Abstract:
A communication apparatus is provided that performs short-range wireless communication in a contactless manner. The communication apparatus includes: a large antenna; a first wireless processing section configured to perform data communication via electromagnetic induction-type using the large antenna; a small antenna placed inside the large antenna; and a second wireless processing section configured to perform data communication using the small antenna.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to Japanese Patent Application JP 2007-319567, filed in the Japan Patent Office on Dec. 11, 2007, the entire contents of which being incorporated herein by reference. 
       BACKGROUND 
       [0002]    The present application relates to a communication apparatus that performs short-range wireless communication in a contactless manner. More specifically, the present application relates to a contactless communication apparatus such as a communication terminal (a transponder) that does not have its own source of radio waves and which transmits data to an apparatus (a reader/writer), such as, a communication partner, in a wireless manner. 
         [0003]    As a communication system in which a communication terminal that does not have its own source of radio waves transmits data to a communication-partner device in a wireless manner, a contactless communication system called radio frequency identification (RFID) is known. The RFID is also referred to as “ID system,” “data carrier system,” and so on, but the name commonly used worldwide is “RFID system,” i.e., “RFID” for short. 
         [0004]    The RFID system is applied to a large number of contactless IC cards. An IC card system is composed of an integrated circuit (IC) card as a transponder and a device (hereinafter referred to as a “reader/writer”) that reads information from the IC card or writes information to the IC card. The IC card system provides great convenience because the IC card and the reader/writer therein exchange the information therebetween in a contactless manner. Thus, the IC card system has been broadening its range of applications. For example, the IC card system has been replacing traditional magnetic cards as commuter passes, identification cards, and so on. Also, the IC card system has been finding wider applications in distribution systems and so on. 
         [0005]    Examples of contactless communication methods as used in the RFID systems include electrostatic coupling, electromagnetic induction, and microwave communication. An RFID system using the electromagnetic induction is composed of a primary coil in the reader/writer and a secondary coil in the card (or the transponder), and these two coils are magnetically coupled to carry out data communication via the coils. Specifically, the reader/writer transmits data by performing amplitude modulation on a magnetic field generated by the primary coil, whereas the transponder demodulates it. The transponder is capable of transmitting data to the reader/writer by performing modulation, such as the amplitude modulation, through load switching (LS) in the secondary coil. 
         [0006]    The coil in each of the transponder and the reader/writer operates as an LC resonant circuit. In general, a range of communication between the transponder and the reader/writer can be set appropriately by adjusting a resonance frequency of the coils to a frequency of a carrier wave used for the communication and allowing them to resonate with each other. Note that the coil in each of the transponder and the reader/writer will be hereinafter referred to also as an “antenna” as appropriate. 
         [0007]      FIG. 17  illustrates an exemplary structure of a contactless communication system using the electromagnetic induction as composed of the transponder and the reader/writer. Antenna resonant circuit sections provided in both the transponder and the reader/writer are electromagnetically coupled with each other to exchange an information signal therebetween. The antenna resonant circuit section of the reader/writer is composed of a resistor R 1 , a capacitor C 1 , and a coil L 1 , and transmits the information signal generated by a processing section to the transponder. Also, the antenna resonant circuit section receives the information signal from the transponder, and supplies the received information signal to the processing section. Note that a resonance frequency specific to the antenna resonant circuit section is set to a predetermined value beforehand by capacitance of the capacitor C 1  and inductance of the coil L 1 . 
         [0008]    The antenna resonant circuit section of the transponder is composed of a resistor R 2 , a capacitor C 2 , and a coil L 2 , and transmits the information signal generated by a processing section and modulated by a load switch modulation circuit section to the antenna of the reader/writer. Also, the antenna resonant circuit section receives the information signal from the reader/writer, and supplies the received information signal to the processing section. Note that a resonance frequency of the antenna resonant circuit section is set to a predetermined value beforehand by capacitance of the capacitor C 2  and inductance of the coil L 2 . 
         [0009]    As an RFID standard, near field communication (NFC) developed by Sony and Philips is known. The NFC was approved as an international standard in December 2003, as ISO/IEC IS 18092. The NFC is originally a communication standard used in Sony&#39;s “FeliCa” and Philips&#39;s “Mifare,” which are widely used as contactless IC cards. The NFC uses a radio wave with a frequency of 13.56 MHz, and is capable of bidirectional communication with a very short communication range of approximately 10 cm. (The NFC specifies passive communication between different reader/writers, in addition to the communication between the card and the reader/writer. The NFC includes FeliCa, TypeA, and TypeB defined in ISO 14443. TypeA corresponds to Philips&#39;s Mifare. A card and a reader/writer as smart cards are standardized as ISO 7816.) 
         [0010]    At present, the NFC is widely used for personal identification, electronic money payment, and so on. For example, an NFC communication apparatus has been proposed that has an active mode in addition to a passive mode (see Japanese Patent Laid-open No. 2005-168069, for example). 
         [0011]    The following table shows transfer directions, and a transfer speed, a modulation scheme, a coding system, and so on for each communication mode as defined in the NFC Interface and Protocol-1 (IP-1) standard. 
         [0000]    
       
         
               
               
               
               
               
             
               
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Transfer 
                 Transfer 
                 Type A 
                 Type B 
                 FeliCa 
               
             
          
           
               
                 Direction 
                 Speed 
                 106 kbps 
                 106 kbps 
                 212 kbps 
                 424 kbps 
               
               
                   
               
             
          
           
               
                 Reader/writer → 
                 Carrier 
                 13.56 MHz 
                 13.56 MHz 
                 13.56 MHz 
               
               
                 Card 
                 Frequency 
               
               
                   
                 Modulation 
                 100% ASK 
                 10% ASK 
                 8-30% ASK 
               
               
                   
                 Scheme 
               
               
                   
                 Coding System 
                 Modified 
                 NRZ 
                 Manchester 
               
