JP4367284B2 - HANDOVER METHOD, MOBILE COMMUNICATION SYSTEM, AND ACCESS POINT - Google Patents

Description

  The present invention relates to a mobile communication system including a plurality of access points and one or more stations moving across the access points, and more particularly to handover of stations.

A conventional wireless LAN device performs an operation conforming to the IEEE 802.11 standard. In 802.11, signals necessary for connection between AP and STA are defined, and reconnection handover across a plurality of cells is also performed within this defined range (for example, Non-Patent Document 1).
Here, AP represents an access point (Access Point), and STA represents a station (Station: wireless terminal device).
A general conventional wireless LAN apparatus handover process operates as follows.
The STA searches for other APs during communication with the handover source AP. Any other AP with the same channel frequency can be searched for by beacon reception and probe transmission. If the other AP uses another channel, buffer or discard the signal being communicated, switch the radio unit to another channel, search by beacon reception and probe transmission, and switch to the original channel and resume communication. To do. This is repeated for a plurality of channels to complete the search for other APs.
The STA determines whether it is necessary to perform handover from the beacon / probe ACK reception strength information of the other AP that is the handover source AP and the handover destination candidate.
When it is determined that a handover is necessary, the communication with the handover source AP is disconnected, the radio unit is switched to the channel of the selected handover destination AP, the authentication and the connection process are executed, and the handover destination AP is reconnected ( For example, Non-Patent Document 2).

IEEE 802.11 Wireless LAN Medium Access Control MAC and Physical Layer PHY Specifications 1999 Edition “802.11 high-speed wireless LAN textbook”, supervised by Hideaki Matsue and Masahiro Morikura, IDC Japan, March 29, 2003, p. 48-64

Since the conventional wireless LAN device is used in a quasi-stationary environment such as using a notebook PC used in an office for a hot spot service at a station on a business trip destination, there is no particular problem with the above operation.
However, if the wireless LAN is applied to a train or the like, a STA in communication moves between APs as the train moves, and a handover process in a short time is required.
In a conventional wireless LAN device, this handover process takes time, and there are problems such as a momentary interruption time becoming longer during high-speed movement and an appropriate handover being impossible.
The present invention has been made to solve the above-described problems. Even when a wireless LAN is applied to a high-speed moving environment, the handover process can be executed in a short time and the instantaneous interruption time of user data can be shortened. With the goal.

  A handover method according to the present invention includes a wireless terminal device that moves on a predetermined linear route, and a plurality of wireless terminal devices that accommodate the wireless terminal devices in a predetermined order according to a moving direction of the wireless terminal device on the linear route. A handover method in a mobile communication system comprising: a plurality of access points, wherein one access point accommodates the wireless terminal devices in an order adjacent to the order of the one access point in the predetermined order Adjacent access point information notification step for notifying adjacent access point information regarding the wireless terminal device accommodated by the one access point and the wireless terminal device receiving adjacent access point information notified by the one access point The adjacent access point information receiving step, and the wireless terminal device, A handover step of performing handover from the one access point to any of the adjacent access points based on the received adjacent access point information and the movement direction information of the wireless terminal device on the predetermined linear path; Is provided.

  According to the present invention, there is an effect that switching from a handover source to a handover destination can be performed in a short time.

Embodiment 1 FIG.
FIG. 1 is a system diagram when the handover method of the present invention is applied, and is common to all embodiments thereafter.
In FIG. 1, 100 is a network for interconnecting each network connection device, 120 is an access point (hereinafter referred to as AP) which is a base station of a wireless LAN, STA 130 is a station (hereinafter referred to as STA) which is a mobile wireless terminal device of wireless LAN, 110a. Is a terminal on the IP network 100, and 110b is a terminal connected under the STA.
It is assumed that the STA 130 moves in one direction on the linear path 140. For convenience, the path 140 is shown as a straight line, but may be a curved line. The APa 120a, APb 120b, and APc 120c sequentially accommodate the STAs 130 in this order, for example, when the STAs 130 move to the right in the figure and perform handover.

FIG. 2 is a diagram showing the internal functions of the AP 120.
In FIG. 2, a wireless LAN PHY 300 is a wireless LAN physical layer processing unit, a network interface (IF) 310 is a network interface processing unit, and a MAC frame receiving unit 320 performs reception wireless LAN MAC processing to separate a main signal and a control signal. A processing unit that performs the wireless LAN MAC process of receiving and transmitting a control signal and a main signal, a neighboring AP registration unit 340 is a storage unit that registers an adjacent AP, and a beacon sending unit 350 is a local AP. A processing unit that generates beacon contents from information and neighboring AP information from the neighboring AP registration unit, and a connection control unit 360 is a processing unit that transmits and receives control information to and from the STA, and performs STA connection processing and handover processing.

