JP7637649B2 - Control device, control method, and program for controlling the setting of a reflector having a metasurface - Google Patents

Description

The present invention relates to a setting control technology for a reflector equipped with a metasurface.

In mobile communications, wireless communication services are provided to terminal devices located in positions where they can receive radio waves sent from base station equipment, so it is essential to make areas where radio waves cannot be received (dead zones) as small as possible. In particular, in today's wireless communication environment, which tends to use higher frequency bands, it is expected that dead zones will occur in the shadows of obstacles such as buildings even if the location is sufficiently close to the base station equipment, so it is important to deal with such dead zones.

The use of reflectors has been considered as a countermeasure to such blind zones. A reflector can change the direction in which a signal is reflected by changing its physical orientation, but a metasurface reflector can reflect radio waves in various directions without changing its physical orientation. A metasurface reflector is composed of multiple reflecting elements, and is configured to form a reflection pattern with a specified direction and beam width by adjusting the reflection phase of each reflecting element. In such a metasurface reflector, the reflection efficiency varies depending on the setting of the reflection phase, so the setting of the reflection phase is important. Non-Patent Document 1 describes a technology in which an initial reflection phase is determined for each of multiple reflecting elements based on a specified direction and beam width, and then the reflection phase of each reflecting element is sequentially adjusted to determine an appropriate reflection phase for each reflecting element.

Samith Abeywickrama, et al., “Intelligent Reflecting Surface: Practical Phase Shift Model and Beamforming Optimization”, IEEE Transactions on Communications, VOL. 68, Issue. 9, pp. 5849-5863, June 2020

In the technology described in Non-Patent Document 1, the reflection phase of each reflection element is changed in sequence to evaluate the effect on the whole, so if the number of reflection elements increases, the processing load for adjusting them becomes excessive.

The present invention provides a technology that improves the reflection efficiency of a metasurface reflector through simple processing.

The control device according to one aspect of the present invention is a control device that controls a reflecting device that reflects radio waves using a metasurface composed of multiple reflecting elements, and includes a determination means that determines a first reflection phase for each of the multiple reflecting elements based on a predetermined direction in which the reflecting device reflects radio waves, a determination means that determines a characteristic value of the reflection of the reflecting device when a uniform first phase shift is added to each of the first reflection phases of the multiple reflecting elements for the multiple first phase shift amounts, and determines an amount of a second phase shift to be used based on the characteristic value, and a setting means that sets the second reflection phase obtained by uniformly adding the amount of the second phase shift to each of the first reflection phases of the multiple reflecting elements as the reflection phase of each of the multiple reflecting elements.

According to the present invention, the reflection efficiency of a metasurface reflector can be improved through simple processing.

FIG. 1 illustrates an example of a system configuration. 11A and 11B are diagrams illustrating changes in characteristic values of a reflector. FIG. 2 is a diagram illustrating an example of a hardware configuration of a control device. FIG. 2 is a diagram illustrating an example of a functional configuration of a control device. FIG. 4 is a diagram illustrating an example of a flow of processing executed by a control device.

The following embodiments are described in detail with reference to the attached drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are necessarily essential to the invention. Two or more of the features described in the embodiments may be combined in any combination. In addition, the same reference numbers are used for the same or similar configurations, and duplicate descriptions are omitted.

(System Configuration)
An example of the configuration of the system according to this embodiment is shown in FIG. 1. In this system, communication between a base station device 111 and a terminal device 131 is performed via a reflector 121. The reflector 121 may be a metasurface reflector that includes multiple reflecting elements 122 and can reflect radio waves in various directions without changing the physical orientation. The metasurface reflector is configured to be able to form a reflection pattern with a predetermined direction and beam width by adjusting the reflection phase of each of the multiple reflecting elements 122. The characteristics of this metasurface reflector change depending on the reflection phase of the reflecting element 122. In this system, a control device 101 is provided to appropriately adjust the reflection phase.

The control device 101 adjusts the reflection phase of the multiple reflecting elements 122 of the reflector 121 so as to form a reflection pattern such that radio waves are reflected, for example, from the base station device 111 to the terminal device 131 and from the terminal device 131 to the base station device 111. For example, in the case of regular reflection, the phase is inverted. A metasurface reflector can be designed by changing the impedance of the reflecting element 122 (the element shape, the dielectric constant of the diode/dielectric, etc.). The control device 101, for example, fixes the reflection phase of one of the multiple reflecting elements 122 and calculates and determines the reflection phase of the other reflecting elements 122. Then, the reflector 121 can obtain a specific reflection pattern by setting the impedance to reflect the determined reflection phase. Note that this setting is performed, for example, when the reflector 121 is manufactured, and can be prevented from fluctuating during operation. The reflector 121 may also be, for example, a reflecting device that is composed of an impedance-variable element and can adaptively change the reflection characteristics by inputting a control signal from the control device 101. Regardless of whether the reflection characteristics can be adaptively changed or not, the reflector 121 may be referred to as a reflecting device in this specification and the appended claims.

