WO2010106397A1 - Method, apparatus and computer readable memory medium for circuit switched fallback and inter-rat selection - Google Patents

Method, apparatus and computer readable memory medium for circuit switched fallback and inter-rat selection Download PDF

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Publication number
WO2010106397A1
WO2010106397A1 PCT/IB2009/051076 IB2009051076W WO2010106397A1 WO 2010106397 A1 WO2010106397 A1 WO 2010106397A1 IB 2009051076 W IB2009051076 W IB 2009051076W WO 2010106397 A1 WO2010106397 A1 WO 2010106397A1
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WO
WIPO (PCT)
Prior art keywords
user equipment
radio access
access technology
circuit switched
information
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PCT/IB2009/051076
Other languages
French (fr)
Inventor
Lars Dalsgaard
Woonhee Hwang
Curt Wong
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Nokia Corporation
Nokia, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Application filed by Nokia Corporation, Nokia, Inc. filed Critical Nokia Corporation
Priority to PCT/IB2009/051076 priority Critical patent/WO2010106397A1/en
Publication of WO2010106397A1 publication Critical patent/WO2010106397A1/en

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/0005—Control or signalling for completing the hand-off
    • H04W36/0011—Control or signalling for completing the hand-off for data sessions of end-to-end connection
    • H04W36/0022—Control or signalling for completing the hand-off for data sessions of end-to-end connection for transferring data sessions between adjacent core network technologies
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/14—Reselecting a network or an air interface
    • H04W36/144—Reselecting a network or an air interface over a different radio air interface technology
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/08—Access point devices

Definitions

  • the exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs and, more specifically, relate to the provision of a circuit switched fallback capability in a packet switched wireless communication system.
  • 3GPP third generation partnership project 5 AS access stratum
  • TAU tracking area update TMSI temporary mobile subscriber identity
  • EUTRAN evolved UTRAN
  • UTRAN-LTE UTRAN-LTE
  • EUTRA evolved UTRAN
  • OFDMA OFDMA
  • SC- FDMA SC- FDMA
  • This system may be referred to for convenience as LTE Rel-8, or simply as Rel-8.
  • the set of specifications given as 3GPP TS 36.xyz (e.g., 36.211, 36.311, 36.312, etc.) may be seen as describing the Rel-8 LTE system.
  • FIG. IA reproduces Figure 4.1 of 3GPP TS 36.300, and shows the overall architecture of the EUTRAN system.
  • the EUTRAN system includes eNBs, providing the EUTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE.
  • the eNBs are interconnected with each other by means of an X2 interface.
  • the eNBs are also connected by means of an Sl interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a Sl MME interface and to a Serving Gateway (SGW) by means of a Sl interface.
  • MME Mobility Management Entity
  • SGW Serving Gateway
  • the Sl interface supports a many to many relationship between MMEs / Serving Gateways and eNBs.
  • the eNB hosts the following functions: functions for Radio Resource Management: Radio Bearer Control, Radio Admission
  • Connection Mobility Control Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
  • IP header compression and encryption of the user data stream selection of a MME at UE attachment; routing of User Plane data towards Serving Gateway; scheduling and transmission of paging messages (originated from the MME); scheduling and transmission of broadcast information (originated from the MME or
  • O&M O&M
  • measurement and measurement reporting configurations to provide mobility and scheduling.
  • 3GPP has defined a CS fallback procedure in Rel-8.
  • the CS fallback in EPS enables the provisioning of voice and other CS-domain services (e.g., CS UDI video/ SMS/ LCS/ USSD) by reuse of CS infrastructure when the UE is served by EUTRAN.
  • a CS fallback enabled terminal, connected to EUTRAN may use GERAN or UTRAN to establish one or more CS domain services. This function is only available in the case where EUTRAN coverage is overlapped by either GERAN coverage or UTRAN coverage.
  • CS Fallback and IMSbased services shall be able to co-exist in the same operator's network.
  • the CS fallback in EPS function is realized by using the SGs interface mechanism between the MSC Server and the MME.
  • the SGs interface functionality is based on the mechanisms specified for the Gs interface, 3GPP TS 23.060.
  • SGs This is the reference point between the MME and MSC server.
  • the SGs reference point is used for the mobility management and paging procedures between EPS and CS domain, and is based on the Gs interface procedures.
  • the SGs reference point is also used for the delivery of both mobile originating and mobile terminating SMS. Additional procedures for alignment with the Gs reference point are not precluded.
  • S3 This is defined in 3GPP TS 23.401, with the additional functionality to support CS fallback with ISR.
  • the CS fallback capable UE supports access to E-UTRAN/EPC, as well as access to the CS domain over GERAN and/or UTRAN.
  • the UE supports the following additional functions: combined procedures specified for EPS/IMSI attach, update and detach; and CS fallback and SMS procedures for using CS domain services.
  • a UE using CS fallback supports ISR according to 3 GPP TS 23.401.
  • a UE deactivates ISR at reception of LAU accept or at reception of combined RAU/LAU accept. IfISR is active the UE can change between all registered areas and RATs without performing update signaling. The UE listens for paging on the RAT it is currently camped on.
  • the CS fallback enabled MME supports the following additional functions: deriving a VLR number and LAI from the GUTI received from the UE or from a default LAI; maintaining of SGs association towards MSC/VLR for EPS/IMSI attached UE; initiating IMSI detach at EPS detach; initiating a paging procedure towards the eNB when the MSC pages the UE for CS services; support for SMS procedures; and rejecting CS Fallback call request (e.g., due to O&M reasons).
  • a MME that supports CS fallback uses the LAI and a hash value from the IMSI to determine the VLR number as defined in 3GPP TS 23.236 when multiple MSC/VLRs serve the same LAI.
  • the same hash value/function is used by SGSN to determine the VLR number.
  • the CS fallback enabled MSC supports the following additional functions: maintaining SGs association towards MME for EPS/IMSI attached UE; paging on SGs and Iu/A in parallel; and support for SMS procedures.
  • the CS fallback enabled E-UTRAN supports the following additional functions: forwarding paging request and SMS to the UE; and directing the UE to the target CS capable cell.
  • the SGSN If the SGSN supports ISR, the SGSN follows the rules and procedures described in 3GPP TS 23.401 and 3GPP TS 23.060 with the following additions and clarifications: the SGSN shall not send the ISR activated indication at combined RAU/LAU procedure.
  • a SGSN that supports Gs uses LAI and a hash value from the IMSI to determine the VLR number as defined in 3GPP TS 23.236 when multiple MSC/VLRs serve the same LAI;.
  • the same hash value/function is used by the MME to determine the VLR number.
  • the UE initiates the attach procedure by the transmission of an Attach Request (parameters as specified in 3GPP TS 3.401 including the Attach Type) message to the MME.
  • the Attach Type indicates that the UE requests a combined EPS/IMSI attach and informs the network that the UE is capable and configured to use CS fallback.
  • the VLR is updated according to the combined GPRS/IMSI Attach procedure in 3GPP TS 23.060 if the Attach Request message includes an Attach Type indicating that the UE requests a combined EPS/IMSI attach.
  • the MME allocates a default LAI, which is configured on the MME and may take into account the current TAI and/or E-CGI.
  • the MME derives a VLR number based on the allocated LAI and on an IMSI hash function defined in 3GPP TS 23.236.
  • the MME starts the location update procedure towards the new MSC/VLR upon receipt of the first Insert Subscriber Data message from the HSS in step 2. This operation marks the UE as EPS-attached in the VLR.
