JP2010114671A - Wireless lan terminal, wireless lan system, state transition method and control program of wireless lan terminal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: a wireless LAN (local area network) terminal capable of appropriately receiving a beacon even though there is an error between a beacon transmission cycle which a wireless LAN base station counts and a beacon receiving cycle which a wireless LAN terminal counts, and consuming no useless power consumption; a wireless LAN system; and a state transition method of the wireless LAN terminal and a control program. <P>SOLUTION: The wireless LAN terminal includes: a communication part for transmitting and receiving data with the wireless LAN base station; a control part for transiting the communication part from a power saving state to a communicatable at a timing to receive the beacon cyclically transmitted from the wireless LAN base station; a beacon receiving cycle difference-storing part for storing a displacement between a time interval stored in the beacon by multiple beacon receptions and a time interval of beacon reception; and an activation cycle-setting part for setting the activation cycle for transiting from the power saving state to the communication-capable-state on the basis of the displacement of the time interval stored in the beacon receiving cycle difference-storing part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wireless LAN terminal, a wireless LAN system, and a wireless LAN terminal state transition method. In particular, the present invention relates to a wireless LAN terminal having a power save mode in which a beacon is received by intermittently switching between a communicable state capable of receiving a beacon periodically transmitted from a wireless LAN base station and a power saving state.

  Some wireless LAN terminals have a power save mode in addition to an active mode in which power is always supplied to a transmission / reception circuit. This power save mode is a state in which a wireless LAN terminal can communicate from a power saving state (also called a sleep state) (awake state) in accordance with the period of beacons periodically sent from a wireless LAN base station (access point). In other words, when a communication is necessary, communication is performed, and when communication is not necessary, power consumption is reduced by returning to a power saving state again.

  In Patent Document 1, in the power save mode, the wireless LAN base station (access point) uses a wireless channel to beacon to transmit a beacon because other wireless LAN terminals use it for communication, so the transmission of the beacon signal is delayed. In order to receive a beacon signal even when the beacon interval (BI) value included in the transmitted beacon is different from the beacon period actually received by the wireless LAN terminal, the beacon signal period is measured multiple times. In addition, it is described that a representative value is determined from a plurality of measurement data and set as a set value of a beacon signal cycle.

Patent Document 2 also provides a beacon delay time estimation means for receiving a beacon and reducing power consumption even when beacon communication is delayed, and the delay time estimated by the delay time estimation means. Accordingly, there is described a wireless LAN terminal that makes a transition from an awake (communicable) state to a power saving state.
JP 2007-104033 A JP 2006-310909 A

  The following analysis is given in the present invention. For beacon transmission delays due to communication complications, beacons are measured multiple times as described in Patent Document 1 and Patent Document 2, and errors due to beacon transmission delays due to communication complications from multiple measurements. It is possible to modify However, according to the inventor's study, even if there is no complication of communication, there is a difference in the time advance between the two due to the accuracy of the timer that measures the time of the wireless LAN base station and the timer that measures the time of the wireless LAN terminal. If so, the beacon cannot be received properly.

  An object of the present invention is to receive beacons appropriately even if there is an error between the beacon transmission cycle timed by the wireless LAN base station and the beacon reception cycle timed by the wireless LAN terminal, and wasteful consumption. An object of the present invention is to provide a wireless LAN terminal, a wireless LAN system, and a wireless LAN terminal state transition method that do not consume power.

  A wireless LAN terminal according to one aspect of the present invention includes a communication unit that transmits and receives data to and from a wireless LAN base station, and the communication at a timing at which a beacon periodically transmitted from the wireless LAN base station is to be received. A beacon reception cycle for storing a shift between a time interval at which the beacon is received a plurality of times and a time interval at which the beacon is received A difference storage unit, and an activation cycle setting unit that sets an activation cycle for transitioning from the power saving state to the communicable state based on a time interval shift stored in the beacon reception cycle difference storage unit.

  In addition, a wireless LAN system according to another aspect of the present invention includes a wireless LAN base station that periodically transmits a beacon including time information, and a transition from a power saving state to a communicable state at a timing at which the beacon is to be received. A wireless LAN system including the wireless LAN terminal that receives the beacon, wherein the wireless LAN terminal includes a beacon transmission cycle timed by the wireless LAN base station from time information included in the beacon and a time when the beacon is received. An error from the beacon reception cycle timed by the wireless LAN terminal is obtained, and a cycle for transition from the power saving state to the communicable state is determined based on the error.

  According to another aspect of the present invention, a wireless LAN terminal state transition method receives a beacon by transitioning from a power saving state to a communicable state at a timing at which a wireless LAN base station should periodically receive a beacon. A wireless LAN terminal state transition method, comprising: a beacon transmission period timed by the wireless LAN base station from a time information included in the beacon and a time when a beacon is received; and a beacon reception period timed by the wireless LAN terminal. An error is obtained, and based on the error, the wireless LAN terminal determines an activation period for transitioning from the power saving state to the communicable state and receives the beacon.

