Abstract:
There is disclosed a communication channel search method for searching for a beacon transmitted from a base station and setting a communication channel with the base station based on a search result and the received beacon. The communication channel search method includes the steps of: transmitting a plurality of beacons from the base station for a fixed transmission time for transmitting each beacon in a predetermined cycle; and searching for the beacon for a time corresponding to the fixed transmission time for transmitting each beacon in each interval corresponding to a transmission interval for transmitting the plural beacons.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention generally relates to a channel search method and a communication apparatus using the same and particularly to a channel search method and a communication apparatus using the same in which a beacon transmitted from a base station is searched for and a communication channel with the base station is set based on a search result and the received beacon. 
         [0003]    2. Description of the Related Art 
         [0004]    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). 
         [0005]    Such an electronic shelf label system employs a communication system for determining a communication channel, in which a beacon is used for communication between the electronic shelf label and the access point. In one method referred to as passive scanning in communication systems using a beacon, when the electronic shelf label searches for a channel used in the communication system, it is impossible to discover the channel if scanning fails to continue for a beacon cycle of Tbcn_cycle millisecond. 
         [0006]    On the other hand, electronic shelf labels are driven by a battery, so that low power consumption is desired. In general, in proportion as the beacon cycle is reduced, scanning time on the electronic shelf label is reduced, so that low power consumption is realized. However, when the beacon cycle is simply reduced, occupancy in a radio channel frequency band is increased and a radio system using the same frequency band is greatly influenced. 
         [0007]    Patent Document 1: Japanese Laid-Open Patent Application No. 2002-304673 
         [0008]    Patent Document 2: Japanese Laid-Open Patent Application No. 2005-99888 
         [0009]    Patent Document 3: Japanese Laid-Open Patent Application No. 2002-109177 
         [0010]    Patent Document 4: Japanese Laid-Open Patent Application No. 2004-265196 
         [0011]    Patent Document 5: Japanese Laid-Open Patent Application No. 9-138892 
         [0012]    Because of this, in electronic shelf label systems in particular, a search method capable of realizing low power consumption without increasing occupancy is desired. 
       SUMMARY OF THE INVENTION 
       [0013]    It is a general object of the present invention to provide an improved and useful channel search method and communication apparatus using the same in which the above-mentioned problems are eliminated. 
         [0014]    A more specific object of the present invention is to provide a channel search method and communication apparatus using the same that can realize low power consumption. 
         [0015]    According to one aspect of the present invention, there is provided a communication channel search method for searching for a beacon transmitted from a base station and setting a communication channel with the base station based on a search result and the received beacon, the communication channel search method comprising the steps of: transmitting a plurality of beacons from the base station for a fixed transmission time for transmitting each beacon in a predetermined cycle; and searching for the beacon for a time corresponding to the fixed transmission time for transmitting each beacon in each interval corresponding to a transmission interval for transmitting the plural beacons. 
         [0016]    According to another aspect of the present invention, the communication channel search method includes the steps of: having a circuit in an operating status during a period for searching for the beacon; and maintaining only a minimum necessary portion of the circuit in operation and shifting other portions of the circuit to a sleep status as a non-operating status during other periods. 
         [0017]    According to another aspect of the present invention, in the communication channel search method, a search operation for the beacon is performed when communication is not established with the base station. 
         [0018]    According to another aspect of the present invention, there is provided a communication apparatus for receiving a plurality of beacons transmitted from a base station for a fixed transmission time for transmitting each beacon in each predetermined cycle and determining a communication channel with the base station, the communication apparatus comprising: a communication channel search unit searching for the beacon for a time corresponding to the fixed transmission time for transmitting each beacon in each interval corresponding to a transmission interval for transmitting the plural beacons; and a communication unit determining a communication channel in accordance with the beacon when the beacon is searched for by the communication channel search unit. 
         [0019]    According to another aspect of the present invention, the communication apparatus includes a control unit shifting the communication unit in an operating status to a sleep status while searching using the communication channel search unit. 
         [0020]    According to the present invention, plural beacons are transmitted from a base station for a fixed transmission time for transmitting each beacon in each predetermined cycle and a beacon is searched for the transmission time in each interval corresponding to an interval for transmitting the plural beacons, so that low power consumption is realized without increasing occupancy. 
         [0021]    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 
         [0022]      FIG. 1  is a configuration diagram of an example of a system according to the present invention; 
           [0023]      FIG. 2  is a block diagram of a relay device; 
           [0024]      FIG. 3  is a block diagram of an electronic shelf label; 
           [0025]      FIG. 4  is a process flow chart of a relay device; 
           [0026]      FIG. 5  is a diagram illustrating a transmission pattern of a beacon transmitted from a relay device; 
           [0027]      FIG. 6  is a process flow chart of a channel search operation by an electronic shelf label; and 
           [0028]      FIG. 7  is a process flow chart of a variation of a channel search operation by an electronic shelf label. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     [System Configuration] 
       [0029]      FIG. 1  is a configuration diagram of an example of a system according to the present invention. 
         [0030]    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] 
       [0031]      FIG. 2  is a block diagram of the relay device  112 . 
