The joint orthogonal projection with the circulating beam forming of the range finder pulse interference suppression method

Technical Field

The invention relates to a range finder pulse interference suppression method. In particular to a joint on the orthogonal projection with the circulating beam forming of the range finder pulse interference suppression method.

Background Art

For the protection of civil aviation a new generation of air traffic management system is safe, reliable, high-efficiency operation, the International civil aviation organization (ICAO) has proposed two ground-to-ground data link candidate technical proposal: L frequency band digital aviation communication system 1 (L - DACS1) with the L frequency band digital aviation communication system 2 (L - DACS2), wherein L - DACS1 system using multi-carrier orthogonal frequency division multiplexing (OFDM) transmission scheme, L - DACS2 system employing a single-carrier Gaussian minimum frequency shift keying (GMSK) transmission scheme. With respect to the L - DACS2 system, L - DACS1 system has higher spectral efficiency, higher transmission capacity, is more suitable for the frequency selective fading channel transmission has the advantages, therefore L - DACS1 system to obtain civil aviation industry wide attention. At the same time, in order to solve the civil aviation very high frequency communication frequency resource shortage, 2007 of the world radio assembly (WRC) to ratify the future civil aviation ground-to-air data link system deployed in aviation radio navigation frequency band, and is embedded to work in the range finder (DME) inter-channel (DME system channel interval is 1 MHz, L - DACS system deployed in the adjacent DME channel central, occupied bandwidth 0.5 MHz). Since the telemeter signal spectrum with L - DACS1 system spectrum have some overlap, and DME transmitter to high power, the work of the burst pulse mode, therefore not can avoid the DME transmitted pulse signal interference L - DACS1 system of the OFDM receiver.

Literature M Schnell, S Brandes, S Gligorevic, Interference Mitigation for Broadband L - DACS, 2008 Digital Avionics Systems Conference (DASC 2008), pp. 1 - 12, St.Paul, MN, USA, October 2008 and documentation S Brandes, M Schnell, Mitigation of Pulsed Interference in OFDM Based Systems, 2008 International OFDM Workshop (InOWo 2008), pp. 193 - 197, Hamburg, Germany, August 2008 to first establish provide the range finder pulse based on raised signal model, and the simulation study pulse extinguishes method to OFDM receiver link error performance impact, simulation studies show that the pulse extinguishes method to a certain extent the elimination of range finder pulse based on raised, but the pulse off will cause the OFDM receiver sub inter-carrier based on raised (ICI); for the application of the pulse extinguishes method to eliminate range finder pulse based on raised, literature U Epple, M Schnell, German Aerospace Center (DLR), Overview of Interference Situation and Mitigation Techniques for LDACS1, 2011 IEEE/AIAA 30 th Digital Avionics Systems Conference (DASC), pp: 4 C5 - 1 - 4 C5 - 12, 2011, provides two range finder pulse based on raised signal of the position detection method, and the simulation study raised the performance of the detection method; against the pulse off method to generate OFDM receiving the machine carrier between the question based on raised, literature S Brandes, M Schnell, Compensation of the Impact of Interference Mitigation by Pulse Blanking in OFDM Systems, 2009 IEEE Global Telecommunications Conference (GLOBECOM 2009), pp. 1 - 6, Honolulu, USA, Nov. 2009, the ICI by iterative reconstruction method based on raised and to compensate, and the simulation study ICI based on raised the performance of the compensation method, the study found that the operation of the compensation method based on raised ICI of high complexity; against the OFDM system of the non-correlated random pulse based on raised, literature G Caire, T Y.Al - Naffouri, and A. Narayanan, Impulse noise cancellation in OFDM: an application of compressed sensing, IEEE Int.Symp.on Inform. Theory, Canada, jul. 2008, will compress the perception theory application OFDM system, the optimized pulse [...] elimination method based on raised; to the power line communication system block sparse non-correlated pulse based on raised, literature L Lampe. Bursty impulse noise detection by compressed sensing, 2011 IEEE International Symposium on Power Line Communications and Its Applications (ISPLC), On page (s): 29 - 34, provide the block based on the sparse compression sensing pulse based on raised eliminating method.