  • the MME sends a Location Update Request (new LAI, IMSI, MME address, Location Update Type) message to the VLR.
  • the MME address is an IP address.
  • the VLR creates an association with the MME by storing the MME address.
  • the VLR performs Location Updating procedure in the CS domain.
  • the VLR responds with a Location Update Accept (VLR TMSI) to the MME. 8) The MME sends an Attach Accept (parameters as specified in 3GPP TS 23.401 , LAI, VLR TMSI) message to the UE.
  • the LAI is as allocated in step 3 above. The existence of the LAI and VLR TMSI indicates successful attach to CS domain.
  • CTl (see 3GPP TS 24.301 V8.0.0 (2008-12) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Non- Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3 (Release 8), in particular the CS mode of operation) has developed a technique for the UE to switch RATs based on the NAS reason, (i.e., CSFB mode in the UE and combine attachment status), and have suggested to override the RAN AS level of RAT control (see Cl-091198).
  • NAS Non- Access-Stratum
  • EPS Evolved Packet System
  • Stage 3 Release 8
  • the EPS For those services delivered via the HPLMN that the HPLMN only supports in the CS domain (e.g. voice services), when such services are invoked while the UE is configured to use CS Fallback and registered in the E-UTRAN (either in the HPLMN or in a VPLMN), it shall be possible for the EPS to request the UE to perform a change of radio access technology in order to deliver the service over UTRAN or GERAN or IxRTT. In the case of an incoming CS service to a UE that is registered for CS services and active in E-UTRAN, the EPS shall transfer the CLI to the UE if available and the calling party has not restricted the presentation, prior to triggering CS fallback.
  • a UE that is configured to use CS fallback registers over E-UTRAN in a VPLMN not supporting CS fallback the default behaviour of the UE is to attempt to select a GERAN/UTRAN/ IxRTT CS radio access technology in the VPLMN or in a PLMN equivalent to the VPLMN.
  • the default behaviour of the UE is not to autonomously attempt to (re-)select the E-UTRAN for the duration of the time the UE stays in a VPLMN and PLMNs equivalent to the VPLMN.
  • the default behaviour may be changed based on user preference settings.
  • the UE may offer the user to perform a PLMN scan and display the list of available PLMNs.
  • the selection of a different PLMN is performed using the manual mode.
  • RAT selection made by the UE is under network control using radio level parameters.
  • the exemplary embodiments of this invention provide a method that comprises receiving information at a network access node of a first radio access technology, the information concerning a user equipment and comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment; and determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
  • the exemplary embodiments of this invention provide a computer-readable memory medium that stores program instructions the execution of which result in operations that comprise receiving at a network access node of a first radio access technology certain information concerning a user equipment, the certain information comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment; and determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
  • the exemplary embodiments of this invention provide an apparatus that comprises a controller configured with a first interface for conducting wireless communications with a user equipment and with a second interface for conducting communications with a mobile management entity.
  • the controller is responsive to a receipt from the second interface of information comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment to determine in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
  • Figure IA reproduces Figure 4.1 of 3GPP TS 36.300, and shows the overall architecture of the EUTRAN system.
  • Figure IB reproduces Figure 4.2-1 : CS fallback in EPS architecture of 3GPP TS 22.272.
  • Figure 1C reproduces Figure 5.2-1: Attach Procedure of 3GPP TS 23.272.
  • Figure 2 A shows a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention.
  • Figure 2B shows a more particularized block diagram of a user equipment such as that shown at Figure 2A.
  • Figure 3 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with the exemplary embodiments of this invention.
  • Figure 4 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with the exemplary embodiments of this invention.
  • Figure 5 is another logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with the exemplary embodiments of this invention.
  • the LTE network i.e., the eNB
  • the eNB can signal a dedicated priority during an RRC Connection Release procedure with a validity timer.
  • the dedicated priority is set based on the parameter "Subscriber Profile ID for RAT/Frequency" which is signaled from the HSS to the eNB via the MME, and this priority is based on the operator's policy and subscription information.
  • the AS may wish to keep the UE in LTE, while the UE may move to another RAT due to the NAS level parameter.
  • the NAS may wish to prioritize UE camping to E-UTRAN, but the UE (e.g., due to user selection of CS as preferred) will on its own initiative camp elsewhere when possible. This will cause confusion at the AS layer.
  • the UE will disappear from the LTE coverage network based on its own logic, it may have an impact on KPI.
  • the statistics being collected at E-UTRAN may not be accurate because it is not known if the UE left the LTE coverage due to CSFB, or due to some UE malfunction, or if the UE lost the coverage due to some coverage-related reason. Therefore, it is important to maintain a principle of a single control point for RAT selection.
  • the UE overwrites the dedicated priority due to the CSFB mode, it is also not clear when this dedicated priority will be invalidated, and when the UE can return to the LTE frequency. Also, due to the existing priority mechanism there may be ping-pong effect on cell reselection between LTE and the overlaid CS RAT. Additional UE complexity is problematic in this case when the UE autonomously changes otherwise network controlled parameters. For example, the UE may be camped on an accessible E-UTRAN CSG cell which has an implicit highest priority. However, if CSFB is not possible at this CSG cell, UE would change to a CS-capable RAT and apply the highest priority for this RAT and make LTE the lowest priority.
  • the CSG cell shall have the highest priority.
  • the UE would search for the CSG cell again.
  • the visibility of usage e.g., an E-UTRAN UE is always camped outside of E-UTRAN due to user choice or network implementation
  • UE mode of operation for CS fallback In Cl-090718, 3GPP TSG CT WGl Meeting #57, San Antonio (TX), USA, 9-19 February 2009, "UE mode of operation for CS fallback", Panasonic, it is proposed at a high level to adopt network-based RAT selection behavior to achieve the current requirement of UE mode of operation for CS fallback.
  • the UE needs to indicate its mode of operation as a UE network capability during the attach procedure.
  • UE mode operation should be known by the network to coordinate the priority and UE mode, there should be further information available (e.g., whether or not the UE managed to successfully perform the combined registration) in order to set the priority correctly.
  • a wireless network 1 is adapted for communication over a wireless link 11 with an apparatus, such as a mobile communication device which may be referred to as a UE 10, via a network access node, such as a Node B (base station), and more specifically an eNB 12.
  • a network access node such as a Node B (base station)
  • eNB 12 evolved Node B
  • the network 1 may include a network control element (NCE) 14 that may include the MME/SGW functionality shown in Figure 1 A (and the MME functionality shown in Figure 1 B), and which provides connectivity with a further network, such as a telephone network and/or a data communications network (e.g., the internet).
  • the UE 10 includes a controller, such as a computer or a data processor (DP) 1OA, a computer-readable memory medium embodied as a memory (MEM) 1OB that stores a program of computer instructions (PROG) 1OC, and a suitable radio frequency (RF) transceiver 1OD for bidirectional wireless communications with the eNB 12 via one or more antennas.
  • DP data processor
  • PROG program of computer instructions
  • RF radio frequency
  • the eNB 12 also includes a controller, such as a computer or a data processor (DP) 12 A, a computer- readable memory medium embodied as a memory (MEM) 12B that stores a program of computer instructions (PROG) 12C, and a suitable RF transceiver 12D for communication with the UE 10 via one or more antennas.
  • the eNB 12 is coupled via a data / control path 13 to the NCE 14.
  • the path 13 may be implemented as the S 1 interface shown in Figures 1 A and 1 B .
  • the eNB 12 may also be coupled to another eNB via data / control path 15, which may be implemented as the X2 interface shown in Figure IA.
