JP3096733B2 - Array antenna beam forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam forming method for an array antenna for automatically directing a reception beam in the direction of arrival of a desired communication signal, capturing and tracking the beam, and reducing interference caused by undesired communication signals. About the method.

[0002]

2. Description of the Related Art Conventionally, it has been desired to be able to selectively receive only a desired communication signal from communication signals transmitted from various directions and at various frequencies. Various techniques for satisfactorily receiving communication signals have been proposed.

As a first prior art, "Equivalence between adaptive array and spatial diversity by MMSE combining"
-Consideration on element spacing and subscriber capacity-, IEICE (Technical Research Report RCS97-249, p73-p80, 1998-02) "
As described in, an initial value is set as a weight for multiplying the received signal of each antenna element, and the difference between the known reference data sequence prepared on the receiving side at that time and the combined output signal of the array antenna is set as an error. This error signal is fed back so that this signal is minimized, and from each received signal by each antenna element and its error signal, a change in weight to multiply each received signal by each antenna element is calculated, and the change is calculated. There is a method in which the weight is repeatedly updated only to form a beam for capturing and tracking a desired communication signal and to suppress interference due to an undesired communication signal.

In the first prior art, weight control is performed so as to minimize the mean square error between the combined output signal of the array antenna and the known reference data sequence of the desired communication signal. Specifically, the peak of the beam is directed in the direction of arrival of the desired communication signal, and the valley of the beam is directed in the direction of arrival of the non-desired communication signal. Therefore, optimal beam formation for receiving the desired communication signal is achieved. The feature is that it can be realized and the operation is relatively simple.

[0005] As a second conventional example, a multi-wave suppression in high-speed digital land mobile communication using an adaptive array based on the SMI method, IEICE (Transactions of BI)
I, Vol. J75-B-II, No. 11, p806-p814, 1992-11) ”, the covariance matrix obtained from the received signal of each antenna element is successively updated every time. From this, the received signal of each antenna element, and a known reference data sequence prepared on the receiving side, a weight for multiplying the received signal of each antenna element is obtained, and a beam for capturing and tracking a desired communication signal is obtained. And suppressing interference by undesired communication signals.

In the above-mentioned second prior art, the feedback control is not performed at all, and the mean square error between the combined output signal of the array antenna and the known reference data sequence of the desired communication signal is minimized. The weight can be obtained. As a result, the peak of the beam is directed in the direction of arrival of the desired communication signal, and the valley of the beam is directed in the direction of arrival of the undesired communication signal, which is optimal for receiving the desired communication signal. Beam forming can be realized at high speed.

[0007] As a third conventional example, a method for constructing a self-beam steering array antenna for mobile satellite communication using DBF, IEICE (Transactions B-II, Vo
l. J79-B-II, No. 8, p448-458, 1996-08) ”and“ Experiment for tracking reception of satellite radio waves using an in-vehicle DBF self-beam steering array antenna ”, IEICE (Transactions B-II, Vol. . J80-B-II, No. 7, p547-p557, 1997-0
7), a reference signal sequence is not used, and a signal received by a specific one of the antenna elements or an antenna element having the strongest reception power, or a plurality of fixed signals oriented in a predetermined direction is used. By using the received signal of the beam having the highest received power among the beams instead of the reference data sequence, a weight for multiplying the received signal of each antenna element or each fixed beam is obtained, and a beam for capturing and tracking a desired communication signal is formed. There is a way.

In the third prior art described above, the beam peak can be directed to the arrival direction of the desired communication signal without performing any feedback control, and the communication signal has a known reference data sequence. It has the feature that there is no need.

[0009]

However, in the first prior art, since the control of the weight is performed by the feedback control, it is difficult to achieve both high speed response and stability or complicated computation. There was a disadvantage.
In addition, when the number of antenna elements in the array antenna is large or when there are many undesired communication signals, the number of weights to be controlled increases, and the possibility that the response speed and stability are impaired increases. There were also points.

In the second prior art, since it is necessary to sequentially calculate an inverse matrix of a covariance matrix composed of sample values of signals received by each antenna element of the array antenna, a high processing capability for complicated calculations is required. In addition, there is a problem that the complexity increases exponentially as the number of antenna elements increases.

