Wireless communication method and wireless communication apparatus

Wireless communication is carried out between devices. A highest frequency band is selected. When the selected frequency band includes an unused channel in which no disturbing wave is present, a maximum transmission rate at which a received field strength value exceeds a threshold value is determined. When the selected frequency band does not include an unused channel or one in which no disturbing wave is present or there is no transmission rate associated with the selected frequency band at which the received field strength value exceeds the threshold value, the next highest frequency band is successively selected and the above is repeated. When the maximum transmission rate is successfully determined, communication is initiated using the unused channel of the selected frequency band at the maximum transmission rate as a communication channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national stage application under 35 U.S.C. §371 of International Application No. PCT/JP03/05107, filed Apr. 22, 2003, which claims priority from Japanese Application No. P2002-120518, filed Apr. 23, 2002, the disclosures of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a wireless communication method for use with a wireless communication system constituted by a plurality of wireless communication apparatuses and to wireless communication apparatuses that composes the wireless communication system.

2. Background Art

A system constituted of a base apparatus and a display terminal has been developed. The base apparatus functions as an information source or as an access point in which or to which a television broadcast receiving tuner is built or connected and that is connected to a telephone line through a modem as one type of a wireless LAN system that is structured in a limited area of a residence, an office, or the like. The display terminal executes functions for issuing a command to the base apparatus through a wireless communication with the base apparatus that includes receiving a picture of the television from the base apparatus, receiving information from the Internet, displaying the picture and information on a display, and transmitting and receiving electronic mail through the base apparatus.

As radio frequency bands that can be used for the wireless communication system, the IEEE 802.11a standard has defined a 5.8 GHz band (in U.S. a 5.2 GHz band, these bands are generally called 5 GHz band), whereas the IEEE 802.11b standard has defined a 2.4 GHz band.

When a wireless communication system deals with both the 5.2 GHz band and the 2.4 GHz band, it can perform a communication over a radio channel (radio frequency) properly selected as a communication channel from the 5.2 GHz band and 2.4 GHz band.

However, in a communicable area of the above-described wireless communication system, another wireless communication system of the same type as the present system or of a different type, such as Bluetooth (a registered trademark), that uses the same frequency bands as the present system might coexist.

In addition, if another system coexists with the present system, a communication radio wave of the other system may become a disturbing wave that causes data streams to be broken, moving pictures streams to be stopped, and images to be disturbed with respect to the data transmission in the present system.

Also, besides those wireless communication systems that interfere with the present system, there may be, for example, microwave ovens and so forth in the vicinity of the present system. When such a device radiates a radio wave of the radio frequency band that the present system uses, the radio wave may act as a disturbing wave and adversely affect the present system.

Furthermore, when a large volume of data, such as picture data from the television and moving picture data of the Internet, are transmitted, it would be desirable to increase the data transmission rate.

However, in the 5.2 GHz band defined in the IEEE 802.11a standard, the maximum transmission rate can be increased up to at most 54 M bps (mega bits/second). In contrast, in the 2.4 GHz band defined in the IEEE 802.11b standard, the transmission rate can be increased up to at most 11 Mbps.

If the transmission rate at which a large volume of data, such as picture data and moving picture data, is transmitted is low, it might be difficult to securely and smoothly transmit the data in a real time basis.

SUMMARY OF THE INVENTION

Therefore, the present invention provides a wireless communication system that deals with a plurality of communicable frequency bands having different transmission rates to allow a large volume of data to be securely and smoothly transmitted in real time without a disturbance from another wireless communication system and so forth and without abnormalities such as the stopping of a moving picture and disturbance of a still image.

A wireless communication method of the present invention is for use with a wireless communication system for performing a communication on a radio channel as a communication channel in a frequency band selected from a plurality of communicable frequency bands having different transmission rates, the wireless communication method comprising the steps of:

detecting radio channels that are not used in the system and that are free of a disturbing wave transmitted from the outside of the system from the frequency bands in decreasing order from relatively higher transmission rates;

detecting whether or not received field strengths at transmission rates of the detected radio channels exceed a predetermined threshold value in decreasing order from the relatively higher transmission rates; and

starting a communication on a channel having a transmission rate at which the received field strength reaches or exceeds the predetermined threshold value in a manner that a communicable frequency band having a relatively higher transmission rate is prioritized and that an unused channel that is free of a disturbing wave and that has a relatively higher transmission rate in one of the frequency bands is prioritized as a communication channel in accordance with the results of the first and second detecting steps.

In the wireless communication method according to the present invention of the above-described method, a frequency band communicable at a high transmission rate is preferentially selected. A communication is started on a communication channel that is free of a disturbing wave preferentially at a high transmission rate. Therefore, the wireless communication method according to the present invention is capable of securely and smoothly transmitting a large volume of data on real time basis without a disturbance of another wireless communication system and abnormalities of stop of a moving picture and a disturbance of an image.

DETAILED DESCRIPTION

Best Mode for Carrying Out the Invention

Next, exemplifying the case in which the present invention is applied to the wireless communication system, which is constituted by the above-described base apparatus and display terminal, an embodiment of the present invention will be described.

External Structures of Display Terminal and Base Apparatus:FIG. 1toFIG. 3:

FIG. 1shows an external structure of an example of the display terminal, andFIG. 2shows an external structure of an example of the base apparatus.

As shown inFIG. 1, an Liquid Crystal Display (LCD)51is disposed at the front of a display terminal50. A touch panel53is disposed on a display screen of the LCD51. Speakers55are disposed at an upper left position and an upper right position of the LCD51. Plain antennas89a,89bfor performing wireless communication with the base apparatus10, which will be described later, are disposed at a lower left position and a lower right position of the LCD51.

The antenna89ais used for a frequency band Ba (5.2 GHz band), whereas the antenna89bis used for a frequency band Bb (a 2.4 GHz band). The left side antenna forms a semi-spherical surface radiation pattern in the forward direction of the display terminal50. The right side antenna forms a semi-spherical surface radiation pattern in the backward direction of the display terminal50. One of the antennas is selected to transmit and receive a radio wave based on reception level information of the left side antenna and the right side antenna. The combination of the left side antenna and the right side antenna forms an antenna that has an all spherical surface radiation pattern. Regardless of the relation of positions of the display terminal50and the base apparatus10, wireless communication between the display terminal50and the base apparatus10is securely performed.

