CN100512047C - Estimating method of reach direction of user signal wave of array antenna MC-CDMA system - Google Patents

Abstract

The invention relates to a user signal wave direction evaluate method of array antenna MC-CDMA system, wherein it comprises that: first, the sub carrier wave de-spread match filter connected to the array antenna separates the user at each sub carrier wave, to obtain the output vector of sub carrier wave on match filter; then processing frequency domain summation on each match filter, to obtain output vector sum of all antenna match filters; then based on sample of vector sum, obtaining the sample evaluated value of output vector relative to the covariance matrix; then processing characteristic decomposition on covariance matrix, to obtain the evaluated value of main characteristic vector of covariance matrix; at last, based on the spatial spectrum function of main characteristic vector, searching the spectrum peak of spatial spectrum function to obtain the evaluated value of user signal wave direction.

Description

Estimating method of reach direction of user signal wave of array antenna MC-CDMA system

Technical field

The invention belongs to multicarrier (MC) code division multiple access (CDMA) cell mobile communication systems field.

Background technology

CDMA is a kind of main technology in the third generation (3G) mobile communication system, and multicarrier (MC) modulation will be the key technology of super three generations (B3G) mobile communication system.Merging CDMA technology with multi-transceiver technology, constitute multi-carrier CDMA system, will be the important directions of future mobile system development.The scheme that merges CDMA with multi-transceiver technology mainly contains CDMA multiple carrier (MC-CDMA), multi-carrier direct sequence spectrum CDMA (MC-DS-CDMA) and three kinds of principal modes of multitone modulation CDMA (MT-CDMA).Wherein, MC-CDMA also is one of the most competitive scheme of future mobile communication system owing to can adopt frequency diversity and good performance to be considered in three kinds of schemes the scheme of tool prospect.

In the MC-CDMA system, further adopt the array antenna technology, make full use of the redundant information on the space, the sky of uniting, the time, signal processing frequently, can improve the performance of MC-CDMA system to a great extent.The direction of arrival of subscriber signal (DOA) estimates that user radio location technology that wave beam to down link forms, reduces to disturb and estimates based on angle etc. has important function in array antenna MC-CDMA system, is one of key technology of array antenna MC-CDMA system.

In the past few decades, many DOA algorithm for estimating based on array antenna have been proposed.Traditional DOA algorithm for estimating such as multiple signal classification method (MUSIC) and require the array number of array antenna more than signal number by invariable rotary technology estimated signal parametric method (ESPRIT), and signal source spatially can not be overlapping, otherwise array antenna can't effectively be estimated the DOA of signal source.And tens users are arranged in sub-district of mobile communication system usually, traditional DOA algorithm for estimating can not be directly applied in the array antenna MC-CDMA system.

Summary of the invention

The present invention has proposed a kind of estimating method of reach direction of user signal wave of array antenna MC-CDMA system for solving the problems of the technologies described above, this method had both been utilized the intrinsic characteristic of the mobile communication system user signal that makes up based on CDMA technology, utilize the frequency diversity characteristic of MC-CDMA system again, solved array antenna MC-CDMA system subscriber signal direction of arrival estimation problem effectively.

The invention provides the technical scheme that a kind of array antenna MC-CDMA system subscriber signal direction of arrival is estimated, may further comprise the steps:

1) signal that receives of each array element of array antenna comprises the stack of each user's signal and noise, at first, utilize the subcarrier despreading and the matched filter banks that connect after each array element of array antenna, despreading and matched filter processing by pairing despreading of each subcarrier and matched filter, realize the separation of user's signal on each subcarrier, obtain the array antenna matched filter output vector of user's sub-carrier signal;

2) secondly, the matched filter output signal of each sub-carrier signal of user is carried out the frequency domain summation operation, obtain all sub-carrier signals of user the output of array antenna matched filter vector and;

3) then, based on to array antenna matched filter output vector and Continuous Observation or sampling, the sampling that obtains the pairing covariance matrix of array antenna output vector is estimated;

4) afterwards, the covariance matrix of subscriber signal is carried out feature decomposition, obtain the estimation of covariance matrix principal eigenvector;

5) last, based on the pairing spatial spectrum function of covariance matrix feature decomposition principal eigenvector, obtain the estimation of subscriber signal direction of arrival by the spectrum peak of search volume spectral function.

