JP6612113B2 - Method and apparatus for estimating direction of arrival and intensity of radio wave - Google Patents

Method and apparatus for estimating direction of arrival and intensity of radio wave Download PDF

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JP6612113B2
JP6612113B2 JP2015232333A JP2015232333A JP6612113B2 JP 6612113 B2 JP6612113 B2 JP 6612113B2 JP 2015232333 A JP2015232333 A JP 2015232333A JP 2015232333 A JP2015232333 A JP 2015232333A JP 6612113 B2 JP6612113 B2 JP 6612113B2
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arrival
antenna
radio wave
intensity
exponential function
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俊浩 ▲瀬▼在
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国立研究開発法人宇宙航空研究開発機構
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  The present invention relates to an arrival direction and intensity estimation device for an arrival radio wave that estimates an arrival direction and intensity when an incoming radio wave is received by an equally spaced linear array antenna.
  There are known a plurality of methods for estimating the direction of arrival of an incoming radio wave by using array antennas arranged linearly at equal intervals. A typical method among these is the MUSIC method.
  However, the MUSIC method has the following problems. First, the direction of arrival of radio waves can be estimated, but the intensity cannot be estimated. In addition, when performing the arrival direction estimation process of radio waves, it is essential to set the number of incoming radio waves, and the number of incoming radio waves is assumed in advance or the number of incoming radio waves is estimated. There is a problem that must be added. And when there are a plurality of incoming radio waves and their correlation is high, there is a problem that the estimation accuracy of the arrival direction is lowered. Furthermore, the result obtained from a single received signal has a low accuracy, and therefore there is a problem that a plurality of received signals must be used.
  The present invention has been made to solve the above-mentioned problems in the MUSIC method, and estimates the arrival direction and intensity of an incoming radio wave using an equally spaced linear array antenna composed of the same antenna elements. It is an object of the present invention to provide an apparatus and method capable of performing the above.
  The present invention is a process for generating a data sequence from a received signal captured by an equally spaced linear array antenna formed by arranging a plurality of identical antenna elements in a straight line at equal intervals, and fitting the data sequence with an exponential function And calculating the direction and intensity of the incoming radio wave from the obtained exponential function argument and amplitude.
  In the process of fitting with the above exponential function, the argument and amplitude of the exponential function to be used can be selected according to the size of the real part of the exponential function argument.
  The process of generating the data series may be performed based on the received signal by capturing the incoming radio wave a plurality of times with the equally spaced linear array antenna and averaging a plurality of received signals for each antenna element.
  The present invention captures incoming radio waves by an equally spaced linear array antenna composed of the same antenna elements, arranges the received signals of each antenna element of the array antenna in order from one end to the other end, and arranges the data series. Since the processing to generate, the processing to fit the data series with an exponential function, and the processing to calculate the direction and intensity of the incoming radio wave from the argument and amplitude of the obtained exponential function, The direction of arrival of radio waves and the intensity thereof can be estimated.
It is the figure which showed typically a mode that the array antenna which has arrange | positioned N antenna elements from # 1 to #N linearly at equal intervals d receives the electromagnetic wave which arrives from angle (theta) direction. 1 is a schematic block configuration diagram of an arrival direction and intensity estimation device for an incoming radio wave according to an embodiment of the present invention. It is the flowchart which showed the procedure of the signal processing performed with a signal processing apparatus. It is the table | surface which showed an example of the simulation result obtained based on the prony method. It is the table | surface which showed an example of the simulation result obtained based on the prony method. It is the table | surface which showed an example of the simulation result obtained based on the prony method. It is the graph which showed the result after processing the result of FIG. 6 with the method of this invention. It is the graph which showed an example of the simulation result obtained based on the MUSIC method. It is the graph which showed an example of the simulation result obtained based on this invention, changing only a phase difference into 90 degrees.
FIG.

Equally spaced antenna elements


The array antenna arranged in a straight line at


A mode that the radio wave which arrives from the direction is received is shown typically. The N antenna elements can be used of any type as long as they are the same.
As shown in FIG.


