KR20190025157A - Method and Apparatus for signal detection in Backscatter system - Google Patents

Abstract

The present invention relates to a method and apparatus for signal detection in a backscatter system. The method for signal detection in a backscatter system comprises the steps of: performing averaging operations on each of a plurality of signals received via a plurality of antennas; calculating channel state information of each subcarrier based on a preamble signal of each signal on which the average operation is performed; and calculating a channel state threshold value of each subcarrier using the channel state information, and selecting one of the plurality of signals based on the corresponding channel state threshold value for each subcarrier.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backscatter system,

The present invention relates to a method and apparatus for detecting a signal in a backscatter system, and more particularly, to a method and apparatus for detecting a signal in a backscatter system capable of selecting a signal having the best reception state from signals received via a plurality of antennas Detection method and apparatus.

Recently, the Internet of Things (IOT), which connects the Internet to all things, has attracted attention. The IOT provides intelligent interfaces and communication protocols to objects so that objects are integrated into the network, autonomously detects changes in objects or environments, and responds to user requests.

What is required to realize IOT technology is the implementation of intelligent interfaces and communication protocols, and the provision of intelligent interfaces to all objects. However, not all things can support LTE (Long Term Evolution), Wi-Fi protocol used in modern smart phones, etc., and the power required for wireless communication can not be periodically supplied through a battery.

In recent years, Wi-Fi backscatter technology has been attracting attention because it is connected with backscatter technology that collects Wi-Fi RF signals and acquires power. Wi-Fi backscatter technology is a promising technology for the IoT field where the Wi-Fi signal transmitted from the Wi-Fi AP (Access Point) is used for communication as an energy source so that the RFID tag can communicate without a separate power supply .

The Wi-Fi backscatter technology described above is largely composed of three devices. A Wi-Fi AP that generates a Wi-Fi signal, a Wi-Fi tag that reflects signals from the AP to transmit its signal, and a Wi-Fi reader that receives the tag information.

Wi-Fi APs and Wi-Fi readers are one of the existing Wi-Fi devices and therefore can send and receive Wi-Fi packets. The tag only reflects the signal generated from the Wi-Fi AP, and if it reflects the signal, it means '1'. The Wi-Fi reader determines what information has been transmitted from the tag through the power of the signal received from the tag.

However, there is a problem that the uplink transmission distance from the conventional tag to the Wi-Fi reader is seriously limited by the interference of the AP signal. In other words, the signal received by the reader reflected by the tag causes more attenuation than the signal coming directly from the Wi-Fi AP, and the signal from the AP acts as a large interference in detecting the tag signal from the signal received by the reader , The transmission distance of the uplink is limited.

A related prior art is Korean Patent No. 0825362 (published on April 28, 2008).

An object of the present invention is to provide a method and an apparatus for detecting a signal in a backscatter system which can solve the problem of transmission distance being limited due to attenuation due to reflection in uplink communication of a backscatter system and interference of an access point signal.

The problems to be solved by the present invention are not limited to the above-mentioned problem (s), and another problem (s) not mentioned can be clearly understood by those skilled in the art from the following description.

A method for detecting a signal in a backscatter system according to an embodiment of the present invention is a method for detecting a signal in a reader in a backscatter system having a reader having a plurality of antennas, a powerless sensor node and an access point, Calculating a channel state information of each subcarrier based on a preamble signal of each signal subjected to the averaging operation, calculating channel state information of each subcarrier based on the channel state information, , And selecting one of the plurality of signals based on the corresponding channel state threshold value for each subcarrier.

Preferably, the plurality of signals received through the plurality of antennas is the same signal reflected from the powerless sensor node, and each signal includes a short training symbol (STS), a preamble including an LTS (Long Training Symbol) , And a data area.

Preferably, the channel state information of each subcarrier may be calculated by dividing the LTS of the frequency domain of each subcarrier by a preset LTS.

Preferably, the step of selecting one of the plurality of signals may include using a channel state information of each subcarrier to determine a first channel state threshold value for the first bit and a second channel state threshold value for the second bit, Calculating a distance between a first channel state threshold value and a second channel state threshold value for each subcarrier, and selecting a signal having the largest calculated distance from the plurality of signals as a signal of the corresponding subcarrier Step < / RTI >

Preferably, the first channel threshold value is calculated by averaging packets transmitted with '1' in the preamble signal, and the second channel threshold value may be calculated by averaging packets transmitted with '0' in the preamble signal have.

