Patent Publication Number: US-2023136032-A1

Title: Wireless communication system, base station control device, evacuation guidance method, and base station control program

Description:
TECHNICAL FIELD 
     The present disclosure relates to a wireless communication system and a wireless communication method. 
     BACKGROUND ART 
     There has been proposed a technique that also uses optical wireless communication (downlink communication using LED lightings or the like) in an RF (radio frequency) communication system such as Wi-Fi (see, e.g., Patent Literature 1). In Patent Literature 1, downlink communication of data such as an SSID (service set identifier) and a password needed for connection authentication of Wi-Fi is performed by optical wireless. As a result, in Patent Literature 1, a user can connect to Wi-Fi only by entering the optical wireless communication area without performing connection/authentication work such as checking which wireless communication is usable and performing input operations of an SSID and a password. 
     There has been proposed a technique in which instead of transmitting connection/authentication information itself for RF communication by optical wireless communication, an optical ID having a small amount of data corresponding thereto is transmitted (see, e.g., Patent Literature 2). In Patent Literature 2, an optical transmitter transmits data of the above optical ID with a color/brightness change under the condition that humans cannot perceive it. Both a base station and a terminal have a correspondence list between the optical ID and the connection/authentication information, and the terminal extracts the connection/authentication information corresponding to the received optical ID, and performs RF communication in accordance with this information. As a result, in Patent Literature 2, in a system that performs connection/authentication control for RF communication using an optical signal, light sources that are used for both optical wireless communication and lighting can be used on the base station side and a terminal such as a normal smartphone can be used on the terminal side. In addition, it has merits in terms of popularization of facilities at the time of introducing the facilities and suppression of cost and power consumption. 
     In the system of Patent Literature 2, the main configuration is a configuration in which an optical base station (such as a smart lighting) and an RF base station are integrated. In this configuration, optical base stations are required depending on the number of RF base stations. Further, in the above configuration, it is difficult to utilize already installed optical base stations as they are. There is a need for a concrete mechanism for integrated management/control of already installed optical base stations and RF base stations. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: US20180139202A1 
         Patent Literature 2: PCT/JP2019/031260 
       
    
     Non-Patent Literature 
     Non-Patent Literature 1: SHIKAKURA Tomoaki et al., “Research on the Perception of Lighting Fluctuation in a Luminous Offices Environment”, Journal of Science and Technology in Lighting Vol.85, No.5, 2001, PP.346-351 
     SUMMARY OF THE INVENTION 
     Technical Problem 
     An object of the present disclosure is to make already installed smart lightings available as optical base stations as they are without modifying them, and perform connection/authentication control for RF communication using an optical signal sent out from the optical base stations. 
     Means for Solving the Problem 
     The present disclosure has a configuration in which optical base stations and RF base stations are separated from each other in an optical/RF wireless hybrid communication system, and controls one or more optical base stations to connect an RF base station and a terminal based on information acquired from the RF base stations. 
     Specifically, a wireless communication system according to the present disclosure includes: 
     one or more wireless base stations that wirelessly communicate with a terminal;   a base station control device that collects wireless base station information from each wireless base station, determines a wireless base station that wirelessly communicates with the terminal using the collected wireless base station information, and transmits an optical ID corresponding to the determined wireless base station; and   one or more optical base stations that receive the optical ID from the base station control device, and transmit the received optical ID to the terminal using an optical signal,   wherein the wireless base station determined by the base station control device wirelessly communicates with the terminal that receives the optical ID.   

     Specifically, a wireless communication method according to the present disclosure is
     a wireless communication method executed by a wireless communication system in which one or more wireless base stations and one or more optical base stations are connected to a base station control device,   wherein the base station control device   collects wireless base station information from each wireless base station,   determines a wireless base station that wirelessly communicates with a terminal using the collected wireless base station information, and   transmits an optical ID corresponding to the determined wireless base station to at least one of the one or more optical base stations,   the optical base station that receives the optical ID transmits the received optical ID to the terminal using an optical signal, and   the wireless base station determined by the base station control device wirelessly communicates with the terminal that receives the optical ID.   

     Specifically, a base station control device according to the present disclosure is 
     a base station control device connected to one or more wireless base stations and one or more optical base stations, wherein the base station control device   collects wireless base station information from each wireless base station,   determines a wireless base station that wirelessly communicates with a terminal using the collected wireless base station information,   transmits an optical ID corresponding to the determined wireless base station to at least one of the one or more optical base stations,   causes the optical base station to transmit the optical ID to the terminal using an optical signal, and   causes the determined wireless base station to wirelessly communicate with the terminal that receives the optical ID.   

