CN1564494A - Self-adaptive beam shaping method of beam space orthogonal FDM medulating system - Google Patents

Abstract

The method is as following: DFT transform is carried out in space domain for signal vector received by array element; transform is carried back to wave beam space; each component of signal vector in wave beam space is corresponding to a receiving signal of one fixed beam former; correlation operation is carried out between each component of signal vector in wave beam space and a known adjustment sequence so as to obtain preliminary estimate of information of the wave beam channel; based on discrimination criterion, the wave beam of receiving interference and noise is determined. Setting correlation sequences values of these wave beams to zero; final estimate of channel information matrix is obtained from multiple paths abstraction of correlation sequences of each wave beam. Based on maximum S/N ratio rule, optimal weight vector in wave beam space is obtained, and then optimal weight vector in array element space is obtained. The invention raises precision of CSI estimation.

Description

Beam space orthogonal FDM modulation system adaptive beam formation method

Technical field

The present invention relates to be used for the digital information radio transmission technical field, be specifically related to a kind of OFDM modulation (OFDM) system self-adaption antenna beam formation method.

Background technology

The OFDM modulation, promptly the OFDM technology is applied to the high speed data transfer field, contrary frequency selectivity decline effectively.Application self-adapting antenna array in OFDM can suppress the multipath interference that cochannel disturbs and time-delay exceeds the protection interval, obtains optimum Signal to Interference plus Noise Ratio (SINR).Adaptive array is according to certain criterion, and the received signal of each array element is weighted and superposes, and forms wave beam adaptively in the space, thereby suppresses to disturb, and extracts useful signal.Be formed on position in the receiver signal processing flow according to wave beam, the OFDM adaptive antenna can be divided into two types of time domain (pre-FFT) and frequency domains (post-FFT), its difference is, the former carried out wave beam to form before the OFDM demodulation, and the latter carries out wave beam formation after each array element is done the OFDM demodulation, and time-domain wave beam forms has the advantage that fast Fourier transform (FFT) element number is few, training sequence length is short, computation complexity is low.

The effect of OFDM adaptive array is to suppress the multipath interference that cochannel disturbed and exceeded the protection interval; " the On a novel pre-FFT OFDM adaptiveantenna array for delayed signal suppression " that M.Budsabathon and S.Hane deliver (can suppress to postpone the novel pre-FFT OFDM adaptive antenna that multipath disturbs; IEICE Trans.Communications; 2003; E86-B (6): 1936-1945); adopt pre-FFT adaptive antenna beam-forming technology; at first utilize training sequence that each array element upper signal channel information (CSI) is estimated; just estimate the time delay and the amplitude-phase information of each useful multipath in each array element received signal; then estimate to carry out on the basis wave beam and form, reach and suppress to exceed the purpose that protection multipath at interval disturbs at CSI.The shortcoming of this method is the robustness of its CSI estimation and the influence that precision is subjected to following two factors:

1) do not consider the existence that strong cochannel disturbs, thereby do not consider the strongly disturbing CSI estimation effect that has caused for each array element.When strong jamming incident, because the training sequence limited length, useful signal information is difficult to be extracted out, thereby the error that CSI is estimated increases even utter failure greatly.

2) even do not exist strong co-channel to disturb, different multipath component interferences also can be estimated to exert an influence to CSI, reduce the accuracy that CSI estimates.

Summary of the invention

The objective of the invention is at the defective of CSI estimation in array element space on precision and robustness, a kind of beam space orthogonal FDM modulation system adaptive beam formation method is proposed, this method by the signal transformation that will receive on the array element to beam space, the different directions incoming signal is projected on the different beams, reduce each multipath component each other influence and interference signal to the influence of desired signal, and handle according to the extraction that the feature of different beams correlated series is carried out non-signal beam, the CSI that can improve the OFDM adaptive antenna greatly estimates the precision and the robustness of (particularly disturb under the existence condition at strong co-channel and estimate), thereby guarantees the performance that wave beam forms.

The present invention is achieved by the following technical solutions, and method step is as follows:

1) by spatial domain discrete Fourier transform (DFT) (DFT) the array element received signal vector is converted into beam space, the received signal of the in fact corresponding fixed beam former of each component of beam space signal vector.

2) each component of beam space signal vector is correlated with known training sequence, and the correlated series that obtains is considered as this beam-channel information according to a preliminary estimate.