  A wireless LAN terminal control program according to still another aspect of the present invention is a wireless LAN terminal control program including a communication unit that performs transmission / reception processing including reception of a periodically transmitted beacon. Time data recorded at the time of receiving the first beacon, time data recorded at the second beacon, time data timed at the time of receiving the second beacon, From the number of beacons received before receiving the second beacon from the beacon, how to advance the time per cycle recorded in the beacon, and how to advance the time per cycle recorded by the wireless LAN terminal And periodically transitioning the communication unit from a power saving state to a communicable state capable of receiving the beacon based on the processing for obtaining the periodic difference Executing the management, to the wireless LAN terminal.

  According to the present invention, even if there is an error in the time advance between the time measured by the wireless LAN base station that periodically transmits beacons and the time measured by the wireless LAN terminal that receives the beacon signal, Since the LAN terminal receives a beacon based on the time interval recorded in the beacon and the time interval when the beacon is received, the frequency of loss of synchronization can be reduced.

  Embodiments of the present invention will be described with reference to the drawings as necessary. In addition, drawing quoted in description of embodiment and the code | symbol of drawing are shown as an example of embodiment, and, thereby, the variation of embodiment by this invention is not restrict | limited.

  For example, as shown in FIG. 1, a wireless LAN terminal 2 according to an embodiment of the present invention periodically transmits data from and to a wireless LAN base station 1 and a communication unit 3 that transmits and receives data to and from the wireless LAN base station 1. The control unit 4 that causes the communication unit 3 to transition from the power saving state to the communicable state at the timing when the beacon to be received is received, the interval between the times when the beacon is received and recorded in the beacon, and the time when the beacon is received A beacon reception cycle difference storage unit 8 that stores a deviation from the interval and a start cycle for transitioning from the power saving state to the communicable state are set based on the difference in time interval stored in the beacon reception cycle difference storage unit 8. And an activation cycle setting unit 6.

  Further, for example, as shown in FIG. 1, the wireless LAN terminal 2 according to the embodiment of the present invention stores a beacon reception time difference storage that stores a plurality of times a difference between a time when the beacon is expected to be received and the time when the beacon is actually received. The startup time for setting the startup time, which is the time from the transition to the communicable state to the return to the power saving state based on the distribution of the reception time deviation stored in the unit 7 and the beacon reception time difference storage unit 7 The setting part 5 may be provided. According to the above configuration, starting from transitioning to the communicable state to returning to the power saving state again according to the distribution of the difference in reception time between the time when the beacon is expected to be received and the time when the beacon is actually received Since the time can be determined, there is no problem that the activation time is too long and power consumption is wasted, or the activation time is too short and a beacon to be received cannot be received. Even when the beacon transmission time is delayed due to communication congestion or the like, an appropriate activation time can be set due to variations in delay.

  Furthermore, in the wireless LAN terminal 2 (FIG. 1) according to the embodiment of the present invention, the activation time setting unit 5 is given in advance an expected probability of succeeding in receiving a beacon with respect to a difference in beacon transmission time. The activation time setting unit 5 sets the activation time so as to satisfy the expected probability with reference to the distribution of the reception time deviation (see, for example, FIG. 6). With the above configuration, the startup time is set so that the expected probability is satisfied with reference to the distribution of the reception time deviation, so the expected probability set in advance is whatever the distribution of the reception time deviation is. Startup time can be set to satisfy Accordingly, it is possible to set an appropriate start-up time that takes into account the congestion state of communication and the like compared to the case where the start-up time is simply set based on the average value of the reception time shift and the maximum value of the shift.

  Further, the wireless LAN terminal 2 (FIG. 1) according to the embodiment of the present invention, as shown in FIG. 3 and FIG. 5, is out of the threshold from the reception time deviation data stored in the beacon reception time difference storage unit 7. Based on the median after the data is removed, the timing for transition from the power saving state to the communicable state is determined. The power saving state is determined because the timing of transition from the power saving state to the communicable state is determined based on the median reception time excluding data that is clearly shifted in reception time due to communication complications. Can be synchronized with beacon reception timing with high accuracy.

  Further, as shown in FIG. 4, the wireless LAN terminal 2 (FIG. 1) according to the embodiment of the present invention is within a range where communication with the base station can be performed from outside the service area when the power is turned on (Yes in step S301). When the movement time is detected (Yes in step S302), or when a certain time has elapsed since the activation time was set in the area (Yes in step S304), the activation time setting unit 5 resets the activation time. Set (step S309). According to the above configuration, since the startup time is reset when moving from outside the service area to within the service area, it is appropriate when there is a possibility that the communication environment may change significantly due to movement from the service area outside the service area, such as a corporate LAN. You can set the startup time.

  In addition, when the wireless LAN terminal 2 (FIG. 1) according to the embodiment of the present invention is turned on or when a certain time has elapsed since the activation time was set, the activation time setting unit 5 is activated. The time may be reset. That is, when the frequency of movement from the outside of the service area to the outside of the service area is low, such as a home LAN, the setting process of the activation time can be simplified by omitting the detection of the movement from the outside of the service area to the service area.

  Further, as shown in FIG. 4, the wireless LAN terminal 2 (FIG. 1) according to the embodiment of the present invention records the activation period set by the activation period setting unit 6 together with identification information unique to the wireless LAN base station. When the wireless LAN base station is a base station recorded in the base station-specific activation cycle storage unit 9 when communication with the wireless LAN base station 1 is started (Yes in step S305). Sets the activation cycle for the base station stored in the activation cycle storage unit 9 for each base station as the activation cycle of the wireless LAN terminal. Even if it is necessary to review the activation time at any time depending on the communication status, the activation period is considered to be fixed for each wireless LAN base station. Therefore, the activation period is the same as the wireless LAN base station for which the activation period has been set in the past. If it is a base station, resetting the start cycle can be simplified by setting again the start cycle set in the past stored in the start cycle storage unit 9 for each base station.

