JP4686374B2 - Access point and wireless LAN system - Google Patents

Description

  The present invention relates to a wireless LAN terminal and an access point that perform wireless communication based on a wireless LAN standard.

  In the wireless LAN system, a method of arranging a plurality of access points is taken for the purpose of expanding the range covered by the access points and the communication capacity. A wireless LAN terminal used in such a wireless LAN system is allowed to freely move between a plurality of access points using a handover technique. Recently, the demand for a wireless LAN telephone system having a wireless LAN terminal having a voice communication function is increasing. However, unlike data communication terminals that can transmit and receive data by repeating retransmission even in situations where communication quality is poor, voice communication terminals are required to have high communication quality sufficient to achieve real-time performance. The In order to maintain high communication quality, it is desired to perform handover to an access point with better received signal quality, but it is important that the received signal level for executing handover is appropriate.

  In order to avoid this, in Patent Document 1, the received radio wave intensity from another access point adjacent to the access point is measured, an optimum handover threshold is determined based on the measured result, and the determined handover threshold is A technique for notifying a wireless LAN terminal is disclosed.

JP 2004-7504 A

  However, when a wireless LAN system is configured by arranging a plurality of access points, the radio waves are not visible, and the intensity of the radio waves transmitted from the access points shows a complicated distribution due to the arrangement of surrounding obstacles, etc. For these reasons, it is difficult to arrange each access point so that it can receive radio waves from other adjacent access points. In addition, it is conceivable to use the technique described in Patent Document 1 by arranging a plurality of access points closely, but the number is larger than the number necessary to secure a desired communication band in a narrow area. Arranging the number of access points is not preferable from the viewpoint of cost effectiveness.

  The present invention has been made in view of the above circumstances, and an object of the present invention is arranged in a wireless LAN system in which a plurality of access points are arranged so that the radio waves of the access points do not reach other access points. Even in this case, it is possible to appropriately calculate the value of the received radio wave intensity for executing the channel search in order to determine the start of the handover.

  In order to solve the above problems, an access point according to the present invention acquires reception signal quality before and after handover from a wireless LAN terminal that has been handed over from another access point, and based on the acquired reception signal quality, the wireless LAN terminal Calculates the value of the received radio wave intensity for performing the channel search for performing handover, and notifies the wireless LAN terminal of it.

For example, one aspect of the present invention is an access point that is used in a wireless LAN system including a wireless LAN terminal and a plurality of access points, and is capable of communication via the LAN, and is from the wireless LAN terminal belonging to itself. Search execution level calculation means for calculating a search execution level used for determining whether to search for an access point other than the access point belonging to, based on the reported received radio wave strength after handover , Search execution level transfer means for transferring the search execution level calculated by the search execution level calculation means to the access point before handover together with the identification information of the own access point based on the identification information of the access point before handover, and other access From the point, the identification information of the other access point When the search execution level is received, the search execution level storage means for storing the search execution level in association with the identification information of the other access point, and the search execution level stored in the search execution level storage means, Provided is an access point comprising: search execution level notification means for notifying a subordinate wireless LAN terminal using wireless communication together with identification information of a corresponding access point.

  According to the wireless LAN system of the present invention, in a wireless LAN system in which a plurality of access points are arranged, even when the access point radio waves are arranged not to reach other access points, the start of handover is performed. In order to make a determination, it is possible to appropriately calculate the value of the received radio wave intensity at which the channel search is executed.

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

  FIG. 1 shows an example of the configuration of a wireless LAN system 10 according to an embodiment of the present invention. The wireless LAN system 10 includes a wireless LAN terminal 20 and a plurality of access points 30. Each access point 30 outputs a radio wave indicating a corresponding radio wave intensity distribution 31. Each radio wave intensity distribution 31 is shown by a straight line for easy explanation.

  The wireless LAN terminal 20 performs wireless communication with the nearest access point 30 based on a wireless LAN standard such as IEEE802.11a or IEEE802.11b. And communication with other communication devices 12 connected to the wired LAN 11.

  Each access point 30 is connected to the wired LAN 11. Each access point 30 relays a communication frame transmitted / received by the wireless LAN terminal 20 to another wireless LAN terminal 20 or the communication device 12 by wireless communication based on the wireless LAN, and is transmitted / received by the communication device 12. Are relayed to the subordinate wireless LAN terminal 20 by wireless communication based on the wireless LAN. In FIG. 1, the wired LAN 11 is described as an example of a network connecting the access points 30, but the present invention is not limited to this, and the wireless communication method used by the wireless LAN terminal 20 is between the access points 30. May be connected by a wireless network of a different method.