Below process that direction of arrival of the present invention is estimated discussed, with the concrete implication of illustrating each step of method of estimation of the present invention and the meaning of related symbol.

1. the array antenna of subscriber signal output

A. the received signal of array antenna

Investigate an array antenna MC-CDMA system, travelling carriage adopts single antenna, and the array antenna with N array element is adopted in the base station.Certain cellular cell has K user in the supposing the system, adopts the MC-CDMA equivalence low pass transmission signal of arbitrary user k of BPSK modulation to be expressed as like this

$s_k\left(t\right)=\underset{l=1}{\overset{L}{\mathrm{\Σ}}}\sqrt{P_{k,l}}{b}_k\left(t\right)c_{k,l}\left(t\right)\cos \left({\mathrm{\ω}}_{l}t\right)$ [formula 1]

In the formula, L is a sub-carrier number, P _{K, l}Be the bit power of l the subcarrier of user k, ω _lIt is the angular frequency of l subcarrier.c _k(t)=[c _{K, 1}(t) L c _{K, L}(t)] be the frequency domain spread spectrum sequence waveform of user k, $c_{k,l}\left(t\right)=c_{k,l}{g}_{T_c}(t-{\mathrm{lT}}_c)$ And c _{K, l}General waveform and spreading code, T are cut in expression accordingly respectively _cBe chip period. $b_k\left(t\right)={\mathrm{\Σ}}_{i=-\∞}^{\∞}{d}_k\left(i\right)g_{T_b}(t-{\mathrm{iT}}_b)$ The signal of expression user k, wherein, d _k(i) i the data bit of expression user k, T _bBe bit period.

With

Be respectively be defined in [0, T _b) and [0, T _c) on the pulse shaping function.To typical MC-CDMA system, T _b=T _c, spread processing gain G=L.

To typical MC-CDMA scheme, what each subcarrier experienced is that frequency non-selective fading channel is to guarantee the orthogonality between each subcarrier.Like this, the impulse response of l subcarrier uplink channel of the user k N dimensional vector that can be expressed as

$h_{k,l}\left(t\right)={\mathrm{\ρ}}_{k,l}{e}^{-j{\mathrm{\φ}}_{k,l}}{a}_k\mathrm{\δ}(t-{\mathrm{\τ}}_{k,l})$ [formula 2]

Wherein, ρ _{K, l}, φ _{K, l}And τ _{K, l}Be respectively amplitude fading, phase shift and the time delay of l sub-carrier channels of user k, δ (t) is the delta function.

$a_k\left({\mathrm{\θ}}_k\right)={[a_{k,1}\left({\mathrm{\θ}}_k\right),...,a_{k,N}\left({\mathrm{\θ}}_k\right)]}^T/\sqrt{N}$ [formula 3]

Be that direction of arrival is θ _kThe array steering vector of user k signal, wherein, () ^TThe computing of expression transposition.

Like this, base station array antenna array element 1 ..., array element N receives total baseband signal and is

$x\left(t\right)={[x_1\left(t\right),K,x_N\left(t\right)]}^T$

$=\underset{k=1}{\overset{K}{\mathrm{\Σ}}}{s}_k{h}_{k,l}\left(t\right)+n\left(t\right)$ [formula 4]

$=\underset{i=-\∞}{\overset{\∞}{\mathrm{\Σ}}}\underset{k=1}{\overset{K}{\mathrm{\Σ}}}\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\μ}}_{k,l}{e}^{-j{\mathrm{\φ}}_{k,l}}{b}_k\left(i\right)a_k{c}_{k,l}(t-{\mathrm{iT}}_b-{\mathrm{\τ}}_{k,l})+n\left(t\right)$

In the formula, ${\mathrm{\μ}}_{k,l}=\sqrt{P_{k,l}}{\mathrm{\ρ}}_{k,l}$ Be the amplitude of the user k l that receives footpath signal, n (t) is that average is 0, covariance matrix is σ ²I _NThe additive white Gaussian noise vector, I _NIt is the unit matrix of N * N.

