Abstract:
A reader device and RF tag improves the efficiency of frequency usage without increasing bandwidth using wireless communication from the reader to the tag and provides a transmission method that improves the power supply efficiency from the reader to the tag to extend the communication distance from the tag to the reader. A reader device for wirelessly communicating with an RF tag, comprises circuitry operable to transmit a wireless signal including information indicating encoding method of data to the RF tag and circuitry operable to receive and demodulate a wireless signal from the RF tag.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a reader/writer (R/W) device, its communication method, and RF tag. For example, this invention is the reader/writer (R/W) device, its transmission method, and tag for RFID systems that executes multi-level ASK modulation.  
         [0003]     2. Description of the Related Art  
         [0004]     Conventionally, RFID communicated with the reader/writer device (herein referred to as a “reader”) and RF tag using amplitude modulation signals. The following is an explanation of an example of the conventional reader and RF tag.  
         [0005]      FIG. 1  shows the configuration of a conventional reader.  FIG. 2  shows the conventional command format.  
         [0006]      FIG. 3  shows the wave pattern of the conventional 1-bit Manchester Encoded ASK signal.  
         [0007]     In  FIG. 1 , reader  10  receives information signals from LAN  21  and transmits timing information through processor  30 . The command generated by processor  30  or the information signal received from LAN  21  is processed into the data shown in the command format in  FIG. 2  and output to filter  11 . The detailed configuration of processor  30  will be explained later.  
         [0008]     Filter  11  outputs the signal, restricting the bandwidth of data from processor  30  to ASK modulator  12 . ASK modulator  12  executes ASK (amplitude shift keying) modulation on the transport signal from oscillator  14  based on the signal from filter  11 . The wave pattern of the amplitude-modulated signal (herein referred to as “ASK signal”) is shown in  FIG. 3 . In addition, the A and B levels are used in the wave pattern of the ASK signal and the modulation index is represented by (A−B)/(A+B). In addition, in type B of ISO/IEC 18000 Part 6, it is stated that 18% or 100% should be used as the degree of modulation index.  
         [0009]     In addition, the ASK signal is amplified with amplifier  13  and is transmitted to the RF tag through the coupling device  15  and antenna  16 .  
         [0010]     The reception of modulated backscatter signals from the RF tag by the reader is explained in the following using  FIG. 1 . The modulated backscatter signal (herein referred to as “modulated signal”) received by antenna  16  is output to down converter  19 , through shared device  15  and amplified in amplifier  20 . Down converter  19  demodulates the amplified modulated signal to an IF signal by the output of oscillator  14 . As filter  18  eliminates high-frequency components with a LPF, the interference between the adjacent channels of the IF signal is controlled. Demodulator  17  demodulates signals from filter  18  into data and outputs them to processor  30 . Processor  30  processes demodulated data and outputs data to LAN  21  received from the tag.  
         [0011]      FIG. 4  shows the processor configuration of the conventional reader.  
         [0012]     In  FIG. 4 , control  31  controls from the upper layer and outputs the control data (refers to the information written to the Delimiter area) of whether to transmit the uplink at a rate of 4-times to the frame assembly  34  from the RF tag. CRC attachment  32  attaches 16 bits for CRC to the command from LAN  21 , parameters, and transmission data from the data and outputs to 1-bit Manchester Encoder  33 .  
         [0013]     The 1-bit Manchester encoder  33  allocates code “1” to the Manchester code “10” of the 1 symbol of the transmission data with 16 bits for CRC attached and allocates code “0” to the Manchester code “01” of the 1 symbol. 1-bit Manchester encoding is executed and a 1-bit Manchester encoded signal is output to the frame assembly  34 . The preamble established by the frame assembly  34 , for example, is configured by a fixed pattern of 16-bit ALL “0” as the Preamble Detect and 9 bits of Manchester code 0 as the Preamble. The Preamble Detect is necessary to dispatch power to each part of the RF tag before data is demodulated. This allows each part of the RF tag to always be ready to receive before the demodulator receives the necessary data. The preamble pattern is known by the RF tag.  
