KR20190086975A - Decoding method using soft-decision in wi-fi backscatter system and wi-fi backscatter system using it - Google Patents

Abstract

Provided is a decoding method using soft determination in a Wi-Fi backscatter system, which is capable of increasing a data transmission rate in an uplink. According to the present invention, the decoding method using soft determination in a Wi-Fi backscatter system allows a reader to receive and decode preamble and data signals from a tag, which have a plurality of levels for each of a plurality of subcarriers. The decoding method of the reader comprises the steps of: receiving the preamble signal and the data signal; calculating a determination variable corresponding to each of the levels based on a difference value between the intensity of the preamble and data signals corresponding to each of the levels for each subcarrier; and decoding the data signal based on at least one determination variable having the least value among the determination variables corresponding to each of the levels.

Description

TECHNICAL FIELD [0001] The present invention relates to a Wi-Fi backscatter system, a Wi-Fi backscatter reader, and a Wi-Fi backscatter system using the soft-decision in a Wi-Fi backscatter system. }

The present invention relates to a decoding method using a soft decision in a Wi-Fi backscatter system, a Wi-Fi backscatter reader, and a Wi-Fi backscatter system using the same. In a Wi-Fi backscatter system using multi- A Wi-Fi backscatter reader, and a Wi-Fi backscatter system using the same.

Today, with the development of the Internet of Things (IoT) technology, battery problems have occurred in IoT devices, and Wi-Fi backscatter technology has emerged to solve them. The technology, launched at the University of Washington, uses wireless signals to charge devices that consume less power through signal strength and backscatter. Simply put, this technology uses RF power to charge the device's battery, which means energy harvesting technology that collects, stores and supplies power through the surrounding wireless signals.

However, existing Wi-Fi backscatter technologies have some problems in real-life applications. First, the existing Wi-Fi backscatter technology can communicate at a relatively high speed in the uplink where tag data is transmitted, but the communication distance is limited. In addition, since the existing Wi-Fi backscatter technology discriminates data according to the presence or absence of reflection of a Wi-Fi packet when transmitting data, there is a problem that a data rate is lowered because one bit is transmitted per packet.

Korean Prior Art No. 10-1590291 (entitled BACKSPACE CAMERA SYSTEM USING PHASE MODULATION AND ULTRA LINK COMMUNICATION METHOD USING THE SAME) discloses a related prior art, which is published on February 1, 2016.

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

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

Preferably, the step of decoding the data signal comprises the steps of: 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 decision variables.

Preferably, in calculating the probability decision variable, after exchanging the two decision variables with each other, dividing each of the two decision variables by the sum of the two decision variables to calculate two probability decision variables have.

Advantageously, the step of decoding the data signal based on the two probability decision variables comprises: calculating, for each of the plurality of levels, a sum of the probability decision variables for the plurality of subcarriers; And decoding the data signal at a level at which the sum is the highest among the plurality of levels.

개의 레벨로 이루어질 수 있다.Advantageously, said plurality of levels

Lt; / RTI > level.

In addition, the Wi-Fi backscatter reader provided in the present invention includes a receiver for receiving a preamble signal and a data signal having a plurality of levels for a plurality of subcarriers from a tag; A calculation unit for calculating a decision variable corresponding to each of the plurality of levels based on a difference between the magnitude of the preamble signal and the data signal magnitude corresponding to a plurality of levels for each of the plurality of subcarriers; And a decoding unit that decodes the data signal based on at least one determination variable having the smallest value among decision variables corresponding to each of the plurality of levels.

Preferably, the calculation unit extracts two decision variables having the smallest value among the decision variables respectively corresponding to the plurality of levels, and uses two values of the two decision variables and the two decision variables to calculate two Calculate a probability decision variable, and decode the data signal based on the two probability decision variables.

Preferably, the calculating unit may calculate the two probability decision variables by exchanging the two decision variables and dividing each of the two decision variables by a sum of the two decision variables.

Preferably, the decoding unit may calculate a sum of the probability decision variables for each of the plurality of levels, and decode the data signal to a level at which the sum is the highest among the plurality of levels .

개의 레벨로 이루어 질 수 있다.Advantageously, said plurality of levels

Lt; / RTI > level.

In addition, the Wi-Fi backscatter system provided in the present invention is a Wi-Fi backscatter system comprising an access point (AP), a tag, and a reader, wherein the tag transmits a preamble signal and a data signal, A receiving unit for receiving a preamble signal and a data signal from a tag; A calculation unit for calculating a decision variable corresponding to each of the plurality of levels based on a difference between the magnitude of the preamble signal and the data signal magnitude corresponding to a plurality of levels for each of the plurality of subcarriers; And a decoding unit that decodes the data signal based on at least one determination variable having the smallest value among decision variables corresponding to each of the plurality of levels.

