CN1156108C

CN1156108C - Method based on known time delay for estimating wave reaching direction

Info

Publication number: CN1156108C
Application number: CNB00128133XA
Authority: CN
Inventors: 雷周; 周雷; 范涛; 曲秉玉
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2000-11-27
Filing date: 2000-11-27
Publication date: 2004-06-30
Anticipated expiration: 2020-11-27
Also published as: CN1355628A

Abstract

The present invention discloses a method for estimating wave reaching directions based on known time delay. In the method, received pilot signals are utilized to estimate wave reaching directions of signals on the basis of time delay estimation so that estimation in the number of signals is considerably simplified. Meanwhile, the method of conjugate gradient or singular value decomposition is adopted to obtain vectors for calculating the wave reaching directions of signals in the present invention so that noise has little influence on estimation in wave reaching directions of signals obtained by the method of the present invention, and estimation values also have little fluctuation.

Description

Direction-of-arrival estimation method based on known time delay

Technical Field

The present invention relates to reception techniques in a receiver of a wireless communication system, and more particularly, to a direction of arrival (DOA) estimation technique of a received signal of a wireless communication system.

Background

Currently, the commonly used DOA estimation method is the Fast Fourier Transform (FFT) method. This method has advantages of simple implementation, but has problems that the number of signals cannot be determined and the variance of estimation errors is large, and since the FFT method is not a statistical method, its performance is greatly affected by noise, and thus the fluctuation of the estimated value is large. In a wireless communication system, estimating the direction of arrival of a signal by the above method does not make good use of the received signal over a period of time to reduce the error in the estimation result.

Disclosure of Invention

In view of the above problems in the prior art, an object of the present invention is to provide a method for estimating a direction of arrival based on a known delay, which greatly simplifies the estimation of the number of signals, and the obtained estimation of the direction of arrival of the signals is less affected by noise and the fluctuation of the estimated value is also less.

In order to achieve the purpose, the invention adopts the technical scheme that: a method for estimating a direction of arrival based on known time delays, the method comprising the steps of:

(1) judging whether the array elements of the antenna are linearly placed at equal intervals or placed on the circular ring at equal intervals, if so, continuing to operate in the step (3), and otherwise, continuing to operate;

(2) for antennas with each array element placed equidistantly on the circumference, the baseband signal received by each array element is expressed by the following formula y (n) T_y0(n) transforming to obtain an equivalent signal column vector y (n);

wherein: y is₀(n) is a column vector of the baseband signal received by the antenna,

(3) despreading a received signal vector of a linear antenna or a transformed equivalent signal column vector y (n) of a loop antenna by using known time delay information to obtain a despread signal column vector x (n);

(4) construction of a reduced-dimension signal vector z using a despread signal column vector x (n)_i(n)，i＝1，…，P-1 according to

The following formula:

and r (n) ═ λ_fR(n-1)+R_ss(n) calculating to obtain instantaneous correlation matrix R_ss(n) and estimation of a correlation matrix r (n);

(5) the instantaneous correlation matrix R obtained according to the step (4)_ss(n) and the correlation matrix r (n) to obtain a desired vector w (n) ═ w₁ w₂]^T(ii) an estimate of (d);

(6) utilizing two weighted weights w contained in the vector obtained in the step (5)₁And w₂And obtaining the estimation of the direction of arrival of the required signal.