On the other hand, the magnitude of loss of each of the reflecting elements 122 may differ depending on the reflection phase. That is, as described above, since loss occurs due to the resistance component of the impedance for varying the reflection phase, the magnitude of loss also differs if the reflection phase differs. If the losses occurring in each of the multiple reflecting elements 122 accumulate and the loss of the reflector 121 as a whole increases, even if the gain is set to be higher in the desired direction compared to other directions, radio waves will be significantly attenuated, and communication services cannot be efficiently provided to the terminal device 131 staying in the blind zone. In order to reduce such losses, in the technology described in Non-Patent Document 1, after determining the initial reflection phase, the reflection phase of each reflecting element is sequentially adjusted to determine the suitable reflection phase of each of the reflecting elements 122. However, such a procedure is cumbersome, and the processing load for determining the reflection phase may become excessive, especially when the number of reflecting elements 122 increases.

In this embodiment, a method is provided for setting a metasurface reflector that can suppress such an increase in processing load while suppressing loss during reflection. Specifically, as described in Non-Patent Document 1, the control device 101 initially determines a first reflection phase for each of the multiple reflecting elements 122 based on a predetermined direction in which radio waves are reflected, and adds a uniform first phase shift to each of the first reflection phases to calculate a characteristic value indicating reflection characteristics such as loss during reflection and reflected power. For example, the control device 101 stores information indicating the relationship between the reflection phase and loss for each of the multiple reflecting elements 122 in advance. Then, the control device 101 can specify the loss in the reflection phase after adding the first phase shift to the first reflection phase, and calculate the loss of the reflector 121 as a whole by adding the loss for each of the multiple reflecting elements 122. Similarly, for each of the multiple reflecting elements 122, the reflected power after adding the first phase shift to the first reflected phase may be calculated based on information indicating the relationship between the reflected phase and the reflected power stored in advance. The reflected power may be a reflection pattern indicated by the power value for each direction of reflected radio waves when, for example, a radio wave of a predetermined power is irradiated. In addition, for example, the reflection characteristic value may be determined by actually irradiating radio waves to the reflecting plate 121 in which the reflecting elements 122 are set to have a reflection phase obtained by adding the first phase shift to the first reflected phase. Then, the control device 101 determines the change in the characteristic value of the reflecting plate 121 as a whole for the multiple values of the first phase shift while varying the first phase shift.

Then, the control device 101 determines the amount of the second phase shift to be used for setting the reflector 121 from among the multiple first phase shift amounts based on the characteristic value. For example, when the characteristic value is loss, the control device 101 specifies, as the amount of the second phase shift, the amount of phase shift whose corresponding loss magnitude is smaller than a predetermined value from among the multiple first phase shift amounts. Note that the predetermined value here may be, for example, a relative value such as a value obtained by multiplying the minimum value of the loss magnitude by a constant value, or may be a value determined in advance. In addition, the control device 101 may specify, as the amount of the second phase shift, the amount of the first phase shift whose corresponding loss magnitude is the smallest from among the multiple first phase shift amounts. The magnitude of the loss may be, for example, the result of adding the magnitude of the loss specified from a value indicating the relationship between the reflection phase value and the magnitude of the loss in each of the reflecting elements 122. In addition, the loss may be specified by the difference between the total amount of power of the radio waves reflected by irradiating a radio wave of a reference power and the power at the time of irradiation.

The characteristic value may be the magnitude of deviation from the theoretical value of the pattern of the reflected power or loss value for each reflection direction when a predetermined direction is the reflection direction. For example, the control device 101 may calculate the relationship between the reflection direction and the reflected power of the entire reflector 121 using the relationship between the reflection direction and the reflected power stored in advance for each of the multiple reflecting elements 122 for the phase value in which the first reflection phase is added with the amount of the first phase shift. Then, the control device 101 may calculate the difference between the calculated reflected power and a theoretical value prepared in advance, for example, by computer simulation, for multiple reflection directions, and specify the result of adding the differences as the magnitude of the deviation. Note that the control device 101 may calculate only the deviation within a predetermined angle range from the direction in which the radio wave should be reflected, for example. The control device 101 may also measure the reflected power of the reflector 121 configured by applying a phase value in which the amount of the first phase shift is added to the first reflection phase to each reflecting element, and specify the deviation from the theoretical value. In this case, the control device 101 specifies, as the second phase shift amount, the amount of phase shift whose corresponding deviation is smaller than a predetermined value among the multiple first phase shift amounts. Note that the predetermined value here may be a relative value, such as a value obtained by multiplying the minimum deviation value by a constant value, or may be a value determined in advance. In addition, the control device 101 may specify, as the second phase shift amount, the amount of first phase shift whose corresponding deviation is the smallest among the multiple first phase shift amounts.

