CN103344951A - Method for selecting signal transmitting frequency of sky wave MIMO-OTH radar - Google Patents

Abstract

The invention discloses a method for selecting a signal transmitting frequency of sky wave MIMO-OTH radar, and belongs to the technical field of sky wave MIMO-OTH radars. According to the technical scheme, a primary alternative signal transmitting frequency is selected from a current usable frequency band based on the current detection range, multipath propagation exists in transmitted signals corresponding to the primary alternative signal transmitting frequency, a secondary alternative signal transmitting frequency is extracted from the primary alternative signal transmitting frequency, all echo signals of transmitted signals corresponding to the secondary alternative signal transmitting frequency are not related to one another, the diversity gain of all the transmitted signals corresponding to the secondary alternative signal transmitting frequency is calculated, M transmitting frequencies corresponding to the maximum diversity gain are taken as the signal transmission frequency of the radar, and the numerical value of M corresponds to the number of radar transmitting antennas. After the method is applied, the maximum diversity gain of the radar can be obtained by the radar, and the detection performance of the sky wave MIMO-OTH radar is effectively improved.

Description

A kind of system of selection of the emission signal frequency for sky wave MIMO-OTH radar

Technical field

The present invention relates to sky wave MIMO-OTH Radar Technology, particularly a kind of method that improves the detection performance of sky wave MIMO-OTH radar.

Background technology

Conventional sky wave OTH radar utilizes ionosphere the reflection of radar signal to be surveyed the target that is positioned at outside the sighting distance.In order to cover the investigative range of 800km～3000km, the wave beam of sky wave OTH radar emission has the wideer angle of pitch at vertical plane, and this just makes the phenomenon that tends to occur multipath transmisstion in the sky wave OTH radar.Know that according to the ray trace technology signal of the different angles of pitch has different travel paths in ionosphere.The angle of pitch is more big, and the ground distance of radiation exposure is relatively more little, and the ray correspondence of the different angles of pitch different ground irradiation distances.But because ionospheric hierarchy, when the reflection spot height of ray just was near two tie points between the different ionosphere, the irradiation distance of ray can sharply increase.This just makes the ray of the different angles of pitch might shine same ground region, makes this zone produce two different echoes, Here it is multipath transmisstion.Multipath transmisstion can make radar to the misjudgment of target number, and the measuring distance error increases.For clutter, multipath transmisstion will make a clutter elementary echo on different range gate noise signal be arranged, and brings difficulty for the detection of target.

The MIMO radar that adopts antenna to split has utilized the principle of signal from different angular illumination targets, make that transmitting and receiving between the signal of different antennae is separate, these signals make radar obtain space diversity gain through after the Combined Treatment, under higher letter miscellaneous noise ratio condition, can effectively improve detection performance (but the concrete list of references: MIMO Radar with Widely Separated Antennas of radar, Alexander M.Haimovich, Rick S.Blum, and Leonard J.Cimini, Jr, IEEE signal processing magazine, Volume25, Issue1, Page (s): 116-129,2008; Spatial Diversity in Radars-Models and Detection Performance, Alexander M.Haimovich, Rick S.Blum, Leonard J.Cimini, D.Chizhik, IEEE transactions on signal processing, Volume:54, Issue:3, Page (s): 823-838, March2006).

The MIMO radar that adopts antenna to put altogether then is to have utilized the diversity gain that transmits to improve detection performance (but the concrete list of references: MIMO radar with colocated antennas of radar, Jian Li, P.Stoic, IEEE signal processing magazine, Volume:24, Issue:5, Page (s): 106-114, September2007).The structure of the MIMO radar that antenna is put is altogether introduced and is just obtained sky wave MIMO-OTH radar in traditional OTH radar, because ionosphere is for the travel path difference of the signal generation of the different angles of pitch, different frequency, so radar has obtained the effect of space diversity gain, improved the detection performance of radar.

Ionosphere MQP model can be good at describing ionospheric electron concentration with the variation tendency of height.Can calculate the correlation parameter of ray in ionosphere according to the MQP model, modeling and closely related (but the list of references: A model of the vertical distribution of the electron concentration in the ionosphere and its application to oblique propagation studies of analysis for sky wave OTH radar signal, P.L.Dyson and J.A.Bennett, journal of atmospheric and terrestrial physics, Volume:50, Issue:3, Page (s): 251-262,1988).

