JP2934426B1 - Arrival wave estimation method - Google Patents

Abstract

An object of the present invention is to reduce the amount of calculation of arrival angle and delay time estimation of an incoming wave when a MUSIC algorithm is applied. SOLUTION: Array outputs from an array antenna 10 and a receiver 20 are input to a covariance matrix operation unit 30 and a simple estimation unit 60. The simple estimation unit 60 performs a simple estimation of the angle of arrival using an algorithm with a relatively small amount of calculation, and based on the result of the simple estimation, calculates the calculation range determination unit 7.
0 is used to determine the calculation range of the MUSIC evaluation function. The covariance matrix calculation unit 30 and the eigenvalue / eigenvector calculation unit 40 determine the eigenvalues and eigenvectors of the covariance matrix of the array output, determine the number of incoming waves based on the eigenvalues, and determine the noise subspace from the eigenvectors. The angle-of-arrival estimating unit 50 obtains a MUSIC evaluation function within the minimum necessary range from the calculation range determining unit 70, and estimates the angle of arrival of the arriving wave. The estimation of the delay time is performed in the same manner.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for estimating an arrival angle or delay time of an incoming wave using a MUSIC algorithm.

[0002]

2. Description of the Related Art In land mobile communications, high-speed, high-quality wireless communication systems are being studied with the development of multimedia in the future. However, the higher the wireless transmission speed, the greater the effect of multipath fading. Therefore, in order to realize this system, it is necessary to take a multipath fading countermeasure technique such as an adaptive array antenna or an adaptive equalizer. When designing and evaluating an adaptive array antenna, an adaptive equalizer, and the like, it is necessary to clarify the propagation characteristics in consideration of the delay time and the angle of arrival of an incoming multiplex wave.

[0003] Therefore, MUSIC (MUltiple Signal Characte), which is one of the super-resolution methods in which the resolution of the estimation of the delay time and the angle of arrival of a multiplex wave is very high.
ROSchmidt: “Multiple Emitter L”
ocation and Signal Parameter Estimation ”, IEEE Tra
ns. Antennas Propagat., AP-34,3, pp.276-280 (March 1
986), Yamada, Ogawa, Omiya, Ito: “Basic study on antenna measurement using super resolution method”, IEICE Technical Report, A ・ P90-47, pp.17-24, (1990), Sekizawa : "Study of Direction of Arrival Estimation by MUSIC applied to Planar Array", IEICE Technical Report, A. P97-117, pp. 21-28 (Oct. 1
997)).

As an example of a method for estimating an incoming wave using such a MUSIC algorithm, a principle diagram in a case where the MUSIC algorithm is used for a received signal received by an array antenna to estimate the arrival angle of a multiplex wave with high resolution. Is shown in FIG. The incoming wave m (m = m
1,2, ..., it is assumed that M) arrives at the arrival angle theta _m with respect to the direction (x-axis) of the alignment of linear array. However, the incoming waves are uncorrelated with each other. Further, the number of elements of the linear array 10 is N. The signals received by the elements of the linear array 10 are input to the receiver 20, and the receiver 20 outputs array outputs X ₁ (t), X ₂ (t),..., X _N (t). Expressing this array output as a vector,
It is expressed as the following equation (1).

(Equation 1) Here, s _m (t) and θ _m are the m-th wave (m = m
1, 2,..., M) and the direction of arrival, Ψ
_n (θ _m ) is the reception phase of the m-th wave in the n-th element, vector a (θ _m ) is the mode vector (direction vector),
Vector n (t) is a noise vector. ^T represents transposition.

Next, an N × N-dimensional covariance matrix R defined by the following equation (2) is created from the array output vector X (t) in the covariance matrix calculation section 30.

