JP2004040373A - Wireless terminal and control method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless LAN terminal capable of being used for a longer time than a conventional terminal by reducing its power consumption and to provide a control method thereof. <P>SOLUTION: A wireless LAN system in compliance with the IEEE 802.11 standards indicates an estimate time of a busy channel called a network assignment vector (NAV) given by RTS and CTS (request to send and clear to send) frames to a third terminal in order to solve a problem of hidden terminals and controls the third terminal not to transmit data within the estimated time. The third terminal needs not to receive data within the estimated time. Then the third terminal may stop supply of power to its reception circuit or stop supply of a synchronizing signal for the NAV period given from the RTS frame when receiving the RTS frame from e.g., a transmission station. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a wireless premises including a plurality of mobile terminals performing communication using a wireless transmission path, or connection control of the mobile terminals, and an access point serving as a base station for connecting the mobile terminals to a wired network. The present invention relates to a network (wireless LAN) system, and in particular, controls access to a wireless medium to a wireless local area network system controlled by a collision avoidance type carrier sense multiple access (CSMA / CA) system. The present invention relates to a possible wireless terminal and a control method thereof.
[0002]
[Prior art]
Conventionally, a wireless LAN system has been used as a highly portable network system that is not restricted by a communication cable. In recent years, in particular, the transmission speed has dramatically increased due to the improvement in transmission speed in a wireless communication section, the spread of notebook computers, and the emergence of applications suitable for mobile communication. Particularly, as a wireless LAN system using radio waves in the 2.4 GHz and 5 GHz bands, a wireless LAN system defined by the IEEE 802.11 standard group has been widely used.
[0003]
An advantage of such a wireless LAN system is that it does not require a cable connection and allows a free device layout in a room. Further, when a portable terminal is used, even if the terminal is moved to a different place such as a room in a company or a conference room, the terminal can be freely connected to the in-house main LAN as long as the terminal is near the connection point. is there. Therefore, the user can do the same work at his desk everywhere, which is very convenient. Further, in recent years, it has become possible to connect to the Internet from a connection point outdoors by a connection service provider, commonly called a hot spot, using a terminal owned by the user.
[0004]
As described above, many terminals mainly used in the wireless LAN system are mobile terminals driven by a battery, and the time during which the terminal can be continuously used is limited by the power consumption of the terminal and the battery capacity. In order to provide a terminal that can be used for a long time, it is necessary to reduce the power consumption of each unit in the terminal, and reducing the power consumption of the wireless LAN module itself is also an important technical problem. Techniques for reducing the power consumption of the wireless LAN module include those that mainly reduce transmission power by optimally controlling the transmission output power and those that reduce reception power by controlling the operation during reception standby. There is a method for reducing power consumption.
[0005]
As a conventional example of a technique for reducing the power consumption of the receiving unit of the wireless module during such reception standby, Japanese Patent No. 2700000 is first mentioned. In this prior art, the radio receiving unit operates only the reception level determining unit when waiting for reception of a packet, and the reception level among other circuit parts included in the radio receiving unit such as an analog-to-digital converter and a digital demodulation unit. All the operations except for the judgment unit are stopped. Then, when the reception of the packet is started and the detection signal is output from the reception level determination unit, the analog-to-digital converter and the digital demodulation unit are activated, and the packet reception and demodulation process is started. In this conventional technique, the effect of reducing the power consumption of other circuit parts is obtained by operating only the reception level determination unit during the period when no packet exists. However, the reception level determination unit as described in the conventional example generally includes an automatic gain control circuit (AGC circuit), and receives a signal with a maximum gain when waiting for reception of a packet. Will be consumed. Further, in this conventional example, not only the reception level determination unit but also the analog circuit parts such as the high-frequency circuit unit from the antenna to the reception level determination unit are all in the operating state, so that sufficient power consumption cannot be reduced. It's hard to say.
[0006]
Another conventional technique for reducing the power consumption of the receiving unit of the wireless module is disclosed in Japanese Patent No. 27131197. According to the conventional technique, when a packet header added to the first part of a packet is received, address information and a packet length included in the header are obtained. When the control unit determines that the address is not the address of the own terminal, the wireless module that has received the packet stops the subsequent reception operation and stops the operation of the receiver until the end of packet reception obtained from the packet length. By doing so, the power consumption is reduced. Also in this conventional example, the operation of the receiver cannot be stopped until all the received packets are received and at least the packet header of each packet is demodulated. In a wireless LAN system, a spread spectrum (SS) system, an orthogonal frequency division multiplex (OFDM) system, or the like is used as a modulation / demodulation system. Therefore, generally, a packet signal is received from an antenna and demodulation processing is completed. Has a relatively large delay due to the numerical operation. Therefore, in this conventional example, when the packet header is analyzed, many parts of the data payload following the packet header have already been demodulated, and the effect of reducing power consumption is small.
[0007]
[Problems to be solved by the invention]
As described above, in the conventional method in which the wireless receiving unit starts receiving a packet once and then determines whether to receive or ignore the packet, it is not possible to sufficiently reduce the power consumption of the wireless LAN module. It was possible.