Current, the main principle that the emission signal frequency of sky wave OTH radar is selected is: detect the frequency range that does not have interference that current period radar can be used by spectrum detector, in these available frequency bands, select to be fit to the radar signal frequency of current detection range then according to the radar illumination distance, in the selection of radar frequency, can avoid use the signal frequency of multipath transmisstion can occur simultaneously as far as possible.And about the research of the detection aspect of performance that improves sky wave MIMO-OTH radar, most of research is about the design of radar emission signal waveform, and the not relevant research of detection performance that the frequency of the correlativity between transmitting based on difference and radar signal selects to improve sky wave MIMO-OTH radar.

Summary of the invention

Goal of the invention of the present invention is: based on correlativity and the diversity gain of the signal frequency of multipath transmisstion, select to be used for the emission signal frequency of sky wave MIMO-OTH radar, to improve the diversity gain of radar, promote it and detect performance.

The system of selection of the emission signal frequency for sky wave MIMO-OTH radar of the present invention comprises the following steps:

Based on current detection range, from current available frequency band, select elementary alternative emission signal frequency, and there is multipath transmisstion in corresponding the transmitting of described elementary alternative emission signal frequency;

Extract the alternative emission signal frequency of secondary from described elementary alternative emission signal frequency, each echoed signal that transmits of the alternative emission signal frequency correspondence of described secondary is uncorrelated mutually;

Calculating is corresponding to the diversity gain that respectively transmits of the alternative emission signal frequency of described secondary, and getting M the corresponding transmission frequency of maximum diversity gain is the emission signal frequency of radar, and the value of described M is corresponding to the number of transmitting radar antenna.

When the present invention selects to be fit to the radar signal frequency of current detection range in these available frequency bands according to the radar illumination distance, opposite with the existing selection principle of the signal frequency that multipath transmisstion can appear in use of avoiding as far as possible, from available frequency band, choose have multipath transmisstion the emission signal frequency that can arrive target to be detected as elementary alternative emission signal frequency, then to all elementary alternative emission signal frequencies, by being transmitted into target to be detected to obtain corresponding waveform signal, and then filter out between same each echoed signal that transmits mutually the incoherent corresponding emission signal frequency that transmits as the alternative emission signal frequency of secondary, at last, screen based on the corresponding diversity gain of the alternative emission signal frequency of secondary again, filter out the emission signal frequency of M maximum diversity gain as the transmission frequency of M emitting antenna, the combination that can obtain diversity gain maximum in the radar emission signal combination of different transmission frequencies makes radar obtain maximum diversity gain, effectively promotes the detection performance of sky wave MIMO-OTH radar.

Further, in the present invention, calculating corresponding to the diversity gain that respectively transmits of the alternative emission signal frequency of described secondary can be: send the detection of a target that transmits signals to corresponding to the alternative emission signal frequency of secondary, determine the bar number in the back-propagating path of current transmission signal, the minterm of then getting the bar number in the number of radar receiving antenna and described back-propagating path is the diversity gain value of current transmission signal, and described back-propagating path is the travel path corresponding to the current echoed signal that transmits.

In sum, owing to adopted technique scheme, the invention has the beneficial effects as follows: the detection performance that effectively promotes the MIMO-OTH radar.

Description of drawings

Fig. 1 is the communication mode of multipath transmisstion sky wave MIMO-OTH radar signal when existing;

Fig. 2 is under the multipath transmisstion condition, samely transmits because multipath transmisstion the correlativity curve between a plurality of echoed signals on the same receiving antenna;

Fig. 3 is the different echoed signal correlativity curve map that transmits and receive at same receiving antenna place;

Fig. 4 does not have under the multipath transmisstion condition, the different radar detedtion probability figure that transmits and receives the antenna correspondence;

Fig. 5 is under the multipath transmisstion condition, the different radar detedtion probability figure that transmits and receives the antenna correspondence;

Fig. 6 is under the multipath transmisstion condition, and the correlativity of echoed signal is for detections of radar Effect on Performance synoptic diagram;

Wherein, M represents number of transmit antennas, N represents the receiving antenna number, K represents propagated forward path bar number (subscript corresponding different transmit 1 or 2), L represents back-propagating path bar number (subscript corresponding different transmit 1 or 2), delta_x represents the length of the horizontal direction of the detection of a target, and delta_f_m represents that emission signal frequency is poor, and f_c represents signal frequency.

Embodiment

Disclosed all features in this instructions, or the step in disclosed all methods or the process except mutually exclusive feature and/or step, all can make up by any way.

Disclosed arbitrary feature in this instructions (comprising any accessory claim, summary and accompanying drawing) is unless special narration all can be replaced by other equivalences or the alternative features with similar purpose.That is, unless special narration, each feature is an example in a series of equivalences or the similar characteristics.

Specific implementation of the present invention comprises the following steps:

Step 1 based on current detection range, is selected elementary alternative emission signal frequency from current available frequency band.

