JP3593960B2 - Multi-beam antenna equipment - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multi-beam antenna, and more particularly to a multi-beam antenna for Global Positioning System (GPS) signals using digital beamforming (DBF).
[0002]
[Prior art]
DGPS that can improve the accuracy of GPS while utilizing private signals is well known. DGPS is a system that transmits the error of a GPS signal at a known point to a mobile station to improve the accuracy and reliability of the mobile station. However, the accuracy and reliability of this system are based on the performance of the reference station. Is clear.
[0003]
In recent years, there has been a movement to use this DGPS system for transportation systems and the like. A system for transmitting a DGPS signal to a mobile using a geostationary satellite has been studied in the aviation field. In such a system, the number of GPS satellites is usually increased apparently, and a pseudo range is provided so that accurate positioning calculation can be performed even when the satellite arrangement is deteriorated. Therefore, the pseudo range providing device is not limited to the GPS satellite, but may be a geostationary satellite, a pseudo satellite installed on the ground, or the like, and the supply sources thereof are increasing.
[0004]
A problem that has always been a top risk in such systems and is being discussed around the world is the presence of interference affecting the GPS spectrum. In particular, there is a concern that the user's reception signal may be unlocked due to interference radio waves. In this case, the navigation signal cannot be received, and the continuity of the system is interrupted. This is because in the aviation and transportation fields, it is required that the system be available at all times due to its public nature.
[0005]
The United States Federal Aviation Administration (FAA) has been considering countermeasures against interfering radio waves since the beginning of system development, and reports on interfering radio wave problems (The Johns Hopkins University, Applied Physics Laboratory, GPS Risk Assessment Research, Japan, Philippines, Republic of Japan). 1999). It has also been considered in other reports (M. Geyer, DOT Volp Center, R. Frazier, FAA, FAA GPS Mitigation Program, ION-99, Nashville, TN, Septmber, 1999) and is considered as an international concern. ing. This is because, in the normal DGPS, when the interference due to the interference radio wave occurs, the accuracy of all the mobile stations using the correction value of the reference station system is deteriorated or the mobile station becomes unusable.
[0006]
Conventionally, as a first countermeasure method for such an interference wave, a method of forming a null in a direction of arrival of the interference wave using a phased array antenna using a phase shifter has been adopted. Further, as a second countermeasure method for the interference radio wave, when the direction of the transmission source such as GPS can be specified, a method of directing the beam of the phased array antenna to the transmitter has been considered.
[0007]
[Problems to be solved by the invention]
However, in the above-mentioned first countermeasure method, the first problem is that it is necessary to know the direction from which the interference radio wave arrives. Usually, the location where the interference wave is generated is unknown, and it is difficult to know the direction of arrival. Since the form of the interfering radio wave is also unknown, the direction can be identified by scanning NULL in the case of relatively easy CW or pulsed interfering wave, but a signal similar to the GPS signal is intentionally interfered with. In this case, it is very difficult to know the direction of arrival accurately (MUSIC method). A second problem is that the satellite near the formed NULL has a low received radio wave intensity.
[0008]
Further, the above-mentioned second countermeasure method has a problem that the apparatus becomes large-scale. This is because a phaser system is required for forming beams by the number of satellites. For example, as shown in FIG. 5, in a multi-beam antenna device using a 5 × 5 element antenna array 110, a GPS signal received by the 5 × 5 element antenna array 110 is transmitted to the first signal by the distributor 111. The signals are distributed and input to four phase shifter arrays from the phase shifter array 112 to the fourth phase shifter array 113.
[0009]
Each of the first to fourth phase shifter arrays 112 to 113 is provided with 25 phase shifters, and the signals from the elements of the antenna array 110 input to each phase shifter are respectively shifted. After being combined, they are supplied to corresponding combiners 114 to 115 and combined to output first to fourth beams toward the transmitter.