Below the speaker55on the right side of the front of the display terminal50, an index button57a, a jump button57b, and channel buttons57c,57dare disposed.

Pressing the index button57acauses an index screen, as shown in the drawing, to be displayed on the LCD51. By touching any item of the menu on the index screen with a touch pen or user's finger, the user can select, for example, a channel of the television, operate an external device that is connected to the base apparatus10, access the Internet, create and transmit e-mail, and/or create and display an album.

Pressing the jump button57b, it allows an immediately preceding television channel to be received. By pressing the channel button57c, the current mode displayed on the LCD51is switched in the order from television→external device→Internet→mail→album→television. By pressing the channel button57d, the operation screen displayed on the LCD51is switched in the reverse order.

An album is a picture or the like that is captured by a digital camera and recorded on a the memory card77and which is then displayed on the LCD51, processed on the LCD51, and attached to e-mail created on the LCD51. Alternatively, an album is a picture that is stored in the display terminal50or in the memory card77, a television image captured as a still picture, a picture received by e-mail, a picture obtained from the Internet, or the like.

On an upper surface of the display terminal50, a groove portion69and so forth are formed. The groove portion69accommodates a touch pen59. On the left side, a knob91and so forth are disposed. The knob91adjusts the brightness of the LCD51. On the right side, a slot79and so forth are formed. In the slot79, the memory card77is attached. At the bottom, charging terminals94,96are disposed.

At a the back surface of the display terminal50, a U-shaped stand99that allows the display terminal50to be raised is extensively and contractively disposed. A battery accommodating portion (not shown) is disposed at a portion surrounded by the stand99. A battery is accommodated in the battery accommodating portion.

As shown inFIG. 2, the base apparatus10is constituted of a front portion12and a rear portion14that are integrally connected. At left and right positions of the front portion12, plain antennas49a,49bfor performing wireless communication with the display terminal50are disposed.

Like the antennas89a,89bof the display terminal50, the antenna49ais used for the frequency band Ba (5.2 GHz band) whereas the antenna49bis used for the frequency band Bb (2.4 GHz band). The left side antenna forms a semi-spherical surface radiation pattern in the forward direction of the base apparatus10. The right side antenna forms a semi-spherical surface radiation pattern in the backward direction of the base apparatus10. In accordance with reception level information of the left side antenna and the right side antenna, one of the antennas is selected to transmit and receive a radio wave. The combination of the right side antenna and left side antenna forms an antenna that has a half-spherical surface radiation pattern. Regardless of the relation of the positions of the base apparatus10and the display terminal50, wireless communication can be securely performed between the base apparatus10and the display terminal50.

The front portion12is slanted backwards and, in a lower center portion thereof, a supporting member16is disposed that causes the display terminal50to be inclined against the base apparatus10. Charging terminals24,26are disposed in the supporting member16. In addition, at a lower portion on the rear surface of the rear portion14, various types of terminals, such as an antenna terminal and a line terminal that will be described later, are disposed.

With respect to the above-described base apparatus10and display terminal50, the user can place the base apparatus10at a fixed position and carry the display terminal50to any place inside a communicable area. The user can execute functions for receiving a television broadcast, accessing the Internet, and transmitting and receiving electronic mail with the display terminal50that the user is holding at any place.

The user can operate the display terminal50by hand or, alternatively, with the stand99extended, as shown inFIG. 3, so that the display terminal50can be raised on a proper surface at a properly inclined angle.

In addition, the display terminal50may be inclined against the front portion12of the base apparatus10. In this case, the charging terminals94,96of the display terminal50are brought into contact with the charging terminals24,26of the base apparatus10and are connected. As a result, the battery accommodated in the display terminal50can be charged by the base apparatus10.

Functional Blocks of Structures of Base Apparatus and Display Terminal:FIG. 4andFIG. 5:

FIG. 4shows the functional blocks of an example of a structure of the base apparatus10. A controlling portion30comprises a CPU31. The CPU31is connected to a bus33. A program executed by the CPU31, fixed data, and so forth are written to a memory35in advance. The memory35also functions as a work area and so forth of the CPU31. The memory35is connected to the bus33.

An antenna1for receiving a television broadcast is connected to an antenna terminal11. A television broadcast signal is received by the antenna1is channel-selected and demodulated by a tuner21. The channel-selected and demodulated signal is then compressed and further converted into video data and audio data. The video data and audio data are then sent to the bus33.

A telephone line3is connected to a line terminal13. The line terminal13is connected to the bus33through a modem23.

In addition, an Ethernet (registered trademark) terminal15, for connecting an ADSL modem, a CATV modem, or the like, is connected to the bus33through an interface25.

A DVD player, a hard disk recorder, a digital CS tuner, or the like is connected as external device7to a terminal17. Video data and audio data from the external device7are sent to the bus33through an interface27.

In addition, an AV mouse9is connected to a terminal19. The terminal19is connected to the bus33through an interface29. An infrared ray remote control signal is emitted by a light emitting portion of the AV mouse9, in accordance with a command signal that is outputted from the controlling portion30, and is received by a light detecting portion disposed in the external device7. As a result, using the infrared ray remote control signal, the external device7is operated.

Base Band Processors (BBP)41a,41bfor the frequency bands Ba, Bb are connected, respectively, to the bus33. Transmitting and receiving portions45a,45bfor the frequency bands Ba, Bb are connected to the BBPs41a,41b, respectively. The above-described antennas49a,49bare connected to the transmitting and receiving portions45a,45b, respectively.

Also, disturbing wave detecting portions43a,43bare connected between the BBPs41a,41band the bus33, respectively. Received field strength detecting portions47a,47bare connected between the transmitting and receiving portions45a,45band the bus33, respectively. The disturbing wave detecting portions43a,43bdetect whether or not a disturbing wave exists on a radio channel selected from the frequency bands Ba, Bb, respectively, by a method that will be described later. The received field strength detecting portions47a,47bdetect the received field strengths of the signals received by the transmitting and receiving portions45a,45bin accordance with control levels of an Automatic Gain Control (AGC) against the signals received by the transmitting and receiving portions45a,45b, respectively.