Preferably, the signal detection method in the backscatter system may further include discriminating bit information by comparing channel state information on the selected signal with the first and second channel state threshold values.

Preferably, the step of discriminating the bit information may include calculating an Euclidian distance between the channel state information of each subcarrier and the first or second channel state threshold value, calculating a Euclidean distance based on the calculated Euclidean distance, And determining the information.

According to another aspect of the present invention, there is provided an apparatus for detecting a signal in a backscatter system, comprising: an averaging unit for averaging each of a plurality of signals received through a plurality of antennas; A channel state measurement unit for calculating channel state information of each subcarrier, calculating a channel state threshold value of each subcarrier using the channel state information, and calculating a channel state threshold value for each subcarrier based on the channel state threshold value, And a signal selector for selecting one of the signals.

Preferably, the plurality of signals received through the plurality of antennas is the same signal reflected from the powerless sensor node, and each signal includes a short training symbol (STS), a preamble including an LTS (Long Training Symbol) , And a data area.

Preferably, the channel state measuring unit divides the LTS of the frequency domain of each subcarrier into a predetermined LTS, and calculates channel state information of each subcarrier.

Preferably, the signal selector includes a threshold value calculating module for calculating a first channel state threshold value for the first bit and a second channel state threshold value for the second bit using the channel state information of each subcarrier, A distance calculation module for calculating a distance between the first channel state threshold value and the second channel state threshold value for each subcarrier, a signal selection module for selecting a signal of the antenna having the largest distance between the thresholds calculated for each subcarrier, . ≪ / RTI >

Preferably, the threshold value calculation module calculates a first channel state threshold value by averaging the packets having transmitted '1' in the preamble signal when the preamble bits are '1' and '0', respectively And a second channel state threshold value can be calculated by averaging the packets having transmitted '0' in the preamble signal.

The signal detection apparatus may further include a discriminator for discriminating bit information by comparing channel state information on the selected signal with the first and second channel state threshold values.

Preferably, the determining unit may calculate the Euclidean distance between the channel state information of each subcarrier and the first or second channel state threshold, and may determine the bit information based on the calculated Euclidean distance.

According to the present invention, in the uplink communication of the backscatter system, the reader receives signals from a plurality of antennas, and determines the states of the reception signals by the estimated CSI based on the preamble of the reception signals, By selecting the best signal, there is an effect of improving the uplink transmission distance.

In addition, there is an effect of improving the signal-to-noise power ratio of the received signal by averaging the signals received by the plurality of antennas.

The effects of the present invention are not limited to the above-mentioned effects, and various effects can be included within the scope of what is well known to a person skilled in the art from the following description.

to be.
2 is a block diagram illustrating a configuration of a reader according to an embodiment of the present invention.
3 is a diagram illustrating a frame structure of a wireless packet according to an embodiment of the present invention.
4 is a block diagram specifically showing a configuration of the signal selector shown in FIG.
FIG. 5 is a complex plane diagram illustrating a difference between a first channel state threshold value and a second channel state threshold value according to an embodiment of the present invention.
6 is a diagram for explaining an uplink communication method using a backscatter system according to an embodiment of the present invention.
7 is a flowchart illustrating a signal detection method of a reader in an uplink communication according to an embodiment of the present invention.
FIG. 8 is a graph illustrating bit error performance when information is detected after performing only an LTS averaging operation.
9 is a graph showing bit error performance when only an optional technique for selecting one of a plurality of signals is applied.
10 is a graph illustrating bit error performance when the present invention is applied.

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.

In the following description and claims, the backscatter system according to the present invention assumes that surrounding Wi-Fi signals are used for backscatter communication. However, the present invention is not limited to Wi-Fi backscatter communication, and the backscatter system of the present invention can be applied to any communication system that can utilize channel state information such as RFID, Zigbee, and BLE.

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

1 is a view for explaining a backscatter system according to an embodiment of the present invention.

