WO2015188846A1 - Scanning for access points in a wireless local area network - Google Patents

Scanning for access points in a wireless local area network Download PDF

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Publication number
WO2015188846A1
WO2015188846A1 PCT/EP2014/061956 EP2014061956W WO2015188846A1 WO 2015188846 A1 WO2015188846 A1 WO 2015188846A1 EP 2014061956 W EP2014061956 W EP 2014061956W WO 2015188846 A1 WO2015188846 A1 WO 2015188846A1
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WO
WIPO (PCT)
Prior art keywords
ap
sta
validity conditions
time interval
access
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PCT/EP2014/061956
Other languages
French (fr)
Inventor
Leif Wilhelmsson
Filip MESTANOV
Stephen Rayment
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Telefonaktiebolaget L M Ericsson (Publ)
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Application filed by Telefonaktiebolaget L M Ericsson (Publ) filed Critical Telefonaktiebolaget L M Ericsson (Publ)
Priority to PCT/EP2014/061956 priority Critical patent/WO2015188846A1/en
Publication of WO2015188846A1 publication Critical patent/WO2015188846A1/en

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W48/00Access restriction; Network selection; Access point selection
    • H04W48/16Discovering, processing access restriction or access information
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W48/00Access restriction; Network selection; Access point selection
    • H04W48/20Selecting an access point

Abstract

There is provided means for scanning for access points (APs) in a wireless local area network. An access point (AP) broadcasts validity conditions of the AP, the validity conditions indicating at least one time interval when the AP is operating. A station (STA) acquires such validity conditions for an AP. The STA sends a request for access to the AP only during the at least one time interval.

Description

SCANNING FOR ACCESS POINTS

IN A WIRELESS LOCAL AREA NETWORK

TECHNICAL FIELD

Embodiments presented herein relate to wireless local area network, and particularly to methods, an access point, a station, computer programs, and a computer program product for scanning for access points in a wireless local area network.

BACKGROUND

In communication networks, there may be a challenge to obtain good performance and capacity for a given communication protocol, its parameters and the physical environment in which the communication network is deployed.

For example, keeping an updated list of what network nodes (e.g., a radio base station or an access point (AP) in a cell site) are available is common in a wireless device (e.g. a station (STA) or a user equipment (UE)). Such a list may be kept in order to support a handover, or it could simply be so that even if the wireless device is connected to one network node in one basic service set (BSS) there is a preference in being connected to another network node in another BSS. In the various versions of Wi-Fi currently employed, e.g. standards according to IEEE 802.11b, g, a, n, or ac, there are two ways for a STA to find out if there is a suitable AP available which the STA may try to associate with. One way is to use passive scanning, where the STA is listening for the beacons sent out by the AP. The other way is to use active scanning where the STA sends a Probe Request to the AP and the AP, if it hears the Probe Request, typically replies with a Probe Response.

Because there are many channels and the beacons are only transmitted every 100ms, active scanning is often used in order to reduce the time it takes for a STA to find and associate with an AP. However, very often the Probe Request is not heard by the AP because the STA is not within the coverage area. This means that the transmitted Probe Request consumed valuable time and resources and may also cause interference to other STAs and APs that are in the vicinity. This means that a significant part of the traffic is useless. Because the access attempts, such as Probe Requests, typically are transmitted using a very robust modulation and coding scheme (MCS), it means that the time needed for these access attempts is relatively long, so that even if the amount of data in an access attempt is not that large, the duration of the packet or packets needed for the access attempt may still be significant.

There have been some proposals that aim at addressing issues relating thereto.

"Location-Aided Probing in Wi-Fi Networks" by Y.S. Kim et. al. makes use of the current location of the STA and takes an intelligent decision whether or not to send probe requests only if there is a high probability that the AP will be in the STA's vicinity.

US2013130680 specifies a method in a mobile device to determine network profiles that could be in the vicinity. How the device actually obtains the location of the network nodes is not discussed. US2012307645 relates to a mobile device determining the location of an AP and its own location and then deciding whether or not to connect to the AP.

There is still a need for an improved scanning for access points in a wireless local area network.

SUMMARY

An object of embodiments herein is to provide efficient scanning for access points in a wireless local area network

One issue with the above referred disclosures is that the Probe Request sent are wasting a lot of time that otherwise could have been used to send user data. This issue gets even more pronounced in case of dense deployments when STAs connected to different APs may hear the Probe Request and as a result thereof defer from transmission.

