HK1079382A - Method and system wherein handover information is broadcast in wireless local area networks - Google Patents

Description

Method and system for broadcasting switching information in wireless local area network

Technical Field

The present invention relates to broadcasting handover or roaming information in a wireless local area network. The present invention relates in particular to providing handover information in a wireless local area network to enable a user to handover from the wireless local area network to another wireless system whose geographical coverage area overlaps with the wireless local area network.

Background

In a Wireless Local Area Network (WLAN), an Access Point (AP) or Base Station (BS) serving a particular cell periodically broadcasts beacon signals (i.e., every 100 ms). An active WTRU scans the beacon signal and associates it with the AP with the strongest beacon. A conventional beacon contains information about the corresponding AP, such as time stamp, beacon interval, capability, Extended Service Set (ESS) Identification (ID), Traffic Indication Map (TIM). The WTRU uses legacy beacons to distinguish between different APs. The WTRU tracks the Received Signal Strength (RSS) of the beacon. When the RSS becomes weaker, the WTRU starts scanning for stronger beacons from neighboring APs.

The WLAN conventional scanning method may be active or passive. In passive scanning, the WTRU sends a probe request to the target station of APs, which can receive its probe. In the active scanning case, each AP receiving a probe responds with a probe response containing the same information as found in a conventional beacon, except for the TIM. The TIM is used to alert or alert APs and is therefore not required when an AP can provide a relevant response in response to a probe request.

To facilitate interoperability between WLANs and an alternative system (i.e., another system whose coverage area overlaps with the WLAN), WTRUs operating within a WLAN are typically caused to detect the presence of such alternative available systems. This is accomplished by performing a cell search for the availability of a Public Land Mobile Network (PLMN) when handing over the PLMN from the WLAN while utilizing the WLAN for communications. This method is implemented by turning on the WLAN receivers of the WTRU's to search for available networks, while the WTRU uses the WLAN for communication. This approach has the disadvantage of being time consuming and requiring simultaneous activation of the WTRAN and PLMN functions of the WTRU's. Thereby resulting in increased battery consumption and an inability of the WLAN to direct communications to a particular PLMN network. Furthermore, this approach is limited to switching from WLANs to PLMNs.

Alternatively, the availability search for a particularly available PLMN is done manually. In this way, in addition to being limited to PLMNs, the user must manually select a network, which is inconvenient and time consuming.

Accordingly, it would be desirable to provide handover information without the disadvantages and limitations of the prior art.

Disclosure of Invention

The present invention provides a method and system for handover of broadcast information from WLANs to available alternative systems. WTRUs can read the selected system information without searching and can switch to any type of available selected system.

A frequently implemented WLAN is an 802.11b network. The 802.11 standard includes "beacon frames" to allow all access points to inform the WTRUs of the parameters of the system. The beacon frame has information available for future service. Some unused information elements may be used to broadcast information of available alternative systems. Rather than tracking beacons based on RSS WTRUs, the present invention enables WTRUs to access alternate system information at any time to allow them to interact with alternate systems as desired. The information broadcasted about available alternative systems may include network type, network name, information about surrounding cells and information about services that the alternative systems may provide.

Drawings

The invention may best be understood by referring to the following examples and accompanying drawings.

Fig. 1 illustrates a WLAN whose geographic coverage area overlaps with other alternative systems.

Fig. 2 illustrates a conventional beacon frame structure for beacon frames used by conventional WLANs.

Fig. 3 is a beacon frame structure according to the present invention.

Fig. 4 is a beacon frame structure according to the present invention.

Figure 5 is a method for automatic handover from WLANs to available alternative systems at WTRUs according to a predetermined scaling.

Figure 6 is a method in which a user operating a wtru in a WLAN can manually switch to an alternative system where geographic coverage overlaps with the WLAN.

Figure 7 is a WLAN wherein operational WTRUs may switch to a backup system whose geographic coverage area overlaps with the WLAN.

The following terms and acronyms are used in this application:

PLAN mobile public land mobile network

Global system for GSM mobile communication

UMTS Global Mobile Telecommunications System

GPRS general packet radio service

IMS IP multimedia system

WLAN wireless local area network

CDMA code division multiple access

UE user equipment

WTRU wireless transmit/receive unit

Detailed Description

By way of introduction, a wireless transmit/receive unit (WTRU) includes, but is not limited to, a UE, a mobile station, fixed or mobile subscriber unit, pager, or other type of client device that may operate in any wireless environment. Examples of wireless environments include, but are not limited to, WLANs and PLMNs. WTRUs described herein preferably operate in the environment of WLANs and PLMNs.

