Patent Publication Number: US-2023142456-A1

Title: Transmission device, reception device, communication system, transmission method, reception method, and communication method

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a U.S. continuation application of PCT International Patent Application Number PCT/JP2017/036597 filed on Oct. 10, 2017, claiming the benefit of priority of U.S. Provisional Patent Application No. 62/407,003 filed on Oct. 12, 2016 and U.S. Provisional Patent Application No. 62/411,035 filed on Oct. 21, 2016. The entire disclosures of the above-identified applications, including the specifications, drawings and claims are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     The present disclosure relates to a transmission device, a reception device, a communication system, a transmission method, a reception method, and a communication method. 
     BACKGROUND 
     Devices can use global positioning system (GPS) as a method for obtaining location information. In such cases, devices receive a modulated signal transmitted from a satellite, and estimate location by positioning calculation. However, it is difficult for the device to estimate location information when the device is indoors, where reception of the radio waves transmitted by the GPS satellite is difficult. 
     For example, one method for overcoming such a problem is disclosed in non-patent literature (NPTL) 1. As disclosed in NPTL 1, there is a method by which the device uses radio waves transmitted from an access point in a wireless local area network (LAN) to estimate location. 
     CITATION LIST 
     Non-Patent Literature 
     
         
         [Non-Patent Literature 1] 
         Santosh Pandey, “NGP Use Case Template” IEEE802.11-16/0137 r4, 2016 Mar. 12 
       
    
     SUMMARY 
     Technical Problem 
     However, the performance of the transmission device and the reception device can be improved upon. 
     Solution to Problem 
     A transmission device according to one aspect of the present disclosure includes: a light source; and a transmitter that generates a modulated signal based on an input signal and transmits the modulated signal from the light source as visible light by changing a luminance of the light source in accordance with the modulated signal. The modulated signal includes a plurality of items of information related to service set identifiers (SSIDs) of a plurality of mutually different access points in a wireless local area network (LAN). 
     Additional benefits and advantages of the disclosed embodiments will be apparent from the Specification and Drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the Specification and Drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
     Advantageous Effects 
     According to the present disclosure, it is possible to improve upon the performance of a communication device and a reception device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       These and other objects, advantages and features of the disclosure will become apparent from the following description thereof taken in conjunction with the accompanying drawings that illustrate a specific embodiment of the present disclosure. 
         FIG.  1    illustrates one example of a configuration of a device and a terminal according to Embodiment 1. 
         FIG.  2    illustrates one example of a frame configuration transmitted in a modulated signal transmitted by a first device according to Embodiment 1. 
         FIG.  3    illustrates one example including a plurality of devices according to Embodiment 2. 
         FIG.  4    illustrates one example of a configuration of a device and a terminal according to Embodiment 3. 
         FIG.  5    illustrates one detailed example of a screen of a display according to Embodiment 3. 
         FIG.  6    illustrates one example of a frame configuration of a modulated signal transmitted by a first device according to Embodiment 3. 
         FIG.  7    illustrates one example of a frame configuration of a modulated signal transmitted by a base station according to Embodiments 3 through 6. 
         FIG.  8    is a flow chart of one example of processes performed by a device, terminal, and base station according to Embodiment 3. 
         FIG.  9    illustrates one example of a map according to Embodiment 3. 
         FIG.  10    illustrates one example of a configuration of a communication system according to Embodiment 4. 
         FIG.  11    illustrates one example of a frame configuration of a modulated signal transmitted by a second device according to Embodiment 4. 
         FIG.  12    illustrates one example of a frame configuration of a modulated signal transmitted by a radio device included in a terminal according to Embodiment 4. 
         FIG.  13    is a flow chart of one example of processes performed by a device, terminal, and base station according to Embodiment 4. 
         FIG.  14    illustrates one example of a configuration of devices, a terminal, and a base station according to Embodiment 5. 
         FIG.  15    illustrates one example of a frame configuration of a modulated signal transmitted by a third device according to Embodiment 5. 
         FIG.  16    illustrates one example of a frame configuration of a modulated signal transmitted by a fourth device according to Embodiment 5. 
         FIG.  17    is a flow chart of a first example of processes performed by a third device, a fourth device, a terminal, and a base station according to Embodiment 5. 
         FIG.  18    is a flow chart of a second example of processes performed by a third device, a fourth device, a terminal, and a base station according to Embodiment 5. 
         FIG.  19    illustrates a space in which a third device, a fourth device, a terminal, and a base station according to Embodiment 5 are disposed. 
         FIG.  20    illustrates one example of a configuration of a communication system according to Embodiment 6. 
         FIG.  21    is a flow chart of one example of processes performed by an element related to, for example, an LED, a terminal, and a radio device included in a base station according to Embodiment 6. 
         FIG.  22    illustrates one example of a configuration of a communication system according to Embodiment 7. 
         FIG.  23    illustrates one example of a frame configuration of a modulated signal transmitted by a device according to Embodiment 7. 
         FIG.  24    illustrates one example of another frame configuration of a modulated signal transmitted by a device according to Embodiment 7. 
         FIG.  25    illustrates one example of another frame configuration of a modulated signal transmitted by a device according to Embodiment 7. 
         FIG.  26    illustrates one example of transmission method using a device according to Embodiment 7. 
         FIG.  27    illustrates one example of an area in which devices and base stations are disposed according to Embodiment 7. 
         FIG.  28    is a flow chart of one example of processes performed by a device, terminal, and base station according to Embodiment 7. 
         FIG.  29    illustrates one example of an automobile including a light source. 
         FIG.  30    illustrates one example of an automobile including a light receiver. 
         FIG.  31    illustrates another example of a communication method. 
         FIG.  32    illustrates one example of line scan sampling. 
         FIG.  33    illustrates an example of a captured image in which a striped pattern does not appear. 
         FIG.  34    illustrates an example of a captured image in which a striped pattern appears. 
         FIG.  35 A  illustrates one example of a 4 PPM modulation scheme. 
         FIG.  35 B  illustrates one example of a Manchester coding scheme. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Underlying Knowledge Forming Basis of the Present Disclosure 
     Devices can use global positioning system (GPS) as a method for obtaining location information. In such cases, devices receive a modulated signal transmitted from a satellite, and estimate location by positioning calculation. However, it is difficult for the device to estimate location information when the device is indoors, where reception of the radio waves transmitted by the GPS satellite is difficult. 
     For example, one method for overcoming such a problem is disclosed in NPTL 1 described above. As disclosed in NPTL 1, there is a method by which the device uses radio waves transmitted from an access point in a wireless local area network (LAN) to estimate location. However, since it is not easy to know the service set identifier (SSID) of an access point that can be securely accessed, when the device attempts to obtain location information, there is a possibility that the device will connect to an insecure SSID access point, leading to the possibility of a compromise of information. 
     In view of this, in the present disclosure, a (optical) modulated signal including information related to a location is transmitted, for example, from, for example, a light emitting diode (LED) lamp, light source, or light that is provided in a room and emits visible light. For example, a terminal (device) receives a (optical) modulated signal via, for example, an image sensor such as a complementary metal oxide semiconductor (CMOS) or organic photoconductive film (OPF) CMOS (i.e., organic CMOS) image sensor, performs demodulation and such, and obtains at least the information related to a location. With this, the terminal can achieve the advantageous effect of being able to securely obtain information related to a location. 
     Alternatively, in the present disclosure, for example, a (optical) modulated signal including information related to an SSID is transmitted, for example, from, for example, a light emitting diode (LED) lamp, light source, or light that is provided in a room and emits visible light. A terminal (device) receives a (optical) modulated signal via, for example, an image sensor such as a complementary metal oxide semiconductor (CMOS) or organic photoconductive film (OPF) CMOS (i.e., organic CMOS) image sensor, performs demodulation and such, and obtains at least the information related to the SSID. With this, the terminal can achieve the advantageous effect of being able to securely connect to an access point. 
     Embodiment 1 
       FIG.  1    illustrates one example of configurations of device  100  including, for example, a light emitting diode (LED) light source, lamp, light source, and/or light that emits visible light, and terminal  150 . Device  100  includes, for example, a light emitting diode (LED) lamp, light source, and/or light that emits visible light. Note that this device is referred to as a “first device”. 
     Transmitter  102  receives an input of information related to a location or information  101  related to a position. Moreover, transmitter  102  may receive an input of information  105  related to a time. Moreover, transmitter  102  may receive an input of both (i) the information related to a location or information  101  related to a position and (ii) information  105  related to a time. 
     Transmitter  102  receives an input of information related to a location or information  101  related to a position and/or information  105  related to a time, and based on the one or more input signals, generates a (optical) modulated signal, and outputs modulated signal  103 . For example, modulated signal  103  is transmitted from light source  104 . 
     Next, examples of the information related to a location or information  101  related to a position will be given. 
     Example 1 
     Information related to a location or information  101  related to a position may be information indicating the latitude and/or longitude of a location or position. For example, the information related to a location or information  101  related to a position may be information indicating “45 degrees north latitude, 135 degrees east longitude”. 
     Example 2 
     Information related to a location or information  101  related to a position may be information indicating an address. For example, the information related to a location or information  101  related to a position may be information indicating “1-1-1 XYZ-machi, Chiyoda-ku, Tokyo-to”. 
     Example 3 
     Information related to a location or information  101  related to a position may be information indicating a building or facility, for example. For example, the information related to a location or information  101  related to a position may be information indicating “Tokyo Tower”. 
     Example 4 
     Information related to a location or information  101  related to a position may be information indicating a fixed location or position of something at a building or facility, for example. 
     For example, assume there are five parking spaces for automobiles in a parking lot. Assume the first through fifth parking spaces are named A- 1  through A- 5 , respectively. In this example, the information related to a location or information  101  related to a position may be information indicating, for example, “A- 3 ”. 
     This example is not limited to only parking spaces in a parking lot. 
     Information related to a location or information  101  related to a position may be for example, information related to a section, a seat, a store, a facility, etc., at, for example, a concert facility, a stadium such as a baseball, soccer, or tennis stadium, an airplane, an airport lounge, a railway, a station, etc. 
     Note that methods for configuring the information related to a location or information  101  related to a position are not limited to the above examples. 
     Terminal  150  receives the modulated signal transmitted by first device  100 . 
     Light receiver  151  is, for example, a CMOS or organic CMOS image sensor. Light receiver  151  receives light including the modulated signal output from the first device, and outputs reception signal  152 . Receiver  153  receives an input of reception signal  152 , performs processing such as demodulation and error correction decoding on the modulated signal included in the reception signal, and outputs reception data  154 . 
     Note that reception signal  152  output from light receiver  151  may be a signal including information on an image or moving picture obtained by the image sensor, and may be an output signal from an element that performs photo-electric conversion (an element that converts light into an electric signal). In the following description, when a reception-side device is described as receiving a modulated signal without giving any further details on the processes performed by light receiver  151 , this means that the reception-side device obtains a signal of an image or moving picture and a modulated signal for transmitting information by photo-electric conversion (converting light into an electric signal) of light including the modulated signal by light receiver  151 . However, the method described above used to receive the modulated signal by the reception-side device is merely one non-limiting example. 
     Data analyzer  155  receives an input of reception data  154 , estimates, for example, the location or position of terminal  150  from reception data  154 , and outputs information  156  including at least information on the location or position of terminal  150 . 
     Display  157  receives an input of information  156 , and displays information related to the location or position of terminal  150  based on the location or position of terminal  150  included in information  156 . 
       FIG.  2    illustrates one example of a configuration of a frame transmitted in a modulated signal transmitted by first device  100 . In  FIG.  2   , time is represented on the horizontal axis. For example, the first device transmits preamble  201  and then transmits control information symbol  202 , symbol  203  related to location information or position information, and symbol  204  related to time information. 
     Here, preamble  201  is a symbol for terminal  150 , which receives the modulated signal transmitted by first device  100 , to perform, for example, signal detection, temporal synchronization, and/or frame synchronization. 
     Control information symbol  202  is, for example, a symbol including data on, for example, the configuration method of the modulated signal, the error correction encoding scheme used, and/or the frame configuration method. 
     Symbol  203  related to location information or position information is a symbol including information related to a location or information related to a position illustrated in  FIG.  1   . 
     The frame may include symbols other than symbols  201 ,  202 , and  203 . For example, as illustrated in  FIG.  2   , the frame may include symbol  204  related to time information. Symbol  204  related to time information includes, for example, information indicating a time of transmission of the modulated signal by the first device. Note that the frame configuration of the modulated signal transmitted by the first device is not limited to the frame configuration illustrated in  FIG.  2   . Moreover, the symbols included in the modulated signal are not limited to the configuration illustrated in  FIG.  2    (the modulated signal may include symbols including other data and/or information). 
     Next, the advantageous effects achieved when the first device transmits a modulated signal and the terminal receives the modulated signal, as described with reference to  FIG.  1    and  FIG.  2   , will be described. 
     Since the first device transmits the modulated signal via visible light, a terminal capable of receiving the modulated signal is not in a location significantly far from the location of the first device. Accordingly, by the terminal obtaining the location or position information transmitted by the first device, the terminal can achieve an advantageous effect whereby it is possible to easily (i.e., without having to perform complicated signal processing) obtain accurate position information. Moreover, when the first device is disposed in a place where reception of satellite radio waves from a GPS satellite is difficult, it is possible to achieve an advantageous effect whereby it is possible for the terminal to securely obtain accurate position information even in locations in which reception of radio waves from a GPS satellite is difficult, by the terminal receiving the modulated signal transmitted by the first device. 
     Embodiment 2 
     In this embodiment, a configuration in which a plurality of the first devices described in Embodiment 1 are provided will be described. 
     In this embodiment, for example, as illustrated in  FIG.  3   , first device # 1   301 - 1  having the same configuration as first device  100  illustrated in  FIG.  1    transmits a modulated signal, and terminal  302  receives the modulated signal. Terminal  302  receives the modulated signal transmitted by first device # 1   301 - 1 , and obtains, for example, information related to first location or position # 1  and information related to first time # 1 . 
     Similarly, first device # 2   301 - 2  having the same configuration as first device  100  illustrated in  FIG.  1    transmits a modulated signal, and terminal  302  receives the modulated signal. Terminal  302  receives the modulated signal transmitted by first device # 2   301 - 2 , and obtains, for example, information related to first location or position # 2  and information related to first time # 2 . 
     With this, terminal  302  can know the distance between first device # 1   301 - 1  and first device # 2   301 - 2  illustrated in  FIG.  3    from the information related to first location or position # 1  and the information related to first location or position # 2 . Moreover, terminal  302  can know the distance between terminal  302  and first device # 1   301 - 1  based on the information related to first time # 1 , and, for example, the time at which the terminal receives the modulated signal transmitted by first device # 1   301 - 1 . Similarly, terminal  302  can know the distance between terminal  302  and first device # 2   301 - 2  based on the information related to first time # 2 , and, for example, the time at which the terminal receives the modulated signal transmitted by first device # 2   301 - 2 . 
     Moreover, terminal  302  knows the position of first device # 1  from the information related to the first location or position # 1 . Moreover, terminal  302  knows the position of first device # 2  from the information related to the first location or position # 2 . Terminal  302  knows the geometry of the triangle formed by first device # 1   301 - 1 , first device # 2   301 - 2 , and terminal  302  from the distance between first device # 1   301 - 1  and first device # 2   301 - 2 , the distance between first device # 1   301 - 1  and the terminal, and the distance between first device # 2   301 - 2  and the terminal. 
     Accordingly, terminal  302  can accurately calculate and obtain the position of terminal  302  from the position of the first device # 1 , the position of the first device # 2 , and the geometry of the triangle formed by first device # 1   301 - 1 , first device # 2   301 - 2 , and terminal  302 . 
     However, the geodetic measurement method used by terminal  302  to obtain the location or position information is not limited to the method described above; any geodetic measurement method may be used. Examines of geodetic measurement methods include triangulation, traverse calculation, leveling, etc. 
     As described above, the terminal can obtain the above-described information from a plurality of devices including light sources that transmit location information, and as a result, it is possible to achieve an advantageous effect whereby the terminal can accurately estimate position. Moreover, as described in Embodiment 1, when the device including a light source that transmits location information is disposed in a place where reception of satellite radio waves from a GPS satellite is difficult, it is possible to achieve an advantageous effect whereby it is possible for the terminal to securely obtain accurate position information even in locations in which reception of radio waves from a GPS satellite is difficult, by the terminal receiving the modulated signal transmitted by the device. 
     Note that in the above example, the terminal receives modulated signals transmitted by two devices, but an embodiment in which the terminal receives modulated signals transmitted by more than two devices can be implemented in the same manner. Note that the more devices there are, the more accurately the terminal can calculate the position information, so from this viewpoint, more devices are more beneficial. 
     Embodiment 3 
       FIG.  4    illustrates one example of configurations of; a device including, for example, an LED light source, lamp, light source, and/or light that emits visible light; a terminal; and, for example, a base station that communicates with the terminal. Device  400  in  FIG.  4    includes, for example, an LED lamp, light source, and/or light that emits visible light. Note that the device is referred to as a “first device”. In first device  400  in  FIG.  4   , elements that operate the same as in first device  100  in  FIG.  1    share like reference marks. 
     Terminal  450  in  FIG.  4    indicates the configuration of a terminal, and elements that are the same as in  FIG.  1    share like reference marks. 
     In first device  400  in  FIG.  4   , transmitter  102  receives inputs of, for example, information related to a location or information  101  related to a position, information  401 - 1  related to a service set identifier (SSID), and information  401 - 2  related to an access destination. Moreover, transmitter  102  may receive an input of information  105  related to a time. 
     Transmitter  102  receives inputs of information related to a location or information  101  related to a position, information  401 - 1  related to an SSID, information  401 - 2  related to an access destination, and/or information  105  related to a time, and based on the one or more input signals, generates a (optical) modulated signal, and outputs modulated signal  103 . For example, modulated signal  103  is transmitted from light source  104 . 
     Note that since examples of the information related to a location or information  101  related to a position are the same as described in Embodiment 1, repeated description will be omitted. 
     Next, information  401 - 1  related to an SSID and information  401 - 2  related to an access destination will be described. 
     First, information  401 - 1  related to an SSID will be described. 
     Information  401 - 1  related to an SSID is information indicating the SSID of the base station (or access point (AP))  470  illustrated in  FIG.  4   . When processing is performed for determining whether or not the SSID notified via the optical signal is the SSID of a secure base station, first device  400  can provide access to base station  470 , which is a secure access destination for terminal  450 . With this, terminal  450  in  FIG.  4    can achieve the advantageous effect of being able to securely obtain information from base station (or AP)  470 . On the other hand, first device  400  can restrict the terminals that access base station  470  to terminals in a space in which it is possible to receive optical signals transmitted (emitted) by first device  400 . 