According to the instantaneous correlation matrix R_ss(n) and the correlation matrix r (n) to obtain a desired vector w (n) ═ w₁ w₂]^TThe estimate of (c) can be obtained as follows:

setting the initial conditions as follows: w (0) ═ 10]^TThe residual vector g (0) [ -10 ]]^TThe gradient vector p (1) is g (0), n is 1, and the update step is calculated sequentially:

wherein: (lambda_f-0.5)≤η≤λ_fThe required vector update is calculated as:

w(n)＝w(n-1)+α(n)p(n)

the residual vector update formula is:

g(n)＝λ_fg(n-1)-α(n)R(n)p(n)-R_ss(n)w(n-1)

the gradient adjustment step size is calculated as follows:

gradient vector update calculation:

p(n)＝g(n)+β(n)p(n)

through each iterative calculation, the required vector w (n) ═ w can be obtained₁ w₂]^T。

According to the instantaneous correlation matrix R_ss(n) and the correlation matrix r (n) to obtain a desired vector w (n) ═ w₁ w₂]^TThe estimate of (c) can also be obtained as follows:

the correlation matrix r (n) is subjected to a singular value decomposition as follows:

R(n)＝U(n)∑(n)U(n)^H＝[u(n)w(n)]diag{λ₁，λ₂}[u(n)w(n)]^H λ₁＞λ₂not less than 0, the required vector w (n) ═ w can be obtained₁ w₂]^T。

The above uses two weighted weights w₁And w₂The estimation of the direction of arrival of the desired signal can be obtained as follows: for antennas with each array element placed equidistantly on the circumference, the signal direction angle phi is equal to angle (w)₂)-angle(w₁) (ii) a For the antennas with linearly and equidistantly arranged array elements, the arrival direction angle of the signals is as follows:

according to the technical scheme adopted by the invention, the problem of signal number estimation is simplified by utilizing the known time delay information, so that the method is easy to realize in practice; the invention can use a plurality of baseband signals received by continuous antennas to carry out statistical signal processing, thereby avoiding the defect that the common FFT method is easily affected by noise, greatly reducing the fluctuation of the estimated result and improving the accuracy, thereby improving the performance of wireless communication receiving.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and examples.

FIG. 1 is a schematic flow diagram of the process of the present invention.

Detailed description of the invention

Generally, in an actual wireless communication system, the change of the direction of arrival of a signal is relatively slow, and the conventional FFT method does not improve the estimation result using the slowly changing information, and therefore, there is inevitably room for improvement in the performance of the signal processing method.

The method of the invention is aimed at processing the baseband signals received by each antenna element and obtained after demodulation. Let the symbol y (n) denote the resulting baseband signal column vector, the number of vector elements is P, i.e. the number of actual antenna elements, and the column vector denotes that n in the symbol corresponds to a sampling time, i.e. the vector is a vector of baseband signal samples obtained at the nth sampling time on each array element.

The method of the present invention also uses different treatments for different antenna shapes. For antennas with linearly equidistant placement of the elements, the method of the invention can be applied directly. For the antenna with each array element placed equidistantly on the ring, the following processing needs to be performed on the signal in advance:

assuming that the actual number of antenna elements is N, the radius of a circular ring is r, the carrier wavelength is lambda, the arrival signal pitch angle theta is epsilon [0, pi/2 ], and let M be 2 pi r/lambda and zeta be Msin theta

Wherein,

j = \sqrt{- 1},

J_m(ζ) is a first type of Bessel function with order m, and diag { a, b } represents a diagonal matrix with major diagonal elements a, b, respectively. Column vector y of baseband signal received by antenna₀(N) (the vector dimension is Nx 1) is transformed as follows

y(n)＝T_y0And (n) the number of elements of the equivalent signal column vector y (n) after conversion is 2M + 1. The above-mentioned transformations are transformations of the signals received on the different elements. And directly despreading a received signal vector of a linear antenna or a transformed equivalent signal column vector y (n) of a loop antenna by using known time delay information. The despread signal column vector is denoted x (n).

