Techniques for region-based scanning of different frequency bands for use in a wireless LAN

A communication method implemented in a mobile device is provided. The communication method includes limiting a frequency band on which the mobile device performs a scanning operation to a first frequency band used for a wireless connection of the mobile device; determining whether it is necessary to scan a second frequency band during a subsequent scanning operation of the mobile device; and in response to determining that it is necessary to scan the second frequency band, allowing the subsequent scanning operation to be performed on a plurality of frequency bands including the first and second frequency bands.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 2013-0108194, filed on Sep. 10, 2013, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates to wireless network technology, and more particularly, to technology for setting a frequency band to be scanned in a wireless local area network (WLAN) in which a plurality of frequency bands are used.

2. Discussion of Related Art

Recently, a demand for mobile devices has been drastically increased. Mobile devices communicate radio signals with access points (APs) that provide access to a wireless network through defined frequency channels. A typical example of such a wireless network that provides a service for a mobile device is a WLAN, which is widely used for business purposes, public facility-related purposes, personal purposes, and so on. The Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard for a WLAN mainly covers a physical layer and a media access control (MAC) layer.

A WLAN system includes one or more basic service sets (BSSs). A BSS is a set of stations that can be synchronized to communicate with one another. In a broad sense, the stations include AP stations and non-AP stations. For the sake of convenience, however, an AP station may be simply referred to as an AP and a non-AP station as a station. Meanwhile, a non-AP station may also be referred to as a mobile station (MS), a mobile terminal, user equipment (UE), or the like.

FIG. 1schematically shows an exemplary configuration of a WLAN.

As shown inFIG. 1, stations152and154may access a WLAN100via APs111,113,115,117,121,123, and125. For example, the access to the WLAN100may be performed according to a protocol of the IEEE 802.11 standard. Such a WLAN100as mentioned above is referred to as an infrastructure network. In the WLAN100, each of the APs111,113,115,117,121,123, and125manages the station(s)152and/or154associated with itself as one or more entities constituting a BSS. The APs111,113,115,117,121,123, and125are identified by basic service set identifiers (BSSIDs).

The exemplary WLAN100includes a distribution system (DS) that interconnects the plurality of APs111,113,115,117,121,123, and125and provides an extended service set (ESS), although it is not shown inFIG. 1. As a mechanism for one AP to communicate with another AP, such a DS enables an AP to transmit a frame to stations connected to a BSS managed by the AP, deliver a frame to a station that has moved to another BSS, or deliver a frame over an external network such as a wired network. As such, APs and stations included in one ESS may communicate with one another. In other words, a single ESS may be considered as a single logic network segment present in one Internet protocol (IP) subnet. Such an ESS is identified by a service set identifier (SSID). As shown inFIG. 1, the SSID “mobile” is an identifier indicating the WLAN100and is transmitted from the APs111,113,115,117,121,123, and125as information indicating the presence of the WLAN100. According to the IEEE 802.11 standard, an SSID may be signaled using a management frame named a beacon frame or another one named a probe response frame.

Under such a scenario, the stations152and154may roam between the different APs111,113,115,117,121,123, and125having the same SSID. In other words, in the WLAN100(SSID: mobile), the stations152and154may move from one BSS to another BSS through roaming. For example, when the station152connected to the AP113moves and a communication signal from the AP113is attenuated, the station152attempts to connect to another AP (e.g., the AP115) to change its connection point before the connection to the AP113is completely lost. In a preparatory process for such roaming, the station152scans frequency bands (e.g., the 2.4 GHz frequency band and the 5 GHz frequency band) used for wireless connections in the WLAN100to search for an AP that sends a signal at a satisfactory level. The scanning may follow either an active scanning mode or a passive scanning mode. According to the active scanning mode, the stations152and154transmit probe request frames and then wait for probe response frames. According to the passive scanning mode, the stations152and154wait for beacon frames from the APs111,113,115,117,121,123, and125. For example, the station152discovers the AP115from which a beacon frame or a probe response frame is received at a higher strength, selects the AP115as an AP to which a new connection is to be made, and sends a reassociation request frame to the AP115.

It is of primary importance to improve the communication performance of a mobile device in a wireless network (e.g., WLAN) for providing a service to the mobile device. Particularly, for an application such as voice over IP (VoIP) or video conference that actually requires real-time delivery of voice/image traffic, it is necessary to maintain such a traffic flow in a stable manner. In addition, it is preferable to prevent degradation of the communication performance caused by radio interference in some frequency band for use in wireless connections in the wireless network.