     Note that when terminal  450  receives an optical signal transmitted via a predetermined scheme, it may be determined that the notified SSID is the SSID of a secure base station, and, alternatively, processing for determining whether the SSID is secure or not may be performed. For example, first device  400  may transmit a predetermined identifier in an optical signal, and the terminal may determine whether the notified SSID is the SSID of a secure base station or not based on the received identifier. Alternatively, the processing for determining whether the base station is secure or not may be omitted by terminal  450 , and instead, the user may select a first device  400  that is highly secure utilizing the characteristics of the visible light, and the SSID of the highly secure base station may be obtained by terminal  450  receiving the optical signal from first device  400 . 
     Note that although  FIG.  4    only illustrates base station (or AP)  470 , for example, when there is a base station (or AP) other than base station (or AP)  470 , terminal  450  in  FIG.  4    accesses base station (or AP)  470  to obtain information. 
     Information  401 - 2  related to an access destination is information related to an access destination for terminal  450  in  FIG.  4    to access base station (or AP)  470  and then obtain information (note that a specific example of operations will be given later). 
     Terminal  450  in  FIG.  4    receives the modulated signal transmitted by first device  400 . Note that in terminal  450  in  FIG.  4   , operations that are the same as in terminal  150  in  FIG.  1    share like reference marks. 
     Light receiver  151  included in terminal  450 , examples of which include an image sensor such as a CMOS or organic CMOS image sensor, receives the modulated signal transmitted by first device  400 . Receiver  153  receives an input of reception signal  152  received by light receiver  151 , performs processing such as demodulation and error correction decoding on the reception signal, and outputs reception data  154 . 
     Data analyzer  155  receives an input of reception data  154 , estimates, for example, the location or position of the terminal from reception data  154 , and outputs information  156  including at least information on the location or position of the terminal, information  451  related to an SSID, and information  452  related to an access destination. 
     Display  157  receives inputs of information  156  including information on the location or position of the terminal, information  451  related to an SSID, and information  452  related to an access destination, and, for example, displays the location or position of the terminal, the SSID of a communication partner that radio device  453  included in terminal  450  accesses, and the access destination (this display is referred to as a “first display”). 
     For example, after the first display, radio device  453  included in terminal  450  in  FIG.  4    receives inputs of information  451  related to an SSID and information  452  related to an access destination. Then, radio device  453  included in terminal  450  in  FIG.  4    connects to the communication partner by using, for example, radio waves, based on information  451  related to an SSID. Note that in the example illustrated in  FIG.  4   , radio device  453  included in terminal  450  in  FIG.  4    connects to base station  470 . 
     Then, based on information  452  related to an access destination, radio device  453  included in terminal  450  in  FIG.  4    generates a modulated signal from data including the information related to an access destination, and transmits the generated modulated signal to base station  470  over, for example, radio waves. 
     Base station (or AP)  470 , which is the communication partner of the terminal in  FIG.  4   , receives the modulated signal transmitted by radio device  453  included in terminal  450  in  FIG.  4   . Then, base station (or AP)  470  performs processing such as demodulation and error correction decoding on the received modulated signal, outputs reception data  471  including information on the access destination transmitted by terminal  450  in  FIG.  4   , and based on the information on the access destination, base station (or AP)  470  accesses a desired access destination over a network and, for example, obtains desired information  472  from the access destination. 
     Then, base station  470  receives an input of the desired information  472 , generates a modulated signal from the desired information  472 , and transmits the modulated signal to terminal  450  in  FIG.  4    over, for example, radio waves. 
     Radio device  453  in terminal  450  in  FIG.  4    receives the modulated signal transmitted by base station  470 , performs processing such as demodulation and error correction decoding, and obtains the desired information  472 . 
     For example, assume the desired information  472  is information related to a section, a seat, a store, a facility, etc., on/at, for example, a map, a map or floor guide for a building, a map or floor guide for a facility, a map or floor guide for a parking lot, a concert facility, a stadium such as a baseball, soccer, or tennis stadium, an airplane, an airport lounge, a railway, a station, etc. 
     Display  157  receives inputs of the desired information  472 , information  156  including, at least information on the location or position of the terminal, information  451  related to an SSID, and after the first display, displays a result of mapping the position of the terminal on the display of the map, floor guide, facility information, seat information, or store information, based on the desired information  472  and information  156  including at least information on the location or position of the terminal. 
     A specific example will be given.  FIG.  5    illustrates one example of a display displayed by display  157 . The display in  FIG.  5    indicates that this is the third floor of a building. Each of A- 1 , A- 2 , A- 3 , A- 4 , A- 21 , A- 22 , A- 23 , and A- 24  indicates a position of a parking space for an automobile. B- 1  and B- 2  indicate positions of elevators. The information on this map is the desired information  472 . As illustrated in  FIG.  5   , the “current location” is mapped on the map. Here, the current location is information obtained from information  156  including at least information on the location or position of the terminal. 
       FIG.  6    illustrates one example of a configuration of a frame of a modulated signal transmitted by first device  400  in  FIG.  4   . In  FIG.  6   , time is represented on the horizontal axis, and symbols that transmit the same information as indicated in  FIG.  2    share like reference marks. Accordingly, repeated description will be omitted 
     First device  400  transmits symbol  600 - 1  related to an SSID and symbol  600 - 2  related to an access destination in addition to preamble  201 , control information symbol  202 , symbol  203  related to location information or position information, and symbol  204  related to time information. 
     Note that symbol  600 - 1  related to an SSID is a symbol for transmitting information  401 - 1  related to an SSID illustrated in  FIG.  4   , and symbol  600 - 2  related to an access destination is a symbol for transmitting information  401 - 2  related to an access destination in  FIG.  4   . Note that in the frame illustrated in  FIG.  6   , symbols other than the symbols shown in  FIG.  6    may be included. Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  6   . 
       FIG.  7    illustrates one example of a frame configuration of a modulated signal transmitted by base station  470  illustrated in  FIG.  4   . Time is represented on the horizontal axis. As illustrated in  FIG.  7   , base station  470  transmits, for example, preamble  701 , and then transmits control information symbol  702  and information symbol  703 . 
     Here, preamble  701  is a symbol for the terminal, which receives the modulated signal transmitted by base station  470 , to perform, for example, signal detection, temporal synchronization, frame synchronization, and/or frequency offset estimation. 
     Control information symbol  702  includes, for example, information related to the error correction encoding scheme method and/or demodulation scheme used in the generation of the modulated signal, and information related to frame configuration. 
     Information symbol  703  is a symbol for transmitting information. Note that in this embodiment, information symbol  703  is a symbol for transmitting the desired information  472  described above. 
     Note that base station  470  in  FIG.  4    may transmit a frame including symbols other than the symbols illustrated in  FIG.  7    (for example, a frame including a pilot symbol (reference symbol) midway through the information symbol). Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  7   . In  FIG.  7   , a plurality of symbols may be present along the frequency axis, that is to say, symbols may be present on a plurality of frequencies (a plurality of carriers). 
     Moreover, for example, a modulated signal that has the frame configuration illustrated in  FIG.  6    and is transmitted by the first device being transmitted at a regular timing, e.g., repeatedly transmitted is conceivable. This makes it possible for a plurality of terminals to implement the operations described above. 
       FIG.  8    is a flow chart illustrating one example of processes implemented by first device  400 , terminal  450 , and base station (or AP)  470  illustrated in  FIG.  4   . 
     First, as  801  in  FIG.  8    illustrates, first device  400  in  FIG.  4    transmits a modulated signal having the frame configuration illustrated in  FIG.  6   . 
     Then, as  802  in  FIG.  8    illustrates, the modulated signal transmitted by first device  400  in  FIG.  4    is received, and terminal  450  in  FIG.  4    performs terminal location or position estimation. 
     Likewise, as  803  in  FIG.  8    illustrates, the modulated signal transmitted by first device  400  in  FIG.  4    is received, and terminal  450  in  FIG.  4    knows the SSID of the base station to be accessed by the terminal. 
     Then, as  804  in  FIG.  8    illustrates, terminal  450  in  FIG.  4    transmits, to base station (or AP)  470  in  FIG.  4   , a modulated signal including data including information related to an access destination for obtaining information, such as a map, using, for example, radio waves. 
     As  805  in  FIG.  8    illustrates, base station (or AP)  470  receives the modulated signal transmitted by terminal  450 , obtains the information on the access destination, accesses the desired access destination and obtains desired information, such as a map, over a network. 
     Then, as  806  in  FIG.  8    illustrates, base station (or AP)  470  in  FIG.  4    transmits a modulated signal including desired information, such as the obtained map, to terminal  450  using, for example, radio waves. 
     As  807  in  FIG.  8    illustrates, terminal  450  receives the modulated signal transmitted by base station (or AP)  470  and obtains (for example) the map. Terminal  450  displays a screen such as the one illustrated in  FIG.  5   , based on information on (for example) the map and the location or position of the terminal already obtained. 
     Next, an example of operations performed when a plurality of first devices  400  and base station (or AP)  470  are disposed in the location illustrated in  FIG.  5     
     Similar to  FIG.  5   ,  FIG.  9    illustrates a map of a given location. 
     As described with reference to  FIG.  5   ,  FIG.  9    is a map of the third floor of a building. Each of A- 1 , A- 2 , A- 3 , A- 4 , A- 21 , A- 22 , A- 23 , and A- 24  indicates a position of a parking space for an automobile, and B- 1  and B- 2  indicate elevators. 
     The position of circle  901 - 1  in  FIG.  9    indicates the location of a first device having the same configuration as device  100  illustrated in  FIG.  4   . A first device having the same configuration as device  100  in  FIG.  4    at the position of  901 - 1  is referred to as “first device # 1 ”. The first device # 1  holds and transmits, as information related to a location or information related to a position, information labeled “A- 1 ”. 
     The position of circle  901 - 2  in  FIG.  9    indicates the location of a first device having the same configuration as device  100  illustrated in  FIG.  4   . A first device having the same configuration as device  100  in  FIG.  4    and located at the position of  901 - 2  is referred to as “first device # 2 ”. The first device # 2  holds and transmits, as information related to a location or information related to a position, information labeled “A- 2 ”. 
     The position of circle  901 - 3  in  FIG.  9    indicates the location of a first device having the same configuration as device  100  illustrated in  FIG.  4   . A first device having the same configuration as device  100  in  FIG.  4    and located at the position of  901 - 3  is referred to as “first device # 3 ”. The first device # 3  holds and transmits, as information related to a location or information related to a position, information labeled “A- 3 ”. 
     The position of circle  901 - 4  in  FIG.  9    indicates the location of a first device having the same configuration as device  100  illustrated in  FIG.  4   . A first device having the same configuration as device  100  in  FIG.  4    and located at the position of  901 - 4  is referred to as “first device # 4 ”. The first device # 4  holds and transmits, as information related to a location or information related to a position, information labeled “A- 4 ”. 
     The position of circle  901 - 21  in  FIG.  9    indicates the location of a first device having the same configuration as device  100  illustrated in  FIG.  4   . A first device having the same configuration as device  100  in  FIG.  4    and located at the position of  901 - 21  is referred to as “first device # 21 ”. The first device # 21  holds and transmits, as information related to a location or information related to a position, information labeled “A- 21 ”. 
     The position of circle  901 - 22  in  FIG.  9    indicates the location of a first device having the same configuration as device  100  illustrated in  FIG.  4   . A first device having the same configuration as device  100  in  FIG.  4    and located at the position of  901 - 22  is referred to as “first device # 22 ”. The first device # 22  holds and transmits, as information related to a location or information related to a position, information labeled “A- 22 ”. 
     The position of circle  901 - 23  in  FIG.  9    indicates the location of a first device having the same configuration as device  100  illustrated in  FIG.  4   . A first device having the same configuration as device  100  in  FIG.  4    and located at the position of  901 - 23  is referred to as “first device # 23 ”. The first device # 23  holds and transmits, as information related to a location or information related to a position, information labeled “A- 23 ”. 
     The position of circle  901 - 24  in  FIG.  9    indicates the location of a first device having the same configuration as first device  400  illustrated in  FIG.  4   . A first device having the same configuration as first device  400  in  FIG.  4    and located at the position of  901 - 24  is referred to as “first device # 24 ”. The first device # 24  holds and transmits, as information related to a location or information related to a position, information labeled “A- 24 ”. 
     The position of double circle  902  in  FIG.  9    indicates the location of a base station (or AP) having the same configuration as base station  470  illustrated in  FIG.  4   . Here, the SSID of a base station (or AP) having the same configuration as base station  470  in  FIG.  4    and located at the position of  902  is “abcdef”. 
     When the terminals located around the positions illustrated in the map in  FIG.  9    communicate wirelessly, the terminals may access a base station (or AP) having the same configuration as base station  470  in  FIG.  4    and located at position  902  in  FIG.  9   . Accordingly, the first device # 1  located at  901 - 1  in  FIG.  9    transmits “abcdef” as information on an SSID (see  401 - 1  in  FIG.  4   ). 
     Similarly, the first device # 2  located at  901 - 2  in  FIG.  9    transmits “abcdef” as information on an SSID (see  400 - 1  in  FIG.  4   ). 
     The first device # 3  located at  901 - 3  in  FIG.  9    transmits “abcdef” as information on an SSID (see  401 - 1  in  FIG.  4   ). 
     The first device # 4  located at  901 - 4  in  FIG.  9    transmits “abcdef” as information on an SSID (see  401 - 1  in  FIG.  4   ). 
     The first device # 21  located at  901 - 21  in  FIG.  9    transmits “abcdef” as information on an SSID (see  401 - 1  in  FIG.  4   ). 
     The first device # 22  located at  901 - 22  in  FIG.  9    transmits “abcdef” as information on an SSID (see  401 - 1  in  FIG.  4   ). 
     The first device # 23  located at  901 - 23  in  FIG.  9    transmits “abcdef” as information on an SSID (see  401 - 1  in  FIG.  4   ). 
     The first device # 24  located at  901 - 24  in  FIG.  9    transmits “abcdef” as information on an SSID (see  401 - 1  in  FIG.  4   ). 
     Next, a specific example of operations will be given. 
     Assume a terminal having the same configuration as terminal  450  in  FIG.  4    is positioned at  903 - 1  in  FIG.  9   . The terminal receives a modulated signal transmitted by the first device # 4  positioned at  901 - 4  in  FIG.  9   , and receives position information referred to as “A- 4 ”. Moreover, the terminal obtains information on the SSID “abcdef”, and as a result, the terminal accesses a base station (or AP) that has the same configuration as base station  470  in  FIG.  4    and is positioned at  902  in  FIG.  9   , whereby the terminal obtains information, such as a map, from the base station (or AP) that has the same configuration as base station  470  in  FIG.  4    and is positioned at  902  in  FIG.  9   . Then, the terminal displays map information and position information (see  FIG.  5   ; however,  FIG.  5    is only one, non-limiting example). 
     Assume a terminal having the same configuration as terminal  450  in  FIG.  4    is positioned at  903 - 2  in  FIG.  9   . The terminal receives a modulated signal transmitted by the first device # 22  positioned at  901 - 22  in  FIG.  9   , and receives position information referred to as “A- 22 ”. Moreover, the terminal obtains information on the SSID “abcdef”, and as a result, the terminal accesses a base station (or AP) that has the same configuration as base station  470  in  FIG.  4    and is positioned at  902  in  FIG.  9   , whereby the terminal obtains information, such as a map, from the base station (or AP) that has the same configuration as base station  470  in  FIG.  4    and is positioned at  902  in  FIG.  9   . Then, the terminal displays map information and position information (see  FIG.  5   ; however,  FIG.  5    is only one, non-limiting example). 
     Note that the terminal stores a map (surrounding information) and position information, such as those illustrated in  FIG.  5   , in storage included in the terminal, and when the user of the terminal needs it, may make more use of the map (surrounding information) and position information by reading the stored information. 
     As described above, since the first device transmits the modulated signal via visible light, a terminal capable of receiving the modulated signal is limited to being located within a region capable of receiving the signal light from the position of the first device. Accordingly, by the terminal obtaining the location or position information transmitted by the first device, the terminal can achieve an advantageous effect whereby it is possible to easily (i.e., without having to perform complicated signal processing) obtain accurate position information. Moreover, when the first device is disposed in a place where reception of satellite radio waves from a GPS satellite is difficult, it is possible to achieve an advantageous effect whereby it is possible for the terminal to securely obtain accurate position information even in locations in which reception of radio waves from a GPS satellite is difficult, by the terminal receiving the modulated signal transmitted by the first device. 
     Furthermore, an advantageous effect is achieved in which, based on information on the SSID transmitted by the first device, the terminal connects to the base station (or AP) and obtains information to securely retrieve information. This is because, when information from a visible light modulated signal is obtained, since it is visible light, the user can easily recognize the first device transmitting the modulated signal, making it possible for the user to determine whether the source of information is secure or not. 
     For example, when an SSID is obtained from a modulated signal transmitted by a wireless LAN over radio waves, it is difficult for the user to determine which device transmitted the radio waves. Accordingly, from the viewpoint of ensuring information security, obtaining the SSID via visible light communication is more suitable. 
     Note that a plurality of input signals may further be in radio device  453  in terminal  450  in  FIG.  4   . For example, a control signal for controlling radio device  453  may be in radio device  453 , and information transmitted by the base station may be in radio device  453  as input signals. Here, based on the control signal, operations for the start of communication by radio device  453  are conceivable as one example. As described above, the configuration of the first device is not limited to the configuration of first device  400  in  FIG.  4   , moreover the configuration of the terminal is not limited to the configuration of terminal  450  in  FIG.  4   , and moreover the device to which base station  470  connects is not limited to the configuration illustrated in  FIG.  4   . 
     Moreover, although only one base station (or AP) is exemplified in the configuration illustrated in  FIG.  4   , a plurality of (secure) base stations (or APs) accessible by the terminal may be included. Here, the symbol related to an SSID transmitted by first device  400  in  FIG.  4    may include information indicating the SSIDs of the plurality of base stations (or APs). Terminal  450  in  FIG.  4    may select a base station (or AP) to wirelessly connect to based on the information on the SSIDs of the base stations (or connect to the plurality of base stations (or APs)). 
     For example, assume there are three base stations (or APs). The three base stations are named base station #A, base station #B, and base station #C. The SSID of base station #A is “abcdef”, the SSID of base station #B is “ghijk”, and the SSID of base station #C is “pqrstu”. In such cases, symbol  600 - 1  related to an SSID in the frame configuration illustrated in  FIG.  6    of the modulated signal transmitted by the first device includes information related to the SSID “abcdef” of base station #A, the SSID “ghijk” of base station #B, and the SSID “pqrstu” of base station #C. Terminal  450  in  FIG.  4    receives symbol  600 - 1  related to an SSID, and based on the SSID “abcdef” of base station #A, the SSID “ghijk” of base station #B, and the SSID “pqrstu” of base station #C, selects a base station (or AP) to wirelessly connect to. 
     Embodiment 4 
       FIG.  10    illustrates one example of a configuration of a communication system according to this embodiment. The communication system illustrated in  FIG.  10    includes, for example: device  1000  including an LED light source, lamp, light source, and/or light that emits visible light; terminal  1050 ; and, for example, base station  470  that communicates with terminal  1050 . Device  1000  in  FIG.  10    includes, for example, an LED lamp, light source, and/or light that emits visible light. Note that device  1000  is referred to as a “second device” in this embodiment. In second device  1000  in  FIG.  10   , elements that operate the same as in first device  100  in  FIG.  1    share like reference marks. 
     In terminal  1050  in  FIG.  10   , components that operate the same as terminal  150  in  FIG.  1    share like reference marks. 
     Note that communication between radio device  453  and base station  470  in  FIG.  10    is performed using, for example, radio waves. 
     In second device  1000  in  FIG.  10   , transmitter  102  receives inputs of information  1001 - 1  related to an SSID, information  1001 - 2  related to an encryption key, and data  1002 , and based on these input signals, generates a (optical) modulated signal, and outputs modulated signal  103 . For example, modulated signal  103  is transmitted from light source  104 . 
     Next, information  1001 - 1  related to an SSID and information  1001 - 2  related to an encryption key will be described. 
     First, information  1001 - 1  related to an SSID will be described. 
     Information  1001 - 1  related to an SSID is information indicating the SSID of base station (or AP)  470  in  FIG.  10   . Note that, in this example, base station (or AP)  470  transmits modulated signals over radio waves, and receives radio wave modulated signals. In other words, second device  1000  can provide access to base station  470 , which is a secure access destination for the terminal. With this, terminal  1050  in  FIG.  10    can achieve the advantageous effect of being able to securely obtain information from base station (or AP)  470 . On the other hand, device  1000  can restrict the terminals that access base station  470  to terminals in a space in which it is possible to receive optical signals transmitted (emitted) by device  1000 . Note that when terminal  1050  receives an optical signal transmitted via a predetermined scheme, it may be determined that the notified SSID is the SSID of a secure base station, and, alternatively, processing for determining whether the SSID is secure or not may be performed. For example, device  1000  may transmit a predetermined identifier in an optical signal, and the terminal may determine whether the notified SSID is the SSID of a secure base station or not based on the received identifier. 
     Note that although  FIG.  10    only illustrates base station (or AP)  470 , for example, when there is a base station (or AP) other than base station (or AP)  470 , terminal  1050  in  FIG.  10    accesses base station (or AP)  470  to obtain information. 
     Information  1001 - 2  related to an encryption key is information related to an encryption key required for terminal  1050  in  FIG.  10    to establish communication with base station (or AP)  470  in  FIG.  10   . Encrypted communication is possible between terminal  1050  in  FIG.  10    and base station (or AP)  470  as a result of terminal  1050  in  FIG.  10    obtaining this information from second device  1000  in  FIG.  10   . 
     Terminal  1050  in  FIG.  10    receives the modulated signal transmitted by second device  1000 . Note that in terminal  1050  in  FIG.  10   , components that operate the same as terminal  150  in  FIG.  1    and terminal  450  in  FIG.  4    share like reference marks. 
     Light receiver  151  included in terminal  1050 , examples of which include an image sensor such as a CMOS or organic CMOS image sensor, receives the modulated signal transmitted by second device  1000 . Receiver  153  receives an input of reception signal  152  received by light receiver  151 , performs processing such as demodulation and error correction decoding on the reception signal, and outputs reception data  154 . 
     Data analyzer  155  receives an input of reception data  154 , and outputs, based on the reception data, for example, information  1051  on the SSID of the base station ( 470 ) to be connected to, and information  1052  on the encryption key for communication with the base station ( 470 ) to be connected to. For example, in a wireless local area network (LAN), examples of encryption schemes include wired equivalent privacy (WEP), Wi-Fi™ protected access (WPA), and Wi-Fi protected access 2 (WPA2) (pre-shared key (PSK) mode, extended authentication protocol (EAP) mode). However, the encryption method is not limited to these examples. 
     Display  157  receives inputs of information  1051  on the SSID and information  1052  on the encryption key, and, for example, displays the SSID of the communication partner to be accessed by radio device  453  included in the terminal, and the encryption key (this display is referred to as a “first display” in this embodiment). 
     For example, after the first display, radio device  453  included in terminal  1050  in  FIG.  10    receives inputs of information  1051  on the SSID and information  1052  on the encryption key, and establishes a connection with base station (or AP)  470  (for example, the connection uses radio waves). Here, when base station (or AP)  470  also communicates with radio device  453  in terminal  1050  in  FIG.  10   , base station (or AP)  470  transmits a modulated signal using, for example, radio waves. 
     Thereafter, radio device  453  included in terminal  1050  in  FIG.  10    receives inputs of data  1053  and control signal  1054 , demodulates data  1053  in accordance with control signal  1054 , and transmits a modulated signal as radio waves. 
     Then, for example, base station (or AP)  470  transmits data to the network ( 471 ) and receives data ( 472 ) from the network. Thereafter, for example, base station (or AP)  470  transmits, to terminal  1050  in  FIG.  10   , a modulated signal as radio waves. 
     Radio device  453  included in terminal  1050  in  FIG.  10    performs processing such as demodulation and error correction decoding on the modulated signal received as radio waves to obtain reception data  1056 . Display  157  displays a display based on reception data  1056 . 
       FIG.  11    illustrates one example of a configuration of a frame of a modulated signal transmitted by second device  1000  in  FIG.  10   . In  FIG.  11   , time is represented on the horizontal axis, and symbols that are the same as in  FIG.  2    and  FIG.  6    share like reference marks. Accordingly, repeated description thereof will be omitted. 
     Symbol  600 - 1  related to an SSID is a symbol for transmitting information  1001 - 1  related to an SSID in  FIG.  10   , and symbol  1101  related to an encryption key is a symbol for transmitting information  1001 - 2  related to an encryption key in  FIG.  10   . Data symbol  1102  is a symbol for transmitting data  1002 . 
     The second device transmits preamble  201 , control information symbol  202 , symbol  600 - 1  related to an SSID, symbol  1101  related to an encryption key, and data symbol  1102 . Note that second device  1000  in  FIG.  10    may transmit a frame including symbols other than the symbols illustrated in  FIG.  11   . Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  11   . 
       FIG.  12    illustrates one example of a configuration of a frame of a modulated signal transmitted by radio device  453  included in terminal  1050  in  FIG.  10   . In  FIG.  12   , time is represented on the horizontal axis. As illustrated in  FIG.  12   , radio device  453  included in terminal  1050  in  FIG.  10    transmits, for example, preamble  1201 , and then transmits control information symbol  1202  and information symbol  1203 . 
     Here, preamble  1201  is a symbol used for base station (or AP)  470  that receives the modulated signal transmitted by radio device  453  in terminal  1050  in  FIG.  10    to perform, for example, signal detection, temporal synchronization, frame synchronization, frequency synchronization, and frequency offset estimation. 
     Control information symbol  1202  includes data such as information related to the error correction encoding scheme method and/or demodulation scheme used in the generation of the modulated signal, information related to frame configuration, and information related to the transmission method used, and base station (or AP)  470 , for example, demodulates the modulated signal based on the information included in control information symbol  1202 . 
     Information symbol  1203  is a symbol for radio device  453  included in terminal  1050  in  FIG.  10    to transmit data. 
     Note that radio device  453  included in terminal  1050  in  FIG.  10    may transmit a frame including symbols other than the symbols illustrated in  FIG.  12    (for example, a frame including a pilot symbol (reference symbol) midway through the information symbol). Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  12   . In  FIG.  12   , a plurality of symbols may be present along the frequency axis, that is to say, symbols may be present on a plurality of frequencies (a plurality of carriers). 
     Note that in Embodiment 3, when radio device  453  included in terminal  1050  in  FIG.  4    transmits a modulated signal, the frame configuration illustrated in  FIG.  12    may be used. 
       FIG.  7    illustrates one example of a configuration of a frame of a modulated signal transmitted by base station  470  in  FIG.  10   . In  FIG.  7   , time is represented on the horizontal axis. As illustrated in  FIG.  7   , base station  470  transmits, for example, preamble  701 , and then transmits control information symbol  702  and information symbol  703 . 
     Here, preamble  701  is a symbol for radio device  453  included in terminal  1050  in  FIG.  10   , which receives the modulated signal transmitted by base station  470 , to perform, for example, signal detection, temporal synchronization, frame synchronization, frequency synchronization, and/or frequency offset estimation. 
     Control information symbol  702  includes data such as information related to the error correction encoding scheme method and/or demodulation scheme used in the generation of the modulated signal, information related to frame configuration, and information related to the transmission method used, and radio device  453  included in terminal  1050  in  FIG.  10   , for example, demodulates the modulated signal based on the information included in this symbol. 
     Information symbol  703  is a symbol for base station (or AP)  470  in  FIG.  10    to transmit data. 
     Note that base station (or AP)  470  in  FIG.  10    may transmit a frame including symbols other than the symbols illustrated in  FIG.  7    (for example, a frame including a pilot symbol (reference symbol) midway through the information symbol). Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  7   . In  FIG.  7   , a plurality of symbols may be present along the frequency axis, that is to say, symbols may be present on a plurality of frequencies (a plurality of carriers). 
     Moreover, for example, a modulated signal that has the frame configuration illustrated in  FIG.  11    and is transmitted by second device  1000  being transmitted at a regular timing, e.g., repeatedly transmitted is conceivable. This makes it possible for a plurality of terminals to implement the operations described above. 
       FIG.  13    is a flow chart illustrating one example of processes implemented by second device  1000 , terminal  1050 , and base station (or AP)  470  in  FIG.  10   . 
     First, as  1301  in  FIG.  13    illustrates, second device  1000  in  FIG.  10    transmits a modulated signal having the frame configuration illustrated in  FIG.  11   . 
     Likewise, as  1302  in  FIG.  13    illustrates, the modulated signal transmitted by second device  1000  in  FIG.  10    is received, and terminal  1050  in  FIG.  10    obtains the SSID of the base station to be accessed by terminal  1050 . 
     Likewise, as  1303  in  FIG.  13    illustrates, terminal  1050  in  FIG.  10    obtains an encryption key to be used for communicating with base station  470  to be accessed by the terminal. 
     Terminal  1050  in  FIG.  10    requests connection with base station  470  in  FIG.  10    over radio waves ( 1304 ). 
     As  1305  in  FIG.  13    illustrates, terminal  1050  in  FIG.  10    completes the connection with base station  470  in  FIG.  10    upon receiving a response from base station  470  in  FIG.  10   . 
     As  1306  in  FIG.  13    illustrates, terminal  1050  in  FIG.  10    transmits information on the connection destination to base station  470  in  FIG.  10    using radio waves. 
     Then, as  1307  in  FIG.  13    illustrates, base station  470  in  FIG.  10    obtains information to be transmitted to terminal  1050  in  FIG.  10    from the network. 
     As  1308  in  FIG.  13    illustrates, base station  470  in  FIG.  10    transmits the obtained information to terminal  1050  in  FIG.  10    using radio waves, and terminal  1050  in  FIG.  10    obtains the information. 
     For example, when necessary, terminal  1050  in  FIG.  10    obtains required information from the network via base station  470  in  FIG.  10   . 
     As described above, based on the SSID information and the encryption key information transmitted from the second device, the terminal connects to the base station (or AP) and obtains information, whereby an advantageous effect that it is possible to securely obtain information via the base station (or AP) whose security has been authenticated can be achieved. This is because, when information from a visible light modulated signal is obtained, since it is visible light, the user can easily determine whether the source of information is secure or not. 
     For example, when an SSID is obtained from a modulated signal transmitted by a wireless LAN over radio waves, it is difficult for the user to determine which device transmitted the radio waves. Accordingly, from the viewpoint of ensuring information security, obtaining the SSID via visible light communication is more suitable. 
     Note that in this embodiment, the second device is exemplified as transmitting encryption key information, but, for example, when the base station (or AP) does not perform encrypted communication using an encryption key, the second device can transmit only the information related to an SSID without transmitting the encryption key information, that is, the second device may be implemented without the configuration related to an encryption key. 
     Moreover, the configuration of the second device is not limited to the configuration illustrated in  FIG.  10   , the configuration of the terminal is not limited to the configuration illustrated in  FIG.  10   , and the configuration of the connection destination of the base station is not limited to the configuration illustrated in  FIG.  10   . 
     Although in this embodiment, only one base station (or AP) is exemplified in the configuration illustrated in  FIG.  10   , a plurality of (secure) base stations (or APs) accessible by the terminal may be included (note that these base stations and the terminal transmit and receive modulated signals using radio waves). Here, the symbol related to an SSID transmitted by second device  1000  in  FIG.  10    may include information indicating the SSIDs of the plurality of base stations (or APs). Moreover, the symbol related to an encryption key transmitted by second device  1000  in  FIG.  10    may include encryption key information used to connect to the plurality of base stations (or APs). Terminal  1050  in  FIG.  10    may select a base station (or AP) to wirelessly connect to based on the information on the SSIDs of the base stations and the encryption key information (or connect to the plurality of base stations (or APs)). 
     For example, assume there are three base stations (or APs). The three base stations are named base station #A, base station #B, and base station #C. The SSID of base station #A is “abcdef”, the SSID of base station #B is “ghijk”, and the SSID of base station #C is “pqrstu”, the encryption key for connecting with base station #A is “123”, the encryption key for connecting with base station #B is “456”, and the encryption key for connecting with base station #C is “789”. 
     In such cases, symbol  600 - 1  related to an SSID in the frame configuration illustrated in  FIG.  11    of the modulated signal transmitted by the second device includes information related to the SSID “abcdef” of base station #A, the SSID “ghijk” of base station #B, and the SSID “pqrstu” of base station #C. The symbol  1101  related to an encryption key having the frame configuration illustrated in  FIG.  11    includes information related to the encryption key “123” for connecting with base station #A, the encryption key “456” for connecting with base station #B, and the encryption key “789” for connecting with base station #C. 
     Terminal  1050  in  FIG.  10    receives symbol  600 - 1  related to an SSID and thus obtains the SSID “abcdef” of base station #A, the SSID “ghijk” of base station #B, and the SSID “pqrstu” of base station #C, receives symbol  1101  related to an encryption key and thus obtains the encryption key “123” for connecting with base station #A, the encryption key “456” for connecting with base station #B, and the encryption key “789” for connecting with base station #C. Then, based on this information, terminal  1050  in  FIG.  10    selects a base station (or AP) to wirelessly connect to (for example, via radio waves), and connects to the selected base station (or AP). 
     As described in this embodiment, as a result of the terminal setting which base station to access, utilizing a light source, exemplified here as an LED light source, a mode for making a special setting for processes for establishing a wireless connection between the terminal and base station in the modulated signal for connection over radio waves that is transmitted by the terminal is not required, and a mode for making a special setting for processes for establishing a wireless connection between the terminal and base station in the modulated signal for connection over radio waves that is transmitted by the base station is not required, whereby an advantageous effect that wireless communication data transmission efficiency improves can be achieved. 
     As described above, the encryption key may be an encryption key for an SSID on a wireless LAN, may be an encryption key for restricting the form of connection used, the form of service used, and/or the connectivity range of the network (in other words, any encryption key that is restrictive is sufficient). 
     Embodiment 5 (SSID and Password Separation) 
       FIG.  14    illustrates one example of configurations according to this embodiment of: devices including, for example, an LED light source, lamp, light source, and/or light that emits visible light; a terminal; and, for example, a base station that communicates with the terminal. The communication system in  FIG.  14    includes: device  1400 A and  1400 B each including, for example, an LED light source, lamp, light source, and/or light that emits visible light; terminal  1050 ; and, for example, base station  470  that communicates with terminal  1050 . Note that device  1400 A in  FIG.  14    is referred to as a “third device” in this embodiment, and device  1400 B in  FIG.  14    is referred to as a “fourth device” in this embodiment. Note that in terminal  1050  in  FIG.  14   , operations that are the same as in  FIG.  1    and  FIG.  10    share like reference marks. Regarding the base station or AP as well, operations that are the same as in  FIG.  4    have the same reference marks as in  FIG.  4   . 
     Note that communication between radio device  453  and base station  470  in  FIG.  14    is performed using, for example, radio waves. 
     In third device  1400 A in  FIG.  14   , transmitter  1404 - 1  receives inputs of information  1401 - 1  related to an SSID and data  1402 - 1 , and based on these input signals, generates a (optical) modulated signal and outputs modulated signal  1405 - 1 . Modulated signal  1405 - 1  is transmitted from light source  1406 - 1 . 
     In fourth device  1400 B in  FIG.  14   , transmitter  1404 - 2  receives inputs of information  1403 - 2  related to an encryption key and data  1402 - 2 , and based on these input signals, generates a (optical) modulated signal and outputs modulated signal  1405 - 2 . Modulated signal  1405 - 2  is transmitted from light source  1406 - 2 . 
     Next, information  1401 - 1  related to an SSID and information  1403 - 2  related to an encryption key will be described. 
     First, information  1401 - 1  related to an SSID will be described. 
     Information  1401 - 1  related to an SSID is information indicating the SSID of base station (or AP)  470  in  FIG.  14   . In other words, third device  1400 A can provide access over radio waves to base station  470 , which is a secure access destination for the terminal With this, terminal  1050  in  FIG.  14    can achieve the advantageous effect of being able to securely obtain information from base station (or AP)  470 . 
     Note that when terminal  1050  receives an optical signal transmitted via a predetermined scheme, it may be determined that the notified SSID is the SSID of a secure base station, and, alternatively, processing for determining whether the SSID is secure or not may be performed. For example, device  1400 A may transmit a predetermined identifier in an optical signal, and the terminal may determine whether the notified SSID is the SSID of a secure base station or not based on the received identifier. 
     Note that although  FIG.  14    only illustrates base station (or AP)  470 , for example, when there is a base station (or AP) other than base station (or AP)  470 , terminal  1050  in  FIG.  14    accesses base station (or AP)  470  to obtain information. 
     Information  1403 - 2  related to an encryption key is information related to an encryption key required for terminal  1050  in  FIG.  14    to establish communication with base station (or AP)  470  in  FIG.  14   . Encrypted communication is possible between terminal  1050  in  FIG.  14    and base station (or AP)  470  as a result of terminal  1050  in  FIG.  14    obtaining this information from fourth device  1400 B in  FIG.  14   . 
     Terminal  1050  in  FIG.  14    receives the modulated signal transmitted by third device  1400 A. 
     Light receiver  151  included in terminal  1050 , examples of which include an image sensor such as a CMOS or organic CMOS image sensor, receives the modulated signal transmitted by third device  1400 A. Receiver  153  receives an input of reception signal  152  received by light receiver  151 , performs processing such as demodulation and error correction decoding on the reception signal, and outputs reception data  154 . 
     Data analyzer  155  receives an input of reception data  154 , and outputs, based on the reception data, for example, information  1051  on the SSID of the base station ( 470 ) to be connected to. 
     Accordingly, radio device  453  included in terminal  1050  obtains information on the SSID of the base station to be connected to over radio waves by radio device  453 , from information  1051  on the SSID. 
     Next, terminal  1050  in  FIG.  14    receives the modulated signal transmitted by fourth device  1400 B. 
     Light receiver  151  included in terminal  1050 , examples of which include an image sensor such as a CMOS or organic CMOS image sensor, receives the modulated signal transmitted by fourth device  1400 B. Receiver  153  receives an input of reception signal  152  received by light receiver  151 , performs processing such as demodulation and error correction decoding on the reception signal, and outputs reception data  154 . 
     Data analyzer  155  receives an input of reception data  154 , and outputs, based on the reception data, for example, information  1052  on the encryption key for communication with the base station ( 470 ) to be connected to. For example, in a wireless local area network (LAN), examples of encryption schemes include wired equivalent privacy (WEP), Wi-Fi protected access (WPA), and Wi-Fi protected access 2 (WPA2) (pre-shared key (PSK) mode, extended authentication protocol (EAP) mode). However, the encryption method is not limited to these examples. 
     Accordingly, radio device  453  included in terminal  1050  obtains encryption key information for the base station to be connected to by radio device  453 , from information  1052  on the encryption key for communication with the base station ( 470 ) to be connected to (for example, over radio waves). 
     Display  157  receives inputs of information  1051  on the SSID and information  1052  on the encryption key, and, for example, displays the SSID of the communication partner to be accessed by radio device  453  included in the terminal, and the encryption key (this display is referred to as a “first display” in this embodiment). 
     For example, after the first display, radio device  453  included in terminal  1050  in  FIG.  14    receives inputs of information  1051  on the SSID and information  1052  on the encryption key, and establishes a connection with base station (or AP)  470  (for example, the connection uses radio waves). Here, when base station (or AP)  470  also communicates with radio device  453  in terminal  1050  in  FIG.  14   , base station (or AP)  470  transmits a modulated signal using, for example, radio waves. 
     Thereafter, radio device  453  included in terminal  1050  in  FIG.  14    receives inputs of data  1053  and control signal  1054 , demodulates data  1053  in accordance with control signal  1054 , and transmits a modulated signal as radio waves. 
     Then, for example, base station (or AP)  470  transmits data to the network ( 471 ) and receives data ( 472 ) from the network. Thereafter, for example, base station (or AP)  470  transmits, to terminal  1050  in  FIG.  14   , a modulated signal as radio waves. 
     Radio device  453  included in terminal  1050  in  FIG.  14    performs processing such as demodulation and error correction decoding on the received modulated signal to obtain reception data  1056 . Display  157  displays a display based on reception data  1056 . 
       FIG.  15    illustrates one example of a configuration of a frame of a modulated signal transmitted by third device  1400 A in  FIG.  14   . In  FIG.  15   , time is represented on the horizontal axis, and symbols that are the same as in  FIG.  2   ,  FIG.  6   , and  FIG.  11    share like reference marks. Accordingly, repeated description thereof will be omitted. 
     Symbol  600 - 1  related to an SSID is a symbol for transmitting information  1401 - 1  related to an SSID in  FIG.  14   . Data symbol  1102  is a symbol for transmitting data  1402 - 1 . 
     Third device  1400 A transmits preamble  201 , control information symbol  202 , symbol  600 - 1  related to an SSID, and data symbol  1102 . Note that third device  1400 A in  FIG.  14    may transmit a frame including symbols other than the symbols illustrated in  FIG.  15   . Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  15   . 
       FIG.  16    illustrates one example of a configuration of a frame of a modulated signal transmitted by fourth device  1400 B in  FIG.  14   . In  FIG.  16   , time is represented on the horizontal axis, and symbols that are the same as in  FIG.  2    and  FIG.  11    share like reference marks. Accordingly, repeated description thereof will be omitted. 
     Symbol  1101  related to an encryption key is a symbol for transmitting information  1403 - 2  related to an encryption key in  FIG.  14   . Data symbol  1102  is a symbol for transmitting data  1402 - 2 . 
     Fourth device  1400 B transmits preamble  201 , control information symbol  202 , symbol  1101  related to an encryption key, and data symbol  1102 . Note that fourth device  1400 B in  FIG.  14    may transmit a frame including symbols other than the symbols illustrated in  FIG.  16   . Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  16   . 
       FIG.  12    illustrates one example of a configuration of a frame of a modulated signal transmitted by radio device  453  included in terminal  1050  in  FIG.  14   . In  FIG.  12   , time is represented on the horizontal axis. As illustrated in  FIG.  12   , radio device  453  included in terminal  1050  in  FIG.  14    transmits, for example, preamble  1201 , and then transmits control information symbol  1202  and information symbol  1203 . 
     Here, preamble  1201  is a symbol used for base station (or AP)  470  that receives the modulated signal transmitted by radio device  453  in terminal  1050  in  FIG.  14    to perform, for example, signal detection, temporal synchronization, frame synchronization, frequency synchronization, and frequency offset estimation. 
     Control information symbol  1202  includes data such as information related to the error correction encoding scheme method and/or demodulation scheme used in the generation of the modulated signal, information related to frame configuration, and information related to the transmission method used, and base station (or AP)  470 , for example, demodulates the modulated signal based on the information included in control information symbol  1202 . 
     Information symbol  1203  is a symbol for radio device  453  included in terminal  1050  in  FIG.  14    to transmit data. 
     Note that radio device  453  included in terminal  1050  in  FIG.  14    may transmit a frame including symbols other than the symbols illustrated in  FIG.  12    (for example, a frame including a pilot symbol (reference symbol) midway through the information symbol). Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  12   . In  FIG.  12   , a plurality of symbols may be present along the frequency axis, that is to say, symbols may be present on a plurality of frequencies (a plurality of carriers). 
       FIG.  7    illustrates one example of a configuration of a frame of a modulated signal transmitted by base station  470  in  FIG.  14   . In  FIG.  7   , time is represented on the horizontal axis. As illustrated in  FIG.  7   , base station  470  transmits, for example, preamble  701 , and then transmits control information symbol  702  and information symbol  703 . 
     Here, preamble  701  is a symbol for radio device  453  included in terminal  1050  in  FIG.  14   , which receives the modulated signal transmitted by base station  470 , to perform, for example, signal detection, temporal synchronization, frame synchronization, frequency synchronization, and/or frequency offset estimation. 
     Control information symbol  702  includes data such as information related to the error correction encoding scheme method and/or demodulation scheme used in the generation of the modulated signal, information related to frame configuration, and information related to the transmission method used, and radio device  453  included in terminal  1050  in  FIG.  14   , for example, demodulates the modulated signal based on the information included in this symbol. 
     Information symbol  703  is a symbol for base station (or AP)  470  in  FIG.  14    to transmit data. 
     Note that base station (or AP)  470  in  FIG.  14    may transmit a frame including symbols other than the symbols illustrated in  FIG.  7    (for example, a frame including a pilot symbol (reference symbol) midway through the information symbol). Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  7   . In  FIG.  7   , a plurality of symbols may be present along the frequency axis, that is to say, symbols may be present on a plurality of frequencies (a plurality of carriers). 
     Moreover, for example, a modulated signal that has the frame configuration illustrated in  FIG.  15    and is transmitted by third device  1400 A being transmitted at a regular timing, e.g., repeatedly transmitted is conceivable. This makes it possible for a plurality of terminals to implement the operations described above. 
     Similarly, a modulated signal that has the frame configuration illustrated in  FIG.  16    and is transmitted by fourth device  1400 B being transmitted at a regular timing, e.g., repeatedly transmitted is conceivable. This makes it possible for a plurality of terminals to implement the operations described above. 
       FIG.  17    is a flow chart illustrating a first example of processes implemented by third device  1400 A, fourth device  1400 B, terminal  1050 , and base station (or AP)  470  in  FIG.  14   . Note that in  FIG.  17   , operations that are the same as in  FIG.  13    share like reference marks. 
     First, as  1701  in  FIG.  17    illustrates, third device  1400 A in  FIG.  14    transmits a modulated signal having the frame configuration illustrated in  FIG.  15   . 
     As  1702  in  FIG.  17    illustrates, the modulated signal transmitted by third device  1400 A in  FIG.  14    is received, and terminal  1050  in  FIG.  14    obtains the SSID of the base station to be accessed by terminal  1050 . 
     Next, as  1703  in  FIG.  17    illustrates, fourth device  1400 B in  FIG.  14    transmits a modulated signal having the frame configuration illustrated in  FIG.  16   . 
     As  1704  in  FIG.  17    illustrates, the modulated signal transmitted by fourth device  1400 B in  FIG.  14    is received, and terminal  1050  in  FIG.  14    obtains an encryption key to be used for communicating with base station  470  to be accessed by the terminal. 
     Terminal  1050  in  FIG.  14    requests connection with base station  470  in  FIG.  14    over radio waves ( 1304 ). 
     As  1305  in  FIG.  17    illustrates, terminal  1050  in  FIG.  14    completes the connection with base station  470  in  FIG.  14    upon receiving a response from base station  470  in  FIG.  14   . 
     As  1306  in  FIG.  17    illustrates, terminal  1050  in  FIG.  14    transmits information on the connection destination to base station  470  in  FIG.  14    using radio waves. 
     Then, as  1307  in  FIG.  17    illustrates, base station  470  in  FIG.  14    obtains information to be transmitted to terminal  1050  in  FIG.  14    from the network. 
     As  1308  in  FIG.  17    illustrates, base station  470  in  FIG.  14    transmits the obtained information to terminal  1050  in  FIG.  14    using radio waves, and terminal  1050  in  FIG.  14    obtains the information. 
     For example, when necessary, terminal  1050  in  FIG.  14    obtains required information from the network via base station  470  in  FIG.  14   . 
       FIG.  18    is a flow chart illustrating a second example of the above-described processes implemented by third device  1400 A, fourth device  1400 B, terminal  1050 , and base station (or AP)  470  in  FIG.  14   . Note that in  FIG.  18   , operations that are the same as in  FIG.  13    share like reference marks. 
     First, as  1801  in  FIG.  18    illustrates, fourth device  1400 B in  FIG.  14    transmits a modulated signal having the frame configuration illustrated in  FIG.  16   . 
     As  1802  in  FIG.  18    illustrates, the modulated signal transmitted by fourth device  1400 B in  FIG.  14    is received, and terminal  1050  in  FIG.  14    obtains an encryption key to be used for communicating with the base station to be accessed by terminal  1050 . 
     Next, as  1803  in  FIG.  18    illustrates, third device  1400 A in  FIG.  14    transmits a modulated signal having the frame configuration illustrated in  FIG.  15   . 
     As  1804  in  FIG.  18    illustrates, the modulated signal transmitted by third device  1400 A in  FIG.  14    is received, and terminal  1050  in  FIG.  14    obtains the SSID of base station  470  to be accessed by the terminal. 
     Terminal  1050  in  FIG.  14    requests connection with base station  470  in  FIG.  14    over radio waves ( 1304 ). 
     As  1305  in  FIG.  18    illustrates, terminal  1050  in  FIG.  14    completes the connection with base station  470  in  FIG.  14    upon receiving a response from base station  470  in  FIG.  14   . 
     As  1306  in  FIG.  18    illustrates, terminal  1050  in  FIG.  14    transmits information on the connection destination to base station  470  in  FIG.  14    using radio waves. 
     Then, as  1307  in  FIG.  18    illustrates, base station  470  in  FIG.  14    obtains information to be transmitted to terminal  1050  in  FIG.  14    from the network. 
     As  1308  in  FIG.  18    illustrates, base station  470  in  FIG.  14    transmits the obtained information to terminal  1050  in  FIG.  14    using radio waves, and terminal  1050  in  FIG.  14    obtains the information. 
     For example, when necessary, terminal  1050  in  FIG.  14    obtains required information from the network via base station  470  in  FIG.  14   . 
     As described above, based on the SSID information and the encryption key information transmitted from the third and fourth devices, the terminal connects to the base station (or AP) and obtains information, whereby an advantageous effect that it is possible to securely obtain information via the base station (or AP) whose security has been authenticated can be achieved. This is because, when information from a visible light modulated signal is obtained, since it is visible light, the user can easily determine whether the source of information is secure or not. 
     For example, when an SSID is obtained from a modulated signal transmitted by a wireless LAN over radio waves, it is difficult for the user to determine which device transmitted the radio waves. Accordingly, from the viewpoint of ensuring information security, obtaining the SSID via visible light communication is more suitable. 
     Note that in this embodiment, the fourth device is exemplified as transmitting encryption key information, but, for example, when the base station (or AP) does not perform encrypted communication using an encryption key, the fourth device can transmit only the information related to an SSID without transmitting the encryption key information, that is, the fourth device may be implemented without the configuration related to an encryption key. 
     Moreover, as described in this embodiment, by separating the device for transmitting information related to an SSID and the device for transmitting information related to an encryption key, the terminal can implement even more secure communication with the base station. 
     For example, consider the space illustrated in  FIG.  19   . As illustrated in  FIG.  19   , the space includes area # 1  and area # 2 , and a wall and a doorway between area # 1  and area # 2 . In this example, movement from area # 1  to area # 2  and movement from area # 2  to area # 1  is only possible through the doorway. 
     A base station (or AP), a third device, and a fourth device are disposed in area # 1  in  FIG.  19   . Only a third device is disposed in area # 2 . 
     Moreover, assume that the radio waves transmitted by the base station (or AP) are receivable in either of areas # 1  or # 2 . Here, a terminal in area # 1  in which a fourth device is disposed can communicate with the base station. Moreover, even when a terminal connected to the base station in area # 1  moves to area # 2 , communication with the base station is still possible. 
     When a terminal connected to the base station in area # 1  moves somewhere other than area # 1  or area # 2 , and then returns to either area # 1  or area # 2 , communication with the base station is possible. 
     However, a terminal that cannot enter area # 1  cannot obtain an encryption key. In such cases, the terminal can only know the SSID of the base station (or AP). Here, communication with the base station via a service that can be accepted with nothing more than knowledge of the SSID may be received by the terminal. 
     Accordingly, only a terminal that can enter area # 1  can communicate with the base station, and as a result, communication security can be assured. Moreover, this makes it possible to construct a system that can provide different services for different areas. 
     Note that when the encryption key for the terminal to communicate with the base station changes (for example, on a per time interval basis), a previous encryption key cannot be used to communicate with the base station. Using such a system makes it possible to provide secure communication. 
     As described above, the encryption key may be an encryption key for an SSID on a wireless LAN, may be an encryption key for restricting the form of connection used, the form of service used, and/or the connectivity range of the network (in other words, any encryption key that is restrictive is sufficient). 
     The configurations of the third and fourth devices are not limited to the configurations illustrated in  FIG.  14   , the configuration of the terminal is not limited to the configuration illustrated in  FIG.  14   , and the configuration of the connection destination of the base station is not limited to the configuration illustrated in  FIG.  14   . 
     In this embodiment, although only one base station (or AP) is exemplified in the configuration illustrated in  FIG.  14   , a plurality of (secure) base stations (or APs) accessible by the terminal may be included. Here, the symbol related to an SSID transmitted by third device  1400 A in  FIG.  14    may include information indicating the SSIDs of the plurality of base stations (or APs). Moreover, the symbol related to an encryption key transmitted by fourth device  1400 B in  FIG.  14    may include encryption key information used to connect to the plurality of base stations (or APs). Terminal  1050  in  FIG.  14    may select a base station (or AP) to wirelessly connect to based on the encryption key information and the information on the SSIDs of the base stations (or connect to the plurality of base stations (or APs)). 
     For example, assume there are three base stations (or APs). The three base stations are named base station #A, base station #B, and base station #C. The SSID of base station #A is “abcdef”, the SSID of base station #B is “ghijk”, and the SSID of base station #C is “pqrstu”, the encryption key for connecting with base station #A is “123”, the encryption key for connecting with base station #B is “456”, and the encryption key for connecting with base station #C is “789”. 
     In such cases, symbol  600 - 1  related to an SSID in the frame configuration illustrated in  FIG.  15    of the modulated signal transmitted by the third device includes information related to the SSID “abcdef” of base station #A, the SSID “ghijk” of base station #B, and the SSID “pqrstu” of base station #C. The symbol  1101  related to an encryption key having the frame configuration illustrated in  FIG.  16    of the modulated signal transmitted by the fourth device includes information related to the encryption key “123” for connecting with base station #A, the encryption key “456” for connecting with base station #B, and the encryption key “789” for connecting with base station #C. 
     Terminal  1050  in  FIG.  14    receives symbol  600 - 1  related to an SSID and thus obtains the SSID “abcdef” of base station #A, the SSID “ghijk” of base station #B, and the SSID “pqrstu” of base station #C, receives symbol  1101  related to an encryption key and thus obtains the encryption key “123” for connecting with base station #A, the encryption key “456” for connecting with base station #B, and the encryption key “789” for connecting with base station #C. Then, based on this information, terminal  1050  in  FIG.  14    selects a base station (or AP) to wirelessly connect to (for example, via radio waves), and connects to the selected base station (or AP). 
     As described in this embodiment, as a result of the terminal setting which base station to access, utilizing a light source, exemplified here as an LED light source, a mode for making a special setting for processes for establishing a wireless connection between the terminal and base station in the modulated signal for connection over radio waves that is transmitted by the terminal is not required, and a mode for making a special setting for processes for establishing a wireless connection between the terminal and base station in the modulated signal for connection over radio waves that is transmitted by the base station is not required, whereby an advantageous effect that wireless communication data transmission efficiency improves can be achieved. 
     Embodiment 6 (Base Station Includes LED) 
       FIG.  20    illustrates one example of a configuration of a communication system according to this embodiment. The communication system illustrated in  FIG.  20    includes, for example: an LED light source, lamp, light source, and/or light that emits visible light; base station  2000  including radio device  2001 ; and terminal  1050 . Note that in  FIG.  20   , operations that are the same as in  FIG.  1    and  FIG.  10    share like reference marks. 
     Note that communication between radio device  2001  and radio device  453  in  FIG.  20    is performed using, for example, radio waves. 
     Base station (or AP)  2000  in  FIG.  20    includes, for example, an LED lamp, light source, and/or light that emits visible light. First, operations of one or more elements related to the LED lamp, light source, and/or light that emits visible light will be described. 
     Transmitter  102  receives inputs of information  1001 - 1  related to an SSID, information  1001 - 2  related to an encryption key, and data  1002 , and based on these input signals, generates a (optical) modulated signal, and outputs modulated signal  103 . For example, modulated signal  103  is transmitted from light source  104 . 
     Next, information  1001 - 1  related to an SSID and information  1001 - 2  related to an encryption key will be described. 
     First, information  1001 - 1  related to an SSID will be described. 
     Information  1001 - 1  related to an SSID is information indicating the SSID of, for example, radio device  2001  that uses radio waves in base station (or AP)  2000  in  FIG.  20   . In other words, an “element related to the LED lamp, light source, and/or light that emits visible light” can provide access to radio device  2001 , which is a secure access destination for the terminal. With this, terminal  1050  in  FIG.  20    can achieve the advantageous effect of being able to securely obtain information from radio device  2001 . 