Moreover, in both the first prior art and the second prior art, the mean square of the reference data sequence and the received signal of the array antenna is mainly set by directing a deep beam valley in the arrival direction of the undesired signal. The error has been minimized, and there is a tendency to aim the beam peak in the direction of arrival of the desired signal, but the problem is that the maximum gain determined by the number of antenna elements is not always aimed. There was a point.
This is a problem particularly when the power that can be received is weak and the communication line itself cannot be established unless the antenna has a gain greater than a certain value.

Further, in both the first prior art and the second prior art, when a transmission beam having a frequency different from that of the reception is formed in the arrival direction of a desired communication signal by using the weight obtained in the reception, the weight is obtained in the reception. Even if frequency conversion is performed on the weights given, if the undesired communication signal is a reflected wave from a wall or the like, the propagation path and the arrival direction may be different due to the difference in frequency. However, there is a problem that the valley of the transmission beam by the array antenna may not be directed but the mountain may be directed.

In the third prior art, when an undesired communication signal arrives at the same time, a small beam peak is also directed in that direction, causing interference. That is, in this method, it is not possible to distinguish whether the signal received by the array antenna is a desired communication signal or a non-desired communication signal. Therefore, it is assumed that the strongest arriving signal is the desired communication signal and the beam is directed to that direction. When the power of the undesired communication signal is higher than the power of the desired communication signal, the undesired communication signal is regarded as the desired communication signal, and there is a problem that the beam peak is directed to that. .

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a beam forming method for an array antenna according to the present invention has an unknown effect on an array antenna composed of a plurality of antenna elements. It is assumed that the desired communication signal modulated from the direction shown in FIG. 2 is received, and that the desired communication signal is accompanied by a predetermined number of bits for each given time with a reference data sequence known on the receiving side, and that the reception timing is known. A signal received from an antenna is converted into a complex baseband signal composed of in-phase and quadrature components by a local oscillator having a common frequency and a common but arbitrary fixed phase for each antenna element, which is output for each antenna element and, by the replica signal converted into complex base band signal is generated at the receiving side the known reference data sequences at the same timing as the reception, the replication Shin Is multiplied by the complex conjugate of the received complex baseband signal for each antenna element, the in-phase and quadrature components are passed through a low-pass filter or a band-pass filter, respectively, and the complex weight is used as the complex weight of the received complex baseband signal for each antenna element. By multiplying each band signal and adding the result of the multiplication by the number of antenna elements, a composite output signal directed to the arrival direction of the desired communication signal is formed as a reception beam of the array antenna.

According to a second aspect of the present invention, there is provided a beam forming method for an array antenna according to the first aspect, wherein a duplicate signal obtained by converting a known reference data sequence prepared on the receiving side into a complex baseband signal, When multiplying the complex weight obtained by passing the multiplication result of the received complex baseband signal with the complex conjugate through a low-pass filter or a band-pass filter to the complex baseband signal received by each of the antenna elements, By forcibly setting the complex weight to zero on condition that the energy of the weight is equal to or less than a predetermined threshold, a plurality of undesired communication signals arrive at the same frequency simultaneously from different directions from the desired communication signal. In this case, the interference due to the undesired communication signal can be suppressed.

According to a third aspect of the present invention, there is provided a beam forming method for an array antenna, wherein a desired communication signal modulated from an unknown direction arrives at an array antenna composed of a plurality of antenna elements, and the desired communication signal is present at a certain time. A predetermined number of bits are associated with a known reference data sequence on the receiving side, and the reception timing is assumed to be known, and a signal received from the array antenna is shared by each antenna element at a common frequency and common but arbitrary Is converted into a complex baseband signal composed of in-phase and quadrature components by a local oscillator having a fixed phase, and a fixed beam directed in a plurality of predetermined directions viewed from the array antenna by a plurality of complex baseband signals by spatial discrete Fourier transform. into a received complex baseband signal by, and outputs it to each fixed beam, same type as the reception The known reference data series replicated signal converted into complex base band signal is generated at the receiving side ring, the replica signal by multiplying the complex conjugate of the received complex baseband signal for each said respective fixed beams, the phase and Each of the orthogonal components is passed through a low-pass filter or a band-pass filter, and the received complex baseband signal for each fixed beam is multiplied as a complex weight.
By adding all the multiplication results by the number of fixed beams, a combined output signal directed to the arrival direction of the desired communication signal is formed as a reception beam of the array antenna.