[0008]
In the present invention, in view of these prior arts, by using a specific media connection protocol used in a wireless LAN system, the power consumption of the wireless LAN module is greatly reduced, and a wireless terminal that can be used for a longer time than before and its control. The aim is to provide a method.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the invention of the present application, when a wireless terminal device of a wireless LAN system receives a frame that is not addressed to the wireless terminal device, the wireless terminal device performs a wireless communication for a period corresponding to a network allocation vector indicated by the frame. The waiting of the signal arrival is stopped by stopping the power supply or the clock.
[0010]
Alternatively, a wireless terminal device connectable to a wireless network,
Receiving means for waiting for an incoming radio signal and receiving the incoming signal;
Acquiring means for acquiring, from a packet received by the receiving means, time information and packet configuration information held by the packet;
When the packet is not addressed to the wireless terminal device, a stop unit for stopping at least a part of the function of the wireless terminal device during a period calculated from the time information and the packet configuration information.
[0011]
Preferably, the stopping means stops waiting for an incoming call by the receiving means.
[0012]
Preferably, the stopping means stops power supply to an electronic circuit included in the receiving means.
[0013]
Also preferably, the stopping unit stops supplying a synchronization signal to an electronic circuit included in the receiving unit.
[0014]
Alternatively, a wireless terminal device conforming to the IEEE 802.11 standard,
When a frame not addressed to the wireless terminal device is received, the operation of the wireless signal receiving circuit is stopped for a period corresponding to the network allocation vector indicated by the frame.
[0015]
Alternatively, a wireless communication system in which the transmitting and receiving terminal presents the expected time that the line is occupied to the third terminal in the exchanged data,
The third terminal that has intercepted the data stops the operation of the circuit that realizes the communication function for the expected time period when the line indicated by the data is occupied.
[0016]
According to this configuration, the packet header of the received packet is analyzed, and the wireless receiving unit is controlled by using packet configuration information and duration information used in the protocol of the wireless LAN. Here, the packet configuration information determines whether or not it is necessary to receive the next packet to be transmitted, and the period information determines the period in which the receiving unit is to be stopped. Has the effect of suppressing the receiving operation from the beginning.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
The operation of the receiving unit of the wireless LAN system in the embodiment according to the present invention will be described with reference to the drawings regarding the protocol of the wireless LAN system.
[0018]
[First Embodiment]
FIG. 8 shows a system configuration diagram of a general wireless LAN system. Now, the wireless LAN system includes three stations, a first station 31 (STA-1), a second station 32 (STA-2), and an access point 33 (AP). In a wireless LAN system, since all stations share and use a single wireless channel, the packet transmission timing of each station is controlled by a Media Access Control (MAC) protocol in order to avoid packet collision. In the wireless LAN system, a method called CSMA / CA is used as the MAC protocol. In the CSMA / CA system, each station must transmit a packet after performing carrier sense on the wireless medium for a predetermined period before confirming that the wireless medium is not occupied before transmitting the packet. However, depending on the location of each terminal, each station may not be able to receive signals transmitted by all stations. For example, in FIG. 8, the AP 33 and the STA-1 and the AP 33 and the STA-2 are within a communication distance from each other, but the STA-1 and the STA-2 are not directly within the communication distance from each other. Cannot be received. In such a case, for example, even if STA-2 performs carrier sense, it cannot receive a signal from STA-1, so that STA-2 may determine that the wireless medium is empty and start transmitting packets. . Such a situation is called a hidden terminal problem, but it means that it is impossible to completely perform access control as a MAC protocol in the CSMA / CA system that simply performs carrier sense. Therefore, in a MAC protocol used for a wireless LAN, a distribution coordination function (DCF) using an RTS / CTS frame based on CSMA / CA and a point coordination function for controlling by polling from an access point are used. A multiple access function is realized by adopting a function (PCF) or the like.
[0019]
FIG. 1 is a timing chart showing a state of packet transmission by the RTS / CTS protocol. In FIG. 1, the operation of the transmitting station of the data packet is represented as “transmitting station”, the operation of the receiving station is represented as “receiving station”, and the operations of the other stations are represented as “third station”. The transmitting station first transmits an RTS frame before transmitting a data packet. The receiving station receiving this RTS returns a CTS frame to the transmitting station. Thereafter, the transmitting station that has received the CTS frame transmits a data packet (data) to the receiving station. When the reception of the data packet is completed, the receiving station returns an ACK frame to the transmitting station, and a series of data packet transmission processing is completed.
[0020]
Now, it is assumed that the third station can receive only the signal transmitted from the transmitting station and is a hidden terminal with respect to the receiving station. At this time, even if the third station performs carrier sense, it can receive only RTS and data among the four frames (RTS, CTS, data, and ACK) used in this series of transmission processing. Therefore, during transmission of CTS and ACK, it cannot be recognized that the wireless medium is occupied. In the wireless LAN protocol, a method called virtual carrier sense is used during the transmission period of the CTS and ACK to inform other stations that cannot directly receive these frames that the wireless medium is being used. use.
