KR101590291B1 - backscatter system using phase modulation and uplink communication method thereof - Google Patents

Abstract

The present invention relates to a backscatter system using phase modulation and an uplink communications method using the same. According to the present invention, an uplink communications method using a backscatter system including a reader, a sensor node, and an access point comprises the steps of: receiving a request signal from the reader by the sensor node; dividing wireless data received according to the time flow from the access point into 2 bit units, and performing phase modulation on a single packet every 2 bits by using a delay value corresponding to the bit combination of the 2 bit units; and sequentially transmitting the phase modulated packet to the reader through an uplink. The backscatter system using phase modulation and the uplink communications method using the same may perform phase modulation on data received from an access point by a sensor node every 2 bit units and transmit the data to enhance a data rate and to provide communications performance less sensitive to a threshold value.

Description

BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to a backscatter system using phase modulation and an uplink communication method using the backscatter system.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backscatter system using phase modulation and an uplink communication method using the same, and more particularly, to a backscatter system capable of phase modulating and transmitting a packet in a uplink, .

Recently, Wi-Fi backscatter technology has been proposed as an energy harvesting technique that is attracting attention as a next generation technology, and a technique of receiving power by using surrounding RF signals to communicate.

Fig. 1 is a diagram showing the configuration of a general back scattering system. The backscatter system consists of a Wi-Fi Helper (Access Point), a Wi-Fi Reader (eg a cell phone) and a tag (Wi-Fi backscatter tag) When the reader requests information from the tag through the uplink, the tag transmits a response to the reader.

Here, the conventional uplink transmission scheme is as follows. The tag modulates the Wi-Fi packet received from the Wi-Fi helper to 0 or 1 through intermittent reflection using the antenna and transmits it to the reader. By adjusting the reflection amount of the antenna, intermittent reflection becomes possible. At this time, only one bit can be transmitted per packet.

As described above, the conventional Wi-Fi backscatter technology can transmit only one bit of data per packet in the uplink transmission, limiting the data rate. In addition, since the tag transmits information using the level modulation method, there is a problem that the communication performance sensitively varies according to the threshold value for determining the levels of 1 and 0 in the reader.

The technique which is the background of the present invention is disclosed in Korean Patent No. 0825362 (published on Mar. 28, 2008).

The present invention relates to a backscatter system capable of improving data rate and less sensitive to a threshold value by phase modulating data received from an access point by a sensor node in units of two bits and transmitting the data, And a communication method.

The present invention provides an uplink communication method using a backscatter system including a reader, a sensor node, and an access point, the method comprising the steps of: receiving a request signal from the reader; Dividing the wireless data into 2-bit units and phase modulating one packet per 2 bits using a delay value corresponding to the 2-bit bit combination, and outputting the phase modulated packet to the reader in sequence And uplink transmitting the uplink data to the base station.

Wherein the bit combination includes 00, 01, 10, and 11, and the phase modulating step includes: a first step of performing a phase modulation on the basis of the first to fourth delay values having a phase difference of? A packet may be phase modulated using one delay value.

In addition, the sensor node may include four reception antennas and four transmission antennas, which correspond to the number of bit combinations and have a mutually parallel structure, and first to fourth transmission antennas for each 2-bit unit of the wireless data received by the reception antennas. A fourth phase modulator for phase modulating the packet by applying a fourth delay value to the phase modulated signal, and a fourth phase modulator connected to the four phase modulators for transmitting the phase modulated signal to each of the transmit antennas at turn- One switch unit of the four switch units is turned on in units of two bits so that one delay value corresponding to the bit combination of the two bits is successively selected every two bits of the wireless data And a switch control unit.

The four phase modulators may have the first to fourth delay values set according to an inductor value and a capacitor value, respectively.

In addition, the reader may detect the wireless data by converting the packets transmitted in the uplink from the sensor node into a signal on a frequency axis and then using a differential phase detection method.

In addition, the present invention provides a backscatter system including a reader, a sensor node, and an access point, wherein the sensor node comprises: a receiver for receiving a request signal from the reader; A phase modulator for phase modulating one packet per 2 bits using a delay value corresponding to the bit combination of 2 bits, and a phase modulator for sequentially phase-modulating the phase modulated packet to the reader A backscatter system including a transmitting unit for transmitting the backscatter system.