Referring to FIG. 1, a backscatter system includes a powerless sensor node 100, a reader 200, and an access point 300.

The access point 300 (Access Point) may correspond to a general wireless router, and transmits a wireless signal (Wi-Fi packet) to peripheral devices to provide a wireless Internet connection. The wireless Internet may be a conventional Wi-Fi, and the access point 300 may be a Wi-Fi wireless router used as a Wi-Fi helper. Of course, wireless Internet is not necessarily a Wi-Fi concept.

The access point 300 broadcasts a wireless signal (ex, Wi-Fi packet) to the surroundings. Accordingly, the wireless signal is transmitted to both the reader 200 and the powerless sensor node 100.

Since the powerless sensor node 100 operates with fine power and has no battery, it is difficult to wirelessly communicate with a large amount of power such as Wi-Fi. However, the wireless sensor node 100 can be connected to the Internet via the reader 200, Lt; / RTI >

The powerless sensor node 200 may be implemented in a tag form. In the embodiment of the present invention, the powerless sensor node 200 may refer to a battery-free passive tag in which a separate power supply (battery) such as an RFID tag is not present.

In a typical backscatter system, the reader 200 can transmit or request information to the powerless sensor node 100 through a downlink, and the powerless sensor node 100 transmits a response to the uplink (Up) Link to the reader 200 via the network.

In the uplink, the powerless sensor node 100 reflects the radio signal received from the access point 300 and transmits information (bit string). That is, the powerless sensor node 100 transmits information to be transmitted to the reader 200 by transmitting the information to the wireless signal received from the access point 300. At this time, the powerless sensor node 200 switches the loads connected to the antenna to transmit the wireless signal. Each load is determined so that the difference of the reflection coefficient of the antenna when it is connected with the antenna becomes the maximum, and the difference of the reflection signal when connected to each load becomes larger as the difference of reflection coefficient is larger. The powerlessness sensor node 200 changes the impedance of the antenna and transmits '1' or '0' as a difference of the reflected peripheral wireless signal (Wi-Fi) signal.

The reader 200 can modulate the wireless signal received from the access point 300 into a signal readable by the powerless sensor node 100 and transmit the modulated signal to the powerless sensor node 100 via the Internet The Internet of things can be realized. The reader 200 may correspond to a user terminal having a built-in wireless Internet function (Wi-Fi function) such as a normal mobile phone, a smart phone, a smart pad, and a notebook computer.

In an embodiment of the present invention, a reader 200 for receiving a signal using a plurality of antennas is provided to improve a transmission distance in an uplink. Since the reader 200 has a plurality of antennas, a plurality of channel environments exist on a signal transmission / reception path, and a signal having the best reception state is selected from the signals received through the plurality of antennas.

The reader 200 receives a radio signal transmitted by the access point 300 and a radio signal reflected by the powerless sensor node 100 together. At this time, the wireless signal reflected and transmitted from the powerless sensor node 200 experiences a large attenuation, and may be vulnerable to various noise and interference generated in the reader 200. [ Therefore, the reader 200 receives a signal using a plurality of antennas and selects a signal having the best reception condition among the signals received through the plurality of antennas, in order to improve signal detection performance.

The reader 200 can use the preamble transmitted before data transmission to select a signal having a good reception state. That is, since the power-free sensor node 100 transmits a pre-determined bit string in advance as a preamble before data transmission, the reader 200 uses a preamble of a signal received through a plurality of antennas to generate a signal that is less distorted Can be detected.

Specifically, the reader 200 receives a signal with a plurality of antennas, estimates the CSI based on the preamble of the received signal, determines the state of the received signal with the estimated CSI, and selects the signal with the best reception state have. The powerless sensor node 100 reflects the surrounding signals to change the channel state, and this change appears in the CSI. Therefore, the reader 200 can calculate the CSI (channel state information) of the received radio signals and measure the change of the CSI to detect the information bits transmitted by the power-free sensor node 100.

Hereinafter, how the reader 200 detects a signal will be described in detail.

The reader 200 performs the averaging operation on the signals received through the plurality of antennas. At this time, the reader 200 performs an averaging operation on a plurality of packets. Since the same bit is transmitted during the packet interval during which the averaging operation is performed, the data transmission rate of the uplink decreases as the averaging interval is extended, but the ratio of CSI signal power to noise power can be improved by averaging received packets.

