KR20170103058A - Wi-Fi backscatter system and method for improving transmission range using the same - Google Patents

Wi-Fi backscatter system and method for improving transmission range using the same Download PDF

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KR20170103058A
KR20170103058A KR1020160025025A KR20160025025A KR20170103058A KR 20170103058 A KR20170103058 A KR 20170103058A KR 1020160025025 A KR1020160025025 A KR 1020160025025A KR 20160025025 A KR20160025025 A KR 20160025025A KR 20170103058 A KR20170103058 A KR 20170103058A
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South Korea
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access point
tag
signal
reader
wireless packet
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KR1020160025025A
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Korean (ko)
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KR101781732B1 (en
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송형규
이성주
고영민
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세종대학교산학협력단
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/155—Ground-based stations
    • H04B7/15521—Ground-based stations combining by calculations packets received from different stations before transmitting the combined packets as part of network coding
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06K—GRAPHICAL DATA READING; PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS
    • G06K19/00—Record carriers for use with machines and with at least a part designed to carry digital markings
    • G06K19/06—Record carriers for use with machines and with at least a part designed to carry digital markings characterised by the kind of the digital marking, e.g. shape, nature, code
    • G06K19/067—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components
    • G06K19/07—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips
    • G06K19/0723—Record carriers with conductive marks, printed circuits or semiconductor circuit elements, e.g. credit or identity cards also with resonating or responding marks without active components with integrated circuit chips the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
    • H02J50/20—Circuit arrangements or systems for wireless supply or distribution of electric power using microwaves or radio frequency waves
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B5/00—Near-field transmission systems, e.g. inductive loop type
    • H04B5/0056—Near-field transmission systems, e.g. inductive loop type for use in interrogation, identification or read/write systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/14—Relay systems
    • H04B7/15—Active relay systems
    • H04B7/155—Ground-based stations
    • H04B7/15507—Relay station based processing for cell extension or control of coverage area
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation

Abstract

The present invention relates to a Wi-Fi backscatter system and a transmission distance improvement method using the same. The transmission distance improvement method uses the Wi-Fi backscatter system including an access point, a reader, and a tag. The transmission distance improvement method comprises: a step in which an access point broadcasts a wireless packet corresponding to a reference signal already shared with the reader; a step in which the reader estimates a first channel value with the access point from the wireless packet received from the access point; a step in which the tag loads own information bits on the wireless packet received from the access point and backscatters the loaded information bits to the reader; a step in which the reader extracts a signal component of the tag and demodulates the information bits by removing the signal component of the access point obtained through the first channel value from the signal received by being summed from the tag and the access point; a step in which the reader estimates a second channel value via the access point and the tag by using a preamble signal included in the signal of the tag and feeds back to the access point; and a step in which the access point applies a precoding value generated by the second channel value to the wireless packet and broadcasts the applied value. The present invention enables reliable communication and increases the transmission range of a tag by offsetting the impact of a channel according to the backscattering environment of the tag by applying a precoding technique to a Wi-Fi signal broadcasted from an access point.

Description

FIELD OF THE INVENTION [0001] The present invention relates to a Wi-Fi backscatter system and a method for improving transmission distance using the Wi-Fi backscatter system.

FIELD OF THE INVENTION The present invention relates to a Wi-Fi backscatter system and a transmission distance improving method using the Wi-Fi backscatter system, and more particularly, to a Wi-Fi backscatter system capable of increasing a transmission range of a tag and a transmission distance improving method using the same.

Recently, IoT (Internet of Things) technology, which connects the Internet to all objects as well as computers, is getting attention. IoT provides intelligent interfaces and communication protocols to objects, allowing objects to be integrated into the network, autonomously detecting changes in objects or environments, and responding to requests for information. In addition, with the public interest in the Internet of things, the development of technology, the demand of industry, the researches about devices capable of communicating without a power supply device are being actively carried out.

Wi-Fi Energy Harvesting technology uses Wi-Fi RF (Radio Frequency) signal as power source to charge electric power. It uses energy discharged from surrounding environment as energy source of communication. Is a promising technology that enables communication without using a separate power supply. In addition, RFID (Radio Frequency Identification) technology suitable for application to low-power communication is a technology that can manage information of various objects through an IC chip and radio, and is a reader for reading information tags and information .