SUMMARY

According to an exemplary embodiment, there is provided a communication method implemented in a mobile device, the communication method including: limiting a frequency band on which the mobile device performs a scanning operation to a first frequency band used for a wireless connection of the mobile device; determining whether it is necessary to scan a second frequency band during a subsequent scanning operation of the mobile device; and in response to determining that it is necessary to scan the second frequency band, allowing the subsequent scanning operation to be performed on a plurality of frequency bands including the first and second frequency bands.

The communication method may further include limiting a frequency band on which another subsequent scanning operation of the mobile device is performed to a frequency band which is used for a wireless connection of the mobile device after the subsequent scanning operation is performed on the plurality of frequency bands.

The determining of whether it is necessary to scan the second frequency band may be based on whether a signal indicating a loss of the wireless connection of the mobile device using the first frequency band is received.

The determining of whether it is necessary to scan the second frequency band may be based on a quality of a link for the wireless connection of the mobile device using the first frequency band.

The communication method may further include measuring the quality of the link using a parameter including a received signal strength indication (RSSI).

The communication method may further include acquiring information indicating one or more wireless devices, and the determining of whether it is necessary to scan the second frequency band may be based on whether a first wireless device connected with the mobile device using the first frequency band is included in the one or more wireless devices.

The one or more wireless devices may provide wireless connections using the first frequency band, and the one or more wireless devices may be located in a boundary region between a first region in which the first frequency band is used for a wireless connection of the mobile device and a second region in which the second frequency band is used for a wireless connection of the mobile device.

The determining of whether it is necessary to scan the second frequency band may be based on a quality of a link for the wireless connection of the mobile device using the first frequency band.

The communication method may further include measuring the quality of the link using a parameter including an RSSI.

The information may be acquired from a server communicatively connected with the first wireless device.

The plurality of frequency bands may include a 2.4 GHz frequency band and a 5 GHz frequency band.

The communication method may further include: monitoring a state of data communication across the wireless connection of the mobile device; and in accordance with the monitored state, selecting one of a plurality of schemes for determining whether it is necessary to scan the second frequency band.

When the monitored state is an inactive state, the selected scheme may include determining, based on whether a signal indicating a loss of the wireless connection of the mobile device is received, whether it is necessary to scan the second frequency band.

When the monitored state is an active state, the selected scheme may include determining, based on a quality of a link for the wireless connection of the mobile device using the first frequency band, whether it is necessary to scan the second frequency band.

The communication method may further include acquiring information indicating one or more mobile devices, and when the monitored state is an active state, the selected scheme may include determining, based on whether a first wireless device connected with the mobile device using the first frequency band is included in the one or more mobile devices, whether it is necessary to scan the second frequency band.

The selected scheme may further include determining, based on a quality of a link for the wireless connection of the mobile device using the first frequency band, whether it is necessary to scan the second frequency band.

According to another exemplary embodiment, there is provided a computer-readable storage medium having computer executable instructions stored thereon which implement the above-described communication method.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, detailed embodiments of the present disclosure will be described with reference to drawings. However, the embodiments are merely examples and are not to be construed as limiting the present disclosure.

Various details already understood by those familiar with this field will be omitted to avoid obscuring the gist of the present disclosure. Terminology described below is defined considering functions in the present disclosure and may vary according to a user's or operator's intention or usual practice. Thus, the meanings of the terminology should be interpreted based on the overall context of the present specification.

The spirit of the present disclosure is determined by the claims, and the following exemplary embodiments are provided only to efficiently describe the spirit of the present disclosure to those familiar with this field.

FIG. 2schematically shows an exemplary configuration of a WLAN.

A WLAN200is different from the WLAN100ofFIG. 1in that APs141,143, and145in an area230are configured to provide wireless connections using a 5 GHz frequency band. The WLAN200is configured in this manner to prevent the communication performance of the station154from being degraded by radio interference from medical/electronic devices, Bluetooth devices, APs of an external WLAN, and the like, which communicate in the 2.4 GHz frequency band through which, in the WLAN100, the APs121,123, and125would provide wireless connections.