  • the UE 10 may be assumed to also include a CS fallback (CSFB) unit or module 1 OE, and the eNB 12 may be assumed to also include a CS fallback unit or module 12E, both of which are assumed to compatible with the exemplary embodiments of this invention as described in further detail below.
  • CSFB CS fallback
  • the MME aspect of the NCE 14 is also assumed to be compatible with the exemplary embodiments of this invention as described in further detail below.
  • At least one of the PROGs 1 OC and 12C is assumed to include program instructions that, when executed by the associated DP, enable the device to operate in accordance with the exemplary embodiments of this invention, as will be discussed below in greater detail. That is, the exemplary embodiments of this invention may be implemented at least in part by computer software executable by the DP 1OA of the UE 10 and/or by the DP 12A of the eNB 12, or by hardware, or by a combination of software and hardware (and firmware).
  • the various embodiments of the UE 10 can include, but are not limited to, cellular telephones, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.
  • PDAs personal digital assistants
  • portable computers having wireless communication capabilities
  • image capture devices such as digital cameras having wireless communication capabilities
  • gaming devices having wireless communication capabilities
  • music storage and playback appliances having wireless communication capabilities
  • Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.
  • the computer readable MEMs 1OB and 12B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory.
  • the DPs 1OA and 12A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multicore processor architecture, as non-limiting examples.
  • Figure 2B illustrates further detail of an exemplary UE 10 in both plan view (left) and sectional view (right), and the invention may be embodied in one or some combination of those more function specific components.
  • the UE 10 has a graphical display interface 20 and a user interface 22 illustrated as a keypad but understood as also encompassing touch screen technology at the graphical display interface 20 and voice recognition technology received at the microphone 24.
  • a power actuator 26 controls the device being turned on and off by the user.
  • the exemplary UE 10 may have a camera 28 which is shown as being forward facing (e.g., for video calls) but may alternatively or additionally be rearward facing (e.g., for capturing images and video for local storage).
  • the camera 28 is controlled by a shutter actuator 30 and optionally by a zoom actuator 30 which may alternatively function as a volume adjustment for the speaker(s) 34 when the camera 28 is not in an active mode.
  • a shutter actuator 30 and optionally by a zoom actuator 30 which may alternatively function as a volume adjustment for the speaker(s) 34 when the camera 28 is not in an active mode.
  • multiple transmit/receive antennas 36 that are typically used for cellular communication.
  • the antennas 36 may be multi-band for use with other radios in the UE.
  • the operable ground plane for the antennas 36 is shown by shading as spanning the entire space enclosed by the UE housing though in some embodiments the ground plane may be limited to a smaller area, such as disposed on a printed wiring board on which the power chip 38 is formed.
  • the power chip 38 controls power amplification on the channels being transmitted and/or across the antennas that transmit simultaneously where spatial diversity is used, and amplifies the received signals.
  • the power chip 38 outputs the amplified received signal to the radio frequency (RF) chip 40 which demodulates and downconverts the signal for baseband processing.
  • the baseband (BB) chip 42 detects the signal which is then converted to a bit stream and finally decoded. Similar processing occurs in reverse for signals generated in the apparatus 10 and transmitted from it.
  • Signals going to and from the camera 28 may pass through an image/video processor 44 that encodes and decodes the various image frames.
  • a separate audio processor 46 may also be present controlling signals to and from the speakers 34 and the microphone 24.
  • the graphical display interface 20 is refreshed from a frame memory 48 as controlled by a user interface chip 50 which may process signals to and from the display interface 20 and/or additionally process user inputs from the keypad 22 and elsewhere.
  • Certain embodiments of the UE 10 may also include one or more secondary radios such as a wireless local area network radio WLAN 37 and a Bluetooth® radio 39, which may incorporate an antenna on the chip or be coupled to an antenna off the chip.
  • secondary radios such as a wireless local area network radio WLAN 37 and a Bluetooth® radio 39, which may incorporate an antenna on the chip or be coupled to an antenna off the chip.
  • various memories such as random access memory RAM 43, read only memory ROM 45, and in some embodiments removable memory such as the illustrated memory card 47 on which the various programs 1 OC are stored. All of these components within the UE 10 are normally powered by a portable power supply such as a battery 49.
  • the processors 38, 40, 42, 44, 46, 50 may operate in a slave relationship to the main processor 1OA, 12A, which may then be in a master relationship to them.
  • Embodiments of this invention may be disposed across various chips and memories as shown, or disposed within another processor that combines some of the functions described above for Figure 2B. Any or all of these various processors of Figure 2B access one or more of the various memories, which may be on chip with the processor or separate there from.
  • Similar function-specific components that are directed toward communications over a network broader than a piconet may also be disposed in exemplary embodiments of the access node 12, which may have an array of tower mounted antennas rather than the two shown at Figure 2B.
  • AS level of RAT control is maintained by incorporating the CS fallback functionality into it. Note that this approach is compatible with SAl, as this method is also part of the EPS in "... it shall be possible for the EPS to request the UE to perform a change of radio access technology in order to deliver the service over UTRAN or GERAN or IxRTT.”
  • exemplary steps of the method are as follows.
  • Block 3 A The UE 10 indicates its mode of operation to the MME 14 during the LTE
  • Attach procedure and TAU procedure If the mode of operation is changed by the user after it is attached to the EPS then the UE 10 performs the TAU procedure to update the
  • MME with the latest mode of operation settings. This information is stored in the MME as a part of the UE context.
  • Block 3B The MME 14 is aware of the status of the combined attach procedure, e.g., whether it is successful or has failed (i.e., the MME 14 is aware of the status of the attach procedure described above with respect to Figure 1C). The MME 14 returns this indication, along with the UE 10 mode of operation indication, to the E-UTRAN (to the eNB 12).
  • Block 3C E-UTRAN now has the information of the UE 10 that is related to the CSFB mode of operation, the result of the combine attach, and also a policy related to RAT/Frequency priority control. Based on this information, E-UTRAN (the eNB 12) determines whether the UE 10 should continue to stay in LTE or should move to another RAT. This is thus the single point of control of RAT selection, hi some embodiments, the E-UTRAN may determine that a UE 10 which didn't succeed in the combined attach would be a candidate for moving to another RAT.
  • Block 3D the eNB 12 can acquire a measurement report from the UE 10.
  • the report may comprise information on accesses that are reachable by the UE 10.
  • Block 3E If the eNB 12 decides to redirect the UE 10 to CS coverage, it triggers a RRC Connection Release procedure to the selected CS RAT with a dedicated priority with the validity timer. Thus, the UE 10 will return to LTE coverage if desired by the network operator.
  • another CSFB mechanism e.g., PS handover or CCO
  • PS handover or CCO can be used to redirect the UE 10 to the CS RAT.
  • the UE 10 sets up the RRC Connection (to perform the NAS procedure). Thus, this redirection can occur immediately after a combined attachment has failed and during the RRC Connection Release.
  • the UE 10 will not receive CS paging (the same situation as if the CS coverage is not provided). However, even for this case the UE 10 still can make (originate) a CS call by signaling its preference as defined for MO CSFB in 3GPP TS 23.272 (e.g., see generally Section 6, Mobile Originating Call).
  • Block 4A The UE 10 sets up the RRC Connection and sends a Service Request to the MME 14 with a MO CS call indication.
  • Block 4B The MME 14 sends the MO CS call indication, the CSFB mode and registration status in an Initial Context Setup to the eNB 12.
  • Block 4C Optionally the eNB 12 can acquire a measurement report from the UE 10.
