Patent Publication Number: US-2021195590-A1

Title: Device provided a plurality of types of wireless communication functions

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/965,204 filed Apr. 27, 2018 which claims priority from Japanese Patent Application No. 2017-090824 filed Apr. 28, 2017. The entire content of the priority applications are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to an image-processing device that performs at least one of an image-forming process and an image-reading process. In the image-forming process, the image-processing device forms images on sheets on the basis of image data. In the image-reading process, the image-processing device reads an original to generate image data. 
     BACKGROUND 
     Wireless LAN (WLAN) communications and Bluetooth communications use the same 2.4 GHz frequency band, but their use of frequencies is different. That is, WLAN communications according to the IEEE 802.11 standard use a single fixed frequency channel among a plurality of channels in an occupied bandwidth of 20 MHz, while Bluetooth communications according to the IEEE 802.15.1 standard switch among a plurality of channels in an occupied bandwidth that is smaller than the bandwidth of channels in WLAN communications (frequency hopping). 
     Since both WLAN communications and Bluetooth communications use the 2.4 GHz frequency band, signal interference can occur when WLAN communications and Bluetooth communications are performed simultaneously in the vicinity of devices equipped with a WLAN communication function and a Bluetooth communication function. The Bluetooth communication function incorporates adaptive frequency hopping spread spectrum (AFH) in order to reduce such interference. AFH technology is used to detect a channel used for WLAN communications, generate a hopping pattern to avoid that channel, and perform frequency hopping according to this hopping pattern. 
     SUMMARY 
     Bluetooth has a maximum transfer rate of approximately 24 Mbps, which is slower than the transfer rate in WLAN communications. Accordingly, Bluetooth communications is primarily used for simple data transfers between a printer and a portable terminal such as a smartphone. However, if a need arises to transfer a large volume of data while communicating with Bluetooth, it is desirable to be able to switch from Bluetooth communications to WLAN communications. 
     Unfortunately, it can take time to search for a channel suitable for WLAN communications from among the plurality of channels. 
     In view of the foregoing, it is an object of the present disclosure to provide a device capable of reducing the time required to search for one first channel suitable for first wireless communications (WLAN) from among a plurality of first channels when switching from a connection according to second wireless communications (Bluetooth) to a connection using the first wireless communications. 
     In order to attain the above and other objects, the present disclosure provides device that includes: a first wireless communication interface; a second wireless communication interface; a storage; and a controller. The first wireless communication interface is configured to perform first wireless communications with an external device using a first communication channel. The first communication channel is determined from among a plurality of first channels. Each of the plurality of first channels occupies a first frequency bandwidth ranging from a minimum frequency to a maximum frequency within a predetermined frequency band. The second wireless communication interface is configured to perform second wireless communications with the external device using a second communication channel The second communication channel is determined from and switched among a plurality of second channels depending on radio wave environment. Each of the plurality of second channels occupies a second frequency bandwidth smaller than the first frequency bandwidth within the predetermined frequency band. The second communication channel has a center communication frequency. The center communication frequency of the second communication channel is a median of the second frequency bandwidth occupied by the second communication channel The controller is configured to perform: storing in the storage the center communication frequency of the second communication channel used for the second wireless communications and picked up every prescribed time interval while the second wireless communication interface is performing the second wireless communications with the external device, the storage being configured to store a plurality of center communication frequencies; determining a search target distribution, the search target distribution being a range defined by a minimum communication frequency and a maximum communication frequency within the predetermined frequency band, the minimum communication frequency being a minimum among a plurality of communication frequencies, the maximum communication frequency being a maximum among the plurality of communication frequencies, the plurality of communication frequencies being at least a part of the plurality of center communication frequencies stored in the storage and being separated from each other by less than the first frequency bandwidth; and determining the first communication channel from among at least one first channel satisfying a candidate condition, the candidate condition requiring that both the minimum frequency and the maximum frequency of each of the at least one first channel be included in the search target distribution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The particular features and advantages of the disclosure as well as other objects will become apparent from the following description taken in connection with the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a structure of a system including a multifunction peripheral (MFP) according to the present disclosure; 
         FIG. 2  is a flowchart illustrating steps in a main process executed by the MFP; 
         FIG. 3  is a flowchart illustrating steps in a WLAN connection process executed by the MFP; 
         FIG. 4  is a flowchart illustrating steps in a first example of a channel selecting process executed by the MFP; 
