HK1185210B - Method and device in a telecommunications system - Google Patents

Description

Method and arrangement in a telecommunication system

Technical Field

The present disclosure relates to methods and devices in a telecommunication system, in particular to methods and devices for providing a preferred distribution of idle User Equipments (UEs) between different Radio Access Technologies (RATs), and further to methods and devices for providing information to RATs in order to obtain a preferred distribution.

Background

Mobile Circuit Switched (CS) services based on global system for mobile communications (GSM) and Wideband Code Division Multiple Access (WCDMA) radio access allow telecommunication services to be obtained with a single subscription in almost all countries around the world. Moreover, the number of CS subscribers is still growing rapidly, now facilitated by the deployment of mobile CS services in densely populated countries such as india and china. Furthermore, the typical Mobile Switching Center (MSC) architecture is changed to a so-called soft-switch solution that allows the use of the packet transport infrastructure for mobile CS services.

The third generation partnership project (3GPP) has completed the work item "evolved UTRA and UTRAN" that defines the long term evolution LTE concept to ensure the competitiveness of 3GPP based access technologies. Heretofore, a broad evaluation phase of possible features and techniques in a Radio Access Network (RAN) working group leading to an agreed system concept could satisfy most needs without identifying serious problems in feasibility.

In parallel with RAN standardization, 3GPP also drives System Architecture Evolution (SAE) work items to develop evolved core networks. The SAE core network consists of core nodes further divided into control plane (mobility management entity, MME) and user plane gateway (serving gateway, S-GW and PDN gateway, PDN-GW) nodes according to the ericsson proposal spirit. The resulting network architecture is shown in fig. 1. Thus, fig. 1 depicts nodes and interfaces in an LTE radio network and terminals (UEs) connected thereto.

Common to LTE and SAE is that only the Packet Switched (PS) domain is specified, i.e. all services are to be supported via this domain. However, GSM and WCDMA provide both PS and CS access.

A solution known as "CS Fallback" (Fallback) has been standardized and a phase 2 solution is defined in the 3GPP technical specification TS23.272, and fig. 2 shows the "CS Fallback" architecture. In fig. 2, nodes of a cellular radio network employing a CS fallback solution and related interfaces between the nodes are depicted. These nodes are typically implemented using hardware and software adapted to perform different tasks associated with the respective nodes and also associated with communication means that digitally connect with other nodes using the depicted interfaces.

The main principle of "CS fallback" is that the terminal, i.e. the Mobile Station (MS) or the User Equipment (UE), performs normal SAE Mobility Management (MM) procedures towards the MME while camping on the LTE radio access. The MME registers the terminal in an MSC server (MSC-S) for CS-based services using an SG-interface. When a page for a CS service is received in the MSC-S, the page is forwarded to the terminal via the MME (using the SG interface), and the terminal then performs a fallback to GSM EDGE Radio Access Network (GERAN) or Universal Terrestrial Radio Access Network (UTRAN) and responds to the page via the selected RAN. Similar behavior applies to CS services originating in a terminal (mobile station). When these are triggered and the terminal is camped on an LTE access (evolved UTRAN, E-UTRAN), the terminal performs a fallback to GERAN or UTRAN and triggers the initiation of the CS service there. Different solutions have been discussed for the "fallback" mechanism, such as PS handover and inter-Radio Access Technology (RAT) cell change order (possibly NACC, network assisted cell change).

Fig. 3 shows a case where a mobile station initiates a call in an active mode and when PS Handover (HO) is supported. This is further described in section 6.2 of 3GPP TS23.272 and a specific step is further described in 3GPP TS23.401 and depicted in fig. 4, step 3.

Once the terminal (MS/UE) has completed CS services in the CS domain, the terminal may return to E-UTRAN using existing mechanisms or may remain in 2G or 3G coverage, i.e. provided with radio access via GERAN or UTRAN.

In idle mode, the mobile station typically performs cell reselection using information received in system information from the network. However, the network may decide to change the cell reselection behavior for individual terminals. For example, the system information may be set to favor LTE over WCDMA and GSM, but the network may detect that a particular user is better served in GSM. In such a case, the network may change the cell reselection parameters for the terminal so that the terminal will remain in GSM while in idle mode. However, it is important and advantageous to maintain a preferred distribution of UEs in idle mode between the GSM/WCDMA system and LTE in general.