Oftentimes, when stations152and154continues to scan both of the 2.4 GHz and the 5 GHz frequency bands to discover a nearby AP111,113,115,117,141,143, or145, an excessive number of such scanning operations may result in an undesirably long time delay. In particular, when an application susceptible to transmission delay, for example, a VoIP or video conference application, is executed in the stations152and154, scanning all frequency bands that are used in the WLAN200may destabilize traffic flows from and/or to the stations152and154. In order to prevent such resultant transmission delay and ensure a quality of service (QoS) of the application at a desired level, it may be preferable for the stations152and154to perform AP discovery only on a particular frequency band, in certain situations. For example, when the station152initially scans both of the 2.4 GHz and the 5 GHz frequency bands in an area210and then connects to the AP113that provides a wireless connection over the 2.4 GHz frequency band, the station152may fix the frequency band to be subsequently scanned to the 2.4 GHz frequency band. In the area210where the station152is located, such an AP discovery scheme is more efficient than a scheme of consistently scanning both the 2.4 GHz and 5 GHz frequency bands for use in the WLAN200.

When the stations152and154, set to scan a particular frequency band as mentioned above, move to an area in which wireless connections are provided in another frequency band, the stations152and154could fail to find any APs that use the particular frequency band and, therefore, might be disconnected from the WLAN200. For example, when the station152set to scan only the 2.4 GHz frequency band in the area210moves to an area230for the 5 GHz frequency band, the station152discovers none of the APs141,143, and145that transmit information indicating the presence of the WLAN200, for example, indicated as “SSID: mobile,” using channels in the 5 GHz frequency band. Accordingly, the station152would lose a connection for providing a service (e.g., VoIP or video conference service) to the station152.

Exemplary embodiments of the present disclosure provide techniques for limiting the frequency band to be scanned by a mobile device (for example, a station) in a wireless network (for example, a WLAN) to a frequency band, and then, if it is necessary to scan a different frequency band, setting the frequency to be scanned as the different frequency band, thereby ensuring service continuity at a sufficient level in a wireless network environment in which multiple frequency bands are used.

FIG. 3shows a wireless local area network (WLAN) environment according to an exemplary embodiment of the present disclosure.

As shown inFIG. 3, an exemplary WLAN300includes access points (APs)131,133,135,137,161,163, and165and a station350. The APs131,133,135,137in an area310deliver information indicating the presence of the WLAN300, for example, a service set identifier indicated as “SSID: mobile,” using a 2.4 GHz frequency band. The APs161,163, and165in an area330deliver information indicating the presence of the WLAN300, for example, indicated as “SSID: mobile,” using a 5 GHz frequency band. In the WLAN300, the APs131,133,135, and137in the area310provide connections through the 2.4 GHz frequency band, and the APs161,163, and165in the area330provide connections through the 5 GHz frequency band. In other words, the 2.4 GHz frequency band is used for a wireless connection over the area310, and the 5 GHz frequency band is used for a wireless connection over the area330.

It is now assumed that in the WLAN300, the station350moves along the arrows shown inFIG. 3. The station350may be initialized in the area310to scan a plurality of frequency bands including the 2.4 GHz and 5 GHz frequency bands. According to a result of the scanning, the station350may connect to the AP131, which provides a wireless connection using the 2.4 GHz frequency band, and limit a frequency band which is to be subsequently scanned by the station350to the 2.4 GHz frequency band. The station350may then be newly connected to the AP135and, in that case, may still remain in an AP discovery mode for scanning the limited frequency band.

On the other hand, as the station350moves further along the arrows, a need may arise for the station350to scan the 5 GHz frequency band. For example, when the station350moves out of the area310or is located in a boundary region between the area310and the area330, the station350may need to scan the 5 GHz frequency band during its subsequent scanning operation. For the sake of illustration, it is assumed that while the station350moves further along the arrows of theFIG. 3after being connected to the AP135, the station350performs a scanning operation on the 2.4 GHz frequency band, discovers the AP137, and connects to the AP137. According toFIG. 3, the AP137provides a wireless connection using the 2.4 GHz frequency band in the area310and, notably, is located in a boundary region between the area310and the area330. It can be said that since the station350is located in the boundary region between the area310and the area330, the station350would possibly soon enter the area330. Moreover, if the station350travels further along the right-hand arrow shown inFIG. 3, the station350may actually move out of the area310and enter the area330. Therefore, there is a need that the station350detects that the station350moves out of the area310or enters the area330, or that the station350would likely soon move out of the area310or enter the area330, and in order to discover the AP161,163or165, which uses the 5 GHz frequency band, changes its AP discovery mode.