  Furthermore, the wireless LAN system according to an embodiment of the present invention, for example, as shown in FIG. 1, saves power at a wireless LAN base station 1 that periodically transmits a beacon including time information and a timing at which a beacon should be received. Wireless LAN terminal 2 that receives a beacon by transitioning from a state to a communicable state, the wireless LAN terminal 2 uses a wireless LAN base station from time information included in the beacon and a time when the beacon is received. An error between the beacon transmission cycle timed by 1 and the beacon reception cycle timed by the wireless LAN terminal is obtained, and the cycle for transition from the power saving state to the communicable state is determined based on the error (for example, step S208 in FIG. 3). , S210, S211). According to the above configuration, the wireless LAN terminal calculates an error between the beacon transmission cycle timed by the wireless LAN base station 1 from the time information included in the beacon and the time when the beacon was received and the beacon reception cycle timed by the wireless LAN terminal. Since the period of transition from the power saving state to the communicable state is determined based on the obtained and error, synchronization can be achieved with high accuracy.

  In addition, the wireless LAN system according to the embodiment of the present invention, for example, as shown in FIGS. 1 and 3, the wireless LAN terminal 2 actually receives the beacon a plurality of times and actually starts receiving the beacon. The time delay distribution of the time when the signal is received is obtained, and the activation time that is the time from the transition to the communicable state to the return to the power saving state is set so that the time delay can be relieved with a preset probability (step S214). S215) When the beacon cannot be received during the activation time, the state transits to the power saving state without waiting for the reception of the beacon. According to the above configuration, as shown in FIG. 5, a beacon is received a plurality of times, a time delay distribution of the time when the beacon is actually received is obtained from a time when the beacon is expected to be received, and the time delay is set in advance based on the distribution. Since the activation time is set so that the time delay can be remedied with the probability, the activation time can be set in accordance with the distribution of the time delay.

  Further, the wireless LAN system according to the embodiment of the present invention is, for example, as shown in FIG. 4, when the wireless LAN terminal is turned on (Yes in step S301), the wireless LAN system cannot communicate with the wireless LAN base station. When it is detected that the mobile terminal has moved to a communicable area from the terminal (Yes in step S302), or when a predetermined time has elapsed after setting the activation time in the area (Yes in step S304), the activation time is reset. You may do. According to the above configuration, since the activation time is reset when necessary, the activation time can be appropriately updated in accordance with the normal state of wireless congestion and the congestion state of communication.

  Furthermore, the wireless LAN terminal state transition method according to an embodiment of the present invention shifts from a power saving state to a communicable state at a timing when a wireless LAN base station should receive a beacon periodically transmitted, as shown in FIG. A wireless LAN terminal state transition method for making a transition and receiving a beacon, wherein the beacon transmission cycle timed by the wireless LAN base station from the time information included in the beacon and the time at which the beacon is received and the beacon timed by the wireless LAN terminal An error with respect to the reception cycle is obtained (step S210), and based on the error, the activation period in which the wireless LAN terminal transitions from the power saving state to the communicable state is determined and the beacon is received (step S211). With the above configuration, even if there is an error in how the time of the wireless LAN base station and the time of the wireless LAN terminal are measured, the activation period is set based on the error, and therefore synchronization is lost as shown in FIG. There is no fear.

  As shown in FIG. 3, the wireless LAN terminal state transition method according to an embodiment of the present invention has a time delay distribution of a time when a beacon is received a plurality of times and a beacon is actually received from a time when the beacon is expected to be received. The activation time, which is the time from the transition to the communicable state to the return to the power saving state so that the time delay can be remedied with a preset probability, is set (steps S214 and S215). If reception is not possible, the communication state is changed to the power saving state without waiting for reception of a beacon. With the above configuration, an appropriate activation time can be set in accordance with the beacon reception delay state.

  Further, as shown in FIG. 3, the wireless LAN terminal control program according to the embodiment of the present invention includes a wireless LAN terminal 2 including a communication unit 3 that performs transmission / reception processing including reception of periodically transmitted beacons. A control program, which is time data recorded in the first beacon (for example, T0 in equation (1)), time data (t0) timed when the first beacon is received, and data recorded in the second beacon. From the time data (T1), the time data (t1) timed when the second beacon is received, and the number of beacons (n1) received from the first beacon until the second beacon is received, Based on the recorded time advance per cycle and the difference between the time advance per time measured by the wireless LAN terminal 2 (step S210 in FIG. 3) and the cycle difference To execute the communication unit process for periodically transition to receivable communicable state the beacon from the power-saving state (step S211 in FIG. 3), to the wireless LAN terminal 2. That is, the control program is stored in, for example, the FLASH ROM 102 of FIG. The CPU 101 shifts the communication unit 3 from the power saving state to the communicable state by executing the control program.

