Abstract:
There is disclosed a communication method of a communication system having a base station for performing a call and a terminal for returning a response to the call from the base station, the communication method including the steps of: transmitting the call by the base station, the call including response probability; and responding to the base station by the terminal based on the response probability when the call from the base station is received.

Description:
CROSS REFERENCES TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. §119(a) to Japanese application number 2006-038664, filed on Feb. 15, 2006, in the Japan Patent Office, which is incorporated herein by reference to its entirety as forth in full. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a communication method, a communication system, and a communication apparatus and particularly to a communication method, a communication system, and a communication apparatus having a base station for calling and a terminal for returning a response to the calling from the base station. 
     2. Description of the Related Art 
     In an electronic shelf label system, an electronic shelf label having rewritable display information is registered in a host computer and then attached to a product shelf. It is possible to rewrite the display information of the electronic shelf label from the host computer by accessing the electronic shelf label through an access point (refer to Patent Documents 1 to 5). 
     Such an electronic shelf label system employs a communication system in which a communication channel for communication between the electronic shelf label and an access point is determined using a beacon. For example, in CSMA/CA employed in IEEE 802.11b and the like, each terminal performs carrier sensing so as to confirm that a radio channel is continuously available for a certain period of time (random) and then transmits data. In accordance with this, collision is avoided. 
     Patent Document 1: Japanese Laid-Open Patent Application No. 2002-304673 
     Patent Document 2: Japanese Laid-Open Patent Application No. 2005-99888 
     Patent Document 3: Japanese Laid-Open Patent Application No. 2002-109177 
     Patent Document 4: Japanese Laid-Open Patent Application No. 2004-265196 
     Patent Document 5: Japanese Laid-Open Patent Application No. 9-138892 
     In view of this, a conventional method has a problem in that when the number of terminals is very large or when an amount of data transmitted by the terminal is very small, each terminal stands by while performing carrier sensing for a longer period of time in comparison with a period of actual data transmission, so that this is inefficient in terms power saving, for example. 
     SUMMARY OF THE INVENTION 
     It is a general object of the present invention to provide an improved and useful communication method, communication system, and communication apparatus in which the above-mentioned problems are eliminated. 
     A more specific object of the present invention is to provide a communication method, communication system, and communication apparatus that can perform communication in an efficient manner. 
     According to one aspect of the present invention, there is provided a communication method of a communication system having a base station for performing a call and a terminal for returning a response to the call from the base station, the communication method including the steps of: transmitting the call by the base station, the call including response probability; and responding to the base station by the terminal based on the response probability when the call from the base station is received. 
     According to another aspect of the present invention, in the communication method, when the terminal decides to make a response based on the response probability, the terminal determines time for the response in a random manner. 
     According to another aspect of the present invention, there is provided a communication system including: a base station for performing a call; and a terminal for returning a response to the call from the base station, wherein the base station transmits the call including response probability, and the terminal makes a response to the base station based on the response probability when the terminal receives the call from the base station. 
     According to another aspect of the present invention, in the communication system, when the terminal decides to make a response based on the response probability, the terminal sets a time slot as time for the response in a random manner. 
     According to another aspect of the present invention, there is provided a communication apparatus for performing a call to a terminal and receiving a response from the terminal, the communication apparatus including: a response probability setting unit setting response probability on the terminal; and a call unit transmitting the call including the response probability set by the response probability setting unit. 
     According to another aspect of the present invention, the communication includes: a communication probability setting unit controlling communication probability in accordance with a status of a communication channel. 
     According to another aspect of the present invention, there is provided a communication apparatus for returning a response to a call from a base station, the communication apparatus including: a response decision unit deciding whether to make a response to the base station based on response probability included in the call; and a response unit returning a response to the base station based on a decision by the response decision unit. 
     According to the present invention, the base station transmits a call including response probability and the terminal makes a response to the base station based on the response probability included in the call when the terminal receives the call from the base station. Thus, it is possible to control probability of collision of responses of terminals, so that it is possible to prevent the collision of responses. In accordance with this, unnecessary communication is reduced, so that it is possible to reduce power consumption. 
