KR102201169B1 - Method for generating time code and space-time code for controlling reflection coefficient of meta surface, recording medium storing program for executing the same, and method for signal modulation using meta surface - Google Patents

Abstract

According to one embodiment of the present invention, a method for generating a time code to control a reflection coefficient of a meta surface comprises the steps of: calculating a reflection amplitude (A_1) for a +1^th harmonic based on a center frequency (f_c) with respect to a first time sign (c_1); determining whether the reflection amplitude (A_1) for the +1^th harmonic is higher than the reflection amplitude for the remaining harmonics by S dB or more and is greater than or equal to a threshold value α; recording a reflection coefficient (a_1) and a reflection phase (φ_1) together with the first time code (c_1) in a codebook for the +1^th harmonic that satisfies the above two conditions; and generating a codebook including a set (C) of time codes by sequentially performing the steps of calculating, determining, and recording for a time code (c_k, k≠1) other than the first time code. According to the present invention, it is possible to implement manual downlink beamforming communication based on PSK modulation.

Description

Time code generation method for controlling reflection coefficient of meta surface, method of generating space-time code for controlling reflection coefficient of meta surface, computer readable recording medium storing a computer program that executes it, and signal modulation method of meta surface using the same {METHOD FOR GENERATING TIME CODE AND SPACE-TIME CODE FOR CONTROLLING REFLECTION COEFFICIENT OF META SURFACE, RECORDING MEDIUM STORING PROGRAM FOR EXECUTING THE SAME, AND METHOD FOR SIGNAL MODULATION USING META SURFACE}

The present invention relates to a method for generating a temporal code for controlling a reflection coefficient of a meta surface, a method for generating a space-time code for controlling a reflection coefficient of a meta surface, a computer readable recording medium storing a computer program that executes the same, and a meta surface using the same. Regarding the signal modulation method, more specifically, when the input signal incident on the meta surface is modulated and output by the meta surface, the reflected phase of the modulated carrier can occupy a wide range of -180° to 180°. It includes a method of generating a temporal code or a space-time code applied to the meta surface to control the properties of the meta surface, that is, reflection coefficients of meta elements constituting the meta surface. Further, it includes a computer-readable recording medium in which a computer program for executing the time code or space-time code generation method is stored, and a method of modulating a signal in the meta surface using the generated space-time code.

In wireless communication technology using radio waves, information to be transmitted is modulated into radio waves, and radio waves are transmitted through a power amplifier (PA), and a receiver demodulates the received radio waves to receive information. The frequency range of radio waves used for such radio wave communication is infinitely wide, and in recent years, research on wireless communication technology using a high frequency band has been actively conducted. Depending on the frequency band, the characteristics of the radio wave reach and data transmission speed are different.The low frequency band has a long wavelength instead of a low speed, so even if it encounters an obstacle, it is bent naturally and can propagate to a long distance. While it has the advantage of being able to transmit the signal quickly, it has the disadvantage of shortening the reception distance due to reflection when it encounters an obstacle due to increased straightness. In other words, if LOS (Line of Sight) is not secured in an environment with many obstacles such as indoors, radio waves are easily absorbed by the obstacles, making communication difficult, and thus the service area of wireless communication is reduced. In addition, in the high frequency band, downlink network congestion burdened by the AP increases.

In such a situation, there is a need for a technology that transmits information to users whose LOS is not secured and reduces network congestion burdened by APs, and recently, meta-materials (have a negative refractive index, There is an attempt to solve the above-described problem by utilizing a meta-surface composed of a material having a diffraction rate of close to 100% that appears as if there is no object).

In a conventional wireless communication technology using a meta surface, a 1-bit or 2-bit digital code is input from an FPGA (Field Programmable Gate Array) to control a reflection coefficient of a meta atom, thereby adjusting the phase or amplitude of an incident carrier. For example, in the conventional meta-surface, using a 1-bit digital code, bit 0 is mapped to have a reflection phase of 0°, and bit 1 is mapped to 180° to perform binary phase shift keying (BPSK) modulation.

However, in this case, since it has a finite set of reflection coefficients for a limited number of bits of the digital code, the phase or amplitude of the reflected wave is fixed and finite. Therefore, only limited applications are possible, and there are problems such as poor fluidity and a quantization error. That is, a modulation technique higher than BPSK cannot be used with a 1-bit digital code, and even when a 2-bit digital code is used, a modulation technique higher than QPSK (Quadrature Phase Shift Keying) cannot be used. To solve this problem, if the number of digital code bits is increased, since a diode must be additionally connected, there is a problem that the complexity increases. In addition, there is a problem in that the phase cannot be precisely adjusted to perform beamforming.

The present invention is to solve the above problems, and an object of the present invention is to reflect the meta surface to have an arbitrary reflection phase within -180° to 180° at a harmonic frequency through a time code composed of a 2-bit digital code. By controlling the coefficient, it is to implement passive downlink beamforming communication based on PSK modulation.

Meanwhile, an object of the present invention is to provide passive beamforming by obtaining an optimal beamforming vector that maximizes the achievable bit rate under the limited power of the carrier generation device and the constraints that minimize interference with other users.

The problem to be solved by the present invention is not limited to the problems mentioned above, and other problems that are not mentioned will be clearly understood by those skilled in the art from the following description.