1 antenna element on a straight line


In the array antenna arranged at equal intervals in the angle


When radio waves arrive from the direction, the received signals at each antenna element are as follows.

In equation (1),


Is the antenna element


Directional antenna pattern, a known function measured in advance. In square brackets in equation (1)


Since the leftmost antenna element in FIG. 1 is used as a phase reference, the leftmost value in the brackets is “1”.


Is the imaginary unit,


Is the wavelength of the incoming radio wave. Data series in which the terms of formula (1) are arranged in order from the left


Create Comparing equation (2) with the Fourier series, the amplitude is


The frequency is


It can be seen that a complex sine wave is shown.
Expression (2) is an expression when the number of incoming radio waves is one, but the number of incoming radio waves is


In the case of individual pieces, it can be expressed as follows.


In equation (3)


Respectively


The direction and intensity of the second incoming radio wave are shown.
The Prony method is known as a method of fitting a data series with an exponential function. Since exponential functions are expressed in terms of amplitude and arguments,


From the data


One exponential function can be fitted.
Therefore, the antenna pattern is


The antenna element that is


so


Wavelengths arriving at array antennas arranged on individual lines


When fitting the data series created from the received signal of the radio wave to the exponential function by the Prony method,


Amplitude


And exponential arguments


Is calculated as a numerical value. Therefore, from equation (3),


The direction of arrival of the second radio wave is


Can be obtained. here


Represents the imaginary part in parentheses.


Is required, the antenna pattern of the antenna element in that direction


Since the value of


The intensity of the second radio wave is


Sought by.
FIG. 2 is a schematic block configuration diagram of an arrival direction and intensity estimation device for an incoming radio wave according to an embodiment of the present invention. In FIG. 2, reference numeral 1 denotes an equally spaced linear array antenna, and 1-1 to 1-N denote the same antenna elements that constitute the equally spaced linear array antenna. As the antenna element, any antenna such as a dipole antenna, a horn antenna, or a parabolic antenna can be used. Reference numeral 2 denotes a receiving device that outputs a signal based on the radio wave captured by each antenna element. The receiving device 2 may output a signal captured by each antenna element as it is as a received signal, or outputs a signal obtained by averaging the signals received by each antenna element a plurality of times as a received signal in order to improve accuracy. You can also. Reference numeral 3 denotes a signal processing device, which is connected to the receiving device 2.


Number of data from received signals


From the result of fitting the created data series to the exponential function using the Prony method,


It is a device that calculates the direction and intensity of each incoming radio wave. Reference numeral 4 denotes a display device that displays the result of the signal processing device.
Next, an operation for estimating the arrival direction and intensity of the radio wave of the apparatus shown in FIG. 2 will be described. The equally spaced linear array antenna 1 is


Each antenna element receives incoming radio waves according to its pattern and position, and outputs an RF reception signal. The receiving device 2


An RF reception signal from each antenna element is converted into a video signal, digitized, and output as a complex signal. The signal processing device 3 performs signal processing according to the procedure shown in FIG. That is, in the data sequence creation process 3-1, the receiving device 2


First complex signal from the first antenna element signal

Arrange the antenna element signals in order and the number of data


Create a data series for. In the Prony method process 3-2, a process of fitting the data series created in the data series creation process 3-1 to an exponential function is performed,


Calculate the exponential argument and amplitude. In the incoming radio wave direction / intensity calculation process 3-3, the direction of the incoming radio wave is calculated from the argument of the exponential function, and the intensity of the incoming radio wave is calculated from the amplitude. The display device 4 displays the output of the incoming radio wave direction / intensity calculation force 3-3 in a table format or a diagram format.
Looking at equation (3), the argument of the exponential function, that is, the braces are purely imaginary numbers.