     On the other hand, an element related to the LED lamp, light source, and/or light that emits visible light in base station  200  can restrict the terminals that access radio device  2001  to terminals in a space in which reception of the optical signal transmitted (emitted) by the element related to the LED lamp, light source, and/or light that emits visible light in base station  200  is possible. Note that when terminal  1050  receives an optical signal transmitted via a predetermined scheme, it may be determined that the notified SSID is the SSID of a secure base station, and, alternatively, processing for determining whether the SSID is secure or not may be performed. For example, an element related to the LED lamp, light source, and/or light that emits visible light in base station  2000  may transmit a predetermined identifier in an optical signal, and the terminal may determine whether the notified SSID is the SSID of a secure base station or not based on the received identifier. 
     Note that although  FIG.  20    only illustrates base station (or AP)  2000 , for example, when there is a base station (or AP) other than base station (or AP)  2000 , terminal  1050  in  FIG.  20    accesses base station (or AP)  2000  to obtain information. 
     Information  1001 - 2  related to an encryption key is information related to an encryption key required for terminal  1050  in  FIG.  20    to establish communication with radio device  2001  in  FIG.  20   . Encrypted communication is possible between terminal  1050  in  FIG.  20    and radio device  2001  as a result of terminal  1050  in  FIG.  20    obtaining this information from an element related to the LED lamp, light source, and/or light that emits visible light. Terminal  1050  in  FIG.  20    receives the modulated signal transmitted by an element related to the LED lamp, light source, and/or light that emits visible light in base station  200 . 
     Note that in terminal  1050  in  FIG.  20   , components that operate the same as terminal  150  in  FIG.  1    and terminal  1050  in  FIG.  10    share like reference marks. 
     Light receiver  151  included in terminal  1050 , examples of which include an image sensor such as a CMOS or organic CMOS image sensor, receives the modulated signal transmitted by an element related to the LED lamp, light source, and/or light that emits visible light in base station  200 . Receiver  153  receives an input of reception signal  152  received by light receiver  151 , performs processing such as demodulation and error correction decoding on the reception signal, and outputs reception data  154 . 
     Data analyzer  155  receives an input of reception data  154 , and outputs, based on the reception data, for example, information  1051  on the SSID of radio device  2001  in the base station to be connected to, and information  1052  on the encryption key for communication with radio device  2001  in the base station to be connected to. For example, in a wireless local area network (LAN), examples of encryption schemes include wired equivalent privacy (WEP), Wi-Fi protected access (WPA), and Wi-Fi protected access 2 (WPA2) (pre-shared key (PSK) mode, extended authentication protocol (EAP) mode). However, the encryption method is not limited to these examples. 
     Display  157  receives inputs of information  1051  on the SSID and information  1052  on the encryption key, and, for example, displays the SSID of the communication partner to be accessed by radio device  453  included in the terminal, and the encryption key (this display is referred to as a “first display” in this embodiment). 
     For example, after the first display, radio device  453  included in terminal  1050  in  FIG.  20    receives inputs of information  1051  on the SSID and information  1052  on the encryption key, and establishes a connection with radio device  2001  in base station (or AP)  2000  (for example, the connection uses radio waves). Here, when radio device  2001  in base station (or AP)  2000  also communicates with radio device  453  in terminal  1050  in  FIG.  20   , radio device  2001  in base station (or AP)  2000  transmits a modulated signal using, for example, radio waves. 
     Thereafter, radio device  453  included in terminal  1050  in  FIG.  20    receives inputs of data  1053  and control signal  1054 , demodulates data  1053  in accordance with control signal  1054 , and transmits a modulated signal as radio waves. Then, for example, radio device  2001  in base station (or AP)  2000  transmits data to the network ( 471 ) and receives data ( 472 ) from the network. Thereafter, for example, radio device  2001  in base station (or AP)  2000  transmits, to terminal  1050  in  FIG.  20   , a modulated signal as radio waves. Radio device  453  included in terminal  1050  in  FIG.  20    performs processing such as demodulation and error correction decoding on the modulated signal received as radio waves to obtain reception data  1056 . Display  157  displays a display based on reception data  1056 . 
       FIG.  11    illustrates one example of a configuration of a frame of a modulated signal transmitted by transmitter  102  and light source  104  in base station (or AP)  2000  in  FIG.  20   . In  FIG.  11   , time is represented on the horizontal axis, and symbols that are the same as in  FIG.  2    and  FIG.  6    share like reference marks. Accordingly, repeated description thereof will be omitted. 
     Symbol  600 - 1  related to an SSID is a symbol for transmitting information  1001 - 1  related to an SSID in  FIG.  20   , and symbol  1101  related to an encryption key is a symbol for transmitting information  1001 - 2  related to an encryption key in  FIG.  20   . Data symbol  1102  is a symbol for transmitting data  1002 . 
     Transmitter  102  and light source  104  in base station (or AP)  2000  transmit preamble  201 , control information symbol  202 , symbol  600 - 1  related to an SSID, symbol  1101  related to an encryption key, and data symbol  1102 . Note that transmitter  102  and light source  104  in base station (or AP)  2000  in  FIG.  20    may transmit a frame including symbols other than the symbols illustrated in  FIG.  11   . Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  11   . 
       FIG.  12    illustrates one example of a configuration of a frame of a modulated signal transmitted by radio device  453  included in terminal  1050  in  FIG.  20   . In  FIG.  12   , time is represented on the horizontal axis. As illustrated in  FIG.  12   , radio device  453  included in terminal  1050  in  FIG.  20    transmits, for example, preamble  1201 , and then transmits control information symbol  1202  and information symbol  1203 . 
     Here, preamble  1201  is a symbol used for radio device  2001  in base station (or AP)  2000  that receives the modulated signal transmitted by radio device  453  in terminal  1050  in  FIG.  20    to perform, for example, signal detection, temporal synchronization, frame synchronization, frequency synchronization, and frequency offset estimation. 
     Control information symbol  1202  includes data such as information related to the error correction encoding scheme method and/or demodulation scheme used in the generation of the modulated signal, information related to frame configuration, and information related to the transmission method used, and radio device  2001  in base station (or AP)  2000 , for example, demodulates the modulated signal based on the information included in control information symbol  1202 . 
     Information symbol  1203  is a symbol for radio device  453  included in terminal  1050  in  FIG.  20    to transmit data. 
     Note that radio device  453  included in terminal  1050  in  FIG.  20    may transmit a frame including symbols other than the symbols illustrated in  FIG.  12    (for example, a frame including a pilot symbol (reference symbol) midway through the information symbol). Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  12   . In  FIG.  12   , a plurality of symbols may be present along the frequency axis, that is to say, symbols may be present on a plurality of frequencies (a plurality of carriers). 
       FIG.  7    illustrates one example of a configuration of a frame of a modulated signal transmitted by radio device  2001  in  FIG.  20   . In  FIG.  7   , time is represented on the horizontal axis. As illustrated in  FIG.  7   , base station  470  transmits, for example, preamble  701 , and then transmits control information symbol  702  and information symbol  703 . 
     Here, preamble  701  is a symbol for radio device  453  included in terminal  1050  in  FIG.  20   , which receives the modulated signal transmitted by radio device  2001  in  FIG.  20   , to perform, for example, signal detection, temporal synchronization, frame synchronization, frequency synchronization, and/or frequency offset estimation. 
     Control information symbol  702  includes data such as information related to the error correction encoding scheme method and/or demodulation scheme used in the generation of the modulated signal, information related to frame configuration, and information related to the transmission method used, and radio device  453  included in terminal  1050  in  FIG.  20   , for example, demodulates the modulated signal based on the information included in the control information symbol. 
     Information symbol  703  is a symbol for radio device  2001  in  FIG.  20    to transmit data. 
     Note that radio device  2001  included in base station  2000  in  FIG.  20    may transmit a frame including symbols other than the symbols illustrated in  FIG.  7    (for example, a frame including a pilot symbol (reference symbol) midway through the information symbol). Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  7   . In  FIG.  7   , a plurality of symbols may be present along the frequency axis, that is to say, symbols may be present on a plurality of frequencies (a plurality of carriers). 
     Moreover, for example, a modulated signal that has the frame configuration illustrated in  FIG.  11    and is transmitted by an element related to the LED lamp, light source, and/or light that emits visible light in base station  200  being transmitted at a regular timing, e.g., repeatedly transmitted is conceivable. This makes it possible for a plurality of terminals to implement the operations described above. 
       FIG.  21    is a flow chart illustrating one example of processes implemented by an element related to the LED lamp, light source, and/or light that emits visible light, terminal  1050 , and radio device  2001  in the base station (or AP) in  FIG.  20   . 
     First, as  1301  in  FIG.  21    illustrates, an element related to the LED lamp, light source, and/or light that emits visible light in  FIG.  20    transmits a modulated signal having the frame configuration illustrated in  FIG.  11   . 
     Then, as  1302  in  FIG.  21    illustrates, the modulated signal transmitted by an element related to the LED lamp, light source, and/or light that emits visible light in  FIG.  20    is received, and terminal  1050  in  FIG.  20    obtains the SSID of the base station to be accessed by terminal  1050 . 
     Likewise, as  1303  in  FIG.  21    illustrates, terminal  1050  in  FIG.  20    obtains an encryption key to be used for communicating with base station  470  to be accessed by the terminal. 
     Terminal  1050  in  FIG.  20    requests connection with radio device  2001  included in base station  2000  in  FIG.  20    over radio waves ( 1304 ). 
     As  1305  in  FIG.  21    illustrates, terminal  1050  in  FIG.  20    completes the connection with radio device  2001  included in base station  2000  in  FIG.  20    upon receiving a response from radio device  2001  included in base station  2000  in  FIG.  20   . 
     As  1306  in  FIG.  21    illustrates, terminal  1050  in  FIG.  20    transmits information on the connection destination to radio device  2001  included in base station  2000  in  FIG.  20    using radio waves. 
     Then, as  1307  in  FIG.  21    illustrates, radio device  2001  included in base station  2000  in  FIG.  20    obtains information to be transmitted to terminal  1050  in  FIG.  20    from the network. 
     As  1308  in  FIG.  21    illustrates, radio device  2001  included in base station  2000  in  FIG.  20    transmits the obtained information to terminal  1050  in  FIG.  20    using radio waves, and terminal  1050  in  FIG.  20    obtains the information. 
     For example, when necessary, terminal  1050  in  FIG.  20    obtains required information from the network via radio device  2001  included in base station  2000  in  FIG.  20   . 
     As described above, based on the SSID information and the encryption key information transmitted from an element related to the LED lamp, light source, and/or light that emits visible light in the base station, the terminal connects to the base station (or AP) and obtains information, whereby an advantageous effect that it is possible to securely obtain information via the base station (or AP) whose security has been authenticated can be achieved. This is because, when information from a visible light modulated signal is obtained, since it is visible light, the user can easily determine whether the source of information is secure or not. 
     For example, when an SSID is obtained from a modulated signal transmitted by a wireless LAN over radio waves, it is difficult for the user to determine which device transmitted the radio waves. Accordingly, from the viewpoint of ensuring information security, obtaining the SSID via visible light communication is more suitable. 
     Note that in this embodiment, an element related to the LED lamp, light source, and/or light that emits visible light in the base station is exemplified as transmitting encryption key information, but, for example, when the base station (or AP) does not perform encrypted communication using an encryption key, the element related to the LED lamp, light source, and/or light that emits visible light in the base station can transmit only the information related to an SSID without transmitting the encryption key information, that is, the element related to the LED lamp, light source, and/or light that emits visible light in the base station may be implemented without the configuration related to an encryption key. 
     As illustrated in  FIG.  20   , the SSID and encryption key for radio device  2001  included in base station  2000  may be overwritten. For example, in  FIG.  20   , information  1001 - 1  related to an SSID and information  1001 - 2  related to an encryption key are received as inputs by radio device  2001 . Radio device  2001  included in base station  2000  overwrites the SSID and encryption key as per the input information  1001 - 1  related to an SSID and information  1001 - 2  related to an encryption key. With this, the security of the communication between the terminal and radio device  2001  included in base station  2000  is assured (however, in  FIG.  20   , although radio device  2001  included in base station  2000  has a function of being able to overwrite the SSID and encryption key, radio device  2001  included in base station  2000  may have a configuration in which this function is not included). 
     Moreover, the configuration of an element related to the LED lamp, light source, and/or light that emits visible light in the base station is not limited to the configuration illustrated in  FIG.  20   , the configuration of the terminal is not limited to the configuration illustrated in  FIG.  20   , and the configuration of the connection destination of the radio device included in the base station is not limited to the configuration illustrated in  FIG.  20   . 
     In this embodiment, although only one base station (or AP) is exemplified in the configuration illustrated in  FIG.  20   , a plurality of (secure) base stations (or APs) accessible by the terminal may be included (note that the radio devices in these base stations transmit and receive modulated signals using radio waves). Here, the symbol related to an SSID transmitted by an element related to the LED lamp, light source, and/or light that emits visible light in  FIG.  20    may include information indicating the SSIDs of the plurality of radio devices in the base stations (or APs). Moreover, the symbol related to an encryption key transmitted by an element related to the LED lamp, light source, and/or light that emits visible light in  FIG.  20    may include encryption key information used to connect to the plurality of radio devices in the base stations (or APs). Terminal  1050  in  FIG.  20    may select a radio device in a base station (or AP) to wirelessly connect to (for example, over radio waves), based on the information on the SSIDs and encryption key information of the radio stations in the base stations (or connect to the plurality of radio devices in the plurality of base stations (or APs)). 
     For example, assume there are three base stations (or APs) that include radio devices. The radio devices are named radio device #A, radio device #B, and radio device #C. The SSID of radio device #A is “abcdef”, the SSID of radio device #B is “ghijk”, and the SSID of radio device #C is “pqrstu”, the encryption key for connecting with radio device #A is “123”, the encryption key for connecting with radio device #B is “456”, and the encryption key for connecting with radio device #C is “789”. 
     In such cases, symbol  600 - 1  related to an SSID in the frame configuration illustrated in  FIG.  11    of the modulated signal transmitted by an element related to the LED lamp, light source, and/or light that emits visible light in base station  200  includes information related to the SSID “abcdef” of radio device #A, the SSID “ghijk” of radio device #B, and the SSID “pqrstu” of radio device #C. The symbol  1101  related to an encryption key having the frame configuration illustrated in  FIG.  11    includes information related to the encryption key “123” for connecting with radio device #A, the encryption key “456” for connecting with radio device #B, and the encryption key “789” for connecting with radio device #C. 
     Terminal  1050  in  FIG.  20    receives symbol  600 - 1  related to an SSID and thus obtains the SSID “abcdef” of radio device #A, the SSID “ghijk” of radio device #B, and the SSID “pqrstu” of radio device #C, receives symbol  1101  related to an encryption key and thus obtains the encryption key “123” for connecting with radio device #A, the encryption key “456” for connecting with radio device #B, and the encryption key “789” for connecting with radio device #C. Then, based on this information, terminal  1050  in  FIG.  20    selects a base station (or AP) to wirelessly connect to (for example, via radio waves), and connects to the selected base station (or AP). 
     As described in this embodiment, as a result of the terminal setting a radio device included in a base station to access using a light source, exemplified here as an LED light source, a mode for making a special setting for processes for establishing a wireless connection between the terminal and base station in the modulated signal for connection over radio waves that is transmitted by the terminal is not required, and a mode for making a special setting for processes for establishing a wireless connection between the terminal and base station in the modulated signal for connection over radio waves that is transmitted by the base station is not required, whereby an advantageous effect that wireless communication data transmission efficiency improves can be achieved. 
     As described above, the encryption key may be an encryption key for an SSID on a wireless LAN, may be an encryption key for restricting the form of connection used, the form of service used, and/or the connectivity range of the network (in other words, any encryption key that is restrictive is sufficient). 
     Embodiment 7 (Plural Base Stations; Access Control Performed) 
       FIG.  22    illustrates one example of a configuration of a communication system according to this embodiment. The communication system illustrated in  FIG.  22    includes, for example: device  1000  including an LED light source, lamp, light source, and/or light that emits visible light; terminal  1050 ; and, for example, base station # 1   470 - 1 , base station # 2   470 - 2 , and base station # 3   470 - 3  that communicate with terminal  1050 . Note that in  FIG.  22   , operations that are the same as in  FIG.  1   ,  FIG.  4   , and  FIG.  10    share like reference marks. 
     Device  1000  in  FIG.  22    includes, for example, an LED lamp, light source, and/or light that emits visible light. Note that device  1000  is referred to as a “fifth device” in this embodiment. Note that communication between radio device radio device  453  and base station # 1   470 - 1 , between radio device  453  and base station # 2   470 - 2 , and between radio device  453  and base station # 3   470 - 3  in  FIG.  22    is performed using, for example, radio waves. 
     In fifth device  1000  in  FIG.  22   , transmitter  102  receives inputs of information  1001 - 1  related to an SSID, information  1001 - 2  related to an encryption key, and data  1002 , and based on these input signals, generates a (optical) modulated signal, and outputs modulated signal  103 . For example, modulated signal  103  is transmitted from light source  104 . 
     Next, information  1001 - 1  related to an SSID and information  1001 - 2  related to an encryption key will be described. 
     First, information  1001 - 1  related to an SSID will be described. 
     For example, information  1001 - 1  related to an SSID is information indicating the SSID of base station (or AP)  470 - 1  in  FIG.  22   , the SSID of base station (or AP)  470 - 2  in  FIG.  22   , and the SSID of base station (or AP)  470 - 3  in  FIG.  22   . Note that, in this example, base stations (or APs)  470 - 1 ,  470 - 2 , and  470 - 3  transmit modulated signals over radio waves, and receive radio wave modulated signals. In other words, fifth device  1000  can provide access to base stations  470 - 1 ,  470 - 2 , and  470 - 3 , which are secure access destinations for the terminal. With this, terminal  1050  in  FIG.  22    can achieve the advantageous effect of being able to securely obtain information from base stations (or APs)  470 - 1 ,  470 - 2 , and  470 - 3 . 
     On the other hand, device  1000  can restrict the terminals that access base stations  470 - 1 ,  470 - 2 , and  470 - 3  to terminals in a space in which it is possible to receive optical signals transmitted (emitted) by device  1000 . Note that when terminal  1050  receives an optical signal transmitted via a predetermined scheme, it may be determined that the notified SSID is the SSID of a secure base station, and, alternatively, processing for determining whether the SSID is secure or not may be performed. For example, device  1000  may transmit a predetermined identifier in an optical signal, and the terminal may determine whether the notified SSID is the SSID of a secure base station or not based on the received identifier. 
     Note that the configuration in  FIG.  22    illustrates base stations (or AP)  470 - 1 ,  470 - 2 , and  470 - 3 , but one or more base stations (or APs) other than base stations (or AP)  470 - 1 ,  470 - 2 , and  470 - 3  may also be included. 
     Information  1001 - 2  related to an encryption key is information related to an encryption key required for terminal  1050  in  FIG.  22    to establish communication with base stations (or AP)  470 - 1 ,  470 - 2 , and  470 - 3  in  FIG.  22   . Encrypted communication is possible between the terminal and base station (or AP)  470 - 1 , between the terminal and base station (or AP)  470 - 2 , and between the terminal and base station (or AP)  470 - 3  as a result of terminal  1050  in  FIG.  22    obtaining this information from fifth device  1000  in  FIG.  22   . 
     Terminal  1050  in  FIG.  22    receives the modulated signal transmitted by fifth device  1000 . Note that in terminal  1050  in  FIG.  22   , components that operate the same as terminal  150  in  FIG.  1    and terminal  450  in  FIG.  4    share like reference marks. 
     Light receiver  151  included in terminal  1050 , examples of which include an image sensor such as a CMOS or organic CMOS image sensor, receives the modulated signal transmitted by fifth device  1000 . Receiver  153  receives an input of reception signal  152  received by light receiver  151 , performs processing such as demodulation and error correction decoding on the reception signal, and outputs reception data  154 . 
     Data analyzer  155  receives an input of reception data  154 , and outputs, based on the reception data, for example, information  1051  on the SSIDs of the base stations ( 470 - 1 ,  470 - 2 , and  470 - 3 ) to be connected to, and information  1052  on the encryption keys for communication with the base stations ( 470 - 1 ,  470 - 2 , and  470 - 3 ) to be connected to. For example, in a wireless local area network (LAN), examples of encryption schemes include wired equivalent privacy (WEP), Wi-Fi protected access (WPA), and Wi-Fi protected access 2 (WPA2) (pre-shared key (PSK) mode, extended authentication protocol (EAP) mode). However, the encryption method is not limited to these examples. 
     Display  157  receives inputs of information  1051  on the SSID and information  1052  on the encryption key, and, for example, displays the SSID of the communication partner to be accessed by radio device  453  included in the terminal, and the encryption key (this display is referred to as a “first display” in this embodiment). 
     For example, after the first display, radio device  453  included in terminal  1050  in  FIG.  22    receives inputs of information  1051  on the SSID and information  1052  on the encryption key, and establishes a connection with any one of base stations (or APs)  470 - 1 ,  470 - 2 , and  470 - 3  (for example, the connection uses radio waves). Here, when the base station also communicates with radio device  453  in terminal  1050  in  FIG.  22   , the base station transmits a modulated signal using, for example, radio waves. 
     Thereafter, radio device  453  included in terminal  1050  in  FIG.  22    receives inputs of data  1053  and control signal  1054 , demodulates data  1053  in accordance with control signal  1054 , and transmits a modulated signal as radio waves. 
     Then, for example, the base station (or AP) connected to transmits data to the network (any one of  471 - 1 ,  471 - 2 , and  471 - 3 ) and receives data (any one of  472 - 1 ,  472 - 2 , and  472 - 3 ) from the network. Thereafter, for example, the base station connected to transmits, to terminal  1050  in  FIG.  22   , a modulated signal as radio waves. 
     Radio device  453  included in terminal  1050  in  FIG.  22    performs processing such as demodulation and error correction decoding on the modulated signal received as radio waves to obtain reception data  1056 . Display  157  displays a display based on reception data  1056 . 
     Assume, in the case of  FIG.  22   , there are three types of frame configurations as modulated signals transmitted by fifth device  1000  in  FIG.  22   .  FIG.  23    illustrates frame # 1   2300 - 1 , which is one of the three types of frame configurations,  FIG.  24    illustrates frame configuration # 2   2300 - 2 , which is one of the three types of frame configurations, and  FIG.  25    illustrates frame configuration # 3   2300 - 3 , which is one of the three types of frame configurations. 
       FIG.  23    illustrates one example of the configuration of frame # 1   2300 - 1  of a modulated signal transmitted by fifth device  1000  in  FIG.  22   . In  FIG.  23   , time is represented on the horizontal axis, and symbols that are the same as in  FIG.  2    and  FIG.  11    share like reference marks. Accordingly, repeated description thereof will be omitted. Frame # 1   2300 - 1  in  FIG.  23    is a frame for transmitting information on the SSID of base station # 1   470 - 1  in  FIG.  22    and an encryption key for base station # 1   470 - 1  (an encryption key for accessing base station # 1   470 - 1 ) in  FIG.  22   . 
     Symbol  2301 - 1  related to an SSID in  FIG.  23    is a symbol for transmitting information  1001 - 1  related to an SSID in  FIG.  22   . Moreover, symbol  2301 - 1  related to an SSID in  FIG.  23    is a symbol for fifth device  1000  in  FIG.  22    to transmit the SSID of base station # 1   470 - 1  in  FIG.  22   . 
     Symbol  2302 - 1  related to an encryption key in  FIG.  23    is a symbol for transmitting information  1001 - 2  related to an encryption key in  FIG.  22   . Moreover, symbol  2302 - 1  related to an encryption key in  FIG.  23    is a symbol for fifth device  1000  in  FIG.  22    to transmit an encryption key for base station # 1   470 - 1  (an encryption key for accessing base station # 1   470 - 1 ) in  FIG.  22   . 
     Fifth device  1000  transmits preamble  201 , control information symbol  202 , symbol  2301 - 1  related to an SSID, symbol  2302 - 1  related to an encryption key, and data symbol  1102 . Note that fifth device  1000  in  FIG.  22    may transmit frame # 1   2300 - 1  including symbols other than the symbols illustrated in  FIG.  23   . Moreover, the configuration of frame # 1   2300 - 1 , including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  23   . 
       FIG.  24    illustrates one example of the configuration of frame # 2   2300 - 2  of a modulated signal transmitted by fifth device  1000  in  FIG.  22   . In  FIG.  24   , time is represented on the horizontal axis, and symbols that are the same as in  FIG.  2    and  FIG.  11    share like reference marks. Accordingly, repeated description thereof will be omitted. Frame # 2   2300 - 2  in  FIG.  24    is a frame for transmitting information on the SSID of base station # 2   470 - 2  in  FIG.  22    and an encryption key for base station # 2   470 - 2  (an encryption key for accessing base station # 2   470 - 2 ) in  FIG.  22   . 
     Symbol  2301 - 2  related to an SSID in  FIG.  24    is a symbol for transmitting information  1001 - 1  related to an SSID in  FIG.  22   . Moreover, symbol  2301 - 2  related to an SSID in  FIG.  24    is a symbol for fifth device  1000  in  FIG.  22    to transmit the SSID of base station # 2   470 - 2  in  FIG.  22   . 
     Symbol  2302 - 2  related to an encryption key in  FIG.  24    is a symbol for transmitting information  1001 - 2  related to an encryption key in  FIG.  22   . Moreover, symbol  2302 - 2  related to an encryption key in  FIG.  24    is a symbol for fifth device  1000  in  FIG.  22    to transmit an encryption key for base station # 2   470 - 2  (an encryption key for accessing base station # 2   470 - 2 ) in  FIG.  22   . 
     Fifth device  1000  transmits preamble  201 , control information symbol  202 , symbol  2301 - 2  related to an SSID, symbol  2302 - 2  related to an encryption key, and data symbol  1102 . Note that fifth device  1000  in  FIG.  22    may transmit frame # 2   2300 - 2  including symbols other than the symbols illustrated in  FIG.  24   . Moreover, the configuration of frame # 2   2300 - 2 , including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  24   . 
       FIG.  25    illustrates one example of the configuration of frame # 3   2300 - 3  of a modulated signal transmitted by fifth device  1000  in  FIG.  22   . In  FIG.  25   , time is represented on the horizontal axis, and symbols that are the same as in  FIG.  2    and  FIG.  11    share like reference marks. Accordingly, repeated description thereof will be omitted. Frame # 3   2300 - 3  in  FIG.  25    is a frame for transmitting information on the SSID of base station # 3   470 - 3  in  FIG.  22    and an encryption key for base station # 3   470 - 3  (an encryption key for accessing base station # 3   470 - 3 ) in  FIG.  22   . 
       FIG.  25    illustrates one example of the configuration of frame # 3   2300 - 3  of a modulated signal transmitted by fifth device  1000  in  FIG.  22   . In  FIG.  25   , time is represented on the horizontal axis, and symbols that are the same as in  FIG.  2    and  FIG.  11    share like reference marks. Accordingly, repeated description thereof will be omitted. Frame # 3   2300 - 3  in  FIG.  25    is a frame for transmitting information on the SSID of base station # 3   470 - 3  in  FIG.  22    and an encryption key for base station # 3   470 - 3  (an encryption key for accessing base station # 3   470 - 3 ) in  FIG.  22   . 
     Symbol  2301 - 3  related to an SSID in  FIG.  25    is a symbol for transmitting information  1001 - 1  related to an SSID in  FIG.  22   . Moreover, symbol  2301 - 3  related to an SSID in  FIG.  25    is a symbol for fifth device  1000  in  FIG.  22    to transmit the SSID of base station # 3   470 - 3  in  FIG.  22   . 
     Symbol  2302 - 3  related to an encryption key in  FIG.  25    is a symbol for transmitting information  1001 - 2  related to an encryption key in  FIG.  22   . Moreover, symbol  2302 - 3  related to an encryption key in  FIG.  25    is a symbol for fifth device  1000  in  FIG.  22    to transmit an encryption key for base station # 3   470 - 3  (an encryption key for accessing base station # 3   470 - 3 ) in  FIG.  22   . 
     Fifth device  1000  transmits preamble  201 , control information symbol  202 , symbol  2301 - 3  related to an SSID, symbol  2302 - 3  related to an encryption key, and data symbol  1102 . Note that fifth device  1000  in  FIG.  22    may transmit frame # 3   2300 - 3  including symbols other than the symbols illustrated in  FIG.  25   . Moreover, the configuration of frame # 3   2300 - 3 , including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  25   . 
       FIG.  26    illustrates an example of a transmission method used by fifth device  1000  in  FIG.  22    upon transmitting frame # 1   2300 - 1  in  FIG.  23   , frame # 2   2300 - 2  in  FIG.  24   , and frame # 3   2300 - 3  in  FIG.  25   . In  FIG.  26   , time is represented on the horizontal axis. 
     In  FIG.  26   , in the frame # 1  group transmissions of  2601 - 1  and  2601 - 2 , one or more of frames # 1   2300 - 1  illustrated in  FIG.  23    are transmitted. In the frame # 2  group transmissions of  2602 - 1  and  2602 - 2 , one or more of frames # 2   2300 - 2  in  FIG.  24    are transmitted. In the frame # 3  group transmissions of  2603 - 1  and  2603 - 2 , one or more of frames # 3   2300 - 3  in  FIG.  25    are transmitted. 
     This will be described in more detail next. 
     The recitation “in the frame # 1  group transmissions of  2601 - 1  and  2601 - 2 , one or more of frames # 1   2300 - 1  illustrated in  FIG.  23    are transmitted” above will be described. 
     For example, when an image sensor, such as a CMOS or organic CMOS image sensor is used in light receiver  151 , it is possible to process the reception signal in units of frames in moving or still images. Note that, for example, when a moving picture is labeled as “4K 30p”, the number of pixels of one frame is 3840×2160, and the moving picture includes 30 frames per second. 
     Accordingly, when fifth device  1000  in  FIG.  22    transmits a modulated signal including frame # 1   2300 - 1  in  FIG.  23   , frame # 2   2300 - 2  in  FIG.  24   , and frame # 3   2300 - 3  in  FIG.  25    in a single frame, terminal  1050  in  FIG.  22    has difficulty in selecting a base station to access from among the plurality of base stations. 
     In view of this, a frame configuration such as illustrated in  FIG.  26    is proposed. 
     Method 1-1: 
     Method 1-1 makes the temporal space that frame # 1  group transmission occupies longer than a frame of a still or moving picture by including a plurality of frames # 1   2300 - 1  illustrated in  FIG.  23   , in frame # 1  group transmissions of  2601 - 1  and  2601 - 2 . 
     This method makes it possible for terminal  1050  in  FIG.  22    to easily select a base station to access from among the plurality of base stations since terminal  1050  in  FIG.  22    can prevent the reception of a modulated signal including, in a single frame of a still or moving picture, frame # 1   2300 - 1  in  FIG.  23   , frame # 2   2300 - 2  in  FIG.  24   , and frame # 3   2300 - 3  in  FIG.  25   , by fifth device  1000 . 
     Method 2-1: 
     Method 2-1 makes the temporal space that frame # 1   2300 - 1  in  FIG.  23    occupies longer than a frame of a still or moving picture. For example, symbol  2301 - 1  related to an SSID in  FIG.  23    may include a plurality of items of the information on the SSID for base station # 1  (the information on the SSID for base station # 1  is repeatedly included), or symbol  2302 - 1  related to an encryption key may include a plurality of items of the information on the encryption key for base station # 1  (the encryption key for connecting with base station # 1 ) (the information on the encryption key for base station # 1  (the encryption key for connecting with base station # 1 ) is repeatedly included). 
     This method makes it possible for terminal  1050  in  FIG.  22    to easily select a base station to access from among the plurality of base stations since terminal  1050  in  FIG.  22    can prevent the reception of a modulated signal including, in a single frame of a still or moving picture, frame # 1   2300 - 1  in  FIG.  23   , frame # 2   2300 - 2  in  FIG.  24   , and frame # 3   2300 - 3  in  FIG.  25   , by fifth device  1000 . 
     Similarly, frame # 2  group transmissions of  2602 - 1  and  2602 - 2  may have the following configurations. 
     Method 1-2: 
     Method 1-2 makes the temporal space that frame # 2  group transmission occupies longer than a frame of a still or moving picture by including a plurality of frames # 2   2300 - 2  illustrated in  FIG.  24   , in frame # 2  group transmissions of  2602 - 1  and  2602 - 2 . 
     Method 2-2: 
     Method 2-2 makes the temporal space that frame # 2   2300 - 2  in  FIG.  24    occupies longer than a frame of a still or moving picture. For example, symbol  2301 - 2  related to an SSID in  FIG.  24    may include a plurality of items of the information on the SSID for base station # 2  (the information on the SSID for base station # 2  is repeatedly included), or symbol  2302 - 2  related to an encryption key may include a plurality of items of the information on the encryption key for base station # 2  (the encryption key for connecting with base station # 2 ) (the information on the encryption key for base station # 2  (the encryption key for connecting with base station # 2 ) is repeatedly included). 
     Similarly, frame # 3  group transmissions of  2603 - 1  and  2603 - 2  may have the following configurations. 
     Method 1-3: 
     Method 1-3 makes the temporal space that frame # 3  group transmission occupies longer than a frame of a still or moving picture by including a plurality of frames # 3   2300 - 3  illustrated in  FIG.  25   , in frame # 3  group transmissions of  2603 - 1  and  2603 - 2 . 
     Method 2-3: 
     Method 2-3 makes the temporal space that frame # 3   2300 - 3  in  FIG.  25    occupies longer than a frame of a still or moving picture. For example, symbol  2301 - 3  related to an SSID in  FIG.  25    may include a plurality of items of the information on the SSID for base station # 3  (the information on the SSID for base station # 3  is repeatedly included), or symbol  2302 - 3  related to an encryption key may include a plurality of items of the information on the encryption key for base station # 3  (the encryption key for connecting with base station # 3 ) (the information on the encryption key for base station # 3  (the encryption key for connecting with base station # 3 ) is repeatedly included). 
     Next, the advantageous effects achieved when fifth device  1000  in  FIG.  22    transmits a frame, such as those illustrated in  FIG.  23    through  FIG.  26   , will be described. 
     Consider area  2700  in  FIG.  27   . Fifth devices  1000  having the configuration illustrated in  FIG.  22    are disposed at circles  2701 - 1 ,  2701 - 2 ,  2701 - 3 ,  2701 - 4 ,  2701 - 5 ,  2701 - 6 ,  2701 - 7 ,  2701 - 8 ,  2701 - 8 ,  2701 - 9 , and  2701 - 10 . Base station # 1   470 - 1  in  FIG.  22    is disposed at double circle  2702 - 1 , base station # 2   470 - 2  in  FIG.  22    is disposed at double circle  2702 - 2 , and base station # 3   470 - 3  in  FIG.  22    is disposed at double circle  2702 - 3 . 
     For example, 99 terminals having the configuration of  1050  in  FIG.  22    are present in the area indicated as  2703 . 
     Here, for example, fifth devices  2701 - 5  and  2701 - 10  both transmit information on the SSID of base station # 3   470 - 3  and information on the encryption key for access to base station # 3   470 - 3  (since the base station closest to fifth devices  2701 - 5  and  2701 - 10  is base station # 3   470 - 3 ). 
     In such cases, all of the 99 terminals having the configuration of  1050  in  FIG.  22    will access base station # 3   470 - 3  in  FIG.  22   . This means there is a high probability that the terminals having the configuration of  1050  in  FIG.  22    will have difficulty accessing base station # 3   470 - 3  in  FIG.  22   . 
     Taking this point into consideration, by making it so that the 99 terminals having the configuration of  1050  in  FIG.  22    access base station # 1   470 - 1  ( 2702 - 1 ) in  FIG.  22   , base station # 2   470 - 2  ( 2702 - 2 ) in  FIG.  22   , and base station # 3   470 - 3  ( 2702 - 3 ) in  FIG.  22    as evenly as possible, it is possible to achieve the advantageous effect of a reduction in terminals having difficulty accessing a base station, as described above. 
     In this embodiment, when fifth device  1000  in  FIG.  22    transmits a frame, such as those illustrated in  FIG.  23    through  FIG.  26   , the 99 terminals having the configuration of  1050  in  FIG.  22    typically access fifth device  1000  in  FIG.  22    at different timings, so the 99 terminals having the configuration of  1050  in  FIG.  22    access base station # 1   470 - 1  ( 2702 - 1 ) in  FIG.  22   , base station # 2   470 - 2  ( 2702 - 2 ) in  FIG.  22   , and base station # 3   470 - 3  ( 2702 - 3 ) in  FIG.  22    as evenly as possible. Accordingly, the previously-described advantageous effect of a reduction in terminals having difficulty accessing a base station can be achieved. In other words, it is possible to achieve an advantageous effect that concentration of access from a plurality of terminals to any given base station can be avoided. 
     Note that although  FIG.  26    illustrates an example of a transmission method used upon fifth device  1000  in  FIG.  22    transmitting frame # 1   2300 - 1  in  FIG.  23   , frame # 2   2300 - 2  in  FIG.  24   , and frame # 3   2300 - 3  in  FIG.  25   , the transmission method used upon fifth device  1000  in  FIG.  22    transmitting frame # 1   2300 - 1  in  FIG.  23   , frame # 2   2300 - 2  in  FIG.  24   , and frame # 3   2300 - 3  in  FIG.  25    is not limited to this example. 