(Equation 2) Here, E ｛·｝ indicates an ensemble average (strictly, an expected value), and H indicates a complex conjugate transpose. The matrix P is a covariance matrix E {s (t) · s (t) ^H } of the signal vector, σ ² I
Is the covariance matrix of the noise vector, the vector I is an N × N unit matrix, and σ ² is the variance of the noise vector n (t).

Then, the eigenvalue / eigenvector operation unit 40
, The eigenvalue λ _i and the eigenvector e _i of the covariance matrix R
(I = 1,..., N). If the covariance matrix R is nonsingular, its eigenvalue λ _i has the relationship shown in the following equation (3).

(Equation 3) Here, the number M of arriving waves can be estimated from the number of eigenvalues larger than the internal noise power σ ² .

Further, as shown by the following equation (4), a space (noise subspace) E _N spanned by NM eigenvectors corresponding to the noise eigenvalue (λ _{M + 1} = λ _N ) is obtained. This noise subspace E _N is orthogonal to the mode vector a (θ _m ) of the incoming wave.

(Equation 4) Therefore, the arrival angle estimating unit 50 uses the property that the noise subspace E _N and the mode vector a (θ _m ) of the arriving wave are orthogonal to each other, and uses the MUSIC evaluation function P
_The angle of arrival of the arriving wave is estimated by _music (θ).

(Equation 5)

FIG. 8 is an explanatory diagram of arrival angle estimation. As shown in FIG. 8, P _music (θ) in equation (5) diverges when θ coincides with the arrival angle θ _{m of the} arriving wave, and has a sharp peak.
Therefore, the estimated value of arrival angle θhat _m is changed by changing θ
It can be obtained by searching for the peak of _music (θ). In the figures and formulas, for characters in which a chevron symbol is attached above the characters, “θhat” is used in the text.
The character is expressed by adding the character "hat". In order to detect the peak of P _music (θ) in this manner, it is necessary to determine the calculation step width of θ according to the estimated resolution of the angle of arrival. The higher the estimated resolution of the angle of arrival, the smaller the calculation step width. There is a need to.

[0009] The MUSIC algorithm can estimate when the incoming waves are uncorrelated with each other. However, in land mobile communications, MUSIC cannot be directly applied to estimation of the angle of arrival because the correlation between incoming waves of multiplex waves is very high. In such a case, a spatial smoothing method or the like (TJShan, M. Wax, and T. Kai
lath, "On Spatial Smoothing for Direction-of-Arriva
l Estimation of Coherent Signals ", IEEE Trans. Acou
st., Speech, Signal Processing, vol.33, no.4, pp.806-81
1, Aug. 1985, RT Williams, S. Prasad, AKmahalanabis,
and LHSibul, "An Improved Spatial Smoothing Tech
nique for Bearing Estimation in a Multipath Enviro
nment ", IEEE Trans. Acoust., Speech, Signal Processin
g, vol. 36, no. 4, pp. 425-432, April 1988, and the like. ) By suppressing the cross-correlation
Estimation by IC becomes possible.

In the above description, it has been described that the arrival angle of an incoming wave can be estimated using a MUSIC for a received signal spatially sampled by a linear array (one-dimensional array antenna). In addition, if the MUSIC algorithm is applied to an array output obtained by a multidimensional array antenna, multidimensional arrival angle estimation becomes possible. Similarly, if the MUSIC algorithm is applied to the frequency-sampled received signal, high-resolution estimation of a delay time of an incoming wave or the like is possible. For example, assuming that N data is obtained by frequency sweeping using one antenna, and a multiplexed wave of M waves arrives, the data vector is expressed by an equation having the same form as the aforementioned equation (1). You. Therefore, the delay time can be estimated by the MUSIC as in the case described above.

