JP2006005630A - Wireless terminal, network connecting device, and method and program for searching for candidate to be switched - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wireless terminal capable of switching an access point in a short time during roaming. <P>SOLUTION: The wireless terminal 1 previously examines a candidate for an access point 2 where a communication line is to newly be established for roaming. The search for the candidate for the access point 2 targets not only an access point 2e of the same channel with an access point 2a which is currently established, but access points 2b, 2c, and 2d of other communication channels. Further, this search is made when the wireless terminal 1 is in a sleep state and while communication with the access point 2a is still established. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a wireless communication technique, and more particularly to a technique for switching communication connection between a wireless terminal and an access point.

  In wireless communication such as a wireless LAN, when the strength of communication established with an access point becomes weak due to movement or the like, the wireless terminal performs roaming for switching communication connection to another access point having higher communication strength.

In this roaming, there is a problem that it takes time for the switching process, but there are, for example, Patent Documents 1, 2, and 3 as techniques for dealing with this point. Among these, in the wireless communication system disclosed in Patent Document 1, when a wireless terminal trying to perform roaming recognizes that there are a plurality of access point candidates that are trying to establish a communication connection, index request information is sent to these The index information transmitted to the candidate access points and returned from each access point is compared to determine which access point to connect to. In Patent Document 2, all access points are operated in synchronization, and each access point stores information about the access point based on hopping information from an adjacent access point in a database, and a wireless terminal. Performs roaming based on information about its neighboring access points. Furthermore, in the system disclosed in Patent Document 3, an access point that can be connected in advance is searched and stored in a table. When the communication state with an access point with which communication is established deteriorates, this table A new communication connection has been established with the access point stored in the network.
JP 2003-264870 A (FIG. 3, paragraphs [0027] to [0028]) JP 2002-26931 A (paragraphs [0039] to [0044]) Japanese Patent Laid-Open No. 08-191305 (FIG. 1, paragraphs [0012] to [0014])

It is an object of the present invention to provide a wireless terminal and a program that reduce the time required for roaming, as in each of the above patent documents.
It is another object of the present invention to provide a terminal device and a program that can establish a communication connection with higher communication quality than conventional methods when establishing new communication by performing roaming.

  It is another object of the present invention to provide a terminal device and a program that can be realized more easily and at a lower cost than conventional methods.

The present invention is premised on a wireless terminal that establishes communication with an access point and performs wireless communication, and includes switching candidate search means and switching candidate storage means in order to solve the above problems.
The switching candidate search means searches for a candidate of an access point that newly establishes communication at the time of roaming that switches the access point that establishes the communication by switching the communication channel prior to the roaming.

The switching candidate storage means stores the access point candidates obtained by the search.
With this configuration, an access point having a communication channel different from the access point with which communication is currently established can be used as a candidate for switching at the time of roaming. An access point that can establish communication with high communication quality can be selected. Furthermore, since access points of different channels can be targeted, the number of access points to be installed can be reduced. Therefore, it can be realized easily and inexpensively.

  The switching candidate search means may be configured to store the access point with the best communication quality as the candidate in the switching candidate storage means when a plurality of access points exist as candidates for one communication channel. I can do it.

  Furthermore, the switching candidate search means can be configured to search for the candidate by switching the communication channel while establishing communication with an access point established for performing the wireless communication.

  As a method of this configuration, for example, when the switching candidate search means is in a sleep state where reception from the access point with which the communication is established is not performed, the communication channel is switched to search for the candidate. To do.

With this configuration, an access point having another communication channel can be searched without disconnecting communication.
Further, when performing the roaming, the apparatus further comprises a roaming processing unit that refers to the switching candidate storage unit and switches an access point that establishes the communication based on the reference result, and the switching candidate search unit includes the access to be the candidate The communication quality of the communication with the point is checked, information indicating the communication quality is stored as information on the candidate in the switching candidate storage unit, and the roaming processing unit is stored in the switching candidate storage unit It can be configured to switch to an access point that shows the best communication quality.

  At this time, for example, the switching candidate search means checks the communication quality from the reception intensity of the beacon from the candidate access point. Alternatively, a probe request is transmitted, and the communication quality is checked from the received intensity of the response to the probe request.