FIG. 3 shows the internal functions of the STA. In the figure, those having the same numbers as those in FIG. 2 have equivalent functions or equivalent functions.
In FIG. 3, a beacon processing unit 390 is a processing unit for notifying connection control of received beacon signal contents, a moving direction registration unit 400 is a storage unit for registering the moving direction of the STA, and a channel control unit 410 is for controlling the channel frequency of the STA. It is a functional part to do.

Next, the operation will be described.
In each AP, neighboring APs that may be handed over from the self AP are registered in the neighboring AP registration unit 340 in advance.
When the AP is linearly arranged along the route 140, two APs of the starting point direction and the ending point direction are registered together with the moving direction information. As a registration method, direct writing to the AP device using a maintenance terminal or the like or remote writing from a network management device or the like can be considered. As the contents to be written, the use frequency of the neighboring AP, the MAC address, and a part of beacon information can be considered. The information registered in the neighboring AP registration unit is transmitted to the beacon transmission unit, merged with the beacon information of the own station, converted into a MAC frame by the MAC frame generation unit, and as a beacon signal as a radio signal by the wireless LAN PHY unit. Informed. FIG. 4 shows an example of a beacon signal in the present invention.

In the STA, in the first connection with the AP after the power is turned on, an AP search for what kind of AP exists around is performed.
In the AP search, the channel control unit 410 sequentially switches according to the channel frequency permitted, waits for a beacon signal that can be detected in the channel, or sends a probe signal and obtains the same content as the beacon reception as a probe ACK signal. The beacon signal is transferred to the wireless LAN PHY, MAC frame reception, and beacon processing unit and notified to the connection control unit.
The connection control unit 360 selects the optimum AP, for example, the AP having the highest received power from the plurality of APs that can be searched, and performs wireless LAN connection control. The connection control here operates as standard. When the connection between the AP and the STA is completed by the connection control unit 360, communication of user data is started via the terminal under the STA, the network IF unit, the MAC frame generation unit, the MAC frame reception unit, and the wireless LNAPHY unit 300. The AP connected here is set as the handover source AP (accommodation step).

  In parallel with the communication of user data, the STA 130 receives information on two handover destination candidate APs (adjacent access point information) in the direction of the start point and the direction of the end point by a beacon signal from the handover source AP at a fixed period (predetermined time interval) Is transmitted (adjacent access point information notifying step), the STA 130 receives this adjacent access point information (adjacent access point information receiving step). In the STA, information (moving direction information) indicating whether the STA is moving in the starting point direction or the ending point direction is registered by the moving direction registration unit. The STA 130 can identify a destination AP to move from the beacon signal received from the handover source AP and its own movement direction information, and obtain the used frequency, MAC address, and beacon information of the handover destination AP.

  That is, in the adjacent access point information notification step, the APa 120a notifies the STA 130 of the adjacent access point information related to the APb 120b that is the adjacent AP that accommodates the STA 130 next to the APa 120a that currently accommodates the STA 130. In step, the STA 130 receives this neighboring access point information.

When the STA 130 tries to perform a handover from the handover source AP to the handover destination AP, the AP search process, the beacon reception or probe signal transmission / reception process from the handover destination AP, and the optimum AP selection process are performed as in the initial AP connection. And handover can be executed (handover step).
Since the use frequency of the handover destination AP is known in advance, when the connection control unit decides to perform handover, the channel used is notified to the channel control unit and the setting is changed to the handover destination frequency. Further, since the connection control unit knows the MAC address and SSID of the handover destination in advance, it is possible to immediately issue a connection request from the STA to the AP without waiting for a beacon or probe ACK signal.
When the connection to the handover destination AP is completed, the handover destination AP is set as the handover source AP to prepare for the next handover. Thereafter, the same operation is repeated to realize high-speed handover.

Moreover, although the example of one line was demonstrated above, even if it branches in three directions, for example, three neighboring AP information such as Osaka direction, Tokyo direction, Nagano direction is put on the AP beacon, and STA If these three directions are set, the same high-speed handover can be realized.
Note that a criterion for determining that the connection control unit 360 is to be handed over will be described later in a sixth embodiment.

In the AP 120, the neighboring AP registration unit 340, the beacon sending unit 350, the MAC frame generating unit 330, and the wireless LAN PHY unit 300 constitute the neighboring access point information notifying means in the present invention.
In the STA 130, the wireless LAN PHY unit 300 and the MAC frame receiving unit 340 form adjacent access information receiving means in the present invention. The connection control unit 360, the channel control unit 410, and the wireless LAN PHY unit 300 form handover means in the present invention. Is formed.

  As described above, according to this embodiment, since the STA can obtain in advance information necessary for connection to the handover destination AP during communication with the handover source, the AP search for the handover destination candidate, the handover destination AP It is not necessary to perform time-consuming processing for beacon reception from the mobile phone, and switching from the handover source to the handover destination can be performed in a short time.