A signal transmitted from the base apparatus10to the display terminal50is processed for a baseband by the BBPs41a,41band is then modulated by the transmitting and receiving portions45a,45b, respectively. The modulated signal is next converted into a signal of a radio channel selected from the frequency bands Ba, Bb. Thereafter, the radio channel signal is transmitted from the transmitting and receiving portions45a,45bto the display terminal50through the antennas49a,49b, respectively.

In addition, a signal of a radio channel selected from the frequency bands Ba and Bb and transmitted from the display terminal50to base apparatus10is received by the transmitting and receiving portions45a,45bthrough the antennas49a,49b, respectively. The received signal is frequency converted by the transmitting and receiving portions45a,45b, respectively. Thereafter, the frequency converted signal is processed for a baseband by the BBPs41a,41band then received by the bus33.

FIG. 5shows functional blocks of an example of a structure of the display terminal50. A controlling portion70comprises a CPU71. The CPU71is connected to a bus73.

A program executed by the CPU71, fixed data, and so forth are written to a memory75in advance. The memory75also functions as a work area and so forth of the CPU71. The memory75is connected to the bus73.

The LCD51is connected to the bus73through a display controlling portion61. A speaker55is connected to the bus73through a D/A converter (DAC)65and an audio amplifying circuit66. In addition, the touch panel53is connected to the bus73through a coordinate detecting portion63. Moreover, a key operation portion57including the index button57ashown inFIG. 1, is connected to the bus73through an interface67.

When the memory card77is attached to the slot79, shown inFIG. 1, the memory card77is connected to the bus73.

In addition, BBPs81a,81bfor the frequency bands Ba, Bb, respectively, are connected to the bus73. Transmitting and receiving portions85a,85bfor the frequency bands Ba, Bb are connected to the BBPs81a,81b, respectively. The above-described antennas89a,89bare connected to the transmitting and receiving portions85a,85b, respectively.

In addition, disturbing wave detecting portions83a,83bare connected between the BBPs81a,81band the bus73, respectively. Received field strength detecting portions87a,87bare connected between the transmitting and receiving portions85a,85band the bus73, respectively. The disturbing wave detecting portions83a,83bdetect whether a disturbing wave is present in a radio channel selected from the frequency bands Ba, Bb, respectively, by a method that will be described later. The received field strength detecting portions87a,87bdetect the received field strengths of signals received by the transmitting and receiving portions85a,85bin accordance with control levels of the AGC against signals received by the transmitting and receiving portions85a,85b, respectively.

A signal transmitted from the display terminal50to base apparatus10is processed for a baseband by the BBPs81a,81band is then modulated by the transmitting and receiving portions85a,85b, respectively. Thereafter, the modulated signal is converted into a signal of a radio channel selected from the frequency bands Ba, Bb. The signal of the radio channel is then transmitted from the transmitting and receiving portions85a,85bto the base apparatus10through the antennas89a,89b, respectively.

In addition, a signal of a radio channel selected from the frequency bands Ba and Bb is transmitted from the base apparatus10to the display terminal50. The signal is received by the transmitting and receiving portions85a,85bthrough the antennas89a,89b, respectively. The received signal is frequency converted and demodulated by the transmitting and receiving portions85a,85b, respectively. Thereafter, the demodulated signal is processed for a baseband by the BBPs81a,81band is then received by the bus73.

The above-described wireless communication system uses the 2.4 GHz band and the 5.2 GHz band, as defined in the IEEE 802.11a standard and the IEEE 802.11b, standard as the frequency bands Ba and Bb, respectively.

It has been determined that when a plurality of radio channels are set in the 5.2 GHz band and 2.4 GHz at the same time and in the same area, as shown inFIG. 6andFIG. 7, the frequency intervals between adjacent radio channels should be apart by 20 MHz or more and by 25 MHz or more to prevent a signal from one radio channel from becoming a disturbing wave to a signal of the other radio channel, respectively.

Therefore, the number of radio channels that can be set at the same time in the 5.2 GHz band is a maximum of four channels C1, C2, C3, and C4, shown inFIG. 6. In the 2.4 GHz band is a maximum of three channels C5, C6, and C7can be set, as shown inFIG. 7.

The transmission rates and modulation systems in the 5.2 GHz can be set in eight modes A1to A8, shown inFIG. 8, and those in the 2.4 GHz band in four modes B1to B4, shown inFIG. 9. The terms “modes A1to A8” and “modes B1to B4” are not defined in the IEEE 802.11a and IEEE 802.11b standards, but are defined in this specification for convenience.

The modulation systems shown inFIG. 8andFIG. 9are multi-value digital modulation (primary modulation) systems for the BBPs41aand41bof the base apparatus10and for the BBPs81aand81bof the display terminal50, respectively. Orthogonal Frequency Division Multiplexing (OFDM) is used as the radio frequency modulation for the frequency band Ba of the transmitting and receiving portion45aof the base apparatus10and for the transmitting and receiving portion85aof the display terminal50. Direct Sequencing (DS) is used as the radio frequency modulation for the frequency band Bb of the transmitting and receiving portion45bof the base apparatus10and of the transmitting and receiving portion85bof the display terminal50.

The transmission rate of the mode B4in the 2.4 GHz band can be higher than that of each of the modes A1and A2in the 5.2 GHz band as shown in theFIG. 8andFIG. 9. Generally, the transmission rate in the 5.2 GHz band can be higher than that in the 2.4 GHz band.

Setting Process Performed Upon Startup of Communication:FIG. 10andFIG. 11:

In the state that the power of the base apparatus10has been turned on in the above-described wireless communication system, when the user turns on the power of the display terminal50and performs an operation for receiving a television broadcast or performs an operation for accessing the Internet using the display terminal50, a connection request and a command are transmitted from the display terminal50to the base apparatus10as signals of a predetermined radio channel of a predetermined frequency band.

After the connection request and command have been received by the base apparatus10and the operation for receiving a television broadcast or for accessing the Internet has been performed, a communication with the display terminal50is started. Picture and audio data of the television, information of the Internet, and so forth are transmitted from the base apparatus10to the display terminal50.

FIG. 10andFIG. 11show an example of a setting process for setting a communication frequency band, a communication channel, and a transmission rate that the controlling portion30(CPU31) of the base apparatus10executes.

First, in step101of the setting process100, the controlling portion30determines whether an unused channel exists in the frequency band Ba (5.2 GHz band) in which a high transmission rate can be set.