According to a fourth aspect of the present invention, there is provided a beam forming method for an array antenna according to the third aspect, wherein a replicated signal obtained by converting a known reference data sequence prepared on the receiving side into a complex baseband signal is directed in a plurality of directions. The complex weights obtained by passing the result of multiplication with the complex conjugate of the received complex baseband signal for each received complex baseband signal by each fixed beam through a low-pass filter or a band-pass filter,
When multiplying the received complex baseband signal by each of the fixed beams, respectively, on condition that the energy of the complex weight is equal to or less than a predetermined threshold, the complex weight is forcibly set to zero, whereby a plurality of Even when the undesired communication signal arrives at the same frequency at the same time from a different direction from the desired communication signal, the interference by the undesired communication signal can be suppressed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a receiving mechanism capable of embodying a beam forming method for an array antenna according to the present invention will be described with reference to the accompanying drawings.

The first embodiment shown in FIG. 1 is a functional block diagram schematically showing a receiving mechanism 1 for forming a beam by the output of an antenna element.

The receiving mechanism 1 includes an array antenna 2 (m
Antenna 2 _{1, 2} 2 of the device, and ... 2 consisting _m), the processing unit 31,3 ₂ before receiving received signals from each antenna element 2 ₁ to 2 _m, ..., 3 _m and each pre-processing unit ( FE) 3 ₁ -3
Each antenna element with respect to the pre-processed signal in _m 2 ₁ to 2
a level adjuster 4 ₁ for setting an excitation amplitude distribution according to _m ,
4 _2, ..., 4 and _m, a power selector 5 the signal level to selectively pass only a signal corresponding to more than a predetermined threshold value from each level adjustment part 4 ₁ to 4 _m, said power selector 5 And a reference data sequence generator (SQG) 7 for supplying a replica signal of a known reference data sequence to the beam forming device 6.

In the first embodiment, the n number of communication signals S _{1 to} S _n of the same frequency including the desired communication signal S _i from different signal sources in different directions are provided to the m-element array antenna 2.
, Arrive at the same time, by directly calculating a copy of the reference data sequence for the antenna element output signal,
Only the arrival direction of the desired communication signal S _i from the incoming signal S ₁ to S _n while suppressing as much as possible interference of the non-desired communication signal directing the beam, as it separates received only S _i obtained as array combining output is there. Note each antenna element 2 ₁ to 2 _m
Is assumed to have a wide beam width including all incoming signal directions.

Hereinafter, the operation principle of this embodiment will be described.

The received signals from the antenna elements 2 ₁ to 2 _m pass through pre-processing sections 3 _{1 to} 3 _{m including} an amplifier, a frequency conversion section, an A / D converter, a quasi-synchronous detection section, and the like. Is input to the beam forming apparatus 6 at the sample period of the. Each input signal to the beam forming apparatus 6 is a complex baseband signal composed of an in-phase component and a quadrature component when viewed from the phase of the local oscillation signal in the quasi-synchronous detection unit. Bn as a function
(t) (n = 1, 2,..., m).

On the other hand, a replica ri (t) of the known reference data sequence included in the desired received signal S _i is also generated as a complex baseband signal in the reference data sequence generator 7 at the same timing as the reception, and the beam forming device 6 To enter.

In the beam forming apparatus 6, each antenna element 2
₁ complex conjugate bn ^* (t) and the reference data sequence replication ri of each input signal from to 2 _m bn (t) a (t) by multiplying each result of each low-pass filter (LPF) 6a ₁ ~ obtaining weights wn (t) for the array combined through 6a _m. Note that a band-pass filter may be used instead of the low-pass filter.

This Wn (t) is expressed by the following equation.