Let x (n) be [ < x >₁(n)x₂(n)…x_p(n)]^TFrom which new reduced-dimension signal vectors are constructed, such that

z₁(n)＝[x₁(n)，x₂(n)]^T

z₂(n)＝[x₂(n)，x₃(n)]^T

*

z_P-1(n)＝[x_P-1(n)，x_P(n)]^T

The calculation was performed according to the following two equations:

R(n)＝λ_fR(n-1)+R_ss(n)

wherein the forgetting factor lambda_fSatisfies 0 < lambda_fLess than or equal to 1. After obtaining the correlation matrix R (n) and the instantaneous correlation matrix R_ssAfter the result of the calculation formula (n), the required vector w (n) can be calculated by two methods:

the first method is a conjugate gradient-based method, and specifically comprises the following steps:

wherein: (lambda_f-0.5)≤η≤λ_f，

The required vector update is calculated as:

w(n)＝w(n-1)+α(n)p(n)

the residual vector update formula is:

g(n)＝λ_fg(n-1)-α(n)R(n)p(n)-R_ss(n)w(n-1)

the gradient adjustment step size is calculated as follows:

gradient vector update calculation:

p(n)＝g(n)+β(n)p(n)

The second method is a method based on singular value decomposition. The decomposition computation is not very computationally intensive due to the small dimension of the matrix. In view of the signal characteristics here, it can be assumed that the singular value decomposition of the correlation matrix r (n) is as follows:

R(n)＝U(n)∑(n)U(n)^H＝[u(n) w(n)]diag{λ₁，λ₂}[u(n)w(n)]^Hλ₁＞λ₂not less than 0, then w (n) ═ w₁ w₂]^TIs the vector we need.

And finally, obtaining the estimation of the signal direction of arrival through the obtained vector. The data required in this case are two weighted weights w contained in a vector w (n)₁And w₂. Calculating the difference between the phase angles of two weighted weights of two elements of vector w (n), and making phi equal to angle (w)₂)-angle(w₁) For antennas with array elements equidistantly placed on the circumference, the angle (in radians) is the azimuth angle of the signal arrival direction to be estimated; for the antennas with linearly and equidistantly arranged array elements, the estimation of the direction angle of arrival of the signal to be estimated can be calculated by the following formula:

λ is also the carrier wavelength, d is the distance between adjacent array elements, sin^-1(. cndot.) represents an arcsine function.

The invention is further described below in terms of its application to a TD-SCDMA (time division synchronous code division multiple access) system.

In the TD-SCDMA system, the signal used for estimating the direction of arrival is a despread intermediate pilot (midamble) code signal, or a channel estimation signal obtained through joint detection. The system antenna is assumed to be an antenna with each array element equidistantly arranged on the circumference, and the signal obtained by the antenna is h_k，l ^(j)(n), where J1, …, J represents different array elements, K1, …, K represents different users, L1, …, L_kRepresenting signals of different paths. The specific implementation of the present invention is described with reference to fig. 1. In step 1, judging whether the array elements of the antenna are linearly placed at equal intervals or are placed on the circular ring at equal intervals, and continuing the following operations because the array elements of the antenna are not linearly placed at equal intervals; in step 2, the baseband signal received by each array element is expressed by the following formula y (n) ═ T_y0(n) transforming to obtain an equivalent signal column vector y (n);

in step 3, the converted equivalent signal column vector y (n) is despread by using the known time delay information, and a despread signal column vector x (n) is obtained; in step 4, a reduced-dimension signal vector z is constructed by using the despread signal column vector x (n)_i(n), i ═ 1, …, P-1, according to the following formula:

and r (n) ═ λ_fR(n-1)+R_ss(n) calculating to obtain instantaneous correlation matrix R_ss(n) and estimation of a correlation matrix r (n); in step 5, the instantaneous correlation matrix R obtained in step 4 is used_ss(n) and the correlation matrix r (n) to obtain a desired vector w (n) ═ w₁ w₂]^T(ii) an estimate of (d); in step 6, the vector obtained in step 5 is usedTwo weighting values w₁And w₂And obtaining the estimation of the direction of arrival of the required signal.