[0021]
FIG. 2 is a diagram showing a frame configuration of an RTS frame used in the present protocol. The RTS frame 101 includes a frame control field, a duration / ID field, a destination address (RA), a source address (TA), and a frame check sequence (FCS). Further, the duration / ID field 203 is a 16-bit field, of which 14 bits are allocated as the duration field 204. In the duration field, time information until packet transmission is completed by the RTS / CTS protocol, that is, time information until the end of ACK transmission is recorded. In virtual carrier sense, a third station acquires the duration field included in this RTS. This value is called a network allocation vector (NAV), which is time information indicating a period during which the wireless medium is occupied. When the RTS frame is not addressed to itself, the third station does not transmit packets from itself during this NAV period, so that the third station performs carrier sense even for the receiving station which is a hidden terminal. It is possible to perform the same operation as.
[0022]
Next, on the contrary, it is assumed that the third station can receive only the signal emitted by the receiving station and is hidden from the transmitting station. At this time, the third station can receive only CTS and ACK among the four frames (RTS, CTS, data, and ACK) used for this series of transmission processing even if the third station performs carrier sensing. However, as shown in the frame format of the CTS frame 102 shown in FIG. 3, since the CTS frame also has a duration field like the RTS, the third station calculates the NAV from this duration field, and Virtual Carrier Sense can be performed in the same manner as described above.
[0023]
Here, other symbols displayed in FIG. 1 will be briefly described. A waiting time is inserted between packets by a time (IFS: Inter-Frame Spacing) in consideration of switching between transmission / reception and propagation delay. DIFS and SIFS in FIG. 1 represent the maximum IFS and the minimum IFS, respectively. In addition, when data to be transmitted occurs in any one of the stations (third station in FIG. 1) while the own station or another station (the transmitting station and the receiving station in FIG. 1) is communicating, this is indicated by NAV. After the elapse of the time, carrier sense is performed after waiting for a time defined by DIFS and further for a time defined by a random number. If the line is free at that time, transmission is started. The collision window shown in FIG. 1 indicates a waiting time determined by this random number. These are all defined in IEEE 802.11.
[0024]
As described above, the virtual carrier sense in the wireless LAN system has been described. However, the present invention uses such a wireless LAN protocol to reduce the power consumption of the receiving unit of the wireless module mounted on the terminal station. Provided is a wireless LAN system that can be driven by a time battery.
[0025]
<When the third station is a hidden terminal with respect to the receiving station>
Now, consider a case where a data packet is transmitted from the AP 33 to the STA-1 in the wireless LAN system in FIG. Here, AP33 corresponds to the transmitting station in FIG. 1, and STA-1 corresponds to the receiving station. The operation of STA-2 at this time is shown as STA-2 (A) in FIG. When the STA-2 receives the RTS from the AP and recognizes that the RTS is not addressed to its own station, the STA-2 starts virtual carrier sense at timing T1. Since the STA-2 reads the duration field of the RTS and knows that this packet transmission process will continue until the timing T3, the STA-2 does not need to receive the wireless medium during this period T1-T3. Accordingly, during this period, the STA-2 has no problem even if the receiving module of the STA-2 is stopped, thereby reducing the power consumption during this period.
[0026]
<When the third station is a hidden terminal with respect to the transmitting station>
Similarly, in the wireless LAN system in FIG. 8, a case is considered in which a data packet is transmitted from STA-1 to AP 33. Here, AP33 corresponds to the receiving station in FIG. 1, and STA-1 corresponds to the transmitting station. The operation of STA-2 at this time is shown as STA-2 (B) in FIG. Since STA-2 is a hidden terminal with respect to STA-1, it cannot receive RTS from STA-1, but can receive CTS from AP 33 following it. When STA-2 receives this CTS, it starts virtual carrier sense at timing T2. Since the STA-2 reads the duration field of the CTS and knows that the packet transmission process will continue until the timing T3, the STA-2 does not need to receive the wireless medium during the period T2 to T3. Therefore, during this period, the STA-2 stops the receiving module of its own station, thereby making it possible to reduce power consumption during this period.
[0027]
FIG. 4 shows a first configuration example of the receiving module of the wireless LAN module according to the present invention. In the figure, a high-frequency signal received by an antenna 10 is converted into a low-frequency intermediate frequency signal or a baseband signal by a high-frequency analog receiving unit 11. These intermediate frequency signals or baseband signals are sampled by an analog / digital converter (AD converter) 12 and converted into digital data. The digital demodulation unit 13 performs a demodulation process on the digital data to demodulate the data of the received frame. The modulation method used for the wireless LAN includes the SS method, the OFDM method, and the like. However, the present invention can be applied to any modulation method or a combination of these modulation methods. It is.
[0028]
The demodulated data thus obtained is sent to the control unit 14. The control unit 14 analyzes the demodulated data and sends the received data to the upper layer of the wireless LAN system as needed. The feature of the control unit 14 in the present invention is that the received RTS frame and CTS frame are analyzed and the time is analyzed. It is to acquire NAV which is information. The control unit 14 determines that it is not necessary to perform reception of the wireless medium during the period indicated by the NAV, and activates the reception stop control line 21 during this period. The reception stop control line 21 is connected to the power supply unit 16. The power supply unit 16 normally supplies power to each unit of the wireless module via the power supply line 22. However, the power supply unit 16 has a function of stopping the power supply while the reception stop control line 21 is active. Power consumption due to useless receiving operation is suppressed.
[0029]
Note that the transmission module may be stopped while the reception module is stopped. Further, power supply to all modules other than the module necessary for restarting power supply may be stopped.
