Abstract:
A communication apparatus and method for preventing interference with information transmitted from one apparatus to another apparatus. The apparatus and method comprising selecting M different numbers, receiving a signal, generating a clock from the received signal, counting the generated clock, and transmitting information according to the clock count and the selected numbers, wherein if the information is determined to be invalid, the information is re-transmitted.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a communication apparatus and method for preventing interference with information transmitted from another communication apparatus. 
   2. Description of the Related Art 
   Radio tags or RF-ID tags for identifying objects have attracted attention as replacements for bar codes. 
   In the near future, a so-called ubiquitous society will be realized in which all objects are assigned a radio tag or RF-ID tag. 
   Japanese Patent Laid-Open No. 2002-162918 describes a poster having a radio tag or an RF-ID tag embedded therein. When a user who sees the poster wants information of the content written in this poster, the user directs his/her receiver to the radio tag or RF-ID tag embedded in the poster to obtain ID information from the poster, and then acquires the desired information via the Internet. 
   However, in a society where every object contains a radio tag or RF-ID tag, users would be surrounded by a plurality of radio tags or RF-ID tags. When a user directs a receiver to the above described poster in order to acquire information from the poster, a plurality of radio tags or RF-ID tags from objects in the vicinity of the poster emit their ID information in response to an ID acquisition instruction signal issued by the receiver, thus interfering with the information the user wants. 
   One approach to prevent interference in acquiring ID information is using a receiver with a highly directional antenna. However, this approach is problematic in that it is inconvenient for a user to direct the antenna or the receiver itself to a radio tag or an RF-ID tag each time the user wants to acquire information. The “Smart Active Label Consortium,” which was established in November 2002, has plans to provide internal batteries for radio tags or RF-ID tags so as to increase the ID information output power. As such radio tags or RF-ID tags that provide stronger transmission power will become wide-spread, thereby increasing the likelihood of interference between the various transmissions of ID information. 
   Japanese Patent Laid-Open No. 8-161653 describes a locator for lost objects in which a transmitter (e.g., radio tag or RF-ID tag) selects one of a plurality of frequencies (e.g., f1 to fn) and sends one ID information, including a pre-sync signal, to a receiver. The receiver receives the same ID information a plurality of the times and synchronizes the pre-sync signals and received one ID information. The goal of this invention is to ensure receipt of ID information from a specific apparatus without interference by ID information transmitted by different apparatuses by selecting the sending and receiving frequency. 
   The locator described in Japanese Patent Laid-Open No. 8-161653 is not useful in a very crowded place, such as an airport. In a crowded place where a plurality of radio waves can be exchanged, when a source of strong radio waves and a desired transmitter, each having different IDs, are near each other, the strong radio waves can cancel the transmission waves of the transmitter. Therefore, a user would not able to receive the ID information of the desired transmitter. Since the transmission frequency is fixed so as to coordinate with a receiver, the locator described in this publication is not suitable for an application to acquire ID information from multiple radio tags or RF-ID tags at the same time. 
   The locator described in Japanese Patent Laid-Open No. 8-161653 has a problem in that, in a case where a user possesses a plurality of objects which the user does not want to leave behind or lose, the user must either carry a plurality of receivers or carry a single receiver having a receiving-frequency changeover switch, which must be switched each time a plurality of objects are to be located. 
   The system described in Japanese Patent Laid-Open No. 8-335238 uses a locating system disclosed in U.S. Pat. No. 5,214,410 entitled “Location of objects” (i.e., so-called “Supertag” technology) to prevent interference. 
   In this system, a transmitter includes an internal clock generator, having the functions of using an ID transmission instruction from a receiver as a timing signal and count clock thereof in synchronization with the timing signal. The transmitter has one number stored in a read-only memory (ROM), and compares the clock count with the stored number. When a match is found, one-time transmission of ID information is carried out. 
   Each radio tag or RF-ID tag has a unique delay time, and has the function of transmitting information after the delay time has elapsed. If a plurality of radio tags or RF-ID tags exists, these tags do not transmit information, such as ID information, at the same time, thus preventing interference. 
   However, when radio tags or RF-ID tags that transmit ID information at the same time are accidentally located near each other, interference occurs. Interference is created, even if a receiver that detects an error sends an ID information re-transmission instruction, because the ID information is sent again at the same time. In other words, an interference error occurs again. 