               
                   
                   
                 Mirror 
               
               
                 Card → 
                 Subcarrier 
                 13.56 MHz/16 
                 13.56 MHz/16 
                 — 
               
               
                 Reader/writer 
                 Frequency 
               
               
                   
                 Modulation 
                 Load 
                 Load 
                 &gt;12% ASK Load 
               
               
                   
                 Scheme 
                 Modulation 
                 Modulation 
                 Modulation 
               
               
                   
                 Coding System 
                 Manchester 
                 BPSK-NRZ-L 
                 Manchester 
               
               
                   
               
             
          
         
       
     
         [0012]    As shown in the above table, a maximum transfer speed as defined in the NFC IP-1 standard is as low as 424 kbps, and very low as compared to that of other general-purpose wireless communication standards (e.g., WiFi, Bluetooth, etc.). Thus, it is difficult to apply the NFC to high-capacity data communication for image data, audio data, video data, and so on. In addition, a maximum possible transfer speed that could be realized is as low as 848 kbps because of physical constraints such as that of the carrier frequency, and a future dramatic increase in the transfer speed cannot be expected. 
         [0013]    As such, actual applications of current NFC communication are limited to electronic money, the personal identification (e.g., ID cards, tickets, etc.), assistance in establishing connection in the general-purpose wireless communication (handover), and transmission of a very small amount of data using a cheap tag (e.g., a smart poster, etc.). 
       SUMMARY 
       [0014]    The present application provides in an embodiment an communication apparatus that is capable of performing data transfer suitably via contactless communication, as a transponder without its own source of radio waves or a reader/writer that transmits a carrier to the transponder. 
         [0015]    Further, the present application provides in an embodiment an communication apparatus that is capable of performing contactless communication suitably via electromagnetic induction, using a primary coil in the reader/writer and a secondary coil in the transponder. 
         [0016]    Still further, the present application provides in an embodiment an excellent communication apparatus that is capable of performing high-speed data communication while maintaining perfect upward compatibility with already established NFC communication systems. 
         [0017]    According to one embodiment, there is provided a communication apparatus that performs short-range wireless communication in a contactless manner, the communication apparatus including: a large antenna; a first wireless processing section configured to perform data communication via electromagnetic induction-type using the large antenna; a small antenna placed inside the large antenna; and a second wireless processing section configured to perform data communication using the small antenna. 
         [0018]    According to another embodiment, there is provided a communication system including: an NFC-capable reader/writer having a large antenna; and an NFC-capable card, or an NFC-capable reader/writer that operates in a card mode, having a large antenna. The reader/writer and the card perform short-range wireless communication therebetween in a contactless manner. The reader/writer and the card each have a small antenna placed inside the large antenna, and use the pair of small antennas to perform multi-communication therebetween via another contactless communication system than NFC communication. 
         [0019]    Note here that the term “system” as in “a communication system” above refers to a logical collection of a plurality of devices (or functional modules that fulfill specific functions), regardless of whether the plurality of devices or functional modules are contained in a single housing. 
         [0020]    A contactless communication system called RFID is known, and the RFID has been broadening its range of applications. The NFC standard using a radio wave with a frequency of 13.56 MHz has been developed as a contactless communication system using electromagnetic induction. The NFC standard allows bidirectional communication with a very short communication range of approximately 10 cm. 
         [0021]    However, the maximum transfer speed as defined in the NFC IP-1 standard is as low as 424 kbps, and very low as compared to that of other general-purpose wireless communication standards, and a future dramatic increase in the transfer speed cannot be expected. 
         [0022]    The communication apparatus according to an embodiment of the present application includes, in addition to the large antenna and the first wireless processing section, which correspond to an NFC-capable reader/writer or transponder, the second wireless processing means and one or more small antennas placed inside the known large antenna. A pair(s) of individual small antennas is used to perform high-speed communication, whereby an improvement will be achieved in the transfer speed of a system as a whole. 
         [0023]    The large antenna has perfect compatibility with the known NFC standard, and is capable of performing the known NFC communication when communication (hereinafter referred to as “multi-communication”) between the small antennas is not used. On the other hand, the small antennas take charge of data communication alone. Thus, supply of power from the reader/writer to the card is also performed by the large antenna. 
         [0024]    Thus, the communication apparatus according to the embodiment has perfect upward compatibility with already established NFC communication systems, and does not require a significant change to a superior software program. The communication apparatus according to an embodiment achieves a dramatic increase in the speed of the data communication as compared to current NFC communication. 
