CN103593509B - Method for analyzing plasma-sheath-caused multipath interference on aircraft surfaces - Google Patents

Abstract

The invention discloses a method for analyzing plasma-sheath-caused multipath interference on aircraft surfaces. The method includes firstly, using a flow field distribution file to input frequency, direction and power of navigation signals; calculating according to the MUSIC algorithm and the decorrelation algorithm to acquire interference signals. Direction of arrival is estimated based on the MUSIC algorithm of the decorrelation processing technology, so that the method is applicable to judgment on influence magnitude of the multipath interference in satellite navigation systems. Since multipath magnitude and incoming direction can be estimated, the method can support for eliminating multipath influences.

Description

The multi-path jamming that a kind of aircraft surface is produced by plasma sheath analyzes method

Technical field

The invention belongs to technical field of satellite navigation, be specifically related to the multipath that a kind of aircraft surface is produced by plasma sheath Interference analysis method.

Background technology

Aircraft is reentried to the process landed and is referred to as reentering process.During reentering, hypersonic aircraft with Atmospheric interaction, forms arch detached shock wave before aircraft, and after shock wave, gas temperature drastically raises and presents " high-temperature effect ", Air molecule dissociates, ionization reaction；Meanwhile, the solar heat protection ablator of aircraft surface burns under high temperature, high hot-fluid effect Erosion, is discharged into ablation resultant around aircraft in flow field, and define the various complexity of composition reenters Flow Field.Reenter around Stream flow field is an ionized gas, and when the ionization degree of gas reaches to a certain degree, ionized gas shows plasma to be had Some collective behavior and become plasma, now reenter Flow Field also known as plasma cladding flow field, reenter plasma Body or plasma sheath.Reenter the formation of plasma so that the power attenuation of electromagnetic wave propagation, and it is anti-to make electromagnetic wave produce Penetrate, reflect and scatter.

Signal produces multiple reflections after plasma sheath aircraft surface and plasma sheath, thus causes Multipath effect.Here multipath effect refer to GPS in addition to directly receiving satellite-signal, be still likely to be received through wait from After daughter sheath is launched, arrive aerial signal through different propagation paths.Thus the position error formed, multipath effect can reduce The positioning precision of receiver, and make the process time lengthen, at WAAS(Wide Area Augmentation System) and DGPS In (Difference Global Positioning System) system, multipath effect error will cause error propagation, seriously The positioning precision of user in reduction system.

The method also not having to analyze multipath effect in existing plasma sheath model, if can effectively estimate The multipath effect that plasma sheath produces, will play an important role for the impact of elimination multipath.

Summary of the invention

It is an object of the invention to provide a kind of multi-path jamming analysis method that aircraft surface is produced by plasma sheath, solve The problem that existing plasma sheath model can not analyze multipath effect.

The technical solution adopted in the present invention is, the multi-path jamming analysis side that a kind of aircraft surface is produced by plasma sheath Method, specifically implements according to following steps:

Step 1: first by Flow Field Distribution file, the frequency of input navigation signal, direction, power；

Step 2: use MUSIC algorithm and Decorrelating algorithm to be calculated interference signal.

The feature of the present invention also resides in,

Step 2 therein is specifically implemented according to following steps:

Input needs the plasma distribution file of prediction, uses FDTD numerical value emulation method, by plasma by input File distribution within the specific limits, according to the navigation frequency of measurement and control signal, direction, the power that set, for the signal of feed-in, at mould The aircraft surface intended arranges M observation station, and the position between observation station is less than half wavelength, is gone out often by FDTD numerical computations Individual observation station, the signal Xp, p that receive are the numbers of sampled point；

M unit observation station is divided into several submatrixs, and the array number of each submatrix is m, and information source number is K, submatrix number p, Then there is M=p+m-1；

Taking first submatrix is with reference to battle array, then i-th submatrix reception data are:

$X_i^f\left(k\right)=[x_i,x_{i+1},\·\·\·,x_{i-m+1}]={\mathrm{AD}}^{(i-1)}s\left(k\right)+n_i\left(k\right),$

WhereinΦ is the phase contrast between adjacent array element, then corresponds to the association side of this submatrix Difference matrix is:

$\begin{array}{c}{R}_i^f=E\left[X_i^f{\left(X_i^f\right)}^H\right]={\mathrm{AD}}^{(i-1)}{R}_s{\left(D^{(i-1)}\right)}^H{A}^H+{\mathrm{\σ}}^2{I}_m\\ ={\mathrm{AD}}^{(i-1)}{R}_s{D}^{-(i-1)}{A}^H+{\mathrm{\σ}}^2{I}_m\end{array},$

In formula, I_mFor m rank unit matrix, R_sFor signal autocorrelation matrix, the covariance matrix of all submatrixs is taken average, Covariance matrix after process, it may be assumed that

$R^f=\frac{1}{p}\underset{i=1}{\overset{p}{\mathrm{\Σ}}}{R}_i^f=A\left(\frac{1}{p}\underset{i=1}{\overset{p}{\mathrm{\Σ}}}{D}^{(i-1)}{R}_s{D}^{-(i-1)}\right)A^H+{\mathrm{\σ}}^2{I}_m,$

Estimate that input covariance matrix is:

${\hat{R}}_x=R^f,$

Covariance matrix is carried out feature decomposition:

${\hat{R}}_{x}V=\mathrm{V\Λ},$

In formula, Λ=diag{ λ₀,…,λ_M-1, λ₀≥…≥λ_M-1It is characterized value, V=[q₀,…,q_M-1] beCorresponding The matrix that characteristic vector is formed；

The tuple L utilizing little eigenvalue determines Signal estimation number:

$\hat{K}=M-L,$

And then determine noise subspace V_n；

Calculating MUSIC spatial spectrum:

${\hat{P}}_{\mathrm{MUSIC}}\left(\mathrm{\θ}\right)=\frac{a^H\left(\mathrm{\θ}\right)a\left(\mathrm{\θ}\right)}{a^H\left(\mathrm{\θ}\right)V_n{V}_n^{H}a\left(\mathrm{\θ}\right)},$

In formula, V_n=[q_K,…,q_M-1]；

Find out'sIndividual peak-peak, in addition to maximum peak value, obtains other multi-path jamming directions and estimates Meter.

The invention has the beneficial effects as follows, present invention MUSIC based on decorrelation LMS treatment technology algorithm carries out direction of arrival and estimates Meter, is suitable in satellite navigation system judging the application affecting size of multipath effect.And can estimate multipath size and come to, Support is provided for removing multi-path influence.

Accompanying drawing explanation

Fig. 1 is plane wave vertical incidence ideal plasma schematic diagram；

Fig. 2 is the multipath effect analysis result that ideal plasma produces；

Fig. 3 is actual plasma sheath electron density distribution figure；

Fig. 4 is the multipath effect analysis result that actual plasma sheath produces.

Detailed description of the invention

The present invention is described in detail with detailed description of the invention below in conjunction with the accompanying drawings.

The multi-path jamming that aircraft surface of the present invention is produced by plasma sheath analyzes method, to existing plasma sheath (can measure or emulate and obtain model data) carries out numerical modeling, analyzes the multi-path jamming letter that this plasma sheath exists Number.Place reception antenna array element (numerical simulation) at aircraft surface, the incidence wave of navigation signal frequency is set, through plasma After body sheath, antenna array receives signal, uses decorrelation LMS algorithm, makes the order of signal covariance matrix be effectively restored.Then Application MUSIC algorithm calculates spatial spectrum, finds out multiple peak-peaks of signal, obtains multi-path jamming and estimates, determines plasma sheath The multi-path jamming direction produced.Specifically implement according to following steps:

Step 1: first by Flow Field Distribution file, the frequency of input navigation signal, direction, power.

Step 2: use MUSIC algorithm and Decorrelating algorithm to be calculated interference signal.

In the method, needed the plasma distribution file of prediction by input, use FDTD numerical value emulation method, will Plasma press input file be distributed within the specific limits, according to set navigation the frequency of measurement and control signal, direction, power, for (can be j signal s), the aircraft surface in simulation arranges M observation station to the signal of feed-in, and the position between observation station is little In half wavelength.Going out each observation station by FDTD numerical computations, the signal Xp, p that receive are the numbers of sampled point.

M unit observation station is divided into several submatrixs, and the array number of each submatrix is m, and information source number is K, submatrix number p, Then there is M=p+m-1.