  The plurality of access points 30 are rarely arranged at equal intervals in an actually used environment. For example, as shown in FIG. 1, the access point 30b is more than the distance between the access point 30a and the access point 30b. And the access point 30c may be arranged to be close to each other. In such a case, if the wireless LAN terminal 20 executes handover between the access point 30a and the access point 30b, the handover is executed after the received radio wave intensity from the access point 30 to which the wireless LAN terminal 20 belongs becomes low. become. When the received radio wave intensity decreases, the received signal quality such as BER (Bit Error Rate) and SNR (Signal to Noise Ratio) may deteriorate.

  Here, when executing the handover, the wireless LAN terminal 20 executes a channel search for measuring the received radio wave intensity of the radio wave transmitted to the radio channel used by another access point 30 prior to the handover. .

  On the other hand, if the wireless LAN terminal 20 executes a handover between the access point 30b and the access point 30c, the handover is performed to another access point 30c while the received radio wave intensity from the access point 30b to which it belongs is high. Therefore, it is possible to perform handover with a good reception signal quality. As described above, the value of the received radio wave intensity at which handover is to be performed may vary depending on the location of the access point 30. Since the radio wave from the access point 30 shows a complicated distribution due to the influence of an obstacle or the like, even if a plurality of access points 30 are arranged at equal intervals, the value of the received radio wave intensity at which handover is to be executed is In many cases, each access point 30 is different.

  Here, it is also conceivable that a handover is executed when another access point 30 having a better received signal quality than the access point 30 to which it belongs is detected by always performing a channel search from a state in which the received radio wave intensity is sufficiently high. It is done. However, constantly performing a channel search causes inconveniences such as a loss of communication data due to an increase in processing load and a decrease in continuous communication time due to an increase in power consumption.

  Therefore, the wireless LAN system 10 of the present invention calculates the search execution level, which is the received radio wave intensity for executing the channel search performed prior to the handover, for each access point 30 and notifies the subordinate wireless LAN terminal 20 of the search execution level. Each wireless LAN terminal 20 acquires the search execution level from the access point 30 to which it belongs, and when the received radio wave intensity from the access point 30 to which it belongs falls within a predetermined range from the search execution level, the handover destination A channel search for searching for another access point 30 is executed.

  As a result, the wireless LAN terminal 20 can reduce the number of times that the channel search is executed, and can appropriately execute the handover without affecting the data communication.

  Hereinafter, a method for calculating the search execution level will be described in detail.

  FIG. 2 shows an example of a detailed functional configuration of the wireless LAN terminal 20. The wireless LAN terminal 20 includes a search execution level acquisition unit 201, a received radio wave intensity measurement unit 200, a channel search unit 202, a handover processing unit 203, a signal quality notification unit 204, a communication data processing unit 205, and a wireless communication unit 206.

  The wireless communication unit 206 performs wireless communication with the access point 30 based on the wireless LAN. In the present embodiment, the wireless communication unit 206 has a function of performing processing related to known wireless LAN communication such as attribution processing and authentication processing. The communication data processing unit 205 has a function of performing data communication via the wireless communication unit 206.

  The search execution level acquisition unit 201 obtains one or more search execution levels from the access point 30 to which the own wireless LAN terminal 20 belongs together with the identification information of the access point 30 corresponding to the search execution level. Get and store through. For example, the search execution level acquisition unit 201 acquires the search execution level from the beacon signal transmitted by the access point 30 when it newly belongs to the access point 30. The search execution level acquisition unit 201 deletes all stored search execution levels when the own wireless LAN terminal 20 executes a handover.

  Received radio wave intensity measuring section 200 measures the received radio wave intensity from belonging access point 30 and sends the measurement result to channel search section 202 and signal quality notifying section 204. The channel search unit 202 has the received radio wave intensity acquired from the received radio wave intensity measuring unit 200 within a predetermined range (for example, within ± 0.5 dB) from the search execution level stored in the search execution level acquisition unit 201. In this case, a channel search is executed via the wireless communication unit 206.

  When the radio wave from the other access point 30 is detected and the received radio wave intensity from the other access point 30 satisfies a predetermined condition, the channel search unit 202 selects the other access point. The handover processing unit 203 is instructed to perform handover to 30. Here, the predetermined condition is, for example, that the received radio wave intensity from another access point 30 is 5 dB or more higher than the search execution level.

  When the search execution level acquisition unit 201 stores a plurality of search execution levels, the channel search unit 202 uses the received radio wave intensity acquired from the received radio wave intensity measurement unit 200 as the search execution level acquisition unit 201. If the search execution level is within a predetermined range, a channel search is executed.

  As another example, the channel search unit 202 holds the reception radio wave intensity acquired last time from the reception radio wave intensity measurement unit 200, and performs a search execution level between the reception radio wave intensity acquired last time and the reception radio wave intensity acquired this time. May be included, channel search may be executed.

  The channel search unit 202 also performs channel search when the received radio wave intensity acquired from the received radio wave intensity measuring unit 200 is equal to or lower than the minimum reception level (eg, −100 dBm). When the received radio wave intensity from the other access point 30 is higher than the received radio wave intensity from the access point 30 to which the own wireless LAN terminal 20 belongs, the channel search unit 202 sends to the other access point 30. The handover processing unit 203 is instructed to perform a handover. Here, the minimum reception level is the minimum reception radio wave intensity at which the wireless LAN terminal 20 can continue communication while causing a certain amount of reception data error.