While communication between the base apparatus10and a display terminal of the same type as that of the display terminal50is performed on a radio channel C1to C4as a communication channel in the frequency band Ba, the radio channel is not an unused channel. An unused channel is a radio channel that is not used as a communication channel by the present system.

When the controlling portion30determines that an unused channel exists in the frequency band Ba in the step101, the flow advances to step102wherein the controlling portion30determines whether a disturbing wave exists on the unused channel based on the detected result of the disturbing wave detecting portion43afor the frequency band Ba.

A disturbing wave is a communication radio wave transmitted from a wireless communication system that is of the same type as or of a different type than the present system. Alternatively, the disturbing wave is a radio wave transmitted from a non-wireless communication apparatus, such as a microwave oven.

When determining whether a signal received by the transmitting and receiving portion45ais a disturbing wave, the disturbing wave detecting portion43aand the controlling portion30detect whether transmission destination address information is contained in a received signal that has been processed in the BBP41a. When the transmission destination address information is contained therein, the controlling portion30determines whether the transmission destination address information matches an apparatus address of the base apparatus10.

When transmission destination address information is contained in the received signal and matches the apparatus address (identification information that identifies an apparatus) of the base apparatus10, the controlling portion30determines that the received signal is not a disturbing signal but is instead a signal transmitted from the display terminal50to the base apparatus10. When the received signal is a radio wave of other than a communication radio wave of another wireless communication system and transmission destination address information is not contained in the received signal or when the received signal is a communication radio wave of another wireless communication system and transmission destination address information contained in the received signal, the controlling portion30determines that the received signal is a disturbing wave.

However, the system may be structured in a manner that, when the controlling portion30has determined that a received signal is a disturbing wave and the received field strength detecting portion47adetermines that the received field strength is so low that it can be ignored, as shown in step102, the controlling portion30determines that a disturbing wave does not exist on the unused channel.

When the controlling portion30has determined that a disturbing wave exists on the unused channel in step102, the flow advances to step103in which the controlling portion30determines whether another unused channel exists. When another unused channel exists, the flow returns to step102where, in the same manner as described above, the controlling portion30determines whether a disturbing wave exists on the unused channel.

When the controlling portion30has determined that a disturbing wave does not exist on the unused channel in step102, the flow advances to step104. After the controlling portion30has set the unused channel as a communication channel in step104, the flow advances to process routine200. In process routine200, the controlling portion30executes a mode setting process for the frequency band Ba.

In the mode setting process200for this frequency band Ba, as will be described later with reference toFIG. 12andFIG. 13, the controlling portion30detects received field strengths at transmission rates in decreasing order starting from higher transmission rates on the communication channel that has been set in step104of process routine100. The controlling portion30sets as a mode the highest transmission rate at which the received field strength reaches or exceeds a predetermined threshold value.

After the controlling portion30has executed the mode setting process200, the flow advances to step105where the controlling portion30determines whether communication should start in the frequency band Ba. When it is determined that the communication should start in the frequency band Ba, the controlling portion30completes the setting process. The controlling portion30starts the communication in the mode (transmission rate) that was set in the process200on the communication channel that was set in step104.

When the controlling portion30has determined that an unused channel does not exist in the frequency band Ba in step101, has determined that an unused channel free of a disturbing wave does not exist in the frequency band Ba) in step103, or has determined that an unused channel free of a disturbing wave exists in the frequency band Ba but the received field strengths at all the transmission rates do not exceed the threshold value) in step105, the flow advances to step111wherein the controlling portion30determines whether an unused channel exists in the frequency band Bb (2.4 GHz band).

When the controlling portion30has determined that an unused channel exists in the frequency band Bb, the flow advances from step111to step112, and the controlling portion30determines whether a disturbing wave exists on the unused channel in accordance with the detected result of the disturbing wave detecting portion43bfor the frequency band Bb.

In this case, the controlling portion30determines whether the signal received by the transmitting and receiving portion45bis a disturbing wave and whether a disturbing wave exists on an unused channel in the same manner as set out in step102.

When the controlling portion30has determined that a disturbing wave exists on the unused channel in step112, the flow advances to step113wherein the controlling portion30determines whether another unused channel exists. When the controlling portion30has determined that another unused channel exists, the flow returns to step112where, in the same manner as described above, the controlling portion30determines whether a disturbing wave exists on the unused channel.

When the controlling portion30has determined that a disturbing wave does not exist on the unused channel in step112, the flow advances to step114wherein the controlling portion30sets the unused channel as a communication channel. Thereafter, the flow advances to process routine300in which the controlling portion30executes a mode setting process for the frequency band Bb.

In the mode setting process300for the frequency band Bb, as will be described later with reference toFIG. 14, the controlling portion30detects a received field strength at the highest transmission rate on the communication channel that was set in step114of the setting process100. When the received field strength reaches or exceeds the threshold value, the controlling portion30sets the transmission rate as a mode. When the received field strength does not reach the threshold value, the controlling portion30sets the next highest transmission rate as a mode.

When the controlling portion30has determined that an unused channel does not exist in the frequency band Bb in step111or has determined that an unused channel free of a disturbing wave does not exist in the frequency band Bb, the flow advances to step115. As step115shows, the controlling portion30sets a predetermined radio channel in a predetermined frequency band as a communication channel and sets a predetermined mode (transmission rate). For example, the controlling portion30sets a particular radio channel in the frequency band Ba (5.2 GHz band) as a communication channel and sets mode A8(transmission rate: 54 Mbps) as a mode of the transmission rate. Thereafter, the controlling portion30completes the setting process performed upon startup of communication and starts the communication.

Alternatively, in place of step115of process100, the controlling portion30transmits a message indicating that data cannot be transmitted due to an improper communication environment between the base apparatus10and the display terminal50and then causes the message to be displayed on the LCD51of the display terminal50or to be outputted as audio data from the speaker55to inform the user.

Mode Setting Process for Frequency Band Ba:FIG. 12andFIG. 13:

FIGS. 12 and 13show an example of a process routine200of a mode setting process for the frequency band Ba (5.2 GHz band).

When the controlling portion30starts communication in mode setting process e200, the controlling portion30has already set an unused channel free of a disturbing wave in the frequency band Ba as a communication channel in setting process100. Thereafter, in step211, the controlling portion30transmits a setup signal in mode A8(transmission rate: 54 Mbps), which has the highest transmission rate in the frequency band Ba, from the base apparatus10to the display terminal50.