     Specifically, a base station control program according to the present disclosure is a program for causing a computer to implement each functional unit provided in the base station control device according to the present disclosure, and is a program for causing a computer to execute each step provided in the wireless communication method according to the present disclosure. 
     Effects of the Invention 
     It is possible to make already installed smart lightings available as optical base stations as they are without modifying them, and perform connection/authentication control for RF communication using an optical signal sent out from the optical base stations. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    shows a basic configuration of a system according to the present disclosure. 
         FIG.  2    shows an example of an optical ID correspondence list. 
         FIG.  3    shows an example of wireless base station information. 
         FIG.  4    shows an example of a configuration of a system according to a second embodiment. 
         FIG.  5    shows an example of a processing flow in the case where an optical base station broadcasts an optical ID regardless of the presence or absence of a terminal. 
         FIG.  6    shows an example of a control signal flow in the second embodiment. 
         FIG.  7    shows an example of a processing flow in the case where a probe request from the terminal is used as the starting point of the flow processing. 
         FIG.  8    shows an example of a configuration of a system according to a third embodiment. 
         FIG.  9    shows an example of a control signal flow in the third embodiment. 
         FIG.  10    shows an example of a configuration of a system according to a fourth embodiment. 
         FIG.  11    shows an example of a control signal flow in the fourth embodiment. 
         FIG.  12    shows an example of a processing flow in a fifth embodiment. 
         FIG.  13    shows an example of a control signal flow in the fifth embodiment. 
         FIG.  14    is a diagram illustrating a configuration of an optical base station in a communication system according to a sixth embodiment. 
         FIG.  15    is a diagram illustrating a configuration of a terminal in the communication system according to the sixth embodiment. 
         FIG.  16    is a diagram illustrating the illuminance of an optical signal received by the terminal according to the sixth embodiment. 
         FIG.  17    is a diagram illustrating a signal binarized by a determination unit of the terminal according to the sixth embodiment. 
         FIG.  18    is a diagram illustrating processing in an analysis unit of the terminal according to the sixth embodiment. 
         FIG.  19    is a diagram illustrating processing in a calculation unit of the terminal according to the sixth embodiment. 
         FIG.  20    is a flowchart illustrating a communication method according to the sixth embodiment. 
         FIG.  21    is a diagram illustrating a configuration of the terminal in the communication system according to the sixth embodiment. 
         FIG.  22    is a diagram illustrating processing in the calculation unit of the terminal according to the sixth embodiment. 
         FIG.  23    is a diagram illustrating a configuration of a terminal in a communication system according to a seventh embodiment. 
         FIG.  24    is a diagram illustrating the illuminance of an optical signal received by the terminal according to the seventh embodiment. 
         FIG.  25    is a diagram illustrating a signal binarized by a determination unit of the terminal according to the seventh embodiment. 
         FIG.  26    is a diagram illustrating processing in an analysis unit of the terminal according to the seventh embodiment. 
         FIG.  27    is a diagram illustrating processing in an optical ID estimation unit of the terminal according to the seventh embodiment. 
         FIG.  28    is a diagram illustrating processing in an optical ID analysis unit of the terminal according to the seventh embodiment. 
         FIG.  29    is a first flowchart illustrating a communication method according to the seventh embodiment. 
         FIG.  30    is a second flowchart illustrating a communication method according to the seventh embodiment. 
         FIG.  31    shows an example of characteristics of an optical signal output from an optical transmitter according to an eighth embodiment. 
         FIG.  32    shows an example of characteristics of an optical signal output from the optical transmitter according to the eighth embodiment. 
         FIG.  33    shows an example of characteristics of an optical signal output from the optical transmitter according to the eighth embodiment. 
         FIG.  34    shows an example of characteristics of an optical signal output from the optical transmitter according to the eighth embodiment. 
         FIG.  35    shows an example of a configuration of a terminal in a communication system according to the eighth embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These examples of embodiment are merely illustrative, and the present disclosure can be embodied with various modifications and improvements based on the knowledge of those skilled in the art. Note that in the present specification and the drawings, components having the same reference numeral shall refer to the same component. 
     Summary of the Present Disclosure 
     
         
         The main configuration is a configuration in which optical base stations and RF base stations are separated from each other, and the already installed optical base stations are flexibly controlled based on some information aggregated from the RF base stations. 
         By providing a base station control device in a network composed of the optical base stations and the RF base stations, information aggregation from the RF base stations and management/control of the optical base stations are executed integrally. 
         A control scheme is proposed in executing information aggregation from the RF base stations and control of the optical base stations. 
       
    
     First Embodiment 
       FIG.  1    shows a basic configuration of a system according to the present disclosure. The system according to the present disclosure includes a base station control device  40 , a single RF base station  10 , and a single optical base station  50 . The RF base station  10  and the optical base station  50  are connected to each other. The RF base station  10  is connected to an upper network  30 . Their connection form may be any form, and may be wired connection or wireless connection. 