[0011]

In the above-described conventional method in which MUSIC is applied to a linear array for estimating the angle of arrival, the method of calculating θ for obtaining P _music (θ) in comparison with the angular resolution of the angle of arrival is described. If the width θ _step is not sufficiently small, there is a disadvantage that the peak of P _music (θ) cannot be detected. FIG. 9A is a diagram showing this state. As shown in FIG. 9, when the calculation step width θ _step is large, the amount of calculation over the entire calculation range θ ^{start to} θ ^stop is small, but the peak is small. , It is difficult to detect the estimated peak θhat _m (m = 1,..., M) with high accuracy.

On the other hand, if the calculation step width θ _step of θ is reduced to detect a sharp peak of P _music (θ), the amount of calculation increases. FIG. 9B shows this state. As shown in FIG. 9, when θ _step is reduced, the estimated peak θhat _m can be detected with high accuracy, but the amount of calculation increases. . In particular, when the number of arrays, the S / N, and the number of snapshots (the number of samples of the array output vector X (t)) are large, it is possible to estimate a high angular resolution. It becomes a serious problem. This is the same problem in the case of estimating the delay time of an incoming wave using the MUSIC algorithm.

Accordingly, the present invention provides an evaluation function P _music for estimating the arrival angle and delay time of an incoming wave by MUSIC.
It is an object of the present invention to provide a method for estimating the arrival angle and delay time of an incoming wave, which can reduce the amount of calculation of (θ) and obtain a highly accurate estimation result with a small amount of calculation.

[0014]

In order to achieve the above object, an arrival wave estimation method of the present invention is an arrival wave estimation method for estimating an arrival angle of an arrival wave using an array antenna,
(1) Estimating the approximate angle of arrival of the arriving wave by calculating from the output of the array antenna by an algorithm based on the discrete Fourier transform with a first calculation step width capable of estimating the approximate angle of arrival , (2)
MU based on the estimation result in the step (1)
Determining the calculation range of the SIC evaluation function; and (3) calculating the calculation range determined by the step (2) using the MUSIC algorithm with a second calculation step width required to obtain a desired resolution. The step of estimating the angle of arrival of the incoming wave. The array antenna is a linear array antenna or a planar array antenna. Further, the step (2) is a step of determining, as the calculation range, an angle at which the power within a predetermined range with respect to the peak value of the power corresponding to the arriving wave in the estimation result of the step (1). Things.

Still another arriving wave estimating method of the present invention is an arriving wave estimating method for estimating a delay time of an arriving wave.
Te, the transfer function output from (1) an antenna,
A first calculation step capable of estimating the approximate delay time
By an algorithm based on the discrete Fourier transform
Estimating the approximate delay time of the arriving wave by performing computation; (2) determining the computation range of the MUSIC evaluation function based on the estimation result in step (1); and (3) performing the step ( In order to obtain the desired resolution for the calculation range determined by 2)
The method has a step of estimating a delay time of an incoming wave by performing an operation using a MUSIC algorithm with a required second operation step width .

According to the arriving wave estimating method of the present invention, first, the arrival angle or delay time of the arriving wave is roughly estimated by the simple estimating method with a small amount of calculation, and based on the estimation result by the simple estimation. Since the minimum necessary calculation range is determined and the MUSIC evaluation function is calculated for the determined calculation range, a highly accurate estimation result can be obtained, and the amount of calculation for that is significantly reduced. It becomes possible.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of an incoming wave estimation method according to the present invention will be described. FIG. 1 is a principle diagram of the angle-of-arrival estimation method of the present invention. Conventionally, as shown in FIG. 7, it was composed of a linear array 10, a receiver 20, a covariance matrix operation unit 30, an eigenvalue and eigenvector operation unit 40, and an arrival angle estimation unit 50 using MUSIC. On the other hand, in the present invention, the simple estimating unit 60
And a calculation range determination unit 70 for the evaluation function. The simple estimating unit 60 estimates the direction of arrival of an incoming wave based on the output of the linear array 10 by using an estimating method that requires less computation than MUSIC. The calculation range determination unit 70 determines a calculation range of the MUSIC evaluation function according to a predetermined algorithm based on the simple estimation result from the simple estimation unit 60, and outputs the calculation range to the arrival angle estimation unit 50. The angle-of-arrival estimating unit 50 calculates the
For the calculation range determined by 0, the MUSIC evaluation function P _music (θ) of the above equation (5) is calculated based on the output from the eigen value / eigen vector calculation unit 40, and the arrival angle is estimated with high accuracy.