  The handover processing unit 203 executes a handover process to another access point 30 detected by the channel search unit 202 in accordance with an instruction from the channel search unit 202. The signal quality notification unit 204 measures the quality of the received signal from the access point 30 to which the own wireless LAN terminal 20 belongs at every predetermined time interval (for example, several milliseconds), and the latest number of the measured received signal quality. Hold ten samples.

  When the signal quality notification unit 204 obtains the completion of the handover from the handover processing unit 203, the signal quality notification unit 204 holds the received signal quality of several tens samples before the handover, and measures the received signal quality after the handovers by several tens samples. . Then, the signal quality notification unit 204 calculates the received signal quality before handover by averaging the received signal quality of several tens samples before handover, and averages the received signal quality of several tens samples after handover. The received signal quality is calculated.

  In addition, when the signal quality notification unit 204 obtains the completion of handover from the handover processing unit 203, the received signal strength from the access point 30 after handover sent from the received signal strength measuring unit 200 is several tens of samples. The received radio wave strength after the handover is calculated by averaging the received radio wave strengths held. Then, the signal quality notification unit 204 notifies the calculated reception signal quality before handover, reception signal quality after handover, and received radio wave strength after handover to the access point 30 after handover via the wireless communication unit 206. To do.

  As another example, the signal quality notification unit 204 measures the received signal quality and the received radio wave intensity before and after a predetermined period (for example, several tens of milliseconds) from the handover time point with reference to the handover time point, And may be notified to the access point 30 after the handover.

  FIG. 3 shows an example of the structure of data stored in the search execution level acquisition unit 201. The search execution level acquisition unit 201 stores the search execution level 2011 in association with the MAC address 2010 acquired from the access point 30 together with the search execution level 2010. The MAC address 2010 is an example of identification information of the access point 30. As another example, the search execution level acquisition unit 201 may use an IP address, a preset identification number, or the like as the identification information of the access point 30.

  When the search execution level acquisition unit 201 acquires a search execution level from the access point 30 together with the same MAC address as the already stored MAC address, the search execution level is stored in association with the MAC address. Replace with the newly acquired search execution level. Thereby, the wireless LAN terminal 20 can store the latest search execution level notified from the access point 30.

  FIG. 4 is a conceptual diagram for explaining an example of processing of the channel search unit 202. In FIG. 4, the radio wave intensity distribution is shown by a straight line for easy explanation.

  The radio wave intensity distribution from the access point 30 becomes lower as indicated by 400 as the wireless LAN terminal 20 moves away from the access point 30. When the wireless LAN terminal 20 moves to the position indicated by 407, the received radio wave intensity 404 from the access point 30 to which the own wireless LAN terminal 20 belongs is, for example, 0.5 dB higher than the search execution level 403. From the search execution level 403, for example, the radio wave intensity 406 is lowered by 0.5 dB, and the channel search unit 202 executes the channel search.

  Then, the channel search unit 202 detects a radio wave from another access point 30, and if the received radio wave intensity from the other access point 30 is higher than the search execution level by, for example, 5 dB or more, The handover processing unit 203 is instructed to perform handover to the access point 30.

  In FIG. 4, when the radio field intensity from other access points 30 is distributed as 401a, the radio field intensity 402a from other access points 30 at the position 407 is 5 dB or more higher than the search execution level 403. The channel search unit 202 instructs the handover processing unit 203 to perform handover to the access point 30 that is transmitting the radio wave of the radio wave intensity distribution 401a.

  On the other hand, when the radio wave intensity from the other access point 30 is distributed like 401b, the radio wave intensity 402b from the other access point 30 at the position 407 is higher than the search execution level 403, but the search execution level 403 Is less than 5 dB, the channel search unit 202 does not instruct the handover processing unit 203 to perform handover to the access point 30 that is transmitting the radio wave having the radio wave intensity distribution 401b.

  Similarly, when the radio wave intensity from the other access point 30 is distributed as 401c, the radio wave intensity 402c from the other access point 30 at the position 407 is lower than the search execution level 403. 202 does not instruct the handover processing unit 203 to perform handover to the access point 30 that is transmitting the radio wave of the radio wave intensity distribution 401c.

  As described above, in the channel search activated when the received radio wave intensity from the access point 30 to which the own wireless LAN terminal 20 belongs is within a predetermined range from the search execution level 403, the channel search is 5 dB higher than the search execution level 403. Since handover is executed only when there is an access point 30 that is higher than the above, it is possible to prevent so-called switch back in which handover is further executed to the original access point 30 after handover. Therefore, the wireless LAN terminal 20 can reliably perform handover.

