KR20090116853A - Preamble detector for miller encoding signal having sub carrier - Google Patents

Abstract

PURPOSE: A preamble detector for a miller encoding signal having a sub carrier is provided to detect a preamble accurately regardless of the number of subcarrier included in one symbol period by using correlation characteristic. CONSTITUTION: In a preamble detector for a miller encoding signal having a sub carrier, a shift register(161) stores a reception signal for one symbol cycle. A shift register outputs a start signal and an end signal of a current symbol period. A shift register simultaneously extracts a waveform of a site x and a waveform of a site y at the same time. At data 0, the waveform of the site x and the waveform of site y have polarities which are different with each other in transmission. At data 1, the waveform of the site x and the waveform of site y have polarities which are different with each other in transmission.

Description

Preamble detection device of Miller encoding signal including subcarrier {PREAMBLE DETECTOR FOR MILLER ENCODING SIGNAL HAVING SUB CARRIER}

The present invention relates to a preamble detector for detecting a preamble in a wireless communication technology, and more particularly, to an apparatus for detecting a preamble of a Miller encoded signal including a subcarrier used in a receiver of a passive RFID reader.

In general, RFID (Radio Frequency IDentification) system consists of tags, readers, back-end databases, and additional systems, which are being standardized by the International Organization for Standardization, manufacturing, logistics, distribution, membership cards, employee cards, It is widely applied in various fields such as visitor certificate.

EPC (Electronic Product Code) is an RFID standard established by MIT's Auto ID Center, and has a tag specification from Class 0 to Class 4, and EPC Global Class 1 Gen 2 The standard is now widely used.

The general EPC architecture proposed by the EPC Global Standard consists of RFID tags, RFID readers, RFID middleware, distributed RFID middleware and EPC Information Server (IS). EPC IS provides services that enable EPC-related data to be exchanged with counterparts through the EPC global network, and RFID middleware manages real-time lead events and information for communication with EPC IS, provides alerts, etc. Manage basic lead information for communication.

An RFID reader is called a transceiver and is a device that sends data to or reads data from an RFID tag through an RF interface. Such an RFID reader should be able to recognize a unique identification code from each tag by avoiding collision with other tags without physical contact with the RFID tag.

 RFID tags, also called transponders, consist of a processor for protocol execution and cryptography, a memory that stores data, and an RF antenna. The RFID tag is divided into an active tag having a built-in battery and a passive tag that receives RF signals from an RFID reader and generates power for operation.

In addition, international communication standards between RFID tags and RFID readers are defined by ISO / IEC 18000-1, 2, 3, 4, 6, and 7. The main RF frequencies are 125KHz, 134KHz, 13.56MHz, 433.92MHz, 860. ~ 930MHz, 2.45GHz band is used. The EPC Global Class 1 GEN2 specification is a protocol standard in the 860-930 MHz band (UHF: ISO / IEC 18000-6).

Meanwhile, in the ISO 18000-6 (EPC global Class1 GEN2) standard, ASK or PSK is used as a modulation method in communication between a tag and a reader, and "FM0" or Miller Subcarrier is used for data coding. As shown in (a) of FIG. 1, the FM0 method has a phase change once in the middle of the signal when data 0, and there is no phase change when it is data 1, and the Miller method is shown in (b) of FIG. As shown in FIG. 2, there is no phase change in data 0, and in data 1, the phase is changed once in the middle of the signal. In the Miller method, as shown in FIG. 2, the link frequency may be adjusted by including 2, 4, or 8 subcarriers M in a symbol period. 2 shows that M = 2, the polarity of the sub-carrier transmitted during one symbol is not changed when data 0 is transmitted, but the polarity of the sub-carrier is changed about 1/2 symbol when data 1 is transmitted. Able to know.

However, when the number M of sub-carriers included in one symbol is different, it is generally complicated to detect the preamble. The most primitive method is to predict and detect the preamble signal in all cases for the number of sub-carriers in one symbol that the tag can select. Another method is to detect a change in the signal, and to detect the change in polarity of the sub-carrier at the 1/2 symbol point.

As described in the background art, the method of detecting whether the polarity of the sub-carrier is changed at the 1/2 symbol point can be detected because the received sub-carrier is normal when there is no noise, but when there is noise, Since the polarity of the signal may be changed by noise even at the symbol point, there is a problem that a preamble detection error may occur due to noise.

The present invention has been proposed to solve the above problems, and an object of the present invention is simple even if the transmission speed is changed by changing the number of sub-carriers included in one symbol period when transmitting a signal using a Miller-encoder. The present invention provides a preamble detection apparatus for a Miller encoded signal including a subcarrier capable of detecting a preamble.