         [0025]    Control for establishing the multi-communication as described above can be accomplished by software programs (e.g., so-called firmware) in CPUs contained in the card and the reader/writer. Alternatively, the above control may be implemented on a physical layer, using hardware (or a microprogram). In the latter case, the software programs are allowed to perform the data communication without regard to which communication is being performed on the physical layer (i.e., the known NFC communication or the multi-communication). In other words, the multi-communication can be accomplished without the need to make any change to the software programs used in the known NFC communication on the upper layer. 
         [0026]    The multi-communication according to an embodiment can also be applied to active-mode bidirectional communication as defined in the NFC IP-1 standard, if synchronous control over radio wave transmission and the operation of the plurality of small antennas is possible in the reader/writer. 
         [0027]    The present application provides in an embodiment an communication apparatus that is capable of performing data transfer suitably via contactless communication, as a transponder without its own source of radio waves or a reader/writer that transmits a carrier to the transponder. 
         [0028]    Also, the present application provides in an embodiment an communication apparatus that is capable of performing contactless communication suitably via electromagnetic induction, using a primary coil in the reader/writer and a secondary coil in the transponder. 
         [0029]    A communication apparatus according to an embodiment has one or more unified small antennas formed inside the large antenna, which is used as a known NFC reader/writer or transponder, and performs the multi-communication using a plurality of antennas. Thus, the communication apparatus maintains perfect upward compatibility with already established NFC communication systems, and does not require a significant change to a superior software program. In addition, the communication apparatus achieves a dramatic increase in the speed of the data communication as compared to the current NFC communication. 
         [0030]    In an embodiment, the present application relates to a communication apparatus that performs contactless communication via electromagnetic induction, using a primary coil in the reader/writer and a secondary coil in the transponder. In an embodiment, the present application relates to a communication apparatus that has perfect upward compatibility with already established NFC communication systems. 
         [0031]    Additional features and advantages are described herein, and will be apparent from the following Detailed Description and the figures. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0032]      FIG. 1  illustrates a basic configuration of an NFC communication system; 
           [0033]      FIG. 2  illustrates an antenna configuration of a common NFC-capable card; 
           [0034]      FIG. 3  illustrates an exemplary antenna configuration of an NFC-capable card and reader/writer according to an embodiment; 
           [0035]      FIG. 4  illustrates multi-communication, i.e., the combination of communication between large antennas and communication between small antennas, as performed between the card and the reader/writer, with the antennas in the card opposed against those in the reader/writer; 
           [0036]      FIG. 5  schematically illustrates the structure of a multi-communication system in which NFC communication is performed using a pair of large antennas while reflected wave transmission is performed using a pair of small antennas placed inside the large antennas; 
           [0037]      FIG. 6  illustrates the structures of backscatter RF function sections of the card and the reader/writer; 
           [0038]      FIG. 7  illustrates exemplary antenna configurations in NFC-capable cards equipped with a plurality of small antennas; 
           [0039]      FIG. 8  illustrates an exemplary antenna configuration in an NFC-capable reader/writer, where a great number of small antennas are arranged in an array; 
           [0040]      FIG. 9  illustrates a procedure for selecting a small antenna to be used for the communication, when the multi-communication is performed between the card and the reader/writer; 
           [0041]      FIG. 10  illustrates a procedure for selecting an antenna to be used for the communication, in accordance with physical arrangements of the reader/writer and the card; 
           [0042]      FIG. 11  is a flowchart illustrating a procedure performed by the reader/writer in order to establish the multi-communication between the reader/writer and the card; 
           [0043]      FIG. 12  is a flowchart illustrating a procedure performed by the card in order to establish the multi-communication between the reader/writer and the card; 
           [0044]      FIG. 13  is a flowchart illustrating a procedure performed by the reader/writer in order to establish the multi-communication between the reader/writer and the card; 
           [0045]      FIG. 14  is a flowchart illustrating a procedure performed by the card in order to establish the multi-communication between the reader/writer and the card; 
           [0046]      FIG. 15  illustrates exemplary antenna arrangements in the case where antenna configurations or characteristics are different between the reader/writer and the card; 
           [0047]      FIG. 16  illustrates an exemplary manner in which antennas in different reader/writers are opposed to one another when the multi-communication is performed between the reader/writers; and 
           [0048]      FIG. 17  illustrates an exemplary structure of a contactless communication system using electromagnetic induction as composed of the transponder and the reader/writer. 
       