  The wireless LAN terminal control program according to the embodiment of the present invention receives a beacon a plurality of times, obtains a time delay distribution of the time when the beacon is actually received from the time when the beacon is expected to be received, and is set in advance. A process of setting a start time (for example, step S214 in FIG. 3) that is a time from transition to the communicable state to return to the power saving state so that the time delay can be remedied with a probability, and a beacon during the start time If the wireless LAN terminal 2 cannot receive the beacon, it causes the wireless LAN terminal 2 to execute a process of shifting from the communicable state to the power saving state without waiting for reception of the beacon (for example, step S215 in FIG. 3). That is, the CPU 101 also performs a process of transitioning from the communicable state to the power saving state based on the control program of the FLASH ROM 102. Hereinafter, the present invention will be described in more detail with reference to the drawings based on examples.

  FIG. 1 is a block diagram illustrating the configuration of the wireless LAN system according to the first embodiment. In FIG. 1, a wireless LAN base station 1 and a wireless LAN terminal 2 communicate with each other wirelessly. Although only one wireless LAN base station 1 and one wireless LAN terminal 2 are shown in FIG. 1, there may be a plurality of wireless LAN base stations 1 and wireless LAN terminals 2. Here, the wireless LAN base station 1 is an access point that outputs a beacon, and the wireless LAN terminal is a terminal that receives the beacon. The wireless LAN terminal 2 includes a communication unit 3 that communicates with the wireless LAN base station 1, a control unit 4 that controls the entire wireless LAN terminal 2, an activation time setting unit 5, an activation cycle setting unit 6, and beacon reception. A time difference (Z1) storage unit 7, a beacon reception cycle difference (Z2) storage unit 8, and a base station-specific activation cycle storage unit 9 are provided.

  The communication unit 3 further includes an RF unit 31 and a baseband unit 32, and performs communication with the wireless LAN base station 1. In the power save mode, the activation time setting unit 5 again saves power when no beacon is received after the beacon can be received from the wireless LAN base station after transition from the power saving state to the communicable state. Set the startup time, which is the time to return to the state. In addition, in the power save mode, the activation cycle setting unit 6 sets a cycle for causing the wireless LAN terminal 2 to transition from the power saving state to the communicable state in order to receive a beacon transmitted from the wireless LAN base station 1.

  Also, the beacon reception time difference (Z1) storage unit 7 stores a difference between the time when the beacon is expected to be received and the time when the beacon is actually received for a plurality of times. The beacon reception cycle difference (Z2) storage unit 8 measures the time interval for transmitting the beacon measured by the wireless LAN base station included in the received beacon and the wireless LAN terminal 2 side at which the wireless LAN terminal 2 has received the beacon. The difference with the time interval is stored. Further, the base station activation cycle storage unit 9 stores the activation cycle set for each wireless LAN base station. The base station activation cycle storage unit 9 may be provided in the MAC address cache, identify the base station by the MAC address, and store the activation cycle for each MAC address.

  Further, the control unit 4 controls the entire wireless LAN terminal. In particular, even if the communication unit 3 is set from the power saving state to the communicable state for each activation cycle set by the activation cycle setting unit 6 and the activation time set by the activation time setting unit 5 has elapsed, Is not received, the communication unit 3 is set from the communicable state to the power saving state. The communicable state is a state in which transmission / reception with the wireless LAN base station 1 can be performed by the communication unit, and the power saving state is a state in which the operation of the communication unit 3 is stopped and power consumption is reduced. is there. In the power saving state, the power of the communication unit 3 may be turned off.

  Next, FIG. 2 shows an example of the hardware configuration of the wireless LAN terminal of the first embodiment. The wireless LAN terminal 2 includes a CPU 101 that controls the device, a RAM 105 that serves as a work area, a FLASH ROM 102 that stores a control program, a communication unit 3 that performs wireless LAN communication, a display unit 106 that displays various types of information, and a data input unit. It includes a key input unit 107 and performs communication with an external access point (wireless LAN base station 1). By the control program stored in the FLASH ROM 102, the wireless LAN terminal 2 functions as the wireless LAN terminal 2 that realizes the function shown in the block diagram of FIG. That is, according to the control program, the CPU 101 functions as the control unit 4, the activation time setting unit 5, and the activation cycle setting unit 6 in FIG. 1, and the FLASH ROM 102 and the RAM 105 are the beacon reception time difference (Z1) storage unit 7 and the beacon reception. It functions as a cycle difference (Z2) storage unit 8 and a base station specific startup cycle storage unit 9. In FIG. 2, the display unit and the key input unit are not indispensable, but are preferably mounted in order to provide a better user interface (UI).

  Next, the beacon reception time difference Z1 stored in the beacon reception time difference (Z1) storage unit 7 and the beacon reception cycle difference Z2 stored in the beacon reception cycle difference (Z2) storage unit 8 will be described here. . The beacon reception time difference Z1 is a difference between an expected value of time for receiving a beacon and a time for actually receiving a beacon. Ideally, the beacon is expected to be received at a predetermined cycle, but when other wireless LAN terminals or the like are using the frequency band that the wireless LAN base station intends to use, The beacon transmission is delayed until the frequency band becomes available. Therefore, a difference occurs between the expected value of the time for receiving the beacon and the time for actually receiving the beacon. This is stored in the beacon reception time difference (Z1) storage unit 7 as Z1.

