CN106576273B

CN106576273B - Circuit switched fallback with improved reliability in pool overlap regions

Info

Publication number: CN106576273B
Application number: CN201580037238.4A
Authority: CN
Inventors: 梁华瑞; 王志伟; D·博埃特格尔; 张大伟; F·贝尔霍尔; K·基斯
Original assignee: Apple Inc
Current assignee: Apple Inc
Priority date: 2014-07-11
Filing date: 2015-07-02
Publication date: 2020-03-10
Anticipated expiration: 2035-07-02
Also published as: CN106576273A

Abstract

The invention discloses performing Circuit Switched Fallback (CSFB) calls with improved reliability. The request to establish the CSFB call may be received by a UE (106) currently located in a pool overlap region. A network resource controller (172) or base station (102) transmits information to the UE indicating the pool in which the neighboring cell is operating. For CSFB operation, the UE uses the information to select a circuit switched cell to operate on, wherein the selected CS cell is located in the same pool area as the current pool area. This prevents the UE from accidentally camping on a CS cell in another pool area, which may lead to a call failure on some networks. The information provided by the base station may include a pool area id or may include mapping relationship information that can be used by the UE to determine the current pool area.

Description

Circuit switched fallback with improved reliability in pool overlap regions

Technical Field

The present patent application relates to wireless devices, and more particularly, to a system and method for establishing a circuit switched fallback call with improved reliability.

Background

The use of wireless communication systems is growing rapidly. In addition, wireless communication technologies have evolved from voice-only communication to also including the transmission of data such as the internet and multimedia content. As wireless communication systems evolve, successive generations of wireless communication technologies tend to be developed. The adoption of a new generation of wireless technology may be a progressive process during which a previous generation or a previous generation of similar technology may coexist with the new generation of technology, for example, for a period of time until the new generation of wireless technology is fully developed.

One example of a transition to the next generation in wireless technology is the transition from GSM and UMTS to LTE. LTE uses a fully packet-switched network without providing circuit-switched services. UMTS provides both circuit switched services and packet switched services. GSM was originally provided only circuit switched services but was later enhanced to also provide some packet switched services. One transition technique to LTE is a Circuit Switched Fallback (CSFB) call. In this case, when the wireless device registers on the CSFB-enabled LTE network and a circuit switched call is initiated, the wireless device is redirected to a 2G/3G network that can support the circuit switched call.

Therefore, improvements in wireless communications, particularly in handling CSFB calls, would be desirable. In particular, it is desirable to improve the reliability of CSFB calls.

Disclosure of Invention

In view of the foregoing and other considerations, it would be desirable to provide a way for a wireless User Equipment (UE) device to perform Circuit Switched Fallback (CSFB) calls with improved reliability.

When a circuit-switched call is initiated (e.g., received) at a wireless device that is camped on a packet-switched network that does not provide circuit-switched services (e.g., an LTE network) and is capable of supporting circuit-switched fallback, the UE may be redirected to fallback to a circuit-switched network that provides circuit-switched services (e.g., UTMS). However, when the UE currently resides on a cell in the first pool during CSFB, the UE may accidentally choose to reside on a cell of a different MSC (mobile switching center) pool when switching to the circuit-switched network if the UE is in the pool overlap area. This may cause the UE to attach to another MSC server and thus may result in a call failure if MTRF (mobile station called roaming forwarding) has not been deployed in the network. Thus, disclosed herein are methods of providing sufficient information for a UE to select a suitable cell on the same pool in which it has operated and thus on the same MSC server to avoid call failure.

In various embodiments, the UE is aware of or provided with information for identifying the current pool on which it resides. For example, the UE may know its current pool, e.g., its pool id, from its own TMSI (temporary mobile station identification). In some embodiments, the UE is also provided with pool information about other neighboring candidate cells. The pool information may include a pool id' of each candidate cell of the plurality of candidate cells. In some operator networks, the pool-id of a cell is part of a Network Resource Identification (NRI), e.g., the NRI bit field includes one or more bits that specify the pool-id. In a first embodiment, a base station subsystem/radio network controller (BSS/RNC) receives and stores a pool id' from each candidate cell, e.g. received from an OAM server or a respective MSC server. The BSS/RNC then broadcasts (transmits) these pool ids' to the UE before or during CSFB operation. In another embodiment, the base station receives the pool-ids' of these candidate cells from the BSS/RNC or from the OAM server or the respective MSC server. The base station may then transmit these pool ids' to the UE. For example, the base station, eNodeB, may transmit the pool-id' in the RRC release message to the UE during CSFB operation. In other embodiments, the UE may be provided with other information to identify one or more MSC servers to which the respective candidate cell is currently attached, such as the MSC address of each MSC server or other information.

When the UE receives a Mobile Terminal (MT) (incoming) call and performs a CSFB operation, the UE may perform cell selection to select a new CS cell to camp on. The UE knows the current pool-id where it resides. The UE may also have received cell frequency/pool id information for a plurality of other cells from the BSS/RNC or base station. The BSS/RNC may then have received this information from the OAM server, which has collected it from the various MSC servers. Alternatively, the UE may receive cell frequency/pool id information from an over-the-air (OTA) server or from possible individual ones of the different neighbor candidate cells. For each respective candidate cell, the information received by the UE may include an identification of the candidate cell (e.g., the frequency of the cell), and also include the pool-id of the respective candidate cell, as well as possibly other information.

When the UE receives information (cell frequency/pool id) about various possible candidate cells, the UE may store each of the candidate cell frequencies and corresponding pool ids in a memory, such as in a data structure. When the UE is searching for a new cell, the UE may then compare the pool id on which it currently resides with the pool ids' of these candidate cells. Therefore, the UE uses this information to select candidate cells that belong to the same pool (with the same pool id) as it resided on before the CSFB operation. This is to prevent call failures that may occur if the UE is camped on another MSC pool and is therefore attached to another MSC server and MTRF is not available. This helps prevent call failures due to lack of MTRF deployment.

Thus, presented herein is an embodiment of a method for performing a CSFB call and a UE and base station or other cellular networking hardware (BSS/RNC) configured to implement the method. The UE, base station, and other hardware may include one or more radios (including one or more antennas) for performing wireless communication with each other. The UE and/or base station may also include device logic (which may include a processor and memory medium and/or hardware logic) configured to implement the method. Also presented herein are embodiments of a memory medium (e.g., a non-transitory computer-accessible memory medium) storing program instructions executable by a processor to perform some or all of the methods.

Drawings

A better understanding of the present invention can be obtained when the following detailed description of the embodiments is considered in conjunction with the following drawings.

Fig. 1 illustrates an exemplary (simplified) wireless communication system according to some embodiments;

fig. 2 illustrates a base station in communication with user equipment, in accordance with some embodiments;

fig. 3 illustrates an exemplary block diagram of a UE according to some embodiments;

fig. 4 illustrates an exemplary block diagram of a UE according to some embodiments;

fig. 5 is a block diagram of an exemplary cellular communication network, in accordance with some embodiments;

fig. 6 is a more detailed block diagram of a cellular communication network including both an LTE network and a 3GPP network;

FIG. 7 illustrates a portion of a cellular network including overlapping MSC pools;

figures 8 and 9 illustrate examples of circuit switched fallback to different pools resulting in a call failure, according to some embodiments;

fig. 10 is a flow chart showing an improved CSFB operation according to the first embodiment, where pool id information is provided from the BSS/RNC to the UE;

fig. 11 is a flow chart illustrating an improved CSFB operation according to a second embodiment, wherein pool-id information is provided from a base station to a UE;

FIG. 12 is a more detailed flow chart illustrating the improved CSFB operation according to the flow chart of FIG. 10;

FIG. 13 is a more detailed flow chart illustrating the improved CSFB operation according to the flow chart of FIG. 11; and is

Fig. 14 illustrates a manner of providing pool id information from an MSC server to a UE, according to some embodiments.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

Detailed Description

Acronyms

The following acronyms are used in this patent application.