[0030]
Here, for example, when the control unit 14 is program-controlled, the control unit 14 can be realized by using a timer and a reception stop control signal port (register) to which a unique address is given. In this case, the control unit 14 receives and analyzes the RTS frame or the CTS frame demodulated from the digital demodulation unit 13 and, if the communication is not related to the own station, acquires the NAV from the communication and expires the value. Set the time as a timer. However, it is desirable to adjust the NAV value in consideration of the signal delay in the receiving module and the value of IFS inserted between packets without setting the NAV value as it is. Then, after setting the NAV value or the adjusted NAV value in the timer, the timer is started immediately. At the same time, the power supply is stopped by rewriting the reception stop control signal port to an active value. When the timer expires, the control unit 14 restarts the power supply by rewriting the reception stop control signal port to a value that becomes inactive.
[0031]
Alternatively, the control unit 14 can activate the reception control stop line 21 for a designated period by providing a timer and a flip-flop with an initial value setting function. In this configuration, the flip-flop holds the value of the reception stop control signal, and its output is connected to the reception stop control signal line 21. It is assumed that the reception stop control signal is active at a value of 1. Then, the expiration signal of the timer is connected to the clock of the flip-flop. This signal becomes 1 upon expiration, and the flip-flop latches the input data at the rising edge of 0 → 1. In this configuration, first, the control unit 14 analyzes the RTS frame or the CTS frame demodulated by the digital demodulation unit 13 and, if the communication is not related to the own station, acquires the NAV from the communication and determines the value. Set the expiration time in the timer. Then, after setting the value of NAV in the timer, the timer is started immediately. At the same time, 1 is set as the initial value of the flip-flop, and 1 is set as its input signal. As a result, the reception stop control signal line 21 becomes active, and the supply of power is stopped. When the expiration signal of the timer is input to the clock of the flip-flop, the flip-flop latches the value 0, the reception stop control becomes inactive, and the power supply is restarted.
[0032]
In this configuration example, the power supply line 22 is connected to all parts of the receiving module. However, for example, a local oscillator such as a phase-locked loop generally mounted in a high-frequency analog receiving unit generally has a power-on and stable operation. Therefore, it is not appropriate to frequently turn on / off the power supply. Such a circuit block may be excluded from a target of power control by the control unit 14 and the power supply unit 16, and the present invention may be applied only to other circuit parts.
[0033]
As described above, in the wireless LAN system according to the present embodiment, when the received RTS frame or CTS frame is not addressed to a terminal including the wireless LAN module, the wireless LAN module uses the NAV indicated by the received RTS frame and CTS frame. The power supply to the circuit blocks related to wireless communication (high-frequency analog receiving unit, AD converter, digital demodulating unit in this embodiment) is stopped for a time corresponding to According to the CSMA / CA method, the NAV is an estimated time until the RTS-CTS-DATA-ACK procedure is completed, during which no frame is transmitted to the third station. For this reason, the third station stops the power supply to the circuit block related to wireless communication, particularly the circuit block activated for standby for reception for a time corresponding to NAV, so that there is no hindrance to wireless communication. Power consumption can be effectively reduced.
[0034]
In the present embodiment, a case has been described where the third terminal is a hidden terminal with respect to either the transmitting station or the receiving station. If the third terminal can receive signals from both the transmitting station and the receiving station, any method can be adopted. However, when the receiving module is stopped based on the RTS frame of the transmitting station, a longer reception stop time can be secured than when the receiving module is based on the CTS frame of the receiving station. Therefore, it is desirable to adopt the former.
[0035]
[Second embodiment]
Next, FIG. 5 shows a configuration example of the second embodiment of the receiving module of the wireless LAN module according to the present invention. This configuration example is characterized by controlling a system clock for operating a digital circuit, instead of controlling a power supply to stop a receiving operation.
[0036]
In FIG. 5, a high-frequency signal received by an antenna 10 is converted into a low-frequency intermediate frequency signal or a baseband signal by a high-frequency analog receiving unit 11. These intermediate frequency signals or baseband signals are sampled by the analog-to-digital converter 12 and converted into digital data. The digital demodulation unit 13 performs a demodulation process on the digital data to demodulate the data of the received frame. The demodulated data thus obtained is sent to the control unit 14. The control unit 14 determines that it is not necessary to perform reception of the wireless medium during the period indicated by the NAV, and activates the reception stop control line 21 during this period. Further, the reception stop control line 21 is connected to the clock generator 17.
[0037]
The clock generator 17 normally supplies the system clock to the analog-to-digital converter 12 and the digital demodulation unit 13 in the wireless module via the clock supply line 23, but during a period when the reception stop control line 21 is active. Has the function of stopping the supply of this system clock. Generally, a digital circuit made by CMOS technology or the like consumes almost no power when switching by a clock signal is stopped. In this way, by stopping the clock supply to the digital circuit during the reception stop period, it is possible to reduce the power consumption of the reception module.
[0038]
Further, in this configuration example, the clock supply line 23 is single, and this one clock line is connected to the analog / digital converter 12 and the digital demodulation unit 13. There can be different clocks. Even in such a case, the present invention can be similarly applied by configuring the clock generator 17 to control the plurality of clock supply lines.
