JP2012237705A - Azimuth and elevation angle measuring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an azimuth and elevation angle measuring system capable of measuring an azimuth and elevation angle of an incoming signal with high precision.SOLUTION: An azimuth and elevation angle measuring system includes: plural antennas 11-11; and a signal processor 15 that performs a radio wave propagation route estimation by ray tracing using an incoming wave number and incoming signals estimated based on plural antenna reception signals obtained from the plural antennas, to determine an incoming direction, and then measures an incoming azimuth and elevation angle with the determined incoming direction as the initial value.

Description

  Embodiments described herein relate generally to an azimuth / elevation angle measurement system that measures arrival directions and elevation angles of radio waves.

  The result of measuring the direction of arrival of radio waves received by the array antenna, that is, the direction of arrival and the elevation angle, includes an error due to the influence of coherent multipath. As a method for reducing this error, for example, the SAGE method is known (see Non-Patent Document 1 and Non-Patent Document 2). In the SAGE method, the number of incoming waves (including multipath waves) and the number of incoming signals are assumed, and an iterative process is performed until the value of an evaluation function for performing convergence determination converges.

  However, in the SAGE method described above, the convergence result may differ depending on the number of initial signals. There is no method for setting an appropriate value as the initial arrival signal. Therefore, generally, an appropriate number of signals is set and an initial arrival signal is randomly determined.

  As one of the initial value setting methods of the SAGE method shown in Non-Patent Document 1, the number of incoming signals is estimated using the method of Akaike's and Rissanen's criteria described in Non-Patent Document 3, and A method is known in which the arrival direction of an incoming signal is estimated by the MUSIC method shown in FIG. 4 and these estimated values are used as initial values. Then, a steering vector in the direction of arrival is generated using this method.

Bernard H. Fleury, et.al .: “Channel Parameter Estimation in Mobile Radio Environments Using the SAGE Algorithm’, IEEE J. Sel. Areas Commun., Vol. 17, no. 3, pp 434-450, March 1999. Yasuhiro Ishiguro, Nobuyoshi Kikuma, Hiroshi Hirayama, Kunio Hagiwara: “Square Weighted Array Antenna Calibration Method for Estimating Direction of Arrival of Radio Waves Using the SAGE Algorithm”, Theory of Science (B), vol.J93-B, No .2,2010. M.Wax and T.Kailath, “Detection of signals by information theoreteic criteria”, IEEE Trans.Acoust., Speech, Signal Processing, Vol.ASSP-33, Apr. 1985. Nobuyoshi Kikuma: "Applied signal processing by array antenna", Science and Technology Publishing, 1999.

  The precondition for using the Akaike's and Rissanen's criteria method described above is that the signal is independent and the noise is normally distributed, but in practice there is a coherent multipath signal that is not independent. Therefore, the number of received signals including coherent multipath signals is unclear. Also, it is difficult to set an appropriate value as an initial value for the direction of arrival of the coherent signal, particularly the elevation angle. As a result, there is a problem that the azimuth and elevation angle of the incoming signal cannot be measured accurately.

  An object of the present invention is to provide an azimuth / elevation angle measurement system capable of accurately measuring the azimuth and elevation angle of an incoming signal.

  According to the azimuth / elevation angle measurement system according to the embodiment, radio wave propagation path estimation is performed by ray tracing using a plurality of antennas and the number of arrival waves and the arrival signals estimated based on the plurality of antenna reception signals obtained from the plurality of antennas. And a signal processing device that measures the arrival direction and the elevation angle using the obtained arrival direction as an initial value.

It is a block diagram which shows the structure of the azimuth | direction / elevation angle measurement system which concerns on 1st Embodiment. It is a flowchart which shows operation | movement of the azimuth | direction / elevation angle measurement system which concerns on 1st Embodiment. It is a flowchart which shows the detail of the radio wave propagation path estimation and attenuation amount estimation which are performed with the azimuth | direction / elevation angle measurement system which concerns on 1st Embodiment. It is a figure for demonstrating the radio wave propagation path estimation performed with the azimuth | direction / elevation angle measurement system which concerns on 1st Embodiment. It is a figure for demonstrating the arrival direction estimation from the calculation position performed with the azimuth | direction / elevation angle measurement system which concerns on 1st Embodiment.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First embodiment

  FIG. 1 is a block diagram illustrating a configuration of an azimuth / elevation angle measurement system according to the first embodiment. The azimuth / elevation angle measurement system includes a signal processing system 1, a satellite signal processing system 2, an ionosphere observation system 3, an internet data processing system 4, and a data server system 5.

