JPH09199926A - Adaptive digital beam forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a digital beam forming device having provision for a broad band desired signal in which the number of weight coefficients to be calculated is reduced between a conversion means and a finite impulse response digital filter. SOLUTION: A multi-beam forming device 7 and a signal selector 8 are provided between low-pass digital filters 5-1 to 5-L and FIR digital filters 9-1 to 9-L. Thus, a beam is generated by the multi-beam forming device 7 and signals y1 (m) to yN(m) of a narrower frequency band are subjected to beam shaping processing by the FIR digital filters again and the resulting signals are summed, then a broad band desired signal is outputted and the number of weight coefficients to be calculated is reduced. A symbol (m) in the signals y1 (m) to yN(m) depicts a time (time number).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a beam in the direction of a desired signal among incoming propagating wave signals and receiving the signal.
The present invention relates to an adaptive digital beamforming apparatus that suppresses nulls by directing them to the arrival direction of an interference signal.

[0002]

2. Description of the Related Art Here, a case where information is transmitted using a carrier wave as a propagating wave signal will be described. High frequency (R
F) A signal in which the bandwidth of the signal is not negligible as compared with the carrier frequency is called a wideband signal. However, the bandwidth is narrower than 1/2 of the carrier frequency. FIG.
In the prior art document 1 “OL Frost, III,“ An alg.
orithm of linearly constrained adaptive array proc
essing ", Proceedings of the IEEE, vol.60,
No. 8, pp. FIG. 9 is a block diagram of a first conventional adaptive digital beamforming apparatus for the above-mentioned wideband signal, to which the adaptive beamformer disclosed in “926-935, August 1972” is applied. The adaptive digital beamforming apparatus of the first conventional example shown in FIG. 3 has L antenna elements 1 having approximately the same directivity and frequency characteristics.
-1 to 1-L array antenna 100, receivers 2-1 to 2-L, and A / D converters 3-1 to 3-L
, Mixers 4-1 to 4-L, low-pass digital filters 5-1 to 5-L, and digital local oscillator 6
And finite impulse response (hereinafter referred to as FIR) type digital filters 9-1 to 9-L, a first coefficient controller 11a, and an adder 10.

A first conventional example will be described below with reference to FIG. The high frequency signals received by the plurality of L antenna elements 1-i are converted into intermediate frequency signals by the receiver 2-i, and converted into digital intermediate frequency signals by the A / D converter 3-i ( Hereinafter, the intermediate frequency is referred to as _fIF .). Here, i = 1, 2, ..., L, and the same applies hereinafter unless otherwise specified in this specification. Then, these digital intermediate frequency signals are respectively mixed with the digital sine wave of the frequency f _IF oscillated by the digital local oscillator 6 by the mixer 4-i, the high frequency components are cut by the low pass digital filter 5-i, A complex digital in-phase / quadrature signal x _i (m) is output from the band-pass digital filter 5-i. Here, in the digital in-phase / quadrature signal x _i (m), the real part is the in-phase component and the imaginary part is the quadrature component. In addition, 2 in the line of the drawing indicates a symbol of a complex number.

L digital in-phase / quadrature signals x
₁ (m), x2 (m), ..., x _L (m) are FIR
Input to the digital filters 9-1 to 9-L.
The FIR digital filter 9-i has a weighting factor w _{i, 0} (m), w input from the first coefficient controller 11 a.
_{Based on i, 1} (m), ..., W _{i, q-1} (m), the input digital in-phase / quadrature signal x _i (m) is digitally filtered to obtain the digital in-phase after filtering.・ Quadrature signal x
_i (m) is output to the adder 10. Here, the first coefficient controller 11a uses the digital in-phase / quadrature signal x
_{Based on 1} (m), x2 (m), ..., X _L (m), a wideband desired signal is extracted and a wideband interference signal is suppressed at the output z _es (m) of the adaptive digital beamforming apparatus. Thus, the load factors w _{i, 0} (m), w _{i, 1} (m),
,, w _{i, q-1} (m) is calculated, and the weighting factor w _{i, 0} (m),
_{w i, 1 (m),} ..., and outputs _{w i, q-1 (m} ) to the FIR type digital filter 9-i.

These weighting factors w _{i, 0} (m), w
_{i, 1} (m), ..., W _{i, q-1} (m) are generally complex numbers.
Here, q is a tap length of the FIR digital filter 9-i and is a predetermined integer. Load factor w _{i, 0} (m),
The calculation method of w _{i, 1} (m), ..., W _{i, q−1} (m) is, for example, LMS (Least Mean Squ) when a reference signal is used.
Known methods such as the ares method and the direction-constrained LMS method can be used if the incident direction of the desired wave is known. Here, as in the first conventional example of FIG. 3, a configuration in which signals from the antenna elements 1-i having the same directivity characteristics are controlled is referred to as an element space configuration.

