JP2007325064A - Radio lan handover method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a time required by a radio LAN terminal at a handover, and to conduct a data communication with a little interruption. <P>SOLUTION: An operation channel of a radio access point during communicating at present is set as a reference channel, a place in a specific range regarding the reference channel as a center is prescribed as a scan object range, a scan channel is extracted by a channel step determined from a youngest number in the scan object range, and a scan is conducted only to the extracted channel. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a handover method in a wireless LAN, and more particularly to a method for shortening the time required for a wireless LAN terminal to perform handover and performing data communication with little interruption.

When it is impossible to cover the area where the wireless LAN terminal moves with one wireless access point, a plurality of wireless access points are arranged to cover the entire area to be used.

When the wireless LAN terminal moves in such an environment, if the data communication quality with the wireless access point in communication starts to deteriorate, the wireless LAN terminal searches for the presence of other adjacent wireless access points with good communication quality. As a result of the search, if there is a wireless access point with good communication quality, a handover operation for switching the connection is performed.

The operation of searching for another adjacent wireless access point with good data communication quality performed at the time of the handover operation is called scanning, and the conventional scanning method uses, for example, wireless access when using a wireless LAN in the 2.4 GHz band. Regardless of the presence or absence of points, scan all channels in order from 1 channel to 14 channels, or register all channels used by multiple wireless access points in the wireless LAN terminal and give priority to registered channels There is a way to scan.

During this scan operation period, the normal wireless LAN terminal cannot perform data communication with the wireless access point for the search operation, and therefore it is desired that the time required for the scan is short.

Therefore, for example, as shown in Japanese Patent Application Laid-Open No. 2005-151433, instead of searching for the presence or absence of wireless access points for all channels in one background scan, all available wireless access points can be used. There is a background scan method in which the time required for one background scan is shortened by dividing the channel into a plurality of groups and performing the background scan a plurality of times, and the scan does not affect the data communication.

Here, FIG. 3 is a time chart for explaining the background scanning method, and FIG. 4 is a flowchart of the background scanning method.

Next, the operation of JP-A-2005-151433 will be described. When the data communication quality with the wireless access point during communication starts to deteriorate, the wireless LAN terminal executes a so-called background scan that searches for the presence of other adjacent wireless access points while performing data communication. In this background scan, after holding the channel value with which it is communicating prior to the start of scanning, the group table holding the channel value to be searched is selected. The group table holding this channel value is created by dividing all channels that can be used by the wireless access point into multiple groups. For example, adjacent wireless access points are usually assigned to adjacent wireless access points. The channels with high probability of being arranged close to the channel of the wireless access point with which they are communicating are grouped together as one group. This multiple grouping reduces the time required for one background scan and prevents the scan from affecting data communication. With respect to one divided group, the presence / absence of a wireless access point using a channel allocated in the group is searched and the result is held. When the search for the group is completed, the operation for searching for the presence / absence of a wireless access point using the channel assigned in the group is similarly performed for the group of the next number at the timing of the next background scan. The background scan ends when all the channels have been searched through a plurality of groups. Thereafter, if there is a wireless access point with good communication quality, a handover is performed.
JP 2005-151433 A

In the conventional scanning method in which the search is performed on all the channels in order from the 1st channel to the 14th channel, since the number of channels is large, it takes about several hundred milliseconds to complete the scan. In addition, if all channels used by the wireless access point are registered in each wireless LAN terminal and the registered channels are scanned preferentially, when the number of channels used increases, the scan ends for several hundred milliseconds as with the former. It takes some time. This causes a problem that leads to interruption of data communication at the time of handover. In particular, in the latter case, there is also a problem of channel registration setting for the wireless LAN terminal.

Also, in the background scan method disclosed in Japanese Patent Application Laid-Open No. 2005-151433, the time required for one background scan can be shortened by dividing all channels that can be used by the wireless access point into a plurality of groups. However, since the scan does not affect the data communication, the background scan is performed a plurality of times to perform the scan of all the channels, so that the time required for the end of the full scan is almost the same as the conventional method. In addition, the wireless LAN terminal cannot be handed over until the end of all scanning, and there is a problem in that the state of data communication with the wireless access point continues to deteriorate in the moving wireless LAN terminal. Furthermore, if the background scan is frequently performed, the processing amount of the wireless LAN terminal increases, and there is a problem that affects data communication.

To achieve the above object, a wireless LAN handover method according to claim 1 is a wireless LAN system hand comprising a wireless LAN terminal, a communication network, and a plurality of wireless access points for connecting the wireless LAN terminal and the communication network. In the over method, when searching for other adjacent wireless access points other than the currently communicating wireless access point, the operation channel of the currently communicating wireless access point is set as the reference channel, and the specific channel range before and after the reference channel is set. A scan channel target range is defined, a scan channel is extracted from the scan channel target range in a predetermined channel step, and scanning is performed using only the extracted channel.