[0027]

(Equation 1)

[0028] In the above equation, "¯" means averaged by the low-pass filter 6a ₁ ~6a _m. Also,
The content of “￣” is an amplitude component proportional to | bn (t) |
The phase difference between n (t) and ri (t) is used as a phase component, and the phase fluctuation component due to data modulation is cancelled, which is a weight for performing maximum ratio combining. This operation is performed by the following in-phase component I and quadrature component Q in an actual signal processing circuit.
And low-pass filtering alone, and the operation is extremely simple.

[0029]

(Equation 2)

[0030] multiplied by this wn (t) to the input bn (t) from the antenna element _{2 1 ~2 m, n = 1,2} , ..., by adding at m, a gain for the desired communication signals S _i Is formed, and the gain in the direction of arrival of another undesired communication signal becomes lower. At this time, the array synthesized output signal is expressed by the following equation.

[0031]

(Equation 3)

In the receiving mechanism 1 according to the first embodiment,
Weight controllers 6c ₁ ~ before each weight multiplier unit 6b ₁ ~6b _m
Comprising a 6c _m, portions other than the reference data sequence in the communication signal for fixing the updating of the weights, and the control by the reference data timing to update or stopping of the weight carried out for each weight. Also, a low-pass filter 6a
₁ to compensate for the processing delays by ~6a _m, and a delay buffer 6d ₁ ~6d _m for timing the input signal bn (t) and the weight wn (t).

[0033] In the present embodiment, in order to reduce the beam sidelobe level for desired communication signals, when the number of antenna elements is large, the antenna elements 2 ₁ to 2 _m
As comprising level adjusting portion 4 ₁ to 4 _m for setting an appropriate excitation amplitude distribution for every effectively lowers the gain for undesired communication signals are also available mitigate interference due to this.

Further, the beam former 6 of the present embodiment, the directivity of the antenna element 2 ₁ to 2 _m is narrow, and each of the antenna elements 2 ₁ to 2 _m are oriented while aligned with each other the different directions In the case where all the signal arrival directions assumed in (1) are covered, that is, assuming a sector antenna or the like, a correlation selection unit 6e is provided, so that interference by undesired communication signals can be further suppressed.
The correlation selector 6e calculates the energy | wn (t) | ² of the weight obtained by the above equation 1, and forcibly sets the weight to zero only when the energy is equal to or less than a certain appropriate threshold value. is there. Thus, the input signal from the antenna element 2 ₁ to 2 _m of correlation facing the direction of arrival of low signal and the reference data sequence is not synthesized, it is possible to further suppress interference from undesired communication signals. In addition, a beam in a direction irrelevant to a desired communication signal can be obtained by the function of the correlation selecting unit 6e.
Since the truncation is performed at an early time, the initial acquisition of the desired communication signal can be accelerated as compared with the case where all the weights are selected.

Since a signal does not always come from all directions, in the case of a sector antenna, a threshold value is provided for the antenna element output, and only a signal having a threshold value or more is selected and selected. In the present embodiment, the power selection unit 5 is provided in preparation for a case where it is desirable to perform a subsequent beam forming operation only with the signal obtained. As a result, unnecessary calculations can be omitted, and the scale and processing time of the signal processing circuit can be saved in some cases.

The second embodiment shown in FIG. 2 is a functional block diagram schematically showing a receiving mechanism 1 'for forming a beam with a fixed multi-beam output.

In the function of the receiving mechanism 1 ', the same functions as those of the receiving mechanism 1 shown in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Thus, the receiving mechanism 1 '
It is characterized in that by interposing a multi-beam forming unit (MBF) 8 between the level adjusting unit 4 ₁ to 4 _m and the power selecting section 5.

[0038] In the second embodiment, the communication signals S ₁ to S _n of the n-number of the same frequency, including a desired communication signal S _i from each other from the different directions of different source array antenna 2 ₁ to 2 _m of m elements In the case of simultaneous arrival, a discrete multi-beam is applied to the antenna element output signal on the spatial axis to form a fixed multi-beam directed in a plurality of predetermined directions, and a reference data sequence is calculated for the output. by, incoming signals S ₁ to S by the arrival direction of the desired communication signal S _i while suppressing as much as possible interference of undesired communication signals from the _n to direct the beam, S _i only separated received by array combining output Is obtained. Directivity of each antenna element 2 ₁ to 2 _m, it is assumed that with a broad beam width including all of the incoming signal direction.

