HK1089578B - Wireless local access network system detection and selection - Google Patents

Description

Detection and selection of wireless local access network systems

Technical Field

The present invention relates generally to communication systems, and more particularly to detection of a Wireless Local Access Network (WLAN) by a mobile station in a cellular communication system.

Background

A Wireless Local Access Network (WLAN) provides wireless access to a communication network within a local geographic area, such as within a building or an internet cafe. Many cellular carriers are currently considering WLANs to reduce the load on cellular systems to increase their capabilities. In addition, users may wish to access local WLANs to increase the reception and data rate of communications through the wireless device. There are problems in detecting and selecting WLAN systems. The purpose of system detection is to detect the availability of a wireless access medium (e.g., cdma2000, WLAN, etc.). The purpose of system selection is to select an access medium for delivery of application content. System selection may be based on availability of access media, preference policy, application state, user intervention, etc., or a combination thereof.

Typically, the cellular system periodically transmits a paging indicator to call the mobile station when there is any pending communication. Similarly, the WLAN may be informed by beacons transmitted by the WLAN. Both paging indicators and beacons require the mobile station to search for transmitted signals. Because the mobile station typically has no information about the location and availability of the WLAN, the mobile station spends considerable power periodically searching for a WLAN. There is therefore a need for an efficient, accurate method of system detection and selection.

Drawings

FIG. 1 is a mobile station adapted for system detection and selection;

fig. 2A is a communication configuration including capabilities of a cellular system and access of a WLAN;

fig. 2B illustrates a signaling message for notifying a WLAN;

FIG. 3A is a timing diagram of signal flow in the system shown in FIG. 2A;

FIG. 3B is a timing diagram of signal flow in the system shown in FIG. 2A;

FIG. 4 is a timing diagram of signal flow in the system shown in FIG. 2A;

FIG. 5A is a mobile station having a display format related to WLAN detection;

FIG. 5B is a flow chart diagram of a system detection and selection method;

fig. 6 is a block diagram of a mobile station with multiple tuners in communication with a WLAN and a cellular system;

FIG. 7 is a flow chart diagram of a system detection method;

FIG. 8 is a communication system supporting wireless cellular communication, wireless local area network communication, and Internet communication;

FIG. 9 is a timing diagram of WLAN detection and selection;

FIG. 10A is a timing diagram of WLAN detection and selection;

FIG. 10B is a timing diagram of WLAN detection and selection;

fig. 10C is a timing diagram of WLAN detection and selection.

Detailed Description

The word "exemplary" is used herein to mean "serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

An HDR subscriber station, referred to herein as an Access Terminal (AT), which may be mobile or stationary, may communicate with one or more HDR base stations, referred to herein as Modem Pool Transceivers (MPTs). An access terminal transmits and receives data packets through one or more modem pool transceivers to an HDR base station controller, referred to herein as a Modem Pool Controller (MPC). The modem pool transceivers and modem pool controllers are parts of what are referred to as access networks. An access network transports data packets between multiple access terminals. The access network may be further connected to other networks outside the access network, such as a common intranet or the internet, and may transport data packets between each access terminal and such outside networks. An access terminal that has established an active traffic channel connection with one or more modem pool transceivers is referred to as an active access terminal and is considered to be in a traffic state. An access terminal that is in the process of establishing an active traffic channel connection with one or more modem pool transceivers is said to be in a connection setup state. An access terminal may be any device that communicates through a wireless channel or through a wired channel, for example using fiber optic or coaxial cables, to carry out any data. The access terminal may further be any of a variety of devices including but not limited to PC card, compact flash, external or internal modem, or wireless or wireline phone. The communication link through which the access terminal sends signals to the modem pool transceiver station is called a reverse link. The communication link through which a modem pool transceiver sends signals to an access terminal is called a forward link.

FIG. 1 illustrates components and interfaces for system detection and selection, according to one embodiment. In system 50, user 52 represents a user of a wireless mobile unit, where user 52 is a person who is able to manually select an access medium or perform an automatic selection process. The application 54 is a computer readable program or protocol stack (e.g., a Transmission Control Protocol (TCP)/Internet Protocol (IP) stack) that requires access to a medium for transport. The application 54 communicates with the user 52 via interface C. The application 54 also communicates with a selection database 56 via interface B and with a selector 58 via interface E.

The selection database 56 is a storage device that stores system selection criteria. The system selection criteria may be manually configured by the user 52 or automatically processed by the application 54. In one embodiment, the system selection criteria considers the availability of wireless access, which selects a WLAN when available. In one example, if the system 50 is currently communicating via a cellular network, such as a cdma2000 network, the system 50 is instructed to continue such communication in addition to continuing to attempt to detect the availability of a WLAN. Application 54 may automatically configure selection database 56. The user 52 may manually configure the selection database 56 and may start or stop the application 54.

An Access Medium Detector (AMD)60 detects the availability of the wireless access medium and reports the results to the selector 58. The selector 58 is responsible for enabling or disabling one or more access medium detectors 60 and selecting an access medium based on the detection results, system selection criteria, application status, and/or user request. Selector 58 may notify user 52 and/or application 54 of the system selection. The selector 58 communicates with the application 54 through interface E, with the selection database 56 through interface F, and with the AMDs 60 through interface G. The selector 58 is further in communication with the user 52 via the interface D.