B. the despreading of each sub-carrier signal of user and matched filter processing

To the mobile communication system that makes up based on CDMA technology, each user has been assigned with unique spreading code, utilize the priori of user's spreading code, subscriber signal is carried out despreading and matched filter processing, realize effective separation of subscriber signal and the inhibition that multiple access is disturbed.

The despreading matched filtering output vector of l sub-carrier signal array antenna of user k is:

$y_{k,l}\left(i\right)={[y_{k,l,1}\left(t\right),K,y_{k,l,N}\left(t\right)]}^T$

$={\∫}_{(i-1)T_b+{\mathrm{\τ}}_{k,l}}^{{\mathrm{iT}}_b+{\mathrm{\τ}}_{k,l}}x\left(t\right)c_{k,l}(t-{\mathrm{iT}}_b-{\mathrm{\τ}}_{k,l})\mathrm{dt}$ [formula 5]

C. the frequency domain of each subcarrier output signal of user merges

MC-CDMA has the frequency diversity characteristic, and each subcarrier output signal of above-mentioned user is carried out the frequency domain summation, and the output vector that obtains all L of user k sub-carrier signal array antenna is:

$y_k\left(i\right)={[y_{k,1}\left(t\right),K,y_{k,N}\left(t\right)]}^T$

$=\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{y}_{k,l}\left(i\right)$ [formula 6]

2. the subscriber signal direction of arrival is estimated

A. Estimation of covariance matrix

Output vector y based on formula 6 array antenna MC-CDMA systems _k(i), can be to the direction of arrival θ of user k signal _kEstimate.This is because the despreading processing of MC-CDMA is disturbed with the multiple access that spreading gain G has suppressed on each bay, and the frequency domain of each sub-carrier signal merges the intensity that has further increased subscriber signal.Therefore, the array antenna MC-CDMA despreading will provide one well to estimate for the direction of arrival of subscriber signal with the principal eigenvector of the pairing covariance matrix of output vector after feature decomposition that merges the back array antenna.

The covariance matrix R of user k _kBe defined as:

R _k=E{y _k(i) (y _k(i)) ^H[formula 7]

Wherein, E{} represents expectation, () ^HThe computing of expression conjugate transpose.

Because can not obtain R in the reality _kAccurate information, must estimate by the data-signal that receives.Covariance matrix R _kCan form true R by Q continuous observation or sampling based on formula 6 _kSampling estimate Promptly

${\hat{R}}_k=\frac{1}{Q}\underset{i=1}{\overset{Q}{\mathrm{\Σ}}}{y}_k\left(i\right){\left(y_k\left(i\right)\right)}^H$ [formula 8]

In the formula, Q is a sampling length.

B. direction of arrival is estimated

To resulting sampling covariance matrix

Carry out following feature decomposition, just can obtain covariance matrix R _kPrincipal eigenvector e _{K, 1}Estimation

R _kE _k=E _kΛ _k[formula 9]

In the formula, Λ _k=diag{ λ _{K, 1}, K, λ _{K, N}, λ _{K, 1}〉=L 〉=λ _{K, N}Be characteristic value, E _k=[e _{K, 1}, L, e _{K, N}] be R _kThe matrix that corresponding characteristic vector is formed.

Afterwards, by being constructed as follows the spatial spectrum function, just can realize the estimation of array antenna MC-CDMA system subscriber signal direction of arrival based on covariance matrix feature decomposition principal eigenvector.To user k signal direction of arrival θ _kConcrete estimating step be:

At first, structure spatial spectrum function:

$P_{\mathrm{MU}}\left({\mathrm{\θ}}_k\right)={[1-{\left|\right|a_k^H\left({\mathrm{\θ}}_k\right){\hat{e}}_{1,k}\left|\right|}^2]}^{-1}$ [formula 10]

In the formula, ‖ ‖ ²Represent 2 norm computings.