When referring to an Access Point (AP), it includes, but is not limited to, a Base Station (BS), node-B, station controller or other interfacing device in a wireless environment. Furthermore, the terms other technology or other alternative system may be used interchangeably to refer to a wireless system to which a WTRU operating in a WLAN may switch.

Referring to fig. 1, a WLAN 10 is shown in which the geographic coverage areas of WLANs overlap the coverage areas a, B, C of various alternative technologies. For purposes of illustrating the present invention, alternative technology a14 is CDMA 2000. Alternative B12 is a UMTS and alternative C15 is an 802.16 network. It should be particularly noted that the alternative technology may be any type of wireless system. Furthermore, the technology that overlaps with the WLAN may be the same type of technology used in the WLAN. That is, the alternative technology may be the same type of system that is handed off from the WTRU. For example, handover information may be broadcast over an 802.11b network to handover to another 802.11b network that has a different operator but overlapping coverage areas.

For purposes of illustrating the preferred embodiment of the present invention, a WLAN may be referred to as 1082.11 b network 10. It should be particularly noted that the WLAN 10 may be any type of WLAN, such as an 802.11a network, an 802.15 WLAN or any other WLAN.

Users operating WTRUs in 802.11b may wish to handover to an alternative system for different reasons. For example, a WTRU may be out of range of an 802.11b network, or a user may require a higher level of security/quality of service (QoS), which may be obtained from an alternative system such as a PLMN. Furthermore, the user needs to switch because of the cost of the alternative system and the WLAN, or the user needs the services of the alternative system because the WLAN it operates cannot be obtained.

For any reason, switching to an alternative technology 12, 14, 15 requires information on the availability of the alternative technology 12, 14, 15 in the zone. According to the present invention, handover information is broadcast over the WLAN 10 so that WTRUs receive the required handover information without having to search themselves. The handover information received from the WTRUs, the WTRUs may determine with which of the available alternative systems 12, 14, 15 to interact.

WLANs typically provide management information for WTRUs in the form of beacons. Referring to fig. 2, a prior art beacon frame structure is shown and indicated generally by the numeral 20. The beacon 20 includes a time stamp 22 that is used by WTRUs to update their local clocks to synchronize between all WTRUs associated with a particular AP. A beacon interval 24 is also included. The beacon interval 24 represents the amount of time between beacon transmissions so that WTRUs are in a sleep mode between transmissions.

The capability information 26 provides a requirement that WTRUs intended to belong to a particular WLAN must meet. A Service Set Identifier (SSID)28 identifies the WLAN. Before an association occurs with a particular WLAN, a WTRU must have the same SSID 28 as the AP via which it can access the WLAN.

The supported rate 30 represents the data rate supported by a particular WLAN. For example, an 802.11b may enable a WTRU to access a WLAN that supports only data rates below 11Mbps, the WTRU will comply with this restriction and limit transmissions below 11 Mbps.

The beacon typically includes information about the particular signaling method in the form of different sets of parameters 32, 34, 36, 38, which are also included in the beacon 20. The parameter set typically includes Frequency Hopping (FH)32, direct sequence spread spectrum (DS)34, Carrier Frequency (CF)36, and Infrastructure Basic Service Set (IBSS)38 information. As described above, for active scanning, a TIM40 is provided. The TIM40 is timed out to identify which sleep mode WTRUs have data frames waiting in an AP buffer.

The prior art beacon frame structure 20 does not include information regarding handover. However, the prior art beacon frame structure 20 may be adapted such that the structure 20 with the presence of additional information elements may be used to broadcast handover information regarding available alternative systems. Referring to fig. 3, information 50 regarding available alternative technologies (i.e., alternative system information) is provided within beacon frames to enable WTRUs to interact with available alternative systems. For a particular available alternative system for which information is to be broadcast, the information 50 preferably includes; network type (GSM, GPRS, CDMA2000, UMTS FDD, UMTS TDD, 802.11a, 802.11b, 802.15, 802.16, bluetooth, etc.) network identification, cell description of surrounding cells and services provided by alternative systems.

In particular, with respect to the network identification, an indication of the service provider is provided. The information preferably includes frequency, channel number, and cell identification associated with the particular technology type, as described with respect to the surrounding cells. For example, in the case of the GSM/GPRS system, the cell identification information typically includes a Base Station Identity Code (BSIC). With respect to the services provided by the alternative system, the data 50 may include an indication of whether the alternative system provides an IP Multimedia System (IMS), Short Message Service (SMS), Multimedia Message Service (MMS), etc.

The information 50 may be downloaded to a WLAN and included in a beacon sent by the WLAN. Alternatively, the WLAN may be equipped for auto-detection of alternative technologies. Other means for providing wlan information 50 for broadcast in the beacon may also be implemented.