     The base station control device  40  is a device that externally controls the optical base station  50 , and includes an authentication information integration control unit  41 , an optical base station control unit  42 , and an optical ID correspondence list. The base station control device  40  of the present disclosure can also be implemented by a computer and a program, and the program can be recorded on a recording medium or provided through a network. 
       FIG.  2    shows an example of the optical ID correspondence list.  FIG.  2    shows an example of four optical IDs with serial numbers of 1 to 4. Connection information for wireless communication is information that defines which wireless scheme, which frequency band, and which radio channel are used for RF wireless communication between the RF base station  10  and the terminal  20 . Authentication information for wireless communication is information that defines an SSID (service set identifier), a password, and an ID (identifier) when the terminal  20  access the RF base station  10 . The authentication information may be one of them, or any two or more may be defined. The connection information for wireless communication and the authentication information for wireless communication are examples, and other necessary information may be defined. 
     The authentication information integration control unit  41  collects wireless base station information from the RF base station  10 , selects an RF base station  10  to which the terminal  20  should connect, and transmits information to the optical base station control unit  42 . 
       FIG.  3    shows an example of wireless base station information. The wireless base station information includes wireless parameters and wired parameters. The wireless parameters are parameters used in performing wireless communication with the terminal  20 , such as a wireless scheme, a frequency band, a radio channel, the number of connected terminals, transmission power, RSSI (received signal strength indicator), a modulation coding scheme, the number of spatial streams, and channel state information. The wired parameters are, for example, a wired interface, and a wired traffic alive monitoring result. 
     The authentication information integration control unit  41  selects the optimum RF base station  10  to which the terminal  20  should connect using the collected wireless base station information, and transmits connection information and authentication information to be used in the RF base station  10  to the optical base station control unit  42 . 
     The optical base station control unit  42  extracts an optical ID, which corresponds to the connection information and authentication information received from the authentication information integration control unit  41 , from the optical ID correspondence list, and transmits optical base station control information indicating transmission of the extracted optical ID to the optical base station  50 . The optical base station control information includes the connection information and authentication information for the RF base station  10  to which the terminal  20  should connect. The optical ID included in the optical base station control information may be the optical ID itself, or may be a signal pattern corresponding to the optical ID. The signal pattern includes a bit pattern of 8 bits, 16 bits, etc. By lengthening the bit pattern, the reception accuracy at the terminal  20  can be improved. 
     The optical base station  50  transmits the optical ID, which is in accordance with the optical base station control information from the base station control device  40 , to the terminal  20  using an optical signal. Any equipment capable of transmitting the optical ID to the terminal  20  can used as the optical base station  50 , for example, non-communication equipment that is not originally used for communication, such as a smart lighting may be used. An optical signal transmitted from the optical base station  50  may be modulated by an orthogonal code or the like so that the reception accuracy at the terminal  20  may be improved. 
     The terminal  20  holds the same optical ID correspondence list as the base station control device  40 . When the terminal  20  receives the optical ID, it refers to the optical ID correspondence list, and uses the connection information and authentication information for RF transmission/reception corresponding to the received optical ID to transmit an authentication request to an appropriate RF base station  10 . This enables communication connection between the RF base station  10  and the terminal  20 . 
     Note that the terminal  20  may not hold the same optical ID correspondence list as the base station control device  40 . For example, the terminal  20  automatically acquires position information from within the terminal  20  when starting an application, and acquires the optical ID correspondence list corresponding to the position information using the application. Further, the terminal  20  may acquire an appropriate optical ID correspondence list according to the corresponding position information from the cloud via mobile communication. 
     Second Embodiment 
       FIG.  4    shows an example of a configuration of a system according to this embodiment. The system according to this embodiment includes the base station control device  40 , a plurality of RF base stations  10 , and a single optical base station  50 . The base station control device  40  is a device that externally controls the optical base station  50 , and includes the authentication information integration control unit  41  and the optical base station control unit  42 . 
     The authentication information integration control unit  41  collects wireless base station information from each RF base station  10 , selects the optimum RF base station  10  to which the terminal  20  should connect, and transmits information to the optical base station control unit  42 . The optical base station control unit  42  transmits control information to the optical base station  50 . 
     The optimum RF base station  10  selected in the authentication information integration control unit  41  is determined, for example, as follows:
     The RF base station  10  having the highest expected communication band is preferentially connected to the terminal  20 .   When there are a plurality of optical base stations  50 , an RF base station  10  is selected so that the number of terminals  20  connected to each RF base station  10  is uniform.   

       FIG.  5    shows an example of a processing flow in the case where the optical base station  50  broadcasts the optical ID regardless of the presence or absence of a terminal.  FIG.  6    shows an example of a control signal flow. 
     Step S 101 : The authentication information integration control unit  41  transmits a request for wireless base station information to each RF base station  10 . 
     Step S 102 : The authentication information integration control unit  41  receives the wireless base station information from each RF base station  10 . 
     Step S 103 : The authentication information integration control unit  41  determines whether or not the wireless base station information has been received from all the RF base stations  10 . 
     Step S 104 : When having received the wireless base station information from all the RF base stations  10  (Yes in S 103 ), the authentication information integration control unit  41  selects the optimum RF base station  10  from among the plurality of RF base stations  10 . 
     Step S 105  and S 106 : The optical base station control unit  42  performs communication negotiation with the optical base station  50  in order to confirm whether the optical base station control information can be transmitted. For example, the optical base station control unit  42  transmits a packet for survival confirmation to the optical base station  50  (S 105 ), and confirms whether a response has been received from the optical base station  50  (S 106 ). 
     Step S 107 : The optical base station control unit  42  transmits the optical base station control information to an optical base station  50  from which a response has been received from the optical base station  50 . 
     The optical base station control information may be transmitted to the optical base station  50  with a probe request from the terminal  20  as a trigger.  FIG.  7    shows an example of a processing flow in the case where a probe request from the terminal is used as the starting point of the flow processing.  FIG.  6    shows an example of a control signal flow. In this case, the base station control device  40  selects the optimum RF base station  10  in advance (S 104 ), and then executes steps S 105  to S 107  in response to receiving the probe request transmitted from the terminal  20 . 
     Further, a function as an RF base station may be provided in the base station control device  40 . For example, the base station control device  40  itself may function as a base station #N+1. 
     Third Embodiment 
       FIG.  8    shows an example of a configuration of a system according to this embodiment. The system according to this embodiment includes a plurality of RF base stations  10  and a plurality of optical base stations  50 . In this embodiment, the plurality of optical base stations  50  perform the same operation. 
       FIG.  5    shows an example of a processing flow in the case where the optical base stations  50  broadcast the optical ID regardless of the presence or absence of terminals.  FIG.  9    shows an example of a control signal flow. In this embodiment, in step S 105 , the optical base station control unit  42  performs communication negotiation with each optical base station  50 . Then, if the optical base station control unit  42  can confirm responses from all the optical base stations  50  (True in S 106 ), it transmits the optical base station control information to each optical base station  50  (S 107 ). Here, the optical base station control information transmitted in step S 107  is common to each optical base station  50 . 
     The optical base station control information may be transmitted to the optical base stations  50  with a probe request from the terminal  20  as a trigger.  FIG.  7    shows an example of a processing flow in the case where a probe request from the terminal is used as the starting point of the flow processing.  FIG.  9    shows an example of a control signal flow. In this case, the base station control device  40  selects the optimum RF base station  10  in advance (S 104 ), and then executes steps S 105  to S 107  in response to receiving the probe request transmitted from the terminal  20 . 
     Further, a function as an RF base station may be provided in the base station control device  40 . For example, the base station control device  40  itself may function as a base station #N+1. 
     Fourth Embodiment 
       FIG.  10    shows an example of a configuration of a system according to this embodiment. The system according to this embodiment includes a plurality of RF base stations  10  and a plurality of optical base stations  50 . In this embodiment, the plurality of optical base stations  50  perform operation individually. 
       FIG.  5    shows an example of a processing flow in the case where the optical base stations  50  broadcast the optical IDs regardless of the presence or absence of terminals.  FIG.  11    shows an example of a control signal flow. In this embodiment, in step S 105 , the optical base station control unit  42  performs communication negotiation with each optical base station  50 . At this time, the optical base station control unit  42  performs communication negotiation for each optical base station  50 . As a result, in this embodiment, the plurality of optical base stations  50  can perform operation individually. Then, if the optical base station control unit  42  can confirm responses from all the optical base stations  50  (True in S 106 ), it transmits individual optical base station control information to each optical base station  50  (S 107 ). 
     The optical base station control information may be transmitted to the optical base stations  50  with a probe request from the terminal  20  as a trigger.  FIG.  7    shows an example of a processing flow in the case where a probe request from the terminal is used as the starting point of the flow processing.  FIG.  11    shows an example of a control signal flow. In this case, the base station control device  40  selects the optimum RF base station  10   in advance (S 104 ), and then executes steps S 105  to S 107  in response to receiving the probe request transmitted from the terminal  20 . 
     Further, a function as an RF base station may be provided in the base station control device  40 . For example, the base station control device  40  itself may function as a base station #N+1. 
     Fifth Embodiment 
     In this embodiment, the position of the terminal  20  is grasped, and the optical base stations  50  each distribute an individual optical ID according to the position of the terminal  20 . The system configuration of this embodiment is the same as that of the fourth embodiment. 
       FIG.  12    shows an example of a processing flow of the base station control device  40 .  FIG.  13    shows an example of a control signal flow. In this embodiment, when having received the wireless base station information from all the RF base stations  10  (Yes in S 103 ), the optical base station control unit  42  executes step S 111  before step S 104 . In step S 111 , the optical base station control unit  42  collects position information of the terminal  20 . For example, the optical base station control unit  42  captures the terminal  20  or its user using a camera, and derives the position information of the terminal  20  using the position in the captured image. Further, it can be exemplified to estimate the terminal  20  using radio waves at the time of the probe request. 
     Then, in steps S 105  and S 106 , the optical base station control unit  42  performs communication negotiation only with the optical base station  50  at a particular location (S 105 ) and transmits the optical base station control information only to the optical base station  50  at the particular location (S 107 ) based on the position information of the terminal  20 . 
     Sixth Embodiment 1 
     This embodiment will describe a configuration for accurately acquiring information of the optical ID regardless of the position and light receiving angle of the terminal. The terminal according to this embodiment has a mechanism for periodically updating a threshold value setting and reading a change in light illuminance according to changes in its own position, light receiving angle, and the like. 
       FIG.  14    is a diagram illustrating a configuration of the optical base station  50 . The optical base station  50  includes an optical transmitter  51  and a beam control unit  52 . The same applies to the following embodiments. 
     The optical transmitter  51  uses a light source such as an LED that can be dimmed or toned. The light source may also be used for the purpose of lighting. The optical transmitter  51  converts the optical ID (modulated signal) from the optical base station control unit  42  into an optical signal having a predetermined wavelength, power, modulation scheme, or data rate. This embodiment will describe a case where the optical transmitter  51  sends out an optical signal (an optical signal modulated by the optical ID under the above conditions) so that the illuminance exceeds a certain level within a predetermined area  60 . 
     The beam control unit  52  controls the beam shape so that the optical signal from the optical transmitter  51  can reach the predetermined area  60 , and then sends out the optical signal into the space. If there are no obstacles that block the light, the optical signal reaches all the terminals  20  in the predetermined area  60 . 
       FIG.  15    is a diagram illustrating a configuration of the terminal  20 . The terminal  20  includes: 
     an optical sensor (optical sensor information acquisition unit  31 ) that receives an optical signal from the optical base station  50 ;   a calculation unit (threshold value calculation unit  38 ) that samples illuminance of the optical signal to acquire a sampling value, and calculates a threshold value for performing binary conversion of the optical signal based on transition of the sampling value; and   a determination unit (threshold value determination unit  37 ) that performs binary conversion of the optical signal based on the threshold value.   

     In addition, the terminal  20  further includes:
     a list (optical ID correspondence list  36 ) that describes correspondence between ID information and authentication information for starting RF wireless communication;   an analysis unit (optical ID analysis unit  35 ) that refers to the list for the ID information obtained through binary conversion of the optical signal by the determination unit, and acquires the corresponding authentication information; and   an RF transmission/reception unit  33  that transmits the authentication information acquired by the analysis unit to the RF base station  10  by RF wireless communication.   

     The optical sensor information acquisition unit  31  converts the optical signal from the optical transmitter  51  into an electrical signal to acquire it as a light illuminance value. The optical sensor information acquisition unit  31  is not limited to an optical receiver dedicated to optical wireless communication, and when the terminal  20  is a smartphone, the camera function may be used. 
     The threshold value calculation unit  38  calculates an optimum threshold value from the light illuminance value acquired by the optical sensor information acquisition unit  31 , and inputs the calculated threshold value to the threshold value determination unit  37 .  FIG.  16    is a diagram illustrating a process performed by the threshold value calculation unit  38 . In  FIG.  16   , p(k) is a sampling value of light illuminance (k is a sampling number), and p th  is the threshold value. As shown in  FIG.  16   , the threshold value calculation unit  38  periodically calculates the threshold value p th  based on sampling values of the illuminance of the optical signal. A threshold value calculation method will be described later. 
     The threshold value determination unit  37  binarizes (into 1/0) the optical signal received by the optical sensor information acquisition unit  31  using the threshold value calculated by the threshold value calculation unit  38 .  FIG.  17    is a diagram illustrating a process performed by the threshold value determination unit  37 . The threshold value determination unit  37  determines that S(k) = 1 when p(k) ≥ p th , and determines that S(k) = 0 when p(k) &lt; p th  to binarize the received signal. Here, S(k) is a determination value of 1 or 0 made by the threshold value determination unit  37  for the illuminance p(k) of the sampling number k. That is, since the threshold value calculation unit  38  adaptively changes the threshold value p th  according to the light illuminance, the threshold value determination unit  37   can accurately acquire information of the optical ID even when the position or light receiving angle of the terminal  20  changes and thereby the illuminance of the optical signal changes. 
     The optical ID analysis unit  35  extracts the optical ID based on the data binarized by the threshold value determination unit  37 .  FIG.  18    is a diagram illustrating a process performed by the optical ID analysis unit  35 . The optical ID analysis unit  35  compares the input binarized data with signal shapes of stored optical IDs, and extracts the optical ID with a signal shape having the maximum correlation. Subsequently, the optical ID analysis unit  35  collates the optical ID with the optical ID correspondence list  36 , and selects the corresponding connection operation/authentication information from the optical ID correspondence list  36 . The contents described in the optical ID correspondence list  36  are the same as those of the optical ID correspondence list  46  of the base station control device  40 . 
     The RF transmission/reception unit  33  transmits/receives RF wireless signals using a corresponding protocol. The corresponding protocol is Wi-Fi, LTE, etc. For example, Wi-Fi may support a plurality of wireless standards such as 2.4 GHz/5 GHz. The RF transmission/reception unit  33  transmits the connection operation/authentication information extracted by the optical ID analysis unit  35  to the RF base station  10 . 
     Threshold Value Calculation Method 
       FIG.  19    is a diagram illustrating a calculation method performed by the threshold value calculation unit  38 .  FIG.  17    is an image of calculating the threshold value p th   [k]  in determining the sample k. The threshold value calculation unit  38  calculates the threshold value p th   [k]  for determining sample k using n past sample values (p [k-n+1]  to p [k] ). Similarly, the threshold value calculation unit  38  calculates the threshold value p th   [k-1  for determining sample k-1 using n past sample values (p [k-n]  to p [k-1] ), a threshold value p th   [k-2]  for determining sample k-2 using n past sample values (p [k-n-1]  to p [k-2] ), and so on. 
     A specific threshold value calculation method will be described. Here, p [k]  is the illuminance value at the time of sample k, p th   [k]  is the threshold value at the time of sample k, n is the number of used data, and α is a smoothing constant. 
     (Example 1) This is an example in which the threshold value calculation unit  38  calculates the threshold value by a moving average method (Math.1) using the plurality of past sampling values. [Math.1] 
     
       
         
           
             
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     (Example 2) This is an example in which the threshold value calculation unit  38  calculates the threshold value by a weighted average method (Math.2) using the plurality of past sampling values. [Math.2] 
     
       
         
           
             
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     (Example 3) This is an example in which the threshold value calculation unit  38  calculates the threshold value by an exponential moving average method (Math.3) using the plurality of past sampling values. [Math.3] 
     
       
         
           
             
               
                 
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     Sixth Embodiment 2 
       FIG.  20    is a flowchart illustrating operation (communication method) of the terminal  20  described in the sixth embodiment 1. This communication method is a communication method in which communication between the terminal  20  and the RF base station  10  is performed by optical wireless communication and RF wireless communication, wherein the terminal  20  performs:
     receiving an optical signal from the optical base station  50  (step S 201 );   sampling illuminance of the optical signal to acquire a sampling value (step S 202 );   calculating a threshold value for performing binary conversion of the optical signal based on transition of the sampling value (step S 203 ); and   performing binary conversion of the optical signal based on the threshold value (step S 204 ).   

     In steps S 201  and S 202 , the optical sensor information acquisition unit  31  converts the optical signal from the optical base station  50  into an electrical signal, and samples a light illuminance value. 
     In step S 203 , the threshold value calculation unit  38  calculates an optimum threshold value from the light illuminance value (sampling value) acquired in step S 202 , and inputs the calculated threshold value to the threshold value determination unit  37 . As shown in  FIG.  16   , the threshold value calculation unit  38  periodically calculates the threshold value p th  based on sampling values of the illuminance of the optical signal. 
     In step S 204 , the threshold value determination unit  37  binarizes (into 1/0) the optical signal based on the sampling value obtained in steps S 201  and S 202  using the threshold value calculated in step S 203 . The threshold value determination unit  37  determines that S(k) = 1 when p(k) ≥ p th , and determines that S(k) = 0 when p(k) &lt; p th  to binarize the received signal. 
     Sixth Embodiment 3 
       FIG.  21    is a diagram illustrating a configuration of the terminal  20  of this embodiment. The terminal  20  of this embodiment includes the terminal  20  of sixth embodiment 1 and further includes a sensor information acquisition unit  32 . The sensor information acquisition unit  32  is a sensor that acquires physical information other than the illuminance of the optical signal. Then, the calculation unit (threshold value calculation unit  38 ) varies the smoothing constant α used in the exponential moving average method based on sensor information output from the sensor. 
     Here, the physical information other than the illuminance of the optical signal is information such as the acceleration of the terminal  20  from an acceleration sensor, the tilt of the terminal  20  from a gyro sensor, and the direction (orientation) of the terminal  20  from a magnetic sensor. 
     The sensor information acquisition unit  32  acquires the physical information and inputs it to the threshold value calculation unit  38 . The threshold value calculation unit  38  of this embodiment uses not only the illuminance of the optical signal but also the physical information when calculating the threshold value.  FIG.  22    is a diagram illustrating an example in which the threshold value calculation unit  38  sets the smoothing constant α using the physical information when calculating the threshold value by the exponential moving average. 
     The acceleration sensor acquires the acceleration of the terminal  20  for each of the three axes (x, y, z). The illuminance value of the background fluctuates as the terminal  20  moves. Therefore, by setting a smoothing constant α corresponding to the acceleration in Math. 3 as shown in  FIG.  22   , it is possible to increase the followability of the threshold value with respect to the illuminance value fluctuation. Specifically, when the illuminance change in the background is small (when the acceleration is small), the followability of the threshold value with respect to the illuminance becomes too high if α is set to be too large, so it is effective to take a moderately small value. On the other hand, when the illuminance change in the background is large (when the acceleration value is large), the followability of the threshold value with respect to the illuminance can be increased by setting α to be relatively large. 
     Note that  FIG.  22    is an example, and the setting value for α may be changed flexibly in consideration of an illuminance profile (directivity of the light source) for a lighting to be used. Further, the threshold value calculation unit  38  may use sensor information other than the acceleration sensor. 
     Seventh Embodiment 1 
     This embodiment will describe a configuration that can reduce the error rate even when the transmitting side and the receiving side are asynchronous. The terminal according to this embodiment samples the optical signal at a sufficiently finer granularity than the transmission pattern of 1/0, and performs majority determination using a plurality of sampling values. 
       FIG.  23    is a diagram illustrating a configuration of the terminal  20 . The terminal  20  includes: 
     an optical sensor (optical sensor information acquisition unit  31 ) that receives an optical signal from the optical base station  50 ;   a determination unit (threshold value determination unit  37 ) that samples illuminance of the optical signal at sampling points with a finer granularity than a bit pattern of the optical signal to acquire sampling values, and converts the optical signal into binary values (0/1) by comparing the sampling values with any threshold value; and   an estimation unit (optical ID estimation unit) that has a determination time which is shorter than the time of one bit of the bit pattern and longer than the time corresponding to the number of intervals between the sampling points included in one bit of the bit pattern, and estimates ID information included in the optical signal using the value of the majority of the binary values included in the determination time as the value of the bit.   