When the control device 101 determines the amount of the second phase shift as described above, it sets the second reflection phase obtained by uniformly adding the determined second phase shift to the first reflection phase for each of the multiple reflection elements 122 as the reflection phase for each of the multiple reflection elements 122.

The change in the characteristics of the reflector 121 due to this process will be explained with reference to FIG. 2. FIG. 2 shows an example of characteristics when 24 reflecting elements 122 are arranged vertically and horizontally, totaling 484, the frequency of the radio wave to be reflected is in the 28 GHz band, and the incident direction and reflection direction are (60°, 0°) and (55°, 180°), respectively. Note that (x, y) indicating the direction indicates (azimuth angle, elevation angle). As shown in FIG. 2, compared to the ideal characteristics shown by the dashed line, the characteristics when the initial setting shown by the thin solid line (the first reflection phase is set) is used cannot obtain sufficient reflected power in the reflection direction, and it can be seen that there is a large loss. In contrast, according to the characteristics improved by the above-mentioned phase shift shown by the thick solid line, the characteristics are sufficiently improved in the reflection direction, and it can be seen that the reflector 121 works sufficiently effectively.

In this embodiment, an initial phase is determined for each of the multiple reflecting elements 122 in the reflector 121 based on a predetermined direction in which the radio waves are reflected, and then the reflection phase is shifted uniformly for the multiple reflecting elements 122 to improve the characteristic value of the entire reflector 121. In this way, because the phase shift is performed uniformly for the multiple reflecting elements 122, the characteristics of the reflector 121 can be improved with a low processing load regardless of the number of reflecting elements 122.

(Device configuration)
An example of the hardware configuration of the control device 101 will be described with reference to FIG. 3. The control device 101 is, for example, a general-purpose computer, and in one example, includes a processor 301, a ROM 302, a RAM 303, a storage device 304, and a communication circuit 305. The processor 301 includes one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and executes the overall processing of the device and each of the above-mentioned processes by reading and executing a program stored in the ROM 302 or the storage device 304. The ROM 302 is a read-only memory that stores information such as programs and various parameters related to the processing executed by each device. The RAM 303 functions as a workspace when the processor 301 executes a program, and is a random access memory that stores temporary information. The storage device 304 is, for example, a removable external storage device. The communication circuit 305 can be configured to communicate with the reflector 121 for setting the reflector 121, for example. The control device 101 may be a stand-alone computer and may not include the communication circuit 305 .

FIG. 4 shows an example of the functional configuration of the control device 101. The control device 101 has, for example, an initial phase identification unit 401, a phase adjustment unit 402, and a setting unit 403 as its functions. Each functional unit can be realized, for example, by the processor 301 executing a program stored in the ROM 302 or the storage device 304. However, this is not limited to this, and some or all of the functional units may be executed by dedicated hardware. The initial phase identification unit 401 identifies an initial phase (the above-mentioned first reflection phase) for each of the multiple reflecting elements 122 of the reflecting plate 121 based on a predetermined direction in which the radio wave should be reflected in the reflecting plate 121. The initial phase identification unit 401 identifies the first reflection phase without considering losses in the reflecting element 122 (for example, assuming that there is no loss). The initial phase identification unit 401 determines the first reflection phase for each of the multiple reflecting elements 122 under the condition that the reflection phase value of one reflecting element is fixed, for example. The phase adjustment unit 402 uniformly adds a first phase shift to the first reflection phases of the multiple reflecting elements 122 identified by the initial phase identification unit 401 as described above, and identifies a change in the characteristic value of the reflector 121. Then, the phase adjustment unit 402 identifies a second phase shift to be used from the multiple amounts of first phase shift based on the characteristic values identified for each of the multiple amounts of first phase shift. Then, the setting unit 403 sets, for each of the multiple reflecting elements 122, a second reflection phase obtained by uniformly applying the second phase shift to the first reflection phase for each of the multiple reflecting elements 122.

