Rfid system and communication method performed by the same

Abstract

Provided is an RFID system and method for maintaining a constant strength of a signal transmitted from an RFID tag to an RFID reader, regardless of a distance between the reader and tag. The RFID signal strength measuring reader measures a signal strength received from the RFID tag, creates control information used to set an amplification amount of the RFID tag by using a value of the measured strength to include the control information in an output signal, and sends the output signal to the RFID tag. The RFID tag, if the signal sent from the RFID reader is received, extracts internal information from the received signal, sends the information to the RFID reader as an output signal, and extracts the control information included in the signal sent from the RFID reader to adjust a strength of the output signal according to a value of the control information.

1 . A radio frequency identification (RFID) system comprising:
 an RFID tag; and   an RFID signal strength measuring reader that measures a strength of a signal received from the RFID tag, creates control information used to set an amplification amount of the RFID tag by using a value of the measured strength to include the control information in an output signal, and sends the output signal to the RFID tag;   wherein the RFID tag, if the signal sent from the RFID reader is received, extracts internal information from the received signal, sends the information to the RFID reader as an output signal, and at this time, extracts the control information included in the signal sent from the RFID reader to adjust a strength of the output signal according to a value of the control information.   
   
   
       2 . The RFID system of  claim 1 , wherein, if the strength of the signal transmitted from the RFID tag to the RFID reader is below a low predetermined value, the RFID reader sets the value of the control information so that the amplification amount of the RFID tag is increased, and if the strength of the signal transmitted from the RFID tag to the RFID reader is above a high predetermined value, the RFID reader sets the value of the control information so that the amplification amount of the RFID tag is reduced. 
   
   
       3 . The RFID system of  claim 1 , wherein the strength of the signal transmitted from the RFID tag to the RFID reader is inversely proportional to a distance between the RFID reader and the RFID tag. 
   
   
       4 . The RFID system of  claim 1 , wherein the RFID tag comprises:
 an antenna that sends a signal to the RFID reader and receives a signal from the RFID reader;   a logic unit that receives the signal from the antenna to extract internal information from the received signal and extracts the control information included in the signal transmitted from the antenna;   a modulating unit that modulates the internal information; and   an output unit connected to the logic unit and the modulating unit, the output unit amplifies an output signal of the modulating unit, adjusts an amplification amount of the output signal of the modulating unit according to the value of the control information to output the amplification amount as an output signal of the RFID tag, and sends the output signal to the antenna.   
   
   
       5 . The RFID system of  claim 4 , wherein the logic unit comprises:
 a signal analyzing unit that extracts and analyzes the control information, and sends an analysis result to the output unit;   a memory storing the information; and   a data processing unit that extracts the information stored in the memory and sends the information to the modulating unit.   
   
   
       6 . The RFID system of  claim 4 , wherein the output unit comprises:
 a variable amplification unit that receives an output signal of the modulating unit and an output signal of the logic unit, and adjusts the amplification amount of the output signal of the modulating unit according to the value of the control information which is output from the logic unit to output the amplification amount; and   a circulator that sends the output signal of the variable amplification unit to the antenna, and sends the signal transmitted from the antenna to the logic unit.   
   
   
       7 . The RFID system of  claim 4 , wherein the output unit comprises an impedance adjusting unit connected to the modulating unit and the logic unit, and adjusts the strength of the output signal of the modulating unit according to the value of the control information which is output from the logic unit. 
   
   
       8 . A communication method performed by a RFID system comprising an RFID reader and an RFID tag, the method comprising:
 if a signal sent from the RFID tag is received, then measuring a strength of the received signal, wherein the RFID reader measures the strength;   creating control information used to set an amplification amount of an output signal of the RFID tag by using a value of the measured strength, wherein the RFID reader creates the control information; and   sending a signal including the control information to the RFID tag, wherein the RFID reader sends the signal.   
   
   
       9 . The method of  claim 8 , wherein, if the strength of the received signal is below a predetermined low value, the RFID reader sets the value of the control information so that the amplification amount of the RFID tag is increased, and if the strength of the received signal is above a predetermined high value, the RFID reader sets the value of the control information so that the amplification amount of the RFID tag is reduced. 
   