         [0014]     Frame assembly  34  generates frame data with preamble detect, preamble, delimiter and Manchester encoded data. The format of this frame data is shown in  FIG. 2 . In addition, the decoder  35  decodes FMO encoded signal from demodulator  17  in  FIG. 1  and outputs to error detector  36 . The error detector  36  detects the errors in the decoded data. Processor  30  confirms the contents of the received data. In addition, processor  30  transmits the data received from the tag to LAN  21  of  FIG. 1 .  
         [0015]      FIG. 5  shows the configuration of the conventional RF tag.  
         [0016]     In  FIG. 5 , RF tag  40  receives the ASK signal from reader  10  in  FIG. 1  with antenna  41 . Electric power generator  46  generate direct-current voltage by rectifying the signal received by antenna  41 . Although this is not illustrated, this direct-current voltage is supplied to each of the parts. ASK demodulator  42  demodulates ASK signals received from antenna  41  and outputs the demodulated Manchester encoded signals to the logic part  44 . Logic part  44  decodes the Manchester encoded signals and extract the command data in the decoded data. If the command refers to a write command, the decoded data is written to memory  45 . When write is complete, logic part  44  FMO encodes the ACKNOWLEDGE information. After the data is modulated by modulator  43 , this is transmitted to reader  10 .  
         [0017]     In addition, logic part  44  confirms the details of the command in the demodulated data and if the command refers to a read command, the information stored in the memory  45  corresponding to the address in the parameter is read and is then FMO encoded. Furthermore, logic part  44  attach the Preamble and CRC bits with the encoded data. After the data is modulated by modulator  43 , this is transmitted to reader  10 .  
         [0018]     The items regarding the configuration of the reader and RF tag in the above are disclosed in Japanese Unexamined Patent Application Publication 2003-158470 and in Published Japanese Translation of a PCT Application 2002-525932  
         [0019]     As explained, demodulation of ASK signal is relatively easy and this is why ASK modulation is popular forward link (reader to tag transmission) modulation in RF tag systems. However, efficiency of frequency usage of 1-bit ASK modulation is low.  
         [0020]     In addition, the frequency bandwidth allocated to the current UHF-band RFID system is narrow in Japan and Europe, compared to the US. When utilizing multiple adjacent readers, each reader must use a different frequency to avoid the effect of mutual interference. However, if the available frequency range is narrow, there is a problem with the limited number of secured frequency channels as the number of readers available is now also limited. As a result, the RFID is a system with bad efficiency of frequency usage. It is anticipated that cases utilizing multiple adjacent readers will increase in the future. An RFID system with improved efficiency of frequency usage without increasing frequency range is needed.  
         [0021]     In addition, the 1-bit Manchester encoded ASK modulation shown in  FIG. 2  allocates data code “1” to the Manchester code “10” of the 1 symbol and allocates data code “0” to the Manchester code “01” of the 1 symbol. In case of Manchester code “1001,” a period of low-level amplitude is generated for 1 symbol-length duration. Therefore, the voltage supplied to the RF tag from the reader is insufficient and there is a problem with the limitations in the communication range between RF tag and the reader in the RFID system using conventional 1-bit Manchester encoded ASK modulation.  
         [0022]     As a result, a system must be constructed with limitations in communication range when the RFID system is used.  
         [0023]     In the RFID system, a technology is needed to extend the conventional communication range between the RF tag and the reader.  
       SUMMARY OF THE INVENTION  
       [0024]     The present invention advantageously improves the efficiency of frequency usage without increasing bandwidth using wireless communication from the reader to the tag. In addition, the present invention provides a transmission method that improves the power supply efficiency from the reader to the tag to extend the communication distance from the tag to the reader. Also, the present invention provides results that were unavailable to conventional technology resulting from the various configurations of the Best Modes of Practicing the Invention mentioned below. This invention&#39;s reader device, communication method, and tag improve the efficiency of frequency usage without increasing bandwidth and make the communication distance from the tag to the reader expandable, compared to conventional means.  