Accordingly, while performing a scanning operation only on the 2.4 GHz frequency band, the station350may determine whether it is necessary to scan the 5 GHz frequency band during a subsequent scanning operation. In response to the determination that it is necessary to scan the 5 GHz frequency band, the station350may perform the subsequent scanning operation on a plurality of frequency bands including the 2.4 GHz and 5 GHz frequency bands. In this example, there may be various ways to determine whether it is necessary to scan the 5 GHz frequency band. Several approaches may be utilized to compare a position of the station350with the range of the area310and that of the area330. For example, determining whether it is necessary to scan the 5 GHz frequency band may involve checking, based on information indicating the position of the station350, whether the station350has left the area310or whether the station350is located in the boundary region between the area310and the area330. Some other approaches will be described below.

Afterwards, the station350may connect to the AP discovered in the subsequent scanning operation and limit the frequency band on which another subsequent scanning operation is to be performed. For example, when the station350scans both of the 2.4 GHz and 5 GHz frequency bands and detects the highest RSSI (Received Signal Strength Indication) from the AP161in the area330, the station350may connect to the AP161and then limit, to the 5 GHz frequency band, the frequency band which is to be scanned after the connection is established.

When the station350moves from the area330to the area310along the backward directions of the arrows shown inFIG. 3, the station350may similarly operate as described above.

FIG. 4shows an exemplary configuration of a WLAN environment according to an exemplary embodiment of the present disclosure.

FIG. 4illustrates that in a WLAN400, a station450may connect to APs410-1to410-n. The APs410-1to410-nmay include all or some of the APs131,133,135,137,161,163, and165shown inFIG. 3. At the back-end of the APs410-1to410-n, a controller420may be communicatively connected to the APs410-1to410-nand control communications through a network430such as the Internet or an intranet. In addition, a access control server440may control a connection of the station450and provide, through the network430to the station450, information related with a connection to the WLAN400. For example, the access control server440may maintain a list of APs located in a boundary region between the area310and the area330, and transmit the list to the station450.

By way of example, the station450may include hardware452, an operating system454, and software modules456-1to456-m. The station350shown inFIG. 3may be configured in the same manner as the station450.

The hardware452may include a processor, a memory, and a transceiver. The operating system454may be a module for acting as an intermediary between the hardware452and the software modules456-1to456-mand provide an environment in which a user of the station450executes the software modules456-1to456-min a convenient manner. For example, the operating system454may be iOS of Apple Inc. or Android of Google Inc.

The software modules456-1to456-mmay include a software module for managing/controlling a connection of the station450to the WLAN400. For example, the software module456-1may have a function of connecting the station only with a predetermined SSID, a function of limiting the frequency band which is to be scanned for AP discovery, a function of changing the AP discovery mode, for example, to allow the scanning of all frequency bands, instead of the limited frequency band, a function of receiving, from the operating system454, a signal indicating a state of a connection of the station450(for example, whether the connection is lost), and/or a function of receiving, from the access control server440, information or a policy related with the connection.

Changing of an AP Discovery Mode

FIG. 5is a flowchart of an exemplary process in which a station sets a frequency band to be scanned, discovers an AP, and connects to the AP in a WLAN according to an embodiment of the present disclosure.

For example, a process500illustrated inFIG. 5may be performed by the station350. In the process500, the station350may adaptively change its AP discovery mode according to a certain condition. First, when operation500is initiated, the station350scans both of the 2.4 GHz and 5 GHz frequency bands for AP discovery as an initial operation (operation502). Such a mode for discovering an AP as mentioned above may be referred to as a full-band scanning mode. When the whole bands for use in the WLAN400are scanned, but the discovery of an AP that uses a particular SSID (e.g., the SSID “mobile”) to announce its own presence fails (operation504), the station350continues to discover an AP in the full-band scanning mode (operation502).

When an AP sending the particular SSID (e.g., the SSID “mobile”) is discovered (operation504), the station350connects to the discovered AP (operation506).

In order that the station350may perform a subsequent scanning operation only on a particular frequency band for available wireless channels, the frequency band to be subsequently scanned by the station350is limited to the frequency band used by the station350to connect to the discovered AP (operation508). Such an AP discovery mode of the station350may be referred to as a limited band scanning mode.

Scanning of the frequency band, which is set as mentioned above, is started (operation510).

When, in the course of the scanning (operation510), it is determined that it is not necessary to scan, during a subsequent scanning operation, a frequency band different from the currently-scanned frequency band (operation512), the process500proceeds to operation510of scanning the currently-set frequency band unless conditions for roaming between APs (for example, the station350has discovered a new AP that represents a greater RSSI than that of the currently-connected AP) are satisfied (operation516). When the roaming conditions are satisfied (for example, when the station350discovers the new AP as described above) (operation516), the station350connects to the new AP (operation518) and then scans the frequency band that has already set and is used for the new connection as well (operation510).

When, in the procedure of the scanning (operation510), it is determined that it is necessary to scan, during a subsequent scanning operation, a frequency band different from the currently-scanned frequency band (operation512), the frequency band to be scanned by the station350is changed to the whole of the frequency bands (operation514). Then, scanning of the whole frequency bands is performed (operation502), and the subsequent operations may be repeatedly in a similar manner.

As a detailed illustration, when the station350moves in the WLAN300along the arrows ofFIG. 3, the process500ofFIG. 5may be performed as follows. The station350that may be present in the WLAN300is initialized and scans both of the 2.4 GHz and 5 GHz frequency bands (operation502). When both of the frequency bands are scanned, but none of the APs131,133,135,137,161,163, and165transmitting the SSID “mobile” are discovered (operation504), the station350continues the AP discovery in the full-band scanning mode (operation506). When the station350is present in the area310of the WLAN300and discovers the AP133transmitting the SSID “mobile” as an AP to which to connect (operation504), the station350connects to the AP133(operation506). As shown inFIG. 3, the AP133provides wireless connections over the 2.4 GHz frequency band. The station350limits the frequency band to be subsequently scanned to the 2.4 GHz frequency band (operation508). Then, the station350scans only the 2.4 GHz frequency band (operation510). When, in the course of the scanning (operation510), it is determined that it is not necessary for the station350to scan the 5 GHz frequency band (operation512), the station350operates as follows. When the 2.4 GHz frequency band is scanned, but the roaming conditions are not satisfied (operation516), a connection between the station350and the AP133is maintained as it is, and the 2.4 GHz frequency band is scanned again (operation510). On the other hand, when the roaming conditions are satisfied (for example, when the new AP135represents a greater RSSI than that of the currently-connected AP133and, therefore, is discovered as an AP to which the station350is to newly connect) (operation516), the station350connects to the AP135and then still scans only the 2.4 GHz frequency band (operation510). Meanwhile, when the station350is set to scan only the 2.4 GHz frequency band but determines that it is necessary to scan the 5 GHz frequency band (operation512), the AP discovery mode of the station350is changed to the full-band scanning mode (operation514). By way of example, it is assumed that the station350determines that the roaming conditions are satisfied through the scanning operation on the 2.4 GHz frequency band (operation516) and connects to the newly discovered AP137(operation518). Then, when the station350receives a signal indicating that the wireless connection between the station350and the AP137is lost (e.g., when the station350has left the region310), the frequency band to be scanned by the station350may be changed from the 2.4 GHz frequency band to the whole frequency bands including the 2.4 GHz and 5 GHz frequency bands (operation514). As another example, when it is recognized that the station350is connected to the AP137(and, therefore, it is highly likely that the station350is located in a boundary region between the area310and the area330since the AP137is located in the boundary region), the AP discovery mode of the station350may be changed into the full-band scanning mode (operation514). The subsequent operations may be the same as those subsequent to operation502for both of the 2.4 GHz and 5 GHz frequency bands.

Exemplary Criterion for Changing AP Discovery Mode

There may be various criteria for changing the AP discovery mode of a station from a limited band scanning mode to a full-band scanning mode. The following examples are illustrative of how to determine whether it is necessary for the station350to scan the 5 GHz frequency band if the AP discovery mode of the station350is set to the mode for scanning only the 2.4 GHz frequency band while the station350moves along the arrows shown inFIG. 3.

As one example, when the station350determines that the station350has passed through a boundary region between the area310and the area330and left the area310, the station350may change its AP discovery mode into the full-band scanning mode. The station350may determine, based on a signal indicating that its wireless connection using the 2.4 GHz frequency band is lost, that the station350has moved out of the area310. The signal indicating such disconnection may be transmitted from the operating system (for example, the operating system454) of the station350to the station350. For instance, if a connection management/control software module such as the software module456-1of the station350receives the signal indicating the disconnection, the AP search mode of the station350may be changed into the full-band scanning mode with support of the software module.

As another example, when the station350determines that the station350is located in a boundary region between the area310and the area330, the station350may change its AP discovery mode into the full-band scanning mode. Unlike the above-mentioned criterion (i.e., whether the station350has actually left the area310), this approach suggests that when the station350is likely to enter the area330soon, the station350performs a scanning operation on the 5 GHz frequency band as well as the 2.4 GHz frequency band. Accordingly, the connection of the station350may be prevented from being lost while the station350is receiving, e.g., a VoIP service. As described below, whether the station350is located in a boundary region between the area310and the area330may be determined based on a quality of a link which it uses for data transmission and/or information indicating one or more wireless devices (for example, APs) located in the boundary region. This is because the quality of the link for use in the data transmission may deteriorate when the station350is located in the boundary region between the area310and the area330, and the station350may be regarded as being located in the boundary region when the station350is connected to an AP located in the boundary region.

First, based on the quality of the link for use in the data transmission, the AP discovery mode may be changed as follows. When the quality of the link has become worse, the station350may determine that it is necessary to scan a frequency band different from the currently-scanned frequency band. For example, the station350may measure the link quality for the wireless connection using the 2.4 GHz frequency band to compare the measured link quality with a certain threshold value, and then determine, based on a result of the comparison, that it is necessary to scan the 5 GHz frequency band.

The link quality may be measured using a parameter including an RSSI. In addition to or instead of the RSSI, the parameter may include a link quality indication (LQI), a frame error rate (FER), a channel rate and/or a noise figure. For example, when the station350is connected to the AP137but an RSSI indicating a level of a signal received from the AP137is equal to or less than a specific level (e.g., RSSI_min), especially when the RSSI is maintained at the specific level (e.g., RSSI_min) or less during more than a specific time (e.g., T_RSSI_max), the station350may determine that the station350is located in the boundary region between the area310and the area330, and change the AP discovery mode into the full-band scanning mode.

Next, based on the information indicating a wireless device (for example, an AP) which is located in a boundary region of the two regions310and330in which the different frequency bands are used for the wireless connection, the AP discovery mode may be changed as follows. For example, the station350may acquire information indicating the AP137which provides a wireless connection using the 2.4 GHz frequency band and is located in the boundary region between the area310and the area330. Based on the acquired information, the station350may check that the currently connected AP for providing a wireless connection over the 2.4 GHz frequency band is located in the boundary region between the area310and the area330. For example, when the station350is connected to the AP137, the station350may check that the AP137is included among the APs indicated by the acquired information, thereby determining that it is necessary to scan the 5 GHz frequency band. In response to such determination, the station350may change its AP discovery mode into the full-band scanning mode.

Moreover, in accordance with certain embodiments, when the station350is connected to the AP137, the station350may check that the AP137to which the station350is connected is included among the APs indicated by the acquired information, and also use the link quality so as to determine that it is necessary to scan the 5 GHz frequency band. For example, in the process600shown inFIG. 6, this approach applies to determining whether it is necessary to scan another frequency band. The other operations of the process600ofFIG. 6may be the same as those of the process500ofFIG. 5. In accordance with these embodiments, it is possible to keep the station350from unnecessarily scanning the whole frequency bands when the station350is located not in the boundary region between the area310and the area330but in a region where the link quality is poor (for example, a shadow region).

With reference toFIG. 6, the following illustration shows where the station350connects to the AP137(operation506) and a subsequent scanning operation is set to be performed on the 2.4 GHz frequency band (operation508). During the subsequent scanning operation on the 2.4 GHz frequency band (operation510), the station350determines whether the AP137connected to the station350is located in a boundary region between the area310and the area330(operation612). When it is determined that the AP137is located in the boundary region, the station350determines whether a quality of a link with the AP137has deteriorated (operation613). As described above, determining whether the link quality has deteriorated may involve measuring the link quality and comparing the measured link quality with a certain threshold value and, in the measurement of the link quality, a parameter including an RSSI may be used. When the link quality has deteriorated, the station350changes its AP discovery mode into the full-band scanning mode (operation514). When the AP connected to the station350is not located in the boundary region between the area310and the area330, or when the station350is located in the boundary region but the quality of the link has not deteriorated, the station350continues to perform scanning of the 2.4 GHz frequency band.