Interface A: the user 52 may manually load new system selection criteria or modify selection criteria already existing in the selection database 56. The system selection criteria are rules that the selector 58 will use to make decisions. For example, if an application is active (i.e., is sending/receiving data) and a WLAN access medium is available, the system should select that WLAN access medium to carry data traffic. The user may enter system selection criteria via a user graphical interface (e.g., a window-based program).

And interface B: the application 54 may automatically load new system selection criteria or modify selection criteria already existing in the selection database 56. For example, the application 54 has the option of using a given access medium X, which is automatically loaded into the options database 56 when the application 54 is downloaded or installed.

And interface C: the user 52 may start or stop the application 54. The user 52 may configure the settings of the application 54 for system selection. For example, when the user 52 decides to manually control the hierarchical selection of the application 54 through interface A, the user 52 may configure the application 54 to disable automatic interaction with the selection database 56.

And interface D: the selector 58 may prompt the user to select an access medium. In another case, without such a prompt, the user 52 may request a particular access medium, where such a request overrides other system selection criteria.

And interface E: the application 54 may provide status information to assist the selector 58 in making system selections. For example, whether the application 54 is enabled or disabled affects the decision of the selector 58 to enable or disable the access medium detector 60. The selector 58 may provide the system selection result to the application 54 based on an indication derived from the system selection criteria stored in the access medium detector and selection database. For example, if the selector 58 selects a higher bandwidth access medium, the application 54 may switch to a codec with better quality. In another example, the selector 58 relays the system detection results obtained from the access medium detector 60 to the application 54 so that the application 54 can display the results to the user 52.

And interface F: the selector 58 obtains system selection criteria from the selection database 56. If there is a change in the system selection criteria (e.g., modified by the user 52), the selector 58 must retrieve the new criteria from the selection database 56. The selector identifies the change in criteria by a number of methods, such as: (1) the user 52 (or the application 54) provides information to the selector 58 via the D (or E) interface indicating that the selection database 56 is updated, or (2) the selector 58 periodically checks the selection database for updates.

And interface G: the selector 58 may enable or disable one or more access medium detectors 60 based on user input, application status, and/or system selection criteria derived from the selection database 56. The access medium detector 60 may inform the selector 58 of the detection result.

Providing WLAN information for MS

The provisioning of WLAN information in a Mobile Station (MS) and methods performed in the MS are discussed in detail below to minimize unnecessary WLAN scanning based on WLAN advertisement from the cellular network via signaling messages. The network support for cdma2000 protocols is exemplified in the discussion that follows. In the context of the present description, provisioning refers to the communication of WLAN parameters and configuration information to the MS that is necessary to establish communication with the WLAN.

Conventional provisioning methods manually configure the MS with the necessary information (e.g., 802.11a/b frequencies, service identifier lists, etc.) for the MS to detect WLAN coverage provided by the service provider. An Extended Service Set Identifier (ESSID) may be used to identify all Access Points (APs) in a WLAN operator network. Different operators will use different ESSIDs. Thus, the ESSID list may correspond to a list of WLAN operators accessible to the MS.

An alternative to manual provisioning is to provision the MS with WLAN information via an over-the-air provisioning (OTAP) type protocol. Details of OTAP are set forth in the IS-683 standard, which can be extended to support provisioning of WLAN parameters. Another alternative is to automatically provision the MS with WLAN information via 1x signaling messages (discussed below). The latter alternative is more flexible than OTAP.

Once the MS has the necessary WLAN information, the MS can decide when to scan for WLAN coverage. Typically, a WLAN will transmit a periodic beacon, which is a signal transmitted to inform the WLAN. The MS can access the WLAN when the MS can receive the beacon. The user 52 may initiate or discontinue WLAN scanning, however, this process may not be user-friendly, as manual operation by the user is required. Automatic operation is more preferred, as is apparent to the user. According to one embodiment, the MS is provided with a search method that is easily used by the user 52 that can perform periodic searches. Periodic searches are expensive when the MS is not within the coverage area of the WLAN, as searches consume battery power.

If a cellular system, such as cdma2000, also provides WLAN service or enters into a roaming agreement with other WLAN operators, several options are implemented to cause the cellular network to publish WLAN information via cellular signaling messages to assist the MS in efficiently scanning for WLAN coverage. Alternative embodiments may be implemented in other cellular systems.

WLAN notification through signaling messaging

In a first embodiment, a Base Station Controller (BSC) and a Base Transceiver System (BTS) are configured to possess knowledge of WLAN coverage in a cell sector. When the cellular service provider also provides WLAN service, WLAN information is available to the cellular system. The BTS periodically broadcasts WLAN provisioning information (e.g., 802.11a/b frequencies, ESSID, preferred roaming list, etc.) as overhead messages over common channels when WLAN coverage exists within the cell sector. The MS receives the WLAN provisioning information and uses the information to scan for a WLAN. The WLAN provisioning information may be included within existing overhead messages. Alternatively, the WLAN provisioning information may be provided in a defined signaling message dedicated for WLAN provisioning.