(Α is a real part and β is an imaginary part). Here, “α” in the real part is called a damping coefficient. However, only the imaginary part is actually required for direction estimation and intensity estimation of the incoming radio wave, and using this imaginary part,

Is required.
According to the Prony method,

N / 2 complex numbers are obtained. The influence of noise is considered to appear not only in α but also in β. And if there is no noise, α is zero in principle. Therefore, among the obtained N / 2 values, if α is large, the corresponding β is not used and α is sufficiently small. If only β is used for a product, it is considered that processing with less influence of noise can be performed. This is the basic idea. Conventionally, since all β obtained by the Prony method was used, β having a large influence of noise was also used. This is considered to be the reason why the Prony method was said to have a large influence of noise.
  The tables in FIGS. 4 to 6 show the simulation results obtained based on the Prony method. Among these, the table of FIG. 4 shows the intensity arriving from the position where the angle is 10 °, the intensity (amplitude) is 1, the phase is zero, and the angle is 20 degrees. This is an example in which there are two radio waves (amplitude) of 0.8 and zero phase (20, 0.8, 0) and the S / N ratio is 20 dB. 10EL) is a simulation result in a case where the signals are received side by side at half wavelength intervals. Since there are ten antenna elements, five values can be obtained by the Prony method.
  Looking closely at the five values in the table of FIG. 4, it can be seen that there is a radio wave with an amplitude of 1 at an arrival angle of about 10 ° and a radio wave with an amplitude of 0.79 at an arrival angle of about 20 °. Show. In addition, although there is a possibility that there is an incoming radio wave at positions of about −13 °, about −46 °, and about −59 °, these amplitudes are very small compared to the first two. On the other hand, since all of these absolute values of α are small enough to be ignored, it can be inferred that the noise shadow for each value obtained by the Prony method is very small. Thus, when the absolute values of all α are small, there are two radio waves indicated by the first value and the second value based on the table of FIG. This indicates that it can be determined that it does not exist.
  The table in FIG. 5 shows the simulation results when there are two radio waves with the same conditions as in FIG. 4 except that the S / N ratio is 15 dB. The result of FIG. 5 is similar to the result of FIG. 4 as a whole, but it is understood that the absolute value of α increases as a whole when noise increases and the S / N ratio decreases. That is, the high reliability of the obtained value can be estimated with high accuracy by the magnitude of α.
  The table of FIG. 6 shows the intensity arriving from the position where the angle is 10 °, the intensity (amplitude) is 1, the phase is zero, and the angle is 12.5 °. This is an example in which there are two radio waves (amplitude) of 1 and zero phase (12.5, 1, 0) and the S / N ratio is 20 dB, and 20 antenna elements (20EL) It is a simulation result at the time of receiving by arranging in half wavelength intervals. Since there are 20 antenna elements, 10 values are obtained by the Prony method. The example of FIG. 6 is a case where the arrival positions of two radio waves are very close to 10 ° and 12.5 °.
  Looking at the top of the table in FIG. 6, the arrival direction is 34.144 °, but there is actually no radio wave in that direction. In other words, if the Prony method is simply used, it may be determined that a radio wave having a large amplitude has arrived from such a direction. However, looking at the absolute value of α here, it is 0.156, which is very large compared to other values. Therefore, it can be assumed that this first one is not due to incoming radio waves but due to noise and does not actually exist. Subsequently, the absolute values of the second and third α are very small compared to the first one. And these arrival directions are about 10 ° and about 13 °, and it can be seen that they are almost coincident with the actual directions. And since the intensity | strength (amplitude) is very small about the 4th or subsequent thing, it can be guessed that these radio waves will also depend on noise and will not actually exist. Therefore, in the example of FIG. 6, it is possible to estimate the amplitude and the arrival direction of the two radio waves based on the second and third values.
  As described above, the Prony method has been considered to be difficult to use in estimating the direction and intensity (amplitude) of the actual incoming radio wave due to the influence of noise. It can be seen that the arrival direction and intensity (amplitude) of the incoming radio wave can be estimated with higher accuracy based on the value and the value of α. The actual threshold value for α varies depending on the application. For example, the experiment is repeated several times, and the α value that can be identified with a probability of, for example, 90% or more or 100% is determined as the threshold value. It is also possible. The threshold value determined in this way is set in the signal processing device 3 in FIG. 2 and is used in the step of calculating the incoming radio wave direction / intensity in FIG. Based on the value of, a process is performed that selects what is considered not to be due to noise.
  The graph of FIG. 7 shows the result of FIG. 6 after processing by the method of the present invention. The horizontal axis represents the angle direction of the incoming radio wave, and the vertical axis represents the intensity (amplitude). In FIG. 7, the value of α is in the range of −0.7 ≦ α ≦ 0.7. As can be seen from FIG. 7, the amplitude of the second radio wave with an arrival angle of 10.451 ° in the table of FIG. 6 and the third radio wave with an arrival angle of 13.242 ° is extremely large, and others can be ignored. I understand. The graph in FIG. 8 is a graph showing the result of simulation by the MUSIC method under the same conditions as in FIGS. 6 and 7. However, MUSIC method processing was performed with two radio waves. As can be seen from the graph of FIG. 8, only one peak appears at an angle of about 11.3 °. Therefore, in the MUSIC method, both the number of incoming radio waves and the angle of arrival are selected from the values obtained using the Prony method based on the amplitude and α values that are considered not to be noise-related. It can be seen that it is less accurate than the method of the invention.
  FIG. 9 shows the calculation result when only the phase difference is changed to 90 ° among the conditions described in relation to FIG. Also in FIG. 9, the value of α is in the range of −0.7 ≦ α ≦ 0.7. The fact that the phase difference between the two radio waves differs by 90 ° means that the correlation between the two radio waves is lower than when the phase difference is zero. For this reason, it can be seen that the estimated arrival directions of the two radio waves are closer to 10 ° and 12.5 °.
  INDUSTRIAL APPLICABILITY The arrival direction and intensity estimation method and estimation apparatus according to the present invention are used in wireless communication such as mobile phones, active radio devices such as radar, and passive radio devices used in radio astronomy and the like. can do.
DESCRIPTION OF SYMBOLS 1 Equally-spaced linear array antenna 1-1 First antenna element 1-2 Second antenna element
2 Receiving device 3 Signal processing device 3-1 Data sequence creation processing 3-2 Prony method processing 3-3 Arrival radio wave direction / intensity calculation processing 4 Display device

