JP5288459B2 - Beacon synchronization method and beacon synchronization program in wireless LAN system - Google Patents

Description

  The present invention relates to a beacon synchronization method and a wireless LAN terminal in a wireless LAN (Local Area Network) system in which beacons are periodically transmitted.

  There are two types of systems that build a wireless LAN network: an infrastructure mode and an ad hoc mode. In the infrastructure mode, an access point is installed, and broadcast information called a beacon is periodically transmitted from the access point. A wireless LAN terminal existing in the vicinity of an access point can check the beacon transmission timing by decoding a TBTT (Target Beacon Transmission Time) included in the beacon. TBTT is a beacon transmission timing time and is defined in IEEE 802.11. Based on this information, the wireless LAN terminal that transitions to the sleep state that is the power save mode enters the sleep state by predicting the next beacon transmission time, and can receive signals from the sleep state at the beacon prediction time timing. Transition to a wake state. When receiving the beacon, the wireless LAN terminal transitions to the sleep state again, so that unnecessary wake time can be reduced and a power saving effect can be obtained.

  However, if the accuracy of the beacon transmitted by the access point is poor, the beacon transmission interval gradually increases, and the beacon timing deviates from the predicted beacon timing notified by the TBTT, the wireless LAN terminal transmits a beacon. Wake up until it can be received.

FIG. 6 is a timing diagram for explaining the above phenomenon. FIG. 6 (1) shows the actual transmission timing of the beacon, and the beacon is transmitted with the transmission interval gradually deviating gradually from T _R0 , T _R1 , T _R2 ,. FIG. 6B is a beacon timing predicted by the wireless LAN terminal based on TBTT. The beacon synchronization timing is set so that the wireless LAN terminal can receive a beacon at a time interval T _S. FIG. 6 (3) shows the wake time of the wireless LAN terminal. The wireless LAN terminal has already set the beacon timing T _S from the TBTT, wakes up ΔT time before the time T _S to receive the next beacon, and has received the beacon transmitted after T _R0 time Return to sleep at that point. Therefore, the wireless LAN terminal has been woken for (T _RO −T _S ) + ΔT = T _W1 time. However, since the subsequent beacon transmission timings T _R1 , T _R2 ,... Gradually increase as T _R0 <T _R1 <T _R2 ,..., The beacon can be received after wake-up before ΔT time. T _W2 , T _W3 , and so on become T _W1 <T _W2 <T _W3 ..., And the wake time gradually increases. As described above, since the wake is performed at the beacon synchronization timing set first, the wake time is gradually increased, leading to an increase in power consumption.

In Cited Document 1, when the accuracy of the reference clock is not sufficient, in order to enable synchronization with the peripheral station when returning from the sleep state, the positional deviation of the start position of the reference time and the speed of clock advancement are described. It is disclosed that two kinds of synchronization processing, that is, the synchronization of the data is performed.
JP 2005-286998 A

  An object of the present invention is to provide a beacon synchronization method and a wireless LAN terminal in a wireless LAN system that can shorten the wake time.

  In the first aspect of the present invention, a beacon in which a wireless LAN terminal transmits a beacon synchronization timing for the wireless LAN terminal to enter a wake mode after a certain period of time has elapsed from the time of belonging processing to the access point. Synchronization processing is performed according to the transmission timing.

  In the second aspect of the present invention, an upper limit value of the wake time is provided, and when the wake time exceeds the upper limit value, the beacon synchronization timing for the wireless LAN terminal to enter the wake mode is assigned. The synchronization processing is performed in accordance with the transmission timing of the beacon transmitted by the access point that has performed.

  In the wireless LAN system in which beacons are periodically transmitted, the present invention forcibly executes synchronization processing after a certain time after performing beacon synchronization for an access point whose beacon period is not constant, or By forcibly executing the synchronization process when the time exceeds the upper limit value, the wake time for receiving a beacon from the access point can be shortened.

  Next, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a block diagram of a main part of a wireless LAN terminal according to the first embodiment of this invention. The wireless LAN terminal 1A includes a wake timing control unit 11, a synchronization timer 12, and a wireless control unit 13. Access point 2 holds TBTT 21.

  The wake timing control unit 11 obtains the TBTT 21 included in the beacon transmitted from the access point 2. The wake timing control unit 11 determines a wake timing (beacon synchronization timing) based on the acquired information, and notifies the radio control unit 13 of the wake timing. The wireless control unit 13 performs attribution processing and switches the wake state / sleep state in synchronization with reception of a beacon based on information from the wake timing control unit 11. In addition, the synchronization timer 12 is activated when the wireless control unit 13 sets the wake timing. When the preset timer time elapses and the synchronization timer 12 times out, the wake timing control unit 11 notifies the radio control unit 13 to perform synchronization processing. The wireless control unit 13 performs a synchronization process that matches the beacon synchronization timing with the timing of the beacon transmitted by the access point 2.