Figure 2A shows sectors within a cell of a cellular communication network. The cell includes sector a 102, sector B104, and sector C106. Inside the cell there are multiple WLANs including WLAN #1120 and WLAN # 2130. WLAN #1120 is labeled ESSID (1). WLAN #2130 is labeled ESSID (2). As shown, WLAN #2130 is contained within sector B104, while WLAN #1120 includes a portion located within sector B104 and a portion located within sector a 102.

The preferred roaming list is a list of ESSIDs, each corresponding to a WLAN provider having a roaming agreement with the cellular system. The broadcast signaling message may be initiated by the cellular system provisioning, i.e., the cellular system broadcasts the message at all times regardless of whether the MS has WLAN capability. The cellular system continuously transmits WLAN provisioning information in order to inform the WLAN. Alternatively, the WLAN provisioning information may be conveyed via a signaling message, wherein the signaling message is triggered upon receipt of at least one registration message, and wherein the registration message indicates that the MS is WLAN capable. Such a WLAN capability indication may be a 1-bit flag in the registration message. Note that one benefit of registration trigger signaling is that the BTS can avoid broadcasting unnecessary WLAN provisioning information.

Upon receiving a WLAN request from the MS, the BS may transmit a WLAN advertisement in a number of ways. The BS may transmit the WLAN broadcast on a common channel where multiple users can access the information. The BS may directly convey the information to the MS using a signaling message. The BS may transmit only specific information, such as information for location identification of the WLAN.

The MS may not be able to detect the AP when receiving the WLAN provisioning information in the overhead signaling message because the WLAN coverage within the cell sector may be inconsistent. In densely populated areas, such as shopping malls, stadiums, etc., the probability of WLAN coverage increases. Cellular systems require increased capacity in populated areas and WLANs provide a means to increase capacity in such areas. Therefore, cellular systems implement WLANs in residential areas. On the other hand, WLAN coverage is not required in rural areas because its capabilities are generally not considered in populated areas.

Within cell 100, the BS (not shown) supporting sector B104 transmits identifiers of those WLANs that the BS knows. For example, if the network has an association with WLAN #1120, the BS in sector B104 may transmit a WLAN #1129 announcement, where the announcement provides ESSID (1). In this way, when the MS (not shown) receives the notification, the MS can scan for WLAN #1129 based on ESSID (1). Similarly, the BS of sector A102 may also advertise WLAN # 1120. In addition, sector B if the cell network has an association with WLAN #2130

The BS in 104 may also inform the WLAN #2130 providing ESSID (2).

Fig. 2B shows two embodiments of signaling messages. In the first embodiment, the system parameter message includes system parameter information 112 and a WLAN advertisement field 116. The WLAN advertisement field 116 may be a bit where one polarity indicates that the WLAN is available and the opposite polarity indicates that it is not available. The WLAN advertisement 116 may be a multi-bit field that provides more information, such as location information, or an indication to the MS about accessing WLAN information. In the second embodiment, the system parameters message includes system parameters information 140, a WLAN advertisement 142, and location information or a Global Positioning System (GPS) 144.

In an alternative embodiment, the WLAN provisioning/advertisement information is not broadcast periodically via overhead messages on a common channel. When the MS wants to receive WLAN provisioning/advertisement information for a specified cell sector, the MS uses a cellular signaling message, such as a cdma2000 registration message, to request the WLAN provisioning/advertisement information from the BSC. Alternatively, the MS may request information using a specific WLAN. In response, the BSC provides the WLAN provisioning/advertisement information as required. If the MS has no traffic channel, the BSC sends an acknowledgement to the MS on the common channel. The reply identifies available WLAN coverage within the specified cell sector. Note that the sector is identified by using an identifier, such as the base station ID used in cdma 2000. The reply from the BSC also includes the necessary WLAN provisioning/advertisement information to allow the MS to scan for WLAN coverage when there is WLAN coverage in the sector.

To avoid additional signaling traffic (e.g., when multiple MSs request WLAN provisioning/advertisement information), the BSC may transmit the reply (i.e., WLAN provisioning/advertisement information) over a common channel. The WLAN information may be redundant. In one embodiment, upon receiving a request for WLAN provisioning/advertisement information from the MS, the BSC transmits the WLAN provisioning/advertisement information for a predetermined period of time. The provision of such information on the common channel avoids causing additional signaling messages when other MSs request the same information at close times.

The MS receives WLAN location information from the cellular network, wherein the WLAN location information identifies APs that support the WLAN. The location information may be a latitude and longitude identifier of the AP. The MS receives the WLAN location information and then displays the WLAN location information at the MS. The display may provide the location of the AP within a local map that may be stored in the MS. The display may be as shown in fig. 5A, where the mobile wireless device 200 includes a keypad 204 and a display 202. The display graphically identifies the location of each WLAN AP. The display may be a text message.

There are several methods available for the MS to acquire location information for APs supporting the WLAN. In one embodiment, the MS obtains location information for each AP from signaling overhead messages communicated over common or dedicated channels, as described above. In an alternative embodiment, the user instructs the MS to request location information for each AP from the application server. In this case the server may be located at the back end of the operator network, so the MS communicates with the server using a higher layer protocol (e.g., IP) to obtain the location information of the AP.