With this configuration, it is possible to perform switching during roaming from among access point candidates having different communication channels.
Further, a means for acquiring a signal indicating whether the mobile unit on which the wireless terminal is mounted is moving or stopped, and a roaming priority mode for actively searching for the candidate when the signal indicates movement Further, it is possible to further comprise means for switching to a power save mode in which priority is given to suppressing power consumption when the signal indicates a stop.

With this configuration, power consumption can be reduced when the vehicle is not moving, that is, when the requirement for roaming is difficult to occur.
The scope of the present invention also includes a network connection device mounted on a wireless terminal, a search method for an access point that is a candidate for switching performed on the wireless terminal, and a program executed on the wireless terminal.

  According to the present invention, since an access point that is a candidate for switching is searched prior to roaming, switching of access points can be performed in a short time during roaming. Therefore, smooth communication can be realized even when roaming frequently occurs.

  In addition, since the switching candidates are searched for a plurality of channels, it is possible to select an access point that can establish communication with higher communication quality than selecting a switching candidate for one channel.

  Furthermore, since access points of different channels can be targeted, the number of access points to be installed can be reduced. Therefore, it can be realized easily and inexpensively.

An embodiment according to the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram for explaining the concept of the roaming method in this embodiment.
In the roaming process, the wireless terminal according to the present embodiment checks in advance candidates for access points for establishing a new communication line during roaming. Also, instead of searching only for access points on the same channel as the currently established line, this access point candidate search is performed by checking the communication strength with access points on multiple channels and selecting the optimal Establish a line with the access point. In addition, this search is performed while the wireless terminal 1 is in the sleep state, so that communication with the currently used access point 2a is established.

  For example, in FIG. 1, when roaming is performed when the wireless terminal 1 establishes communication with the access point 2a, conventionally, only the access point 2e having the same channel A as the access point 2a is subject to switching. In the present embodiment, access points 2b, 2c, and 2d having channels B and C different from the access point 2a are also examined as candidates, and connected to the access point that can establish the best communication connection among them. Switch.

  Thereby, the optimal access point can be selected from a larger number of candidates than in the conventional method. Therefore, it is possible to establish a communication connection with higher communication quality than the conventional method. Also, since access points having different channels can be switched, the number of installed access points as a whole can be reduced as compared with the case where only one channel is targeted. Therefore, the entire system can be easily realized at low cost.

  FIG. 2 is a diagram illustrating a configuration example of the wireless terminal 1 in the present embodiment. As long as the wireless terminal 1 has a function capable of wirelessly communicating with an access point, the form of the device is not particularly limited, and examples thereof include a PDA, a portable PC, an in-vehicle communication device, and the like.

  The wireless terminal 1 shown in FIG. 1 includes a CPU 11, a main storage device 12 including a ROM, a RAM, a large-capacity auxiliary storage device 13 such as a hard disk, an input / output device 14 including a display, a keyboard, and an access point. A network connection device 15 such as a LAN adapter for wireless connection and a portable storage medium 17 such as a CD, a DVD, an optical disk, a flexible disk, and a memory card are mounted, and a medium reading device 16 that reads out the stored content from the medium storage device 16. The buses 18 are connected to each other. The network connection device 15 may be configured as an external device mounted on the wireless terminal 1, such as a LAN card, instead of being one of the components of the wireless terminal 1.

  In the processing according to the present embodiment, the CPU 11 uses a driver stored in the main storage device 12 or the auxiliary storage device 13, or the control unit in the network connection device 15 executes firmware to perform processing described later. Can be realized.

  In addition, various processes in the present embodiment can be realized by providing dedicated hardware in the wireless terminal 1, but the medium reader 16 reads out programs and data stored in the portable storage medium 17, This is loaded or stored in the main storage device 12 or the auxiliary storage device 13. Each process according to the present embodiment can be realized by software by the CPU 11 loading and executing the program and data on the main storage device 12. In this case, the switching candidate search means and the roaming processing means are realized by the CPU 11 executing a program using the main storage device 12 as a work memory, and the switching candidate storage means is stored on the main storage device 12 or the auxiliary storage device 13. Built in.