   
       10 . A communication method performed by an RFID system comprising an RFID reader and an RFID tag, the method comprising:
 if a signal sent from the RFID reader is received,
 then checking if control information used to set an amplification amount of the RFID tag is included in the received signal, wherein the RFID tag performs checking; 
 if the control information is included in the received signal, then extracting the control information and information stored in the RFID tag and modulating the extracted information, wherein the RFID tag performs extraction; and 
 amplifying the modulated signal, and adjusting and outputting an amplification amount of the modulated signal according to a value of the control information, wherein the RFID tag performs amplification and adjustment. 
   
   
   
       11 . The method of  claim 10 , wherein the control information is set by the RFID reader to increase the amplification amount of the RFID tag if the RFID reader and the RFID tag are a long distance from each other, and to reduce the amplification amount of the RFID tag if the RFID reader and the RFID tag are a short distance from each other. 
   
   
       12 . An RFID tag that communicates with an RFID reader wirelessly, the RFID tag comprising:
 a signal strength measuring unit that receives a signal from the RFID reader and measures a strength of the received signal; and   an output unit that receives a signal that is output from the signal strength measuring unit, adjusts a strength of an RFID tag signal, and sends the RFID tag signal to the RFID reader.   
   
   
       13 . The RFID tag of  claim 12 , wherein if the strength of the signal which is input into the signal strength measuring unit is above a predetermined high value, the output unit reduces the strength of the input signal, and if the strength of the signal which is input into the signal strength measuring unit is below a predetermined low value, the output unit increases the strength of the input signal. 
   
   
       14 . The RFID tag of  claim 12 , further comprising:
 a logic unit connected to the signal strength measuring unit, the logic unit receives the signal which is output from the signal strength measuring unit, outputs data stored in the logic unit, and sends the data to the output unit.   
   
   
       15 . The RFID tag of  claim 14 , further comprising:
 a modulating unit connected between the logic unit and the output unit, the modulating unit modulates the signal which is output from the logic unit, and sends the modulated signal to the output unit.   
   
   
       16 . The RFID tag of  claim 12 , further comprising:
 an antenna that receives the signal from the RFID reader, transmits the signal to the signal strength measuring unit, and sends the signal which is output from the output unit to the RFID reader.   
   
   
       17 . The RFID tag of  claim 12 , wherein the output unit adjusts the strength of the output signal by adjusting an internal impedance thereof. 
   
   
       18 . An RFID tag that communicates with an RFID reader, the RFID tag comprising:
 an antenna that receives and sends a signal from and to the RFID reader;   a signal strength measuring unit that receives the signal from the RFID reader and measures a strength of the received signal;   a variable amplification unit that amplifies an input signal, receives an output signal of the signal strength measuring unit, adjusts an amplification amount of the input signal, and outputs the adjusted signal; and   a circulator connected to the variable amplification unit, the signal strength measuring unit, and the antenna, that transmits the signal which is output from the variable amplification unit to the antenna, and sends the signal which is output via the antenna to the signal strength measuring unit.   
   
   
       19 . The RFID tag of  claim 18 , wherein, if the strength of the signal which is input to the signal strength measuring unit is above a predetermined high value, the variable amplification unit reduces the strength of the input signal, and if the strength of the signal which is input to the signal strength measuring unit is below a predetermined low value, the variable amplification unit increases the strength of the input signal. 
   
   
       20 . The RFID tag of  claim 18 , further comprising: a logic unit connected to the signal strength measuring unit, that receives the signal which is output from the signal strength measuring unit, outputs data stored in the logic unit, and sends the data to the variable amplification unit. 
   
   
       21 . The RFID tag of  claim 20 , further comprising: a modulating unit connected to the logic unit and the variable amplification unit, that modulates the signal that is output from the logic unit, and sends the modulated signal to the variable amplification unit. 
   
   
       22 . A method of operating an RFID tag that communicates with an RFID reader, the method comprising:
 measuring a strength of a signal sent from the RFID reader and outputting the signal as a control signal;   extracting information stored in the RFID tag;   modulating a signal of the extracted information; and   adjusting a strength of the modulated signal according to the control signal and sending the modulated signal to the RFID reader.   
   
   
       23 . The method of  claim 22 , wherein the adjusting comprises:
 if the strength of the signal transmitted from the RFID reader to the RFID tag is below a predetermined low value, then increasing the strength of the signal which is output from the RFID tag, and   if the strength of the signal transmitted from the RFID reader to the RFID tag is above a high predetermined value, reducing the strength of the signal which is output from the RFID tag.