JP2003318920A - Wireless LAN system - Google Patents

Abstract

(57) [Summary] [PROBLEMS] When a wireless terminal is located in an overlap area between two cells, an access point to be connected can be selected stably and reliably. Also, the restriction on the installation location of the wireless terminal is relaxed. SOLUTION: If there is a wireless terminal in the overlap area, means for comparing a "distance" between the wireless terminal and the access point to determine a connection destination is provided. In addition, when the vehicle enters the overlap area from other than the overlap area, means for switching the access point earlier is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless LAN system, and more particularly to a method for selecting an access point of a wireless terminal and its system.

[0002]

2. Description of the Related Art There are mainly two known methods for selecting an access point of a wireless terminal in a conventional wireless LAN system. One is a method of selecting the stronger access point by measuring the electric field strengths of radio waves from two access points and comparing the electric field strengths of the two. The other is a method of storing the ESS-ID of the connection destination access point in advance in the terminal and not connecting to other access points.

ESS-ID stands for Extended Service Set
It is an abbreviation of Identity and is defined by the IEEE 802.11b wireless LAN specification. Enables communication between access points and wireless terminals having the same ESS-ID,
This is to prevent communication with an access point or wireless terminal having an S-ID. Also, the same ESS-ID
Between the access points, the wireless terminal can communicate by crossing (roaming) the access points. ESS-
The fact that the ID has the specifications of IEEE 802.11 means that "Dictionary of Digital Terms" (issued by Nikkei BP, ISBN4-8
222-7231-1 C3055). Also, for the explanation of the function, please refer to "Can wireless LAN 2nd Ed
version Air Station compatible "(Issue:
Impress Co., Ltd., ISBN4-8443-1543-
9 C3055.

When installing a plurality of access points,
As shown in FIG. 3, the communication ranges (cells) where the radio waves of the access point reach and are communicable are arranged so as to overlap each other.
This overlapping portion is called an overlap area. This enables smooth roaming even if the wireless terminal moves.

The electric field strength at the time of receiving a radio wave is generally attenuated in inverse proportion to the distance from the access point. Therefore, the overlap region is the outer edge of the area covered by the access point, and the electric field strength is weaker than that of the central portion. At the left end of the overlap region, the electric field strength of one access point is slightly strong, and at the right end, the electric field strength of the other access point is slightly strong. Further, there is a boundary line having the same electric field strength near the center of the overlap region (see FIG. 3).

[0006] Generally, in a mobile terminal such as a mobile phone, when roaming, communication with a connected base station is continued unless the electric field strength falls below a certain threshold. Even if an access point with a strong electric field strength is found, switching is not performed. A method of selecting an access point having a good electric field strength is also described in "Access Point Selection Method and Wireless LAN Device in Wireless LAN", Japanese Patent Laid-Open No. 2001-308866.

[0007]

Of the above-mentioned conventional techniques,
The method of comparing the electric field strengths and connecting to the stronger access point is difficult to determine in the vicinity of the boundary where the electric field strength values compete with each other. The result of the electric field strength comparison is determined to be greater equal (≧) or less (<), but the result may be opposite in the next time zone even if it is once decided. In that case, since the connection destination access point is changed, switching loss (transmission performance deterioration) occurs. Due to such circumstances, in a radio wave simulation or the like that decides the wireless terminal arrangement in the office in advance, the wireless terminals are restricted from being arranged in the overlap area.

On the other hand, the conventional method of assigning an ESS-ID to a terminal is to reliably select the access point that matches the ESS-ID of the wireless terminal in the overlap area of access points of different ESS-IDs. Although there is an effect that it can be done, two access points have the same ESS-I
In the case of D, the connection destination of the overlap area is not determined.

Further, the effective radius of the access point in the wireless LAN system in the office is from several meters to 10 meters.
It is small and there is no large radius of several kilometers like the base station of a mobile phone. Therefore, if the communication is sticky in the overlap area, the state of the radio wave will be deteriorated immediately.

It is an object of the present invention to provide a connection method in which even if a wireless terminal is located near the boundary of the overlap area, there is no "judgment fluctuation" of the access point of the connection destination. In addition, there is no restriction on the installation location of wireless terminals.

