JP2010028874A - Terminal station - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a terminal station for preventing the interruption of data from being increased, when executing handover. <P>SOLUTION: The movable terminal station performs wireless communication with one of a plurality of base stations while performing handover of switching the base station to be connected on a communication system having the plurality of base stations connected by a cable LAN. The terminal station includes: a transmission rate change part 31 for determining which of the change of a transmission rate to the base station under the wireless communication and the handover is to be performed; and a storage part 23 for storing a transmission rate reference value to be the comparison reference of the transmission rate to the base station. The transmission rate change part 31 determines which of the change of the transmission rate to the base station and the handover is to be performed on the basis of the transmission rate to the base station under the wireless communication and the transmission rate reference value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a terminal station in a mobile communication system.

  In recent years, wireless LAN technology has been rapidly developed. In a wireless LAN, it is desired to efficiently process reconnection to a handover destination in a handover when a mobile terminal moves from a base station at a high speed. In wireless LAN standardized by IEEE (Inter-Access Point Protocol) 802.11, there is no clear definition regarding handover. Therefore, IAPP (Inter) used for roaming between different vendors defined by IEEE 802.11f. -Access Point Protocol) protocol is often used.

  For example, when a mobile terminal (terminal station) moves and performs a handover, the mobile terminal hands over a deauthentication frame or a disassociation frame for disconnecting from the handover source base station. Transmit to former base station. Thereafter, the mobile terminal transmits a reassociation request frame for reconnection to the handover destination base station. Then, information related to the mobile terminal handed over between the handover destination base station and the handover source base station is transferred by IAPP, and the mobile terminal and the base station (handover destination base station) are reconnected.

  In such a handover, when the mobile terminal station leaves the handover source base station rapidly, the Ack (acknowledgment response) of the data transmitted to the handover source base station may not be returned to the mobile terminal station. In such a case, in IEEE 802.11, data retransmission is defined by “Recovery Procedure and retransmit limit”, and data loss is prevented and data communication throughput is stabilized by using the defined data retransmission.

  In the mobile communication system described in Patent Document 1, the radio mobile station sets the number of times of retransmission of radio control data of the radio communication protocol layer 2 or layer 3 according to the degree of deterioration of downlink communication quality from the radio base station. is doing.

  In addition, a technology has been developed for a mobile terminal that can be connected to a plurality of base stations to select a connection with a base station that can perform efficient radio communication by comparing radio degradation with each radio base station. ing.

  In the wireless communication system described in Patent Literature 2, a user terminal located in an overlap zone in which zones of a plurality of access points overlap each other selects which access point is connected to perform wireless communication. The user terminal first recognizes the access point candidate in the overlap zone by referring to the value (information) of Supported rates (communication speed at which the access point can operate) included in the beacon based on the IEEE 802.11 standard. . Then, the access point to be used is selected from the recognized access point candidates.

JP 2003-318804 A JP 2003-264870 A

  According to the former conventional technique, it is possible to stabilize the throughput of data transfer by setting the number of times of retransmission of the radio control data, but the deauthentication frame or the disassociation frame that is a call disconnection frame is used. In the case of transmission, since the mobile terminal station already wants to connect to the handover destination base station, the data is retransmitted even though it is unnecessary to retransmit the data to the mobile terminal station. Therefore, there is a problem that the call disconnection time at the time of handover becomes long.

  In the latter prior art, since an access point is selected based on radio degradation or the like, there is a possibility of selecting a base station having a low maximum transmission rate with a supported base station when a handover is detected. There is. For this reason, even if data is buffered and transferred between base stations by the handover source base station in order to prevent data loss, there is a problem that a delay or a momentary interruption due to a low transmission rate with the base station occurs. It was.

  The present invention has been made in view of the above, and an object of the present invention is to obtain a terminal station that prevents an increase in data loss when executing a handover.

  In order to solve the above-described problems and achieve the object, the present invention provides a communication system having a plurality of base stations connected by a wired LAN while performing a handover for switching the connected base stations. A determination unit for determining whether to change the transmission rate for the base station during wireless communication or the handover in a mobile terminal station that performs wireless communication with one of the communication terminal, and a reference for comparing the transmission rate for the base station A storage unit that stores a transmission rate reference value to be, and the determination unit changes the transmission rate for the base station based on the transmission rate for the base station in wireless communication and the transmission rate reference value, or It is determined which of the handover is performed.

  According to the present invention, it is determined whether to change the transmission rate for the base station or to perform the handover based on the transmission rate for the base station in radio communication and the transmission rate reference value. There is an effect that it can be prevented.

FIG. 1 is a diagram showing a configuration of a communication system according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a configuration of the terminal station according to the first embodiment. FIG. 3 is a block diagram showing a configuration of the base station according to Embodiment 1. In FIG. FIG. 4 is a sequence diagram illustrating a handover processing procedure according to the first embodiment. FIG. 5 is a sequence diagram illustrating a handover processing procedure according to the second embodiment. FIG. 6 is a sequence diagram illustrating a handover processing procedure according to the third embodiment. FIG. 7 is a block diagram showing a configuration of a base station according to the fourth embodiment. FIG. 8 is a sequence diagram illustrating a handover processing procedure according to the fourth embodiment. FIG. 9 is a diagram showing a basic format of a MAC frame. FIG. 10 is a diagram showing the configuration of the IP header. FIG. 11 is a diagram showing the structure of UDP data. FIG. 12 is a diagram illustrating a configuration of TCP data. FIG. 13 is a sequence diagram illustrating a handover processing procedure according to the fifth embodiment. FIG. 14 is a diagram of a configuration of a communication system according to the sixth embodiment. FIG. 15 is a block diagram showing a configuration of a terminal station according to Embodiment 6. In FIG. FIG. 16A is a flowchart of a procedure for selecting one base station from a plurality of base stations. FIG. 16B is a flowchart of the transmission rate control process.

  Embodiments of a handover method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration of a communication system according to Embodiment 1 of the present invention. The communication system includes a plurality of base stations (AP (Access Point)) 1X and 1Y and a plurality of terminal stations (STA) 2A to 2D, and includes a plurality of base stations 1X and 1Y and a plurality of terminal stations 2A to 2D. Both comply with the wireless LAN (IEEE802.11a, b, g). The base stations 1X and 1Y are connected by a wired LAN 3.

  The terminal stations 2A to 2D are movable terminal devices such as PDAs (Personal Digital Assistants) and notebook personal computers, and transmit / receive information to / from the base stations 1X and 1Y including computer devices.

  Here, a case will be described in which the terminal station 2A moving at high speed performs a handover from the handover (handoff) source base station 1X to the handover destination base station 1Y. That is, the terminal station 2A moves between the base station 1X and the base station 1Y at a high speed, and the terminal station 2A moves from the plurality of base stations to the base station based on a predetermined standard as the radio section with the base station 1X deteriorates. 1Y is selected to perform handover.