A particular object is therefore to provide efficient scanning for access points in a wireless local area network without wasting unnecessary network resources.

According to a first aspect there is presented a method for scanning for access points (APs) in a wireless local area network. The method is performed by a station (STA). The method comprises acquiring validity conditions for an AP. The validity conditions indicate at least one time interval when the AP is operating. The method comprises sending a request for access to the AP only during the at least one time interval.

Advantageously this provides efficient scanning for access points in a wireless local area network. Advantageously this provides efficient scanning for access points in a wireless local area network and does not waste unnecessary network resources.

Advantageously this enables the number of useless Probe Requests that are sent from a STA to be reduced and does in this way save power in the STAs as well as reduce the amount of caused interference e.g. to other STAs in the wireless local area network.

According to a second aspect there is presented a STA for scanning for access points in a wireless local area network. The STA comprises a processing unit. The processing unit is configured to cause the STA to acquire validity conditions for an AP. The validity conditions indicate at least one time interval when the AP is operating. The processing unit is configured to cause the STA to send a request for access to the AP only during the at least one time interval.

According to a third aspect there is presented a computer program for scanning for APs in a wireless local area network, the computer program comprising computer program code which, when run on a processing unit of the STA, causes the STA to perform a method according to the first aspect.

According to a fourth aspect there is presented a method for enabling a STA to scan for APs in a wireless local area network. The method is performed by an AP. The method comprises broadcasting validity conditions of the AP. The validity conditions indicate at least one time interval when the AP is operating.

According to a fifth aspect there is presented an AP for enabling a STA to scan for APs in a wireless local area network. The AP comprises a processing unit. The processing unit is configured to cause the AP to broadcast validity conditions of the AP. The validity conditions indicate at least one time interval when the AP is operating.

According to a sixth aspect there is presented a computer program for enabling a STA to scan for APs in a wireless local area network, the computer program comprising computer program code which, when run on a processing unit of the AP, causes the AP to perform a method according to the fourth aspect.

According to a seventh aspect there is presented a computer program product comprising a computer program according to at least one of the third aspect and the sixth aspect, and a computer readable means on which the at least one computer program is stored. The computer readable means may be non- transitory computer readable means.

It is to be noted that any feature of the first, second, third, fourth, fifth, sixth and seventh aspects may be applied to any other aspect, wherever

appropriate. Likewise, any advantage of the first aspect may equally apply to the second, third, fourth, fifth, sixth, and/or seventh aspect, respectively, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings. Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

Figs la and lb are schematic diagrams illustrating a communication network according to embodiments;

Fig 2a is a schematic diagram showing functional units of an access point according to an embodiment; Fig 2b is a schematic diagram showing functional modules of an access point according to an embodiment;

Fig 3a is a schematic diagram showing functional units of a station according to an embodiment;

Fig 3b is a schematic diagram showing functional modules of a station according to an embodiment;

Fig 4 shows one example of a computer program product comprising computer readable means according to an embodiment; and

Figs 5, 6, 7, and 8 are flowcharts of methods according to embodiments.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description. Any step or feature illustrated by dashed lines in the drawings should be regarded as optional.

Fig la is a schematic diagram illustrating a communication network 10a where embodiments presented herein can be applied. The communication network 10a comprises network nodes in the form of access points (APs) na, lib. The APs na-b are configured to provide network coverage to wireless devices or stations (STAs) 12a, 12b within a network coverage as

schematically illustrated at reference numerals 16a, 16b. The APs na-b thus define a wireless local area network. The STAs I2a-b may be any combination of hand-held wireless transceiver devices, such as mobile phones,

smartphones, tablet computers, or laptop computers or the like, or other types of user equipment (UE). The APs na-b thus act as radio base stations for the STAs i2a-b. Each STA i2a-b is configured to be operatively connected to at least one AP na-b via a wireless link 15a, 15b. The communication network 10a further comprises a core network 13. The APs na-b are operatively connected to the core network 13. The core network 13 is in turn operatively connected to an Internet Protocol (IP) based service network 14. The STAs i2a-b are thereby enabled to access content and services as provided by the IP based service network 14. The communication network 10a may be a wireless local area network

(WLAN). In WLANs basic access to the communication channel is based on carrier sense multiple access with collision avoidance (CSMA/CA). When the access to the communication channel is handled in a completely distributed fashion, this is referred to as a distributed coordination function (DCF). This means that all STAs, as well as the AP, contend for the communication channel. There are also possibilities for a more centralized channel access scheme where the AP polls the different STAs, and in addition it is possible to combine the DCF with more centralized scheme in a hybrid manner, referred to as hybrid coordination function, HCF.