In order to achieve the above object, the wireless LAN handover method according to claim 2 is characterized in that in the wireless LAN handover method according to claim 1, the channel step can be arbitrarily changed according to a scan result.

According to the first aspect of the present invention, no specific registration or setting is required for the wireless LAN terminal, and the number of channels to be scanned at the time of handover is reduced, so that the scanning is completed in a shorter time than the conventional method. Uninterrupted data communication is possible.

According to the invention of claim 2, by setting the scan channel step to be thin or coarse, scanning is performed according to various channel setting conditions of the wireless access point, so the scan is completed in a shorter time than the conventional method, Data communication without interruption is possible at the time of handover.

Embodiments of a wireless LAN handover method according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a conceptual diagram illustrating a wireless LAN handover method according to an embodiment of the present invention. FIG. 2 is a diagram illustrating processing operations of a scanning method at a wireless LAN terminal that performs wireless LAN handover according to an embodiment of the present invention. It is a flowchart.

In the embodiment of the present invention, when the communication quality with the wireless access point during communication starts to deteriorate, the wireless LAN terminal performs a scan to check whether there is another adjacent wireless access point with good communication quality. At this time, all channels are not scanned, the operation channel of the wireless access point currently communicating is set as a reference channel, and a specific range of ± 10 channels, for example, is defined as a scan channel target range centering on the reference channel. The scan channel is intermittently extracted in 5 channel steps from the smallest number within the scan channel target range, and only the extracted channel is scanned. There may be any number of specific ranges of ± 10 channels, and the details of setting the channel step this time to 5 will be described later, but the channel step can also be set arbitrarily.

In FIG. 1, for example, it is assumed that a wireless access point currently communicating with a 2.4 GHz band wireless LAN terminal is set to 11 channels, and another adjacent wireless access point is set to 1 channel. At this time, the scan reference channel is 11 channels, and the scan channel is a target range of the scan channel from 1 channel to 21 channels of ± 10 channels centering on 11 channels. However, in the 2.4 GHz band wireless LAN, since there is no channel setting larger than 14 channels, the scan channel target range finally becomes 1 channel to 14 channels. When the scan channel target range is determined, scanning is performed every 5 channels from the smallest channel in a predetermined channel step. In this case, scanning is performed in the order of 1 channel first, then 6 channels, and finally 11 channels. If the scan performed in this way confirms the presence of other adjacent wireless access points with good communication quality, handover is performed. If it cannot be confirmed, the scan channel step is reduced and scanning is started again from the smallest channel. Whether the communication quality is good or bad is determined by the received signal strength (RSSI).

Next, the processing operation in the embodiment of the present invention performed by the wireless LAN terminal will be described with reference to the flow shown in FIG.

The wireless LAN terminal sets a channel currently being communicated as a reference channel, and determines a ± 10 channel range around the reference channel as a scan channel target range. A value obtained by subtracting 10 from the reference channel is stored in the internal buffer as a scan channel target range start value, and a value obtained by adding 10 to the reference channel is stored as a scan channel target range end value. Next, the scan channel step is set. Normally, channel steps are 5 channel steps (steps 201, 202, 203, 204).

At 205, the scan channel start value is read and stored in the buffer as the scan channel initial value. In practical wireless LAN systems, there are no channels of 0 or less, so it is determined whether the buffer value is 0 or less. If it is 0 or less, the buffer value is added by the scan channel step. If it is 0 or less after the addition, the scan channel step is added to the buffer value again, and the process is repeated until the buffer value becomes 1 or more. (Steps 205, 206, 207)

If it is determined that the buffer value is 1 or more, the channel is set to the value and scanning is performed. After scanning on the channel, the channel step is added to the buffer, and the addition result is within the scan channel target range or 14 or less of the maximum usable channel value set in the 2.4 GHz band wireless LAN system. If the determination result is true, the channel is set to the numerical value and scanning is performed. If not, the scanning is terminated. (Steps 208, 209, 210, 211, 212, 213)

After the scan is completed, the channel is set as a reference channel and communication is performed. The communication quality of the adjacent wireless access point is judged from the scan result. If the presence of another adjacent wireless access point with good communication quality can be confirmed, the handover is performed. If the existence is not confirmed, the scan channel is confirmed. The step is set small, and a series of processes from 205 is performed again. The quality of the communication quality is determined by the received signal strength (RSSI). (Steps 213, 214, 215, 216, 217)

Next, a method for determining a scan channel step will be described. The wireless LAN channels allocated to the 2.4 GHz band include channel 1 to channel 14. Of these, channels 1 to 13 are arranged at intervals of 5 MHz, and use bands overlap between adjacent channels. For this reason, when wireless access points are arranged close to each other, it is usually difficult to use adjacent channels. For example, a combination of channel 1, channel 6, and channel 11, or channel 2, channel 7, and channel 12 are used. Are often used at intervals of 5 channels. In the embodiment of the present invention, the channel step of scanning is set to 5 in consideration of the above-described characteristics.