OFDM receiver pulse interference cancellation method mainly comprises: pulse out method, pulse clipping method, the joint pulse extinguishment and ICI interference compensation method, compression sensing pulse interference reconstruction and eliminating method, the following are described the defects and disadvantages of these technologies.

A basic idea of the pulse extinguishes method: receiver according to the amplitude of the received signal, it first determines the position of the pulse interference signal is present, then, there will be a pulse interference signal samples is set to zero, in order to eliminate the influence of the pulse interference. In practical application, the method exists when the following two problems: pulse interference signal is not easy to determine the position of the, pulse after the extinction of the LED to the ICI interference. In determining the position of the pulse interference signal when there, usually the threshold comparison method, when the received signal amplitude exceeds the set threshold, the receiver considers that these signal samples includes the pulse interference, because the OFDM signal self-peak-to-average ratio (PAPR) is relatively high, and the dissemination through the multi-path channel, the receiver is usually not easily confirm the pulse off threshold, this will lead to the receiver bit error performance loss. In another aspect, the pulse after the extinction of the receiver, so that the receiving signal sub inter-carrier interference (ICI), inter-carrier interference will eventually lead to the deterioration of the bit error performance of the receiver.

A basic idea of the pulse amplitude limiting method: the receiver the received signal according to OFDM signal to determine the peak amplitude, then the received signal is in excess of the OFDM signal peak amplitude of the peak amplitude sample are set, in order to reduce the pulse effect of interfering signal. Pulse clipping method there is also the problem of two respects: pulse amplitude value not easy to determine, after the pulse amplitude of the signal pulse interference still remain. Because the OFDM signal self-peak-to-average ratio (PAPR) is relatively high, and the dissemination through the multi-path channel, the receiver is usually not easily confirm the pulse of limiting, pulse amplitude value not reasonably will lead to the receiver bit error performance loss; in addition, pulse clipping method cannot completely eliminate the pulse interference, limiting signal still include portion of the pulse interference, these residual pulse interference will lead to the deterioration of the bit error performance of the receiver.

The joint pulse extinguishment and ICI interference compensation method of the basic idea: first of all the use of pulse extinguishes method to eliminate the pulse interference, then further heavy hanger inter-carrier interference (ICI), the last pulse of the extinguished ICI interference compensation, thereby reducing the pulse extinguishes method to generate ICI interference, improve the reliability of the transmission link. The method of the existence of two aspects, 1st pulse extinguishing threshold not easy to determine, 2nd iterative ICI interference reconstruction and compensated operational complexity is higher.

OFDM system against the existence of sparse, non-correlated pulse interference, can also be used to reconstruct the compression perception and the elimination of the pulse interference, the scope of application of the compression sensing method: pulse interference signal with sparse characteristic, pulse interference signal is non-correlated random interference. In the L band digital aviation communication system 1 (L - DACS1) in, range finder generates pulse interference strong correlation pulse interference, therefore the compression sensing method is difficult to be directly applied to the OFDM system range finder pulse interference suppression.

Content of the invention

The invention aims to solve the technical problem, to provide a range finder can be effectively overcome the pulse and scattering of a multipath signal interference, improve the L frequency band digital aviation communication system link transmission reliability of the joint on the orthogonal projection with the circulating beam forming of the range finder pulse interference suppression method.

The present invention adopts the technical scheme is: a combined orthogonal projection with the circulating beam forming of the range finder pulse interference suppression method, comprising: from the array antenna of the radio frequency signal through the radio frequency front end into an analog baseband signal, the analog baseband signal through the A/D is converted to a digital baseband signal, a plurality of receiving channel output digital baseband signal by orthogonal projection algorithm to calculate the interference signal obtained orthogonal complement the projection matrix, the projection matrix is applied to the received signal vector for the pulse signal of the interference elimination of range finder, after the elimination of pulse interference signal vector further through the circulating beam forming method to obtain the array antenna beam forming weight vector, using the obtained weight vector to the elimination of the pulse interference after the signal vector for the beam forming extracting OFDM direct path signal; beam forming device output of the OFDM direct path signals after removing the cyclic prefix, through the FFT operation is converted to a frequency domain signal, and further through 4 down-sampling time of frequency range, sampler under output signal through the channel estimation to estimate the channel characteristics, and a channel equalization by the equalizer, the equalizer output signal passes through the demodulator, de-interleaver and decoder to get an estimate of the bit sequence.