In recent years, Wi-Fi backscatter technology that combines Wi-Fi RF signals with RFID backscattering technology to transmit information of battery-free devices is attracting attention. In Wi-Fi backscatter technology, an RFID tag can communicate without a separate power supply by using a Wi-Fi signal transmitted from an access point as an energy source of communication.

The Wi-Fi backscatter system uses the Wi-Fi frequency of the 2.4 GHz band instead of the frequency band used by the existing RFID. In the RF backscatter system, an RFID tag (RF backscatter tag) has the purpose of enabling the Internet connection without a battery using a Wi-Fi signal if the purpose of use of the conventional RFID is for unique information identification.

Currently, the trend of RFID devices in the Internet industry is not simply for the recognition and use of RFID devices, but for the purpose of storing and managing various information for a long period of time. To expand the tag memory size and to read and write the information in tags Is also being studied.

Wi-Fi backscatter system that combines backscatter technology and RFID technology of RFID tag conducts communication procedure based on backscatter method between reader and tag. Typically, a Wi-Fi backscatter system includes a Wi-Fi helper, a Wi-Fi reader, a Wi-Fi backscatter tag, Device). The Wi-Fi helper and Wi-Fi reader is one of the Wi-Fi devices and can send and receive Wi-Fi packets.

Tag is a battery-free tag with RF-powered capability. Unlike other elements, it is not a Wi-Fi device and therefore can not transmit Wi-Fi packets and can not read incoming Wi-Fi packets . However, the tag can transmit the information that it wants to transmit to the reader through the backscattering using the Wi-Fi packet, and the Internet-connected technique is defined as the Wi-Fi backscatter. However, existing Wi-Fi backscatter technology has the advantage of providing a Wi-Fi connection even when the tag does not have a power supply, but it has a limited transmission range.

The technology that becomes the background of the present invention is disclosed in Korean Patent Publication No. 2008-0042578 (published May 15, 2008).

It is an object of the present invention to provide a Wi-Fi backscatter system capable of extending a transmission range in a Wi-Fi backscatter system and a method of improving transmission distance using the same.

The present invention relates to a method for improving transmission distance using a Wi-Fi backscatter system including an access point, a reader and a tag, wherein the access point broadcasts a wireless packet corresponding to a reference signal shared with the reader Estimating a first channel value with the access point from a wireless packet received from the access point; and writing the information bit of the wireless packet received from the access point to the reader The reader extracts a signal component of the access point obtained through the first channel value from a signal received from the access point and the tag, and extracts a signal component of the tag, Demodulating the information bits, the reader comprising: To estimate a value of the second channel via the access point and the tag using a preamble signal comprising the steps of feedback to the access point; And the access point applies a pre-coding value generated according to the second channel value to the wireless packet and broadcasts the wireless packet.

The step of demodulating the information bits may demodulate one bit per packet by dividing a signal of the extracted tag by a packet and comparing the level of the divided signal with a preset threshold value.

Also, the generated precoding value may be an inverse of the second channel value.

Further, a signal received by the reader after broadcasting the precoded wireless packet at the access point may be defined by the following equation.

Figure pat00001

Where X is a wireless packet, P is the precoding value (P = 1 / H 2 ), PX is the precoded wireless packet, H 1 is the first channel value corresponding to the direct signal path to the access point H 2 denotes the second channel value corresponding to the signal path passing through the access point and the tag, and N denotes a noise component.

According to another aspect of the present invention, there is provided a Wi-Fi backscatter system including an access point, a reader, and a tag, wherein the access point broadcasts a wireless packet corresponding to a reference signal shared by the reader, A receiver for receiving a signal broadcasting by the access point and receiving a signal for backscattering the information packet with a radio packet received from the access point by the tag; A first channel estimator for estimating a first channel value with the access point from a received wireless packet; a first channel estimator for estimating a first channel value with the access point from the access point and the tag after backscattering of the tag, And outputs the signal of the tag And an information bit demodulator for demodulating the information bit from the signal of the tag, and a second demodulator for demodulating the information bit from the signal of the tag using a preamble signal included in the signal of the tag, A second channel estimator for estimating a channel value, and a feedback unit for feeding back the second channel value to the access point, wherein the access point notifies the precoding value generated according to the fed- The present invention provides a Wi-Fi backscatter system that applies a broadcast packet to a wireless packet and broadcasts it.