  • the report may comprise information on accesses that are reachable by the UE 10.
  • Block 4D The eNB 12 redirects the UE 10 to the CS RAT based on the CSFB procedure
  • the eNB 12 determines which CSFB procedure to be used and a timer value if needed based on the information from the MME
  • Block 4E If the UE 10 is re-directed, after the CS call is terminated the UE 10 applies a normal reselection rule and AS RAT priority parameter. IfLTE has a higher priority, the
  • UE 10 returns to LTE coverage.
  • the eNB 12 may advantageously set the duration of the validity timer for the UE 10 using the information received from the MME 14 which includes, in accordance with an exemplary aspect of this invention, the CFSB mode and registration status of the UE 10, and not just the MO CS call indication.
  • FIG. 5 is another logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions, in accordance with the exemplary embodiments of this invention.
  • a method performs, at Block 5A, a step of receiving information at a network access node of a first radio access technology, the information concerning a user equipment and comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment.
  • Block 5B there is a step of determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
  • the information is received from a mobile management entity with which the user equipment has performed the combined attach procedure.
  • the combined attach procedure may be is a general packet radio service/international mobile subscriber identity attach procedure.
  • determining comprises an initial step of requesting a measurement report from the user equipment, which report may comprise information on accesses that are reachable by the user equipment.
  • the first radio access technology comprises an evolved universal terrestrial radio access network technology
  • the radio access node is embodied as an evolved Node B.
  • the radio access node determines to not redirect the user equipment, further comprising steps and operations of receiving further information at the network access node from the mobile management entity, the further information comprising a mobile originated circuit switched call indication that the mobile management entity received from the user equipment; and redirecting the user equipment to another radio access technology to obtain circuit switched service for making a mobile originated circuit switched call.
  • the exemplary embodiments of this invention provide a method, apparatus and computer program(s) to establish the decision point of RAT selection in one network node, enabling a harmonized and coordinated decision to be made.
  • this NAS-based approach does not interfere with any existing AS-based RAT selection mechanisms.
  • the RRC Connection Release can be still be controlled by the network, unlike a UE-based approach.
  • the eNB 12 can signal the timer for the validity of the dedicated priority, the use of these exemplary embodiments can ensure that the UE 10 will return to LTE coverage.
  • An illustrative aspect of the exemplary embodiments of this invention is an apparatus that comprises means for receiving information at a network access node of a first radio access technology, the information concerning a user equipment and comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment.
  • the apparatus further comprises means for determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
  • the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof.
  • some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto.
  • firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto.
  • While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.
  • the integrated circuit, or circuits may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.
  • UTRAN-LTE Rel-8 E-UTRAN
  • LTE-A LTE- Advanced
  • connection means any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are “connected” or “coupled” together.
  • the coupling or connection between the elements can be physical, logical, or a combination thereof.
  • two elements may be considered to be “connected” or “coupled” together by the use of one or more wires, cables and/or printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as several non- limiting and non-exhaustive examples.
  • the various names used for the described parameters are not intended to be limiting in any respect, as these parameters may be identified by any suitable names.
  • the various names assigned to different functional units e.g., MME, etc.
  • reference points and interfaces e.g., SGs, S 1 , etc.
  • various procedures e.g., RRC Connection Release, etc.

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Abstract

A method includes receiving information at a network access node of a first radio access technology, the information concerning a user equipment and including a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment. The method further includes determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.

Description

METHOD, APPARATUS AND COMPUTER READABLE MEMORY MEDIUM FOR CIRCUIT SWITCHED FALLBACK AND INTER-RAT SELECTION
TECHNICAL FIELD: 5
The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs and, more specifically, relate to the provision of a circuit switched fallback capability in a packet switched wireless communication system. 0
BACKGROUND:
This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are5 not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section. 0 The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
IxRTT single carrier radio transmission technology
3GPP third generation partnership project 5 AS access stratum
CCO cell change order
CS circuit switched
CSFB circuit switched fall back
CSG closed subscriber group 0 DL downlink (eNB towards UE) eNB EUTRAN Node B (evolved Node B)
EPC evolved packet core EPS evolved packet system
EUTRAN evolved UTRAN (LTE)
CDM code division multiplexing
CQI channel quality indicator
FDD frequency division duplex
FDMA frequency division multiple access
FDPS frequency domain packet scheduler
GERAN GSM/EDGE radio access network
GPRS general packet radio service
GUTI globally unique temporary identity
HO handover
HPLMN home PLMN
HSS home subscriber server
IMSI international mobile subscriber identity
ISR idle mode signaling reduction
KPI key performance indicators
LAI location area identity
LTE long term evolution
MAC medium access control
MM/MME mobility management/mobile management entity
MO mobile originated
MSC mobile switching center
MT mobile terminated
NACC network assisted cell change
NAS non access stratum
Node B base station
OFDMA orthogonal frequency division multiple access
O&M operations and maintenance
PDCP packet data convergence protocol
PHY physical
PLMN public land mobile network
PS packet switched RAN radio access network
RAT radio access technology
RLC radio link control
RRC radio resource control SGSN serving GPRS support node
SGW serving gateway
SMS short message service
SC-FDMA single carrier, frequency division multiple access
TAU tracking area update TMSI temporary mobile subscriber identity
UE user equipment
UL uplink (UE towards eNB)
UTRAN universal terrestrial radio access network
VLR visitor location register VPLMN visited PLMN
The specification of a communication system known as evolved UTRAN (EUTRAN, also referred to as UTRAN-LTE or as EUTRA) is nearing completion within the 3GPP. As specified the DL access technique is OFDMA, and the UL access technique is SC- FDMA.
One specification of interest is 3GPP TS 36.300, V8.7.0 (2008-12), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Access Network (EUTRAN); Overall description; Stage 2 (Release 8). This system may be referred to for convenience as LTE Rel-8, or simply as Rel-8. In general, the set of specifications given as 3GPP TS 36.xyz (e.g., 36.211, 36.311, 36.312, etc.) may be seen as describing the Rel-8 LTE system.
Figure IA reproduces Figure 4.1 of 3GPP TS 36.300, and shows the overall architecture of the EUTRAN system. The EUTRAN system includes eNBs, providing the EUTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an Sl interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a Sl MME interface and to a Serving Gateway (SGW) by means of a Sl interface. The Sl interface supports a many to many relationship between MMEs / Serving Gateways and eNBs.
The eNB hosts the following functions: functions for Radio Resource Management: Radio Bearer Control, Radio Admission
Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);
IP header compression and encryption of the user data stream; selection of a MME at UE attachment; routing of User Plane data towards Serving Gateway; scheduling and transmission of paging messages (originated from the MME); scheduling and transmission of broadcast information (originated from the MME or
O&M); and measurement and measurement reporting configurations to provide mobility and scheduling.
3GPP has defined a CS fallback procedure in Rel-8.
For example, reference may be made to 3GPP TS 22.272 V8.2.0 (2008-12) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Circuit Switched Fallback in Evolved Packet System; Stage 2 (Release 8). Figure IB herein reproduces Figure 4.2-1 : CS fallback in EPS architecture of 3GPP TS 22.272.
As is stated in Section 4, the CS fallback in EPS enables the provisioning of voice and other CS-domain services (e.g., CS UDI video/ SMS/ LCS/ USSD) by reuse of CS infrastructure when the UE is served by EUTRAN. A CS fallback enabled terminal, connected to EUTRAN may use GERAN or UTRAN to establish one or more CS domain services. This function is only available in the case where EUTRAN coverage is overlapped by either GERAN coverage or UTRAN coverage.
