KR102097110B1 - Decoding method using soft-decision in wi-fi backscatter system and wi-fi backscatter system using it - Google Patents

Abstract

The Wi-Fi backscatter system provides a decoding method using soft decision. The decoding method using soft decision in the Wi-Fi backscatter system provided by the present invention is a method in which a reader receives and decodes a preamble signal and a data signal having multiple levels from a tag for a plurality of subcarriers. Receiving a preamble signal and the data signal; Calculating, by the reader, a decision variable corresponding to each of the plurality of levels based on a difference between the size of the preamble signal corresponding to each of the plurality of levels for each of the plurality of subcarriers and the size of the data signal; And the reader decoding the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to the plurality of levels.

Description

Decoding method using soft decision in Wi-Fi backscatter system, Wi-Fi backscatter reader and Wi-Fi backscatter system using it {DECODING METHOD USING SOFT-DECISION IN WI-FI BACKSCATTER SYSTEM AND WI-FI BACKSCATTER SYSTEM USING IT }

The present invention relates to a decoding method using soft decision in a Wi-Fi backscatter system, a Wi-Fi backscatter reader, and a Wi-Fi backscatter system using the same, which is soft decision in a Wi-Fi backscatter system using multiple levels Decryption method using, Wi-Fi backscatter reader and relates to a Wi-Fi backscatter system using the same.

Today, as the Internet of Things (IoT) technology has developed, a battery problem required for IoT devices has occurred, and a Wi-Fi Backscatter technology has emerged to solve the problem. The technology, which originated from the University of Washington, uses wireless signals to charge devices that consume less power through signal strength and backscatter. In short, this technology uses RF power to charge the device's battery, which means energy harvesting technology that collects, stores, and supplies power through ambient wireless signals.

However, the existing Wi-Fi backscatter technology has some problems to be applied in real life. First, the existing Wi-Fi backscatter technology can communicate at a relatively high speed in the uplink where the tag data is transmitted, but the communication distance is limited. In addition, in the existing Wi-Fi backscatter technology, when data is transmitted, data is determined according to whether or not the Wi-Fi packet is reflected, and thus, only one bit per packet is transmitted, and thus the data transmission rate decreases.

Related prior art is Korean Registered Patent No. 10-1590291 (Invention name: backscatter system using phase modulation and uplink communication method using the same, publication date: February 1, 2016).

The present invention provides a decoding method using soft decision and a Wi-Fi backscatter reader and system using the same, which can improve the data transmission rate in the uplink of the Wi-Fi backscatter system and reduce the probability of errors when transmitting data. I want to.

In order to achieve the above object, the decoding method using soft decision in the Wi-Fi backscatter system provided by the present invention is a method in which a reader receives and decodes preamble signals and data signals having multiple levels from a tag for each subcarrier. The method of claim 1, wherein the reader receives the preamble signal and the data signal; Calculating, by the reader, a decision variable corresponding to each of the plurality of levels based on a difference between the size of the preamble signal corresponding to each of the plurality of levels for each of the plurality of subcarriers and the size of the data signal; And the reader decoding the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to the plurality of levels.

Preferably, the decoding of the data signal may include extracting two decision variables having the smallest value among the decision variables respectively corresponding to the plurality of levels; Calculating two probability decision variables using the sum of the two decision variables and the two decision variables; And decoding the data signal based on the two probability determination variables.

Preferably, in the step of calculating the probability decision variable, after exchanging the two decision variables, each of the two decision variables is divided by the sum of the two decision variables, and the two probability decision variables can be calculated. have.

Preferably, the decoding of the data signal based on the two probability determination variables comprises: calculating, for each of the plurality of levels, the sum of the probability determination variables for each of the plurality of subcarriers; And decoding the data signal to the level where the sum is the largest among the plurality of levels.

개의 레벨로 이루어질 수 있다.Preferably, the plurality of levels

It can consist of two levels.

In addition, the Wi-Fi backscatter reader provided by the present invention includes a receiver configured to receive preamble signals and data signals having a plurality of levels for each subcarrier from a tag; A calculator configured to calculate a decision variable corresponding to each of the plurality of levels based on a difference between the size of the preamble signal corresponding to each of the plurality of levels for each of the plurality of subcarriers and the size of the data signal; And a decoding unit that decodes the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to each of the plurality of levels.