    
    
     DETAILED DESCRIPTION 
       [0049]    An embodiment of the present application will be described in detail with reference to the accompanying drawings. 
         [0050]    The NFC standard was established as an RFID communication standard for the 13.56 MHz band, and is now widely used for personal identification, electronic money payment, and so on, using RFID cards. In the NFC IP-1 standard, transfer speeds, modulation schemes, and coding systems are defined depending on transfer direction and communication mode (see Table 1), but a maximum transfer speed is 424 Kbps of Felica, which is very low compared to that of other wireless communication standards (e.g., Bluetooth communication, IEEE 802.11, etc.). 
         [0051]    On the other hand, NFC technology has several advantages as follows. 
         [0052]    (1) The NFC technology uses a contactless interface, which is allowed great flexibility in shape, whose contact point is free from abrasion or deterioration, and which allows countermeasures against dust accumulation, water splashing, and so on at an interface port. 
         [0053]    (2) A transponder, such as a card, is of the passive type, and it therefore does not need to be equipped with its own power supply. 
         [0054]    (3) It is possible to provide electrical isolation between a reader/writer and the transponder. 
         [0055]    (4) A maximum possible distance that a signal can cover is as short as 10 cm, and this physical characteristic ensures great security. 
         [0056]    The above characteristics are very attractive when employing the card as the transponder for storage purposes (e.g., when using the card in a manner similar to that in which a USB memory is used), or for high-capacity data communication between portable devices, such as when exchanging image data, audio data, video data, or the like between the portable devices. Thus, there is an increasing desire for improvement in transfer speed of the NFC technology. 
         [0057]    Communication apparatuses according to one embodiment correspond to an NFC-capable reader/writer and transponder, each of which has a large antenna used for existing NFC communication and is provided with a unified array of one or more small antennas inside the large antenna. A pair(s) of individual small antennas communicate with each other at a high speed to improve a transfer speed of a system as a whole. Therefore, the communication apparatuses according to an embodiment maintain perfect upward compatibility with already established NFC communication systems, and do not require a significant change to a superior software program. In addition, the communication apparatuses according to an embodiment achieve a dramatic increase in speed of the data communication as compared to that of current NFC communication. 
         [0058]    The NFC communication system allows an NFC reader/writer and an NFC card to communicate with each other, or passive NFC reader/writers to communicate with each other.  FIG. 1  illustrates a basic configuration of the NFC communication system. The NFC communication system is composed of an initiator that initiates communication and a target to which the communication is directed. 
         [0059]    Specifically, the initiator is an NFC-capable reader/writer (R/W) that operates in a reader/writer mode. The reader/writer as the initiator is connected to a host device via a host interface such as a universal asynchronous receiver-transmitter (UART). The host device corresponds to a personal computer (PC), a central processing unit (CPU) contained in the reader/writer, or the like. 
         [0060]    On the other hand, the target is a transponder such as an NFC-capable card, or an NFC-capable reader/writer that operates in a card mode (hereinafter, the target will also be referred to simply as a “card,” which encompasses all of them). The card may function on a standalone basis or be connected to a host device. 
         [0061]    Upon receipt of a communication start command from the host device (as indicated by (1) in  FIG. 1 ), the reader/writer connected to the host device first transmits a carrier wave. Thereafter, the NFC-capable reader/writer transmits a response request signal in a manner defined in the standard (i.e., using a specified carrier frequency, a specified data modulation rate, and specified data contents) in order to check whether any NFC-capable card (or any NFC-capable reader/writer that operates in the card mode) exists within an area covered by the communication ability of the NFC-capable reader/writer (as indicated by (2) in  FIG. 1 ). 
         [0062]    On the other hand, the card is first supplied with power by an induced electromotive force of the carrier transmitted by the reader/writer so as to be activated and become capable of reception. Thereafter, the card receives the response request signal transmitted from the reader/writer. If the received response request signal matches the type of the card, the card transmits a response signal including identification information (i.e., a card ID) of its own in a manner defined in the standard (i.e., using a specified data modulation rate, specified response timing, and specified data contents), by performing load modulation on the carrier transmitted from the reader/writer (as indicated by (3) in  FIG. 1 ). 
         [0063]    The reader/writer receives the response signal from the card, and then transfers information about the response signal to the host device (as indicated by (4) in  FIG. 1 ). The host device recognizes the number of cards that exist in the area covered by the communication ability of the reader/writer, and the identification information of each of such cards, and proceeds to a phase of communication with a particular card in accordance with an operation program (firmware). Thus, communication between the reader/writer and the card (or communication between the passive NFC-capable reader/writers) is established. After the communication is established, the reader/writer as the initiator continues to transmit the carrier wave constantly, thereby sending necessary power to the card as the target, until end of the required communication. 
         [0064]    At the time of data communication, as at the time of the above-described response request operation, the reader/writer performs intensity modulation on the carrier wave to transmit data to the card, whereas the card performs the load modulation on the unmodulated carrier to transmit data to the reader/writer. Note that the coding system depends on the communication mode. For details, see Table 1. 
         [0065]      FIG. 2  illustrates an antenna configuration of a common NFC-capable card. The antenna configuration as illustrated in  FIG. 2  is used in FeliCa, RC-S860, and so on. 
         [0066]    A rectangular antenna coil is arranged along edges of the card, which has the size of a common IC card, i.e., 85.6 mm by 54.0 mm, as defined in ISO/IEC 7816-2, JIS 6301-2, and so on, in order to secure as much power as possible. 
         [0067]    Note that ISO 14443 does not specify the configuration of the antenna coil or the number of turns of the coil, but recommends that the antenna coil be arranged so as to surround a contact of a contact IC card as defined in the ISO/IEC 7816-2 standard. 
         [0068]      FIG. 3  illustrates an exemplary antenna configuration of the NFC-capable card and reader/writer according to an embodiment of the present application. A small-sized antenna (hereinafter referred to as a “small antenna”) is placed in the middle of an existing large-sized antenna (hereinafter referred to as a “large antenna”), and connected to a control IC chip. 
         [0069]    The large antenna maintains perfect compatibility with the known NFC standard, and is capable of performing known NFC communication when the communication between the small antennas (hereinafter referred to as “multi-communication”) is not used. Thus, the large antenna is also used to supply the power from the reader/writer to the card. 
         [0070]    On the other hand, the small antenna is used only for the data communication. Physical configurations, including that of a wire connecting the small antenna to the control IC chip, the frequency of the carrier wave, output of the carrier from the reader/writer, and so on are adjusted properly in order not to cause mutual interference between the communication between the small antennas and the communication between the large antennas, or interfere with the supply of the power from the reader/writer to the card using the large antenna. The small antenna has a capability to perform the data communication independently of the large antenna. 