  Note that the channel search unit 202 may prohibit the next channel search for a predetermined period (for example, several seconds) when the handover is not executed after the channel search. As a result, when the received wireless LAN terminal 20 stays at a position where the received radio wave intensity is in the vicinity of the search execution level 403 and the access point 30 having a received radio wave intensity higher than the search execution level 403 by 5 dB or more does not exist. Can be prevented from being repeated unnecessarily and increasing the processing load.

  5 and 6 are conceptual diagrams for explaining an example of a handover process of the wireless LAN terminal 20. In FIG. 5 and FIG. 6, the radio wave intensity distribution is shown by a straight line for easy explanation.

  Reference numeral 410a denotes an area transmitted from the access point 30a and having a radio wave intensity equal to or higher than the search execution level. Reference numeral 410b denotes an area transmitted from the access point 30b and having a radio wave intensity equal to or higher than the search execution level. Reference numeral 415 denotes a search execution level. Reference numeral 416 denotes RBmin. Reference numeral 417 denotes the minimum reception level.

  When the wireless LAN terminal 20 passes through the moving route 411 passing through the vicinity of the access point 30a and the access point 30b, the radio wave intensity distribution on the moving route 411 is as indicated by 412a and 412b. When the wireless LAN terminal 20 moves from the vicinity of the access point 30a through the movement route 411 to the position shown in FIG. 5, the received radio wave intensity from the access point 30a becomes a value indicated by 414 near the search execution level 415. The channel search unit 202 of the wireless LAN terminal 20 performs a channel search.

  Channel search section 202 detects the radio wave from access point 30b and measures the received radio wave intensity indicated by 413. In FIG. 5, it is assumed that the radio wave intensity 413 and the search execution level 415 have a difference of 10 dB. Since the channel search unit 202 detects the access point 30b to which a radio wave having a received radio wave intensity higher than the search execution level 415 by 5 dB or more is transmitted, the channel search unit 202 instructs the handover processing unit 203 to perform a handover to the access point 30b.

  On the other hand, as shown in FIG. 6, when the wireless LAN terminal 20 passes the moving route 420 that is farther from the access point 30a and the access point 30b than in the case shown in FIG. As shown in 421a and 421b. When the wireless LAN terminal 20 moves to the position shown in FIG. 6 along the movement route 420, the received radio wave intensity from the access point 30a becomes a value indicated by 422 in the vicinity of the search execution level 415. The channel search unit 202 performs channel search.

  Then, the channel search unit 202 detects the radio wave from the access point 30b and measures the received radio wave intensity indicated by 423. In FIG. 6, since the radio wave intensity 423 is lower than the search execution level 415, the channel search unit 202 does not instruct the handover processing unit 203 to perform handover at the position shown in FIG.

  After that, when the wireless LAN terminal 20 moves along the movement route 420 and reaches the position of the radio wave intensity 425 (the reception radio wave intensity becomes the minimum reception level 417 or less), the channel search unit 202 performs a channel search. Then, the channel search unit 202 detects the radio wave from the access point 30b and measures the received radio wave intensity indicated by 424. Since the radio field intensity 424 is greater than or equal to the radio field intensity 425, the channel search unit 202 instructs the handover processing unit 203 to perform handover to the access point 30b.

  Note that when the radio wave intensity indicated by 413 in FIG. 5 is 5 dB or more lower than the search execution level 415, the search is repeated, causing unnecessary processing and inconvenience such as dropping a communication packet. May occur. On the other hand, when the radio wave intensity indicated by 413 is 20 dB or more higher than the search execution level 415, it is appropriate to perform handover at an earlier stage in view of communication quality. Therefore, it is desired that the search execution level 415 can be dynamically changed for each access point 30. In the present invention, the received radio wave intensity of the route on which the user using the wireless LAN terminal 20 travels the most is calculated from the statistical data of the handover result, and as shown in FIG. 5, the search execution level 415 and the adjacent access point 30 The search execution level 415 can be changed so that the relationship with the received radio wave intensity becomes appropriate.

  As described above, since the channel search is executed when the received radio wave intensity from the access point 30 to which the own wireless LAN terminal 20 belongs is near the search execution level or below the minimum reception level, the channel search is executed. The number of executions can be reduced. As a result, an increase in processing load and power consumption due to channel search can be suppressed.

  FIG. 7 shows an example of a detailed functional configuration of the access point 30. The access point 30 includes a search execution level storage unit 300, a search execution level notification unit 301, a search execution level transfer unit 302, a search execution level calculation unit 303, a signal quality acquisition unit 304, a wireless LAN processing unit 305, a wired communication unit 306, And a wireless communication unit 307.

  The wireless communication unit 307 performs wireless communication based on the wireless LAN with the wireless LAN terminal 20, sends the communication data received from the wireless LAN terminal 20 to the wired communication unit 306, and transmits the data received from the wired communication unit 306 by wireless communication. The data is sent to the wireless LAN terminal 20. In the present embodiment, the wireless communication unit 307 performs known wireless LAN communication processing such as attribution processing and authentication processing. The wired communication unit 306 performs wired communication with other communication devices via the wired LAN 11 based on, for example, Ethernet (registered trademark).

