WO2009025425A1

WO2009025425A1 - Rfid reader supporting dense mode

Info

Publication number: WO2009025425A1
Application number: PCT/KR2008/000035
Authority: WO
Inventors: Won Sang Jo; Sang Hun Kim; Kyung Il Lee; Ji Heon Song; Chul Min Jun; Young Hee Chun; Ki Ho Lee
Original assignee: Victek Co., Ltd.
Priority date: 2007-08-20
Filing date: 2008-01-03
Publication date: 2009-02-26
Also published as: KR20090019227A; KR100886631B1

Abstract

Disclosed herein is a passive Radio Frequency Identification (RFID) reader supporting a dense mode. The RFID reader includes a modulator, a Radio Frequency (RF) transmitter, an RF receiver, a demodulator, a coupler, a scan receiver, and a microcontroller. The modulator encodes and modulates interrogation signals, and converts resulting signals into analog signals. The RF transmitter performs frequency up-conversion and power amplification on the analog signals, and radiates resulting signals. The RF receiver receives response signals from tags, and performs frequency down-conversion and then power amplification on the response signals. The demodulator converts the response signals into digital signals, and demodulates and decodes the digital signals. The coupler samples interrogation signals from other readers. The scan receiver scans the frequency channels of all sampled interrogation signals. The microcontroller receives the results of the scanning, detects a currently unoccupied frequency channel, and communicates with a tag using the detected frequency channel.

Description

Description RFID READER SUPPORTING DENSE MODE

Technical Field

[1] The present invention relates, in general, to a passive Radio Frequency Identification

(RFID) reader supporting a dense mode, and, more particularly, to a passive RFID reader supporting a dense mode that searches for a unoccupied channel using a realtime radio wave monitoring device, and communicates with a tag over the found channel, thereby supporting a dense mode, in which radio wave interference between readers can be prevented. Background Art

[2] Generally, RFID is a technology that is capable of identifying, tracing and managing animals and humans, to which tags are attached, by reading and recording information from and on the tags having unique identification information using radio frequencies in a non-contact manner. Such an RFID system includes a plurality of electronic tags (alternatively referred to as 'transponders'; hereinafter abbreviated as 'tags'), which have unique identification information and are attached to products or animals; and an RFID reader (alternatively referred to as an 'interrogator'; hereinafter abbreviated as a 'reader'), which is used to read or write information from or on the tags. Such RFID systems are classified into a mutual induction type and an electromagnetic wave type depending on the method of communication between the reader and the tags, into a passive type and an active type depending on whether tags are operated using their own power sources, and into a long- wave type, a medium- wave type, a short-wave type, an ultrashort- wave type, and a microwave type depending on the frequency used. Based on these classifications, various types of standards have been established, or are undergoing preparation for the establishment thereof.

[3] Meanwhile, an Ultrahigh Frequency (UHF) band of 860 to 960 MHz is expected to be widely used as a frequency band for RFID radio equipment. In particular, it has been prescribed in Korea that passive RFID equipment should make access using a frequency occupying method such as Frequency Hopping Spread Spectrum (FHSS) or Listen Before Talk (LBT). In the case of the FHSS method, it is prescribed that a channel bandwidth of 200 kHz within a range of 910 to 914 MHz should be used. Therefore, for the FHSS method, the total number of theoretically available channels is 20. Here, the FHSS method is a method in which hopping to another frequency band is performed using a plurality of frequency bands (channels) so as to avoid interference, and which was adopted in the U.S. etc., where the band of usable frequencies is wide. The LBT method is a method in which an available channel is detected before the transmission of data so as to share a frequency and performs communication only when a channel is unoccupied, and which was adopted as a standard in Europe, etc. where the band of usable frequencies is narrow.