Acquiring of Information Indicating an AP Located in a Boundary Region

The station350may acquire information indicating one or more APs (e.g., the AP137) located in a boundary region between the area310and the area330. The acquiring of the information may be performed as follows. However, the following examples are merely illustrative.

The station350may has stored therein (e.g., in a memory of the station350) information regarding which AP(s) is(are) located in the boundary region between the area310and the area330. For example, the station350may maintain the information in such a manner as to store a history that the station350has been connected to the AP137to move from the area310to the area330, and if necessary, may use the information.

The station350may receive, from an AP, information regarding whether the AP is located in a boundary region between the area310and the area330. For example, the station350may receive boundary region AP information included in a beacon frame of the AP137. This information may indicate that the AP137is located in the boundary region between the area310and the area330. By way of another example, the station350may transmit a probe request message to the AP137, and then receive, from the AP137, a probe response message including boundary region AP information.

The station350may acquire, from a certain server (e.g., the access control server440) communicatively connected with all or some of the APs131,133,135,137,161,163, and165, information regarding an AP located in a boundary region between the area310and the area330. The information may be acquired from the above-mentioned server after the station350is connected to the AP131,133,135,137,161,163, or165, or may be acquired when the station350inquires of the server after entering into the area310or330. The server may control the connection of the station350, and have a variety of information for supporting the APs131,133,135,137,161,163, and165at the backend of the APs131,133,135,137,161,163, and165. For instance, the server may have a list of the APs131,133,135,137,161,163, and165located in the boundary region between the area310and the area330.

A proper combination of the aforementioned approaches may be adopted. In conjunction withFIGS. 7 and 8, the following description provides exemplary processes performed by a station for acquiring, from such a access control server, information indicating an AP located in a boundary region. These processes are described below as being performed in the WLAN400environment ofFIG. 4, although such description is merely exemplary. In the following description, it should be appreciated that operations of the station450can be implemented by the software module456-1of the station450.

According to the process700shown inFIG. 7, the station450loads previously-stored information regarding an AP which is located in a boundary region between two areas where different frequency bands are used for wireless connections (and also may hereinafter be referred to as a “boundary region AP”) (operation702). For example, the boundary region AP information may have a structure of a list form. Next, the station450connects to the AP410-1(operation704). If the connected AP410-1is listed in the boundary region AP information, then the station450may roam to another AP (e.g., AP410-n) (operation714). When the connected AP410-1is not listed in the boundary region AP information, the station450sends, to the access control server440, a request for confirmation as to whether the AP410-1is a boundary region AP (operation708). The station450receives, from the access control server440, a result of the confirmation (operation710). While transmitting the confirmation result, the access control server440may also transmit information indicating a boundary region AP among APs located around the AP410-1. The station450updates the boundary region AP list with the confirmation result and the information received from the access control server440(operation712). Then, the station450may roam to another AP (e.g., the AP410-n) (operation714). After the station450is connected to the AP410-nthrough the roaming operation, the station450may perform operations similar to those performed after its connection to the AP410-1. That is, when the connected AP410-nis listed in the boundary region AP information (operation716), the station450may roam to still another AP (not shown). When the connected AP410-1is not listed in the boundary region AP information (operation716), the station450requests the access control server440to confirm whether the AP410-nis a boundary region AP (operation718). The station450receives, from the access control server440, a result of the confirmation (operation720). While transmitting the confirmation result to the station450, the access control server440may also transmit information indicating a boundary region AP among APs located around the AP410-n. The station450updates the boundary region AP list again with the confirmation result and the information received from the access control server440(operation722).

According to operation800shown inFIG. 8, the station450establishes an initial connection with the AP410-1(operation802), and then informs the access control server440of a version of the boundary region AP information stored in the station450(operation804). The access control server440confirms whether the version is the latest one (operation806). When the boundary region AP information of the station450is not the latest version, the access control server440transmits the latest version of the boundary region AP information to the station450(operation808), and the station450updates the boundary region AP information (operation810). When the boundary region AP information of the station450is the latest version, the access control server440transmits a message confirming the latest information (operation812).

Application of a Criterion for Changing an AP Discovery Mode According to a Communication State

The above-mentioned criteria for changing an AP discovery mode may be used selectively or in any proper combination according to a data communication state.

The station350may monitor a state of data communication across a wireless connection of the station350, and adaptively apply a criterion for determining whether it is necessary to change its AP discovery mode according to the monitored data communication state. Such monitoring and application may be implemented by the software module (for example, the software module456-1) of the station350.