         FIGS. 5A through 5C  are explanatory diagrams for describing the channel selecting process illustrated in  FIG. 4 , in which  FIG. 5A  illustrates a plurality of WLAN channels ch-1 through ch-13 used for WLAN communications in frequency,  FIG. 5B  illustrates a sample distribution of Bluetooth communication frequencies that were stored in a RAM over time, and  FIG. 5C  illustrates a selection result of a WLAN channel used for WLAN communications in the channel selecting process illustrated in  FIG. 4 ; 
         FIG. 6  is a flowchart illustrating steps in an all channels scanning process executed by the MFP; 
         FIG. 7  is a flowchart illustrating steps in a second example of a channel selecting process executed by the MFP; 
         FIGS. 8A through 8C  are explanatory diagrams for describing the channel selecting process illustrated in  FIG. 7 , in which  FIG. 8A  illustrates a plurality of WLAN channels ch-1 through ch-13 used for WLAN communications in frequency,  FIG. 8B  illustrates a sample distribution of Bluetooth communication frequencies that were stored in a RAM over time, and  FIG. 8C  illustrates a selection result of a WLAN channel used for WLAN communications in the channel selecting process illustrated in  FIG. 7 ; 
         FIG. 9  is a flowchart illustrating steps in a third example of a channel selecting process executed by the MFP; 
         FIGS. 10A through 10C  are explanatory diagrams for describing the channel selecting process illustrated in  FIG. 9 , in which  FIG. 10A  illustrates a plurality of WLAN channels ch-1 through ch-13 used for WLAN communications in frequency,  FIG. 10B  illustrates a sample distribution of Bluetooth communication frequencies that were stored in a RAM over time, and  FIG. 10C  illustrates a selection result of a WLAN channel used for WLAN communications in the channel selecting process illustrated in  FIG. 9 ; 
         FIG. 11  is a flowchart illustrating steps in a fourth example of a channel selecting process executed by the MFP; and 
         FIGS. 12A through 12C  are explanatory diagrams for describing the channel selecting process illustrated in  FIG. 11 , in which  FIG. 12A  illustrates a plurality of WLAN channels ch-1 through ch-13 used for WLAN communications in frequency,  FIG. 12B  illustrates a sample distribution of Bluetooth communication frequencies that were stored in a RAM over time, and  FIG. 12C  illustrates a selection result of a WLAN channel used for WLAN communications in the channel selecting process illustrated in  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
     Next, embodiments of the present disclosure will be described in detail while referring to the accompanying drawings. 
     Structure of System 
     A system  1  illustrated in  FIG. 1  includes a multifunction peripheral (MFP)  2 , and a wireless terminal  3 . 
     The MFP  2  (an example of the device) possesses a plurality of functions, such as an image-forming function for forming images on printing paper or other sheets on the basis of image data, and an image-reading function for generating image data by reading an image. 
     The wireless terminal  3  is a smartphone or a tablet computer, for example. 
     Both the MFP  2  and wireless terminal  3  are equipped with a wireless LAN (WLAN) communication function employing the IEEE 802.11 standard, and a Bluetooth communication function employing the IEEE 802.15.1 standard. While both WLAN communications and Bluetooth communications use the same 2.4 GHz frequency band ranging from 2.4 GHz to 2.4835 GHz in frequency, their method of using frequencies differs. Specifically, on one hand, WLAN communications use a single fixed channel among a plurality of WLAN channels having an occupied bandwidth of 20 MHz, for example, 13 WLAN channels ch-1 through ch-13 within which center frequencies of the occupied bandwidth for two neighboring WLAN channels are separated by 5 MHz. On the other hand, Bluetooth communications use adaptive frequency hopping spread spectrum (AFH) technology to switch channels over the course of time among 40 Bluetooth channels in an occupied bandwidth of 2 MHz, while avoiding frequencies occupied by other wireless stations (frequency-hopping spread spectrum). Further, the transfer rate in Bluetooth communications is a maximum 24 Mbps, which is slower than the transfer rate of WLAN communications. 
     The MFP  2  also has an image-forming unit  11  (an example of the image processor), an image-reading unit  12  (an example of the image processor), a display unit  13 , an operating unit  14 , a WLAN interface (WLAN I/F)  15  (an example of the first wireless communication interface), and a Bluetooth interface (Bluetooth I/F)  16  (an example of the second wireless communication interface). 
     The image-forming unit  11  forms images (color or monochrome images) on the basis of image data onto sheets conveyed one at a time along a conveying path in the MFP  2 . The method of image formation may be the electro-photographic method or the inkjet method. 
     The image-reading unit  12  reads an image formed on a sheet and outputs image data for that image. Image reading may be done according to the contact image sensor (CIS) method, for example. 
     The display unit  13  is a liquid crystal display unit, for example. 
     The operating unit  14  is provided with operating keys (for example, a start key, the ten numerical keys, cursor keys, and a return key). Through operations on the operating keys, the user can input various commands and the like into the operating unit  14 . Note that the operating unit  14  may also be configured of touch keys superimposed over the display unit  13 . 
     The WLAN interface  15  is provided with a circuit, an antenna, and the like required for WLAN communications. 
     The Bluetooth interface  16  is provided with a circuit, an antenna, and the like required for Bluetooth communications. 
     The MFP  2  is also provided with an application-specific integrated circuit (ASIC)  21 , a read-only memory (ROM)  22 , and a random access memory (RAM)  23  (an example of the storage). 
     The image-forming unit  11 , image-reading unit  12 , display unit  13 , operating unit  14 , WLAN interface  15 , Bluetooth interface  16 , ROM  22 , and RAM  23  are all electrically connected to the ASIC  21 . The ASIC  21  has a built-in central processing unit (CPU)  24  (an example of the controller). The CPU  24  executes programs for implementing various processes on the basis of information inputted into the ASIC  21 . When executing these programs, the CPU  24  controls operations of the image-forming unit  11 , image-reading unit  12 , display unit  13 , WLAN interface  15 , Bluetooth interface  16 , and other components. 