Another object of the present invention is to provide a preamble detection apparatus resistant to noise using a partial correlator.

In order to achieve the above object, an apparatus of the present invention includes a shift register for receiving a received signal and storing the received signal for one symbol period and outputting a start signal of the current symbol period and a end signal of the current symbol period; A correlator for receiving a start signal of the current symbol period and a signal received at the end of the current symbol period to calculate and output a correlation; And determining the output of the correlator to determine data 0 when the correlation is large, and determining the data to be data 1 when the correlation is low.

The correlator is represented by the following equation from a received signal transmitted including M subcarriers in one symbol period T.

The correlation value is calculated according to the method. The correlation between the signal waveform of the subcarrier period at the start of one symbol of the same symbol period and the signal waveform of the subcarrier period at the end of one symbol is compared. If is low, it outputs negative value.

The determining unit may determine the output of the correlator to determine data 0 as a positive value and data 1 as a negative value, and the preamble detection unit receives a response signal from an RFID reader. Can be implemented in

Since the preamble detecting apparatus of the present invention uses the correlation characteristic, it can quickly and accurately detect the preamble irrespective of the number of subcarriers included in one symbol period while having a strong characteristic against noise. In addition, the preamble detection apparatus of the present invention can reduce the hardware size and simplify the control while maintaining good preamble detection characteristics even in noise, and thus can be manufactured at low cost and have stable operation.

The technical problem achieved by the present invention and the practice of the present invention will be more clearly understood by the preferred embodiments of the present invention described below. The following examples are merely illustrated to illustrate the present invention and are not intended to limit the scope of the present invention.

3 is a block diagram illustrating an RFID reader and an RFID tag suitable for applying the present invention. The RFID reader 10 includes an MCU 11, a transmitter 12, an oscillator 13, a circulator 14, An antenna 15, a receiver 16, and the RFID tag 20 includes an antenna 21, a demodulator 22, a power supply 23, a control logic 24, an EEPROM 25, and a modulator 26. It is composed.

The communication between the RFID reader 10 and the tag 20 consists of a forward link from the RFID reader 10 to the tag 20 and a reverse link from the tag 20 to the RFID reader 10. In the reverse link from the 20 to the reader 10, a power is generated using the CW signal output by the reader 10, and a back scatter modulated data is used.

The backscattering method is used as a data transmission method of the passive tag 20, and can drive the chip of the tag 20 from the RF signal radiated from the reader 10, which rectifies the DC current to drive its own chip to respond. ASK coded by the ASK of changing the amplitude or PSK method of changing the phase is transmitted.

As shown in FIG. 4, the format of the response signal formed by the tag 20 includes a preamble, an ID or data (Data), and a CRC. Detection of the preamble signal in the RFID system is a prerequisite for obtaining a link from the reader 10 to the tag 20 and from the tag 20 to the reader 10. A preamble detection device for detecting a preamble transmitted from the Miller encoder method is implemented.

FIG. 5 is a diagram illustrating a concept of detecting a preamble of a Miller encoding signal including a subcarrier according to the present invention, and shows an RFID tag transmission Miller encoding preamble signal using different Ms. In FIG. 5, (a) shows a preamble signal when M = 2, (b) shows a preamble signal when M = 4, and (c) shows a preamble signal when M = 8. .

Referring to FIG. 5, the Miller encoding signal including the subcarriers has no phase change when the data is zero even though the number M of the subcarriers is different, and the characteristic that the phase is changed once in the middle of the signal when the data is 1 is the same. It can be seen. That is, when data 0 is transmitted, the polarity of the subcarrier transmitted during one symbol is not changed, but when data 1 is transmitted, the polarity of the subcarrier is changed about 1/2 symbol. This can be seen from the polarity change of the signal at the 1/2 symbol point, but as shown in Fig. 5, the point " x " which is the period of the subcarrier at the start of one symbol and the period of the subcarrier at the end of one symbol This can also be seen by comparing the waveforms at point "y".

In the preamble signal of M = 2, as shown in FIG. 5A, when the data is 0, the subcarrier at the x point and the subcarrier at the y point are in phase, and when the data 1 is the subcarrier at the x point and the y point, respectively. It can be seen that the subcarriers are out of phase. In the preamble signal of M = 4, as shown in (b), the subcarrier at the x point and the subcarrier at the y point are in phase when the data is 0, and the subcarrier at the x point and the subcarrier at the y point in the case of data 1, respectively. It can be seen that the phases are reversed, and as shown in (c), when the data is 0 in the preamble signal of M = 8, the subcarrier at the x point and the subcarrier at the y point are in phase, and the x point when the data is 1 It can be seen that the subcarriers at and the subcarriers at point y are opposite in phase.