Next, a specific implementation example of the roaming process in the present embodiment will be shown. The following example shows a case where it is realized in a wireless LAN according to the IEEE 802.11 standard.
In the present embodiment, in order to reduce the time required for roaming, the wireless terminal 1 performs an access point search using the switching candidate search unit before the communication quality with the access point is deteriorated, and performs this as a switching candidate storage unit. To remember. At this time, the search is also performed for access points having channels other than the channel with which communication is currently established.

In this example, power management is used for searching for the switching target.
In IEEE 802.11, a power management function is provided to suppress power consumption of the wireless terminal 1.

  The wireless terminal 1 has a PS (Power Save) mode that regularly transitions between the Awake state and the Doze state that operates with the minimum amount of power in addition to the Active mode that is always in the Awake state in which frames can be received from the access point. And two operation modes.

  When the wireless terminal 1 declares use of the PS mode to the access point, when the access point receives a message frame addressed to the wireless terminal 1, the wireless terminal 1 is in a sleep state (such as a Doze state). For example, the frame is held without being transmitted. This frame is acquired by polling by the wireless terminal 1 or the wireless terminal 1 rises at every predetermined beacon reception interval, and is held by the access point according to the frame accumulation notification (TIM, DTIM) included in the beacon. Get the message frame.

FIG. 3 is an explanatory diagram of the operation in this power management.
In the figure, when the wireless terminal 1 polls and acquires the frame held by the access point (PSP (Power Save Polling)), the frame held by the access point is acquired according to the frame accumulation notification included in the beacon. In this case, an example of operation (PSNP (Power Save Non Polling)) is shown.

  In the PSP mode, the wireless terminal 1 looks at the information of TIM (Traffic Indication Map) or DTIM (Delivery Traffic Indication Message) in the received beacon signal and knows that the access point has a message addressed to itself. In the case of communication, the access point is polled from the wireless terminal 1 to receive communication data. Further, in the PSNP mode, the wireless terminal 1 recognizes that the access point holds a message addressed to itself by DTIM (in the beacon signal), and continues the Awake state to receive a message from the access point.

  In the case of a broadcast that sends a broadcast data frame to an unspecified number of terminals, in both the PSP mode and the PSNP mode, it is recognized that the message held by the broadcast is sent by DTIM, and the Awake state is continued. The message is received as a broadcast data frame from the access point. In FIG. 3, at the beacon generation interval A, the access point notifies the wireless terminal 1 in the PSNP mode of data frame accumulation by DTIM and transfers the data frame. Also, at the beacon generation interval B, the access point notifies the wireless terminal 1 in the PSP mode of frame accumulation by TIM, and in response to this, the wireless terminal 1 transmits a poll frame, and as a response, the access point transfers a data frame. ing. At the beacon generation interval C, no frame reception processing is performed because there is no stored frame addressed to the wireless terminal 1 at the access point. At the beacon generation interval D, the access point notifies the accumulation of the broadcast data frame by DTIM and broadcasts the data frame.

  Except when these beacons and message frames are received, the access point recognizes that the wireless terminal 1 is in the sleep state, and the message frame received during this time is retained by the access point as described above. In this sleep state, the wireless terminal 1 maintains communication with the access point if it returns to the original channel by the next beacon interval, even if the wireless terminal 1 switches from the currently established channel to another channel. I can do it.

  Therefore, in the present embodiment, during the period of the sleep state, the switching candidate search means searches for an access point to be switched during roaming while switching channels. As a method of this search, for example, during a sleep state in which a channel can be switched, a probe request is transmitted while switching the channel, and communication quality information is acquired from the reception intensity of the probe response received from the access point of that channel. Alternatively, a beacon transmitted from the access point of the channel is received while switching the channel during the sleep state, and communication quality information is acquired from the received intensity. Then, the MAC address and communication quality information of the access point having the best communication quality on the same channel are held on the main storage device 12 or the auxiliary storage device 13 (hereinafter referred to as internal memory) as switching candidate storage means.

  When the communication quality with the connection access point with which communication is established deteriorates and it becomes necessary to perform roaming, the wireless terminal 1 uses the roaming processing means to communicate from the list of candidates in the internal memory. Obtain an access point whose quality information indicates the best communication quality, switch communication to the channel used by the access point, send a connection request to the held MAC address, and Connecting.