     The function and operation of the optical sensor information acquisition unit  31  are the same as those in the sixth embodiment. 
     In addition, the terminal  20  further includes:
     a list (optical ID correspondence list  36 ) that describes correspondence between ID information and authentication information for starting the RF wireless communication;   an analysis unit (optical ID analysis unit  35 ) that refers to the list for the ID information estimated by the estimation unit, and acquires the corresponding authentication information; and   an RF transmission/reception unit  33  that transmits the authentication information acquired by the analysis unit to the RF base station  10  by the RF wireless communication.   

     The function and operation of the RF transmission/reception unit  33  are the same as those in the sixth embodiment. 
     The threshold value determination unit  37  binarizes (into 1/0) the optical signal received by the optical sensor information acquisition unit  31  using the preset threshold value p th .  FIG.  24    and  FIG.  25    are diagrams illustrating a process performed by the threshold value determination unit  37 . First, a received signal is input from the sensor information acquisition unit  31  to the threshold value determination unit  37 . As shown in  FIG.  24   , the threshold value determination unit  37  samples this electrical signal at a finer granularity than the pattern of the optical ID. Here, “finer granularity than the pattern of the optical ID” means an interval shorter than the length (time) of each bit constituting the optical ID. In the example of  FIG.  24   , the granularity is an interval in which each bit constituting the optical ID can be sampled three times. In  FIG.  24   , p(k) is a sampling value and k is a sampling number. The sampling value may be a higher value or a lower value than the true value due to various factors. Here, attention will be paid to the sampling value p(k-2). 
     The threshold value determination unit  37  determines that S(k) = 1 when p(k) ≥ p th , and determines that S(k) = 0 when p(k) &lt; p th  to binarize the received signal. Here, S(k) is a determination value of 1 or 0 made by the threshold value determination unit  37  for the illuminance p(k) of the sampling number k.  FIG.  25    shows the sampling values in  FIG.  24    binarized with the threshold value p th . At the point A in  FIG.  25   , the sampling value p(k-2) should normally be determined as “0”, but it is erroneously determined as “1” due to the large influence of noise. 
     The optical ID estimation unit  34  estimates each bit value of the received signal by a majority determination scheme using a determination processing window.  FIG.  26    is a bit pattern of the received signal estimated by the optical ID estimation unit  34 . Since the optical ID estimation unit  34  has estimated the bit values by the majority determination scheme, the bit value of the bit  61  can be correctly acquired regardless of the influence of the point A. The majority determination scheme performed by the optical ID estimation unit  34  will be described later. 
     The optical ID analysis unit  35  extracts an optical ID from the bit pattern estimated by the threshold value calculation unit  34 .  FIG.  28    is a diagram illustrating a process performed by the optical ID analysis unit  35 . The optical ID analysis unit  35  compares the input bit pattern with the signal shapes of the stored optical IDs, and extracts the optical ID with a signal shape having the maximum correlation. Subsequently, the optical ID analysis unit  35  collates the optical ID with the optical ID correspondence list  36 , and selects the corresponding connection operation/authentication information from the optical ID correspondence list  36 . The contents described in the optical ID correspondence list  36  are the same as those of the optical ID correspondence list  46  of the base station control device  40 . 
     Majority Determination Scheme 
       FIG.  27    is a diagram illustrating a majority determination scheme performed by the optical ID estimation unit  34 .  FIG.  27    shows a state in which the transmitting side and the receiving side are out of synchronization.  FIG.  27   (A) and  FIG.  27   (B) show cases where all of the sampling points are not in an uncertain region,  FIG.  27   (C) shows a case where one of the sampling points is in an uncertain region. 
     The optical ID estimation unit  34  has a determination processing window  81  that is used when performing majority determination. The time of the determination processing window  81  (determination time) t h  is shorter than the time t bit  of one bit of the bit pattern and longer than the time (1/f s ×n) corresponding to the number n of intervals between the sampling points included in one bit of the bit pattern. In the example of  FIG.  27   , three sampling points are included in the time t bit  of one bit, so the number n of intervals between the sampling points is 2. Therefore, the determination time is as follows: 1/f s ×2&lt;t h &lt;t bit   
     The majority determination scheme is performed as follows. The optical ID estimation unit  34  performs majority determination for the binarized data to determine which determination value (0/1) is greater in number within the determination processing windows  81 . That is, when the number of observations of the determination value of “1” is 2 or 3 within the determination processing window  81 , “1” is assigned to the determination processing window  81  (bit), and when the number of observations of the determination value of “1” is 0 or 1 within the determination processing window  81 , “0” is assigned to the determination processing window  81  (bit). 
     By performing such majority determination, it is possible to avoid erroneous bit determination not only in the case where all of the sampling points are not in an uncertain region as in  FIG.  27   (A) and  FIG.  27   (B), but also in the case where one of the sampling points is in an uncertain region as in  FIG.  27   (C). 
     Such majority determination can avoid erroneous bit determination even when there is the erroneously determined sample A as shown in  FIG.  25   . 
     Seventh Embodiment 2 
       FIG.  29    is a flowchart illustrating operation (communication method) of the terminal  20  of this embodiment. This communication method is a communication method in which communication between the terminal  20  and the RF base station  10  is performed by optical wireless communication and RF wireless communication, wherein the terminal  20  performs: 
     receiving an optical signal from the optical base station  50  (step S 301 );   sampling illuminance of the optical signal at sampling points with a finer granularity than a bit pattern of the optical signal to acquire sampling values (step S 302 );   converting the optical signal into binary values by comparing the sampling values with any threshold value (step S 303 );   setting a determination time which is shorter than the time of one bit of the bit pattern and longer than the time corresponding to the number of intervals between the sampling points included in one bit of the bit pattern (step S 304 ); and   estimating ID information included in the optical signal using the value of the majority of the binary values included in the determination time as the value of the bit (step S 305 ).   