The time code generation method for controlling the reflection coefficient of the meta surface according to an embodiment of the present invention is a reflection amplitude for a +1 th harmonic based on a center frequency (f _c ) for a first time code (c ₁ ). Calculating (A ₁ ); Determining whether a reflection amplitude (A ₁ ) for the +1 th harmonic is higher than the reflection amplitude for the remaining harmonics by S dB or more and a threshold value α or more; Recording a reflection coefficient (a ₁ ) and a reflection phase (φ ₁ ) in a codebook together with the first time code (c ₁ ) for a +1 harmonic that satisfies the two conditions of the determining step; And generating a codebook including a set of time codes (C) by sequentially performing the calculating, determining, and recording steps for time codes (c _k , k ≠ 1) other than the first time code. It includes;

In addition, the step of calculating the reflection amplitude (A ₁ ) includes a reflection coefficient (a _m ) for the -m-th harmonic to the +m-th harmonic based on the center frequency (f _c ) for the first time sign (c ₁ ). ) Calculating; And calculating reflection amplitudes (A _m ) for the -mth to +mth harmonics from the reflection coefficients (a _m ).

In addition, the first time code (c ₁ ) is composed of L 2-bit digital codes arranged in time series, and the number (K) of time codes constituting the set of time codes (C) is at most 4 ^L And the step of generating the codebook may be performed until k becomes K.

In addition, bit rate control may be possible by adjusting the number (L) of the 2-bit digital code.

In addition, in the step of recording in the codebook, when two or more time codes having the same reflection phase appear, a time code having a large difference in reflection amplitude for the +1 harmonic and other harmonics may be selected and recorded in the codebook. have.

In addition, the S dB may be 10 dB.

Meanwhile, the present invention includes a computer-readable recording medium storing a computer program for performing the method for generating time codes for controlling the reflection coefficient of the meta-surface described above.

Meanwhile, a method for generating a space-time code for controlling a reflection coefficient of a meta surface according to another embodiment of the present invention includes: estimating a channel between a carrier wave generator and a meta surface and a channel of the meta surface and a receiver; Calculating a phase change during carrier modulation by the meta-surface based on the estimated channel; Selecting a time code (c _k ) having a reflection phase (φ) closest to the calculated phase from the codebook generated by the method of claim 1; And obtaining a space-time code by calculating the selected time code (c _k ) for each element of the meta surface.

In addition, the step of calculating the phase change may be calculating a phase change during differential BPSK (DBPSK) or differential QPSK (DQPSK) modulation.

Meanwhile, the present invention includes a computer-readable recording medium in which a computer program for performing a method for generating a space-time code for controlling a reflection coefficient of a meta surface is stored.

Meanwhile, a method for modulating a signal of a meta surface according to another embodiment of the present invention includes the steps of: receiving a carrier wave from a carrier wave generator; Generating a space-time code according to the above-described time code generation method based on the frequency of the received carrier; Inputting the generated space-time code to the meta surface to control a reflection coefficient of the meta surface; Modulating the carrier wave using the meta surface; And transmitting the modulated signal to a receiver.

In addition, in the step of receiving the carrier wave, a carrier wave having a frequency of f _c -f ₀ is received from the carrier wave generator, and f ₀ may be an interval between harmonic frequencies.

According to the present invention, by generating a time code with a digital code of a limited number of bits, it is possible to control the meta surface to have most of the reflection phase values between -180° to 180°, and communication based on PSK modulation can be performed. .

In addition, the wireless communication technology using the meta-surface according to the present invention does not require a transmission RF chain used for each antenna in the existing active RF communication, thereby reducing power consumption.

In addition, according to the present invention, passive beamforming may be performed by precisely controlling the phase of each meta surface element through a space-time code. Since a large amount of information requested by a user can be transmitted through such downlink passive beamforming, it is possible to reduce the downlink network congestion of an AP (Access Point).

In addition, since the meta-surface has an advantage that can be easily installed on a wall or a ceiling, the present invention using the meta-surface can provide relatively stable downlink communication even in a high frequency band.

In addition, it is possible to provide an effect of supporting large-scale downlink communication by using a meta surface that can be implemented at a low cost and uses less power than an AP in an indoor environment where a line of sight is not well secured due to many obstacles.

Meanwhile, the effects of the present invention are not limited to the above-mentioned effects, and various effects may be included within a range that is apparent to a person skilled in the art from the contents to be described below.

1 is a diagram schematically showing a basic model of a wireless communication system using a meta surface.
2 is a graph showing a reflection phase with respect to a voltage according to a frequency incident on the meta surface.
3 is a diagram illustrating an algorithm for a time code generation method for controlling a reflection coefficient of a meta surface according to an embodiment of the present invention.
4 is a diagram illustrating an exemplary reflection amplitude for each harmonic when a +1 th harmonic is generated using a time sign.
5 is a diagram illustrating a reflection phase region that appears when a +1th harmonic is generated.
6 is a diagram illustrating an example of a codebook obtained through a time code generation method according to an embodiment of the present invention.
7 shows a part of a set (C) of time codes derived by applying an algorithm for a time code generation method according to an embodiment of the present invention.
8 is a block diagram showing a large-scale passive downlink communication scheme based on 802.11b communication using a meta surface.