Another object of the present invention is to switch early when a wireless terminal such as a notebook PC having a wireless function moves, instead of switching after communication is disabled.

[0012]

The wireless terminal of the wireless LAN system of the present invention has means for determining the connection destination based on the distance between the wireless terminal and the access point. In the overlap area where the electric field strength is similar, an access point closer to the wireless terminal is selected.

Further, the wireless terminal of the wireless LAN system of the present invention, when the wireless terminal moves and enters the overlapping area where the access points do not overlap with each other, when the wireless terminal does not perform the transmission / reception operation, the access point is activated. It has a switching means. Since the switching is performed early, it is possible to avoid a case where the wireless terminal enters the overlap area, then enters the transmission / reception operation, rushes out of the area of the cell, and becomes unable to communicate and is retransmitted.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a control program for selecting a connection destination access point of a wireless terminal. It consists of three modules.

As a premise of the control of this embodiment, it is assumed that the wireless terminal receives radio waves from a maximum of two access points AP1 or AP2 but does not receive radio waves from three access points. The access points are arranged so that this condition is satisfied. That is, the layout is designed so that three or more access points do not overlap. A notebook personal computer (PC) having a wireless function will be described as an example of the wireless terminal. Although the notebook PC is portable, it is often used by placing it on the seat without moving it. Mainly used in the office.

The first module 101 selects an access point by judging the threshold value of the electric field strength. If not settled here, the second module 102 is entered.

The second module determines the distance between the wireless terminal and the access point and selects the access point. Also, when the area is changed, control is performed to switch the access point. If it is not determined by the distance determination, the third module 103 is reached. The third module urges the user to move the wireless terminal because the radio wave condition is bad. This warning is not issued if it is determined that the wireless terminal is moving. Whether it is moving can be determined by monitoring whether the distance has changed.

Next, the details of each module will be described.

The module 101 searches for an access point with which the wireless terminal can communicate. The search detects the beacon from the access point and determines whether the electric field strength is above the threshold value (E ≧ threshold value). Communication is possible if it is above the threshold. If there is one communicable access point, the connection destination is that access point.
Here, in the present embodiment, when there are two or more communicable access points, the area in which the wireless terminal exists is assumed to be the overlap area.

Immediately after the wireless terminal is powered on, the wireless terminal registers the device address once with the access point. The access point registers this wireless terminal in the management table, and thereafter manages transmitted / received data.

In module 101, if the field strengths from the two access points are greater than the threshold value, the next step is to go to module 102.

The module 102 (1) first compares the distances from the wireless terminal to both access points. The reason why the electric field strengths from both access points are not compared is that the electric field strengths are almost equal in the overlap region, and there is often no significant difference even if the electric field strengths are compared at this stage. .

The relationship between the electric field strength E and the distance r is shown in the equation (1) of FIG. In this equation, the distance r is the route of the product of the transmission output p of the access point and the gain g divided by the electric field strength E.

Here, if the electric field intensities E1 and E2 are substantially equal and the gain g and the coefficient a are the same at both access points, there is no problem in comparing the distances r1 and r2 even if comparing the transmission outputs p1 and p2. . The access point notifies the wireless terminal of the transmission output p, the gain g, and the coefficient a by a beacon. Therefore, if the electric field strength E is measured and pga is known, the distance r can be calculated.

In this way, the comparison of the distances r1 and r2 between the access point and the wireless terminal can be reduced to the comparison of the transmission outputs p (1) and p (2) of the access point. For example, if there is a difference between p (1) and p (2), E
Even if 1 and E2 are the same, there will be a large difference between r1 and r2. The transmission power depends on the model of the access point. If the wireless terminals hold the transmission outputs of these models in correspondence with the access point models, the distances can be easily compared by identifying the access point models. In addition, this comparison result is stored in a memory of a wireless terminal (not shown),
It is used for movement determination in the next step described later.

According to the above simple determination method, if the electric field strength is the same, the distance from the access point with a large transmission output is far, and the distance from the access point with a small transmission output is short. Therefore, p (1)> p (2) means r (1)> r (2), and since the wireless terminal is located near the access point 2, the access point 2 is selected. Conversely, if p (1) <p (2), then r
(1) <r (2), that is, the wireless terminal is located near the access point 1. Therefore, the wireless terminal selects the access point 1 as the connection destination.