UE: user equipment

BS: base station

ENB: eNodeB (base station)

GSM: global mobile communication system

UMTS: universal mobile communication system

LTE: long term evolution

CS: circuit switching

PS: packet switching

CSFB: circuit switched fallback

MME: mobility management entity

MSC: mobile switching center

RNC: radio network controller

OAM: operation, administration and management

RRC: radio resource control

MT: mobile station called party

MTRF: mobile station called roaming forwarding

Term(s) for

The following is a glossary of terms used in this patent application:

memory mediumAny of various types of memory devices or storage devices. The term "memory medium" is intended to include mounting media such as CD-ROMs, floppy disks 104, or tape devices; computer system memory or random access memory such as DRAM, DDR RAM, SRAM, EDO RAM, Rambus RAM, etc.; non-volatile memory, such as flash memory, magnetic media, e.g., hard disks or optical storage devices; registers, or other similar types of memory elements, etc. The storage medium may also include other types of memory or combinations thereof. Further, the memory medium may be located in a first computer executing the program, or may be located in a different second computer connected to the first computer through a network such as the internet. In the latter case, the second computer may provide the program instructions for the first computer for execution. The term "memory medium" may include two or more memory media that may reside in different locations, such as different computers connected by a network.

Carrier medium-a memory medium as described above, and a physical transmission medium such as a bus, a network and/or a transmission signal such as an electrical, electromagnetic or digital signalOther physical transmission media.

Computer systemAny of various types of computing systems or processing systems, including Personal Computer Systems (PCs), mainframe computer systems, workstations, network appliances, internet appliances, Personal Digital Assistants (PDAs), television systems, grid computing systems, or other devices or combinations of devices. In general, the term "computer system" may be broadly defined to encompass any device (or combination of devices) having at least one processor that executes instructions from a memory medium.

User Equipment (UE) (or "UE device")Any of various types of computer systems or devices that perform wireless communication. Examples of UE devices include mobile phones or smart phones (e.g., iphones)^TMBased on Android^TMTelephone), wearable device (such as a smart watch), portable gaming device (e.g., Nintendo DS)^TM、PlayStationPortable^TM、Gameboy Advance^TM、iPhone^TM) A laptop computer, a PDA, a portable internet appliance, a music player, a data storage device, or other handheld device, etc. In general, the term "UE" or "UE device" may be broadly defined to include any electronic device, computing device, and/or telecommunications device (or combination of devices) capable of wireless communication. UE devices may generally be mobile or portable and easily transported by a user, but in some cases, substantially stationary devices may also be configured to perform wireless communications.

Channel with a plurality of channels-a medium for transferring information from a sender (transmitter) to a receiver. It should be noted that, as the term "channel" is defined differently for different wireless protocols, it should be considered to be used in a manner that conforms to the standard for the type of device that refers to the term being used. In some standards, the channel width may be variable (e.g., depending on device capabilities, band conditions, etc.). For example, LTE may support a scalable channel bandwidth of 1.4MHz to 20 MHz. In contrast, a WLAN channel may be 22MHz wide, while a bluetooth channel may be 1MHz wide. Other protocolsAnd the standard may include different definitions for the channel. Further, some standards may define and use multiple types of channels, e.g., different channels for uplink or downlink and/or different channels for different purposes such as data, control information, etc.

AutomaticRefers to an action or operation performed by a computer system (e.g., software executed by a computer system) or a device (e.g., a circuit, a programmable hardware element, an ASIC, etc.) without user input directly specifying or performing the action or operation. Thus, the term "automatically" is in contrast to a user manually performing or specifying an operation in which the user provides input to directly perform the operation. An automatic process may be initiated by input provided by a user, but subsequent actions performed "automatically" are not specified by the user, i.e., are not performed "manually" in which the user specifies each action to be performed. For example, by selecting each field and providing input specifying information, a user filling out an electronic form (e.g., by typing in information, selecting check boxes, single-selection selections, etc.) is manually filling out the form, even though the computer system must update the form in response to the user action. The form may be automatically filled in by a computer system, wherein the computer system (e.g., software executing on the computer system) analyzes the fields of the form and fills in the form without any user entering answers specifying the fields. As indicated above, the user may invoke automatic filling of the form, but not participate in the actual filling of the form (e.g., the user does not manually specify answers for the fields but rather they are automatically completed). This specification provides a number of examples of automatically performing an operation in response to an action that a user has taken.

Fig. 1 and 2-communication system

Fig. 1 illustrates an exemplary (simplified) wireless communication system according to some embodiments. It is noted that the system of fig. 1 is only one example of a possible system, and that embodiments of the present invention may be implemented in any of a variety of systems, as desired.

As shown, the exemplary wireless communication system includes a base station 102 that communicates with one or more user devices 106-a through 106-N over a transmission medium. Each of the user equipments may be referred to herein as a "user equipment" (UE). Thus, the user equipment 106 is referred to as a UE or UE device.

The base station 102 may be a Base Transceiver Station (BTS) or a cell site and may include hardware to enable wireless communication with the UEs 106A-106N. Base stations 102 may also be equipped to communicate with network 100. Accordingly, base station 102 may facilitate communication between UEs and/or between UEs and network 100. The communication area (or coverage area) of a base station may be referred to as a "cell". The base station 102 and the UEs may be configured to communicate over a transmission medium using any of a variety of wireless communication technologies, such as GSM, UMTS, LTE, CDMA, WLL, WAN, WiFi, WiMAX, or the like. Base station 102 and other similar base stations operating according to the same or different cellular communication standards may thus be provided as a network of cells that may provide continuous or near-continuous overlapping service to UEs 106 and similar devices over a wide geographic area via one or more cellular communication standards.

In some embodiments, the UE106 may be capable of communicating using multiple wireless communication standards. For example, the UE106 may be configured to communicate using two or more of GSM, UMTS, LTE, CDMA2000, WiMAX, WLAN, bluetooth, one or more global navigation satellite systems (GNSS, such as GPS or GLONASS), one and/or more mobile television broadcast standards (e.g., ATSC-M/H or DVB-H), and so forth. Other combinations of wireless communication standards, including more than two wireless communication standards, are also possible.

Fig. 2 illustrates a user equipment 106 (e.g., one of the devices 106-a through 106-N) in communication with a base station 102, in accordance with some embodiments. As described above, the UE106 may be a device with wireless network connectivity, such as a mobile phone, a handheld device, a computer or tablet, or virtually any type of wireless device.

The UE may include a processor configured to execute program instructions stored in a memory. The UE may perform any of the method embodiments described herein by executing such stored instructions. In some embodiments, the UE may comprise a programmable hardware element, such as an FPGA (field programmable gate array), configured to perform any of the method embodiments described herein, or any portion of any of the method embodiments described herein.