When a CS connection is to be terminated/released for an E-UTRAN enabled MS/UE connected to a 2G or 3G network, a base station controller/radio network controller (BSC/RNC) may decide whether to:

-sending MS/UE to E-UTRAN using explicit signaling, also known as release in GERAN or Radio Resource Control (RRC) connection release with redirection in UTRAN, or by including "cell selection indicator after TCH and SDCCH release" in channel release (CHANNEL RELEASE);

keeping the UE in the current RAT (e.g. GSM or WCDMA).

Also, US 2010/317347 describes a method designed to improve the reliability of circuit switched fallback.

It is desirable to improve performance in cellular radio networks. In particular, it is desirable to improve performance in deployment scenarios where many radio access technologies, such as GERAN/UTRAN and E-UTRAN, are employed in the same area and fall back to CS is used.

Disclosure of Invention

An aspect of the present disclosure is to provide an improved method and apparatus for maintaining a preferred distribution of idle UEs between GERAN/UTRAN and E-UTRAN.

This is achieved by a method and apparatus as recited in the appended claims.

In some embodiments explicit signalling may be used in the radio access network to decide whether the UE should remain in GERAN/UTRAN (also referred to as 2G/3G) or move back to E-UTRAN in a fast manner taking into account, for example, the fact that: this fact is the fact that the CS call is performed as a result of a native CS fallback (CSFB) procedure, i.e. as a result of a procedure by which the above-mentioned UE moves from E-UTRAN coverage to 2G/3G coverage so that the CS call can be performed.

When making such a decision, knowledge about whether the CS call is executed due to CSFB and whether it is a native CSFB is advantageous. According to some embodiments, the mobile station returns to the E-UTRAN if the call has used the CSFB procedure, but remains in the 2G/3G cell with E-UTRAN coverage if the call is initially established in the 2G/3G cell.

Aspects of the present disclosure also provide methods and arrangements for notifying a base station controller/radio network controller (BSC/RNC) whether a CS call has used a CSFB procedure.

These methods are described in more detail in the detailed description.

Thus, according to some embodiments, a method in a central node of a cellular radio network is provided, the central node being provided, wherein the central node is adapted to decide whether a mobile station connected to the cellular radio network via a first radio access technology controlled by the central node is to move to another radio access technology at the end of a circuit switched call of the mobile station. It is assumed that the cellular radio network is adapted to use a "fall back" to the circuit switched procedure. First, it is decided that a CS call for a specific mobile station has ended. It is then checked whether the CS call is the result of a fallback to CS procedure. The central node then decides whether the mobile station is to move to another radio access technology based at least in part on the determination, i.e., based at least in part on whether the CS call is the result of a CS fallback procedure.

For example, if a mobile station that performed a fall back to a circuit switched procedure makes a circuit switched call, the mobile station may return to the original radio access technology from which the fall back to the circuit switched procedure was performed. According to some embodiments, the original radio access technology may be evolved UTRAN or a similar radio access technology that does not support CS connections.

According to some embodiments, the central node, which may be an RNC or a BSC, may receive information in a message from the mobile switching center as to whether the circuit switched call was caused by a fall back to the circuit switched procedure.

The disclosure also extends to a node such as an RNC or BSC, and also to a mobile switching centre in a cellular radio system configured to perform the method as described above. The node may be provided with controller/controller circuitry for performing the above-described processes. The controller may be implemented using suitable hardware and software. The hardware may include one or more processors that may be arranged to execute software stored in a readable storage medium. The processor may be implemented by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some of which may be shared or distributed. Further, the processor may alternatively include, but is not limited to, Digital Signal Processor (DSP) hardware, ASIC hardware, Read Only Memory (ROM), Random Access Memory (RAM), and/or other storage media.

Drawings

The invention will now be described in more detail, by way of non-limiting example, and with reference to the accompanying drawings, in which:

figure 1 shows an SAE/LTE architecture,

figure 2 illustrates a CS fallback architecture,

figure 3 shows CS fallback-mobile originated call in active mode PS HO,

figure 4 shows a PS HO from E-UTRAN to GERAN preparation phase,

figure 5 is a view of an exemplary radio network,

figure 6 is a diagram of an exemplary mobile station,

figure 7 is a view of an exemplary radio base station,

FIG. 8 is a view of an exemplary central node, an

Figure 9 is a flow chart illustrating some steps performed in the central node.