According to the Wi-Fi backscatter system and the transmission distance improving method using the Wi-Fi backscatter system according to the present invention, a precoding scheme is applied to a Wi-Fi signal broadcast from an access point, thereby canceling the influence of a channel depending on the backscattering environment of the tag It is possible to perform more reliable communication than before and to increase the transmission range of the tag.

1 is a diagram illustrating a configuration of a Wi-Fi backscatter system according to an embodiment of the present invention.
FIG. 2 is a diagram showing a configuration of the reader shown in FIG. 1. FIG.
FIG. 3 is a view for explaining a transmission distance improving method using the Wi-Fi backscatter system shown in FIG. 1. FIG.
4 is a diagram illustrating a packet structure in a Wi-Fi backscatter system according to an embodiment of the present invention.
5 is a diagram illustrating an improved error performance of an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

FIELD OF THE INVENTION The present invention relates to a Wi-Fi backscatter system and a transmission distance improving method using the Wi-Fi backscatter system, and more particularly, We propose a scheme that overcomes the limitation of the transmission range by canceling the influence and extending the transmission range of the tag through it.

1 is a diagram illustrating a configuration of a Wi-Fi backscatter system according to an embodiment of the present invention. Referring to FIG. 1, a Wi-Fi backscatter system includes an access point 100, a reader 200, and a tag 300.

An access point (AP) 100 may correspond to a general wireless router, and transmits a wireless packet (Wi-Fi packet) to peripheral devices to provide a wireless Internet connection. The access point 100 may refer to a Wi-Fi wireless router used as a Wi-Fi helper.

The access point 100 broadcasts the wireless packet around. The broadcast wireless packet is transmitted to the nearby reader 200 and the tag 300.

The reader 200 can be connected to the Internet through a Wi-Fi packet received from the access point 100. [ The reader 200 may correspond to a personal portable terminal that supports Wi-Fi transmission such as a normal mobile phone, a smart phone, a smart pad, and a notebook computer capable of wireless Internet access.

The tag 300 corresponds to an RFID tag and is capable of transmitting a tag 300 using a backscattering technique even though it is not capable of demodulating a wireless packet (Wi-Fi packet) received from the access point 100. [ It is possible to transmit unique information to the reader 200. Backscatter technology utilizes reflection control of the antenna.

The tag 300 level-modulates the Wi-Fi packet received from the access point 100 through the adjustment of the reflection amount of the antenna, and transmits the Wi-Fi packet to the reader 200. For example, when the information to be transmitted to the reader 200 is '1', the tag 300 reflects the Wi-Fi packet at a high level (size), and when it is '0' Modulated and transmitted. The reader 200 may restore the data using the level difference at the time of demodulating the received signal.

The tag 300 may be a battery-free passive tag in which a separate power supply (battery) is not present. Of course, the tag 300 may correspond to a sensor node (power-free sensor node). In the case of the RFID tag, the 900 MHz Gen2 protocol and the 13.56 MHz similar Gen2 protocol have already been selected as the standard technology in the domestic market and can be used in the present invention.

The following embodiments of the invention may be supported by standard documents disclosed in IEEE (Institute of Electrical and Electronics Engineers) 802 systems.

In the embodiment of the present invention, the access point 100 broadcasts a wireless packet corresponding to a reference signal shared with the reader 200. [ This access point 100 continuously broadcasts the wireless packet.

Since the reader 200 knows the reference signal in advance, the reader 200 can easily estimate the channel H 1 from the received signal with the access point 100 after receiving the signal broadcasted by the access point 100.

If there is a request from the reader 200 in the future, the tag 300 can transmit back information bits to a wireless packet broadcasted by the access point 100 and transmit the information bit back to the reader 200. At this time, 200 are received in a form in which a signal broadcast by the access point 100 and a signal backscattered by the tag 300 are added together.