Hereinafter, the operation principle of the second embodiment will be described.

[0040] Also in the receiving mechanism 1 ', the same as the first embodiment, the received signal from each antenna element 2 ₁ to 2 _m, the amplifier, frequency converter, A / D converter, before consisting quasi synchronous detector, etc. processor 3 through the ₁ to 3 _m, is input to the beam forming device 6 in the sample period where the a / D converter has. These input signals are complex baseband signals composed of an in-phase component and a quadrature component when viewed from the phase of the local oscillation signal in the quasi-synchronous detection unit. The input signal from the k-th antenna element is expressed as xk (t ) (K = 1,
2, ..., m). At this time, the discrete Fourier transform on the spatial axis is represented by the following equation.

[0041]

(Equation 4)

In the above equation (4), ω is a rotator of the Fourier transform, and satisfies the following equation.

[0043]

(Equation 5)

Equation (4) shows that a fixed multi-beam is formed from the m-element antenna in m different directions orthogonal to each other, and the output is bn (t). The multi-beam forming unit 8 performs the processing. The output signals from the multi-beam forming unit 8, the fixed beam output of the incoming signal direction, even if the signal-to-noise power ratio of the signal received by each antenna element 2 ₁ ~2 _m (SNR) is low, the array antenna gain Since the SNR is increased by an amount closer to, the accuracy of the subsequent weight calculation can be improved.

Next, the above equation (1) is obtained by using the sequence copy ri (t).
(Or Equation 2) and by carrying out calculation according to formula 3, to maximize the gain for the desired communication signals S _i, the gain for the arrival direction of the other non-desired communication signal is formed beams, such as lower than, S An array composite output signal obtained by separating and receiving only _i is obtained.

In the second embodiment, since the beam width formed by the multi-beam forming unit 8 is narrow even though the beam width of each of the antenna elements 2 ₁ to 2 _m is wide, a sector antenna is used as the antenna element. As in the first embodiment used, a correlation selection unit 6e may be provided. In this case, interference by undesired communication signals can be further suppressed, and initial acquisition of desired communication signals can be accelerated.

Also, in the second embodiment, as in the case of the first embodiment in which the antenna element is a sector antenna, an incoming signal does not always come from all directions. A configuration in which a certain threshold value is provided, and only an output that exceeds the threshold value by the power selection unit 5 is selectively input to the beam forming apparatus 6, and a subsequent beam forming operation is performed using only the selected signal. There is.
As a result, unnecessary calculations can be omitted, and the scale of the signal processing circuit and the processing time can be saved in some cases.

Further, also in the second embodiment, as in the case of using a wide directivity antenna as the antenna element in the first embodiment, the number of antenna elements is reduced in order to reduce the side lobe of the beam for the desired communication signal. If large, the antenna elements 2 ₁ level adjustment unit 4 for each to 2 _{m 1} to 4 _m
With a configuration that gives an appropriate excitation amplitude distribution,
By combining this level adjusting unit 4 ₁ to 4 _m and the correlation selecting section 6e, and freely controlling the gain of the non-desired wave arrival direction can be reliably suppress interference due to this.

The third embodiment shown in FIG. 3 is a receiving mechanism 1 ″ that performs beam forming by fixed multi-beam output in a space division multiple access system by simultaneous acquisition and tracking of a plurality of incoming signals.
It is a functional block diagram showing the outline of.

In the function of the receiving mechanism 1 ″, the same functions as those of the receiving mechanisms 1 and 1 ′ shown in the first and second embodiments are denoted by the same reference numerals, and description thereof will be omitted. This receiving mechanism 1 ″ includes n ′ distributors (DIVs) 9 _{1 to} 9 _n ′, a channel converter 10, and a first
It is characterized by providing the n 'number of beamformer consisting beamformer 6 ₁ through n' beamformer 6 _n '.

