JP2011193101A - Wireless lan system, access point, channel control method used by them, and program thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly change channels by shortening a required time other than a time required for radar search processing as much as possible when changing the channels by a DFS function stipulated in IEEE802. 11h for dynamically changing a frequency when a radar wave is detected. <P>SOLUTION: This access point in a radio LAN system includes: a BSS including an access point provided with a DFS function stipulated in IEEE802. 11h for dynamically changing a frequency when a radio wave is detected. The access point includes: a radar wave detecting means for detecting a radar wave for a channel used by a BSS; and the next channel candidate selecting means for selecting a change destination channel as a candidate on the basis of change channel information in which a change destination channel candidate is defined in advance on the basis of the positional relation of each BSS when the radar wave is detected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a channel control method considering a dynamic frequency selection function (DFS function) in an IEEE802.11 wireless LAN system.

  Wireless LAN systems that have been rapidly spreading in recent years have been standardized by IEEE 802.11. In particular, for a system using a frequency of 5 GHz band, IEEE 802.11h defines a dynamic frequency selection function (hereinafter referred to as DFS function) and a transmission power control function (TPC function). These functions are for reducing interference with other systems (meteorological radars and various radars) that use the same frequency, and are required to be implemented on the wireless LAN system side.

  When the DFS function detects a radar wave of another system using the same frequency, the used frequency is changed to another empty channel frequency. At that time, the radar wave detected by the DFS function is changed. The operation prohibition within 30 minutes on the same channel and the radar search for 60 seconds before the operation start on the channel whose radar presence / absence information is not known in advance are essential.

  However, the method for determining the channel to be changed by the DFS function has no specific definition in the standard, and in many cases, is a system-specific implementation. For example, there exists a thing like patent document 1. FIG.

JP 2007-181200 A

  In Patent Document 1, when it is determined that a channel change by the DFS function is necessary, a new channel to be used is determined based on the quality among a plurality of empty channels at that time.

  However, in the system of Patent Document 1, when the channel is changed by the DFS function, the access point itself has to scan the empty channel and determine the quality, and if the number of channels to be scanned is large, it takes a corresponding time. It will be. This is a time required separately from the radar search for 60 seconds before the start of operation.

  As described above, the DFS function requires a radar search process for 60 seconds before the start of operation according to the standard, and communication between the access point and the station cannot be performed during that period. In order to shorten such communication impossible time as much as possible, it is necessary to shorten the time required in addition to the time required for the radar search process as much as possible. However, since the invention according to Patent Document 1 requires a relatively long time for channel change, it cannot be said to be a sufficient solution to this problem.

 The access point according to the first embodiment of the present application is an access point in a wireless LAN system including a BSS including an access point having a DFS function defined in IEEE802.11h that dynamically changes a frequency when a radar wave is detected. The radar wave detecting means for detecting the radar wave for the channel used by the BSS, and when the radar wave is detected, the change destination channel candidate is selected as a candidate based on the change channel information defined in advance. And a next channel candidate selection means.

 More preferably, the wireless LAN system is a wireless LAN system including a predetermined number of BSSs having a predetermined positional relationship, and the change channel information is defined in advance as a change destination channel candidate based on information including the predetermined positional relationship. Access point.

  More preferably, in an arbitrary BSS, the changed channel information is defined as an initial channel separated by a predetermined number of channels from another BSS that has the strongest radio wave influence on the BSS, and is determined by the next channel candidate selection unit. In the channel change based on the changed channel information, an access point that requires at least two channel changes until each BSS becomes the same channel.

  According to the present invention, when a channel is changed by the DFS function, a change candidate channel can be immediately determined by changing the channel based on a predetermined channel change table. Furthermore, since the initial channel and the channel to be changed are defined on the table so that duplication with other BSS does not occur immediately, the risk of interference with other BSS after the channel change may be reduced. There is also an effect that can be done.

Embodiments according to the present invention will be described below with reference to the drawings. In addition, the same number is attached | subjected to the element which is common in each drawing, and description is not repeated.
[Overview of wireless LAN system]

  FIG. 1 is a schematic diagram of a wireless LAN system according to the present invention. A set of the access point 101 and the station 103 communicating with the access point 121, and the access point 121 and the station 123 communicating with the access point 101 are referred to as a BSS (Basic Service Set). BSS is a set of access points and stations in an infrastructure mode standardized by IEEE 802.11. In FIG. 1, there are two BSSs, BSS0 and BSS1.