Embodiment 2. FIG.
The second embodiment will be described with reference to FIG.
In the first embodiment, an example in which the moving direction of the STA is registered in the moving direction registration unit 400 is shown, but in this embodiment, an example in which the moving direction is not registered in advance is shown.
FIG. 5 is a diagram illustrating an internal configuration of the STA 130 according to the second embodiment.
In FIG. 5, a movement direction detection unit 410 is a processing unit that identifies the movement direction of the own STA based on movement result information from the connection control unit 360.
In the second embodiment, the configuration of the AP is the same as in the first embodiment.

Next, the operation will be described.
In the STA of the second embodiment, the movement direction is not registered in advance in the movement direction registration unit 400.
The operation up to the connection with the first AP after the power is turned on is the same as in the first embodiment.
When the connection with the first AP is completed, the connection control unit 360 transmits the MAC address of the connected AP from the beacon or probe ACK received from the connected AP, the MAC address of the AP in the start direction, and the AP in the end direction. The MAC address is notified to the movement direction detection unit 410.

In the operation so far, the STA 130 cannot specify the handover destination AP. Since the connection control unit 360 can grasp the two handover destination AP candidates from the beacon information similar to that of the first embodiment received from the handover source AP, it temporarily stops communication of user data, and the channel control unit determines the two candidate APs. The channel to be used is sequentially switched to perform an AP search operation.
For example, when the STA 130 is mounted on a train, the STA 130 moves in one direction on the track. Therefore, even if either of the two beacons can be received or two of the candidate APs can be received, either reception strength is received. Is getting smaller. Based on this, the connection control unit 360 performs AP selection processing, specifies a handover destination AP, and performs connection processing. When the connection with the handover destination AP is completed, the connection control unit notifies the MAC address (connection access point information which is a predetermined signal) of the AP connected (received) to the moving direction detection unit (connection access point information reception step) ).
That is, in the connection access point information reception step, the STA 130 receives the MAC address of the AP that accommodates the STA 130.
The movement direction detection unit 410 compares the MAC address of the AP in the start point direction obtained from the AP of the handover source and the MAC address of the AP in the direction of the end point with the MAC address of the handover destination AP obtained from the handover destination AP, and Specify the direction of movement. The identified movement direction (movement direction information) is registered in the movement direction registration unit 400 (movement direction information generation step).
That is, in the movement direction information generation step, the STA 130 generates movement direction information from the beacon or probe ACK information and the MAC address transition.
The operation after the movement direction is registered in the movement direction registration unit is the same as in the first embodiment.

The movement direction identification process by the movement direction detection unit 410 is performed by confirming that the N movements are the same movement direction as in the case of registering in the movement direction registration unit with only two AP connections as described above. It is possible to register in the movement direction registration unit.
Further, after the registration of the movement direction in the movement direction registration unit is completed, the movement direction is continuously confirmed, and if the movement direction is changed, the movement direction registration can be changed.

  As described above, according to the second embodiment, since it is configured as described above, the switching from the handover source to the handover destination can be performed in a short time, and the movement direction of the train can be changed without registering the movement direction in advance. It is possible to automatically set it accordingly. In addition, the train can be automatically and flexibly updated when the moving direction of the train changes.

Embodiment 3 FIG.
The third embodiment will be described with reference to FIGS.
The system in this embodiment is provided with an authentication server (not shown) in FIG. 1 described in the first embodiment.
FIG. 6 shows the internal functions of AP 120 in the third embodiment.
In FIG. 6, an inter-AP information transmission unit 370 is a processing unit that transmits STA information and the like to a neighboring AP prior to handover, and an inter-AP information reception unit 380 is a processing unit that receives STA information and the like from the adjacent AP prior to handover.
In the third embodiment, the configuration of the STA is the same as that of the first embodiment.
FIG. 8 is a diagram showing an outline of a sequence example in the third embodiment. FIG. 8 is a sequence example for explaining the outline of the operation, and detailed signal contents and the like are omitted.

Next, the operation will be described.
The operations described in the first and second embodiments are similar here. The STA 130 performs authentication and connection association with the AP to be connected for the first time or at an appropriate interval, and this is, for example, the handover source APa. In this connection, the STA 130 waits for reception of a beacon or requests a probe, receives a probe ACK, and obtains information on the APa 120a. The STA sends a connection request to the APa and performs a connection process with the APa 120a. Here, a plurality of signals are transferred (connection request / response), and the connection between the STA and the APa is established. The STA 130 reads movement direction information from the movement direction registration unit 400 during this connection process, and notifies the APa 120a of its movement direction.
Next, the STA 130 performs an authentication process with the authentication server. The authentication related signal is transferred to the authentication server via the APa 120a. Again, a plurality of signals are passed to the authentication server (authentication request / response), and the authentication of the STA 130 by the authentication server is completed. When the authentication of the STA 130 is completed, the authentication server passes pre-key information that is a key generation source to the APa 120a and the STA 130.
When the advance key information is notified, the APa 120a notifies the STA 130 of the APa information, and the STA 130 notifies the STA information to the APa 120a to generate a key. Thereafter, in order to use the generated key for communication, key introduction processing is performed, and encrypted communication is started.