That is, in the third embodiment, the first,
A plurality (n ′) of beam forming devices 6 in the second embodiment
And a plurality of beams are simultaneously directed to a plurality of communication signals transmitted at the same frequency from different communication partner stations located in different directions from each other, separated from each other, and obtained as separate array combined outputs. .

[0052] In this reception mechanism 1 ", the first beam forming units ₆₁ to a desired communication signal S _{1, 2} second beamformer 6 that a desired communication signal and S _2, ... a desired communication signal S _n N 'beamformer 6 _n '
comprising a n 'number of beamformer, each antenna element 2 ₁ -
Signal received by 2 _m are respectively distributed to the beam former in the distributor 9 ₁ ~9 _n '. Each beam forming device 6 ₁
In to 6 _n 'each generates a replica of separate reference data sequences, capture separate desired communication signal.
However, the distributor 9 ₁ to 9 _n 'is for performing a digital signal, there is no decrease in power due to distribution.

Further, since a plurality of communication signals arriving from close directions corresponding to the same beam width of the array antenna 2 cannot be spatially separated by beams, when frequency division multiple access is used together, Assign a different channel to each beam former 6 ₁ to 6 _n 'by means such as using a separate control channel, performs channel converted by the channel converting unit 10 corresponding, respectively proximity separate beams separated by frequency Form in the incoming signal direction.

Therefore, according to the third embodiment, communication signals arriving at the same frequency from different directions can be received while being separated from each other by the number (n ′) of beam forming devices 6 provided on the receiving side. . Also, a plurality of communication signals arriving from close directions can be received while being separated from each other by the number of available channels.
Therefore, compared to the case where the communication signal is separated and received only by the channel alone, the spatial separation is performed, so that the communication capacity can be greatly increased, and the peak of the reception beam of the array antenna 2 always becomes the communication partner. Since the transmission is directed toward the station, the transmission power of the partner station can be saved. Furthermore, since the receiving mechanism 1 ″ in the present embodiment does not include a feedback loop and can be realized only by simple arithmetic processing, the circuit scale can be saved, high-speed and stable operation can be expected, and a large number of antenna elements are provided. It is suitable for an array antenna or a fixed or mobile communication system having a high transmission rate.

The above-mentioned channel can be replaced with a time slot in time division multiple access, a spreading code in code division multiple access, or the like, in addition to the frequency.

Hereinafter, the operation of the third embodiment will be described with reference to computer simulation results. In the simulation, it is assumed that communication signals of the same frequency, the same level, and the same modulation scheme come from three different directions by a linear array in which 16 antenna elements are arranged on a straight line at half-wavelength intervals. The modulation method was four-phase phase shift keying (QPSK), the reference data sequence was a pseudo-random noise (PN) code of 10 symbols, and the sampling by the A / D converter was 16 samples per symbol. For clarifying the basic characteristics, the signal power to noise power ratio (CNR) of the received signal was set to 30 dB per antenna element. Each antenna element is omnidirectional, and a multi-beam forming unit (M
BF).

FIG. 4 shows three beam patterns when three beam forming devices (first to third beam forming devices 6 _{1 to} 6 ₃ ) perform beam forming on three arriving signals, respectively. Is shown. However, the excitation amplitude distribution was uniform, and power selection and correlation selection of the MBF output were not performed. From this figure, different beam peaks are automatically directed to each incoming signal direction,
It can be seen that the gain in the direction of arrival of the undesired communication signal is low, and three incoming signals are separated and received. However, small beam peaks of about −11 dB to −16 dB are also formed in the direction of the undesired communication signal, and it can be seen that the interference of the undesired communication signal is slightly received.

FIG. 5 shows the setting of the excitation amplitude distribution in the level adjustment section so that a low side lobe pattern called a Chebyshev directivity pattern is obtained,
3 shows three beam patterns when the correlation selection of the F output is performed. In each case, the beam in the desired communication signal direction hardly changes, and the gain in the non-desired communication signal direction is -30.
It can be seen that the interference is greatly reduced to less than dB, and interference due to this is suppressed.