In the analog baseband signal is converted into a digital signal, in order to avoid range finder pulse signal samples to produce the frequency spectrum of the received OFDM signal aliasing interference, the receiver using the four times over sampling.

The orthogonal projection algorithm to calculate the interference signal obtained orthogonal complement the projection matrix, including:

The use of the assumption that the received signal even array, the array element number of channels is M, the array element interval is the λ / 2, then the array antenna receiving signal vector x (n) is expressed as:

Wherein n represents the number of sampling a signal, s (n) on behalf of the OFDM signal, a_θ On behalf of the OFDM signal that corresponds to the guide vector, w_k (N) on behalf of a k interference signal, d_k K interference signal on behalf of a corresponding guide vector, K represents the total number of interference sources, n (n) representative channel input of the complex Gaussian white noise vector;

Will (1) type further is expressed as:

X (n)=s_θ (N)+ w (n)+ n (n) (2)

Wherein s_θ (N)=s (n) a_θ ,

The array antenna receiving signal vector x (n) of the covariance matrix is defined as:

R_Xx =E {x (n) ·x^H (N)} (3)

Taking into account the OFDM signal, range finder pulse signal, the noise signal statistics independent, then (3) type dization is:

R_Xx =R_s + R_w + R_n (4)

Wherein R_s The representatives of the covariance matrix of the OFDM signal; R_w The representatives of the covariance matrix of the interference signal; R_n The representatives of the covariance matrix of the noise signal;

The range finder of the pulse signal is far greater than the strength of the OFDM signal and the noise signal, so (4) type further abbreviation for:

R_Xx =R_w + R_v (5)

Wherein R_v =R_s + R_n ;

The matrix R_Xx Characteristic value is decomposed to get:

Wherein On behalf of the covariance matrix R_Xx Of non-vanishing characteristic value, e_i , I=1, 2...M representative R_Xx The non-zero value corresponding to the feature vector, Representative R_Xx The non-zero value of the diagonal matrix, the representative of the U R_Xx The proper value of the column vector corresponding to a characteristic of the unitary matrix, meet the UU^H =I, the definition of a K pulse interference signal corresponding to the feature value is λ_i , Wherein i=1, 2, .. K, because the range finder pulse interference signal strength is far greater than the OFDM signal with the noise signal, therefore λ_i The value of the characteristic value is significantly greater than the The K pulse interference signal corresponding to the characteristic value of the λ_i Known as the main characteristic value, the characteristic value of the λ main_i Eigenvectors corresponding interference signal sub-space, for S entry_w =span {e₁ , E₂ , ..., E_K }, It is S_w =span {e₁ , E₂ , ..., E_K }, Wherein e_i , I=1, 2... K on behalf of the covariance matrix R_Xx The main characteristic of a λ K_i The corresponding feature vector;

Interference signal obtained after the sub-space, to calculate the interference signal of the orthogonal complement space projection matrix:

Then, the role of the projection matrix for the received signal vector in order to dispel the range finder pulse signal interference.

The projection matrix is applied to the received signal vector in order to dispel the range finder pulse signal interference, including:

The received signal vector x (n) of the interference signal of the orthogonal complement space projection to obtain:

(8) in the formula, Representative of the interference signal of the orthogonal complement space projection matrix, x (n) on behalf of the array antenna receiving signal vector, s_θ (N) on behalf of the array antenna receiving to the OFDM signal vector, n (n) representative channel input of the complex Gaussian white noise vector. Taking into account the The final (8) type dization is:

(9) type that: by the received signal vector of the interference signal orthogonal complement space projection can eliminate the channel input of the range finder pulse interference.

