JP5006287B2 - Tablet computer and wireless communication system control method - Google Patents

Description

  The present invention relates to a technique for controlling transmission of radio waves from an antenna equipped in a tablet computer, and more particularly to a technique for controlling transmission of radio waves based on the positional relationship between the antenna and a human body.

  Among personal computers (hereinafter referred to as PCs), a thin computer that can be operated by pen input to a display is referred to as a tablet PC. The tablet PC provides a function equivalent to that of a notebook computer (hereinafter referred to as a notebook PC) by operating with a pen input without using a keyboard. There are two types of tablet PCs: a convertible type and a pure tablet type. The convertible type has a structure that can be used as a tablet PC by changing the display direction of a notebook PC with a built-in keyboard. The pure tablet type has a structure in which only a pen input operation is performed without a built-in keyboard.

  Regardless of the type, the tablet PC can be connected to a network via a wireless local area network (LAN) or a wireless wide area network (WAN) by being equipped with a wireless communication device and an antenna. . At this time, the antenna of the tablet PC is provided on any one of a plurality of edges of the housing in order to improve radio wave transmission / reception sensitivity. The user may operate the tablet PC while holding it on his / her arm. At that time, the user holds the main body of the tablet PC with one hand and operates the touch pen with respect to the display with the other hand. In this posture, the edge of the case of the tablet PC may contact or approach the user's chest or abdomen.

  As wireless communication devices that are used in close proximity to human bodies, such as mobile phones and wireless LANs, are becoming more and more concerned about the effects on the human body of radio waves emitted from these communication devices. Therefore, in many countries, standards are set for the allowable amount of SAR (Specific Absorption Rate), which is an index of the amount of radio wave power absorbed by the human body. SAR means energy absorbed per unit time by a human body tissue of unit mass. For example, in Japan, according to the Ministry of Internal Affairs and Communications or radio equipment regulations, land mobile stations that perform mobile radio communications are required to have a local SAR, which is an SAR for a specific part of the human body, of 2.0 W / kg or less. Similarly, standards for local SAR are established such as 1.6 W / kg in the United States and 0.8 W / kg in Sweden. In a notebook PC, the local SAR is not usually a problem because the casing on the display side is located away from the human body during use, but in a tablet PC, it may be a problem due to its specific operation method.

  Patent Document 1 discloses a technique for controlling an antenna unit without impairing the communication speed and quality of a tablet PC. In the present invention, the tablet PC uses a plurality of antennas on different sides of the housing and uses the diversity method. Usually, among these antennas, those having better transmission / reception conditions are used for communication. When the direction of the screen displayed on the display is switched by the operation of the display direction rotation button, any of the plurality of antennas may be arranged in the direction of the user's body. Therefore, in the present invention, when the screen direction is changed so that one of the antennas is arranged in the direction of the user's body, the use of the antenna is stopped and only the other antenna is used. Yes.

Patent Document 2 discloses a technique for changing the display direction of a screen while maintaining the continuity of wireless communication in a tablet PC and avoiding the problem of local SAR. The present invention is based on the premise that the user uses the tablet PC by being positioned on the lower side of the screen in the normal usage method. Then, a state in which the tablet PC is used with the antenna attachment position approaching the user is detected based on the antenna position and the screen display direction. And when there is a request to change the display direction of the screen so that the antenna emitting radio waves approaches the human body, the radio waves are prevented from being transmitted from the antenna that is close to the user by not changing the display direction. .
JP 2006-340180 A JP 2008-90345 A

  In the invention according to Patent Document 1, since a plurality of diversity antennas are arranged on different edges of the tablet PC, wireless communication can be continued even if transmission from any one of the antennas is stopped. A wireless communication apparatus for connecting to a wireless network such as a wireless MAN (Wireless Metropolitan Area Network) typified by a wireless WAN or WiMAX (registered trademark) is not a diversity system but is often a single antenna system. . When such a wireless communication device is installed in a tablet PC, if the emission of radio waves from the antenna is stopped at the moment when the display direction of the screen is changed, the connection to the wireless network used until then is suddenly disconnected. Therefore, it is not convenient. Even if the antenna is a diversity antenna, the communication performance deteriorates when the operation of one antenna stops.

  The invention according to Patent Document 2 can solve the problem of local SAR while maintaining continuity of wireless communication even when there is only one antenna. However, in the invention according to Patent Document 2, since it is determined that the antenna has approached the user only by the display direction of the screen and the screen change instruction is ignored, the switching of the screen is restricted and the tablet PC is used. This will impair the workability.

  The problem of the local SAR does not occur when the display direction of the screen is changed on the assumption that the user is positioned on the lower side of the screen, but actually occurs when the antenna and the user's body are close to each other. Therefore, in the invention according to Patent Document 1 and Patent Document 2, communication performance and operability are deteriorated by stopping transmission of radio waves from the antenna or prohibiting a change in the display direction of the screen more than necessary. It will be. Moreover, it is desirable to solve the local SAR problem without mounting a special device on the tablet PC.

  Accordingly, an object of the present invention is to provide a tablet computer that can cope with a local SAR while avoiding a decrease in communication performance. A further object of the present invention is to provide a tablet computer that can cope with a local SAR while avoiding a decrease in operability. A further object of the present invention is to provide a tablet computer capable of supporting local SAR in a practical wireless system. It is a further object of the present invention to provide a method for controlling a wireless communication system in such a tablet computer and a computer program for causing the tablet computer to function as such.

