CN100492954C - Space characteristic extracting and signal reaching direction estimating method for CDMA wireless telecommunication - Google Patents

Abstract

The method includes following steps: a) the time space impulse response of relative subscriber channel is estimated by using the data received from antenna array; b) the time space impulse response of main propagation path is selected and separated from results of time space impulse response of the subscriber channel; c) the space impulse response extracted from main propagation path is used to estimate space feature of the main propagation path and corresponding arrival direction. Due to only using space impulse response of main propagation path of subscriber signal to estimate relevant DOA, so the white noise and interference between multi path signals are avoided.

Description

The space characteristics of cdma wireless communication extracts and the direction of arrival of signal method of estimation

Technical field

The present invention relates to a kind of mobile communication technology, the space characteristics that relates to a kind of code division multiple access (CDMA) radio communication or rather extracts and direction of arrival of signal (DOA) estimation approach.This method is not subjected to the influence of signal correlation and signal DOA spacing, is suitable for estimating in CDMA mobile communication system the space characteristics and the DOA of multipath signal.The wireless channel space characteristics that is extracted can be used for the signal that receives or launch is carried out space filtering, and the DOA of estimation can be used for moving target is positioned and wave beam forming.

Background technology

In mobile communication system, use aerial array and can suppress effectively to disturb, improve power system capacity, effectively suppress to disturb by spatial filter and/or beamformer are set in having the mobile communication system of aerial array.The method for designing of spatial filter roughly can be divided into " blind " and " non-blind " two big classes.Wherein the method for " non-blind " is to utilize the space characteristics of training sequence estimation channel (or by estimating that DOA obtains the space characteristics of channel) to finish.DOA estimates can also be used for moving target is positioned and follows the tracks of.

For single (the nothing diffusion) wireless channel propagation path, after antenna array structure is determined, the space characteristics of channel and the DOA of signal are (mapping relations) one to one, therefore the space characteristics of channel can be estimated and the DOA estimation of signal be handled as same problem.

The method of estimated signal DOA has a lot, most typical have beam scanning (Classic) method (a kind of traditional DOA method of estimation), the undistorted response of the minimum variance of Capon (MVDR) method and feature structure method (as MUSIC, ESPRIT and extended method thereof).Traditional beam sweeping method is the form that the hypothesis space filter has array steering vector, with those peak values of certain angle intervals search volume filter power output maximum, the pairing angle of those peak values is exactly the DOA that will estimate in the certain range of observation in space.The optimization criterion of the MVDR method of Capon is under the constraints that guarantees the main lobe energy, makes spatial filter power output minimum, thereby reaches the purpose that suppresses interference.Therefore when differentiating the close a plurality of signal of DOA, has better resolution performance than traditional beam sweeping method.The feature structure method is by carrying out characteristic value decomposition to the space covariance matrix of exporting with array way, definition signal subspace and noise subspace, and then utilize the orthogonality (to MUSIC and expansion thereof) of signal subspace and noise subspace or utilize the rotational invariance (to ESPRIT and expansion thereof) of signal subspace to obtain the estimation to signal DOA.The feature structure method is when estimating the DOA of a plurality of independent signals, and its angular resolution has substantially exceeded traditional Classic algorithm, and high resolution technique therefore is otherwise known as.

Above-mentioned DOA algorithm for estimating requires the number of signal source less than the antenna element sum in the aerial array when differentiating the DOA of a plurality of signals.This requirement makes these algorithms can not be directly used in cdma communication system, because in cdma communication system, the number of signal source is generally greater than the antenna element sum.Therefore the DOA method of estimation of existing C DMA signal is all carried out based on the CDMA signal after the demodulation.