According to the backscatter system and the uplink communication method using the backscatter system according to the present invention, the sensor node phase-modulates data received from the access point in units of two bits and transmits the data, thereby improving the data rate and reducing the communication performance Can be provided.

Fig. 1 is a diagram showing the configuration of a general back scattering system.
2 is a diagram illustrating a configuration of a backscatter system according to an embodiment of the present invention.
3 is a diagram illustrating the configuration of the sensor node shown in FIG.
4 is a flowchart illustrating a method of transmitting the uplink signal to the reader by the sensor node of FIG.
FIG. 5 is a diagram showing the configuration of the sensor node of FIG. 3 in more detail.

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.

2 is a diagram illustrating a configuration of a backscatter system according to an embodiment of the present invention. Referring to FIG. 2, the backscatter system includes a sensor node 100, a reader 200, and an access point 300.

First, an access point (AP) 300 may correspond to a general wireless router, and may transmit a Wi-Fi packet to a peripheral device as wireless data.

In the embodiment of the present invention, the wireless Internet may be a general Wi-Fi. In this case, the access point 300 may be a Wi-Fi wireless router (Wi-Fi AP) used as a Wi-Fi helper It can mean. Of course, wireless Internet is not necessarily a Wi-Fi concept. In the following embodiments of the present invention, Wi-Fi will be described as a representative example for convenience of explanation.

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. The sensor node 100 may be implemented as a tag. The sensor node 100 may refer to a passive tag of a non-battery type in which there is no separate power supply device (battery) such as an RFID tag.

The reader 200 requests information from the sensor node 100 through a down link and the sensor node 100 transmits the response to the reader node 200 through an uplink do.

In the embodiment of the present invention, the sensor node 100 phase-modulates and transmits a packet in the uplink. Specifically, the sensor node 100 divides the wireless data received by the access point 300 in units of two bits over a time period, and uses the delay value corresponding to the bit combination of the two bits, Modulates and transmits the packet.

A typical phase modulation technique modulates the phase in frequency, but in the present system the sensor node 100 modulates the phase in such a way that it reflects the packet with a time delay. Since the delay changes the phase of the signal, when the reader 200 demodulates the packet to which the delay value is applied, the data may be recovered using the phase difference.

Hereinafter, the uplink transmission method in the sensor node 100 will be described in more detail.

FIG. 3 is a diagram illustrating a configuration of the sensor node shown in FIG. 2, and FIG. 4 is a flowchart illustrating a method of transmitting an uplink signal to a reader by the sensor node of FIG. 3 and 4, a sensor node 100 according to an embodiment of the present invention includes a receiving unit 110, a phase modulator 120, and a transmitting unit 130.

The receiving unit 110 receives a request signal from the reader 200 (S410). Then, the phase modulator 120 divides the wireless data (Wi-Fi packet) received by the access point 300 in units of 2 bits, and outputs the wireless data One packet per 2 bits is phase-modulated (S420). Then, the transmitter 130 sequentially transmits the phase-modulated packet to the reader 200 in an uplink.

In the embodiment of the present invention, the bit combination of 2 bits includes 00, 01, 10, and 11 as four types. A delay value corresponding to each of these four bit combinations is set in advance. Each delay value can have a phase difference of [pi] / 2 (90 [deg.]).

Table 1 below illustrates delay values applied to each bit combination in this embodiment.

data Phase modulation 00 (0) 1 * e ^? 01 (1) 1 * e ^{&thetas; + 90} 10 (2) 1 * e ^{[theta] + 180} 11 (3) 1 * e ^{&thetas; + 270}

In Table 1, a delay value of 0 ° for '00', 90 ° for '01', 180 ° for '10', and 270 ° for '01' is set. Of course, the delay value applied to each bit combination is not necessarily limited thereto. For example, for each bit combination, the phase corresponding to the delay value may be shifted in a batch and the interval between the phases may be smaller.

In this way, during phase modulation, the packet can be phase-modulated using one delay value corresponding to the current 2-bit combination of bits among the first to fourth delay values having a phase difference of? / 2. For example, if the wireless data is 01100011 ... The first packet is delayed by 90 degrees corresponding to '01', the second packet is delayed by 180 degrees corresponding to '10', and the second packet is delayed by 0 degree corresponding to '00' The third packet, and the fourth packet, which is delayed by 270 degrees corresponding to '11', to the reader 200 in order.