Preferably, the calculator extracts two decision variables having the smallest value among the decision variables corresponding to the plurality of levels, and uses the sum of the two decision variables and the two decision variables to create two The probability determination variable is calculated, and the data signal can be decoded based on the two probability determination variables.

Preferably, after the two decision variables are exchanged with each other, the calculator calculates two probability decision variables by dividing each of the two decision variables by a sum of the two decision variables.

Preferably, the decoding unit may calculate, for each of the plurality of levels, the sum of the probability determination variables for each of the plurality of subcarriers, and decode the data signal to the level of which the sum is the largest among the plurality of levels. .

개의 레벨로 이루어 질 수 있다.Preferably, the plurality of levels

It can consist of two levels.

In addition, the Wi-Fi backscatter system provided by the present invention is a Wi-Fi backscatter system composed of an access point (AP), a tag, and a reader, wherein the tag transmits a preamble signal and a data signal, and the reader comprises the A receiver configured to receive a preamble signal and a data signal from a tag; A calculator configured to calculate a decision variable corresponding to each of the plurality of levels based on a difference between the size of the preamble signal corresponding to each of the plurality of levels for each of the plurality of subcarriers and the size of the data signal; And a decoding unit that decodes the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to each of the plurality of levels.

The present invention can improve the data rate by using multiple levels when transmitting a signal from a tag to a reader in an uplink of a Wi-Fi backscatter system.

In addition, the present invention can improve reliability by reducing an error occurrence probability when transmitting a signal from a tag to a reader in an uplink of a Wi-Fi backscatter system.

1 is a view showing the configuration of a Wi-Fi backscatter system according to an embodiment of the present invention.
2 is a diagram illustrating the configuration of a backscatter signal according to an embodiment of the present invention.
3 is a flowchart of a decoding method using soft decision in a Wi-Fi backscatter system according to an embodiment of the present invention.
4 is a diagram illustrating the structure of a preamble signal according to an embodiment of the present invention.
5 is a flowchart of a step of decoding a data signal according to an embodiment of the present invention.
6 is a schematic conceptual diagram for explaining the steps of extracting two decision variables according to an embodiment of the present invention.
7 is a flowchart of a step of decoding a data signal based on two probability determination variables according to the present invention.
8 is a diagram showing the configuration of a Wi-Fi backscatter reader according to an embodiment of the present invention.

The present invention can be applied to various changes and may have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and 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 are used for similar components.

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

When an element is said to be "connected" or "connected" to another component, it is understood that other components may be directly connected to or connected to the other component, but other components may exist in the middle. It should be. On the other hand, when a component is said to be "directly connected" or "directly connected" to another component, it should be understood that no other component exists in the middle.

The terms used in this 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 this application, the terms "include" or "have" are intended to indicate the presence of features, numbers, steps, actions, components, parts or combinations thereof described herein, one or more other features. It should be understood that the existence or addition possibilities of fields or numbers, steps, operations, components, parts or combinations thereof are not excluded in advance.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by a person skilled in the art to which the present invention pertains. Terms such as those defined in a commonly used dictionary should be interpreted as having meanings consistent with meanings in the context of related technologies, and should not be interpreted as ideal or excessively formal meanings unless explicitly defined in the present application. Does not.

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

1 is a view showing the configuration of a Wi-Fi backscatter system according to an embodiment of the present invention. Referring to Figure 1, the Wi-Fi backscatter system is composed of an access point (100, Access Point), a reader 200 and a tag 300, the reader 200 through a downlink (Down link) tag (300) When requesting information from), the tag 300 may respond to the reader 200 through an uplink.

The access point 100 is configured to transmit and receive wireless signals such as Wi-Fi, and the reader 200 can receive signals from the access point 100 and tags 300, for example, communication such as a smartphone. The device may be configured as a reader 200.

The tag 300 is a component capable of receiving and reflecting a signal from the access point 100, and is preferably configured to include an antenna to receive and backscatter the signal from the access point 100.

First, to describe the conventional uplink transmission method, the tag 300 level modulates the signal received from the access point 100 to 0 or 1 through intermittent reflection using an antenna and transmits it to the reader (if there are 4 levels) In case of modulated transmission, it can be transmitted in the form of 00, 01, 10, 11). At this time, if the reflection amount of the antenna included in the tag 300 is adjusted, intermittent reflection is possible. That is, the uplink can be viewed as the reader 200 receives the signal reflected by the tag 300.