Because in CDMA mobile communication system, the CDMA signal of DOA method of estimation after based on demodulation carries out.And must contain this user's multi-path signal-component and additive noise in the signal after certain user's demodulation, and have following feature: there is very strong correlation between the multipath component of (1) signal; (2) interval of the DOA between the multipath component of signal (spacing) is very little; (3) owing to the nonorthogonality of spreading code in the cdma system, the noise after the demodulation is coloured noise often.Signal for height correlation, when adopting the DOA method of estimation of traditional C lassic algorithm, angle resoluting ability is seriously descended, though adopt the high-resolution method to make its performance improvement of differentiating coherent signal, the deficiency of loss array aperture and increasing algorithm computation amount arranged in conjunction with Search Space Smoothing.In mobile communication system, angle between multipath component often is separated by very near, and is subjected to the influence of system cost, and the antenna element sum in the array antenna again can not be a lot, therefore for the not only relevant but also close multipath component of angle, high-resolution algorithm is also with powerless.Above-mentioned analysis explanation, existing space feature extraction and DOA method of estimation, it is very big that the ability of resolution multipath component is influenced by signal correlation and DOA spacing.This is because of the space covariance matrix of these technology based on user's multipath data of noise pollution, if multipath signal is relevant, these correlation energies will influence resolution performance when differentiating multipath.On the other hand, in the DOA spacing hour, prior art is subjected to antenna number and the Effect on Performance of technology own, makes it can't differentiate the less multipath of these DOA spacings.

One solves the approach of differentiating multipath component and utilizes the structural characteristics of RAKE receiver to carry out, promptly estimate the DOA (being undertaken) in this footpath by the footpath with the signal after the paths demodulation, but this method still will be subjected to having a strong impact on of additivity coloured noise, and this is based on additive white noise because of existing technology and grows up.In addition, when differentiating a plurality of signal source, the advantage of high resolution DOA estimation technology is mainly reflected in traditional beam scanning technology and compares, but will spend bigger consumption on calculating, because it will carry out the characteristic value decomposition of complex matrix.When carrying out the DOA estimation with the signal after the individual paths demodulation, high resolution technique has just lost its superiority.In addition, carry out DOA with the signal after every footpath demodulation of RAKE receiver structure and estimate also receiver is had following requirement: (1) receiver must be that RAKE receives form; (2) the demodulation process ability of separating every footpath is arranged.Otherwise, only bring extra complexity to receiver for DOA estimates separation tracking and the demodulation meeting of carrying out multipath component.

Summary of the invention

The objective of the invention is to design the space characteristics extraction and the direction of arrival of signal method of estimation of cdma wireless communication, be not subjected to the influence of signal correlation and direction of arrival of signal spacing, the channel space feature of extracting can be used for the signal that receives and launch is carried out space filtering, and the arrival direction of estimation (DOA) can be used for target is positioned and wave beam forming.

The technical scheme that realizes the object of the invention is such: a kind of space characteristics of cdma wireless communication extracts and the direction of arrival of signal method of estimation, it is characterized in that may further comprise the steps:

A. the user data that utilizes aerial array to receive estimate impulse response when being concerned about subscriber channel empty;

Isolate the impulse response intensity of every propagation path the impulse response result during B. from this subscriber channel of estimating empty, and select the wherein space impulse response of main propagation path;

C. with the space impulse response of the main propagation path that extracts, estimate the space characteristics and the corresponding arrival direction of every main propagation path.

Described step B isolates the impulse response intensity of every propagation path, and selects the wherein space impulse response of main propagation path, further comprises:

The impulse response result obtains the wherein impulse response intensity of every propagation path on each antenna element, each time delay tap during B1. according to this subscriber channel empty;

B2. utilize impulse response intensity, press the maximum principle of impulse response average power and determine and the main corresponding time delay tap of propagation path;

B3. extract the channel space impulse response of the time delay tap corresponding with main propagation path.

Described step B2 further comprises: the impulse response average power of obtaining corresponding each antenna element of this user, each time delay tap; The time delay tap of choosing corresponding maximum q average power is as the time delay tap corresponding with main propagation path.

Described q is under the different channels environment, the existing main propagation path number that satisfies certain signal-noise ratio threshold.

Described step B2 further comprises: set a power threshold; Choose all time delay tap conducts with the main propagation path corresponding time delay tap of the power average value of the space impulse response that satisfies a certain footpath correspondence more than or equal to power threshold.

Described power average value is based on whole antenna elements in the aerial array or part antenna element.

Described power threshold based on the current time slots channel when empty the impulse response data determine, or unite the channel of considering current time slots and current time slots front time slot when empty the impulse response data determine.

The described channel of considering current time slots and current time slots front time slot impulse response data when empty of uniting are impulse response data when current time slots begins to consider that by the principle of exponential damping the channel of front time slot is empty.

