three groups of I / Q values. The optimal group of I / Q values ​​corresponding to the radius r is selected as the current compensation radius.

[0072] S105 , calculating a rotated NCO value and then using the rotated NCO value to correct the carrier NCO value.

[0073] The rotating NCO is similar to the carrier NCO and code NCO, and the step value is related to the rotation speed.

[0074] Taking GPS L1 as an example, if the carrier NCO accumulator bit width is 32 bits and the signal sampling rate is f s , the signal intermediate frequency is f i , the satellite Doppler is f d , the code rate is f ca , the rotation speed is n rpm, then the step values ​​of carrier NCO (without rotation compensation), code NCO (without rotation compensation), and rotation NCO are:

[0075] f carrystep =(f i +f d )*2 32 / f s (5)

[0076] f castep =(f ca +f d / 1540)*2 32 / f s (6)

[0077] f rotatestep =n*2 32 / f s (7)

[0078] After obtaining the phase value of the rotated NCO, perform the rotation phase difference to obtain Δθ rotate , and then the rotation phase difference Δθ rotate Adding it to the carrier NCO and code NCO can effectively compensate for the rotation phase:

[0079] f carrystep =(f i +f d )*2 32 / f s +Δθ rotate (8)

[0080] f castep =(f ca +f d / 1540)*2 32 / f s +Δθ rotate / 1540 (9)

[0081] After obtaining the value of the rotation NCO, the value is added to the carrier NCO and the code NCO to obtain effective rotation compensation.

[0082] The following calculation and simulation examples take GPS L1 as an example. C / A code modulation, code rate 1.023MHz, navigation receiver installed in the projectile warhead, sampling ring microstrip antenna, projectile rotation speed 30000 rpm, antenna rotation center and antenna phase center distance is 0.05 meters. The actual elevation angle of the satellite is 30° (the angle with the zenith direction is 60°), Doppler is 0Hz, and loop tracking period is 1 millisecond.

[0083] Figure 3 , Figure 4 The I / Q integration output and Doppler output without rotation compensation are given. Figure 5 , Figure 6 The I / Q integral value and Doppler output result after rotation compensation are given. Figure 3-Figure 6 The unit of the horizontal axis is milliseconds. Figure 3 , Figure 5 The ordinate is the relevant amplitude value, Figure 4 , Figure 6 The vertical axis unit is Hz. As can be seen from the figure, the performance is significantly improved after compensation.

[0084] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for rotation compensation and tracking of a missile-borne navigation receiver, characterized in that: include: separating the rotational Doppler from the Doppler shift of the received satellite navigation signal; Establish a warhead rotation analysis model to determine the Doppler shift of the carrier and the Doppler shift of the code caused by the rotation; The Doppler frequency shift of the carrier Δf=2πnrsin(2πnt-β)cosαf / c; the Doppler frequency shift of the code Δf C =2πnrsin(2πnt-β)cosαf C / c; where t is time, f is carrier frequency, and f C is the code rate, n is the rotation speed of the warhead, r is the distance from the antenna phase center to the rotation center, α is the angle between the satellite signal ray and the projection line of the satellite signal ray on the vertical projection plane passing through the rotation axis of the projectile; β is the angle between the projection line of the satellite signal ray on the vertical projection plane passing through the rotation axis of the projectile and the vertical direction; Estimate and obtain the warhead rotation speed; Initialize and track the space cone angle formed by the satellite signal ray and the vertical direction and the distance r from the antenna phase center to the rotation center respectively; The rotated NCO value is calculated, and then the rotated NCO value is added to the carrier NCO value to obtain the corrected carrier NCO value.

2. The method according to claim 1, characterized in that: The estimation of the warhead rotation speed is performed by performing FFT on the product sequence of the I / Q values ​​before compensation to obtain the rotation speed value; specifically, it includes: Demodulate and despread the satellite signal received before compensation to obtain an I / Q integral value; Perform dot multiplication on the integral value of I / Q to obtain a set of IQ sequences; Perform FFT processing on the IQ sequence to obtain the spectrum sequence IQ of the IQ sequence spectrum = abs(fft(IQ,M)); where abs() means taking absolute value calculation, and M means the number of points of FFT calculation; Find the peak of the spectrum sequence and note its unit m, and finally calculate the speed n = f s *(m-1) / M, where f s Indicates the frequency of the IQ sequence.

3. The method according to claim 1, characterized in that The initialization and tracking of the space cone angle formed by the satellite signal ray and the vertical direction specifically include: Three sets of local codes and local carriers are generated at three angles of β+θ, β, and β-θ, respectively, where β is approximately equal to the spatial cone angle and θ is the convergence step size; then the compensation amount is calculated according to the Doppler frequency shift of the carrier and the Doppler frequency shift of the code, and the rotation compensation amount is obtained and then applied to the rotating NCO; Three groups of local codes and local carriers are used for demodulation and despreading respectively to obtain three groups of I / Q values. The angle corresponding to the best group of I / Q values ​​is selected as a new reference, and the NCO is updated.

4. The method according to claim 1, characterized in that Initializing and tracking the distance r from the antenna phase center to the rotation center specifically includes: A step value is added and subtracted from the current r, and then the rotation compensation is calculated, and then demodulated and despread to obtain three groups of I / Q values. The optimal group of I / Q values ​​corresponding to r is selected as the current compensation amount.

5. The method according to claim 1, characterized in that Calculating the rotated NCO value and then adding the rotated NCO value to the carrier NCO value to obtain the corrected carrier NCO value specifically includes: When it is the L1 signal of GPS, the accumulator bit width of the carrier NCO is 32 bits, and the signal sampling rate is f s , the signal intermediate frequency is f i , the satellite Doppler is f d , the code rate is f ca , the rotation speed is n rpm, then the step values ​​of the carrier NCO without rotation compensation, the code NCO without rotation compensation, and the rotation NCO are: f carrystep =(f i +f d )*2 32 / f s f castep =(f ca +f d / 1540)*2 32 / f s f rotatestep =n*2 32 / f s After obtaining the phase value of the rotated NCO, perform the rotation phase difference to obtain Δθ rotate , and then the rotation phase difference Δθ rotate Adding it to the carrier NCO and code NCO can effectively compensate for the rotation phase; f carrystep =(f i +f d )*2 32 / f s +Δθ rotate f castep =(f ca +f d / 1540)*2 32 / f s +Δθ rotate / 1540。

Images