     For example, in  FIG.  26   , the order of frame # 1  group transmission, frame # 2  group transmission, and frame # 3  group transmission is repeated, but the order in which frame # 1  group transmission, frame # 2  group transmission, and frame # 3  group transmission are transmitted is not limited to the example given in  FIG.  26   . For example, the transmission of frame group # 1 , the transmission of frame group # 2 , and the transmission of frame group # 3  may be temporally randomized, and, alternatively, the order of the transmission of frame group # 1 , the transmission of frame group # 2 , and the transmission of frame group # 3  may be a regular order different than the example given in  FIG.  26   . It is sufficient so long as fifth device  1000  in  FIG.  22    transmits frame # 1  group, frame # 2  group, and frame # 3  group. For example, when fifth device  1000  temporally randomizes the transmission of frame group # 1 , the transmission of frame group # 2 , and the transmission of frame group # 3 , a random number may be generated at a given timing, and the frame group specified by that random number may be transmitted at that time. Note that the usage of a random number is merely one non-limiting example. 
     Moreover, in  FIG.  26   , frame # 1  group transmission, frame # 2  group transmission, and frame # 3  group transmission are exemplified as being performed consecutively, but these transmissions do not necessarily need to be performed consecutively. For example, in  FIG.  26   , there may be a time interval between frame # 1  group transmission  2601 - 1  and frame # 2  group transmission  2602 - 2 . 
     In  FIG.  26   , the example includes only frame # 1  group transmission, frame # 2  group transmission, and frame # 3  group transmission, but other symbols and/or frames may be included. Furthermore, in  FIG.  26    and  FIG.  22   , there are three base stations, but the number of base stations is not limited to this example. As long as there are two or more base stations, they can operate the same as when there are three. Accordingly, for example, when there are N base stations (N is an integer of 2 or more), when transmission such as that illustrated in  FIG.  26    is performed, frame #k group transmission is performed. Note that k is an integer greater than or equal to 1 and less than or equal to N. Then, in the transmission of frame #k group, there is a symbol related to an SSID (information on the SSID of base station #k) and a symbol related to an encryption key (information on an encryption key for base station #k). 
       FIG.  12    illustrates one example of a configuration of a frame of a modulated signal transmitted by radio device  453  included in terminal  1050  in  FIG.  22   . In  FIG.  12   , time is represented on the horizontal axis. As illustrated in  FIG.  12   , radio device  453  included in terminal  1050  in  FIG.  22    transmits, for example, preamble  1201 , and then transmits control information symbol  1202  and information symbol  1203 . 
     Here, preamble  1201  is a symbol used for base stations (or APs)  470 - 1 ,  470 - 2 , and  470 - 3  that receive the modulated signal transmitted by radio device  453  in terminal  1050  in  FIG.  22    to perform, for example, signal detection, temporal synchronization, frame synchronization, frequency synchronization, and frequency offset estimation. 
     Control information symbol  1202  includes data such as information related to the error correction encoding scheme method and/or demodulation scheme used in the generation of the modulated signal, information related to frame configuration, and information related to the transmission method used, and base stations (or APs)  470 - 1 ,  470 - 2 , and  470 - 3 , for example, demodulate the modulated signal based on the information included in control information symbol  1202 . 
     Information symbol  1203  is a symbol for radio device  453  included in terminal  1050  in  FIG.  22    to transmit data. 
     Note that radio device  453  included in terminal  1050  in  FIG.  22    may transmit a frame including symbols other than the symbols illustrated in  FIG.  12    (for example, a frame including a pilot symbol (reference symbol) midway through the information symbol). Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  12   . In  FIG.  12   , a plurality of symbols may be present along the frequency axis, that is to say, symbols may be present on a plurality of frequencies (a plurality of carriers). 
       FIG.  7    illustrates one example of a configuration of a frame of a modulated signal transmitted by base stations  470 - 1 ,  470 - 2 , and  470 - 3  in  FIG.  22   . In  FIG.  7   , time is represented on the horizontal axis. As illustrated in  FIG.  7   , base stations  470 - 1 ,  470 - 2 , and  470 - 3  transmit, for example, preamble  701 , and then transmit control information symbol  702  and information symbol  703 . 
     Here, preamble  701  is a symbol for radio device  453  included in terminal  1050  in  FIG.  22   , which receives the modulated signals transmitted by base stations  470 - 1 ,  470 - 2 , and  470 - 3 , to perform, for example, signal detection, temporal synchronization, frame synchronization, frequency synchronization, and/or frequency offset estimation. 
     Control information symbol  702  includes data such as information related to the error correction encoding scheme method and/or demodulation scheme used in the generation of the modulated signal, information related to frame configuration, and information related to the transmission method used, and radio device  453  included in terminal  1050  in  FIG.  22   , for example, demodulates the modulated signal based on the information included in the control information symbol. 
     Information symbol  703  is a symbol for base stations (or APs)  470 - 1 ,  470 - 2 , and  470 - 3  in  FIG.  22    to transmit data. 
     Note that base stations (or APs)  470 - 1 ,  470 - 2 , and  470 - 3  in  FIG.  22    may transmit a frame including symbols other than the symbols illustrated in  FIG.  7    (for example, a frame including a pilot symbol (reference symbol) midway through the information symbol). Moreover, the frame configuration, including the order in which the symbols are transmitted, is not limited to the configuration illustrated in  FIG.  7   . In  FIG.  7   , a plurality of symbols may be present along the frequency axis, that is to say, symbols may be present on a plurality of frequencies (a plurality of carriers). 
       FIG.  28    is a flow chart illustrating one example of processes implemented by fifth device  1000 , terminal  1050 , and base station #X (or AP #X) in  FIG.  22   . Note that X is 1, 2, or 3. 
     First, as  2801  in  FIG.  28    illustrates, fifth device  1000  in  FIG.  22    transmits a modulated signal having the frame configuration illustrated in  FIG.  26   . 
     Likewise, as  2802  in  FIG.  28    illustrates, the modulated signal transmitted by fifth device  1000  in  FIG.  22    is received, and terminal  1050  in  FIG.  22    selects the base station to be accessed by terminal  1050  from among base station # 1   470 - 1 , base station # 2   470 - 2 , and base station # 3   470 - 3  in  FIG.  22   . 
     This point will be discussed next. Terminal  1050  in  FIG.  22    attempts to access a base station, and receives a modulated signal transmitted by fifth device  1000  in  FIG.  22   . Here, for example, in one frame of a moving or still picture, any one of frame # 1  group transmission, frame # 2  group transmission, and frame # 3  group transmission in  FIG.  26    is obtained. Then, from the obtained information on the base station (for example, the SSID), terminal  1050  in  FIG.  22    determines which of base station # 1   470 - 1 , base station # 2   470 - 2 , and base station # 3   470 - 3  in  FIG.  22    to access. 
     For example, terminal  1050  selects the frame group transmission first received from among frame # 1  group transmission, frame # 2  group transmission, and frame # 3  group transmission, and determines the base station to access from the information on the base station from that frame group transmission (for example, the SSID). 
     As  2803  in  FIG.  28    illustrates, the modulated signal transmitted by fifth device  1000  in  FIG.  22    is received, and terminal  1050  in  FIG.  22    obtains the SSID of base station #X to be accessed by terminal  1050 . 
     Likewise, as  2804  in  FIG.  28    illustrates, terminal  1050  in  FIG.  22    obtains an encryption key to be used for communicating with base station #X to be accessed by the terminal. 
     Terminal  1050  in  FIG.  22    then requests connection with base station #X over radio waves ( 2805 ). 
     As  2806  in  FIG.  28    illustrates, terminal  1050  in  FIG.  22    completes the connection with base station #X upon receiving a response from base station #X. 
     As  2807  in  FIG.  28    illustrates, terminal  1050  in  FIG.  22    transmits information on the connection destination to base station #X using radio waves. 
     Then, as  2808  in  FIG.  28    illustrates, base station #X obtains information to be transmitted to terminal  1050  in  FIG.  22    from the network. 
     As  2809  in  FIG.  28    illustrates, base station #X transmits the obtained information to terminal  1050  in  FIG.  22    using radio waves, and terminal  1050  in  FIG.  22    obtains the information. 
     For example, when necessary, terminal  1050  in  FIG.  22    obtains required information from the network via base station #X. 
     As described above, based on the SSID information and the encryption key information transmitted from the fifth device, the terminal connects to the base station (or AP) and obtains information, whereby an advantageous effect that it is possible to securely obtain information via the base station (or AP) whose security has been authenticated can be achieved. This is because, when information from a visible light modulated signal is obtained, since it is visible light, the user can easily determine whether the source of information is secure or not. 
     For example, when an SSID is obtained from a modulated signal transmitted by a wireless LAN over radio waves, it is difficult for the user to determine which device transmitted the radio waves. Accordingly, from the viewpoint of ensuring information security, obtaining the SSID via visible light communication is more suitable. 
     Note that in this embodiment, the fifth device is exemplified as transmitting encryption key information, but, for example, when the base station (or AP) does not perform encrypted communication using an encryption key, the fifth device can transmit only the information related to an SSID without transmitting the encryption key information, that is, the fifth device may be implemented without the configuration related to an encryption key. 
     Moreover, the configuration of the fifth device is not limited to the configuration illustrated in  FIG.  22   , the configuration of the terminal is not limited to the configuration illustrated in  FIG.  22   , and the configurations of the connection destination of base stations # 1 , # 2 , and # 3  are not limited to the configurations illustrated in  FIG.  22   . 
     Accordingly, when a configuration such as the one described in this embodiment is implemented, when there are a plurality of terminals in a given area, an advantageous effect of a reduction in terminals having difficulty accessing a base station can be achieved. 
     Note that in  FIG.  27   , the frame configurations of the modulated signals transmitted by the fifth devices disposed at circles  2701 - 1 ,  2701 - 2 ,  2701 - 3 ,  2701 - 4 ,  2701 - 5 ,  2701 - 6 ,  2701 - 7 ,  2701 - 8 ,  2701 - 8 ,  2701 - 9 , and  2701 - 10  may all be the same as illustrated in  FIG.  26   , the frame configurations of the modulated signals transmitted by the fifth devices may be mutually different, and two or more of the fifth devices may transmit modulated signals having the same frame configuration. 
     Moreover, in this embodiment, the terminal connects to the base station or access point in a wireless LAN using radio waves, but the device that the terminal connects to may be any device that the terminal can connect to using radio waves, and is not limited to a base station or access point in a wireless LAN. For example, the device may be a base station such as a mobile phone, or a relay station. Moreover, in this embodiment, an example is given in which information on an SSID is included in the modulated signal, but the SSID is merely one non-limiting example. In other words, the information included in the modulated signal may be any information from which a secure base station to which the terminal may connect to can be identified; the information is not limited to including an SSID. Moreover, the terminal may be any device that has the functions that terminal  1050  in  FIG.  22    has, and may, for example, may be a vehicle itself or be a device including transmitting and receiving functions that is included in a vehicle. 
     Embodiment 7 Summary 
     As described above, the transmission device according to this embodiment is, for example, device  1000  described above, and includes light source  104  and transmitter  102  that that generates a modulated signal based on an input signal and transmits the modulated signal from light source  104  as visible light by changing the luminance of light source  104  in accordance with the modulated signal. The modulated signal includes a plurality of items of information related to service set identifiers (SSIDs) of a plurality of mutually different access points in a wireless local area network (LAN). 
     Here, the modulated signal may include a plurality of frame groups respectively corresponding to the plurality of mutually different access points and each including one or more frames, and each of the one or more frames included in the plurality of frame groups may include the information related to the SSID of the access point corresponding to the frame group including the frame. 
     Moreover, the time required to transmit one of the plurality of frame groups may be longer than the time required to image one frame of a moving or still image by the reception device that receives the modulated signal. 
     Alternatively, the modulated signal may include a plurality of frames respectively corresponding to the plurality of mutually different access points, and each of the plurality of frames may include one or more items of the information related to the SSID of the access point corresponding to the frame. The time required to transmit one of the plurality of frames may be longer than the time required to image one frame of a moving or still image by the reception device that receives the modulated signal. 
     Moreover, transmitter  102  may transmit the plurality of frame groups respectively corresponding to the plurality of mutually different access points in random order along a time or frequency axis. 
     Alternatively, transmitter  102  may transmit the plurality of frame groups respectively corresponding to the plurality of mutually different access points in a regular order along a time or frequency axis. 
     The reception device according to the present embodiment is terminal  1050  that, for example, receives modulated signal transmitted as visible light from the transmission device. More specifically, the reception device includes: light receiver  151  that receives a modulated signal transmitted as visible light from a transmission device; data analyzer  155  that outputs analysis information by analyzing data based on the modulated signal; and a radio unit configured to, based on the analysis information, connect to an access point in a wireless local area network (LAN) using radio waves. For example, the radio unit is radio device  453 . Here, the modulated signal includes a plurality of items of information related to service set identifiers (SSIDs) of a plurality of mutually different access points in the wireless LAN. Data analyzer  155  selects any one of the plurality of items of the information related to the SSIDs of the plurality of mutually different access points included in the modulated signal, and outputs, as the analysis information, the information related to the SSID selected. The radio unit connects to, using radio waves, the access point corresponding to the information related to the SSID output from data analyzer  155 , from among the plurality of mutually different access points. 
     Here, the modulated signal may include a plurality of frame groups respectively corresponding to the plurality of mutually different access points and each including one or more frames, and each of the one or more frames included in the plurality of frame groups may include the information related to the SSID of the access point corresponding to the frame group including the frame. 
     The time required to receive one of the plurality of frame groups by light receiver  151  may be longer than the time required to image one frame of a moving or still image by light receiver  151 . 
     Alternatively, the modulated signal may include a plurality of frames respectively corresponding to the plurality of mutually different access points, and each of the plurality of frames may include one or more items of the information related to the SSID of the access point corresponding to the frame. The time required to receive one of the plurality of frames by light receiver  151  may be longer than the time required to image one frame of a moving or still image by light receiver  151 . 
     Moreover, light receiver  151  may receive the plurality of frame groups respectively corresponding to the plurality of mutually different access points in random order along a time or frequency axis. 
     Alternatively, light receiver  151  may receive the plurality of frame groups respectively corresponding to the plurality of mutually different access points in a regular order along a time or frequency axis. 
     The communication system according to the present embodiment includes a transmission device and a plurality of mutually different access points in a wireless local area network (LAN). The transmission device is, for example, device  1000 , and the plurality of access points include, for example, base station # 1   470 - 1 , base station # 2   470 - 2 , and base station # 3   470 - 3 . The transmission device includes: light source  104 ; and transmitter  102  that generates a modulated signal based on an input signal and transmits the modulated signal from light source  104  as visible light by changing the luminance of light source  104  in accordance with the modulated signal. The modulated signal includes a plurality of items of information related to service set identifiers (SSIDs) of the plurality of mutually different access points, and at least one of the plurality of mutually different access points connects, using radio waves, to a reception device that received the modulated signal, and transmits information to the reception device. 
     Moreover, the transmission method according to the present embodiment includes: generating a modulated signal based on an input signal; and transmitting the modulated signal from a light source as visible light by changing a luminance of the light source in accordance with the modulated signal. The modulated signal includes a plurality of items of information related to service set identifiers (SSIDs) of a plurality of access points on mutually different wireless local area networks (LANs). 
     The reception method according to the present embodiment includes: receiving a modulated signal transmitted as visible light from a transmission device; outputting analysis information by analyzing data based on the modulated signal; and based on the analysis information, connecting to an access point in a wireless local area network (LAN) using radio waves. Here, the modulated signal includes a plurality of items of information related to service set identifiers (SSIDs) of a plurality of mutually different access points in the wireless LAN. The outputting of analysis information includes: selecting any one of the plurality of items of the information related to the SSIDs of the plurality of mutually different access points included in the modulated signal; and outputting, as the analysis information, the item of information related to the SSID selected. The connecting to the access point in the wireless LAN includes connecting to, using radio waves, the access point corresponding to the item of information related to the SSID output via the analyzing, from among the plurality of mutually different access points. 
     Moreover, the communication method according to the present embodiment includes: generating a modulated signal based on an input signal; and transmitting the modulated signal from a light source as visible light by changing a luminance of the light source in accordance with the modulated signal. The modulated signal includes a plurality of items of information related to service set identifiers (SSIDs) of a plurality of mutually different access points in a local area network (LAN). At least one of the plurality of mutually different access points connects, using radio waves, to a reception device that received the modulated signal, and transmits information to the reception device. 
     Supplemental Information 1 for Above Embodiments 
     Note that at least one of the field programmable gate array (FPGA) and central processing unit (CPU) may be configured to be able to download all or part of software required for implementing the communication method described in the present disclosure via wireless or wired communication, and moreover may be configured to be able to download all or part of software for receiving updates via wireless or wired communication. The downloaded software may be stored in storage, and the digital signal processing described in the present disclosure may be implemented by operating at least one of the FPGA and CPU based on the stored software. 
     Here, a device including at least one of the FPGA and CPU may be connected to a telecommunications modem via a wireless or wired connection, and the communication method described in the present disclosure may be implemented by the device and the telecommunications modem. 
     For example, a communication device, such as the base station, AP, terminal described in the present specification may include at least one of an FPGA and a CPU, and may include an interface for obtaining software for operating the at least one of an FPGA and a CPU from an external source. Furthermore, the communication device may include storage for storing software obtained from an external source, and may implement the signal processing described in the present disclosure by operating the FPGA and/or CPU based on the stored software. 
     The transmission device described in the present specification may be included in a first automobile or vehicle, and the reception device described in the present specification may be included in a second automobile or vehicle, and the transmission and receiving of data may be implemented under such a configuration. 
     The transmission device or part of the functions of the transmission device described in the present specification may be connected to the first automobile or vehicle via an interface, and the reception device or part of the functions of the reception device described in the present specification may be connected to the second automobile or vehicle via an interface, and the transmission of data may be implemented via transmission and reception thereby. 
     The transmission device described in the present specification may be included in a first automobile or vehicle, and the transmission and receiving of data between this transmission device and the reception device described in the present specification may be implemented under such a configuration. 
     The reception device described in the present specification may be included in a second automobile or vehicle, and the transmission and receiving of data between this reception device and the transmission device described in the present specification may be implemented under such a configuration. 
     Furthermore, the transmission device or part of the functions of the transmission device described in the present specification may be connected to the first automobile or vehicle via an interface, and the transmission and receiving of data between this string of transmission devices and the reception device described in the present specification may be implemented under such a configuration. 
     The reception device or part of the functions of the reception device described in the present specification may be connected to the second automobile or vehicle via an interface, and the transmission and receiving of data between this string of reception devices and the transmission device described in the present specification may be implemented under such a configuration. 
     When the automobile or vehicle includes the transmission device or part of the transmission device described in the present specification, or when the automobile or vehicle and the transmission device described in the present specification or part of the functions of the transmission device described in the present specification are connected via an interface, the light source included in the transmission device described in the present specification may be a light source included in the automobile or vehicle. 
