JP2013247532A - Access point finding method for controlling timing with which radio terminal searches for access point - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an access point finding method and system which can control the timing with which a radio terminal searches for an access point, requiring only low power consumption and a short standby time.SOLUTION: The access point finding method includes: a first step in which a radio terminal transmits a probe request including a broadcast address to a destination address; a second step in which an access point, after receiving the probe request, returns a probe response including information on a time difference till a time at which a next beacon is transmitted; a third step in which the radio terminal, after receiving the probe response, stands by till a beacon standby time of day based on the information on a time difference; a fourth step in which, after the beacon standby time of day, the radio terminal begins a beacon standby in a passive scan mode; a fifth step in which the access point transmits a beacon by broadcasting; and a sixth step in which the radio terminal, after receiving the beacon, executes a connection sequence between the access point and itself.

Description

  The present invention relates to a communication sequence technique for a wireless terminal to find an access point for a wireless local area network (LAN).

  FIG. 1 is a system configuration diagram including a wireless terminal and an access point.

  According to FIG. 1, the access point 2 is connected to the Internet via one access network and communicates with the wireless terminal 1 via the other. A wireless terminal 1 located in a wireless LAN area around the access point can connect to the Internet (upper network) via the access point 2. According to FIG. 1, the wireless terminal 1 is located at a place where it can communicate with the three access points 2. For example, the wireless terminal 1 discovers an access point AP2 for connection purpose, and then tries to connect to the Internet via the access point AP2.

  A wireless LAN employs a MAC (Media Access Control) layer technique for controlling packet transmission between a wireless terminal and an access point. The MAC frame exchanged between the wireless stations by the MAC layer is defined by, for example, the IEEE 802.11 standard.

According to the infrastructure mode of IEEE802.11, there are two methods, “active scan method” and “passive scan method”, for a wireless terminal to discover an access point via a wireless LAN.
In the “active scan method”, a wireless terminal broadcasts a probe request toward an access point and receives a probe response from the access point, thereby discovering the access point.
In the “passive scan method”, an access point periodically broadcasts a beacon, and a wireless terminal receives the beacon, thereby discovering the access point.
Note that a beacon, a probe request, and a probe response are a type of management control signal exchanged between an access point and a wireless terminal.

  Generally, a wireless terminal is equipped with functions of both an active scan method and a passive scan method. A wireless terminal that has found an access point by one of these two methods executes a connection sequence for the access point to be connected.

  FIG. 2 is a sequence diagram based on the active scan method.

  According to FIG. 2, first, the wireless terminal 1 broadcasts a probe request. When transmitting such a frame, the power consumption of the wireless terminal 1 increases. The probe request transmitted by the wireless terminal 1 is received by all the access points 2 (AP1, AP2, AP3) that exist within the reachable range of the radio wave and operate on the same channel.

  On the other hand, each access point 2 returns a probe response to the wireless terminal 1. At this time, according to the MAC layer technology of the wireless LAN, the transmission timing of each access point 2 is controlled so that probe responses transmitted to each other do not collide. For example, according to wireless LAN, a CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) method is adopted in which the same channel is temporally transferred to establish communication between a plurality of terminals.

  On the other hand, the wireless terminal 1 waits for a probe response for a relatively short time with relatively small power consumption. When the wireless terminal 1 receives a probe response from the access point AP2 for connection within the standby time range, the wireless terminal 1 executes a connection sequence for the access point AP2.

  FIG. 3 is a sequence diagram based on the passive scan method.

  According to FIG. 3, each access point 2 transmits beacons periodically and in a broadcast manner. At this time, the wireless terminal 1 waits for a beacon with a relatively small power consumption and for a relatively long time at least equal to or greater than the beacon cycle time. When the wireless terminal 1 receives a beacon from the access point AP2 for connection within the standby time, the wireless terminal 1 executes a connection sequence for the access point AP2.

The access point broadcasts a beacon at all times (for example, at intervals of about 100 ms) in the 2.4 GHz band, for example. The wireless terminal needs to sense (search) whether there is a notification of a beacon from an access point that is a partner to which each of the 2.4 GHz band, for example, 10 channels is connected. In this case, the wireless terminal needs to wait for a beacon for at least 100 ms in each channel. Then, at least about 1 second of standby time is required to sense all channels as follows.
100 msec x 10 channels = 1 sec
When the wireless terminal 1 is a mobile phone or a smartphone that operates on a battery, it is effective from the viewpoint of suppressing power consumption to shorten such a standby time as much as possible.