Then, by search volume spectral function P _MUThe spectrum peak obtain the estimation of user k signal direction of arrival.User k signal direction of arrival θ _kBe estimated as:

${\widehat{\mathrm{\θ}}}_k=\arg \underset{{\mathrm{\θ}}_k}{\max }\left\{{[1-{\left|\right|a_k^H\left({\mathrm{\θ}}_k\right){\hat{e}}_{1,k}\left|\right|}^2]}^{-1}\right\}$ [formula 11]

In the formula,

Pairing θ when getting maximum for { } _kEstimated value.

Beneficial effect of the present invention:

At first, the present invention has made full use of the priori that each user of mobile communication system who makes up based on CDMA technology has been assigned with unique spreading code, by subscriber signal is carried out despreading and matched filter processing, realized effective separation of subscriber signal and the inhibition that multiple access is disturbed; Secondly, estimation to the subscriber signal direction of arrival is directly to have utilized the output of array antenna MC-CDMA system to realize, and this is the necessary link of array antenna MC-CDMA system subscriber signal demodulating process, so method has direct, the simple advantage of processing; MC-CDMA has the characteristic of frequency diversity, and the frequency domain of each subcarrier output signal merges, and has further increased the intensity of array antenna output signal, can guarantee the validity of estimating; In addition, because this method only need be searched for single spatial spectrum peak, therefore, corresponding estimated result is very reliable.These all make the present invention be very suitable for the array antenna MC-CDMA system practical application.

Description of drawings

Fig. 1 is the procedure chart that the arbitrary user k of a kind of array antenna MC-CDMA system signal direction of arrival is estimated;

Fig. 2 carries out the spatial spectrum of independent estimations respectively to 4 subscriber signal direction of arrival for method of the present invention;

Fig. 3 is the relation curve of the root-mean-square error RMSE of Wave arrival direction estimating method of the present invention to signal to noise ratio snr.

Embodiment

The present invention is described in further detail below in conjunction with accompanying drawing.

The method according to this invention can be applied to the MC-CDMA mobile communication system of any employing array antenna.

Fig. 1 has provided this method and has been applied to the process that array antenna MC-CDMA system is estimated arbitrary user k signal direction of arrival.

Concrete estimating step is as follows:

1) at first, with base station array antenna array element 1 ..., the baseband signal x that array element N receives (t)=[x ₁(t), K, x _N(t)] ^TSend into the despreading and the matched filter pack module 11 of each subcarrier, by pairing despreading of each subcarrier and matched filter 11-1, ..., the despreading of 11-L and matched filter processing realize user's the separating of signal on each subcarrier, obtain the array antenna matched filter output vector y of user k l sub-carrier signal _{K, l}(i),

$y_{k,l}\left(i\right)={[y_{k,l,1}\left(t\right),K,y_{k,l,N}\left(t\right)]}^T$

$={\∫}_{(i-1)T_b+{\mathrm{\τ}}_{k,l}}^{{\mathrm{iT}}_b+{\mathrm{\τ}}_{k,l}}x\left(t\right)c_{k,l}(t-{\mathrm{iT}}_b-{\mathrm{\τ}}_{k,l})\mathrm{dt}$ [formula 5]

In the formula, x (t)=[x ₁(t), K, x _N(t)] ^TBe base station array antenna array element 1 ..., array element N receives total baseband signal, c _{K, l}(t) be the frequency domain spread spectrum waveform of l subcarrier of k user, T _bBe bit interval time, τ _{K, l}Be the time delay of signal on l subcarrier of k user, its result offers frequency domain combination module 12;

2) secondly, in frequency domain combination module 12, the matched filter output signal of each sub-carrier signal of user is carried out the frequency domain summation operation, obtain the vector and the y of all L of user k sub-carrier signal array antenna matched filter outputs _k(i),