Next, the beacon reception cycle difference Z2 will be described. The beacon transmitted by the wireless LAN base station (access point) includes time information timed by the wireless LAN base station. Therefore, by comparing the progress of the time information included in the beacon and the time measured by the wireless LAN terminal for each beacon reception period, the beacon transmission period timed by the wireless LAN base station and the wireless LAN terminal It is possible to recognize an error from the period in which the beacon to be timed is expected to be received. When the time recorded in the reference beacon is T0, the time measured by the wireless LAN terminal when the beacon is received is t0, the time recorded in the beacon received thereafter is T1, and the beacon is received If the time measured by the wireless LAN terminal is t1, and the total number of beacons received from the reference beacon is n1, the beacon reception cycle difference Z2 is
Z2 (n1) = {(T1-T0)-(t1-t0)} / n1 (Formula 1)
Can be obtained.

  FIG. 3 is a process flowchart in which the wireless LAN terminal 2 sets the activation cycle and activation time for beacon reception in the first embodiment. As an initial state, since neither the activation cycle nor the activation time is determined, it is assumed that both the “accuracy flag” and the “time flag” are “0”. The “accuracy flag” is a flag indicating whether or not it is necessary to set the activation cycle. If “0”, it is necessary to set the activation cycle. If “1”, The activation cycle has been set, and it is not necessary to set the activation cycle. The “time flag” is a flag indicating whether or not the activation time needs to be set. If “0”, it means that the activation time needs to be set. If so, it indicates that the startup time has already been set and does not need to be reset. In addition, the beacon transmission cycle is determined in advance excluding time errors. For example, it is assumed that a beacon is transmitted every second. Further, it is assumed that the initial values of n1 which is the counter of Z1 and n2 which is the counter of Z2 are both zero.

  First, in order to initialize the reception timing, beacons are continuously received until the number of samples becomes Y or more (step S202). Every time a beacon is received, a time difference Z1 from the temporarily determined beacon reception time is obtained and stored temporarily until the number of samples reaches Y (step S201). If the number of samples is equal to or greater than Y, the beacon reception timing is initialized (step S203). Specifically, after receiving a beacon with the number of samples Y, the expected beacon reception time is set so that the expected beacon reception time becomes 0 with reference to the smallest value in the distribution of Z1.

  When the initial setting is completed, the wireless LAN terminal thereafter records the time when receiving a beacon from the wireless LAN base station (access point), and calculates a difference Z1 from the expected beacon reception time (determined in step S203). And it memorize | stores in the beacon reception time difference (Z1) memory | storage part 7 (step S204). Moreover, 1 is added to n1 which is a counter of Z1. Next, in step S205, the “accuracy flag” and the “time flag” are checked, and the process branches depending on the state. If the setting of the start cycle has not been completed, the “accuracy flag” is “0”, so the process proceeds to step S206. If the start cycle has been set, but the start time needs to be set, the "accuracy flag" is "1" and the "time flag" is "0", so the process branches to step S213. To do. If both the start cycle and start time have been set and there is no need to review them, the “accuracy flag” and “time flag” are both “0”, so the process proceeds to “END” and the start cycle and start time are set. The setting process ends.

  In step S206, it is checked whether or not the time difference Z1 is equal to or less than the threshold value A. When the time difference Z1 exceeds the threshold value A, the beacon reception timing is deviated due to the reasons described above, such as wireless congestion and communication congestion, and is not used for setting the activation cycle. In this case, if the “time flag” is “0”, the process proceeds to the activation time setting process (step S213), but the “time flag” is “1” and the activation time has already been set. If so, the process moves to step S204 and waits for the reception of the next beacon. If it is less than or equal to the threshold A, it is assumed that a beacon has been received at regular timing, and processing proceeds to step S208.

  In step S <b> 208, the period difference Z <b> 2 is obtained by the above-described equation (1). The obtained period difference Z <b> 2 is recorded in the beacon period difference (Z <b> 2) storage unit 8. Moreover, 1 is added to n2 which is a counter of Z2.

  In step S209, it is checked whether n2 which is a counter of Z2 is equal to or greater than a specified value B. If n2 is less than B, the process returns to step S204 and waits for reception of the next beacon. If n2 is greater than or equal to B, the process proceeds to step S210, and the start cycle is set.

  In step S210, the median value of sampled Z1 and the average value of Z2 are calculated. In step S211, the activation cycle determined in advance is corrected by the average value of Z2 obtained in step S210. In other words, the beacon transmission cycle itself is determined in advance, but the beacon transmission cycle timed by the wireless LAN base station (access point) and the period at which the wireless LAN terminal expects beacon transmission are counted by the wireless LAN base station. And the progress of timing on the wireless LAN terminal side, there may be a difference in synchronization due to an error in timer accuracy. In this embodiment, the start cycle is corrected in step S211. There is a low possibility that synchronization loss will occur between the LAN base station and the wireless LAN terminal. In step S211, the timing at which the wireless LAN terminal transitions from the power saving state to the communicable state is determined based on the median value of Z1. Therefore, it is possible to determine the timing of transition from the power saving state to the communicable state by sufficiently synchronizing with the beacon reception timing. For example, if the median value of Z1 is +0.1 seconds and the average value of Z2 is -0.02 seconds with respect to the beacon interval of 1 second, the activation time is set to 0.1 seconds with respect to the reference value. Reset the startup period to 0.98 seconds. By doing so, beacon transmission from the wireless LAN base station and activation time of the wireless LAN terminal can be synchronized in an ideal environment regardless of the correlation time difference between the internal clocks of the wireless LAN base station and the wireless LAN terminal.