  Next, the configuration of the terminal stations 2A to 2D will be described. Since the terminal stations 2A to 2D have the same configuration, the terminal station 2A will be described here as an example. FIG. 2 is a block diagram showing a configuration of the terminal station according to the first embodiment. The terminal station 2A includes an input unit 21, an output unit 22, a storage unit 23, a communication IF unit 24, a calculation unit (detection unit) 25, a setting unit 26, and a control unit 29.

  The input unit 21 includes a keyboard, a mouse, and the like, and inputs various information. The output unit 22 includes a liquid crystal display or the like, and displays and outputs various information. The storage unit 23 includes an HDD (Hard Disk Drive), a RAM (Random Access Memory), and the like, and stores various types of information.

  The communication IF unit 24 is an interface that transmits and receives information to and from the base stations 1X and 1Y. Between the communication IF unit 24 and the base stations 1X and 1Y, as a MAC frame to be described later, a beacon frame, a probe request frame, a probe response frame, an authentication frame, Deauthentication frame, association request frame, association response frame, disassociation frame, reassociation request frame, reassociation request frame, reassociation request frame (Occurrence Response) frame and the like are transmitted and received.

  The beacon frame is a frame transmitted to notify various information necessary for communication in the communication network to the radio stations (base stations 1X and 1Y, terminal stations 2A to 2D). The probe request frame is a frame for inquiring the presence or absence of a base station (wireless cell) in the vicinity of the terminal station. The probe response frame is a frame for the wireless station to respond to the probe request frame from the terminal station. is there.

  The authentication (authentication) frame is a frame (connection request information) for performing authentication between wireless stations, and the deauthentication (deauthentication) frame is a frame for canceling authentication between wireless stations (disconnection). Information).

  The association request frame is a frame for the terminal stations 2A to 2D to request connection relations to the base stations 1X and 1Y, and the association response frame is a response to the association request from the terminal stations 2A to 2D by the base stations 1X and 1Y. The disassociation (connection relationship release) frame is a frame for releasing the connection relationship between the terminal stations 2A to 2D and the base stations 1X and 1Y (connection release information). ).

  The reassociation request frame is a frame (connection request information) for requesting a connection relationship to the handover destination base station when the terminal stations 2A to 2D are handed over. The reassociation response frame is transmitted from the base station to the terminal stations 2A to 2A. This is a frame for responding to whether or not to accept a connection relationship in response to a reassociation request from 2D.

  The calculation unit 25 calculates various settings related to handover detection and information transmission / reception based on information received from the base stations 1X and 1Y and information stored in the storage unit 23 and the setting unit 26. The calculation unit 25 detects the base station 1Y as a handover destination base station based on, for example, information received from the base station 1Y.

  The setting unit 26 stores various settings related to information transmission / reception. For example, the number of retransmissions (retry number) and Ack (acknowledgment) reception timer of a deauthentication frame and a disassociation frame for disconnecting a call to the base station 1X are set.

  When the terminal station 2A transmits a deauthentication frame or a disassociation frame from the terminal station 2A to the base stations 1X and 1Y, the number of retransmissions is determined when there is no response from the base stations 1X and 1Y. This is the number of times a frame or disassociation frame is retransmitted.

  The Ack reception timer is a time for waiting for a response from the base station 1X, 1Y to this transmission when the terminal station 2A transmits a deauthentication frame or a disassociation frame to the base station 1X, 1Y. The control unit 29 controls the input unit 21, output unit 22, storage unit 23, communication IF unit 24, calculation unit 25, and setting unit 26.

  Next, the configuration of the base stations 1X and 1Y will be described. Since the base stations 1X and 1Y have the same configuration, the base station 1X will be described here as an example. FIG. 3 is a block diagram showing a configuration of the base station according to Embodiment 1. In FIG. The base station 1X includes a terminal station 2A that includes an input unit 11, an output unit 12, a storage unit 13, a communication IF unit 14, a calculation unit 15, and a control unit 19.

  The input unit 11 includes a keyboard, a mouse, and the like, and inputs various information. The output unit 12 includes a liquid crystal display or the like, and displays and outputs various information. The storage unit 13 includes an HDD, a RAM, and the like, and stores various information.

  The communication IF unit 14 is an interface that transmits / receives information to / from the terminal stations 2A to 2D and other base stations (here, the base station 1Y). The communication IF unit 14 communicates with the terminal stations 2A to 2D by wireless communication, and communicates with other base stations via the wired LAN 3.

  The calculation unit 15 calculates various settings related to transmission / reception of information based on information received from the terminal stations 2A to 2D and other base stations 1Y and information stored in the storage unit 13. The control unit 19 controls the input unit 11, the output unit 12, the storage unit 13, the communication IF unit 14, and the calculation unit 15.

  Next, the operation of each component of the communication system shown in FIG. 1 will be described. FIG. 4 is a sequence diagram illustrating a handover processing procedure according to the first embodiment. When the terminal station 2A moves in the direction of the base station (new base station) 1Y from the state in which the terminal station 2A transmits and receives data (information) to and from the base station (old base station) 1X, the calculation unit of the terminal station 2A 25 detects a handover (detection of a handover destination base station).

  When the terminal station 2A moves in the zone (wireless zone) of the base station 1X in the zone direction of the base station 1Y (overlap zone connectable with the base stations 1X and 1Y), for example, the communication station 24 from the communication station 24 of the terminal station 2A Based on whether or not the communication IF unit 24 has received a probe response frame for the probe request frame from the base station 1Y, the calculation unit 25 detects a handover.

  When the terminal station 2A detects the handover, the deauthentication set in the setting unit 26 is transmitted before transmitting the deauthentication frame or the disassociation frame for disconnecting the call to the handover source base station 1X. The number of retransmissions of the application frame or disassociation frame is stored in the storage unit 23 (10). Then, the number of retransmissions of the deauthentication frame or disassociation frame in the setting unit 26 is temporarily set to a minimum value (11).

  Here, the minimum value of the number of retransmissions is set in advance by the user (user) of the terminal station 2A. For example, if the minimum value is set to 0, the deauthentication frame or the disassociation frame is retransmitted. Do not do. Thereafter, the communication IF unit 24 transmits a deauthentication frame or a disassociation frame to the handover source base station 1X.

  The terminal station 2A receives an Ack (acknowledgment response) for the transmitted deauthentication frame or disassociation frame from the handover source base station 1X or an Ack reception timer (response waiting time) set in the setting unit 26 At the expiration of (12) (connection release confirmation), the number of retransmissions of the deauthentication frame or disassociation frame stored in the storage unit 23 is reset in the setting unit 26 (13).