In one embodiment, as shown in fig. 5B, method 250 provides a method of manual WLAN selection. At step 252, the user selects a map display function for identifying the WLAN location on the wireless device. At step 254, the WLAN is identified as being within range. If an auto-scan is enabled at decision diamond 256, processing continues to step 258 where the device scans for WLANs. Otherwise processing continues to step 260 where the user searches for a WLAN. If the WLAN is accessible at decision diamond 262, the wireless device sends a WLAN registration request at step 264. Otherwise, the process returns to step 254 to await identification of a WLAN within range.

Fig. 3A is a timing diagram for WLAN detection, wherein the MS sends a WLAN query or request for specific WLAN information to the BS. In response, the BS transmits WLAN information, such as a WLAN advertisement, to the MS, which is conveyed over a common channel. When a WLAN is available, the MS scans for the WLAN based on WLAN information provided by the BS and sends a registration request to the WLAN to establish communication.

Fig. 3B is a timing diagram for WLAN detection, where the MS sends a registration request to the BS (i.e., cellular network). The registration request may include a specific request for WLAN information. Alternatively, the registration request may not be a specific request for WLAN information, but rather prompts the BS to provide the WLAN information. In response to the registration request, the BS provides the MS with WLAN information. When a WLAN is available, the MS scans for the WLAN based on WLAN information provided by the BS and sends a registration request to the WLAN to establish communication.

Fig. 4 is a timing diagram for WLAN detection, where the MS sends a registration request to the BS (i.e., cellular network). The registration request may include a specific request for WLAN information. Alternatively, the registration request may not be a specific request for WLAN information, but rather prompts the BS to provide the WLAN information. In response to the registration request, the BS broadcasts WLAN information on the common channel. When a WLAN is available, the MS scans for the WLAN based on WLAN information provided by the BS and sends a registration request to the WLAN to establish communication.

MS with a tuner

The Mobile Station (MS) has a tuner for communication. In such a device, the one tuner is used for communication with both the cellular system and the WLAN system. The MS detects WLAN coverage and performs system selection between WLAN and cellular systems, where the MS may only tune to one system (WLAN or cellular) at a given time.

The MS performs system detection and selection in the following cases: (1) the MS is idle (not in use in communication) with respect to the cellular network, has no dedicated channel, and wants to scan for WLAN; (2) the MS has an active packet data session (session) with the cellular network, has a dedicated channel, and wants to scan for WLAN; (3) the MS is tuned to the WLAN and wants to receive cellular pages; and (4) the MS is tuned to the WLAN but its signal strength is small.

In case (1) above, if the MS is idle in the cellular network (i.e., no dedicated channel), the MS may decide to scan for WLAN coverage based on one or more factors, such as user requirements, pre-configured choices, WLAN availability notifications received from the cellular network, and the like. The MS tunes to the cellular network at each set paging slot interval. In this way, the MS can receive any paging indicator from the cellular network. Once the MS monitors the cellular paging indicator, the MS can tune to the WLAN frequency and use passive or active scanning to detect WLAN coverage.

In case (2) above, the MS has an active packet data session (i.e., there is a dedicated channel) in the cellular network. The MS may choose not to scan for WLANs during an active data session in the cellular network. In this case, when the MS is in an active state in the cellular network, the MS does not switch to the WLAN even though it may access the WLAN. Although the MS may not be able to take advantage of high speed WLAN access, the MS does not experience service disruption. After the MS becomes idle in the cellular network, the MS tunes away from the cellular network to scan for WLANs.

Alternatively, the cellular network may direct the MS to scan for WLAN coverage. In this case, the cellular network instructs the MS to scan for WLAN coverage. If there is WLAN coverage, the network may direct the MS to handoff its packet data session to WLAN. This procedure may be useful when the network is overloaded or when the power strength of the MS is too small. This process will be discussed below and is similar to the candidate frequency search process in a system supporting cdma 2000.

The MS may inform the cellular network of any WLAN capabilities via over-the-air registration. If the MS is located in a cell sector with WLAN hot spots, the network may send a signaling message to request the MS to scan for WLAN coverage. The signaling request message contains WLAN information (e.g., frequency, ESSID, etc.) and is sent on a dedicated channel of the MS. The MS tunes to the WLAN frequency and actively or passively scans for WLAN beacons. Then, the MS may have several behaviors: (1) if the MS detects WLAN coverage, the MS tunes back to the cellular network to inform the WLAN search results. The cellular network then sends a signaling message to instruct the MS to handoff to the WLAN. The MS tunes to the WLAN and performs access authentication and optionally mobile IP registration to transfer its packet data session to the WLAN. If access authentication or mobile IP registration fails, the MS may tune back to the cellular network and start the packet data service option.

(2) If the MS detects WLAN coverage, the MS does not return to the cellular network to inform the WLAN search results. Instead, the MS proceeds to perform WLAN access authentication, optionally mobile IP registration to transfer its packet data session to WLAN. In this case, if the cellular network does not receive the signaling reply message after a timeout, the network assumes that the MS has left the cellular system and therefore removes the packet data session for the MS.

(3) If the MS fails to detect WLAN coverage, the MS re-tunes to the cellular network and sends a signaling reply message to inform the cellular network about the WLAN search results, and the network restores the active state of the MS's packet data session.