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

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

1 is a diagram illustrating a configuration of a Wi-Fi backscatter system according to an embodiment of the present invention.
2 is a diagram illustrating a configuration of a backscatter signal according to an embodiment of the present invention.
3 is a flowchart illustrating a method of decoding a soft Wi-Fi backscatter system using a soft decision according to an embodiment of the present invention.
4 is a diagram illustrating a 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 diagram for explaining a step of extracting two decision variables according to an embodiment of the present invention.
Figure 7 is a flow diagram of the step of decoding a data signal based on two probability decision variables according to the present invention.
FIG. 8 is a diagram illustrating a configuration of a Wi-Fi backscatter reader according to an embodiment of the present invention.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the invention is not intended to be limited to the particular embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. Like reference numerals are used for like elements in describing each drawing.

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

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms such as those defined in commonly used dictionaries are to be interpreted as having a meaning consistent with the contextual meaning of the related art and are to be interpreted as either ideal or overly formal in the sense of the present application Do not.

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

1 is a diagram illustrating a configuration of a Wi-Fi backscatter system according to an embodiment of the present invention. 1, a Wi-Fi backscatter system includes an access point 100, a reader 200, and a tag 300, and a reader 200 transmits a tag 300 The tag 300 can respond to the reader 200 through an up link.

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 the tag 300. For example, The device may be configured as a reader 200. [

The tag 300 is preferably a component that can receive and reflect a signal from the access point 100 and is configured to include an antenna for receiving and backscattering signals from the access point 100.

First, the conventional uplink transmission method will be described. The tag 300 modulates the signal received from the access point 100 to 0 or 1 through intermittent reflection using an antenna, and transmits the signal to the reader 01, 10, 11 in the case of modulating and transmitting). At this time, if the reflection amount of the antenna included in the tag 300 is adjusted, intermittent reflection becomes possible. That is, the uplink can be regarded as the reader 200 receiving the signal reflected by the tag 300.

Prior to a specific description of a decoding method using a soft decision in a Wi-Fi backscatter system according to the present invention, a configuration of a signal used in an uplink of a Wi-Fi backscatter system, that is, Let's look at the composition of the backscatter signal that is sent. FIG. 2 shows 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 interval in which real data is stored and a preamble interval in front of a data interval. In other words, the backscatter signal in the present invention can be considered to include a preamble signal and a data signal.

The preamble signal may include channel state information (CSI). In the modulation scheme of the Wi-Fi backscatter system, the tag determines the packet type signal received from the access point 100 from the module and connects different capacitances to the antenna through the switch, impedance, and the maximum and minimum values of the reflected amount (the amount of the signal transmitted by the tag) are obtained through the channel state information before the communication, and if the packet is not reflected, Signal is transmitted, and if the packet is completely reflected, a signal corresponding to '11' may be transmitted.

In addition, the reader 200 obtains the minimum value and the maximum value of the reflection amount of the tag 300 using the channel state information of the received preamble signal, and then obtains a predetermined threshold value, 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 a plurality of levels. For example,

Lt; / RTI > level. For example, the present invention can be configured such that the preamble signal and the data signal are reflected by the tag 300 so that the preamble signal and the data signal have four levels, wherein the reader 200 can determine the level of the received signal on the basis of the predetermined threshold have.

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 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 can transmit a signal with the basic unit signal having any one of 00, 01, 10, and 11 .

At this time, since the unique characteristic of the Wi-Fi backscatter system (the tag 300 does not operate with the battery or the inherent power source but operates by the energy of the RF signal) The receiving side receives a signal that is somewhat fluctuated by the channel state, not the original signal.

That is, in the Wi-Fi backscatter system, when the tag 300 transmits a signal having any one of a plurality of levels to the basic unit signal, the reader 200 determines that the received signal is a signal The determination of the level of the basic unit signal may become inaccurate.

For example, when the tag 300 transmits signals in the order of 00, 01, 10, and 11, the reader 200 can 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.

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

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

Also, the preamble signal may include a plurality of sub-carriers. For example, in the present invention, a 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 a preamble signal from the tag 300 and then receives a data signal. The reader 200 can receive and store a plurality of preamble signals having a plurality of levels for each of a plurality of subcarriers. At this time, the reader 200 can sort the channel information values extracted by each class according to the size as shown in Equation (1) below and store the changed size position 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 a j-th subcarrier of a level i received by the reader 200,

Is the level value relocated in ascending order, and k is the order of i that is rearranged and stored.