The reader 200 calculates the channel state values of the respective subcarriers on the basis of the preamble signals of the averaged signals. Then, the reader 200 calculates a first channel state threshold value by averaging the packets having transmitted '1' in the preamble signal for each of the preamble bits '1' and '0' And a second channel state threshold value is calculated by averaging the packets having transmitted '0' in the signal.

Then, the reader 200 calculates the distance between the first channel state threshold value and the second channel state threshold value for each subcarrier, and determines whether the distance between the first channel state threshold value and the second channel state threshold value is the largest The signal is determined to be the signal having the best reception state and is selected. The reader 200 then compares the channel state value for the selected signal with the first and second channel state thresholds to determine the information bits.

As described above, in the uplink communication of the backscatter system, the reader 200 receives a signal with a plurality of antennas, determines the state of the reception signal with the channel state value (CSI) calculated based on the preamble of the reception signal, By selecting a signal having the best reception state among the reception signals, the uplink transmission distance can be improved.

FIG. 2 is a block diagram illustrating a configuration of a reader according to an embodiment of the present invention. FIG. 3 is a diagram illustrating a frame structure of a wireless packet according to an embodiment of the present invention. FIG. 5 is a diagram illustrating a complex plane of a difference between a first channel state threshold value and a second channel state threshold value according to an exemplary embodiment of the present invention. Referring to FIG.

2, the reader 200 includes a plurality of antennas 210, an averaging operation unit 220, a channel state measurement unit 230, a signal selection unit 240, and a determination unit 250.

The plurality of antennas 210 receive signals reflected from the powerless sensor node, respectively.

The averaging operation unit 220 performs averaging operation on a plurality of signals received through the plurality of antennas 210, respectively. That is, the averaging unit 220 averages the signals received through the plurality of antennas 210 before selecting the best received signal among the plurality of signals, thereby increasing the signal-to-noise power ratio of the signal have.

The signal reflected by the powerless sensor node has a frame structure including a preamble (PLCP preamble), a header, and a data area as shown in FIG. The preamble is composed of a Short Training Symbol (STS) and a Long Training Symbol (LTS), and each of the STS and LTS can have a length of 8 mu s. The header may have a length of 4 mu s and the data symbols of the data area may have a length of 4 mu s each.

The reader 200 estimates a channel using a preamble, and can use an LTS among the preambles.

Therefore, the LTS received through the plurality of antennas is expressed by Equation 1 described below.

은 프리앰블 내의 반복되는 LTS 중 하나를 나타내는 인덱스, l은 수신 패킷의 인덱스, w_l(t)는 additive white Gaussian noise(AWGN)를 나타낸다. 수학식 1에서

은 액세스포인트로부터 수신된 신호,

는 무전력 센서 노드로부터 반사되어 수신된 신호를 나타낸다.

은 무전력 센서 노드 안테나에서의 감쇠 계수,

은 l번째 패킷에 실린 정보로 0 또는 1이 할당된다. _Here, h _{sr, l} (t) is a transmission channel coefficient, x _Tn (t) to the reader from the access point is an access point is broadcasting a radio _signal, h _{tr, l} (t) is the reader from the non-power sensor node, transmission channel coefficient, h _{st, l} (t) is a transmission channel coefficient of a non-power sensor node from the access point,

1 denotes an index indicating one of the repeated LTSs in the preamble, 1 denotes an index of a received packet, and w ₁ (t) denotes additive white Gaussian noise (AWGN). In Equation (1)

A signal received from the access point,

Represents a received signal reflected from the powerless sensor node.

Is the attenuation coefficient of the powerless sensor node antenna,

0 " or " 1 "

In order to solve this problem, a data estimating index that requires less variation with time and does not significantly change the value by multipath is necessary. The channel state information has a frequency diversity characteristic that represents propagation characteristics in 64 subcarrier units. The channel state information measured in different subcarriers clearly indicates the received signal strength represented by a single index. And can be effectively applied to a data demodulation method using a power magnitude. Therefore, in order to estimate the channel state information, it is necessary to convert the signal in the time domain as shown in Equation (1) into the signal in the frequency domain.