Thereafter, the flow advances to step212wherein the controlling portion30determines whether the received field strength at the time reaches or exceeds the threshold value.

As an example, the following method for detecting and determining the received field strength may be used. The transmitting and receiving portion85aof the display terminal50receives a signal transmitted from the base apparatus10. The received field strength detecting portion87aof the display terminal50detects the received field strength. The controlling portion70of the display terminal50determines whether the received field strength reaches or exceeds the threshold value and transmits the result from the display terminal50to the base apparatus10. The controlling portion30of the base apparatus10then determines whether the received field strength reaches or exceeds the threshold value.

Alternatively, when the display terminal50has received a signal from the base apparatus10, the display terminal50transmits an acknowledge signal to the base apparatus10that notifies the base apparatus10that the display terminal50has received the signal. The transmitting and receiving portion45aof the base apparatus10receives the acknowledge signal. The received field strength detecting portion47aof the base apparatus10then detects the received field strength. The controlling portion30of the base apparatus10next determines whether the received field strength reaches or exceeds the threshold value.

When the controlling portion30has determined that the received field strength in mode A8reaches or exceeds the threshold value in step212, the controlling portion30completes the mode setting process for the frequency band Ba. When the controlling portion30starts the communication, the flow advances to step105of the setting process100. In step105, the controlling portion30determines that the communication should start in the frequency band Ba and then starts communication in mode A8on the communication channel that was set in step104.

When the controlling portion30has determined that the received field strength in mode A8does not reach the threshold value in step212, the flow advances to step221. Here, the controlling portion30transmits a setup signal in mode A7(transmission rate: 48 Mbps), which has the second highest transmission rate in the frequency band Ba, from the base apparatus10to the display terminal50. Thereafter, the flow advances to step222wherein the controlling portion30determines whether the received field strength at the time reaches or exceeds the threshold value in the same manner as described above.

Thereafter, when the controlling portion30has determined that the received field strength in mode A7reaches or exceeds the threshold value in step222, the controlling portion30completes the mode setting process for the frequency band Ba. When the controlling portion30starts communication, the flow advances to step105of the setting process100wherein the controlling portion30determines that the communication should start in the frequency band Ba and starts the communication in mode A7on the communication channel that was set in step104.

When the controlling portion30has determined that the received field strength in mode A7does not reach the threshold value in step222, the flow advances to step231. Here, the controlling portion30transmits a setup signal in mode A6(transmission rate: 36 Mbps) from the base apparatus10to the display terminal50. Thereafter, the flow advances to step232wherein the controlling portion30determines whether the received field strength at the time reaches or exceeds the threshold value in the manner described above.

When the controlling portion30has determined that the received field strength in mode A6reaches or exceeds the threshold value in step232, the controlling portion30completes the mode setting process for the frequency band Ba. When the controlling portion30starts communication in the setting process100, the controlling portion30starts the communication in mode A6in the same manner as described above.

When the controlling portion30has determined that the received field strength in mode A6does not reach the threshold value in step232, the flow advances to step241. Here, the controlling portion30transmits a setup signal in mode A5(transmission rate: 24 Mbps) from the base apparatus10to the display terminal50. Thereafter, the flow advances to step242. The controlling portion30determines whether the received field strength at the time reaches or exceeds the threshold value in the above-described manner.

When the controlling portion30has determined that the received field strength in mode A5reaches or exceeds the threshold value in step242, the controlling portion30completes the mode setting process for the frequency band Ba. When the controlling portion30then starts communication in the setting process100, the controlling portion30starts the communication in mode A5in the same manner as described above.

When the controlling portion30has determined that the received field strength in mode A5does not reach the threshold value in step242, the flow advances to step251. Now, the controlling portion30transmits a setup signal in mode A4(transmission rate: 18 Mbps) from the base apparatus10to the display terminal50. Thereafter, the flow advances to step252in which the controlling portion30determines whether the received field strength at the time reaches or exceeds the threshold value as described above.

When the controlling portion30has determined that the received field strength in mode A4reaches or exceeds the threshold value in step252, the controlling portion30completes the mode setting process for the frequency band Ba. When the controlling portion30next starts communication in the setting process100, the controlling portion30starts the communication in mode A4in the manner as described above.

When the controlling portion30has determined that the received field strength in mode A4does not reach the threshold value in step252, the flow advances to step261. Wherein, the controlling portion30transmits a setup signal in mode A3(transmission rate: 12 Mbps) from the base apparatus10to the display terminal50. Thereafter, the flow advances to step262in which the controlling portion30determines whether the received field strength at the time reaches or exceeds the threshold value in the same method as described above.

When the controlling portion30has determined that the received field strength in mode A3reaches or exceeds the threshold value in step262, the controlling portion30completes the mode setting process for the frequency band Ba. When the controlling portion30thereafter starts communication in process routine100, the controlling portion30starts the communication in mode A3in the manner described above.

When the controlling portion30has determined that the received field strength in mode A3does not reach the threshold value in step262, the flow advances to step271. Here, the controlling portion30transmits a setup signal in mode A2(transmission rate: 9 Mbps) from the base apparatus10to the display terminal50. Thereafter, the flow advances to step272. The controlling portion30determines whether the received field strength at the time reaches or exceeds the threshold value in the same method as described above.

When the controlling portion30has determined that the received field strength in mode A2reaches or exceeds the threshold value in step272, the controlling portion30completes the mode setting process for the frequency band Ba. When the controlling portion30subsequently starts a communication in the process100, the controlling portion30starts the communication in mode A2in the same manner as described above.

When the controlling portion30has determined that the received field strength in mode A2does not reach the threshold value in step272, the flow advances to step281. Where, the controlling portion30transmits a setup signal in mode A1(transmission rate: 6 Mbps), which has the lowest transmission rate in the frequency band Ba, from the base apparatus10to the display terminal50. Thereafter, the flow advances to step282in which the controlling portion30determines whether the received field strength at the time reaches or exceeds the threshold value as described above.

When the controlling portion30has determined that the received field strength in mode A1reaches or exceeds the threshold value in step282, the controlling portion30completes the mode setting process for the frequency band Ba. When the controlling portion30next starts a communication in the process100, the controlling portion30starts the communication in mode A1in the same manner as described above.