In some embodiments, the UE106 may be configured to communicate using any of the plurality of wireless communication protocols described above. The UE106 may include one or more antennas for communicating using one or more wireless communication protocols. In some embodiments, the UE106 may share one or more portions of a receive chain and/or a transmit chain among multiple wireless communication standards; the shared radio may include a single antenna or may include multiple antennas for performing wireless communications (e.g., for MIMO). In other embodiments, the UE106 may include separate transmit and/or receive chains (e.g., including separate antennas and other radios) for each wireless communication protocol configured to communicate therewith. In further embodiments, the UE106 may include one or more radios shared between multiple wireless communication protocols, as well as one or more radios dedicated for use with a single wireless communication protocol. For example, in one set of embodiments, the UE106 may include a shared radio for communicating using either LTE or 1xRTT, and a separate radio for communicating using each of Wi-Fi and bluetooth. Other configurations are also possible.

In some embodiments, the UE106 may be configured to establish and perform a Circuit Switched Fallback (CSFB) call. For example, the UE106 may be configured to communicate using either a first wireless communication technology that provides Packet Switched (PS) services but not Circuit Switched (CS) services and a second wireless communication technology that provides PS services and CS services. If the UE106 is using a first wireless communication technology and a CS call is initiated or received, the UE106 may be able to switch to using a second wireless communication technology in order to establish the call.

In particular, in one set of embodiments, the UE106 may be configured to perform CSFB calls in a manner that advantageously improves reliability by ensuring that the UE selects a suitable cell when in a pool overlap region, as described further below.

FIG. 3-exemplary block diagram of a UE

Fig. 3 illustrates an exemplary block diagram of a UE106 according to some embodiments. As shown, the UE106 may include a system on a chip (SOC)300, which may include various portions for various purposes. For example, as shown, SOC 300 may include one or more processors 302 that may execute program instructions of UE106 and display circuitry 304 that may perform graphics processing and provide display signals to display 340. The one or more processors 302 may also be coupled to a Memory Management Unit (MMU)340, which may be configured to receive addresses from the one or more processors 302 and translate those addresses to locations in memory (e.g., memory 306, Read Only Memory (ROM)350, NAND flash memory 310) and/or other circuits or devices, such as display circuitry 304, radio 330, connector I/F320, and/or display 340. MMU 340 may be configured to perform memory protections and page table translations or settings. In some embodiments, MMU 340 may be included as part of one or more processors 302.

In the illustrated embodiment, the ROM 350 may include a boot loader that may be executed by the one or more processors 302 during startup or initialization. Further as shown, the SOC 300 may be coupled to various other circuitry of the UE 106. For example, the UE106 may include various types of memory (e.g., including NAND flash memory 310), a connector interface 320 (e.g., for coupling to a computer system), a display 340, and wireless communication circuitry (e.g., for LTE, CDMA2000, bluetooth, WiFi, etc.).

The UE device 106 may include at least one antenna, and in some embodiments may include multiple antennas for performing wireless communications with base stations and/or other devices. For example, UE device 106 may perform wireless communication using antenna 335. As described above, in some embodiments, a UE may be configured to wirelessly communicate using multiple wireless communication standards.

As described herein, the UE106 may include hardware components and software components for implementing methods for performing CSFB calls in accordance with embodiments of the present disclosure.

The processor 302 of the UE device 106 may be configured to implement a portion or all of the methods described herein, for example, by executing program instructions stored on a memory medium (e.g., a non-transitory computer-readable memory medium). In other embodiments, the processor 302 may be configured as a programmable hardware element, such as an FPGA (field programmable gate array) or as an ASIC (application specific integrated circuit).

FIG. 4-base station

Fig. 4 illustrates an example block diagram of a base station 102 in accordance with some embodiments. It is noted that the base station of fig. 4 is only one example of a possible base station. As shown, base station 102 may include one or more processors 404 that may execute program instructions for base station 102. The one or more processors 404 may also be coupled to a Memory Management Unit (MMU)440, or other circuit or device. The MMU may be configured to receive addresses from the one or more processors 404 and translate the addresses to locations in memory (e.g., memory 460 and Read Only Memory (ROM) 450).

The base station 102 may include at least one network port 470. The network port 470 may be configured to couple to a telephone network and provide access to the telephone network for a plurality of devices, such as the UE device 106, as described above.

The network port 470 (or additional network port) may also or alternatively be configured to couple to a cellular network, such as a core network of a cellular service provider. The core network may provide mobile-related services and/or other services to multiple devices, such as UE device 106. In some cases, the network port 470 may be coupled to a telephone network via a core network, and/or the core network may provide the telephone network (e.g., in other UE devices 106 served by a cellular service provider).

Base station 102 may include at least one antenna 434. The at least one antenna 434 may be configured to function as a wireless transceiver and may be further configured to communicate with the UE device 106 via the radio 430. Antenna 434 communicates with radio 430 via communication link 432. Communication chain 432 may be a receive chain, a transmit chain, or both. Radio 430 may be configured to communicate via various RATs including, but not limited to, GSM, UMTS, LTE, WCDMA, CDMA2000, and the like.

The processor 404 of the base station 102 may be configured to implement a portion or all of the methods described herein, for example, by executing program instructions stored on a memory medium (e.g., a non-transitory computer-readable memory medium). Alternatively, the processor 404 may be configured as a programmable hardware element, such as an FPGA (field programmable gate array) or as an ASIC (application specific integrated circuit), or a combination thereof.

FIG. 5-communication System

Fig. 5 illustrates an exemplary (simplified) wireless communication system according to some embodiments. It is noted that the system of fig. 5 is only one example of a possible system, and that the embodiment may be implemented in any of a variety of systems, as desired.

As shown, the exemplary wireless communication system includes base stations 102A and 102B that communicate with one or more User Equipment (UE) devices, represented as UE106, over a transmission medium. The base station 102 may be a Base Transceiver Station (BTS) or a cell site and may include hardware to enable wireless communication with the UE 106. Each base station 102 may also be equipped to communicate with the core network 100. For example, base station 102A may be coupled to core network 100A, while base station 102B may be coupled to core network 100B. Each core network may be operated by a respective cellular service provider or multiple core networks 100A may be operated by the same cellular service provider. Each core network 100 may also be coupled to one or more external networks, such as external network 108, which may include the internet, a Public Switched Telephone Network (PSTN), and/or any other network. Thus, the base station 102 may facilitate communication between the UE devices 106 and/or between the UE devices 106 and the

networks

100A, 100B, and 108.

Base station 102 and UE106 may be configured to communicate over a transmission medium using any of a variety of radio access technologies (RATs, also referred to as wireless communication technologies or telecommunication standards), such as GSM, UMTS (WCDMA), LTE-advanced (LTE-a), 3GPP2 CDMA2000 (e.g., 1xRTT, 1xEV-DO, HRPD, eHRPD), IEEE 802.11(WLAN or Wi-Fi), IEEE 802.16(WiMAX), and so on.

The base station 102A and the core network 100A may operate according to a first RAT (e.g., LTE), while the base station 102B and the core network 100B may operate according to a second (e.g., another) RAT (e.g., GSM, CDMA2000, or other conventional or circuit-switched technologies). The two networks may be controlled by the same network operator (e.g., a cellular service provider or "operator") or may be controlled by different network operators as desired. Furthermore, the two networks may operate independently of each other (e.g., if they operate according to different RATs), or may operate in a somewhat coupled or tightly coupled manner.

It is also noted that while two different networks may be used to support two different RATs (such as shown in the exemplary network configuration shown in fig. 5), other network configurations implementing multiple RATs are also possible. For example, base stations 102A and 102B may operate according to different RATs, but are coupled to the same core network. As another example, a multi-mode base station capable of simultaneously supporting different RATs (e.g., LTE and GSM, LTE and CDMA 20001 xRTT, and/or any other RAT combination) may be coupled to a core network that also supports different cellular communication technologies. In one embodiment, the UE106 may be configured to use a first RAT (e.g., LTE) as a packet-switched technology and a second RAT (e.g., GSM or 1xRTT) as a circuit-switched technology.