  The signal quality acquisition unit 304 transmits the received signal quality from the access point 30 before and after the handover from the wireless LAN terminal 20 that has been handed over from the other access point 30, and the access point 30 to which the wireless LAN terminal 20 belonged before the handover. Together with the identification information of the pre-handover access point, which is obtained via the wireless communication unit 307. Further, the signal quality acquisition unit 304 sends the received signal quality of the radio wave transmitted from the wireless LAN terminal 20 to the wired communication unit 306 from the access point 30 to which the wireless LAN terminal 20 belonged before the handover. To get through. Further, the signal quality acquisition unit 304 acquires the received signal quality of the radio wave transmitted from the wireless LAN terminal 20 measured by the quality measurement unit 308.

  The quality measurement unit 308 measures the received signal quality from the wireless LAN terminal 20 to which it belongs, and notifies the access point 30 after the handover via the wired communication unit 306, and the wireless LAN terminal 20 after the handover. A function of measuring the received signal quality and notifying the signal quality acquiring unit 304 of the received signal quality.

Based on the received signal quality acquired by the signal quality acquisition unit 304, the search execution level calculation unit 303 calculates a search execution level that is referred to when handing over from the pre-handover access point to the own access point 30. The search execution level calculation unit 303 calculates a search execution level Rth (dBm) based on the following relational expression, for example.
Rth = RBmin + 0.5 × (RAave−RBmin)

  Here, RBmin (dBm) is a predetermined received radio wave intensity, and is set to, for example, the minimum reception level +10 dB. RAave (dBm) is an average of received radio wave intensity after handover reported from a plurality of wireless LAN terminals 20.

  Further, the search execution level calculation unit 303 sets the search execution level calculated by the above formula 1 when the received signal quality before handover is worse than the received signal quality after handover by a predetermined amount (for example, BER is 1%) or more. By adding a predetermined value (5 dB), the handover may be executed early in a state where the received radio wave intensity before the handover is high.

  Further, the search execution level calculation unit 303 calculates the search execution level calculated by the above equation 1 when the received signal quality before the handover is better than the reception signal quality after the handover by a predetermined amount (for example, BER is 1%). By subtracting the predetermined value (5 dB), the handover may be executed after the received radio wave intensity from the handover destination access point 30 becomes high.

  The search execution level transfer unit 302 uses the search execution level calculated by the search execution level calculation unit 303 based on the identification information (the MAC address in this example) of the access point before handover based on the identification information (the MAC address in this example). Together with the MAC address in the example) via the wired communication unit 306 to the pre-handover access point.

  When the search execution level storage unit 300 receives the identification information and the search execution level of the other access point 30 from another access point 30 via the wired communication unit 306, the search execution level storage unit 300 sets the search execution level to the other access point 30. Stored in association with the identification information of the access point 30. When a plurality of search execution levels associated with different identification information are received, the search execution level storage unit 300 stores a plurality of search execution levels in a format as shown in FIG. 3 for each identification information.

  The search execution level notification unit 301 uses a beacon when the search execution level stored in the search execution level storage unit 300 is updated, when the wireless LAN terminal 20 newly belongs to the own access point 30, or the like. The search execution level stored in the search execution level storage unit 300 is periodically notified to the subordinate wireless LAN terminal 20 using the wireless communication together with the identification information of the corresponding access point 30.

  FIG. 8 is a flowchart showing an example of the operation of the wireless LAN terminal 20. For example, by starting wireless communication, the wireless LAN terminal 20 starts the processing shown in this flowchart.

  First, the received radio wave intensity measuring unit 200 measures the received radio wave intensity from the access point 30 to which the own wireless LAN terminal 20 belongs via the wireless communication unit 206 (S100). Then, the channel search unit 202 determines whether or not the received radio wave intensity is within a predetermined range from the search execution level (S101). When the wireless LAN terminal 20 is within the predetermined range from the search execution level (S101: Yes), the wireless LAN terminal 20 executes a channel search process activated by the search execution level (S110) and determines whether or not to end communication (S110). S102).

  When communication is continued (S102: No), the received radio wave intensity measuring unit 200 executes the process shown in step 100 again. When the communication is to be ended (S102: Yes), the wireless LAN terminal 20 ends the communication and ends the processing shown in this flowchart.

  If the received radio wave intensity is not within the predetermined range from the search execution level (S101: No), the channel search unit 202 determines whether the received radio wave intensity is equal to or lower than the minimum reception level (S103). If the received radio wave intensity is not equal to or lower than the minimum reception level (S103: No), the wireless LAN terminal 20 executes the process shown in step 102. If the received radio wave intensity is equal to or lower than the minimum reception level (S103: Yes), the wireless LAN terminal 20 executes a channel search process activated by the minimum reception level (S120).