In FIG. 1, the channel H 2 corresponds to a path for backscattering the wireless packet received from the access point 100 by the tag 300. Tag 300 is prior to the backs Catering reader 200 has received only the signal of the access point 100 via the H 1 channel is and, Bax if catering reader 200, the access point (100 through the H 1 channel ) Together with the backscattering signal of the tag 300 via the H 2 path.

Since the reader 200 knows the reference signal and the channel value H 1 from the signal received through the two paths H 1 and H 2 during backscattering of the tag 300, By removing the signal component of the access point 100 by one path, only the signal component of the tag 300 by the H 2 path can be extracted.

The reader 200 can also demodulate the information bits transmitted from the tag 300 from the signal components of the extracted tag 300 and estimate the channel H 2 from the preamble signals included in the signal components of the tag 300 And can feed back to the access point 100.

Accordingly, the access point 100 applies the precoding value generated using the H 2 value to the wireless packet for broadcasting. Access point 100 transmits a wireless packet because the pre-coding, the channel H 2 In other words, it is possible to offset the effect of the channel H 2 according to the backs catering environment of the tag.

FIG. 2 is a diagram showing a configuration of the reader shown in FIG. 1. FIG. 2, the reader 200 includes a receiving unit 210, a first channel estimating unit 220, a tag signal extracting unit 230, an information bit demodulating unit 240, a second channel estimating unit 250, And a feedback unit 260.

1 and 2, the receiving unit 210 can receive a signal broadcasted by the access point 100 and also transmits an information bit to the wireless packet received from the access point 100 It is possible to receive a signal to carry back-to-back catering.

The first channel estimator 220 estimates a first channel value H 1 from the wireless packet received from the access point 100 with the access point 100 prior to backscattering the tag 300. Here, the concept of not backscattering as well as the concept of not backscattering may be included.

The tag signal extracting unit 230 extracts the tag 300 from the access point 100 and the tag 300 through the access point 100 obtained through the first channel value H 1 100), and extracts only the signal component of the tag 300. [0053] FIG.

The information bit demodulator 240 demodulates the information bits from the signal of the tag 300 thus extracted. The second channel estimating unit 250 estimates a second channel value H 2 through the tag 300 using the preamble signal included in the extracted signal of the tag 300 ).

The feedback unit 260 feeds back the estimated second channel value (H 2 ) to the access point. Then, the access point 100 applies the precoding value generated according to the feedback second channel value (H 2 ) to the wireless packet and broadcasts the precoded value. Accordingly, it is possible to minimize the influence of the second channel value (H 2 ) in the Wi-Fi backscatter system as shown in FIG. 1, thereby substantially improving the transmission distance of the tag 300.

Hereinafter, a transmission distance improving method using a Wi-Fi backscatter system according to an embodiment of the present invention will be described in detail. FIG. 3 is a view for explaining a transmission distance improving method using the Wi-Fi backscatter system shown in FIG. 1. FIG.

First, the access point 100 broadcasts a wireless packet corresponding to a reference signal (S310). The reference signal corresponds to a signal previously agreed between the access point 100 and the reader 200 to establish Wi-Fi backscatter communication. A wireless packet broadcasted by the access point 100 is received in the reader 200 and the tag 300.

Then, the reader 200 estimates a first channel value (H 1 ) with the access point 100 from the wireless packet received from the access point 100 (S320). At this time, the signal received by the reader 200 can be expressed simply as in Equation (1).

Figure pat00002

In Equation (1), X is a wireless packet broadcasted by the access point 100, and H 1 is a channel between the access point 100 and the reader 200. N represents a noise component.

Since the reader 200 already knows the reference signal, the reader 200 can easily estimate the channel H 1 by reflecting the reference signal to the signal received from the access point 100. That is, the first channel value (H 1 ) can be obtained through channel state information (CSI) calculated on the sub-channel of the frequency axis of the reference signal portion in the received signal. As a result, the reader 200 can acquire XH 1 , which is a signal component received from the access point 100, and the reader 200 can reproduce the signal of the access point 100 at any time.