As described above, the UE106 may be capable of communicating using multiple RATs, such as those in 3GPP, 3GPP2, or any desired cellular standard. The UE106 may also be configured to communicate using WLAN, bluetooth, one or more global navigation satellite systems (GNSS, such as GPS or GLONASS), one and/or more mobile television broadcast standards (e.g., ATSC-M/H or DVB-H), and so on. Other combinations of network communication standards are possible.

The base stations 102A and 102B and other base stations operating according to the same or different RATs or cellular communication standards may thus be provided as a network of cells that may provide continuous or near-continuous overlapping service to the UE106 and similar devices over a wide geographic area via one or more Radio Access Technologies (RATs).

FIG. 6-Communication scenario with CSFB

Fig. 6 shows an example of a communication scenario that may involve circuit switched fallback according to the prior art. Fig. 6 depicts the current prior art CSFB operation and certain problems that arise in prior art CSFB operation. As shown, fig. 6 shows a simplified view of an exemplary network architecture with parallel LTE and 2G/3G networks. As shown, LTE network 142 and legacy 2G/3G network 144 may coexist in the same geographic area, with both networks residing between a mobile user's User Equipment (UE) and a common core network. The common core network may include an MME (mobility management entity) 152, an SGSN (serving GPRS support node) 154, and an MSC (mobile switching center) server 156. GPRS refers to general packet radio service, which is a packet-oriented mobile data service over 2G and 3G GSM (global system for mobile communications) networks.

MME 152 is used to serve UEs during communications using LTE. SGSN 154 is used to serve the UE when the UE is communicating using data services in a 2G/3G network. The MSC server 156 is used to serve the UE when voice services are utilized in the 2G/3G network. The MSC server 156 is connected to the telephone network of the operator (carrier). MME 152 is connected to MSC server 156 to support CS fallback (CSFB) signaling and SMS transport for LTE devices.

The interface (SG) between the MSC server 156 and the LTE Mobility Management Entity (MME)152 enables the UE to conduct both Circuit Switched (CS) and Packet Switched (PS) registrations while on the LTE access network. The interface also enables CS paging as well as SMS communications to be delivered via LTE access, while the UE has to leave the LTE network.

The CSFB operation generally operates as follows. Assume that a mobile station called (incoming) CS voice call arrives at MSC server 156 when the UE is currently communicating with the LTE network, i.e., the default LTE data network connection is in operation. The incoming CS voice call triggers paging of the user's UE device via LTE. The page causes CSFB operation. In performing the CSFB operation, the UE sends an extended service request to the network to transition to 2G/3G. The base station responds with a Radio Resource Control (RRC) release message to release the UE from the LTE network. Once the UE has transitioned from LTE to 2G/3G, conventional call setup procedures are performed to establish the CS call. The mobile station originating (outgoing) call follows the same transition from lte (ps) to 2G/3G (cs), but does not require a paging step. When performing CSFB from LTE to 3G network, PS data sessions can also be moved to 3G network for simultaneous voice and data services. When performing CSFB from LTE to the 2G network, the PS data session may be suspended until the voice call ends and the device returns to LTE unless the 2G network supports Dual Transfer Mode (DTM) allowing simultaneous voice and data. When the voice call ends, the UE device returns to LTE via either idle mode or connected mode mobility procedures.

Thus, as described above, the UE device switches from LTE to 2G/3G when an incoming call arrives or when the UE initiates an outgoing call. The acquisition of the 2G/3G network and the establishment of the call may employ either of two procedures, which are handover or redirection. During handover, the target cell is selected by the network and prepared in advance, and the UE may enter the cell directly in connected mode. While still in LTE, inter-radio access technology (IRAT) measurements of signal strength measurements may be performed before handover occurs. In the redirection process, rather than pre-selecting a target cell for the UE, the UE is provided with one or more possible candidate frequencies for multiple cells. The UE is then allowed to select any cell on one of these candidate frequencies. The UE may also attempt other frequencies/RATs if no cells can be found on the provided candidate frequencies. The UE may thus be provided with a frequency list containing possible frequencies of the cells it can select. Once the UE selects a cell, the UE initiates normal call setup procedures. Therefore, CSFB performed using redirection may require less time to identify the best cell than the handover procedure.

Call setup reliability is an important issue for voice call user experience. Call setup reliability refers to the ability to successfully establish an incoming or outgoing call within a certain time frame without indicating a call setup failure, preferably in the first attempt. A desired goal for CSFB call setup is to at least match legacy performance. Therefore, improvements in this area are desired.

An LTE cell may overlap two or more 2G/3G cells. Therefore, it is often uncertain which 2G/3G cell is the best target for handover from an LTE cell. In some cases, an LTE to 2G/3G cell handover may occur in an MSC server "border" area, where the LTE to 2G/3G handover involves a possible change in the MSC server. However, this can create problems on certain networks if the UE selects a new cell during CSFB that causes it to attach to another MSC server.

The MSC pool architecture may be deployed to address setup delays and failure risks in MSC "border" areas and eliminate LAU delay times. The MSC pool architecture follows the 3GPP Release 5 specification to connect Radio Access Network (RAN) nodes to multiple Core Network (CN) nodes (MSC servers). With the MSC pool architecture, all MSC servers in the pool area serve all cells in the pool, eliminating MSC "borders" within the pool and time delays of LAUs between MSCs. However, the MSC pool architecture is not widely implemented in at least some networks.

MT roaming forwarding (MTRF) may also be used as a supplement to the MSC pool architecture. MTRF is a newer version of the MT roaming retry (MTRR) standard. When performing fallback across an MSC boundary, the MTRF forwards the call directly from the old MSC server to the new MSC server, thereby overcoming the MSC server boundary problem. MTRF has the following advantages over MTRR (MT roaming retry): no agreement between operators is required and calls are not rerouted back to the GMSC for the second HLR query. This makes MTRF more reliable and easier to deploy. Again, however, MTRF is not widely implemented in at least some networks.

Fig. 7 shows most of the possible pool area configurations that can be done in a typical network. The UE is served by a dedicated Core Network (CN) node (MSC server) of the pool area as long as it is in the radio coverage of the pool area. As shown, fig. 7 contains a circuit-switched (CS) pool-area 1 (RAN-

areas

1, 2, 5, 6 served by

MSCs

1, 2, 3), a CS pool-area 2 (RAN-

areas

2, 3, 6, 7 served by

MSCs

4, 5, 6), a PS pool-area 1 (RAN-

areas

1, 5 served by SGSNs 1, 2), and a PS pool-area 2 (RAN-

areas

2, 3, 6, 7 served by

SGSNs

3, 4, 5). Further, RAN areas 4 and 8 are served by MSC 7 and SGSN 6 without using intra-domain connectivity of RAN nodes with multiple CN nodes.

CS pool areas

1 and 2 show the possibility of configuring overlapping pool areas. The

PS pool areas

1 and 2 are configured not to overlap. The pool-areas of the CS and PS domains may be identically configured to the CS pool-area 2 and the PS pool-area 2, or they may be differently configured, as shown for the CS pool-area 1 and the PS pool-area 1. The number or capacity of CN nodes (MSC servers) may be configured independently for each pool area.