The through circulation beam forming method to obtain the array antenna beam forming weight vector, comprising:

Firstly the following parameter, N_s On behalf of a OFDM symbol sampling points of, N_g OFDM symbol representative of the sampling points of the cyclic prefix, N_u In addition to the cyclic prefix representative of the sampling points of the outer symbols, and N_s =N_u + N_g ;

In response to the orthogonal projection pulse after eliminating the interference output signal vector, defined two vector z (j, i) and z (j, i + N_u ):

Z (j, i)=[z₁ [(J - 1) ·N_s + I], ..., z_m [(J - 1) ·N_s + I], ..., z_M [(J - 1) ·N_s + I]]^T(10)

Z (j, i + N_u )=[z₁ [(J - 1) N_s + N_u + I], ..., z_m [(J - 1) N_s + N_u + I], ..., z_M [(J - 1) N_s + N_u + I]]^T ·E^{J2 π α} (11)

Wherein z_m [(J - 1) ·N_s + I] its representative M continuity of m in the channel of a channel of the OFDM symbols of a j of the i sampling samples, wherein i=1, ..., N_g , J=1, ..., N, m=1, ..., M; z (j, i) on behalf of all the M continuity of a channel of the OFDM symbol of the j of a i sampling values of the signal vector; z (j, i + N_u ) Representative of the Doppler frequency offset in the received signal after correcting all M channel of one of the OFDM symbol of the j of a i sampling values of the signal vector, wherein α represents the normalized doppler frequency offset of the received signal, α=delta f/F_S ; Delta f representative of the received signal Doppler frequency offset; F_S The sub-carrier interval on behalf of the OFDM system;

On the assumption that the receiver has established full symbol timing synchronization, then the receiver circulating beam forming of the target: the search for the optimal weight vector ω ω desired signal^H Z (j, i) with a reference signal c^H Z (j, i + N_u ) Between the maximum of the correlation value, the correlation value is maximized is a mathematical description of a:

(12) in the formula of the ω ω and c meet the^H Ω=c^H C=1

Wherein I=1, 2, ..., N_g , J=1, ..., N, N representative of the total number of OFDM symbols in a frame, further the definition Is (12) type further is expressed as:

Wherein c represents the auxiliary vector; (13) is expressed as in formula further|_AO7 C X0AO_ ω|_AO7 C X0AO_=|_AO7 C X0AO_ c _AO7 C X0AO_ _AO7 C X0AO_=1 under constraint, ω^H Rcc^H R^H The problem of maximizing ω, to (13) type using Lagrange multiplier france asks differential satisfies equation is zero can be obtained abbreviation:

ω^H Rc=ξ_Max (14)

Wherein ξ_Max The representatives of the largest singular value R, when the optimal weight vector ω and auxiliary vector c R value is the largest singular value ξ_Max When the left and right singular value corresponding to the vector, (13) fetch maximum value, the optimal weight vector ω is OFDM signal corresponding to a guide vector_θ Direct estimation, namely ω ∝a_θ .

The channel estimation is estimated in the frequency domain and the frequency domain interpolation LS obtained by the method.

The joint of the present invention orthogonal projection with the circulating beam forming of the range finder pulse interference suppression method, which can effectively overcome the range finder pulse and scattering of a multipath signal interference, improve the L frequency band digital aviation communication system of the reliability of the transmission link. Has the following results:

1. the method of the invention does not exist pulse off threshold setting issues, there is no inter-carrier interference (ICI) problem, can be directly received signal vector construct the interfering signal orthogonal complement space projection matrix and then acting on receiving the signal, thereby effectively inhibiting the range finder pulse signal.

2. the method does not exist pulse the clipping threshold sets up the question, not the existence of residual pulse interference problem, has better link error transmission performance.

3. the method does not exist pulse off threshold setting problem, also without iterative reconstruction ICI interference, so this invention the calculation complexity relatively low.

4. the method can not only eliminate random pulse interference, at the same time taking advantage of the OFDM cyclic prefix symmetrical characteristic of effectively extract the desired signal. The invention has wider application range, and interference suppression effect is better.