[4] Meanwhile, the operational environment of a reader is determined depending on how many readers are present within a predetermined region, for example, a region having a radius of 1 km. That is, a single-interrogator environment refers to an environment in which a single reader is present in an environment in which 20 frequency channels are available, a multiple-interrogator environment refers to an environment in which two to five readers exist in a 20-available frequency channel environment, and a dense- interrogator environment (dense mode environment) refers to an environment in which 20 or more readers are present in an environment in which 20 frequency channels are available.

[5] However, in a dense mode environment in which a plurality of readers operate in a specific space in such a UHF band passive RFID system, the performance of the system is considerably reduced by radio wave interference between readers. In order to prevent this, that is, in order to overcome radio wave interference between readers, conventionally, a narrow-band spectrum mask has been implemented, or a time division method has been used. Of these schemes, the time division method is one method that is generally and widely used to implement a dense mode, but it has problems in that a separate device for synchronizing readers with each other in order to implement the function is required, and complicated software technology is demanded. Furthermore, in the case in which even one reader that does not support the time division method exists in an operational space, there is a problem in that the performance and reliability of the system are significantly reduced. Furthermore, in the case in which the time division method is used, there is a problem in that an idle period occurs between the operational cycles of the reader and the reader cannot recognize a tag during the idle period. Disclosure of Invention Technical Problem

[6] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a passive RFID reader supporting a dense mode, which searches for an unoccupied channel using a real-time radio wave monitoring device, and communicates with a tag over a found channel, so that a dense mode, in which the radio wave interference between readers can be reliably prevented, is supported, and the idle period of the reader can be eliminated, thereby maximizing communication efficiency. Technical Solution [7] In order to accomplish the above object, the present invention provides a passive

RFID reader supporting a dense mode, including a modulator for encoding and modulating various types of interrogation signals, converting the encoded and modulated interrogation signals into analog signals, and outputting these analog signals; a Radio Frequency (RF) transmitter for performing frequency up-con version and power amplification on the analog signals, modulated and output by the modulator, and radiating resulting signals through a transmitting antenna; an RF receiver for receiving response signals received from tags through a receiving antenna, and performing frequency down-conversion and then power amplification on the response signals; a demodulator for converting the response signals, provided through the RF receiver, into corresponding digital signals, and demodulating and decoding these digital signals; a coupler disposed between the receiving antenna and the RF receiver so as to search for a currently unoccupied frequency channel and configured to sample interrogation signals from other readers; a scan receiver for scanning frequency channels of all interrogation signals sampled by the coupler; and a microcontroller for receiving results of the scanning from the scan receiver, detecting a currently unoccupied frequency channel, and communicating with a tag using the detected frequency channel.

[8] Additionally, the present invention provides a passive RFID reader supporting a dense mode, including a modem for encoding and modulating various types of interrogation signals, converting the encoded and modulated interrogation signals into analog signals and outputting the analog signals, and converting response signals into corresponding digital signals and demodulating and decoding the digital signals; an RF transceiver for performing frequency up-conversion and then power amplification on the analog signals, modulated and output by the modem, and radiating resulting signals through a transmitting/receiving antenna, and performing power amplification and then frequency down-conversion on response signals received from tags through the transmitting/receiving antenna; a circulator for causing signals from an output port of the RF transceiver to be transmitted only to the transmitting/receiving antenna without being transmitted to an input port thereof at a time of transmitting interrogation signals, and causing signals, detected by the transmitting/receiving antenna, to be transmitted to the input port of the RF transceiver without being transmitted to the output port thereof at a time of receiving response signals from tags and searching for an unoccupied frequency channel; a coupler disposed between the circulator and an input port of the RF receiver and configured to sample interrogation signals from other readers; a scan receiver for scanning frequency channels of all interrogation signals sampled by the coupler; and a microcontroller for receiving results of the scanning from the scan receiver, detecting a currently unoccupied frequency channel, and com- municating with a tag using the detected frequency channel.