A pool (or pool area) may be defined as an area in which a UE may roam without changing the serving CN node (MSC server 156). The pool areas may be served in parallel by one or more CN nodes (MSC servers). The complete service area of the RAN node (RNC or BSC) belongs to one or more identical pool areas. The RAN node service area may belong to a plurality of pool areas, which is the case when a plurality of overlapping pool areas comprise the RAN node service area. The pool areas of the CS and PS domains may be independently configured with the granularity of the RAN node service area.

A Network Resource Identifier (NRI) uniquely identifies each CN node (MSC server) from among all CN nodes of a service pool area. The length of the NRI is the same in all nodes of a domain in one pool area. In areas where pool areas overlap, the NRI uniquely identifies a CN node from all CN nodes serving all these overlapping pool areas, i.e. the NRI may uniquely identify a CN node within a RAN node. For overlapping pool areas, the NRI length may be configured to be the same in all nodes of a particular domain serving these pool areas. The NRIs of the CS and PS domains may be independent of each other, since the PS and CS domain CN nodes are independently addressed. More than one NRI may be allocated to a CN node.

The NRI is part of a temporary identity TMSI (CS domain) or P-TMSI (PS domain) allocated to the UE by the serving CN node (MSC server). Each CN node supporting "inter-domain connectivity of the RAN node with multiple CN nodes" is configured with its specific NRI or NRIs. A (P-) TMSI allocation mechanism in the CN node generates a (P-) TMSI containing the configured NRI in the relevant location position. NRIs have a flexible length between 10 bits and 0 bits (note that 0 bits means that NRIs are not used and this feature is not implemented).

Thus, as described above, and as shown in fig. 7, Circuit Switched (CS) pool areas may overlap in certain geographic areas. When the UE starts the CSFB procedure, it will disconnect from the LTE network, so that the base station sends a Radio Resource Control (RRC) release message to the UE. However, RRC release in LTE may include cell candidate frequencies from different MSC pools, and thus the UE may inadvertently select a cell in another MSC pool and thus need to attach to another MSC server. Therefore, a problem arising here is that if the UE is in a CS pool overlap area during a CSFB Mobile Terminated (MT) (incoming) call procedure, the UE may eventually select and camp on a different MSC pool than it was on before the MT call. This may result in MT call failure if MTRF is not already deployed in the network system. In addition, the UE sends an extended service request message to the network to initiate a CSFB or CSFB call, or responds to an MT CS fallback request from the network. In general, when an ESR failure occurs, the UE may select a GSM or UTMS (GERAN/UTRAN) cell in another Radio Access Network (RAN), which may increase the failure rate. For example, assume that the UE initiates an ESR for a CSFB Mobile Terminated (MT) call in RAN (radio access network) service area 2, where MSC1 is the serving MSC. After the ESR has failed in the current cell selection, the UE may camp in a cell belonging to RAN service area 3. In this example, then the MSC4 would be the serving MSC. In a network where MTRF capability has not been deployed, the CSFB MT call will fail. This will adversely affect the user experience. One example of a network that has not deployed MTRF capability is the China Mobile (CMCC) network, i.e., CMCC deploys only a small amount of MTRF capability in its current network.

FIGS. 8 and 9-CSFB to different pools causing call failure

Fig. 8 illustrates an example of a CSFB fallback procedure resulting in an MT call failure in accordance with some embodiments. As shown, when an MT (incoming) call arrives via a paging message 802 to a base station and a page is provided to a UE (not shown), the UE issues an Extended Service Request (ESR)804 to the base station in response to the MT call. The base station (eNodeB) then responds with an RRC release 806 to release the UE from the LTE network. The RRC release message 806 from the base station may include one or more Absolute Radio Frequency Channel Numbers (ARFCNs). The RRC release message may include Absolute Radio Frequency Channel Numbers (ARFCNs) belonging to two or more different MSC pools. It is noted that in GSM cellular networks, the Absolute Radio Frequency Channel Number (ARFCN) is a code that specifies a pair of physical radio carriers, one for uplink signals and one for downlink signals, for transmission and reception in a mobile radio network. Thus, the uplink/downlink channel pairs in GSM are identified by ARFCNs.

In response to the RRC release message received from the base station, the UE performs a fallback to the 2G/3G network 808. During CS fallback, the UE may select a 2G/3G cell from a different MSC pool than the pool on which it camped when the MT call arrived. Note that in this example, the UE chooses to camp on a cell from another MSC pool (MSC pool 2). The UE electing to camp on another MSC pool may cause the MT call to fail. As shown in fig. 8, the failure may be due to the fact that the IAM message cannot be forwarded between MSC servers operating these different pools, i.e. the IAM message cannot be forwarded between the previous MSC pool (pool 1) and the newly selected MSC pool (pool 2). Therefore, the CC _ setup 810 is not provided to the UE, resulting in a call failure.

Fig. 9 shows another example of a CSFB fallback procedure resulting in an MT call failure in case an ESR failure scenario is involved. As shown, as in fig. 8, when an MT (incoming) call page 802 arrives and is provided to the UE, the UE issues an Extended Service Request (ESR)804 to the base station in response to the MT call. However, in this example, the ESR message sent by the UE ends with an ESR failure 807. When an ESR failure 807 occurs, the UE may perform normal cell selection for GERAN (gsm), which will likely be located in another MSC pool. This may result in a call failure, e.g., no CC setup 810. Note that ESR failure has a higher probability than RRC release to cause the UE to select another MSC pool. For example, note that the Network (NW) may take some action to avoid sending the ESR failure, which may include allocating a cell belonging to another MSC pool to the UE. Such allocation of a cell belonging to another MSC pool will cause the UE to camp on this other MSC pool, resulting in MT call failure.

Therefore, for each of the examples of fig. 8 and 9, an MT call failure occurs, resulting in performance degradation. This performance degradation occurs in either case of RRC release or ESR failure.

Fig. 10 and 11: flow chart embodiments

Fig. 10 and 11 are simple flow diagrams illustrating an embodiment of a method for providing improved reliability of CSFB call operation. Here, the UE is provided with information about the MSC server to which its respective neighboring or candidate cell is currently attached, so that it can select a cell corresponding to the same MSC server. This is used to help prevent call failures due to lack of MTRF deployment.

In embodiments described herein, the UE receives information about the current MSC server currently serving the UE. For example, the UE may know its own MSC server, e.g. its own pool-id from its TMSI (temporary mobile station identifier). The UE may also receive information about the MSC server of the neighboring candidate cell. One way to provide this current MSC server information is to provide the UE with the pool area id ' (or pool id ') of each candidate cell, in particular the pool id ' of the pool in which this respective other cell is currently operating. Since cells in the same pool use the same MSC server, this pool id information enables the UE to select a cell corresponding to the same MSC server by selecting a cell in the same pool. Thus, the pool id serves as a proxy for identifying the current MSC server for each of these candidate cells. Note that other information identifying the current MSC server (to which the respective candidate cell is currently attached) may be provided to the UE instead of or in addition to the pool ids' of these cells, such as the MSC server address, or any of various other types of MSC server identification information. For example, in some implementations where cells in the same pool do not necessarily use the same MSC server, other information may be used to identify the MSC servers of the candidate cells, such as MSC server addresses.