In WLAN, such as Wi-Fi, significant interference may be caused by that STAs sends Probe Requests to determine whether a certain AP is available, rather than performing passive scanning and just listen for the beacons that are transmitted by APs. As a STA typically have been connected to a large number of APs, a significant number of Probe Requests may be sent by each STA. As an illustrative, non-limiting, example, consider STA 12b in Fig la. The STA 12b is outside network coverage 16a, 16b of both AP 11a and AP lib but still transmits Probe Requests, as schematically illustrated by the wireless links 15b. These transmissions of Probe Requests consume power of the STA 12b and may in addition cause interference at the STA 12a.

The location of a STA 12a, 12b may be available. This may for instance be the case when the STA 12a, 12b is integrated in a mobile phone, as then the location information can be obtained from the cellular network, by the global positioning system (GPS), or even from the WLAN or Wi-Fi network. For other devices, there is a trend that Wi-Fi is integrated together with

Bluetooth and Bluetooth Low Energy (BLE). As one use case for BLE is indoor positioning, location information may be available also in other equipment.

It is also noted that many of the APs 11a, lib that a STA 12a, 12b connects to are of a temporary character, i.e., the STA 12a, 12b may connect to this AP 11a, 11b only once, or may connect to it occasionally only during a very limited time. An example of this is when a user carrying a STA 12a, 12b is travelling and uses Wi-Fi to connect to an AP 11a, lib at an airport or a hotel. Fig lb is a schematic diagram illustrating a communication network 10b where embodiments presented herein can be applied. The communication network 10b is similar to the communication network 10a except that in the communication network 10b the AP lib is not operating or active (as schematically illustrated by the absence of a network coverage 16b for AP 11b; see Fig la). By active is meant that an AP lib is in operation. Hence according to the illustrative example of Fig lb the AP lib is not operative to provide network access to any of the STAs I2a-b. As an illustrative, non-limiting, example, consider STA 12b in Fig lb. The STA 12b is what would have been inside network coverage of AP lib if AP lib would have been operating. But although AP lib is not operating, STA 12b still transmits Probe Requests, as schematically illustrated by the wireless links 15b. These transmissions of Probe Requests consume power of the STA 12b and may in addition cause interference at the STA 12a.

The herein disclosed embodiments are based on the STA 12a, 12b before sending a Probe Request to an AP 11a, 11b first determines that there is a reasonable likelihood that the AP 11a, lib is within range and whether the AP 11a, 11b is operating (active) at the time. The means to determine this may be based on having certain location information or other relevant information associated with the AP 11a, lib and using this information together with some information about where the STA 12a, 12b currently is located. Only if it is determined that the STA 12a, 12b is reasonable close to an operating AP 11a, 11b a Probe Request is transmitted from the STA 12a, 12b. As most of the APs 11a, 11b that a STA 12a, 12b has been connected to are not within range, the number of transmitted Probe Requests is thereby largely reduced, without reducing the likelihood of finding a suitable AP 11a, 11b.

Hence, by accessing location information of the STA 12b and its relative position to the APs 11a, lib, the STA 12b may in the scenario of Fig la determine that it is out of coverage of both AP 11a and AP 11b and therefore refrain from sending Probe requests. Further, by accessing information that the AP 11b, is not operating the STA 12b may in the scenario of Fig lb determine that it is out of coverage of AP 11a and that AP lib is not operating and therefore refrain from sending Probe requests.

The embodiments disclosed herein particularly relate to scanning for APs 11a, 11b in a wireless local area network 10a, 10b, and to enabling a STA 12a, 12b to scan for an AP 11a, 11b. In order to obtain this there is provided an access point 11a, 11b, a method performed by the access point 11a, 11b, a station 12a, 12b, a method performed by the station 12a, 12b, at least one computer program comprising code, for example in the form of a computer program product, that when run on a processing unit, causes the processing unit to perform at least one of the method of the access point 11a, 11b and the station 12a, 12b.