According to the instantaneous correlation matrix R_ss(n) and the correlation matrix r (n) to obtain a desired vector w (n) ═ w₁ w₂]^TThe estimate of (d) is obtained as follows:

what is needed is

The required vector update is calculated as:

w(n)＝w(n-1)+α(n)p(n)

the residual vector update formula is:

g(n)＝λ_fg(n-1)-α(n)R(n)p(n)-R_ss(n)w(n-1)

the gradient adjustment step size is calculated as follows:

gradient vector update calculation:

p(n)＝g(n)+β(n)p(n)

Obtaining the desired vector w (n) ═ w₁ w₂]^TThe estimate of (c) can also be obtained as follows: the correlation matrix r (n) is subjected to a singular value decomposition as follows:

R(n)＝U(n)∑(n)U(n)^H＝[u(n) w(n)]diag{λ₁，λ₂}[u(n)w(n)]^H λ₁＞λ₂not less than 0, the required vector w (n) ═ w can be obtained₁ w₂]^T。

Using two weighted weights w₁And w₂In the process of obtaining the desired estimation of the direction of arrival of the signal, the signal direction angle phi is equal to angle (w) for the antennas having the array elements disposed at equal distances on the circumference₂)-angle(w₁) (ii) a For the antennas with linearly and equidistantly arranged array elements, the arrival direction angle of the signals is as follows:

it can be seen from the above detailed implementation process of the present invention that the present invention is applicable to a mobile communication system requiring DOA estimation, and can provide DOA estimation with small variance.

Claims

1. A method for estimating a direction of arrival based on a known time delay is characterized by comprising the following steps:

(2) for the antennas with the array elements equidistantly arranged on the circumference, the baseband signals received by the array elements are according to the following formula y (n) T_y0(n) transforming to obtain an equivalent signal column vector y (n);

wherein,

j = \sqrt{- 1},

J_m(ζ) is a first type of bessel function having an order m, m being an integer greater than or equal to 0, diag { a, b } representing a diagonal matrix with major diagonal elements a, b, respectively;

wherein, N is the number of the actual array elements of the antenna, M is 2 pi r/λ, ζ is Msin θ, r is the radius of the circular ring, λ is the carrier wavelength, and θ is the arrival signal pitch angle [0, pi/2 ].

(4) construction of a reduced-dimension signal vector z using a despread signal column vector x (n)_i(n), i-1, …, P-1, according to

The following formula:

and r (n) ═ λ_fR(n-1)+R_ss(n) calculating to obtain instantaneous correlation matrix R_ss(n) and estimation of a correlation matrix r (n); where P ═ 2M +1 is the number of elements in the transformed equivalent signal column vector y (n), and the forgetting factor λ_fSatisfies 0 < lambda_f≤1。

2. The method of claim 1, wherein the direction of arrival estimation is based on an instantaneous correlation matrix R_ss(n) and the correlation matrix r (n) to obtain a desired vector w (n) ═ w₁ w₂]^TIs estimatedThe meter is obtained according to the following method:

wherein: (lambda_f-0.5)≤η≤λ_f

The required vector update is calculated as:

w(n)＝w(n-1)+α(n)p(n)

the residual vector update formula is:

g(n)＝λ_fg(n-1)-α(n)R(n)p(n)-R_ss(n)w(n-1)

the gradient adjustment step size is calculated as follows:

gradient vector update calculation:

p(n)＝g(n)+β(n)p(n)

3. The method according to claim 1, wherein the estimation is based on the instantaneous correlation matrix R_ss(n) and the correlation matrix r (n) to obtain a desired vector w (n) ═ w₁ w₂]^TThe estimation of (a) is obtained according to the following method: the correlation matrix r (n) is subjected to a singular value decomposition as follows:

4. The method according to claim 1, wherein the two weighted weights w are used to estimate the direction of arrival₁And w₂The estimation of the direction of arrival of the desired signal is obtained as follows: for antennas with each array element equidistantly placed on the circumference, the signal direction angle phi is equal to angle (w)₂)-angle(w₁) (ii) a For the antennas with linearly and equidistantly arranged array elements, the arrival direction angle of the signals is as follows: