HK1089038B - Multi-access call setup - Google Patents

Description

Multiple access call setup

Technical Field

The present invention relates generally to multiple access communication systems, and more particularly to mobile terminal call setup in such systems.

Background

In the development of mobile communication systems, different radio access technologies have been developed. In recent years, it has been recognized that multiple parallel systems can be utilized by the same mobile terminal. Therefore, solutions have been developed to connect networks employing different access technologies to allow users to switch between different access modes.

A mobile communication system comprising a plurality of radio access networks employing different radio access technologies is referred to as a multiple access communication system in the present disclosure. It is assumed that a user can move between different access networks using different access technologies and that the user should always be connected to an access network defined by some criteria that is considered "optimal".

Some types of applications require that the party can reach the user, such as a telephony application, a video technology application or an instant messaging application, where the user should be able to receive incoming calls. These applications place some specific requirements on the multiple access system. First, a mechanism is needed to determine which access networks a user may find. Secondly, resources are consumed to remain reachable within the access network: user battery and access network capacity.

The possibility to utilize multiple access technologies and to select the best one depending on current needs, circumstances etc. is a hot topic discussed in various publications today. Most of the published material on multiple access communication systems focuses on how to maintain and move sessions when switching between different access types. Typical examples of such handover and mobility publications can be found in published U.S. patent applications US20020147008a1 and US2002/0160785a 1.

In order to save battery of the user equipment, it is possible to let the user equipment be reachable by only one access network at a time, even if there are other access networks. In many multiple access communication systems, user equipment is accessed through the unique access network even though another technique is better suited for handling the call. The setup procedure needs to be run before switching to the better access technology. The disadvantages of this approach are: significant delay may be incurred before a more suitable access technology can be used.

For example, the setup procedure in the cellular access network must at least include paging from the network, the terminal answering on a random access channel and sending some signaling between the two, in order to establish a communication channel to carry the call and subsequent signaling. Only after these steps is it possible to perform the signalling required for switching another access type. The specific operation process differs between the various cellular technologies, but the main principle is the same.

In published US patent application US2002/0090975a1 a multiple access communication system is disclosed comprising two cellular access networks, namely UMTS and GSM. Since the two access networks are coordinated by the same MSC, the MSC has inherent information about the coverage of the two access networks. When a request for a call or other type of communication session is received, paging is performed in one of the two access networks. The page contains a request to switch access networks if the requested communication session is of a type that is more suitable for handling by other access networks. The call setup is done directly in the most suitable access network. This ensures that the call is not rejected for establishment on an access network that cannot support the call. The request for switching access networks is based on intrinsic knowledge about the coverage of the two coordinated access networks.

One problem with the system disclosed in US2002/0090975a1 is that it is limited to a system in which two or more cellular access networks are supported by a common control.

Disclosure of Invention

A problem with many prior art multiple access communication systems is that: it is generally inefficient to maintain the resources reachable by a terminal in more than one access network at the same time. Another problem with prior art multiple access communication systems is that the delay in performing call setup in any preferred access network is generally too long.

It is therefore an object of the present invention to provide a multiple access communication system that supports call setup in any reachable access network in a manner that is not only fast but also resource efficient.

The above object is achieved by a method and a device according to the appended patent claims. In general, a terminal is kept reachable through a first access network, which is the most resource efficient one of the available access networks for keeping the terminal reachable. The terminal passively scans for the presence of available base stations of other access networks of the system and reports data relating to the presence to the first access network. The passive scanning is resource efficient and may be performed continuously or intermittently according to a predetermined scheme or according to instructions from the first access network. Performing paging in the first access network when a call request to a terminal is received. The paging message contains information about the preferred access network based on the reported data of the presence of available base stations or access points of other access networks. The terminal connects to the preferred access network and performs call setup directly in the preferred access network.

The present invention is advantageous in that the resource efficiency required to keep the terminal reachable is kept at an optimal level by utilizing the most efficient access network selected. Another advantage is that call setup to the terminal can be performed in the preferred access network without any unnecessary delay. Yet another advantage is reduced signaling during interaction and during actual call setup.

Drawings

The invention, together with further objects and advantages thereof, may best be understood by reference to the following drawings and the accompanying description.

Fig. 1 is a block diagram of an embodiment of a multiple access communication system according to the present invention;

fig. 2a is a schematic block diagram of the multiple access communication system of fig. 1 in standby mode;

fig. 2b is a block diagram of the multiple access communication system of fig. 1 during a paging procedure;

fig. 2c is a block diagram of the multiple access communication system of fig. 1 during a call setup procedure;

fig. 2d is a block diagram of the multiple access communication system according to fig. 1 during an ongoing call;

fig. 3a is a block diagram of a multiple access communication system according to fig. 1 during WCDMA call setup;

fig. 3b is a block diagram of the multiple access communication system according to fig. 1 during an ongoing WCDMA call;

fig. 4 is an embodiment of a call setup sequence including scanning for WLAN beacons, in accordance with the present invention; and

FIG. 5 is a flow chart of an embodiment of a method according to the present invention;

Detailed Description

The present invention is based on three main bases. The first basis is to achieve reachability of all access networks through only the most resource efficient one of them, thereby providing more resource efficient reachability. The second basis is to make information about the availability of other access networks available through a single associated connection. The terminal thus performs passive scanning for any base stations of other access networks and reports the results. The third basis is the idea of using the neighbor access network information to request a change of access network during the paging phase of the call setup.

For ease of discussion, a model multiple access communication system is employed. It should be noted, however, that the scope of protection of the present patent should not be limited thereto, as this model system is only taken as an example.

Fig. 1 schematically shows a model multiple access communication system 1. The model multiple access communication system 1 comprises two radio access networks: a WCDMA access network 10 and a WLAN access network 20. The access networks 10 and 20 are interconnected by a re-routing means 8 handling the relationship between them. The two access networks 10 and 20 are basically uncoordinated, i.e. in terms of coverage area, resources, etc., except for the rerouting means 8. The re-routing means 8 are connected to the external communication system via a connection 5.

The WCDMA access network 10 includes several base stations 14 (only two shown). Each base station 14 is associated with at least one cell. The base stations 14 are connected by means of different types of control devices 12, and the base stations 14 communicate with the re-routing means 8 via these control devices 12.

The WLAN access network 20 comprises several Access Points (APs) 24, which are interconnected by means of the control device 22, the APs 24 being in contact with the re-routing means 8 via the control device 22.

The actual access network is not described much since it is only important to the invention in a few respects. The rest of the access network operates according to principles known to those skilled in the art.

A terminal 30 supporting communication through the WLAN 20 and the WCDMA 10 access network exists within an area covered by the WCDMA access network 10. During periods of inactivity, the terminal 30 is associated with one cell of the base station 14 of the WCDMA access network 10. This is indicated by the dashed line 16. The terminal 30 monitors the cellular network by monitoring the paging channel of the network.

The AP24 of the WLAN access network 20 sends out a beacon signal 26 which preferably contains an identifier of the WLAN network. One possibility is to employ Service Set Identification (SSID). The terminal 30 is not associated with the WLAN 20 but is able to detect the SSID and the signal strength of the beacon 26 carrying the SSID. Thus, the WLAN 20 is not aware of the presence of the terminal 30, but the terminal 30 is aware of the presence of the WLAN 20.

Fig. 2a shows a situation where the terminal 30 is associated with the WCDMA network 10 but only listens to the WLAN network 20. As described above, the WLAN AP24 transmits the beacon signal 24 including the SSID. The terminal 30 has a passive scanner 32 that performs intermittent scanning for beacons. The passive scanner 32 is adapted to read the SSID of the beacon signal 26. In addition, the passive scanner 32 is adapted to detect the signal strength of the beacon signal 26. The reporting means 34 is connected to the passive scanner 32 and forms an alternative access network report message 36 based on the results obtained by the passive scanner 32 to the base station 14 of the WCDMA network 10. An alternative access network report message 36 is transmitted to the base station 14 which preferably contains data about the SSID and signal strength. The base station 14 receives the alternative access network report message in the paging data means 18. The data is evaluated and the current presence information of any alternative access networks is stored.

Reporting from the terminal 30 to the paging data device 18 may be done continuously or intermittently, such as when any significant state change occurs. The paging data means 18 therefore has up-to-date information about the current terminal 30 condition. The terminal 30 is reachable through the WCDMA network 10, and the WCDMA network 10 is resource efficient in terms of the task of keeping the terminal reachable. The WLAN network 20 is currently unaware of the presence of the terminal 30. As discussed further below, call setup time may be greatly reduced if the terminal 30 passively continuously or intermittently scans for WLAN 20 cells even though the terminal 30 is only registered in the cellular network 10 and is not associated with any WLAN AP 24.

Cellular standards include mechanisms for reaching users that are very efficient in conserving terminal battery, radio resources, and network resources. Paging is a basic function that minimizes the time required for a terminal to monitor the network to be able to receive traffic. Moreover, paging eliminates the need for the terminal to update the network at each cell change even during inactivity. This makes it possible for the cellular terminal to remain up to several days before the battery needs to be recharged. Furthermore, paging mechanisms in cellular systems are designed for fast, upper-bound response times.

However, for e.g. WLAN (broadband local area network) technology, there is only basic support for mobility. There is no particular mechanism by which a user can remain reachable at all times without actively communicating while moving between different cells. To remain reachable, the terminal needs to initiate a reassociation procedure, including some signaling transmitted between the terminal and the WLAN Access Point (AP), each time the terminal moves to a new WLAN cell.

Since some access technologies are more resource demanding than others, it is a resource efficient strategy to stay reachable by the most suitable access means. Thus, one simple solution to the inefficiency problem of remaining reachable in a WLAN system is to only remain reachable through cellular access.

In fig. 2b, an incoming call to a terminal 30 enters the communication system 1 via the external connection 5. Since the WCDMA network 10 is an access network for keeping the terminal 30 reachable, a paging procedure is initiated in the WCDMA network 10. The paging message is prepared based on the characteristics of the incoming call and the saved data about the current availability of the alternative access network. The call requirements, e.g. a data rate as high as possible or a certain guaranteed QoS (quality of service), are matched to the stored data of the available access networks. Since the terminal reports measurements on WLAN cells over the cellular access, the network has valuable information whether the terminal is located within the WLAN coverage area. In this way, a preferred access network may be determined. Information about such preferred access networks, such as an "access reselection indicator" information element or a paging cause value, is preferably included in the paging message. The paging message 19 is sent and received by the terminal 30.

Upon receiving the paging message, the terminal is ready to immediately start performing association with the WLAN network 20. The terminal 30 has previous passive scanning results available or it starts to search for a suitable WLAN cell. The terminal may then associate itself with the WLAN AP according to normal routines. This stage is shown in figure 2 c. The call set-up means 28 in the WLAN AP24 communicates with the WLAN call set-up means 38 of the terminal 30 via call set-up messages 36.

The cellular access setup procedure may be avoided by indicating in a paging message on the cellular access that the user should perform WLAN access. Thus the setup procedure is left to be performed only for paging (i.e. procedure start-up) and subsequent steps are dispensed with. This process is facilitated by, for example, a specific paging cause value or a specific information element. The operator may set the paging cause value to "perform WLAN access", e.g. when paging the user for an incoming call that is best suited to be handled by the WLAN. This is based on the operator knowing that the user is within the WLAN coverage area. Upon receiving the paging message, the user equipment may immediately start to search for WLAN cells and associate itself with a certain WLAN AP. Whereby the call can be routed to the correct wlan ap.

The terminal 30 may reply to the paging message by receiving an acknowledgement message 39. The receipt acknowledgement message 39, which is a reply to the "reselection" paging message, indicates to the base station 14 that the paging message has been received and is attempting to establish contact with another access network. If no contact can be established with the WLAN AP24, the base station 14 should be notified and the call should be received over WCDMA instead.

The terminal can maintain the idle mode in WCDMA even though the actual call is transferred to WLAN.

Passive scanning of alternative access networks is the gist of the present invention. The time for the whole call setup is reduced by using the principle of passively scanning alternative access network beacons and reporting them through the access network in which the terminal is reachable. The terminal is prepared to immediately associate itself with another access network, with available scanning results before receiving the page. Furthermore, since the scanning result is also communicated to the access network in which the terminal is reachable, the paging message may even be adapted accordingly.