Description of drawings

Figure 1 is the block diagram of the form of the invention the joint orthogonal projection with the circulating beam forming of the range finder pulse interference suppression method;

Figure 2 a is a spectrogram of the OFDM transmission signal power;

Fig. 2 b is the residual interference after filtering the signal power spectrum;

Fig. 2 c is a receiver the received signal power spectrogram;

Figure 2d is the signal power spectrogram of after suppression pulse interference;

Figure 3 is a range finder pulse interference suppression front and rear time domain signal waveform diagram (a single DME interference, signal-to-interference ratio=- 10dB, noise power=0);

Figure 4 is the beam pattern of the circulating beam forming (400 times Monte carlo test);

Figure 5 is a system error performance curve (QPSK modulation).

Mode of execution

The following combined embodiment and with photos to the combination of the present invention orthogonal projection with the circulating beam forming of the range finder pulse interference suppression method to make detailed description.

In order to solve the L frequency band digital aviation communication system 1 (L - DACS1) is embedded to deployed in the L frequency band generated by the range finder strong pulse interference L frequency band digital aviation communication system of the OFDM receiver. The invention provides joint orthogonal projection with the circulating beam forming pulse interference suppression method of the range finder, the method utilizes the aircraft in route flight stage, air channel mainly to direct channel, scattering mode propagation, and direct drive and scattering path wave incident angle and expanded the greater characteristic, made joint orthogonal projection with the circulating beam forming of the range finder pulse interference suppression method, the receiver of the signal through the first orthogonal projection method to eliminate the high strength range finder pulse interference, then the use of OFDM signal cyclic prefix symmetrical characteristic of, using the circulation a beam forming method extracting OFDM direct path signal. The use of the invention can effectively overcome the range finder pulse and scattering of a multipath signal interference, improve the L frequency band digital aviation communication system of the reliability of the transmission link.

As shown in Figure 1, the joint of the present invention orthogonal projection with the circulating beam forming of the range finder pulse interference suppression method, comprising: from the array antenna of the radio frequency signal through the radio frequency front end into an analog baseband signal, the analog baseband signal through the A/D is converted to a digital baseband signal, in converting the analog baseband signal is a digital signal, in order to avoid range finder pulse signal samples to produce the spectrum aliasing interference OFDM (orthogonal frequency division multiplexing) of the received signal, the receiver using the four times over sampling (L - DACS1 receiver standard sampling frequency is 625 kHz, four-times over-sampling frequency is 2.5 MHz). A plurality of receiving channel output digital baseband signal by orthogonal projection algorithm to calculate the interference signal obtained orthogonal complement the projection matrix, the projection matrix is applied to the received signal vector for the interference elimination of range finder of the pulse signal, after the elimination of pulse interference signal vector further through the circulating beam forming method to obtain the array antenna beam forming weight vector, using the obtained weight vector to the elimination of the pulse interference after the signal vector for the beam forming extracting OFDM direct path signal; beam forming device output of the OFDM direct path signals after removing the cyclic prefix, through the FFT operation is converted to a frequency domain signal, and further through 4 down-sampling time of frequency range, sampler under output signal through the channel estimation to estimate the channel characteristics, and a channel equalization by the equalizer, the equalizer output signal passes through the demodulator, de-interleaver and decoder to get an estimate of the bit sequence. The channel estimation is estimated in the frequency domain and the frequency domain interpolation LS obtained by the method. And compared with the conventional OFDM receiving method, the receiving scheme of a Patent mainly reflect the following two aspects: a signal orthogonal projection pulse interference suppression and circulating beam forming OFDM direct path signal extraction.