Taking first submatrix is with reference to battle array, then i-th submatrix reception data are

$X_i^f\left(k\right)=[x_i,x_{i+1},\·\·\·,x_{i-m+1}]={\mathrm{AD}}^{(i-1)}s\left(k\right)+n_i\left(k\right)---\left(1\right)$

WhereinΦ is the phase contrast between adjacent array element, then corresponds to the association of this submatrix Variance matrix is

$\begin{array}{c}{R}_i^f=E\left[X_i^f{\left(X_i^f\right)}^H\right]={\mathrm{AD}}^{(i-1)}{R}_s{\left(D^{(i-1)}\right)}^H{A}^H+{\mathrm{\σ}}^2{I}_m\\ ={\mathrm{AD}}^{(i-1)}{R}_s{D}^{-(i-1)}{A}^H+{\mathrm{\σ}}^2{I}_m\end{array}---\left(2\right)$

In formula, I_mFor m rank unit matrix, R_sFor signal autocorrelation matrix.The covariance matrix of all submatrixs is taken average, Covariance matrix after process, it may be assumed that

$R^f=\frac{1}{p}\underset{i=1}{\overset{p}{\mathrm{\Σ}}}{R}_i^f=A\left(\frac{1}{p}\underset{i=1}{\overset{p}{\mathrm{\Σ}}}{D}^{(i-1)}{R}_s{D}^{-(i-1)}\right)A^H+{\mathrm{\σ}}^2{I}_m---\left(3\right)$

(1) estimate that input covariance matrix is

${\hat{R}}_x=R^f---\left(4\right)$

(2) covariance matrix is carried out feature decomposition

${\hat{R}}_{x}V=\mathrm{V\Λ}---\left(5\right)$

In formula, Λ=diag{ λ₀,…,λ_M-1, λ₀≥…≥λ_M-1It is characterized value, V=[q₀,…,q_M-1] beCorresponding The matrix that characteristic vector is formed.

(3) the tuple L utilizing little eigenvalue determines Signal estimation number:

$\hat{K}=M-L---\left(6\right)$

And then determine noise subspace V_n。

(4) MUSIC spatial spectrum is calculated:

${\hat{P}}_{\mathrm{MUSIC}}\left(\mathrm{\θ}\right)=\frac{a^H\left(\mathrm{\θ}\right)a\left(\mathrm{\θ}\right)}{a^H\left(\mathrm{\θ}\right)V_n{V}_n^{H}a\left(\mathrm{\θ}\right)}---\left(7\right)$

In formula, V_n=[q_K,…,q_M-1]。

(5) find out'sIndividual peak-peak, in addition to maximum peak value, obtains other multi-path jamming directions Estimate.

Embodiment 1

Numerical value emulation method use FDTD, computation model plasma as shown in Figure 1 () starting point coordinate in Fig. 1 3. be (1, 30), terminal point coordinate is (1000,330), i.e. with aircraft surface angle α=16.7 °.Plasma thickness be 6cm(12 × Dy).FDTD zoning is total up to 400 × 1000 grids, in PML(Fig. 1 2.) thickness is 10 grids, mesh generation dx=dy =0.5cm, uniform plasma body thickness 6cm(12 × dy) it is positioned at y direction 30～41 grid, plasma collision frequency υ= 1e10Hz, electron density ne=10¹⁷m^-3.Aircraft surface () is positioned at y direction 19 grid in Fig. 1 5..Each antenna () in Fig. 1 4. Being spaced apart 9cm, coordinate is respectively (50,20), (68,20), (86,20), (104,20), (122,20), (140,20), (158, 20), (176,20).Added source is gps signal mid frequency 1.57542GHz plane wave () in Fig. 1 1..During Mutual coupling, Using MUSIC algorithm, and signal carries out forward direction smoothing solution Coherent processing, wherein total array number is M=8, submatrix array number m =4.As can be seen from Figure 20 ° is direct wave, 2 α=-33.4 °, the incoming wave in 3 three directions, α=-66.8 °, and energy is with angle Degree increase and reduce, this is completely the same with theoretical analysis result.And thus know multi-path jamming come to for-33.4 ° with- 66.8°。

Embodiment 2

Numerical value emulation method uses FDTD, the actual plasma () that computation model imports as shown in Figure 3 in Fig. 3 3.) thick Degree is 10 grids, mesh generation dx=dy=0.5cm, plasma collision frequency υ=1e9Hz, electron density ne=10¹⁸m^-3.Aircraft surface () is positioned at y direction, length 2m in Fig. 3 5..Each antenna () is spaced apart 9cm in Fig. 3 4., coordinate be respectively (50, 20), (68,20), (86,20), (104,20), (122,20), (140,20), (158,20), (176,20).Added source is 1.57542GHz plane wave () in Fig. 3 1..During Mutual coupling, use MUSIC algorithm, and it is smooth that signal carries out forward direction Decorrelation LMS processes, and wherein total array number is M=8, submatrix array number m=4.As can be seen from Figure 4 21.7 °, 59.2 ° is multipath Interference radiating way.