(2) of the module 102 shows the processing when the wireless terminal is moving. If the wireless terminal is placed corresponding to the desk and does not move, the determination in 102 (1) is sufficient, but if there is movement, the access point switching determination is performed according to the change in the situation after once determining the access point. I need to do it. In the determination of the electric field strength of 101, the determination is performed by periodically observing the beacon from the access point.

Here, unlike the previous determination, it is detected that the wireless terminal has entered the overlap area. Since the effective radius of the access point used in the office environment is relatively small, the switching timing may be delayed if the access point is switched by detecting that it has exited the overlap area. Therefore, when entering the overlap area, a new registration request is issued to an access point different from the previous connection destination. With such a configuration, it is possible to prevent at least communication from becoming impossible due to transmission / reception after entering the overlap area.

That is, in this step, the determination result stored in the memory in the previous step 102 (1) is compared with the determination result of this time. If the determination result is different from the previous determination result, the wireless terminal is moving. Judge that. Information on the access point connected so far and the other access point causing the overlap is obtained from, for example, a beacon transmitted from the access point. When that information is used, when it enters the overlap area, an access point different from the access point that has been accessed until then is selected, and the access point of the connection destination is switched.

Note that the transmission / reception time is IEEE802.11.
The maximum speed is 11 Mbps in the b specification, but about 6 m assuming an effective rate of 5 Mbps and a packet length of 4 kB.
s, 64 kB length is about 102 ms. Even if the time required for one transmission / reception is 0.2 seconds with a margin, it is possible to cross the cell boundary (outer edge). If it can be switched early, transmission / reception during the time when moving in the overlap area will not be a problem, and transmission / reception started before entering the overlap area will be retransmitted unless it passes through the overlap area in 0.2 seconds. No need arises.

The module 103 is for display control. If p (1) = p (2) of module 102 (1),
Proceed to the next step, module 103. The module 103 notifies the user that the wireless terminal is in the overlapping area and can communicate with either of the access points, but is in the area which does not connect with either one. Such a case occurs when there is a wireless terminal in the overlap area of access points having the same transmission output.

When a warning is given to the wireless terminal in this way, the user of the wireless terminal selects either access point to perform communication. The choice depends on the firmware of the wireless terminal. At the preliminary stage, it is undecided which of the access points will be loaded, so it is urged to change the location.

If the cells have the same size as described above, the electric field strength and the distance are close to each other in the overlap region. The module 103 displays that fact, but upon receiving this notification, the mobile terminal is set to move. In that case, the module 102 (2) captures and displays the timing when the wireless terminal enters the overlap area and when the wireless terminal exits the overlap area. With such a configuration, the user can know in which area the wireless terminal is located, and can determine the installation location of the wireless terminal suitable for communication.

Next, a method of calculating the distance from the access point to the wireless terminal will be described in detail.

FIG. 2 shows a general relationship between electric field strength and distance. The electric field strength E is obtained by dividing the square root of the product of the transmission output p of the access point and the gain g by the distance r and further multiplying it by a constant a (equation (1) in FIG. 2). The access point periodically puts this information in a beacon to notify the wireless terminal.

The wireless terminal measures the electric field strength E, pga
The distance r is calculated by substituting it into the equation (1) together with the value of.
Usually, as described above, the transmission output p is limited to several depending on the model of the access point. For example, transmission output 30m
W, 5 mW, 1 mW, etc. The effective radii of radio waves are 50 m, 20 m, 10 m, etc., respectively. When this is plotted on the graph of electric field strength and distance r, 201 is 3
0mW, 201 is 5mW, 203 is 1mW
In the case of. Assuming that the lower limit of field strength communication is "1"
Then, the value to be compared as an overlap of 5 m is a value near “1”. The smaller the transmission output, the steeper the curve.

FIG. 3 shows a wired Ethernet (registered trademark)
An example of overlapping of cells of an access point 1 having a large transmission output and an access point 2 having a small transmission output, which are connected to each other, is shown. The overlap area is shown at 304. It is assumed that the wireless terminal 307 is located here. The range of the radio wave of AP (1) is 301, and the range of the radio wave of AP (2) is 302. Also, the changes in the respective radio field intensities are shown by curves 305 and 306.