It is also possible to save terminal battery and radio interface and network hardware resources of any alternative access network if the scanning is performed passively, i.e. without establishing a connection or association with any alternative access network base station. The passive scanning may be performed continuously, periodically and/or after receiving the instruction/recommendation over the first access network. The network may use the terminal location information, e.g. by GPS measurements, in combination with coverage maps of alternative access networks to determine when the terminal should be instructed/advised to initiate scanning for beacons. Another way for the network to determine whether the terminal is likely to be located in the coverage area of the alternative access network is to make use of knowledge about the coverage of the alternative access network in relation to the current area (cell or set of cells) in the currently used access system in which the terminal is to be paged.

As mentioned above, if the terminal reports the measurement result of the alternative access network beacon signal by the current access mode, the network will get more accurate information about whether the terminal is in the coverage of the alternative access network related to the current access.

Fig. 2d shows the situation when the WLAN call setup procedure is completed. The call is connected from the external connection 5 to the terminal 30 via the WLAN access network 20.

When the call is ended, the situation of fig. 2a is preferably restored. The terminal 30 is disconnected from the WLAN access network.

Fig. 4 shows an exemplary execution sequence illustrating a process with a cellular access network and a WLAN access network. The execution sequence begins with the terminal scanning for a WLAN beacon 101, which is a signal being broadcast from the WLAN. These measurements are reported 102 over the cellular access. The measurement report 102 may contain the signal strength of the detected beacon and an identifier of the detected WLAN network. One possibility is to use the SSID carried by the WLAN beacon as an identifier. The transmission of the beacon signal is performed in a continuous or intermittent manner, as indicated by arrow 109. Also, the measurements on the terminal are made in a continuous or intermittent manner, as indicated by arrow 110. The report 102 is preferably sent when a change occurs. Next, the cellular network receives the calling party's request for an incoming call 103 and determines that the call is well suited for delivery over the WLAN. Since the WCDMA access network has recently received a measurement report from the terminal indicating that it is within the WLAN coverage, the cellular network decides 104 to attempt to perform an incoming call in the WLAN. The cellular network pages 105 the terminal with a paging cause value indicating that the terminal should attempt to access the WLAN. The terminal initiates an association procedure 106 with the WLAN AP, i.e. establishes a connection between the terminal and the WLAN AP. The call is rerouted to WLAN AP 107 via existing technologies like mobile IP to complete the call setup. The call is then placed over WLAN 108.

Alternatively, the process may be represented as a flow chart as shown in fig. 5. The process starts at step 200. In step 202, the terminal associates with the first access network, which is resource efficient in terms of reachability. In step 204, a passive scan for the presence of alternative access networks is preferably performed in an intermittent manner. At step 206, the scan results are reported back in the first access network. When an incoming call arrives for a terminal, the terminal is paged in the first access network, the paging message containing information about the preferred access network. At step 210, the call is established according to the preferred access network information. The process ends at step 212.

Now consider the case where the passive scanning of the terminal 30 indicates that no alternative access networks are available and reports this to the WCDMA access network (as shown in fig. 2 a). When an incoming call occurs, the paging device processes the available information and concludes that the preferred access network is WCDMA. Likewise, if WCDMA access is the preferred option for the incoming call anyway, WCDMA is selected as the preferred access network regardless of whether there is an available WLAN. At this point a paging message 19 associated with the incoming call is sent and the paging message 19 is received by the terminal 30. However, this paging message does not contain any request to change access networks. The call is set up by the call set-up means 13 of the base station 14 and the WCDMA call set-up means 35 in the terminal 30 by means of standard call set-up signalling 15. This is shown in figure 3 a. The call is finally connected from the external connection 5 to the terminal 30 via the WCDMA access network 10 as shown in fig. 3 b.

The invention is easily implemented in today's general cellular networks. For WCDMA access networks, paging for mobile terminal call setup is described in detail in the standard. In particular, for user equipments in idle mode or in RRC connected mode CELL _ PCH or URA _ PCH state, the operation upon reception of paging messages is well described in the standard specifications. The message content is also described in detail. The main features are as follows.