  The principle of the present invention for solving the above-described problem is that the possibility that a problem of local SAR occurs in a tablet computer is detected by a spurious signal when the human body is regarded as a propagation loss of radio waves. In the present invention, since the possibility of the occurrence of local SAR is detected based on the approaching state of the actual human body, the operation of the antenna is stopped more than necessary or the screen is rotated as compared with the case of detecting in the conventional screen direction. There is no need to constrain.

  In one aspect of the present invention, a first antenna, a second antenna, and a third antenna are attached to the periphery of a case of a tablet computer. The first antenna constitutes a first radio communication system, and the second antenna and the third antenna constitute a second radio communication system. The first wireless communication system and the second wireless communication system operate in different frequency bands. For example, the first wireless communication system can be configured as a wireless WAN system including a wireless WAN module, and the second wireless communication system can be configured as a wireless LAN system including a wireless LAN module.

  The control unit transmits the reference signal of the first frequency from the first antenna, and the human body and any of the antennas based on the received power of the spurious signal with respect to the reference signal received by the second antenna and the third antenna, respectively. It is judged whether or not. Both the first wireless communication system and the second wireless communication system according to the present invention can be connected to a network and are put to practical use. In the present invention, since it is possible to transmit and receive spurious signals between both radio communication systems in different frequency bands, it is not necessary to provide a special receiving device in order to realize the present invention. The control unit can be mainly composed of a device driver, an operating system, and a wireless connection application program.

  The control unit further recognizes which of the three antennas is approaching the human body. The recognition can be performed by binarizing the reception power value of the spurious signal based on the reference value. By binarizing, the received power of the spurious signal can be classified into strong and weak. A spurious signal propagated via a human body between antennas for transmission and reception is identified as weak, and a spurious signal propagated without passing through a human body is identified as strong. Therefore, an antenna approaching the human body can be recognized based on a combination of received power strengths received by the second antenna and the third antenna.

  The control unit displays a message prompting the antenna to be separated from the human body on the display unit, and the first wireless communication system is configured to prohibit transmission of radio waves from the recognized antenna until it is determined that the antenna is actually separated from the human body. And / or the second wireless communication system. As a result, the user can recognize that the housing needs to be separated from the body in order to use the antenna, and can transmit radio waves from the antenna after avoiding the problem of local SAR. In addition, since transmission of radio waves from only the antenna that is actually recognized as approaching the human body is prohibited, transmission from other antennas is possible, and communication performance is not deteriorated more than necessary.

  If a carrier wave is used for the reference signal, detection of spurious signals becomes easy. In addition, the control unit determines whether or not the spurious signal is a spurious signal with respect to the reference signal, thereby preventing detection of spurious signals and noise of other signals. If the frequency of the spurious signal is selected as the nth harmonic or the 1 / n harmonic of the reference signal, detection is facilitated. When the peripheral part of the housing is composed of four edges, the antenna close to the human body can be accurately identified by attaching the second antenna and the third antenna for reception to different edges. .

  According to the present invention, it is possible to provide a tablet computer that can cope with a local SAR while avoiding a decrease in communication performance. Furthermore, according to the present invention, it is possible to provide a tablet computer that can cope with a local SAR while avoiding a decrease in operability. Furthermore, according to the present invention, it is possible to provide a tablet computer that can cope with local SAR in a practical wireless system. Further, according to the present invention, it is possible to provide a method for controlling a wireless communication system in such a tablet computer, and a computer program for causing the tablet computer to function as such.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. FIG. 1 is an external view of a tablet PC 10 according to an embodiment of the present invention. The tablet PC 10 is a convertible type, and includes a system-side casing 11 and a display-side casing 13 that are both substantially rectangular parallelepipeds. The system-side casing 11 includes an input unit 15 including a keyboard and a pointing device, and the display-side casing 13 enables display and input with a touch pen by overlaying a touch panel input unit on a liquid crystal display (LCD). An input display panel 17 is provided.

  Further, the system-side casing 11 and the display-side casing 13 are connected by a connecting portion 21 at the center of each end portion. The connecting portion 21 supports these casings so as to be rotatable in a direction to open and close each other. Further, the display-side housing 13 can be rotated at least 180 degrees around the connecting portion 21 in a state where the display-side housing 13 is opened with respect to the system-side housing 11. In the PC usage mode shown in FIG. 1A, the tablet PC 10 can be used by operating the input unit 15 like a normal notebook PC. Further, the display-side casing 13 is rotated as shown in FIG. 1B, and the display-side casing 13 is folded over the system-side casing 11 as shown in FIG. If the display panel 17 faces the front, the tablet use mode shown in FIG. In the tablet use mode, the tablet PC 10 can be used by operating the input display panel 17.

  The display-side housing 13 includes four edges 12a, 12b, 12c, and 12d at the periphery of the input display panel 17. A display direction rotation button 23 is provided on the edge 12a. Each time the user presses the display direction rotation button 23, the direction of the screen displayed on the input display panel 17 is rotated by 90 degrees in a predetermined direction. The direction of rotation can be a set clockwise, counterclockwise, or any selected direction. Furthermore, when rotating 180 degree | times, you may make it rotate 180 degree | times at once, without rotating 90 degree | times at a time.

  A WAN antenna 25 used for the wireless WAN and a LAN antenna 29 used for the wireless LAN are attached to the edge 12c, and a LAN antenna 27 used for the wireless LAN is attached to the edge 12b. The LAN antenna 27 and the LAN antenna 29 are used for communication by a diversity system or a MIMO (Multiple Input Multiple Output) system, and the performance of both is configured to be equal. When the LAN antenna 27 and the LAN antenna 29 are used in a diversity system, an antenna having a large reception power is used for reception and functions as reception diversity, and when the antenna used for reception is used for transmission, transmission is performed. Functions as diversity.

  The WAN antenna 25, the LAN antenna 27, and the LAN antenna 29 are preferably provided on any of the four edges of the display-side casing 13 from the viewpoint of transmission / reception performance. Therefore, as described above, the human body may approach or touch any one of the edges, which may cause a local SAR problem specific to the tablet PC. As will be described in detail later, in the present invention, when a human body approaches the antenna, transmission from the antenna attached to the edge is prohibited in order to avoid the problem of local SAR. The LAN antenna 27 and the LAN antenna 29 exhibit maximum communication performance when both operate, but communication is possible with low communication performance even when only one of them operates.

  A characteristic arrangement of these antennas in the tablet PC 10 is that the LAN antenna 27 and the LAN antenna 29 are not attached to one edge. The user's body usually approaches or contacts only one of the edges. Therefore, with such an antenna arrangement, transmission from one of the LAN antennas can always be enabled regardless of the proximity of the human body and the tablet PC 10.

  FIG. 2 is a block diagram illustrating a schematic configuration of hardware of the notebook PC 10. The CPU 51 is an arithmetic processing unit having a central function of a notebook PC, and executes an OS, a BIOS, a device driver, an application program, or the like. The CPU 51 controls each device connected to a chip set mainly composed of the north bridge 33 and the south bridge 55 via various buses.

  The north bridge 53 has a memory controller function for controlling an access operation to the main memory 57, a data buffer function for absorbing a difference in data transfer speed between the CPU 51 and another device, and the like. Including. The main memory 57 is a writable memory connected to the north bridge 53 and used as a reading area for programs executed by the CPU 51 and a work area for writing processing data. The video controller 59 is connected to the north bridge 53 and has a video chip (not shown) and a VRAM (not shown). The video controller 59 receives a drawing command from the CPU 51 and generates an image to be drawn. The image written in the VRAM and the image read from the VRAM are sent as drawing data to the LCD 17b constituting the input display panel 17.

  The wireless LAN module 61 and the wireless WAN module 63 are each connected to the south bridge 55. The wireless LAN module 61 is connected to the LAN antenna 27 and the LAN antenna 29, and the wireless WAN module 63 is connected to the WAN antenna 25. As a result, the wireless LAN module 61 and the wireless WAN module 63 can perform wireless communication in the respective frequency bands.

  The wireless LAN module 61 can be configured to have functions of either or both of the diversity communication scheme and the MIMO communication scheme. When both functions are provided, the user switches to one of the communication methods depending on the situation. The wireless LAN module 61 and the wireless WAN module 63 can perform wireless communication using a plurality of channels. When a predetermined channel is set, transmission power for each predetermined frequency included in the bandwidth of the channel is set. The value or the received power value is stored in the memory while being refreshed at a predetermined cycle.

  The south bridge 55 also includes functions as a serial ATA interface and a USB interface (not shown), and is connected to a hard disk drive (HDD) 65, an optical drive (not shown), and the like via the serial ATA. . The HDD 65 stores an OS, a device driver, an application program, or the like. Further, an embedded controller (EC) 69, an I / O controller 75, and the like are connected to the south bridge 55 via an LPC bus 67. An acceleration sensor 71 and a power supply device 73 are connected to the embedded controller (EC) 69. The acceleration sensor 71 is composed of a piezoelectric ceramic element or the like, and detects the direction and magnitude of acceleration given from the outside to the tablet PC 10.

  Specifically, the acceleration sensor 71 detects acceleration generated when the tablet PC 10 is lifted by the user and outputs it to the EC 69 as an analog signal. The EC 69 converts the acceleration information received from the acceleration sensor 71 into a digital signal, stores it in the internal RAM, and further notifies the CPU 51 by interrupting it. The power supply device 73 includes a charger, a battery pack, a control hardware logic circuit, and the like. The I / O controller 75 is connected to an input unit 15 such as a keyboard and a mouse and a touch panel input unit 17 a constituting the input display panel 17.

  Note that FIGS. 1 and 2 merely describe the main hardware configuration and connection relations related to the present embodiment in a simplified manner in order to describe the present embodiment. In addition to those mentioned above, many devices are used to configure the tablet PC 10, but these are well known to those skilled in the art and will not be described in detail here. A person skilled in the art also arbitrarily selects a plurality of blocks described in the figure as one integrated circuit or device, or conversely, a block is divided into a plurality of integrated circuits or devices. Is included in the scope of the present invention.

  In the present embodiment, the tablet PC 10 detects that the WAN antenna 25 and the LAN antennas 27 and 29 mounted on the edge of the display-side casing 12 have actually approached the human body, and transmits radio waves from the antenna. To deal with the problem of local SAR. The operation in which the tablet PC 10 controls the transmission of radio waves from the antenna in this way is referred to as antenna processing in this specification.

  FIG. 3 is a block diagram illustrating a software and hardware configuration related to antenna processing. The wireless connection application 101, the OS 103, the wireless LAN driver 105, and the wireless WAN driver 107 stored in the HDD 65 are read into the main memory 57 and executed by the CPU 51 when the tablet PC 10 is activated. The wireless connection application 101 is an application program that runs on the OS 103 and resides in the main memory 57 and plays a central role in antenna processing described below. Note that the OS 103 intervenes in all exchanges of data or commands between the wireless connection application 101 and each device driver.

  The wireless LAN driver 105 is a device driver corresponding to the wireless LAN module 61. The wireless connection application 101 can connect, disconnect, and reconnect to the wireless LAN by controlling the wireless LAN module 61 via the wireless LAN driver 105. Further, the wireless connection application 101 can inquire through the wireless LAN driver 105 and acquire the frequency and power intensity of the radio wave currently transmitted to the wireless LAN module 61 and the received radio wave. The wireless LAN module 61, the LAN antenna 27, and the LAN antenna 29 are collectively referred to as a wireless LAN system 60.

  The wireless WAN driver 107 is a device driver corresponding to the wireless WAN module 63. The wireless connection application 101 can connect, disconnect, and reconnect to the wireless LAN by controlling the wireless WAN module 63 through the wireless WAN driver 107. The wireless connection application 101 can also inquire and acquire the frequency and power intensity of the signal currently transmitted to the wireless WAN module 33 and the received signal through the wireless WAN driver 107. The wireless WAN module 63 and the WAN antenna 25 are collectively referred to as a wireless WAN system 62.

  In this embodiment, the wireless LAN uses the 2.4 GHz band (2400 to 2500 MHz), and the wireless WAN uses the GSM850 (upstream 824 to 849 MHz) frequency band. However, these frequency bands are examples for carrying out the present invention. In the wireless LAN and the wireless WAN, a plurality of channels are set in an assigned frequency band, and a center frequency and a bandwidth are defined for each channel. In principle, the frequency of the radio wave transmitted by the wireless LAN system 60 and the wireless WAN system 62 corresponds to the frequency of each channel set in each frequency band.

  However, the frequency of the radio waves received by the wireless LAN system 60 and the wireless WAN system 62 is not limited to the center frequency set for the channel, but also receives radio waves of frequencies included in the frequency band, and stores their power intensity in the memory. Store. The wireless connection application 101 can acquire the power intensity for each predetermined frequency included in the bandwidth from the wireless LAN system 60 or the wireless WAN system 62. Now, it is assumed that the wireless WAN system 62 emits a radio wave having a center frequency of 824.2 MHz corresponding to the channel 128 in the vicinity of the lower limit of the GSM850 frequency band with a predetermined output. This signal is only a carrier wave and does not include a frequency component due to modulation.

  Since the wireless LAN system 60 has a frequency band different from that of the wireless WAN system 62, the wireless LAN system 60 does not receive this 824.2 MHz radio wave. However, spurious emission is simultaneously performed from a frequency band outside the necessary frequency band with transmission of the carrier wave of 824.2 MHz. Since the 824.2 MHz radio wave does not include a frequency component due to modulation, the nth harmonic or the 1 / n subharmonic is generated so as to be distinguishable from other frequency components. Since the signal of 2472.6 MHz, which is the third harmonic of 824.2 MHz, is included in the frequency band used in the wireless LAN system 60, it can be received by the wireless LAN system 60.

  In addition, in response to the revision of the radio communication rules regarding the permissible value of the spurious emission of radio equipment at the WRC (World Radio Communication Conference), the intensity of spurious emission of radio equipment in Japan in December 2005 was revised. Relevant ministerial ordinances and notifications such as technical standards related to tolerances have been revised. Among them, the emission generated outside the necessary frequency band is collectively referred to as unnecessary emission, and out-of-band emission and spurious emission are defined as unnecessary emission. However, in this specification, signals emitted outside the necessary frequency band are collectively referred to as spurious. Accordingly, the radio waves of the nth order harmonic and the 1 / nth order subharmonic are not limited to the order but are treated as spurious emission.

  Both the wireless LAN system 60 and the wireless WAN system 62 are mounted as the original wireless function of the tablet PC 10. If the transmission power and antenna gain of the WAN antenna 25 are Pt and Gt, the reception power and antenna gain of the LAN antenna 27 or the LAN antenna 29 are Pr and Gr, and the propagation loss between both antennas is Lp, then Pr = The relationship is Pt−Lp + Gt + Gr.

  FIG. 4 is a diagram for explaining the positional relationship between the human body and the antenna when the user operates the tablet PC 10. The state when the user operates the tablet PC 10 includes a state where the antenna is separated from the human body as shown in FIG. 4A and a state where the antenna is close to the human body as shown in FIG. A human body existing in a radio wave propagation path between the WAN antenna 25 and the LAN antenna 27 or the LAN antenna 29 affects the received power Pr as a propagation loss Lp. That is, when the human body is close to any antenna for transmission / reception, the received power decreases.