The averaging unit 220 performs FFT on the LTS included in the received signal and converts the LTS into a frequency-domain LTS. The LTS in the frequency domain is as shown in Equation 2 below.

은 프리앰블 내의 반복되는 LTS 중 하나를 나타내는 인덱스, l은 수신 패킷의 인덱스, W_l(t)는 additive white Gaussian noise(AWGN)를 나타낸다.

은 무전력 센서 노드 안테나에서의 감쇠 계수,

은 l번째 패킷에 실린 정보로 0 또는 1이 할당된다. Here, k is an _index, H _{sr, l} (k) is accessed the transmission channel coefficient from the point to the reader, X _Tn (k) is an access point is broadcasting a radio _signal, H _{tr, l} (t) of the sub-carriers are non-power sensor transmission channel coefficient of the reader from the node, H _{st, l} (t) is a transmission channel coefficient of a non-power sensor node from the access point,

Denotes an index indicating one of the repeated LTSs in the preamble, l denotes an index of a received packet, and W _l (t) denotes additive white Gaussian noise (AWGN).

Is the attenuation coefficient of the powerless sensor node antenna,

0 " or " 1 "

When the signal is transformed into the frequency domain signal as shown in Equation (2), the averaging unit 220 averages the subcarriers included in the frequency domain LTS. At this time, the averaging operation unit 220 may perform an averaging operation on the packets corresponding to the predetermined number. That is, the averaging unit 220 performs averaging on the received signal as shown in Equation (3) below.

는 부 반송파의 인덱스, Y_Tn,l[k]는 k 부반송파의 주파수 영역의 LTS, L은 패킷 개수를 의미한다. here,

Is the index of the subcarrier, Y _{Tn, l} [k] is the LTS in the frequency domain of k subcarriers, and L is the number of packets.

By performing averaging on the signals received by the plurality of antennas, the signal-to-noise power ratio of the signal can be increased.

The channel state measurement unit 230 calculates channel state information of each subcarrier based on the preamble signal of each signal on which the averaging operation is performed.

The reader 200 measures the channel state information of the received signals because it can detect the information bits transmitted by the powerless sensor node by measuring the change of the channel state information of the received signals.

The channel state measurement unit 230 divides the received LTS into a predetermined LTS to calculate channel state information (CSI). That is, the channel state measurement unit 230 can calculate the channel state information (CSI) of each subcarrier by dividing the LTS of the frequency domain of each subcarrier by the predetermined LTS. Then, channel state information (CSI) such as Equation (4) described below can be calculated, respectively.

는 k 부반송파의 채널상태정보로, 값으로 산출될 수 있다.

는 검출하려는 백스케터 신호의 상향 링크 채널,

는 액세스 포인트와 리더기 사이의 채널,

는 액세스 포인트로부터의 잡음을 나타낸다.

은

번째 패킷에 실린 정보로 0 또는 1일 수 있으며, 이 값은 데이터 전송 전에 무전력 센서 노드가 반사하여 전송한 프리앰블들을 이용한다. here,

Is the channel state information of the k subcarriers, and can be calculated as a value.

The uplink channel of the backscatter signal to be detected,

A channel between the access point and the reader,

Represents the noise from the access point.

silver

The information contained in the first packet may be 0 or 1, and this value uses the preambles transmitted and reflected by the power-free sensor node before data transmission.

When the channel state information of each subcarrier is calculated, the information bit transmitted from the powerless sensor node can be determined using the channel state information. However, since the reader 200 receives the same number of signals corresponding to the number of antennas through a plurality of antennas, it selects a signal having the best reception state from a plurality of reception signals, and discriminates the information bit from the selected signal .

The signal selector 240 calculates the channel state threshold value of each subcarrier using the channel state information of each subcarrier and selects one of the plurality of signals based on the corresponding channel state threshold value for each subcarrier do. That is, the signal selector 240 calculates the first channel state threshold value for the first bit and the second channel state threshold value for the second bit using the channel state information of each subcarrier, A signal of the antenna having the largest difference between the one channel state threshold value and the second channel state threshold value is selected. Here, the first bit may be '1' and the second bit may be '0'.