  FIG. 9 is a flowchart showing an example of detailed processing in step 110.

  When the received radio wave intensity is within a predetermined range from the search execution level (S101: Yes), the channel search unit 202 executes a channel search (S111). Then, the channel search unit 202 determines whether another access point 30 has been detected (S112). When no other access point 30 is detected (S112: No), the channel search unit 202 determines whether or not the channel search has been executed for all the usable channels set in advance in the wireless LAN system 10. (S117).

  When the channel search is executed for all channels (S117: Yes), the received radio wave intensity measurement unit 200 executes the process shown in step 100 again. When channel search is not executed for all channels (S117: No), the channel search unit 202 changes the channel and executes the process shown in step 111 again.

  When another access point 30 is detected by the channel search (S112: Yes), the channel search unit 202 determines that the received radio wave intensity from the other access point 30 is a predetermined value (eg, a search execution level). It is determined whether or not it is higher than 5 dB) (S113). When the detected radio wave intensity from the other access point 30 has a difference from the search execution level that is less than a predetermined value or less than the search execution level (S113: No), the channel search unit 202 indicates in step 117. Execute the process.

  When the received radio wave intensity from the detected other access point 30 is higher than the search execution level by a predetermined value or more (S113: Yes), the channel search unit 202 performs handover processing for the detected handover to the other access point 30. The unit 203 is instructed. The handover processing unit 203 executes a handover process to another access point 30 detected by the channel search unit 202 (S114).

  Then, the search execution level acquisition unit 201 deletes all the search execution levels stored before the handover, and acquires and stores the search execution level newly notified from the access point 30 after the handover (S115). Then, the signal quality notification unit 204 notifies the received signal quality before and after the handover to the access point 30 after the handover via the wireless communication unit 206 (S116), and the wireless LAN terminal 20 executes the processing shown in step 102. To do.

  FIG. 10 is a flowchart illustrating an example of detailed processing in step 120.

  When the received radio wave intensity is equal to or lower than the minimum reception level (S103: Yes), the channel search unit 202 performs a channel search (S121). Then, the channel search unit 202 determines whether another access point 30 is detected (S122). If no other access point 30 is detected (S122: No), the channel search unit 202 executes the process shown in step 126.

  When another access point 30 is detected (S122: Yes), the channel search unit 202 determines that the received radio wave intensity from the other access point 30 is the same as the access point 30 to which the own wireless LAN terminal 20 belongs. It is determined whether the received radio wave intensity is higher than (S123).

  When the detected radio wave intensity from the other access point 30 is higher than the radio wave intensity received from the access point 30 to which the own wireless LAN terminal 20 belongs (S123: Yes), the channel search unit 202 detects The handover processing unit 203 is instructed to perform handover to another access point 30. The handover processing unit 203 executes a handover process to another access point 30 detected by the channel search unit 202 (S124). Then, the search execution level acquisition unit 201 deletes all the search execution levels stored before the handover, acquires and stores the search execution level newly notified from the access point 30 after the handover (S125). The LAN terminal 20 executes the process shown in step 102.

  When the detected radio wave intensity from the other access point 30 is lower than the radio wave intensity received from the access point 30 to which the own wireless LAN terminal 20 belongs (S123: No), the channel search unit 202 It is determined whether or not channel search has been executed for all usable channels preset in the system 10 (S126). When the channel search is not executed for all channels (S126: No), the channel search unit 202 executes the process shown in step 121 again.

  When the channel search is executed for all channels (S126: Yes), the wireless LAN terminal 20 determines whether or not communication can be continued (S127). If the communication can be continued (S127: Yes), the wireless LAN terminal 20 executes the process shown in step 102. If data errors occur frequently and communication cannot be continued (S127: No), the wireless LAN terminal 20 ends the communication and ends the processing shown in this flowchart.

  FIG. 11 is a flowchart showing an example of the operation of the access point 30. For example, at a predetermined timing such as when the power is turned on, the access point 30 starts the processing shown in this flowchart.

  First, the signal quality acquisition unit 304 identifies the received signal quality before and after the handover from the wireless LAN terminal 20 that has been handed over from another access point 30, and the identification information of the access point 30 to which the wireless LAN terminal 20 belonged before the handover. At the same time, it is determined whether or not it has been acquired via the wireless communication unit 307 (S200). When the received signal quality is received (S200: Yes), the search execution level calculation unit 303 calculates the search execution level based on the above-described Equation 1 using the received radio wave intensity after the handover (S201). Then, the search execution level calculation unit 303 determines whether the received signal quality before the handover is worse than the received signal quality after the handover by a predetermined amount or more (S202).