  In step S212, since the setting of the activation cycle is completed, the accuracy flag is set to 1, and the MAC address of the wireless LAN base station and the set activation cycle value are stored in the activation cycle storage unit 9 for each base station.

  Here, referring to FIG. 5, the effect of the present invention by synchronizing the activation times and setting the activation period accurately based on the error between the time measurement of the wireless LAN base station and the time measurement of the wireless LAN terminal is a conventional example. This will be explained in comparison with FIG. 5A shows a case where the beacon interval is longer than the expected value. In the conventional technique of FIG. 5 (a1), synchronization is initially established, but since the beacon period is longer than the expected value, the beacon reception timing is gradually delayed, and synchronization is not performed in B14. On the other hand, if the startup time is long, it is possible to receive beacons as in B15 and B16, but as long as the synchronization is shifted, either cannot be received. In addition, if the startup time is increased, power consumption increases.

  On the other hand, according to the present invention, as shown in FIG. 5 (a2), if the start cycle is accurately set based on the error between the time measurement of the wireless LAN base station and the time measurement of the wireless LAN terminal, the probability of loss of synchronization is remarkably high. Decrease.

  Similarly, as shown in FIG. 5 (b1), when the beacon interval is shorter than the expected value, in the conventional technique, once synchronization is lost, it is impossible to synchronize even if the activation time is extended. . On the other hand, as shown in FIG. 5 (b2), if the activation period is set accurately based on the error between the time measured by the wireless LAN base station and the time measured by the wireless LAN terminal, the probability of loss of synchronization is significantly reduced.

  Returning to FIG. 3, the step of setting the activation time from step S213 will be described. In step S213, it is determined whether or not the value of the sample number n1 is C or more. When the sample number n1 is less than C, the process returns to step S204 and waits for reception of the next beacon. If the number of samples n1 is C or more, the process proceeds to step S214.

  In step S214, the activation time is set. The length of the activation time is determined so as to satisfy a predetermined expected probability D% in consideration of the variation of Z1 indicating the difference between the time when the beacon is expected to be received and the time when the beacon is actually received. The setting of the expected probability D% and the activation time will be described with reference to FIG. FIG. 6A shows a conventional method for determining the activation time, and FIG. 6B shows a method for determining the activation time according to the present invention. If there is no delay in the reception time of the beacon, the frequency should concentrate on the activation time 0. However, as described above, when another wireless LAN terminal or the like uses a frequency band in which the wireless LAN base station intends to transmit a beacon, the transmission of the beacon is delayed until the channel becomes free. Therefore, as communication becomes congested or the wireless environment worsens, the variation in beacon reception time increases, and even if there is a variation in reception time, in order to receive beacons with a certain probability, the wireless LAN terminal The start-up time, which is the time from when the communicable state is reached to when the power-saving state is restored, must be lengthened. In the conventional technique of FIG. 6A, since the magnitude of the beacon reception time shift, that is, the quality of the wireless environment is not taken into consideration, if the activation time is set according to the bad wireless environment, the wireless environment If it is good, the startup time is too long, and extra power is consumed.

  On the other hand, as shown in FIG. 6B, the probability of satisfying a predetermined expected probability D% according to the variation in Z1 indicating the difference between the time when the beacon is expected to be received and the time when the beacon is actually received. Since the start-up time is set so that the beacon can be received, the optimal start-up time can be set. That is, in both cases where the wireless environment is bad and good, the start-up time is set so as to satisfy the expected probability D%. Therefore, when the wireless environment is good, the start-up time can be shortened. The power can be lowered. On the other hand, when the wireless environment is bad, the activation time is set so as to satisfy the expected probability D% even if the wireless environment is bad. Therefore, even if the wireless environment is bad, a beacon can be received with a certain probability. I can expect.

  Returning to FIG. 3, the description will be continued. In step S214, a specific method for determining the activation time may directly obtain the activation time satisfying the expected probability D% from the variation of Z1, or obtain the distribution function of Z1 from the variation of Z1 to obtain the distribution of Z1. The activation time may be obtained from the function and the expected probability D%. If the activation time is found in step S214, the activation time setting unit 5 changes the activation time setting in step S215, and thereafter, the control unit 4 activates according to the activation time set by the activation time setting unit 5. When the beacon cannot be received within the time, control is performed to shift from the communicable state to the power saving state. Finally, in step S216, the “time flag” is changed from “0” to “1”, and the activation time changing process is terminated.

  The start cycle, start time, and timing for transition from the power saving state to the communicable state are set at the start cycle first, then the timing for transition to the communicable state is determined, and finally the start time is set. It is originally desirable to set it. However, since Z2 for determining the activation cycle, Z1 median for determining the timing for transition to the communicable state, and the magnitude of the activation time setting value are Z2 << Z1 <“activation time setting value”, FIG. As shown in the flowchart of FIG. 3, even if the “start cycle”, “start time”, and “timing to transition to the communication state” are simultaneously set in parallel, there is no big problem.