  In the active scan method, power consumption temporarily increases in order to transmit a probe request, but the standby time for probe response is relatively short. On the other hand, although the passive scan method consumes relatively little power, the beacon standby time is relatively long. As a result, the active scan method that can find an access point in a relatively short time consumes less overall power than the passive scan method. For this reason, the “active scan method” that can find an access point in a relatively short time is generally used frequently in a wireless terminal. When the wireless terminal enters the area of the access point to be connected, the wireless terminal transmits a probe request in the active scan method and receives a probe response to the probe request, thereby discovering the access point.

  As a conventional technique, there is a technique for switching to either an active scan method or a passive scan method based on whether a wireless terminal is within or out of service to find an access point (see, for example, Patent Document 1).

JP 2005-12539 A

  However, according to the active scan method, a wireless terminal is detected by a plurality of access points located in the vicinity thereof in order to transmit a probe request by broadcast, and a probe response is returned from these access points. On the other hand, the wireless terminal connects only to the access point that has returned the probe response including the service identifier of the access point that is the connection purpose. That is, the probe response transmitted by the access point other than the connection purpose is simply ignored, and the radio resource is merely wasted.

  On the other hand, according to the passive scan method, since it is not necessary to transmit a probe request from a wireless terminal, it is not necessary to receive a probe response from an access point other than the connection purpose, and wireless resources are not wasted. .

  In general, when a wireless terminal recognizes that it is located under an access point (or when operated by a user or requested by a data transmission / reception application), an active scan method is executed. Send a probe request. On the contrary, when it is recognized that it is not located under the access point, a passive scan is executed, and a beacon standby state is set.

  However, in an area under the access point, an active scan method that further consumes radio resources is executed in spite of having to save radio resources as much as possible. On the other hand, in a place where wireless resources are not wasted relatively, and where there is no area under the access point, a passive scan method is executed in which power consumption increases due to a relatively long standby time. In the first place, since the radio waves from the access point are not visible to the user, it is impossible to know whether or not the user is in the area under the access point.

  Therefore, the present invention provides an access point discovery method and system capable of controlling the timing at which a wireless terminal searches for an access point so that the power consumption is relatively small and the standby time is relatively short. For the purpose.

According to the present invention, there is provided an access point discovery method in which a wireless terminal discovers an access point via a wireless LAN,
A first step in which a wireless terminal transmits a probe request including a broadcast address as a destination address by an active scan method;
A second step in which the access point returns a probe response including time difference information up to the transmission timing of the next beacon after receiving the probe request;
A third step in which the wireless terminal waits until the beacon standby time based on the time difference information without executing a connection sequence with the access point after receiving the probe response;
A fourth step in which the wireless terminal starts beacon standby in the passive scan mode after the beacon standby time;
A fifth step in which the access point broadcasts a beacon;
The wireless terminal has a sixth step of executing a connection sequence with the access point after receiving the beacon.

According to another embodiment of the access point discovery method of the present invention,
For the third step, the wireless terminal shifts the wireless communication unit to the power saving mode until the beacon standby time,
Regarding the fourth step, the wireless terminal preferably returns the wireless communication unit from the power saving mode after the beacon standby time.

According to another embodiment of the access point discovery method of the present invention,
Regarding the sixth step, when the wireless terminal receives a beacon from an access point and the reception level of the beacon is equal to or lower than a predetermined threshold, the wireless terminal does not execute a connection sequence with the access point,
It is also preferable to wait until the beacon standby time that becomes the periodic transmission timing of the next beacon and repeat the fourth step and the sixth step until the reception level of the beacon becomes higher than a predetermined threshold.

According to another embodiment of the access point discovery method of the present invention,
About a 4th step, it is also preferable that a radio | wireless terminal waits for a beacon in the predetermined time range containing beacon standby time.

According to another embodiment of the access point discovery method of the present invention,
Regarding the second step, it is also preferable that the access point transmits a normal beacon without returning a probe response when the beacon transmission timing is within a predetermined time.

According to another embodiment of the access point discovery method of the present invention,
Regarding the first step, it is also preferable that the wireless terminal includes a service identifier of an access point for connection purpose or a service identifier of a wild card as a network connection identifier in the probe request.