Continuing with case (2) given above, further, when the MS tunes away to scan for WLAN coverage, the MS may send a request to the cellular network to save the MS's state information. In this case, the MS requests the cellular network to save state information while scanning for WLAN coverage. The MS transmits a signaling request message (similar to a CDMA idle time (offtime) report message) to the 1x network. If the MS is located in a cell sector with WLAN hot spots, the network may send a signaling reply message containing the WLAN information necessary for the MS to scan for WLAN coverage. If the MS detects WLAN coverage and is authenticated for access, the MS may continue Mobile IP registration to handoff its packet data session over WLAN for delivery. If the MS fails to detect WLAN coverage or fails access authentication, the MS re-tunes to the cellular network and sends a signaling message requesting the cellular network to restore the active state of the MS's packet data session. If the cellular network does not receive the signaling request message after the expiration of the specified time period, the network assumes that the MS has left the cellular system, thus eliminating the MS's packet data session.

According to case (3) the MS is currently tuned to the WLAN. If the MS is not transmitting or receiving frames over the WLAN, the MS periodically tunes back to the cellular network and monitors the quick paging channel for a paging indicator. If the paging indicator is "0", there is no page to the MS and the MS immediately tunes back to the WLAN frequency. In this case, the time the MS spends on the cellular frequency is minimal (in the order of MS). If the paging indicator is "1", the MS monitors the paging channel at its paging slot. In cdma2000 type networks, the paging indicator occurs at most 100MS before the paging slot of the MS. The paging slot is 80 ms. A paging indicator of "1" does not guarantee that the page is for the MS because it is likely that the International Mobile Subscriber Identifier (IMSI) of the second MS is accidentally interfered with as with the paging indicator of the first MS. Thus, the MS may spend up to 180MS on the paging channel without doing anything. If the page is for the MS, it will answer with a page response and stay in the cellular network to receive the incoming circuit-switched voice call.

At the time the MS is scheduled to monitor cellular network pages, if the MS is transmitting or receiving frames on the WLAN, the MS should stay within the WLAN to complete the data transfer and thus skip the paging cycle. Potentially, the MS may miss pages and the call setup time for incoming circuit-switched voice calls may increase. If the MS receives a page for an incoming circuit-switched voice call, the MS may respond as follows:

1. upon receiving the page, the MS may remain tuned to the cellular network to send a page response and accept the call. After the voice call, the MS may tune to the WLAN to continue the packet data session (if the MS still has WLAN coverage).

2. Upon receiving the page, the MS immediately tunes back to the WLAN and sends a Disassociation message (Disassociation message) to the AP. The MS then switches to the cellular network, sends a page response, and accepts the call. After the voice call, the MS may need to start a new packet data session in the cellular network or WLAN.

According to scenario (4), if the MS is tuned to the WLAN, but detects that the signal strength has dropped below an acceptable threshold, the MS may tune to the cellular network and proceed to transfer the packet data session to the cellular network.

Fig. 10A shows an example of scenario (2) where the MS 702 is currently in a packet data session with the cell network 706. The MS 702 scans for WLAN indication messages sent from the cellular network. Using the WLAN indication message intended for the MS, the MS scans for WLAN coverage. Upon detecting a WLAN, the MS 702 informs the cellular network of the result. As shown, the MS 702 detects the WLAN (AP 704), and in response sends a search result notification to the cellular network. The cellular network may then instruct the MS 702 to switch to the WLAN. The decision to switch from the cellular network 706 to the WLAN is made based on network load, bandwidth of the user, data requirements, etc. Once the cellular network 706 instructs the MS 702 to handover, the cellular network 706 eliminates the data session. The MS 702 then initiates authentication with the AP 704. Note that the MS may need to re-establish with the cellular network if authentication fails.

Fig. 10B shows another example of scenario (2) where the MS 702 currently has a packet data session with the cell network 706. The MS 702 scans for WLAN indication messages sent from the cell network 706. Using the WLAN indication message intended for the MS, the MS scans for WLAN coverage. Upon detecting a WLAN, the MS 702 informs the cellular network of the result. As shown, the MS 702 detects a WLAN (AP 704) and in response initiates authentication with the AP 704. The cellular network 706 then starts a timer and when timed out, the cellular network 706 eliminates the data session.

Fig. 10C shows yet another example where the MS 702 is currently in a packet data session with the cell network 706. The MS 702 scans for WLAN indication messages sent from the cell network 706. Using the WLAN indication message intended for the MS, the MS scans for WLAN coverage. When no WLAN is detected, the MS 702 sends the search results to the cellular network 706. The MS 702 continues the data session with the cell network 706.

Two tuners

In the following example, a Mobile Station (MS) has two tuners that are capable of tuning to both cellular and WLAN frequencies. As shown in fig. 6, MS300 has an ESSID list 302, a first tuner (tuner a 304), and a second tuner (tuner B306) that are stored in memory. Tuner a is configured for communication with a WLAN. Tuner B306 is configured for communication with a wireless cellular network. As shown, when the MS300 is within range of the access AP320, tuner A304 scans for WLAN beacons transmitted by the AP 320. The WLAN beacon is transmitted periodically and identifies the WLAN supported by the AP 320. Tuner B306 searches for a paging indicator sent from the cellular network that is transmitted by Base Transceiver System (BTS) 322. In this way, the MS300 may scan for WLAN coverage while also scanning for cellular pages. Thus, the MS300 detects WLAN coverage and performs system selection between WLAN and cellular systems using one tuner per access medium.