Fig 2a schematically illustrates, in terms of a number of functional units, the components of an access point (AP) 11a, lib according to an embodiment. A processing unit 21 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate arrays (FPGA) etc., capable of executing software instructions stored in a computer program product 41a (as in Fig 4), e.g. in the form of a storage medium 23. Thus the processing unit 21 is thereby configured to execute methods as disclosed herein. The storage medium 23 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The AP 11a, lib may further comprise a communication interface 22 for communication with another AP 11a, 11b, the core network 13, and at least one station 12a, 12b. As such the communication interface 22 may comprise one or more transmitters and receivers, comprising analogue and digital components such as a digital-to- analogue converter and an analogue-to-digital converter, a suitable number of antennas for radio communication, and a suitable number of ports for wired communication. The processing unit 21 controls the general operation of the AP 11a, 11b e.g. by sending data and control signals to the

communication interface 22 and the storage medium 23, by receiving data and reports from the communication interface 22, and by retrieving data and instructions from the storage medium 23. Other components, as well as the related functionality, of the AP 11a, 11b are omitted in order not to obscure the concepts presented herein.

Fig 2b schematically illustrates, in terms of a number of functional modules, the components of an AP 11a, lib according to an embodiment. The AP 11a, lib of Fig 2b comprises a send and/or receive module 21a. The AP na, lib of Fig 2b may further comprise a number of optional functional modules, such as a generate module 21b. The functionality of each functional module 2ia-b will be further disclosed below in the context of which the functional modules 2ia-b may be used. In general terms, each functional module 2ia-b may be implemented in hardware and/or in software. The processing unit 21 may thus be configured to fetch instructions from the storage medium 23 as provided by a functional module 2ia-b and to execute these instructions, thereby performing any steps as will be disclosed hereinafter. Fig 3a schematically illustrates, in terms of a number of functional units, the components of a station (STA) 12a, 12b according to an embodiment. A processing unit 31 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), application specific integrated circuit (ASIC), field programmable gate arrays (FPGA) etc., capable of executing software instructions stored in a computer program product 41b (as in Fig 4), e.g. in the form of a storage medium 33. Thus the processing unit 31 is thereby configured to execute methods as herein disclosed. The storage medium 33 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The STA I2a-b may further comprise a communication interface 32 for communication with an AP 11a, 11b or another STA I2a-b. As such the communication interface 32 may comprise one or more transmitters and receivers, comprising analogue and digital components, such as a digital-to-analogue converter and an analogue- to-digital converter, and a suitable number of antennas for radio

communication, components for infrared communication, etc. The processing unit 31 controls the general operation of the STA I2a-b e.g. by sending data and control signals to the communication interface 32 and the storage medium 33, by receiving data and reports from the communication interface 32, and by retrieving data and instructions from the storage medium 33. Other components, as well as the related functionality, of the STA i2a-b are omitted in order not to obscure the concepts presented herein.

Fig 3b schematically illustrates, in terms of a number of functional modules, the components of a STA I2a-b according to an embodiment. The STA I2a-b of Fig 3b comprises a number of functional modules; an acquire module 31a, and a send and/or receive module 31b. The STA I2a-b of Fig 3b may further comprises a number of optional functional modules, such as any of a discard module 31c, a store module 3 id, a delete module 3ie, and a sense module 3 if. The functionality of each functional module 3ia-f will be further disclosed below in the context of which the functional modules 3ia-d may be used. In general terms, each functional module 3ia-f may be implemented in hardware and/or in software. The processing unit 31 may thus be configured to from the storage medium 33 fetch instructions as provided by a functional module 3ia-f and to execute these instructions, thereby performing any steps as will be disclosed hereinafter.

Figs 5 and 6 are flow charts illustrating embodiments of methods for scanning for APs 11a, 11b in a wireless local area network 10a, 10b as performed by a STA I2a-b. Figs 7 and 8 are flow charts illustrating

embodiments of methods for enabling a STA 12a, 12b to scan for APs 11a, lib in a wireless local area network 10a, 10b as performed by an AP 11a, lib. The methods are advantageously provided as computer programs 42a, 42b. Fig 4 shows one example of a computer program product 41a, 41b comprising computer readable means 43. On this computer readable means 43, at least one computer program 42a, 42b can be stored, which computer program 42a can cause the processing unit 21 and thereto operatively coupled entities and devices, such as the communication interface 22 and the storage medium 23, to execute methods according to embodiments described herein, and which computer program 42b can cause the processing unit 31 and thereto operatively coupled entities and devices, such as the communication interface 32 and the storage medium 33, to execute methods according to

embodiments described herein. The at least one computer program 42a, 42b and/or computer program product 41a, 41b may thus provide means for performing any steps as herein disclosed.