Detect when front space available spectrum section by spectrum detector, alternative emission signal frequency as radar, and then based on the search coverage position, filter out can satisfy current detection range emission signal frequency as elementary alternative emission signal frequency, and this elementary alternative emission signal frequency can produce multipath transmisstion.In the present invention, can adopt arbitrary mature technology to filter out the emission signal frequency that satisfies current detection range, preferred, can screen based on ionosphere MQP model.

In order to make up ionosphere MQP model, at first utilize the ionosphere checkout equipment that ionospheric current state is detected, obtain the parameter between ionospheric different layers: the thickness y of each layer _m, the height z _m, and maximum electron concentration N _m

The computing formula of MQP model is as shown in Equation (1):

Wherein z is height, z ₀Be earth radius, N _e(z) be electron concentration on height z.According to formula (1), can be in order to time delay τ and the ground distance R that calculates radar echo signal _D, reflection height h etc.Simultaneously, can determine the radar emission signal s of different frequency _m(t) signal strips that shines the propagated forward path of the detection of a target from emitting antenna m is counted K ^m, and the bar that the signal of detection of a target scattering (echoed signal) can be received the back-propagating path that antenna n receives is counted L ^Mn

Step 2 is extracted the alternative emission signal frequency of secondary from elementary alternative emission signal frequency.

Based on discovering in a large number, when mutual when uncorrelated between same each echoed signal that transmits, transmitting to obtain maxgain value.So in step 2, screen based on the correlativity of each echoed signal that transmits, filter out the mutual incoherent corresponding emission signal frequency that transmits of each echoed signal as the alternative emission signal frequency of secondary from elementary alternative transmitting.

Preferably, the present invention realizes the extraction of the alternative emission signal frequency of secondary is handled through the following steps.

(1) sets up the echo signal model of sky wave MIMO-OTH radar.

Suppose that the detection of a target and the radar that are positioned at earth surface are on the same vertical plane, for example set the target that the detection of a target is the Swerling-I type, namely the detection of a target is (x by being evenly distributed on a center ₀, y ₀), the length of side is that infinite a plurality of independent identically distributed scattering point on the rectangle of Δ x * Δ y constitutes.(x y) represents to be positioned at (x+x with U ₀, y+y ₀) reflection coefficient of the scattering point located, (Δ x/2)≤x≤(Δ x/2) wherein, (Δ y/2)≤y≤(Δ y/2), and U (x y) is the multiple Gaussian random variable of 0 average, variance E{|U (x, y) | ²}=1/ (Δ x Δ y).Considering that sky wave MIMO-OTH radar signal communication mode is seen Fig. 1 under the situation of earth curvature, m(m=1 wherein, 2 ..., M) position of the individual corresponding emitting antenna that transmits is

The signal s of its emission _m(t) expression, λ _mIt is the wavelength of this signal correspondence.N(n=1,2 ..., N) position of individual receiving antenna is Definition

The expression s emission signal s _m(t) (x y) propagates into point (γ, time delay β) of the detection of a target through k bar forward path from launching site.Same,

Expression signal s _m(t) (γ is β) through arriving point (x, time delay y) to propagated behind the l bar from point.M of receiving of n receiving antenna transmits through k(k=1 so ..., K ^m) bar propagated forward path and l(l=1 ..., L ^Mn) echoed signal in bar back-propagating path is expressed as:

Wherein

The phase place of introducing when representing signal by k bar propagated forward path, l bar back-propagating path is polluted,

The Doppler of having reflected the detection of a target, E represent the energy that transmits.

In the present invention, so-called propagated forward path refers to transmit signals to the travel path of search coverage, and the back-propagating path refers to that corresponding echo is to the travel path of receiving antenna.

For formula (2) is carried out conversion so that calculate definition

${\mathrm{\φ}}_{\mathrm{lk}}^{\mathrm{mn}}=2\mathrm{\π}{f}_m[{\mathrm{\τ}}_k^m(x_m^t,y_m^t,x_0,y_0)-{\mathrm{\τ}}_1^m(x_m^t,y_m^t,x_0,y_0)+{\mathrm{\τ}}_l^{\mathrm{mn}}(x_n^r,y_n^r,x_0,y_0)-{\mathrm{\τ}}_1^{\mathrm{mn}}(x_n^r,y_n^r,x_0,y_0)]---\left(3\right)$

${\mathrm{\ρ}}_{m,k}={\left\{(4z_0^2-A{C}_m^2)\right[{(h_m^k+z_0)}^2+z_0^2-(h_m^k+z_0)\sqrt{4z_0^2-A{C}_m^2}\left]\right\}}^{0.5}---\left(4\right)$