In the first conventional example, when handling a wideband signal in which the bandwidth of the target high-frequency signal is not negligible compared to the carrier frequency, in order to form a wideband beam or null, a simple weight independent of frequency is used. Since it is necessary to realize a "weighting coefficient" that depends on the frequency instead of the coefficient, the FIR digital filter is used.

Further, FIG. 4 shows an adaptive digital beamforming apparatus which can deal with a wide band signal and requires a small number of weighting factors to be calculated.
F. Yang et al., “Wideband adaptive arrays based on
the coherent signal-subspace transformation ", I
EEE International Confererence on Acoustic
s, Speech, and Signal Processing, pp. 2011
FIG. 6 is a block diagram of a second conventional example disclosed in “-2014, 1987”. The second conventional example deals with a wideband signal by performing a non-linear preprocessing called coherent subspace conversion on the received signal by the signal converter 20. After this conversion, adaptive processing is performed with one weighting factor per path without using the FIR digital filter.

[0008]

However, in the case of the first conventional example of the element space configuration, the _weighting factors w _1,0 (m), w to be calculated in the FIR digital filters 9-1 to 9-L are used. _1,1 (m), ..., w
_{The number of 1, q-1} (m), w _2,0 (m), ..., W _{L, q-1} (m) is q × L, and the tap length q of the FIR digital filter 9-i and the antenna When both the number of elements L is large,
There is a problem in that the number of weighting factors to be controlled becomes very large, and thus the amount of signal processing calculation for calculating the weighting factor also increases dramatically. Also,
The second conventional example has a problem that the coherent subspace conversion in the signal converter 20 requires accurate prior knowledge about the incident direction of the signal.

An object of the present invention is to solve the above problems, to deal with a desired signal in a wide band, to reduce the number of weighting factors to be calculated, and to have prior knowledge about the incident direction of the desired signal. An object of the present invention is to provide an adaptive digital beamforming device that does not.

[0010]

According to a first aspect of the present invention, there is provided an adaptive digital beamforming apparatus comprising a plurality of L
An array antenna consisting of a plurality of antenna elements and each received signal received by each antenna element are
A conversion unit that performs D / D conversion to output each digital signal corresponding to each received signal, and a plurality of N weight coefficient units corresponding to each antenna element, and a plurality of N to be formed.
A plurality of N weight coefficient units are provided so as to correspond to the respective beams, and a plurality of (L × N) weight coefficient units respectively output the respective digital signals by multiplying them by a predetermined weight coefficient. And a plurality of N adders that add and output the plurality of L signals output from the plurality of L weight coefficient units for forming the beams, respectively, and are output from the conversion means. Beam forming means for forming beams in a plurality of N different directions based on each digital signal and outputting a plurality of N beam reception signals corresponding to the beams, and a plurality of beam forming means output from the beam forming means. Signal selection means for selecting and outputting a plurality of M beam reception signals from the N beam reception signals, and the plurality of M pieces input from the signal selection means based on a plurality of filter coefficients. Based on a plurality of M finite impulse response type digital filters for filtering the beam reception signal and outputting the beam reception signal, and a plurality of the M number of beam reception signals output from the signal selecting means, a predetermined signal including at least the frequency of the desired signal is provided. In the frequency range, a plurality of filter coefficients for directing the main beam of the array antenna in the direction of arrival of the desired signal and zeroing the level of the received signal in the direction of arrival of the interference signal are applied to the finite impulse response type digital filters. And a plurality of M filters output from the plurality of M finite impulse response digital filters, the coefficient control means outputting the plurality of filter coefficients to the corresponding finite impulse response digital filters. And adding means for adding and outputting the post-wave beam reception signals.

The adaptive digital beamforming apparatus according to a second aspect is the adaptive digital beamforming apparatus according to the first aspect, wherein the coefficient control means determines the envelope of the signal output from the adaptive digital beamforming apparatus. Each of the above filter coefficients is calculated so as to be kept constant.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment> FIG. 1 is a block diagram showing the configuration of an adaptive digital beamforming apparatus according to an embodiment of the present invention. The adaptive digital beamforming apparatus of the embodiment shown in FIG. 1 has the multi-layered structure between the low-pass digital filters 5-1 to 5-L and the FIR digital filters 9-1 to 9-L in the first conventional example. A beam former 7 and a signal selector 8 are provided. As a result, in the present embodiment, the signals y ₁ (m) to y _N (m), which are beam-formed by the multi-beam former 7 and have a narrower frequency band than the desired signal, are re-generated by the FIR digital filter 9-k. By performing beam forming processing and adding, a wideband desired signal is output, and the number of weighting factors to be calculated is reduced to q × M, which is smaller than q × L in the first conventional example. Reducing. Where the signal y
_{In the} parentheses () in ₁ (m) to y _N (m), m represents time (time number).