3) according to given criterion, judge and receive to disturb and the wave beam of noise, and with the correlated series value zero setting of these wave beams, with the elimination strong jamming to the CSI estimation effect.

4) each wave beam correlated series is carried out the extraction of multipath, obtain the final estimation of channel information matrix.

5) obtain the optimal weight vector of beam space according to maximum Signal to Interference plus Noise Ratio criterion.

6) the array element space is gone back in the optimal weight vector conversion of beam space, obtained the optimal weight vector in array element space.

Below each step of the present invention is described in further detail:

1, described step 1) is implemented as follows:

Carry out the DFT conversion in space at first to received signal, with r=[r ₁, r ₂..., r _M] ^TExpression array element space received signal, $r_b(={[r_1^b,r_2^b,\&CenterDot;\&CenterDot;\&CenterDot;,r_M^b]}^T)$ Expression is converted into the signal of beam space, and subscript T represents transposition, and M is the bay number, with $F={[f_0^T,f_1^T,\&CenterDot;\&CenterDot;\&CenterDot;,f_{M-1}^T]}^T$ Expression DFT transformation matrix $(f_1={[1,e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20041001736800121.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;t}}{M}},\&CenterDot;\&CenterDot;\&CenterDot;,e^{-\mathrm{<figure-callout\; id="2"\; label="j"\; filenames="A20041001736800121.png"\; state="\{\{state\}\}">j</figure-callout>}\frac{2\mathrm{\&pi;t}(M-1)}{M}}]}^T),$ Then conversion expression formula is: r ^b=Fr.

2, described step 2), be implemented as follows:

r ^bEach component be L with being used for the length that CSI estimates _TrTraining sequence Tr (k) be correlated with, with

$c_i={[c_{i,0},c_{i,1},\&CenterDot;\&CenterDot;\&CenterDot;c_{i,L_g}]}^T$ The correlated series of representing i beam component correspondence, L _gBe OFDM protection gap length, the correlometer formula is

$c_{i,n}=\frac{1}{L_{\mathrm{tr}}}\underset{k=0}{\overset{L_{\mathrm{tr}}-1}{\mathrm{\&Sigma;}}}{r}_i^b(k+n)\mathrm{Tr}\left(k\right),i=1...M,n=0...L_g$

3, described step 3) is implemented as follows:

As follows each wave beam is differentiated and handled: to the c of each wave beam correspondence _iSequence is with the average c of this sequence minimax mould value _{I_th}Be standard, judge that the mould value is greater than the number of this standard value, if number is greater than predetermined threshold values N in the sequence _Th, think that this wave beam is non-signal beam, with this correlated series zero setting, with c ' _iSequence after expression is handled, this procedural representation is:

The element number of Num () expression set in the formula.

4, described step 4) is implemented as follows:

Extract the multipath information in each wave beam, obtain the final estimation of Beam-Space CSI matrix

Extracting method is, to the c ' of each wave beam correspondence _iSequence keeps the bigger some values of its mould value, and to other value zero setting, differentiates threshold values by factor alpha and c ' _iIn maximum determine.

5, described step 5) is implemented as follows:

By finding the solution following generalized eigenvalue equation, obtain the beam space optimal weight vector W under the maximum Signal to Interference plus Noise Ratio criterion _Opt ^b:

E express time expectation in the formula, subscript H represents conjugate transpose,

$S_d={[S_{d,l},S_{d,l-1},\&CenterDot;\&CenterDot;\&CenterDot;,S_{d,l-L_g}]}^T$ Be that l snap moment time delay is less than protection required multipath signal vector at interval.This expectation computing can be used and be used for the training sequence that weights generate in the OFDM frame.λ _MaxBe eigenvalue of maximum.

6, described step 6) is implemented as follows:

With W _Opt ^bThe array element space is gone back in conversion, obtains the optimal weight vector w in array element space _Opt, transform is:

$w_{\mathrm{opt}}=F^H{w}_{\mathrm{opt}}^b$

The present invention has following advantage: 1) in the existing array element space-wise, the signal of all directions is superimposed upon in each array element received signal, influence each other, in the present invention, the signal of different directions is mapped on the different wave beams, influencing each other each other is greatly diminished, and the precision that CSI estimates can improve greatly.2) by differentiating the interference noise wave beam, the wave beam that mainly receives only interference and noise can be extracted, the influence that cochannel disturbs and useless multipath disturbs can further suppress.3) based on above reason, array element space-wise poor performance even can't work under the condition that strong co-channel disturb to exist, and the method applied in the present invention still has good performance.Even when no strong co-channel disturbed, this method still can obtain more performance than existing methods.