  The communication IF unit 24 of the terminal station 2A transmits an authentication frame (authentication request) for newly connecting to the handover destination base station 1Y or a reassociation request frame for reconnection.

  The handover destination base station 1Y receives the authentication frame or the reassociation request frame from the terminal station 2A by the communication IF unit 14. When receiving the authentication frame from the terminal station 2A, the handover destination base station 1Y transmits an authentication frame (establishment of authentication) from the communication IF unit 14 to the terminal station 2A in order to establish a connection with the terminal station 2A. .

  Further, when the handover destination base station 1Y receives the reassociation request frame from the terminal station 2A, the communication IF unit 14 transmits a reassociation response frame to the terminal station 2A in order to establish a connection with the terminal station 2A. Then, the communication IF unit 24 of the terminal station 2A receives an authentication frame and a reassociation response frame from the handover destination base station 1Y, and establishes a connection between the terminal station 2A and the base station 1Y.

  As a result, the handed over terminal station 2A responds to the deauthentication frame or disassociation frame transmitted to the handover source base station 1X with the number of retransmissions of the deauthentication frame or disassociation frame set to the minimum value. When Ack is received from the handover source base station 1X or when the Ack reception timer expires, a new connection process with the handover destination base station 1Y can be started.

  As described above, according to the first embodiment, the terminal station 2A that has performed the handover performs the transmission of the de-authentication frame or disassociation frame to the handover source base station 1X in a state where the number of retransmissions is set to the minimum value. The Ack for the sensation frame or the disassociation frame is received from the handover source base station 1X, or when the Ack reception timer expires, a new connection process with the handover destination base station 1Y can be started. The call disconnection time can be shortened, and the data interruption time can be reduced. Therefore, efficient wireless communication can be performed.

Embodiment 2. FIG.
A handover method according to the second embodiment will be described with reference to FIGS. In the second embodiment, before receiving the Ack for the deauthentication frame or disassociation frame transmitted to the handover source base station 1X from the handover source base station 1X or before the expiration of the Ack reception timer, the handover destination base station 1Y A new connection process is started.

  FIG. 5 is a sequence diagram illustrating a handover processing procedure according to the second embodiment. When the terminal station 2A moves in the direction of the base station (new base station) 1Y from the state in which the terminal station 2A transmits and receives data (information) to and from the base station (old base station) 1X, the calculation unit of the terminal station 2A 25 detects a handover.

  When the terminal station 2A detects the handover, the deauthentication set in the setting unit 26 is transmitted before transmitting the deauthentication frame or the disassociation frame for disconnecting the call to the handover source base station 1X. The number of retransmissions of the application frame or disassociation frame is stored in the storage unit 23 (20). Then, the number of retransmissions of the deauthentication frame or disassociation frame of the setting unit 26 is temporarily set to the minimum value (21).

  The terminal station 2A transmits a deauthentication frame or a disassociation frame from the communication IF unit 24 to the handover source base station 1X. Thereafter, the terminal station 2A resets the number of retransmissions of the deauthentication frame or disassociation frame stored in the storage unit 23 in the setting unit 26 (22). Then, after the shortest time for receiving Ack after transmitting the deauthentication frame or disassociation frame (time that does not affect other base stations etc. even if the next processing is performed) has passed, the terminal The communication IF unit 24 of the station 2A transmits an authentication frame (authentication request) for newly connecting to the handover destination base station 1Y or a reassociation request frame for reconnection.

  That is, in the second embodiment, the terminal station 2A does not wait for the Ack (acknowledgment response) to the transmitted deauthentication frame or disassociation frame from the handover source base station 1X or the expiration of the Ack reception timer. The connection process with the base station 1Y is started (without running the Ack reception timer).

  Thereafter, the handover process is executed by the same processing procedure as in the first embodiment. That is, when receiving the authentication frame from the terminal station 2A, the handover destination base station 1Y transmits an authentication frame (establishment of authentication) from the communication IF unit 14 to the terminal station 2A.

  Further, when the handover destination base station 1Y receives a reassociation request frame from the terminal station 2A, the communication IF unit 14 transmits a reassociation response frame to the terminal station 2A. Then, the communication IF unit 24 of the terminal station 2A receives an authentication frame and a reassociation response frame from the handover destination base station 1Y, and establishes a connection between the terminal station 2A and the base station 1Y.

  As a result, it is possible to start a new connection process with the handover destination base station 1Y after the shortest time for Ack reception has elapsed. In addition, the base station 1X can detect that the terminal station 2A has moved and left the coverage area by receiving the de-authentication frame from the terminal station 2A. For this reason, the terminal station 2A can detect the terminal station 2A in a shorter time than when the terminal station 2A moves and detects that the area in which the terminal station 2A has moved away is detected when the timer of the base station 1X expires (monitors whether there is data access from the terminal station 2A). It becomes possible to detect movement, and information related to the terminal station 2A that has become out of service can be deleted early from the information management table. Therefore, the base station 1X can accommodate new users at an early stage.

  As described above, according to the second embodiment, since the new connection process with the handover destination base station 1Y is started after the elapse of the shortest time for Ack reception, the call disconnection time at the time of handover becomes the shortest time for Ack reception. It can be shortened and efficient wireless communication can be performed.

Embodiment 3 FIG.
A handover method according to the third embodiment will be described with reference to FIGS. In the third embodiment, a new connection process with the handover destination base station 1Y is started immediately after the handover is detected.

  FIG. 6 is a sequence diagram illustrating a handover processing procedure according to the third embodiment. When the terminal station 2A moves in the direction of the base station (new base station) 1Y from the state in which the terminal station 2A transmits and receives data (information) to and from the base station (old base station) 1X, the calculation unit of the terminal station 2A 25 detects a handover.

  When the calculation unit 25 of the terminal station 2A detects a handover, the communication IF unit 24 of the terminal station 2A makes an authentication frame (authentication request) or reconnection for newly connecting to the handover destination base station 1Y. To transmit a reassociation request frame.

  Thereafter, the handover process is executed by the same processing procedure as in the first embodiment. That is, when receiving the authentication frame from the terminal station 2A, the handover destination base station 1Y transmits an authentication frame (establishment of authentication) from the communication IF unit 14 to the terminal station 2A. Further, when the handover destination base station 1Y receives a reassociation request frame from the terminal station 2A, the communication IF unit 14 transmits a reassociation response frame to the terminal station 2A. Then, the communication IF unit 24 of the terminal station 2A receives an authentication frame and a reassociation response frame from the handover destination base station 1Y, and establishes a connection between the terminal station 2A and the base station 1Y.

  As described above, according to the third embodiment, after the handover is detected, a new connection process with the handover destination base station 1Y is started, so that the call disconnection time at the time of handover can be shortened and efficient wireless communication can be performed. Can be done.

Embodiment 4 FIG.
A handover method according to the fourth embodiment will be described with reference to FIGS. In the fourth embodiment, after the terminal station 2A performs handover, data is buffered by transmitting a deauthentication frame or the like to the base station 1X to prevent data loss due to handover.

  FIG. 7 is a block diagram showing a configuration of a base station according to the fourth embodiment. Among the constituent elements in FIG. 7, constituent elements that achieve the same functions as those of the base station 1 </ b> X according to Embodiments 1 to 3 shown in FIG. 3 are assigned the same numbers, and redundant descriptions are omitted.

  As illustrated in FIG. 7, the base station 1 </ b> X includes a buffering unit 16. The buffering unit 16 performs buffering of data addressed to the terminal station 2A (data to be transmitted to the terminal station 2A) when the terminal station 2A is handed over. The buffered data is transferred to the handover destination base station 1Y of the terminal station 2A.

  FIG. 8 is a sequence diagram illustrating a handover processing procedure according to the fourth embodiment. When the terminal station 2A moves in the direction of the base station (new base station) 1Y from the state in which the terminal station 2A transmits and receives data to and from the base station (old base station) 1X, the calculation unit 25 of the terminal station 2A performs handover. Is detected.

  When the terminal station 2A detects a handover, the terminal station 2A transmits a deauthentication frame or a disassociation frame for disconnecting the call to the handover source base station 1X to the base station 1X.

  In order to perform wireless communication with less traffic, IEEE 802.11 defines a power saving mode of a terminal station as “Power Management”. In the sleep state in the power save mode, the terminal station performs transmission by setting a “power management bit” of a transmission frame such as a deauthentication frame in order to reduce power consumption. When the terminal station is in the sleep state, the base station performs buffering of data. If there is data addressed to the terminal station, the base station addresses the terminal station using the TIM (Traffic Indication Map) information at the time of beacon transmission. Is notified to the terminal station. The terminal station periodically receives a beacon, and when it is recognized by TIM information that the data addressed to the terminal station has reached the base station 1X, the terminal station collects this data by PS (Power Save) -POLL.

  Further, when data transfer is performed by IAPP (Inter-Access Point Protocol), at the time of registration information transfer of the terminal station (STA) from the handover source base station (old AP) to the handover destination base station (new AP), the handover source base station There is a possibility that data addressed to the terminal station is transferred to the station, and data to be delivered to the terminal station handed over to the handover destination base station may be lost.

  Accordingly, in the fourth embodiment, the “power management” bit is set in the MAC frame for the deauthentication frame or disassociation frame transmitted to the base station 1X when the terminal station 2A is handed over. Send in state. As a result, it is possible to cause the base station 1X to perform data buffering and prevent data loss due to handover.

  Here, an IEEE 802.11 MAC frame will be described. FIG. 9 is a diagram showing a basic format of an IEEE 802.11 MAC frame. The MAC frame 40 includes “frame control”, “Duration / ID”, “MAC address 1”, “MAC address 2”, “MAC address 3”, “sequence control”, “MAC address 4”, “frame body”, It consists of “FCS (Frame Check Sequence)”.

  “Duration / ID” is used when identifying a terminal station in the power saving mode. “Sequence control” is used for a sequence number of a MAC frame or the like. The “frame body” stores transmission data. “FCS” stores the MAC header and the error detection code of the frame body. In “MAC address 1”, “MAC address 2”, “MAC address 3”, and “MAC address 4”, a receiving station address, a transmitting station address, a destination station address, a transmitting source station address, and the like are stored.

  “Frame control” includes “protocol version”, “Type”, “Sub-Type”, “To Ds”, “From DS”, “More Flag”, “Retry”, “Power management”, “More Data”. , “Wep”, “Order”.

  “Protocol version” indicates the version of the IEEE 802.11 MAC protocol, “Type” and “Sub-Type” indicate the frame type, and “To Ds” indicates whether the receiving station is a base station or a terminal station. “From DS” indicates whether the transmitting station is a base station or a terminal station, and “More Flag” indicates whether there is a fragment frame following this frame when the upper layer is divided into a plurality of frames. “Retry” indicates whether the frame is a retransmitted frame, “Power management” indicates whether the power save mode is set, and “More Data” indicates a frame addressed to the radio station in the power save mode. If used, indicates whether there is a frame addressed to the power save mode station following this frame. (Transmit data) indicates whether it is encrypted, "Order" indicates whether or interchanged relay order when relaying a packet.

  The “Power management” bit indicates a power save (power saving) mode when “1”, and indicates a non-power save mode when “0”. In the fourth embodiment, the MAC frame is transmitted with the “Power management” bit set (the “Power management” bit is “1”).

  When the terminal station 2A transmits a deauthentication frame or a disassociation frame to the base station 1X with the “Power management” bit set in the MAC frame (30), the communication IF unit 14 of the base station 1X The communication IF unit 14 receives the deauthentication frame or the disassociation frame with the power management bit ON transmitted from the station 2A.

  The calculation unit 15 of the base station 1X that has received the deauthentication frame or the disassociation frame checks whether the management bit of the received frame is ON. When the buffering unit 16 of the base station 1X confirms that the management bit of the received frame is ON, the buffering unit 16 immediately starts buffering the data addressed to the terminal station 2A without performing the disconnection process with the terminal station 2A. (31).

  The terminal station 2A detects a handover, transmits a deauthentication frame or a disassociation frame to the base station 1X, and then transmits a reassociation request frame for requesting connection to the base station 1Y.

  The handover source base station 1X and the handover destination base station 1Y execute an IAPP sequence process defined in IEEE 802.11. That is, the base station 1Y that has received the reassociation request frame from the terminal station 2A receives an “IAPP: Send Security Block” frame (transfer request information) including information related to encryption for ensuring data security from the communication IF unit 14. Is transmitted to the base station 1X.

  When the communication IF unit 14 receives the “IAPP: Send Security Block” frame, the base station 1X transmits “IAPP: Ack Security Block” including information related to the terminal station 2A from the communication IF unit 14 as a confirmation response to this frame. Transmit to station 1Y.

  When the communication IF unit 14 receives “IAPP: Ack Security Block”, the base station 1Y transmits an “IAPP: Move Request” frame including information related to movement of the terminal station 2A from the communication IF unit 14 to the base station 1X. .

  When the communication IF unit 14 receives the “IAPP: Move Request” frame, the base station 1X transmits an “IAPP: Move Response” frame including information related to the movement of the terminal station 2A from the communication IF unit 14 to the base station 1Y. .

  Thereafter, when the base station 1X buffers the data addressed to the terminal station 2A for the base station 1Y, the communication IF unit 14 of the base station 1X transfers the buffered data to the base station 1Y ( 32). After the data transfer to the base station 1X, the base station 1X deletes the registration information of the terminal station 2A from the storage unit 13 when it was connected to the terminal station 2A (before detection of handover) (33) .

  The communication IF unit 14 of the handover destination base station 1Y transmits a reassociation response frame as a connection response to the connection request to the terminal station 2A. Then, when the communication IF unit 24 of the terminal station 2A receives the reassociation response frame, the connection between the terminal station 2A and the base station 1Y is established. Then, the terminal station 2A receives the data buffered by the base station 1X at the time of handover from the base station 1Y.

  If the terminal station 2A can receive a beacon from the base station 1X, the base station 1X can perform handover switching by the same method as the power save mode defined in IEEE 802.11. Even in the middle, the data being buffered can be received from the base station 1X. That is, when there is data addressed to the terminal station 2A, the base station 1X notifies the terminal station 2A that the data addressed to the terminal station 2A has arrived by TIM information at the time of beacon transmission. The terminal station 2A periodically receives a beacon, and when the TIM information recognizes that the data addressed to the terminal station has reached the base station 1X, the terminal station 2A collects this data by PS-POLL.

  In the fourth embodiment, when the terminal station 2A detects a handover, the terminal station 2A transmits the MAC frame with the “power management” bit set to the base station 1X. The terminal station 2A may select whether or not to set the “power management” bit in the MAC frame transmitted from the base station 1X to the base station 1X according to the service or protocol being connected.

  In this case, in order to grasp the service used by the terminal station 2A, the protocol type 50 of the IP header, the source port number 51 located at the head of the TCP header or UDP header, which is an upper layer of the IP layer, and the destination port number 52 is monitored and the monitored information is saved (stored). Then, based on the stored protocol type 50, source port number 51, and destination port number 52 information, it is determined whether or not to set the “power management” bit.

  FIG. 10 is a diagram showing the configuration of the IP header, FIG. 11 is a diagram showing the configuration of UDP data, and FIG. 12 is a diagram showing the configuration of TCP data. As shown in FIG. 10, the IP header 60 includes a protocol type 50. The protocol type 50 indicates the type of the upper protocol used in the data portion subsequent to the IP header.

  As shown in FIG. 11, the UDP data 61 includes a source port number 51 and a destination port number 52. As shown in FIG. 12, the TCP data 62 includes a source port number 51 and a destination port number 52. A source port number 51 indicates an application program that is a data transmission source, and a destination port number 52 indicates an application program that is a data reception destination.

  When the service used by the terminal station 2A is grasped by the protocol type 50, the protocol type 50 of the terminal station 2A is extracted by the calculation unit 25 and stored in the storage unit 23. Then, when instructing handover to the base station 1X (when transmitting a deauthentication frame or a disassociation frame), the data currently being communicated by the terminal station 2A is UDP data (real time) having a strong real time property. In this case, the processing by the handover method described in FIG. 8 is not executed. As described above, when the communication currently being performed by the terminal station 2A is UDP data with strong real-time characteristics, the real-time characteristics of data communication are maintained by not executing the processing by the handover method described in FIG.

  On the other hand, when instructing the base station 1X to perform handover, if the data currently being communicated by the terminal station 2A is TCP data with high reliability, the processing by the handover method described in FIG. 8 is executed. That is, in this case, when transmitting the deauthentication frame or the disassociation frame to the base station 1X, the terminal station 2A sets the “power management bit” of the transmission frame for transmission. As a result, if the communication currently being performed by the terminal station 2A is TCP data with high reliability, data loss in the wireless LAN (L2 (layer 2)) is performed by executing the processing according to the handover method described in FIG. To prevent.

  Further, when the service used by the terminal station 2A is grasped by the source port number 51 and the destination port number 52 at the head of the TCP header or UDP header, each port number is previously stored in the storage unit 23 of the terminal station 2A. ON / OFF of handover for (maximum 65536) is stored as a port number table. Here, ON of the handover indicates that processing by the handover method described in FIG. 8 is executed, and OFF of handover indicates that processing by the handover method described in FIG. 8 is not executed. In the port number table, ON / OFF of handover for each port number can be arbitrarily set, and handover is set to ON for the port number of the service for which processing by the handover method described in FIG. 8 is to be executed. .

  After the terminal station 2A confirms the TCP data and UDP data in communication with the protocol number, the port number is stored in the storage unit 23 together with the protocol number. Then, when the terminal station 2A instructs the base station 1X to perform handover, whether or not to execute the processing by the handover method described in FIG. 8 based on the handover ON / OFF information for each port number in the port number table. Decide whether or not.

  In this way, since the deauthentication frame or disassociation frame to be transmitted to the base station 1X when the terminal station 2A is handed over is transmitted with the “power management” bit set in the MAC frame, the base station 1X Can be made to buffer data.

  Further, when selecting whether or not to set the “power management” bit by the terminal station 2A, it is determined whether or not the base station 1X is to perform data buffering according to the service communicated by the terminal station 2A. It becomes possible to select whether to give priority to preventing data loss or to give priority to real-time data communication according to the contents of the service.

  As described above, according to the fourth embodiment, when the terminal station 2A is handed over, the MAC frame with the “power management” bit set is transmitted, so that the base station 1X can perform data buffering. It becomes. Therefore, it is possible to prevent data loss due to handover. In addition, since it is possible to select whether or not the “power management” bit is set by the terminal station 2A, it is possible to prevent data loss due to handover depending on the service communicated by the terminal station 2A.

Embodiment 5 FIG.
A handover method according to the fifth embodiment will be described with reference to FIGS. In the fifth embodiment, after the terminal station 2A has performed a handover, data is buffered by transmitting a reassociation request frame to the base station 1X to prevent data loss due to the handover. FIG. 13 is a sequence diagram illustrating a handover processing procedure according to the fifth embodiment.

  When the terminal station 2A moves in the direction of the base station (new base station) 1Y from the state in which the terminal station 2A transmits and receives data to and from the base station (old base station) 1X, the calculation unit 25 of the terminal station 2A performs handover. Is detected.

  When the terminal station 2A detects a handover, the terminal station 2A transmits a reassociation request frame (connection switching request) for handover to a new base station to the handover source base station 1X. At this time, the reassociation request frame transmitted from the terminal station 2A to the base station 1X is transmitted with the “power management” bit set in the MAC frame (40).

  The communication IF unit 14 of the base station 1 </ b> X receives the power management bit ON reassociation request frame transmitted from the terminal station 2 </ b> A by the communication IF unit 14. Receiving the reassociation request frame, the calculation unit 15 of the base station 1X checks whether the management bit of the received frame is ON. Then, when the calculation unit 15 of the base station 1X confirms that the management bit of the received frame is ON, whether or not the terminal station 2A requests connection with another base station to be handed over by movement To check.

  In order to confirm whether or not the terminal station 2A wants to establish a connection with another base station to be handed over, the calculation unit 15 of the base station 1X receives the destination of the reassociation request frame (MAC frame) received from the terminal station 2A. Check whether the MAC address matches its own MAC address. Further, it confirms whether or not the handover source MAC address of the MAC frame received from the terminal station 2A matches its own MAC address.

  When the calculation unit 15 of the base station 1X confirms that the destination MAC address of the MAC frame received from the terminal station 2A matches its own MAC address and the handover source MAC address matches its own MAC address. The terminal station 2A determines that it is requesting connection with the handover destination base station 1Y, and starts buffering of data addressed to the terminal station 2A (41).

  Further, the handover source base station 1X does not wait for the reception of “IAPP: Send Security Block” from the handover destination base station 1Y defined by IEEE802.11f, but itself “IAPP: Security” to the handover destination base station 1Y. Information related to the terminal station 2A is transferred by "Block Ack" (42).

  Thereafter, the same processing as in the second embodiment is performed. That is, when the base station 1Y receives “IAPP: Ack Security Block”, the base station 1Y transmits an “IAPP: Move Request” frame to the base station 1X.

  When the base station 1X receives the “IAPP: Move Request” frame, the base station 1X transmits an “IAPP: Move Response” frame to the base station 1Y. When the base station 1X buffers the data addressed to the terminal station 2A for the base station 1Y, the communication IF unit 14 of the base station 1X transfers the buffered data to the base station 1Y (43). After the data transfer to the base station 1X, the base station 1X deletes the registration information of the terminal station 2A from the storage unit 13 when connected to the terminal station 2A (44).

  Similarly to the case described in the fourth embodiment, whether or not the “power management” bit is set in the MAC frame transmitted from the terminal station 2A to the base station 1X depends on the service or protocol to which the terminal station 2A is connected. It is good also as a structure selected according to it.

  In this way, the base station 1X receives the reassociation request frame in which the “power management” bit is set from the terminal station 2A when the terminal station 2A is handed over, and the destination MAC address of this frame is itself Since the base station 1X confirms that the handover source MAC address matches its own MAC address, the base station 1X decides whether or not the terminal station 2A wants to establish a connection with the other base station of the handover destination by movement. Can be confirmed.

  Thereby, the base station 1X can transfer information on the terminal station 2A by “IAPP: Security Block Ack” without waiting for the reception of “IAPP: Send Security Block” from the base station 1Y.

  As described above, according to the fifth embodiment, when the terminal station 2A is handed over, it is possible to cause the base station 1X to perform data buffering, and “IAPP: Send Security Block” from the base station 1Y. It is possible to transfer information related to the terminal station 2A by “IAPP: Security Block Ack” without waiting for the reception of. Therefore, it is possible to shorten the reconnection process between the terminal station 2A and the base station 1Y and to prevent data loss due to handover.

Embodiment 6 FIG.
A handover method according to the sixth embodiment will be described with reference to FIGS. In the sixth embodiment, when a base station to be connected is selected from a plurality of base stations based on the received power value and the maximum transmission rate value, the received power value of the base station with the maximum maximum transmission rate value is set to a predetermined value. Weighting is performed, the received power values of the base stations are compared, and a base station connected to the terminal station is selected.

  FIG. 14 is a diagram showing the configuration of the communication system according to the sixth embodiment. Among the components shown in FIG. 14, the components that achieve the same functions as the communication systems of the first to fifth embodiments shown in FIG. Are given the same numbers, and redundant explanations are omitted.

  FIG. 15 is a block diagram showing the configuration of the terminal station according to the sixth embodiment, and achieves the same functions as the terminal stations of the first to fifth embodiments shown in FIG. Constituent elements are given the same numbers, and duplicate descriptions are omitted.

  As shown in FIG. 14, the communication system includes a plurality of base stations (AP (Access Point)) 1X, 1Y, 1Z and a plurality of terminal stations (STA (Station)) 2A to 2D. Both 1Y and 1Z and the plurality of terminal stations 2A to 2D comply with the wireless LAN (IEEE802.11a, b, g). Each base station 1X, 1Y, 1Z is connected by a wired LAN 3. Here, a case where the terminal station 2A moving at a high speed moves from the zone of the handover source base station 1X to the zone (overlap zone) of the base station 1Y and the base station 1Z is shown.

  As illustrated in FIG. 15, the terminal station 2A includes an AP selection unit 30 (selection unit, determination unit), a transmission rate change unit 31, and a transmission rate measurement unit 32. The AP selection unit 30 extracts candidates for a base station (AP) that can be handed over by movement of the terminal station 2A, and stores this base station as Index information of the selection candidate AP. In the index information of the selection candidate AP, a different selection candidate number i (i is a natural number) is assigned to each base station that can be handed over. The candidate of the base station that can be handed over is performed by identifying information received from the base station by the calculation unit 25 or the like.

  The transmission rate changing unit 31 compares the transmission rate value of the terminal station 2A with a reference transmission rate value, which will be described later, and compares the reception power value of the terminal station 2A with a reference reception power value, which will be described later. Based on the comparison result Instructs transmission rate control and base station selection processing. The transmission rate measuring unit 32 measures the transmission rate of data transmitted from the communication IF unit 24.

  Next, a procedure for selecting one base station from a plurality of base stations at the time of handover will be described. Here, the terminal station 2A moves at a high speed from the radio zone of the base station 1X, and the terminal station 2A follows a predetermined standard from a plurality of base stations (base stations 1Y, 1Z) as the radio section with the base station 1X deteriorates. A case will be described in which the base station 1Y is selected on the basis of which a handover is performed.

  FIG. 16A is a flowchart illustrating a procedure for selecting one base station from a plurality of base stations at the time of handover. The terminal station 2A stores the determination transmission rate β and the determination reception power Γ in the storage unit 23 in advance.

  The transmission rate for determination β is a maximum transmission rate between the base stations 1Y and 1Z and the terminal station 2A, which becomes a determination criterion when selecting a base station connected to the terminal station 2A. Here, the maximum value of the maximum transmission rate between the base station and the terminal is extracted by comparing each maximum transmission rate between the base station and the terminal with the transmission rate for determination β.

  The determination reception power Γ is reception power (RSSI (Receive Signal Strength Indicator)) between the base station and the terminal, which is a determination criterion when selecting a base station connected to the terminal station 2A.

  When the terminal station 2A becomes able to connect to a plurality of base stations due to high-speed movement or the like, the terminal station 2A is handed over to any one of the base stations (selection candidate APs). Obtain from frame or probe response frame.