  The process so far takes a certain amount of time. In a normal handover, this operation is repeated every time a handover is performed, so that the handover time becomes longer.

In this embodiment, when authentication of the STA 130 is completed via the handover source APa 120a, even if the STA 130 is handed over to the APb 120b, authentication processing and key generation are not performed there, and the handover time is shortened. In order to realize this, the connection information and authentication information of the STA 130 are passed from the APa 120a to the APb 120b in advance (connection step). As connection information, the MAC address and AID of the STA, and as authentication information, a PMK (Pairwise Master Key), a random number, the MAC address of the AP, and the like are conceivable.
The generic name of the connection information and the authentication information is the connection information in the present invention, but the connection information is not limited to those listed here.

As described above, since the STA 130 notifies the APa 120a of its movement direction during the connection process, the APa 120a obtains the movement direction information of the STA 130 during the connection process with the STA 130. In the APa 120a, two adjacent APs in the starting point direction and the ending point direction are registered in the adjacent AP registration unit 340 in advance. The APa 120a compares the moving direction information of the STA 130 and the neighboring AP information, specifies the AP that is the handover destination of the STA 130, and sets the identified AP as the handover destination access point APb.
When the user data communication with the STA 130 is started, the APa 120a notifies the APb 120b of the connection information and authentication information in advance to the APb 120b via a wired line during the communication. In APb 120b, processing up to key generation performed by AP A 120a before starting user data communication with STA 130 is performed in advance. It is conceivable that the key generation process includes registration of PMK, generation of PTK (Pairwise Transient Key), and the like.
The connection information and the authentication information are “connection information” in the present invention. The “connection information” may be one other than the connection information and the authentication information, or may be other information.

Thereafter, with the movement of the STA 130, the STA 130 is unable to continue the connection with the APa 120a, and it is determined that the handover to the APb 120b is performed. Similar to the operation of the first embodiment, since the STA knows the APb information in advance, the STA switches its own channel frequency to the channel used by the APb 120b. When the switching is completed, a connection request signal is sent to the APb 120b without waiting for a beacon or the like based on the APb information already known in advance. Since APb 120b also obtains STA information in advance via a wired line, it can send a connection completion response to STA 130 without time-consuming processing. Next, a key introduction process is performed between the STA and the APb using the key generated in advance by the APb and the key used by the STA 130 for communication with the APa. Thereafter, communication of user data is started between the STA 130 and the APb 120b.
After user data communication between the STA 130 and the APb 120b is started, in parallel with the user data communication, an instruction to disconnect the STA 130 corresponding to the APa is issued from the APb to the APa via a wired line. The APa 120a releases the connection with the corresponding STA 130 by receiving a disconnection instruction from the APb 120b.
In addition, the STA disconnection process of the handover source AP has the same effect even if it is disconnected by a timer or the like that monitors the absence of communication traffic with the corresponding STA.
When the processing so far is completed, the APb 120b is set as the handover source AP, and the handover is repeated to the next AP in the same manner.

  In this third embodiment, since it is configured as described above, the normal interruption of user data requires long time such as channel switching, connection control, authentication control, and key control. It takes only a part of the control and part of the key control, and the instantaneous interruption time of the user data can be shortened.

In the above example, the first authentication information is used to the end. For example, during normal communication with APx, the authentication information is updated at a certain interval, for example, every 10 minutes, when APx and authentication-included reconnection is executed. Is also possible.
Further, in the above description, the configuration of the STA 130 is the same as that of the first embodiment. However, similarly to the second embodiment, the movement direction detection unit 410 may detect the movement direction and register it in the movement direction registration unit 400. Good.

  In the above embodiment, an example is shown in which the APa 120a that is the movement source AP acquires the movement direction of the STA 130 and notifies the AP in the movement direction in advance of authentication information and connection information. Authentication information and connection information may be notified in advance to both APs without acquiring STA movement information.

Embodiment 4 FIG.
The fourth embodiment will be described with reference to FIGS.
FIG. 9 is a diagram showing an outline of a sequence example in the fourth embodiment. FIG. 9 is a sequence example for explaining the outline of the operation, and detailed signal contents and the like are omitted.

Next, the operation will be described.
In the fourth embodiment, the operation from when the STA 130 is connected to the first APa 120a until the APa 120a notifies the APb 120b of STA information and authentication information via a wired line is the same as that of the third embodiment.
In the fourth embodiment, the APb 120b that has received the STA information and the authentication information completes the connection process of the corresponding STA 130 at this time. Although the connection completion signal is not sent to the STA 130, the process proceeds to a state similar to the state in which the STA 130 is connected to the APb 120b. Regarding the key processing, the APb 120b completes the processing from the generation of the key to the introduction of the key at this point.
Thereafter, the STA 130 is unable to continue the connection with the APa 120a with the movement, and determines that the handover to the APb 120b is performed. Since the STA 130 knows the information of the APb 120b in advance, the STA 130 switches its own use channel frequency to the channel used by the APb. When the switching is completed, the STA 130 switches the destination of its own signal to the APb 120b, and directly enters the user data communication without the connection process with the APb 120b and the key introduction process.
The subsequent disconnection processing of the handover source APa 120a is the same as that in the third embodiment.
Since the fourth embodiment is configured as described above, the instantaneous interruption time of user data can be further reduced as compared with the third embodiment.

  In the above description, an example is described in which the processing up to the key generation and key introduction is performed in advance at the handover destination AP. However, the key itself generated by the handover source AP may be sent in advance to the handover destination AP.

Embodiment 5.
A fifth embodiment will be described with reference to FIG.
In the first embodiment, an example is shown in which adjacent AP information is registered in the neighboring AP registration unit 340. However, in this embodiment, an example in which neighboring AP information is not registered in advance is shown.
FIG. 7 is a diagram showing an internal configuration of the AP 120 in the fifth embodiment.
In FIG. 7, the neighboring AP registration unit 340 is a storage unit that stores neighboring AP information corresponding to the moving direction of the STA based on the STA movement result information from the connection control unit 360.
In the fifth embodiment, the configuration of the STA is the same as that of the first embodiment.

Next, the operation will be described.
In the AP of the fifth embodiment, the neighboring AP information is not registered in the neighboring AP registration unit 340 in advance.
The operation until the connection with the first AP 120a of the STA after the power is turned on is the same as in the first embodiment. At this time, the neighboring AP information is not registered in the neighboring AP registration unit 340 of the AP 120a. After that, when the STA 130 moves and tries to connect to the next handover destination AP 120b, a normal handover process is performed without neighboring AP information being included in the beacon or probe ACK received from the handover source AP 120a. When the connection with the handover destination AP 120b is completed, the STA 130 notifies the handover destination AP 120b of the movement direction information registered in the movement direction registration unit 400 and the AP information such as the MAC address of the handover source AP 120a. The handover destination AP 120b receives information notification from the connection control unit 360, and registers the neighboring AP information in the direction opposite to the moving direction of the STA 130 in the neighboring AP registration unit 340. Further, the inter-AP information transmission unit 370 notifies the handover source AP 120a of the MAC address of the STA 130, the moving direction information, the MAC address of the AP 120b, and the like via a wired line. The handover source AP 120a that has received the notification releases the connection with the STA and registers the neighboring AP information in the moving direction of the STA 130 in the neighboring AP registration unit 340. The AP whose contents are registered in the adjacent AP registration unit 340 adds the adjacent AP information to the beacon or probe ACK signal transmitted by the local station and transmits the AP.
Thereafter, the handover source AP and the handover destination AP are sequentially updated. The operation after the contents are registered in the neighboring AP registration unit 340 and the neighboring AP information is added to the beacon or probe ACK signal is the same as that in the first embodiment.

In the above description, the neighbor AP information is updated by one handover, but it is also conceivable to update the neighbor AP information with a plurality of handover results.
In addition, after the registration of the neighboring AP information to the neighboring AP registration unit 340 is completed, the handover status is continuously confirmed, and if there is a change in the content, the moving direction registration can be changed.

  As described above, in the fifth embodiment, since it is configured as described above, it is possible to switch from a handover source to a handover destination in a short time, and without registering neighboring AP information in advance, the moving direction of the train It becomes possible to set automatically according to. In addition, the train can be automatically and flexibly updated when the moving direction of the train changes.

Embodiment 6 FIG.
The operation of the sixth embodiment will be described.
In the first to fifth embodiments, the STA connected to the handover source AP needs to perform a process of making a handover to the APb 120b by some method. In the sixth embodiment, a method for determining to perform handover will be described. This handover determination operation is performed by the connection control unit 360 of the STA 130 in the first to fourth embodiments.

In a normal handover method, the STA 130 temporarily stops communication with the APa 120a, switches to a frequency used by another AP, waits for a beacon, or receives an AP signal by a probe. The STA 130 repeats this operation, collects the beacon reception strength, and determines the optimum handover destination AP from the reception strength. However, this method does not allow user data to be communicated while receiving a handover candidate beacon.
In the sixth embodiment, the start of handover is determined by making the following determination.
When the reception level of the beacon signal of the handover source AP is lower than a certain level occurs a specified number of times.
• When the specified number of times that the reception level of the main signal during communication falls below a certain level.
• When the specified number of times that the transmission speed of the main signal during communication falls below a certain level.
It decides to hand over to the handover destination APb under the AND or OR condition of the above conditions. Also, AND and OR may be combined. For example, condition A AND condition B OR condition C
It may be as follows. It is arbitrary whether the conditions A, B, and C are any of the above conditions, and the combination of AND and OR is also arbitrary, such as taking the AND of two conditions and the OR of one other condition.
In other words, in this embodiment, in the handover step, the STA 130 determines the timing of the handover in consideration of the quality of the signal received from the AP (the reception level of the beacon signal, the reception level of the main signal, the transmission speed of the main signal, etc.). It will be decided.

  As described above, in the handover method according to the sixth embodiment, in a wireless LAN system in which APs are linearly arranged, handover start determination can be made without receiving beacon information of the handover destination AP, and beacon information collection of the handover destination AP is performed. Handover can be performed without causing a momentary interruption of user data for a period of time.

Embodiment 7 FIG.
FIG. 10 is a configuration diagram of the STA in the seventh embodiment.
In the figure, a data copy unit 420 copies a transmission signal as necessary and sends it to two wireless LANPHY units 300a and 300b, and a data synthesis unit 430 receives both signals received from two wireless LANPHYs as necessary. Is a processing unit that transmits the MAC frame to the MAC frame receiving unit 340.

Next, the operation will be described.
In the seventh embodiment, the operation will be described with reference to the STA 130 in FIG. 10, the AP 120 in FIG. 6, and the sequence in FIG.
Operations until the STA 130 decides to perform handover are the same as those in the first to fifth embodiments. The STA 130 attempts to perform a handover, and attempts to perform connection processing or data communication with the handover destination APb 120b. If communication with the handover destination APb 120b is possible, a wireless ACK signal is returned from the APb 120b in response to the wireless signal from the STA. However, if the APb 120b cannot be normally connected and the wireless ACK signal cannot be received, the STA 130 operates to perform connection processing or data communication with the handover destination AP while maintaining the connection with the handover source AP. Since this STA 130 has two wireless LAN PHYs, this operation is possible.

At the time of double connection, in the STA to AP direction, the uplink data input from the terminal under the STA to the STA is copied by the data copying unit and transmitted to the handover source APa and the handover destination APb via the respective wireless LAN PHYs. The When the handover destination APb is in the process of connection, data is transmitted only to the handover source APa. In the AP to STA direction, signals from the two wireless LAN PHYs are input to the data synthesis unit. The data synthesis unit sends both reception signals from the two wireless LAN PHYs to the MAC frame reception unit.
When the wireless ACK signal is returned from the handover destination APb, the double connection operation is stopped. The data copy unit transfers data only to the wireless LAN PHY corresponding to the handover destination APb. The data combining unit sends only a signal from the wireless LAN PHY corresponding to the handover destination APb to the MAC frame receiving unit.

  Since the handover method according to the seventh embodiment is configured as described above, the data interruption time can be reduced even when a new AP is not immediately connected during the handover operation. Further, even when a new AP is immediately connected, the data interruption time can be reduced.

Embodiment 8 FIG.
The operation of the eighth embodiment will be described. The operation will be described with reference to the STA of FIG. 5, the AP of FIG. 6, and the sequence of FIG.
In the eighth embodiment, the sequence from the handover source APa to the handover destination APb is the same as in any one of the first to seventh embodiments. In the eighth embodiment, the transmission interval of beacons (notification information) transmitted from the AP is controlled.

Also in this embodiment, as in the first embodiment, the STA performs an AP search as to what kind of AP is present in the first AP connection after the power is turned on.
The AP transmits a beacon, and the STA receives this beacon signal (access point information notification step).
In AP search, the channel control unit 410 is sequentially switched according to the permitted channel frequency, and a beacon signal that can be detected in the channel is waited, or a probe signal is sent and the same contents as beacon reception are obtained as a probe ACK signal. The beacon signal is transferred to the wireless LAN PHY, MAC frame reception, and beacon processing unit and notified to the connection control unit.
The connection control unit 360 selects the optimum AP, for example, the AP having the highest received power from the plurality of APs that can be searched, and performs wireless LAN connection control. The connection control here operates as standard. When the connection between the AP and the STA is completed by the connection control unit 360, communication of user data is started via the terminal under the STA, the network IF unit, the MAC frame generation unit, the MAC frame reception unit, and the wireless LNAPHY unit 300. The AP connected here is set as the handover source AP (accommodation step).

