WO2009054568A1

WO2009054568A1 - Rfid reader supporting dense mode using fft algorithm

Info

Publication number: WO2009054568A1
Application number: PCT/KR2008/000042
Authority: WO
Inventors: Won Sang Jo; Sun Ho Choi; Gwan Tae Kim; In Chur Jin; Won Choi; Myeong Ryeol Choi; Seong Yong Shim
Original assignee: Victek Co., Ltd.
Priority date: 2007-10-24
Filing date: 2008-01-04
Publication date: 2009-04-30
Also published as: KR20090041553A; KR100907212B1

Abstract

Disclosed herein is a passive Radio Frequency Identification (RFID) reader supporting a dense mode using a Fast Fourier Transform (FFT). The RFID reader includes a modulator, a Radio Frequency (RF) transmitter, an RF receiver, a demodulator, a coupler, an FFT receiver, and a microcontroller. The modulator encodes and modulates interrogation signals, and converts resulting signals into analog signals. The RF transmitter performs up- conversion and power amplification on the analog signals, and radiates resulting signals. The RF receiver receives response signals, and performs frequency down-conversion and 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. The FFT receiver scans the frequency channels of the interrogation signals using an FFT algorithm. The microcontroller receives the results of the scanning, detects a currently unoccupied frequency channel, and communicates with a tag using the frequency channel.

Description

[DESCRIPTION]

[Invention Title]

RFID READER SUPPORTING DENSE MODE USING FFT ALGORITHM

[Technical Field]

<i> The present invention relates, in general, to a passive Radio Frequency Identification (RFID) reader supporting a dense mode using a Fast Fourier Transform (FFT) algorithm, and, more particularly, to a passive RFID reader supporting a dense mode using an FFT algorithm that searches for an unoccupied channel using a real-time 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]

[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 using an FFT algorithm, which searches for an unoccupied channel using a real-time radio wave monitoring device implemented using an FFT receiver, 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 an RFID reader supporting a dense mode using a FFT algorithm, 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-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; an FFT receiver for scanning frequency channels of all interrogation signals, sampled by the coupler, using an FFT algorithm; and a microcontroller for receiving results of the scanning from the FFT receiver, detecting a currently unoccupied frequency channel, and communicating with a tag using the detected frequency channel.

<8> In order to accomplish the above object, the present invention provides a passive RFID reader supporting a dense mode using an FFT algorithm, 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; an FFT receiver for scanning frequency channels of all interrogation signals, sampled by the coupler, using an FFT algorithm; and a microcontroller for receiving results of the scanning from the FFT receiver, detecting a currently unoccupied frequency channel, and communicating with a tag using the detected frequency channel.

<9> In the above construction, the FFT receiver includes an RF down- converter for down-converting an RF signal, that is, an interrogation signals sampled by the coupler and received from each of other readers, into an intermediate frequency signal; an A/D converter for converting the analog intermediate frequency signal, output from the RF down-converter, into a corresponding magnitude digital signal; a digital down-converter for down- converting the digital intermediate frequency signal, output from the A/D converter, into baseband digital data; and an FFT processing unit for processing the baseband digital data from the digital down-converter using an FFT algorithm, searching for all frequency channels currently occupied by the other readers, and transferring information about the occupied channels to the microcontroller.

<io> Meanwhile, the FFT processing unit generates the amplitude information of a frequency signal of each of the found frequency channels and transfers the amplitude information to the microcontroller. [Advantageous Effects]

<ii> 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 implemented using an FFT receiver, 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.

[Description of Drawings] <12> Fig. 1 is a block diagram showing a passive RFID reader supporting a dense mode according to an embodiment of the present invention; <13> Fig. 2 is a block diagram showing a passive RFID reader supporting a dense mode according to another embodiment of the present invention; <14> Fig. 3 is a block diagram showing the FFT processing unit of Figs. 1 and 2; and <15> Fig. 4 is a detailed block diagram showing an embodiment of the FFT processing unit of Fig. 3. <i6> *** Description of reference characters of principal elements in the drawings ***

<i7> 100: transmitting antenna 110: RF transmitter <18> 120: modulator 130: receiving antenna

<19> 140: RF receiver 150: demodulator

<20> 160: coupler 170: FFT receiver

<2i> 172: RF down-converter 174: A/D converter <22> 176: digital down-converter 178: FFT processing unit <23> 178a: FPGA 178al: FIFO memory

<24> 178a2: FFT performance unit 178a3: high-speed amplitude calculation unit

<25> 178a4: control interface 178a5: buffer

<26> 178b: DSP 178c: D-Random Access Memory (RAM)

<27> 180: microcontroller 200: transmitting/receiving antenna <28> 210: circulator 220: RF transceiver

<29> 230: modem

[Mode for Invention] <30> A passive RFID reader supporting a dense mode using an FFT algorithm according to preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

<3i> 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-SideBand 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-conversion 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.

<32> 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 an FFT 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 O

detects an unoccupied frequency channel based on the results of the scanning from the FFT receiver 170, and communicates with a tag over the found frequency channel.

<33> 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.