The adaptive digital beam forming apparatus (beam forming apparatus) of the embodiment will be described in detail below with reference to FIG. In the adaptive digital beamforming apparatus of the embodiment, the high-frequency signals received by the plurality of L antenna elements 1-i juxtaposed on one straight line are respectively the same as in the adaptive digital beamforming apparatus of the first conventional example. It is converted into an intermediate frequency signal by the receiver 2-i, and converted into a digital intermediate frequency signal by the A / D converter 3-i. Here, in the adaptive digital beamforming apparatus of the embodiment, the array antenna 100 in which a plurality of L antenna elements 1-i are juxtaposed on one straight line is used, but the present invention is not limited to this and, for example, 2
An array antenna in which antenna elements are appropriately arranged, such as a two-dimensionally arrayed array antenna, may be used. Then, these digital intermediate frequency signals are respectively mixed with the digital sine wave having the intermediate frequency f _IF oscillated by the digital local oscillator 6 by the mixer 4-i, and the high frequency component is cut by the low pass digital filter 5-i, Complex digital in-phase / quadrature signals x ₁ (m), x from the low-pass digital filter 5-i
₂ (m), ..., X _L (m) are output.

The multi-beam former 7, as shown in FIG. 6, has weighting factors 71-11 to 71-NL and an adder 72.
, -1 to 72-N and outputs L digital in-phase / quadrature signals x ₁ (m), x ₂ (m), ..., X _L (m) output from the low-pass digital filter 5-i. Beam forming processing is performed to obtain a plurality N of beam formed signals y.
Outputs ₁ (m), y ₂ (m), ..., Y _N (m). When N = L, the multi-beam former 7 can be constructed by using a fast Fourier transformer, which enables high-speed and efficient processing. Here, the multi-beam former 7 is composed of weight coefficient units 71-11 to 71-.
Since the NL and the adders 72-1 to 72-N are included, in the present embodiment in which the desired signal has a wide band, as will be described later, each of the N signals y ₁ (m in the narrow band compared to the desired signal. ), Y ₂ (m), ..., Y _N (m) are output.

Next, the multi-beam former 7 will be described in more detail. As shown in FIG. 6, in the multi-beam former 7, the digital in-phase / quadrature signal x ₁ (m)
Is input to the load coefficient units 71-11 to 71-N1, and the digital in-phase / quadrature signal x ₂ (m) is input to the load coefficient unit 71-
12 through 71-N2. Similarly, the digital in-phase / quadrature signal x _i (m) (i = 3, 4, ..., L) is input to the weight coefficient units 71-1i to 71-Ni. FIG.
, The load coefficient unit 71-1i (i = 1, 2,
, L) is the input digital in-phase / quadrature signal x _i
(M) is multiplied by the _weighting factor W _1i, and the multiplication result x
_i (m) · W _1i is output to the adder 72-1. Adder 7
2-1 adds a plurality of L multiplication results x _i (m) · W _1i input from each weighting coefficient unit 71-1i and adds the signal y ₁ (m) as the addition result to the signal selector 8 Output to. Here, the load coefficient W _1i in each load coefficient unit 71-1i is
A beam is formed in a predetermined direction and a signal y ₁ (m) corresponding to the beam is output from the adder 72-1.
It is set to a predetermined value in advance.

The weight coefficient unit 71-2i also receives the input digital in-phase / quadrature signal x _i (m) and the weight coefficient W _2i.
Are multiplied and the multiplication result x _i (m) · W _2i is added to the adder 72.
-2. The adder 72-2 is used for each load coefficient unit 71.
-I is input from a plurality of L multiplication results x _i (m)
W _2i is added and the resulting signal y ₂ (m) is output to the signal selector 8. Here, each load coefficient unit 71-2i
The weighting factor W _{2i at} is such that a beam is formed in a predetermined direction and the signal y ₂ (m) corresponding to the beam is added by the adder 72-
It is preset to a predetermined value so that it is output from 1.

Further, the load coefficient unit 71-bi (b = 3,
4, ..., N) are similarly input digital in-phase
The quadrature signal x _i (m) is multiplied by the _weighting coefficient W _bi, and the multiplication result x _i (m) · W _bi is output to the adder 72-b. The adder 72-b adds a plurality of L multiplication results x _i (m) · W _bi input from each weighting coefficient unit 71-bi and selects a signal y _b (m) which is the addition result. Output to the container 8. Here, weighting factor W _bi at each load coefficient units 71-bi is the signal y _b (m) is output from the adder 72-b corresponding to the beam to form a plurality of N beams in a predetermined direction Is set in advance to a predetermined value. The multi-beam former 7 configured as described above forms beams in a plurality of N different preset directions, respectively, and a plurality of N signals y _b (m) corresponding to the beams are formed.
Is output.

Here, the signals output from the multi-beam former 7 are N signals y ₁ (m), y ₂ (m), ..., Y.
_N (m) can be expressed by the following equation 1 using the _weighting coefficient W _bi . This equation 1 holds even when N = L is set and the multi-beam former 7 is configured by using the fast Fourier transform (FFT).

[0019]

[Equation 1]

Further, the radiation power intensity H of the beam when the beam is formed by using the multi-beam former 7.
_b (f, θ) can be expressed by the following equation 2.