Described step C presses θ _i, $a\left({\mathrm{\&theta;}}_i\right)=\underset{\mathrm{\&theta;}\&Element;\left[\mathrm{0,2}\mathrm{\&pi;}\right)}{\arg \max }|<a\left(\mathrm{\&theta;}\right),h^{\left(k\right)}\left({\mathrm{\&tau;}}_i\right)>|$ Calculate the space characteristics of every main propagation path i and corresponding arrival direction,＜, the expression inner product operation, be the array steering vector a (θ) and the space impulse response h of a main propagation path i correspondence wherein ^(k)(τ _i) inner product, k represents k user, τ _iExpression and the main corresponding time delay tap of propagation path i.

Technical scheme of the present invention, impulse response during based on the subscriber channel sky, estimate each user's channel when empty behind the impulse response, isolate the channel space impulse response (useful information) of the main propagation path of every bars again, only with the channel space impulse response of the main propagation path of each subscriber signal, rather than utilize the space impulse response data of all propagation paths, estimate the DOA in corresponding footpath, not only avoid the influence of white noise, also avoided the phase mutual interference of multipath information.Even the correlation of multipath signal is very high, DOA is identical, and the inventive method also is effective.And other existing method can not be differentiated the multipath signal of height correlation effectively, can not differentiate the close multipath of DOA.

In addition, the inventive method is calculated simple, is fit to the engineering application and especially uses in cdma system.

Description of drawings

Fig. 1 is that the long or tap number of the aerial array of 8 antenna elements and impulse response window is 16 o'clock an impulse response intensity schematic diagram;

Fig. 2 is the average power schematic diagram of the impulse response of corresponding diagram 1;

Fig. 3 is that the DOA that uses the inventive method estimates, is the both direction angle effect signal of step size computation with 1 °.

Embodiment

The present invention proposes the method for estimation of a kind of simple and effective wireless channel space characteristics extraction and direction of arrival of signal (DOA), the DOA method of estimation of impulse response when being based on the channel sky, this method is not subjected to the influence of signal correlation and signal DOA spacing, is suitable for use in the channel space feature and the DOA that estimate multipath component in the mobile communication system.The channel space feature of extracting can be used for the signal that receives and launch is carried out space filtering, and the DOA of estimation can be used for target is positioned and wave beam forming.

The present invention is primarily aimed at the multiuser mobile communication system, cdma system especially, the DOA method of estimation of proposition a kind of channel estimating during based on sky.Describe its technical scheme in detail below in conjunction with accompanying drawing, its major technique step comprises: impulse response when the estimating user channel is empty; The separate users multipath signal is also chosen tap by the maximum principle of impulse response average power; Space characteristics extracts and DOA estimates with carrying out.

In conjunction with referring to Fig. 1, for user k, impulse response was when the subscriber channel after supposing to estimate was empty:

$=\left[\begin{array}{cccc}{h}_1^{\left(k\right)}\left(0\right)& h_1^{\left(k\right)}\left(1\right)& & h_1^{\left(k\right)}(W-1)\\ h_2^{\left(k\right)}\left(0\right)& h_2^{\left(k\right)}\left(1\right)& & h_2^{\left(k\right)}(W-1)\\ & & & \\ h_M^{\left(k\right)}\left(0\right)& h_M^{\left(k\right)}\left(1\right)& & h_M^{\left(k\right)}(W-1)\end{array}\right]---\left(2\right)$

(1) formula is a matrix expression, and (2) formula is the column vector expression formula, and M is an antenna number in the formula, the long or tap number of impulse response window when W is empty.In the inventive method, impulse response in the time of can adopting any existing estimation technique to come the estimating user channel empty, the method for impulse response is without limits during promptly to estimating user channel empty.Impulse response can be the result after any form normalization.

The impulse response intensity that defines i+1 tap of corresponding m antenna element is

(intensity is absolute value), when Fig. 1 signal had provided M=8 and W=16, the impulse response intensity in corresponding each antenna element of user k, each tap illustrated with circle.Through computing, suppose the wherein signal h of two multipaths ^(k)(0) and h ^(k)(3) the corresponding tap τ of (the 1st, the 4th liang of row in the formula 2, promptly the 1st, the 2nd footpath) difference ₁=0 and τ ₂=3 (transverse axis is represented time delay tap τ among the figure, and the longitudinal axis is represented impulse response intensity.