$o_{\mathrm{mn},l}={\left\{(4{\mathrm{<figure-callout\; id="0"\; label="z"\; filenames="HDA00003405682100021.png,HDA00003405682100022.png"\; state="\{\{state\}\}">z</figure-callout>}}_0^2-B{C}_n^2)\right[{(h_l^{\mathrm{mn}}+z_0)}^2+{\mathrm{<figure-callout\; id="0"\; label="z"\; filenames="HDA00003405682100021.png,HDA00003405682100022.png"\; state="\{\{state\}\}">z</figure-callout>}}_0^2-(h_l^{\mathrm{mn}}+z_0)\sqrt{4z_0^2-B{C}_n^2}\left]\right\}}^{0.5}---\left(5\right)$

AC wherein _mRepresent that m emitting antenna is to the air line distance of target's center, BC _nRepresent n receiving antenna to the air line distance of target,

The reflection spot height of representing k bar propagated forward path,

The reflection height of representing l bar back-propagating path.After corresponding calculating, variable being changed to of formula (2):

Wherein

${\mathrm{\&epsiv;}}_{\mathrm{lk}}^{\mathrm{mn}}={\&Integral;}_{-\frac{\mathrm{\&Delta;<figure-callout\; id="2"\; label="x"\; filenames="HDA00003405682100022.png,HDA00003405682100031.png"\; state="\{\{state\}\}">x</figure-callout>}}{2}}^{\frac{\mathrm{\&Delta;x}}{2}}{\&Integral;}_{-\frac{\mathrm{\&Delta;<figure-callout\; id="2"\; label="y"\; filenames="HDA00003405682100022.png,HDA00003405682100031.png"\; state="\{\{state\}\}">y</figure-callout>}}{2}}^{\frac{\mathrm{\&Delta;<figure-callout\; id="2"\; label="y"\; filenames="HDA00003405682100022.png,HDA00003405682100031.png"\; state="\{\{state\}\}">y</figure-callout>}}{2}}\exp \{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="HDA00003405682100022.png,HDA00003405682100031.png"\; state="\{\{state\}\}">j</figure-callout>}2\mathrm{\&tau;}{f}_m[-\frac{(h_k^m+z_0)[\mathrm{\&gamma;}(x_m^t-x_0)+\mathrm{\&beta;}(y_m^t-y_0)]}{c{\mathrm{\&rho;}}_{m,k}}$

(7)

$-\frac{(h_l^{\mathrm{mn}}+z_0)[\mathrm{\&gamma;}(x_n^r-x_0)+\mathrm{\&beta;}(y_n^r-y_0)]}{c{o}_{\mathrm{mn},l}}\left]\right\}U(\mathrm{\&gamma;},\mathrm{\&beta;})\mathrm{d\&beta;d\&gamma;}$

The expression detection of a target on k bar propagated forward path, l bar back-propagating path the detection of a target for signal s _m(t) reflection coefficient,

Reacted the time delay between travel path k, l and arbitrary other travel paths (as the 1st propagated forward path, the 1st back-propagating path).

(2) correlativity between the echoed signal of the different paths of calculating.

Referring to Fig. 2, it has provided the detection of a target that is on the different detection ranges, same transmitting because multipath transmisstion, correlativity curve between a plurality of echoed signals on the same receiving antenna, wherein Δ x represents the length on the horizontal direction of the detection of a target, as the Δ x of the detection of a target during greater than the curve among the figure, each echoed signal is only incoherent.Analysis can obtain: along with the increase of detection range, make echoed signal uncorrelated, need the Δ x of bigger value; Simultaneously, the frequency that transmits is more big, and the Δ x of the uncorrelated needs of different echoed signals is more little.

Referring to Fig. 3, it has shown the correlativity curve map of the different echoed signals that receive at same receiving antenna place of transmitting.Based on Fig. 3 as can be known, two frequency distance that transmit are more big, and uncorrelated required Δ x is more little between its echoed signal separately.

Based on above-mentioned analysis as can be known, the signal of different travel paths

With

Correlativity C by their reflection coefficient

With

Determine, satisfy

$C=E\left\{r_{\mathrm{lk}}^{\mathrm{mn}}\left(t\right){\left[r_{l^{\&prime;}{k}^{\&prime;}}^{m^{\&prime;}{n}^{\&prime;}}\left(t\right)\right]}^{*}\right\}=E\left\{{\mathrm{\&epsiv;}}_{\mathrm{lk}}^{\mathrm{mn}}{\left({\mathrm{\&epsiv;}}_{l^{\&prime;}{k}^{\&prime;}}^{m^{\&prime;}{n}^{\&prime;}}\right)}^{*}\right\}---\left(8\right)$