The signal selection unit 240 includes a threshold value calculation module 242, a distance calculation module 244, and a signal selection module 246 as shown in FIG.

The threshold value calculation module 242 calculates a first channel state threshold value by averaging the packets having transmitted '1' in the preamble signal when the preamble bits are '1' and '0', respectively, And a second channel state threshold value is calculated by averaging the packets having transmitted '0' in the signal. The first channel state threshold value can be calculated using Equation (5) described below, and the second channel state threshold value can be calculated using Equation (6) described below.

는 k 부반송파의 제1 채널상태 임계값을 의미한다. N은 프리앰블에 전송된 패킷의 수를 의미하고, ‘1’과‘0’을 보낸 패킷의 수는 동일하도록 할 수 있다. here,

Denotes a first channel state threshold value of k subcarriers. N means the number of packets transmitted in the preamble, and the number of packets sent '1' and '0' can be the same.

는 k 부 반송파의 제2 채널상태 임계값을 의미한다.here,

Denotes a second channel state threshold value of the k subcarriers.

As described above, the threshold value calculation module 242 can calculate the first channel state threshold value and the second channel state threshold value by averaging the packets having transmitted '1' and '0' in the preamble.

The distance calculation module 244 calculates the distance between the first channel state threshold value and the second channel state threshold value for each subcarrier. That is, the distance calculation module 244 may calculate the distance d between the first channel state threshold value and the second channel state threshold value using Equation (7) described below.

The distance between the first channel state threshold value and the second channel state threshold value on the subcarrier k is expressed in a complex plane as shown in FIG.

The signal selection module 246 selects signals of the antenna having the largest distance between the two threshold values for each sub-carrier wave. That is, the greater the distance between the first channel state threshold value and the second channel state threshold value, the more suitable the threshold value for discriminating the information bits transmitted from the powerless sensor node. Therefore, the signal selection module 246 can select the signal of the antenna having the greatest distance between the two channel state threshold values for the subcarriers of the plurality of signals received through the plurality of antennas 210 as the signal having the best reception state .

The determination unit 246 compares the channel state information of the signal selected by the signal selection unit 240 with the first and second channel state threshold values to determine bit information. That is, the determination unit 246 calculates the Euclidean distance between the channel state information of each subcarrier and the first or second channel state threshold, and determines the information based on the calculated Euclidean distance.

Specifically, the determination unit 246 calculates the Euclidean distance between the channel state information of the selected signal and the first and second channel state threshold values. At this time, the determination unit 246 may calculate the Euclidean distance D _i using the following equation (8).

Here, D _i denotes the Euclidean distance between the channel state threshold of the packets sent i and the channel state information of the data packet, i may be '0' or '1', and K is the number of subcarriers , and k denotes an index of a subcarrier.

When the Euclidean distance is calculated as shown in Equation (8), the determining unit 246 can determine the information bit ( _Bl ) using Equation (9) using the Euclidean distance.

That is, the Euclidean distance D ₁ between the second channel state threshold value of the packets that transmitted '1' and the channel state information of the data packet is greater than the first channel state threshold value of the packets that transmitted '0' Is greater than the Euclidean distance D ₂ between the channel state information, the information bit can be determined as '0'. In addition, the Euclidean distance D ₁ between the second channel state threshold value of the packets sent '1' and the channel state information of the data packet is greater than the first channel state threshold value of the packets that sent '0' Is smaller than the Euclidean distance (D ₂ ) between the channel state information, the information bit can be determined as '1'.

6 is a diagram for explaining an uplink communication method using a backscatter system according to an embodiment of the present invention.

Referring to FIG. 6, the access point 300 broadcasts a radio signal (S610). That is, the access point 300 transmits a radio signal to the reader 200 and the powerless sensor node 100 in the vicinity.

In step S610, the powerless sensor node 100 transmits information to be transmitted to the reader 200 to the wireless signal received from the access point 300 (S620).

When step S620 is performed, the reader 200 receives signals reflected from the powerless sensor node 100 through a plurality of antennas (S630). At this time, the reader 200 receives the same number of signals corresponding to the number of antennas.