In step S320, the reader 200 calculates a decision variable corresponding to a plurality of levels based on the difference between the size of the preamble signal corresponding to each of a plurality of levels and the data signal size for each of a plurality of subcarriers. For example, the decision variable can be calculated using the following equation (2).

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 in the preamble signal,

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

As described above, according to the present invention, a preamble signal is transmitted first and a value corresponding to each of a plurality of levels can be stored in advance for each of a plurality of subcarriers. For example, if the preamble signal used in the present invention has 64 subcarriers and has four levels, the reader 200 can store a preamble signal corresponding to four levels for each of 64 subcarriers.

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

FIG. 4 is a diagram illustrating a structure of a preamble signal according to an embodiment of the present invention. In the present invention, a preamble signal may have a plurality of levels. As shown in FIG. 4, Lt; RTI ID = 0.0 > 11. ≪ / RTI > In addition, the data signal may also be composed of four levels so as to correspond thereto.

In the present invention, a data signal transmitted after a preamble signal can be decoded using information on a preamble signal stored in advance. If the preamble signal and the data signal have four levels, The decoding of the data signal can be performed by determining which of the two levels has the level value.

Therefore, at the moment when the reader 200 receives the data, it is not possible to determine which level of the four levels the received data signal has, and only the magnitude of the received data signal can be measured, A determination variable is calculated by a difference value between the magnitude corresponding to each of the four levels of the stored preamble signal and the magnitude of the transmitted data signal and by determining which level value of the four levels the data signal has based on the calculated determination 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, the step of decoding a data signal according to an embodiment of the present invention includes extracting two decision variables having the smallest value among decision variables corresponding to a plurality of levels (S331) ; Calculating (S332) 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 decision variables (S333).

In step S331, two decision variables having the smallest value among the decision variables corresponding to the plurality of levels are extracted. The data signal can be decoded based on the two decision variables thus extracted. For example, when the preamble signal and the data signal have four levels, four decision variables may be calculated so as to correspond to each of the four levels in step S320. In this case, The 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 minima of the jth subcarrier, respectively.

와

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

Wow

0.3 and 0.5, 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 decision variables by using a sum of two decision variables and two decision variables. In order to apply the decision variable obtained above to the probability value, two The two probability decision variables can be obtained by dividing the decision variables by the sum. At this time

Since it is desirable to have a higher probability value as the value is smaller, it is desirable to exchange the two judgment variables and divide each of the two judgment variables into a sum of the two judgment variables. This can be expressed by Equation (4) below.

=

=

=

=

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

Figure 7 is a flow diagram of the step of decoding a data signal based on two probability decision variables according to the present invention. Referring to FIG. 7, decoding (S333) a data signal based on two probability decision variables includes calculating (S333-1) a sum of probability decision variables for a plurality of subcarriers for each of a plurality of levels; And a step (S333-2) of decoding the data signal at the highest level among the plurality of levels.

The step S333-1 is a step of calculating a sum of probability decision variables for a plurality of subcarriers for each of a plurality of levels, and a step S333-2 is a step for calculating a sum of probability decision variables for a plurality of subcarriers, The data signal can be decoded at the highest level among the plurality of levels. The step S333 may be expressed by the following equation (5).

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, a probability decision variable calculated for each sub-

And the level at which the summed value has the largest value, that is, the kth level value of the probability determination variable, can be determined as the data to be decoded.

In this case, N may be the number of subcarriers, and the number of subcarriers may be a predetermined number of subcarriers having the greatest size difference of subcarriers according to level through experiments. For example, when the total number of subcarriers included in the preamble signal and the data signal is 64, only 32 subcarriers having a large size difference between levels can be selected and applied to Equation (5). When a predetermined number of subcarriers are selected and applied, the accuracy of the decoding of the data signal can be improved as compared with the case where the entire subcarrier is applied.

FIG. 8 is a diagram illustrating a 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 a preamble signal and a data signal from a plurality of tags 300; A calculation unit 220 for calculating a decision variable corresponding to each of a plurality of levels based on a magnitude of a preamble signal corresponding to each of a plurality of levels for each of a plurality of subcarriers and a difference value between the data signal magnitudes; And a decoding unit (230) for decoding the data signal based on at least one decision variable having a smallest value among 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 respectively corresponding to the plurality of levels, divides the two decision variables by the sum of the two decision variables for each of the two decision variables, The judgment variable can be calculated.

Also, the calculation unit 220 may calculate two probability decision variables by replacing the two decision variables with each other, and dividing each of the two decision variables by the sum of the two decision variables.