  The WAN antenna 25, the LAN antenna 27, and the LAN antenna 29 are attached to the same display-side casing 13, and the distance between them and the positional relationship between them are always constant. Therefore, if the wireless LAN system 60 and the wireless WAN system 62 operate normally and the 824.2 MHz radio wave emitted from the WAN antenna 25 is stable at a known transmission power Pt, the LAN antenna 27 or the LAN antenna 29 The received power Pr of the 2472.6 MHz spurious signal received by is also stabilized at a substantially constant value. Therefore, the received power Pr of the LAN antenna 27 is larger at the position of the human body in FIG. 4A than at the position of the human body in FIG. However, the received power Pr of the LAN antenna 29 does not change between the position of the human body in FIG. 4A and the position of the human body in FIG. In the antenna processing according to the present embodiment, this characteristic is used to detect which antenna is actually approaching the user's human body.

  FIG. 5 is a diagram illustrating a result of measuring the reception power of the spurious signal received by the LAN antenna 27. FIGS. 5A and 5B both show a case where 824.2 MHz transmission radio waves (hereinafter referred to as reference signals) having the same transmission power are output from the WAN antenna 25 and simultaneously received by the LAN antenna 27. This is a typical reception characteristic obtained by scanning the received power value of the received signal at a predetermined frequency interval in the range of 2457 ± 20 MHz. 5A shows the received power of the LAN antenna 27 corresponding to the state of FIG. 4A, and FIG. 5B shows the received power of the LAN antenna 27 corresponding to the state of FIG. 4B. Show.

  In both FIG. 5A and FIG. 5B, a waveform 201 corresponding to the waveform of the received signal used in the 2.4 GHz band channel 10 (2457 ± 11 MHz) of the wireless LAN is observed. A peak 203 isolated from the waveform of the channel signal is observed near 2472.6 MHz. This peak 203 corresponds to the received power of the third harmonic of the reference signal emitted from the WAN antenna 25. The waveform 201 is substantially the same between FIG. 5A and FIG. 5B, but the received power value of the peak 203 is measured in the state where the LAN antenna 27 and the human body are close to each other in FIG. ) Is in the vicinity of −110 dBm, whereas in FIG. 5A measured in a state where the LAN antenna 27 is separated from the human body, it is in the vicinity of −100 dBm.

  At this time, in the above formula, there is no change between FIG. 5 (A) and FIG. 5 (B) except for the distance between the LAN antenna 27 and the human body. It can be said that a difference of about 10 dBm occurs due to the approach of the human body. Note that the difference in received power based on the distance from the human body can be similarly detected for the LAN antenna 29. Therefore, the wireless connection application 101 inquires the wireless LAN module 61 for the received power value in the vicinity of 2472.6 MHz received by the LAN antenna 27 and the LAN antenna 29, and acquires any of the received power values based on the strength of the received power value. It can be determined whether the antenna is close to the human body.

  The wireless connection application 101 uses a reference value of −105 dBm, which is an intermediate value between the received power value (−100 dBm) of the LAN antenna 25 when the human body is separated and the received power value (−110 dBm) when the human body is approaching. As 207, the received power value is binarized into strong and weak data for determination. FIG. 6 is a diagram illustrating a method for identifying the antenna that the wireless connection application 101 is approaching to the human body.

  In FIG. 6, the antennas are displayed as A, B, and C, and the positions of the human body are displayed as 1, 2, and 3 in order to generalize and judge. The human body position 1 indicates that the human body is away from the tablet PC, and the human body positions 2 and 3 indicate that the human body and the tablet PC are close to each other at the edge. 6C and 6D correspond to FIG. 6A, and FIGS. 6E and 6F correspond to FIG. 6B. Here, a method will be described in which a reference signal is transmitted from any one of the antennas A, B, and C, and an antenna approaching the human body is identified by the received power of spurious signals received from the other two antennas. 6 (C), (D), (E), and (F), a circle indicates that the received power is strong because neither the human body nor the antenna for transmission / reception is close, and a triangle indicates a human body. It indicates that one of the antennas for transmission and reception approaches and the received power is weak.

  6A is the same as the antenna arrangement shown in FIG. FIG. 6C shows a result of transmitting the reference signal from the antenna A and measuring the reception power of the spurious signal by the antenna B and the antenna C. When the position of the human body is 1, the received power of antenna B and antenna C are both strong. However, at this time, it is not necessary to prohibit transmission from any antenna.

  When the human body position is 2 and the human body position is 3, the received power of the antenna B and the antenna C is weak. Therefore, in the antenna arrangement shown in FIG. 1A, when the reference signal is transmitted from the antenna A and the power intensity of the spurious signals received by the antenna B and the antenna C is measured, However, it is impossible to identify an antenna that is close to the human body. As shown in FIG. 6D, when the reference signal is transmitted from the antenna B and the received power of the spurious signal is measured by the antenna A and the antenna C, the antenna A for each of the positions 1, 2, and 3 of the human body. The pattern of the received power of antenna C is different.

  In the case of the position 1 of the human body, the received power of both the antenna A and the antenna C is strong, and there is no need to prohibit transmission to any antenna. In the case of the human body position 2, the received power of the antenna A is weak and the received power of the antenna C is strong. In the case of position 3 of the human body, the received power of both antenna A and antenna C becomes weak. Therefore, the wireless connection application 101 detects the human body position 2 or the human body position 3 from the reception intensity patterns of the two antennas, and prohibits transmission from the antenna A when the human body position is 2, and the human body position When 3, the transmission from the antenna B and the antenna C is prohibited. Note that, when the reference signal is transmitted from the antenna C, the antenna approaching the human body can be identified by the pattern of FIG. 6D in which the antenna B and the antenna C are interchanged.

