Abstract:
A method of controlling a receiving operation includes, receiving a transmission frame into a wireless device, and decoding the transmission frame. A header information in the transmission frame is analyzed. Then, the receiving operation is suspended in response to the header information.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     A claim of priority under 35 U.S.C. §119 is made to Japanese Patent Application No. 2004-115312, filed Apr. 9, 2004, which is herein incorporated by reference in its entirety for all purposes.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a method of controlling a receiving operation which is used for wireless LAN(Local Area Network).  
         [0004]     2. Description of the Related Art  
         [0005]     Wireless LAN terminals are increasingly a part of modern life. The wireless LAN terminals do not need a network cable. Therefore, in the wireless LAN terminal which is driven by a battery, the terminal can be used as a mobile device in a communication area. For making a communication between the wireless LAN terminals and an accessing point, CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance) is used as a wireless LAN standard. The CSMA/CA is used by a 2.4-GHz band wireless LAN standard such as an IEEE(Institute of Electrical and Electrical Engineers) 802.11b standard and an IEEE 802.11g standard.  
         [0006]     A maximum transmission speed of the IEEE 802.11g is 54-Mbps and a maximum transmission speed of the IEEE 802.11b is 11-Mbps. The IEEE 802.11g has an upward compatibility to the IEEE 802.11b. Therefore, a device which uses the IEEE 802.11g can communicate to a device which uses the IEEE 802.11g and the IEEE 802.11b. Both of the IEEE 802.11b and the IEEE 802.11g adopt DSSS(Direct Sequence Spread Spectrum) and OFDM(orthogonal frequency division multiplexing). A synchronizing portion and a header portion of a transmission frame are modulated by a DBPSK of 1 Mbps mode or a QPSK of 2 Mbps mode for making the compatibility of these standards. The IEEE 802.11b and an IEEE 802.11a are described in reference 1: Japanese Patent Laid-Open No. 2003-299141.  
         [0007]     In the mobile terminal of the wireless LAN system, low power consumption is desired. A technique for achieving the low power consumption is described in reference 2: Japanese Patent Laid-Open 8-195754. In reference 2, a standby period is extended by receiving a beacon signal for reducing the power consumption during waiting time. The mobile terminal may be called a mobile station or simply called a wireless LAN station in this invention.  
         [0008]     The beacon signal is transmitted from the access point every 100 msec. Therefore, the mobile station which has a power saving mode can be changed between an awake mode and a doze mode in response to the beacon signal from an access point. The access point changes the condition of the mobile station to the awake mode or the doze mode by checking whether the mobile station is in a power consumption mode or not. An information which indicates an interval of the transmitting operation of the beacon signal is included in a frame body which is next to a MAC header portion.  
         [0009]     In the wireless LAN station, further low power consumption has been desired. In particular, the device which is driven by a battery desires the low power consumption. In the CSMA/CA, the mobile station receives carriers continually for checking a data sending timing. Therefore, it is difficult to reduce the power consumption in such device.  
         [0010]     For example, when the access point and one mobile station communicate using the IEEE 802.11b, and the other mobile station which uses the IEEE 802.11b and a mobile station which uses the IEEE 802.11g are located in the same communication area, a radio wave of the IEEE 802.11b is transferred to each station in the communication area. The station of the IEEE 802.11g waiting to send a signal may wait until the communication which is performed by the IEEE 802.11b is completed. Therefore, the station which uses the IEEE 802.11g and is waiting to send the signal, consumes powers receiving the unneeded signal.  
         [0011]     Also, when a plurality of mobile stations which use the IEEE 801.11g make a communication link to the access point, the stations waiting to send the signal may wait while receiving the unneeded signal until the communication by the other station is completed. Therefore, it is difficult to reduce power consumption.  