The MS300 may implement any of a variety of practical configurations. For example, a "type a" device is a manual device (phone, Personal Digital Assistant (PDA)) with a built-in WLAN tuner and cellular network tuner, or a mounted WLAN tuner card and cellular tuner card (e.g., CDMA2000 card). Further, a "type B" device is a portable computing device, such as a personal computer with a WLAN tuner card, wherein the portable computing device is connected to a cellular handset, such as a handset supporting cdma2000 communications.

For type a devices, the MS300 is a physical device (e.g., handset, PDA) that supports both WLAN and serving network protocols. The MS300 has two Radio Frequency (RF) tuners: the first for cellular networks; the second for WLAN.

Returning to fig. 6, note that the WLAN beacon and the paging indicator need not be transmitted at the same time or at the same period. The MS300 scans for WLAN beacons over a period having a first period of time with tuner a 304. The MS300 searches for the paging indicator of the cellular network over a period having a second period of time. Typically, the second period of time is shorter than the first period of time. In other words, the paging indicator is generated more frequently than the WLAN beacon.

Power conservation is an important criterion in system detection and selection design. Conservation of power on mobile devices is highly desirable to extend the device operating time to the time during which the battery is recharged. If the MS300 decides to scan for WLAN coverage, it needs to minimize power consumption during such a scan while still monitoring for cellular pages.

The MS300 may decide to scan for WLAN coverage based on one or more factors, such as user command, pre-configured selections, application status (e.g., an ongoing packet data session), WLAN availability advertisement received from the cellular network, and the like. A WLAN protocol defined by IEEE802.11, referred to herein as "802.11," allows the MS300 to scan for WLAN coverage passively or actively. In passive scanning, the MS300 listens for a WLAN beacon transmitted by the AP320 on a WLAN frequency. The WLAN beacon contains the ESSID of AP320, also referred to as ESSID (AP 320). If the ESSID (AP 320) matches an ESSID stored in the MS300 ESID list 302, this indicates that the MS300 has detected WLAN coverage, and this coverage information is provided by the MS300 service provider. In active scanning, the MS300 sends a probe request (ProbeRequest) containing the ESSID of the MS 300. If the AP320 receives the Probe request and the ESSID of the MS300 matches the ESSID of the AP320, the AP320 sends a Probe Response (Probe Response) to the MS 300. If the MS includes a list of multiple ESSIDs, the MS may transmit a Probe request containing the ESSID with the highest preference. The ESSID selection may be stored as a system selection parameter in a selection database (as described above).

To conserve power, the sleep mode of the MS300 needs to be maximized. In other words, it is desirable to maximize the time that the MS300 uses reduced power or is in a sleep mode. Furthermore, as a result of such maximization, it is desirable to minimize the MS's wake-up time, or full power operation time. Thus, when the MS300 wakes periodically, such as checking for paging or WLAN beacons, the MS300 should monitor for the cellular paging indicator while scanning for any WLAN beacon. If the paging cycle and the beacon cycle are not synchronized, the MS300 wakes up according to the paging cycle to monitor the paging indicator. In this case, the MS300 uses active scanning to scan for WLAN beacons when the MS300 wakes. If the paging cycle and beacon cycle are synchronized, the MS wakes up periodically to monitor the paging indicator and passively listen for any WLAN beacon. Synchronizing paging and beacon periods provides more power efficient operation because passive searching is used; however, this synchronization requires the AP320 clock to be synchronized with the timing of the cellular network.

One way to synchronize the paging cycle with the WLAN beacon cycle is to schedule the WLAN beacon to arrive at the same time as the first paging indicator in the quick paging channel. According to this method, each MS is scheduled to wake up just before the scheduled WLAN beacon arrival time. Note that because of the potential for collisions, the WLAN beacon may not be transmitted at the scheduled time; thus, there is no guarantee that a given WLAN beacon will arrive at a scheduled or expected time. The WLAN beacon is transmitted as a data frame and thus follows the same rules of accessing the shared medium as other transmissions. Some MSs may need to stay awake longer after receiving the WLAN beacon in order to scan for the paging indicator. In addition, this method requires clock synchronization for generating the WLAN beacon and the cellular network paging indicator. Such synchronization is not always possible or available.

After the MS300 detects WLAN coverage, and receives the WLAN beacon, the MS300 switches the packet data session from the cellular network to the WLAN using certain criteria. These criteria may include whether the MS in the cellular network is idle (i.e., no dedicated channel) or whether the WLAN signal strength is stable, etc. The MS300 may wait for pending packet data sessions in the cellular network until it stops. The MS300 d then performs a packet data session handoff (i.e., sends a mobile IP registration over the WLAN). This may be helpful to minimize service disruption. Similarly, the MS300 may perform a packet data session handoff when the WLAN signal strength is greater than an acceptable threshold for a particular time period. In this way, the MS300 can ensure that access to the WLAN is maintained. This metric may be any metric of channel quality and/or signal strength. The threshold may be predetermined or may be dynamically adjusted based on the actual performance of the communication. This helps to avoid any ping-pong effect whereby the MS300 hands off between WLAN access and cellular network access due to changing conditions or signal strength at the margin of operational margin. Further, upon detecting a WLAN, the MS300 may notify the user and wait for the user to manually select a WLAN.