  Next, the operation of this embodiment will be described with reference to the flowchart of FIG. When the wake timing control unit 11 receives the beacon transmitted from the access point 2, the wireless control unit 13 performs attribution processing for the access point 2 (step 101). In the belonging process, a probe request (Probe Request) is transmitted to inquire about the presence or absence of a wireless cell (access point) existing in the vicinity. If there is a corresponding wireless cell, a response is received from the access point, and then authentication processing of the wireless section, a connection request to the access point are performed, and it belongs to the access point. The wake timing control unit 13 confirms the TBTT 21 included in the beacon in the belonging process (step 102). Then, the beacon synchronization timing (wake timing) is confirmed and notified to the wireless control unit 13 (step 103). After starting the synchronization timer 12 (step 104), the wireless control unit 13 causes the wireless LAN terminal 1 to transition to the sleep state (step 105). The wireless control unit 13 determines whether or not the next beacon synchronization timing has come (step 106). When the beacon synchronization timing is reached, wake is performed (step 107), and after receiving the beacon (step 108), the mode transits to the sleep mode again (step 109). After sleep, the wake timing control unit 11 determines whether the synchronization timer 12 has timed out (step 110). If the synchronization timer 12 has not timed out, the process returns to step 106, wakes up again at the beacon synchronization timing (step 107), and receives a beacon (step 108). When the synchronization timer 12 times out, the wireless control unit 13 performs a synchronization process that matches the beacon synchronization timing currently held by the wireless LAN terminal 1 with the transmission timing of the beacon transmitted by the access point 2 (step 111). For example, scanning is performed only for the access point 2 to which it belongs, a beacon is acquired, the TBTT 21 included in the beacon is confirmed, and set as a new beacon synchronization timing.

  In this embodiment, a beacon synchronization timer value is set in advance in the wireless LAN terminal 1A. This beacon synchronization timer value is the time from the time of belonging to a certain access point until beacon synchronization is established again, and an area for storing the beacon synchronization timer value is provided in a storage unit such as a ROM (Read Only Memory) inside the terminal. A parameter may be set so that the user can change the resynchronization time depending on the accuracy of the beacon transmitted by the access point.

[Second Embodiment]
FIG. 3 is a block diagram of the main part of the wireless LAN terminal according to the second embodiment of the present invention. The wireless LAN terminal 1B includes a wake timing control unit 14, a synchronization timer 15, a wireless control unit 16, and memories 17 and 18. Access point 2 holds TBTT 21.

  Similar to the first embodiment, the TBTT 21 included in the beacon transmitted from the access point 2 is obtained by the wake timing control unit 14 of the wireless LAN terminal 1B, and the wake timing control unit 14 wakes up based on the obtained information. The timing is determined and notified to the wireless control unit 16. The wireless control unit 16 performs attribution processing, and switches between wake / sleep in synchronization with the beacon based on information from the wake timing control unit 14. The wake time measuring unit 15 measures the wake time for each wake. When the measured wake time exceeds the wake time upper limit value set in advance in the memory 17, the wake timing control unit 14 notifies the radio control unit 16 to perform synchronization processing. The wireless control unit 16 performs the same synchronization process as in the first embodiment.

  Next, the operation of this embodiment will be described with reference to the flowchart of FIG.

  In the first embodiment, as described with reference to FIG. 2, when the wake timing control unit 14 receives a beacon transmitted from the access point 2, the radio control unit 16 performs attribution processing for the access point 2. In step 201, the wake timing control unit 14 confirms the TBTT included in the beacon in the belonging process (step 202). The wireless control unit 16 sets the confirmed timing as a beacon synchronization timing (wake timing) inside (step 203), and transitions to a sleep state (step 204). The wireless control unit 16 determines whether or not the next beacon synchronization timing has come (step 205). When the beacon synchronization timing comes, the wireless control unit 16 wakes up (step 206) and receives a beacon (step 207). At this time, the wake timing control unit 14 stores in the memory 18 the wake time measured by the wake time measurement unit 15 until the beacon is received (step 207) after the transition to the wake mode (step 206). Every time (step 208), a transition is made to the sleep mode (step 209). Thereafter, the wake timing control unit 14 determines whether or not the wake time stored in the memory 18 has exceeded the upper limit value stored in the memory 17 (step 210). If the upper limit is not exceeded, the process returns to step 205, and when the beacon synchronization timing comes, wake (step 206) and receive the beacon (step 207). If the wake time exceeds the upper limit value, the same synchronization process as in the first embodiment is performed, the TBTT included in the beacon is confirmed, and a new beacon synchronization timing is set (step 211).