       SUMMARY OF THE INVENTION  
       [0012]     Accordingly, in one aspect of the present invention, a method of controlling a receiving operation for achieving low power consumption is provided. The method of controlling a receiving operation includes, receiving a transmission frame into a wireless device, and decoding the transmission frame. A header information in the transmission frame is analyzed. Then, the receiving operation is suspended in response to the header information. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  is a block diagram showing a receiving controlling unit in a wireless LAN device of a present invention.  
         [0014]      FIG. 2  is a block diagram showing the wireless LAN device of the present invention.  
         [0015]      FIG. 3  is a schematic diagram showing a wave receiving condition in the wireless LAN device.  
         [0016]      FIG. 4  is a block diagram showing a structure of a header of a PLCP frame.  
         [0017]     FIGS.  5  is a block diagram showing a field of a MAC header, frame body, and an FSC.  
         [0018]      FIG. 6  is a block diagram showing a structure of a beacon frame.  
         [0019]      FIG. 7  is a timing chart showing a sleep timer operation.  
         [0020]      FIG. 8  is a timing chart showing a sleep timer operation.  
         [0021]      FIG. 9  is a timing chart showing a suspending time in response to the PLCP header.  
         [0022]      FIG. 10  is a timing chart showing a receiving operation in the wireless LAN device.  
         [0023]      FIG. 11  is a block diagram showing a structure of a receiving controlling unit of another embodiment of the present invention.  
         [0024]      FIG. 12  is a schematic diagram showing a wave receiving condition in the wireless LAN device.  
         [0025]      FIG. 13  is a table showing a receiving condition.  
         [0026]      FIG. 14  is a timing chart showing a receiving timing.  
         [0027]      FIG. 15  is flowchart showing a judgment operation in the receiving controlling unit. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]     A method of controlling a receiving operation according to preferred embodiments of the present invention will be explained hereinafter with reference to the accompanying figures. In order to simplify the explanation, like elements are given like or corresponding reference numerals. Dual explanations of the same elements are avoided.  
         [0029]      FIG. 2  is a block diagram showing a wireless LAN device  200 . The wireless LAN device  200  is compliant with the IEEE 802.11b and the IEEE 802.11g standards. In this embodiment, the wireless LAN device  200  can be operated with low power consumption independently of a beacon signal, while the wireless LAN device  200  makes a communication link to an access point in an infrastructure mode. The wireless LAN device  200  communicate with other wireless LAN devices directly in an ad hoc mode.  
         [0030]      FIG. 3  is a schematic diagram showing a wave receiving condition in the wireless LAN device  200 . In  FIG. 3 , a communication is performed between the access point  300  and the wireless LAN device  310  by the IEEE 802.11b. The wireless LAN devices  200 ,  320 , and  330  receive a carrier from the access point  300 .  
         [0031]     The wireless LAN device  200  includes an antenna  210 , a transmitting/receiving unit  220  which transmits and receives a radio frequency signal, a modem unit  240  which is connected to the transmitting/receiving unit  220  via a connecting line  230 , and a receiving controlling unit  260  which is connected to the modem unit  240  via a connecting line  250 , as shown in  FIG. 2 . The modem unit  240  demodulates a receiving signal to a receiving frame and modulates a transmitting frame to a radio frequency signal. The receiving controlling unit  260  is operated for achieving low power consumption operation in response to the receiving frame. The receiving controlling unit  260  outputs a control signal to the transmitting/receiving unit  220  and the modem unit  240  via a connecting line  270 .  
         [0032]     The transmitting/receiving unit  220  is an RF circuit for transmitting and receiving a  2 . 4 -GHz band wireless signal. The transmitting/receiving unit  220  includes an automatic gain control circuit  222  which amplifies the received signal in response to a level of the received signal. The automatic gain control circuit  222  suspends the amplifying operation in response to the control signal from the receiving controlling unit  260 . While the amplifying operation is suspended, the power consumption in the wireless LAN device  200  is reduced. A gain control signal is supplied from a digital analog converter  242  in the modem unit  240  to the automatic gain control circuit  222  via a connecting line  244 .  