  In addition, since the error in the activation cycle is considered as an individual difference in hardware, and changes with time are unlikely to occur, in step S212, the activation cycle error is combined with the MAC address of the wireless LAN base station (access point). By storing the set value in the base station-by-base station activation cycle storage unit 9, it is possible to reduce the subsequent calculations.

  As described above, the activation cycle and the activation time can be set by the procedure described with reference to FIG. However, when moving to a different wireless LAN base station area, or when the wireless environment has changed since the activation time was set, it is necessary to review the set activation cycle and activation time. FIG. 4 is a flowchart for reviewing the setting of the start cycle and start time in such a case.

  In FIG. 4, first, in step S301, it is checked whether or not the power is newly turned on. If the power is newly turned on, the activation cycle and activation time are set or reset, and the process proceeds to step S305. If the power has not been newly turned on, the process proceeds to step S302, and it is checked whether or not the mobile station has moved from a location outside the range where communication with the wireless LAN base station is impossible to a range where communication with the base station is possible. When moving to the vicinity, the activation cycle and activation time are set or reset, and the process proceeds to step S305. If it has not moved to the vicinity, the process proceeds to step S303, and it is checked whether communication with the wireless LAN base station is not possible. If it is out of the service area, the process returns to step S302, and the loop of steps S302 and S303 is repeated until it moves into the service area. If it is within the range, the process proceeds to step S304.

  In step S304, it is checked whether or not a fixed time has elapsed since the previous activation time was reviewed. Even if the area is always within range, the radio conditions are not always constant, so it is desirable to evaluate at regular intervals. In step S305, it is confirmed whether or not there is cache data of the wireless LAN base station stored in association with the MAC address of the wireless LAN base station in the base station activation period storage unit 9 when the activation period is set. If the wireless LAN base station activation cycle data exists in the MAC address cache, the “accuracy flag” is set to “1”, the “time flag” is set to “0”, and n1 is set to 0, step S307 In step S309, the timer accuracy and activation time setting sequence (steps S213 to S216) in FIG. 3 is performed. On the other hand, if the wireless LAN base station data is not stored in the base station activation cycle storage unit 9 (MAC address cache), the process proceeds to step S308, where the accuracy flag and the time flag are set to 0, and n1 = With n2 = 0, the process proceeds to step S309, and the activation cycle setting and activation time setting in FIG. 3 are performed again.

  By performing the above processing, the activation cycle and the activation time can always be set to optimum values. As shown in FIG. 4, when the wireless LAN is an in-company LAN, wireless LAN base stations (access points) are arranged so that there is no area outside the service area on the same floor in the company. In many cases, an out-of-service-> in-service situation occurs only when the employee leaves the office or moves to the floor. In other words, since there is a possibility that the wireless environment changes significantly from outside the area to within the area, the flow is such that the quality evaluation of the wireless section is performed even when the area is outside the area → the area. However, if it is difficult to consider that the use of the wireless LAN terminal goes out of the general household, etc., the system can be further simplified by reducing the determination in step S302.

  In the above embodiment, the MAC address is used to identify the wireless LAN base station, and the activation period value for each wireless LAN base station is associated with the MAC address and described in the activation period storage unit 9 for each base station. However, if the wireless LAN base station can be identified, it goes without saying that information other than the MAC address may be used to identify the wireless LAN base station.

  The present invention has been described with reference to the embodiments. However, the present invention is not limited to the configurations of the above embodiments, and various modifications that can be made by those skilled in the art within the scope of the present invention. Of course, modifications are included.

It is a block diagram which shows the structure of the wireless LAN system by one Example of this invention. It is a block diagram which shows the hardware constitutions of the wireless LAN terminal by one Example of this invention. 4 is a flowchart of setting a start cycle and start time of a wireless LAN terminal according to an embodiment of the present invention. 4 is a flowchart of reviewing the activation period and activation time of a wireless LAN terminal according to an embodiment of the present invention. 6 is a timing chart for explaining a difference in operation between a wireless LAN terminal according to the prior art and a wireless LAN terminal according to an embodiment of the present invention when the activation cycle is deviated. 6 is a diagram for explaining a difference in activation time setting between a wireless LAN terminal according to the prior art and a wireless LAN terminal according to an embodiment of the present invention in different communication environments.

Explanation of symbols

1: wireless LAN base station 2: wireless LAN terminal 3: communication unit 4: control unit 5: activation time setting unit 6: activation cycle setting unit 7: beacon reception time difference (Z1) storage unit 8: beacon reception cycle difference (Z2) ) Storage unit 9: Base station-specific activation cycle storage unit 31: RF unit 32: Baseband unit 101: CPU
102: FLASH ROM
105: RAM
106: Display unit 107: Key input unit

Claims (16)