     Other objects, features and advantage of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a configuration diagram of an example of a system according to the present invention; 
         FIG. 2  is a block diagram of a relay device; 
         FIG. 3  is a block diagram of an electronic shelf label; 
         FIG. 4  is a process flow chart of a call process operation of a relay device; 
         FIG. 5  is a process flow chart of a response process operation of an electronic shelf label; and 
         FIG. 6  is a diagram illustrating a response time determination operation. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     System Configuration 
       FIG. 1  is a configuration diagram of an example of a system according to the present invention. 
     An electronic shelf label system  100  according to the example includes a management device  111 , a relay device  112 , and an electronic shelf label  113 . The electronic shelf label system  100  has the relay device  112  for relaying communication between the electronic shelf label  113  and the management device  111  managing the electronic shelf label  113  and manages the electronic shelf label  113  attached to a product shelf. 
     [Relay Device] 
       FIG. 2  is a block diagram of the relay device  112 . 
     The relay device  112  includes a communication unit  141 , a process unit  142 , a storage unit  143 , a radio communication unit  144 , a power supply circuit  145 , and a battery  146 . 
     The communication unit  141  is connected to the management device  111  via a network such as LAN, WAN, a dedicated line, or the like. The communication unit  141  performs communication with the management device  111 . 
     The process unit  142  includes a microcomputer and the like and performs a process for relaying communication, for example, between the management device  111  and the electronic shelf label  113  based on a program installed on the storage unit  143 . 
     The storage unit  143  includes a rewritable non-volatile memory such as EEPROM, for example, ROM, RAM, and the like. In the storage unit  143 , information  131  on electronic shelf labels within a communication range is stored in addition to a communication control program. 
     The radio communication unit  144  performs radio communication with the electronic shelf label  113 . 
     The power supply circuit  145  is connected to an alternating-current power supply such as an external commercial power supply. The power supply circuit  145  converts the connected alternating-current power into a direct-current voltage and supplies the direct-current voltage as a driving voltage to the communication unit  141 , the process unit  142 , the storage unit  143 , and the radio communication unit  144 . 
     The battery  146  includes a Ni—Cd battery, a lithium ion battery, an electric double layer capacitor, or the like as a chargeable battery unit. The battery  146  is charged from the direct-current voltage generated in the power supply circuit  145  and supplies electric power for driving the communication unit  141 , the process unit  142 , the storage unit  143 , and the radio communication unit  144  for a certain period of time so as to execute an end program when alternating-current power is cut. 
     [Electronic Shelf Label] 
       FIG. 3  is a block diagram of the electronic shelf label  113 . 
     The electronic shelf label  113  includes a radio communication unit  151 , a process unit  152 , a storage unit  153 , a display device  154 , and a battery  155 . 
     The radio communication unit  151  performs radio communication with the relay device  112 . 
     The process unit  152  includes CPU, for example. The process unit  152  controls communication with the relay device  112  and also controls display of the display device  154  based on a program stored in the storage unit  153 . 
     The storage unit  153  includes a rewritable non-volatile storage device such as EEPROM, for example. In the storage unit  153 , a program executed in the process unit  152  is installed and shelf label IDs and product codes are stored. Some of the shelf label IDs and product codes are registered in advance and can be changed by the relay device  112 . 
     The display device  154  includes LCD, an EL panel, electronic paper, or the like. The display device  154  displays product names, product codes, prices and the like. 
     The battery  155  includes a small battery and supplies electric power for driving the radio communication unit  151 , the process unit  152 , the storage unit  153 , and the display device  154 . 
     First, status transition of the electronic shelf label  113  from an unregistered status to a normal operation status is described. 
     The electronic shelf label  113  has three statuses, namely, an ID assignment waiting status where an ID is not assigned from the relay device  112 , an ID registration waiting status where the ID assigned from the relay device  112  is not registered in the management device  111 , and a normal status where the ID is registered in the management device  111 . 
     In the following, a transition process from the ID assignment waiting status to the ID registration waiting status is described. A transition process from the ID registration waiting status to the normal status is omitted since this is the same process as the transition process from the ID assignment waiting status to the ID registration waiting status. 
     [Operation] 
     First, a call process of the relay device  112  is described. 