Another consideration is to minimize power consumption when the MS300 monitors cellular pages while receiving data over the WLAN. After the MS300 hands off the packet data session to the WLAN, the MS300 may receive data via the WLAN and may also accept incoming circuit-switched voice calls via the cellular network. The MS300 relies on the cellular sleep mode to conserve power when monitoring for cellular pages. The 802.11 protocol is similar for the method by which the MS300 conserves power while waiting for incoming data. If the cdma2000 quick paging channel, or other similar mechanism, is supported, the MS300 may further conserve power by synchronizing the cellular sleep mode with the 802.11 power-saving mode.

According to the 802.11 power saving mode, the MS300 sends an Association Request (AR) to the AP320, where the AR indicates a number (e.g., N) of beacon periods during which the MS300 will be in the power saving mode. The AP320 keeps track of a list of MSs that have initiated the power save mode. When the MS300 is in the power save mode, the AP320 buffers frames destined for the MS 300. AP320 periodically transmits a beacon containing a Traffic Indication Map (TIM) (not shown) indicating whether each MS has buffered frames within AP 320. The MS300 wakes up every N beacon periods to monitor the beacon and the included TIM. If the TIM indicates that the MS300 has a pending frame, the MS300 sends a Power-Save Poll (Power-Save Poll) to the AP320, to which the AP320 responds by sending a frame of data to the MS 300. This frame will include a control field where the control bit indicates whether there are more buffered frames for the MS 300. If the control bit is set, the MS300 needs to send another power saving registration information to the AP 320. If the control bit is cleared, there are no pending frames for the MS 300.

When the 802.11 power save mode is synchronized with the cellular sleep mode, the MS300 may receive more power savings. In this way, the MS wakes up periodically to monitor for beacons (the included TIM) and to monitor for cellular paging indicators. Synchronization is achieved by synchronizing the AP320 clock to the cellular timing, where the cellular paging interval and the WLAN beacon interval are immediately preceded (lock-step). For example, when the WLAN beacon interval is equal to the cellular paging interval, the beacon may be scheduled to arrive at the same time as the first paging indicator in the cellular system, such as is performed on the cdma2000 quick paging channel. Each MS wakes up before the beacon arrives. Some MSs may need to stay a long time (e.g., 40MS after the WLAN beacon arrives) to receive the paging indicator.

For systems without the cdma2000 quick paging channel, the beacon period and paging period are typically not synchronized, i.e., the time difference between the WLAN beacon and the cellular paging slot may vary from MS to MS. If the time difference is small, the MS can wake up to monitor the beacon and its paging slot before going back to sleep mode. If the time difference is large, this procedure may not be power efficient for every MS to wake up and stay awake to monitor the WLAN beacon and paging slot. Note that each MS may have a designated paging slot, and thus, the differential time required to receive the WLAN beacon and the paging indicator may not be the same for each MS and will typically be different.

Fig. 7 illustrates a process 350 that may be applied to the MS 300. The MS300 first wakes for a cellular paging indicator (step 354). The MS300 may schedule it to wake up to coincide with the common time of the first paging indicator slot and the WLAN beacon, or may use some other criteria to determine when to wake up. The MS300 determines (decision diamond 356) whether to perform an active WLAN scan or a passive WLAN scan. For active scanning, the MS300 sends a WLAN beacon request (step 358), and then continues to scan for WLAN beacons (step 360). In this way, the MS300 avoids additional power consumption while waiting for the next scheduled WLAN beacon transmission. For passive scanning, the MS scans for WLAN beacons (step 360) until a beacon is detected.

Fig. 8 illustrates communication flows within a network 500, including cellular communications and Internet Protocol (IP) communications. The internet 502 is connected to a Home Agent (HA)516 associated with the MS 508. The internet is further connected to a File Transfer Protocol (FTP) server 514, an access router 510, and a Packet Data Serving Node (PDSN) 504. The access router 510 communicates with the AP 512 over a wireless interface. The interface between the access router 510 and the AP 512 is a WLAN interface, wherein the access router 510 and the AP 512 are part of a WLAN. When the MS 508 is set up to communicate with the AP 512, the MS 508 accesses the WLAN through the wireless interface and the AP 512. For cellular communication, the MS 508 communicates with the BS 506 over the air. The BS 506 is configured for communication with the PDSN 504 via an interface identified as cdma 2000. Such an interface may be compliant with another cellular protocol.

Note that the wireless device may include multiple tuners, each of which is adapted to communicate with a different access medium, such as WLAN and cellular networks. Alternatively, a wireless device may be connected to another wireless device, where each device includes a tuner, resulting in a combination with multiple tuners. In one such configuration, a laptop (computing device) operates in conjunction with a cellular handset. The laptop includes a WLAN card or built-in WLAN port, while the handset supports cellular communication. WLAN information (e.g., ESSID) is provided to the laptop for scanning for WLAN coverage.