Prior to the detailed description of the decoding method using soft decision in the Wi-Fi backscatter system according to the present invention, the configuration of the signal used in the uplink of the Wi-Fi backscatter system, that is, from the tag 300 to the reader 200 Look at the configuration of the backscatter signal being sent. 2 illustrates a configuration of a backscatter signal according to an embodiment of the present invention.

Referring to FIG. 2, the backscatter signal of the present invention may be composed of a data section carrying actual data and a preamble section before the data section. In other words, in the present invention, the backscatter signal can be regarded as including a preamble signal and a data signal.

The preamble signal may include channel state information (CSI). The modulation method of the Wi-Fi backscatter system determines the packet type signal received from the access point 100 by the tag 300 in the module, and connects different capacitances to the antenna through a switch to connect the impedance of the signal ( Impedance) is transmitted differently. At this time, the maximum and minimum values of the reflected amount (the amount of the signal transmitted by the tag) are determined through the channel status information before communication, and then the packet is not reflected. When a signal is transmitted and all packets are reflected, a signal corresponding to '11' may be transmitted.

In addition, the reader 200 may obtain the minimum and maximum values of the reflection amount of the tag 300 using the channel state information of the received preamble signal, and then obtain a predetermined threshold through this, and receive based on the obtained predetermined threshold It is possible to determine the value of the signal.

개의 레벨을 갖도록 구성될 수 있다. 가령 본 발명은 프리앰블 신호 및 데이터 신호가 4개의 레벨을 갖도록 태그(300)가 반사할 수 있도록 구성될 수 있고, 이때 리더기(200)는 상기 소정 임계치를 기준으로 수신된 신호의 레벨을 판정할 수 있다.In the present invention, the preamble signal and the data signal have multiple levels, for example

It can be configured to have two levels. For example, the present invention may be configured so that the tag 300 can reflect such that the preamble signal and the data signal have four levels, and the reader 200 can determine the level of the received signal based on the predetermined threshold. have.

In addition, in the present invention, as shown in FIG. 2, the preamble signal and the data signal may be divided into a plurality of basic unit signals, and the basic unit signal may be configured to have any one of a plurality of levels. For example, in the present invention, when the preamble signal and the data signal are configured to have four levels, the tag 300 may transmit the signal by having any one of 00, 01, 10, and 11 in the basic unit signal. .

At this time, however, the signal reflected from the tag 300 is reflected due to the unique characteristics of the Wi-Fi backscatter system (the characteristic that the tag 300 does not operate with a battery or a unique power source, but is operated by energy of the RF signal). The receiving side receives a signal that has been changed to some extent by the channel state, not the original signal.

That is, in the Wi-Fi backscatter system, when the tag 300 transmits a basic unit signal having one of a plurality of levels, the reader 200 receives the received signal by a channel state to some extent. Since it is received, the determination of the level of the basic unit signal may not be accurate.

For example, when the tag 300 transmits signals in the order of 00, 01, 10, and 11, the reader 200 may determine the signals in the order of 00, 01, 11, and 10. Therefore, there is a need to accurately decode the signal received by the reader 200 in the Wi-Fi backscatter system.

3 is a flowchart of a decoding method using soft decision in the Wi-Fi backscatter system according to the present invention. Referring to FIG. 3, a decoding method using soft decision in a Wi-Fi backscatter system according to the present invention includes: a step in which the reader 200 receives a preamble signal and a data signal (S310); The reader 200 calculates a determination variable corresponding to each of the plurality of levels based on a difference between the size of the preamble signal corresponding to each of the plurality of levels for each of the plurality of subcarriers and the size of the data signal (S320); And the reader 200 decoding the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to the plurality of levels (S330).

In step S310, the reader 200 receives a preamble signal and a data signal. As described above, the preamble signal may be configured to have multiple levels, specifically, the preamble signal may be composed of multiple basic unit signals, and each basic unit signal may be configured to have multiple levels.

Also, the preamble signal may include a plurality of sub-carriers. For example, in the present invention, the Wi-Fi backscatter signal (preamble signal and data signal) may be configured to have 64 subcarriers.

In summary, in step S310, the reader 200 receives the preamble signal from the tag 300 and then receives the data signal. The preamble signal having a plurality of levels for each subcarrier may be first received and stored. At this time, the reader 200 may sort the channel information values extracted for each level by size as shown in Equation 1 below, and store the location of the changed size for each subcarrier.