According to another embodiment of the access point discovery method of the present invention,
Regarding the second step, the access point preferably also includes the MAC (Media Access Control) address of the wireless terminal that is the source of the probe request as the destination MAC address of the probe response.

According to another embodiment of the access point discovery method of the present invention,
The non-request source wireless terminal other than the wireless terminal that transmitted the probe request is in a range where the radio waves of the access point can be received,
For the second step, the access point includes the broadcast address in the destination MAC address of the probe response,
For the third step, the non-request source wireless terminal waits until the beacon standby time based on the time difference information by receiving the probe response addressed to the broadcast immediately before attempting to transmit the probe request,
Regarding the fourth step, when the non-request source wireless terminal reaches the beacon standby time, it waits for a beacon in the passive scan method,
Regarding the sixth step, it is also preferable that the non-request source wireless terminal has a sixth step of executing a connection sequence with the access point when receiving the beacon.

According to the present invention, a system in which a wireless terminal discovers an access point via a wireless LAN,
Wireless terminal
Probe request transmission means for transmitting a probe request including a broadcast address as a destination address by an active scan method;
Standby control means for waiting until the beacon standby time based on the time difference information without executing a connection sequence with the access point after receiving the probe response;
Beacon standby means for waiting for a beacon in the passive scan method after the beacon standby time;
A connection sequence establishing means for executing a connection sequence with the access point after receiving the beacon;
The access point
After receiving the probe request, a probe response return means for returning a probe response including time difference information until the next beacon transmission timing;
And a beacon transmitting means for transmitting a beacon by broadcast.

According to another embodiment of the system of the present invention,
The standby control means of the wireless terminal is
Until the beacon standby time, shift the wireless communication unit to the power saving mode,
It is also preferable to return the wireless communication unit from the power saving mode after the beacon standby time.

According to another embodiment of the system of the present invention,
When a wireless terminal receives a beacon from an access point and the reception level of the beacon is equal to or lower than a predetermined threshold, the wireless terminal performs a periodic transmission timing of the next beacon without executing the process of the connection sequence establishment unit. It is also preferable to further include a beacon reception level determination unit that waits until the beacon standby time and controls to repeat the processes of the standby control unit and the beacon standby unit until the beacon reception level becomes higher than a predetermined threshold.

According to another embodiment of the system of the present invention,
It is also preferable that the beacon standby unit of the wireless terminal waits for a beacon within a predetermined time range including a beacon standby time.

According to another embodiment of the system of the present invention,
When the beacon transmission timing is within a predetermined time, the access point probe response return means preferably does not return a probe response and then transmits a normal beacon by the beacon transmission means.

According to another embodiment of the system of the present invention,
The probe request transmission means of the wireless terminal preferably includes the service identifier of the access point for connection or the wild card service identifier as the network connection identifier in the probe request.

According to another embodiment of the system of the present invention,
The probe response return means of the access point preferably includes the MAC address of the wireless terminal that is the source of the probe request as the destination MAC address of the probe response.

According to another embodiment of the system of the present invention,
The non-request source wireless terminal other than the wireless terminal that has transmitted the probe request is in a range where the radio waves of the access point can be received via the wireless LAN,
The probe response return means of the access point includes the broadcast address in the destination MAC address of the probe response,
The standby control means of the wireless terminal as the non-request source wireless terminal waits until the beacon standby time based on the time difference information by receiving the probe response addressed to the broadcast immediately before attempting to transmit the probe request,
The beacon standby means of the wireless terminal as the non-request source wireless terminal waits for the beacon in the passive scan method after the beacon standby time,
It is also preferable that the connection sequence establishment means of the wireless terminal as the non-request source wireless terminal executes the connection sequence with the access point after receiving the beacon.

  According to the access point discovery method and system of the present invention, it is possible to control the timing at which a wireless terminal searches for an access point so that the power consumption is relatively small and the standby time is relatively short.

1 is a system configuration diagram including a wireless terminal and an access point. It is a sequence diagram based on an active scan system. It is a sequence diagram based on a passive scan system. It is a MAC frame format in the present invention. It is a sequence diagram in the present invention. It is a sequence diagram in which a non-request source wireless terminal controls the start timing of a connection sequence by receiving a probe response from an access point. It is a sequence diagram which controls the start timing of a connection sequence according to the reception level of the beacon which a wireless terminal receives from an access point. It is a function block diagram of the radio | wireless terminal in this invention. It is a function block diagram of the access point in this invention.