     In steps S 301  and S 302 , the optical sensor information acquisition unit  31  converts the optical signal from the optical base station  50  into an electrical signal, and samples a light illuminance value. 
     In step S 303 , the threshold value determination unit  37  binarizes (into 1/0) the optical signal based on the sampling value obtained in steps S 301  and S 302  using a predetermined threshold value. The threshold value determination unit  37  determines that S(k) = 1 when p(k) ≥ p th , and determines that S(k) = 0 when p(k) &lt; p th  to binarize the received signal. 
     In step S 304 , the optical ID estimation unit  34  sets the determination processing window  81  described in  FIG.  27   . 
     In step S 305 , the optical ID estimation unit  34  determines each bit value of the received signal from the binarized data using the majority determination scheme. 
       FIG.  30    is a flowchart illustrating operation (communication method) of the terminal  20  of this embodiment. In this communication method, this operation may be performed after the operation described in  FIG.  29   . In other words, this communication method further performs:
     referring to a list (optical ID correspondence list  36 ) that describes correspondence between ID information and authentication information for starting the RF wireless communication for the estimated ID information, and acquiring the corresponding authentication information (step S 306 ), and   transmitting the authentication information to the RF base station  10  by the RF wireless communication (step S 307 ).   

     The authentication information transmitted in step S 307  is received by the RF base station  10 . Then, the terminal  20  for which matching of the authentication information can be confirmed by the RF base station  10  is permitted to communicate with the upper network  30 . 
     Eighth Embodiment 
     This embodiment will describe a configuration for limiting the communication area and ensuring the safety of communication and the stability of communication. The optical base station  50  according to this embodiment generates a signal pattern corresponding to the optical ID, outputs an optical signal corresponding to the generated signal pattern, controls the beam shape of the output optical signal, and sends it out into the space. 
     The optical base station control unit  42  extracts the optical ID, and generates a signal pattern corresponding to the extracted optical ID. For example, when using the connection information and authentication information of the serial number of “1” shown in the optical ID correspondence list shown in  FIG.  2   , the optical base station control unit  42  generates “1010” as the signal pattern when extracting “1010” as the optical ID. It is not necessary that the signal pattern is also set to “1010” in response to the optical ID of “1010”, for example, a signal pattern such as “101011” may be used. In the case where the signal pattern is analog, for example, a repetitive signal pattern at a frequency of 1 Hz is used when the optical ID is “1010”. When the optical ID is “1000”, for example, a repetitive signal pattern at a frequency of 2 Hz is used. 
     The optical transmitter  51  outputs an optical signal with the signal pattern from the optical base station control unit  42 . When the owner of the wireless terminal device  20  has entered the area of the RF base station  10 , discomfort is not given to the person if the fluctuation in the optical signal sent out from the beam control unit  52  has such a modulation degree that it cannot be perceived by humans. According to Non-Patent Literature 1, the optical modulation degree is preferably 20% or less. If it is at this level of modulation degree, humans cannot perceive fluctuation in light intensity in a situation where they are concentrating on some work. More preferably, the optical modulation degree is 7% or less. If it is at this level of modulation degree, humans cannot perceive fluctuation in light intensity regardless of their activity states. 
     Examples of the optical ID generated by the optical base station control unit  42  and the optical signal output from an optical transmission circuit  13  are shown in  FIGS.  31  to  34   .  FIG.  31    shows an example in which the optical base station control unit  42  generates a signal pattern of “1010” which is a digital signal, and the optical transmitter  51  outputs an optical signal of “1010” as a digital signal. In this case, the optical signal output from the optical transmitter  51  and light from a lighting device other than the optical transmitter  51  are combined, and a configuration is made such that both types of light result in an optical modulation degree equal to or less than a predetermined percentage. 
       FIG.  32    shows an example in which the optical base station control unit  42  generates a signal pattern of “1010” which is an electrical signal, and the optical transmitter  51  outputs an optical signal of “1010” as a digital signal. The optical transmitter  51  is configured so that the optical signal of “1010” itself contains bias light and the optical modulation degree of the optical signal output from the optical transmitter  51  is equal to or less than a predetermined percentage. In this case, the optical transmitter  51  has both the function of outputting an optical signal and the function of lighting. 
       FIG.  33    shows an example in which the optical base station control unit  42  generates an analog repetitive signal pattern which is an electrical signal, and the optical transmitter  51  outputs a repetitive optical signal as an analog signal. In this case, the optical signal output from the optical transmitter  51  and light from a lighting device other than the optical transmitter  51  are combined. Here, a configuration is made such that the combined light results in an optical modulation degree equal to or less than a predetermined percentage. 
       FIG.  34    shows an example in which the optical base station control unit  42  generates an analog repetitive signal pattern which is an electrical signal, and the optical transmitter  51  outputs a repetitive optical signal as an analog signal. In  FIG.  34   , the optical transmitter  51  is configured so that the repetitive optical signal itself contains bias light and the optical modulation degree of the optical signal output from the optical transmitter  51  is equal to or less than a predetermined percentage. In this case, the optical transmitter  51  has both the function of outputting an optical signal and the function of lighting. 
     The optical transmitter  51  may have a configuration in which frequency modulation or wavelength modulation is used instead of intensity modulation. In this case, the frequency or wavelength of an optical signal of the optical transmission circuit is varied according to the intensity of the signal pattern. 
     The beam control unit  52  controls the beam shape of the optical signal from the optical transmitter  51 , and sends it out into the set space of the RF base station  10 . This is to set the communicable area of this wireless communication system. By utilizing the linearity of output of light waves, it is possible to limit the communication area and ensure the safety of communication. A reflector or a transparent refractive index body can be used for controlling the beam shape. 
       FIG.  35    is a diagram illustrating a configuration of the terminal  20 . The terminal  20  includes:
     an optical receiver  21  that receives an optical signal from the beam control unit  52  and converts it into a signal pattern;   a terminal-side optical ID list  22  that includes combination information of an optical ID and connection information and authentication information for wireless communication corresponding thereto;   an optical ID analysis circuit  23  that reproduces an optical ID from the signal pattern from the optical base station  50 , collates the optical ID with the terminal-side optical ID correspondence list  26 , and extracts the corresponding connection information /authentication information; and   a terminal-side RF transmitter  24  that transmits the authentication information from the optical ID analysis circuit  23  by predetermined RF wireless which is in accordance with the connection information from the optical ID analysis circuit  23 .   