In the present invention, various modifications may be made and various embodiments may be provided, and specific embodiments will be illustrated in the drawings and described in detail. However, this is not intended to limit the present invention to a specific embodiment, and it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing each drawing, similar reference numerals have been used for similar elements.

Terms such as first, second, A, and B may be used to describe various elements, but the elements should not be limited by the terms. These terms are used only for the purpose of distinguishing one component from another component. For example, without departing from the scope of the present invention, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element. The term and/or includes a combination of a plurality of related listed items or any of a plurality of related listed items.

When a component is referred to as being "connected" or "connected" to another component, it is understood that it may be directly connected or connected to the other component, but other components may exist in the middle. Should be. On the other hand, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there is no other component in the middle.

The terms used in the present application are only used to describe specific embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the presence of features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, but one or more other features. It is to be understood that the presence or addition of elements or numbers, steps, actions, components, parts, or combinations thereof, does not preclude in advance.

Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms such as those defined in commonly used dictionaries should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in this application. Does not.

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

1 is a diagram schematically showing a basic model of a wireless communication system using a meta-surface, FIG. 2 is a graph showing a reflection phase of a voltage according to a frequency incident on the meta-surface, and FIG. 3 is an embodiment of the present invention. Algorithm for a time code generation method for controlling the reflection coefficient of the meta-surface according to this, FIG. 4 is a diagram showing an exemplary reflection amplitude for each harmonic when a +1th harmonic using a time code is generated, and FIG. 5 is +1 A diagram showing an exemplary reflection phase region appearing when a th harmonic is generated, FIG. 6 is a diagram illustrating an example of a codebook obtained through a time code generation method according to an embodiment of the present invention, and FIG. 7 is an embodiment of the present invention. A diagram showing a part of a set of time codes (C) derived by applying an algorithm for a time code generation method according to an example. FIG. 8 is a block diagram showing a large-scale passive downlink communication scheme based on 802.11b communication using a meta surface. .

As shown in FIG. 1, the wireless communication system includes a meta surface 100, a carrier wave generator 200, and a receiver 300.

When explaining the operating mechanism of the wireless communication system using the meta surface, the carrier wave generator 200 transmits an unmodulated carrier signal to the meta surface, and the meta surface 100 modulates the incident carrier signal to the receiver 300 ). An example of the modulation method used at this time may be a phase shift keying (PSK) method such as binary phase shift keying (BPSK) or quadrature phase shift keying (QPSK), but the modulation method is not limited thereto.

Here, the metasurface refers to a two-dimensional surface consisting of a pattern of meta-atoms, and each meta-atom is composed of switches that control the meta-surface by arranging a conductive square patch and a diode. do. These meta-atoms are reflected to the receiver after adjusting characteristics such as the phase, amplitude, and polarization of the carrier wave incident on the meta surface according to electrical characteristics such as dielectric constant and permeability, respectively. Accordingly, the carrier signal incident on the meta surface can be modulated according to the reflection coefficient of each meta surface element.

At this time, by applying a voltage to each diode, it becomes possible to modulate the carrier wave by controlling the electrical properties of the meta-atoms, that is, the reflection coefficient. That is, by controlling the voltage applied to the meta surface, the reflection coefficient of the meta atom can be controlled, and accordingly, the phase and amplitude of the electromagnetic wave modulated and reflected from the meta surface can be variously modulated. Here, the voltage may be applied to the meta atom in the form of a digital code. In other words, a voltage may be applied independently to each diode of the meta surface.

The meta surface 100 of FIG. 1 can be applied to wireless communication as follows. In the carrier wave generator 200, an unmodulated carrier signal is incident on the meta surface 100. In the meta-surface, 1-bit or 2-bit digital code is input to the FPGA (Field Programmable Gate Array), and the corresponding voltage is applied to the meta-surface elements.

The reflection coefficient of each meta surface element is controlled by a voltage applied through an FPGA or the like to modulate the phase or amplitude of an incident carrier signal. For example, in the case of a communication system using a PSK modulation method such as BPSK (Binary Phase Shift Keying) or QPSK (Quadrature Phase Shift Keying), the meta surface 100 modulates the phase of the carrier signal and transmits it to the receiver 300. have.

In this case, as shown in FIG. 2, even if the same voltage is applied through the FPGA, the reflection phase and amplitude are different according to the frequency of the incident carrier wave. However, in order to perform PSK modulation, the range of the reflection phase that can be obtained according to the voltage in the frequency band to be used must occupy most of -180° to 180°. For example, when it is possible to occupy a range of reflection phases from 0° to 270° at least, QPSK modulation can be performed so that each carrier wave has a phase difference of 90° through the meta surface. Therefore, it is necessary to design the meta surface so that the reflection phase that the meta surface can have in the frequency band to be used occupies the widest range as possible.

The present invention relates to a large-scale passive downlink communication technique using a software-controlled meta-surface, and performs communication based on PSK modulation by controlling the characteristics of the meta-surface so that the range of the reflection phase at the harmonic frequency occupies most of -180° to 180°. This is possible, and the characteristics of the meta surface can be controlled by software such as a computer program. Hereinafter, a method for generating a temporal code, a method for generating a space-time code, and a method for modulating a signal of a meta surface for controlling a reflection coefficient of a meta surface according to the present invention will be described.