When the controlling portion30has determined that the received field strength in mode A1does not reach the threshold value in step282, the flow advances to step291. In step291, the controlling portion30has determined that no mode should be set in the frequency band Ba and completes the mode setting process for the frequency band Ba. When the controlling portion30starts communication, the flow advances to step105of the setting process100wherein the controlling portion30has determined that a communication should not start in the frequency band Ba. Here, as when the controlling portion30has determined that an unused channel does not exist in the frequency band Ba in step101or30has determined that an unused channel free of a disturbing wave does not exist in the frequency band Ba in step103, the flow advances to step111as described above.

When the communication environment does not vary, the received sensitivity point, namely the received field strength of which the bit error rate of the received data does not reach a predetermined value, becomes higher, as the transmission rate is increased. Therefore, the threshold values at the above-described steps212,222,232,242,252,262,272, and282are increased as the transmission rate increases.

Mode Setting Process for Frequency Band Bb:FIG. 14:

FIG. 14shows an example of a mode setting process300for the frequency band Bb (2.4 GHz band).

When the controlling portion30starts communication in the process300, the flow first returns to step114of the process100. In step114, the controlling portion30sets an unused channel free of a disturbing wave in the frequency band Bb as a communication channel. Thereafter, the flow advances to step311where the controlling portion30transmits a setup signal in mode B4, which has the highest transmission rate in the frequency band Bb (transmission rate: 11 Mbps), from the base apparatus10to the display terminal50.

Thereafter, the flow advances to step312in which the controlling portion30determines whether the received field strength at the time reaches or exceeds the threshold value.

As an example, the following method for detecting and determining the received field strength may be used. The transmitting and receiving portion85bof the display terminal50receives a signal transmitted from the base apparatus10. The received field strength detecting portion87bof the display terminal50then detects the received field strength. The controlling portion70of the display terminal50then determines whether the received field strength reaches or exceeds the threshold value and transmits the result from the display terminal50to the base apparatus10. The controlling portion30of the base apparatus10thereafter determines whether the received field strength reaches or exceeds the threshold value.

Alternatively, when the display terminal50has received a signal transmitted from the base apparatus10, the display terminal50transmits an acknowledge signal to the base apparatus10that notifies the base apparatus that the display terminal50has received the signal. The transmitting and receiving portion45bof the base apparatus10next receives the acknowledge signal. The received field strength detecting portion47bof the base apparatus10then detects the received field strength. The controlling portion30of the base apparatus10subsequently determines whether the received field strength reaches or exceeds the threshold value.

When the controlling portion30has determined that the received field strength in mode B4reaches or exceeds the threshold value in step312, the controlling portion30completes the mode setting process for the frequency band Bb and starts the communication in mode B4on the communication channel that has been set in step114of the process100.

When the controlling portion30has determined that the received field strength in mode B4does not reach the threshold value in step312, the flow advances to step313. Here, the controlling portion30sets mode B3(transmission rate: 5.5 Mbps), which has the second highest transmission rate in the frequency band Bb, completes the mode setting process for the frequency band Bb and then starts the communication in mode B3on the communication channel that has been set in step114of the setting process100.

When the received field strength in mode B4does not reach the threshold value, the controlling portion30sets mode B3without determining whether the received field strength in mode B3reaches or exceeds the threshold value because if the received field strength in mode B3did not exceed the threshold value and the controlling portion30were to set mode B2(transmission rate: 2 Mbps) or mode B1(transmission rate: 1 Mbps), the resulting transmission rate would become too low.

Alternatively, the mode setting process300may be structured in the following manner. When the controlling portion30has determined that the received field strength in mode34does not reach the threshold value in step312, the controlling portion30transmits a setup signal in mode B3to the display terminal50and then determines whether the received field strength in mode B3reaches or exceeds the threshold value. When the received field strength reaches or exceeds the threshold value, the controlling portion30sets mode B3. When the received field strength does not reach the threshold value, the controlling portion30determines that no mode is to be set in the frequency band Bb.

When the controlling portion30has determined that no mode is to be set in the frequency band Bb in the process300, in the same manner that the controlling portion30determines that an unused channel exists in the frequency band Bb in step111or determines that an unused channel free of a disturbing wave does not exist in the frequency band Bb in step113, the flow advances to step115. In step115, the controlling portion30sets a predetermined radio channel of a predetermined frequency band as a communication channel, sets a predetermined mode (transmission rate), and starts the communication.

Changing Process that is Performed During Communication:FIG. 15toFIG. 21:

Changing Process that is Performed During Normal Communication:FIG. 15toFIG. 18:

When the controlling portion30starts communication at a high transmission rate in the frequency band Ba, if a disturbing wave is present in a communication channel, it is desirable to change the communication channel. Moreover, when the controlling portion30starts communication at a low transmission rate in the frequency band Bb and an unused channel now exists in the frequency band Ba, it is desirable to change the communication channel to the unused channel in the frequency band Ba to increase the transmission rate.

Therefore, the above-described wireless communication system is structured such that while the base apparatus10is communicating with the display terminal50, the controlling portion30of the base apparatus10executes a changing process.

Changing Process Performed During Communication in Frequency Band Ba:FIG. 15andFIG. 16:

FIG. 15andFIG. 16show an example of a changing process120performed during communication in the frequency band Ba.

While the controlling portion30is communicating in the frequency band Bb, in step129of process routine120, the controlling portion30periodically determines whether a disturbing wave exists on a communication radio channel in the frequency band Ba in accordance with the detected result of the disturbing wave detecting portion43a.

In this case, as in the setting process100performed upon startup of communication, when the controlling portion30determines whether a signal received by the transmitting and receiving portion45ais a disturbing wave, the above-described method for detecting/identifying transmission destination address information is used.

When the controlling portion30has determined that a disturbing wave exists on the communication radio channel in step129, the controlling portion30, in step121, determines whether an unused channel exists in the frequency band Ba. When it is determined that an unused channel exists, the flow advances to step122wherein the controlling portion30determines whether a disturbing wave exists on the unused channel. When such a disturbing wave is found to exist, the flow advances to step123where the controlling portion30determines whether or not another unused channel exists. When it is determined that an unused channel exists, the flow returns to step122in which the controlling portion30determines whether a disturbing wave exists on the unused channel.