In the example of Fig 4, the computer program product 41a, 41b is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 41a, 41b could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory. Thus, while each computer program 42a, 42b is here schematically shown as a track on the depicted optical disk, each computer program 42a, 42b can be stored in any way which is suitable for the computer program product 41a, 41b.

Reference is now made to Fig 5 illustrating a method for accessing APs 11a, 11b in a wireless local area network 10a, 10b according to an embodiment. The method is performed by a STA 12a, 12b.

Before sending any requests for access, the STA 12a, 12b acquires validity conditions for at least one AP 11a, lib. The method thus comprises acquiring, in a step S104, validity conditions for an AP 11a, lib. The validity conditions indicate at least one time interval when the AP 11a, lib is operating. The processing unit 31 is configured to perform step S104, for example by executing functionality of the acquire module 31a.

Once the validity conditions have been acquired, the validity conditions may be used by the STA 12a, 12b to determine when requests for access should be sent. The method therefore comprises sending, in a step S108, a request for access to the AP 11a, lib only during the at least one time interval (i.e., when the validity conditions are met). The processing unit 31 is configured to perform step S108, for example by executing functionality of the send and/or receive module 31b. This may reduce the number of unnecessary access requests that are sent by the STA 12a, 12b, thus reducing power consumption at the STA 12a, 12b and possibly also reducing any interference that the STA 12a, 12b may cause by sending unnecessary access requests.

Reference is now made to Fig 7 illustrating a method for enabling a STA 12a, 12b to scan for APs 11a, 11b in a wireless local area network 10a, 10b according to an embodiment. The method is performed by an AP 11a, lib.

The AP 11a, 11b is configured to report when it is available to be accessed by a STA 12a, 12b. This is accomplished by the AP 11a, lib broadcasting validity conditions which then may be acquired by the STA 12a, 12b (as in step S104, see above). The method comprises broadcasting, in a step S204, validity conditions of the AP 11a, 11b. The validity conditions indicates at least one time interval when the AP 11a, 11b is operating. The processing unit 21 is configured to perform step S204, for example by executing functionality of the send and/or receive module 21a. The AP 11a, 11b may thus provide information about the validity conditions of the wireless local area network 10a, 10b to the STA 12a, 12b. The validity conditions may include, but not be limited to, indication of a certain day, time of the day, etc., during which the (APs 11a, 11b of the) wireless local area network 10a, 10b will be active. The validity conditions may thus indicate when the AP 11a, lib allows transmission to, and reception from, the STA 12a, 12b. The validity conditions may comprise a service set identifier (SSID) of the AP 11a, 11b. The validity conditions may comprise a time stamp. The time stamp may define at least one of a start point and an end point of the at least one time interval. The validity conditions may be transmitted in the beacon, in a control message, or the validity conditions may be requested by the STA 12a, 12b. For example, the validity conditions may by the STA 12a, 12b be received directly from the AP 11a, lib. The request for access may be sent as a broadcast transmission. The request for access may be an IEEE 802.11 probe request.

Reference is now made to Fig 6 illustrating a method for accessing APs 11a, 11b in a wireless local area network 10a, 10b according to further

embodiments. The methods are performed by the STA 12a, 12b.

The method may comprise an optional step S106 of acquiring location information indicating that the STA 12a, 12b is within network coverage 16a, 16b of the AP 11a, 11b; and an optional step Sio8a of sending the request for access only when the STA 12a, 12b is within the network coverage. The method may comprise an optional step S112 of storing a list of SSIDs, each SSID of which is associated with at least one AP 11a, 11b; and an optional step S114 of deleting an SSID from the list once said validity conditions of its associated at least one AP 11a, 11b are no longer satisfied. The processing unit 31 may be configured to perform step S112, for example by executing functionality of the store module 3id and to perform step S114, for example by executing functionality of the delete module 3ie. Thus, in a first

embodiment, the validity conditions can then be used to remove SSID from a list of saved SSID when the time indicated by the time stamp has passed. Alternatively, the SSID may not be removed, but the current time may be compared with the validity conditions associated with the SSID and only if the SSID is determined to be active, a request for access, such as a Probe Request, is sent.