Detailed Description

In the following description describing some exemplary embodiments, two scenarios are analyzed: a mobile originated Circuit Switched Fall Back (CSFB) call, and a corresponding mobile terminated CSFB call. In connection with these two exemplary scenarios, it is assumed here that CSFB enabled long term evolution/wideband code division multiple access/global system for mobile communications/(LTE/WCDMA/GSM) mobile terminals in idle mode are distributed over a combined GSM/WCDMA/LTE network based on some criteria, e.g. CS center users are kept in GSM while fewer CS center users mainly using Packet Switched (PS) data services are kept in LTE and/or WCDMA. To further simplify the description, the term mobile station will be used to refer to any device connectable to a cellular radio network, such as any user equipment or (mobile) terminal.

In a GSM/WCDMA network, this scenario means that a CS voice call is either a normal mobile station originated/terminated CS language call originating in a GSM/WCDMA radio network or a mobile station originated/terminated CSFB call originating from an LTE or WCDMA radio network. A terminal that has performed a CSFB call is advantageously directed back to the radio network from which the CSFB call originated after the CSFB call has ended if the distribution of mobile stations supporting CSFB remains the same in idle mode.

In order to enable the network to return the mobile station to another radio access technology, the central node in GERAN or UTRAN, i.e. the base station controller/radio network controller (BSC/RNC), needs to have information whether to initiate a voice call using a CSFB procedure.

Mobile originated call:

in this case, when the mobile station originates (MO) CS call, i.e., when the mobile station originates the CS call, the mobile station performs CSFB for the 2G or 3G network (i.e., GERAN or UTRAN network). The mobile station indicates to the Mobile Switching Center (MSC) in a CM service request (CMSERVICE REQUEST) message in 3GPP24.008 that the MO call is due to a CSFB generated by setting a new Information Element (IE), referred to herein as CSMO. As a result, the MSC knows that the call is due to CSFB, however, the message is transparent to the BSC/RNC and thus the nodes remain unknown.

According to some embodiments, new information elements are added on the a and Iu interfaces. According to some embodiments, the new IE may be added to a sub-part of an existing Base Station Subsystem (BSS) management application/radio access network application part (BSSMAP/RANAP) message. For example, the BSC/RNC may receive new information elements from the MSC regarding whether the call is due to CSFB added to existing messages specifying:

for the a interface in 3GPP TS 48.008:

○ assignment request

○ Release order

O common ID

O handover request

For the Iu interface in 3GPP TS 25.413:

○ RAB assignment request

O IU Release Command

O common ID

○ relocation request

Mobile station terminated calls

In this example, assume that the MSC knows that the call is due to a CSFB because the call has triggered the CSFB. Two different scenarios are described.

In the first scenario, the mobile station is already connected to the network in E-UTRAN when paged by the MME. The MSC knows that the mobile station is registered in the SG and can inform the BSC/RNC that the CS call is due to CSFB in the same manner as described above.

In the second scenario, the mobile station has performed a combined tracking area update/location area update (TAU/LAU), however, thereafter the mobile station reselects/moves to 2G/3G coverage. This situation exists if S4-SGSN (serving GPRS support node) is deployed and ISR is supported in the network, which will be discussed further below. Otherwise, moving to 2G/3G will typically trigger RAU (routing area update) and LAU or combined RAU/LAU procedures.

It is assumed that the mobile station moves to the same Location Area (LA) as the registered location area by using the combined TAU/LAU. The mobile station will then perform RAU to obtain its PS service in the 2G/3 GPS network, however the mobile station has not performed a new LAU procedure. The results were:

MSC with active registration associated with MME over SG interface

-MME knows that Mobile station is registered to 2G/3G SGSN

Thus, assuming the mobile station is still in E-UTRAN coverage, the MSC that established the CS call for the mobile station will page the mobile station via the MME.

Assuming the MME knows that the mobile station is now registered with a particular 2G/3G SGSN, it will forward the paging message to the appropriate 2G/3G SGSN. The paging procedure will be completed by the 2G/3G SGSN using existing procedures.

The mobile station may access the MSC, i.e. send a paging response of 3GPP TS44.018 in response to a CS page received via the SGSN, in exactly the same way as it had been paged by the MME.

Thus, the MSC will assume that this is a CSFB call, while the mobile station is under 2G/3G coverage when performing the paging procedure, and therefore the call is not actually a local CSFB. In other words, the procedure is not a procedure by which the mobile station moves from E-UTRAN coverage to 2G/3G coverage so that a CS call can be performed. The information that the mobile station is actually under 2G/3G coverage may be important in the algorithm implemented in the central node BSC/RNC, which decides how the mobile station should be managed at the release of the CS call for the inter-RAT scenario.