Referring now to fig. 10, the network system includes a base station subsystem/radio network controller (BSS/RNC)172 in wireless communication with the UE 106. The BSS/RNC 172 is coupled to the MSC server 156. BSS/RNC 172 is also coupled to OAM server 174, OAM server 174 in turn being coupled to MSC server 156 and MME 152. At "1" in fig. 10, the BSS/RNC may obtain the current UE MSC pool frequencies and NRI pool ids' of these candidate cells from the OAM server, which may in turn have obtained this information from the MSC server. This step will typically be performed before the MT call request, but may also be performed during CSFB operation. Thus, as further depicted in fig. 13, the BSS/RNC may also obtain cell frequency/pool id information for a plurality of other cells and may broadcast this information to the UE. The BSS/RNC may obtain cell frequency/pool id information for a plurality of other cells from the respective MSC server collected by the OAM server.

More specifically, when the UE initially connects to the network, it is attached to the MSC server via the 2G/3G network. The MSC server then allocates a valid TMSI (temporary mobile station ID) to the UE. The TMSI includes 32 bits, with a portion of the TMSI having an NRI field. The NRI field may be included in the middle 0-10 bits of the TMSI. One or more bits of the NRI field contain the pool-id of the pool (or pool area) on which the UE currently resides.

The BSS/RNC may obtain the NRI from the MSC server, either directly or via an OAM server, for each of a plurality of possible candidate cells. As described above, the NRI field contains the pool id of the pool on which the cell is currently operating, thus allowing the BSS/RNC to know the pool id. For 3GPP Iu mode, the BSS/RNC can acquire NRI via IDNNS in RRC. The BSS/RNC may additionally (or alternatively) obtain other information, such as MSC addressing information, that can be used to identify the current MSC server for these neighboring cells.

Before or during CSFB fallback operation, the BSS/RNC broadcasts the frequency list of potential fallback cells and their respective pool ids' to the UE via SI/SIB (system information/system information block).

At "2" of fig. 10, the UE then performs cell selection based on the information to select a cell mapped to the same pool as the initial cell or to the same MSC server. More specifically, when the UE receives a mobile station called (MT) (incoming) call and performs a CSFB operation, the UE performs cell selection to select a new CS cell to camp on. The UE knows the current pool-id on which it resides, which has been obtained from its own TMSI or received from the BSS/RNC or base station. The UE may also know the cell frequency/pool id information for multiple candidate cells, which has been received from the BSS/RNC or possibly from the OTA server as described above. Alternatively, the UE receives broadcasts from respective ones of the different neighboring cells, and for each respective cell, the broadcast information includes the cell's frequency and the pool-id (or other pool or MSC identification information) of the respective cell.

When the UE receives cell frequency/pool id information for each possible cell, the UE may store the frequency of the new cell and the corresponding pool id of the respective cell in a memory, such as a data structure. The UE then compares the pool-ids of these potential cells (at least a complex subset of these candidate cells) with the pool-ids of the cells on which it currently resides. Therefore, the UE uses this information to select a cell belonging to the same pool as it resided on before the CSFB operation.

Thus, the UE selects the cell in the same pool it was in before the MT call request arrived and therefore continues to use the same MSC server as before. In other words, the cells in the same pool are selected such that the MSC server is unchanged. In other embodiments, the UE selects a cell known to be associated with the same MSC server to which it is currently attached based on other information, such as the MSC server address, or other id, or other type of information that can identify the MSC server.

Fig. 11 is a simple flow diagram of a second embodiment similar to that described above with reference to fig. 10. Only the main differences from fig. 10 are specified in detail. In this embodiment, the base station (eNodeB) stores the same pool id information (or possibly other information such as MSC addressing information) as that stored by the BSS/RNC described above. In this embodiment, it is assumed that the network operator has deployed an OAM system between the base station and the BSS/RNC. The OAM system is then configured by the network operator as a type of relay node where the BSS/RNC communicates cell frequency/pool id information to the OAM and the OAM communicates that information to the base station (eNodeB). The base station then forwards the cell frequency/pool id information to the UE in an RRC release message, such as during CSFB. Thus, during CSFB, the UE will have the necessary information to know the pool-id' of the current MSC pool and a large number of other cells, and can select cells belonging to the same pool.

As shown in fig. 11, at "1", the base station (eNodeB) acquires pool id information of each candidate cell from the OAM server. As described above, the OAM server will have received this information in advance from the MSC server or possibly from the BSS/RNC. At "2", the base station transmits an RRC release message to the UE during CSFB call operation. The base station transmits the pool-id information (and/or MSC addressing information) of the neighboring cell to the UE as part of the RRC release message. The RRC release message may thus include a list/pool id' of frequencies corresponding to the candidate cell. As described above, the UE may additionally or alternatively receive cell frequency and pool id information for each of these candidate cells from the OTA server or from the cell itself. The UE then selects an appropriate CS cell belonging to the same pool based on the received pool id information of the respective candidate cells received from the base station. In other words, the UE then performs cell selection, wherein the UE uses the received pool id information of the candidate cell to determine the appropriate CS cell to select that belongs to the same pool area as it is currently operating in.

FIG. 12-Detailed flow chart

Fig. 12 is a more detailed flow chart of the method shown in fig. 10. The method shown in fig. 12 corresponds to the flow shown in fig. 10. In the embodiment depicted in fig. 10, prior to or during CSFB operation, BSS/RNC 172 may transmit pool information to the UE at 801 regarding the pool in which the respective candidate cells are operating (shown in fig. 14). Note that the BSS/RNC may alternatively or additionally send other information that can identify the current MSC server of these candidate cells, such as the current MSC server address.

The BSS/RNC apparatus therefore broadcasts cell frequency/pool id information for these various candidate cells to the UE at 801, where this information may have been collected by the OAM server from different MSC servers. This operation is described with reference to fig. 14. When the UE receives broadcast information about various possible cells from the BSS/RNC apparatus, the UE stores, for each respective cell, the frequency of the respective cell and the corresponding pool-id of the respective cell. For example, the UE may store this information in a data structure, such as a table, to allow for easy searching during cell reselection (during CSFB). The BSS/RNC or UE may alternatively (or additionally) receive cell frequency/pool id information of other cells from the OTA server.

As shown in fig. 12, assume that the network receives a Mobile Terminating (MT) call request to establish a CSFB call with a UE while the UE is camped on or operating on a Packet Switched (PS) network. It is noted that embodiments of the present invention may operate with calls originating from a UE as well as calls to a UE (MT calls). The MT call request may be received in the form of a paging message 802 received by a base station (eNodeB), which is then provided to the UE at 803. One example of such a PS network is LTE. Before the MT call (or when the MT call is received), the UE resides on MSC pool 1, as shown. In response to an MT call received over the network, MSC p1 issues paging message 802 to the base station, which then pages the UE at 803. As shown, in response to the paging message, the UE transmits an Extended Service Request (ESR) to a base station (eNodeB) at 804, as shown.

The base station (eNodeB) then responds with an RC release 806 to release the UE from the LTE network. The RRC release message from the base station may include a frequency list of cells on which the UE may camp, i.e., may include one or more Absolute Radio Frequency Channel Numbers (ARFCNs) including Absolute Radio Frequency Channel Numbers (ARFCNs) of cells belonging to two or more different MSC pools.

During cell selection at 82, the UE then compares the pool-id of the cell on which it currently resides with the pool-ids' of the potential cells (e.g., at least a subset, preferably a complex subset, of the potential cells). For example, the UE may use the pool-id of its current cell to search for other candidate cell frequencies with the same pool-id and select one of these cells with the same pool-id. It is noted that the UE may of course additionally use other criteria in performing its cell selection, such as received signal strength, etc. Thus, performing the selection of the candidate cell based on the pool information comprises performing the selection based at least in part on the pool information, i.e. the selection may also be based on other factors. The UE then selects a cell, e.g., cell 1, at 828 that is in the same MSC pool as the pool in which the UE was previously operating, i.e., has the same pool-id of the cell on which it has camped. This results in a successful call.