         [0071]      FIG. 4  illustrates the multi-communication, i.e., the combination of the communication between the large antennas and the communication between the small antennas, as performed between the card and the reader/writer, with the antennas in the card opposed against those in the reader/writer. 
         [0072]    In the reader/writer, the small antenna, as well as the large antenna, transmits the carrier wave, and modulates the carrier wave to send a signal to the card. On the other hand, the card sends a response signal to the reader/writer without using its own power. Thus, even when performing the data communication using the pair of small antennas, the card does not need to be equipped with its own power supply, as an existing NFC-capable card is not. 
         [0073]    Note here that the communication between the small antennas is not limited to use of the known NFC standard using the 13.56 MHz band, and that another wireless communication technology, using a different carrier frequency band or a different communication mode, or having different coverage, may be applied to the communication between the small antennas, as long as neither the power supply nor the NFC communication using the large antennas is disturbed. 
         [0074]    As an exemplary wireless communication technology applied to the communication between the small antennas, the present inventors propose an RFID system using microwave communication. According to this communication system, the transponder, such as the card, is equipped with a reflector for transmitting data via a reflected wave obtained by modulating the unmodulated carrier, whereas the reader/writer is equipped with a reflected wave reader for reading data from the modulated reflected wave signal transmitted from the reflector. If the unmodulated carrier is sent from the reflected wave reader to the reflector, the reflector performs reflected wave transmission, also called “backscatter,” by modulating the reflected wave based on an operation of changing antenna load impedance or the like to superimpose transmission data upon the reflected wave. 
         [0075]      FIG. 5  schematically illustrates the structure of a multi-communication system in which the NFC communication is performed using a pair of large antennas while the reflected wave transmission is performed using a pair of small antennas placed inside the large antennas. As shown in  FIG. 5 , the card includes an NFC-capable large antenna, an NFC-capable RF function section, a small antenna, a backscatter RF function section, and a processing section, which corresponds to a superior protocol. On the other hand, the reader/writer includes an NFC-capable large antenna, an NFC-capable RF function section, a small antenna, a backscatter RF function section, and a processing section, which corresponds to a superior protocol. 
         [0076]    The structures of the NFC-capable RF function sections of the card and the reader/writer are the same as those illustrated in  FIG. 17 . Therefore, descriptions thereof are omitted here. 
         [0077]      FIG. 6  illustrates the structures of the backscatter RF function sections of the card and the reader/writer. In the present embodiment, the 2.4 GHz band is used as frequencies of radio waves. 
         [0078]    A backscatter RF function section  300  of the card includes an antenna  309 , an antenna switch  310 , an antenna load  311 , a band-pass filter  312 , and an ASK detection section  313 . 
         [0079]    When the reflected wave transmission is performed, an on/off operation of the antenna switch  310 , which is connected to the antenna  309 , is performed in accordance with a bit image of transmission data supplied from the processing section. For example, the antenna switch  310  is turned on when data represents 1 and turned off when data represents 0. The antenna switch  310  is formed by a gallium arsenide IC, for example, and power consumption at the time of the on/off operation is less than tens of microwatts. 
         [0080]    As shown in  FIG. 6 , when the antenna switch  310  is in an ON position, the antenna  309  is terminated with the antenna load  311  of 50Ω, whereas when the antenna switch  310  is in an OFF position, the antenna  309  is open. According to this operation, in relation to a radio wave transmitted from a destination of the transmission data, the antenna  309  is terminated when the antenna switch  310  is in the ON position while the antenna  309  causes a reflection when the antenna switch  310  is in the OFF position. Accordingly, the reader/writer is able to read the data by detecting reflection of the transmitted radio wave. This reflected wave signal is equivalent to an ASK modulated wave. Note, however, that PSK modulation and FSK modulation are also applicable. 
         [0081]    The band-pass filter (BPF)  312  and the ASK detection section  313  are used at a time when an acknowledgement signal subjected to ASK modulation has been received from the reader/writer, for example. 
         [0082]    On the other hand, a backscatter RF function section  400  of the reader/writer includes an antenna  401  using the 2.4 GHz band, a circulator  402 , a reception section  403 , a transmission section  406 , and a frequency synthesizer  409 . The reception section  403  includes a quadrature detection section  404  and an AGC amplifier  405 . The transmission section  406  includes a mixer  408  and a power amplifier  407 . 
         [0083]    When the unmodulated carrier is transmitted, a certain direct-current voltage is applied to the mixer  408 . A frequency of the unmodulated carrier to be transmitted is determined by a frequency of the frequency synthesizer controlled by a communication control section (not shown). The 2.4 GHz band is used in the present embodiment. The unmodulated carrier outputted from the mixer  408  is amplified by the power amplifier  407  to a predetermined level, and then outputted by the antenna  401  via the circulator  402 . 
         [0084]    The reflected wave signal transmitted from the backscatter RF function section  300  of the card has the same frequency as the unmodulated carrier. This reflected wave signal is received by the antenna  401 , and inputted to the reception section  403  via the circulator  402 . The same local frequency as used for the transmission is inputted to the quadrature detection section  404 , and therefore, the ASK modulated wave as transmitted from the image transmission apparatus  300  appears as an output from the quadrature detection section  404 . However, because the signal received differs from a local signal in phase, modulated signals corresponding to a phase difference appear in an I-axis signal and a Q-axis signal. Gain is controlled to an optimum value in the AGC amplifier  405 , and a signal outputted from the AGC amplifier  405  is supplied to the processing section. The processing section demodulates the I-axis and Q-axis signals to obtain digital data, and the proper data is transferred to the processing section. 
         [0085]    While frequencies from several megahertz to hundreds of megahertz (e.g., 13.56 MHz) are used in the NFC communication system, the reflected wave transmission system as illustrated in  FIG. 6  uses the 2.4 GHz band (microwaves) called an industrial, scientific and medical (ISM) band, which is a high-frequency band, for example, to carry out high-speed data transmission of the order of Mbps. Thus, a dramatic improvement in the transfer speed of the NFC communication can be achieved by performing the multi-communication using the small antennas while performing the NFC communication using the pair of large antennas. 
         [0086]    The reflected wave transmission system is described in Japanese Patent Laid-open Nos. 2005-136666, 2005-136943, 2005-323267, and so on, which have been transferred to the present assignee, for example. 
         [0087]    A plurality of small antennas may be placed inside the large antenna, as long as each of the small antennas is allowed to perform communication independently, without interfering with the communication of any other small antenna, and does not disturb the NFC communication or the power supply by the large antenna.  FIG. 7  illustrates exemplary antenna configurations in NFC-capable cards equipped with a plurality of small antennas. 