Wherein, function E{} represents to get average, and conjugation is got in symbol " * " expression, according to the definition of correlativity, when the value of the correlativity C of two signals is tending towards 0, thinks that two signals are incoherent; And when the value of C is tending towards 1, think that these two signals are to have strong spatial coherence.After formula (8) carried out corresponding conversion, obtaining C, to be tending towards 0 condition be signal

With

Parameter satisfy below in the inequality one:

$\frac{(h_{k^{\&prime;}}^{m^{\&prime;}}+z_0)(x_{m^{\&prime;}}^t-x_0)}{{\mathrm{\&lambda;}}_{m^{\text{\&prime;}}}{\mathrm{\&rho;}}_{m^{\&prime;},k^{\&prime;}}}+\frac{(h_{l^{\&prime;}}^{m^{\&prime;}{n}^{\&prime;}}+z_0)(x_{n^{\&prime;}}^r-x_0)}{{\mathrm{\&lambda;}}_{m^{\&prime;}}{o}_{m^{\&prime;}{n}^{\&prime;},l^{\&prime;}}}$

(9)

$-\frac{(h_k^m+z_0)(x_m^t-x_0)}{{\mathrm{\&lambda;}}_m{\mathrm{\&rho;}}_{m,k}}-\frac{(h_l^{\mathrm{mn}}+z_0)(x_n^r-x_0)}{{\mathrm{\&lambda;}}_m{o}_{\mathrm{mn},l}}>\frac{1}{\mathrm{\&Delta;x}}$

$\frac{(h_{k^{\&prime;}}^{m^{\&prime;}}+z_0)(y_{m^{\&prime;}}^t-y_0)}{{\mathrm{\&lambda;}}_{m^{\&prime;}}{\mathrm{\&rho;}}_{m^{\&prime;},k^{\&prime;}}}+\frac{(h_{l^{\&prime;}}^{m^{\&prime;}{n}^{\&prime;}}+z_0)(y_{n^{\&prime;}}^r-y_0)}{{\mathrm{\&lambda;}}_{m^{\&prime;}}{o}_{m^{\&prime;}{n}^{\&prime;},l^{\&prime;}}}$

(10)

$-\frac{(h_k^m+z_0)(y_m^t-y_0)}{{\mathrm{\&lambda;}}_m{\mathrm{\&rho;}}_{m,k}}-\frac{(h_l^{\mathrm{mn}}+z_0)(y_n^r-y_0)}{{\mathrm{\&lambda;}}_m{o}_{\mathrm{mn},l}}>\frac{1}{\mathrm{\&Delta;y}}$

Wherein,

The reflection height of representing the k bar propagated forward path of m emitting antenna,

The reflection height of representing the l bar back-propagating path of m emitting antenna,

The reflection height of representing the k ' bar propagated forward path of the individual emitting antenna of m ',

The reflection height of representing the l ' bar back-propagating path of the individual emitting antenna of m '.

By top formula, can calculate different paths on radar echo signal between correlativity.By top formula as can be seen, the correlation between signals of different travel paths is mainly determined by position, aerial position and signal frequency, this Several Parameters of signal reflex height of the detection of a target.For a given detection of a target, differing between the travel path of two echoed signals is more big, and the parameter of these two signals more might satisfy two top inequality, and two signals also just more are tending towards uncorrelated.

Step 3 is calculated the diversity gain that respectively transmits corresponding to the alternative emission signal frequency of described secondary.This step can be that existing arbitrary method realizes.

The optimal way of this embodiment is: signal s _m(t) the diversity gain g that provides _mValue be: g _m=min{N, L ^Mn, make a concrete analysis of as follows:

According to the radar signal model, since the influence of ionosphere multipath transmisstion, n the s emission signal s that receiving antenna receives _m(t) all echoed signals of Chan Shenging should satisfy

(11)

τ wherein _MnExpression signal s _m(t) the arbitrary travel path of process (as the 1st propagated forward path, the 1st back-propagating path) is transmitted into the time delay of n receiving antenna.For the receiving antenna of uniform linear array, the reception signal of same detection of a target reflected signal on different receiving antennas is difficult to satisfy incoherent condition, thus think that they are linear dependences, so can make

L ^M1=...=L ^MN=L ^mBecause be linear evenly receiving array, suppose that the luffing angle in l back-propagating path is

So

N=1,2 ..., N, wherein c represents the light velocity, then formula (11) but abbreviation be:

(12)

In formula (12), w _n(t) the clutter plus noise composition in the signal received of expression receiving antenna n.Be mutually orthogonal because transmit, with the reception signal r on n the receiving antenna _n(t) pass through matched filter

Obtain:

W wherein _MnBe that clutter and noise are by the output of matched filter.