[0021]

[Equation 2]

In Equation 2, b is the beam number, d is the element spacing between adjacent antenna elements 1-i, and a linear array with equal spacing is assumed. Also, f _c
Is the carrier frequency and λ _c is the carrier wavelength. Further, θ is the incident angle of the desired signal, and the antenna element 1-k
Is defined by the angle between the perpendicular of the juxtaposed lines and the incident direction of the desired signal. Here, in the case of N = L, considering the case where the multi-beam former 7 is configured by using the fast Fourier transform (FFT), the weighting factor W _bi can be expressed by the following _Expression 3.

[0023]

Equation 3 W _bi = (1 / N) · exp {j2π (b-1) (i-1) /
N}, i = 1, 2, 3, ..., L

In Equation 3, b = 1 corresponds to a beam having an incident angle θ = 0 °. Substituting 0 ° for the incident angle θ in Equation 2,
The radiated power intensity H ₁ (f, θ) expressed by Equation 2 is a constant that does not depend on the frequency f. Therefore, the broadband signal incident at the incident angle θ = 0 ° is received as it is. However, b = 1
The radiated power intensity H _b (f, θ) of the beams other than is dependent on the frequency f, and the received power of a signal having a frequency apart from the carrier frequency f _c is attenuated. For example, when L = 16, the incident angle θ
The beam (b = 8) formed in the direction of = 61 ° is shown in FIG.
Radiated power intensity H ₈ (f, θ) as shown in FIG. Here, in FIG. 7, the vertical axis represents relative power based on the power at the carrier frequency f _c , and the horizontal axis represents the carrier frequency f.
It is represented by a standardized frequency standardized with c as a reference.
That is, since the multi-beam former 7 operates as a kind of band pass filter for a signal incident from a direction other than the incident angle θ = 0, the multi-beam former 7 has a wider frequency range than the pass band of the band pass filter. Of the wide band signal that it has, a signal outside the pass band having a frequency away from the carrier frequency f _c is attenuated and output as a narrow band signal. Here, the pass band of the band pass filter is determined corresponding to the incident angle θ. Thus, the load factor W _bi
A multi-beam former 7 configured by using a weight coefficient unit 71-bi preset as a value independent of frequency.
Operates as a kind of band-pass filter for a signal incident from a direction other than the incident angle θ = 0. Therefore, in the present embodiment in which the desired signal has a wide band, the narrow band is smaller than that of the desired signal. N signals y ₁ (m), y of
₂ (m), ..., Y _N (m) are output.

The signal selector 8 outputs N signals y ₁ (m), y ₂ (m), ..., Y from the multi-beam former 7.
_A plurality of M signals are selected from _N (m) and the selected signals yn _{1 to} yn _M are output to the FIR digital filters 9-1 to 9-M, respectively. Here, in the present embodiment, the selection method is such that a plurality of M signals are selected in descending order of power. However, the present invention is not limited to this, and another method such as selecting a signal having power equal to or higher than a predetermined threshold may be used. Further, the number M of signals to be selected is a predetermined integer equal to or less than the number N of beams and is determined according to the number L of antenna elements and the number of expected interference waves.
Preferably, it is set to about half to 1/4 of the number L of antenna elements.

As shown in FIG. 2, the FIR digital filter 9-k includes (q-1) delay units 91-1 to 9-1.
1- (q-1) and a plurality of q multipliers 92-1 to 92
-Q and (q-1) adders 93-1 to 93- (q
-1) and. Here, k = 1, 2, ..., M, and the same applies hereinafter unless otherwise specified in this specification. The signal yn _k (m) input to the FIR digital filter 9-k is supplied to the delay unit 91-1 and the multiplier 9
2-1, and part of the signal yn _k (m) is input to the first coefficient controller 11a. Also, FI
Weighting factor w input to R-type digital filter 9-k
_{k, s-1} is input to the multiplier 92-s (s = 1, 2, ..., Q).

In the FIR type digital filter 9-k, the delay device 91-s (s = 1, 2, ..., Q-2) delays the input signal yn _k (m-s + 1) by one sample period. The signal yn _k (m-
s) to delay device 91- (s + 1) and multiplier 92- (s +
1) and the first coefficient controller 11a. Further, the delay device 91- (q-1) outputs the input signal yn _k (m-
q + 2) is delayed by one sample period and delayed by one sample period, and the signal yn _k (m−q + 1) is multiplied by the multiplier 92-q.
And to the first coefficient controller 11a. Multiplier 92-
1 is the input signal yn _k (m) and the weighting factor w
It is multiplied by _{k, 0} (m) and output to the adder 93-1.
The multiplier 92-s (s = 2, 3, ..., Q) multiplies the input signal yn _k (m−s + 1) by the weighting coefficient w _{k, s−1} (m), and the adder 93 -(S-1). The adder 93-1 adds the signal input from the multiplier 92-1 and the signal input from the multiplier 92-2, and adds the signal to the adder 9-1.
Output to 3-2. Adder 93-s (s = 2, 3, ...,
q-2) adds the signal input from the adder 93- (s-1) and the signal input from the multiplier 92- (s + 1), and outputs the result to the adder 93- (s + 1). Adder 9
3- (q-1) adds the signal input from the adder 93- (q-2) and the signal input from the multiplier 92-q and outputs the result to the adder 10.