Thereafter, the tag 300 transmits its information bit to the wireless packet received from the access point 100 and backscatter it to the reader 200 (S330). In general, a lot of fading occurs in the backscattering process, so that there is a limitation in the distance for transmitting the information of the correct tag 300 to the reader 200. [

The backscattering method is as follows. The tag 300 carries its own information bit by transmitting the Wi-Fi packet received from the access point 100 in a level-modulated manner by adjusting the reflection amount of the antenna. That is, the information bits of 1 and 0 can be transmitted to the reader 200 by adjusting the magnitude of the reflection amount of the wireless packet received from the access point 100.

The access point 100 continuously broadcasts the wireless packet and therefore in step S330 the signal broadcast by the access point 100 and the signal backscattered by the tag 300 are added to the reader 200 .

Here, the reader 200 calculates the signal component (XH 1 ) of the access point 100 obtained through the first channel value (H 1 ) from the signals received from the access point 100 and the tag 300 in total , thereby extracting a signal component (XH 2) of the tag according to the removing (S340).

The concrete principles are as follows. First, the signal received by the reader 200 after step S330 can be expressed in the form of equation (2).

Figure pat00003

That is, in this case, the signals XH 1 and XH 2 passing through the two channels are summed and received. Of course, N represents a noise component. XH 1 corresponds to the signal broadcast by the access point 100 according to the path of the channel H 1 , that is, the signal component of the access point 100, and XH 2 corresponds to the path of the channel H 2 , That is, a signal component of the tag 300. [

The reader 200 previously reserves the signal component XH 1 of the access point as a result of the channel estimation in step S320. Therefore, by removing these components by the signal 1 XH of formula (2) can be obtained XH 2 component. As a result, when at Y = XH 1 + XH 2 + N except for the XH 1 the signal components of the access point (100), XH 2 + N this there is left, such a remaining signal is the signal component of the tag 300.

Then, the reader 200 demodulates the information bits from the signal components of the extracted tag 300 (S350). The reader 200 can determine the bit by comparing the remaining signals based on a threshold value by dividing the remaining signals into Wi-Fi packet units.

That is, the reader 200 divides the signal of the extracted tag 300 into packet units and then compares the level of each divided signal with a preset threshold value, so that the reader 200 can demodulate one bit per packet do. Through the step S350, the reader 200 can determine the information (eg, unique information of the tag, etc.) sent from the tag 300 to the reader 200.

The reader 200 estimates the second channel value H 2 via the access point 100 and the tag 300 by using a preamble signal included in the signal of the extracted tag 300 (S360).

The preamble signal is a predetermined signal between the access point 100 and the reader 200 and is a value that the access point 100 and the reader 200 know in advance. If the preamble signal is used, the channel state information received from the access point 100 through the tag 300 can be estimated.

4 is a diagram illustrating a packet structure in a Wi-Fi backscatter system according to an embodiment of the present invention. It can be seen that the packet structure in the backscatter system uses a configuration different from the packet configuration method of transmitting the existing Wi-Fi signal.

FIG. 4 shows a structure of a Wi-Fi packet in a Wi-Fi backscatter system. In this embodiment, the Wi-Fi packet includes a CTS-to-Self, a preamble, and a payload interval. CTS (clear to send) means ready to transmit. The preamble signal uses a predetermined fixed value.

In the embodiment of the present invention, the reader 200 can grasp the channel state (H 2 ) using the preamble signal portion of the signals of the tag 300 extracted above. Since the reader 200 already knows the preamble signal, the reader 200 transmits the second channel value (H 2 ) through the channel state information (CSI) calculated on the sub-channel on the frequency side of the preamble signal portion in the signal component of the tag 300, Can be easily estimated.

Thereafter, the reader 200 feeds the estimated second channel value H 2 back to the access point 100 for use in pre-coding (S 370). In the case of the precoding scheme, the transmitter uses the channel information. When the transmitter knows the information of the channel in advance, it transmits the coded information to the receiver, thereby reducing the effect of the channel and reducing the complexity of the system Increase reliability.