A communication unit that transmits and receives data to and from the wireless LAN base station;
A control unit that causes the communication unit to transition from a power saving state to a communicable state at a timing at which a beacon periodically transmitted from the wireless LAN base station is to be received;
The beacon is received a plurality of times, a beacon reception period difference storage unit that stores a difference between an interval of time recorded in the beacon and an interval of time when the beacon is received;
An activation period setting unit that sets an activation period for transitioning from the power saving state to the communicable state based on a time interval shift stored in the beacon reception period difference storage unit;
Wireless LAN terminal equipped with. A beacon reception time difference storage unit that stores the difference between the time when the beacon is expected to be received and the time when the beacon is actually received, for a plurality of times,
An activation time setting unit that sets an activation time, which is a time from when the communication time transitions to the return to the power saving state, based on the distribution of reception time deviations stored in the beacon reception time difference storage unit When,
The wireless LAN terminal according to claim 1, further comprising:   The activation time setting unit is given in advance an expected probability of successful beacon reception with respect to a beacon transmission time shift, and the activation time setting unit refers to the distribution of the reception time shift. 3. The wireless LAN terminal according to claim 2, wherein a startup time is set so as to satisfy the expected probability.   The timing for transition from a power saving state to a communicable state is determined based on a median value after removing data outside a threshold from reception time deviation data stored in the beacon reception time difference storage unit. Or the wireless LAN terminal of 3.   When the power is turned on, when it is detected that the mobile station has moved from outside the area where communication with the base station is possible, or when a certain period of time has elapsed since the activation time was set in the area, the activation time The wireless LAN terminal according to claim 2, wherein the setting unit resets the activation time.   5. The start time setting unit resets the start time when the power is turned on or when a predetermined time elapses after the start time is set. 5. The wireless LAN terminal according to the item.   The wireless LAN base station further includes an activation cycle storage unit for each base station that records the activation cycle set by the activation cycle setting unit together with identification information unique to the wireless LAN base station, and when the wireless LAN base station starts communication with the wireless LAN base station, When the base station is recorded in the station-by-station start-up cycle storage unit, the start-up cycle for the base station stored in the base-station start-up cycle storage unit is set as the start-up cycle of the wireless LAN terminal. 6. The wireless LAN terminal according to any one of claims 6. A wireless LAN base station that periodically transmits a beacon including time information;
A wireless LAN terminal that receives the beacon by transitioning from a power saving state to a communicable state at a timing to receive the beacon;
In a wireless LAN system including
The wireless LAN terminal obtains an error between the beacon transmission cycle timed by the wireless LAN base station and the beacon reception cycle timed by the wireless LAN terminal from the time information included in the beacon and the time when the beacon was received, A wireless LAN system that determines a period of transition from the power saving state to a communicable state based on an error.   The wireless LAN terminal receives the beacon a plurality of times, obtains a time delay distribution of the time when the beacon is actually received from the time when the beacon is expected to be received, and can relieve the time delay with a preset probability. Set the activation time, which is the time from the transition to the communicable state to the return to the power saving state, and when the beacon cannot be received during the activation time, without waiting for the reception of the beacon, The wireless LAN system according to claim 8, wherein the wireless LAN system transitions to a power saving state.   When the wireless LAN terminal is turned on, when it is detected that the wireless LAN terminal has moved from a non-communication area where communication with the wireless LAN base station is possible, or after the activation time is set in the area. The wireless LAN system according to claim 9, wherein the activation time is reset when a predetermined time has elapsed. A wireless LAN terminal state transition method for receiving a beacon by transitioning from a power saving state to a communicable state at a timing when a wireless LAN base station should periodically receive a beacon,
Obtaining the error between the beacon transmission period timed by the wireless LAN base station and the beacon reception period timed by the wireless LAN terminal from the time information included in the beacon and the time when the beacon was received, based on the error, A wireless LAN terminal state transition method for receiving a beacon by determining a start cycle in which a wireless LAN terminal transitions from the power saving state to a communicable state.   The beacon is received a plurality of times, a time delay distribution of the time when the beacon is actually received is obtained from the time when the beacon is expected to be received, and the communication delay state is set so that the time delay can be relieved with a preset probability. A startup time that is a time from the transition to the return to the power saving state is set, and when the beacon cannot be received during the startup time, the communication from the communicable state without waiting for the reception of the beacon. The wireless LAN terminal state transition method according to claim 11, wherein the wireless LAN terminal transitions to a power state.   When the power is turned on, when it is detected that it has moved from outside the service area to a range where communication with the base station is possible, or when a certain time has elapsed since the activation time was set in the area The wireless LAN terminal state transition method according to claim 12, wherein the time is reset.   13. The wireless LAN terminal state transition method according to claim 12, wherein the activation time is reset when the power is turned on or when a certain time has elapsed since the activation time was set. A wireless LAN terminal control program including a communication unit that performs transmission / reception processing including reception of beacons periodically transmitted,
Time data recorded in the first beacon, time data timed when the first beacon is received, time data recorded in the second beacon, time data timed when the second beacon is received, From the number of beacons received from the first beacon until the second beacon is received, how the time per period recorded in the beacon progresses, and the period per period counted by the wireless LAN terminal A process for obtaining a period difference in how time advances,
A control program for causing the wireless LAN terminal to execute a process of periodically transitioning the communication unit from a power saving state to a communicable state capable of receiving the beacon based on the period difference. The beacon is received a plurality of times, a time delay distribution of the time when the beacon is actually received is obtained from the time when the beacon is expected to be received, and the communication delay is set so that the time delay can be relieved with a preset probability. A process of setting a start-up time that is a time from the transition to the return to the power-saving state;
If the beacon could not be received during the startup time, a process of transitioning from the communicable state to the power saving state without waiting for the reception of the beacon;
16. The control program according to claim 15, which causes the wireless LAN terminal to execute.

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