는 리더기(200)가 수신한 레벨 i의 j번째 부반송파를 의미하고,

는 오름차순으로 재배치된 레벨 값이며, k는 재배치되어 저장된 i의 순서를 의미한다.here

Denotes the j-th subcarrier of level i received by the reader 200,

Is a level value rearranged in ascending order, and k denotes the order of i reordered and stored.

In step S320, the reader 200 calculates a determination variable corresponding to each of the multiple levels based on the difference between the size of the preamble signal corresponding to each of the multiple levels for each of the plurality of subcarriers and the size of the data signal. For example, the determination variable may be calculated using Equation 2 below.

는 레벨 k의 j번째 부반송파에 대응되는 프리앰블 신호이고,

는 j번째 부반송파에 대응되는 데이터 신호이다. 다시 말해

는 프리앰블 신호 중 레벨 k의 j번째 부반송파에 대응되는 값을 의미하고,

는 데이터 신호 중 j번째 부반송파에 대응되는 값을 의미한다. 또한 abs는 절대값을 의미한다.here,

Is a preamble signal corresponding to the j-th subcarrier of level k,

Is a data signal corresponding to the j-th subcarrier. In other words

Denotes a value corresponding to the j-th subcarrier of level k among the preamble signals,

Denotes a value corresponding to the j-th subcarrier of the data signal. Also, abs means absolute value.

As described above, in the present invention, a preamble signal may be first transmitted and a value corresponding to each of a plurality of levels may be previously stored for a plurality of subcarriers. For example, if the preamble signal used in the present invention has 64 subcarriers and has 4 levels, the reader 200 may store the size of the preamble signal corresponding to each of the 4 levels for each of the 64 subcarriers.

Step S330 is a step in which the reader 200 decodes the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to each of the multiple levels.

4 is a diagram showing the structure of a preamble signal according to an embodiment of the present invention. In the present invention, the preamble signal may be composed of multiple levels. As shown in FIG. 4, the preamble signal is 00, 01, 10, It can consist of 4 levels with a value of 11. In addition, the data signal can also be made up of four levels to correspond to this.

As described above, in the present invention, the information on the preamble signal stored in advance can be used to decode the data signal transmitted after the preamble signal. If the preamble signal and the data signal have four levels, the transmitted data signal is 4 Decoding of the data signal can be performed by determining which level value among the dog's levels.

Therefore, at the moment when the reader 200 receives the data, it is impossible to determine which level value of the four data levels the received data signal has, and only the magnitude of the received data signal can be measured. By calculating a decision variable based on a difference between a size corresponding to each of the four levels of the stored preamble signal and the size of the transmitted data signal, and determining which of the four levels the data signal has based on the calculated decision variable The received data signal can be decoded.

5 is a flowchart of a step of decoding a data signal according to an embodiment of the present invention. Referring to FIG. 5, in the step of decoding a data signal according to an embodiment of the present invention, extracting two decision variables having the smallest value among decision variables corresponding to multiple levels (S331) ; Calculating two probability decision variables using the sum of the two decision variables and the two decision variables (S332); And decoding the data signal based on two probability determination variables (S333).

In step S331, two decision variables having the smallest values among the decision variables corresponding to the plurality of levels are extracted. The data signal may be decoded based on the two decision variables. For example, if the preamble signal and the data signal have four levels, in step S320, four decision variables may be calculated to correspond to each of the four levels. Two decision variables can be extracted using Equation (3).

와

는 각각 j번째 부반송파의 1번째 최솟값과 2번째 최솟값이다.here,

Wow

Are the first and second minimum values of the j-th subcarrier, respectively.

와

로 각각 0.3과 0.5를 추출할 수 있다.FIG. 6 is a schematic conceptual diagram for explaining the step of extracting two decision variables according to an embodiment of the present invention, and continues with the description of the step of extracting the decision variables with reference to FIG. 6. 6 shows the difference between the data received on the j-th subcarrier and the preamble signal when the reader 200 receives the data signal. Specifically, the difference between the size of the received data and the size corresponding to level 0 of the preamble signal is 0.6, the difference between the size of the received data and the size corresponding to level 1 of the preamble signal is 0.3, the size of the received data And a difference in size corresponding to level 2 of the preamble signal is 0.5, and a difference in size between the size of the received data and the level 4 of the preamble signal is 0.9. At this time, using Equation 3 above,

Wow

0.3 and 0.5 can be extracted respectively.