   Another problem with the “Supertag” system is that one-time transmission of ID information causes a high probability of reception errors in a high-noise environment. 
   Moreover, since each tag contains a phase-locked loop (PLL) circuit that internally generates a timing signal and that synchronizes the generated timing signal with an ID transmission instruction, the chip size and the cost increase. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to prevent interference caused by information transmitted from another communication apparatus or due to noise. 
   It is another object of the present invention to differentiate the information transmission timing of a given communication apparatus from the transmission timing of another communication apparatus. 
   It is still another object of the present invention to improve the noise resistance of an information receiver. 
   One of the foregoing objects is achieved by an aspect of the present invention through the provision of a communication apparatus including a selecting unit for selecting M different numbers, a receiving unit for receiving a signal, a clock generating unit for generating a clock from the signal received by the receiving unit, a counting unit for counting the generated clock, and a transmitting unit for transmitting information according to the clock count obtained by the counting unit and the selected numbers by the selecting unit. 
   One of the foregoing objects is achieved by another aspect of the present invention through the provision of a communication apparatus including a transmitting unit for transmitting a signal to supply a clock and power to at least one other different communication apparatus, a receiving unit for receiving information from the at least one other different communication apparatus, a determining unit for determining whether or not the receiving unit has received the same information a plurality of times, and an outputting unit for outputting the information received a plurality of times according to a determination result of the determining unit. 
   One of the foregoing objects is achieved by still another aspect of the present invention through the provision of a communication method including a selecting step of selecting M different numbers, a receiving step of receiving a signal, a clock generating step of generating a clock from the signal received in the receiving step, a counting step of counting the generated clock, and a transmitting step of transmitting information according to the clock count obtained in the counting step and the selected numbers in the selecting step. 
   One of the foregoing objects is achieved by still another aspect of the present invention through the provision of a communication method including a transmitting step of transmitting a signal to supply a clock and power to at least one other different communication apparatus, a receiving step of receiving information from the at least one other different communication apparatus, a determining step of determining whether or not the same information has been received a plurality of times in the receiving step, and an outputting step of outputting the information received a plurality of times according to a determination result obtained in the determining step. 
   Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a circuit diagram of a transmitting apparatus  10  according to a first embodiment of the present invention. 
       FIG. 2  is a circuit diagram of a receiving apparatus  20  according to the first embodiment of the present invention. 
       FIG. 3  is a diagram showing the principle of the transmitting apparatus  10  and the receiving apparatus  20  according to the present invention. 
       FIG. 4  is a flowchart showing the operation of the receiving apparatus  20  in accordance with the first and second embodiments of the present invention. 
       FIG. 5  is a flowchart showing the operation of the transmitting apparatus  10  in accordance with the first embodiment of the present invention. 
       FIG. 6  is a circuit diagram of a transmitting apparatus  30  according to the second embodiment of the present invention. 
       FIG. 7  is a view showing that L numbers and ID information are stored in a storage unit  36  in accordance with the second embodiment of the present invention. 
       FIG. 8  is a flowchart showing the operation of the transmitting apparatus  30  in accordance with the second embodiment of the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   First Embodiment 
     FIG. 1  is a circuit diagram of a transmitting apparatus  10  according to a first embodiment of the present invention. 
   The transmitting apparatus  10  is preferably a radio tag or an RF-ID tag, including an antenna A 1 , a receiving unit  11 , a signal processing unit  12 , a power supply unit  13 , a transmitting unit  14 , a random number generating unit  15 , and a storage unit  16 . Though the transmitting apparatus  10  is preferably a radio tag or an RFID-tag, any apparatus (e.g., Bluetooth) allowing practice of the present invention is applicable. 
   When the antenna A 1  receives an ID transmission instruction sent from a receiving apparatus  20  shown in  FIG. 2 , the power supply unit  13  generates the power necessary for operating the overall circuit of the transmitting apparatus  10  based on the received ID transmission instruction. The generated power is supplied to the respective circuit components. D.C. power is obtained by rectifying and smoothing the ID transmission instruction (i.e., radio wave). Processing such as rectification and smoothing is performed by the power supply unit  13 . 