[Time Code Generation Method for Controlling Reflection Coefficient of Meta Surface]

The time code generation method for controlling the reflection coefficient of the meta surface according to an embodiment of the present invention is a reflection phase of the carrier after the meta surface 100 receives an unmodulated carrier from the carrier wave generator 200. Phase) is intended to control the properties of meta surface elements, that is, reflection coefficients, to occupy most of the range of -180° to 180°, and to accomplish this, unlike wireless communication technology using conventional meta surfaces, 2 Provides a method of generating a time code (c _k ) having a period composed of -bit digital codes.

3 is a diagram illustrating an algorithm for a time code generation method for controlling a reflection coefficient of a meta surface according to an embodiment of the present invention. Referring to the drawing, in the method for generating a time code according to an embodiment of the present invention, a reflection amplitude (A ₁ ) for a +1 th harmonic based on a center frequency (f _c ) with respect to a first time code (c ₁ ) ) Calculating; Determining whether the reflection amplitude (A ₁ ) for the +1 th harmonic is higher than the reflection amplitude for the remaining harmonics by S dB or more and is higher than the threshold value α; Recording a reflection coefficient (a ₁ ) and a reflection phase (φ ₁ ) in a codebook together with a first time code (c ₁ ) for a +1 harmonic that satisfies the two conditions of the determining step; And by sequentially performing the step of calculating, determining, and recording a time code other than the first time code (c _k , k ≠ 1), a codebook including a set of time codes (C) is generated. It includes;

A method of generating a time code according to an embodiment of the present invention includes generating a harmonic using a time code having a period, which is composed of a 2-bit digital code, and this will be described in detail as follows.

First, the reflection amplitude (A ₁ ) for the +1 th harmonic is calculated based on the center frequency (f _c ) for the first time sign (c ₁ ). Here, the equations for calculating the reflection coefficient (a _m ) and reflection amplitude (A _m ) of the m-th harmonic when a harmonic is generated by inputting a time sign having a period are shown below [Equation 1] and [Equation 2] Same as

[Equation 1]

[Equation 2]

은 시간 부호의 길이이고,

은 시간 부호의 n번째 디지털 코드에 의한 반사 계수이다(예컨대, 시간 부호의 길이 L=10이라면, n은 1 부터 10이 될 것이다). 반송파가 메타 표면에 입사되면 메타 표면 요소들의 반사 계수에 따라 위상, 진폭 등이 변조되어 반사된다. 메타 표면 요소들의 반사 계수

는 2-bit 디지털 코드에 대하여 다음과 같이 맵핑할 수 있다. here,

Is the length of the time sign,

Is the reflection coefficient by the nth digital code of the time code (for example, if the length of the time code L=10, n will be from 1 to 10). When the carrier wave is incident on the meta surface, the phase and amplitude are modulated and reflected according to the reflection coefficients of the meta surface elements. Reflection coefficient of meta surface elements

Can be mapped as follows for a 2-bit digital code.

* 2-bit code '00'=

* 2-bit code '01'=

* 2-bit code '10'=

* 2-bit code '11'=

라고 하면, 하모닉 주파수 사이의 간격은

이 되므로, 시간 부호의 주기를 제어하여

를 조절할 수 있다. Since 2-bit is used, it is irrelevant to use any value if the phase is different by 90°. However, it is possible to set the reflection coefficient so as to have a gastric window difference of 90° by occupying a reflection phase of at least 270° for the voltage applied to the meta surface. In this way, the reflection coefficient (a _m ) for the m-th harmonic of each element of the meta surface can be calculated using the time sign. Also, the period of the time sign

, The interval between harmonic frequencies is

Therefore, by controlling the period of the time sign

Can be adjusted.

The step of calculating the above-described reflection amplitude (A ₁ ) includes reflection coefficients (a _m ) for the -m-th harmonic to the +m-th harmonic based on the center frequency (f _c ) for the first time sign (c ₁ ). Calculating; And calculating reflection amplitudes (A _m ) for the -mth to +mth harmonics from the reflection coefficients (a _m ), respectively. If reflection coefficients (a _m ) for each harmonic are calculated based on Equation 1, the reflection amplitude (A _m ) for each harmonic may be calculated based on Equation 2. In the case of FIG. 3, it is assumed that m is 7, but the value of m is not limited thereto. Since the amplitude of each harmonic is attenuated as the distance from the center frequency f _c increases, the following description will be made on the assumption that the reflection amplitude is sufficiently small from the eighth harmonic. According to an embodiment, reflection coefficients from -7th to +7th harmonics are calculated for a given time sign (c _k ) (ie, m=7).

) 판단한다. 이는 다른 하모닉을 억제함과 동시에 +1번째 하모닉에서의 충분한 송신 전력을 확보하기 위함이다. Next, whether the reflection amplitude (A ₁ ) for the +1 harmonic is higher than the reflection amplitude (Am) for the remaining harmonics by S dB or more (λ> S dB), and is more than the threshold α (

) Judge. This is to suppress other harmonics and secure sufficient transmit power at the +1 harmonic.