By such processing, the wireless terminal 1 in the present embodiment can search for an access point to be switched over a plurality of channels in advance.
FIG. 4 is a flowchart showing search processing for an access point to be switched, which is performed by the wireless terminal 1 in the present embodiment.

  The process shown in FIG. 6 is started when the wireless terminal 1 enters the sleep state shown in FIG. 2. First, in step S 1, the value of the variable CNT storing the channel switching counter value is read from the saving memory. In step S2, the communication channel is switched to the channel indicated by the variable CNT.

  In this state, the wireless terminal 1 derives the communication quality with the access point having the channel switched in step S2 as step S3. There are various methods for deriving the communication quality. For example, the reception level of the beacon received from the access point is obtained and set as a value indicating the communication quality, or the wireless terminal 1 emits a probe request, A value indicating the reception level communication quality of the probe response returned as a response by the access point that has received this.

  In step S4, the access point from which the communication quality is derived in step S3 is used as a candidate for switching, and the communication quality information indicating the MAC address and the communication quality is displayed in the list table for recording the candidate. Register with. When there are a plurality of candidates in one channel, such as receiving beacons from a plurality of access points, the communication quality with each of the plurality of access points is determined in step S3, and the best communication among them is determined in step S4. Only access points that indicate quality are registered in the table. In step S3, if no candidate exists in the channel, such as when no beacon of the channel is received, NULL is registered at the position of the target channel in the table.

FIG. 5 is a diagram illustrating a configuration example of a table for registering access points serving as switching candidates.
In this example, the access points having channels 1 to 14 are to be switched. In the example of FIG. 6, the MAC addresses of candidate access points and the communication lines with the access points are displayed in the columns of channels 1 to 14, respectively. Information for communication quality indicating communication quality is stored.

When roaming, the wireless terminal 1 refers to this table created in advance, selects the access point with the best communication quality, and establishes communication.
When registration in the table is completed, the value of the variable CNT is checked in step S5. If the variable CNT indicates the maximum value of the channel (14 in this example) (step S5, Y), the CNT is set to the initial value “ If it is 1 ″ (step S7) and it is not the maximum value (step S5, N), the CNT value is incremented by +1.

  If the search time has not ended (step S8, N), the process returns to step S2 to switch to the next channel, and the communication quality with the access point of that channel is checked.

  In step S8, if the search time has ended (step S8, Y), the value of the variable CNT is saved in the memory in step S9, and then the channel of the access point that is currently in communication is switched in step S10. This process is terminated. Whether or not this search time has expired, there is a margin until the next beacon occurs, and it switches to the next channel before returning the channel to receive the beacon from the access point with which communication is currently established. Judgment is made based on whether or not a candidate can be searched.

FIG. 6 is a flowchart showing an operation process performed by the wireless terminal 1 when performing roaming.
This processing is started when communication with a connection access point with which communication has been established or communication quality deteriorates due to a cause such as the movement of the position of the wireless terminal 1, and as shown in FIG. 5 as step S21. The communication quality information in the list table of new access point access points stored in the internal memory is referred to. In step S22, the channel and MAC address of the access point having the best communication quality in the communication quality information are acquired from the list table.

  Then, after switching communication to the channel obtained in step S22 as step S23, a connection request is transmitted to the MAC address acquired in step S22 as step S24, and the connection is made with the access point of the switching destination, and this process is performed. finish.

Through such processing, the wireless terminal 1 of the present embodiment selects an access point with the best communication quality with reference to a table in which switching candidates created in advance are registered when roaming. Since communication can be established, the access point can be switched in a short time. Therefore, although it is difficult to establish communication if it takes a long time for one roaming, according to this embodiment, switching can be performed in a short time. Even when roaming frequently occurs, smooth communication can be realized.

  In addition, since the switching candidates are searched for a plurality of channels, it is possible to select an access point that can establish communication with higher communication quality than selecting a switching candidate for one channel.

  Further, until now, access points had to be provided separately for each channel. However, in this embodiment, access points of different channels can be targeted, and the number of necessary access points can be reduced. Also, since the configuration of the access point is not different from the conventional one, there is no need to change the access point side when introducing the system of this embodiment. Therefore, it can be introduced inexpensively and easily.