[0059] Figure 6, when changing the excitation amplitude distribution set in the level adjusting unit 4 ₁ to 4 _m by the side lobe level set value shows a beam pattern directed to S ₁ arrival direction when three waves arriving . The gain of the S ₁ direction without substantial change, it can be seen that the S ₂ and S ₃ the direction of the gain which is undesired communication signals can be effectively reduced.

[0060]

As described above, the beam forming method for the array antenna according to the first aspect has the following effects.

(1) Even when a plurality of communication signals of the same frequency and the same modulation method arrive at the array antenna at the same time, if the arrival directions of the desired communication signal and the non-desired communication signal are not so close as to be indistinguishable. While automatically aiming and tracking the beam peak only in the direction of arrival of the desired communication signal, at the same time automatically reducing the gain in the direction of arrival of the undesired communication signal while reducing interference by the undesired communication signal Desired communication signals can be spatially separated and received.

(2) When a plurality of different communication signals arrive at the same frequency from different directions, separate beams can be formed in these directions of arrival, and these beams can be spatially separated from each other and received. Since the incoming signal is spatially separated, the communication capacity can be significantly increased as compared with a system that only performs channel separation.

(3) The operation for beam forming does not include a feedback loop and can be realized only by simple arithmetic processing. Therefore, the operation is fast and stable, the scale of the arithmetic processing circuit can be saved, and many operations can be performed. It is suitable for an array antenna having an antenna element and a beam forming method for a high-speed transmission system.

Also, in the beam forming method for an array antenna according to claim 2 which is dependent on claim 1,
Further, the following effects can be obtained.

(4) When each antenna element is a sector antenna, by performing correlation selection of the antenna element output, the gain in the undesired communication signal arrival direction can be further suppressed, and unnecessary output can be suppressed. Since early truncation occurs, early acquisition can be expedited.

(5) Even when each antenna element has a wide directivity, the gain in the arrival direction of the undesired communication signal can be largely suppressed by performing the correlation selection of the output of the multi-beam forming unit. In addition, since unnecessary outputs are truncated at an early stage, initial capture can be hastened.

(6) When a multi-beam forming unit is provided, the gain in the arrival direction of the undesired communication signal is further suppressed by a combination of the correlation selection of the output of the multi-beam forming unit and the setting of the excitation amplitude distribution by the level adjusting unit. And it can be controlled freely.

Further, in the beam forming method for an array antenna according to the third aspect, in addition to the effects (1) to (3) provided by the first aspect, a signal-to-noise power ratio of a received signal by the antenna element is provided. Even when (SNR) is low, the fixed beam output in the arriving signal direction among the output signals of the multi-beamformer increases the SNR by an amount close to the gain of the array antenna, so that the accuracy of the subsequent weight calculation can be improved. There is also an effect.

The beam forming method for an array antenna according to claim 4 which is a dependent claim of claim 3 further has the above-mentioned effects (4) to (6).

[Brief description of the drawings]

FIG. 1 is a functional block diagram showing a first embodiment of a receiving mechanism capable of implementing a beam forming method for an array antenna according to the present invention.

FIG. 2 is a functional block diagram showing a second embodiment of a receiving mechanism capable of embodying the array antenna beam forming method according to the present invention.

FIG. 3 is a functional block diagram showing a third embodiment of a receiving mechanism capable of realizing the array antenna beam forming method according to the present invention.

FIG. 4 shows a third embodiment having three beam forming devices.
FIG. 11 is a beam pattern characteristic diagram showing a computer simulation result when beam formation is performed on three incoming signals by the receiving mechanism according to the embodiment.

FIG. 5 shows a third example provided with three beam forming devices.
FIG. 8 is a beam pattern characteristic diagram showing a computer simulation result when beam forming is performed on three arriving signals under the condition that a Chebyshev directional pattern is obtained by the receiving mechanism according to the embodiment.

FIG. 6 shows a third example provided with three beam forming devices.
A beam pattern characteristic diagram showing a computer simulation result in a case where the excitation amplitude distribution setting in the level adjustment unit is changed by the side lobe level setting value and beam forming is performed on each of three incoming signals in the receiving mechanism according to the embodiment. It is.