For example, assume that an access point with a radius of 50 m and an access point with a radius of 10 m overlap by 5 m. If the access points are arranged so that the overlap does not become large, the middle point of the distance between them will be 303, which is about 27.5 m from the center of the access point 2.
Since it is on the line of, it can be outside (on the left side) of the overlap area. In this case, the distances r1 and r2 will not be equal no matter where the wireless terminal is in the overlap area. Always r1> r2. Therefore, the determination result becomes more reliable.

On the other hand, the electric field strengths are almost equal in the overlap area, and the boundary line of the electric field strength exists in the overlap area. Looking at the electric field strength in detail, since the rising slope of the curve 306 is slightly steeper than the falling slope of the curve 305, the boundary line is closer to the AP (1) side of the overlap region. If the determination based on the electric field strength D difference is accurate, the wireless terminal in the overlap area will mostly select AP (2). Since the determination method of FIG. 1 this time introduces the determination based on the distance, all the wireless terminals in the overlap area select AP (2) here.

FIG. 4A is an enlarged representation of the overlap area of FIG. 3 and expresses the point of switching the access point of (2) of the module 102 of FIG. Four
03 is a change in electric field strength of AP (1), 404 is AP
The change in electric field strength in (2) is shown. A dotted line 401 indicates that the wireless terminal starts moving from the state of being connected to AP (1), and switches to AP (2) indicated by the electric field strength 404 when entering the overlap area. After that, the AP (2) is continuously connected. A dotted line 402 indicates that the wireless terminal starts moving from the state of being connected to AP (2) and switches to AP (1) indicated by the electric field strength 403 when entering the overlap area. After that, the AP (1) is continuously connected.

FIGS. 4B-1 and 4B-2 are schematic diagrams of access point switching. FIG. 4B-1 is a conventional method, and FIG. 4B-2 is a method according to an embodiment of the present invention. Is. Conventionally, when moving from AP (1) to AP (2), the current stable communication connection destination is continued as much as possible as indicated by a broken line 411, and switching is performed when the threshold value is exceeded.
In the case of moving from AP (2) to AP (1), the broken line 4
As shown in 12, the current connection destination AP is continued and switched when the threshold value is exceeded.

In (B-2), AP (1) to AP
When moving to (2), when it enters the overlap area as shown by the polygonal line 413, it switches from AP (1) to AP (2). Switching is faster than B-1.

In the configuration of FIG. (B-2), the electric field strength 403
From the middle of the mountain to the bottom of the electric field strength 404, 404
It looks like climbing a mountain. AP (2) to AP (1)
Also in the case of moving to, as shown by the polygonal line 414, when the overlap area is entered, the AP (2) is switched to the AP (1). Switching is faster than B-1. The reason is that the effective radius of the access point is so small that the electric field strength drops sharply before the distance advances.

When moving from the overlap area to the non-overlap area, the access point is not changed. By doing so, it is possible to change the access point earlier and prevent the connection from being interrupted due to the change of the access point.

In this embodiment, it is premised that the layout is designed so that three or more access points do not overlap each other, but the same can be realized in the case of three or more. In that case, the number of overlapping units is stored in the memory each time.

For example, even if three access points overlap each other, the two access points always enter the overlapping area before entering the area. Therefore, when entering the overlap area of the two access points, as in the above-described embodiment, the access point different from the one that has been accessed until now is entered, and three access points are overlapped. When entering the area, the connection destination may be changed to a new access point.

If the number of overlapping access points becomes small, for example, when the user further moves and the two access points enter the overlap area from the overlap areas of the three access points, the access points are not changed. Whether or not the change is necessary can be performed by determining whether or not the number of previous overlapping access points stored in the memory has decreased. Alternatively, instead of the number of overlapping access points, a kind of identification ID may be stored in the memory to determine whether or not there is a new access point.

As described above, when the number of overlapping access points increases, the number of connecting access points is increased. When the number of overlapping access points decreases, the number of access points is not changed. With such a configuration, even when three or more access points overlap with each other, it is possible to appropriately change the access points forward and prevent access disconnection.