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

  First, the control frame MAC frame format used in the present invention will be described. Specifically, the present invention relates to beacons, probe requests, and probe responses based on the IEEE 802.11 standard.

FIG. 4 is a MAC frame format in the present invention. According to FIG. 4, the MAC frame format is composed of the following information items.
"Frame control"
"DurationID"
"Destination MAC address"
"Source MAC address"
"BSSID (Basic Service Set IDentifier)"
"Sequence control"
"Frame body"
"FCS (Frame Check Sequence)"

  FIG. 5 is a sequence diagram in the present invention.

(S0) At this time, the wireless terminal 1 is not located in a position where it can communicate with each access point 2. At this time, each access point 2 transmits a beacon (control frame) periodically (for example, about every 100 ms) and broadcast. The “beacon” advertises the presence of the access point to neighboring wireless terminals, and includes a service identifier SSID (Service Set IDentifier, 0 to 32 character strings) in the frame body. The wireless terminal 1 can find an access point by receiving a beacon.

(S1) It is assumed that the wireless terminal 1 is located under the access point AP2 for connection. Initially, the wireless terminal 1 operates in the power saving mode without supplying power to the wireless communication unit. The wireless terminal 1 returns from the power saving mode by supplying power to the wireless communication unit when a connection operation to the wireless LAN is executed by a user operation or a request from the data communication application.

  Next, in order to discover the access point 2, the wireless terminal 1 transmits a “probe request” including a broadcast address as a destination address by an active scan method.

FIG. 4A shows the MAC frame format of the “probe request”.
"Frame control": The first 8 bits are 00000100 = Probe request "Destination MAC address": Broadcast address (FF: FF: FF: FF: FF: FF)
“Source MAC address”: MAC address of wireless terminal “BSSID”: Broadcast address (FF: FF: FF: FF: FF: FF)
"Frame body"
-SSID: SSID / wildcard of access point for connection purpose
At least.

  When an access point for connection is designated in advance, the wireless terminal 1 includes the SSID of the access point in the SSID. Otherwise, the SSID includes a wild card SSID (arbitrary character string). The wild card SSID is specified by setting the information length of the SSID to zero. As a result, all of the access points 2 that are within reach of the radio wave from the wireless terminal 1 can request to return a probe response to the probe request.

(S2) After receiving the probe request, the access point returns a “probe response” including time difference information until the next beacon transmission timing. According to FIG. 5, all the access points 2 return a probe response to the wireless terminal 1.

FIG. 4B shows a MAC frame format of “probe response”.
“Frame control”: first 8 bits are 00000101 = probe response “destination MAC address”: MAC address of wireless terminal / * broadcast address “source MAC address”: MAC address of access point “BSSID”: MAC address of access point “ Frame body "
-Timestamp: Time stamp of transmission time (μs unit)
・ Beacon Interval: Beacon period (interval) (in units of 1024 μs)
-SSID: SSID of the access point
・ "Time difference information until next beacon transmission timing"
Information length: 4 bytes (μs unit)
The destination MAC address includes the MAC address of the wireless terminal that is the source of the probe request. Thereby, the probe response is received by the wireless terminal that has transmitted the probe request. Note that setting the destination MAC address to “broadcast address” will be described later with reference to FIG.

Here, as a feature of the present invention, the probe response returned by the access point 2 includes “time difference information until the next beacon transmission timing”. The wireless terminal 1 can know the next beacon transmission timing (beacon standby time) by the following formula.
Beacon standby time = Time stamp held in the wireless terminal + Time difference information Here, when waiting for N beacons ahead, it is also preferable to calculate as follows.
Beacon standby time = Time stamp stored in the wireless terminal + Time difference information
+ Beacon period x N

(S3) After receiving the probe response, the wireless terminal 1 waits until the beacon standby time based on the time difference information without executing a connection sequence with the access point. Here, the wireless terminal 1 shifts the wireless communication unit to the power saving mode and stands by until the beacon standby time. As a result, the power consumption of the wireless terminal can be reduced as much as possible.