[0039]
[Third embodiment]
The operation of the receiving unit of the wireless LAN system according to the third embodiment of the present invention will be described with reference to the drawings regarding the protocol of the wireless LAN system. In the present embodiment, the DCF protocol used when fragmenting relatively large data into a plurality of wireless LAN data packets (Fragmentation) and transmitting the divided data is referred to.
[0040]
<When the third station is a hidden terminal with respect to the receiving station>
FIG. 6 is a diagram showing the operation of the RTS / CTS protocol in the wireless LAN when transmitting a plurality of wireless LAN data packets. Here, as in FIG. 1, the operation of the transmitting station of the data packet is represented by the transmitting station, the operation of the receiving station is represented by the receiving station, and the operations of the other stations are represented by the third station. The data packets to be transmitted are three packets represented by Frag0, Frag1, and Frag2. First, the transmitting station transmits an RTS frame before transmitting a data packet. The receiving station receiving this RTS returns a CTS frame to the transmitting station. Thereafter, the transmitting station that has received the CTS frame transmits the first data packet (Frag0) to the receiving station. When the reception of the first data packet is completed, the receiving station returns a first ACK frame (Ack0) to the transmitting station. Then, without exchanging the RTS / CTS frame, the transmitting station immediately transmits the second data packet (Frag1), and the receiving station that has received the second data packet (Frag1) returns the second ACK frame (Ack1). Thereafter, the transmitting station transmits the last data packet (Frag2), and the receiving station receiving this transmits the last ACK frame (Ack2). Through these series of processes, the transmission process of the data packet divided into three packets is completed.
[0041]
It should be noted here that in such a fragmented packet transmission, the RTS / CTS protocol determines whether there is a next fragmented data packet transmission to follow the current fragmented data packet. It is the exchange of information. Specifically, the frame control field 201 in the RTS frame 101 shown in FIG. 2 includes one bit of a more fragment field (more fragment bit), and there is a fragment packet to be transmitted next. This bit is set. Further, similarly to the duration field, this more fragment bit is defined not only in the RTS frame but also in the CTS frame 102, the ACK frame 104, and the MAC header 103 added to the head of the data packet shown in FIG. Have been.
[0042]
Here, how the wireless LAN system performs virtual carrier sense in such divided packet transmission will be described with reference to FIG. 6 again. Now, it is assumed that the third station can receive only the signal transmitted from the transmitting station and is a hidden terminal with respect to the receiving station. At this time, even if the third station performs carrier sensing, it can receive only RTS, Frag0, Frag1, and Frag2 among the frames used for this series of transmission processing.
[0043]
First, when the third station receives the RTS frame, it reads the destination address, and if this packet transmission is not addressed to itself, sets the NAV (RTS) based on the time information indicated in the duration field in the RTS frame. Start. At the same time, the more fragment bit included in the RTS frame is read, and if this bit is set, it is recognized that there is a divided data packet following the current packet. In this case, the third station receives the MAC header of the first data frame Frag0. The third station stores the duration field included in the MAC header, and after the NAV based on the RTS frame ends, newly starts the NAV (Frag0) based on the duration field information of Frag0.
[0044]
In this way, the third station sequentially receives the MAC header in which the more fragment bit is set, and sequentially starts NAV using the respective duration fields. Regarding the last received data packet Frag2, since there is no subsequent divided data packet, the more fragment bit of Frag2 is not set, so that the third station can set the current NAV (Frag1) to the last virtual data packet. Recognize that it is the carrier sense period, and after this NAV (Frag1) ends, transition to the normal reception operation mode. In this way, virtual carrier sense in divided data packet transmission can be realized.
[0045]
Here, it is shown that the present invention can be applied to such a MAC protocol as in the first embodiment. In the wireless LAN system in FIG. 8, a case is considered where a divided data packet is transmitted from AP 33 to STA-1. Here, AP33 corresponds to the transmitting station in FIG. 6, and STA-1 corresponds to the receiving station. The operation of STA-2 at this time is shown as STA-2 in FIG. When the STA-2 receives the RTS from the AP 33 and recognizes that the RTS is not addressed to its own station, the STA-2 starts virtual carrier sense at a timing T1. At the same time, STA-2 reads the duration field of the RTS, and can know that this packet transmission process will continue until timing T2 *. However, STA-2 must receive the MAC header of the first fragmented data packet Frag0 in order to obtain the next NAV information because the more fragment bit of the RTS frame is set. Since the CTS frame has a fixed length, the STA-2 knows the timing T1 * at which the transmission of Frag0 is started even if the CTS cannot be received. Therefore, STA-2 does not need to receive the wireless medium during this period T1-T1 *. Accordingly, during this period, the STA-2 has no problem even if the receiving module of the STA-2 is stopped, thereby reducing the power consumption during this period. For example, the timing T1 * can be expected to be a timing later than the timing T1 by the time of the CTS frame and the time corresponding to the insertion of the IFS before and after the CTS frame. The reception stop can be realized in the manner described in the first embodiment with reference to FIGS. However, the period T1-T1 * during which reception is stopped is a value obtained by adding the time of inserting the IFS before and after the time of the CTS frame.