     The ROM  22  stores programs executed by the CPU  24 , various data, and the like. 
     The RAM  23  is used as a work area when the CPU  24  executes programs. The RAM  23  also temporarily stores image data for images that the image-forming unit  11  will form on sheets, image data read by the image-reading unit  12 , data to be transferred by the WLAN interface  15  and Bluetooth interface  16 , and the like. 
     The wireless terminal  3  has a display unit  31 , an operating unit  32 , a WLAN interface (WLAN I/F)  33 , a Bluetooth interface (Bluetooth I/F)  34 , a control unit  35 , a read-only memory (ROM)  36 , and a random access memory (RAM)  37 . 
     The display unit  31  is a liquid crystal display unit, for example. 
     The operating unit  32  is configured of touch keys superimposed over the display unit  31 , for example. 
     The WLAN interface  33  is provided with a circuit, an antenna, and the like required for WLAN communications. 
     The Bluetooth interface  34  is provided with a circuit, an antenna, and the like required for Bluetooth communications. 
     The display unit  31 , operating unit  32 , WLAN interface  33 , Bluetooth interface  34 , ROM  36 , and RAM  37  are all electrically connected to the control unit  35 . The control unit  35  has a built-in central processing unit (CPU)  38 . The CPU  38  executes programs for implementing various processes on the basis of information inputted into the control unit  35 . When executing these programs, the CPU  38  controls operations of the display unit  31 , WLAN interface  33 , Bluetooth interface  34 , and other components. 
     The ROM  36  stores programs executed by the CPU  38 , various data, and the like. 
     The RAM  37  is used as a work area when the CPU  38  executes programs. The RAM  23  also temporarily stores data to be transferred by the WLAN interface  15  and Bluetooth interface  16 , and the like. 
     Main Process 
     The CPU  24  built into the ASIC  21  of the MFP  2  executes a main process illustrated in  FIG. 2  while power to the MFP  2  is on. 
     In S 11  of the main process, the CPU  24  controls the Bluetooth interface  16  to transmit an advertising signal. The advertising signal is an example of the searching signal. 
     After transmission of the advertising signal, the CPU  24  waits for receiving a scan request (Scan-Req) signal. The scan request signal is an example of the response signal. Specifically, in S 12  the CPU  24  determines whether the Bluetooth interface  16  has received a scan request signal and repeats this determination while a scan request signal has not been received (S 12 : NO). 
     Upon receiving the advertising signal, the wireless terminal  3  transmits a scan request signal to the MFP  2 . When the Bluetooth interface  16  receives the scan request signal (S 12 : YES), in S 13  the CPU  24  uses the Bluetooth interface  16  to initiate a connection (pairing) according to Bluetooth communications between the wireless terminal  3  that transmitted the scan request signal and the MFP  2 . 
     Once a connection according to Bluetooth communications (hereinafter called a “Bluetooth connection”) has been established between the MFP  2  and wireless terminal  3 , in S 14  the CPU  24  stores the center frequency of the Bluetooth channel (hereinafter called the “Bluetooth communication frequency”) used for Bluetooth communications with the wireless terminal  3  in the RAM  23  while the channel is switched over time. Thereafter the CPU  24  accumulates the Bluetooth communication frequencies used at the current point in time after each prescribed interval elapsed in the RAM  23 . 
     If the Bluetooth interface  16  subsequently receives a transmission/reception command from the wireless terminal  3  (S 15 : YES), in S 16  the CPU  24  determines whether the transmission/reception command includes a WLAN connection command The transmission/reception command is a command to either transmit data of various types from the wireless terminal  3  to the MFP  2  or a command to receive data transmitted from the MFP  2  to the wireless terminal  3 . A WLAN connection command is a command to establish a connection according to WLAN communications (hereinafter called a “WLAN connection”) between the MFP  2  and wireless terminal  3 . 
     If the transmission/reception command does not include a WLAN connection command (S 16 : NO), in S 17  the CPU  24  controls the Bluetooth interface  16  to transmit or receive data with the Bluetooth interface  34  of the wireless terminal  3  according to Bluetooth communications. For example, when the wireless terminal  3  issues a command to execute a print job with the image-forming function of the MFP  2 , data for various settings required to execute this print job (sheet size and number of copies, for example) is exchanged between the wireless terminal  3  and MFP  2 . At this time, Bluetooth communications can be used since the data size is relatively small. 
     When the transmission/reception command includes a WLAN connection command (S 16 : YES), in S 18  the CPU  24  executes a WLAN connection process. The WLAN connection process is a process for establishing a WLAN connection between the MFP  2  and wireless terminal  3  in order to transmit or receive data through WLAN communications. For example, when the wireless terminal  3  issues a command to execute a print job with the image-forming function of the MFP  2 , image data for the print job must be transferred from the wireless terminal  3  to the MFP  2 . In this case, it is preferable to use WLAN communications since the data size is relatively large. The WLAN connection process will be described later in greater detail. 
     After completing the WLAN connection process, in S 19  the CPU  24  determines whether the Bluetooth interface  16  received a command from the wireless terminal  3  to end all connections (both WLAN and Bluetooth connections) between the MFP  2  and wireless terminal  3 . If a command to end all connections was received (S 19 : YES), the CPU  24  temporarily ends the main process and starts a new main process. 