The signal processing system 1 is a part that performs array signal processing, and includes p antennas 11 _{1 to} 11 _p and p amplifiers 12 _{1 to} 12 _p and p antennas (p is an integer of 2 or more). Frequency converters 13 _{1 to} 13 _p , p digitizers 14 _{1 to} 14 _p , a signal processing device 15, and a display unit 16.

The p antennas 11 _{1 to} 11 _p receive radio waves coming from the outside, convert them into analog electric signals, and send them to the _p amplifiers 12 _{1 to} 12 _p , respectively.

The p amplifiers 12 _{1 to} 12 _p amplify the electric signals transmitted from the _p antennas 11 _{1 to} 11 _p , respectively, and send the amplified signals to the p frequency conversion units 13 _{1 to} 13 _p , respectively.

The p frequency conversion units 13 _{1 to} 13 _p convert the frequencies of the amplified electrical signals respectively transmitted from the _p amplifiers 12 _{1 to} 12 _p, and respectively convert them to the p digitizers 14 _{1 to} 14 _p . send.

The p digitizers 14 _{1 to} 14 _p convert the frequency-converted analog signals respectively transmitted from the _p frequency converters 13 _{1 to} 13 _p into digital signals, and send them to the signal processing device 15 as antenna reception signals. send.

The signal processing device 15 is a main part of the azimuth / elevation angle measurement system, and performs the arrival direction measurement of the incoming signal. The signal processing device 15 estimates the ionospheric electron density based on the p antenna reception signals respectively transmitted from the _p digitizers 14 _{1 to} 14 _{p in} order to estimate the direction of arrival, and performs radio wave propagation path estimation. .

  For the estimation of the ionospheric electron density, an IRI (International Reference Ionosphere) model or a TEC (Total Electron Contents) obtained by correcting the IRI model with a GPS signal from a GPS (Global Positioning System) satellite or the like can be used. The signal processing device 15 also performs ionospheric electron density estimation using ionosphere actual measurement data sent from the ionosphere observation system 3 and the Internet data observation system 4.

  The arrival direction estimation, ionospheric electron density estimation and radio wave propagation path estimation performed by the signal processing device 15 can be performed by a single CPU (Central Processing Unit) or in parallel by a plurality of CPUs. In the case of radio wave propagation path estimation, a predetermined calculation start location and arrival direction can be calculated simultaneously by a plurality of CPUs, and the results of arrival direction measurement can be combined.

  The display unit 16 is composed of a personal computer including a display, and displays a processing result in the signal processing device 15. The display unit 16 can be configured to prepare a plurality of personal computers and perform processing in parallel.

  The satellite signal processing system 2 includes a satellite signal receiving antenna 21, a satellite signal receiver 22, and a satellite signal processing device 23. The satellite signal receiving antenna 21 receives a plurality of radio waves transmitted from GPS satellites or Galileo satellites, etc., converts them into electrical signals, and sends them to the satellite signal receiver 22.

  The satellite signal receiver 22 amplifies a plurality of electrical signals sent from the satellite signal receiving antenna 21 and sends them to the satellite signal processing device 23. The satellite signal processing device 23 acquires pseudoranges, phases, and orbits from a plurality of signals sent from the satellite signal receiver 22 and sends them to the signal processing system 1 and the data server system 5.

  The ionosphere observation system 3 includes an ionosonde antenna 31, an ionosonde 32, and an ionosonde collection data processing device 33. The ionosonde antenna 31 radiates pulse radio waves to the sky, receives radio waves reflected by the ionosphere, converts them into electrical signals, and sends them to the ionosonde 32.

  The ionosonde 32 generates an ionogram representing the distribution of the ionized gas from the electrical signal sent from the ionosonde antenna 31 to obtain the delay time from the emission of the pulse radio wave to the reception of the reflected wave, and the ionosonde collection data processing device Send to 33. The ionosonde collection data processing device 33 calculates the coastal frequency of the ionosphere from the ionogram sent from the ionosonde 32 and sends it to the signal processing system 1 and the data server system 5.