  FIG. 6B shows a state where the antenna C of FIG. 6A is moved to another edge. 6E shows the measurement result of the received power of the spurious signal transmitted from the antenna A and received by the antennas B and C. FIG. 6F shows the result of transmitting the reference signal from the antenna B. The measurement result of the reception power of the spurious signal received by the antennas A and C is shown. In the case of FIG. 6E, since the received power patterns are all different at the positions 1, 2, 3, and 4 of the human body, the wireless connection application 101 determines whether the human body is approaching and the antenna that is approaching is specified. Is possible. The wireless connection application 101 does not restrict transmission from any antenna when the human body is at position 1, and prohibits transmission from the antennas A, B, and C at human positions 2, 3, and 4, respectively. .

  In the case of FIG. 6F as well, since the received power patterns are all different at positions 1, 2, 3, and 4 of the human body, the wireless connection application 101 determines whether the human body is approaching and the antenna that is approaching is specified. Is possible. The wireless connection application 101 prohibits transmission from the antennas A, B, and C at the positions 2, 3, and 4 of the human body, respectively. As is apparent from FIG. 6, in the present invention, when two antennas that receive spurious signals are provided on the same edge, the antenna that is close to the human body cannot be specified. The selection is made in consideration of this characteristic.

  FIG. 7 is a flowchart illustrating a procedure in which the wireless connection application 101 performs antenna processing. The antenna processing according to this procedure is performed at a timing when neither the wireless WAN system 62 nor the wireless LAN system 60 is communicating with the network. It is assumed that the wireless connection application 101 has acquired the reference value 207 shown in FIG. The antenna processing is performed when the wireless connection application 101 uses the wireless LAN driver 105 or the wireless WAN driver 107 when the user tries to start using either the wireless WAN system 62 or the wireless LAN system 60 through an application program involving wireless communication. From this, it is possible to start by receiving information that there has been an access (step 301). Alternatively, the wireless connection application 101 may start processing upon receiving a notification from the EC 69 that the posture of the tablet PC 10 has changed based on a signal from the acceleration sensor 71. This is because the change in the posture of the tablet PC 10 suggests the possibility of the human body and the antenna approaching each other.

  In block 303, the wireless connection application 101 causes the wireless WAN system 62 to transmit a reference signal from the WAN antenna 25 with the same frequency (here, 824.2 MHz) and transmission power as when the reference value 207 was acquired. This reference signal is a carrier wave that is not modulated with a data signal. The wireless WAN system 62 may send the carrier wave after variable-length coding such as Morse code. The wireless LAN system 60 uses a channel including a frequency of a spurious signal (here, 2472.6 MHz which is a frequency of the third harmonic of the reference frequency) with respect to the reference signal, and the frequency of each of the LAN antennas 27 and 29 is determined. The frequency included in the band is scanned at a predetermined interval, and the frequency and the received power value corresponding to the frequency are stored in the memory.

  At this time, the LAN antennas 27 and 29 operate in a communication system using independent antennas instead of the MIMO system. In block 305, the wireless connection application 101 receives the received power value for the LAN antennas 27 and 29 from the wireless LAN system 60. In block 305, the wireless connection application 307 acquires the reception power of the spurious signal with respect to the reference signal from the data received from the wireless LAN system 60. The reception power of the spurious signal is obtained by averaging reception power of a frequency around 2472.6 MHz or by receiving data for a plurality of times from the wireless LAN system 60 and averaging them.

  In block 307, the wireless connection application 101 checks whether the acquired spurious signal is a spurious signal of the reference signal. The wireless connection application 101 transmits a reference signal that is variable-length encoded from the wireless WAN system 62, determines whether or not the received signal received by the wireless LAN system is variable-length encoded with the same pattern, and It can be confirmed that the signal is a spurious signal. Alternatively, the transmission and reception of the reference signal can be repeated several times to determine whether or not the acquired spurious signal matches the timing.

  In addition, radio waves received by the wireless LAN system 60 may include noise. FIG. 8 is a diagram for explaining the relationship between the received power of the spurious signal received by the LAN antenna 27 and the received power of noise. As the received power, the same waveform 201 and peak 203 as in FIG. 5 are observed, but noise 205 from the outside is mixed in the frequency range including the frequency f1 of the peak 203. If such noise is mixed, it is impossible to identify the antenna that is close to the human body from the reception power of the spurious signal described with reference to FIG.

  The frequency range in which the peak 203 due to the spurious signal is observed is a relatively narrow range of 10 MHz or less including the frequency f1. On the other hand, the frequency range of the noise 205 such as a microwave oven is generally a relatively wide range of several tens of MHz or more. Therefore, the reception power at another frequency f2 around the frequency f1 and not included in the frequency range of the peak 203 is acquired, and this reception power value is compared with the reference value 209. The reference value 209 is a value smaller than the reference value 207 with respect to the peak 203. If the received power value of the signal of the frequency f2 is smaller than the reference value 209, it can be determined that the influence of the noise 205 is not a problem.