   The receiving unit  11  receives the ID transmission instruction and decodes a clock contained in the ID transmission instruction. The decoded clock is transmitted to the signal processing unit  12 . The signal processing unit  12  counts the clock, and instructs the random number generating unit  15  to generate M random numbers. 
   The random number generating unit  15  transmits the M generated random numbers to the signal processing unit  12  in ascending order. The signal processing unit  12  compares the received clock count with the received random numbers. When a match is found, the signal processing unit  12  obtains ID information for identifying the transmitting apparatus  10  stored in the storage unit  16 . The signal processing unit  12  transmits the obtained ID information to the transmitting unit  14 . The transmitting unit  14  transmits the ID information to the receiving apparatus  20  via the antenna A 1 . 
     FIG. 2  is a circuit diagram of the receiving apparatus  20  according to the first embodiment of the present invention. 
   The receiving apparatus  20  is an apparatus that receives ID information, including an antenna A 2 , a receiving unit  21 , a storage unit  22 , a signal processing unit  23 , a transmitting unit  24 , and a clock generating unit  25 . 
   In the receiving apparatus  20 , the clock generating unit  25  generates a clock and sends the clock to the signal processing unit  23 . The signal processing unit  23  generates an ID transmission instruction signal using the clock, and sends the generated signal to the transmitting unit  24 . The transmitting unit  24  transmits the ID transmission instruction to the transmitting apparatus  10  shown in  FIG. 1  via the antenna A 2 . The receiving unit  21  receives the ID information transmitted by the transmitting apparatus  10  via the antenna A 2 , and the received ID information is stored in storage unit  22 . 
   The operation of the transmitting apparatus  10  and the receiving apparatus  20  according to this embodiment will now be described. 
     FIG. 3  is a diagram showing the principle of the transmitting apparatus  10  and the receiving apparatus  20  according to the embodiment. 
   The receiving apparatus  20  transmits a clock to the transmitting apparatus  10 . The clock is represented by a power supply signal to supply power to the transmitting apparatus  10 , and is also represented by an ID transmission instruction to instruct the transmitting apparatus  10  to transmit the ID information of the transmitting apparatus  10 . 
   The transmitting apparatus  10 , which receives the clock from the receiving apparatus  20  and uses the received clock, does not include an oscillator, such as a PLL circuit. When the transmitting apparatus  10  receives the ID transmission instruction, M random numbers are internally generated, and a counter counts the received clock. Each time the counter value matches the value of one of the generated random numbers, the ID information is transmitted. In other words, the transmitting apparatus  10  transmits the ID information M times. 
   The receiving apparatus  20  transmits an ID information transmission instruction containing a clock to the transmitting apparatus  10 . The transmitting apparatus  10  generates power for operating the transmitting apparatus  10  from the ID transmission instruction transmitted in a period A, i.e., a charging/ID pre-transmission period, shown in  FIG. 3 , and supplies the power to the components of the transmitting apparatus  10  so as to prepare for transmission of the ID. 
   At the rise time of the ID transmission instruction to 1 after a long period of 0, the signal processing unit  12  counts the clock. Each time the clock count matches one of five random numbers (5, 8, 14, 18, and 127 in the example shown in  FIG. 3 ) generated by the transmitting apparatus  10 , the transmitting apparatus  10  transmits the ID information thereof to the receiving apparatus  20 . 
   Only when the same ID information is received more than once does the receiving apparatus  20  determine that the ID information is valid. If the same ID information is not received, the receiving apparatus  20  determines that an error occurs, and sends the ID information transmission instruction to the transmitting apparatus  10  to transmit the ID information again. 
   The probability of interference occurring in this embodiment will now be described, presuming that the clock count is N and the number of random numbers generated by the random number generating unit  15  is M, where, for example, N=128 and M=5. 
   The probability that two different transmitting apparatuses  10  originate ID information five times at the same time is given by 1/ 128 P 5 =1/3.1×10 10 . The probability that the two transmitting apparatuses  10  originate ID information four times at the same time is given by 1/ 128 P 4 =1/256032000, and the probability that the two transmitting apparatuses  10  originate ID information three times at the same time is given by 1/ 128 P 3 =1/2048256. The probability that ID signals occur at the same time three times in an environment where K different transmitting apparatuses  10  exist is given by (K−1) 3 / 128 P 3 =(K−1) 3 /2048256. 