[9] In the passive RFID reader, the scan receiver may include a chirp local oscillator for outputting a local oscillation signal that linearly increases at predetermined time intervals; a mixer for mixing a signal, output from the chirp local oscillator, with an interrogation signal, received from each of other readers, and outputting a sum of frequencies thereof or a difference between the frequencies thereof; a weighted filter for strengthening a center frequency component of the sum or difference signal output from the mixer and weakening peripheral frequency components thereof; a delay filter for outputting the signal, passed through the weighted filter, at a different time delay according to a frequency channel thereof; a logarithmic detector for detecting an envelope of the signal passed through the delay filter and outputting the power of the signal as an equivalent DC voltage; and an A/D converter for converting the signal, passed through the logarithmic detector, into digital data and then outputting the digital signal so that the microcontroller can process the signal.

Advantageous Effects

[10] In accordance with the passive RFID reader supporting a dense mode according to the present invention, all occupied frequency channels currently used are searched for using a real-time radio wave monitoring device, and communication with a tag is performed via the frequencies of an unoccupied channel, thereby completely preventing radio wave interference between readers. Furthermore, in accordance with the passive RFID reader supporting a dense mode according to the present invention, a frequency channel is searched in a time shorter than the frequency hopping time of the FHSS method, and then the frequencies of an unoccupied channel can be utilized, so that the idle period of the reader is substantially shortened, thereby maximizing the communication efficiency of the reader. Furthermore, even if some other reader that does not support such a function exists in an operational space, there is an advantage in that the performance of the system is not considerably reduced. Brief Description of the Drawings

[11] Fig. 1 is a block diagram showing a passive RFID reader supporting a dense mode according to an embodiment of the present invention;

[12] Fig. 2 is a block diagram showing a passive RFID reader supporting a dense mode according to another embodiment of the present invention; and

[13] Fig. 3 is a detailed block diagram showing the scan receiver of Figs. 1 and 2.

[T 4] *** Description of reference characters of principal elements in the drawings ***

[15] 100: transmitting antenna 110: RF transmitter

[16] 120: modulator 130: receiving antenna

[17] 140: RF receiver 150: demodulator [18] 160: coupler 170: scan receiver

[19] 171: mixer 172: chirp LO

[20] 173: weighted filter 174: delay filter

[21] 175: logarithmic detector 176: Analog-to-Digital (A/D) converter

[22] 180: microcontroller 200: transmitting/receiving antenna

[23] 210: circulator 220: RF transceiver

[24] 230: modem 240: coupler

Mode for the Invention

[25] A passive RFID reader supporting a dense mode according to preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[26] Fig. 1 is a block diagram showing a passive RFID reader supporting a dense mode according to an embodiment of the present invention. As shown in Fig. 1, the passive RFID reader supporting a dense mode according to the present invention basically includes a microcontroller 180 for selecting a communication frequency channel and then communicating with a host system while controlling the overall operation of the system; a modulator 120 for, under the control of the microcontroller 180, performing encoding and modulation of various types of interrogation signals, such as Pulse- Interval Encoding (PIE)-type encoding, and Double- SideB and Amplitude- Shift Keying (DSB-ASK), Single-SideBand Amplitude-Shift Keying (SSB-ASK) or Phase-Reversal Amplitude- Shift Keying (PR-ASK)-type modulation, converting the encoded and modulated signals into analog signals, and outputting the analog signals; a Radio Frequency (RF) transmitter 110 for performing frequency up-con version and power amplification on the analog signals, modulated and output by the modulator 120, and radiating resulting signals through the transmitting antenna 100; an RF receiver 140 for receiving response signals from tags, received through the receiving antenna 130, and performing frequency down-conversion and then power amplification on the response signals; and a demodulator 150 for converting the response signals, provided through the RF receiver 140, into corresponding digital signals, demodulating and decoding the digital signals, and providing the demodulated and decoded digital signals to the microcontroller 180.