     The optical receiver  21  receives an optical signal from the beam control unit  52  and converts it into a signal pattern of an electrical signal. For receiving light, it is sufficient to select a light receiving element according to the wavelength of light generated by the optical transmitter  51 . Only when the wireless terminal device  20  is in the communicable area set by the beam control unit  52 , the optical receiver  21  can receive an optical signal from the beam control unit  52 . Since a high-speed demodulation circuit is not required for receiving an optical signal, a wireless terminal device having a simple configuration can be realized. The optical receiver  21  receives the optical signal, and removes the bias component to extract the electrical signal pattern. When the optical signal is a digital signal of “1010”, for example, the optical signal is converted into an electrical signal pattern of “1010”. When the optical signal is an analog signal, for example, it is converted into an electrical signal pattern having a repetition frequency of 1 Hz. 
     The optical ID analysis circuit  23  reproduces an optical ID from the signal pattern from the optical receiver  21 , and collates the optical ID with the terminal-side optical ID correspondence list  26 . Next, the connection information and authentication information corresponding to the optical ID are extracted. For example, the optical ID analysis circuit  23  reproduces an optical ID of “1010” from the signal pattern of “1010” from the optical receiver  21 , and collates the optical ID of “1010” with the terminal-side optical ID correspondence list  26 . For example, the optical ID analysis circuit  23  reproduces an optical ID of “1010” from the signal pattern having a repetition frequency of 1 Hz from the optical receiver  21 , and collates the optical ID of “1010” with the terminal-side optical ID correspondence list  22 . The optical ID analysis circuit  23  extracts the connection information and authentication information of the serial number of “1” corresponding to the optical ID of “1010”. When the optical ID analysis circuit  23  collates the reproduced optical ID with the terminal-side optical ID correspondence list  22 , the optical ID that completely matches it may be detected, or the optical ID having the maximum correlation coefficient may be detected. When the wireless terminal device  20  is present in the areas of a plurality of RF base stations  10 , it will receive an optical signal from each of the plurality of optical base stations  50 , and reproduce a plurality of optical IDs. In this case, the priorities of the plurality of serial numbers are extracted from within the terminal-side optical ID correspondence list  22 , and the connection information and authentication information of the serial number having high priority are extracted. 
     The terminal-side RF transmitter  24  sets an RF wireless standard such as a predetermined wireless scheme, frequency, and channel in accordance with the connection information extracted by the optical ID analysis circuit  23 . Next, the terminal-side RF transmitter  24  transmits the authentication information extracted by the optical ID analysis circuit  23  by RF wireless set toward the RF base station  10 . The stability of communication of the wireless communication system according to the present disclosure can be ensured by utilizing the diffusivity of radio waves for transmission of the authentication information and information communication after authentication. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure can be applied to the information communication industry. 
     REFERENCE SIGNS LIST 
     
         
           10  RF base station 
           20  Terminal 
           21  Optical receiver 
           23  Optical ID analysis circuit 
           24  Terminal-side RF transmitter 
           30  Upper network 
           31  Optical sensor information acquisition unit 
           33  RF transmission/reception unit 
           34  Optical ID estimation unit 
           35  Optical ID analysis unit 
           37  Threshold value determination unit 
           38  Threshold value calculation unit 
           40  Base station control device 
           41  Authentication information integration control unit 
           42  Optical base station control unit 
           26 ,  36 ,  46  Optical ID correspondence list 
           50  Optical base station 
           51  Optical transmitter 
           52  Beam control unit