FIG. 2 is an explanatory diagram of the arrival angle estimation by the method of the present invention. First, as shown in FIG. 2A, the simple angle-of-arrival estimating unit 60 sets the MUSI in the calculation step width θ _step ^rough for the entire calculation range from θ ^start to θ ^stop.
A rough arrival angle θhat _{m ′} ^rough of the m ′ (m ′ = 1, 2,..., M ′) th arriving wave is estimated by using an estimation algorithm whose calculation amount is much smaller than that of C. However, this simple estimation does not always satisfy M ′ = M because the angular resolution is lower than that of MUSIC. The calculation range determination unit 7
0 is the calculation range θ _{m ′} ^start and θ _{m ′} ^stop (m ′ = 1,...,...) Of the evaluation function based on the estimated value θhat _{m ′} ^rough .
M ′) is determined. Next, as shown in FIG. 2B, the arrival angle estimating unit 50 determines the calculation range θ _{m ′} ^start
MUSI from θ _{m '} ^stop (m' = 1, ..., M ')
The C evaluation function P _music (θ) is obtained. The operation step width θ _{step at} this time is a step width necessary to obtain a desired resolution.

As described above, the arrival angle estimation method of the present invention is as follows.
In the first stage, the approximate peak position is estimated by the simple estimation unit 60 using an estimation method with a small amount of calculation,
In the step, highly accurate estimation is performed using the MUSIC algorithm for the vicinity of the peak position estimated in the first step. As described above, by executing the MUSIC algorithm requiring a large amount of calculation only at necessary places, the amount of calculation can be reduced, and a highly accurate estimation result can be obtained.

FIG. 3 is a diagram showing a configuration example of an embodiment in which the arriving wave estimating method of the present invention is applied to the arrival angle estimation using a linear array. In this embodiment, as a simple estimating unit for the angle of arrival, the amount of calculation for estimating the angle of arrival is MUSIC.
A simple estimator 61 using a beamformer method based on a discrete Fourier transform (DFT) is used, which is much less than that of the first embodiment. Further, the DFT uses a fast Fourier transform (FFT) to further reduce the amount of calculation.

FIG. 4 is a diagram for explaining the state of arrival angle estimation of a multiplex wave in this embodiment. In the simple estimating unit 61, the arrival angle θ by the ^DFT with the step width θ _step ^DFT for the entire calculation range from θ ^{start to} θ ^stop
Relative power P _DFT (theta) is calculated, and angle of arrival Shitahat _{m ^'DFT} of P _DFT (theta) peak of M' number detected and incoming waves m 'for
(M ′ = 1, 2,..., M ′) is estimated. When the calculation range determination unit 70 of the evaluation function defines the threshold level as A [dB] based on the peak value P _DFT (θhat _{m '} ^DFT ) of the relative power output from the simple estimation unit 61, , P _DFT (θ) is relative power P _DFT lower by A [dB]
(Θ _{m ^'start)} and P _DFT (θ _m' ^stop) the determined, theta _{m '}
The range (m ′ = 1,..., M) from ^start to θ _{m ′} ^stop is determined as the calculation range of the MUSIC evaluation function in the angle-of-arrival estimation unit 50. The value of A is determined in consideration of the angular resolution of the DFT, the SNR, and the like. Finally, this θ _{m '}
^By calculating the MUSIC evaluation function P _music (θ) in the calculation range from ^start to θ _{m '} ^stop and estimating the angle of arrival, the amount of calculation can be reduced.