     However, if the Bluetooth interface  16  did not receive a command to end all connections from the wireless terminal  3  after completing the WLAN connection process (S 19 : NO), the CPU  24  maintains the Bluetooth connection between the MFP  2  and wireless terminal  3  and in S 14  continues to store the Bluetooth communication frequency in the RAM  23 . 
     On the other hand, if the Bluetooth interface  16  has not received a transmission/reception command from the wireless terminal  3  while a Bluetooth connection is established between the MFP  2  and wireless terminal  3  (S 15 : NO), in S 20  the CPU  24  determines whether the Bluetooth interface  16  received a command from the wireless terminal  3  to end the Bluetooth connection. 
     While the Bluetooth interface  16  has not received a command from the wireless terminal  3  to end the Bluetooth connection (S 20 : NO), in S 14  the CPU  24  continues storing the Bluetooth communication frequency in the RAM  23 . 
     If the Bluetooth interface  16  has received a command from the wireless terminal  3  to end the Bluetooth connection (S 20 : YES), in S 21  the CPU  24  stops storing the Bluetooth communication frequencies in the RAM  23 . 
     In S 22  the CPU  24  ends the Bluetooth connection between the MFP  2  and wireless terminal  3  and quits the main process. 
     WLAN Connection Process 
     Next, steps in the WLAN connection process executed in S 18  of the main process will be described with reference to  FIG. 3 . 
     When the Bluetooth interface  16  receives a WLAN connection command from the wireless terminal  3 , in S 1801  the CPU  24  controls the Bluetooth interface  16  to transmit through Bluetooth communications a service set identifier (SSID) and a password necessary for a WLAN connection. 
     In S 1802  the CPU  24  reads the previously used Bluetooth communication frequencies from the RAM  23 . 
     In S 1803  the CPU  24  determines the existence of a search target distribution within the distribution of Bluetooth communication frequencies read from the RAM  23 . The search target distribution is a collection of Bluetooth communication frequencies within which no two neighboring frequencies are separated by a gap that is greater than or equal to the occupied bandwidth of a WLAN channel used for WLAN communications, and specifically by a gap that is greater than or equal to 20 MHz. 
       FIG. 5B  illustrates a sample distribution of Bluetooth communication frequencies that were stored in the RAM  23  over time. In  FIG. 5B , a collection of Bluetooth communication frequencies denoted by lines (center communication frequencies) having no gaps of 20 MHz or greater between neighboring frequencies (center communication frequencies) is the search target distribution.  FIG. 5B  also indicates the existence of two Bluetooth communication frequencies that fall outside of the search target distribution. One of these Bluetooth communication frequencies is separated more than 20 MHz from the minimum communication frequency of the search target distribution, and the other is separated more than 20 MHz from the maximum communication frequency of the search target distribution. 
     When a search target distribution such as that in the example of  FIG. 5B  exists (S 1803 : YES), in S 1804  the CPU  24  executes a channel selecting process. In the channel selecting process, the CPU  24  selects a WLAN channel to be used for WLAN communications between the MFP  2  and wireless terminal  3 . This process will be described later in greater detail. 
     If a search target distribution does not exist (S 1803 : NO), in S 1805  the CPU  24  executes an all channels scanning process. In the all channels scanning process, the CPU  24  selects a WLAN channel to be used for WLAN communications between the MFP 2  and wireless terminal  3 . This process will be described later in greater detail. 
     After the CPU  24  has selected a WLAN channel through either the channel selecting process or the all channels scanning process, in S 1806  the CPU  24  sets the WLAN channel to be used for WLAN communications between the MFP  2  and wireless terminal  3  to the WLAN channel selected in the above process. 
     After setting the WLAN channel, the CPU  24  waits for receiving a transmission/reception command to transmit or receive image data. Specifically, in S 1807  the CPU  24  determines whether the Bluetooth interface  16  has received a transmission/reception command and repeats this determination while a transmission/reception command has not been received (S 1807 : NO). 
     When the Bluetooth interface  16  receives a transmission/reception command from the wireless terminal  3  to transmit or receive image data (S 1807 : YES), in S 1808  the CPU  24  controls the WLAN interface  15  to transmit or receive image data between the WLAN interface  33  of the wireless terminal  3  through WLAN communications on the WLAN channel set in S 1806 . As an example, when the wireless terminal  3  issues a command to execute a print job with the image-forming function of the MFP  2 , image data related to this print job is transmitted from the WLAN interface  33  of the wireless terminal  3  to the WLAN interface  15  of the MFP  2  through WLAN communications on the previously set WLAN channel. 
     In S 1809  the CPU  24  waits while transmission or reception of image data has not completed (S 1809 : NO). After transmission or reception of image data with the WLAN interface  15  is completed (S 1809 : YES), in S 1810  the CPU  24  commands the WLAN interface  15  to terminate the WLAN connection between the MFP  2  and wireless terminal  3  and ends the WLAN connection process. At this time, the WLAN interface  15  terminates the WLAN connection with the WLAN interface  33 . 
     First Example of Channel Selecting Process 
     Next, steps in the channel selecting process executed in S 1804  of the WLAN connection process will be described with reference to  FIG. 4 .  FIG. 4  illustrates steps in the first example of the channel selecting process. 