         [0088]    Regarding the antennas in the reader/writer, a great number of small antennas may be arranged in an array in the case where a sufficiently wide area can be secured for the antennas.  FIG. 8  illustrates an exemplary antenna configuration in an NFC-capable reader/writer, where a great number of small antennas are arranged in an array. In this case, the reader/writer and the card are equipped with a section for distributing data to be communicated appropriately among the small antennas so that each of the small antennas will transmit a separate portion of the data, or a section for integrating data received by each of the small antennas into one unit appropriately, and each pair of small antennas performs independent communication in parallel so as to improve the transfer speed of the multi-communication. 
         [0089]      FIG. 9  illustrates a procedure for selecting a small antenna to be used for the communication, when the multi-communication is performed between the card and the reader/writer. 
         [0090]    The reader/writer and the card are equipped with a section for, before starting the multi-communication, determining whether each of the small antennas is capable of communicating with the other party individually. The reader/writer and the card allow any small antenna that has been determined to be incapable of communicating with the other party to enter a suspend mode, and carry out the multi-communication using only a pair(s) of antennas that are capable of communicating with each other (see ( 1 ) in  FIG. 9 ). 
         [0091]    At this time, if more than one small antenna in the reader/writer or the card is capable of communicating with the same small antenna in the other party (see ( 2 ) in  FIG. 9 ), one of the multiple small antennas that is capable of communicating most excellently is selected, and the rest of the multiple small antennas is caused to enter the suspend mode (see ( 3 ) in  FIG. 9 ). 
         [0092]      FIG. 10  illustrates a procedure for selecting an antenna to be used for the communication, in accordance with physical arrangements of the reader/writer and the card. 
         [0093]    When the physical arrangements of the reader/writer and the card are ideal with the help of a card holder attached to the reader/writer, for example, the multi-communication is performed at a maximum possible transfer speed allowed by the pair of the reader/writer and the card (see ( 1 ) in  FIG. 10 ). 
         [0094]    Meanwhile, when the physical arrangements of the reader/writer and the card are not favorable, such as when a user holds the card by hand or places the card close to the reader/writer, the multi-communication is performed at a maximum transfer speed allowed in this situation (see ( 2 ) in  FIG. 10 ). 
         [0095]    Meanwhile, when no pairs of small antennas are capable of communication, the NFC communication is performed in the existing manner using the large antennas (see ( 3 ) in  FIG. 10 ). 
         [0096]    During this procedure for selecting the antenna(s) to be used for the communication, the power is constantly supplied from the reader/writer to the card using the large antennas, regardless of whether the data communication is performed using the large antennas. 
         [0097]      FIG. 11  is a flowchart illustrating a procedure performed by the reader/writer in order to establish the communication between the reader/writer and the card. Notice that steps enclosed by a dotted line in this figure correspond to a novel procedure for establishing the multi-communication. 
         [0098]    After power-up (step S 1 ), the reader/writer waits until receipt of a reader/writer start command from the host, to which the reader/writer is connected via the UART or the like (step S 2 ). 
         [0099]    Upon receipt of the reader/writer start command from the host, the reader/writer uses the large antenna to transmit the response request signal to any NFC-capable card within its coverage (step S 3 ), and waits for receipt of a response from any NFC-capable card (step S 4 ). If time-out occurs while the reader/writer is waiting for a response from any card, control returns to step S 2 , and the reader/writer waits again until receipt of the reader/writer start command from the host. 
         [0100]    Meanwhile, if the reader/writer receives, from any NFC-capable card, a response to the response request signal, the reader/writer uses the large antenna to transmit, to that card, a “multi-communication support check signal” to check whether that card is capable of high-speed communication using the small antenna, i.e., whether that card supports the multi-communication (step S 5 ). Then, the reader/writer waits for a response from the card (step S 6 ). 
         [0101]    Here, if time-out occurs while the reader/writer is waiting for a response from the card, the reader/writer, determining not to perform the multi-communication with the card, enters an NFC communication mode that involves use of only the large antenna (step S 12 ), and transmits an NFC communication command to the card via the large antenna. 
         [0102]    Meanwhile, if the reader/writer receives, from the card, a response to the multi-communication support check signal, the reader/writer uses the small antennas to transmit “multi-communication response request signals” to the card at a time (step S 7 ), and waits for a response from the card (step S 8 ). The multi-communication response request signal transmitted from each of the small antennas contains an ID number that indicates the small antenna from which it is transmitted. 
         [0103]    If time-out occurs while the reader/writer is waiting for a response from the card, the reader/writer, determining not to perform the multi-communication, enters the NFC communication mode that involves use of only the large antenna (step S 12 ), and transmits the NFC communication command to the card via the large antenna. 
         [0104]    The response to the multi-communication response request signal contains an ID number that indicates a small antenna in the card from which it is transmitted (details thereof will be described later). If any of the small antennas in the reader/writer receives a multi-communication response signal (i.e., a response to the multi-communication response request signal) from the card, the reader/writer causes all small antennas that have not received the multi-communication response signal to enter the suspend mode (step S 9 ). In addition, the reader/writer compares the ID numbers contained in the response signals received by the small antennas with one another to determine whether more than one small antenna has received the same ID number as contained in the multi-communication response signal (step S 10 ). If it is determined that more than one small antenna has received the same ID number as contained in the multi-communication response signal, the reader/writer selects one of the multiple small antennas that is capable of communicating most excellently, and causes the rest of the multiple small antennas to enter the suspend mode. Then, control returns to step S 7 , and the reader/writer transmits the multi-communication response request signal via each of the remaining small antennas at a time again. The reader/writer repeats the above-described multi-communication response request operation several times in relation to the card, to establish pairs of small antennas, one in the reader/writer and the other in the card, that are capable of communicating with each other in a one-to-one manner without overlapping. 
         [0105]    Then, when it has been determined that no two multi-communication response signals received by the small antennas contain the same ID number (i.e., when it has been determined that more than one small antenna has not received the same ID number as contained in the multi-communication response signal), the reader/writer shifts to a multi-communication mode in which the reader/writer performs the high-speed communication using the small antennas in addition to the NFC communication using the large antennas. In this case, the reader/writer transmits a multi-communication command to the card via each of the small antennas that are capable of communicating (step S 11 ). 
         [0106]      FIG. 12  is a flowchart illustrating a procedure performed by the card in order to establish the communication between the reader/writer and the card. Note that steps enclosed by a dotted line in this figure correspond to a novel procedure for establishing the multi-communication. 