And, in order to compare the reflection amplitude (A ₁ ) for the +1 harmonic with the reflection amplitude (A _m ) for the remaining harmonics, calculate λ according to [Equation 3] below, and then determine whether λ> S dB. Confirm. In this case, the S dB may be 10 dB.

[Equation 3]

4 is a diagram exemplarily showing a reflection amplitude for each harmonic when a +1 th harmonic is generated using a time sign, and FIG. 5 is a diagram exemplarily illustrating a reflection phase region that appears when a +1 th harmonic is generated. For example, when the algorithm shown in FIG. 3 is applied using a time code with a threshold value α of 0.5 and L=10, the reflection amplitude (0.67) for the +1 harmonic as shown in FIG. 4 is the most amplitude among other harmonics. It was more than 10dB higher than the large -1st harmonic and was more than 0.5 threshold (α). And, as can be seen in FIG. 5, it can be seen that the reflection phase of the +1st harmonic whose amplitude is greater than the threshold value (α) of 0.5 and is 10dB larger than other harmonics occupies most of the reflection phase between -180° and 180°. have.

Next, the reflection coefficient (a ₁ ) and reflection phase (φ ₁ ) are recorded in the codebook together with the first time code (c ₁ ) for the +1 th harmonic that satisfies the above two conditions of the second step. Here, the equation for calculating the reflection phase (φ _m ) for the m-th harmonic is as shown in [Equation 4] below.

[Equation 4]

In the present invention, a time code composed of a 2-bit digital code is used, and L digital codes are arranged in a time series in a set of time codes. Therefore, when setting a time code of length L (n=1,2,3,...,L) with a 2-bit digital code, four types of digital codes (00,01,10,11) are L times. As can be specified over, the set of time codes (C) is all 4 ^L. That is, the number (K) of time codes constituting the set of time codes (C) may be up to 4 ^L.

Here, the present invention has one technical feature in using a time code having a period composed of a 2-bit digital code, unlike a conventional wireless communication technology using a meta surface. If a 1-bit digital code is used, the reflection amplitude of the harmonic is always symmetrical with respect to the center frequency (f _c ), so other harmonics other than the intended harmonic cannot be suppressed. In other words, when a 1-bit digital code is used, the +1 harmonic and the -1st harmonic always appear together, so unused harmonics cannot be suppressed. Therefore, when the number of bits of the digital code is at least 2-bit or more, this symmetry can be eliminated to suppress signals other than the +1th harmonic.

However, as the number of digital code bits increases, an additional diode must be connected and the complexity increases. In the present invention, a time code is configured using a 2-bit digital code.

Next, by sequentially performing the calculating, determining, and recording steps for time codes (c _k , k ≠ 1) other than the first time code, a codebook including a set of time codes (C) is obtained. Generate.

6 is a diagram illustrating an example of a codebook obtained through a time code generation method according to an embodiment of the present invention, and FIG. 7 is a time code generation for controlling a reflection coefficient of a meta surface according to an embodiment of the present invention. It shows a part of the set (C) of time codes derived by applying the algorithm for the method.

As shown in FIG. 6, in the codebook generated through the above-described process, information of L digital codes constituting the time code for each time code (c ₁ , c ₂ , c ₃ , …, c _k ) and When each time sign is applied to the meta surface, the reflection coefficient (a ₁ ) of the meta surface with respect to the +1th harmonic and the reflection phase (φ ₁ ) of the +1th harmonic are recorded. For reference, time codes having a reflection phase between 100° and 110° are shown in FIG. 7. If, in the step of recording in the above-described codebook, when two or more time codes having the same reflection phase calculation result appear, a time sign in which the difference in reflection amplitude for the +1 harmonic and other harmonics is larger is selected. Record it in the codebook. This is to maximize the strength of the signal received by the receiver and suppress other harmonics to minimize interference in other frequency bands.

와 같은 관계에 있고, 이들 둘 사이는 반비례 관계에 있으므로, 시간 부호의 주기 T₀를 조절함으로써 비트 전송률 R_b 제어가 가능하다. 여기서, 시간 주기 T₀는 디지털 코드의 수 L, 그리고 디지털 코드를 구성하는 비트의 주기와 각각 비례 관계에 있다. 이에 따라, 시간 부호의 주기 T₀를 제어하는 하나의 방법으로서, 2-bit 디지털 코드의 수(L)를 조절하는 방법이 있다. 시간 부호의 주기 T₀는 디지털 코드의 수 L과 비례 관계에 있으므로, L을 조절함으로써 비트 전송률 R_b의 제어가 가능하다. 한편, 시간 부호의 주기 T₀를 제어하는 또 다른 방법으로서 FPGA에서 디지털 코드를 입력할 때의 비트 주기(FPGA의 Clock 주기가 될 수 있음)를 짧게 또는 길게 하여 주기 T₀를 조절하는 방법이 있다. Meanwhile, the bit rate R _b can be controlled by adjusting the period T ₀ of the time code. The bit rate R _b is the period T ₀ of the time sign and

Since the relationship is the same as and there is an inverse relationship between the two, it is possible to control the bit rate R _b by adjusting the period T ₀ of the time code. Here, the time period T ₀ is proportional to the number L of digital codes and the period of bits constituting the digital code, respectively. Accordingly, as one method of controlling the period T ₀ of the time code, there is a method of adjusting the number L of 2-bit digital codes. Since the period T ₀ of the time code is proportional to the number L of digital codes, it is possible to control the bit rate R _b by adjusting L. On the other hand, as another method of controlling the period T ₀ of the time code, there is a method of adjusting the period T ₀ by shortening or lengthening the bit period (which can be the clock period of the FPGA) when the digital code is input in the FPGA. .