[0010]
As described above, the conventional multi-beam antenna apparatus shown in FIG. 5 requires 25 phase shifters to form one beam, whereas the GPS system receives GPS signals from at least four satellites or more. There is a need. Therefore, in order to stably track these satellites, it is necessary to control four or more beams. Therefore, it is necessary to prepare four phase shifter arrays each composed of 25 phase shifters and use a distributor 111 for coupling the antenna array 110 to the phase shifter array. Further, as shown in FIG. 5, combiners 114 to 115 for combining the output signals of the phase shifter arrays 112 to 113 are also required.
[0011]
Further, as a conventional multi-beam antenna device, a phased array antenna for obtaining a wide band using a DBF has been conventionally known (Japanese Patent Application Laid-Open No. 10-303634). In this conventional device, a virtual antenna is assumed in an area surrounded by a plurality of antenna elements, and an estimating unit obtains a coefficient corresponding to each of the plurality of antenna elements from the position vector of the virtual antenna and the plurality of antenna elements. The received I / Q data of the virtual antenna is estimated from the coefficients and the received I / Q data at the plurality of antenna elements. By estimating the virtual antenna, a combined output equivalent to that when the virtual antenna actually exists can be obtained. Since the size of the antenna can be increased by that amount, the band of the antenna element can be widened.
[0012]
However, in this conventional apparatus, there is a problem that the interference prevention function cannot be realized because there is no cooperation with the GPS. That is, the sampling between the DBF and the GPS correlator is asynchronous, so that a temporal quantum error occurs in the correlation result. At the same time, since only one direction can be obtained, the satellite necessary for the positioning calculation is obtained. This is a problem in that radio waves cannot always be received.
[0013]
The present invention has been made in view of the above points, and an object of the present invention is to provide a multi-beam antenna device for homing a GPS satellite or the like with a simplified device configuration.
[0014]
It is another object of the present invention to provide a multi-beam antenna apparatus capable of improving the reception sensitivity of each satellite and improving the reliability of GPS reception in an environment where an interfering wave exists.
[0015]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides n (n is an integer of 2 or more) antenna elements constituting an array antenna having digital beamforming, and satellites received by each of the n antenna elements. After detecting and separating the high-frequency signal into an I signal and a Q signal based on the local signal, and converting the signal into a digital signal synchronized with the local signal, n receiving modules provided for each of the n antenna elements, K signals (k is a number) that receive signals output from the receiving module as inputs, perform phase delay and weighting on a plurality of input signals, and then perform vector synthesis to output virtual directional signals, respectively. (Integer of 2 or more), a pseudo-random code generator for generating a pseudo-random code corresponding to a satellite to be received, and k signal processing units K correlators for correlating the output signal of the signal processing unit with the pseudo-random code and outputting the time of the largest correlation as the arrival time of the high-frequency signal; and k signals from the k correlators. Decoding means for decoding the information on the orbit data of the satellites contained in the satellite, and the direction of the signal output from the signal processing section for each of the k signal processing sections based on the information on the orbit data from the decoding means. Directivity control means for controlling the phase delay amount and the weighting value so as to track the satellite corresponding to the characteristic, and a pseudo-random code from a pseudo-random code generator is input as a synchronization signal to generate a local signal And a local signal generating means.
[0016]
According to the present invention, the relative position of the satellite is known based on the information on the orbit data of the satellite to be received from the decoding means, and the output signal of the directivity control means calculates the direction of the satellite by using the control signal. For each of the signal processing units, while controlling the amount of phase delay and weighting each so that the directivity of the signal output from the signal processing unit tracks the corresponding satellite, and a signal receiver from the satellite By using an array antenna (DBF antenna) with digital beamforming (DBF) with an interface, a large number of satellites can be tracked. According to the present invention, a virtual beam having directivity can be formed for each satellite.
[0017]
Here, each of the k signal processing units receives the signals output from the n receiving modules as inputs, and inputs a plurality of input signals based on a control signal from the directivity control unit. Phase delay and weighting means for varying the amount of phase delay and weighting given to the signal, and combining the signals from the phase delay and weighting means for vector synthesis and outputting a signal with virtual directivity Means, and is constituted by software or firmware. According to the present invention, since the signal processing unit is configured by software or firmware, the configuration of the signal processing unit can be simplified as compared with the case where the signal processing unit is configured by hardware.