         [0107]    After power-up (step S 21 ), the card waits until receipt of the response request signal from any NFC-capable reader/writer within its coverage (step S 22 ). Then, in response to receipt of the response request signal from any reader/writer, the card transmits a response to the response request signal via the large antenna (step S 23 ). Then, the card shifts to a selection mode for determining whether to perform the NFC communication with the reader/writer or to perform the multi-communication with the reader/writer, which involves simultaneous performance of the NFC communication and the high-speed communication using the small antennas (step S 24 ). If time-out occurs while the card is in this selection mode, the card, determining not to perform the multi-communication, enters an NFC communication mode that involves use of only the large antenna (step S 31 ). 
         [0108]    Meanwhile, if the card receives the multi-communication support check signal from the reader/writer while in the selection mode, the card transmits, via the large antenna, a response to notify the reader/writer that the card supports the multi-communication (step S 25 ). Then, the card waits for receipt of the multi-communication response request signal from the reader/writer (step S 26 ). If time-out occurs while the card is waiting for receipt of the multi-communication response request signal from the reader/writer, the card, determining not to perform the multi-communication, enters the NFC communication mode that involves use of only the large antenna (step S 31 ). 
         [0109]    If the card receives the multi-communication response request signal from the reader/writer, the card transmits a response signal via the small antenna. At this time, the card causes all small antennas that have not received the multi-communication response request signal from the reader/writer to enter a suspend mode (step S 27 ). In addition, the card compares the ID numbers contained in the response request signals received by the small antennas with one another to determine whether more than one small antenna has received the same ID number as contained in the multi-communication response request signal. If it is determined that no two small antennas have received the same ID number as contained in the multi-communication response request signal, the card transmits the response signal via each of all small antennas that have received the multi-communication response request signal at a time (step S 28 ). Meanwhile, if it is determined that more than one small antenna has received the same ID number as contained in the multi-communication response request signal, the card selects one of the multiple small antennas that is capable of communicating most excellently, and, after causing the rest of the multiple small antennas to enter the suspend mode (step S 27 ), transmits the response signal via each of the remaining small antennas at a time (step S 28 ). The response signal transmitted via each of these small antennas contains the ID number that indicates the small antenna in the card from which the response signal is transmitted. Then, the card shifts to a mode for waiting for the multi-communication (step S 29 ). 
         [0110]    If time-out occurs while the card is in the mode for waiting for the multi-communication (or if the card receives the NFC communication command from the reader/writer), the card, determining not to perform the multi-communication, enters the NFC communication mode that involves use of only the large antenna (step S 31 ). 
         [0111]    Meanwhile, if the card receives the multi-communication command from the reader/writer while in the mode for waiting for the multi-communication, the card shifts to a multi-communication mode in which the card performs the high-speed communication using the small antennas in addition to the NFC communication using the large antennas (step S 30 ). 
         [0112]    The control in each of the procedures as illustrated in  FIGS. 11 and 12  can be accomplished by software programs (e.g., so-called firmware) in CPUs contained in the card and the host device connected to the reader/writer via the UART. Alternatively, the above control may be implemented on a physical layer, using hardware (or a microprogram). In the latter case, the software programs are allowed to perform the data communication without regard to which communication is being performed on the physical layer (i.e., the existing NFC communication or the multi-communication). In other words, the multi-communication can be accomplished without the need to make any change to the software programs used in the existing NFC communication on the upper layer. 
         [0113]    In the procedures as illustrated in  FIGS. 11 and 12 , the procedure of exchanging the multi-communication support check signal and the response to this signal between the reader/writer and the card is required for each of the reader/writer and the card to recognize whether or not the multi-communication is supported by the other party. Note, however, that the procedure for each of the reader/writer and the card to recognize whether the multi-communication is supported by the other party can be made simpler by storing information indicating whether or not the multi-communication is supported in an unused bit (RFU) within the response request signal and the response signal as used in the existing NFC communication. 
         [0114]      FIGS. 13 and 14  are flowcharts illustrating procedures performed by the reader/writer and the card, respectively, in order to establish the communication between the reader/writer and the card, in the case where the information indicating whether or not the multi-communication is supported is stored in the unused bit (RFU) in the response request signal and the response signal as used in the NFC communication. Notice that steps enclosed by a dotted line in these figures correspond to a novel procedure for establishing the multi-communication. 
         [0115]    After power-up (step S 41 ), the reader/writer waits until receipt of the reader/writer start command from the host, to which the reader/writer is connected via the UART or the like (step S 42 ). 
         [0116]    Upon receipt of the reader/writer start command from the host, the reader/writer uses the large antenna to transmit the response request signal to any NFC-capable card within its coverage (step S 43 ), and waits for receipt of a response from any NFC-capable card (step S 44 ). Information indicating that the reader/writer supports the multi-communication is stored in the unused bit (RFU) within the response request signal. 
         [0117]    If time-out occurs while the reader/writer is waiting for a response from any card, control returns to step S 42 , and the reader/writer waits again until receipt of the reader/writer start command from the host. Meanwhile, if the reader/writer receives, from any NFC-capable card, a response to the response request signal, the reader/writer checks whether information indicating that the card supports the multi-communication is stored in an unused bit (RFU) within this response (step S 45 ). Notice that the operation of transmitting the multi-communication support check signal is omitted in this procedure. 
         [0118]    If it is not determined based on the unused bit (RFU) within the response received from the card that the card supports the multi-communication, the reader/writer, determining not to perform the multi-communication with the card, enters the NFC communication mode that involves use of only the large antenna (step S 51 ), and transmits the NFC communication command to the card via the large antenna. 
         [0119]    Meanwhile, if it is determined based on the unused bit (RFU) within the response received from the card that the card supports the multi-communication, the reader/writer uses the small antennas to transmit the “multi-communication response request signals” to the card at a time (step S 46 ), and waits for a response from the card (step S 47 ). The multi-communication response request signal transmitted from each of the small antennas contains the ID number that indicates the small antenna from which it is transmitted. 
         [0120]    If time-out occurs while the reader/writer is waiting for a response from the card, the reader/writer, determining not to perform the multi-communication, enters the NFC communication mode that involves use of only the large antenna (step S 51 ), and transmits the NFC communication command to the card via the large antenna. 