The FIR type digital filter 9-k constructed as described above has the respective weighting factors w _{k, 0} (m), w _{k, 1} (m), ... Which are inputted from the first coefficient controller 11a. , W
_{Based on k, q-1} (m), the signal yn _k (m) input from the signal selector 8 is digitally filtered to adder 10
Output to The structure of the FIR digital filters 9-1 to 9-M in FIG. 2 is a direct type, but other structures,
For example, a cascade type or a lattice type may be used. However, FIR
The calculation method of the weighting factor input to the digital filter of the digital type differs depending on the structure of the digital filter of the FIR type.

Further, the first coefficient controller 11a of the adaptive digital beamforming apparatus is based on the signal yn _k (m) input from the FIR digital filter 9-k, as in the first conventional example. In the output signal z (m), the weighting factors w _{k, 0} (m), w _{k, 1} (m), ..., To extract a wideband desired signal and suppress a wideband interference signal.
By calculating w _{k, q-1} (m), the weighting factors w _{k, 0} (m), w
Output _{k, 1} (m), ..., W _{k, q-1} (m) to the FIR digital filter 9-k. Here, in the embodiment,
The first coefficient controller 11a uses the FIR, as will be described later in detail.
Weighting factors w _{k, 0} (m), w so that the envelope of the signal output from the digital filter 9-k is kept constant.
_{k, 1} (m), ..., W _{k, q-1} (m) are calculated. In addition, in the embodiment, the number of weighting factors to be calculated is q × M, which is a smaller number than the q × L number of the first conventional example. Furthermore, each of these weighting factors w _{k, 0} (m), w
_{k, 1} (m), ..., W _{k, q-1} (m) are generally complex numbers.

The adder 10 adds the output signals of the FIR digital filters 9-1 to 9-M and outputs a desired output signal z (m) in which the added interference signal is suppressed. Here, FIR digital filters 9-1 to 9
-M causes the multi-beam former 7 to attenuate and output a signal having a frequency distant from the carrier frequency as described above. Therefore, for the input signals yn ₁ (m) to yn _M (m), It is configured to have a frequency characteristic that cancels the influence of the multi-beam former 7. For example, the desired signal y corresponding to a beam with an incident angle θ = 61 °
₈ (m) is selected by the signal selector 8 and the signal yn ₁
If it is input as, to correct the frequency characteristic of FIG. 7, as compared to the gain of the frequency near the carrier frequency f _c, FIR type digital filter so that the gain becomes large at a frequency away from the carrier frequency f _c The gain of 9-k is set so that the amplitude characteristics of the multi-beam former 7 and the FIR digital filter 9-k are flat in the frequency range of the wideband signal. Further, since the null formed by the multi-beam former 7 has a narrow band, the amplitude characteristics of the multi-beam former 7 and the FIR type digital filter 9-k are the same as those of the interference signal of the wide band for the interference signal. The amplitude value is configured to be almost 0 in the frequency range. As a result, a wideband beam is directed in the direction of arrival of the desired signal, and a wideband null is formed in the direction of the interference signal. That is, the signal y ₁ beam-formed by the multi-beam former 7
Although (m) to y _N (m) are narrow band signals as described above, they are subjected to beam forming processing again by the subsequent FIR digital filter 9-k and added to form a wide band desired signal. It is corrected and output. The configuration in which some of the signals output from the multi-beam former 7 are selected and the beam forming process is performed again as described above is called a beam space type configuration because the beam is the control target.

Next, the arithmetic processing in the first coefficient controller 11a will be described in detail. As described above, in the adaptive digital beamforming apparatus of FIG. 1, the first coefficient controller 11a uses the FIR digital filter so as to keep the envelope of the output signal z (m) of the adaptive digital beamforming apparatus constant. 9-k weighting factor w
_{k, 0} (m), w _{k, 1} (m), ..., W _{k, q-1} (m) are calculated and output.

An algorithm for suppressing the interference signal by controlling the weighting factor so as to keep the envelope of the output signal of the adaptive digital beam forming apparatus constant is a CMA (Const).
ant Modulus Algorithm) processing. This is a signal where the envelope of the desired signal is constant, eg FM signal, F
This is effective for SK signals and PSK signals. LMS
Unlike the (Least Mean Square) algorithm, there is an advantage that a reference signal is not required. Regarding the CMA processing, the prior art document 3 “J. Tre Trechler et al.,“ Anew ”
approach to multipath correction of constant modul
us signals ”, IEEE Transactions on Acoustic
s, Speech, and Signal Processing, vol. ASS
P-31, No. 2, pp. 459-472, 1983 4
Details are given in the month.