For example, when a plurality of BSSs are operated in one location such as an office, normally, in order to avoid radio wave interference between the BSSs, the respective BSSs are arranged at some physical distance, and adjacent BSSs are separated from each other. Use channels with different frequency bands.
[Overview of wireless LAN system]

  FIG. 2 is an overall view of a wireless LAN system according to the present invention. A total of 11 BSSs of BSS0 to BSS10 are operated on one straight line, and each BSS is under the influence of a radar wave emitted from the antenna 201.

As described in the background art, when an access point detects a radar wave that interferes with a channel used by its own BSS, the access point must change its own channel. That is, when radar waves are detected in all the BSSs 0 to 10, the used channels must be changed.
[Function block diagram]

  FIG. 3 is a block diagram of functions executed by the wireless LAN system according to the present invention, particularly an access point. The functions described below are executed by the CPU, ROM, and RAM provided in the access point, but may be executed by dedicated hardware. Since such a configuration is obvious to those skilled in the art, illustration is omitted.

  The radar wave detection means 301 detects a radar wave emitted from the antenna 201 or the like. The radar wave detection technique is not described in detail because the conventional technique may be used. Although the concept of “neighboring channel” will be described later, this is a concept limited to channels between BSSs, and does not indicate the channel relationship between BSS and radar waves.

The channel candidate selection unit 303 includes a table reading unit 305 and a next channel reading unit 307. The table reading means 305 reads a channel change table, which will be described in detail later, and recognizes the channel position of the own BSS on the table. The next channel reading means 307 reads the channel corresponding to the position next to the channel position of the own BSS in the table. Through the above processing, the channel candidate selection unit 303 selects the change destination channel as a candidate. At this point, the change destination channel is only a candidate and is not actually used.
Note that the position of the selected channel on the table is maintained unless explicitly reset as will be described later.

  The radar search means 309 performs a 60-second search for the channel selected as a candidate, and detects whether it is being used. This process is essential as a DFS function.

  The determination unit 311 determines whether to change the channel based on the result of the search, and the channel setting unit 313 determines the channel selected by the channel candidate selection unit 303 as the BSS when it is determined to change the channel. Set as the operation channel. At this point, the BSS channel is actually changed.

The selection position reset means 315 resets the position of the selected channel on the channel change table selected by the channel candidate selection means 303 and returns it to the initial position.
[flowchart]

FIG. 4 is a flowchart of processing executed by the wireless LAN system according to the present invention, particularly an access point.
In step 401, the radar wave detecting means 301 tries to detect a radar wave. If detected, the process proceeds to step 403, and if not, the detection process is repeated.

  In step 403, the channel candidate selection unit 303 selects a channel candidate to be changed. Specifically, in step 451, the table reading means 305 reads the channel change table and specifies the current channel position of the own BSS on the table. Next, in step 453, the next channel reading means 307 reads the next channel based on the table.

In step 405, the radar search unit 309 performs a search process for 60 seconds, and the determination unit 311 determines the result in step 407. If a radar wave is detected as a result of the determination, the process returns to step 403 to select a channel candidate again. At this time, as the position of the selected channel on the table, the channel corresponding to the next change order is selected with reference to the already held selection position (details will be described later). On the other hand, if no radar wave is detected, the process proceeds to step 409.
In step 409, the channel setting means 313 sets the currently selected channel on the table as the BSS operational channel.
In step 411, the selected position reset means 315 resets the currently selected channel position on the table.
[Initial channel]

  FIG. 5 shows the initial values of the channels operated by each BSS. As is apparent from the figure, each BSS starts operation on a different initial channel. In addition, adjacent BSSs are largely separated from each other. For example, the initial channels of adjacent BSSs BSS0 and BSS1 are 100 and 136, respectively.

  In this embodiment, this initial value is defined based on the actual physical distance between the BSSs. In the case of this embodiment, since each BSS is arranged on the same straight line, four BSSs are operated between the channel of the BSS that is operated by itself and the BSS that operates the neighboring channel (the same channel and the four channels before and after the channel). Channel separation corresponding to the distance used by the BSS is provided. For example, the 104 channel which is a neighboring channel with respect to the 100 channel of BSS0 is the initial channel of BSS5, and there is a channel divergence corresponding to the distance of four BSSs between them.