         [0121]    The response to the multi-communication response request signal contains an ID number that indicates the small antenna in the card from which it is transmitted. If any of the small antennas in the reader/writer receives the multi-communication response signal from the card, the reader/writer causes all small antennas that have not received the multi-communication response signal to enter the suspend mode (step S 48 ). In addition, the reader/writer compares the ID numbers contained in the response signals received by the small antennas with one another to determine whether more than one small antenna has received the same ID number as contained in the multi-communication response signal (step S 49 ). If it is determined that more than one small antenna has received the same ID number as contained in the multi-communication response signal, the reader/writer selects one of the multiple small antennas that is capable of communicating most excellently, and causes the rest of the multiple small antennas to enter the suspend mode. Then, control returns to step S 46 , and the reader/writer transmits the multi-communication response request signal via each of the remaining small antennas at a time again. The reader/writer repeats the above-described multi-communication response request operation several times in relation to the card, to establish pairs of small antennas, one in the reader/writer and the other in the card, that are capable of communicating with each other in a one-to-one manner. 
         [0122]    Then, when it has been determined that no two multi-communication response signals received by the small antennas contain the same ID number (i.e., when it has been determined that more than one small antenna has not received the same ID number as contained in the multi-communication response signal), the reader/writer shifts to the multi-communication mode in which the reader/writer performs the high-speed communication using the small antennas in addition to the NFC communication using the large antennas. In this case, the reader/writer transmits the multi-communication command to the card via each of the small antennas that are capable of communicating (step S 50 ). 
         [0123]    On the other hand, after power-up (step S 61 ), the card waits until receipt of the response request signal from any NFC-capable reader/writer within its coverage (step S 62 ). Then, if the card receives the response request signal from the reader/writer, the card recognizes that the information indicating that the reader/writer supports the multi-communication is stored in the unused bit (RFU) within the received signal, and then transmits a response to this signal via the large antenna (step S 63 ), and waits for receipt of the multi-communication response request signal from this reader/writer (step S 64 ). The information indicating that the card supports the multi-communication is stored in the unused bit (RFU) within the response to the response request signal. Notice that the selection mode for determining whether to perform the NFC communication with the reader/writer or to perform the multi-communication with the reader/writer is omitted in this procedure. Also notice that the process of transmitting the response to the multi-communication support check signal is omitted in this procedure. 
         [0124]    If time-out occurs while the card is waiting for the receipt of the multi-communication response request signal from the reader/writer, the card, determining not to perform the multi-communication, enters the NFC communication mode that involves use of only the large antenna (step S 69 ). 
         [0125]    If the card receives the multi-communication response request signal from the reader/writer, the card transmits the response signal via the small antenna. At this time, the card causes all small antennas that have not received the multi-communication response request signal from the reader/writer to enter the suspend mode (step S 65 ). In addition, the card compares the ID numbers contained in the response request signals received by the small antennas with one another to determine whether more than one small antenna has received the same ID number as contained in the multi-communication response request signal. If it is determined that no two small antennas have received the same ID number as contained in the multi-communication response request signal, the card transmits the response signal via each of all small antennas that have received the multi-communication response request signal at a time (step S 66 ). Meanwhile, if it is determined that more than one small antenna has received the same ID number as contained in the multi-communication response request signal, the card selects one of the multiple small antennas that is capable of communicating most excellently, and, after causing the rest of the multiple small antennas to enter the suspend mode (step S 65 ), transmits the response signal via each of the remaining small antennas at a time (step S 66 ). The response signal transmitted via each of these small antennas contains the ID number that indicates the small antenna in the card from which the response signal is transmitted. Then, the card shifts to the mode for waiting for the multi-communication (step S 67 ). 
         [0126]    If time-out occurs while the card is in the mode for waiting for the multi-communication (or if the card receives the NFC communication command from the reader/writer), the card, determining not to perform the multi-communication, enters the NFC communication mode that involves use of only the large antenna (step S 69 ). 
         [0127]    Meanwhile, if the card receives the multi-communication command from the reader/writer while in the mode for waiting for the multi-communication, the card shifts to the multi-communication mode in which the card performs the high-speed communication using the small antennas in addition to the NFC communication using the large antennas (step S 68 ). 
         [0128]    At the time of the multi-communication mode, the large antennas are used to perform the NFC communication between the reader/writer and the card and supply the power from the reader/writer to the card, while the pair(s) of small antennas, which are placed inside the large antennas, are used to perform the data communication between the reader/writer and the card. The reflected wave transmission using the 2.4 GHz band, for example, may be applied to the data communication using the pair(s) of small antennas. In this case, the data communication using the pair(s) of small antennas can be performed at a high speed, without interfering with the NFC communication using the large antennas. 
         [0129]    The present invention has been described in detail above with reference to the specific embodiments. However, it should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof. 
         [0130]    It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present subject matter and without diminishing its intended advantages. It is therefore intended that such changes and modifications be covered by the appended claims. 
         [0131]    The foregoing descriptions of the specific embodiments have focused on contactless communication between the reader/writer and the card. However, for example, the present application is similarly applicable to passive-mode bidirectional communication between different reader/writers as defined in the NFC IP-1 standard according to an embodiment. 
         [0132]    Note that in the case where the structures of the reader/writer and the card are asymmetrical (i.e., in the case where the antenna configurations or characteristics are different between the reader/writer and the card) as in the above-described communication technology using the reflected wave transmission in the communication via the small antennas, ingenuities are necessary regarding the arrangements of the antennas in the reader/writer and the card.  FIG. 15  illustrates exemplary antenna arrangements in the case where the antenna configurations or characteristics are different between the reader/writer and the card. 
         [0133]    Further, in the case where the multi-communication is performed between different reader/writers, relative positions (orientations) of the reader/writers also need care.  FIG. 16  illustrates an exemplary manner in which the antennas in the different reader/writers are opposed to one another when the multi-communication is performed between the reader/writers. 
         [0134]    The multi-communication according to an embodiment can also be applied to active-mode bidirectional communication as defined in the NFC IP-1 standard, if synchronous control over radio wave transmission and the operation of the plurality of small antennas is possible in the reader/writer.