CS Fallback and IMSbased services shall be able to co-exist in the same operator's network.
The CS fallback in EPS function is realized by using the SGs interface mechanism between the MSC Server and the MME. The SGs interface functionality is based on the mechanisms specified for the Gs interface, 3GPP TS 23.060.
In the EPS architecture shown in Figure IB there are several reference points.
SGs: This is the reference point between the MME and MSC server. The SGs reference point is used for the mobility management and paging procedures between EPS and CS domain, and is based on the Gs interface procedures. The SGs reference point is also used for the delivery of both mobile originating and mobile terminating SMS. Additional procedures for alignment with the Gs reference point are not precluded. S3: This is defined in 3GPP TS 23.401, with the additional functionality to support CS fallback with ISR.
With regard to the functional entities shown in Figure IB, the CS fallback capable UE supports access to E-UTRAN/EPC, as well as access to the CS domain over GERAN and/or UTRAN. The UE supports the following additional functions: combined procedures specified for EPS/IMSI attach, update and detach; and CS fallback and SMS procedures for using CS domain services.
A UE using CS fallback supports ISR according to 3 GPP TS 23.401. In particular, a UE deactivates ISR at reception of LAU accept or at reception of combined RAU/LAU accept. IfISR is active the UE can change between all registered areas and RATs without performing update signaling. The UE listens for paging on the RAT it is currently camped on.
The CS fallback enabled MME supports the following additional functions: deriving a VLR number and LAI from the GUTI received from the UE or from a default LAI; maintaining of SGs association towards MSC/VLR for EPS/IMSI attached UE; initiating IMSI detach at EPS detach; initiating a paging procedure towards the eNB when the MSC pages the UE for CS services; support for SMS procedures; and rejecting CS Fallback call request (e.g., due to O&M reasons).
A MME that supports CS fallback uses the LAI and a hash value from the IMSI to determine the VLR number as defined in 3GPP TS 23.236 when multiple MSC/VLRs serve the same LAI. The same hash value/function is used by SGSN to determine the VLR number.
The CS fallback enabled MSC supports the following additional functions: maintaining SGs association towards MME for EPS/IMSI attached UE; paging on SGs and Iu/A in parallel; and support for SMS procedures.
The CS fallback enabled E-UTRAN supports the following additional functions: forwarding paging request and SMS to the UE; and directing the UE to the target CS capable cell.
If the SGSN supports ISR, the SGSN follows the rules and procedures described in 3GPP TS 23.401 and 3GPP TS 23.060 with the following additions and clarifications: the SGSN shall not send the ISR activated indication at combined RAU/LAU procedure.
A SGSN that supports Gs uses LAI and a hash value from the IMSI to determine the VLR number as defined in 3GPP TS 23.236 when multiple MSC/VLRs serve the same LAI;. The same hash value/function is used by the MME to determine the VLR number.
The above-referenced combined procedures specified for EPS/IMSI attach are described in Section 5.2, "Attach procedure" of 3GPP TS 23.272. Reference can be made herein to Figure 1C, which reproduces Figure 5.2-1 of 3GPP TS 23.272. As described, the attach procedure for the CS fallback in EPS is realized based on the combined GPRS/IMSI Attach procedure specified in 3 GPP TS 23.060. As is shown in Figure 1 C, the following steps/procedures are executed:
1) The UE initiates the attach procedure by the transmission of an Attach Request (parameters as specified in 3GPP TS 3.401 including the Attach Type) message to the MME. The Attach Type indicates that the UE requests a combined EPS/IMSI attach and informs the network that the UE is capable and configured to use CS fallback.
2) The EPS Attach procedure is performed as specified in 3GPP TS 23.401.
3) The VLR is updated according to the combined GPRS/IMSI Attach procedure in 3GPP TS 23.060 if the Attach Request message includes an Attach Type indicating that the UE requests a combined EPS/IMSI attach. The MME allocates a default LAI, which is configured on the MME and may take into account the current TAI and/or E-CGI. The MME derives a VLR number based on the allocated LAI and on an IMSI hash function defined in 3GPP TS 23.236. The MME starts the location update procedure towards the new MSC/VLR upon receipt of the first Insert Subscriber Data message from the HSS in step 2. This operation marks the UE as EPS-attached in the VLR. 4) The MME sends a Location Update Request (new LAI, IMSI, MME address, Location Update Type) message to the VLR. The MME address is an IP address.
5) The VLR creates an association with the MME by storing the MME address.
6) The VLR performs Location Updating procedure in the CS domain.
7) The VLR responds with a Location Update Accept (VLR TMSI) to the MME. 8) The MME sends an Attach Accept (parameters as specified in 3GPP TS 23.401 , LAI, VLR TMSI) message to the UE. The LAI is as allocated in step 3 above. The existence of the LAI and VLR TMSI indicates successful attach to CS domain.
In SAl, 3GPP TS 22.278 V9.2.0 (2008-12) Technical Specification 3rd Generation Partnership Proj ect; Technical Specification Group Services and System Aspects; Service requirements for the Evolved Packet System (EPS) (Release 9), it is defined that the default behavior of the UE is to switch to a RAT that supports CS service if the serving network does not support CSFB, and that the UE is configured to use CSFB. In the RAN side, RAN2 has specified AS-based RAT/Frequency priority control which is also used to control the UE on RAT selection/retunes. Reference in this regard may be made to 3GPP TS 36.331 V8.4.0 (2008-12) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) Radio Resource Control (RRC); Protocol specification (Release 8), as well as to 3GPP TS 36.304 V8.4.0 (2008-12) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA); User Equipment (UE) procedures in idle mode (Release 8).
This RAN2 method, thus far, has not taken the CS fallback SAl requirements into account. Meanwhile, CTl (see 3GPP TS 24.301 V8.0.0 (2008-12) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Core Network and Terminals; Non- Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3 (Release 8), in particular the CS mode of operation) has developed a technique for the UE to switch RATs based on the NAS reason, (i.e., CSFB mode in the UE and combine attachment status), and have suggested to override the RAN AS level of RAT control (see Cl-091198).
From 3GPP TS 22.278 V9.2.0 (2008-12) Technical Specification 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; Service requirements for the Evolved Packet System (EPS) (Release 9):
7.1.7 CS fallback
7.1.7.1 General
For those services delivered via the HPLMN that the HPLMN only supports in the CS domain (e.g. voice services), when such services are invoked while the UE is configured to use CS Fallback and registered in the E-UTRAN (either in the HPLMN or in a VPLMN), it shall be possible for the EPS to request the UE to perform a change of radio access technology in order to deliver the service over UTRAN or GERAN or IxRTT. In the case of an incoming CS service to a UE that is registered for CS services and active in E-UTRAN, the EPS shall transfer the CLI to the UE if available and the calling party has not restricted the presentation, prior to triggering CS fallback.
7.1.7.2 Roaming in a VPLMN not supporting CS fallback When a UE that is configured to use CS fallback registers over E-UTRAN in a VPLMN not supporting CS fallback the default behaviour of the UE is to attempt to select a GERAN/UTRAN/ IxRTT CS radio access technology in the VPLMN or in a PLMN equivalent to the VPLMN. The default behaviour of the UE is not to autonomously attempt to (re-)select the E-UTRAN for the duration of the time the UE stays in a VPLMN and PLMNs equivalent to the VPLMN. The default behaviour may be changed based on user preference settings.
The UE may offer the user to perform a PLMN scan and display the list of available PLMNs. The selection of a different PLMN is performed using the manual mode.