The access point 100 generates a precoding value using the second channel value H 2 fed back from the reader 200 and precodes the pre-coding value by applying the precoding value to the wireless packet at step S380. The access point 100 applies precoding to the transmission signal in advance to compensate for the influence of the channel to be experienced, thereby reducing the influence of fading. As a result, it enables more reliable communication and improves the transmission distance than the existing technique. Here, the precoding value uses 1 / H 2 , which is an inverse number of the second channel value.

The access point 100 broadcasts the precoded wireless packet as described above (S390). At this time, the signal received by the reader 200 can be expressed as Equation (3) below.

Figure pat00004

Here, X denotes a wireless packet, P denotes the precoding value (P = 1 / H 2 ), PX denotes a precoded wireless packet, and N denotes a noise component. H 1 is a first channel value corresponding to a direct signal path between the reader 200 and the access point 100 and H 2 is a value of a first channel corresponding to a direct signal path between the reader 200 and the access point 100 via the access point 100 and the tag 300, Is the second channel value corresponding to the incoming signal path.

In Equation 3, P = 1 / H 2 Since reader and writer 200 are known values and X and H 1 are values already known to reader 200, reader 200 can remove them by applying them to the received signal of Equation (3). As a result, the signal remaining in Equation (3) can be expressed as Equation (4) below.

Figure pat00005

Since the remaining signal corresponds to the backscattered signal from the tag 300, it is represented by Y tag , and it can be confirmed that the influence of the corresponding channel (H 2 ) is removed according to the precoding technique.

In the embodiment of the present invention, since the accuracy and the noise component of CSI can substantially affect the performance, the effect of cancellation of the influence of the channel to be experienced in the future can be canceled as described above. Therefore, in the backscattering environment, 300 can be improved.

The embodiment of the present invention performs Wi-Fi backscatter communication through feedback through continuous channel estimation in the above-described manner.

As described above, according to the embodiment of the present invention, the Wi-Fi signal broadcasted from the access point 100 in the Wi-Fi backscatter system is channel-backed from the tag 300 to the reader 200, The reader 200 transmits the feedback information to the access point 100. The access point 100 multiplies the transmission signal by the reciprocal of the influence of the channel to be experienced by using the feedback information, To minimize and minimize the effects of

In general, the backscattering environment through the tag 300 has the greatest influence on the transmission range, but the embodiment of the present invention can minimize the influence of the corresponding portion, and thus can increase the transmission range of the Wi-Fi backscattering communication . That is, an improved transmission distance of the signal back to the reader 200 from the tag 300 can be provided.

The effect according to the embodiment of the present invention can be confirmed through the following simulation results. 5 is a diagram illustrating an improved error performance of an embodiment of the present invention.

FIG. 5 compares the performance of the conventional technique (Conv), which does not apply precoding, and the technique of the present embodiment, in which precoding is applied, according to distances. It can be seen that when the signal is transmitted using the technique according to the embodiment of the present invention, the error performance is improved compared to the same signal strength.

FIG. 5 is a graph comparing the AWGN environment and the distance (distance between the tag and the reader) of 1 m, 3 m, and 5 m. For simulation, Wi-Fi packets Were modulated and coded. From the simulation results, it can be seen that the error probability is significantly improved when precoding is applied.

Also, in the case of the conventional technique, as the distance increases, the attenuation of the performance is serious. In the case of the technique according to the embodiment of the present invention, it is confirmed that the performance degradation depending on the distance is considerably small. As a result, using the technique of the embodiment of the present invention provides reliable communication and improves the transmission distance.

According to the Wi-Fi backscatter system and the transmission distance improving method using the Wi-Fi backscatter system according to the present invention, precoding is applied to a Wi-Fi signal broadcast from an access point, It is possible to cancel the influence and to perform more reliable communication than before and to increase the transmission range of the tag.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

100: access point 200: reader
210: Receiver 220: First channel estimator
230: tag signal extracting unit 240: information bit demodulating unit
250: second channel estimator 260: feedback unit
300: Tag

Claims (8)