Accordingly, the present invention utilizes such characteristics, and the apparatus for detecting a preamble of the Miller encoded signal including the subcarrier according to the present invention is illustrated in FIG. 6.

As shown in FIG. 6, the preamble detecting apparatus according to the present invention receives a received signal and stores the received signal for one symbol period, and outputs a shift register for outputting a reception signal at the beginning of the current symbol period and a reception signal at the end of the current symbol period. 161 and the correlation of the signal waveform of the sub-carrier period (point "x") at the start of one symbol of the same symbol period with the waveform of the signal of the subcarrier period (point "y") at the end of one symbol. Is correlated 162 outputting a positive value if the correlation is low, and outputs a negative value if the correlation is low, and the output of the correlator 162 is judged to be determined as data 0 if it is a positive value, and data if it is a negative value. It consists of a decision unit 163 which determines 1 and detects the preamble.

Referring to FIG. 6, the shift register 161 stores a received signal r (t) by a sample corresponding to one symbol. In order to simultaneously extract the waveform of the point x and the waveform of the point y, It is necessary. When data 0 is transmitted, the waveform of point x and the waveform of point y are the same, but when data 1 is transmitted, the waveform of point x and the waveform of point y have different polarities.

The correlator 162 receives the starting signal r (kT + t) of the current symbol period and the receiving signal r ((k + 1) TT / M + t) of the current symbol period from the shift register 161. The correlation value c (k) between the waveform at point x and the waveform at point y is obtained. At this time, if the correlation value c (k) is positive, 'data 0' is transmitted to the preamble, and if negative, 'data 1' is transmitted from the preamble. In this way, the role played by the correlator 162 is expressed by the following equation (1).

In Equation 1, r (t) is a received signal, c (k) is an output of a correlator, T is a symbol period, and M is the number of subcarriers.

The determination unit 163 determines that 'data 0' is transmitted when c (k) output from the correlator 162 is positive, and determines that 'data 1' is transmitted when c (k) is negative. The determination unit 163 detects a point corresponding to '010111', which is the preamble data transmitted in the correlation value sequence of c (k).

The present invention has been described above with reference to one embodiment shown in the drawings, but those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom.

1 is an example of a data coding scheme of a tag in a general RFID system,

2 is an example of a Miller subcarrier coding scheme when M = 2;

3 is a block diagram showing an RFID reader and an RFID tag suitable for applying the present invention;

4 is an example of a format of a response signal formed by a tag shown in FIG. 3;

5 is a view illustrating a concept of detecting a preamble of a Miller encoded signal including a subcarrier according to the present invention;

FIG. 6 is a block diagram illustrating an apparatus for detecting a preamble of a Miller encoded signal including a subcarrier according to the present invention. FIG.

* Explanation of symbols for main parts of the drawings

10: RFID Reader 20: Tag

161: shift register 162: correlator

163: decision

Claims (5)

A shift register which receives a received signal and stores the received signal for one symbol period and outputs a received signal at the beginning of the current symbol period and a received signal at the end of the current symbol period; A correlator for receiving a start signal of the current symbol period and a signal received at the end of the current symbol period to calculate and output a correlation; And Determining the output of the correlator includes a determination unit for determining a data 0 if the correlation is large, and a data 1 if the correlation is low, and detecting the preamble by detecting the preamble. Device. The method of claim 1, wherein the correlator, The following equation is obtained from a received signal transmitted including M subcarriers in one symbol period T.

And a correlation value is calculated according to the preamble detection apparatus of the Miller encoded signal including the subcarrier. The method of claim 1, wherein the correlator, Compare the signal waveform of the subcarrier period at the start of one symbol of the same symbol period with the signal waveform of the subcarrier period at the end of one symbol, and output a positive value if the correlation is high, and output a negative value if the correlation is low. Preamble detection device of a Miller encoded signal comprising a sub-carrier, characterized in that. The method of claim 3, wherein the determining unit, And an output value of the correlator to determine data 0 if it is a positive value and data 1 if it is a negative value. The apparatus according to any one of claims 1 to 4, wherein the preamble detection device Preamble detection device of a Miller encoded signal comprising a sub-carrier, characterized in that implemented in the receiving unit of the RFID reader for receiving a response signal from the passive tag.

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