Thus far, RAT selection made by the UE is under network control using radio level parameters.
SUMMARY
The foregoing and other problems are overcome, and other advantages are realized, by the use of the exemplary embodiments of this invention.
In a first aspect thereof the exemplary embodiments of this invention provide a method that comprises receiving information at a network access node of a first radio access technology, the information concerning a user equipment and comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment; and determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
In a further aspect thereof the exemplary embodiments of this invention provide a computer-readable memory medium that stores program instructions the execution of which result in operations that comprise receiving at a network access node of a first radio access technology certain information concerning a user equipment, the certain information comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment; and determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
In yet another aspect thereof the exemplary embodiments of this invention provide an apparatus that comprises a controller configured with a first interface for conducting wireless communications with a user equipment and with a second interface for conducting communications with a mobile management entity. The controller is responsive to a receipt from the second interface of information comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment to determine in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
BRIEF DESCRIPTION OF THE DRAWINGS
In the attached Drawing Figures:
Figure IA reproduces Figure 4.1 of 3GPP TS 36.300, and shows the overall architecture of the EUTRAN system.
Figure IB reproduces Figure 4.2-1 : CS fallback in EPS architecture of 3GPP TS 22.272.
Figure 1C reproduces Figure 5.2-1: Attach Procedure of 3GPP TS 23.272.
Figure 2 A shows a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention. Figure 2B shows a more particularized block diagram of a user equipment such as that shown at Figure 2A.
Figure 3 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with the exemplary embodiments of this invention.
Figure 4 is a logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with the exemplary embodiments of this invention.
Figure 5 is another logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with the exemplary embodiments of this invention.
DETAILED DESCRIPTION
There are various problems associated with the currently specified CS fallback procedures. For example, to influence a cell (re-)selection, the LTE network (i.e., the eNB) broadcasts a priority per frequency or RAT. Also the eNB can signal a dedicated priority during an RRC Connection Release procedure with a validity timer. The dedicated priority is set based on the parameter "Subscriber Profile ID for RAT/Frequency" which is signaled from the HSS to the eNB via the MME, and this priority is based on the operator's policy and subscription information.
One problem that may arise is that the AS may wish to keep the UE in LTE, while the UE may move to another RAT due to the NAS level parameter. Stated differently, the NAS may wish to prioritize UE camping to E-UTRAN, but the UE (e.g., due to user selection of CS as preferred) will on its own initiative camp elsewhere when possible. This will cause confusion at the AS layer. Also, as the UE will disappear from the LTE coverage network based on its own logic, it may have an impact on KPI. In other words, the statistics being collected at E-UTRAN may not be accurate because it is not known if the UE left the LTE coverage due to CSFB, or due to some UE malfunction, or if the UE lost the coverage due to some coverage-related reason. Therefore, it is important to maintain a principle of a single control point for RAT selection.
If the UE overwrites the dedicated priority due to the CSFB mode, it is also not clear when this dedicated priority will be invalidated, and when the UE can return to the LTE frequency. Also, due to the existing priority mechanism there may be ping-pong effect on cell reselection between LTE and the overlaid CS RAT. Additional UE complexity is problematic in this case when the UE autonomously changes otherwise network controlled parameters. For example, the UE may be camped on an accessible E-UTRAN CSG cell which has an implicit highest priority. However, if CSFB is not possible at this CSG cell, UE would change to a CS-capable RAT and apply the highest priority for this RAT and make LTE the lowest priority. However, according to the rule for CSG cell reselection the CSG cell shall have the highest priority. Thus, the UE would search for the CSG cell again. Additionally, the visibility of usage (e.g., an E-UTRAN UE is always camped outside of E-UTRAN due to user choice or network implementation) for the user becomes unclear.
In Cl-090718, 3GPP TSG CT WGl Meeting #57, San Antonio (TX), USA, 9-19 February 2009, "UE mode of operation for CS fallback", Panasonic, it is proposed at a high level to adopt network-based RAT selection behavior to achieve the current requirement of UE mode of operation for CS fallback. The UE needs to indicate its mode of operation as a UE network capability during the attach procedure. However, even though UE mode operation should be known by the network to coordinate the priority and UE mode, there should be further information available (e.g., whether or not the UE managed to successfully perform the combined registration) in order to set the priority correctly.
Before describing in further detail the exemplary embodiments of this invention, reference is made to Figure 2 A for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing the exemplary embodiments of this invention. In Figure 2A a wireless network 1 is adapted for communication over a wireless link 11 with an apparatus, such as a mobile communication device which may be referred to as a UE 10, via a network access node, such as a Node B (base station), and more specifically an eNB 12. The network 1 may include a network control element (NCE) 14 that may include the MME/SGW functionality shown in Figure 1 A (and the MME functionality shown in Figure 1 B), and which provides connectivity with a further network, such as a telephone network and/or a data communications network (e.g., the internet). The UE 10 includes a controller, such as a computer or a data processor (DP) 1OA, a computer-readable memory medium embodied as a memory (MEM) 1OB that stores a program of computer instructions (PROG) 1OC, and a suitable radio frequency (RF) transceiver 1OD for bidirectional wireless communications with the eNB 12 via one or more antennas. The eNB 12 also includes a controller, such as a computer or a data processor (DP) 12 A, a computer- readable memory medium embodied as a memory (MEM) 12B that stores a program of computer instructions (PROG) 12C, and a suitable RF transceiver 12D for communication with the UE 10 via one or more antennas. The eNB 12 is coupled via a data / control path 13 to the NCE 14. The path 13 may be implemented as the S 1 interface shown in Figures 1 A and 1 B . The eNB 12 may also be coupled to another eNB via data / control path 15, which may be implemented as the X2 interface shown in Figure IA.
For the purposes of describing the exemplary embodiments of this invention the UE 10 may be assumed to also include a CS fallback (CSFB) unit or module 1 OE, and the eNB 12 may be assumed to also include a CS fallback unit or module 12E, both of which are assumed to compatible with the exemplary embodiments of this invention as described in further detail below. The MME aspect of the NCE 14 is also assumed to be compatible with the exemplary embodiments of this invention as described in further detail below.
At least one of the PROGs 1 OC and 12C is assumed to include program instructions that, when executed by the associated DP, enable the device to operate in accordance with the exemplary embodiments of this invention, as will be discussed below in greater detail. That is, the exemplary embodiments of this invention may be implemented at least in part by computer software executable by the DP 1OA of the UE 10 and/or by the DP 12A of the eNB 12, or by hardware, or by a combination of software and hardware (and firmware).
In general, the various embodiments of the UE 10 can include, but are not limited to, cellular telephones, personal digital assistants (PDAs) having wireless communication capabilities, portable computers having wireless communication capabilities, image capture devices such as digital cameras having wireless communication capabilities, gaming devices having wireless communication capabilities, music storage and playback appliances having wireless communication capabilities, Internet appliances permitting wireless Internet access and browsing, as well as portable units or terminals that incorporate combinations of such functions.
The computer readable MEMs 1OB and 12B may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, flash memory, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The DPs 1OA and 12A may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multicore processor architecture, as non-limiting examples.