         [0025]     In one embodiment of the present invention, a reader device for wirelessly communicating with an RF tag comprises circuitry operable to transmit a wireless signal including information indicating coding method used to the RF tag and circuitry operable to receive and demodulate a wireless signal from the RF tag. The reader device further comprises circuitry operable to each symbol with same peak level of encoded signals, circuitry operable to transmit signals without varying amplitudes of each symbol and to receive, and circuitry operable to demodulate the signal from the tag. An encoding modulation is N-bit Manchester Encoding, wherein N is at least 2. The reader device further comprises circuitry operable to generate a preamble pattern signal and a signal indicating an encoding method of data and circuitry operable to output data attaching the preamble pattern signal and the signal indicating an encoding method of data as transmission data. The reader device further comprises circuitry operable to generate a signal with information indicating the encoding method and circuitry operable to modulate the generated signal. The reader device further comprises circuitry operable to generate a preamble pattern signal, circuitry operable to generate a signal indicating an encoding method of data, and circuitry operable to attach and transmit data to the preamble and the signal indicating an encoding method of data. The reader device further comprises circuitry operable to offset and transmit constant peak values of each symbol&#39;s multi-level signals. The encoding modulation is Manchester Encoding Amplitude Modulation.  
         [0026]     In one embodiment of the present invention, an RF tag for wirelessly communicating with a reader device comprises circuitry operable to receive modulated signals attached with information identifying encoding method of Manchester code before modulation, circuitry operable to detect demodulation procedures and information to identify the corresponding encoding method, and circuitry operable to switch the demodulation process in response to the information identifying the encoding method. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0027]     The preferred embodiments of the present invention will be described with reference to the accompanying drawings.  
         [0028]      FIG. 1  illustrates the conventional reader configuration.  
         [0029]      FIG. 2  illustrates the conventional command format configuration.  
         [0030]      FIG. 3  illustrates the conventional 1-bit Manchester encoded ASK signal.  
         [0031]      FIG. 4  illustrates the conventional processor configuration.  
         [0032]      FIG. 5  illustrates the conventional RF tag configuration.  
         [0033]      FIG. 6  illustrates this invention&#39;s reader configuration.  
         [0034]      FIG. 7  illustrates this invention&#39;s first command format configuration.  
         [0035]      FIG. 8  illustrates this invention&#39;s processor configuration.  
         [0036]      FIG. 9  illustrates this invention&#39;s 2-bit Manchester encoded ASK signal wave pattern.  
         [0037]      FIG. 10  illustrates this invention&#39;s 3-bit Manchester encoded ASK signal wave pattern  
         [0038]      FIG. 11  illustrates this invention&#39;s RF tag configuration.  
         [0039]      FIG. 12  illustrates this invention&#39;s RF tag logic part configuration.  
         [0040]      FIG. 13  illustrates this invention&#39;s second command format configuration. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0041]     The explanations of this invention&#39;s format refer to the figures below.  
         [0042]     Explanation of this invention&#39;s format  
         [0043]      FIG. 6  shows the configuration of this invention&#39;s reader.  FIG. 7  shows the configuration of this invention&#39;s first command format.  
         [0044]     In  FIG. 6 , LAN  21  transmits instruction commands or information signals written to tag to the reader&#39;s  100  processor  50  and receives timing information from the reader&#39;s  100  processor  50 . Before processor  50  starts communicating with an RF tag, the protocol processing at the processor&#39;s  50  higher layer confirms the RF tag compatible Manchester encoding multi-values (for example, 4-bit) by acquiring the ID of the RF tag. The command generated by processor  50  or the information signal received from LAN  21  is processed into the data shown in the command format in  FIG. 2  and output to filter  11 . The detailed configuration of processor  50  will be explained later.  
         [0045]     Filter  11  outputs the signal restricting the bandwidth of data from processor  50  to ASK modulator  60 . ASK modulator  60  executes ASK modulation on the transport signal from oscillator  14  based on the signal from filter  11 . ASK modulator  60  executes ASK modulation on the data from Preamble Detect, Preamble, Delimiter, Command, Parameter, Data, and CRC-16, shown in  FIG. 7 , from filter  11 .  
         [0046]     The modulated signal is output to amplifier  13 . Amplifier  13  amplifies the modulation signal from ASK modulator  60  and transmits this as a wireless signal to the RF tag through the shared device  15  and antenna  16 .  