Referring to fig. 4, if multiple alternative systems are available, the systems should be listed in order. For example, as in area 3 of fig. 1, information 60 about alternative technology a should be followed by information 62 about alternative information B, as shown in fig. 4.

Referring to fig. 5, a method 100 is shown for automatically handing over WTRUs from WLANs to an available alternative system according to predetermined criteria. For purposes of illustrating the present invention, the WLAN is designated as an 802.11b network.

The method 100 begins at step 104 by determining which alternative system is the candidate system. This determination may be made by the WTRU or the 802.11b network or a combination of both, or may indicate when to switch to an available alternative system based on predetermined criteria.

The predetermined criteria may be based on a minimum criteria, based on factors of an exemplary reason to switch from more than one prepared WLAN, or based on any other reason. For example, the criteria may relate to quality. That is, if the quality of service (QoS) drops below a predetermined value in 802.11b (or other type of WLAN), the criteria may specify that the user should switch to any available alternative system, regardless of other factors. Alternatively, the standard may indicate that where the QoS is below a predetermined value, the user should switch unless the monetary cost of using the alternative system is greater than a certain percentage of the monetary cost of using the WLAN in which the user is operating.

The criteria may also be associated with service, mobility, battery consumption, or any criteria associated with wireless communications. Different criteria may also be combined. For example, the user may wish to switch to an alternative technology with MMS, but not with battery power below a predetermined level.

Once the relevant alternative systems have been determined, the method 100 proceeds to step 106. In step 106, the WTRUs determine which alternative systems are available (i.e., which alternative systems have coverage overlap with the 802.11b implementing the method 100). As described above, information related to the guest alternative system is obtained by the 802.11b network and a beacon is broadcast. Therefore, in step 106, the WTRUs read the 802.11b beacon frame to determine which alternative systems are available. When reading the beacon frame, the WTRU preferably extracts cell data related to the available alternative systems (step 108). This is preferred because, although an alternative system has yet to be selected, it is more efficient to obtain cell information (step 108) about all alternative systems when reading beacons (step 106), rather than reading beacons after an alternative system has been selected.

Next, at step 110, the available alternative systems are compared to the relevant systems. Based on this comparison, it is determined at step 112 that the criteria associated with the system are met by no alternative systems, e.g., none, and the method 100 ends and may be re-implemented if desired. If so, the method 100 proceeds to step 114, where an alternative system that satisfies the criteria is selected. In step 116, coverage and QoS measurements for the selected system are performed. The registration measurement may be performed using the cell information extracted in step 108 and procedures known to those skilled in the art.

Once the measurement is complete, the method 100 proceeds to step 118. In step 118, it is determined whether the coverage area and QoS of the selected candidate system are sufficient. With respect to coverage areas, it may be considered sufficient that a user does not switch to an alternative system or return to an 802.11b network when switching to an alternative system. That is, the signal strength of the selected alternative system must be strong enough to support the desired communication. If the signal strength is not strong, the WTRU will easily switch back to the 802.11b network for another alternative system at the time of the handover. This determination may serve as a double check because although the 802.11b network should not broadcast information related to the alternative system, it may be that the information has changed because it is unable to accept WTRUs operating in the 802.11b network coverage area. For example, the information may change because the alternative system is unavailable due to a power failure.

With respect to QoS, QoS may be considered sufficient, e.g., QoS may reach a predetermined value. The criteria for implementing decision 118 (i.e., whether coverage and/or QoS is sufficient) may be set according to operator preference.

If the measurement is insufficient, the method 100 ends and the user remains in the 802.11b network. If the measurement is sufficient, the user switches to the selected alternative system (step 120). After the handoff has occurred, the method 100 ends.

Referring to fig. 6, a method 200 is shown in which users operating WTRUs in a WLAN may manually switch to an alternative system whose coverage area overlaps with the WLAN. Initially, the user indicates an interest in activating manual selection in the WTRU (step 202) to effect a handover to an alternative system. The manual selection may be activated using any type of manual activation, such as a button, voice activation, etc. Next, in step 204, the WTRU may read an 802.11b network beacon frame provided by the 802.11b network to determine which alternative systems are available, as described above (step 204). When reading the beacon frame, the WTRU preferably extracts all information about available alternative systems (206). At step 208, the WTRU determines which of the available alternative systems the user's WTRU can support.

In step 201, the user selects a desired available alternative system. Note that in this step the user preferably selects only the alternative systems that the user's WTRU can support.