Although the above procedure is also acceptable for the case of mobile terminated calls, it is advantageous in some embodiments if the BSC/RNC is configured to distinguish between the cases of circuit switched fallback when the mobile terminates a call: namely, the case where the mobile station is connected via LTE radio access, and the case where the mobile station is connected via 2G/3G radio access.

According to some embodiments, the Gb/Iu _ PS interface is modified in such a way that the BSC/RNC can distinguish between CS paging messages received from the MME via the S3 interface. According to one embodiment, this is achieved by adding e.g. a new information element or a new flag to an existing information element appended to the CS paging message.

In some embodiments, the BSC/RNC then buffers such CS paging messages and stores the included international mobile subscriber identity/temporary mobile subscriber identity (IMSI/TMSI) values to identify the CS call indicated by using the following procedure: this procedure is the same as the procedure proposed above for mobile originated calls, as a CSFB depending on whether the CS call was initiated when the mobile station was under LTE or 2G/3G coverage.

Alternative embodiments will use the following facts: in the case of circuit switched fallback for mobile terminated calls, the MME always sends an SG service request message to the MSC when the mobile experiencing paging is camped on LTE. However, if the mobile station is camped on 2G/3G during a circuit switched fallback for mobile-terminated call procedures, the message is not sent from the MME.

Thus, the MSC may use the receipt of the SG service request message to decide whether the CSFB indication described above for the mobile station originated call should be sent to the BSC/RNC in an assignment request/RAB assignment request.

Exemplary implementation

Although the described solution may be implemented in any suitable type of telecommunications system supporting any suitable communication standard and using any suitable components, specific embodiments of the described solution may be implemented in an LTE network, such as that illustrated in fig. 5.

As shown in fig. 5, an exemplary cellular radio network 11 may include one or more instances of mobile stations 13 and one or more base stations 12 capable of communicating with the mobile stations, as well as any other elements suitable for supporting communication between mobile stations or between a mobile station and another communication device, such as a landline telephone. Although the mobile stations shown may represent communication devices including any suitable combination of hardware and/or software, in particular embodiments, the mobile stations may represent devices such as the exemplary mobile station illustrated in greater detail in fig. 6. Similarly, although the illustrated base stations may represent network nodes that may include any suitable combination of hardware and/or software, in particular embodiments, these base stations may represent devices such as the exemplary base station illustrated in more detail by fig. 7.

As shown in this fig. 6, exemplary mobile station 13 includes a processor 111, a memory 113, a transceiver 112, and an antenna 23. In particular embodiments, some or all of the above functionality, as provided by a mobile communication device or other form of mobile station, may be provided by mobile station processor 111 executing instructions stored on a computer-readable medium, such as memory 113 shown in fig. 6. Alternative embodiments of the mobile station may include other components in addition to those shown in fig. 6, which may be responsible for providing certain aspects of the mobile station's functionality, including any of the above-described functionality and/or any functionality needed to support the above-described solution.

As shown in fig. 7, exemplary base station 12 includes a processor 101, a memory 103, a transceiver 102, and an antenna 108. The exemplary base station may also include a network interface 104. In particular embodiments, some or all of the above functionality, as provided by a base station, a base station controller, a node B, an enhanced node B, and/or any other type of mobile communication node, may be provided by a mobile station processor executing instructions stored on a computer-readable medium, such as the memory shown in fig. 7. Alternative embodiments of the base station may include other components responsible for providing other functions, including any of the above functions and/or any functions required to support the above-described solution.

Further, fig. 8 depicts an exemplary central node 20, such as an RNC or BSC. The exemplary central node 20 includes a processor 201, memory 203 and a network interface 204 for connecting to other nodes in a cellular network, such as base stations and mobile switching centers. In particular embodiments, some or all of the functionality described above as being provided by a central node may be provided by processor 201 executing instructions stored on a computer-readable medium, such as memory 203.