When the controlling portion30has determined that a disturbing wave does not exist on the unused channel in step122, the flow advances to step124wherein the controlling portion30sets the unused channel as a communication channel. Thereafter, the controlling portion30executes the mode setting process200for the frequency band Ba. Thereafter, the flow advances to step125in which the controlling portion30determines whether the communication should be continued in the frequency band Ba in accordance with the result of the execution of the process200. When the controlling portion30has determined that the communication should be continued in the frequency band Ba, the controlling portion30restores the communicating state in the frequency band Ba.

When the controlling portion30has determined that an unused channel does not exist in the frequency band Ba in step121, has determined that an unused channel free of a disturbing wave does not exist in the frequency band Ba in step123, or has determined that an unused channel free of a disturbing wave exists in the frequency band Ba but the received field strengths at all the transmission rates in the frequency band Ba do not exceed the threshold value in step125, the flow advances to step131. Namely, the controlling portion30determines whether an unused channel exists in the frequency band Bb.

When the controlling portion30has determined that an unused channel exists in the frequency band Bb, the flow advances from step131to step132wherein the controlling portion30determines whether a disturbing wave exists on the unused channel. When it is determined that a disturbing wave exists, the flow advances to step133in which the controlling portion30determines whether another unused channel exists. When another unused channel exists, the flow returns to step132. Namely, the controlling portion30determines whether or not a disturbing wave exists on the unused channel.

When the controlling portion30has determined that a disturbing wave does not exist on the unused channel in step132, the flow advances to step134wherein the controlling portion30sets the unused channel as a communication channel. Thereafter, the controlling portion30executes the mode setting process300for the frequency band Bb. The controlling portion30completes the changing process performed during communication in the frequency band Ba and enters a communicating state in the frequency band Bb.

When the controlling portion30has determined that an unused channel does not exist in the frequency band Bb in step131or has determined that an unused channel free of a disturbing wave does not exist in the frequency band Bb in step133, the flow advances to step135. Namely, the controlling portion30continues the current communication for a predetermined time period and restores the communicating state in the frequency band Ba.

Changing Process Performed During Communication in Frequency Band Bb:FIG. 17andFIG. 18:

FIG. 17andFIG. 18show an example of a changing process performed during communication in the frequency band Bb.

In changing process routine140, while the controlling portion30is communicating, in step147, the controlling portion30periodically determines whether a disturbing wave exists on a communication radio channel in accordance with the detected result of the disturbing wave detecting portion43b.

In this case, as in the setting process routine100performed upon startup of communication, when the controlling portion30determines whether a signal received by the transmitting and receiving portion45bis a disturbing wave, the above-described method for detecting/identifying transmission destination address information is used.

When the controlling portion30has determined that a disturbing wave exists on the communication radio channel in step147, the flow directly advances from step147to step141. When the controlling portion30determines that the disturbing wave does not exist on the communication radio channel, the flow advances from step147to step149wherein the controlling portion30continues the current communication for a predetermined time period. Thereafter, the flow advances to step141.

In step141, the controlling portion30determines whether an unused channel exists in the frequency band Ba, and when an unused channel exists, the flow advances to step142. Namely, the controlling portion30determines whether or not a disturbing wave exists on the unused channel and when a disturbing wave exists, the flow advances to step143wherein the controlling portion30determines whether another unused channel exists. When it is determined that another unused channel exists, the flow returns to step142so that the controlling portion30determines whether a disturbing wave exists on the unused channel.

When the controlling portion30has determined that a disturbing wave does not exist on the unused channel in step142, the flow advances to step144wherein the controlling portion30sets the unused channel as a communication channel. Thereafter, the controlling portion30executes a mode setting process200for the frequency band Ba. The flow then advances to step145in which the controlling portion30determines whether the communication should be continued in the frequency band Ba. When it is determined that the communication should be continued in the frequency band Ba, the controlling portion30completes the changing process performed during communication in the frequency band Ba. Thereafter, the controlling portion30enters a communicating state in the frequency band Ba.

When the controlling portion30has determined that an unused channel does not exist in the frequency band Ba in step141, has determined that an unused channel free of a disturbing wave does not exist in the frequency band Ba) in step143, or has determined that an unused channel free of a disturbing wave exists in the frequency band Ba but the received field strengths at all the transmission rates in the frequency band Ba do not exceed the threshold value) in step145, the flow advances to step151. Namely, the controlling portion30determines whether an unused channel exists in the frequency band Bb.

When the controlling portion30has determined that an unused channel exists in the frequency band Bb, the flow advances from step151to step152wherein the controlling portion30determines whether a disturbing wave exists on the unused channel. When it is determined that a disturbing wave exists, the flow advances to step153in which the controlling portion30determines whether another unused channel exists. When the controlling portion30has determined that another unused channel exists, the flow returns to step152. Namely, the controlling portion30determines whether or not a disturbing wave exists on the unused channel.

When the controlling portion30has determined that a disturbing wave does not exist on the unused channel in step152, the flow advances to step154in which the controlling portion30sets the unused channel as a communication channel. Thereafter, the controlling portion30executes the mode setting process300for the frequency band Bb and restores the communicating state in the frequency band Bb.

When the controlling portion30has determined that an unused channel does not exist in the frequency band Bb in step151or has determined that an unused channel free of a disturbing wave does not exist in the frequency band Bb in step153, the flow advances to step155. Namely, the controlling portion30sets, for example, a predetermined radio channel of a predetermined frequency band as a communication channel, sets a predetermined mode (transmission rate), and completes the changing process performed during communication in the frequency band Bb.

The Case in which Transmission Rate is Increased:FIG. 19:

When the controlling portion30starts a communication in the frequency band Ba, even if the transmission rate cannot be increased because the electric field is weak, if the environment of the electric field varies, the transmission rate may be increased. Thus, the system is structured so that in that case the transmission rate can be increased.

FIG. 19shows an example of a mode changing process160that the controlling portion30of the base apparatus10executes in such a case.

In the mode changing process160, while the controlling portion30is communicating in the frequency band Ba, it periodically determines whether a mode having a higher transmission rate than the current mode exists. When such a mode does not exist, namely, while the controlling portion30is communicating in mode A8(transmission rate: 54 Mbps), the flow advances to step162wherein the controlling portion30continues the communication in the current mode (transmission rate).