[Explanation of symbols]

1 receiving mechanism _{2 1, 2 2, ... 2} m antenna elements _{31, 3 2, ..., 3} m preprocessing unit _{4 1, 4 2, ...,} 4 m level adjuster 5 power selector 6 beamformer 7 reference data Sequence generator

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-199927 (JP, A) JP-A-3-276903 (JP, A) JP-A-9-246843 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01Q 3/26

Claims (4)

(57) [Claims] 1. A desired communication signal modulated from an unknown direction arrives at an array antenna composed of a plurality of antenna elements, and a predetermined number of bits of the desired communication signal is provided at each reception time by a known reference signal on a receiving side. It is accompanied by a data sequence, and its reception timing is known. The received signal from the array antenna is converted from in-phase and quadrature components by a local oscillator having a common frequency and a common but arbitrary fixed phase for each antenna element. A complex baseband signal is converted into a complex baseband signal, and this is output for each antenna element. At the same timing as reception, a duplicate signal obtained by converting a known reference data sequence into a complex baseband signal is generated on the receiving side. Is multiplied by the complex conjugate of the received complex baseband signal for each antenna element, and its in-phase and quadrature components are respectively low-pass filtered. Or a band-pass filter, multiplies the received complex baseband signal for each antenna element as a complex weight, and adds all of the multiplication results by the number of antenna elements, thereby obtaining the arrival direction of the desired communication signal. A beam forming method for an array antenna, characterized in that a combined output signal directed to the antenna is formed as a receiving beam of the array antenna. 2. A low-pass filter or a multiplication result of a duplicate signal obtained by converting a known reference data sequence prepared on a receiving side into a complex baseband signal and a complex conjugate of a received complex baseband signal for each antenna element. When the complex weights obtained by passing through the band-pass filters are respectively multiplied by the complex baseband signals received by the antenna elements, the complex weights are set on condition that the energy of the complex weights is equal to or less than a predetermined threshold. By forcibly setting the weight to zero, even when a plurality of undesired communication signals simultaneously arrive at the same frequency from a different direction from the desired communication signal, interference by the undesired communication signal can be suppressed. The method of forming a beam of an array antenna according to claim 1, wherein: 3. A desired communication signal modulated from an unknown direction arrives at an array antenna constituted by a plurality of antenna elements, and a predetermined number of bits of the desired communication signal are provided for each predetermined time by a known reference signal on a receiving side. It is accompanied by a data sequence, and its reception timing is known. The received signal from the array antenna is converted from in-phase and quadrature components by a local oscillator having a common frequency and a common but arbitrary fixed phase for each antenna element. And converting the plurality of complex baseband signals into a received complex baseband signal by a fixed beam directed in a plurality of predetermined directions as viewed from the array antenna by a spatial discrete Fourier transform. outputs for each fixed beam, the known reference data sequences at the same timing as the reception complex base band signal Generate the converted duplicated signal on the receiving side, multiply this duplicated signal by the complex conjugate of the received complex baseband signal for each fixed beam, and convert the in-phase and quadrature components to a low-pass filter or a band-pass filter, respectively. Then, the complex output is multiplied by the received complex baseband signal for each fixed beam as a complex weight, and the multiplied results are all added by the number of fixed beams, thereby obtaining a combined output signal directed to the arrival direction of the desired communication signal. Is formed as a reception beam of the array antenna. 4. A duplication signal obtained by converting a known reference data sequence prepared on the receiving side into a complex baseband signal, and a reception complex baseband signal for each reception complex baseband signal by each fixed beam directed in a plurality of directions. When multiplying a complex weight obtained by passing a result of multiplication with a complex conjugate through a low-pass filter or a band-pass filter to a complex baseband signal received by each of the fixed beams,
On condition that the energy of the complex weight is equal to or less than a predetermined threshold, by forcibly setting the complex weight to zero, a plurality of undesired communication signals are simultaneously transmitted from different directions from the desired communication signal at the same frequency. 4. The array antenna beam forming method according to claim 3, wherein interference due to the undesired communication signal can be suppressed even when the signal arrives.