[0046]
STA-2 receives the MAC header of Frag0 after stopping the reception in the period T1-T1 *. Since the data payload portion of Frag0 is information unnecessary for STA-2, STA-2 again stops receiving from time T2 when receiving the MAC header. The timing T2 * at which the second divided data packet Frag1 is transmitted is the end of the NAV (RTS) included in the first received RTS frame, and the STA-2 knows this timing information, so the period T2- * At T2 *, STA-2 can stop receiving. The reception suspension period T2-T2 * is a time obtained by subtracting T1-T1 * and the time required for receiving the MAC header of the fragmented packet Frag0 from the NAV (RTS). The timing obtained by adding this time to the timing T2 is the timing T2 * known to the STA-2. In addition, the reception stop can be realized in the manner described with reference to FIGS. 4 and 5 in the first embodiment. However, the period during which reception is stopped is a period obtained by subtracting T1-T1 * and the time required for receiving the MAC header of the fragmented packet Frag0 from NAV (RTS).
[0047]
The STA-2 receives the Frag1 MAC header after stopping the reception in the period T2-T2 *. Since the data payload part of Frag1 is information unnecessary for STA-2, STA-2 stops receiving again from time T3 when receiving the MAC header. The timing T3 * at which the third divided data packet Frag2 is transmitted is the end of the NAV (Frag0) included in the received first divided frame Frag0, and the STA-2 knows this timing information. At T3-T3 *, STA-2 can stop receiving. The reception suspension period T3-T3 * is a time obtained by subtracting the time required for receiving the MAC header of the fragmented packet Frag1 from the NAV (Frag0). The timing obtained by adding this time to the timing T3 is the timing T3 * known to the STA-2. In addition, the reception stop can be realized in the manner described with reference to FIGS. 4 and 5 in the first embodiment. The period during which reception is stopped is a period obtained by subtracting the time required for receiving the MAC header of the fragmented packet Frag1 from NAV (Frag0).
[0048]
When the fragment packet Frag2 is finally received, the time required for receiving the MAC header of the fragment packet Frag2 is subtracted from NAV (Frag1) from the time T4 when the MAC header of Frag2 is received in the same manner as in the period T3-T3 *. Reception can be stopped until the timing T4 * after the lapse of the period. Since the more fragment bit of the received packet Frag2 is not set, it can be determined that there is no subsequent divided packet. Therefore, if data to be transmitted is generated at the timing T1-T4 *, the reception is restarted after the timing T4 *, a period DIFS is inserted, and after a collision window is generated, if a carrier cannot be detected, the timing is changed. Start sending data.
[0049]
In this way, the third station STA-2, which is a hidden terminal with respect to the receiving station STA-1, can receive the MAC header of each divided data packet transmitted by the transmitting station PA33. Then, by acquiring duration information from the RTS frame and the MAC header of each divided data packet, the STA-2 can transmit T1-T1 *, T2-T2 *, T3-T3 *, T4 during this series of divided data packet transmission. At -T4 *, the operation of the receiving module can be stopped. That is, when the fragment function is performed, the period from the time when the transmitting station transmits the RTS frame to the time when the receiving station transmits the last ACK frame, excluding the receiving period of the MAC header of the data packet, is the third period. The station can suppress the power consumption by stopping the receiving module.
[0050]
As described with reference to FIG. 4 in the first embodiment, the stop operation of the receiving module is to supply power to the receiving module such as the high-frequency analog receiving unit 11, the AD converter 11, and the digital demodulating unit 13 by the power supply unit 16. It is realized by stopping. Alternatively, as described with reference to FIG. 5 in the second embodiment, this is realized by stopping the supply of the clock by the clock generator 17 to the receiving module such as the AD converter 11 and the digital demodulation unit 13. This stopping operation of the receiving module can reduce the power consumption in the receiving module of the third station, which is a hidden terminal with respect to the receiving station, even when the fragment function is used.
[0051]
<When the third station is a hidden terminal with respect to the transmitting station>
Contrary to the case described above, FIG. 7 shows an operation timing diagram in the case where the third station can receive only the signal emitted by the receiving station and is a hidden terminal with respect to the transmitting station. It is. Now, even if the third station performs carrier sense, it can receive only CTS, Ack0, Ack1, and Ack2 among the frames used for this series of transmission processing. First, upon receiving the CTS frame, the third station starts NAV based on the time information indicated in the duration field in the CTS frame. At the same time, the more fragment bit included in the CTS frame is read, and if this bit is set, it is recognized that there is a divided data packet following the current packet. In this case, the third station receives the first ACK frame (Ack0) arriving at the end of the NAV period. Read the more fragment bit contained in this ACK frame, and when this bit is set, the third station recognizes that the second data transmission will be performed next, and at the same time, from the duration field in this ACK frame, NAV is started again based on the obtained time information. By starting NAV every time an ACK frame with more fragment bits set is received, virtual carrier sense can be realized even in transmission of a plurality of data packets. When the third station receives the last ACK frame (Ack2), it reads that the more fragment bit of this frame is not set, terminates the virtual carrier sense, and shifts to the normal receiving operation.