When APs are arranged linearly and adjacent APs use the same channel frequency, the channel used by the handover destination APb need not be taught by the beacon signal of the handover source APa as in the first embodiment. Cases are also conceivable. In this case, the STA can detect the beacon of the handover destination APb at the same frequency during communication with the handover source APa.
The beacon is transmitted at a constant cycle, but the cycle is set to be longer (for example, a cycle of 100 mS) so as not to compress the use band of user data. It takes a worst time of 100 ms for the STA to be under the handover destination APb and discover the beacon.

On the other hand, when a wireless LAN is applied to a train or the like, there is little possibility that an adjacent AP has a STA (train). In such a situation, the handover destination APb does not need to consider compressing the user data band.
Therefore, in the eighth embodiment, when the STA is not connected to the handover destination APb, the beacon transmission cycle is shortened, for example, 10 mS, and the beacon detection time of the STA handover destination APb is shortened.
When the STA is connected to the handover destination APb (handover step), the handover destination APb returns the beacon transmission cycle to the original long cycle.

  In the eighth embodiment, since it is configured as described above, the beacon detection time in the handover process can be shortened without squeezing the band of user data.

Embodiment 9 FIG.
The operation of the ninth embodiment will be described. The operation will be described with reference to the STA of FIG. 5, the AP of FIG. 6, and the sequence of FIG.
In the ninth embodiment, the sequence from the handover source APa to the handover destination APb is the same as in the third embodiment. In the ninth embodiment, control is performed so as to increase the reliability of radio communication between the STA and the AP at the time of handover.
When a handover is performed, both the handover source APa and the handover destination APb operate in the periphery of the cell, and the radio transmission between the AP and the STA is often in a severe situation (see FIG. 1). In such a situation, a radio transmission error occurs, the retransmission process operates, and the handover time becomes long.
On the other hand, a wireless LAN supports a plurality of physical speeds. For example, in 802.11a, 54 Mbps, 48 Mbps, 36 Mbps,..., 12 Mbps, 9 Mbps, 6 Mbps. In general, the slower the physical speed, the higher the resistance to radio degradation.

  For this reason, in the ninth embodiment, radio signal transmission / reception related to handover uses a low physical speed that is highly resistant to radio degradation. For example, even if the last communication with the handover source is performed at 24 Mbps, the connection request signal, the connection response signal, and the key introduction signal for connecting to the APb are communicated at 6 Mbps.

  As another implementation method, when transmitting directly from user data without exchanging connection signals with the handover destination APb as in the sequence of FIG. 9 of the fourth embodiment, the data to be transmitted to the handover destination APb for the first time is If transmission is possible at a low rate and communication is possible without error, a method of increasing the transmission speed sequentially can be considered.

  In the ninth embodiment, since it is configured as described above, it is possible to reduce the possibility of a long handover time such as a retransmission process due to a data error even in a state where the radio environment at the time of handover is deteriorated.

  As described above, the handover method and the mobile communication system according to the present invention are effective for the handover of a station in a mobile communication system including a plurality of access points and one or more stations moving across the access points. This is suitable for a mobile communication system in which access points accommodate stations in a predetermined order.

The figure which shows an example of the system which applies the hand-over method in this invention. The figure which shows an example of the internal mechanism of the access point in this invention. The figure which shows one example of the internal mechanism of the station in this invention. The figure which shows one example of the beacon signal in this invention. The figure which shows an example of the internal structure of the station in this invention. The figure which shows an example of the internal mechanism of the access point in this invention. The figure which shows an example of the internal mechanism of the access point in this invention. The figure which shows the outline | summary of the sequence example in this invention. The figure which shows the outline | summary of the sequence example in this invention. The figure which shows one example of the internal mechanism of the station in this invention.

Explanation of symbols

  100 network, 110 terminal, 120 access point, 130 station, 140 route, 300 wireless LAN PHY unit, 310 network interface, 320 MAC frame reception unit, 330 MAC frame generation unit, 340 neighbor AP registration unit, 350 beacon transmission unit, 360 connection Control unit, 370 inter-AP information transmission unit, 380 inter-AP information reception unit, 390 beacon processing unit, 400 movement direction registration unit, 410 channel control unit, 410 movement direction detection unit, 420 data copy unit, data composition unit.

Claims (12)