Through this process, it is possible to obtain a set of time codes (C) that occupy most of the reflection phases in the range of -180° to 180° while having a reflection amplitude that is 10 dB or more higher than that of other harmonics for the +1th harmonic.

According to the present invention, since the carrier wave can be modulated with most of the reflection phase between -180° and 180° through the time code even with a limited digital code compared to the prior art, communication based on PSK modulation can be performed on the meta surface. . For example, wireless communication of the Wi-Fi 802.11b standard based on ISM (Industrial Scientific Medical) band and DQPSK modulation may be performed through the method of generating a space-time code for a meta surface according to the present invention.

[Space-Time Code Generation Method for Controlling Reflection Coefficient of Meta Surface]

Meanwhile, the present invention further includes a method of generating a space-time code for controlling a reflection coefficient of a meta surface by using a time code obtained by the above-described time code generation method. That is, the method of generating a space-time code according to the present invention includes: estimating a channel between a carrier generator and a meta surface and a channel of the meta surface and a receiver; Calculating a phase change during carrier modulation by the meta-surface based on the estimated channel; Selecting a time code (c _k ) having a reflection phase closest to the calculated phase from the codebook generated by the time code generation method described above; And obtaining a space-time code by calculating the selected temporal code (c _k ) for each element of the meta surface.

8 is a block diagram showing a large-scale passive downlink communication scheme based on 802.11b communication using a meta surface. Referring to the drawings, in the method for generating a space-time code according to the present invention, a channel between a carrier generator and a meta surface, and a channel between the meta surface and a receiver are estimated. Subsequently, the amplitude and phase required to generate a beamforming vector may be calculated based on the estimated channel.

Next, based on the estimated channel, a phase change during carrier modulation by the meta surface 100 is calculated. In this step, a phase change during differential BPSK (DBPSK) or differential QPSK (DQPSK) modulation may be calculated. As described above, according to the present invention, communication based on the PSK modulation method can be performed by controlling the reflection phase for the +1 th harmonic through a time code composed of a 2-bit digital code. According to the present invention, since sophisticated phase modulation for a carrier is possible, the method for generating a space-time code according to the present invention uses a signal encoded with Direct-Sequence Spread Spectrum (DSSS) or Complementary Code Keying (CCK) through DBPSK and DQPSK It can be applied to the transmitting Wi-Fi 802.11b communication system. That is, in order to perform communication according to the Wi-Fi 802.11b standard, in this step, the phase change when the carrier is modulated using the DBPSK or DQPSK method may be calculated.

Next, a time code (c _k ) having a reflection phase closest to the calculated phase is selected from the codebook obtained through the time code generation method described above, and this time code is calculated for each element of the meta surface to generate a space-time code. Get Thereafter, the obtained space-time code is repeated a certain number of times to have periodicity.

According to the embodiment of the present invention, passive beamforming can be performed by precisely controlling the phases of meta elements constituting the meta surface through space-time codes. That is, if the length L of the time code is set to be long, the phase of the reflected wave can be more precisely controlled through the meta surface. However, at the same time, since the period (T ₀ ) of the space-time code increases, the length (L) of the time code and the period (T ₀ ) of the space-time code can be adjusted according to the required conditions of each system. Further, according to an embodiment of the present invention, it is possible to reduce downlink network congestion of an access point (AP) by transmitting large amounts of information requested by a user through such downlink passive beamforming.

[Computer readable recording medium in which computer programs are stored]

The present invention further includes a computer-readable recording medium storing a program for implementing a method for generating a temporal code for controlling a reflection coefficient of a meta surface and a method for generating a space-time code for controlling a reflection coefficient of a meta surface. In addition, a program stored in a computer-readable recording medium for implementing the time code generation method or the space-time code generation method can also be implemented.

That is, it will be easily understood by those skilled in the art that the above-described time/space-time code generation method may be provided in a recording medium that can be read through a computer by tangibly implementing a program of instructions for implementing this.

In other words, it is implemented in the form of a program command that can be executed through various computer means, and can be recorded on a computer-readable recording medium. The computer-readable recording medium may include program instructions, data files, data structures, etc. alone or in combination. The program instructions recorded on the computer-readable recording medium may be specially designed and constructed for the present invention, or may be known and usable to those skilled in computer software. Examples of the computer-readable recording medium include magnetic media such as hard disks, floppy disks, and magnetic tapes, optical media such as CD-ROMs and DVDs, and floptical disks. Magneto-optical media and hardware devices specially configured to store and execute program instructions such as ROM, RAM, flash memory, USB memory, and the like. Examples of program instructions include not only machine language codes such as those produced by a compiler but also high-level language codes that can be executed by a computer using an interpreter or the like. The hardware device may be configured to operate as one or more software modules to perform the operation of the present invention, and vice versa.