Clearly, this moment, the feature of channel can be by h to k user ^(k)(0) and h ^(k)(3) definite fully.In fact, under the smaller situation of every paths angular spread, we can be with h ^(k)(0) and h ^(k)(3) approximate representation becomes impulse response function:

α in the formula ₀, α ₁The amplitude fading coefficient of expression channel,

Be respectively the phase place in the 1st, the 2nd footpath, be expressed as

A (θ ₀), a (θ ₁) representing the space characteristics in the 1st, the 2nd footpath respectively, δ (τ) and δ (τ-3) do not have the meaning in the computing.Therefore through above-mentioned calculating process, from H ^(k)In extracted h ^(k)(0) and h ^(k)(3), just can estimate the space characteristics a (θ of this two paths ₀) and a (θ ₁) and their each self-corresponding arrival direction angle θ ₀And θ ₁

But in practice, we also do not know that channel has several main propagation paths (as two above-mentioned multipath signal h ^(k)(0) and h ^(k)(3)), do not know that the pairing time delay tap in these paths is (as above-mentioned tap τ yet ₁=0 and τ ₂=3).Therefore, must judge and how the main propagation path that selects signal (promptly obtains above-mentioned two multipath signal h according to certain criterion ^(k)(0) and h ^(k)(3) and respectively corresponding time delay tap τ ₁=0 and τ ₂=3).Can adopt two kinds of choosing methods:

First kind of choosing method is the time delay tap of choosing q maximum average power of fixing, in other words based on the q that chooses the average power maximum footpath.

To k user, the average power that defines the impulse response of corresponding i time delay tap is:

P ^(k)(i)＝‖h ^(k)(i)‖ ²/M，i＝0，…，W-1 (4)

Corresponding diagram 1 can obtain the average power of 8 antenna channel space impulse responses, shown in circle among Fig. 2.During enforcement, calculate average power and can carry out (being the value of M) based on part antenna element or all antenna elements.

By wireless channel is measured and is analyzed, suppose that under different channel circumstances total the existence is no less than the individual main propagation path of q (for example q=2) and satisfies certain signal-noise ratio threshold, therefore, we are after the average power of the impulse response that has calculated all tap correspondences, just can choose the tap of corresponding maximum q average power, extract space impulse response (the corresponding time delay tap τ of these tap correspondences ₁=0 and τ ₂=3 position).

Second kind of choosing method is to set a power threshold earlier, chooses all taps that average power surpasses this thresholding, based on certain threshold value of setting, chooses the footpath of average power greater than this thresholding in other words.

In mobile communication environment, the variation of environment and the decline of channel all can bring the variation of multipath number and multipath intensity.Method 1 is selected fixing q bar footpath estimation (q is too big) just may occur or is owed the situation of estimation (q is too little).The method that a kind of self adaptation is chosen q is to set certain threshold value according to estimated channel space impulse response

, choose then and satisfy following formula (5)

All taps as main footpath tap, the power average value of the channel space impulse response that promptly a certain footpath is corresponding more than or equal to

The footpath, and being lower than thresholding

The footpath work as noise processed.This user's that thresholding can be only estimated with this time slot impulse response data are determined, also can unite the impulse response data of considering this time slot and front time slot and determine, such as the effect that begins from this time slot by the principle consideration front time slot data of exponential damping.

Making space characteristics extraction and DOA at last estimates.When we by H ^(k)Selected the space impulse response h of certain signal multipath ^(k)(τ _i) (as the h of corresponding diagram 2 ^(k)(0), h ^(k)(3)) after, just can estimate the space characteristics (is variable with a (θ)) and the corresponding DOA (is variable with θ) of respective path by following rule:

${\mathrm{\&theta;}}_i,a\left({\mathrm{\&theta;}}_i\right)=\underset{\mathrm{\&theta;}\&Element;\left[\mathrm{0,2}\mathrm{\&pi;}\right)}{\arg \max }|<a\left(\mathrm{\&theta;}\right),h^{\left(k\right)}\left({\mathrm{\&tau;}}_i\right)>|---\left(6\right)$

Wherein＜, the expression inner product operation, be the array steering vector a (θ) (array steering vector can be the result after the normalization in any form) and the space impulse response h of a footpath correspondence wherein ^(k)(τ _i) inner product.By following formula as seen, the estimated accuracy of DOA is determined by two factors.First h ^(k)(τ _i) estimated accuracy, it two is to calculate consumption function f _i(θ)=|＜a (θ), h ^(k)(τ _i) | the time, the choosing of angle searching step-length.