When the UE is in idle mode or in RRC connected mode CELL _ PCH or URA _ PCH state, it listens to the Paging Control Channel (PCCH), which transmits paging messages. Associated with the paging channel is a Paging Indicator Channel (PICH) which transmits a short burst informing the UE that there is information on the PCCH to read. For a particular UE, the bursts are only sent at a certain time, with a certain periodicity called paging occasions. This allows the UE to turn off its radio receiver- "discontinuous reception" in the time between paging occasions. This paging mechanism saves a lot of battery power on the mobile terminal and significantly extends the battery life of the UE in "standby mode".

When the UE receives the paging message, it will decode the message and look for all paging records. Each paging record carries a specific UE identity and a paging cause value. Several paging records may be included in the same paging message in order to page multiple UEs with the same message. For each paging record, the UE compares the contained UE identity with the UE's own identity. If there is a match, the UE then reads the paging cause of the paging record and uses that cause to learn why the network paged the UE. Examples of paging cause values are "terminate session call", "terminate streaming call", "terminate background call", etc., which indicate the QoS class of the service that the network is attempting to establish with the paging message.

The paging cause value is delivered to an upper layer in the UE. In response to the paging indication with the cause value, an upper layer in the UE transmits a paging response message/service request message. The message is looped back to the network and core network node that is attempting to establish the call.

If the UE was originally in RRC idle mode, i.e. not in CELL _ PCH or URA _ PCH state, the response message to the core network node needs to be sent over the air interface before a signalling connection is established and thus transmitted back to the core network node. This is done through the RRC connection establishment procedure.

Very limited changes to these standard procedures are required to implement the present invention. These changes will be summarized below.

A new information element needs to be added to the paging message. This may be a new paging cause value or a different information element. This information element may be an indicator indicating, for example, "reselect to another access". Or it may be a special access indication such as "reselect to WLAN".

In the above access information, a direct reference to the preferred access network is transmitted by means of a paging message. Another possibility is to instead transmit other types of data that can be processed by the UE to determine a preferred access network. A typical example is to convey the quality of service (QoS) requirements for a call to be established. Such QoS requirements may be included in the paging message. Based on this information, the UE may utilize knowledge about the characteristics of the possible different access networks to determine the preferred access network. These knowledge are preferably stored in a memory means within the UE and may contain data indicating, for example, the maximum data rate or allowed delay for each particular access network. Subsequent communications may then be conducted utilizing the selected access network. The page response may also be transmitted through the network that sent the page message or the newly selected network.

The action to be taken by the UE upon reception of this new cell needs to be added to the current standard specification. These operations should be the UE scanning for alternative access systems. If an alternative access system is found, a connection to the alternative access system is established and the connection with the current access is released. Further, the UE will remain associated with the new access system for time T and wait for incoming data related to the call initiated by the paging message. The time T may be a separate parameter in the paging message or may be set to a certain value according to any specification.

The paging concept in GSM is very similar to that of WCDMA. The MS employs discontinuous reception to conserve battery power and listen for paging messages based on the time they can be sent.

In GSM, paging messages are transmitted on paging subchannels on the PCCCH or CCCH. As in WCDMA, the paging message contains the mobile identity of the MS being paged. In addition, the paging message also contains "paging mode" and "required channel (channel)". These two information elements describe how the MS should handle the page and which channel the MS should use for the response message.

The above embodiments have described solutions for combining WLAN access technology and cellular radio access technology. The cellular radio access technology can be almost any, such as WCDMA, GSM/GPRS or CDMA 2000. However, it is also possible to employ multiple access communication systems with access networks operating according to other technologies in accordance with the present invention. For example, WPAN (wireless personal area network) solutions are also potentially very interesting objects. The solution according to the invention can be applied in more general cases where multiple radio access technologies (not necessarily WLAN and/or cellular) are combined and these technologies differ in terms of resource efficiency.

It will be understood by those skilled in the art that various modifications and changes may be made to the present invention without departure from the scope thereof, which is defined by the appended claims.