     In S 1841  at the beginning of the channel selecting process, the CPU  24  identifies the lowest Bluetooth communication frequency in the search target distribution (hereinafter simply called the “minimum communication frequency f MIN ”; indicated in  FIG. 5B ). The search target distribution comprises a cluster of Bluetooth communication frequencies among which neighboring frequencies are separated by less than 20 MHz. 
     In S 1842  the CPU  24  identifies the highest Bluetooth communication frequency in the search target distribution (hereinafter simply called the “maximum communication frequency f MAX ”; indicated in  FIG. 5B ). 
     In S 1843  the CPU  24  determines the existence of a WLAN channel that satisfies a candidate condition. The candidate condition requires that both the minimum frequency F MIN  and maximum frequency F MAX  of the occupied bandwidth for the WLAN channel be included in the search target distribution between the minimum communication frequency f MIN  and maximum communication frequency f MAX  (hereinafter called the “minimum-to-maximum frequency range”). In  FIG. 5C , the minimum frequency F MIN  and maximum frequency F MAX  of the occupied bandwidth for the seventh WLAN channel from the low frequency side (ch-7) are indicated. 
     Using the sample distribution illustrated in  FIG. 5B  as the distribution of Bluetooth communication frequencies stored in the RAM  23  over time, the sixth through eighth WLAN channels from the low frequency side (ch-6 through ch-8) satisfy the candidate condition since both the minimum frequencies F MIN  and maximum frequencies F MAX  of the occupied bandwidth for WLAN channels ch-6 through ch-8 fall within the minimum-to-maximum frequency range. 
     Here, the minimum frequencies F MIN  of the occupied bandwidth for WLAN channels ch-9 through ch-12 fall within the search target distribution (the minimum-to-maximum frequency range), but the maximum frequencies F MAX  of the occupied bandwidth for WLAN channels ch-9 through ch-12 do not fall in this search target distribution (the minimum-to-maximum frequency range). Accordingly, none of WLAN channels ch-9 through ch-12 meets the candidate condition. 
     When WLAN channels satisfying the candidate condition exist (S 1843 : YES), in S 1844  the CPU  24  selects all WLAN channels that satisfy this candidate condition as candidate channels. In the example shown in  FIGS. 5A through 5C , WLAN channels ch-6 through ch-8 are set as candidate channels. 
     In S 1845  the CPU  24  selects one of the candidate channels, controls the WLAN interface  15  to receive radio waves from the selected candidate channel, and measures the reception strength of these radio waves over a prescribed period of time. 
     In S 1846  the CPU  24  determines whether reception strength has been measured for all candidate channels. While there remain candidate channels for which reception strength has not been measured (S 1846 : NO), in S 1847  the CPU  24  selects one of the candidate channels that has not yet been targeted for reception strength measurements and in S 1845  measures the reception strength of radio waves from the newly selected candidate channel. 
     When measurements of reception strength have been completed for all candidate channels (S 1846 : YES), in S 1848  the CPU  24  selects the candidate channel having the lowest reception strength as the WLAN channel to be used for WLAN communications. Subsequently, the CPU  24  ends the channel selecting process and returns to the WLAN connection process. 
     On the other hand, when the CPU  24  determines in S 1843  that there exist no WLAN channels satisfying the candidate condition (S 1843 : NO), in S 1849  the CPU  24  executes the all channels scanning process (described later). After completing the all channels scanning process, the CPU  24  ends the channel selecting process and returns to the WLAN connection process. 
     All Channels Scanning Process 
     In the all channels scanning process executed in S 1805  of the WLAN connection process and in S 1849  of the channel selecting process, the CPU  24  sets all WLAN channels that can be used for WLAN communications as candidate channels, measures the reception strength of radio waves for each of the candidate channels, and selects the candidate channel having the lowest reception strength as the WLAN channel to be used for WLAN communications. 
     Here, steps in the all channels scanning process will be described with reference to  FIG. 6 . In S 1851  the CPU  24  resets a count value N for a counter provided in the RAM  23  to zero. 
     In S 1852  the CPU  24  increments the count value N. When the count value N is zero, the CPU  24  increments the count value N to one. 
     In S 1853  the CPU  24  controls the WLAN interface  15  to receive radio waves from WLAN channel ch-N (i.e., WLAN channel ch-1 when N=1) and measures the reception strength over a prescribed period of time. 
     After measuring reception strength, in S 1854  the CPU  24  determines whether the reception strength of radio waves has been measured for all candidate channels (all WLAN channels that are available for WLAN communications) using the WLAN interface  15 . Specifically, the CPU  24  determines whether the count value N of the counter matches the number of the WLAN channels that are available for WLAN communications. Note that the number of WLAN channels that are available for WLAN communications differs according to the communication standard used for WLAN communications from among the IEEE 802.11b standard, the IEEE 802.11g standard, and the like. 
     If reception strength has not been measured for all candidate channels (S 1854 : NO), in S 1852  the CPU  24  increments the count value N and in S 1553  measures the reception strength for radio waves received from the WLAN channel ch-N corresponding to the new count value N. In S 1854  the CPU  24  again determines whether reception strength has been measured for all candidate channels. 