[0019]
Further, in order to achieve the above object, the present invention is provided corresponding to k correlators, measures the variance of the correlation result output from the correlators, and the measured value is larger than a predetermined value. Signal quality determination means for comparing whether the measured value is greater than a predetermined value and outputting a flag signal indicating that interference has been received to the positioning calculation processing, and excluding the corresponding signal from the positioning calculation. It is characterized by having. According to the present invention, when the direction of the pseudo range providing device of the satellite coincides with the direction of the interference source by accident, a flag signal is output from the signal quality determination means to the positioning calculation processing, and the corresponding signal is excluded from the positioning calculation. Therefore, it is possible to avoid using a satellite that matches the direction of the interference source.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of a multi-beam antenna device according to the present invention. As shown in the figure, the multi-beam antenna device according to the present embodiment has n antenna elements 10 ₁ to 10 _n and _{n provided} in one-to-one correspondence with these antenna elements 10 ₁ to 10 n. number of the receiving module ₂₀ 1 to 20 _n, k-number of the signal processing unit ₃₀ 1 to 30 _k and the correlator provided in one-to-one correspondence with the output side of the signal processing unit ₃₀ 1 to 30 _k 41 _{1 to} 41 _k , signal quality determining means 42 _{1 to} 42 _k provided on the output side of these correlators on a one-to-one basis, message decoding means 43, pseudo random code generating means 44, pseudo random code receiving a pseudo random code from the code generator 44 as an input, a local signal generator 45 for supplying a local signal to the receiving module 20 ₁ to 20 _n, receiving the decoding result of the message decoding means 43 as an input, It is more configuration and directional control means 46 supplies a control signal to the No. processor ₃₀ 1 to 30 _k.
[0021]
Receiving module 20 _1, and one vector generating means 21 ₁ is composed of two A / D converters 22 ₁ and 23 ₁ Tokyo. Similarly, each of the other receiving modules ₂₀ 2 to 20 _n, is composed of one and the vector generating means ₂₁ 2 through 21 _n of the two A / D converter ₂₂ 2 through 22 _n and ₂₃ 2 ~ 23 _n ing. Further, the signal processing unit 301 has m inputs, m phase delay units 31 _{1 to} 31 _m , m weighting units 32 _{1 to} 32 _m, and m weighting units 32 _1. And a vector synthesizing means 33 for adding and synthesizing each output signal of .about.32 _m . Similarly, a signal processing unit 30 ₁ other signal processing unit 30 ₂ to 30 _m, and a and the m phase delay means, and the m weighting addition means, and one of the vector combining means.
[0022]
Next, the operation of the present embodiment will be described. RF signals received by the antenna elements ₁₀ 1 to 10 _n are supplied to the receiving module ₂₀ 1 to 20 _n provided correspondingly. In the receiving module ₂₀ 1 to 20 _n, on the basis of a local signal output from the local signal generator 45 an input high-frequency signal in the vector generating means ₂₁ 1 through 21 _n, frequency conversion to an intermediate frequency (IF) signal. Here, in frequency conversion performed using a mixer or the like, input phase information is stored. For this reason, the vector generating means 21 _{1 to} 21 _n separate the local signals output from the local signal generator 45 into signals orthogonal to each other, act on each of them with the input high-frequency signal, and perform frequency conversion to convert the I signal and the Q signal. It is possible to separate
[0023]
The I signal and the Q signal output from the vector generators 21 _{1 to} 21 _n respectively correspond to a real axis component and an imaginary axis component when the input RF signal is represented by a vector. These I signal and Q signal are supplied to A / D converters 22 _{1 to} 22 _n and 23 ₁ to 23 _n , respectively, where they are digitalized based on a sampling clock synchronized with a local signal from a local signal generator 45. converted to a signal, is distributed to the k is the signal processing unit ₃₀ 1 to 30 _k.