         [0047]     Reader  100  receives the wireless signals from RF tag with the antenna  16 . The received wireless signals are amplified at amplifier  20  through shared device  15  and output to down converter  19 . Down converter  19  mixes the amplified signal with the transport signal from oscillator  14  and outputs both demodulated signals, I (inphase) and Q (quadrature) signals, to filter  18 . Filter  18  eliminates high-frequency components with an LPF and outputs the signal to demodulator  17 . Demodulator  17  demodulates the signal from filter  18  to data and outputs to processor  50 .  
         [0048]     The following is an explanation regarding the operation of processor  50 , utilizing the configuration of processor  50  shown in  FIG. 8 .  
         [0049]     In  FIG. 8 , control  51  outputs the control signal to frame assembly  56 , based on the higher layer instructions of processor  50 . After receiving the transmission data, a command generated by the CRC attachment  52  or an information signal from LAN  21 , the data is output to 1-bit/2-bit Manchester encoder  54  attaching the CRC 16-bit. In response to the enable and disable signals from processor  50 , 1-bit/2-bit Manchester encoder  54  switches between encoding the 2-bit or 1-bit Manchester code and outputs the data to the frame assembly  56 . Frame assembly  56  acquires the coded data in the format shown in  FIG. 7  by attaching the uplink transmission rate information from control  51 , delimiter indicating the Manchester encoding method used the following data part, and Manchester encoded data from the 1-bit/2-bit Manchester encoder  54  to the head of Preamble (Preamble Detect, Preamble).  
         [0050]     In addition, the demodulated data is input into decoder  55 . Decoder  55  decodes FMO encoded data demodulated from demodulator  17  and outputs to error detector  53 . Error detector  53  utilizes the CRC bit of the decoded data and detects errors. The result of error detection is output with the received data.  
         [0051]      FIG. 9  shows the wave pattern of this invention&#39;s 2-bit Manchester encoded modulation signal. The wave pattern signal in this figure corresponds to the signal output from the ASK modulator  60 . This figure shows the waveform signal of each value of the 2-bit and the amplitude value is scaled vertically. The peak value of any value symbol of this wave pattern is equal. However, the amplitudes of wave pattern signals of certain values (for example, Manchester codes “11” and “00”) are different from the amplitudes of wave pattern signals of other values (for example, Manchester codes “10” and “01”). This signal is transmitted from the reader to the RF tag and the amplitude components of this signal are utilized as the electrical power supply for the RF tag. Increasing the amplitude value of this signal increases the electrical power supplied to the RF tag. As a result, the transmission distance from the RF tag to the reader can be extended, when compared to conventional means. Comparing “10” of this 2-bit and “1” of the 1-bit, the 1 symbol at the same time as shown in the conventional  FIG. 3 , the power of “10” is 1.5 times that of “1.” The communication distance in this comparison is equivalent to the square root of the power ratio, therefore, the distance extends about 1.2 times further than conventional means.  
         [0052]      FIG. 10  shows the wave pattern of this invention&#39;s 3-bit Manchester encoded modulation signal. The wave pattern signal in this figure corresponds to the signal output from the ASK modulator  60  in  FIG. 6 . This figure shows the waveform signal of each value of the 3-bit and the amplitude value is scaled vertically. The peak value of any value symbol of this wave pattern is equal. However, the amplitudes of wave pattern signals of the first value (for example, Manchester codes “000” and “100”), the amplitudes of wave pattern signals of the second value (for example, Manchester codes “001” and “101”), the amplitudes of wave pattern signals of the third value (for example, Manchester codes “010” and “110”), and the amplitudes of wave pattern signals of the fourth value (for example, Manchester codes “011” and “111”) are all different.  
         [0053]     This signal is transmitted from the reader to the RF tag and the amplitude components of this signal are utilized as the electrical power supply at the RF tag. Increasing the amplitude of this signal increases the electrical power supplied to the RF tag. As a result, the transmission distance from the RF tag to the reader can be extended, when compared to conventional means.  
         [0054]      FIG. 11  shows the configuration of this invention&#39;s RF tag.  FIG. 12  shows the configuration of this invention&#39;s RF tag logic part.  