     Once the reception strength has been measured for all candidate channels through the WLAN interface  15  (S 1854 : YES), in S 1855  the CPU  24  selects the candidate channel having the lowest reception strength as the WLAN channel to be used for WLAN communications. Subsequently, the CPU  24  ends the all channel scanning process and returns to the WLAN connection process. 
     Effects 
     As described above, a Bluetooth connection is first established between the MFP  2  and wireless terminal  3  in order to perform wireless communications between the MFP  2  and wireless terminal  3 . While a Bluetooth connection is established between the MFP  2  and wireless terminal  3 , the Bluetooth communication frequency is stored in the RAM  23 . The Bluetooth communication frequency is the center communication frequency of the Bluetooth channel used for Bluetooth communications between the MFP  2  and wireless terminal  3 . If the MFP  2  receives a transmission/reception command from the wireless terminal  3 , the MFP  2  determines that this transmission or reception with the wireless terminal  3  should be performed using WLAN communications. Therefore, the MFP  2  establishes a WLAN connection. Therefore, the MFP  2  establishes a WLAN connection with the wireless terminal  3  and data is transmitted or received between the MFP  2  and wireless terminal  3  through WLAN communications according to the transmission/reception command. Note that the MFP  2  determines to execute WLAN communications with the wireless terminal  3  when the size of data to be transmitted or received is large, such as in the case of image data. 
     When establishing a WLAN connection with the wireless terminal  3 , the MFP  2  checks the distribution of center communication frequencies for Bluetooth channels previously used in Bluetooth communications that are stored in the RAM  23 . The MFP  2  checks this distribution for the existence of a search target distribution configured of a cluster of center communication frequencies for Bluetooth channels that are separated by less than the occupied bandwidth of a WLAN channel to be used for WLAN communications. If such a search target distribution does not exist, the MFP  2  selects one of the available WLAN channels to be the channel for WLAN communications. However, if a search target distribution does exist, the MFP  2  identifies the minimum and maximum communication frequencies f MIN  and f MAX  of the search target distribution, and determines whether there exist WLAN channels whose minimum and maximum frequencies F MIN  and F MAX  of the occupied bandwidth fall within the minimum-to-maximum frequency range. 
     If there are no such WLAN channels that satisfy the above condition (candidate condition), the MFP  2  selects one of the available WLAN channels to be used for WLAN communications. 
     A WLAN channel that satisfies the above condition (candidate condition) occupies a frequency bandwidth that includes Bluetooth channels those have been used for Bluetooth communications before the wireless connection was switched. Accordingly, this frequency bandwidth was not used for WLAN communications between other devices in the vicinity. 
     Therefore, when there exist WLAN channels that meet the above condition (candidate condition), all WLAN channels satisfying this condition (candidate condition) are set as candidate channels, and one of these candidate channels is selected as the channel for WLAN communications. By narrowing down the candidate channels for use in WLAN communications and selecting one of the remaining candidates as the WLAN channel to be used for WLAN communications in this way, this process can shorten the time required for selecting (searching for) a WLAN channel. As a result, this process can reduce the time required to switch from a Bluetooth connection to a WLAN connection. 
     Second Example of Channel Selecting Process 
     A channel selecting process illustrated in  FIG. 7  may be executed in place of the channel selecting process illustrated in  FIG. 4 .  FIG. 7  illustrates steps in the second example of the channel selecting process. 
     In S 1861  of the channel selecting process illustrated in  FIG. 7 , the CPU  24  identifies the minimum communication frequency f MIN  in the search target distribution (see  FIG. 8B ) configured of a cluster of Bluetooth communication frequencies separated from each other by less than 20 MHz. 
     In S 1862  the CPU  24  identifies the maximum communication frequency f MAX  in the search target distribution. 
     In S 1863  the CPU  24  determines whether there exist any WLAN channels that meet the candidate condition. The candidate condition requires that both the minimum frequency F MIN  and maximum frequency F MAX  of the occupied bandwidth for the WLAN channel fall within the minimum-to-maximum frequency range. 
     If there exist any WLAN channels that satisfy the candidate condition (S 1863 : YES), in S 1864  the CPU  24  determines these channels as candidate channels. 
     In S 1865  the CPU  24  determines whether the latest Bluetooth communication frequency f LATEST  falls within the occupied bandwidth for the candidate channel whose center frequency is closest to the latest Bluetooth communication frequency f LATEST  among the candidate channels. The latest Bluetooth communication frequency f LATEST  is the most recently stored Bluetooth communication frequency among the plurality of Bluetooth communication frequencies stored in the RAM  23 . The candidate channel whose center frequency is closest to the latest Bluetooth communication frequency f LATEST  is hereinafter called the “closest candidate channel”. That is, the CPU  24  determines whether the latest Bluetooth frequency f LATEST  falls within a range defined by the minimum frequency F MIN  and maximum frequency F MAX  of the occupied bandwidth for the closest candidate channel. 
     If the latest Bluetooth communication frequency f LATEST  falls within the occupied bandwidth for the closest candidate channel (S 1865 : YES), that is, if the latest Bluetooth communication frequency f LATEST  takes a value between the minimum frequency F MIN  and maximum frequency F MAX  of the occupied bandwidth for the closest candidate channel (S 1865 : YES), in S 1865  the CPU  24  selects this closest candidate channel as the WLAN channel to be used for WLAN communications. Subsequently, the CPU  24  ends the channel selecting process and returns to the WLAN connection process. 