In the adaptive digital beamforming apparatus shown in FIG. 1, the first coefficient controller 11a executes the following CMA processing to execute the FIR of the direct type configuration shown in FIG.
Coefficient w of the digital filters 9-1 to 9-M
_{k, 0} (m), w _{k, 1} (m), ..., W _{k, q-1} (m) are calculated. Next, the CMA processing used in this embodiment will be described. First, the evaluation function J is defined as in Expression 4.
Here, Ε [·] is an expected value and σ is a desired envelope value.

[0034]

[Equation 4] J = (1/4) E [│z (m) │ ² −σ ² ]

Further, as in equations (5) and (6), the signal vector Y (m) at time m and the weighting factors w _{k, 0} (m), w of the FIR digital filters 9-1 to 9-M are _obtained.
A coefficient vector W consisting of _{k, 1} (m), ..., W _{k, q-1} (m)
Define (m). Here, only the elements of the kth block are shown in the equations 5 and 6, but k = 1, 2, ..., M, and the right side of the equations 5 and 6 is a column of the number of elements (M × q). Is a vector. Further, in Expressions 5 and 6, [·] ^T represents a transposed matrix.

[0036]

## EQU5 ## Y (m) = [yn _k (m), yn _k (m-1), ..., y
n _k (m−q + 1)] ^T

## EQU6 ## W (m) = [w _{k, 0} (m), w _{k, 1} (m), ..., W _{k, q-1} (m)] ^T

The coefficient vector W (m) that minimizes the evaluation function J of Equation 4 cannot be analytically obtained. Therefore,
The coefficient vector W (m) is sequentially updated using the gradient method. The updating equation of the coefficient vector W (m) in this case can be expressed as in Expression 7. Where the output signal z
(M) is expressed by Equation 8.

[0038]

(7) W (m + 1) = W (m) −μ [{│z (m) │2-σ
2} z (m) Y * (m)]

[Equation 8] ^{z (m) = W T (} m) Y (m)

In Expression 7, μ represents an appropriate positive constant and * represents a complex conjugate. μ is determined so that the coefficient vector W (m) converges. The initial value W (0) of the coefficient vector W (m) is set to 1 as the first coefficient of the FIR digital filter 9-k to which the signal with the maximum power is input among the output signals of the signal selector 8. , And set all other coefficients to 0.

By updating the coefficients of the FIR digital filters 9-1 to 9-M as shown in Equation 7, the FM signal, the FSK signal, and the PSK signal in which the envelope of the transmission signal transmitted from the transmitter is constant When receiving, for example, the interference signal can be suppressed and the desired signal can be extracted. At this time, a wideband beam is formed in the incident direction of the desired signal, and a wideband null is formed in the incident direction of the interference signal. This method limits the types of signals,
Since the prior knowledge about the incident direction of the signal is not required and the method is more practical than the coefficient control method with a constraint condition, the present embodiment is configured to update the load coefficient according to the equation (7).

In the adaptive digital beamforming apparatus of the embodiment described in detail above, the desired signal, which is a wideband propagating wave signal, is received by the L antenna elements 1-1 to 1-L together with the wideband interference signal. Then, the received signals received by the antenna elements 1-1 to 1-L are converted into digital signals by the A / D converters 3-1 to 3-L and low-pass filtered, respectively. The multi-beam former 7, which forms beams in different directions, performs beam forming processing once and outputs as _N signals y _{1 to} y _N. Then, the signal selector 8 selects and outputs the M signals yn _{1 to} yn _M among the _N signals y _{1 to} y _N , and the selected signal signals yn _{1 to} yn _M are respectively output. FIR type digital filters 9-1 to 9-
A weighting factor w _{k, 0} (m) calculated to extract a wideband desired signal and suppress a wideband interference signal by M,
The desired output signal z (m) in which the desired signal is extracted and the interference signal is suppressed is obtained by filtering and synthesizing based on w _{k, 1} (m), ..., W _{k, q-1} (m). Is output as an output signal of the adaptive digital beam forming apparatus.

As described above, the adaptive digital beam forming apparatus of the beam space type configuration according to the embodiment of the present invention includes the signal selector 8 and is the same as the first conventional example of the conventional element space type configuration shown in FIG. Since the number of weighting factors q × M to be calculated can be reduced as compared with the adaptive digital beam forming apparatus, the amount of calculation and the amount of hardware required for calculating the weighting factor can be greatly reduced.

Further, the adaptive digital beam forming apparatus of the embodiment of the beam space type has excellent noise resistance because the multi-beam former 7 also functions as a band pass filter so as to suppress noise. The calculation processing of the load coefficient in the coefficient controller 11a can be accurately executed.

<Modification> In the above embodiment, the mixer 4-k and the low-pass digital filter 5-k are used as the means for generating the digital in-phase / quadrature signal from the digital intermediate frequency signal. Of course, other methods are also possible. For example, it can be realized by using a digital Hilbert transformer and a mixer. Further, analog in-phase / quadrature signals may be generated from the analog intermediate frequency signal by analog signal processing, and then sampling and A / D conversion may be performed. The structure as described above has the same effect as that of the embodiment.