[0052]
Next, in the wireless LAN system in FIG. 8, a case where a divided data packet is transmitted from STA-1 to AP 33 will be considered. Here, AP33 corresponds to the receiving station in FIG. 7, and STA-1 corresponds to the transmitting station. The operation of STA-2 at this time is shown as STA-2 in FIG. The STA-2 receives the CTS from the AP 33 and starts virtual carrier sense at a timing T1. The STA-2 reads the duration field of the CTS, and can know that this packet transmission process continues until timing T2. However, STA-2 must receive the first ACK frame (Ack0) to obtain the next NAV information because the bit of the more fragment field of this CTS frame is set. Since the ACK frame has a fixed length, the STA-2 can start receiving from the timing T1 * obtained by subtracting the transmission period for the ACK frame from the obtained end timing T2 of the NAV period. Accordingly, since STA-2 does not need to receive the wireless medium during this period T1-T1 *, STA-2 can reduce the power consumption without any problem even if the receiving module of its own station is stopped. Become.
[0053]
When the STA-2 receives the first ACK frame after stopping the reception of the period T1-T1 * and recognizes that the more fragment bit is set, the STA-2 obtains the time information obtained from the duration field of the ACK frame as before. The reception can be stopped until the timing T2 * at which the next ACK frame, which can be calculated from, arrives. By repeating this operation until an ACK frame in which no more fragment bit is set is received, the STA-2 performs the periods T1-T1 *, T2-T2 *, and T3- during this series of divided data packet transmission. At T3 *, the operation of the receiving module can be stopped. In other words, during the fragmentation function, the third station receives the CTS frame from the time when the receiving station transmits the last ACK frame until the receiving station transmits the last ACK frame. The power consumption can be suppressed by stopping the module.
[0054]
As described above, even in the transmission of the fragmented data packet, the terminal station not involved in the packet transmission does not need to receive the wireless medium by using the function of the virtual carrier sense. The period can be known, and the receiving operation of the receiving module is stopped during this period, so that the power consumption of the terminal station can be reduced. As examples of the configuration of the receiving module that performs the power saving operation according to the second embodiment of the present invention, those shown in FIGS. 4 and 5 cited in the first embodiment can be similarly used.
[0055]
In the present embodiment, a case has been described where the third terminal is a hidden terminal with respect to either the transmitting station or the receiving station. If the third terminal can receive signals from both the transmitting station and the receiving station, any method can be adopted. However, when the receiving module is stopped based on the RTS frame of the transmitting station, a longer reception stop time can be secured than when the receiving module is based on the CTS frame of the receiving station. Therefore, it is desirable to adopt the former.
[0056]
As described above, in the wireless LAN terminal according to the present invention, while the NAV is valid, the power supply to the receiving module or the supply of the clock signal is stopped, thereby reducing power consumption.
[0057]
If it is determined that the fragment function is used by receiving the RTS frame or the CTS frame first, even if the NAV is valid, the MAC header or the ACK frame of the fragmented packet is received. During the period, the receiving module is returned to the standby state. Then, while referring to the more fragment bits included in the received MAC header or ACK frame, the value of the duration field is obtained, and the timing to be in the reception standby state in order to receive the next MAC header or ACK frame is determined. I do. Then, during that period, the receiving module is stopped as described in the first embodiment or the second embodiment. In this way, even when the fragment function is used, the power consumption can be effectively reduced.
[0058]
<Operation of Control Unit 14 (All Embodiments)>
Here, an example of the operation of the control unit 14 will be described again. The operations of the first and second embodiments and the operation of the present embodiment are not incompatible with each other, and one wireless LAN terminal functions as the device of both embodiments by changing the processing content according to the presence or absence of a fragment. I can do it. Therefore, for example, the operation of the control unit 4 will be described with reference to FIGS. 9 to 11 assuming that the control unit 14 is program-controlled.
[0059]
When the program is controlled, the control unit 14 can be realized by using a timer and a signal port (register) that holds an output value to a reception stop control signal to which a unique address is given.
[0060]
In FIG. 9A, when receiving a demodulated RTS frame or CTS frame from the digital demodulation unit 13, the control unit 14 analyzes the contents thereof and determines whether the communication is not related to the own station ( Step S901). If relevant, appropriate communication processing is performed. If not relevant, a value for activating the reception stop signal is written to the signal port, and the reception is stopped (step S903). Then, fragment bits are referenced from the received frame (step S905). If the fragment bit has not been set, as described in the first embodiment, the timer is started with the value of the NAV given in the duration field in the frame as the expiration time (step S907).
[0061]
On the other hand, if the fragment bit is set, the processing is divided depending on whether the received frame is RTS or CTS (step S909). In the case of the RTS frame, the timer is started with the time corresponding to the CTS frame length as the expiration time (step S911. In addition, the time corresponding to the CTS frame length is determined from the value of the duration field (ie, NAV) included in the RTS frame. (Step S913) In the case of the CTS frame, the time corresponding to the ACK frame length is subtracted from the time (NAV) indicated by the duration value included therein. The timer is started using the value as the expiration time (step S915) When subtracting the time corresponding to the frame length from the NAV, the IFS (see FIG. 1) inserted before and after the frame is also subtracted. The same applies to the case of.
[0062]
In FIG. 9B, when the started timer expires, a value for inactivating the reception stop signal is written to the signal port (step S921). As a result, a reception standby state is set.