The communication rate used during normal scanning is 1 Mbps or 2 Mbps. At this communication rate, even if there is a difference of one channel or two channels between the operation setting channel of the wireless access point and the scan channel, the above-mentioned use is performed. Due to the overlapping of bands, the received signal strength is 10 to 20 dB lower than that received by the same channel, but the wireless LAN terminal and the wireless access point each have a characteristic capable of receiving signals. Using the above characteristics, even when a wireless access point is used at a channel interval different from the 5-channel interval, the presence or absence of another adjacent wireless access point can be searched by scanning in a 5-channel step.

There are various classification methods using the above characteristics, but for example, there are 6 fixed channels of 1, 4, 7, 10, 13, 14 and 8 fixed channels of 1, 3, 5, 7, 9, 11, 13, 14 You may scan.

An example of the operation is shown below. Assume that the wireless LAN terminal is connected to a wireless access point that is set to operate for one channel. When the received signal strength from the wireless access point deteriorates, the wireless LAN terminal sets one channel whose operation is being set as a reference channel, and defines a ± 10 channel range as a scan channel target range around the reference channel.
Since the scan channel target range is obtained by numerical calculation, a channel value that does not actually exist may be obtained. In this example, -9 to +11 are obtained as the calculation results as the ± 10 scan channel target range of one channel which is the reference channel. There is no channel less than 1 in practical wireless LAN channels, but the scan channel target range is set and held in the internal buffer with -9 as the scan channel target range start value and +11 as the scan channel target range end value. The set value of the scan channel step is 5. Next, the scan channel target range start value is set in the buffer as the scan channel initial value. Since a numerical value of 0 or less cannot be set as a channel, the scan channel step is added to the buffer without doing anything. The value after addition is -4, which is also equal to or less than 0, so the scan channel step is added to the buffer without doing anything. Since the buffer value after addition is 1 and can be set as a channel larger than 0, scanning is performed on the channel having the same value as the buffer value, and the scan result is stored. After saving the result, the scan channel step is added to the buffer. The value after the addition is 6, which is greater than 0, less than or equal to 11 which is the scan channel target range end value, and smaller than 14 which is the maximum usable channel value set in the 2.4 GHz band wireless LAN system. Scan the channel with the same value as the buffer value and save the scan result. After saving the result, the scan channel step is added to the buffer. The value after addition is 11, which is greater than 0, is less than or equal to 11 which is the scan channel target range end value, and is smaller than 14 which is the maximum usable channel value set in the 2.4 GHz band wireless LAN system. Scan the channel with the same value as the buffer value and save the scan result. After saving the result, the scan channel step is added to the buffer. The value after addition is 16, which is 11 or more, which is the scan channel target range end value, so the scan is terminated. After the scan is completed, the channel is temporarily set as a reference channel to perform communication, and another wireless access point with good communication quality is selected using the received signal strength as a criterion for acceptability. If there is another wireless access point with good communication quality, the handover is performed. If there is no other wireless access point, the scan is performed again on the six fixed channels 1, 4, 7, 10, 13, and 14 determined in advance. . After the scanning of up to 14 channels is completed, the handover process is performed in the same manner using the received signal strength as a pass / fail criterion.

The conceptual diagram which shows an example of the channel range used as the scanning object by this invention, The flowchart explaining the processing operation in the wireless LAN terminal of this invention, Time chart explaining the background scan method by the conventional method, A flowchart for explaining processing operations in a wireless LAN terminal of a conventional method;

Explanation of symbols

101: Connected wireless access point operating channel (1 channel)
102: Adjacent wireless access point 1 operation channel (6 channels)
103: Adjacent wireless access point 2 operation channel (11 channels)
104: Scan channel target range 105: 2.4 GHz band wireless LAN channel

Claims (2)

In a handover method of a wireless LAN system having a wireless LAN terminal, a communication network, and a plurality of wireless access points for connecting the wireless LAN terminal and the communication network, other adjacent wireless access other than the wireless access point in communication When searching for a point, the operating channel of the wireless access point in communication is set as a reference channel, a specific channel range before and after the reference channel is set as a scan channel target range, and the scan channel target range is set in advance. A wireless LAN handover method, wherein a scan channel is extracted in a channel step, and scanning is performed using only the extracted channel.
2. The wireless LAN handover method according to claim 1, wherein the channel step can be arbitrarily changed according to a scan result.

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