[Meta surface signal modulation method]

The present invention further includes a method of modulating a single frequency signal in a meta surface by using the space-time code obtained by the above-described space-time code generation method. That is, receiving a carrier wave from the carrier wave generating device; Generating a space-time code based on the above-described space-time code generation method based on the frequency of the received carrier; Inputting the generated space-time code to the meta surface to control a reflection coefficient of the meta surface; Modulating the carrier wave using the meta surface; And transmitting the modulated signal to a receiver.

After generating the space-time code, it is preferable to repeat the space-time code a certain number of times to have periodicity, and the generated space-time code can be input to the meta surface through the FPGA. In the meta-surface, the incident single frequency signal can be modulated by controlling the reflection coefficient for the harmonic according to the input space-time code. The modulated signal can then be transmitted to a receiver based on a wireless communication standard. For example, a signal transmitted according to the Wi-Fi standard may be received by a Wi-Fi chip of a user terminal.

At this time, the carrier generating device 200 generates a carrier signal having a frequency of f _c -f ₀ by moving from the center frequency (f _c ) to the interval between the harmonic frequencies (f ₀ ), and in the step of receiving the carrier wave A carrier wave having a frequency of f _c -f ₀ is received from the generator 200. Thereafter, in the step of transmitting the modulated signal to the receiver, a harmonic is generated through a space-time code, and the frequency of f _c -f ₀ is shifted to the center frequency f _c region to be used again, and the reflection phase is controlled. Based communication and beamforming can be implemented.

On the other hand, the present invention provides a passive beamforming performance by obtaining an optimal beamforming vector that maximizes the achievable bit rate under the limited power of the carrier generation device and the constraints that minimize interference with other users. Make it one of the tasks.

으로, 시간 부호의 주기에 따라 하모닉 주파수가 결정되기 때문에, 정해진 하모닉 주파수에 대하여 고정된 비트 전송률(bit rate)을 가진다. 만일, 다양한 비트 전송률을 얻기 위하여 시간 부호의 주기를 변경하면 그에 따라 하모닉 주파수 간격이 변하기 때문에, 사용하고자 하는 주파수 대역에서 원하는 비트 전송률을 얻는데 문제가 발생한다.If the period of the time sign is T ₀ , the interval between each harmonic frequency is

Thus, since the harmonic frequency is determined according to the period of the time code, it has a fixed bit rate for the determined harmonic frequency. If the period of the time code is changed to obtain various bit rates, the harmonic frequency interval changes accordingly, so a problem occurs in obtaining a desired bit rate in a frequency band to be used.

와 같이 계산할 수 있다. b는 변조 기법에 따른 비트 수이다. 따라서, 시간 부호의 주기 T₀를 조절하여 비트 전송률 R_b을 제어할 수 있다. 예를 들면, 2-bit 디지털 코드 10개로 이루어진 시간 부호를 4번 반복하여 하모닉을 생성하는 경우, FPGA에서 40MHz 클록을 사용하여

인 시간 부호를 입력함으로써 DQPSK 변조의 경우 1Mbps의 비트 전송률을 달성할 수 있다. 여기서 최대 비트 전송률은 802.11b 통신 규격에 의해 최대 11Mbps를 달성할 수 있다.The bit rate R _b has the following relationship with the period T ₀ of the time code. For the symbol period T _s , T _s =kT ₀ and k represents the number of times the time code is repeated. Where the bit rate is

It can be calculated as b is the number of bits according to the modulation technique. Therefore, it is possible to control the bit rate R _b by adjusting the period T ₀ of the time code. For example, if a time code consisting of 10 2-bit digital codes is repeated 4 times to generate a harmonic, a 40MHz clock is used in the FPGA.

By entering the in-time code, a bit rate of 1Mbps can be achieved for DQPSK modulation. Here, the maximum bit rate can achieve a maximum of 11 Mbps according to the 802.11b communication standard.

Meanwhile, the present invention also supports downlink passive beamforming through space-time codes by utilizing the fact that meta-surface elements occupy most of the reflection phases between -180° and 180° with respect to the harmonic. The number of elements constituting the meta surface is N, the power of the single frequency signal generated by the carrier wave generator is P _c , the phase shift of each element for performing passive beamforming on the meta surface is N x N diagonal matrix θ, each The reflection amplitude according to the temporal sign of the elements is N x N diagonal matrix Λ, the channels between the carrier generator and each meta surface element are N x 1 matrix g, and the channels between each meta surface element and the receiver are N x For one matrix h, the achievable rate can be calculated using the following [Equation 5].