When the step S630 is performed, the reader 200 performs an averaging operation on each received signal (S640), and calculates channel state information of each subcarrier based on the preamble signal of each signal subjected to the averaging operation S650). At this time, performing the averaging operation on each signal improves the signal-to-noise power ratio of the signal, and consequently the ratio of the signal power to the noise power of the channel state information can be improved.

When the step S650 is performed, the reader 200 selects the signal having the best reception state among the reception signals based on the channel state information of each subcarrier (S660). A detailed description of a method for the reader 200 to select a signal having the best reception state among a plurality of reception signals will be described with reference to FIG.

7 is a flowchart illustrating a signal detection method of a reader in an uplink communication according to an embodiment of the present invention.

Referring to FIG. 7, the reader receives the signals reflected from the powerless sensor node through a plurality of antennas (S710), and performs the averaging operation on each received signal (S720). At this time, the reader can convert the LTS included in the preamble of each signal into the LTS in the frequency domain, and perform the averaging operation on the LTS in the frequency domain. By performing averaging on the signals received by the plurality of antennas, the signal-to-noise power ratio of the signal can be increased.

When the step S720 is performed, the reader calculates the channel state information of each subcarrier based on the preamble signal of each signal on which the averaging operation is performed (S730). At this time, the reader can calculate the channel state information of each subcarrier by dividing the LTS in the frequency domain by the predetermined LTS.

When step S730 is performed, the reader calculates a first channel state threshold value by averaging the packets having transmitted '1' in the preamble signal when the preamble bits are '1' and '0', respectively, The second channel state threshold value is calculated by averaging the packets having transmitted '0' in step S740.

When the step S740 is performed, the reader calculates the distance between the first channel state threshold value and the second channel state threshold value for each subcarrier (S750). If the distance between the two channel state threshold values is the largest (S760). That is, the reader can select a signal having the largest distance between the first channel state threshold value and the second channel state threshold value as a signal having the best reception state and select the signal.

When the step S760 is performed, the reader compares the channel state information of the selected signal with the first and second channel state thresholds to determine the information bits (S770). At this time, the reader calculates the Euclidean distance between the channel state information of each subcarrier and the first or second channel state threshold value, and determines the information bit based on the calculated Euclidean distance. That is, the Euclidean distance D ₁ between the second channel state threshold value of the packets that transmitted '1' and the channel state information of the data packet is greater than the first channel state threshold value of the packets that transmitted '0' Is greater than the Euclidean distance D ₂ between the channel state information, the information bit can be determined as '0'. In addition, the Euclidean distance D ₁ between the second channel state threshold value of the packets sent '1' and the channel state information of the data packet is greater than the first channel state threshold value of the packets that sent '0' Is smaller than the Euclidean distance (D ₂ ) between the channel state information, the information bit can be determined as '1'.

FIG. 8 is a graph illustrating bit error performance when information is detected after performing only the LTS averaging operation.

은 5, 10, 20인 경우의 결과 성능이다. 결과 성능을 보면,

이 커질수록 최대 비트 레이트는 감소하지만, 기준 비트 오류율(예컨대, 10^-2)을 달성할 수 있는 무전력 센서 노드와 리더기 사이의 거리는 증가함을 알 수 있다. 8, the horizontal axis represents the distance between the powerless sensor node 100 and the reader, the vertical axis represents the bit error rate, the distance between the access point and the powerless sensor node is 2 m, the number of packets used for averaging

Is 5, 10, and 20, respectively. As a result,

It can be seen that the maximum bit rate decreases but the distance between the powerless sensor node and the reader that can achieve the reference bit error rate (e.g., 10 ^-2 ) increases.

9 is a graph showing bit error performance when only an optional technique for selecting one of a plurality of signals is applied. The number of multiple antennas used for reception is set to two, four, and eight. Referring to FIG. 9, the bit error rate according to the transmission distance is improved as the number of antennas increases. Also, it can be seen that the better the signal of the received signal is, the better the performance is, and the closer the distance is, the larger the performance improvement is.

10 is a graph illustrating bit error performance when the present invention is applied.