The reader 200 receives the phase-modulated packets and detects the wireless data through a differential phase detection method. Specifically, the reader 200 converts the uplink transmitted packets from the sensor node 100 into a frequency-axis signal through an FFT (Fast Fourier Transform), and then detects the wireless data using a differential phase detection method. It is assumed that the reader 200 knows the information as shown in Table 1 in order to detect the wireless data based on the phase detection.

As described above, in the embodiment of the present invention, the sensor node 100 phase-modulates one packet for every two bits of the wireless data received from the access point 300. That is, the sensor node 100 varies the phase of the transmission packet corresponding to the bit combination of 2 bits and sequentially transmits the transmission packet.

With this configuration, a 2-bit signal can be transmitted per transmission packet, and the data rate can be doubled. In addition, since the sensor node 100 transmits the uplink data to the reader 200 through a phase modulation method instead of a level modulation method, the reader 200 can demodulate data using a phase difference that is not a threshold value, Can provide a communication environment that is less sensitive to the threshold value, and can improve the reliability and accuracy of the signal.

FIG. 5 is a diagram showing the configuration of the sensor node of FIG. 3 in more detail. Hereinafter, a specific embodiment in which the sensor node 100 selects a delay value corresponding to the combination of bits and performs phase modulation will be described in detail with reference to FIG.

The sensor node 100 has four rows of transmission / reception modules corresponding to the number of bit combinations, and the transmission / reception modules have a parallel structure with each other. Correspondingly, the receiving unit 110 includes four receiving antennas, and the wireless data transmitted from the access point 300 are simultaneously received by the four receiving antennas.

The wireless data received by each of the reception antennas is transmitted to four corresponding lines in the phase modulation unit 120, respectively. The phase modulator 120 also has four lines, and each of the phase modulators 121 phase-modulates one packet per two bits of the received data with a predetermined delay value. At this time, the delay value is set differently for each line. For example, the phase modulator of the first column is designed to apply a first delay value to the packet to be transmitted and the phase modulator of the second column is designed to apply a second delay value to the packet.

Each phase modulator 121 phase-modulates the packet by applying first to fourth delay values, which are predetermined for each 2-bit unit, to the reception antennas corresponding to the respective reception antennas. The respective delay values are individually set according to the inductor value and the capacitor value (L, C element value) used in each phase modulating section 121, and the LC delay refers to Equation 1 below.

T _d represents total delay (ns). The embodiment of the present invention modulates the phase by using the difference of the delay value T _d according to L and C according to Equation (1).

The first column in FIG. 5 omits the configuration of L and C because it corresponds to a line with a delay value of 0 ° in Table 1. Of course, it is also possible to arrange an LC delay circuit for all the lines and control the phase modulation circuit as necessary or not.

According to the above-described configuration, the same wireless data is simultaneously received on each line, and each line simultaneously carries out an operation of generating one packet per 2 bits for the received data. 5, the configuration for generating a packet is omitted for convenience of explanation.

Here, the phase delay values of the packets generated in the respective lines are different for each line. For example, in the first line, the packet is delayed by 0 ° for the same signal, the packet is delayed by 90 ° in the second line, the packet is delayed by 180 ° in the third line, and the packet is delayed by 270 ° in the fourth line .

While these operations are performed at the same time as this, the embodiment of the present invention transmits only the signal of one of the four lines to the transmitter 130. In the embodiment of the present invention, each of the switch units 122 (S1 to S4) is connected to each phase modulating unit 121, and the switch control unit 123 simultaneously controls the ON / OFF of these switches.

Specifically, the switch control unit 123 turns on one of the four switch units for each 2-bit unit so that one delay value corresponding to a bit combination of 2 bits is sequentially selected every 2 bits of the wireless data, . The concrete control method will be described as follows.

Each switch unit 122 receives the phase-modulated packet at the front end at the time of turn-on and transmits the packet to the corresponding transmission antenna. However, in this embodiment, the four switch parts are not simultaneously turned on, and only one switch is turned on.

If the currently input 2-bit signal is '01', each phase modulation line generates one packet and phase-modulates each packet with a predetermined delay value, and transmits the packet to each switch unit 122. Here, the switch control unit 123 turns on only the second switch S2 corresponding to '01' and turns off the remaining switches S1, S3, and S4. Therefore, in this case, only packets delayed by 90 deg. Can be transmitted through the second transmission antenna of the transmitter 130 through the second switch S2. For example, if the received data is '01', only the second switch S2 is turned on and one packet delayed by 90 is transmitted in the uplink. If the next received data is '11', only the fourth switch S4 is turned on And one packet delayed by 18O is transmitted in the uplink.