     For example, automobile B 100  illustrated in  FIG.  29    includes light sources B 101 _ 1 , B 101 _ 2 , B 101 _ 3 , and B 101 _ 4 , and one or more of these light sources may be the light source to be used by the transmission device according to the present specification for transmitting the optical modulated signal. 
     Moreover, the function for selecting which light source among the plurality of light sources included in automobile B 100  the transmission device according to the present specification uses for transmitting the optical modulated signal may be included in the transmission device or a device connected to the transmission device. Moreover, the brightness of the light source, the angle of emission of the light source, the positioning of the light source may be configurable. 
     When the automobile or vehicle includes the reception device or part of the reception device described in the present specification, or when the automobile or vehicle and the reception device described in the present specification or part of the functions of the reception device described in the present specification are connected via an interface, the light receiver included in the reception device described in the present specification may be a light receiver included in the automobile or vehicle (for example, an image sensor or photodiode). 
     For example, automobile B 100  illustrated in  FIG.  30    includes light receivers B 201 _ 1 , B 201 _ 3 , B 201 _ 4 , and B 201 _ 5 , and one or more of these light receivers may be the light receiver to be used by the reception device according to the present specification for receiving the optical modulated signal. 
     Moreover, the function for selecting which light receiver among the plurality of light receivers included in automobile B 100  the reception device according to the present specification uses for receiving the optical modulated signal may be included in the reception device or a device connected to the reception device. Moreover, the angle of the light receiver and the positioning of the light receiver may be configurable. 
     Furthermore, the reception device described in the present specification may display, on the front panel included in the automobile or in the cockpit of the vehicle, a notification indicating that data has been received. Moreover, the reception device described in the present specification may notify a user that data has been received by vibrating the steering wheel of, for example, the automobile, or vibrating a vibrator included on the steering wheel. 
     Moreover, an automobile including the reception device according to the present specification and the terminal may be connected via an interface, and data obtained from the reception device may be stored in storage included in the terminal. Moreover, the automobile may also include a storage, and the automobile may store received data therein. Moreover, the storage included in the terminal and the storage included in the automobile may both store received information. 
     In the present specification, a server may provide an application related to processes pertaining to the reception device, and the functions of the reception device according to the present specification may be implemented by the terminal installing the application. Note that the application may be provided to the terminal by the communication device including in the transmission device according to the present specification connecting to a server over a network, and may be provided to the terminal by a communication device including a different transmission function connecting to a server over a network. 
     Similarly, in the present specification, a server may provide an application related to processes pertaining to the transmission device, and the functions of the transmission device according to the present specification may be implemented by the terminal installing the application. Note that a method in which the application is provided to a different communication device by the communication device connecting to a server over a network is conceivable. 
     Moreover, a server may provide software related to the light source included in the transmission device and the light receiver included in the reception device, and transmission and reception of the optical modulated signal by the light source included in the transmission device and the light receiver included in the reception device, respectively, may be supported by obtaining this software. 
     Furthermore, the transmission device according to the present specification may function as a server, and an application included in the transmission device may be provided to the communication device using some communication means, and the reception device according to the present specification can be implemented by the application obtained by the communication device downloading the application. 
     Note that in the present specification, there is reference to a “lamp” and a “light source”, but the method may be a method of a projector displaying, for example, a still picture, moving picture, or advertisement, and the optical modulated signal being included in that light. In other words, the “lamp” and a “light source” may include functions other than the emission of light. Moreover, the “lamp” and a “light source” may comprise a plurality of lamps and light sources. 
     Furthermore, the transmission method used by the communication device that generates an optical modulated signal and emits light may be a method other than the transmission method described in the present specification. Moreover, the optical modulated signal may include information other than what is described in the present specification. 
     Moreover, the lamp and/or light source, such as an LED lamp and/or light source, may itself include the functions of the transmission device described in the present specification. 
     Furthermore, the device that generates the optical transmission modulated signal may not include a lamp or light source, and may be connected to a lamp and/or light source via an interface. 
     The communication method between the transmission device and the reception device described in the present specification and the present embodiment may be the communication method illustrated in  FIG.  31   . Hereinafter,  FIG.  31    will be described. 
     The symbol mapper receives an input of transmission data, performs mapping based on a modulation scheme, and outputs a symbol sequence (ci). 
     The pre-equalizer receives an input of the symbol sequence, performs pre-equalizing processing on the symbol sequence to reduce the equalizing processes on the reception-side, and outputs a pre-equalized symbol sequence. 
     The Hermitian symmetry processor receives an input of the pre-equalized symbol sequence, allocates sub-carriers to the pre-equalized symbol sequence to secure Hermitian symmetry, and outputs parallel signals. 
     The inverse (fast) Fourier transformer receives inputs of the parallel signals, applies an inverse (fast) Fourier transform to the parallel signals, and outputs inverse (fast) Fourier transformed signals. 
     The parallel serial and cyclic prefix adder receives an input of the inverse (fast) Fourier transformed signals, performs parallel conversion and adds cyclic prefix, and outputs the signal-processed signal. 
     The digital-to-analog converter receives an input of the signal-processed signal, performs digital-to-analog conversion, outputs an analog signal, and the analog signal is emitted as light from, for example, one or more LEDs. 
     Note that the pre-equalizer and the Hermitian symmetry processor need not be included. In other words, there may be instances in which the pre-equalizer and the Hermitian symmetry processor do not perform their respective processes. 
     The photodiode receives an input of light, and obtains a reception signal via a transimpedance amplifier (TIA). 
     The analog-to-digital converter performs an analog-to-digital conversion on the reception signal, and outputs a digital signal. 
     The cyclic prefix subtractor and serial parallel converter receives an input of the digital signal, subtracts the cyclic prefix, and then performs serial parallel conversion, and receives an input of parallel signals. 
     The (fast) Fourier transformer receives inputs of the parallel signals, applies a (fast) Fourier transform to the parallel signals, and outputs (fast) Fourier transformed signals. 
     The detector receives inputs of the (fast) Fourier transformed signals, performs detection, and outputs a series of reception symbols. 
     The symbol demapper receives an input of the series of reception symbols, performs demapping, and obtains a series of reception data. 
     In this way, even when such a transmission device that transmits the optical modulated signals and such a reception device that receives the optical modulated signals are applied to the amendments according to the present specification, the embodiments can be implemented in the same manner. 
     Moreover, the communication method between the transmission device and the reception device described in the present embodiment may be the following communication method. 
     Line Scan Sampling 
     An image sensor such as a complementary metal oxide semiconductor (CMOS) sensor is included in a smartphone or digital camera or the like. For example, the entire scene in a single image captured by the CMOS sensor is not captured at a single instant, but rather, for example, captured line by line using a rolling shutter method, whereby the sensor reads out the amount of light received line by line. Accordingly, the amount of time required for the reading out is calculated, and exposure start and end times are controlled for each line by implementing a time delay. In other words, images captured by the CMOS sensor are constructed from a plurality of lines captured with a slight time lag between each line. 
     This exploits the rolling shutter effect of the CMOS sensor to allow for an improvement in visible light signal reception speeds. 
     In other words, in a first example of a visible light communication scheme, as illustrated in  FIG.  32   , utilizing the slight time lag between the exposure period of each line, the luminance and color of the light source across a plurality of points in time can be calculated line by line from a single image (image captured by the image sensor), making it possible to capture a signal modified faster than the frame rate of the image sensor. 
     This sampling method is referred to as “line scan sampling”, and a single row of pixels exposed at the same time is referred to as an “exposure line”. 
     Note that line scan sampling can be implemented using the rolling shutter effect of a CMOS sensor, but even when the rolling shutter effect is implemented using a sensor other than a CMOS sensor, such as a charge-coupled device (CCD) sensor or an organic CMOS sensor, the line scan sampling can be implemented in the same manner. 
     However, in the settings used when capturing an image in the camera functions (capturing functions for moving or still images), even if a rapidly flashing light source is captured, the flashing will not appear as a striped pattern extending along the exposure lines. This is because, with this setting, the exposure period is sufficiently longer than the flash cycle of the light source, so, as illustrated in  FIG.  33   , the changes in luminance resulting from the flashing (light emission pattern) of the light source are uniform, resulting in a substantially small variation in pixel values between exposure lines, producing an approximately uniform image. 
     In contrast, as illustrated in  FIG.  34   , by setting the exposure period equal to or slower than the flash cycle of the light source, the state (light emission pattern) of the flashing of the light source can be observed as variations in luminance between exposure lines. 
     For example, the exposure lines are designed to extend parallel lengthwise relative to the image sensor. In such cases, as one example, assuming the frame rate is 30 frames per second (fps), when the resolution is 1920×1080, at least 32400 samples are obtained per second, and when the resolution is 3840×2160, at least 64800 samples are obtained per second. 
     Line Scan Sampling Application Example 
     Note that the above described line scan sampling in which a signal indicating an amount of light received per line is read out, but methods of sampling an optical signal using an image sensor such as a CMOS sensor are not limited to this example. A variety of methods that can obtain a sampled signal at a sampling rate that is higher than the frame rate used to capture a normal moving picture, can be used as the sampling method to be used to receive the optical signals. For example, a method of controlling the exposure time per pixel and reading out a signal or a method of controlling the exposure time per group of pixels arranged in a shape other than a line and reading out a signal may be used by utilizing a global shutter method that has a shutter function for each pixel. Moreover, a method of reading out signals a plurality of times from the same pixel in a period equivalent to one frame in the frame rate used in the capture of a normal moving picture may be used. 
     Frame Sampling 
     Furthermore, with a frame rate method that gives a shutter method for each non-pixel, it is possible to sample optical signals even in a method by which the frame rate is sped up. 
     For example, the present specification can be implemented in any of the line scan sampling, line scan sampling application example, and frame sampling methods described above. 
     Light Source and Modulation Scheme 
     With visible light communication, for example, a light emitting diode (LED) can be used as a transmitter. LEDs are commonly used in lamps and in backlit light sources in displays, and can flash at high speeds. 
     However, light sources that are used as visible light communication transmitters cannot be allowed to flash uncontrolled when performing visible light communication. If the changes in luminance made for visible light communication are recognizable to the human eye, the original functionality of a light source as a lamp will be lost. Accordingly, the transmission signal needs to be emitted at a desired brightness and needs to be imperceptible to the human eye. 
     One modulation scheme that meets these requirements is 4-pulse position modulation (4 PPM). As illustrated in  FIG.  35 A , 4 PPM is a scheme in which two bits are represented by a group of four time slots each indicating either bright or dark light emitted by a light source. Moreover, as illustrated in  FIG.  35 A , in 4 PPM, each group of the four time slots includes three light slots and one dark slot. Accordingly, regardless of the content of the signal, the average brightness (average luminance) is ¾=75%. 
     For comparison, as a similar scheme, consider the Manchester coding scheme illustrated in  FIG.  35 B . In the Manchester coding scheme, one bit is expressed with two states, and the modulation efficiency is 50%, which is the same as 4 PPM, but among the two states, one is bright and one is dark, so the average luminance is ½=50%. In other words, 4 PPM is more suitable than the Manchester coding scheme as a visible light communication scheme. However, since communication capability is not adversely affected by changes in luminance from visible light communication that are recognizable to the human eye, depending on the application, there may be no problem in using a method in which the changes in luminance are recognizable to the human eye. Accordingly, the transmitter (light source) may use, for example, an amplitude shift keying (ASK) method, a phase shift keying (PSK) method, or a pulse amplitude modulation (PAM) method to generate the modulated signal and pulse the light source to emit light. 
     Note that the communication method between the transmission device and the reception device described in the present specification is not limited to the above example. Even frequency-based wireless communication methods such as optical, visible light, infrared, ultraviolet methods can be implemented in the same manner. Moreover, in the above description, an example is given in which optical modulated signals are received via an image sensor, but a photodiode may be used in place of the image sensor to receive the optical modulated signals. Alternatively, a device other than an image sensor or photodiode may be used to receive the optical modulated signals. 
     In the present specification, a symbol related to location or position information, a symbol related to time information, a symbol related to an SSID, a symbol related to an access destination, and a symbol related to an encryption key are described using the terminology “symbol”, but these may be referred to as “data” or “information” or “field” or “bit” or “region” instead of “symbol”, and the embodiments can be implemented in the same manner. They may be referred to as something other than “data” or “information” or “field” or “bit” or “region” as well. Moreover, the transmission device may transmit any type of symbol configuration, such as a symbol related to location or position information, a symbol related to time information, a symbol related to an SSID, a symbol related to an access destination, and a symbol related to an encryption key. What is important is that data related to location or position information, data related to time information, data related to an SSID, data related to an access destination, data related to an encryption key is transmitted to the communication partner. 
     In the present specification, in the transmission device that includes, for example, a light source and/or lamp, the light source may be comprised of a plurality of light sources, and/or the lamp may be comprised of a plurality of lamps. 
     Supplemental Information 2 for Above Embodiments 
     It goes without saying that the embodiments described in the present specification may be combined with other aspects. 
     Moreover, the embodiments are merely examples. For example, while a modulation scheme, an error correction coding method (error correction code, code length, encode rate, etc., to be used), control information, etc., are exemplified, it is possible to carry out the present disclosure with the same configuration even when other types of a modulation scheme, an error correction coding method (error correction code, code length, encode rate, etc., to be used), control information, etc., are applied. 
     Regarding the modulation schemes, even when a modulation scheme other than the modulation schemes described herein is used, it is possible to carry out the embodiments and the other subject matter described herein. For example, amplitude phase shift keying (APSK) (such as 16APSK, 64APSK, 128APSK, 256APSK, 1024APSK and 4096APSK), pulse amplitude modulation (PAM) (such as 4PAM, 8PAM, 16PAM, 64PAM, 128PAM, 256PAM, 1024PAM and 4096PAM), phase shift keying (PSK) (such as BPSK, QPSK, 8PSK, 16PSK, 64PSK, 128PSK, 256PSK, 1024PSK and 4096PSK), and quadrature amplitude modulation (QAM) (such as 4QAM, 8QAM, 16QAM, 64QAM, 128QAM, 256QAM, 1024QAM and 4096QAM) may be applied, or in each modulation scheme, uniform mapping or non-uniform mapping may be performed. Moreover, a method for arranging 2, 4, 8, 16, 64, 128, 256, 1024, etc., signal points on an I-Q plane (a modulation scheme having 2, 4, 8, 16, 64, 128, 256, 1024, etc., signal points) is not limited to a signal point arrangement method of the modulation schemes described herein. 
     In the present specification, conceivable devices that include the radio device described in the present specification include a communications and broadcast apparatus, such as a broadcast station, a base station, an access point, a terminal or a mobile phone, or a communication apparatus such as a television, a radio, a terminal, a personal computer, a mobile phone, an access point, or a base station. Moreover, the radio device described in the present specification is conceivably a device having communication functions that is connectable via some interface to a device for executing an application in, for example, a television, a radio, a personal computer or a mobile phone. 
     In the present specification, conceivable devices that include the receiver described in the present specification include a communications and broadcast apparatus, such as a broadcast station, a base station, an access point, a terminal or a mobile phone, or a communication apparatus such as a television, a radio, a terminal, a personal computer, a mobile phone, an access point, or a base station. 
     Moreover, in the radio-wave communication radio device according to this embodiment, symbols other than data symbols, such as pilot symbols (preamble, unique word, post-amble, reference symbol, etc.) or symbols for control information, may be arranged in any way in a frame. Here, the terms “pilot symbol” and “control information symbol” are used, but the naming of such symbols is not important; the functions that they perform are. 
     A pilot symbol may be a known symbol that is modulated using PSK modulation in a transceiver (alternatively, a symbol transmitted by a transmitter can be known by a receiver by the receiver being periodic), and the receiver detects, for example, frequency synchronization, time synchronization, and a channel estimation (channel state information (CSI)) symbol (of each modulated signal) by using the symbol. 
     Moreover, the symbol for control information is a symbol for transmitting information required to be transmitted to a communication partner in order to establish communication pertaining to anything other than data (such as application data) (this information is, for example, the modulation scheme, error correction encoding scheme, or encode rate of the error correction encoding scheme used in the communication, or settings information in an upper layer). 
     Note that the present disclosure is not limited to each exemplary embodiment, and can be carried out with various modifications. For example, in each embodiment, the present disclosure is described as being performed as a communication device. However, the present disclosure is not limited to this case, and this communication method can also be used as software. 
     Note that a program for executing the above-described communication method may be stored in read only memory (ROM) in advance to cause a central processing unit (CPU) to operate this program. 
     Moreover, the program for executing the communication method may be stored in a computer-readable storage medium, the program stored in the recording medium may be recorded in random access memory (RAM) in a computer, and the computer may be caused to operate according to this program. 
     Each configuration of each of the above-described embodiments, etc., may be realized as a large scale integration (LSI) circuit, which is typically an integrated circuit. These integrated circuits may be formed as separate chips, or may be formed as one chip so as to include the entire configuration or part of the configuration of each embodiment. LSI is described here, but the integrated circuit may also be referred to as an integrated circuit (IC), a system LSI circuit, a super LSI circuit or an ultra LSI circuit depending on the degree of integration. Moreover, the circuit integration technique is not limited to LSI, and may be realized by a dedicated circuit or a general purpose processor. After manufacturing of the LSI circuit, a field programmable gate array (FPGA) or a reconfigurable processor which is reconfigurable in connection or settings of circuit cells inside the LSI circuit may be used. Further, when development of a semiconductor technology or another derived technology provides a circuit integration technology which replaces LSI, as a matter of course, functional blocks may be integrated by using this technology. Adaption of biotechnology, for example, is a possibility. 
     Note that in the present specification, for example, in Embodiments 4, 5, 6, and 7, an encryption key for a terminal to connect to a base station over radio waves is described, but the encryption key is not limited to an encryption key for connection over radio waves. 
     For example, assume the base station is connected to a network and the terminal communicates with the network via the base station. In such cases, the encryption key may be an encryption key for the terminal to connect to the network. Accordingly, information on an encryption key is included in the optical modulated signal described in the present specification, and even in this cases, the embodiments can be implemented in the same way, and the same advantageous effects can be achieved. 
     Moreover, the optical modulated signal may include at least one of an encryption key for connecting with a base station (for example, an encryption key for an SSID) and an encryption key for connecting to a network. 
     Although only some exemplary embodiments have been described above, the scope of the Claims of the present application is not limited to these embodiments. Those skilled in the art will readily appreciate that various modifications may be made in these exemplary embodiments and that other embodiments may be obtained by arbitrarily combining the structural elements of the embodiments without materially departing from the novel teachings and advantages of the subject matter recited in the appended Claims. Accordingly, all such modifications and other embodiments are included in the present disclosure. 
     INDUSTRIAL APPLICABILITY 
     The present disclosure is applicable to a wide range of communication systems that transmit and receive optical modulated signals.