$y_k\left(i\right)={[y_{k,1}\left(t\right),K,y_{k,N}\left(t\right)]}^T$

$=\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{y}_{k,l}\left(i\right)$ [formula 6]

3) then, in covariance matrix module 13, based on to y _k(i) Q continuous observation or sampling obtains y _k(i) pairing covariance matrix R _kSampling estimate

${\hat{R}}_k=\frac{1}{Q}\underset{i=1}{\overset{Q}{\mathrm{\Σ}}}{y}_k\left(i\right){\left(y_k\left(i\right)\right)}^H$ [formula 8]

In the formula, Q is a sampling length;

4) afterwards, in the feature decomposition module 14 of covariance matrix, to the covariance matrix of subscriber signal

Carry out following feature decomposition, obtain covariance matrix Principal eigenvector e _{K, 1}Estimation

R _kE _k=E _kΛ _k[formula 9]

In the formula, Λ _k=diag{ λ _{K, 1}, K, λ _{K, N}, λ _{K, 1}〉=L 〉=λ _{K, N}Be characteristic value, E _k=[e _{K, 1}, L, e _{K, N}] be R _kThe matrix that corresponding characteristic vector is formed;

5) last, in direction of arrival estimation module 15, be constructed as follows the spatial spectrum function based on covariance matrix feature decomposition principal eigenvector,

$P_{\mathrm{MU}}\left({\mathrm{\θ}}_k\right)={[1-{\left|\right|a_k^H\left({\mathrm{\θ}}_k\right){\hat{e}}_{1,k}\left|\right|}^2]}^{-1}$ [formula 10]

In the formula, ‖ ‖ ²Represent 2 norm computings.

By search volume spectral function P _MUThe spectrum peak obtain user k signal direction of arrival θ _kEstimation,

${\widehat{\mathrm{\θ}}}_k=\arg \underset{{\mathrm{\θ}}_k}{\max }\left\{{[1-{\left|\right|a_k^H\left({\mathrm{\θ}}_k\right){\hat{e}}_{1,k}\left|\right|}^2]}^{-1}\right\}$ [formula 11]

For investigating the array antenna MC-CDMA system user Wave arrival direction estimating method that is proposed, carried out Computer Simulation research.In the emulation, suppose that channel is a rayleigh fading channel, multidiameter delay [0, T _b) upward evenly distribute.Having adopted array element distance is the even equidistant 9 array element linear array antennas of half-wavelength, and sampling length is 50.Spreading code is that the length of picked at random is 36 PN sequence, and the sub-carrier number of MC-CDMA system also is 36.Supposing has 4 users in certain sub-district, the direction of arrival of each subscriber signal is respectively from 10 °, 25 °, 45 ° and 45 °.

Fig. 2 carries out the result of independent estimations respectively for adopting institute's extracting method to above-mentioned 4 subscriber signal direction of arrival.Can clearly find out from Fig. 2, adopt method of the present invention to realize effective estimation to array antenna MC-CDMA system user direction of arrival, owing to the estimation to each subscriber signal direction of arrival is independently to carry out, it is identical therefore allowing the direction of arrival of subscriber signal simultaneously.

Be further to estimate the performance of the inventive method, to 1000 times independently simulation result carried out on average having adopted the root-mean-square error RMSE that is defined as following formula as evaluation index,

$\mathrm{RMSE}=\sqrt{\frac{1}{K}\underset{k=1}{\overset{K}{\mathrm{\Σ}}}\frac{1}{U}\underset{u=1}{\overset{U}{\mathrm{\Σ}}}{({\widehat{\mathrm{\θ}}}_{k,u}-{\mathrm{\θ}}_{k,u})}^2}$ [formula 12]

u＝1，K，U；k＝1，K，K

Wherein, U is the number of times of independent experiment.

As can be seen from Figure 3, adopt the inventive method very effective to the estimation of array antenna MC-CDMA system user signal direction of arrival, its result is suitable for practical application.