In the above description, the calculation range is determined by determining the threshold level A [dB], but the calculation range determination method is not limited to this. For example, various methods can be adopted, such as a method in which a predetermined angle before and after the arrival angle θhat _{m ′} ^DFT estimated by the simple estimation unit 60 is set as a calculation range.

The above-described embodiment uses a one-dimensional array antenna. Next, an embodiment using a planar array antenna will be described. FIG. 5 is a diagram showing an example of a configuration in an embodiment in which the arriving wave estimating method of the present invention is applied to the arrival angle estimation using a planar array antenna (two-dimensionally arranged array antenna). In FIG. 5, an incoming wave m (m = 1, 2,..., M) is x in the planar array 11.
It is assumed that the angle of arrival α _m with respect to the axis and the angle of arrival β _{m with} respect to the y axis come from. When the plane array is used as described above, the arrival angle estimating unit 50 calculates the evaluation function P
The arrival angles α _m and β _m of the arriving wave _m are estimated by _music (α, β).

(Equation 6)

In the case of a planar array, P _music (α, β)
Since it is necessary to change two variables α and β in order to perform the peak search, the amount of calculation is significantly increased as compared with the case of the linear array described above. Therefore, as shown in FIG. 5, a simple estimating unit 62 for the angle of arrival in this embodiment.
Performs simple estimation using a two-dimensional discrete Fourier transform (2D-DFT), which has a very small amount of computation for arrival angle estimation compared to MUSIC. Then, a rough angle of arrival is estimated by 2D-DFT, and the calculation range determination unit 70 of the evaluation function calculates the two variable calculation range α _{m ′} ^start of the MUSIC evaluation function in the same manner as in the case of the linear array described with reference to FIG. , Α _{m '} ^stop , β _m' ^start and β _{m '} ^stop (m'
= 1, 2,..., M ′), and for the determined calculation range, the arrival angle estimation unit 50 calculates the evaluation function P _music (α, β) shown in the expression (6). Do. With this configuration, it is possible to greatly reduce the amount of calculation, and the effect of reducing the amount of calculation is greater than in the case of the linear array antenna described above. Furthermore, the method for estimating an incoming wave of the present invention can be similarly applied to an array antenna having a three-dimensional arrangement by determining the operation range of three variables of the MUSIC evaluation function and calculating the evaluation function.

Next, an embodiment in which the estimation method of the present invention is applied to the case of estimating the delay time of an incoming wave will be described. FIG. 6 shows a configuration example of an embodiment in which the arrival wave estimation method of the present invention is applied to the case where the delay time of an arrival wave is estimated from frequency characteristics (discrete data) of a transmission line received by one antenna. FIG. Incoming wave m on antenna 12
Assume that (m = 1, 2,..., M) arrives with a delay time τ _m . In the case of estimating the delay time of the arriving wave, the delay time τ _m of the arriving wave _m is estimated by the following MUSIC evaluation function P _music (τ).

(Equation 7) Here, the vector a (τ) is a mode vector determined by the delay time.

In equation (7), P _music (τ) is τ where arriving wave m
And a sharp peak is formed when the delay time τ _m coincides. Therefore, the estimated value Tauhat _m of the delay time can be determined by searching for the peak of the P _music (tau) is changed to tau. In order to detect the peak of P _music (τ), it is necessary to determine the calculation step width of τ according to the estimated resolution of the delay time, and it is necessary to reduce the calculation step width as the estimated resolution of the delay time is higher. . Therefore, as in the case described above, the simple estimator 6 using DFT
In 3, estimate the rough delay time by DFT,
In the same manner as in the case of the linear array described with reference to FIG.
By determining the calculation range of the USIC evaluation function and performing the calculation of the evaluation function, it is possible to greatly reduce the amount of calculation.