A wireless terminal device moving on a predetermined linear route connecting the first point and the second point, and accommodating the wireless terminal device in a predetermined order according to the moving direction of the wireless terminal device on the linear route A handover method in a mobile communication system comprising a plurality of access points,
Each of the plurality of access points includes information necessary for communication with a first adjacent access point adjacent to the access point on the first point side, and a second adjacent point adjacent to the access point on the second point side. Holding adjacent access point information including information required for communication with the access point, and information on the direction of the first adjacent access point and the second adjacent access point viewed from the access point;
1 access point
The neighboring access point information notifying upper Kitonari contact access point information to the wireless terminal by the access point of the one is accommodated notifying step and said wireless terminal device,
An adjacent access point information receiving step for receiving adjacent access point information notified by the access point in 1 above;
The wireless terminal device is
Based on the received adjacent access point information and the moving direction information of the wireless terminal device on the predetermined linear route, the first direction is set when the moving direction of the wireless terminal device is the first point direction. A handover method comprising: a handover step of performing handover to an adjacent access point and performing handover to the second adjacent access point when the moving direction of the wireless terminal apparatus is the second point direction . 2. The neighboring access point information notifying step, wherein the one access point notifies the neighboring access point information to a wireless terminal device accommodated in the one access point at a predetermined time interval. The handover method described in 1. The wireless terminal device is
A connection access point information receiving step for receiving connection access point information, which is a predetermined signal of an access point accommodating the wireless terminal device;
The handover method according to claim 1, wherein the wireless terminal device includes a moving direction information generation step of generating the moving direction information from the received connection access point information and the transition thereof. A connection step in which the access point performs connection processing by exchanging predetermined connection information for connection with the wireless terminal device accommodated by the access point with the wireless terminal device;
The access point includes a connection information notification step of notifying one of the adjacent access points of the connection information acquired from the wireless terminal device in the connection step based on the movement direction information. Item 2. The handover method according to Item 1. The connection information is connection information and authentication information. When the adjacent access point is notified of the connection information and authentication information from an access point that accommodates the wireless terminal device, connection processing with the wireless terminal device is performed. The handover method according to claim 4, wherein an encryption key is generated from the notified connection information and authentication information before starting the operation. When the wireless terminal device performs handover, it notifies the access point of the handover source AP information and the moving direction;
The access point updating neighboring AP information based on information notified from the wireless terminal device; and
The access point notifying neighboring access point information based on the updated neighboring AP information;
The handover method according to claim 1, further comprising: In the handover step,
The handover method according to claim 1, wherein the wireless terminal apparatus determines a handover timing in consideration of a quality of a signal received from the one access point.   2. The handover method according to claim 1, wherein, in the handover step, the wireless terminal apparatus can simultaneously communicate with a plurality of access points. Movement comprising: a wireless terminal device that moves on a predetermined linear route; and a plurality of access points that accommodate the wireless terminal device in a predetermined order according to the moving direction of the wireless terminal device on the linear route A handover method in a communication system, comprising:
An access point information notification step in which each access point transmits notification information for notifying the existence of the access point to the wireless terminal device, and the wireless terminal device,
Receiving step for receiving broadcast information from the access point of 1 and being accommodated in the access point that has transmitted the broadcast information;
The wireless terminal device is
In a handover method comprising: a broadcast step of receiving broadcast information from an access point adjacent to the one access point and performing handover to the adjacent access point;
In the access point information notification step, the time interval at which each access point reports the notification information varies depending on whether or not the access point accommodates a wireless terminal device. In the handover step, the communication speed between the wireless terminal apparatus and the access point adjacent to the one access point that is the handover destination is made slower than the communication speed between the wireless terminal apparatus and the one access point that is the handover source. 10. The handover method according to claim 1 or 9, wherein: A wireless terminal device moving on a predetermined linear route connecting the first point and the second point, and accommodating the wireless terminal device in a predetermined order according to the moving direction of the wireless terminal device on the linear route In a mobile communication system comprising a plurality of access points,
The access point is
Information required for communication with the first adjacent access point adjacent to the access point on the first point side, information required for communication with the second adjacent access point adjacent to the access point on the second point side, And an adjacent access point for notifying the wireless terminal device accommodated by the access point of adjacent access point information including the information on the direction of the first adjacent access point and the second adjacent access point viewed from the access point Provided with information notification means,
The wireless terminal device is
Neighboring access point information receiving means for receiving neighboring access point information notified by the access point;
Based on the received adjacent access point information and the moving direction information of the wireless terminal device on the predetermined linear route, the first direction is set when the moving direction of the wireless terminal device is the first point direction. A mobile communication system comprising: handover means for performing handover to an adjacent access point and performing handover to the second adjacent access point when the moving direction of the wireless terminal device is the second point direction . A wireless terminal device moving on a predetermined linear route connecting the first point and the second point, and accommodating the wireless terminal device in a predetermined order according to the moving direction of the wireless terminal device on the linear route An access point in a mobile communication system comprising a plurality of access points,
Information required for communication with the first adjacent access point adjacent to the access point on the first point side, information required for communication with the second adjacent access point adjacent to the access point on the second point side, And holding adjacent access point information including information on the direction of the first adjacent access point and the second adjacent access point viewed from the access point,
On Kitonari contact access point information to a wireless terminal device to which the access point is contained, the movement direction of the wireless terminal device in the case of the first point direction handover to the first neighboring access point, the access point moving direction, wherein the case of the second point direction with a neighboring access point information notifying means for notifying the wireless terminal, for handover to the second neighboring access point of a wireless terminal device.

Images