(S4) When the wireless terminal 1 reaches the beacon standby time as time elapses, the wireless terminal 1 starts waiting for a beacon in the passive scan method. Here, when the wireless communication unit is in the power saving mode, power is supplied to the wireless communication unit to return from the power saving mode. As a result, the wireless terminal 1 can receive a beacon transmitted from the access point 2.

  Here, it is preferable that the wireless terminal waits for a beacon within a predetermined time range including a beacon standby time. This is because a beacon from the access point 2 is received as reliably as possible by having a certain time width. Specifically, the beacon is received with a time width of several milliseconds before and after because the transmission timing slightly varies according to the CSMA / CA method.

(S5) The access point 2 broadcasts a beacon using the passive scan method.

FIG. 4C shows a MAC frame format of “beacon”.
“Frame control”: First 8 bits are 00001000 = Beacon “Destination MAC address”: Broadcast address (FF: FF: FF: FF: FF: FF)
“Source MAC address”: MAC address of access point “BSSID”: MAC address of access point “Frame body”:
-Timestamp: Time stamp of transmission time (μs unit)
・ Beacon Interval: Beacon period (interval) (in units of 1024 μs)
-SSID: Access point service identifier

  In another embodiment, it is also preferable that the access point transmits a normal beacon without returning a probe response when the beacon transmission timing is within a predetermined time. Within the predetermined time, the wireless terminal 1 can receive the beacon transmitted from the access point 2 because it is within the probe response standby time range.

  That is, if the timing at which the probe response should be returned and the timing at which the next beacon is transmitted are close in time, the probe response is not transmitted intentionally. Thereby, waste of radio resources is slightly suppressed. When the timing is close, the time difference from when the probe request is received until the next beacon is transmitted may be 15 milliseconds or less, or a shorter time may be set.

(S6) The wireless terminal 1 executes a connection sequence with the access point 2 when receiving a beacon.

  FIG. 6 is a sequence diagram in which the non-request source wireless terminal controls the start timing of the connection sequence by receiving the probe response from the access point.

  As described above in S2 of FIG. 5 (FIG. 4B), the access point 2 basically includes the MAC address of the wireless terminal 1 that is the source of the probe request in the destination MAC address of the probe response. On the other hand, according to FIG. 6, the access point 2 includes the broadcast address in the destination MAC address of the probe response. As a result, non-request source wireless terminals other than the wireless terminal that has transmitted the probe request can also receive the probe response when in a reception state.

According to FIG. 6, the non-request source wireless terminal also operates in the same sequence as in FIG.
(S3) The non-request source wireless terminal waits until the beacon standby time based on the time difference information after receiving the probe response.
(S4) Next, when the non-request source wireless terminal reaches the beacon standby time, it starts beacon standby in the passive scan method.
(S6) Then, when the non-request source wireless terminal receives a beacon from the access point 2, it executes a connection sequence with the access point 2.
Accordingly, even a non-request source wireless terminal can receive a beacon transmitted from the access point 2 in a relatively short standby time without requiring power consumption for transmitting a probe request.

  FIG. 7 is a sequence diagram in which the wireless terminal controls the start timing of the connection sequence according to the reception level of the beacon received from the access point.

  FIG. 7 shows that the wireless terminal 1 is gradually approaching the connection-purpose access point AP2. First, the wireless terminal 1 transmits a probe request (S1) and receives a probe response from the access point 2 (S2). The wireless terminal 1 knows that the access point AP2 to be connected exists nearby, and waits until the beacon standby time calculated from the time difference information included in the probe response (S3). When the beacon standby time is reached, the wireless terminal 1 starts waiting for a beacon (S4).

  Here, when the wireless terminal 1 receives a beacon from an access point, the wireless terminal 1 determines the reception level of the beacon. If the reception level of the beacon is equal to or lower than the predetermined threshold, the connection sequence is not immediately executed with the access point (S51). And it waits until the beacon standby time which becomes a periodic transmission timing of the next beacon (S52). Thereafter, S3 to S5 are repeated until the reception level of the beacon becomes higher than a predetermined threshold (S53). When the reception level of the beacon becomes higher than a predetermined threshold (S53), the wireless terminal 1 executes a connection sequence for the access point 2. As a result, the connection sequence can be executed only when the reception level between the wireless terminal 1 and the access point 2 is higher than a predetermined threshold.