The decoding unit 240 calculates a sum by adding all the values for each of the two sub-carriers to each of the two probability decision variables, and sets the level corresponding to the probability decision variable whose sum is larger than the sum of the two probability decision variables as the data to be decoded .

1, the tag 300 transmits a preamble signal and a data signal having a plurality of levels for a plurality of subcarriers, and the reader 200 transmits the preamble signal and the data signal, A reception unit 210 for receiving a preamble signal and a data signal; A calculation unit 220 for calculating a decision variable corresponding to each of a plurality of levels based on a magnitude of a preamble signal corresponding to each of a plurality of levels for each of a plurality of subcarriers and a difference value between the data signal magnitudes; And a decoding unit (230) for decoding the data signal based on at least one decision variable having a smallest value among decision variables corresponding to each of the plurality of levels.

The above-described embodiments of the present invention can be embodied in a general-purpose digital computer that can be embodied as a program that can be executed by a computer and operates the program using a computer-readable recording medium.

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

The present invention has been described with reference to the preferred embodiments. It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the disclosed embodiments should be considered in an illustrative rather than a restrictive sense. The scope of the present invention is defined by the appended claims rather than by the foregoing description, and all differences within the scope of equivalents thereof should be construed as being included in the present invention.

100: access point 200: reader
210: Receiving unit 220:
230: decryption unit 300: tag

Claims (11)

A method for a receiver to receive and decode a preamble signal and a data signal having a plurality of levels for a plurality of subcarriers from a tag,
Receiving the preamble signal and the data signal by the reader;
Calculating a decision variable corresponding to each of the plurality of levels based on a difference between a size of the preamble signal corresponding to each of the plurality of levels and a size of the data signal for each of the plurality of subcarriers; And
Decrypting the data signal based on at least one decision variable having a smallest value among decision variables each corresponding to the plurality of levels
Wherein the soft decision is performed in a Wi-Fi backscatter system.
The method according to claim 1,
The step of decoding the data signal
Extracting two decision variables having the smallest value among 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 decision variables
Wherein the soft decision is performed in a Wi-Fi backscatter system.
3. The method of claim 2,
In calculating the probability decision variable,
Characterized in that the two decision variables are exchanged with each other, and then each of the two decision variables is divided by a sum of the two decision variables to calculate two probability decision variables. In the Wi-Fi backscatter system, / RTI >
3. The method of claim 2,
Wherein the step of decoding the data signal based on the two probability decision variables comprises:
Calculating, for each of the plurality of levels, a sum of the probability decision variables for the plurality of subcarriers; And
Decoding the data signal with the highest level among the plurality of levels
The method of claim 1, wherein the Wi-Fi backscatter system is a Wi-Fi backscatter system.
The method according to claim 1,
The plurality of levels

Level back-to-back system in a Wi-Fi back-scattering system.
A receiver for receiving a preamble signal and a data signal having a plurality of levels for a plurality of subcarriers from a plurality of tags;
A calculation unit for calculating a decision variable corresponding to each of the plurality of levels based on a difference between the magnitude of the preamble signal and the data signal magnitude corresponding to a plurality of levels for each of the plurality of subcarriers; And
And a decoding unit that decodes the data signal based on at least one determination variable having a smallest value among decision variables corresponding to each of the plurality of levels
Gt; Wi-Fi backscatter < / RTI > reader.
The method according to claim 6,
The calculation unit
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 decodes the data signal based on the two probability decision variables.
8. The method of claim 7,
The calculation unit
Wherein the two decision variables are calculated by dividing the two decision variables by the sum of the two decision variables after exchanging the two decision variables with each other. .
8. The method of claim 7,
The decoding unit
And for each of the plurality of levels, calculates a sum of the probability decision variables for the plurality of subcarriers, and decodes the data signal at a level at which the sum is the highest among the plurality of levels -Fi backscatter reader.
The method according to claim 6,
The plurality of levels

Level back-to-back reader.
A Wi-Fi backscatter system comprising an access point (AP), a tag, and a reader,
The tag
A preamble signal and a data signal,
The reader
A receiver for receiving the preamble signal and the data signal from a tag;
A calculation unit for calculating a decision variable corresponding to each of the plurality of levels based on a difference between the magnitude of the preamble signal and the data signal magnitude corresponding to a plurality of levels for each of the plurality of subcarriers; And
And a decoding unit that decodes the data signal based on at least one determination variable having a smallest value among decision variables corresponding to each of the plurality of levels
Gt; Wi-Fi backscatter system. ≪ / RTI >

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