[0024]
The signal processing unit 30 ₁ to 30 _k is a processing unit that is built in software, is performed by the software of k distribution. Since all the signal processing unit ₃₀ 1 to 30 _k performs the same processing with the same configuration, it will be representatively described signal processing unit 30 _1, the signal processing unit 30 ₁ is input from the reception module ₂₀ 1 to 20 _n The output of the directivity control unit 46 is controlled by the amount of phase shift given to the digital signal by the m (= 2n) phase delay units 31 _{1 to} 31 _m and the value of the weight to be multiplied by the weighting units 32 _{1 to} 32 _m. The signals are controlled independently so that the maximum gains are directed in the directions of the n satellites according to the instruction of the signal, and the combining means 33 performs a vector combining operation to obtain virtual directivity. In this process, the interference wave components included in each of the antenna elements 10 ₁ to 10 _n are canceled and attenuated.
[0025]
Signal output from the signal processing unit ₃₀ 1 to 30 _k are supplied to the correlator ₄₁ 1 to 41 _k, where the correlation between the pseudo-random code corresponding to the GPS satellite to be received from the pseudo-random code generating means 44 Is taken. The correlators 41 _{1 to} 41 _k output the time of the output having the largest correlation to the positioning calculation processing as the arrival time of the GPS signal. The output signals of the correlators 41 _{1 to} 41 _k include information on the orbit data of the GPS satellite called a navigation message. This information is input to the message decoding means 43.
[0026]
The message decoding means 43 determines the arrangement of the GPS satellites based on the input orbit data and the current time, outputs the arrangement to the directivity control means 46, and generates a pseudo-random signal corresponding to the visible satellite. The satellite arrangement is transmitted to the code generation means 44. In the case of DGPS, the phase center coordinates of the antenna are known. Therefore, the relative direction of the pseudorange supply device such as a satellite can be calculated geometrically. Based on the calculated value, the value required to form a directional beam toward each GPS satellite is inputted from the directional control means 46 to the signal processing unit 30 ₁ to 30 _k.
[0027]
On the other hand, a synchronization signal is supplied from the pseudo random code generation means 44 to the local generator 45. Thus, I in the receiving module ₂₀ 1 to 20 _n, a signal that is detected in the Q baseband, the output digital signal of the A / D converter ₂₂ 1 through 22 _n and ₂₃ 1 ~ 23 _n is the GPS code and coherent , The quantization error in the correlation processing of the correlators 41 _{1 to} 41 _k can be minimized.
[0028]
The signal quality determination means 42 _{1 to} 42 _k measure the variance of the detection results of the correlators 41 _{1 to} 41 _k , and when the measured value is larger than a predetermined measured value, the signal Output to positioning calculation processing. Here, the positioning calculation process is a process of calculating the coordinates of the phase center of the GPS antenna based on the pseudo distance from each GPS satellite. If the flag signal is output from the a-th (a = 1 to k) signal quality determination unit 42a to the positioning calculation processing, it is determined that the signal quality from the GPS satellite located in the a-th beam direction has deteriorated. Exclude the pseudorange from that GPS satellite.
[0029]
It is known that the sun is also a kind of interference source. Even when the direction of the GPS satellite coincides with the direction of the sun, the signal quality from the GPS satellite deteriorates. Exclude However, even when the pseudo distance from the GPS satellite is excluded, the directivity of the virtual beam with respect to the GPS satellite is maintained. After that, there is a possibility that the interference will disappear.
[0030]
In this way, according to the present embodiment, a so-called DBF antenna for constructing a phased array antenna by software and a GPS receiving circuit are linked, and virtual n multi-beams are transmitted to n GPS satellites. Pointing and secure the required signal-to-jamming ratio.
[0031]
Next, the effect of the present embodiment will be described with reference to FIGS. FIG. 2 is a system diagram showing an example of the relationship between the multibeam antenna apparatus of the present invention, GPS satellites, and interference sources. In the figure, in a multi-beam antenna device 51 of the present invention, n virtual virtual beams 53 _{1 to} 53 having directivity are virtually provided by antenna elements (10 ₁ to 10 _{n in} FIG. 1) arranged on a hemisphere 53. _n is formed. Since each of the virtual beams 53 _{1 to} 53 _n has directivity to each of the GPS satellites SV # 1 to SV # n, an interference radio wave from the interference source 56 which can be considered to have been emitted from an unknown direction. 57 and the level of the interference wave caused by the multipath 55 in which the radio wave from the GPS satellite SV # 1 is reflected by the reflecting object 54 can be relatively reduced. Moreover, the use of the GPS satellites SV # 1~SV # n separate virtual beams ₅₃ 1 to 53 _n for each interference of the satellite each other can be reduced so-called internal interference.