On the basis of the inventive point of the present invention is that FDTD emulation gathers M array element signal, forward direction is used to smooth MUSIC algorithm can accurately estimate multi-path jamming direction.The direction of multi-path jamming finally can be found by the combination of several algorithms. After finding direction, just there is a lot of easy way can eliminate multi-path jamming such as Beam synthesis method etc..

Claims (1)

1. the multi-path jamming analysis method that an aircraft surface is produced by plasma sheath, it is characterised in that specifically according to following Step is implemented:

Step 1: first according to plasma distribution file, the frequency of setting navigation signal, direction, power；

Step 2: use MUSIC algorithm and Decorrelating algorithm to be calculated interference signal, specifically implement according to following steps:

Input needs the plasma distribution file of prediction, uses FDTD numerical value emulation method, plasma is pressed input file Distribution within the specific limits, according to the frequency of navigation signal set, direction, power, for the signal of feed-in, in the flight of simulation Device surface configuration M observation station, the position between observation station is less than half wavelength, goes out each sight by FDTD numerical calculations Measuring point, the signal Xp, p that receive are the numbers of sampled point；

M unit observation station is divided into several submatrixs, and the array number of each submatrix is m, and information source number is K, and submatrix number p then has M =p+m-1；

Taking first submatrix is with reference to battle array, then i-th submatrix reception data are:

$X_i^f\left(k\right)=\[x_i,x_{i+1},...,x_{i-m+1}\]={\mathrm{AD}}^{(i-1)}s\left(k\right)+n_i\left(k\right),$

WhereinΦ is the phase contrast between adjacent array element, then corresponds to the covariance square of this submatrix Battle array is:

$\begin{array}{c}{R}_i^f=E\[X_i^f{\left(X_i^f\right)}^H\]={\mathrm{AD}}^{(i-1)}{R}_s{\left(D^{(i-1)}\right)}^H{A}^H+{\mathrm{\σ}}^2{I}_m\\ ={\mathrm{AD}}^{(i-1)}{R}_s{D}^{-(i-1)}{A}^H+{\mathrm{\σ}}^2{I}_m\end{array},$

In formula, I_mFor m rank unit matrix, R_sFor signal autocorrelation matrix, the covariance matrix of all submatrixs is taken average, obtain everywhere Covariance matrix after reason, it may be assumed that

$R^f=\frac{1}{p}\underset{i=1}{\overset{p}{\Σ}}{R}_i^f=A\left(\frac{1}{p}\underset{i=1}{\overset{p}{\Σ}}{D}^{(i-1)}{R}_s{D}^{-(i-1)}\right)A^H+{\mathrm{\σ}}^2{I}_m,$

Estimate that input covariance matrix is:

${\hat{R}}_x=R^f,$

Covariance matrix is carried out feature decomposition:

${\hat{R}}_{x}V=V\mathrm{\Λ},$

In formula, Λ=diag{ λ₀,…,λ_M-1, λ₀≥…≥λ_M-1It is characterized value, V=[q₀,…,q_M-1] beCharacteristic of correspondence The matrix that vector is formed；

The tuple L utilizing little eigenvalue determines Signal estimation number:

$\hat{K}=M-L,$

And then determine noise subspace V_n；

Calculating MUSIC spatial spectrum:

${\hat{P}}_{MUSIC}\left(\mathrm{\θ}\right)=\frac{a^H\left(\mathrm{\θ}\right)a\left(\mathrm{\θ}\right)}{a^H\left(\mathrm{\θ}\right)V_n{V}_n^{H}a\left(\mathrm{\θ}\right)},$

In formula, V_n=[q_K,…,q_M-1]；

Find out'sIndividual peak-peak, in addition to maximum peak value, obtains other multi-path jamming direction estimation.