$a_{\mathrm{mn}}={\left[\begin{array}{cccc}{a}_{\mathrm{mn}11}& a_{\mathrm{mn}12}& \&CenterDot;\&CenterDot;\&CenterDot;& a_{\mathrm{mn}{L}^m{K}^m}\end{array}\right]}^T$

k＝1,2,…,K ^m,l＝1,2,…,L ^m

${\mathrm{\&epsiv;}}_m={\left[\begin{array}{cccc}{\mathrm{\&epsiv;}}_{11}^m& {\mathrm{\&epsiv;}}_{12}^m& \&CenterDot;\&CenterDot;\&CenterDot;& {\mathrm{\&epsiv;}}_{L^m{K}^m}^m\end{array}\right]}^T$

Getting approximately in the top formula, is because for same radar emission signal, and the difference of propagating between the mulitpath that causes in ionosphere is not too large, their angle

Differ very little, make target Doppler on the different paths

Differ very little.

By m the corresponding matched filter that transmits, its output result is arranged in a column vector r ' with the reception signal of all receiving antennas _m

r′ _m＝[r′ _m1 r′ _m2 … r′ _mN] ^T

＝[a _m1 a _m2 … a _mN] ^Tε _m+[w _m1 w _m2 … w _mN] ^T

＝A _mε _m+w _m

Wherein

A _m＝[a _m1 a _m2 … a _mN] ^T

w _m＝[w _m1 w _m2 … w _mN] ^T

With all M matched filtering output r ' _mBe arranged in a column vector r ', just obtained sky wave MIMO-OTH radar system and received signal model:

$r^{\&prime;}={\left[\begin{array}{cccc}{\mathrm{<figure-callout\; id="1"\; label="r"\; filenames="HDA00003405682100031.png"\; state="\{\{state\}\}">r</figure-callout>}}_1^{\&prime;\mathrm{<figure-callout\; id="2"\; label="T\; r"\; filenames="HDA00003405682100022.png,HDA00003405682100031.png"\; state="\{\{state\}\}">T</figure-callout>}}& r_{}^{}{}_2^{\&prime;T}& \&CenterDot;\&CenterDot;\&CenterDot;& {r_M^{\&prime;}}^T\end{array}\right]}^T$

$=\sqrt{\frac{E}{M}}\mathrm{Diag}\{A_1,A_2,\&CenterDot;\&CenterDot;\&CenterDot;,A_M\}{\left[\begin{array}{cccc}{\mathrm{\&epsiv;}}_1^T& {\mathrm{\&epsiv;}}_2^T& \&CenterDot;\&CenterDot;\&CenterDot;& {\mathrm{\&epsiv;}}_M^T\end{array}\right]}^T$

(13)

$+{\left[\begin{array}{cccc}{w}_1^T& w_2^T& \&CenterDot;\&CenterDot;\&CenterDot;& w_M^T\end{array}\right]}^T$

$=\sqrt{\frac{E}{M}}\mathrm{A\&epsiv;}+w$

Wherein

A＝Diag{A ₁,A ₂,…,A _M} (14)

$\mathrm{\&epsiv;}={\left[\begin{array}{cccc}{\mathrm{\&epsiv;}}_1^T& {\mathrm{\&epsiv;}}_2^T& \&CenterDot;\&CenterDot;\&CenterDot;& {\mathrm{\&epsiv;}}_M^T\end{array}\right]}^T---\left(15\right)$

$w={\left[\begin{array}{cccc}{w}_1^T& w_2^T& \&CenterDot;\&CenterDot;\&CenterDot;& w_M^T\end{array}\right]}^T---\left(16\right)$

Diag{*} represents the arrangement of piece diagonal angle.

According to document " Qian He; R. S. Blum. Diversity gain for MIMO radar employing nonorthogonal waveforms[C]. 2010 4th International Symposium on Communications; Control and Signal Processing (ISCCSP); Limassol; 2010; 1-6 " in lemma, can prove s emission signal s in the sky wave MIMO-OTH radar _m(t) the diversity gain g that provides _mSatisfy

g _m≤min{N,L ^mn} (17)

In the formula (17), when all being incoherent between all echoed signals of m signal correspondence, equal sign is set up, g _mObtain maximal value, the maximum diversity gain that the signal of this frequency that Here it is can provide to radar system.When not being complete incoherent the time (having correlativity) between the echoed signal, formula (17) is got in-less-than symbol.So need elder generation by the correlativity between formula (9) and (10) judgement echoed signal, and then obtain the diversity gain of the signal of this frequency.In the present invention, in order to make the corresponding diversity gain of transmitting of each emitting antenna get maximal value, so corresponding each echoed signal that transmits of the alternative emission signal frequency of each secondary that extracts is uncorrelated mutually.Thereby the minterm that the back-propagating path bar of directly getting the number of radar receiving antenna and transmitting is counted among both is the diversity gain value of current transmission signal.