         [0055]     RF tag  400  receives wireless signals from reader  100  by antenna  41 . The signals received by antenna  41  are output to ASK demodulator  401  and power generator  46 . Although power generator  46  has not been illustrated in detail, the power is rectified by a rectifier generating a direct-current voltage and supplied to each circuit part. ASK modulator  401  demodulates the received data and transmits the demodulated data to logic part  44 .  
         [0056]     The operation of logic part  44  is explained in the following using  FIG. 12 .  
         [0057]     Identifier  447 , in logic part  44 , acquires the demodulated data shown in  FIG. 7 , and identifies the Manchester encoding method as either 2-bit or 1-bit by the Delimiter (identifying information). This also identifies whether the information to increase the transmission rate of return link to 4-times is written. If the 2-bit Manchester encoding is applied in the following part, the identifying information is transmitted to decoder  446 . If the information specifies an increase in transmission rate of return link to 4-times, the information is transmitted to command processor  441 . Furthermore, identifier  447  outputs only the demodulated data up to the Delimiter and subsequent data not including the header, Command, Parameter, Data, and CRC-15 information to decoder  446 . As identifier  447  identifies the contents of the Delimiter, decoder  446  outputs the Command, Parameter, Data, and CRC-15 decoded information to error detector  445 , based on the identifying information indicating the encoding method. Specifically, if the identifying information is 2-bit Manchester encoding, the subsequent data is coded by 2-bit Manchester encoding and the data is decoded as a 2-bit Manchester encoded signal by decoder  446 . In addition, if the information is not 2-bit Manchester code, decoder  446  decodes the information as a 1-bit Manchester encoded signal. Error detector  454  detects any errors in the data utilizing CRC bits in the data after it has been decoded.  
         [0058]     Furthermore, error detector  445  outputs the received data to command processor  441 . Command processor  441  identifies the command contents. If the command refers to a read command, this is compared to the ID in the parameter and memory  45  (not shown in  FIG. 12 ) following the command. If these match, the information stored in the memory  45  corresponding to the address in the parameter is read. If information specifying the increase of return link transmission rate to 4-times from identifier  447  is received by command processor  441 , the transmission rate is increased by modulator  43  to 4-times.  
         [0059]     The following explains the transmission process of RF tag.  
         [0060]     CRC attachment  442  attaches a CRC bit to the transmitting data read from command processor  441  and outputs the signal to FMO encoder  443 . FMO encoder  443  encodes the signal attached to the CRC bit as an FMO and attaches a Preamble at frame assembly  444 . This is output to modulator  43  as encoded data. Modulator  43  modulates the encoded data and transmits it to reader  10 .  
         [0061]     In addition, regarding command processor  441 , error detector  445  utilizes CRC 16-bit to detect errors in the decoded CRC-16 data. Command processor  441  identifies the command contents in the received data. If the command refers to a write command to the RF tag&#39;s memory  45 , this is compared to the ID in the parameter and memory  45  following the command. If these match, the data following the parameter in the address of the parameter is written in memory  45 .  
         [0062]      FIG. 13  shows the configuration of the second command format.  
         [0063]      FIG. 13  explains items differing from the first command format in  FIG. 7 .  
         [0064]     This format has added a Multilevel preamble after Delimiter.  
         [0065]     This multilevel preamble can be used to adjust the optimum threshold level for detecting multilevel signal shown in  FIG. 9 . For example, based on the wave patterns in  FIG. 9 , the information indicating the threshold of the individual data ID are transmitted in the order of Manchester codes “00,” “01,” “10,” and “11.” 
         [0066]     The above was an explanation of Manchester encoding. If the encoding process utilizes differential Manchester codes and the decoding timing is off, decoding is still possible.  
         [0067]     In the Best Modes of Practicing the Invention mentioned above, the ASK modulation was explained. However, other modulation formats, such as, QPSK and QAM can be utilized and in addition to 2-bit and 3-bit Manchester encoding.  
         [0068]     Although specific embodiments of the present invention have been described, it will be understood by those of skill in the art that there are other embodiments that are equivalent to the described embodiments. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiments, but only by the scope of the appended claims.