<34> Fig. 3 is a detailed block diagram showing the FFT 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 FFT receiver 170 includes an RF down-converter 172 for down-converting a received RF signal, that is, an interrogation signal sampled by the coupler 160 and received from each of the other readers, for example, an RF signal in a UHF band (ranging from 860 to 960 MHz), into a signal at an intermediate frequency, for example, 10.7 MHz or 21.4 MHz; an A/D converter 174 for converting the analog intermediate frequency signal, output from the RF down-converter 172, into a corresponding magnitude digital signal; a digital down-converter 176 for down-converting the digital intermediate frequency signal, output from the A/D converter 174, into baseband digital data! and an FFT processing unit 178 for processing the baseband digital data from the digital down-converter 176 using an FFT algorithm, searching for all frequency channels currently occupied by the other readers, and transferring information about the occupied channels to the microcontroller 180.

<35> In the above-described construction, Fourier transform is a technique that is used in various fields, such as noise suppression, amplification technology, and voice and image compression. Fourier transform is an algorithm for interconvert ing time and a frequency signal between the time domain and the frequency domain. FFT is an algorithm that is conceived to reduce the excessively long calculation time of Discrete Fourier Transform (DFT) in which a continuous signal is considered to be signals sampled over time and then a Fourier transform equation is calculated without modification. FFT is a well-known algorithm in which all sampled signals are not converted, but only necessary signals are selected and then Fourier transform is performed on the selected signals at high speed.

<36> Fig. 4 is a detailed block diagram showing an embodiment of the FFT processing unit of Fig. 3. As shown in Fig. 4, an FFT processing unit 178 according to an embodiment of the present invention may include a Field Programmable Gate Array (FPGA) unit 178a for performing FFT in real time, searching for frequency channels currently occupied by the other readers, and outputting relevant frequency information; and a Digital Signal Processor (DSP) unit 178b for controlling the operation of the FPGA unit 178a and transferring the frequency information, output from the FPGA unit 178a, to the microcontroller 180 via a D-RAM 178c.

<37> In the above-described construction, the FPGA unit 178a includes First Input & First Output (FIFO) memory 178a1 for storing the baseband digital data from the digital down-converter 172, and outputting the data in sequence of input; an FFT performance unit 178a2 for processing the baseband digital data from the FIFO memory 178al using an FFT algorithm and generating frequency information based on the results of scanning all frequency channels currently occupied by the other readers; a buffer 178a5 for temporarily storing the frequency information from the FFT performance unit 178a2 so that the DSP unit 178b can read the frequency information; and, preferably, Dual Port RAM. The FPGA unit 178a not only outputs frequency information about frequency channels currently occupied by other readers, but also further includes a high-speed amplitude calculation unit 178a3 for calculating the amplitudes of signals at high speed. Reference numeral 178a4 designates a control interface 178a4 that is responsible for the interfacing among the FFT performance unit 178a2, the high-speed amplitude calculation unit 178a3 and the D-RAM 189c.

<38> According to the present invention having the above-described construction, the time required to scan frequency channels, currently occupied and used by the other readers, using the FFT receiver is less than 5 ms at the very most, so that it is shorter than frequency hopping time, with the result that a currently unoccupied channel can be used within a time period shorter than the hopping time.

<39> The passive RFID reader supporting a dense mode using an FFT algorithm 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. For example, although, in the above-described embodiments, the FPGA unit and the DSP unit have been described as being separate from each other, all the functions of the FPGA unit may be implemented within the DSP unit.

Claims

[CLAIMS] [Claim 1] <4i> A passive Radio Frequency Identification (RFID) reader supporting a dense mode using a Fast Fourier Transform (FFT) algorithm, comprising: <42> 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; <43> 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; <44> 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; <45> a demodulator for converting the response signals, provided through the

RF receiver, into corresponding digital signals, and demodulating and decoding these digital signals; <46> 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; <47> an FFT receiver for scanning frequency channels of all interrogation signals, sampled by the coupler, using an FFT algorithm; and <48> a microcontroller for receiving results of the scanning from the FFT receiver, detecting a currently unoccupied frequency channel, and communicating with a tag using the detected frequency channel.

[Claim 2] <49> A passive RFID reader supporting a dense mode using an FFT algorithm, comprising: <50> 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",

<5i> 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;

<52> 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 ;

<53> a coupler disposed between the circulator and an input port of the RF receiver and configured to sample interrogation signals from other readers;

<54> an FFT receiver for scanning frequency channels of all interrogation signals, sampled by the coupler, using an FFT algorithm; and

<55> a microcontroller for receiving results of the scanning from the FFT receiver, detecting a currently unoccupied frequency channel, and communicating with a tag using the detected frequency channel. [Claim 3]

<56> The passive RFID reader as set forth in claim 1 or 2, wherein the FFT receiver comprises:

<57> an RF down-converter for down-converting an RF signal, that is, an interrogation signals sampled by the coupler and received from each of other readers, into an intermediate frequency signal;

<58> an A/D converter for converting the analog intermediate frequency signal, output from the RF down-converter, into a corresponding magnitude digital signal; <59> a digital down-converter for down-converting the digital intermediate frequency signal, output from the A/D converter, into baseband digital data; and

<60> an FFT processing unit for processing the baseband digital data from the digital down-converter using an FFT algorithm, searching for all frequency channels currently occupied by the other readers, and transferring information about the occupied channels to the microcontroller. [Claim 4]

<6i> The passive RFID reader as set forth in claim 3, wherein the FFT processing unit generates amplitude information of a frequency signal of each of the found frequency channels and transfers the amplitude information to the microcontroller.