After the available alternative systems are selected, coverage area and QoS measurements for the selected systems are performed at step 212. As with the method 100, if coverage and QoS are determined to be adequate at step 214, the WTRU switches to the selected system at step 216. Once the WTRU has switched, the method 200 ends.

Referring to fig. 7, a WLAN 300 of the present invention is shown. For purposes of illustrating the present invention, the WLAN 300 includes an AP 302 to provide an interface between a Local Area Network (LAN)304 and WTRUs 306 and 308 operating within the coverage area of the WLAN 300. WLANs may include any number of Aps and WTRUs. LANs are well known in the art and may include a server 314 and a plurality of computers 316, 318.

As explained above, the WLAN 300 broadcasts handover information in beacon frames, allowing WTRUs 306,308 to easily retrieve the information and handover to (manually or automatically) available alternative systems. The handoff information may be downloaded or automatically detected (periodically or when true) by the WLAN 300 and reassigned to Aps. Handover information may be assigned or provided to Aps. For example, handoff information related to geographic coverage areas serviced by the AP 300 may be stored in the local memory 310. When the AP 300 broadcasts its beacon signal, a processor 312 is provided to cause handover information appropriate for the coverage area of the AP 300 to be accessed from the memory 310 and broadcast to WTRUs 306,308 in the coverage area. Of course, the manner in which the handover information is provided and stored in the Aps, and the manner in which the handover information is broadcast, can be implemented as desired.

Although the invention has been described in detail, it is to be understood that the invention is not limited thereto, as various changes may be made without departing from the scope of the appended claims.

Claims (25)

1. A wireless local area network, comprising:

an access point connected to the local area network, the access point being configured to provide a plurality of WTRUs having wireless access to the local area network;

the wlan is configured to broadcast a beacon frame including handover information to handover WTRUs from the wlan to available alternative systems; and

wherein the geographic coverage area of available alternative systems overlaps with a geographic coverage area of the wireless local area network.

2. The wireless local area network of claim 1, wherein the handover information includes information related to network type.

3. The wireless local area network as in claim 1, wherein the handoff information comprises information associated with a network tag.

4. The wireless local area network of claim 1, wherein the handover information includes cell information surrounding a cell served by the access point.

5. The wireless local area network as in claim 1, wherein the handover information includes information related to the type of service provided by the available alternative systems.

6. The wireless local area network of claim 1, wherein the at least one available alternative technology is a PLMN.

7. The wireless local area network of claim 1, wherein at least one alternative technology is available for another wireless local area network.

8. The wlan as claimed in claim 1 wherein the wlan is an 802.11b network.

9. A method of handing off a WTRU from a wireless local area network to an available alternative system, comprising:

broadcasting handover information in a beacon frame;

determining a system of interest to the WTRU user;

reading the handover information in the beacon frame to determine which alternative systems are available;

extracting cell information about available alternative systems from the handover information in the beacon frame;

selecting an available system of interest to the user;

performing coverage and qos measurements on the selected system;

the user is switched to the selected available system that is measured to be sufficient.

10. The method of claim 9, wherein the step of selecting an available system of interest to the user further comprises comparing the available system to the system of interest to the user.

11. The method of claim 9, wherein the handover information includes information about a network type.

12. The method of claim 9, wherein the handover information includes information on a network flag.

13. The method of claim 9, wherein the handover information includes cell information of surrounding cells served by the access point.

14. The method of claim 9, wherein the handover information includes information of service types provided by available alternative systems.

15. The method of claim 9, wherein the at least one available alternative technology is a PLMN.

16. The method of claim 9, wherein the at least one available alternative technology is another wireless local area network.

17. The method of claim 9 wherein the wlan is an 802.11b network.

18. A method of handing off a WTRU from a wireless local area network to an available alternative system, comprising:

broadcasting handover information in a beacon frame;

reading the switching information to determine whether the alternative system is available for switching;

extracting cell information about available alternative systems, which is interesting information from beacon frames;

determining whether the WTRU can support available alternative systems;

selecting an available system that is of interest and that the WTRU has the capability to support;

performing coverage and qos measurements for the selected system;

switching to a selection system where a measurement is sufficient.

19. The method of claim 18, wherein the handover information includes information related to network type.

20. The method of claim 18, wherein the handover information includes information on a network flag.

21. The method of claim 18, wherein the handover information includes surrounding cell information served by the access point.

22. The method of claim 18, wherein the handover information includes information of service types provided by available alternative systems.

23. The method of claim 18, wherein the at least one available alternative technology is a PLMN.

24. The method of claim 18, wherein the at least one available alternative technology is another wireless local area network.

25. The method of claim 18 wherein the wlan is an 802.11b network.