[0045]

EXAMPLE Next, the result of a simulation performed to confirm the operation of the adaptive digital beamforming apparatus of the embodiment will be described. FIG. 5 is a graph showing a radiation pattern of the array antenna 100 as a result of the simulation. The graph of FIG. 5 shows the relative power with respect to the angle indicating the beam emission direction. Here, the angle indicating the radiation direction of the beam is the antenna element 1-
It is represented by an angle between a straight line of straight lines 1 to 1-L and the radiation direction of the beam, and the relative power on the vertical axis is standardized with the power of the main beam as a reference. In the graph of FIG. 5, simulations are performed for three cases, where the frequency f is set to the carrier frequency fc, the frequency f is set to 0.95fc, and the frequency f is set to 1.05fc. Is shown for each case.

As is clear from the graph of FIG. 5, the arrival of the desired signal in both the case of the frequency f = fc, the case of the frequency f = 0.95fc and the case of the frequency f = 1.05fc. The main beam can be formed in the direction of 40 degrees, which is 60 degrees in the direction of arrival of the interference signal.
Nulls can be formed in the direction of degrees. That is, 10% of the carrier frequency fc in the incident direction of the desired signal.
It is shown that it is possible to form a relatively wideband beam having a band of 10 .ANG. And to form a relatively wideband null having a band of 10% with respect to the carrier frequency fc in the incident direction of the interference signal. . That is, according to the adaptive digital beamforming apparatus of the embodiment, it is possible to extract a desired signal in a relatively wide band and suppress an interference signal in a relatively wide band.

[0047]

According to the adaptive digital beamforming apparatus of the first aspect of the present invention, the weighting coefficient unit and the addition are provided between the plurality of conversion means and the plurality of M finite impulse response type digital filters. Beam forming means for outputting a plurality of N beam reception signals, and
Signal selecting means for selecting and outputting a plurality of M beam reception signals from the plurality of N beam reception signals output from the beam forming means. As a result, it is possible to provide an adaptive digital beamforming apparatus capable of coping with a wideband signal and reducing the number of weighting factors to be calculated as compared with the conventional example.

The adaptive digital beamforming apparatus according to a second aspect of the present invention is the adaptive digital beamforming apparatus according to the first aspect, wherein the coefficient control means determines the envelope of the signal output from the adaptive digital beamforming apparatus. Each of the above filter coefficients is calculated so as to keep it constant. As a result, when receiving an FM signal, an FSK signal, a PSK signal, etc. in which the envelope of the transmission signal transmitted from the transmitter is constant, the interference signal can be suppressed without requiring prior knowledge about the incident direction of the desired signal. Then, the desired signal can be extracted.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an adaptive digital beamforming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of an FIR digital filter 9-k of the adaptive digital beamforming apparatus of FIG.

FIG. 3 is a block diagram showing a configuration of a first conventional adaptive digital beamforming apparatus.

FIG. 4 is a block diagram showing a configuration of a second conventional adaptive digital beamforming apparatus.

5 is a graph showing a radiation pattern of a radiation beam emitted by the adaptive digital beamforming apparatus of FIG.

FIG. 6 is a block diagram showing a configuration of a multi-beam former 7 of FIG.

7 is a graph showing frequency characteristics of beams formed by the multi-beam former 7 of FIG.

[Explanation of symbols]

1-1 to 1-L ... Antenna element, 3-1 to 3-L ... A / D converter, 4-1 to 4-L ... Mixer, 5-1 to 5-L ... Low-pass digital filter, 6 ... digital local oscillator, 7 ... multi-beam former, 8 ... signal selector, 9-1 to 9-M ... FIR digital filter, 11a ... first coefficient controller, 10, 72-1 to 72-N, 93-1 to 93- (q
-1) ... Adder, 71-11 to 71-NL ... Weighting coefficient device, 91-1 to 91-q ... Delay device, 92-1 to 92-q ... Multiplier, 100 ... Array antenna.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 16, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction contents]

The signal selector 8 outputs N signals y ₁ (m), y ₂ (m), ..., Y from the multi-beam former 7.
_A plurality of M signals are selected from _N (m) and the selected signals yn ₁ (m) to yn _M (m) are output to FIR digital filters 9-1 to 9-M, respectively. Here, in the present embodiment, the selection method is such that a plurality of M signals are selected in descending order of power. However, the present invention is not limited to this, and another method such as selecting a signal having power equal to or higher than a predetermined threshold may be used. Also,
The number M of signals to be selected is a predetermined integer equal to or less than the number N of beams, and is determined according to the number L of antenna elements and the number of expected interference waves, but preferably from half the number L of antenna elements to 1 / It is set to about 4.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