  In order to know that the wireless terminal 1 has approached the access point 2, in general, the signal reception level is confirmed. However, when the reception level of the probe response is measured using active scan, it is within the range under the access point. Wireless resources are wasted. Therefore, the wireless terminal 1 can determine whether or not it has approached the access point 2 while measuring only the reception level of the beacon.

  FIG. 8 is a functional configuration diagram of the wireless terminal in the present invention.

  According to FIG. 8, the wireless terminal 1 includes, as hardware, an antenna 10 that wirelessly communicates with an access point, a circulator 11 that distributes wireless signals by transmission / reception, and a wireless communication unit 12 that includes a demodulation unit and a modulation unit. Have The wireless communication unit 12 radiates a transmission signal from the antenna 10 at a timing that does not collide with a radio wave transmitted from another wireless terminal or access point by the CSMA / CA method.

  A circulator is a passive circuit element having three or more ports, and has a characteristic that a high-frequency signal input to the first port is output only to the second port. For example, by connecting a matched load to a three-port circulator (Y-junction type), a signal is transmitted only in one direction between the remaining two ports. Specifically, an input signal from port A is output to port B, and an input signal from port B is output to port C.

  In addition, the wireless terminal 1 connects a reception frame analysis unit 131, a standby control unit 132, a beacon standby unit 133, a beacon reception level determination unit 134, a transmission frame generation unit 141, and a probe request transmission unit 142. A sequence establishing unit 15 and a data transmission / reception application 16 are included. These functional components are realized by executing a program that causes a computer installed in the wireless terminal to function. The connection sequence establishment unit 15 executes a connection sequence with the access point 2 via the reception frame analysis unit 131 and the transmission frame generation unit 141. The data transmission / reception application 16 transmits / receives user data to / from the access point 2 via the reception frame analysis unit 131 and the transmission frame generation unit 141.

  The probe request transmission unit 142 outputs to the transmission frame generation unit 141 to transmit a probe request including a broadcast address as a destination MAC address by an active scan method in response to a user operation or a data transmission / reception application request (described above). (See S1 in FIG. 5). The transmission frame generation unit 141 generates a MAC frame format of the probe request and outputs it to the wireless communication unit 12. The probe request transmission unit 142 includes the service identifier of the access point for connection purpose or the service identifier of the wild card as the SSID in the probe request.

  The reception frame analysis unit 131 buffers reception data in units of MAC frames and analyzes the MAC frame format. Here, if the destination MAC address of the received frame is not the MAC address or broadcast address of the wireless terminal, the received frame analysis unit 131 discards the received frame. When the reception frame analysis unit 131 detects reception of a probe response, the reception frame analysis unit 131 outputs the frame to the standby control unit 132. When the reception frame analysis unit 131 detects reception of a beacon, the reception frame analysis unit 131 outputs the frame to the beacon reception level determination unit 134.

  The standby control unit 132 receives the probe response from the reception frame analysis unit 131 and then waits for the beacon standby based on the time difference information to wait until the beacon standby time based on the time difference information without executing a connection sequence with the access point. Wait until the reception time (see S3 in FIG. 5). Here, the standby control unit 132 shifts the wireless communication unit to the power saving mode until the beacon standby time, and returns the wireless communication unit from the power saving mode after the beacon standby time.

  When the beacon standby time reaches the beacon standby time, the beacon standby unit 133 instructs the received frame analysis unit 131 to wait for a beacon in the passive scan method (see S4 in FIG. 5 described above). The beacon standby unit 133 instructs to wait for a beacon within a predetermined time range including the beacon standby time.

  When the beacon reception level determination unit 134 receives a beacon from the reception frame analysis unit 131 and the reception level of the beacon is equal to or lower than a predetermined threshold value, the beacon reception level determination unit 134 performs the next process without executing the process to the connection sequence establishment unit 15. Control waits until the beacon standby time at which the beacon is periodically transmitted, and repeats the processes of the standby control unit 132 and the beacon standby unit 133 until the reception level of the beacon becomes higher than a predetermined threshold.

  The beacon standby time is also preferably specified to wait for N-th ahead beacons (for example, a beacon after about 5 seconds).

  In addition, when the SSID included in the beacon is not the SSID of the access point for connection, the connection sequence establishment unit 15 discards the beacon.

  FIG. 9 is a functional configuration diagram of the access point in the present invention.