In this embodiment several options exist for implementing the functionality to determine whether a SSID is active or not, but exactly how this is achieved is out of the scope of the present disclosure; rather, this embodiment is applicable regardless which option is used. As examples for options to accomplish the validity conditions functionality one may associate a last day for when the SSID is valid, or one may associate a duration time, such that the SSID is only valid for, say, three days and then the SSID is expired.

Particularly, the method may comprise an optional step S110 of discarding the SSID once the time stamp has expired. The processing unit 31 may be configured to perform step S110, for example by executing functionality of the discard module 31c. One exemplary scenario of this time limited SSID could be a three day event which takes place at a certain location. A wireless local area network (WLAN) service may be provided and a group of users of the STA 12a, 12b may be provided with the SSID of the WLAN and thus be able to access the wireless local area service. However, once the event is over, the WLAN may be taken down as there is no longer a need for a WLAN being able to support the group of users. With the use of a time stamp, the SSID used during the event will simply be removed from the list of SSIDs in the STA 12a, 12b used to find an AP 11a, lib to connect to.

The validity conditions may comprise information indicating a collection of SSIDs. The information may further indicate locations of APs 11a, lib associated with the collection of SSIDs and time intervals for when the APs 11a, 11b are operating. The APs 11a, 11b may be associated with at least two locations. Each location may have its own time interval for when the AP or APs 11a, 11b in that location is operating. Thus, in a second embodiment, the AP 11a, 11b communicates to the STA 12a, 12b the validity conditions in terms of policy (i.e., which SSIDs are valid in which location, during which time periods).

The validity conditions may comprise an SSID, for example of the AP from which the validity conditions were acquired in a step S104. The validity conditions may additionally or alternatively comprise an SSID of a further AP. Further, the at least one time interval may comprise a first time interval and at least one second time interval. The method may comprise an optional step S116 of storing the SSID after expiry of the first time interval and until expiry of a last of the at least one second time interval. The processing unit 31 may be configured to perform step S116, for example by executing

functionality of store module 3id. The method may comprise an optional step Sio8b of sending the request for access to the AP 11a, lib only during the first time interval or during the at least one second time interval. The processing unit 31 may be configured to perform step Sio8b, for example by executing functionality of the send and/or receive module 31b. Thus, in a third embodiment, the SSID has not expired, but rather specific times when the SSID is valid are associated with the SSID. This embodiment may reflect a scenario where an AP 11a, lib is operating at regular occurrences, for example corresponding to a meeting which takes place, say, every two months and where the time for the meeting is known in advance. In this case, the SSID is thus not deleted from the list, but rather the time for the next meeting is associated with the SSID. Thus, when one meeting has ended, no requests for access, such as Probe Requests, will be sent to the AP associated with this SSID until the following meeting starts, and then again the STA 12a, 12b may start to send requests for access, such as Probe Requests, to the corresponding AP.

The method may comprise an optional step acquiring (S118) a list of frequencies associated at least with said AP; and an optional step S120 of sending the request for access on at least one of the acquired frequencies. The processing unit 31 may be configured to perform step S118, for example by executing functionality of the acquire module 31a and to perform step S120, for example by executing functionality of the send and/or receive module 31b. The method may comprise an optional step S122 of sensing APs 11a, lib on at least one of the acquired frequencies. The processing unit 31 may be configured to perform step S122, for example by executing functionality of the send and/or receive module 31b. Thus, in a fourth embodiment, a list of SSIDs, APs 11a, 11b, and corresponding frequencies are provided, and active scanning as performed by the STA 12a, 12b, for example using Probe

Requests, uses this information to determine what frequency or channel to use for searching for the SSID and what SSID to search for. As an example, this embodiment may reflect a scenario where a few different SSIDs are used, and a few hundreds of APs are deployed using, say, about 10 different frequencies or channels. A provided list and/or map over the APs 11a, lib and the used frequencies or channels can be used when determining what frequency and what SSID should be used for the requests for access, such as Probe Requests, in order to avoid scanning for SSIDs which are not active in the area or avoid scanning on channels that do not have any active APs.