For example, it is assumed that the AP discovery mode of the station350is set such that the station350scans the 2.4 GHz frequency band. The station350monitors a data communication state, and according to the monitored state, selects one of a plurality of schemes for determining whether it is necessary to scan the 5 GHz frequency band.

When the monitored state is an inactive state (for example, there is no data communication on the station350), a scheme may be selected for determining, based on whether a signal indicating a loss of the wireless connection of the station350over the 2.4 GHz frequency band is received, whether it is necessary to scan the 5 GHz frequency band.

Meanwhile, when the monitored state is an active state (for example, when VoIP communication continues on the station350), a scheme may be selected for using an RSSI or link quality and/or boundary region AP information. Specifically, a scheme may be selected for determining, based on a link quality for the wireless connection of the station350over the 2.4 GHz frequency band, whether it is necessary to scan the 5 GHz frequency band. On the other hand, a scheme may be selected for determining, based on whether the AP connected to the station350over the 2.4 GHz frequency band (for example, the AP137) is included in the boundary region APs, whether it is necessary to scan the 5 GHz frequency band may be selected. In the latter scheme, whether it is necessary to scan the 5 GHz frequency band may be further based on the link quality for the wireless connection of the station350over the 2.4 GHz frequency band.

Ensuring of Service Continuity for a Terminal that does not Support a Particular Frequency Band

For example, when the station350supports only the 2.4 GHz frequency band in the WLAN300, the station350cannot connect to the APs161,163, and165that support only the connections over the 5 GHz frequency band in the area330, even if the station350enters the area330. Therefore, in order to prevent an interruption to the service provided to the station350, a certain AP that propagates an SSID dedicated to the station350, for example, indicated as “SSID: mobile_2G,” in the 2.4 GHz frequency band may be placed in the area330. When a moderate number of stations that do not support the 5 GHz frequency band but support only the 2.4 GHz frequency band exist in the WLAN300, such an approach may be useful to provide service continuity to the stations while reducing radio interference caused in the area330by the 2.4 GHz frequency band.

FIG. 9shows block diagrams of a wireless device and a mobile device for implementing an exemplary embodiment of the present disclosure.

A mobile device900includes a processor912, a memory914, and a transceiver916. A wireless device920includes a processor922, a memory924, and a transceiver926. The mobile device900may be a station (e.g., the stations350and450) in a WLAN. The wireless device920may be an AP (e.g., the APs131,133,135,161,163,165, and410-1to410-n) in the WLAN.

The transceivers916and926are connected to the processors912and922to exchange radio signals under the control of the processors912and922, respectively. For example, the transceivers916and926may implement the physical layer conforming to the IEEE 802.11 standard. According to the above-described exemplary embodiments of the present disclosure, the processors912and922may operate the devices900and920, respectively. The processors912and922may execute instructions stored in the memories914and924, respectively. When the instructions stored in the memories914and924are executed by the processors912and922, respectively, the devices900and920may be caused to perform operations according to the above-described exemplary embodiments of the present disclosure. The memories914and924may be inside or outside the processors912and922, respectively, and connected to the processors912and922by various well-known means, respectively.

Meanwhile, an exemplary embodiment of the present disclosure can include a computer-readable storage medium including a program for performing the methods described herein on a computer. The computer-readable storage medium may separately include program commands, local data files, local data structures, etc. or include a combination of them. The computer-readable storage medium may be specially designed and configured for the present disclosure, or known and available to those of ordinary skill in the field of computer software. Examples of the computer-readable storage medium include magnetic media, such as a hard disk, a floppy disk, and a magnetic tape, optical recording media, such as a CD-ROM and a DVD, magneto-optical media, such as a floptical disk, and hardware devices, such as a ROM, a RAM, and a flash memory, specially configured to store and execute program commands. Examples of the program commands may include high-level language codes executable by a computer using an interpreter, etc., as well as machine language codes made by compilers.

According to exemplary embodiments of the present disclosure, it is possible to maintain a high quality of service (QoS) and ensure service continuity for a mobile device that is provided with a service through a wireless network in which multiple frequency bands are used.

It will be apparent to those familiar with this field that various modifications can be made to the above-described exemplary embodiments of the present disclosure without departing from the spirit or scope of the present disclosure. Thus, it is intended that the present disclosure covers all such modifications provided they come within the scope of the appended claims and their equivalents.