[27] Meanwhile, the present invention further includes a coupler 160 for sampling interrogation signals, received through the receiving antenna 130 from other readers, between the receiving antenna 130 and the RF receiver 140 so as to search for a currently unoccupied frequency channel; and a scan receiver 170 for scanning the frequency channels of all interrogation signals sampled by the coupler 160 and transmitting the results of the scanning to the microcontroller 180. In this construction, the microcontroller 180 detects an unoccupied frequency channel based on the results of the scanning from the scan receiver 170, and communicates with a tag over the found frequency channel.

[28] Fig. 2 is a block diagram supporting a dense mode according to another embodiment of the present invention. In the following description, the same reference numerals are assigned to elements identical to those of Fig. 1, and detailed descriptions thereof are omitted. As shown in Fig. 2, the present embodiment includes a single transmitting/ receiving antenna 200, a single RF transceiver 220 for performing RF transmission and reception functions, and a single modem 230 for performing modulation and demodulation, unlike the embodiment shown in Fig. 1. Therefore, a three-port circulator 210 is disposed between the transmitting/receiving antenna 200 and the RF transceiver 220. The circulator 210 functions to cause signals from the output port of the RF transceiver 220 to be transmitted only to the transmitting/receiving antenna 200, without being transmitted to the input port thereof at the time of transmitting interrogation signals, and functions to cause signals, detected by the transmitting/ receiving antenna 200, to be transmitted to the input port of the RF transceiver 220 without being transmitted to the output port thereof at the time of receiving response signals from tags and searching for an unoccupied frequency channel.

[29] Fig. 3 is a detailed block diagram showing the scan receiver of Figs. 1 and 2. As shown in Fig. 3, in the passive RFID reader supporting a dense mode according to the present invention, the scan receiver includes a chirp local oscillator 172 for outputting a local oscillation signal that linearly increases at predetermined time intervals; a mixer 171 for mixing a signal, output from the chirp local oscillator 172, with an interrogation signal, received from each of other readers, and outputting the sum of the frequencies thereof or the difference between the frequencies thereof; a weighted filter 173 for strengthening the center frequency component of the sum or difference signal output from the mixer 171 and weakening the peripheral frequency components thereof; a delay filter 174 for outputting the signal, passed through the weighted filter 173, at a different time delay according to the frequency channel thereof; a logarithmic detector 175 for detecting and outputting the envelope of the signal passed through the delay filter 174; and an A/D converter 176 for converting the signal, passed through the logarithmic detector 175, into digital data and outputting the digital signal so that the microcontroller 180 can process the signal.

[30] In the above-described construction, the interrogation signal received through the antenna 130 or 200, that is, an RF signal output and received from another reader, may be a signal in a frequency range of 910 to 914 MHz, as described above. The chirp local oscillator 172 may output an oscillation signal, which increases from, for example, 800 MHz, at predetermined time intervals, for example, 8 ?s, by 1 MHz so as to develop a received RF signal. Accordingly, the mixer 171 mixes a received RF signal with the output signal of the chirp local oscillator 172 and outputs the sum of the signals or the difference between the signals. In the present invention, it is preferable to use the difference signal. Next, the weighted filter 173 is a bandpass filter that allows only frequency components in a predetermined frequency band to pass therethrough. In order to prevent a center frequency signal from being mixed with adjacent sidelobe signals, the weighted filter 174 outputs a signal with the center frequency component thereof strengthened and adjacent frequency components weakened. The delay filter 174 is also referred to as a dispersive delay line, and may be implemented using a surface acoustic filter. The delay filter 174 outputs a signal having a higher frequency faster, and outputs a signal having a lower frequency slower. As a result, when signals, output from the weighted filter 173, pass through the delay filter 174, the signals are arranged along the time axis in a range of a lower frequency channel to a higher frequency channel. The logarithmic detector 175 envelope-detects a signal, including a high frequency component, and outputs the power of the signal as an equivalent DC voltage. The A/D converter 176 converts the resulting DC voltage into a corresponding digital signal, and provides it to the microcontroller 180.