  If the received power value of the signal of frequency f2 is smaller than the reference value 209, it can be determined that there is no influence of the noise 205. If the received power value of the signal of frequency f2 is larger than the reference value 209, it can be determined that there is an influence of the noise 205. As another method for determining the influence of noise, after measuring the reception power value of the spurious signal, the reception power value near the frequency f1 can be measured in a state where transmission of the reference signal is once stopped. Even if the reference signal is stopped, it can be determined that noise is received when a reception power value approximately equal to that before the stop is measured in the vicinity of the frequency f1.

  The wireless connection application 101 determines that the data acquired from the data received from the wireless LAN system 60 on the assumption that the received power of the spurious signal with respect to the reference signal is noise or other signals and is not normal. If so, the process moves to block 309 to interrupt the antenna processing, returns to block 301, and waits until the next antenna processing start opportunity. When the wireless connection application 101 determines that the data acquired as the received power of the spurious signal with respect to the reference signal from the data received from the wireless LAN system 60 is normal, the process proceeds to block 311 and refers to FIG. The method described above is used to determine whether any antenna is approaching the human body.

  When the wireless connection application 101 determines that no antenna is in contact with the human body, the wireless connection application 101 returns to block 301 and waits until the next antenna processing start opportunity. When the wireless connection application 101 determines in block 313 that one of the antennas is close to the human body, the antenna provided on which edge is close to the human body by the method described with reference to FIG. To identify antennas that should be prohibited from transmitting.

  In block 315, the wireless connection application 101 controls the wireless LAN module 61 and / or the wireless WAN module 63 so as not to transmit radio waves from the antenna that is close to the human body. Specifically, the wireless LAN driver 105 and the wireless WAN driver 107 are set so as to prohibit a request accompanied by transmission of radio waves from an antenna close to a human body from any application program. In block 317, since the antenna is close to the human body, the wireless connection application 101 displays a message on the input display panel 17 for urging the tablet PC 10 to be separated from the human body in order to perform wireless communication. The user sees this message and recognizes that the body needs to be separated from the housing when wireless communication is necessary.

  In block 319, the wireless connection application 101 repeats the procedure from block 303 to block 311 every predetermined time to determine whether the user has removed his / her body from the housing. When it is determined in block 319 that there is no antenna approaching the human body, the wireless connection application 101 permits transmission of radio waves from the antenna in block 321. In block 323, the wireless connection application 101 displays a message indicating that transmission is possible on the input display panel 17 and returns to block 301.

  The embodiment described above uses a GSM850 wireless WAN and a 2.4 GHz band wireless LAN, transmits a reference signal of 824.2 MHz on the wireless WAN side, and is the third harmonic on the wireless LAN side. It was performed by the method of acquiring the reception power value of the signal of 2472.6 MHz. However, the implementation of the present invention is not limited to the frequency band of this embodiment. For example, contrary to the embodiment, a 2472 MHz reference signal corresponding to the center frequency of the 13th channel of the 2.4 GHz band wireless LAN is transmitted on the wireless LAN system 60 side, and the wireless WAN system 62 performs the first third low adjustment. It can also be performed by a method of acquiring a received power value of a 824 MHz signal that is a wave.

  Standards and frequency assignments applied in wireless communication vary depending on the country, region, and carrier. For example, the frequency band of GSM850 is currently allocated in the North American region, but not allocated in other countries. Therefore, in implementing the present invention, it is necessary to determine the frequency of the reference signal to be used and its spurious signal in accordance with the country and region in which the tablet PC 10 is used, and the communication carrier. Since the frequency of the reference signal needs to be determined based on the communication standard supported by the wireless module, there are frequencies that are difficult to select as the frequency of the reference signal in the assigned frequency band. However, when the receiving system receives a spurious signal, it can scan the frequency of the frequency band assigned to the receiving system and obtain an arbitrary received power value.

  In Japan, KDDI Corporation is assigned a transmission frequency band of 815 to 830 MHz for the CDMA2000 series. When this transmission frequency band is tripled, it becomes 2445 to 2490 MHz, so that all third harmonics of signals transmitted from this band are included in the 2.4 GHz band (2400 to 2500 MHz). NTT DOCOMO, Inc. is assigned a transmission frequency band of 830 to 845 MHz for W-CDMA. When this transmission frequency band is tripled, it becomes 2490 to 2535 MHz, so that the third harmonic of the signal transmitted from this band overlaps with the 2.4 GHz band.

  Therefore, even if the GSM850 wireless WAN for North America in the above-described embodiment is replaced with the CDMA2000 series or W-CDMA for Japan, the reference signal transmission frequency is selected so that the third harmonic is included in the 2.4 GHz band. For example, the present invention can be carried out in exactly the same manner as in the previous embodiments. In Japan, 1749.9 to 1784.9 MHz are allocated for W-CDMA, and 1925 to 1980 MHz are allocated for W-CDMA and CDMA2000 series. The third harmonic of these frequency bands is also allocated. Are included in 5150 to 5845 MHz, which is the receivable range of the 5 GHz band wireless LAN module, or partially overlap, so the present invention can be implemented by selecting the reference signal transmission frequency in the same manner.

  Besides the wireless LAN and the wireless WAN, Bluetooth (registered trademark), One Seg, UWB, and the like can be applied to the present invention. In particular, UWB is allowed in the US from 3.1 to 10.6 GHz and in Japan is expected to be allowed from 3.4 to 4.8 GHz and 7.25 to 10.25 GHz, so a wide frequency band can be used, If a spurious signal of a signal transmitted in another band is received using UWB, the present invention can be applied to more types of wireless communication.