     Using the sample distribution illustrated in  FIG. 8B  as the distribution of Bluetooth communication frequencies stored in the RAM  23  over time, WLAN channels ch-6 through ch-8 satisfy the candidate condition because both of their minimum and maximum frequencies F MIN  and F MAX  of the occupied bandwidth fall within the minimum-to-maximum frequency range. Here, the WLAN channels ch-6 through ch-8 are the sixth through eighth channels in order from the lowest frequency. Thus, the CPU  24  sets the WLAN channels ch-6 through ch-8 to the candidate channels. 
     In the sample distribution illustrated in  FIG. 8B , the WLAN channel ch-8 is the closest channel closest to the latest Bluetooth communication frequency f LATEST  among the candidate channels. Since the latest Bluetooth communication frequency f LATEST  falls within the occupied bandwidth for the WLAN channel ch-8 as illustrated in  FIGS. 8A through 8C , the CPU  24  selects the WLAN channel ch-8 as the WLAN channel to be used for WLAN communications in this case. 
     If the latest Bluetooth communication frequency f LATEST  does not fall within the occupied bandwidth for the closest candidate channel (S 1865 : NO), that is, if the candidate channel whose center frequency is closest to the latest Bluetooth communication frequency f LATEST  among the candidate channels determined in S 1864  does not fall within the range defined by the minimum frequency F MIN  and maximum frequency F MAX  of the occupied bandwidth for the closest candidate channel, in S 1867  the CPU  24  selects one of the candidate channels, controls the WLAN interface  15  to receive radio waves from the selected candidate channel, and measures the reception strength over a prescribed period of time. 
     In S 1868  the CPU  24  determines whether the reception strength has been measured for all candidate channels. While there remain candidate channels to be measured (S 1868 : NO), in S 1869  the CPU  24  selects another candidate channel to be subjected to reception strength measurements, and in S 1867  measures the reception strength of the newly selected candidate channel. 
     After the CPU  24  has completed measurements of reception strength for all candidate channels using the WLAN interface  15  (S 1868 : YES), in S 1870  the CPU  24  selects the candidate channel having the lowest reception strength as the channel to be used for WLAN communications. Subsequently, the CPU  24  ends the channel selecting process and returns to the WLAN connection process. 
     However, if the CPU  24  determines in S 1863  that there exist no WLAN channels that satisfy the candidate condition (S 1863 : NO), in S 1871  the CPU  24  executes the all channels scanning process of  FIG. 6  in which all WLAN channels available for WLAN communications are set as candidate channels. After completing the all channels scanning process, the CPU  24  ends the channel selecting process and returns to the WLAN connection process. 
     Effects 
     Through the channel selecting process shown in  FIG. 7 , the WLAN channel (closest candidate channel) whose center frequency is closest to the latest Bluetooth communication frequency f LATEST  among the WLAN channels (candidate channels) those minimum and maximum frequencies F MIN  and F MAX  fall within the minimum-to-maximum frequency range has the least probability of being used by another wireless station if the latest Bluetooth communication frequency f LATEST  falls within the occupied bandwidth for this WLAN channel (closest candidate channel). By selecting this WLAN channel to be used for WLAN communications, it is possible to reduce the time required for setting the WLAN channel. However, even if the latest Bluetooth communication frequency f LATEST  does not fall within the occupied bandwidth for this WLAN channel (closest candidate channel), one channel is selected for use in WLAN communications not from all channels but from the candidate channels which has been previously selected from among all channels. Thus, the time required for setting the WLAN channel can be reduced. Therefore, this method can reduce the time required for switching from a Bluetooth connection to a WLAN connection. 
     Third Example of Channel Selecting Process 
     A channel selecting process illustrated in  FIG. 9  may be executed in place of the channel selecting process illustrated in  FIG. 4 .  FIG. 9  illustrates steps in the third example of the channel selecting process. In the channel selecting process illustrated in  FIG. 9 , the processes in S 1844  through S 1848  of the channel selecting process illustrated in  FIG. 4  are replaced with a process in S 1884 . 
     In S 1881  of the channel selecting process illustrated in  FIG. 9 , the CPU  24  identifies the minimum communication frequency f MIN  in the search target distribution configured of a cluster of Bluetooth communication frequencies separated from each other by less than 20 MHz (see  FIG. 10B ). 
     In S 1882  the CPU  24  identifies the maximum frequency f MAX  of the search target distribution. 
     In S 1883  the CPU  24  determines whether there exist any WLAN channels that satisfy the candidate condition. The candidate condition requires that both the minimum and maximum frequencies F MIN  and F MAX  of the occupied bandwidth for the WLAN channel fall within the minimum-to-maximum frequency range. 
     If there exist WLAN channels that satisfy this candidate condition (S 1883 : YES), in S 1884  the CPU  24  sets the WLAN channel to be used for WLAN communications to the WLAN channel whose center frequency is closest to the median f MED  of the minimum-to-maximum frequency range. Subsequently, the CPU  24  ends the channel selecting process and returns to the WLAN connection process. 