In this way, the embodiment of the present invention increases the data rate by transmitting two bits of information in one packet using the phase modulation method. Also, since the phase-modulated packet can be demodulated into the original 2-bit data through the phase difference detection in the reader 200, the reliability of data detection can be increased.

In the conventional backscatter system, when the sensor node transmits the signal received from the access point to the reader in the uplink, it uses a level modulation that transmits a reflection signal when the received signal is 1 and does not transmit when the received signal is 0. However, Since the embodiment uses a phase modulation method, a method of transmitting a certain level of packets even when the received signal is 0 is used. That is, in the embodiment of the present invention, all the packets transmitted by the sensor node 100 in the uplink are signals that are reflected with a size (level), and each packet can be classified according to the phase value.

According to the backscatter system and the uplink communication method using the backscatter system according to the present invention, the sensor node phase-modulates data received from the access point in units of two bits and transmits the data, thereby improving the data rate, There is an advantage that it can provide sensitive communication performance.

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: sensor node 110:
120: phase modulating unit 130: transmitting unit
200: reader 300: access point

Claims (10)

An uplink communication method using a backscatter system including a reader, a sensor node, and an access point,
The sensor node receiving a request signal from the reader;
Demultiplexing the wireless data received from the access point over time in units of two bits and phase modulating one packet per two bits using a delay value corresponding to the bit combination of two bits; And
And sequentially up-linking the phase-modulated packet to the reader,
The sensor node comprises:
Four receive antennas and four transmit antennas corresponding to the number of bit combinations and having mutually parallel structures;
Four phase modulators for phase modulating the packets by applying first to fourth delay values preset in units of two bits of the wireless data received by the receiving antenna;
Four switch parts respectively connected to the four phase modulating parts and transmitting the phase modulated signal to each of the transmission antennas when turned on; And
And a switch control unit for turning on one of the four switch units in units of two bits so that one delay value corresponding to the bit combination of two bits is successively selected every two bits of the wireless data, ,
Wherein the four phase modulators comprise:
Wherein the first to fourth delay values are set in accordance with an inductor value and a capacitor value using an LC delay circuit, respectively. The method according to claim 1,
The bit combination includes 00, 01, 10, 11,
Wherein the phase modulating comprises:
and phase modulating the packet using one delay value corresponding to the bit combination of the 2 bits among the first to fourth delay values having a phase difference of? / 2. delete delete The method according to claim 1,
The reader includes:
Wherein the sensor node converts the uplink transmitted packets into a frequency-axis signal and then detects the wireless data using a differential phase detection method. A backscatter system comprising a reader, a sensor node, and an access point,
The sensor node comprises:
A receiver for receiving a request signal from the reader;
A phase modulator for dividing the wireless data received by the access point in time according to a unit of 2 bits and phase modulating one packet per 2 bits using a delay value corresponding to the bit combination of 2 bits; And
And a transmitter for sequentially up-linking the phase-modulated packet to the reader,
Wherein the receiving unit and the transmitting unit,
Each of which includes four receive antennas and four transmit antennas corresponding to the number of bit combinations and having mutually parallel structures,
Wherein the phase modulator comprises:
Four phase modulators for phase modulating the packets by applying first to fourth delay values preset in units of two bits of the wireless data received by the receiving antenna;
Four switch parts respectively connected to the four phase modulating parts and transmitting the phase modulated signal to each of the transmission antennas when turned on; And
And a switch control unit for turning on one of the four switch units in units of two bits so that one delay value corresponding to the bit combination of two bits is successively selected every two bits of the wireless data, ,
Wherein the four phase modulators comprise:
And the first to fourth delay values are set in accordance with an inductor value and a capacitor value using an LC delay circuit, respectively. The method of claim 6,
The bit combination includes 00, 01, 10, 11,
Wherein the modulator comprises:
and phase modulates the packet using one delay value corresponding to the bit combination of the 2 bits among the first through fourth delay values having a phase difference of? / 2. delete delete The method of claim 6,
The reader includes:
A backscatter system for converting uplink transmitted packets from the sensor node into signals of a frequency axis and then detecting the wireless data using a differential phase detection method.

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