  The access point 2 includes, as hardware, an antenna 20 that wirelessly communicates with a wireless terminal, a circulator 21 that distributes wireless signals by transmission / reception, a wireless communication unit 22 that includes a demodulation unit and a modulation unit, and an access network side communication interface 26.

  Further, the access point 2 includes a reception frame analysis unit 231, a probe response reply unit 232, a transmission frame generation unit 241, a beacon transmission unit 242, and a connection sequence establishment unit 25. These functional components are realized by executing a program that causes a computer mounted on the access point to function.

  After receiving the probe request, the probe response return unit 232 instructs the transmission frame generation unit 241 to return a probe response including time difference information up to the next beacon transmission timing (see S2 in FIG. 5 described above). . In addition, when the beacon transmission timing is within a predetermined time, the probe response reply unit 232 controls the beacon transmission unit 242 to transmit a normal beacon without returning a probe response. Further, the probe response reply unit 232 includes the MAC address of the wireless terminal that is the source of the probe request as the destination MAC address of the probe response. It is also preferable to broadcast the destination MAC address of the probe response.

  The beacon transmission unit 242 broadcasts a beacon (see S5 in FIG. 5 described above).

  As described above in detail, according to the access point discovery method and system of the present invention, the wireless terminal searches for an access point so that the power consumption is relatively small and the standby time is relatively short. Timing can be controlled.

  Further, according to the present invention, outside the range under the access point for connection purpose, it operates to discover the access point by intermittently performing active scan, and at other times, it shifts to the power saving mode. Reduces power consumption of wireless terminals.

  Furthermore, in the range under the access point for connection purposes, the frequency of executing active scan is reduced, and waste of radio resources can be suppressed. In addition, the power consumption of the wireless terminal can be reduced by executing the passive scan in a short time range.

  Normally, the beacon is waited for a longer time than the transmission interval because the beacon transmission timing is unknown. On the other hand, according to the present invention, since the beacon transmission timing is known from the probe response, the time interval up to that time shifts the wireless communication unit to the power saving mode and reduces the power consumption as much as possible. Can do. In addition, since exchange of the probe request and probe response is executed only once, waste of radio resources under the access point can be suppressed.

  Also, with respect to the probe response to the probe request, by setting the destination MAC address as the broadcast address, even if it is a non-request source wireless terminal, the probe response is received when it is in the reception state and waits for the next beacon signal of the access point You can know the timing.

  Various changes, modifications, and omissions of the above-described various embodiments of the present invention can be easily made by those skilled in the art. The above description is merely an example, and is not intended to be restrictive. The invention is limited only as defined in the following claims and the equivalents thereto.

DESCRIPTION OF SYMBOLS 1 Wireless terminal 10 Antenna 11 Circulator 12 Wireless communication part 131 Reception frame analysis part 132 Standby control part 133 Beacon standby part 134 Beacon reception level determination part 141 Transmission frame generation part 142 Probe request transmission part 15 Connection sequence establishment part 16 Data transmission / reception application DESCRIPTION OF SYMBOLS 2 Access point 20 Antenna 21 Circulator 22 Wireless communication part 231 Reception frame analysis part 232 Probe response reply part 241 Transmission frame generation part 242 Beacon transmission part 25 Connection sequence establishment part 26 Access network side communication interface

Claims (16)