(Processing flow)
Next, the flow of the process executed by the control device 101 will be outlined with reference to FIG. 5. In this process, the control device 101 first specifies a first reflection phase in each of the multiple reflecting elements 122 to realize a desired reflection pattern, assuming, for example, that there is no reflection loss (lossless) (S501). Then, the control device 101 uniformly adds a first phase shift to the first reflection phase value specified in S501 to specify a characteristic value corresponding to, for example, the magnitude of loss or deviation from a theoretical value. Then, the control device 101 specifies a characteristic value for each of the multiple first phase shift values, and specifies, as the amount of the second phase shift, one phase shift amount among the multiple first phase shift amounts that, for example, makes the magnitude of loss or deviation from a theoretical value sufficiently small. Then, the control device 101 specifies, as the second reflection phase to be set for each of the multiple reflecting elements 122 in the reflector 121, the reflection phase obtained by uniformly adding a second phase shift to the first reflection phase (S502). Thereafter, for example, under the control of the control device 101, a corresponding second reflection phase is set for each of the multiple reflection elements 122 in the reflector 121 (S503). Note that the control device 101 may notify the reflector 121 of the value of the second reflection phase, thereby setting the reflector 121, or, for example, adjustment of the manufacturing of the reflector 121 may be performed based on the setting by the control device 101.

As described above, the setting method according to this embodiment can improve the characteristics of the reflector with a low processing load, regardless of the number of reflecting elements that make up the metasurface.

The above configuration makes it possible to configure an appropriately configured reflector while minimizing the processing load. This makes it possible to contribute to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "build resilient infrastructure, promote sustainable industrialization and foster innovation."

The invention is not limited to the above-described embodiment, and various modifications and variations are possible within the scope of the invention.

Claims (8)

A control device that controls a reflection device that reflects radio waves using a metasurface composed of a plurality of reflection elements,
a determination means for determining a first reflection phase for each of the plurality of reflecting elements based on a predetermined direction in which the reflecting device reflects a radio wave;
a determination means for determining a characteristic value of the reflection of the reflecting device when a uniform first phase shift is added to each of the first reflection phases of the plurality of reflecting elements, for each of the first phase shift amounts, and determining an amount of a second phase shift to be used based on the characteristic value;
a setting means for setting a second reflection phase obtained by uniformly adding the amount of the second phase shift to each of the first reflection phases for the plurality of reflection elements as a reflection phase for each of the plurality of reflection elements;
A control device comprising: the characteristic value indicates a magnitude of loss in the predetermined direction,
the specifying means specifies, as the amount of the second phase shift, an amount of phase shift in which the loss is smaller than a predetermined value, among the plurality of amounts of the first phase shift.
The control device according to claim 1 . the characteristic value indicates a magnitude of loss in the predetermined direction,
2. The control device according to claim 1, wherein the specifying means specifies, as the amount of the second phase shift, an amount of phase shift that causes the smallest loss, among a plurality of amounts of the first phase shift. The control device according to claim 2 or 3, characterized in that the identification means identifies, as the characteristic value, the loss when the first phase shift is uniformly applied to each of the first reflection phases for the plurality of reflection elements, based on information indicating the relationship between the reflection phase and the loss for each of the plurality of reflection elements. the characteristic value indicates a magnitude of deviation from a theoretical value when the predetermined direction is a reflection direction,
the specifying means specifies, as the amount of the second phase shift, an amount of phase shift in which the magnitude of deviation is smaller than a predetermined value, among the plurality of amounts of the first phase shift.
The control device according to claim 1 . the characteristic value indicates a magnitude of deviation from a theoretical value when the predetermined direction is a reflection direction,
2. The control device according to claim 1, wherein the specifying means specifies, as the amount of the second phase shift, an amount of phase shift having a minimum deviation from among a plurality of amounts of the first phase shift. A control method executed by a control device that controls a reflection device that reflects radio waves using a metasurface configured with a plurality of reflection elements,
determining a first reflection phase for each of the plurality of reflecting elements based on a predetermined direction in which the reflecting device reflects radio waves;
determining a characteristic value of the reflection of the reflecting device when a uniform first phase shift is added to each of the first reflection phases for the plurality of reflecting elements for each of the first phase shift amounts, and determining an amount of a second phase shift to be used based on the characteristic value;
setting a second reflection phase obtained by uniformly adding the amount of the second phase shift to each of the first reflection phases for the plurality of reflection elements as a reflection phase for each of the plurality of reflection elements;
A control method comprising: A computer provided in a control device that controls a reflection device that reflects radio waves using a metasurface configured with a plurality of reflection elements,
determining a first reflection phase for each of the plurality of reflecting elements based on a predetermined direction in which the reflecting device reflects radio waves;
determining a characteristic value of the reflection of the reflecting device when a uniform first phase shift is added to each of the first reflection phases for the plurality of reflecting elements, for each of the first phase shift amounts, and determining an amount of a second phase shift to be used based on the characteristic value;
a second reflection phase obtained by uniformly adding the amount of the second phase shift to each of the first reflection phases for the plurality of reflection elements is set as a reflection phase for each of the plurality of reflection elements;
Program for.

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