The method may comprise an optional step S102 of acquiring auxiliary information. The method may comprise an optional step Si04a of acquiring the validity conditions based on the auxiliary information. The processing unit 31 may be configured to perform step S102, for example by executing functionality of the acquire module 31a. Thus, in a fifth embodiment, no information from the network is used but the decision is made autonomously in the STA based on auxiliary information, such as local information of the STA 12a, 12b and/or the user of the STA 12a, 12b. The STA 12a, 12b does in this embodiment associate a certain time with the SSID and only if the present time matches the time associated with the SSID the STA 12a, 12b may send the request for access (e.g., by performing a Probe Request procedure). As an example of this embodiment, the associated certain time may correspond to a time interval, such as weekly working hours, say from about 7 a.m. (ante meridiem) to about 5 p.m. (post meridiem) during Monday to Friday and the SSID may be the one used by the company. This means that no requests for access, such as Probe Requests, will be sent outside this time interval, e.g. during weekends when it can be expected that the person operating the STA 12a, 12b is not at work and therefore this SSID may not be within range.

In a sixth embodiment, SSID and respective validity conditions are received from a third party network node. The third party network node may be an access network discovery and selection function (ANDSF). Alternatively, the third party network node is an AP. The third party network node may utilize another radio access technology than is used by the STA 12a, 12b to send the request for access. The STA 12a, 12b, for instance provided as a mobile phone, a tablet computer, or a laptop computer, is then provided with what SSID to use and is also explicitly informed not to try to connect to any other SSID in order to reduce the amount of useless requests for access, such Probe Requests, sent. l8

The request for access may be sent as a unicast transmission. Alternatively the request for access may be sent as a multicast transmission. Thus, in a seventh embodiment, the STA 12a, 12b being aware of the validity conditions sends a request for access , such as Probe Requests, to only those APs 11a, 11b that the STA 12a, 12b knows are active. In this case, instead of using a broadcast address, which triggers responses from all the APs on a certain channel, the STA 12a, 12b may send unicast or multicast Probe Requests, asking for a particular AP or group of APs. The STA 12a, 12b may be configured to perform this by either including the last-known address of the AP in the "Destination Address" field of the Probe Request, or asking for a specific SSID in the "SSID Parameter set" field of the Probe Request.

Reference is now made to Fig 8 illustrating methods for enabling a STA 12a, 12b to scan for APs 11a, 11b in a wireless local area network 10a, 10b according to further embodiments. The methods are performed by the AP 11a, 11b.

The AP 11a, 11b may be configured to either generate validity conditions, such as policies, autonomously or to receive them from a central policy

management entity in the wireless local area network 10a, 10b. Hence, the method may comprise an optional step S202a of generating the validity conditions. The processing unit 21 may be configured to perform step S202a, for example by executing functionality of the generate module 21b.

Alternatively the method may comprise an optional step S202b of receiving the validity conditions from a central policy management node. The processing unit 21 may be configured to perform step S202b, for example by executing functionality of the send and/or receive module 21a. The policies may be generally semi-static and may usually not be a subject to frequent changes. Once the policies have been provided to the STA 12a, 12b, the STA 12a, 12b may compare observed conditions (e.g., date, time of day, SSID, etc.) with the conditions specified in the policies in order to select SSIDs to which a request, such as a Probe Request, for accessing the channel should be sent. The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

For example, some embodiments have been described for being used for IEEE 802.11 systems, and therefore the notation Access Point (AP) and Station (STA) has been used to denote the network node (base station) and the wireless devices or mobile stations (user equipment; UE), respectively. However, as is obvious for the person skilled in the art, the herein disclosed embodiments are not limited to this standard, but may be applied also to other standards, mutatis mutandis.