The adder 10 adds the output signals of the FIR digital filters 9-1 to 9-M and outputs a desired output signal z (m) in which the added interference signal is suppressed. Here, FIR digital filters 9-1 to 9
-M causes the multi-beam former 7 to attenuate and output a signal having a frequency distant from the carrier frequency as described above. Therefore, for the input signals yn ₁ (m) to yn _M (m), It is configured to have a frequency characteristic that cancels the influence of the multi-beam former 7. For example, the desired signal y corresponding to a beam with an incident angle θ = 61 °
₈ (m) is selected by the signal selector 8 and the signal yn ₁
When input as (m), the FIR is set so that the gain at a frequency distant from the carrier frequency f _c is larger than the gain at a frequency near the carrier frequency f _c so as to correct the frequency characteristic of FIG. 7. Type digital filter 9-
The gain of k is set so that the amplitude characteristics of the multi-beam former 7 and the FIR digital filter 9-k are flat in the frequency range of the wideband signal. Further, since the null formed by the multi-beam former 7 has a narrow band, the amplitude characteristics of the multi-beam former 7 and the FIR type digital filter 9-k are the same as those of the interference signal of the wide band with respect to the interference signal. The amplitude value is configured to be almost 0 in the frequency range. As a result, a wideband beam is directed in the direction of arrival of the desired signal, and a wideband null is formed in the direction of the interference signal. That is, the signals y ₁ (m) to y _N (m) beam-formed by the multi-beam former 7 are narrow-band signals as described above, but they are beam-formed again by the subsequent FIR digital filter 9-k. By being processed and added, the desired signal having a wide band is corrected and output. The configuration in which some of the signals output from the multi-beam former 7 are selected and the beam forming process is performed again as described above is called a beam space type configuration because the beam is the control target.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0041

[Correction method] Change

[Correction contents]

In the adaptive digital beamforming apparatus of the embodiment described in detail above, the desired signal, which is a wideband propagating wave signal, is received by the L antenna elements 1-1 to 1-L together with the wideband interference signal. Then, the received signals received by the antenna elements 1-1 to 1-L are converted into digital signals by the A / D converters 3-1 to 3-L and low-pass filtered, respectively. The beam forming process is once performed by the multi-beam former 7 that forms beams in different directions, and the N signals y ₁ (m) to y
It is output as _N (m). Then, the signal selector 8 selects and outputs the M signals yn ₁ (m) to yn _M (m) of the _N signals y ₁ (m) to y _N (m), and selects them. Signal signals yn ₁ (m) to yn _M (m)
Is a weighting factor w calculated by each FIR type digital filter 9-1 to 9-M so as to extract a wideband desired signal and suppress a wideband interference signal.
_{k, 0 (m), w} k, 1 (m), ..., desired that w k, are synthesized after the wave Iro based on _q-1 (m), the desired signal is extracted, the interference signal is suppressed Output signal z (m) is output as an output signal of the adaptive digital beam forming apparatus.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Ryu Miura, Ryo Miura, 5 Seiraya-cho, Seika-cho, Soraku-gun, Kyoto Pref., Arai Optical Radio Communications Research Institute, Inc. (72) Inventor Yoshio Karasawa, Soraku, Kyoto Prefecture Gunma Seika-cho, Osamu Osamu, Osamu Osamu, 5 Mihiraya, AT Optical Optical Communication Laboratory

Claims (2)

[Claims] 1. An array antenna comprising a plurality of L antenna elements and respective reception signals received by the respective antenna elements are subjected to A / D conversion to output respective digital signals corresponding to the respective reception signals. A conversion means is provided so that a plurality L of weight coefficient units correspond to each of the antenna elements and a plurality N of weight coefficient units correspond to a plurality of N beams to be formed. A plurality of (L × N) weight coefficient units for multiplying each digital signal by a predetermined weight coefficient and outputting the result, and a plurality of L coefficient units for forming each of the beams. A plurality of N adders for adding and outputting L signals, and forming beams in a plurality of N different directions based on the respective digital signals output from the converting means, Beam forming means for outputting a plurality of N beam reception signals corresponding to the beam, and a signal for selecting and outputting a plurality of M beam reception signals from the plurality of N beam reception signals output from the beam forming means Selecting means, a plurality of M finite impulse response type digital filters for filtering and outputting the plurality of M beam reception signals inputted from the signal selecting means based on a plurality of filter coefficients, respectively, Based on the plurality of M beam reception signals output from the selecting means, the main beam of the array antenna is directed to the arrival direction of the desired signal and the arrival direction of the interference signal is within a predetermined frequency range including at least the frequency of the desired signal. Calculate a plurality of filter coefficients for the finite impulse response type digital filter to make the received signal level of Then, coefficient control means for outputting the plurality of filter coefficients to the corresponding finite impulse response type digital filters, respectively, and a plurality of M after filtering output from the plurality of M finite impulse response type digital filters. Means for adding and outputting the beam reception signals of the above, and an adaptive digital beamforming apparatus. 2. The adaptive controller according to claim 1, wherein the coefficient control means calculates each filter coefficient so that an envelope of a signal output from the adaptive digital beamforming apparatus is kept constant. Digital beam forming device.