Thus, in summary, the BSS/RNC broadcasts to the UE the pool area id' (or possibly other information such as the MSC address) of the current pool area of each possible candidate cell. Thus, the UE has received pool information of these neighboring cells from the BSS/RNC in advance, and when the UE is performing CSFB operation and the corresponding UE is in the pool overlap region, the UE uses this information to select a cell located in the same pool area in which it is currently operating (i.e., in which it was previously). Cells located in the same pool as before will also share the same MSC server. This serves to prevent the UE from inadvertently selecting a cell in another pool area and thus using another MSC server, thereby providing improved reliability of CSFB operation. In other words, this helps to avoid call failures that may result if the UE selects a cell in another pool area and thus selects another MSC server.

FIG. 13: second embodiment

Referring now to fig. 13, the method will now be described with reference to the flow shown in fig. 11. As shown in fig. 13, assume that the network receives a Mobile Terminating (MT) call request to establish a CSFB call with a UE while the UE is camped or operating on a Packet Switched (PS) network. One example of such a PS network is LTE. Prior to the MT call, the UE camps on MSC pool 1, as shown. In response to an MT call received over the network, MSC p1 issues paging message 802 to the base station, which then pages the UE at 803. As shown, in response to the paging message, the UE transmits an Extended Service Request (ESR)804 to the base station (eNodeB), as shown.

The base station (eNodeB) then responds with an RRC release at 826 to release the UE from the LTE network. The RRC release message 826 from the base station may include a frequency list containing cell frequencies on which the UE can camp, and corresponding pool id information for those cell frequencies. In other words, the information may include one or more Absolute Radio Frequency Channel Numbers (ARFCNs) including Absolute Radio Frequency Channel Numbers (ARFCNs) belonging to two or more different MSC pools, and corresponding pool id information for each of the cell frequencies. The RRC release message sent by the base station at 826 may also include other information, such as an MSC server address, for identifying the MSC server or pool associated with each candidate cell.

Thus, when a UE is performing a CSFB operation and the respective UE is in a pool overlap region, in this embodiment, the base station (eNodeB 102) broadcasts the cell frequency and corresponding pool id' of the neighboring or candidate cell to the UE in an RRC message at 826. The UE receives cell frequency/pool id information from each candidate cell in an RRC message and uses this information to select at 828 a cell that is located in the same pool area it was located before. For example, the UE may store cell frequency/pool id information for various cells in a data structure and use searching, as described above. This helps to avoid call failures that may result if the UE selects a cell in another pool area and is therefore served by another MSC server. In other words, when the UE then performs cell selection, the UE uses its own pool id and the pool id' of the other candidate cells to select a CS cell belonging to the same pool area as that in which it is currently operating. This serves to prevent the UE from inadvertently selecting a cell in another pool area, thus preventing possible call failures and providing improved reliability of CSFB operation.

FIG. 14-Providing information to a UE

Fig. 14 shows two different methods for providing MSC server information of candidate cells to a UE, as depicted in fig. 12 and 13 above. As described above, in the embodiments described herein, the MSC server information provided includes pool information, such as the current pool id' of each respective cell. Thus, the pool id 'for each cell is transmitted to the UE, where the pool id' is used in cell selection, as described herein.

In the first embodiment, the pool ids' of the other candidate cells are transmitted to the UE in a BSS/RNC broadcast message. As shown, the OAM server collects MSC server information (pool id information) and Location Area Codes (LACs) from each of a plurality of MSC servers for a plurality of candidate cells. The pool id information takes the form of NRI bits. Thus, the information collected from the OAM server may take the form of, for example:

MSC pool 1: NRI 00011, LAC1 and NRI 00013, LAC 2;

MSC pool 2: NRI 00112, LAC 3;

MSC pool 3: NRI 00212, LAC 4;

the OAM server then provides the BSS/RNC servers of the respective one or more UEs with the corresponding pool id information and LAC numbers for the multiple cells, and may in fact provide this information to multiple BSS/RNC servers, as shown. The BSS/RNC server may then add additional information, such as frequency and cell ID, to each set of information. Thus, the BSS/RNC may generate information such as:

BSS/RNC 1: ARFCN 1, NRI 00011, cell ID A, LAC1

BSS/RNC 2: ARFCN 2, NRI 00011, cell ID B, LAC1

BSS/RNC 3: ARFCN 3, NRI 00013, cell ID C, LAC2

BSS/RNC 4: ARFCN 4, NRI 00111, cell ID D, LAC3

BSS/RNC 5: ARFCN 5, NRI 00112, cell ID E, LAC3

BSS/RNC 6: ARFCN 6, NRI 00212, cell ID F, LAC4

The BSS/RNC broadcasts the set of cell frequency/pool ID information/cell ID/LAC to the UE as shown. As shown, the OAM server provides this set of information, including the respective cell frequencies and corresponding pool id information, to a plurality of different BSS/RNC servers, so that the method can be implemented in a plurality of different cell areas, i.e. for UEs served by different BSS/RNC devices.

In a second embodiment, the pool-id' of other candidate cells is transmitted from the base station (eNB) to the UE in an RRC release message. As shown, the OAM server collects MSC server information (pool id information) and Location Area Code (LAC) from each of a plurality of MSC servers for a plurality of candidate cells, as described above, and provides it to the base station (eNB). The base station then transmits this information to the UE along with the cell frequency information, such as during an RRC release message and during CSFB. Note that here, the base station may not have cell ID or LAC number information as the BSS/RNC does, and therefore does not include this information. Thus, the base station may transmit information to the UE like:

ARFCN 1，NRI 00011，

ARFCN 2，NRI 00011，

ARFCN 3，NRI 00013，

ARFCN 4，NRI 00111，

ARFCN 5，NRI 00112，

ARFCN6，NRI 00212，

as described above, the UE may utilize information received from the base station to select cells in the same pool (with the same pool id) as the pool on which it currently resides during CSFB.

The following paragraphs describe additional embodiments.

A. A non-transitory computer accessible memory medium containing program instructions for a wireless User Equipment (UE) device to establish a Circuit Switched Fallback (CSFB) call, wherein the program instructions are executable to:

receiving a request to establish a CSFB call, wherein a UE is operating in a current pool having a first pool-id;

receiving a pool id for each candidate cell of a plurality of candidate cells, wherein the pool id for each respective candidate cell identifies a pool in which the respective cell is operating;

selecting a circuit switched cell to camp on based at least in part on the first pool id and a pool id' of at least a complex subset of each of the plurality of candidate cells, wherein the selected circuit switched cell is located in the current pool.

B. A method for a wireless User Equipment (UE) device to establish a Circuit Switched Fallback (CSFB) call, the method comprising:

establishing a first wireless link with a first cell, wherein the first cell provides a connection to a network, wherein the first cell provides packet switched service, wherein the first cell does not provide circuit switched service, wherein the first cell is located in a first pool;

receiving a request to establish a call;

receiving an instruction via the first radio link originating from setting up the call as a CSFB call, wherein the instruction instructs the UE to release the first radio link with the first cell and to set up a second radio link with the second cell;

receiving pool information from a base station, wherein the pool information identifies pools corresponding to a plurality of candidate cells adjacent to a UE; and

selecting a circuit switched cell to camp on based on the received pool information, wherein the selected circuit switched cell is located in the first pool.