Fig. 9 shows the signal and message flow in this configuration. As shown, a laptop 600 is connected to an MS 602 for communication. The laptop 600 has a tuner that is currently used to communicate with a cellular network 606, such as a cdma2000 network.

In the configuration shown in FIG. 9, the laptop 600 is currently processing a packet data session with the cellular network 606 through the MS 602. During the packet data session, when the MS 602 receives a WLAN availability notification from the cellular network 606, the MS 602 may notify the laptop 600 via a signaling protocol defined between the MS 602 and the laptop. Upon receiving such a notification, the laptop 600 may choose to scan for WLAN coverage. The laptop 600 may then perform system selection based on WLAN signal strength and obtain WLAN signals from the AP 604. The laptop 600 and AP 604 then authenticate the connection. Once authentication is complete, the laptop 600 disconnects from the cellular network through the MS 602. Then MS

602 disconnects the packet data session with the cellular network 606. In this regard, a packet data session is conducted between the laptop 600 and the AP 604.

As detailed in the example given above and with reference to fig. 9, when the laptop 600 has an ongoing packet data session with the cellular network 606, the laptop may detect a strong WLAN signal through the inherent tuner. The laptop 600 may choose to switch to WLAN access immediately. After WLAN detection, the laptop 600 needs to authenticate WLAN access. This secret information is stored in the handset's User Interface Module (UIM) (not shown), which may or may not be removable, for individual subscription/authentication of WLAN and cdma 2000. Thus, signaling messages are required between the laptop 600 and the MS 602 to perform WLAN access authentication. If the WLAN access authentication is successful, the laptop 600 performs Mobile IP registration via the WLAN (i.e., via the AP 604). If the mobile IP registration is successful, the laptop 600 sends a message (e.g., AT command) to the MS 602 to release the packet data session. The MS 602 may identify the data session through a Service Option (SO), such as SO 33 in cdma 2000. The laptop 600 may then maintain the packet data session through the cellular network until the handoff of the packet data session to the WLAN is completed.

Alternatively, if the packet data session does not currently have data to transfer, the laptop may switch to the WLAN in order to minimize service (e.g., file download) disruption. Upon detecting a strong WLAN signal, the laptop 600 waits for a given period of time (e.g., a few seconds) to detect any activity of the data transfer. If no activity is detected, the laptop 600 performs WLAN access authentication, followed by mobile IP registration through the WLAN, and finally releases the cellular packet data service option, as described above.

When the laptop 600 is accessing the WLAN and the signal strength degrades below an acceptable threshold, the laptop 600 may trigger the MS 602 to initiate a packet data service option. The trigger may be a direct signaling message (e.g., an AT command) or a mobile IP registration message, etc., where the laptop 600 wants to send a message over a cellular network. If the mobile IP registration is successful, the laptop 600 continues the packet data session through the cellular network. To avoid the ping-pong effect between the WLAN and the cellular network, a hysteresis mechanism may be used, for example, to switch to the WLAN only after a certain period of time when the WLAN signal remains above a certain threshold. The laptop may be automatically switched between the WLAN and the cellular network (e.g., operation is readily apparent to the user) or manually triggered by the user.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The various illustrative logical blocks, modules, and circuits described in connection with the embodiments disclosed herein may be implemented or performed with a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may be integrated in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (7)

1. A method for a mobile station, comprising:

receiving a Wireless Local Area Network (WLAN) notification; and

searching for the WLAN in response to the WLAN advertisement;

wherein receiving the WLAN advertisement comprises:

receiving a WLAN advertisement including at least one Extended Service Set Identifier (ESSID), each said ESSID corresponding to a WLAN;

comparing the at least one ESSID to a list of ESSIDs stored in the mobile station; and

searching for the WLAN in response to an ESSID in the ESSID list matching the at least one ESSID in the WLAN advertisement.

2. The method of claim 1, further comprising:

automatically initiate a WLAN scan in response to receiving the WLAN advertisement.

3. The method of claim 1, wherein receiving the WLAN advertisement comprises:

receiving a WLAN advertisement including location information of an Access Point (AP) supporting the WLAN;

comparing the location information with a current location of the mobile station; and

searching for the WLAN if the current location of the mobile station is proximate to the AP.

4. The method of claim 3, wherein the location information comprises a latitude and longitude of the AP.

5. The method of claim 3, further comprising:

displaying the location information of the AP on the mobile station.

6. The method of claim 5, further comprising:

initiating a WLAN search in response to displaying the location information.

7. An apparatus for a mobile station, comprising:

means for receiving a Wireless Local Area Network (WLAN) notification; and

means for searching for the WLAN in response to the WLAN advertisement;

wherein the means for receiving a Wireless Local Area Network (WLAN) notification comprises:

means for receiving a WLAN advertisement including at least one extended service set identifier, ESSID, each said ESSID corresponding to a WLAN;

means for comparing the at least one ESSID to a list of ESSIDs stored in the mobile station; and

means for searching for the WLAN in response to an ESSID in the ESSID list matching the at least one ESSID in the WLAN advertisement.