     Using the sample distribution illustrated in  FIG. 10B  as the distribution of Bluetooth communication frequencies stored in the RAM  23  over time, WLAN channels ch-6 through ch-8 satisfy the candidate condition because both of their minimum and maximum frequencies F MIN  and F MAX  of the occupied bandwidth fall within the minimum-to-maximum frequency range. Here, the WLAN channels ch-6 through ch-8 are the sixth through eighth channels in order from the lowest frequency. Since among the center frequencies of the WLAN channels ch-6 through ch-8 satisfying the candidate condition, the center frequency of WLAN channel ch-7 is closest to the median f MED  of the minimum-to-maximum frequency range illustrated in  FIG. 10B , the CPU  24  sets WLAN channel ch-7 as the WLAN channel to be used for WLAN communications. 
     However, if there exist no WLAN channels that satisfy the candidate condition (S 1883 : NO), in S 1885  the CPU  24  executes the all channels scanning process of  FIG. 6 . After completing the all channels scanning process, the CPU  24  ends the channel selecting process and returns to the WLAN connection process. 
     Effects 
     Through the channel selecting process of  FIG. 9 , when both the minimum and maximum frequencies F MIN  and F MAX  of the occupied bandwidth for the WLAN channel whose center frequency is closest to the center of the search target distribution (the median f MED  of the minimum-to-maximum frequency range) fall within this search target distribution, this WLAN channel is set to be used for WLAN communications. Accordingly, this method can reduce the time required to set the WLAN channel, thereby reducing the time required to switch from a Bluetooth connection to a WLAN connection. 
     Fourth Example of Channel Selecting Process 
     A channel selecting process illustrated in  FIG. 11  may be executed in place of the channel selecting process illustrated in  FIG. 4 .  FIG. 11  illustrates steps in the fourth example of the channel selecting process. In the channel selecting process illustrated in  FIG. 11 , the processes in S 1844  through S 1848  of the channel selecting process illustrated in  FIG. 4  are replaced with processes in S 1894  and S 1895 . 
     In S 1891  of the channel selecting process illustrated in  FIG. 11 , the CPU  24  identifies the minimum communication frequency f MIN  of the search target distribution configured of a cluster of Bluetooth communication frequencies separated from each other by less than 20 MHz (see  FIG. 12B ). 
     In S 1892  the CPU  24  identifies the maximum communication frequency f MAX  of the search target distribution. 
     In S 1893  the CPU  24  determines whether there exist any WLAN channels that satisfy the candidate condition. The candidate condition requires that both the minimum and maximum frequencies F MIN  and F MAX  of the occupied bandwidth for the WLAN channel fall within the minimum-to-maximum frequency range. 
     If there exist WLAN channels that satisfy this candidate condition (S 1893 : YES), in S 1894  the CPU  24  divides the minimum-to-maximum frequency range into segments of 20 MHz, equivalent to the occupied bandwidth of each WLAN channel, and acquires the number of Bluetooth communication frequencies from the RAM  23  that fall within each segment. 
     In S 1895  the CPU  24  sets the WLAN channel to be used for WLAN communications to the WLAN channel whose center frequency is nearest the median f MED OF SEG  of the frequency bandwidth of the segment for which the largest number of Bluetooth communication frequencies was acquired, i.e., the segment in which Bluetooth communication frequencies are most densely distributed (most densely distributed segment). Subsequently, the CPU  24  ends the channel selecting process and returns to the WLAN connection process. 
     Using the sample distribution shown in  FIG. 12B  as the distribution of Bluetooth communication frequencies stored in the RAM  23  over time, WLAN channels ch-6 through ch-8 satisfy the candidate condition requiring that both the minimum and maximum frequencies F MIN  and F MAX  of the occupied bandwidth for the WLAN channel fall within the minimum-to-maximum frequency range. Here, the WLAN channels ch-6 through ch-8 are the sixth through eighth channels in order from the lowest frequency. Since the center frequency of WLAN channel ch-7 is closest to the median f MED OF SEG  of the most densely distributed segment in which Bluetooth communication frequencies are most densely distributed within the minimum-to-maximum frequency range, the CPU  24  selects WLAN channel ch-7 to be the WLAN channel to be used for WLAN communications. 
     However, if there exist no WLAN channels that satisfy the candidate condition (S 1893 : NO), in S 1896  the CPU  24  executes the all channels scanning process of  FIG. 6 . After completing the all channels scanning process, the CPU  24  ends the channel selecting process and returns to the WLAN connection process. 
     Effects 
     Through the channel selecting process of  FIG. 11 , the WLAN channel whose center frequency is closest to the median of the segment in which Bluetooth communication frequencies are most densely distributed is selected as the WLAN channel to be used for WLAN communications. Accordingly, this method can reduce the time required to set the WLAN channel, thereby reducing the time required to switch from a Bluetooth connection to a WLAN connection. 
     Variations of the Embodiments 
     While the description has been made in detail with reference to the specific embodiment thereof, it would be apparent to those skilled in the art that many modifications and variations may be made thereto without departing from the spirit of the disclosure, the scope of which is defined by the attached claims. 
     For example, the ASIC  21  may include a plurality of CPUs that work in concert to execute each process.