         [0032]    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 . 
         [0033]    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 . 
         [0034]    The process unit  142  includes a microcomputer and the like and performs processing 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 . 
         [0035]    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. 
         [0036]    The radio communication unit  144  performs radio communication with the electronic shelf label  113 . 
         [0037]    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 . 
         [0038]    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] 
       [0039]      FIG. 3  is a block diagram of the electronic shelf label  113 . 
         [0040]    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 . 
         [0041]    The radio communication unit  151  performs radio communication with the relay device  112 . 
         [0042]    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 . 
         [0043]    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 . 
         [0044]    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. 
         [0045]    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 . 
       [Communication Data] 
       [0046]    In the following, communication data exchanged between the relay device  112  and the electronic shelf label  113  is described. 
         [0047]    The relay device  112  transfers a message referred to as a beacon to the electronic shelf label  113  in every two seconds in order to notify a status regarding communication. An interval of beacons is referred to as a frame. The frame is used as a base unit of communication between the relay device  112  and the electronic shelf label  113 . The beacon includes call information of the electronic shelf label  113  communicating within the frame following the beacon such as an identification number of the electronic shelf label  113 . 
         [0048]    Each frame is divided into sixteen intervals. Each interval (125 millisecond) of the divided sixteen portions is referred to as a data slot. 
         [0049]    A top of the frame has a period for transferring the message referred to as a beacon. Thus, a top of a first data slot within a frame is used as an interval for transferring the beacon. 
         [0050]    Second to fifteenth data slots within a frame have the same structure. However, data to be transferred is different. At tops of these data slots, a message referred to as a null beacon having a function differing from that of the beacon is transferred. 
         [0051]    The relay device  112  transfers a beacon in every two seconds and transfers a null beacon in every 125 millisecond thereafter. The transfer of null beacon is performed in every 125 millisecond is repeated until the next beacon is transferred. 
         [0052]    Within one frame, there are one interval for transferring a beacon and fifteen intervals for transferring a null beacon. Functions of the beacon and bull beacon are different. 
         [0053]    The normal beacon has a function of calling the electronic shelf label  113  and call information includes an identification number of the electronic shelf label  113 . 
         [0054]    On the other hand, the null beacon is used when the electronic shelf label  113  performs channel search for discovering the relay device  112 . The electronic shelf label  113  uses the null beacon solely for the channel search. 
         [0055]    The null beacon includes a time offset value for the beacon transfer interval. In accordance with this information, when one null beacon is obtained, it is possible to obtain timing of the beacon transfer interval. 
       [Operation] 
       [0056]    Next, a channel search operation of the present example is described. 
         [0057]    First, transmission processing of the relay device  112  is described. 
         [0058]      FIG. 4  is a process flow chart of a relay device. 
         [0059]    In the relay device  112 , when a beacon transmission cycle of Tbcn_cycle millisecond has elapsed in step S 2 - 1 , the relay device  112  transmits plural beacons in step S 2 - 2 . 
         [0060]      FIG. 5  is a diagram illustrating a transmission pattern of a beacon transmitted from the relay device  112 . 
         [0061]    The relay device  112  transmits a beacon group B made of plural beacons b in every beacon transmission cycle of Tbcn_cycle millisecond. A transmission interval of the beacon group B is Tbcn_intrvl millisecond. In this case, transmission interval Tbcn_intrvl&lt;transmission cycle Tbcn_cycle. 
         [0062]    Further, regarding the transmission interval Tbcn_intrvl, when the number of beacons b included in the beacon group B is N and transmission time of each beacon b is Tbcn millisecond, Tbcn_intrvl=N×Tbcn. 
         [0063]    In addition, the transmission time Tbcn millisecond of each beacon b is set to be a time such that the electronic shelf label  113  is capable of reception. 
         [0064]    Next, the channel search operation by the electronic shelf label  113  is described. 
         [0065]      FIG. 6  is a process flow chart of the channel search operation by the electronic shelf label  113 . 
         [0066]    When the electronic shelf label  113  is incapable of synchronizing with any of the relay devices  112  in step S 2 - 1 , the electronic shelf label  113  starts channel scanning in step S 2 - 2 . 
         [0067]    When the electronic shelf label  113  receives a beacon b in step S 2 - 3  as a result of the channel scanning, the electronic shelf label  113  performs a communication channel determination process so as to determine a communication channel in step S 2 - 4 . In accordance with this, the electronic shelf label  113  is capable of synchronizing with the relay device  112  and communicating with the relay device  112 . 
         [0068]    When the electronic shelf label  113  is incapable of receiving a beacon b in step S 2 - 3 , the electronic shelf label  113  determines whether the transmission time Tbcn millisecond of each beacon b has elapsed in step S 2 - 5 . When the transmission time Tbcn millisecond of each beacon b has elapsed in step S 2 - 5 , the electronic shelf label  113  shifts an inner circuit thereof to a sleep status. In the sleep status, only a minimum portion of the circuit necessary for returning to a normal operation capable of communication with the relay device  112  is in an operating status and operations of other portions of the circuit are in a stopped status, for example. 