       FIG. 4  is a process flow chart of a call process of the relay device  112 . 
     When a call request is generated in step S 1 - 1  so as to assign an ID to the unregistered electronic shelf label  113 , for example, the process unit  142  of the relay device  112  sets response probability to the call in step S 1 - 2 . 
     Next, the process unit  142  generates a beacon for calling including the response probability in step S 1 - 3  and transmits the beacon via the radio communication unit  144  in step S 1 - 4 . 
     When a response from the electronic shelf label  113  is an error in step S 1 - 5 , the process of the process unit  142  returns to step S 1 - 2 . In the response probability setting process in step S 1 - 2 , when the response probability is reset due to errors and the like, a process for reducing the response probability from 50% to 30%, for example, is performed. 
     Next, a response process in the electronic shelf label  113  is described. 
       FIG. 5  is a process flow chart of a response process of the electronic shelf label  113 . 
     The process unit  152  of the electronic shelf label  113  shifts from a sleep status to a communication status in step S 2 - 1 . When the calling of the beacon from the relay device  112  is received in step S 2 - 2 , the process unit  152  extracts the response probability included in the received beacon in step S 2 - 3 . 
     The process unit  152  generates a random number from 1 to 100 in step S 2 - 4  and compares the generated random number with a response probability parameter of the extracted response probability in step S 2 - 5 . The response probability parameter is set such that when the extracted response probability is 100%, a response must be made and when the extracted response probability is 50%, a response is made with a probability of 50%. 
     The process unit  152  compares the response probability parameter with the generated random number in step S 2 - 5 . When the response probability parameter is less than the generated random number in step S 2 - 5 , the process unit  152  decides to respond to the relay device  112  and creates response information in accordance with the call in step S 2 - 6 . Further, the process unit  152  determines a response time in step S 2 - 7 . The response time is determined by generating a random number and the like and determining the number of a communication slot inserted into a contended access period in accordance with the generated random number. 
       FIG. 6  is a diagram illustrating a response time determination operation. In  FIG. 6 , a horizontal axis indicates time. In this case, after a beacon b for calling is transmitted, a contended access period T 0  is set. In the contended access period T 0 , N communication slots SL 1  to SLN are set. The process unit  152  selects one communication slot SLi in a random manner from the communication slots SL 1  to SLN in accordance with the random number for example. 
     At a response time in step S 2 - 8 , namely, time of the selected communication slot SLi, the process unit  152  transmits the created response in step S 2 - 9 . When the transmission of the response is finished, the process unit  152  shifts to a sleep status in step S 2 - 10 . In the sleep status, only minimum necessary circuits are in operation and operations of unnecessary circuits are stopped. 
     When the response probability parameter is more than the generated random number in step S 2 - 5 , the process unit  152  decides not to respond and immediately shifts to the sleep status in step S 2 - 10 . In accordance with this, it is possible to reduce unnecessary power consumption. 
     When the response information from the electronic shelf label  113  is received in step S 2 - 9 , the relay device  112  obtains the ID of the unregistered electronic shelf label  113  included in the response information, transmits a call to the electronic shelf label  113  having the obtained ID, and transmits ID assignment information to the unregistered electronic shelf label  113 . 
     As mentioned above, according to the present example, the relay device  112  sets the response probability and transmits the beacon for calling including the response probability and the electronic shelf label  113  receives the beacon for calling, extracts the response probability included in the beacon for calling, and makes a response in accordance with the response probability, so that it is possible to prevent collision of responses from plural electronic shelf labels  113  to the relay device  112 . 
     In this case, in the present example, when response is decided, a communication slot for transmitting the response is determined in a random manner, so that it is possible to further reduce the probability of collision of responses, thereby enabling efficient communication. 
     Moreover, plural electronic shelf labels  113  are capable of certainly returning a response to the call from the relay device  112  without error, so that it is possible to reduce unnecessary calls and responses, thereby reducing power consumption. 
     The present invention is not limited to the specifically disclosed embodiment, and variations and modifications may be made without departing from the scope of the present invention. 
     The present application is based on Japanese priority application No. 2006-038664 filed Feb. 15, 2006, the entire contents of which are hereby incorporated herein by reference.