Claims

1. A method for scanning for access points, APs, (na, lib) in a wireless local area network (10a, 10b), the method being performed by a station, STA, (12a, 12b) and comprising the steps of:
acquiring (S104) validity conditions for an AP, said validity conditions indicating at least one time interval when said AP is operating; and
sending (S108) a request for access to said AP only during said at least one time interval.
2. The method according to claim 1, further comprising:
acquiring (S106) location information indicating that said STA is within network coverage of said AP; and
sending (Sio8a) said request for access only when the STA is within said network coverage.
3. The method according to any one of the preceding claims, wherein said validity conditions indicate when said AP allows transmission to, and reception from, the STA.
4. The method according to any one of the preceding claims, wherein said request for access is sent as a broadcast transmission.
5. The method according to any one of the preceding claims, wherein said request for access is an IEEE 802.11 probe request.
6. The method according to any one of the preceding claims, wherein said validity conditions are received from said AP.
7. The method according to any one of the preceding claims, wherein said validity conditions comprises a service set identifier, SSID, of said AP.
8. The method according to claim 7, wherein said validity conditions comprises a time stamp, said time stamp defining at least one of a start point and an end point of said at least one time interval; the method further comprising:
discarding (Sno) said SSID once said time stamp has expired.
9. The method according to any one of the preceding claims, further comprising:
storing (S112) a list of service set identifiers, SSIDs, each SSID of which is associated with at least one AP; and
deleting (S114) an SSID from said list once said validity conditions of its associated at least one AP are no longer satisfied.
10. The method according to any one of the preceding claims, wherein said validity conditions comprise information indicating a collection of service set identifiers, SSIDs, said information further indicating locations of APs associated with said collection of SSIDs, and time intervals for when said APs are operating.
11. The method according to claim 10, wherein the APs are associated with at least two locations, each location of which having its own time interval for when said APs are operating.
12. The method according to any one of the preceding claims, wherein said validity conditions comprises a service set identifier, SSID, of said AP, wherein said at least one time interval comprises a first time interval and at least one second time interval, the method further comprising:
storing (S116) said SSID after expiry of said first time interval and until expiry of a last of said at least one second time interval; and
sending (Sio8b) said request for access to said AP only during said first time interval or during said at least one second time interval.
13. The method according to any one of the preceding claims, further comprising:
acquiring (S118) a list of frequencies associated at least with said AP; and
sending (S120) said request for access on at least one of said acquired frequencies.
14. The method according to claim 13, further comprising:
sensing (S122) APs on at least one of said acquired frequencies.
15. The method according to any one of the preceding claims, further comprising:
acquiring (S102) auxiliary information; and
acquiring (Si04a) said validity conditions based on said auxiliary information.
16. The method according to any one of the preceding claims, wherein said validity conditions are received from a third party network node.
17. The method according to any one of the preceding claims, wherein said request for access is sent as a unicast transmission.
18. The method according to any one of claims 1 to 16, wherein said request for access is sent as a multicast transmission.
19. A method for enabling a station, STA, (12a, 12b) to scan for access points, APs, (11a, 11b) in a wireless local area network (10a, 10b), the method being performed by an access point, AP, (11a, lib) and comprising the step of: broadcasting (S204) validity conditions of the AP, said validity conditions indicating at least one time interval when said AP is operating.
20. The method according to claim 19, further comprising:
generating (S202a) said validity conditions.
21. The method according to claim 19, further comprising:
receiving (S202b) said validity conditions from a central policy management node.
22. A station, STA, (12a, 12b) for scanning for access points, APs, (11a, lib) in a wireless local area network (10a, 10b), the STA comprising a processing unit (31) configured to cause the STA to:
acquire validity conditions for an AP, said validity conditions indicating at least one time interval when said AP is operating; and send a request for access to said AP only during said at least one time interval.
23. An access point, AP, (11a, lib) for enabling a station, STA, (12a, 12b) to scan for access points, APs, (11a, 11b) in a wireless local area network (10a, 10b), the AP comprising a processing unit (21) configured to cause the AP to: broadcast validity conditions of the AP, said validity conditions indicating at least one time interval when said AP is operating.
24. A computer program (42b) for scanning for access points, APs, (11a, 11b) in a wireless local area network (10a, 10b), the computer program comprising computer code which, when run on a processing unit (31) of a station, STA, causes the processing unit to cause the STA to:
acquire (S104) validity conditions for an AP, said validity conditions indicating at least one time interval when said AP is operating; and
send (S108) a request for access to said AP only during said at least one time interval.
25. A computer program (42a) for enabling a station, STA, (12a, 12b) to scan for access points, APs, (11a, 11b) in a wireless local area network (10a, 10b), the computer program comprising computer code which, when run on a processing unit (21) of an AP, causes the processing unit to cause the AP to: broadcast (S204) validity conditions of the AP, said validity conditions indicating at least one time interval when said AP is operating.
26. A computer program product (41a, 41b) comprising a computer program (42a, 42b) according to at least one of claims 24 and 25 and a computer readable means (43) on which the computer program is stored.
PCT/EP2014/061956 2014-06-10 2014-06-10 Scanning for access points in a wireless local area network WO2015188846A1 (en)

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