  If the received signal quality before the handover is worse than the received signal quality after the handover by a predetermined amount or more (S202: Yes), the signal quality acquisition unit 304 determines the received signal quality from the wireless LAN terminal 20 handed over to the own access point 30. Obtained from the quality measuring unit 308 (S203). Then, the quality measuring unit 308 acquires the received signal quality before the handover of the wireless LAN terminal 20 from the access point 30 to which the wireless LAN terminal 20 handed over to the own access point 30 belonged before the handover. The data is sent to the quality acquisition unit 304 (S204).

  Next, the search execution level calculation unit 303 adds a predetermined value to the search execution level calculated in step 202 (S205). Then, the search execution level transfer unit 302 sets the search execution level calculated by the search execution level calculation unit 303 together with the identification information of the access point 30 before the handover together with the identification information of the own access point 30 to the wired communication unit. The data is transferred to the access point 30 before the handover through 306 (S206), and the signal quality acquisition unit 304 executes the process shown in step 200 again.

  When the received signal quality before handover is not worse than the received signal quality after handover by a predetermined amount or more (S202: No), the search execution level calculation unit 303 determines that the received signal quality before handover is higher than the received signal quality after handover. It is determined whether it is better than a predetermined amount (S207). When the received signal quality before the handover is not better than the received signal quality after the handover by a predetermined amount (S207: No), the signal quality acquisition unit 304 executes the process shown in step 200 again.

  When the received signal quality before handover is better than the received signal quality after handover by a predetermined amount or more (S207: Yes), the search execution level calculation unit 303 subtracts the predetermined value from the search execution level calculated in step 202 (S208). The search execution level transfer unit 302 executes the process shown in step 206.

  If the received signal quality is not received in step 200 (S200: No), the search execution level storage unit 300 has been notified of the search execution level from another access point 30 via the wired communication unit 306. Is determined (S209). When the search execution level is notified from another access point 30 (S209: Yes), the search execution level storage unit 300 acquires and stores the notified search execution level. Then, the search execution level notifying unit 301 notifies the search execution level newly stored in the search execution level storage unit 300 to the currently belonging wireless LAN terminal 20 (S210), and the signal quality acquisition unit 304 again The process shown in step 200 is executed.

  When the search execution level is not notified from another access point 30 (S209: No), the search execution level notification unit 301 determines whether or not the wireless LAN terminal 20 newly belongs (S211). When the wireless LAN terminal 20 newly belongs (S211: Yes), the search execution level notification unit 301 transfers the search execution level stored in the search execution level storage unit 300 to the newly assigned wireless LAN terminal 20. Notification is made via the wireless communication unit 307 (S212), and the signal quality acquisition unit 304 executes the process shown in step 200 again.

  When the wireless LAN terminal 20 is not newly assigned (S211: No), the quality measurement unit 308 determines whether or not the wireless LAN terminal 20 belonging to the own access point 30 has been handed over to another access point 30. Determination is made (S213). When the wireless LAN terminal 20 belonging to the own access point 30 has not handed over to another access point 30 (S213: No), the signal quality acquisition unit 304 executes the process shown in step 200 again.

  When the wireless LAN terminal 20 belonging to the own access point 30 is handed over to another access point 30 (S213: Yes), the quality measurement unit 308 before the hand-over of the wireless LAN terminal 20 to another access point 30 is performed. The received signal quality is recorded (S214). Then, the quality measurement unit 308 transmits the recorded received signal quality to the handover destination access point 30 of the wireless LAN terminal 20 via the wired communication unit 306 (S215), and the signal quality acquisition unit 304 performs the step again. The process indicated at 200 is executed.

  The first embodiment of the present invention has been described above.

  As is clear from the above description, according to the wireless LAN system 10 of the present embodiment, in a wireless LAN system in which a plurality of access points are arranged, the radio waves of the access points are arranged so as not to reach other APs. Even so, the threshold for determining the start of the handover can be calculated appropriately. In addition, the number of channel searches when performing handover can be reduced, and increases in processing load and power consumption can be suppressed.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in embodiment mentioned above. It will be apparent to those skilled in the art that various modifications or improvements can be made to the above-described embodiment. Furthermore, it is apparent from the scope of the claims that the embodiments added with such changes or improvements can be included in the technical scope of the present invention.