Claims (6)

  1. A receiving device for receiving incoming radio waves captured by an equally spaced linear array antenna configured by arranging a plurality of identical antenna elements in a straight line at equal intervals;
    A signal processing device that performs signal processing on a received signal output by the receiving device;
    The signal processing device generates a data series from the received signals of each antenna element of the equally spaced linear array antenna, performs a process of fitting the data series with an exponential function, and an argument of the obtained exponential function An apparatus for estimating an arrival direction and intensity of radio waves, which performs a process of calculating the arrival direction and intensity of an incoming radio wave from amplitude.
  2.   2. The direction of arrival of radio waves according to claim 1, wherein the signal processing device selects an exponential function argument and an amplitude to be used according to the size of the real part of the exponential function argument in the process of fitting with an exponential function. And intensity estimation device.
  3.   3. The receiving device according to claim 1, wherein the receiving device captures an incoming radio wave a plurality of times with the equally spaced linear array antenna, and outputs a signal obtained by averaging a plurality of received signals for each antenna element as a received signal. The radio wave arrival direction and intensity estimation device described.
  4.   A data sequence is generated from a received signal captured by an equally spaced linear array antenna configured by arranging a plurality of identical antenna elements in a straight line at equal intervals, and the data sequence is fitted with an exponential function to obtain a data sequence. A method for estimating the arrival direction and intensity of a radio wave, which performs a process of calculating the arrival direction and intensity of an incoming radio wave from the exponential function argument and amplitude obtained.
  5.   5. The method of estimating the direction of arrival and intensity of radio waves according to claim 4, wherein in the process of fitting with an exponential function, an argument and amplitude of the exponential function to be used are selected according to the size of the real part of the argument of the exponential function.
  6.   The processing for generating the data series is performed based on a received signal by capturing an incoming radio wave a plurality of times with the equally spaced linear array antenna and averaging a plurality of received signals for each antenna element. Item 6. The radio wave arrival direction and intensity estimation method according to Item 4 or 5.
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