Claims (1)

1. an estimating method of reach direction of user signal wave of array antenna MC-CDMA system is characterized in that, the estimation of arbitrary user k signal direction of arrival be may further comprise the steps:

1) at first, with base station array antenna array element (1 ..., the baseband signal x that N) receives (t)=[x ₁(t), K, x _N(t)] ^TSend into the despreading and the matched filter pack module (11) of each subcarrier, by pairing despreading of each subcarrier and matched filter (11-1, ..., despreading 11-L) and matched filter processing obtain the array antenna matched filter output vector y of user k l sub-carrier signal _{K, l}(i),

$y_{k,l}\left(i\right)={[y_{k,l,1}\left(t\right),K,y_{k,l,N}\left(t\right)]}^T$

$={\∫}_{(i-1)T_b+{\mathrm{\τ}}_{k,l}}^{{\mathrm{iT}}_b+{\mathrm{\τ}}_{k,l}}x\left(t\right)c_{k,l}(t-{\mathrm{iT}}_b-{\mathrm{\τ}}_{k,l})\mathrm{dt}$

In the formula, x (t)=[x ₁(t), K, x _N(t)] ^TBe base station array antenna array element 1 ..., array element N receives total baseband signal, () ^TThe computing of expression transposition, c _{K, l}(t) be the frequency domain spread spectrum waveform of l subcarrier of k user, T _bBe bit interval time, τ _{K, l}Be the time delay of signal on l subcarrier of k user, its result offers frequency domain combination module (12);

2) secondly, in frequency domain combination module (12), the matched filter output signal of each sub-carrier signal of user is carried out the frequency domain summation operation, obtain the vector and the y of all L of user k sub-carrier signal array antenna matched filter outputs _k(i),

$y_k\left(i\right)={[y_{k,1}\left(t\right),K,y_{k,N}\left(t\right)]}^T$

$=\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{y}_{k,l}\left(i\right)$

3) then, in covariance matrix module (13), based on to y _k(i) Q continuous observation or sampling obtains y _k(i) pairing covariance matrix R _kThe sampling estimated matrix

${\hat{R}}_k=\frac{1}{Q}\underset{i=1}{\overset{Q}{\mathrm{\Σ}}}{y}_k\left(i\right){\left(y_k\left(i\right)\right)}^H$

In the formula, Q is a sampling length, () ^HThe computing of expression conjugate transpose;

4) afterwards, in the feature decomposition module (14) of covariance matrix, to the covariance matrix of subscriber signal

Carry out following feature decomposition, obtain covariance matrix

Principal eigenvector e _{K, 1}Estimation

R _kE _k＝E _kΛ _k

In the formula, Λ _k=diag{ λ _{K, 1}, K, λ _{K, N}, λ _{K, 1}〉=L 〉=λ _{K, N}Be characteristic value, E _k=[e _{K, 1}, L, e _{K, N}] be R _kThe matrix that corresponding characteristic vector is formed;

5) last, be constructed as follows the spatial spectrum function based on covariance matrix feature decomposition principal eigenvector,

$P_{\mathrm{MU}}\left({\mathrm{\θ}}_k\right)={[1-{\left|\right|a_k^H\left({\mathrm{\θ}}_k\right){\hat{e}}_{k,1}\left|\right|}^2]}^{-1}$

In the formula, ‖ ‖ ²Represent 2 norm computings,

Be covariance matrix

Principal eigenvector e _{K, 1}Estimation, θ _kThe direction of arrival of expression user k signal,

By search volume spectral function P _MUThe spectrum peak obtain user k signal direction of arrival θ _kEstimated value,

${\widehat{\mathrm{\θ}}}_k=\arg \underset{{\mathrm{\θ}}_k}{\max }\left\{{[1-{\left|\right|a_k^H\left({\mathrm{\θ}}_k\right){\hat{e}}_{k,1}\left|\right|}^2]}^{-1}\right\}$

In the formula,

Pairing θ when getting maximum for { } _kEstimated value.

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