[0032]
In addition, since a GPS satellite orbits the earth in one day, its angular velocity changes as slowly as the sun. In the present invention, the reception sensitivity to each GPS satellite is improved because the virtual beam always tracks the satellite direction instead of time division while the GPS satellite is visible.
[0033]
FIG. 3 shows a pattern calculation result of an antenna array having an opening surface of 2500 mm to 300 mm. As shown in the figure, the beam width is about 5 degrees, which is an angle at which a GPS satellite passes in about 20 minutes. With this directivity, it is possible to attenuate signals outside the beam by about 30 degrees. In other words, it is possible to improve the interference resistance performance by 30 dB.
[0034]
Further, in the multi-beam antenna device of this embodiment, a multi-order beam signal processor required to form a 30 ₁ to 30 _n are implemented in software or firmware, the multi-beam antenna device across a relatively simple hardware It can be realized by. In addition, since the reception sensitivity is improved and the S / N from each GPS satellite is improved, the fluctuation component included in the pseudorange is reduced, and the beam tracks the satellite direction while the satellite is visible. available pseudoranges same time satellite positioning calculation, it is possible to exclude the pseudoranges from more signal quality judging means 42 ₁ through 42 _k satellite signal quality is deteriorated by, accuracy can be improved.
[0035]
Further, in the present embodiment, when the direction of the sun coincides with the direction of the GPS satellite, the GPS satellite can not be used, and therefore, it is possible to cope with solar interference. In the above embodiment, n virtual beams are directed to n GPS satellites, but one or more of them may be directed to a terrestrial pseudo satellite. In that case, the level change of the signal from the pseudo satellite installed on the ground is much larger than the level change of the GPS signal from the GPS satellite. In the present embodiment, however, the directivity to the pseudo satellite installed on the ground is changed. Since the gain can be made smaller than that for the GPS satellites by the message decoding means 43 and the directivity control means 46, the near-far problem of the pseudolite can be solved.
[0036]
Next, embodiments of the antenna system according to the present invention will be described. FIG. 4A shows an example in which elements are arranged on a hemisphere. By arranging a plurality of antenna elements on this hemisphere as shown by 52 in FIG. It has the ideal property that the gain change is small.
[0037]
The antenna system shown in FIG. 4B is a simple configuration example in which planes are connected to each other, and a multi-element antenna element is arranged on the planes 61 and 62 and the like. This antenna array does not require a curved surface correction operation. FIG. 4C shows a simpler antenna array. In FIG. 9C, a vertical array 63 has a plurality of antenna arrays, and constitutes an antenna system having directivity only in the vertical direction. This is a configuration in which one antenna element 64 is combined. In this antenna array, the ability to remove interference is reduced, but an antenna can be easily constructed.
[0038]
It should be noted that the arrangement of the antenna elements may be a configuration other than that shown in FIG. The signal processing unit 30 ₁ to 30 _k has been described as being configured by software can also be implemented in firmware, such as a digital signal processor (DSP).
[0039]
【The invention's effect】
As described above, according to the present invention, there are a number of features as follows.
(1) Directivity can be given to each satellite direction, so that the level of interference waves can be relatively reduced.
(2) Since directivity is provided in the direction of each satellite and multi-beams can be tracked, reception sensitivity to each satellite can be improved.
(3) Since different beams are used for each satellite, interference between satellites, so-called internal interference, can be reduced.
(4) Since a distributor, a phase delay unit, a weighting unit, a combining unit, and the like necessary for multi-beam formation are realized by software or firmware, these multi-beam antennas must be realized by relatively simple hardware. Can be.
(5) Since the receiving sensitivity is improved and the S / N from each satellite is improved for the reason of (4), the fluctuation component included in the pseudo range is reduced, and the time division is performed while the satellite is visible. Since the multi-beams are always tracked in the direction of the satellite, the pseudo-range of each satellite at the same time can be used for positioning calculation.In addition, the pseudo-range from the satellite whose signal quality has deteriorated can be excluded by the signal quality judgment means. Can be improved.