Description of drawings

Fig. 1 is an ofdm system time-domain adaptive antenna receiver module map.

Fig. 2 is beam space channel information estimation module figure.

Fig. 3 is for adopting this method and adopting the simulation result of array element space-wise to compare

Fig. 3-a does not have cochannel interference simulation result

Fig. 3-b has strong co-channel interference simulation result

Embodiment

As shown in Figure 1 and Figure 2, for understanding the present invention better, be further described below in conjunction with the realization of the drawings and specific embodiments to method, instance parameter is provided with as follows: bay is counted M=16, OFDM protection gap length L _gBe 16 OFDM sampling lengths; be provided with 4 road multipath components and one road cochannel and disturb incident; one the tunnel outside protection at interval in the multipath component; be to disturb multipath; other three the tunnel are useful multipath, and the Bo Dajiao of each incoming signal spends to equally distributed independent random variable between 90 degree-90, and the time delay of useful multipath is taken as equally distributed independent random variable in 0～16; disturb the time delay of multipath to be taken as 18,4 road multipath constant power incidents.The specific implementation process of this example is as follows:

1) at first 16 * 1 received signals is carried out the discrete Fourier transform (DFT) (DFT) in space, the received signal r in array element space is converted into the received signal of beam space $r_b(={[r_1^b,r_2^b,\&CenterDot;\&CenterDot;\&CenterDot;,r_{16}^b]}^T),$ Represent 16 * 16DFT transformation matrix with F, r is arranged ^b=Fr.

2) r ^bEach component be L with being used for the length that CSI estimates _Tr=80 training sequence Tr (k) is correlated with, with c _i=[c _{I, 0}, c _{I, 2}... c _{I, 16}] ^TThe correlated series of representing i beam component correspondence has

$c_{i,n}=\frac{1}{80}\underset{k=0}{\overset{80-1}{\mathrm{\&Sigma;}}}{r}_i^b(k+n)\mathrm{Tr}\left(k\right),i=1...16,n=0...16$

3) to each c _lSequence is with the average c of this sequence minimax mould value _{I_th}Be standard, judge that the mould value is greater than the number of this standard value, if number is greater than predetermined threshold values N in the sequence _Th, be taken as 4 here, think that then this wave beam is non-signal beam, with this correlated series zero setting, with c ' _iSequence after expression is handled, this procedural representation is:

4) extract multipath information in each wave beam, obtain the estimation of 16 * 17 Beam-Space CSI matrixes

The extraction formula is as follows, to the c ' of each wave beam correspondence _iSequence keeps the bigger some values of its mould value, and to other value zero setting, differentiates threshold values by factor alpha and c ' _iIn maximum determine that α gets 0.5 here.

5) find the solution following generalized eigenvalue equation, obtain the beam space optimal weight vector W under the maximum Signal to Interference plus Noise Ratio criterion _Opt ^b:

S wherein _d=[S _{D, l}, S _{D, l-1}..., S _{D, l-16}] ^TBe that l snap moment time delay is less than protection required multipath signal vector at interval.

6) with W _Opt ^bThe array element space is gone back in conversion, obtains the optimal weight vector in array element space:

$w_{\mathrm{opt}}=F^H{w}_{\mathrm{opt}}^b$

Fig. 3 has provided the error rate Monte Carlo simulation result that adopts this method and adopt the array element space-wise to obtain, and simulation times is 1000 times.Provide simultaneously be under the ideal communication channel information estimation condition the result as a reference, cochannel disturbs and to be made as 0 among Fig. 3-a, disturbs than the result under high 10dB of useful signal level and the 20dB condition and provide cochannel among Fig. 3-b respectively.As we can see from the figure, do not having under the strongly disturbing condition, this method has suitable performance boost than array element space-wise, and under the strong jamming condition, array element space-wise poor performance, even failure, but and this method operate as normal still.