         [0033]     The modem unit  240  includes an analog digital converter  246  which converts an analog received signal to a digital signal. Also, the modem unit  240  has a function for modulating the converted digital signal to a PLCP(Physical Layer Convergence Procedure) frame and a MAC(Media Access Control) frame. The modem unit  240  measures the level of the receiving signal and supplies the gain control signal to the automatic gain control circuit  222  for controlling receiver sensitivity.  
         [0034]     A beginning portion of the PLCP frame and the MAC frame are shown in  FIG. 4  and  FIG. 5 . The beginning portion of the PLCP frame includes a PLCP preamble and a PLCP header. The PLCP preamble includes a synchronization signal field SYNC and a starting field SFD. The SYNC field is used for deciding whether the communication type is the IEEE 802.11b or the IEEE 802.11g. The PLCP header includes a SIGNAL field, a SERVICE field, a LENGTH field, and a CRC field. The SIGNAL field shows a transferring speed of the MAC frame. The SERVICE field is used for setting a modulation type. The LENGTH field shows a period of time for transmitting data. The CRC field is used for checking redundancy.  
         [0035]     The MAC frame is appended to the PLCP header. The MAC frame includes a MAC header, a frame body, and an FCS frame. The MAC header includes a FRAME CONTROL field, a TIME/ID field, a DESTINATION ADDRESS field, and a SOURCE ADDRESS field. The frame body and the FCS field are appended to the MAC header. A combination of the PLCP frame and the MAC frame is called PPDU(PLCP Protocol Data Unit).  
         [0036]     A beacon frame  600  which is transmitted from the access point  300  is described by referring to  FIG. 6 . The beacon frame  600  includes the MAC header which includes the FRAME CONTROL field, the TIME/ID field, the DESTINATION ADDRESS field, BSSID field, and a SEQUENCE CONTROL field. The frame body includes a TIME STAMP field, a BEACON INTERVAL field, a CAPABILITY INFORMATION field, a SSID field, and a SUPPORT RATE field.  
         [0037]     A structure of the receiving controlling unit  260  is described in  FIG. 1 . The receiving controlling unit  260  has a PLCP header decoder  100 . The PLCP header decoder has input thereto a receiving signal of the IEEE 802.11b or the IEEE 802.11g, and extracts the PLCP preamble and the PLCP header from the receiving signal. The PLCP header decoder  100  checks data validity by using the CRC field. If the data validity is confirmed, the extracted PLCP data  110  is output to a length data extracting circuit  102 . If the data validity is not confirmed, the receiving operation is continued. The PLCP header decoder  100  judges the communication type based on the synchronizing signal in the PLCP preamble. If the communication type is different, the PLCP header decoder  100  outputs a judgment information  120  to a power controlling circuit  106 .  
         [0038]     When the mobile station which is used exclusively for the IEEE 802.11g receives the signal of the IEEE 802.11b, the mobile station sets data which is included in the LENGTH field to a sleep timer  104 , and the receiving circuit is suspended during when the set time is counted. Also, when the mobile station which is used exclusively for the IEEE 802.11b receives the signal of the IEEE 802.11g, the mobile station sets data which is included in the LENGTH field to a sleep timer  104 , and the receiving circuit is suspended during the set time is counted.  
         [0039]     The length data extracting circuit  102  extracts the length data which shows a length of time of data transmitting from the PLCP frame and sets the extracted data  130  to the sleep timer  104 . The time of data transmitting is set in 1 μs units. The sleep timer  104  is operated by a clock of 1 μs units. For example, when the length data  130  which has  100  values is set in the sleep timer  104 , the sleep timer  104  outputs a receiving enable signal  140  having a low level while decrementing the set length data in response to the 1 μs cycle clock, as shown in  FIG. 7 . When the counted value becomes 0 value, the receiving enable signal  140  turns to a high level, as shown in  FIG. 8 . The sleep timer  104  outputs the receiving enable signal  140  to a power controlling circuit  106 .  