[31] Finally, the microcontroller 180 detects an unoccupied frequency channel by checking sequentially input digital signals, and communicates with a tag using the frequency channel detected as described above. The microcontroller also provides a trigger signal to the chirp local oscillator 182, and thus it performs control so that the chirp local oscillator 172 operates within a predetermined frequency range. Meanwhile, during the search for a frequency channel, only a time equal to or less than 1 ms is required, so that the operation of searching for an unoccupied frequency channel and communicating with a tag using a found frequency channel is performed before hopping to another channel.

[32] The passive RFID reader supporting a dense mode according to the present invention is not limited to the above-described embodiments, but may be modified and practiced in various manners within the scope of the technical spirit of the present invention.

Claims

[1] A passive Radio Frequency Identification (RFID) reader supporting a dense mode, comprising: a modulator for encoding and modulating various types of interrogation signals, converting the encoded and modulated interrogation signals into analog signals, and outputting these analog signals; a Radio Frequency (RF) transmitter for performing frequency up-conversion and power amplification on the analog signals, modulated and output by the modulator, and radiating resulting signals through a transmitting antenna; an RF receiver for receiving response signals received from tags through a receiving antenna, and performing frequency down-conversion and then power amplification on the response signals; a demodulator for converting the response signals, provided through the RF receiver, into corresponding digital signals, and demodulating and decoding these digital signals; a coupler disposed between the receiving antenna and the RF receiver so as to search for a currently unoccupied frequency channel and configured to sample interrogation signals from other readers; a scan receiver for scanning frequency channels of all interrogation signals sampled by the coupler; and a microcontroller for receiving results of the scanning from the scan receiver, detecting a currently unoccupied frequency channel, and communicating with a tag using the detected frequency channel.

[2] A passive RFID reader supporting a dense mode, comprising: a modem for encoding and modulating various types of interrogation signals, converting the encoded and modulated interrogation signals into analog signals and outputting the analog signals, and converting response signals into corresponding digital signals and demodulating and decoding the digital signals; an RF transceiver for performing frequency up-conversion and then power amplification on the analog signals, modulated and output by the modem, and radiating resulting signals through a transmitting/receiving antenna, and performing power amplification and then frequency down-conversion on response signals received from tags through the transmitting/receiving antenna; a circulator for causing signals from an output port of the RF transceiver to be transmitted only to the transmitting/receiving antenna without being transmitted to an input port thereof at a time of transmitting interrogation signals, and causing signals, detected by the transmitting/receiving antenna, to be transmitted to the input port of the RF transceiver without being transmitted to the output port thereof at a time of receiving response signals from tags and searching for an unoccupied frequency channel; a coupler disposed between the circulator and an input port of the RF receiver and configured to sample interrogation signals from other readers; a scan receiver for scanning frequency channels of all interrogation signals sampled by the coupler; and a microcontroller for receiving results of the scanning from the scan receiver, detecting a currently unoccupied frequency channel, and communicating with a tag using the detected frequency channel.

[3] The passive RFID reader as set forth in claim 1 or 2, wherein the scan receiver comprises: a chirp local oscillator for outputting a local oscillation signal that linearly increases at predetermined time intervals; a mixer for mixing a signal, output from the chirp local oscillator, with an interrogation signal, received from each of other readers, and outputting a sum of frequencies thereof or a difference between the frequencies thereof; a weighted filter for strengthening a center frequency component of the sum or difference signal output from the mixer and weakening peripheral frequency components thereof; a delay filter for outputting the signal, passed through the weighted filter, at a different time delay according to a frequency channel thereof; a logarithmic detector for detecting an envelope of the signal passed through the delay filter and outputting the power of the signal as an equivalent DC voltage; and an Analog-to-Digital (AfD) converter for converting the signal, passed through the logarithmic detector, into digital data and then outputting the digital signal so that the microcontroller can process the signal.