Figure 2B illustrates further detail of an exemplary UE 10 in both plan view (left) and sectional view (right), and the invention may be embodied in one or some combination of those more function specific components. At Figure 2B the UE 10 has a graphical display interface 20 and a user interface 22 illustrated as a keypad but understood as also encompassing touch screen technology at the graphical display interface 20 and voice recognition technology received at the microphone 24. A power actuator 26 controls the device being turned on and off by the user. The exemplary UE 10 may have a camera 28 which is shown as being forward facing (e.g., for video calls) but may alternatively or additionally be rearward facing (e.g., for capturing images and video for local storage). The camera 28 is controlled by a shutter actuator 30 and optionally by a zoom actuator 30 which may alternatively function as a volume adjustment for the speaker(s) 34 when the camera 28 is not in an active mode. Within the sectional view of Figure 2B are seen multiple transmit/receive antennas 36 that are typically used for cellular communication. The antennas 36 may be multi-band for use with other radios in the UE. The operable ground plane for the antennas 36 is shown by shading as spanning the entire space enclosed by the UE housing though in some embodiments the ground plane may be limited to a smaller area, such as disposed on a printed wiring board on which the power chip 38 is formed. The power chip 38 controls power amplification on the channels being transmitted and/or across the antennas that transmit simultaneously where spatial diversity is used, and amplifies the received signals. The power chip 38 outputs the amplified received signal to the radio frequency (RF) chip 40 which demodulates and downconverts the signal for baseband processing. The baseband (BB) chip 42 detects the signal which is then converted to a bit stream and finally decoded. Similar processing occurs in reverse for signals generated in the apparatus 10 and transmitted from it.
Signals going to and from the camera 28 may pass through an image/video processor 44 that encodes and decodes the various image frames. A separate audio processor 46 may also be present controlling signals to and from the speakers 34 and the microphone 24. The graphical display interface 20 is refreshed from a frame memory 48 as controlled by a user interface chip 50 which may process signals to and from the display interface 20 and/or additionally process user inputs from the keypad 22 and elsewhere.
Certain embodiments of the UE 10 may also include one or more secondary radios such as a wireless local area network radio WLAN 37 and a Bluetooth® radio 39, which may incorporate an antenna on the chip or be coupled to an antenna off the chip. Throughout the apparatus are various memories such as random access memory RAM 43, read only memory ROM 45, and in some embodiments removable memory such as the illustrated memory card 47 on which the various programs 1 OC are stored. All of these components within the UE 10 are normally powered by a portable power supply such as a battery 49.
The processors 38, 40, 42, 44, 46, 50, if embodied as separate entities in a UE 10 or eNB 12, may operate in a slave relationship to the main processor 1OA, 12A, which may then be in a master relationship to them. Embodiments of this invention may be disposed across various chips and memories as shown, or disposed within another processor that combines some of the functions described above for Figure 2B. Any or all of these various processors of Figure 2B access one or more of the various memories, which may be on chip with the processor or separate there from. Similar function-specific components that are directed toward communications over a network broader than a piconet (e.g., components 36, 38, 40, 42-45 and 47) may also be disposed in exemplary embodiments of the access node 12, which may have an array of tower mounted antennas rather than the two shown at Figure 2B.
Note that the various integrated circuits (e.g., chips 38, 40, 42, etc.) that were described above may be combined into a fewer number than described and, in a most compact case, may all be embodied physically within a single chip.
Describing now in further detail the exemplary embodiments of this invention, AS level of RAT control is maintained by incorporating the CS fallback functionality into it. Note that this approach is compatible with SAl, as this method is also part of the EPS in "... it shall be possible for the EPS to request the UE to perform a change of radio access technology in order to deliver the service over UTRAN or GERAN or IxRTT."
Referring to Figure 3, exemplary steps of the method are as follows.
Block 3 A: The UE 10 indicates its mode of operation to the MME 14 during the LTE
Attach procedure and TAU procedure. If the mode of operation is changed by the user after it is attached to the EPS then the UE 10 performs the TAU procedure to update the
MME with the latest mode of operation settings. This information is stored in the MME as a part of the UE context.
Block 3B: The MME 14 is aware of the status of the combined attach procedure, e.g., whether it is successful or has failed (i.e., the MME 14 is aware of the status of the attach procedure described above with respect to Figure 1C). The MME 14 returns this indication, along with the UE 10 mode of operation indication, to the E-UTRAN (to the eNB 12). Block 3C: E-UTRAN now has the information of the UE 10 that is related to the CSFB mode of operation, the result of the combine attach, and also a policy related to RAT/Frequency priority control. Based on this information, E-UTRAN (the eNB 12) determines whether the UE 10 should continue to stay in LTE or should move to another RAT. This is thus the single point of control of RAT selection, hi some embodiments, the E-UTRAN may determine that a UE 10 which didn't succeed in the combined attach would be a candidate for moving to another RAT.
Block 3D: Optionally the eNB 12 can acquire a measurement report from the UE 10. The report may comprise information on accesses that are reachable by the UE 10. Block 3E. If the eNB 12 decides to redirect the UE 10 to CS coverage, it triggers a RRC Connection Release procedure to the selected CS RAT with a dedicated priority with the validity timer. Thus, the UE 10 will return to LTE coverage if desired by the network operator. In a case where the UE 10 already has a PS bearer another CSFB mechanism (e.g., PS handover or CCO) can be used to redirect the UE 10 to the CS RAT.
Reference with regard to the RRC Connection Release procedure may be made to Section 5.3.8 of the above-mentioned 3GPP TS 36.331 V8.4.0 (2008-12).
In order to make the combined attachment, the UE 10 sets up the RRC Connection (to perform the NAS procedure). Thus, this redirection can occur immediately after a combined attachment has failed and during the RRC Connection Release.
However, if the network determines to keep the UE 10 under LTE coverage for some reason, the UE 10 will not receive CS paging (the same situation as if the CS coverage is not provided). However, even for this case the UE 10 still can make (originate) a CS call by signaling its preference as defined for MO CSFB in 3GPP TS 23.272 (e.g., see generally Section 6, Mobile Originating Call).
Referring to Figure 4, further exemplary steps of the method are as follows.
Block 4A: The UE 10 sets up the RRC Connection and sends a Service Request to the MME 14 with a MO CS call indication. Block 4B: The MME 14 sends the MO CS call indication, the CSFB mode and registration status in an Initial Context Setup to the eNB 12.
Block 4C: Optionally the eNB 12 can acquire a measurement report from the UE 10.
The report may comprise information on accesses that are reachable by the UE 10. Block 4D: The eNB 12 redirects the UE 10 to the CS RAT based on the CSFB procedure
(e.g., PS-HO or CCO+NACC, or RRC redirection). The eNB 12 determines which CSFB procedure to be used and a timer value if needed based on the information from the MME
14 (that is, based on the MO CS call indication, the CSFB mode and the registration status). Block 4E: If the UE 10 is re-directed, after the CS call is terminated the UE 10 applies a normal reselection rule and AS RAT priority parameter. IfLTE has a higher priority, the
UE 10 returns to LTE coverage.
Note that the eNB 12 may advantageously set the duration of the validity timer for the UE 10 using the information received from the MME 14 which includes, in accordance with an exemplary aspect of this invention, the CFSB mode and registration status of the UE 10, and not just the MO CS call indication.
Figure 5 is another logic flow diagram that illustrates the operation of a method, and a result of execution of computer program instructions, in accordance with the exemplary embodiments of this invention. In accordance with these exemplary embodiments a method performs, at Block 5A, a step of receiving information at a network access node of a first radio access technology, the information concerning a user equipment and comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment. At Block 5B there is a step of determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
In accordance with the method, and the execution of the computer program of Figure 5, the information is received from a mobile management entity with which the user equipment has performed the combined attach procedure.