  The Internet data processing system 4 includes a network connection device 41 and a GEONET collection data processing device 42. The network connection device 41 is composed of a switching hub or a router, and connects the Internet data processing system 4 to another system. The GEONET collection data processing device 42 is constituted by, for example, a personal computer including a display, obtains ionospheric observation information or satellite observation information, and sends it to the signal processing system 1 and the data server system 5. The GEONET collected data processing device 42 is connected to an external Internet network.

  The data server system 5 includes a data collection server 51 and a recording device 52 which are personal computers including a display. The data collection server 51 receives the data processed by the signal processing system 1, the satellite signal processing system 2, the ionosphere observation system 3, and the Internet data processing system 4 described above and records the data in the recording device 52. The recorded data is read out and transmitted to the signal processing system 1, the satellite signal processing system 2, the ionosphere observation system 3, and the Internet data processing system 4, and the data recorded in the recording device 52 is deleted.

  Next, the operation of the azimuth / elevation angle measurement system according to the first embodiment configured as described above will be described. FIG. 2 is a flowchart showing an arrival direction initial value estimation process executed in the azimuth / elevation angle measurement system according to the first embodiment. The processing shown below is mainly executed in the signal processing system 1.

In the arrival direction initial value estimation process, first, reception signal covariance matrix creation / eigenvalue / eigenvector calculation is executed (step S11). Details will be described below. The signal s received by the antennas 11 _{1 to} 11 _p of the signal processing system 1 is expressed by the following equation (1).

here,

Here, E [•] means that an expected value is calculated, R is a covariance matrix of the observed signal, Es is a signal eigenvector, Λ is a matrix having eigenvalues as diagonal elements, and σ is a noise standard Deviation, I represents a unit matrix, and H represents Hermitian transpose. m ₁ ~m _p shows the eigenvalues. Among these, m _{1 to} m _M correspond to signals, and m _{M + 1 to} m _p are eigenvalues corresponding to noise.

Next, the number of incoming signals is estimated (step S12). The estimation of the number of incoming signals is performed by a method based on Akaike's (AIC) or Rissanen's (MDL) using statistical properties (see Non-Patent Document 3), or a number in which the eigenvalue of equation (7) is larger than a preset threshold value. Set as. The method using AIC or MDL is a method of changing k in the following formula (8) or (9) and using k when the value of AIC or MDL is minimized as the estimated number of signals.

here,
m ₁ > m ₂ >...> m _M
k = 0, 1,..., p−1
It is.

Next, the arrival direction is estimated (step S13). There are a beamformer method, a CAPON method, a MUSIC method, an ESPRIT method (see Non-Patent Document 4), and the like, and any method may be used as an arrival direction estimation method. Below, the MUSIC method in this is demonstrated.

here,
E _n : Noise eigenvector θ, φ: Peak search elevation angle / azimuth angle.

  The MUSIC method is a method that utilizes the property that the noise eigenvalue of the covariance matrix and the eigenvalue corresponding to the signal are orthogonal. The steering vector is calculated by changing the azimuth / elevation angle for searching the arrival direction, and the direction in which equation (10) reaches a peak is detected.

  Next, it is checked whether or not the number of incoming signals estimated in step S12 is plural (step S14). If it is determined in step S14 that the number of signals is plural, signal extraction is performed (step S15).

There are an MSN method, a DCMP method, an ICA (independent component analysis) method, a zero forcing (ZF) method, an MMSE method (see Non-Patent Document 4), and the like, and any method can be used. . Hereinafter, the MSN method and the ZF method will be described. In these methods, a steering vector a (θ _k , φ _k ) (k = 1 to s) and a covariance matrix with respect to the arrival direction of a signal to be extracted are used. In Equation (11), m _k and σ indicate the corresponding eigenvalue and noise standard deviation, respectively.

The extraction method by the MSN method is shown in the equations (11) and (12).

E in the equations (11) and (12) _represents the eigenvector of the eigenvalue m _k , s ⁰ _k in the equation (12) represents the received signal with the calculated initial value, and X represents the antenna received signal. ing.

The extraction method by the ZF method is shown in equation (13).

  When the above signal extraction process ends, the process proceeds to step S16. If it is determined in step S14 that the number of signals is not plural, the process in step S15 is skipped and the process proceeds to step S16.