Give an example as checking, two paths that Fig. 3 has provided in the corresponding diagram 2 are being supposed [θ ₀, θ ₃20 ° of]=[, 60 °] time, in 0 to 2 π scope, be the f of step size computation (scanning) with 1 ° ₀(θ)=|＜a (θ), h ^(k)(0)〉| (the first half among the figure) and f ₁(θ)=|＜a (θ), h ^(k)(3)〉| value (the latter half among the figure).Demonstrate when θ is respectively 20 ° and 60 ° the f that calculates among the figure ₀(θ) and f ₁(θ) maximum has illustrated the accuracy of the inventive method.

Claims (9)

1. the space characteristics of a cdma wireless communication extracts and the direction of arrival of signal method of estimation, it is characterized in that may further comprise the steps:

A. the user data that utilizes aerial array to receive estimate impulse response when being concerned about subscriber channel empty;

Isolate the impulse response intensity of every propagation path the impulse response result during B. from this subscriber channel of estimating empty, and select the wherein space impulse response of main propagation path;

C. with the space impulse response of the main propagation path that extracts, estimate the space characteristics and the corresponding arrival direction of every main propagation path.

2. the space characteristics of a kind of cdma wireless communication according to claim 1 extracts and the direction of arrival of signal method of estimation, it is characterized in that: described step B, isolate the impulse response intensity of every propagation path, and select the wherein space impulse response of main propagation path, further comprise:

The impulse response result obtains the wherein impulse response intensity of every propagation path on each antenna element, each time delay tap during B1. according to this subscriber channel empty;

B2. utilize impulse response intensity, press the maximum principle of impulse response average power and determine and the main corresponding time delay tap of propagation path;

B3. extract the channel space impulse response of the time delay tap corresponding with main propagation path.

3. the space characteristics of a kind of cdma wireless communication according to claim 2 extracts and the direction of arrival of signal method of estimation, it is characterized in that described step B2 further comprises: the impulse response average power of obtaining corresponding each antenna element of this user, each time delay tap; The time delay tap of choosing corresponding maximum q average power is as the time delay tap corresponding with main propagation path.

4. the space characteristics of a kind of cdma wireless communication according to claim 3 extracts and the direction of arrival of signal method of estimation, and it is characterized in that: described q is under the different channels environment, the existing main propagation path number that satisfies certain signal-noise ratio threshold.

5. the space characteristics of a kind of cdma wireless communication according to claim 2 extracts and the direction of arrival of signal method of estimation, it is characterized in that described step B2 further comprises: set a power threshold; Choose all time delay tap conducts with the main propagation path corresponding time delay tap of the power average value of the space impulse response that satisfies a certain footpath correspondence more than or equal to power threshold.

6. the space characteristics of a kind of cdma wireless communication according to claim 5 extracts and the direction of arrival of signal method of estimation, it is characterized in that: described power threshold based on the current time slots channel when empty the impulse response data determine, or unite the channel of considering current time slots and current time slots front time slot when empty the impulse response data determine.

7. the space characteristics of a kind of cdma wireless communication according to claim 6 extracts and the direction of arrival of signal method of estimation, it is characterized in that: the described channel of considering current time slots and current time slots front time slot impulse response data when empty of uniting are impulse response data when current time slots begins to consider that by the principle of exponential damping the channel of front time slot is empty.

8. the space characteristics of a kind of cdma wireless communication according to claim 5 extracts and the direction of arrival of signal method of estimation, and it is characterized in that: described power average value is based on whole antenna elements in the aerial array or part antenna element.

9. the space characteristics of a kind of cdma wireless communication according to claim 1 extracts and the direction of arrival of signal method of estimation, it is characterized in that:

Described step C presses θ _i, $a\left({\mathrm{\&theta;}}_i\right)=\underset{\mathrm{\&theta;}\&Element;\left[\mathrm{0,2}\mathrm{\&pi;}\right)}{\arg \max }|<a\left(\mathrm{\&theta;}\right),h^{\left(k\right)}\left({\mathrm{\&tau;}}_i\right)>|$ Calculate the space characteristics of every main propagation path i and corresponding arrival direction,＜, the expression inner product operation, be the array steering vector a (θ) and the space impulse response h of a main propagation path i correspondence wherein ^(k)(τ _i) inner product, k represents k user, τ _iExpression and the main corresponding time delay tap of propagation path i.

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