A method for improving transmission distance using a Wi-Fi backscatter system including an access point, a reader, and a tag,
The access point broadcasting a wireless packet corresponding to a reference signal shared by the reader;
The reader estimating a first channel value with the access point from a wireless packet received from the access point;
The tag loading the information bits of the wireless packet received from the access point backscattering to the reader;
Wherein the reader removes a signal component of the access point obtained through the first channel value from a signal received from the access point and the tag, and extracts a signal component of the tag and demodulates the information bit ;
Estimating a second channel value via the access point and the tag using the preamble signal included in the signal of the tag, and feeding back the estimated second channel value to the access point; And
And the access point applies broadcasting to the wireless packet by applying a precoding value generated according to the second channel value to the wireless packet. The method according to claim 1,
Wherein demodulating the information bits comprises:
Dividing a signal of the extracted tag by a packet unit, comparing the level of the divided signal with a predetermined threshold value, and demodulating one bit per packet. The method according to claim 1,
Wherein the generated precoding value is an inverse of the second channel value. The method of claim 3,
Wherein the signal received at the reader after broadcasting the precoded wireless packet at the access point is defined by the following equation:

Where X is a wireless packet, P is the precoding value (P = 1 / H 2 ), PX is the precoded wireless packet, H 1 is the first channel value corresponding to the direct signal path to the access point H 2 denotes the second channel value corresponding to the signal path passing through the access point and the tag, and N denotes a noise component. A Wi-Fi backscatter system including an access point, a reader, and a tag,
The access point comprising:
Broadcasts a wireless packet corresponding to a reference signal shared by the reader,
The reader includes:
A receiver for receiving a signal broadcasted by the access point, and receiving a signal for backscattering the information packet by placing the information bit in a wireless packet received from the access point by the tag;
A first channel estimator for estimating a first channel value with the access point from a wireless packet received from the access point prior to backscattering of the tag;
Extracting a signal component of the access point obtained through the first channel value from a signal summed and received from the access point and the tag after backscattering of the tag, part;
An information bit demodulator for demodulating the information bits from the signal of the tag;
A second channel estimator estimating a second channel value via the access point and the tag using a preamble signal included in a signal of the tag; And
And a feedback unit for feeding back the second channel value to the access point,
The access point comprising:
And applying the pre-coding value generated according to the feedback second channel value to the wireless packet and broadcasting the pre-coding value. The method of claim 5,
Wherein the information bit demodulator comprises:
A Wi-Fi backscatter system for dividing a signal of the extracted tag by a packet unit, and comparing the level of the divided signal with a predetermined threshold value to demodulate one bit per packet. The method of claim 5,
Wherein the generated precoding value is an inverse of the second channel value. The method of claim 7,
Wherein the signal received at the reader after broadcasting the precoded wireless packet at the access point is defined by the following equation: Wi-Fi backscatter system:
Figure pat00007

Where X is a wireless packet, P is the precoding value (P = 1 / H 2 ), PX is the precoded wireless packet, H 1 is the first channel value corresponding to the direct signal path to the access point H 2 denotes the second channel value corresponding to the signal path passing through the access point and the tag, and N denotes a noise component.
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Publication number Priority date Publication date Assignee Title
KR20190048690A (en) * 2017-10-31 2019-05-09 세종대학교산학협력단 Decoding method using weight in wi-fi backscatter system and wi-fi backscatter system using it
CN112311422A (en) * 2019-07-29 2021-02-02 华为技术有限公司 Signal transmission method and device
WO2023231908A1 (en) * 2022-06-01 2023-12-07 维沃移动通信有限公司 Information transmission method and apparatus for backscatter communication, and terminal and network-side device

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KR101590292B1 (en) * 2015-01-29 2016-02-01 세종대학교산학협력단 Backscatter System and Method For Adaptive Encoding using The Same
KR101590295B1 (en) * 2015-01-30 2016-02-01 세종대학교산학협력단 Wi-Fi Backscatter System Including Intermediate reader and Method For Cooperative Communication using The Same

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20190048690A (en) * 2017-10-31 2019-05-09 세종대학교산학협력단 Decoding method using weight in wi-fi backscatter system and wi-fi backscatter system using it
CN112311422A (en) * 2019-07-29 2021-02-02 华为技术有限公司 Signal transmission method and device
WO2023231908A1 (en) * 2022-06-01 2023-12-07 维沃移动通信有限公司 Information transmission method and apparatus for backscatter communication, and terminal and network-side device

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