   Thus, the probability that ID signals occur at the same time three times in an environment where two different transmitting apparatuses  10  exist, i.e., K=2, is 1/2048256. This results in a very low likelihood of not being able to acquire ID information due to interference. 
   In an environment where 10 transmitting apparatuses  10  exist, i.e., K=10, the probability is 9 3 /2048250=1/2809, which is also very low. In a case where one transmitting apparatus  10  exists, the same ID information is received five times, with the merit of high noise resistance even in a high-noise environment. 
   If the number of transmitting apparatuses  10  is large (i.e., K is a high value), the clock count, i.e., N, must increase. Given that, for example, N=1000 and M=5, the probability that signals from K different transmitting apparatuses  10  occur at the same time three times is given by (K−1) 3 / 1000 P 3 =(K−1) 3 /997002000, and the probability for K=100 is 1/1027, which is also very low. This embodiment provides extensibility by supporting a large number of transmitting apparatuses. 
   The operation of the receiving apparatus  20  that receives ID information from the transmitting apparatus  10  having no internal battery (i.e., power is externally supplied to the transmitting apparatus  10 ) in accordance with this embodiment will now be described. 
     FIG. 4  is a flowchart showing the operation of the receiving apparatus  20  that receives ID information from the transmitting apparatus  10  having no internal battery in accordance with the embodiment. 
   In step S 200 , the receiving apparatus  20  originates an ID transmission instruction containing a clock to the transmitting apparatus  10 . In step S 201 , the receiving apparatus  20  receives ID information sent from the transmitting apparatus  10 . The received ID information is stored in step S 202 . In step S 203 , the stored ID information is read. In step S 204 , it is determined whether or not there is more than one identical ID. 
   If there is not more than one identical ID, it is determined that an error occurred, and the operation returns to step S 200 , where the ID transmission instruction is transmitted again. If there is more than one identical ID, flow proceeds to step S 205 , where all identical IDs are output and it is determined that the transmitting apparatuses  10  having the output IDs exist. The process then terminates. 
   The operation of the transmitting apparatus  10  having no internal battery, that is, power is externally supplied to the transmitting apparatus  10  in accordance with this embodiment will now be described. 
     FIG. 5  is a flowchart showing the operation of the transmitting apparatus  10  having no internal battery in accordance with the embodiment. 
   In step S 210 , the transmitting apparatus  10  that has received an ID transmission instruction generates a clock from the ID transmission instruction. In step S 211 , a counter starts in synchronization with the start time of the clock. In step S 212 , the clock count is compared with the value of the random number selected in step S 219 . Generation and selection of the random number is described below with respect to steps S 217  through S 219 . 
   In step S 213 , it is determined whether or not a match is found. If a match is not found, the counter value and the random number are compared again. If a match is found, ID information is transmitted to the receiving apparatus  20  in step S 214 . In step S 215 , the number of times ID transmission was carried out is counted. If the ID information has been transmitted M times, the operation ends. If the ID information has been transmitted less than M times, flow proceeds to step S 216  which is described below. 
   A procedure of generating random numbers in accordance with the embodiment will now be described. 
   In step S 217 , M random numbers are generated and arranged in ascending order. In step S 218 , K is set to 1, and, in step S 219 , the first random number is invoked. Jumping to step S 215 , if ID information has been transmitted less than M times, K=K+1 is calculated in step S 216 . When K=2 is obtained, the second random number is selected in step S 219 , and this random number is compared with the clock count in step S 212  as discussed above. 
   The ID information transmitted by the transmitting apparatus  10  is received by the receiving unit  21  of the receiving apparatus  20  shown in  FIG. 2  via the antenna A 2 , and the received ID information is stored in the storage unit  22 . The signal processing unit  23  accesses the storage unit  22 , and compares the received ID information. If the same ID information is received more than once, it is determined that the received ID information is valid, and the received ID information is output. Unless the same ID information is received more than once, the ID transmission instruction is transmitted again. 