[Equation 5]

은 잡음 전력, W는 반송파의 주파수 대역폭이다. 그리고,ζ는 실제 변조를 반영한 성능 차이를 나타낸다. (QPSK 변조를 사용하였을 경우, 약 ζ=9.8dB의 성능 저하가 발생한다). 이때, 메타 표면 요소들과 수신기 사이의 채널을 추정하기 위해서는 메타 표면에 채널을 추정하기 위한 수신 RF chain이 존재하게 된다. 따라서, 제한된 반송파 발생 장치의 전력, 그리고 다른 사용자에게 간섭을 최소화하는 제약 조건하에 달성 가능한 비트 전송률을 최대화하는 최적의 빔포밍 벡터를 구하여 수동 빔포밍을 수행할 수 있다.here,

Is the noise power, and W is the frequency bandwidth of the carrier. And, ζ represents the difference in performance reflecting the actual modulation. (When QPSK modulation is used, performance degradation of about ζ = 9.8 dB occurs). At this time, in order to estimate a channel between meta surface elements and a receiver, a reception RF chain for estimating a channel exists on the meta surface. Accordingly, passive beamforming can be performed by obtaining an optimal beamforming vector that maximizes the achievable bit rate under the limited power of the carrier generating device and the constraints that minimize interference to other users.

According to the present invention as described above, by using a time code composed of a 2-bit digital code on the meta surface, the reflection coefficient for harmonics is freely controlled, so that the meta surface effectively has a large number of reflection coefficients in a wide range without increasing the number of bits. You can design the surface. Therefore, wireless communication can be performed more practically than wireless communication using a conventional meta surface.

In addition, it is possible to reduce the downlink network congestion burdened by the AP through the downlink passive beamforming using this meta surface.

In addition, when the same information is transmitted to multiple receivers, information can be transmitted to multiple receivers through multicast beamforming in the meta surface. In addition, it can be used to broadcast information about smart factories and smart homes.

So far, the present invention has been looked at around its preferred embodiments. Those of ordinary skill in the art to which the present invention pertains will be able to understand that the present invention can be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative point of view rather than a limiting point of view. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope equivalent thereto should be construed as being included in the present invention.

100: meta surface
200: carrier sending device
300: receiver

Claims (12)

As a time code generation method for controlling the reflection coefficient of the meta surface,
Calculating a reflection amplitude (A ₁ ) for a +1 th harmonic based on a center frequency (f _c ) for a first time sign (c ₁ );
Determining whether a reflection amplitude (A ₁ ) for the +1 th harmonic is higher than the reflection amplitude for the remaining harmonics by S dB or more and a threshold value α or more;
Recording a reflection coefficient (a ₁ ) and a reflection phase (φ ₁ ) in a codebook together with the first time code (c ₁ ) for a +1 harmonic that satisfies the two conditions of the determining step; And
A codebook including a set of time codes (C) is generated by sequentially performing the calculating, determining, and recording steps for time codes (c _k , k ≠ 1) other than the first time code. The step of doing;
It includes,
Time code generation method to control the reflection coefficient of meta surface. The method of claim 1,
Calculating the reflection amplitude (A ₁ ),
Calculating reflection coefficients (a _m ) for the -mth to +mth harmonics based on the center frequency (f _c ) for the first time code (c ₁ ); And
Calculating reflection amplitudes (A _m ) for -mth to +mth harmonics from the reflection coefficients (a _m );
It characterized in that it further comprises,
Time code generation method to control the reflection coefficient of meta surface. The method of claim 1,
The first time code (c ₁ ) is composed of L 2-bit digital codes arranged in time series, and the number (K) of time codes constituting the set of time codes (C) is at most 4 ^L , , The step of generating the codebook is characterized in that it is performed until the k becomes K,
Time code generation method to control the reflection coefficient of meta surface. The method of claim 3,
It characterized in that the bit rate control is possible by adjusting the period T ₀ of the time code,
Time code generation method to control the reflection coefficient of meta surface. The method of claim 1,
In the step of recording in the codebook, when two or more time codes having the same reflection phase appear, a time code having a large difference in reflection amplitude between the +1 harmonic and other harmonics is selected and recorded in the codebook. doing,
Time code generation method to control the reflection coefficient of meta surface. The method of claim 1,
The S dB is characterized in that 10 dB,
Time code generation method to control the reflection coefficient of meta surface. A computer-readable recording medium in which a computer program performing the method of claim 1 is stored. Estimating a channel between a carrier generator and a meta surface and a channel of the meta surface and a receiver;
Calculating a phase change during carrier modulation by the meta-surface based on the estimated channel;
Selecting a time code (c _k ) having a reflection phase closest to the calculated phase from the codebook generated by the method of claim 1; And
Obtaining a space-time code by calculating the selected temporal code (c _k ) for each element of the meta surface;
Containing,
A method of generating a space-time code to control the reflection coefficient of a meta surface. The method of claim 8,
The step of calculating the phase change is calculating a phase change during a differential BPSK (DBPSK) or a differential QPSK (DQPSK) modulation,
A method of generating a space-time code to control the reflection coefficient of a meta surface. A computer-readable recording medium storing a computer program that performs the method of claim 8. Receiving a carrier wave from a carrier wave generating device;
Generating the space-time code according to claim 8 based on the frequency of the received carrier;
Inputting the generated space-time code to the meta surface to control a reflection coefficient of the meta surface;
Modulating the carrier wave using the meta surface; And
Transmitting the modulated signal to a receiver;
Containing,
Signal modulation method of meta surface. The method of claim 11,
In the step of receiving the carrier wave, the carrier wave having a frequency of f _c -f ₀ is received from the carrier wave generator,
F ₀ is the interval between harmonic frequencies,
Signal modulation method of meta surface.

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