Step 4, based on the diversity gain that respectively transmits of the alternative emission signal frequency of secondary, M maximum diversity gain is worth corresponding emission signal frequency for to make up as sky wave MIMO-OTH radar emission signal frequency before getting.

According to the conclusion of formula (17), the diversity gain g of sky wave MIMO-OTH radar system satisfies

$g\&le;\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}{g}_m=\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}\min \{N,L^{\mathrm{mn}}\}---\left(18\right)$

Wherein M is number of transmit antennas, and N is the receiving antenna number, L ^MnIt is the bar number in m back-propagating path that transmits.When the element among the ε was separate, radar can access maximum diversity gain.

The emission signal frequency of avoiding selecting multipath transmisstion that contrast is habitual, sky wave MIMO-OTH radar of the present invention can obtain being analyzed as follows of best detection performance:

Referring to Fig. 4, having provided among the figure is not having under the multipath transmisstion condition, the different radar detedtion probability figure that transmits and receives the antenna correspondence, and slope of a curve just in time equals the diversity gain of radar among the figure.Based on Fig. 5 as can be known, along with the raising of letter miscellaneous noise ratio, the false dismissal probability P_M of radar is more and more littler, and the detection performance of corresponding radar is more good.The number of transmit antennas that increases radar can increase the diversity gain of radar, improves the detection performance of radar, and the number that still increases receiving antenna can not increase the diversity gain of radar.

Fig. 5 has then provided under the multipath transmisstion condition, the different radar detedtion probability figure that transmits and receives the antenna correspondence (slope of a curve just in time equals the diversity gain of radar among the figure), based on Fig. 6 as can be known, the bar number that increases the back-propagating path can increase the diversity gain of radar, but increases the diversity gain that travel path bar number on the forward path but can not increase radar.

Fig. 6 has then provided under the multipath transmisstion condition, and the correlativity of signal is for detections of radar Effect on Performance comparison diagram, and among the figure, each rate of curve is the diversity gain of radar.As can be seen, when all uncorrelated between the echoed signal, the diversity gain maximum of radar, when having correlativity between the echoed signal, the diversity gain of radar diminishes.So the present invention by between each echoed signal of selecting to transmit mutually uncorrelated corresponding emission signal frequency as the alternative transmission frequency of sky wave MIMO-OTH radar, can make radar system obtain maximum diversity gain, thereby obtain best detection performance.

The present invention is not limited to aforesaid embodiment.The present invention expands to any new feature or any new combination that discloses in this manual, and the arbitrary new method that discloses or step or any new combination of process.

Claims (5)

1. a system of selection that is used for the emission signal frequency of sky wave MIMO-OTH radar is characterized in that, comprises the following steps:

Based on current detection range, from current available frequency band, select elementary alternative emission signal frequency, and there is multipath transmisstion in corresponding the transmitting of described elementary alternative emission signal frequency;

Extract the alternative emission signal frequency of secondary from described elementary alternative emission signal frequency, each echoed signal that transmits of the alternative emission signal frequency correspondence of described secondary is uncorrelated mutually;

Calculating is corresponding to the diversity gain that respectively transmits of the alternative emission signal frequency of described secondary, and getting M the corresponding transmission frequency of maximum diversity gain is the emission signal frequency of radar, and the value of described M is corresponding to the number of transmitting radar antenna.

2. the method for claim 1 is characterized in that, the diversity gain that respectively transmits that calculates corresponding to the alternative emission signal frequency of described secondary is:

Transmission is corresponding to the detection of a target that transmits signals to of the alternative emission signal frequency of secondary, determine the bar number in the back-propagating path of current transmission signal, the minterm of then getting the bar number in the number of radar receiving antenna and described back-propagating path is the diversity gain value of current transmission signal, and described back-propagating path is the travel path corresponding to the current echoed signal that transmits.

3. method as claimed in claim 1 or 2 is characterized in that, based on ionosphere MQP model, selects to satisfy the emission signal frequency of current detection range as elementary alternative emission signal frequency from current available frequency band.