  When the communication IF unit 24 of the terminal station 2A receives the beacon frame and the probe response frame from the selection candidate AP, the AP selection unit 30 extracts the maximum transmission rate and the received power value from the beacon frame and the probe response frame for each selection candidate AP. , And stored as Index information of the selection candidate AP. Further, the AP selection unit 30 assigns a selection candidate number i to each selection candidate AP.

  The AP selection unit 30 of the terminal station 2A first initializes the determination transmission rate β and the determination reception power Γ, which are base station selection criteria (determination transmission rate β = 0, determination reception power Γ = 0). Perform (step S100). Further, the AP selection unit 30 initializes the selection candidate number i (i is a natural number) of the selection candidate AP to be determined (i = 1) (step S110).

  In order to extract the base station with the maximum transmission rate from the selection candidate base stations, the AP selection unit 30 checks the maximum transmission rate in order from the base station with the selection candidate number i = 1. First, the AP selection unit 30 exceeds the number of base station registrations (the number of base stations that can be connected to the terminal station 2A) registered in the terminal station 2A at the present time. It is determined whether or not (step S120).

  When the AP selection unit 30 determines that the selection candidate number i does not exceed the current number of registered base stations (step S120, Yes), the AP selection unit 30 receives the selection candidate number i from the base station and stores it in the storage unit 23. The maximum transmission rate of the selected candidate number i base station (selection candidate APi) is loaded into the AP selection unit 30 (step S130). Then, the AP selection unit 30 compares the loaded maximum transmission rate of the base station of the selection candidate number i with the transmission rate for determination β, and the value of the maximum transmission rate of the base station of the selection candidate number i is the transmission rate for determination β It is determined whether or not the value is larger than (step S140).

  If the AP selection unit 30 determines that the value of the maximum transmission rate of the base station of the selection candidate number i is larger than the value of the determination transmission rate β (step S140, Yes), the current determination transmission rate β is overwritten. Update. That is, the value of the current determination transmission rate β is rewritten to the value of the maximum transmission rate of the base station of the selection candidate number i (the base station of the selection candidate number i (the selection candidate APi) to the value of the current transmission rate for determination β). Substitute the maximum transmission rate value of Further, the selection candidate number i is stored as the selection number I in the Index information of the selection candidate AP (step S150). Thereafter, the selection candidate number i is updated to i = i + 1 (step S160).

  Also, when the AP selection unit 30 determines that the value of the maximum transmission rate of the base station of the selection candidate number i is not larger than the value of the transmission rate for determination β (No in step S140), the selection candidate number i is set to i = Update to i + 1 (step S160).

  Thereafter, until the AP selection unit 30 determines that the selection candidate number i of the base station that confirms the maximum transmission rate exceeds the number of base station registrations currently registered in the terminal station 2A, steps S120 to S160 are performed. Repeat the process.

  The selection candidate number i of the base station with which the AP selection unit 30 confirms the maximum transmission rate exceeds the number of base station registrations currently registered in the terminal station 2A (the last base registered in the terminal station 2A) (No in step S120), the AP selection unit 30 stores the received power value of the base station corresponding to the stored selection number I in the index information of the selection candidate AP stored in the storage unit 23. And a predetermined value α is added to the received power value (step S170). α itself is a parameter (value) that can be arbitrarily set, and is set in advance by calculating an appropriate value from an actual measurement value in the environment of the communication system. For example, if you want to preferentially select a base station with a large maximum transmission rate with a high priority, set α high, and if you want to preferentially select a base station with a large maximum transmission rate with a low priority, select α. Set smaller. The received power value of the base station corresponding to the selection number I obtained by adding the predetermined value α is stored in the storage unit 23.

  After initialization of the selection candidate number i in the index information of the selection candidate AP (step S180), the AP selection unit 30 confirms the reception power value in order from the base station of the selection candidate number i = 1 (reception for determination). Comparison with power value Γ).

  First, the AP selection unit 30 determines whether or not the selection candidate number i of the base station that confirms the received power value exceeds the number of base station registrations currently registered in the terminal station 2A (step S190).

  When the AP selection unit 30 determines that the selection candidate number i does not exceed the current number of registered base stations (step S190, Yes), the AP selection unit 30 receives the selection candidate number i from the base station and stores it in the storage unit 23. The received power value of the base station of the selected candidate number i is loaded into the AP selection unit 30 (step S200). At this time, the received power value of the base station corresponding to the selection number I is loaded with the received power value obtained by adding the predetermined value α. Then, the AP selection unit 30 compares the received power value of the base station of selection candidate number i with the received power value for determination Γ, and the received power value of the base station of selection candidate number i is the received power value for determination Γ. It is determined whether or not the value is larger than (step S210).

  When the AP selection unit 30 determines that the received power value of the base station of the selection candidate number i is larger than the determination received power value Γ (step S210, Yes), the current determination received power value Γ is overwritten. Update. That is, the value of the current determination reception power value Γ is rewritten to the value of the reception power value of the base station of selection candidate number i (the reception power value of the base station of selection candidate number i is replaced with the current reception power value of determination Γ). substitute). Further, the selection candidate number i is stored as the selection number J in the Index information of the selection candidate AP (step S220). Thereafter, the selection candidate number i is updated to i = i + 1 (step S230).

  Also, when the AP selection unit 30 determines that the received power value of the base station of the selection candidate number i is not larger than the determination reception power value Γ (No in step S210), the selection candidate number i is set to i = i + 1. (Step S230).

  Thereafter, until the AP selection unit 30 determines that the selection candidate number i of the base station that confirms the received power value exceeds the number of base station registrations currently registered in the terminal station 2A, steps S190-230 Repeat the process.

  When the AP selection unit 30 determines that the selection candidate number i of the base station that confirms the received power value exceeds the number of base station registrations currently registered in the terminal station 2A (step S190, No), the AP The selection unit 30 determines to connect to the base station corresponding to the selection number J stored in the AP selection unit 30 (step S240). Thereafter, the terminal station 2A performs connection switching processing from the base station 1X to the selected base station 1Y.

  Thus, after adding the predetermined value α to the received power value of the base station with the maximum maximum transmission rate, the received power values of the base stations are compared, so that the base station with the maximum maximum transmission rate is the terminal station 2A. It becomes easy to be selected as a connection destination.

  Note that the base station is not limited to selecting a base station to be connected from a plurality of base stations based on the received power value and the maximum transmission rate value, but is a base for connecting from a plurality of base stations based on the transmission rate and the maximum transmission rate value. A station may be selected. In this case, a predetermined weight is applied to the transmission rate of the base station having the maximum maximum transmission rate value, the transmission rates of the base stations are compared, and the base station connected to the terminal station 2A is selected.