  In step S16, radio wave propagation path estimation and attenuation estimation are performed. In the radio wave propagation path estimation, a process of estimating the extracted k signal propagation path by ray tracing is performed. For radio propagation path estimation by ray tracing, see “Kenichi Maeda, Mitsuo Goto:“ Radio propagation ”, Iwanami Zensho, February 1953”, “KGBuden:“ The Propagation of radio waves ”, Cambridge University Press, 1988. Or “Iwane Kimura:“ Effects of Ions on Whistler-Mode Ray Tracing ”, Radio Science. Vol. I, No. 3, 269-283, March 1966.”, etc.

  In radio wave propagation path estimation by ray tracing, the number of hops of a received signal is unknown, so hop number propagation paths are estimated for the number of hops. At this time, estimation is performed for both the left polarization (O mode) and the right polarization (X mode), or one of the propagation modes (see FIGS. 3 and 4).

  In the estimated propagation path, radio wave propagation path estimation is executed in reverse from the position (calculation position) reaching the ground surface to the reception position. FIG. 4 shows the reverse calculation of 1 hop, 2 hops, 3 hops,... From the calculation position 2. Also at this time, inverse calculation is performed for both the O mode and the X mode, or one of them.

By performing the above-described radio wave propagation path estimation, it is possible to estimate the attenuation generated in the propagation process (see “Maeda Kenichi, Goto Mio:“ Radio wave propagation ”, Iwanami Zensho, February 1953)”. The following formulas (14) to (16) show an approximate attenuation calculation method.

here,
E: Received electric field strength E0: Transmission field strength R1: Total propagation distance between surface and ionosphere R2: Total ionosphere passage distance Γ: Attenuation by ionosphere q: Electron charge c: Light speed me: Electron mass ε0 : Dielectric constant of vacuum f: Radio frequency STEP: Total number of calculation steps ν 0: Average number of collisions at the bottom of the ionosphere α: Rate of change with respect to height zk: Height at step k Nk: Electron density at height zk nk: Height Refractive index Δl at zk: distance between step k and step k + 1 FIG. 5 is a flowchart showing details of the above-described radio wave propagation path estimation and attenuation estimation processing. In the radio wave propagation path estimation and attenuation amount estimation processing, first, an inverse calculation elevation angle initial setting is performed (step S21). Next, ray tracing is performed with the calculated position as the start position (step S22). Next, it is examined whether or not ionosphere penetration has occurred (step S23). If it is determined in step S23 that ionosphere penetration has occurred, the process proceeds to step S28.

  On the other hand, if it is determined in step S23 that the ionosphere has not penetrated, it is then checked whether the absolute value of the difference between the calculation position and the reception position is smaller than ε (step S24). If it is determined in step S24 that the absolute value of the difference between the calculation position and the reception position is not smaller than ε, the inverse calculation elevation angle is changed (step S25), and then the process returns to step S22 and described above. The process is repeated.

  On the other hand, if it is determined in step S24 that the absolute value of the difference between the calculated position and the received position is smaller than ε, the calculated arrival elevation angle and azimuth angle are stored (step S26). Next, the attenuation is calculated and stored (step S27). Thereafter, the process proceeds to step S28.

  In step S28, it is checked whether the O mode and the X mode are completed. If it is determined in step S28 that the O mode and the X mode have not been completed, the mode change from the O mode to the X mode or from the X mode to the O mode is performed (step S29), and then in step S22. Returning to the process, the process described above is repeated.

  If it is determined in step S28 that the O mode and the X mode have been completed, it is then checked whether the hop has become larger than the maximum number of hops (step S30). If it is determined in step S30 that the hop is not larger than the maximum hop count, the hop count is incremented (+1) (step S31). Next, the inverse calculation elevation angle initial setting is performed (step S32), and then the process returns to step S22 and the above-described process is repeated.

  If it is determined in step S30 that the number of hops is greater than the maximum number of hops, it is then checked whether or not the processing for all reverse calculation start positions has been completed (step S33). If it is determined in step S33 that processing for all the reverse calculation start positions has not been completed, the process returns to step S22 and the above-described processing is repeated. On the other hand, if it is determined in step S33 that the processing for all the reverse calculation start positions has been completed, the radio wave propagation path estimation and attenuation estimation processing ends.