Claims (18)

1. Method for performing call setup in a multiple access communication system (1), comprising the steps of:

paging a mobile terminal (30) through a first access network (10);

the page includes access information;

the access information allowing a determination of a preferred access network among at least the first access network (10) and a second access network (20) to which the mobile terminal (30) is connectable; and

establishing a call according to the access information;

the method is characterized in that: also comprises the following steps:

passively scanning, in the mobile terminal (30), for the presence of an available access point (24) of the second access network (20);

the second access network (20) having a lower resource efficiency than the first access network (10) in terms of keeping mobile terminals (30) reachable; and

reporting data relating to said presence from said mobile terminal (30) to said first access network (10);

whereby said access information is based on said data relating to said presence.

2. The method of claim 1, wherein: the first access network (10) is a cellular network and the second access network (20) is a non-cellular network.

3. The method of claim 2, wherein: the second access network (20) is selected from the group consisting of: WLAN and WPAN.

4. A method according to claim 2 or 3, characterized by: the first access network (10) is selected from the group consisting of: GSM, GPRS, WCDMA and CDMA 2000.

5. The method of any of claims 1 to 3, wherein: the access information contains a direct reference to the preferred access network.

6. The method of any of claims 1 to 3, wherein: the access information contains quality of service requirements of the call to be established, whereby the method further comprises the step of determining the preferred access network based on the quality of service requirements and predetermined knowledge about the characteristics of at least the first access network and the second access network.

7. The method of any of claims 1 to 3, wherein: said step of establishing a call comprises the steps of:

associating the mobile terminal (30) with the second access network (20) in response to access information indicating that the second access network (20) is a preferred access network,

whereby said establishing step is performed directly with said second access network (20).

8. The method of any of claims 1 to 3, wherein:

the passive scanning step further comprises the steps of:

identifying a base station (24) transmitting the beacon signal; and

measuring a signal strength of the beacon signal.

9. Mobile terminal (30) connectable to a multiple access communication system (1), the mobile terminal (30) being reachable through a first access network (10) of the multiple access communication system (1), the mobile terminal (30) comprising:

means for receiving a paging message from the first access network (10);

the paging message contains access information;

the access information allows determining a preferred access network among at least the first access network (10) and a second access network (20) of the multiple access communication system (1); and

means for establishing a call according to the access information;

characterized in that, the mobile terminal further comprises:

means for passively scanning for any presence of an available access point (24) of the second access network (20) of the multiple access system (1);

the second access network (20) having a lower resource efficiency than the first access network (10) in terms of keeping the mobile terminal (30) reachable; and

means for reporting data relating to said presence from said mobile terminal (30) to said first access network (10);

whereby said access information is based on said data relating to said presence.

10. The mobile terminal (30) of claim 9, wherein: the first access network (10) is a cellular network and the second access network (20) is a non-cellular network.

11. The mobile terminal (30) of claim 10, wherein: the second access network (20) is selected from the group consisting of: WLAN and WPAN.

12. The mobile terminal (30) of claim 10, wherein: the first access network (10) is selected from the group consisting of: GSM, GPRS, WCDMA and CDMA 2000.

13. The mobile terminal (30) of any of claims 9-12, wherein: said access information contains the quality of service requirements of the call to be established, whereby said mobile terminal (30) further comprises storage means for storing data about the characteristics of at least said first access network and said second access network and means for determining said preferred access network to connect to said storage means and said means for receiving paging messages.

14. A node of a first access network of a multiple access communication system (1), comprising:

means for paging a mobile terminal (30);

the means for paging is adapted to provide access information;

the access information allows determining a preferred access network among at least the first (10) and second (20) access networks of the multiple access communication system (1) to which the mobile terminal (30) is connectable;

characterized in that the node further comprises:

means for receiving data from the mobile terminal (30) relating to any presence of an available access point (24) of the second access network (20); the means for receiving data is connected to the means for paging;

the second access network (20) having a lower resource efficiency than the first access network (10) in terms of keeping mobile terminals (30) reachable; and

whereby said means for paging is further adapted to provide access information based on said data relating to said presence.

15. The node of claim 14, wherein: the first access network (10) is a cellular network.

16. The node of claim 15, wherein: the first access network (10) is selected from the group consisting of: GSM, GPRS, WCDMA and CDMA 2000.

17. The node according to any of claims 14 to 16, characterized by: the access information contains a direct reference to the preferred access network.

18. The node according to any of claims 14 to 16, characterized by: the access information contains the quality of service requirements of the call to be established.