Claims (7)

1, a kind of beam space orthogonal FDM modulation system time-domain adaptive wave beam formation method is characterized in that method step is as follows:

1) the array element received signal vector is carried out the spatial spreading Fourier transform, be converted into beam space, the received signal of the in fact corresponding fixed beam former of each component of beam space signal vector;

2) each component of beam space signal vector is correlated with known training sequence, and the correlated series that obtains is considered as this beam-channel information according to a preliminary estimate;

3) according to given criterion, judge and receive to disturb and the wave beam of noise, and with the correlated series value zero setting of these wave beams, with the elimination strong jamming to the CSI estimation effect;

4) each wave beam correlated series is carried out the extraction of multipath, obtain the final estimation of channel information matrix;

5) obtain the optimal weight vector of beam space according to maximum Signal to Interference plus Noise Ratio criterion;

6) the array element space is gone back in the optimal weight vector conversion of beam space, obtained the optimal weight vector in array element space.

2, beam space orthogonal FDM modulation system time-domain adaptive wave beam formation method according to claim 1 is characterized in that described step 1) is implemented as follows:

Carry out spatial spreading Fourier transform (DFT) at first to received signal, with r=[r ₁, r ₂..., r _M] ^TExpression array element space received signal, $r_b(=[r_1^b,r_2^b,...,r_M^b{]}^T)$ Table transform is to the signal of beam space, and subscript T represents transposition, and M is the bay number, with $F={[f_0^T,f_1^T,...,f_{M-1}^T]}^T$ Expression DFT transformation matrix $(f_i={[1,e^{-j\frac{2\mathrm{\&pi;i}}{M}},...,e^{-j\frac{2\mathrm{\&pi;i}(M-1)}{M}}]}^T),$ Then conversion expression formula is: r ^b=Fr.

3, beam space orthogonal FDM modulation system time-domain adaptive wave beam formation method according to claim 1 is characterized in that described step 2), be implemented as follows:

With r ^bEach component be L with being used for the length that CSI estimates _TrTraining sequence Tr (k) be correlated with, with $c_i={[c_{i,0},c_{i,1},...c_{i,L_g}]}^T$ The correlated series of representing i beam component correspondence, L _gBe OFDM protection gap length, the correlometer formula is

$c_{i,n}=\frac{1}{L_{\mathrm{tr}}}\underset{k=0}{\overset{L_{\mathrm{tr}}-1}{\mathrm{\&Sigma;}}}{r}_i^b(k+n)\mathrm{Tr}\left(k\right),i=1...M,n=0...L_g.$

4, beam space orthogonal FDM modulation system time-domain adaptive wave beam formation method according to claim 1 is characterized in that described step 3) is implemented as follows:

As follows each wave beam is differentiated and handled: to the c of each wave beam correspondence _iSequence is with the average c of this sequence minimax mould value _{I_th}Be standard, judge that the mould value is greater than the number of this standard value, if number is greater than predetermined threshold values N in the sequence _Th, think that this wave beam is non-signal beam, with this correlated series zero setting, with c ' _iSequence after expression is handled, this procedural representation is:

The element number of Num () expression set in the formula.

5, beam space orthogonal FDM modulation system time-domain adaptive wave beam formation method according to claim 1 is characterized in that described step 4) is implemented as follows:

Extract the multipath information in each wave beam, obtain the final estimation of Beam-Space CSI matrix

Extracting method is, to the c ' of each wave beam correspondence _iSequence keeps the bigger some values of its mould value, and to other value zero setting, differentiates threshold values by factor alpha and c ' _iIn maximum determine,

6, beam space orthogonal FDM modulation system time-domain adaptive wave beam formation method according to claim 1 is characterized in that described step 5) is implemented as follows:

By finding the solution following generalized eigenvalue equation, obtain the beam space optimal weight vector w under the maximum Signal to Interference plus Noise Ratio criterion _Opt ^b:

E express time expectation in the formula, subscript H represents conjugate transpose,

$S_d={[S_{d,l},S_{d,l-1},...,S_{d,l-L_g}]}^T$ Be the required multipath signal vector of l snap moment time delay less than the protection interval, this expectation computing is used and is used for the training sequence that weights generate, λ in the OFDM frame _MaxBe eigenvalue of maximum.

7, beam space orthogonal FDM modulation system time-domain adaptive wave beam formation method according to claim 1 is characterized in that described step 6) is implemented as follows:

With w _Opt ^bThe array element space is gone back in conversion, obtains the optimal weight vector w in array element space _Opt, transform is:

$W_{\mathrm{opt}}=F^H{W}_{\mathrm{opt}}^b.$

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