  For example, 2.3 to 2.4 GHz (2.5 GHz band), 2.5 to 2.7 GHz (2.5 GHz band), 3.3 to 3.8 GHz (3.5 GHz band), etc. allocated by WiMAX The present invention can be applied by receiving a spurious signal by UWB even in the frequency band. Since the present invention can cope with the problem of local SAR by using a plurality of practical wireless communication systems with different frequency bands mounted on a tablet PC, there is no need to mount a special device on the tablet PC 10.

  Although the present invention has been described with the specific embodiments shown in the drawings, the present invention is not limited to the embodiments shown in the drawings, and is known so far as long as the effects of the present invention are achieved. It goes without saying that any configuration can be adopted.

  The present invention can be used in a wireless device including a plurality of wireless communication systems having different frequency bands.

It is a perspective view which shows the external appearance of the tablet PC concerning embodiment of this invention. It is a block diagram which shows schematic structure of the hardware of the tablet PC concerning this Embodiment. It is a block diagram which shows the structure of the software and hardware relevant to this Embodiment. It is a figure explaining the positional relationship of a human body and an antenna when a user operates tablet PC. It is a figure showing the result of having measured the reception power of the spurious signal received by the LAN antenna. It is a figure explaining the method in which the wireless connection application identifies the antenna which is approaching the human body. It is a flowchart which shows the procedure in which a wireless connection application controls transmission of the electromagnetic wave from an antenna. It is a figure explaining the relationship between the reception power of the spurious signal received by the LAN antenna, and the reception power of noise.

Explanation of symbols

10 ... Tablet PC
DESCRIPTION OF SYMBOLS 11 ... System side housing | casing 12a, 12b, 12c, 12d ... Edge 13 ... Display side housing | casing 17 ... Input display panel 25 ... WAN antenna 27, 29 ... LAN antenna 60 ... Wireless LAN system 62 ... Wireless WAN system

Claims (15)

A tablet computer having a display unit and covered with a housing,
A first wireless communication system including a first antenna attached to a peripheral portion of the housing and capable of wireless communication with a network;
A second wireless communication system including a second antenna and a third antenna, which are respectively attached to the periphery of the housing, and capable of wireless communication with a network in a frequency band different from that of the first wireless communication system; ,
A reference signal having a first frequency is transmitted from the first antenna, and the human body and any one of the antennas based on reception power of a spurious signal with respect to the reference signal received by the second antenna and the third antenna, respectively. And a control unit for determining whether or not the two are approaching.   The tablet computer according to claim 1, wherein the controller recognizes an antenna approaching a human body from the first antenna, the second antenna, and the third antenna.   The tablet computer according to claim 2, wherein the control unit binarizes a reception power value of the spurious signal based on a reference value to recognize an antenna approaching a human body.   The control unit displays a message prompting the antenna to be separated from the human body on the display unit, and the first wireless communication is prohibited so as to prohibit transmission of radio waves from the antenna until it is determined that the antenna is actually separated from the human body. The tablet computer according to claim 2 or 3, which controls a system and / or the second wireless communication system.   The tablet computer according to any one of claims 1 to 4, wherein the reference signal is an unmodulated carrier wave.   The tablet computer according to claim 1, wherein the control unit determines whether the spurious signal is a spurious signal with respect to the reference signal.   The tablet computer according to any one of claims 1 to 6, wherein the frequency of the spurious signal is n times the frequency of the reference signal or 1 / n times the frequency of the reference signal when n is an integer.   8. The tablet computer according to claim 1, wherein the first wireless communication system includes a wireless WAN module, and the second wireless communication system includes a wireless LAN module.   The tablet computer according to any one of claims 1 to 8, wherein a peripheral portion of the casing is configured by four edges, and the second antenna and the third antenna are attached to different edges. A first antenna attached to the periphery of the housing; and a second antenna and a third antenna attached to the periphery of the housing and used in a frequency band different from the first antenna. A method of controlling the wireless communication system in a tablet computer equipped with a wireless communication system,
Transmitting a first frequency reference signal from the first antenna;
Measuring the received power of a spurious signal with respect to the reference signal respectively received by the second antenna and the third antenna;
Determining whether there is an antenna approaching a human body based on the received power received by the second antenna and the received power received by the third antenna by the tablet computer. Control method.   The control method according to claim 10, further comprising the step of recognizing an antenna approaching the human body by the tablet computer.   The control method according to claim 10 or 11, wherein the transmission of the reference signal is executed immediately before the wireless communication system is used.   The control method according to any one of claims 10 to 12, wherein the transmission of the reference signal is executed when an attitude of the tablet computer changes.   The control method according to any one of claims 11 to 13, wherein the tablet computer includes a step of prohibiting transmission of radio waves from the antenna until it is determined that the recognized antenna is not approaching a human body. A first antenna attached to the periphery of the housing; and a second antenna and a third antenna attached to the periphery of the housing and used in a frequency band different from the first antenna. To tablet computer equipped with wireless communication system,
A function of transmitting a reference signal of a first frequency from the first antenna;
A function of measuring received power of a spurious signal with respect to the reference signal respectively received by the second antenna and the third antenna;
A computer program for realizing a function of determining whether or not there is an antenna approaching a human body based on received power received by the second antenna and received power received by the third antenna.

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