값이 작을수록 높은 확률 값을 가지는 것이 바람직하기 때문에, 두 개의 판정변수를 서로 교환한 후, 두 개의 판정변수 각각을 두 개의 판정변수를 합한 값으로 나누는 것이 바람직하다. 이를 식으로 표현하면 아래의 수학식 4와 같다.Step S332 is a step of calculating two probability determination variables using the sum of two determination variables and two determination variables, and in order to apply the determination variables obtained above as probability values, two for each of the two determination variables. By dividing the decision variable by the sum, two probability decision variables can be obtained. At this time

Since it is preferable to have a higher probability value as the value is smaller, it is preferable to exchange two decision variables, and then divide each of the two decision variables by the sum of the two decision variables. This is expressed as Equation 4 below.

=

=

=

=

Step S333 is a step of decoding the data signal based on the two probability determination variables calculated in step S332.

7 is a flowchart of a step of decoding a data signal based on two probability determination variables according to the present invention. Referring to FIG. 7, decoding a data signal based on two probability determination variables (S333) includes: calculating a sum of a plurality of probability determination variables for each subcarrier for each level (S333-1); And decoding the data signal to the level with the largest sum among the plurality of levels (S333-2).

Step S333-1 is a step of calculating the sum of a plurality of subcarrier probability determination variables for each of the levels, and step S333-2 is a step of calculating the sum of a plurality of subcarrier probability determination variables for each of the plurality of levels. Decoding the data signal by using, it is possible to decode the data signal to the level of the largest sum of the plurality of levels. The step S333 may be expressed by Equation 5 below.

를 모두 합하고, 합해진 값이 가장 큰 값을 갖는 레벨, 즉 확률 판정변수의 k번째 레벨 값이 복호화될 데이터로 결정될 수 있다.That is, in the present invention, for each of a plurality of levels, the probability determination variable calculated for each subcarrier

All of them are summed, and a level at which the summed value has the largest value, that is, a k-th level value of the probability determination variable may be determined as data to be decoded.

At this time, N may be the number of subcarriers, and the number of subcarriers may be a predetermined number of subcarriers having the largest difference in size of subcarriers for each level through experiments. For example, when the total number of subcarriers of the preamble signal and the data signal is 64, only 32 large differences in the size of subcarriers for each level may be selected and applied to Equation 5. When a predetermined number of subcarriers are selected and applied in this way, accuracy may be improved in a process of decoding a data signal than when all of the subcarriers are applied.

8 is a diagram showing the configuration of a Wi-Fi backscatter reader according to an embodiment of the present invention. Referring to FIG. 8, a Wi-Fi backscatter reader according to an embodiment of the present invention includes a receiver 210 for receiving preamble signals and data signals from a plurality of tags 300; A calculation unit 220 for calculating a determination variable corresponding to each of a plurality of levels based on a difference between a size of the preamble signal corresponding to each of a plurality of levels for each subcarrier and a size of the data signal; And a decoder 230 for decoding the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to each of the plurality of levels.

The calculation unit 220 extracts two decision variables having the smallest value among the decision variables corresponding to a plurality of levels, and divides the two decision variables into a sum value for each of the two decision variables, thereby providing two probabilities. Decision variables can be calculated.

In addition, the calculator 220 may replace the two decision variables, and then divide each of the two decision variables by the sum of the two decision variables, and calculate two probability decision variables.

The decoder 240 calculates a sum by adding values for each subcarrier to each of the two probability determination variables, and data to be decoded to a level corresponding to the probability determination variable having a larger value among the two probability determination variables. You can decide.

Lastly, referring to FIG. 1, in the Wi-Fi backscatter system according to an embodiment of the present invention, the tag 300 transmits a preamble signal and a data signal having a plurality of levels for a plurality of subcarriers, and a reader 200 The receiver 210 receives a preamble signal and a data signal; A calculation unit 220 for calculating a determination variable corresponding to each of a plurality of levels based on a difference between a size of the preamble signal corresponding to each of a plurality of levels for each subcarrier and a size of the data signal; And a decoder 230 for decoding the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to each of the plurality of levels.

Meanwhile, the above-described embodiments of the present invention can be written in a program executable on a computer, and can be implemented on a general-purpose digital computer that operates the program using a computer-readable recording medium.