(6) When the direction of the GPS satellite coincides with the direction of the sun, the signal quality of the GPS signal received from the GPS satellite deteriorates. Therefore, by excluding the pseudorange, the GPS satellite can be not used. When it is a kind of interference source and is located outside the directional beam, sufficient attenuation is obtained, and the problem of solar interference can be solved.
(7) Since the directivity gain for the pseudo satellite installed on the ground can be set independently of the directivity gain for other GPS satellites, it is possible to solve the distance problem of the pseudo satellite.
[Brief description of the drawings]
FIG. 1 is a block diagram of one embodiment of the present invention.
FIG. 2 is a system diagram showing an example of a relationship between the multi-beam antenna device of the present invention, a GPS satellite, and an interference source.
FIG. 3 is a diagram illustrating an example of a pattern calculation result of an antenna array.
FIG. 4 is a diagram showing each example of an antenna array.
FIG. 5 is a block diagram of an example of the related art.
[Explanation of symbols]
10 ₁ to 10 _n antenna ₂₀ 1 to 20 _n receive module ₂₁ 1 through 21 _n vector generating means _{22 1 ~22 n, 23 1 ~23} n A / D converters ₃₀ 1 to 30 _k signal processing unit ₃₁ 1 to 31 _m Phase delay means 32 _{1 to} 32 _m weighting means 33 combining means 41 _{1 to} 41 _k correlator 42 _{1 to} 42 _k signal quality determining means 43 message decoding means 44 pseudo-random code generating means 45 local signal generator 46 directivity control means 51 Multibeam antenna device 52 Antenna arrays 531 to 53n arranged on a hemisphere Virtual beam 54 Reflecting object 55 Multipath 56 Interference source 57 Interfering radio waves SV # 1 to SV # n GPS satellites

Claims (3)

N (n is an integer of 2 or more) antenna elements constituting an array antenna having digital beamforming;
After the high-frequency signal from the satellite received by each of the n antenna elements, and detection and separated into I and Q signals based on the station unit signal into a digital signal synchronized with the local signal, the n receiving modules provided for every n antenna elements,
The signals output from the receiving module are respectively received as inputs, and a plurality of input signals are subjected to phase delay and weighting, and then vector-combined to output virtual directivity signals. Is an integer of 2 or more),
A pseudo-random code generator for generating a pseudo-random code corresponding to a satellite to be received;
The k signal processing units are provided corresponding to the k signal processing units, take a correlation between the output signal of the signal processing unit and the pseudo random code, and output a time having the largest correlation as an arrival time of the high frequency signal. A correlator,
Decoding means for decoding information on the orbit data of the satellite included in the signals from the k correlators,
On the basis of information on the orbit data from the decoding means, for each of the k signal processing units, the phase delay is set so that the directivity of a signal output from the signal processing unit tracks a corresponding satellite. Directivity control means for controlling the amount and the weighting value,
A local signal generating unit that receives the pseudo random code from the pseudo random code generator as a synchronization signal and generates the local signal ;
Provided corresponding to the k correlators, measures the variance of the correlation result output from the correlator, compares whether the measured value is greater than a predetermined value, and determines whether the measured value is a predetermined value. Signal quality determination means for outputting a flag signal indicating that interference has occurred to the positioning operation processing when the value is larger than the value, and excluding the corresponding signal from the positioning operation. Multi-beam antenna device. Each of the k signal processing units receives a signal output from each of the n receiving modules as an input, and inputs a plurality of input signals based on a control signal from the directivity control unit. Phase delay and weighting means for varying the amount of phase delay and weighting given to the signal, and a vector synthesis operation of the signal from the phase delay and weighting means to output a signal having virtual directivity 2. The multi-beam antenna according to claim 1, wherein said multi-beam antenna is composed of software or firmware. It said satellite is a multi-beam antenna device according to claim 1 or 2, characterized in that it includes at least a GPS satellite.

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