         [0069]    When Tbcn_intrvl−Tbcn millisecond has elapsed in step S 2 - 7 , the electronic shelf label  113  returns the inner circuit in the sleep status to the normal operation capable of receiving a beacon b in step S 2 - 8  and the process returns to step S 2 - 2 , where the electronic shelf label  113  performs channel scanning again. 
         [0070]    In this manner, the electronic shelf label  113  scans a radio channel for substantially the beacon transmission time Tbcn millisecond. When the electronic shelf label  113  is incapable of receiving a beacon, namely, incapable of discovering an available channel, the electronic shelf label  113  shifts to the sleep status for Tbcn_intrvl−Tbcn millisecond. 
         [0071]    By repeating the above-mentioned operation for a maximum of [(Tbcn_cycle/Tbcn_intrvl)+1] times, it is possible to discover an available channel. 
         [0072]    Although a maximum search interval is about Tbcn_cycle, the electronic shelf label  113  performs scanning for a maximum of [(Tbcn_cycle/Tbcn_intrvl)+1] millisecond in practice. 
         [0073]    For example, when a beacon or a null beacon is transferred for an interval of at least 15 millisecond in every 125 millisecond, it is sufficient to search at each point obtained by dividing the 125 millisecond into nine (≧125/15=8.3333) portions for one millisecond. This is due to the fact that each point exists at 13.8 millisecond intervals and a beacon transfer interval a width exceeding the interval must include one of the points. 
         [0074]    In a search stage, when a sub-beacon or a null beacon is obtained in the beacon transfer interval or the null beacon transfer interval, synchronization is possible. Information sufficient for synchronization is obtained from a single sub-beacon or a single null beacon. A length thereof is not more than 504 microsecond, so that reception is sufficiently possible with one millisecond. 
         [0075]    When it is assumed that probability of appearance of UID, which is a unique ID of each electronic shelf label  113  included in a beacon issued from the relay device  112 , in each bit is obtained with equal probability, and a sub beacon number (position of sub beacon) that the shelf label stats obtaining is determined at random, an average number of sub beacons received by the electronic shelf label  113  is one. 
         [0076]    Thus, in comparison with a case without division, time when a radio communication block is on, namely, time for checking radio waves is reduced to ⅙. 
         [0077]    In comparison with a conventional method, scanning time is reduced to ([(Tbcn_cycle/Tbcn_intrvl)+1]*Tbcn)/Tbcn_cycle time. 
         [0078]    For example, when Tbcn_cycle=125 millisecond, Tbcn_intrvl=15 millisecond, Tbcn=1 millisecond, a maximum search time is about 125 millisecond, a maximum scanning time is 9 millisecond, so that it is possible to reduce to 9/125 time in comparison with a conventional method. 
         [0079]    Since it is possible to reduce the search time and scanning time, it is possible to reduce power consumption of the electronic shelf label  113 . 
         [0080]    In the above example, although a single channel and the search operation are described, plural channels may be searched for. 
         [0081]      FIG. 7  is a process flow chart of a variation of a channel search operation by the electronic shelf label  113 . 
         [0082]    When the electronic shelf label  113  is incapable of synchronizing with any of the relay devices  112  in step S 3 - 1 , the electronic shelf label  113  starts channel scanning in step S 3 - 2 . 
         [0083]    When the electronic shelf label  113  receives a beacon b in step S 3 - 3  as a result of the channel scanning, the electronic shelf label  113  performs a communication channel determination process so as to determine a communication channel in step S 3 - 4 . In accordance with this, the electronic shelf label  113  is capable of synchronizing with the relay device  112  and communicating with the relay device  112 . 
         [0084]    When the electronic shelf label  113  is incapable of receiving a beacon b in step S 3 - 3 , the electronic shelf label  113  determines whether the transmission time Tbcn millisecond of each beacon b has elapsed in step S 3 - 5 . When the transmission time Tbcn millisecond of each beacon b has elapsed in step S 3 - 5 , the electronic shelf label  113  determines whether all channels are searched for in step S 3 - 6 . 
         [0085]    When all channels are not searched for in step S 3 - 6 , the electronic shelf label  113  changes a search channel in step S 3 - 7  and the process returns to step S 3 - 2 , where the electronic shelf label  113  performs channel search. When all channels are searched for in step S 3 - 6 , the electronic shelf label  113  shifts an inner circuit thereof to a sleep status in step S 3 - 8 . 
         [0086]    When Tbcn_intrvl−Tbcn millisecond has elapsed in step S 3 - 9 , the electronic shelf label  113  returns the inner circuit in the sleep status to the normal operation capable of receiving a beacon b in step S 3 - 10  and the process returns to step S 2 - 2 , where the electronic shelf label  113  performs channel scanning again. 
         [0087]    In accordance with this, it is possible to perform channel search with minimum electric power and to improve a battery life in a terminal operating by a battery. 
         [0088]    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. 
         [0089]    The present application is based on Japanese priority application No. 2006-038660 filed Feb. 15, 2006, the entire contents of which are hereby incorporated herein by reference.