The computer-readable recording medium includes a magnetic storage medium (eg, ROM, floppy disk, hard disk, etc.), an optical reading medium (eg, CD-ROM, DVD, etc.).

So far, the present invention has been focused on the preferred embodiments. Those skilled in the art to which the present invention pertains will 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 in terms of explanation, not limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the equivalent range should be interpreted as being included in the present invention.

100: access point 200: reader
210: receiving unit 220: calculating unit
230: decoding unit 300: tag

Claims (11)

A method for a reader to receive and decode a preamble signal and a data signal having a plurality of levels for a plurality of subcarriers from a tag,
The reader receiving the preamble signal and the data signal;
Calculating, by the reader, a decision variable corresponding to each of the plurality of levels based on a difference between the size of the preamble signal corresponding to each of the plurality of levels for each of the plurality of subcarriers and the size of the data signal; And
The reader decoding the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to the plurality of levels.
Including,
Decoding the data signal is
A decoding method using soft decision in a Wi-Fi backscatter system, characterized in that two determination variables each having the smallest value among the determination variables corresponding to the plurality of levels and a sum of the two determination variables are used.
According to claim 1,
Decoding the data signal is
Extracting two decision variables having the smallest value among the decision variables corresponding to the plurality of levels;
Calculating two probability decision variables using the sum of the two decision variables and the two decision variables; And
Decoding the data signal based on the two probability determination variables
Decoding method using soft decision in the Wi-Fi backscatter system, characterized in that it comprises a.
According to claim 2,
In the step of calculating the probability determination variable,
After the two decision variables are exchanged with each other, each of the two decision variables is divided by the sum of the two decision variables, and the two judgment variables are calculated, thereby calculating two probability decision variables. Decoding method using.
According to claim 2,
Decoding the data signal based on the two probability determination variable is
For each of the plurality of levels, calculating a sum of the probability determination variables for each of the plurality of subcarriers; And
Decoding the data signal to the level where the sum is the largest among the plurality of levels
Decoding method using soft decision in the Wi-Fi backscatter system, characterized in that it comprises a.
According to claim 1,
The multiple levels

Decoding method using soft decision in the Wi-Fi backscatter system, characterized in that it consists of two levels.
A receiver configured to receive preamble signals and data signals having multiple levels for each subcarrier from a plurality of tags;
A calculator configured to calculate a decision variable corresponding to each of the plurality of levels based on a difference between the size of the preamble signal corresponding to each of the plurality of levels for each of the plurality of subcarriers and the size of the data signal; And
A decoding unit decoding the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to each of the plurality of levels
Including,
The decoding unit
Wi-Fi backscatter reader, characterized in that it uses the sum of the two decision variables and the two decision variables having the smallest value among the decision variables corresponding to the plurality of levels.
The method of claim 6,
The calculation unit
The two decision variables having the smallest value among the decision variables corresponding to the plurality of levels are extracted, and two probability decision variables are calculated using the sum of the two decision variables and the two decision variables, Wi-Fi backscatter reader, characterized in that for decoding the data signal based on the two probability determination variables.
The method of claim 7,
The calculation unit
Wi-Fi backscatter reader, characterized in that, after exchanging the two judgment variables, each of the two judgment variables is divided by the sum of the two judgment variables, and two probability judgment variables are calculated. .
The method of claim 7,
The decoding unit
Wi for each of the plurality of levels, characterized in that the sum of the probability determination variable for each of the plurality of sub-carriers is calculated, and the data signal is decoded to the level with the largest sum among the plurality of levels. -Fi backscatter reader.
The method of claim 6,
The multiple levels

Wi-Fi backscatter reader, characterized in that it consists of two levels.
In the Wi-Fi backscatter system consisting of an access point (AP), a tag and a reader,
The tag is
A preamble signal and a data signal are transmitted for each subcarrier,
The reader
A receiver configured to receive the preamble signal and data signal from a tag;
A calculator configured to calculate a decision variable corresponding to each of the plurality of levels based on a difference between the size of the preamble signal corresponding to each of the plurality of levels for each of the plurality of subcarriers and the size of the data signal; And
A decoding unit decoding the data signal based on at least one decision variable having the smallest value among the decision variables corresponding to each of the plurality of levels
Including,
The decoding unit
A Wi-Fi backscatter system characterized by using a value obtained by adding two decision variables having the smallest value among the decision variables corresponding to the plurality of levels and the two decision variables.

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