The orthogonal projection algorithm to calculate the interference signal obtained orthogonal complement the projection matrix, in the signal orthogonal projector, the array antenna output signal vector to calculate the reception signal vector covariance matrix, the covariance matrix of the received signal vector after decomposition characteristic value, determining the number of large characteristic value corresponding to the large characteristic value and determining the feature vector, then by using the characteristic value of the eigenvectors corresponding to the interference signal sub-space, the interference sub-space structure by the orthogonal complement space projection matrix, the role of the matrix for the received signal vector can eliminate range finder pulse interference. Specifically comprises:

The use of the assumption that the received signal even array, the array element number of channels is M, the array element interval is the λ / 2, λ received signal in the wavelength of the signal, then the array antenna receiving signal vector x (n) is expressed as:

Wherein n represents the number of sampling a signal, s (n) on behalf of the OFDM signal, a_θ On behalf of the OFDM signal that corresponds to the guide vector, w_k (N) on behalf of a k interference signal, d_k K interference signal on behalf of a corresponding guide vector, K represents the total number of interference sources, n (n) representative channel input of the complex Gaussian white noise vector;

Will (1) type further is expressed as:

X (n)=s_θ (N)+ w (n)+ n (n) (2)

Wherein s_θ (N)=s (n) a_θ ,

The array antenna receiving signal vector x (n) of the covariance matrix is defined as:

R_Xx =E {x (n) ·x^H (N)} (3)

Taking into account the OFDM signal, range finder pulse signal, the noise signal statistics independent, then (3) type dization is:

R_Xx =R_s + R_w + R_n (4)

Wherein R_s The representatives of the covariance matrix of the OFDM signal; R_w The representatives of the covariance matrix of the interference signal; R_n The representatives of the covariance matrix of the noise signal;

In the question in this study, because the range finder is far greater than the pulse signal of the OFDM signal and the strength of the noise signal, so (4) type further abbreviation for:

R_Xx =R_w + R_v (5)

Wherein R_v =R_s + R_n ;

The matrix R_Xx Characteristic value is decomposed to get:

Wherein On behalf of the covariance matrix R_Xx Of non-vanishing characteristic value, e_i , I=1, 2...M representative R_Xx The non-zero value corresponding to the feature vector, Representative R_Xx The non-zero value of the diagonal matrix, the representative of the U R_Xx The proper value of the column vector corresponding to a characteristic of the unitary matrix, meet the UU^H =I, the definition of a K pulse interference signal corresponding to the feature value is λ_i , Wherein i=1, 2, .. K, because the range finder pulse interference signal strength is far greater than the OFDM signal with the noise signal, therefore λ_i The value of the characteristic value is significantly greater than the The K pulse interference signal corresponding to the characteristic value of the λ_i Known as the main characteristic value, the characteristic value of the λ main_i Eigenvectors corresponding interference signal sub-space, it is S_w =span {e₁ , E₂ , ..., E_K }, Wherein e_i , I=1, 2... K on behalf of the covariance matrix R_Xx The main characteristic of a λ K_i The corresponding feature vector;

Interference signal obtained after the sub-space, to calculate the interference signal of the orthogonal complement space projection matrix:

Then, the role of the projection matrix for the received signal vector in order to dispel the range finder pulse signal interference.

The projection matrix is applied to the received signal vector in order to dispel the range finder pulse signal interference, including:

The received signal vector x (n) of the interference signal of the orthogonal complement space projection to obtain:

(8) in the formula, Representative of the interference signal of the orthogonal complement space projection matrix, x (n) on behalf of the array antenna receiving signal vector, s_θ (N) on behalf of the array antenna receiving to the OFDM signal vector, n (n) representative channel input of the complex Gaussian white noise vector. Taking into account the The final (8) type dization is:

(9) type that: by the received signal vector of the interference signal orthogonal complement space projection can eliminate the channel input of the range finder pulse interference.

The through circulation beam forming method to obtain the array antenna beam forming weight vector, in the circulating beam shaping device, using the OFDM signal cyclic prefix of the symmetrical characteristic, to the desired signal with the reference signal correlation value maximum into the objective function to find the optimal weight vector. At the same time, in order to OFDM signal cyclic prefix signal vector with its own frequency shift signal vector construction a cyclic correlation matrix. The optimal weight vector is finally confirmed as a cyclic correlation matrix of left singular value corresponding to the largest singular value of the vector, the vector role has been eliminated range finder for pulse interference signal vector and further through the circulating beam forming method of OFDM direct path signal is extracted. Specifically comprises:

For the convenience of the description of the OFDM receiver cycle the working principle of the beam forming method, firstly the following parameter, N_s On behalf of a OFDM symbol sampling points of, N_g OFDM symbol representative of the sampling points of the cyclic prefix, N_u In addition to the cyclic prefix representative of the sampling points of the outer symbols, and N_s =N_u + N_g ;

In response to the orthogonal projection pulse after eliminating the interference output signal vector, defined two vector z (j, i) and z (j, i + N_u ):

Z (j, i)=[z₁ [(J - 1) ·N_s + I], ..., z_m [(J - 1) ·N_s + I], ..., z_M [(J - 1) ·N_s + I]]^T(10)

Z (j, i + N_u )=[z₁ [(J - 1) N_s + N_u + I], ..., z_m [(J - 1) N_s + N_u + I], ..., z_M [(J - 1) N_s + N_u + I]]^T ·E^{J2 π α} (11)

Wherein z_m [(J - 1) ·N_s + I] its representative M continuity of m in the channel of a channel of the OFDM symbols of a j of the i sampling samples, wherein i=1, ..., N_g , J=1, ..., N, m=1, ..., M; z (j, i) on behalf of all the M continuity of a channel of the OFDM symbol of the j of a i sampling values of the signal vector; z (j, i + N_u ) Representative of the Doppler frequency offset in the received signal after correcting all M channel of one of the OFDM symbol of the j of a i sampling values of the signal vector, wherein α represents the normalized doppler frequency offset of the received signal, α=delta f/F_S ; Delta f representative of the received signal Doppler frequency offset; F_S The sub-carrier interval on behalf of the OFDM system;

On the assumption that the receiver has established full symbol timing synchronization, then the receiver circulating beam forming of the target: the search for the optimal weight vector ω ω desired signal^H Z (j, i) with a reference signal c^H Z (j, i + N_u ) Between the maximum of the correlation value, the correlation value is maximized is a mathematical description of a:

(12) in the formula of the ω ω and c meet the^H Ω=c^H C=1

Wherein I=1, 2, ..., N_g , J=1, ..., N, N representative of the total number of OFDM symbols in a frame, further the definition Is (12) type further is expressed as:

Wherein c represents the auxiliary vector; (13) is expressed as in formula further|_AO7 C X0AO_ ω|_AO7 C X0AO_=|_AO7 C X0AO_ c _AO7 C X0AO_ _AO7 C X0AO_=1 under constraint, ω^H Rcc^H R^H The problem of maximizing ω, to (13) type using Lagrange multiplier france asks differential satisfies equation is zero can be obtained abbreviation:

ω^H Rc=ξ_Max (14)

Wherein ξ_Max The representatives of the largest singular value R, when the optimal weight vector ω and auxiliary vector c R value is the largest singular value ξ_Max When the left and right singular value corresponding to the vector, (13) fetch maximum value, the optimal weight vector ω is OFDM signal corresponding to a guide vector_θ Direct estimation, namely ω ∝a_θ .

Using the obtained weight vector to the elimination of the pulse interference after the signal vector for the beam forming, OFDM can be extracting the direct path signal.

Circulating beam forming device output signal by the cyclic prefix remover removing the cyclic prefix, through FFT converter conversion into a frequency domain signal, and further through 4 down-sampling time of frequency range, sampler under output signals are sent into the channel estimator, the channel estimator by frequency domain and frequency domain interpolation algorithm LS estimated estimated channel characteristics, and then by the channel equalizer through a channel equalization processing algorithm compels zero to be balanced, the equalizer output signal is sent to the signal demodulator demodulates the output, through the completion of the de-interleaver de-interleaving processing, finally by the channel decoder to recover the original transmitted information bit estimate.

The Figure below illustrate the invention joint orthogonal projection with the circulating beam forming of the range finder pulse interference suppression effectiveness of the method.