As another example, as shown in FIG. 6, when the BSSs are arranged on the circumference, the initial value is defined according to the actual distance between the BSSs. However, in any arrangement, it is not necessary to define the initial value according to only the distance, but it is defined according to the strength of radio waves received from other BSSs. In this case, in addition to the distance, the radio wave output of each BSS and the presence of a shield are taken into consideration.
[Channel change table]

  FIG. 7 shows a table read by the table reading unit 305, which is used to select a channel candidate next to a channel operated by each BSS when the radar wave detecting unit 301 detects a radar wave. As apparent from the table, in this table, the next channel candidates to be selected by each BSS are defined in advance in the order of change. As already described for the initial channel, the arrangement of the BSSs in this table is defined according to the strength of radio waves received by each BSS from other BSSs. For example, BSS0 and BSS1 are defined adjacently because they are the BSSs that are most susceptible to the influence of radio waves when the physical distance is actually the shortest and all other conditions are the same.

  One feature of this table is that, as already described, the initial channel (change order 1) between adjacent BSSs is not a neighboring channel. Referring to FIG. 8, for example, looking at the change order 1 (that is, the initial channel) of BSS0 and BSS1, they are 100 and 136, respectively, and are not adjacent channels. The same applies to other adjacent BSSs.

  Another feature is that, even if a channel change occurs in a certain BSS, channel candidates are defined in advance in a table so that the channel does not become a neighboring channel with respect to the adjacent BSS by at least two changes. In general, it is estimated that channel change due to radar wave detection does not occur so frequently. However, when a channel change occurs, if it immediately becomes a neighboring channel of an adjacent BSS, there is a risk that it will hinder the operation, so in this embodiment at least twice. Referring to FIG. 9, even if a channel change needs to be made in channel 100 of BSS0 change order 1, the next channel is 120 according to the table, and the change order of BSS1, which is a BSS adjacent to BSS0, is changed. Neither 1 (channel 136) nor 2 (channel 112) is a neighboring channel. However, if the change is repeated, in this example, if the BSS1 repeats the change twice from the initial channel (100), the channel becomes 140 and becomes a channel adjacent to the channel 136 of the adjacent BSS. However, even if it is actually a nearby channel, communication is often possible as long as it is not the same channel. In this table, it is defined that an additional channel change step is required for the same channel. is doing. In the previous example, in order for the change order 3 of BSS0 to be the same channel as the channel 136 of the adjacent BSS, it is necessary to reach the change order 5, and the channel change is further required twice.

  As described above, according to the present invention, when a channel is changed by the DFS function, a change candidate channel can be immediately determined by changing the channel based on a predetermined channel change table. Furthermore, since the initial channel and the channel to be changed are defined on the table so that duplication with other BSS does not occur immediately, the risk of interference with other BSS after the channel change may be reduced. There is also an effect that can be done.

Wireless LAN system overview Overall view of wireless LAN system Functional block diagram of access point flowchart BSS initial channel Diagram of BSS placed on the circumference Channel change table Adjacent BSS channel (1) Adjacent BSS channel (2)

101 Access point 301 Radar wave detection means 303 Channel candidate selection means

Claims (3)

An access point in a wireless LAN system including a BSS including an access point having a DFS function defined in IEEE802.11h that dynamically changes a frequency when a radar wave is detected,
Radar wave detecting means for detecting a radar wave for a channel used by the BSS;
An access point comprising: next channel candidate selection means for selecting a change destination channel as a candidate based on change channel information in which a change destination channel candidate is defined in advance when a radar wave is detected. The wireless LAN system is a wireless LAN system including a predetermined number of BSSs in a predetermined positional relationship,
2. The access point according to claim 1, wherein the change channel information includes a change destination channel candidate defined in advance based on information including the predetermined positional relationship. In an arbitrary BSS, the change channel information is defined as an initial channel separated by a predetermined number of channels from another BSS having the strongest radio wave influence on the BSS.
The channel change based on the changed channel information by the next channel candidate selecting means requires at least two channel changes until each BSS becomes the same channel. access point.