         [0040]     The power controlling circuit  106  generates a suspending signal  270  in response to the judgment information  120  and the receiving enable signal  140  as shown in  FIG. 1 . The suspending signal  270  is supplied to the automatic gain controlling circuit  222  and the digital analog converter  242  as shown in  FIG. 2 . Therefore, during when the suspending signal  270  is output, the receiving circuit is operated in the power saving mode as shown in  FIG. 9 . The power saving mode is performed by suspending the clock to the automatic gain controlling circuit  222  and the digital analog circuit  242 .  
         [0041]     Next, a receiving controlling operation of the wireless LAN device  200  is described by referring to  FIG. 10 . First, a beacon signal  1000  is transmitted from the access point at “t 1 ”. Then, the communication to the wireless LAN device STA( 1 ) by the IEEE 802.11b or the IEEE 802.11g is started at “t 2 ”. When the wireless LAN device STA( 2 ) receives a transmitting frame  1010  for the wireless LAN device STA( 1 ), the PLCP header decoder  100  in the wireless LAN device STA( 2 ) extracts the PLCP header from the receiving frame. Then, the length data is extracted by the length data extracting circuit  102 . The validity of the PLCP header is confirmed by using the CRC. When the PLCP header is valid and the receiving frame has different communication type from the wireless LAN device STA( 2 ), the value of the extracted length data is set to the sleep timer  104  in the wireless LAN device STA( 2 ). Then, the low level of the receiving enable signal  140  is output to the power controlling circuit  106  at “t 3 ”. If the PLCP header is invalid, the receiving operation is continued.  
         [0042]     The power controlling circuit  106  outputs the suspending signal  270  to the transmitting/receiving unit  220  and the modem unit  240  during the time when the length data is decreased in the sleep timer  104 . The transmitting/receiving unit  220  and the modem unit  240  enter a suspend mode in response to the suspending signal  270 . Then, the receiving circuit starts working in response to the 0 value of the sleep timer at “t 4 ”. Accordingly, the receiving operation is suspended in a period from “t 3 ” to “t 4 ”, and the power consumption is reduced in this period.  
         [0043]     Then, the wireless LAN device STA( 2 ) transmits a transmitting frame  1020  to the access point AP during a period from “t 5 ” to “t 6 ”. In this period, the suspending signal  270  is output to the receiving circuit, and the receiving circuit is suspended. Then, the wireless LAN device STA( 2 ) starts the receiving operation at “t 6 ”. When the wireless LAN device STA( 2 ) receives the PLCP header in the transmitting frame  1030  which is sent from the wireless LAN device STA( 1 ) to the access point AP, the receiving operation in the wireless LAN device STA( 2 ) is suspended at “t 7 ”. Also, the same operation is performed from “t 8 ” to “t 10 ”.  
         [0044]     In this embodiment, the judgment that whether the receiving operation can be suspended or not is decided based on the preamble of the PLCP frame. Further, the suspending time is decided by the header of the PLCP frame. As a result, when the wireless LAN device receives the different type of the receiving frame, the wireless LAN device can be suspended during the time which is set by the length data of the PLCP header. Therefore, the low power consumption operation is achieved.  
         [0045]     Next, another embodiment is described by referring to  FIG. 11 . A receiving controlling unit  700  includes a destination address extracting circuit  710 . The destination address extracting circuit  710  has input thereto the receiving signal  250  and outputs an output signal to the power controlling circuit  720 .  
         [0046]     The destination address extracting circuit  710  judges whether the receiving frame is sent for the wireless LAN device or not based on data of a DESTINATION ADDRESS field. If the receiving frame is exclusively available for another wireless LAN device, the suspending signal  270  is output from the power controlling circuit  720  based on a detecting signal  712  and the receiving enable signal  140 . The suspending time is defined by the LENGTH field in the PLCP header. The transmitting/receiving unit  220  and the receiving circuit in the modem unit  240  are suspended by the suspending signal  270 . Also, if the receiving frame is a different communication type, the suspending signal  270  is generated and the receiving circuit is suspended.  