According to some embodiments, the steps as shown in fig. 9 may be performed by a central node. Thus, in fig. 9 a flow chart is shown illustrating some steps performed in a central node such as a Radio Network Controller (RNC) or a Base Station Controller (BSC). Thus, in a method in a central node of a cellular radio network, the central node is adapted to decide, when a circuit switched call of a mobile station ends, whether the mobile station connected to the cellular radio network via a first radio access technology controlled by the central node is to move to another radio access technology. It is assumed that the cellular radio network is adapted to use fallback to circuit switched procedures. First, in step 901, it is decided that a CS call for a specific mobile station has ended. Then, in step 903, it is checked whether the CS call is the result of a fallback to CS procedure. Then, in step 905, the central node decides whether the mobile station is to move to another radio access technology based at least in part on the determination in step 903, i.e. whether the CS call is the result of a CS fallback procedure.

For example, if a circuit switched call is made by a mobile station that has performed a fall back to a circuit switched procedure, the mobile station may be returned to the original radio access technology from which the fall back to the circuit switched procedure was performed. According to some embodiments, the original radio access technology may be evolved UTRAN or a similar radio access technology that does not support CS connections.

According to some embodiments, the central node receives information in a message from the mobile switching center as to whether the mobile switched call was caused by a fallback to circuit switched procedure.

Claims (12)

1. A method for use in a central node of a cellular radio network for deciding whether a mobile station connected to the cellular radio network via a first radio access technology controlled by the central node is to move to another radio access technology, wherein the cellular radio network is adapted to use a fallback to circuit switched procedure, the method comprising:

determining (901) that a circuit switched call of the mobile station has ended,

the method is characterized in that:

receiving information in a message from a mobile switching center as to whether the circuit switched call was caused by a fallback to circuit switched procedure; and

deciding whether the mobile station is to move to the other radio access technology based on whether the circuit switched call is caused by a fallback to circuit switched procedure.

2. The method according to claim 1, wherein if the circuit switched call is made by a mobile station that has performed a fallback to circuit switched procedure, the mobile station returns to an original radio access technology from which the fallback to circuit switched procedure was performed.

3. The method according to claim 2, wherein the original radio access technology is evolved UTRAN.

4. A method according to any of claims 1-3, wherein said central node is a base station controller, BSC, or a radio network controller, RNC.

5. A central node (20) of a cellular radio network (11), the central node being configured to decide whether a mobile station (13) connected to the cellular radio network via a first radio access technology controlled by the central node is to move to another radio access technology,

wherein the cellular radio network is adapted to use fallback to a circuit switched procedure, the central node comprising a controller (201) adapted to:

determining that a circuit switched call of the mobile station has ended,

the central node is characterized in that the controller (201) is adapted to:

receiving information in a message from a mobile switching center as to whether the circuit switched call was caused by a fallback to circuit switched procedure; and

deciding whether the mobile station is to move to the other radio access technology based on whether the circuit switched call is caused by a fallback to circuit switched procedure.

6. The central node of claim 5, wherein the controller is configured to return the mobile station to an original radio access technology from which a fallback to circuit switched procedure was performed, if the circuit switched call was made by a mobile station that has performed a fallback to circuit switched procedure.

7. The central node according to claim 6, wherein the original radio access technology is evolved UTRAN.

8. The central node according to any of claims 5-7, wherein the central node is a base station controller, BSC, or a radio network controller, RNC.

9. In a mobile switching center of a cellular radio network adapted to use fallback to circuit switched procedures, a method for supporting a central node of the cellular radio network to decide whether a mobile station connected to the cellular radio network via a first radio access technology controlled by the central node is to move to another radio access technology, the method comprising:

determining whether the circuit switched call is caused by a fallback to circuit switched procedure;

transmitting a message to the central node of the cellular radio network, the message comprising information on whether the circuit switched call was caused by a fallback to circuit switched procedure.

10. The method according to claim 9, wherein the central node is a base station controller, BSC, or a radio network controller, RNC.

11. A mobile switching center for a cellular radio network, wherein the cellular radio network is adapted to use fallback to circuit switched procedures, the mobile switching center supporting a central node of the cellular radio network deciding whether a mobile station connected to the cellular radio network via a first radio access technology controlled by the central node is to move to another radio access technology,

the method comprises the following steps:

a processor; and

a memory including instructions executable by the processor,

wherein the mobile switching center is operable to:

determining whether the circuit switched call is caused by a fallback to circuit switched procedure;

transmitting a message to the central node of the cellular radio network, the message comprising information on whether the circuit switched call was caused by a fallback to circuit switched procedure.

12. A mobile switching center according to claim 11, wherein the central node is a base station controller BSC or a radio network controller RNC.