When the radio wave propagation path estimation and attenuation amount estimation processing in step S16 of the flowchart shown in FIG. 2 is completed, arrival direction initial value setting is performed (step S17). In step S17, the arrival direction (θ _u , φ _u ) = (θ ^h _k , φ ^h _k ) (h: number of reverse calculation hops, k: calculation position number) (u = 1 to m) and attenuation is used. Here, m is the obtained number of multipaths. The signal s ⁰ obtained by the equation (12) is expressed as a sum of m coherent multipaths.

The signal x ⁰ _u received by each antenna element is obtained by multiplying the steering vector corresponding to the direction of arrival of the signal u.

After the above processing, the arrival azimuth elevation angle precision measurement is performed. That is, based on the initial value of the arrival direction estimation of the incoming signal s ⁰ determined in step S17, is performed more detailed arrival direction elevation estimation. An example using the SAGE method as an example of the estimation method is shown below. A signal s ⁰ composed of a plurality of multipaths is expressed by equation (24).

Here, k in the equation (25) indicates the number of repetitions.

  The processing of the SAGE method is mainly composed of two steps of E (Expectation) -Step and M (Maximization) -Step. First, E-Step is performed, then M-Step is performed, and these steps are repeated until a preset evaluation value becomes equal to or less than a threshold value.

[E-Step]
First, among the signals composed of a plurality of signals, each antenna reception signal of the signal u is updated by the equation (26).

[M-Step]
Next, the covariance matrix of the signal u updated at E-Step is calculated.

Here, E [•] in the equation (27) is an operation for taking an average in parentheses. Using this covariance matrix, the arrival direction is obtained by a beamforming algorithm (see Non-Patent Document 2).

Next, only the steering vector of the u signal is updated using the arrival direction of the u signal calculated in M-Step. An updated array manifold (mixing matrix) A is then generated. Next, using this, signal separation is performed by the ZF method.

  At this time, εI in parentheses in the equation (29) is a parameter for regularization when the matrix is irregular. When ε is zero, when it is not regular, a sufficiently small value (0.001 to 0.00001) is set.

The end condition of the iterative process is when the change in E-Step is reduced. An example of the convergence condition is shown below.

  In the equation (30), ε is a preset threshold value.

  With the above processing, the azimuth angle and elevation angle obtained by the equation (28) are set as the precise azimuth elevation angle. As described above, according to the azimuth / elevation angle measurement system according to the first embodiment, the number of incoming waves and the incoming signal are estimated by using the radio wave propagation path estimation by ray tracing, and an algorithm represented by the SAGE algorithm is used. Initial settings can be made. As a result, processing can be performed more efficiently than when the initial signal is set at random, and a result closer to the actual signal can be obtained. As a result, the azimuth and elevation angle of the incoming signal can be accurately measured.

  As mentioned above, although several embodiment was described, these embodiment is shown as an example and is not intending limiting the range of invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

1 signal processing system 2 satellite signal processing system 3 ionospheric observation system 4 Internet Data processing system 5 data server system ₁₁ 1 to 11 _p antenna ₁₂ 1 to 12 _p amplifier ₁₃ 1 to 13 _p frequency converting unit ₁₄ 1 to 14 _p digitizer 15 signals Processing device 16 Display unit 21 Satellite signal receiving antenna 22 Satellite signal receiver 23 Satellite signal processing device 31 Ionosonde antenna 32 Ionosonde 33 Ionosonde collection data processing device 41 Network connection device 42 GEONET collection data processing device 51 Personal computer 52 including display Recording apparatus

Claims (2)

Multiple antennas,
The arrival direction is obtained by estimating the radio wave propagation path by ray tracing using the arrival wave number and the arrival signal estimated from the plurality of antenna reception signals obtained from the plurality of antennas, and the arrival direction is determined with the obtained arrival direction as an initial value. And a signal processing device for measuring an elevation angle;
An azimuth / elevation angle measurement system comprising:   The azimuth according to claim 1, wherein the signal processing device estimates a radio wave propagation path by estimating an ionospheric electron density using an IRI model or a model obtained by correcting the IRI model with a GPS signal based on an antenna reception signal.・ Elevation angle measurement system.

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