1 is a system configuration diagram showing an example of a configuration of a wireless LAN system 10 according to an embodiment of the present invention. 2 is a block diagram illustrating an example of a detailed functional configuration of a wireless LAN terminal 20. FIG. 6 is an explanatory diagram illustrating an example of a structure of data stored in a search execution level acquisition unit 201. FIG. 6 is a conceptual diagram for explaining an example of processing of a channel search unit 202. FIG. 3 is a conceptual diagram for explaining an example of a handover process of a wireless LAN terminal 20. FIG. 3 is a conceptual diagram for explaining an example of a handover process of a wireless LAN terminal 20. FIG. 3 is a block diagram illustrating an example of a detailed functional configuration of an access point 30. FIG. 4 is a flowchart showing an example of the operation of the wireless LAN terminal 20. It is a flowchart which shows an example of the detailed process of step 110. FIG. 7 is a flowchart showing an example of detailed processing in step 120. 3 is a flowchart showing an example of the operation of an access point 30.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Wireless LAN system, 11 ... Wired LAN, 12 ... Communication apparatus, 20 ... Wireless LAN terminal, 200 ... Received radio wave intensity measurement part, 201 ... Search execution level acquisition part, 2010 ... MAC address, 2011 ... Search execution level, 202 ... Channel search unit, 203 ... Handover processing unit, 204 ... Signal quality notification unit, 205 ... Communication data processing unit, 206 ... Wireless communication unit, 30 ... Access point, 300 ... Search execution level storage unit, 301 ... Search execution level notification unit, 302 ... Search execution level transfer unit, 303 ... Search execution Level calculation unit 304 ... Signal quality acquisition unit 306 ... Wired communication unit 307 ... Wireless communication unit 308 ... Quality measurement unit 31,400,401, 12, 421 ... Radio wave intensity distribution, 402, 405, 406, 413, 414, 422, 423, 424, 425 ... Radio wave intensity, 403, 415 ... Search execution level, 404 ... Received radio wave intensity 407 ... position 410 ... region 411 ... travel route 420 ... travel route 416 ... Rmin 417 ... minimum reception level

Claims (6)

An access point used for a wireless LAN system including a wireless LAN terminal and a plurality of access points, capable of communication via a LAN,
Search execution level used to determine whether to search for other access points other than the belonging access point based on the received radio wave strength after handover reported from the wireless LAN terminal belonging to itself Search execution level calculating means for calculating
Search execution level transfer means for transferring the search execution level calculated by the search execution level calculation means to the access point before handover together with the identification information of the own access point based on the identification information of the access point before handover;
Search execution level storage means for storing the search execution level in association with the identification information of the other access point when receiving the identification information of the other access point and the search execution level from another access point; ,
Search execution level notifying means for notifying the subordinate wireless LAN terminal of the search execution level stored in the search execution level storing means together with the identification information of the corresponding access point using wireless communication. And an access point. The access point according to claim 1,
The search execution level calculation means includes
Using RBmin (dBm), which is a predetermined received radio wave intensity, and RAave (dBm), which is an average of received radio wave intensity after handover, reported from a plurality of the wireless LAN terminals, An access point that calculates the search execution level Rth (dBm) based on the access point.
Rth = RBmin + 0.5 × (RAave−RBmin) The access point according to claim 2,
Acquisition of signal quality from a wireless LAN terminal that has been handed over from another access point, together with the identification information of the pre-handover access point that is the access point to which the wireless LAN terminal belonged before the handover. Further comprising means,
The search execution level calculation means includes
Received signal quality before and after handover received from the wireless LAN terminal, and received signal quality of radio waves transmitted from the wireless LAN terminal notified from an access point to which the wireless LAN terminal belonged before performing handover Based on the received signal quality of the radio wave transmitted from the wireless LAN terminal measured by the own access point,
A value obtained by subtracting a predetermined second value from the calculated search execution level when the received signal quality before the handover is better than the predetermined first value than the received signal quality after the handover, Calculate as a new search execution level,
When the received signal quality before handover is worse than the received signal quality after handover by a predetermined third value or more, a value obtained by adding a predetermined fourth value to the calculated search execution level is: An access point that is calculated as a new search execution level. The access point according to any one of claims 1 to 3,
The search execution level calculation means includes
Each time the signal quality acquisition means acquires the received signal quality before and after handover from the wireless LAN terminal that has been handed over from another access point, it calculates a new search execution level based on the received signal quality,
The search execution level transfer means includes:
An access point, wherein each time a new search execution level is calculated by the search execution level calculation means, the calculated new search execution level is transferred to the pre-handover access point. An access point according to claim 3 or 4,
With wireless LAN terminal
With
The wireless LAN terminal is
Search execution level acquisition means for acquiring a search execution level corresponding to the received radio wave strength used for determining whether or not to search for an access point other than the access point currently belonging to, from the access point belonging to,
A received radio field strength measuring means for measuring the received radio field strength from the access point to which it belongs,
Channel search means for searching for a radio channel used by another access point when the received radio wave intensity measured by the received radio wave intensity measuring means is within a predetermined range from the search execution level;
Handover processing means for executing handover processing to another access point when the received radio wave intensity from another access point using the radio channel detected by the channel search means satisfies a predetermined condition; ,
Signal quality notification means for measuring the received signal quality before and after the handover and notifying the measured received signal quality to the access point belonging after the handover together with the identification information of the access point belonging before the handover A wireless LAN system . The wireless LAN system according to claim 5,
The handover processing means includes
When the received radio wave intensity from another access point detected by the channel search means is higher than the received radio wave intensity from the belonging access point by a predetermined value or more, handover to the other access point A wireless LAN system that executes processing.

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