         [0047]     In response to the suspending signal, the power or the clock signal for the transmitting/receiving unit  220  and the receiving circuit in the modem unit  240  is suspended as shown in  FIG. 14 .  
         [0048]     Accordingly, since the suspending signal  270  is generated based on the extracted destination address, a timing for starting the low power consumption operation can be accelerated. A judgment table is shown in  FIG. 13 . If the extracted destination address data which corresponds to the wireless LAN station is received and is judged true by using the FCS, the destination address is truly sent to the targeted wireless LAN station. If the extracted destination address data which corresponds to the wireless LAN station is received and is judged as being in error by using the FCS, the destination address has no relationship to the targeted wireless LAN station. If the extracted destination address data does not correspond to the targeted wireless LAN station, the real destination address has no relationship to the targeted wireless LAN station. That is, if the receiving operation is suspended by using the extracted destination address data without using the FCS, the receiving frame for the targeted wireless LAN station can be received correctly.  
         [0049]     The judgment operation in the receiving controlling unit  700  is described by referring to  FIG. 15 . When the communication signal of the IEEE 802.11b or the IEEE 802.11g is received and the receiving frame of the communication signal is input to the PLCP header decoder  100  and the destination address extracting circuit  710 , the PLCP header decoder  100  judges whether the type of the receiving frame signal is available for the wireless LAN device or not at step S 1500 . If the communication type is the same as the communication type which is used in the wireless LAN device, a step S 1510  is applied as the next step. If the communication type is different from the communication type which is used in the wireless LAN device, a step S 1520  is applied as the next step.  
         [0050]     Further, the transmitting time length in the LENGTH field is received in the step S 1520 . Also, the validity of the PLCP header is verified by using the CRC field. The LENGTH data  130  is set in the sleep timer  104  after the validity is verified. Then, the low level of the receiving enable signal  140  is output from the sleep timer  104  to the power controlling circuit  720 , and countdown is started. If the validity of the PLCP header is not verified, the receiving operation is continued.  
         [0051]     Then, the power controlling circuit  720  generates the suspending signal  270  in response to the receiving enable signal  140  and the result of the judgment in the PLCP header decoder  100 , and outputs the suspending signal  270  to the transmitting/receiving unit  220  and the modem unit  240 . As a result, while the suspending signal  270  is output from the power controlling circuit  720 , operating of the automatic gain controlling circuit  222  and the digital analog converter  242  are suspended. The suspending operation can be performed by suspending the clock signal which is input to the automatic gain controlling circuit  222  and the digital analog converter  242 .  
         [0052]     If the communication type is the same as the station as shown in  FIG. 12 , a step  1510  is applied as the next step. When the MAC header destination address field is received in the step S 1510 , the destination address is extracted by the destination address extracting circuit  710 , and it is judged whether the receiving frame is valid for the station or not. If the receiving frame is not valid for the station, the step S 1520  is applied and the LENGTH data  130  is set in the sleep timer  104 . The sleep timer  104  outputs the low level of the receiving enable signal  140  to the power controlling circuit  720  in response to setting the LENGTH data  130 . Then the suspending operation is performed in the step S 1530 . When the counting value in the sleep timer  104  becomes “0”, the high level of the receiving enable signal  140  is supplied to the power controlling circuit  720 . As a result, the power controlling circuit  720  stops outputting the suspending signal  270 , and the receiving operation is restarted.  
         [0053]     If the receiving frame signal is judged valid for the station, the receiving operation is continued as a step S 1540 .  
         [0054]     In this embodiment, if the receiving frame has the same communication type for the station, the suspending operation can be performed.  
         [0055]     While the preferred form of the present invention has been described, it is to be understood that modifications will be apparent to those skilled in the art without departing from the spirit of the invention. The scope of the invention is to be determined solely by the following claims.