Further, in the present embodiment, there is a case where there are a plurality of access points having a radio field intensity capable of communication exceeding the certain threshold in the overlap area. However, another overlap determination for newly defining the overlap area is made. It may be configured to provide a threshold value for the. In other words, if there are multiple access points with radio field strength higher than this threshold,
The control of FIG. 1 described above may be performed as the overlap area.

[0051]

The effects of the present invention are listed below.

Since the connection destination determination based on "distance" is introduced, the connection destination can be clearly determined without the fluctuation of the determination like the radio field intensity. The answer remains the same no matter how many times you judge. Further, wireless terminals may be arranged in the overlap area of access points having different transmission outputs. This alleviates the restrictions on the arrangement of wireless terminals.

Since the wireless terminal is configured to "detect the movement to the overlap area and switch the access point early" from the non-overlapping area, it is possible to prevent the communication from being interrupted and to be retransmitted.

Since the case where the wireless terminal enters the overlapping area from the area where the cells do not overlap and the case where the wireless terminal exits the overlapping area are displayed, the user can know whether or not the wireless terminal is in the overlapping area. You can know the proper installation location.

[Brief description of drawings]

FIG. 1 is a flow chart of a configuration and determination operation of a control program for determining a connection destination of a wireless terminal according to the present invention.

FIG. 2 is a diagram illustrating a general relationship between electric field strength and distance.

FIG. 3 is a diagram illustrating electric field strength when a large cell and a small cell overlap each other.

FIG. 4 is a diagram showing an access point switching point according to the present invention.

[Explanation of symbols]

101: Module for searching access points with which wireless terminal can communicate 102 (1): Module for comparing wireless terminal with access point 102 (2): Module for judging switching of access point 103: Position at wireless terminal A module 201 that prompts the user to move because it is not appropriate: a graph showing the relationship between the electric field strength of a radio wave with a large transmission output and a distance 202: a graph 203 showing the relationship between the electric field strength of a radio wave with a medium transmission output and a distance 203: a small transmission output A graph 301 showing the relationship between the electric field strength of radio waves and the distance: 302 showing a communicable area of a large cell 302: showing a communicable area of a small cell 303: an intermediate point between two access points 304: an overlapping area 305 between two cells : Large cell field intensity graph 306: Small cell field intensity graph 401 Switching route 402 for moving from AP (1) to AP (2): Switching route 403 for moving from AP (2) to AP (1): Electric field strength distribution of AP (1) signal detected by the wireless terminal 404: Electric field intensity distribution 411 of AP (2) signal detected by the wireless terminal 411: Switching route from AP (1) to AP (2) (conventional) 412: Switching route from AP (2) to AP (1) ( Conventional) 413: Switching route from AP (1) to AP (2) (present invention) 414: Switching route from AP (2) to AP (1) (present invention)

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yuju Aihara             810 Shimo-Imaizumi Stock Exchange, Ebina City, Kanagawa Prefecture             Hitachi Platform Platform             Home Office (72) Inventor Kenichi Saito             810 Shimo-Imaizumi Stock Exchange, Ebina City, Kanagawa Prefecture             Hitachi Platform Platform             Home Office F-term (reference) 5K033 AA02 DA02 DA19

Claims (3)

[Claims] 1. A wireless communication unit that receives a radio wave transmitted from an access point, a storage unit that stores first information about a connected access point, and a measurement that measures the radio wave intensity of the radio wave received by the wireless communication unit. Section and the access point that can be connected is determined from the radio field intensity measured by the measurement unit, and if there are multiple determined connectable access points, the distance from the connectable access point is calculated, and the calculated distance is calculated. A wireless terminal comprising a control unit that rewrites the first information by comparing and selecting an access point closer thereto as a connection destination. 2. The wireless terminal according to claim 1, wherein:
When the difference between the distances calculated by the control unit is within a predetermined range, the control unit determines that an access point different from the access point stored in the storage unit is selected from the connectable access points. Characterized wireless terminal. 3. The wireless terminal according to claim 2,
The storage unit further stores second information regarding the determined plurality of connectable access points, and the control unit refers to the second information to determine whether or not to change the access point. Characteristic wireless terminal.