In accordance with the method, and the execution of the computer program of Figure 5, the combined attach procedure may be is a general packet radio service/international mobile subscriber identity attach procedure.
In accordance with the method, and the execution of the computer program of Figure 5, where determining comprises an initial step of requesting a measurement report from the user equipment, which report may comprise information on accesses that are reachable by the user equipment.
In accordance with the method, and the execution of the computer program of Figure 5, where if the radio access node determines to redirect the user equipment, further comprising a step of triggering a radio resource control connection release procedure for the user equipment to the second radio access technology for enabling the user equipment to return to the first radio access technology.
In accordance with the method, and the execution of the computer program of Figure 5, where the first radio access technology comprises an evolved universal terrestrial radio access network technology, and where the radio access node is embodied as an evolved Node B.
In accordance with the method, and the execution of the computer program of Figure 5, where if the radio access node determines to not redirect the user equipment, further comprising steps and operations of receiving further information at the network access node from the mobile management entity, the further information comprising a mobile originated circuit switched call indication that the mobile management entity received from the user equipment; and redirecting the user equipment to another radio access technology to obtain circuit switched service for making a mobile originated circuit switched call.
The various blocks shown in Figures 3, 4 and 5 may be viewed as method steps, and/or as operations that result from operation of computer program code, and/or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s).
Based on the foregoing it should be apparent that the exemplary embodiments of this invention provide a method, apparatus and computer program(s) to establish the decision point of RAT selection in one network node, enabling a harmonized and coordinated decision to be made. Note as well that this NAS-based approach does not interfere with any existing AS-based RAT selection mechanisms. Also, the RRC Connection Release can be still be controlled by the network, unlike a UE-based approach. As the eNB 12 can signal the timer for the validity of the dedicated priority, the use of these exemplary embodiments can ensure that the UE 10 will return to LTE coverage.
An illustrative aspect of the exemplary embodiments of this invention is an apparatus that comprises means for receiving information at a network access node of a first radio access technology, the information concerning a user equipment and comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment. The apparatus further comprises means for determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the invention is not limited thereto. While various aspects of the exemplary embodiments of this invention may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.
It should thus be appreciated that at least some aspects of the exemplary embodiments of the inventions may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.
Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this invention.
For example, while the exemplary embodiments have been described above in the context of the Rel-8 E-UTRAN (UTRAN-LTE) system, it should be appreciated that the exemplary embodiments of this invention are not limited for use with only this one particular type of wireless communication system, and that they may be used to advantage in other wireless communication systems. In addition, the exemplary embodiments may be utilized in beyond Release 8 embodiments of LTE, including LTE- Advanced (LTE-A) system types.
It should be noted that the terms "connected," "coupled," or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are "connected" or "coupled" together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be "connected" or "coupled" together by the use of one or more wires, cables and/or printed electrical connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as several non- limiting and non-exhaustive examples.
Further, the various names used for the described parameters are not intended to be limiting in any respect, as these parameters may be identified by any suitable names. Further, the various names assigned to different functional units (e.g., MME, etc.), reference points and interfaces (e.g., SGs, S 1 , etc.), and to various procedures (e.g., RRC Connection Release, etc.), are not intended to be limiting in any respect, as these various functional units, reference points and procedures may be identified by any suitable names.
Furthermore, some of the features of the various non-limiting and exemplary embodiments of this invention may be used to advantage without the corresponding use of other features. As such, the foregoing description should be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

Claims

CLAIMSWhat is claimed is:
1. A method, comprising:
receiving information at a network access node of a first radio access technology, the information concerning a user equipment and comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment; and
determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
2. The method of claim 1 , where the information is received from a mobile management entity with which the user equipment has performed the combined attach procedure.
3. The method as in any preceding claim, where the combined attach procedure is a general packet radio service/international mobile subscriber identity attach procedure.
4. The method as in any preceding claim, where determining comprises an initial step of requesting a measurement report from the user equipment.
5. The method as in any preceding claim, where if the radio access node determines to redirect the user equipment, further comprising triggering a radio resource control connection release procedure for the user equipment to the second radio access technology for enabling the user equipment to return to the first radio access technology.
6. The method as in any preceding claim, where the first radio access technology comprises an evolved universal terrestrial radio access network technology, and where the radio access node is embodied as an evolved Node B.
7. The method as in claim 2, where if the radio access node determines to not redirect the user equipment, further comprising:
receiving further information at the network access node from the mobile management entity, the further information comprising a mobile originated circuit switched call indication that the mobile management entity received from the user equipment; and
redirecting the user equipment to another radio access technology to obtain circuit switched service for making a mobile originated circuit switched call.
8. A computer-readable memory medium that stores program instructions the execution of which result in operations that comprise:
receiving at a network access node of a first radio access technology certain information concerning a user equipment, the certain information comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment; and
determining at the network access node in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
9. The computer-readable memory medium of claim 8, where the information is received from a mobile management entity with which the user equipment has performed the combined attach procedure.
10. The computer-readable memory medium as in any preceding claim, where the combined attach procedure is a general packet radio service/international mobile subscriber identity attach procedure.
11. The computer-readable memory medium as in any preceding claim, where the operation of determining comprises an initial operation of requesting a measurement report from the user equipment.
12. The computer-readable memory medium as in any preceding claim, where if the radio access node determines to redirect the user equipment, further comprising triggering a radio resource control connection release procedure for the user equipment to the second radio access technology for enabling the user equipment to return to the first radio access technology.
13. The computer-readable memory medium as in any preceding claim, where the first radio access technology comprises an evolved universal terrestrial radio access network technology, and where the radio access node is embodied as an evolved Node B.
14. The computer-readable memory medium as in claim 9, where if the radio access node determines to not redirect the user equipment, further comprising operations of:
receiving further information at the network access node from the mobile management entity, the further information comprising a mobile originated circuit switched call indication that the mobile management entity received from the user equipment; and
redirecting the user equipment to another radio access technology to obtain circuit switched service for making a mobile originated circuit switched call.
15. An apparatus, comprising:
a controller configured with a first interface for conducting wireless communications with a user equipment and with a second interface for conducting communications with a mobile management entity, said controller being responsive to a receipt from the second interface of information comprising a status of a combined attach procedure and a circuit switched fallback mode of operation of the user equipment to determine in accordance with the received information, and in accordance with radio access technology/frequency priority information, whether to redirect the user equipment to a second radio access technology to obtain circuit switched service or whether to maintain the user equipment in the first radio access technology.
16. The apparatus as in claim 15, where the combined attach procedure is a general packet radio service/international mobile subscriber identity attach procedure.
17. The apparatus as in any preceding claim, where if the controller determines to redirect the user equipment, said controller is further configured to trigger a radio resource control connection release procedure for the user equipment to the second radio access technology for enabling the user equipment to return to the first radio access technology.
18. The apparatus as in any preceding claim, where if the controller determines to not redirect the user equipment said controller is further configured to receive further information from the mobile management entity, the further information comprising a mobile originated circuit switched call indication that the mobile management entity received from the user equipment, said controller responding to the further information to redirect the user equipment to another radio access technology to obtain circuit switched service for making a mobile originated circuit switched call.
19. The apparatus as in any preceding claim, where the first radio access technology comprises an evolved universal terrestrial radio access network technology, and where the controller is embodied as a part of an evolved Node B.
20. The apparatus as in any preceding claim, where at least said controller is embodied as an integrated circuit.
PCT/IB2009/051076 2009-03-16 2009-03-16 Method, apparatus and computer readable memory medium for circuit switched fallback and inter-rat selection WO2010106397A1 (en)

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