   When the transmitting apparatus  10  receives the ID transmission instruction again, the random number generating unit  15  generates M random numbers different from the previous random numbers, and the transmitting apparatus  10  originates information, such as ID information, based on the new random numbers. Accordingly, new random numbers are generated after the ID information is transmitted and determination of the re-transmission timing of the ID information is based on the new random numbers. This prevents a recurrence from interference. 
     FIG. 6  is a circuit diagram of a transmitting apparatus  30  according to a second embodiment of the present invention. 
   The transmitting apparatus  30  includes a storage unit  36  having L numbers recorded therein, where L&gt;M, in place of the random number generating unit  15  of the transmitting apparatus  10  shown in  FIG. 1 . 
   The transmitting apparatus  30  includes an antenna A 3 , a receiving unit  31 , a signal processing unit  32 , a power supply unit  33 , a transmitting unit  34 , and the storage unit  36 . 
     FIG. 7  depicts the preferred structure of storing the L numbers and ID information in the storage unit  36  in accordance with the second embodiment. The structure of storing the L numbers and ID information is not limited to example depicted in  FIG. 7 , and any storage method that would allow practice of the present invention is applicable. 
   The L numbers achieve substantially the same function as that of the random numbers generated by the random number generating unit  15  shown in  FIG. 1 . When an ID transmission instruction is received by the antenna A 3 , power is generated by the power supply unit  33 , and is supplied to the respective components. Based on the power supplied by the power supply unit  33 , the receiving unit  31  receives the ID transmission instruction, extracts clock information from the received ID transmission instruction, and then transmits it to the signal processing unit  32 . 
   The signal processing unit  32  generates a timing signal in coordination with the received clock information to count the clock. Furthermore, M numbers are selected from the L numbers and are arranged in ascending order. The M numbers are compared with the count of the timing signal. Each time a match is found, the ID information retrieved from the storage unit  36  is transmitted to the transmitting unit  34 , and the transmitting unit  34  transmits the ID information to the receiving apparatus  20  shown in  FIG. 2  via the antenna A 3 . 
   Where L is set to a non-integer multiple of M, a combination of M numbers shifts each time M numbers are selected from the L numbers. This prevents the same combination on every (L/M)+1. 
     FIG. 8  is a flowchart showing the operation of the transmitting apparatus  30 . 
   The operation shown in the flowchart of  FIG. 8  is performed using the transmitting apparatus  30  shown in  FIG. 6  and the receiving apparatus  20  shown in  FIG. 2 . 
   In step S 701 , a clock is decoded from the received ID transmission instruction. In step S 702 , a counter starts to count the clock. In step S 703 , the number selected in step S 708  (described below) is compared with the counter value obtained in step S 702 . If it is determined in step S 704  that a match is found, ID information is transmitted in step S 705 . If it is determined that a match is not found, the selected value and the clock count are compared again in step S 703 . 
   As indicated above, ID information is transmitted in step S 705 . Flow then proceeds to step S 706 , where the number of times ID transmission was carried out is counted. If the number of times transmission was carried out is M, the operation ends. If the number of times transmission was carried out is less than M, flow proceeds to step S 709  (described below). 
   In step S 707 , K is set to 1. In step S 708 , first M numbers are selected from the L numbers and are arranged in ascending order. Then, the first number is selected from the M numbers. In step S 703 , as discussed above, the selected number is compared with the counter value obtained from step S 702 . Jumping to step S 706 , if ID information has been transmitted less than M times, K=K+1 is calculated in step S 709 . When K=2 is obtained, the second number is selected in step S 708 . 
   According to the foregoing embodiments, information, such as ID information, is transmitted a plurality of times, and when the receiving apparatus  20  receives the same information more than once, it is determined that the received ID information is valid. This enhances the noise resistance. Moreover, the ID transmission timing changes each time ID information is transmitted M times, thus reducing the likelihood of interference. 
   According to the present invention, in an environment surrounded by a plurality of transmitting apparatuses, a receiving apparatus is able to correctly receive information from each of the transmitting apparatuses. 
   A high noise resistance and high reliability information acquisition can also be achieved. 
   The above described embodiment provides extensibility in that a large number of transmitting apparatuses may be supported by changing parameters. 
   While the present invention has been described with reference to what are presently considered to be the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.