  Next, transmission rate control processing will be described. The wireless LAN supports multirate. For example, in the case of IEEE802.11a, multi-rates of 54, 48, 36, 24, 18, 12, 9, and 6 Mbps are supported as wireless transmission rates, and in the case of IEEE802.11b, Multi-rate of 11, 5.5, 2, 1 Mbps is supported.

  The wireless LAN chip attempts to transmit data at the highest possible transmission rate. However, when the wireless quality deteriorates, the wireless LAN chip lowers the transmission rate to maintain data conduction (maintain the connection with the handover source base station). For example, if the connection is made at the maximum rate, the data continuity with the base station connected so far is maintained by reducing the rate step by step.

  When the terminal station 2A moves at a high speed, such an algorithm causes severe radio degradation. Therefore, in this case, even if the connection to the handover source base station is not possible, the data rate is increased because the base station is selected after the transmission rate is lowered to the minimum rate.

  Therefore, in the sixth embodiment, a transmission rate that is a determination criterion when performing a handover is set in advance, and when the transmission rate becomes lower than this transmission rate, data continuity with a base station that is in the area is established. Without searching for a new base station (base station selection process).

  FIG. 16B is a flowchart of the process procedure of the transmission rate control process. The transmission rate changing unit 31 of the terminal station 2A executes a handover with a transmission rate value (reference transmission rate value) serving as a criterion for determining whether to change the transmission rate or perform a base station selection process when executing a handover. In this case, the reception power value (reception power value) that is a criterion for determining whether to change the transmission rate or perform the base station selection process is loaded from the storage unit 23 (step S300). The transmission rate measuring unit 32 of the terminal station 2A measures the transmission rate of data transmitted from the communication IF unit 24.

  Then, the transmission rate changing unit 31 compares the current transmission rate value of the terminal station 2A with the reference transmission rate value, and determines whether or not the current transmission rate value of the terminal station 2A is larger than the reference transmission rate value. This is performed (step S310).

  When the transmission rate changing unit 31 determines that the current transmission rate value of the terminal station 2A is larger than the reference transmission rate value (step 310, Yes), the transmission rate changing unit 31 receives the current received power value of the terminal station 2A. And the reference received power value are compared, and it is determined whether or not the current received power value of the terminal station 2A is larger than the reference received power value (step S320). Here, even if the transmission rate is good, if the terminal station 2A moves at a high speed, the received power value may suddenly deteriorate. Therefore, the received power value of the terminal station 2A is compared with the reference received power value. ing.

  When the transmission rate changing unit 31 determines that the current transmission rate value of the terminal station 2A is not larger than the reference transmission rate value (No in step 310), or the transmission rate changing unit 31 determines that the current terminal station 2A has When it is determined that the received power value is not greater than the received power value (No at Step S320), the AP selection unit 30 selects a base station from the selection candidate base stations (Step S330). At this time, the AP selection unit 30 selects one base station from the plurality of base stations according to the processing procedure shown in FIG. Thereby, it is not necessary to lower the transmission rate to the minimum rate, and it is possible to prevent an increase in data loss.

  When the transmission rate changing unit 31 determines that the current received power value of the terminal station 2A is larger than the received power value (Yes in step S320), the transmission rate changing unit 31 changes the transmission rate by the communication IF unit 24. Control is made to lower (step S340).

  That is, when the transmission rate changing unit 31 determines that the current transmission rate value of the terminal station 2A is larger than the reference transmission rate value and the current reception power value of the terminal station 2A is larger than the reception power value, Controlled to reduce the rate. This makes it possible to maintain the communication that has been connected so far.

  In Embodiment 6, the received power value of the base station with the maximum maximum transmission rate value is subjected to predetermined weighting, the received power values of the base stations are compared, and the base station connected to the terminal station is selected. However, the weighting to the received power value is not limited to the received power value of the base station with the maximum maximum transmission rate value, and the received power value may be weighted according to the maximum transmission rate value. .

  In the sixth embodiment, both the transmission rate value of the terminal station 2A and the reference transmission rate value are compared and the reception power value of the terminal station 2A and the reference reception power value are compared. Only one of the comparisons may be made.

  Thus, according to the sixth embodiment, when a base station to be connected is selected from a plurality of base stations based on the received power value and the maximum transmission rate value, the received power of the base station with the maximum maximum transmission rate is selected. Since the predetermined weighting (addition process of the predetermined value α) is performed on the value, it becomes easy to preferentially select the base station with the maximum maximum transmission rate. Therefore, it is possible to shorten the data transfer time for the terminal station after handover switching. In addition, since it is determined whether to lower the transmission rate or to perform base station selection processing based on the reference transmission rate value or the received power value, the data interruption is large depending on the transmission rate value or received power value of the terminal station 2A. It is possible to prevent the occurrence of the failure and maintain the communication that has been connected so far. Therefore, the communication efficiency in the communication system is improved.

  In the first to sixth embodiments, the base stations 1X and 1Y include the input unit 11 and the output unit 12, and the terminal stations 2A to 2D include the input unit 21 and the output unit 22, but the base station 1X , 1Y and the configurations of the terminal stations 2A to 2D are not limited to these configurations. For example, the base stations 1X and 1Y may be connected to external input devices and output devices, and the terminal stations 2A to 2D may be connected to external input devices and output devices.

  As described above, the handover method, communication system, and terminal station are suitable for handover when the terminal station moves at high speed.

1X, 1Y, 1Z Base station 2A to 2D Terminal station 3 Wired LAN 3
11, 21 Input unit 12, 22 Output unit 13, 23 Storage unit 14, 24 Communication IF unit 15, 25 Calculation unit 16 Buffering unit 19, 29 Control unit 26 Setting unit 30 AP selection unit 31 Transmission rate change unit 32 Transmission rate Measurement unit 40 MAC frame 60 IP header 61 UDP data 62 TCP data

Claims (2)

In a mobile terminal station that performs wireless communication with one of the plurality of base stations while performing handover for switching the connected base station on a communication system having a plurality of base stations connected by a wired LAN,
A determination unit for determining whether to change a transmission rate for the base station during wireless communication or the handover;
A storage unit that stores a transmission rate reference value serving as a reference for comparison of the transmission rate for the base station,
The determination unit determines whether to change the transmission rate for the base station or to perform the handover based on a transmission rate for the base station in wireless communication and the transmission rate reference value Bureau. The storage unit further stores a received power reference value serving as a reference for comparison of received power values from the base station,
The determination unit is configured to transmit a transmission rate for the base station in the wireless communication, the transmission rate reference value,
2. The method according to claim 1, wherein it is determined whether to change a transmission rate for the base station or to perform the handover based on a received power value from the base station in radio communication and the received power reference value. The listed terminal station.

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