When a mode that has a higher transmission rate than the current mode exists, namely, during communication in a mode lower than mode A7, the flow advances from step161to step163wherein the controlling portion30changes the current mode to a mode having a higher transmission rate. Thereafter, in step164, the controlling portion30determines whether the received field strength at the changed transmission rate reaches or exceeds the threshold value.

When the received field strength at the changed transmission rate does not reach the threshold value, the flow advances from step164to step165so that the controlling portion30restores the preceding mode (transmission rate) from which the transmission rate was changed in step163and continues the communication. When the received field strength at the changed transmission rate reaches or exceeds the threshold value, the flow advances from step164to step166wherein the controlling portion30determines whether a mode having a higher transmission rate than the current mode exists. When such a mode exists, the controlling portion30executes steps163and the steps after step163. When a mode having a higher transmission rate than the current mode does not exist, the flow advances to step167. Namely, the controlling portion30continues the communication in the mode (transmission rate) that was changed in step163.

For example, while the controlling portion30is communicating in mode A4, if the received field strength reaches or exceeds the threshold value in mode A5, but not in mode A6, the controlling portion30successively executes steps161,163,164,166,163,164, and165. As a result, the controlling portion30changes mode A4to mode A4.

In contrast, while the controlling portion30is communicating in mode A7, if the received field strength reaches or exceeds the threshold value in mode A8, the controlling portion30successively executes steps161,163,164,166, and167. As a result, the controlling portion30changes mode A7to mode A8.

The Case in which Transmission Rate is Decreased:FIG. 20andFIG. 21:

In a good environment in which a radio wave is free of a disturbing wave while the controlling portion30is communicating at a high transmission rate in the frequency band Ba, if the user having the display terminal50goes away from the base apparatus10, the electric field will vary because the distance between the base apparatus10and the display terminal50becomes large. In such case, the received field strength becomes lower than the received sensitivity point and as a result, the bit error rate of the received data becomes large and communication cannot be securely performed. Thus, the system is structured for the case where the transmission rate is decreased and the received field strength becomes larger than the received sensitivity point.

FIGS. 20 and 21show an example of a mode changing process180that the controlling portion30of the base apparatus10executes in such a case.

In the mode changing process180, while the controlling portion30is communicating in the frequency band Ba, it periodically determines whether the received field strength at the current transmission rate reaches or exceeds the received sensitivity point in step181. When the received field strength does reach or exceed the received sensitivity point, the flow advances to step182wherein the controlling portion30continues the communication in the current mode (transmission rate).

When the received field strength at that transmission rate does not reach the received sensitivity point, the flow advances from step181to step183. Namely, the controlling portion30determines whether a mode having a lower transmission rate than the current mode exists. When such a mode is determined to exist, the flow advances from step183to step184wherein the controlling portion30changes the current mode to a mode having a lower transmission rate by one level. Thereafter, the flow advances to step185in which the controlling portion30determines whether the received field strength at the changed transmission rate reaches or exceeds the received sensitivity point.

When the received field strength at the changed transmission rate reaches or exceeds the received sensitivity point, the flow advances from step185to step186. Namely, the controlling portion30continues the communication in the mode (transmission rate) changed in step184. When the received field strength at the changed transmission rate does not reach the received sensitivity point, the flow advances from step185to step187wherein the controlling portion30determines whether a mode having a lower transmission rate than the current mode exists. When such a mode exists, the controlling portion30repeats the steps starting from step184.

For example, while the controlling portion30is communicating in mode A4, and if the received field strength does not reach the received sensitivity point but does reach or exceed the received sensitivity point in mode A3, the controlling portion30successively executes steps181,183,184,185, and186. As a result, the controlling portion30changes from mode A4to mode A3.

In contrast, when the controlling portion30has determined that a mode having a lower transmission rate than the current mode does not exist in step183, namely, while the controlling portion30is communicating in mode A1, if the received field strength does not reach the received sensitivity point, the flow advances to stop191. Also, when the controlling portion30has determined that a mode having a lower transmission rate than the current mode does not exist in step187, namely even if the controlling portion30decreases the transmission rate to mode A1but the received field strength does not reach the received sensitivity point, the flow advances to step191. In step191, the controlling portion30determines whether or not an unused channel exists in the frequency band Bb.

When the controlling portion30has determined that an unused channel exists in the frequency band Bb, the flow advances from step191to step192wherein the controlling portion30determines whether or not a disturbing wave exists on the unused channel. When it is determined that a disturbing wave exists, the flow advances to step193. Namely, the controlling portion30determines whether another unused channel exists. When another unused channel exists, the flow returns to step192in which the controlling portion30determines whether a disturbing wave exists on the unused channel.

When the controlling portion30has determined that a disturbing wave does not exist on the unused channel in step192, the flow advances to step194, namely, the controlling portion30sets the unused channel as a communication channel. Thereafter, the controlling portion30executes the mode setting process300for the frequency band Bb. Thereafter, the controlling portion30enters a communicating state in the frequency band Bb.

When the controlling portion30has determined that an unused channel does not exist in the frequency band Bb, in step191, or has determined that an unused channel free of a disturbing wave does not exist in the frequency band Bb, in step193, the flow advances to step195. Here, the controlling portion30continues the communication in mode A1having the lowest transmission rate on the original communication channel in the frequency band Ba, thus providing the highest possibility that the received field strength reaches or exceeds the received sensitivity point.

Other Embodiments

Frequency bands are currently defined in the IEEE standard and domestic standard only at 5.2 GHz (5 GHz band) and at 2.4 GHz. However, it is possible to use other frequency bands as the radio frequency bands of the invention. Other frequency bands may be defined in future. Thus the two frequency bands of the invention are not limited to 5.2 GHz (5 GHz band) and 2.4 GHz. In addition, the present invention can be applied to the case in which three or more frequency bands are used.

In addition, the wireless communication apparatuses that compose the wireless communication system are not limited to the above-described base apparatus and display terminal.

INDUSTRIAL APPLICABILITY

As described above, according to the present invention, in a wireless communication system that deals with a plurality of communicable frequency bands having different transmission rates, a large volume of data can be securely and smoothly transmitted in real time without a disturbance from another wireless communication system and so forth, and abnormalities such as the stopping of a moving picture or a disturbance of a still picture are avoided.