  In the case of a configuration mounted on a moving body such as an in-vehicle wireless LAN used in a factory or a plant, a signal indicating whether the vehicle is moving or stopped is obtained from an external device, and the vehicle is It may be configured to switch to a roaming priority mode that actively searches for switching candidates when the vehicle is operating, and to a power save mode that prioritizes suppressing power consumption when the vehicle is stopped.

  Further, in the above example, candidates are searched for in all channels. However, not all channels may be searched, and a plurality of channels may be searched for candidates instead of all channels. . In this case, the processing time required for the search can be shortened compared to the case where all channels are targeted.

  Further, in the above example, the selection of the switching candidate is performed based only on the communication quality, but an access point that is a switching candidate may be selected in consideration of other conditions such as a channel.

  In the above example, a case where the wireless LAN is constructed by the IEEE802.11 standard is taken as an example. However, if the present embodiment has the same use as the power management function by the IEEE802.11, other examples are used. It can also be applied to wireless communication according to standards.

It is explanatory drawing about the method of roaming in this embodiment. It is a figure which shows the structural example of the radio | wireless terminal in this embodiment. It is explanatory drawing of operation | movement in power management. It is a flowchart which shows the search process of the access point used as the switching object which the radio | wireless terminal in this embodiment performs. It is a figure which shows the structural example of the list table which registers the access point used as a switching candidate. It is a flowchart which shows the operation | movement process at the time of performing the roaming of the wireless terminal in this embodiment.

Explanation of symbols

1 wireless terminal 2 access point 11 CPU
12 Main storage device 13 Auxiliary storage device 14 Input / output device 15 Network connection device 16 Medium reader 17 Portable storage medium 18 Bus

Claims (11)

In a wireless terminal that establishes communication with an access point and performs wireless communication,
Switching candidate search means for searching for access point candidates for newly establishing communication during roaming for switching the communication channel prior to the roaming, for switching the access point for establishing the communication;
Switching candidate storage means for storing the access point candidates obtained by the search;
A wireless terminal comprising:   The switching candidate search means stores an access point with the best communication quality as the candidate in the switching candidate storage means when there are a plurality of access points as candidates for one communication channel. Item 2. The wireless terminal according to Item 1.   3. The switching candidate search unit searches for the candidate by switching a communication channel while establishing communication with an access point established for performing the wireless communication. Wireless terminal.   The switching candidate search means searches for the candidate by switching the communication channel when in a sleep state where reception from the access point with which the communication is established is not performed. The wireless terminal described. Roaming processing means for switching the access point for establishing the communication based on the reference result, referring to the switching candidate storage means when performing the roaming,
The switching candidate search means examines communication quality of communication with the candidate access point, stores information indicating the communication quality in the switching candidate storage means as information on the candidate, and the roaming processing means The wireless terminal according to any one of claims 1 to 4, wherein the information indicating the communication quality stored in the switching candidate storage means switches to an access point indicating the best communication quality.   6. The wireless terminal according to claim 5, wherein the switching candidate search means checks the communication quality from reception strength of a beacon from the candidate access point.   6. The wireless terminal according to claim 5, wherein the switching candidate search means transmits a probe request and examines the communication quality from the reception strength of a response to the probe request. Means for obtaining a signal indicating whether the moving body on which the wireless terminal is mounted is moving or stopped;
Means for switching to a roaming priority mode that actively searches for the candidate when the signal indicates movement, and a power saving mode that prioritizes holding down power consumption when the signal indicates stop; The wireless terminal according to claim 1, wherein: In a network connection device that is mounted on a wireless terminal that establishes communication with an access point and performs wireless communication,
Switching candidate search means for searching for access point candidates for newly establishing communication during roaming for switching the communication channel prior to the roaming, for switching the access point for establishing the communication;
Switching candidate storage means for storing the access point candidates obtained by the search;
A network connection device comprising: A method for searching for an access point that is a candidate for switching when roaming is performed in a wireless terminal that establishes communication with an access point to perform wireless communication, and switches the access point for establishing the communication,
Prior to the roaming, the candidate is searched by switching communication channels,
An access point obtained by the search is stored as the candidate. A search method for a candidate for switching. A program executed in a wireless terminal that establishes communication with an access point and performs wireless communication,
Prior to the roaming, the candidate searches for the candidate by switching communication channels;
A function of storing the access point obtained by the search as the candidate;
A program that realizes

Images