Figure 2 a, fig. 2 b, fig. 2 c, Figure 2 d display provides pulse interference suppression front and rear signal power spectrum of a comparison curve. Each of the graphs of the abscissa represents the frequency (MHz), the ordinate represents the signal power (dBw). Wherein fig. 2 a display OFDM transmission signal power spectrum (transmission signal power is 1), by fig. 2 a can be observed: the main frequency component of the OFDM signal at the - 250KHz - + 250 KHz, OFDM pass-band of the signal in the power spectrum takes a value of - 30dBw. Figure 2 b display range finder pulse signal by the equivalent of the anti-aliasing filter after the residual interference signal power spectrum (range finder signal carrier bias 500 KHz, signal-to-interference ratio SIR=- 10dB), by fig. 2 b can be observed: through the receiver of the anti-aliasing filter after the residual interference of the main frequency component of the signal at the + 250 KHz the left and right, and the residual interference signal has a relatively strong signal power. Figure 2 c display gives the power spectrum of the signals received by the receiver (part 1 receiving channel, range finder carrier bias + 500 KHz, SIR=- 10dB, noise power is 0), by fig. 2 c can be observed: in - 250KHz - + 150 KHz frequency within the frequency range, the power spectrum of the OFDM signal takes a value of - 30dBw, in the + 150 KHz - + 250 KHz band obviously can be observed within the range of the residual pulse frequency of the interfering signal component, and the value of the interference signal to the highest intensity for - 10dBw. Figure 2 d display provides the pulse interference suppression after the power spectrum of the signal (article 1 output channel), by fig. 2 d can be observed: in - 250KHz - + 250 KHz of frequency within the frequency range, the power spectrum of the OFDM signal takes a value of - 30dBw, in 150 KHz - 250 KHz frequency within the frequency range observation less than range finder pulse interference signal component. Figure 2 a - Figure 2 d the comparison indicates that the: the orthogonal projection method can remarkably inhibit the range finder pulse interference.

Figure 3 display provide the orthogonal projection algorithm inhibiting range finder front and rear time domain waveform interference, in the Figure abscissa represents time, the ordinate represents the signal amplitude (real), Figure 3 is marked with "-. -" in the curve representative of the time-domain signal before the pulse interference suppressing waveform (article 1 input channel), marked "—" of the curve represents the pulse interference suppression after time-domain signal waveform (article 1 output channel). Curve the comparison indicates that the: use of array antenna orthogonal projection method can remarkably inhibit the range finder pulse interference.

Figure 4 display provides array antenna circulating beam forming algorithm of the beam pattern, Figure 4 abscissa representative of the angle of arrival of a signal (degrees), indicating on the ordinate a normalized beam gain (dB). In the simulation test, OFDM signal to perpendicular incidence diameter to 20 degrees, scattering path to to 80 degrees, the signal to noise ratio is 6 dB, DME interference signal to to 60 degrees, signal-to-interference ratio is - 20dB, DME carrier biased as the 500 KHz. Figure 4 can be observed to: (1) the array antenna main beam pointing OFDM direct path direction; (2) the array antenna in the range finder to the direction of the pulse signal to 60 degrees to form relatively deep beam forming, signal attenuation to achieve - 45dB; (3) multi-simulation display array antenna beam forming the rear main flap prominent, the stability of the antenna beam direction.

Figure 5 display provides the L - DACS1 system bit error performance curve, Figure 5 in horizontal coordinate represent the signal to noise ratio, indicating on the ordinate a bit error probability. Figure 5 is marked with "▲" in the curve representative of the DME system without interference when the bit error performance curve; marked "■" curve represents the existence of a single DME interference when the bit error performance curve (DME carrier bias 500 KHz, signal-to-interference ratio SIR=- 3dB); marked "●" of the curve represents the existence of two DME of interference when the bit error performance curve (DME carrier bias are 500 KHz and - 500KHz, SIR1=- 10dB, SIR2=- 5dB). Curve the comparison indicates that the: (1) the presence of the pulse interference when a single range finder, the method of the invention can be completed the elimination of range finder pulse interference, system bit error performance and range finder pulse interference does not exist when the bit error performance of the system is the same as the curve; (2) when the system of the existence of two range finder when the pulse interference, the proposed method can still obtain satisfactory bit error performance.