[0063]
In FIG. 10, when receiving the MAC header of the data packet from the digital demodulation unit 13, the control unit 14 receives and analyzes the MAC header and determines whether the communication is not related to the own station (step S1001). ). If not related, the fragment bit is referred to from among them (step S1003). If the fragment bit is not set, a separately determined process such as ignoring the packet is performed. On the other hand, if the fragment bit is set, a value for activating the reception stop signal is written to the signal port, and the reception operation is stopped (step S1005). Then, the time corresponding to the MAC header is subtracted from the stored value of the NAV length, and the timer is started using the value as the expiration time (step S1007). Then, the value of the duration field (ie, NAV) included in the received MAC header is stored as a new NAV length (step S1009).
[0064]
In FIG. 11, when receiving an ACK frame from the digital demodulation unit 13, the control unit 14 receives and analyzes the ACK frame, and determines whether the communication is not related to the own station (step S1101). If not related, a fragment bit is referred to from among them (step S1103). If the fragment bit is not set, a separately determined process such as ignoring the packet is performed. On the other hand, if the fragment bit is set, a value for activating the reception stop signal is written to the signal port, and the reception operation is stopped (step S1105). Then, the time corresponding to the ACK frame length is subtracted from the value of the duration field (that is, NAV) included in the ACK frame, and the timer is started using the value as the expiration time (step S1107).
[0065]
【The invention's effect】
As described above, according to the present invention, it is possible to reduce the power consumption of the wireless receiving module by suppressing unnecessary receiving operations. In particular, a battery-powered wireless terminal can be used for a long time despite being driven by a battery. In particular, in the prior art, at least only the level determination unit had to be operated for all packets, or at least the header information of all packets had to be read. By using this protocol, a receiving operation is not performed for an unnecessary packet, so that a great effect of reducing power consumption can be obtained.
[Brief description of the drawings]
FIG. 1 is a timing chart illustrating an operation of a wireless LAN system according to a first embodiment of the present invention.
FIG. 2 is a configuration diagram of an RTS frame used for a wireless LAN.
FIG. 3 is a configuration diagram of a CTS, an ACK frame, and a MAC header used for a wireless LAN.
FIG. 4 is a first configuration diagram of a wireless module according to an embodiment of the present invention.
FIG. 5 is a second configuration diagram of the wireless module according to the embodiment of the present invention.
FIG. 6 is a timing chart illustrating an operation of a wireless LAN system according to another embodiment of the present invention.
FIG. 7 is a timing chart illustrating an operation of a wireless LAN system according to another embodiment of the present invention.
FIG. 8 is a system configuration diagram of a wireless LAN system.
FIG. 9 is a flowchart illustrating an example of a control procedure performed by the control unit 14.
FIG. 10 is a flowchart illustrating an example of a control procedure performed by a control unit 14;
FIG. 11 is a flowchart illustrating an example of a control procedure performed by the control unit 14.
[Explanation of symbols]
10. Antenna
11 High frequency analog receiver
12 ... Analog to digital converter
13 Digital demodulation unit
14 ... Control unit
15 ... CPU
16 Power supply unit
17… Clock generator
21 ... Reception stop control signal
22 Power supply line
23: Clock supply line
31 ... First station
32 ... Second station
33 ... Access point
34 Wired network

Claims (10)

A wireless terminal device connectable to a wireless network,
Receiving means for waiting for an incoming radio signal and receiving the incoming signal;
Acquiring means for acquiring, from a packet received by the receiving means, time information and packet configuration information held by the packet;
When the packet is not addressed to the wireless terminal device, the wireless terminal device has a stopping unit that stops at least a part of functions of the wireless terminal device during a period calculated from the time information and the packet configuration information. Terminal device. The wireless terminal device according to claim 1, wherein the stopping unit stops waiting for an incoming call by the receiving unit. The wireless terminal device according to claim 2, wherein the stopping unit stops power supply to an electronic circuit included in the receiving unit. The wireless terminal device according to claim 2, wherein the stopping unit stops supplying a synchronization signal to an electronic circuit included in the receiving unit. A wireless communication system in which the transmitting and receiving terminal presents the expected time that the line is occupied to the third terminal in the exchanged data,
A wireless communication system, wherein a third terminal that has intercepted the data stops operation of a circuit that realizes a communication function for a period of an expected time when a line indicated by the data is occupied. A wireless terminal device conforming to the IEEE 802.11 standard,
A wireless terminal device, wherein, when a frame not addressed to the wireless terminal device is received, the operation of a wireless signal receiving circuit is stopped for a period corresponding to a network allocation vector indicated by the frame. A method for controlling a wireless terminal device that waits for an incoming radio signal by a receiving circuit and receives the incoming signal,
Obtaining, from the packet received by the receiving unit, time information and packet configuration information held by the packet;
When the packet is not addressed to the wireless terminal device, a period calculated from the time information and the packet configuration information includes a stop control step of stopping at least a part of the function of the wireless terminal device. A method for controlling a wireless terminal device. The control method for a wireless terminal device according to claim 7, wherein the stop control step stops waiting for an incoming call by the receiving unit. The control method for a wireless terminal device according to claim 8, wherein in the stop control step, power supply to an electronic circuit included in the receiving unit is stopped. The control method for a wireless terminal device according to claim 8, wherein the stop control step stops the supply of a synchronization signal to an electronic circuit included in the receiving unit.

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