4. method as claimed in claim 3 is characterized in that, determines that the mutual incoherent computing formula of each echoed signal that transmits is:

$\frac{(h_{k^{\&prime;}}^{m^{\&prime;}}+z_0)(x_{m^{\&prime;}}^t-x_0)}{{\mathrm{\&lambda;}}_{m^{\&prime;}}{\mathrm{\&rho;}}_{m^{\&prime;},k^{\&prime;}}}+\frac{(h_{l^{\&prime;}}^{m^{\&prime;}{n}^{\&prime;}}+z_0)(x_{n^{\&prime;}}^r-x_0)}{{\mathrm{\&lambda;}}_{m^{\&prime;}}{o}_{m^{\&prime;}{n}^{\&prime;},l^{\&prime;}}}-\frac{(h_k^m+z_0)(x_m^t-x_0)}{{\mathrm{\&lambda;}}_m{\mathrm{\&rho;}}_{m,k}}-\frac{(h_l^{\mathrm{mn}}+z_0)(x_n^r-x_0)}{{\mathrm{\&lambda;}}_m{o}_{\mathrm{mn},l}}>\frac{1}{\mathrm{\&Delta;x}},$

Wherein,

The reflection height of representing the k bar propagated forward path of m emitting antenna,

Represent the reflection height in the l bar back-propagating path of m emitting antenna, n represents receiving antenna,

The horizontal coordinate of expression emitting antenna m,

The horizontal coordinate of expression receiving antenna n, λ _mThe corresponding wavelength that transmits of expression emitting antenna m, z ₀The expression earth radius, x ₀The horizontal coordinate of the center of expression search coverage;

Parameter ${\mathrm{\&rho;}}_{m,k}={\left\{(4z_0^2-A{C}_m^2)\right[{(h_m^k+z_0)}^2+z_0^2-(h_m^k+z_0)\sqrt{4z_0^2-A{C}_m^2}\left]\right\}}^{0.5},$

Parameter $o_{\mathrm{mn},l}={\left\{(4z_0^2-B{C}_n^2)\right[{(h_l^{\mathrm{mn}}+z_0)}^2+z_0^2-(h_l^{\mathrm{mn}}+z_0)\sqrt{4z_0^2-B{C}_n^2}\left]\right\}}^{0.5},$

AC wherein _mCenter (the x that represents m emitting antenna and search coverage ₀, y ₀) air line distance, BC _nCenter (the x of expression receiving antenna n and search coverage ₀, y ₀) air line distance;

Δ x represents search coverage length in the horizontal direction.

5. method as claimed in claim 3 is characterized in that, determines that the mutual incoherent computing formula of each echoed signal that transmits is:

$\frac{(h_{k^{\&prime;}}^{m^{\&prime;}}+z_0)(y_{m^{\&prime;}}^t-y_0)}{{\mathrm{\&lambda;}}_{m^{\&prime;}}{\mathrm{\&rho;}}_{m^{\&prime;},k^{\&prime;}}}+\frac{(h_{l^{\&prime;}}^{m^{\&prime;}{n}^{\&prime;}}+z_0)(y_{n^{\&prime;}}^r-y_0)}{{\mathrm{\&lambda;}}_{m^{\&prime;}}{o}_{m^{\&prime;}{n}^{\&prime;},l^{\&prime;}}}-\frac{(h_k^m+z_0)(y_m^t-y_0)}{{\mathrm{\&lambda;}}_m{\mathrm{\&rho;}}_{m,k}}-\frac{(h_l^{\mathrm{mn}}+z_0)(y_n^r-y_0)}{{\mathrm{\&lambda;}}_m{o}_{\mathrm{mn},l}}>\frac{1}{\mathrm{\&Delta;y}},$

Wherein,

The reflection height of representing the k bar propagated forward path of m emitting antenna,

Represent the reflection height in the l bar back-propagating path of m emitting antenna, n represents receiving antenna,

The vertical coordinate of expression emitting antenna m,

The vertical coordinate of expression receiving antenna n, λ _mThe corresponding wavelength that transmits of expression emitting antenna m, z ₀The expression earth radius, y ₀The vertical coordinate of the center of expression search coverage;

Parameter ${\mathrm{\&rho;}}_{m,k}={\left\{(4z_0^2-A{C}_m^2)\right[{(h_m^k+z_0)}^2+z_0^2-(h_m^k+z_0)\sqrt{4z_0^2-A{C}_m^2}\left]\right\}}^{0.5},$

Parameter $o_{\mathrm{mn},l}={\left\{(4z_0^2-B{C}_n^2)\right[{(h_l^{\mathrm{mn}}+z_0)}^2+z_0^2-(h_l^{\mathrm{mn}}+z_0)\sqrt{4z_0^2-B{C}_n^2}\left]\right\}}^{0.5},$

AC wherein _mCenter (the x that represents m emitting antenna and search coverage ₀, y ₀) air line distance, BC _nCenter (the x of expression receiving antenna n and search coverage ₀, y ₀) air line distance;

Δ y represents search coverage length in the vertical direction.

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