An access point discovery method in which a wireless terminal discovers an access point via a wireless LAN,
A first step in which the wireless terminal transmits a probe request including a broadcast address as a destination address by an active scan method;
A second step in which the access point returns a probe response including time difference information until the next beacon transmission timing after receiving the probe request;
A third step of waiting until a beacon standby time based on the time difference information without executing a connection sequence with the access point after the wireless terminal receives the probe response;
A fourth step in which the wireless terminal starts beacon standby in the passive scan mode after the beacon standby time;
A fifth step in which the access point broadcasts a beacon;
And a sixth step of executing a connection sequence with the access point after the wireless terminal receives the beacon. For the third step, the wireless terminal shifts the wireless communication unit to the power saving mode until the beacon standby time,
The access point discovery method according to claim 1, wherein the wireless terminal returns the wireless communication unit from the power saving mode after the beacon standby time for the fourth step. Regarding the sixth step, when the wireless terminal receives a beacon from the access point, and the reception level of the beacon is equal to or lower than a predetermined threshold, without executing a connection sequence with the access point,
The system waits for a beacon standby time that is a periodic transmission timing of the next beacon, and repeats the fourth step and the sixth step until the reception level of the beacon becomes higher than a predetermined threshold. Item 3. The access point discovery method according to Item 1 or 2.   4. The access point discovery method according to claim 1, wherein, in the fourth step, the wireless terminal waits for the beacon within a predetermined time range including the beacon standby time. 5.   Regarding the second step, when the beacon transmission timing is within a predetermined time, the access point transmits a normal beacon without returning the probe response thereafter. The access point discovery method according to any one of the above.   6. The wireless terminal according to claim 1, wherein the wireless terminal includes a service identifier of an access point for connection purpose or a service identifier of a wild card as a network connection identifier in the probe request. The access point discovery method according to the item.   The access point includes the MAC (Media Access Control) address of the wireless terminal that is the transmission source of the probe request as the destination MAC address of the probe response with respect to the second step. The access point discovery method according to the item. The non-request source wireless terminal other than the wireless terminal that transmitted the probe request is in a range where the radio waves of the access point can be received,
For the second step, the access point includes the broadcast address in the destination MAC address of the probe response,
For the third step, the non-request source wireless terminal waits until the beacon standby time based on the time difference information by receiving the probe response addressed to the broadcast immediately before attempting to transmit the probe request,
Regarding the fourth step, when the non-request source wireless terminal reaches the beacon standby time, it waits for a beacon in the passive scan method,
The sixth step according to claim 1, further comprising: a sixth step of executing a connection sequence with an access point when the non-request source wireless terminal receives the beacon. The access point discovery method according to any one of the preceding claims. A system in which a wireless terminal discovers an access point via a wireless LAN,
The wireless terminal is
Probe request transmission means for transmitting a probe request including a broadcast address as a destination address by an active scan method;
Waiting control means for waiting until the beacon standby time based on the time difference information without executing a connection sequence with the access point after receiving the probe response;
Beacon standby means for waiting for a beacon in the passive scan method after the beacon standby time;
Connection sequence establishment means for executing a connection sequence with the access point after receiving the beacon;
The access point is
After receiving the probe request, probe response return means for returning a probe response including time difference information until the next beacon transmission timing;
And a beacon transmitting means for broadcasting the beacon. The standby control means of the wireless terminal is
Until the beacon standby time, the wireless communication unit is shifted to the power saving mode,
The system according to claim 9, wherein the wireless communication unit is returned from the power saving mode after the beacon standby time.   When the wireless terminal receives a beacon from the access point and the reception level of the beacon is equal to or lower than a predetermined threshold, the wireless terminal periodically transmits the next beacon without executing the processing of the connection sequence establishment unit. The system further includes a beacon reception level determination unit that waits until a beacon standby time as a timing, and controls to repeat the processes of the standby control unit and the beacon standby unit until the reception level of the beacon becomes higher than a predetermined threshold. The system according to claim 9 or 10, characterized in that   The system according to any one of claims 9 to 11, wherein the beacon standby unit of the wireless terminal waits for the beacon within a predetermined time range including the beacon standby time.   When the beacon transmission timing is within a predetermined time, the probe response return means of the access point does not return the probe response and then transmits a normal beacon by the beacon transmission means. The system according to any one of claims 9 to 12.   The probe request transmission means of the wireless terminal includes a service identifier of a connection purpose access point or a wild card service identifier as a network connection identifier in the probe request. The system according to item 1.   The probe response return means of the access point includes the MAC address of the wireless terminal that is the transmission source of the probe request as the destination MAC address of the probe response. System. The non-request source wireless terminal other than the wireless terminal that has transmitted the probe request is further in a range where radio waves of the access point can be received via the wireless LAN,
The probe response return means of the access point includes a broadcast address in the destination MAC address of the probe response,
Until the beacon standby time based on the time difference information, the standby control means of the wireless terminal as a non-request source wireless terminal receives a probe response addressed to the broadcast immediately before attempting to transmit the probe request. Wait,
The beacon standby unit of the wireless terminal as a non-request source wireless terminal waits for a beacon in a passive scan method after the beacon standby time,
The connection sequence establishment means of the wireless terminal as a non-request source wireless terminal executes a connection sequence with the access point after receiving the beacon. The system according to item 1.

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