Next, specific operation examples of the first and second embodiments will be described with reference to FIG. FIG. 5 (1) shows the actual transmission timing of the beacons, and the beacons are transmitted with the transmission intervals gradually deviating gradually from T _R0 , T _R1 , T _R2 ,. FIG. 5 (2) shows the beacon timing predicted by the wireless LAN terminals 1A and 1B based on TBTT. The beacon synchronization timing is set so that the wireless LAN terminals 1A and 1B can receive beacons at the time interval T _S1 . FIG. 5 (3) shows the wake time of the wireless LAN terminals 1A and 1B. The wireless LAN terminals 1A and 1B have already set the beacon timing to T _S1 from TBTT, and wake up ΔT time before T _S time to receive the next beacon,
_When the beacon transmitted after the _RO time can be received, it returns to the sleep state. Therefore, the wireless LAN terminals 1A and 1B are waked for (T _RO −T _S1 ) + ΔT = T _W1 time. However, since the subsequent beacon transmission timings T _R1 , T _R2 , and T _R3 gradually increase as T _R0 <T _R1 <T _R2 <T _R3 , the time until the beacon can be received after wake-up before ΔT time. T _W2 , T _W3 , T _W4 , and T _W1 <T _W2 <T _W3 <T _W4 , and the wake time gradually increases. However, the synchronization process when the transmission interval of the beacon of T _R4 (step 111 or step 211) is performed, beacon synchronization timing, the access point 2 is the timing of the beacons transmitted by the next wake time T _W5 becomes smaller.

  In addition, although the method of achieving synchronization for every beacon reception can be considered, this method may increase the scale of processing.

  According to the present embodiment, since the wireless LAN terminal predicts the wake timing based on the TBTT frame at the time of synchronization processing, the wake time can be minimized. The synchronization processing time can be minimized by performing the synchronization processing only on the belonging ESSID and channel. Therefore, depending on the beacon transmission interval, the synchronization process ends before the next beacon is transmitted, and the wireless LAN terminal can wake up with a new beacon synchronization timing, so the wake time can be shortened without missing a beacon. can do.

  The operation of the wireless LAN terminal shown in FIGS. 2 and 4 is performed by recording a program for realizing the operation on a computer-readable recording medium and reading the program recorded on the recording medium into the computer. May be executed. The computer-readable recording medium refers to a recording medium such as a flexible disk, a magneto-optical disk, and a CD-ROM, and a storage device such as a hard disk device built in a computer system. Further, the computer-readable recording medium is a medium that dynamically holds the program for a short time (transmission medium or transmission wave) as in the case of transmitting the program via the Internet, and in the computer serving as a server in that case Such as a volatile memory that holds a program for a certain period of time.

FIG. 1 is a block diagram of a wireless LAN terminal according to the first embodiment of the present invention. FIG. 2 is a flowchart showing the operation of the wireless LAN terminal according to the first embodiment. FIG. 3 is a block diagram of a wireless LAN terminal according to the second embodiment of the present invention. FIG. 4 is a flowchart showing the operation of the wireless LAN terminal according to the second embodiment. FIG. 5 is a timing chart showing an operation example of the first and second embodiments. FIG. 6 is a timing chart showing the operation of the conventional wireless LAN system.

Explanation of symbols

1A, 1B Wireless LAN terminal 2 Access point 11 Wake timing control unit 12 Synchronization timer 13 Wireless control unit 14 Wake timing control unit 15 Wake timing time measurement unit 16 Wireless control unit 17, 18 Memory 21 TBTT
101-111, 201-211 steps

Claims (2)

A beacon synchronization method performed in a wireless LAN terminal of a wireless LAN system in which beacons are periodically transmitted,
A step of setting a beacon synchronization timing based on TBTT included in the beacon and starting a synchronization timer during the belonging process to the access point;
Transitioning the mode of the wireless LAN terminal to a sleep mode;
Determining whether the current time is the beacon synchronization timing;
If the current time is the beacon synchronization timing, the step of transitioning the mode of the wireless LAN terminal to a wake mode;
Receiving a beacon, transitioning the mode of the wireless LAN terminal to a sleep mode;
Determining whether a predetermined time has elapsed and the synchronization timer has timed out;
When the synchronization timer times out, performing a synchronization process that matches the beacon synchronization timing to the transmission timing of the beacon transmitted by the access point that performed the attribution process;
Have
If the synchronization timer has not timed out, the beacon synchronization method returns to the step of determining whether the process is the beacon synchronization timing. A beacon synchronization program for causing a computer to execute beacon synchronization performed in a wireless LAN terminal of a wireless LAN system in which beacons are periodically transmitted,
During the process of belonging to the access point, a procedure for setting the beacon synchronization timing based on the TBTT included in the beacon and starting the synchronization timer;
A procedure for transitioning the mode of the wireless LAN terminal to a sleep mode;
A procedure for determining whether the current time is the beacon synchronization timing;
If the current time is the beacon synchronization timing, a procedure for transitioning the mode of the wireless LAN terminal to a wake mode;
When receiving a beacon, a procedure for transitioning the mode of the wireless LAN terminal to a sleep mode;
A procedure for determining whether a predetermined time has elapsed and the synchronization timer has timed out;
When the synchronization timer times out, a procedure for performing a synchronization process that matches the beacon synchronization timing with the transmission timing of the beacon transmitted by the access point that has performed the attribution process;
Have
The synchronization If the timer has not timed out, beacon synchronization program for executing the pre-Symbol beacon synchronization back to the timing determining whether instructions processed in a computer.

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