[0027]

As described above, according to the present invention, M
The amount of calculation required for high-resolution estimation of the angle of arrival and delay time of an incoming wave by the USIC algorithm can be reduced.
Especially. Since the amount of calculation can be greatly reduced for array antennas with two or more dimensions, real-time processing can be realized when MUSIC is applied to an actual wireless communication system, and enormous propagation data can be processed in a short time. This will greatly contribute to research and development of advanced mobile radio technology and elucidation of land mobile propagation.

[Brief description of the drawings]

FIG. 1 is a configuration diagram for explaining the principle of an angle-of-arrival estimation method according to the present invention.

FIG. 2 is a diagram for explaining an angle-of-arrival estimation method of the present invention.

FIG. 3 is a diagram showing an example of a configuration of an embodiment in which the arrival wave estimation method of the present invention is applied to the case of arrival angle estimation using a linear array antenna.

FIG. 4 is a diagram for explaining the operation of the embodiment shown in FIG. 3;

FIG. 5 is a diagram showing a configuration example of an embodiment in which the arrival wave estimation method of the present invention is applied to the case of arrival angle estimation using a planar array antenna.

FIG. 6 is a diagram showing a configuration example of an embodiment in which the arriving wave estimation method of the present invention is applied to the case of estimating the delay time of an arriving wave.

FIG. 7 is a diagram for explaining the principle of a conventional angle-of-arrival estimation method.

FIG. 8 is a diagram for explaining a conventional angle of arrival estimation method.

FIG. 9 is a diagram for explaining a problem of the conventional angle of arrival estimation.

[Explanation of symbols]

 Reference Signs List 10 linear array antenna 11 planar array antenna 12 antenna 20 receiver 30 covariance matrix calculation unit 40 eigenvalue / eigenvector calculation unit 50 arrival angle estimation unit 60 simple arrival angle estimation unit 61 simple arrival angle estimation unit using DFT 62 2D -Simplified angle of arrival estimator using DFT 63 Simple estimator for delay time using DFT 70 Calculation range determining unit for evaluation function

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-8-201498 (JP, A) JP-A-7-140221 (JP, A) JP-A-9-61471 (JP, A) JP-A-60-1985 JP-A-62-233781 (JP, A) JP-A-9-33628 (JP, A) JP-A-9-171069 (JP, A) JP-A-8-29513 (JP, A) JP-A-61-272669 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01S 3/00-3/74

Claims (4)

(57) [Claims] 1. An arrival wave estimation method for estimating an arrival angle of an arrival wave using an array antenna, wherein (1) a rough arrival angle can be estimated from an output of the array antenna. Estimating the approximate angle of arrival of the arriving wave by calculating with an algorithm based on the discrete Fourier transform with the first calculation step width; (2) calculating the MUSIC evaluation function based on the estimation result in the step (1). Determining a calculation range; and (3) arriving wave by calculating the MUSIC algorithm with the second calculation step width necessary for obtaining a desired resolution in the calculation range determined in step (2). A step of estimating the angle of arrival of the incoming wave. 2. The method according to claim 1, wherein said array antenna is a linear array antenna.
Tena incoming wave estimation how of claim 1, wherein the a or planar array antenna. 3. The step (2) is a step of determining, as the calculation range, an angle at which power within a predetermined range with respect to a peak value of power corresponding to the arriving wave in the estimation result of the step (1). claim 1 or 2 incoming wave estimation method of the arrival wave, wherein the certain. 4. An incoming wave estimation for estimating a delay time of an incoming wave.
A method for the transfer function output from (1) an antenna, schematically
Calculation step capable of estimating the delay time of
Calculated by algorithm based on discrete Fourier transform with width
Estimating a delay time of the outline of the incoming wave by, (2) on the basis of the estimation result in step (1), determining a calculation range of MUSIC evaluation function, and (3) the step (2 ), The second calculation process required to obtain the desired resolution.
Calculate by MUSIC algorithm with step width
Incoming wave estimation method characterized by comprising the step of estimating a delay time of an incoming wave by.