Referring to FIG. 10, it can be seen that the signal averaging operation improves the state of signals received by a plurality of antennas first, so that it is possible to further improve the performance by selectively selecting a signal. In addition, it can be confirmed that the transmission distance is improved by two times or more as compared with Figs. 8 and 9.

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: No power sensor node
200: reader
210: antenna
220: averaging operation unit
230: channel state measuring unit
240: Signal selector
242: Threshold Calculation Module
244: Distance calculation module
246: Signal selection module
250:

Claims (14)

A method of detecting a signal in a reader in a backscatter system having a reader having a plurality of antennas, a powerless sensor node and an access point,
Performing averaging operation on each of a plurality of signals received through the plurality of antennas;
Calculating channel state information of each subcarrier based on the preamble signal of each signal on which the averaging operation is performed; And
Calculating a channel state threshold value of each subcarrier using the channel state information, and selecting one of the plurality of signals based on the corresponding channel state threshold value for each subcarrier
/ RTI > The method of claim 1,
The method according to claim 1,
Wherein the plurality of signals received via the plurality of antennas includes a plurality of antennas,
Power sensor node, and each signal has a frame structure composed of a preamble including a short training symbol (STS), a long training symbol (LTS), a header, and a data area. / RTI >
3. The method of claim 2,
The channel state information of each sub-
And dividing the LTS of the frequency domain of each subcarrier by a preset LTS.
The method according to claim 1,
Wherein selecting one of the plurality of signals comprises:
Calculating a first channel state threshold value for the first bit and a second channel state threshold value for the second bit using the channel state information of each subcarrier;
Calculating a distance between a first channel state threshold value and a second channel state threshold value for each subcarrier; And
And selecting a signal having the largest calculated distance from among the plurality of signals as a signal of the corresponding subcarrier.
5. The method of claim 4,
Wherein the first channel threshold value is calculated by averaging the packets having transmitted '1' in the preamble signal, and the second channel threshold value is calculated by averaging the packets transmitted with '0' in the preamble signal. / RTI >
The method according to claim 1,
And comparing the channel state information for the selected signal with the first and second channel state threshold values to determine bit information.
The method according to claim 6,
Wherein the step of determining the bit information comprises:
Calculating a Euclidean distance between the channel state information of each subcarrier and the first or second channel state threshold value; And
And determining an information bit based on the calculated Euclidean distance. ≪ Desc / Clms Page number 19 >
An averaging operation unit performing averaging operation on each of a plurality of signals received through a plurality of antennas;
A channel state measurement unit for calculating channel state information of each subcarrier based on the preamble signal of each signal on which the averaging operation is performed; And
And a signal selector for selecting one of the plurality of signals based on the corresponding channel state threshold value for each subcarrier, the channel state threshold value for each subcarrier being calculated using the channel state information,
And a signal detector for detecting a signal in the backscatter system.
9. The method of claim 8,
A plurality of signals received via the plurality of antennas
Power sensor node, and each signal has a frame structure composed of a preamble including a short training symbol (STS), a long training symbol (LTS), a header, and a data area. / RTI >
10. The method of claim 9,
The channel state measuring unit
Wherein the channel state information of each subcarrier is calculated by dividing an LTS of a frequency domain of each subcarrier by a preset LTS.
9. The method of claim 8,
The signal selector
A threshold value calculation module for calculating a first channel state threshold value for the first bit and a second channel state threshold value for the second bit using the channel state information of each subcarrier;
A distance calculation module for calculating a distance between a first channel state threshold value and a second channel state threshold value for each subcarrier; And
And a signal selection module for selecting a signal having the largest calculated distance among the plurality of signals as a signal of the corresponding subcarrier.
12. The method of claim 11,
The threshold value calculation module
For each of the preamble bits '1' and '0', a first channel state threshold value is calculated by averaging the packets having transmitted '1' in the preamble signal, and '0' is transmitted from the preamble signal And a second channel state threshold value is calculated by averaging one packet.
9. The method of claim 8,
Further comprising a discriminator for discriminating bit information by comparing channel state information on the selected signal with the first and second channel state threshold values.
14. The method of claim 13,
The determination unit
Calculating a Euclidean distance between the channel state information of each subcarrier and the first or second channel state threshold value and discriminating bit information based on the calculated Euclidean distance; Device.

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