C. A method for a wireless User Equipment (UE) device to perform a Circuit Switched Fallback (CSFB) call, the method comprising:

is performed by the UE in a manner that,

receiving a request to establish a CSFB call, wherein a UE is operating in a current pool;

receiving first pool information regarding a plurality of candidate cells from a base station, wherein the pool information identifies a respective pool for each of the plurality of candidate cells;

selecting a circuit switched cell to camp on based on the first pool information, wherein

The selected circuit switched cell is located in the current pool.

Embodiments of the invention may be implemented in any of various forms. For example, in some embodiments, the invention may be implemented as a computer-implemented method, a computer-readable memory medium, or a computer system. In other embodiments, the invention may be implemented using one or more custom designed hardware devices, such as ASICs. In other embodiments, the invention may be implemented using one or more programmable hardware elements, such as FPGAs.

In some embodiments, a non-transitory computer-readable memory medium may be configured such that it stores program instructions and/or data, wherein the program instructions, if executed by a computer system, cause the computer system to perform a method, e.g., any of the method embodiments described herein, or any combination of the method embodiments described herein, or any subset of any of the method embodiments described herein, or any combination of such subsets.

In some embodiments, an apparatus (e.g., a UE) may be configured to include a processor (or a set of processors) and a memory medium, wherein the memory medium stores program instructions, wherein the processor is configured to read and execute the program instructions from the memory medium, wherein the program instructions are executable to implement any of the various method embodiments described herein (or any combination of the method embodiments described herein, or any subset of any of the method embodiments described herein, or any combination of such subsets). The apparatus may be embodied in any of a variety of forms.

Although the embodiments above have been described in considerable detail, numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations and modifications.

Claims

1. A method for a wireless user equipment, UE, device to perform a circuit switched fallback, CSFB, call, the method comprising:

performing, by the wireless User Equipment (UE) device:

receiving a request to perform a CSFB operation to process a call, wherein the wireless User Equipment (UE) device is operating in a current pool when the request is received;

receiving pool information identifying a plurality of pools in which each candidate cell of a plurality of candidate cells is operating;

selecting a circuit switched cell to camp on, wherein the circuit switched cell is selected based on the pool information such that the selected circuit switched cell is operating in the current pool; and

performing the CSFB operation with the selected circuit-switched cell to process the call.

2. The method of claim 1, wherein the pool information comprises a pool id for each of the candidate cells.

3. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein said receiving said pool information occurs prior to said receiving said request to perform said CSFB operation.

4. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein the wireless User Equipment (UE) device is operating in a pool overlap region during the receiving the request to perform the CSFB operation and the performing the CSFB operation.

5. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein said receiving said pool information occurs during said performing said CSFB operation.

6. The method of claim 5, wherein the first and second light sources are selected from the group consisting of,

wherein the receiving the pool information comprises receiving the pool information in a Radio Resource Control (RRC) release message from a base station during the CSFB operation.

7. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein for each respective candidate cell of the plurality of candidate cells, the pool information comprises a frequency of the respective candidate cell and a pool id of a pool in which the respective candidate cell is operating;

wherein the selecting the circuit switched cell to camp on comprises selecting the circuit switched cell based on comparing a pool id of the current pool in which the wireless user equipment, UE, device is operating with a pool id' of at least a subset of each of the plurality of candidate cells.

8. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein the pool information comprises, for each candidate cell of the plurality of candidate cells, a cell frequency, a pool id, a cell id, and a location area code.

9. The method of claim 1, wherein the first and second light sources are selected from the group consisting of,

wherein the current pool in which the wireless user equipment, UE, device is operating has a first pool-id;

wherein the selecting the circuit switched cell to camp on comprises selecting a first cell frequency of the selected circuit switched cell from a plurality of candidate cell frequencies;

the method further includes storing, by the wireless user equipment, UE, device, the pool information for each candidate cell of the plurality of candidate cells in a data structure, wherein for each candidate cell, the data structure stores a candidate cell frequency and a corresponding pool-id of a pool to which the cell frequency belongs;

wherein the selecting the circuit switched cell to camp on comprises comparing the first pool id to a pool id' in the data structure to select the first cell frequency.

10. A wireless user equipment, UE, device, the wireless user equipment, UE, device comprising:

a radio comprising one or more antennas to perform wireless communication;

a processor;

a memory medium having stored thereon program instructions executable by the processor to:

receiving a request to perform a circuit switched fallback, CSFB, operation to handle a call, wherein the wireless user equipment, UE, device is operating in a current pool when the request is received:

receiving first information, wherein the first information identifies a plurality of pools in which each candidate cell of a plurality of candidate cells is operating;

selecting a circuit switched cell to camp on, wherein the circuit switched cell is selected based on the received first information such that the selected circuit switched cell is operating in the current pool;

11. The wireless user equipment, UE, device of claim 10, wherein the first information includes a plurality of MSC addresses, wherein each of the MSC addresses identifies a respective MSC server for at least one of the plurality of candidate cells;

wherein the circuit switched cell is selected such that the circuit switched cell is served by a current MSC server currently serving the wireless user equipment, UE, device.

12. The wireless user equipment, UE, device of claim 10, wherein the first information comprises pool information for each candidate cell of the plurality of candidate cells;

wherein the circuit switched cell is selected based on the received pool information such that the selected circuit switched cell is located in the same pool as the pool in which the wireless user equipment, UE, device is currently operating.

13. The wireless user equipment, UE, device of claim 10,

wherein the wireless user equipment, UE, device has a current pool-id;

wherein the first information comprises a list of cell frequencies and a corresponding pool id for each of the cell frequencies;

wherein the selecting the circuit switched cell to camp on comprises selecting a cell frequency of the circuit switched cell based on the current pool id of a current pool in which the wireless user equipment, UE, device is operating and a pool id' of each cell of at least a subset of the plurality of cells.

14. The wireless user equipment, UE, device of claim 13,

wherein the memory medium is further configured to store a data structure containing the first information, wherein the data structure stores a cell frequency and a pool id for each of the plurality of cells;

wherein the program instructions are further executable to select the circuit switched cell to camp on by comparing the current pool id to at least one complex subset of pool ids' stored in the data structure.

15. The wireless user equipment, UE, device of claim 10,

wherein the first information is received from a radio network controller.

16. The wireless user equipment, UE, device of claim 10,

wherein the first information is received in a Radio Resource Control (RRC) release message from a base station during the CSFB operation.

17. The wireless user equipment, UE, device of claim 10,

wherein the wireless user equipment UE device is operating in a network that does not support MT roaming Forwarding (MTRF).

18. A base station, comprising:

a radio comprising one or more antennas to perform wireless communication;

a processor;

a memory medium having stored thereon program instructions executable by the base station to:

receiving and storing first information, wherein the first information includes a pool id identifying a plurality of pools in which each cell of a plurality of cells is operating;

sending a request to a first user equipment, UE, device to perform a circuit switched fallback, CSFB, operation to handle a call;

transmitting the first information to the first user equipment, UE, device in a Radio Resource Control (RRC) release message;

wherein the first information is usable by the first user equipment, UE, device to select a circuit switched cell to camp on during the CSFB operation, wherein the circuit switched cell is selected based on the received first information such that the circuit switched cell is located in a same pool in which the first user equipment, UE, device was previously operating.

19. The base station as set forth in claim 18,

wherein the first information comprises a list of cell frequencies and a corresponding pool id'.

20. The base station as set forth in claim 19,

wherein each of the pool ids' is derived from a Network Resource Information (NRI) field obtained from the MSC server.