WO2014117390A1

WO2014117390A1 - Single radio tune-away for lte voice without csfb

Info

Publication number: WO2014117390A1
Application number: PCT/CN2013/071269
Authority: WO
Inventors: Xipeng Zhu; Reza Shahidi; Shyamal Ramachandran; Miguel Griot
Original assignee: Qualcomm Incorporated
Priority date: 2013-02-01
Filing date: 2013-02-01
Publication date: 2014-08-07

Abstract

A method, an apparatus, and a computer program product for wireless communication are provided. In one aspect, an apparatus supports multiple radio access technologies (RATs), and has a single radio configured to provide a circuit-switched (CS) and packet switched (PS) connectivity. The apparatus sends a request for combined registration to a first network entity and detects whether circuit-switched fallback (CSFB) support is available to the apparatus in the first network. The request for combined registration may include a request for concurrent registration with a packet switched (PS) service of the first network and a CS service of a second network using a second RAT. The apparatus enables a single radio LTE (SR-LTE) operation, to maintain the availability of PS service in the first network, when the requested combined registration is not accepted by the first network entity. The SR-LTE operation and related techniques provided herein enable CS and PS service for voice- centric devices without regard to network support for CSFB operation.

Description

SINGLE RADIO TUNE- A WAY FOR LTE VOICE WITHOUT CSFB

BACKGROUND

Field

[0001] The present disclosure relates generally to communication systems, and more particularly, to a user equipment (UE) having a single radio to provide a circuit- switched (CS) service while maintaining registration for packet-switched service (e.g., LTE network) in the absence of circuit-switched fallback (CSFB) or voice over LTE (VoLTE) services.

Background

[0002] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources (e.g., bandwidth, transmit power). Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems.

[0003] These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example of a n emerging telecommunication standard is Long Term Evolution (LTE). LTE is a set of enhancements to the Universal Mobile Telecommunications System (UMTS) mobile standard promulgated by Third Generation Partnership Project (3 GPP). It is designed to better support mobile broadband Internet access by improving spectral efficiency, lowering costs, improving services, making use of new spectrum, and better integrating with other open standards using OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), and multiple-input multiple-output (MIMO) antenna technology. However, as the demand for mobile broadband access continues to increase, there exists a need for further improvements in LTE technology. Preferably, these improvements should be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

[0004] In an aspect of the disclosure, a method, a computer program product, and an apparatus are provided. The apparatus supports multiple radio access technologies (RATs), and has a single radio to provide circuit-switched (CS) and packet-switched (PS) connectivity. The apparatus sends a request for combined registration to a first network entity using a first RAT to detect whether circuit-switched fallback (CSFB) is available at the first network entity. The apparatus may optionally send the request upon a determination that voice over LTE (VoLTE) service is not available in the first network. The request for combined registration can include a request for concurrent registration with a PS service of the first network and a CS service of a second network using a second RAT. The apparatus enables a single radio LTE (SR-LTE) operation, instead of disabling a registration with the PS network of the first RAT, when it is determined that the requested combined registration is not accepted at the first network entity, the SR-LTE operation facilitating the CS service independent of the availability of CSFB or VoLTE support in the first network.

[0005] In an aspect, the apparatus may be a mobility management entity (MME) communicating with a user equipment (UE). The UE may support communication on multiple radio access technologies (RATs) using a single radio. The MME receives from the UE a request for combined registration. The request for combined registration may include a request for concurrent registration with a packet-switched (PS) network of a first RAT and a circuit-switched (CS) network of a second RAT. The MME indicates to the UE that the request for combined registration is not accepted when circuit-switched fallback (CSFB) is not available, and receives an extended service request from the UE relating to the UE's registration with the PS network after indicating that the request for combined registration is not accepted.

[0006] In a further aspect, the UE may support communication on a circuit-switched

(CS) and a packet-switched (PS) radio access network using a single radio. Accordingly, the MME receives a request from the UE via a tracking area update, the request requesting a short message service (SMS) in the MME. The MME then sends a request to a home subscriber server (HSS) to register an address of the MME as a serving GPRS support node (SGSN) for receiving a mobile terminated short message service (MT-SMS). When the HSS supports the SMS in the MME, the MME receives from the HSS an acknowledgment that the SMS is supported in the MME in response to the request from the MME. Thereafter, the MME sends to the UE confirmation that the SMS in the MME is enabled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a network architecture.

FIG. 2 is a diagram illustrating an example of an access network.

FIG. 3 is a diagram illustrating an example of a DL frame structure in LTE.

FIG. 4 is a diagram illustrating an example of an UL frame structure in LTE.

FIG. 5 is a diagram illustrating an example of a radio protocol architecture for the user and control planes.

FIG. 6 is a diagram illustrating an example of an evolved Node B and user equipment in an access network.

FIG. 7 is a diagram illustrating SRVCC in a wireless communication network.

FIG. 8 is a diagram of a 3GPP circuit-switched fallback (CSFB) architecture.

FIG. 9 is a diagram illustrating a call flow of a power-on registration procedure.

FIG. 10 is a diagram illustrating a call flow of a UE requesting suspension of a PS operation.

FIG. 11 is a diagram illustrating a call flow for registering an address of the MME as an SGSN for receiving MT-SMS.

FIG. 12 is a diagram illustrating a call flow for MT-SMS delivery.

FIG. 13 is a diagram illustrating a call flow for PS mobility to SGSN.

FIG. 14 is a flow chart of a method of wireless communication.

FIG. 15 is a data flow diagram illustrating the data flow between different modules/means/components in an exemplary apparatus.

FIG. 16 is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system.

FIG. 17 is a flow chart of a method of wireless communication.

FIG. 18 is a flow chart of a method of wireless communication. [0025] FIG. 19 is a data flow diagram illustrating the data flow between different modules/means/components in an exemplary apparatus.

[0026] FIG. 20 is a diagram illustrating an example of a hardware implementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

[0027] The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

[0028] Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as "elements"). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

[0029] By way of example, an element, or any portion of an element, or any combination of elements may be implemented with a "processing system" that includes one or more processors. Examples of processors include microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software modules, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

[0030] Accordingly, in one or more exemplary embodiments, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer- readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), and floppy disk where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer- readable media.

[0031] FIG. 1 is a diagram illustrating an LTE network architecture 100. The LTE network architecture 100 may be referred to as an Evolved Packet System (EPS) 100. The EPS 100 may include one or more user equipment (UE) 102, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) 104, an Evolved Packet Core (EPC) 110, a Home Subscriber Server (HSS) 120, and an Operator's Internet Protocol (IP) Services 122. The EPS can interconnect with other access networks, but for simplicity those entities/interfaces are not shown. As shown, the EPS provides packet-switched services, however, as those skilled in the art will readily appreciate, the various concepts presented throughout this disclosure may be extended to networks providing circuit-switched services.

[0032] The E-UTRAN includes the evolved Node B (eNB) 106 and other eNBs 108.

The eNB 106 provides user and control planes protocol terminations toward the UE 102. The eNB 106 may be connected to the other eNBs 108 via a backhaul (e.g., an X2 interface). The eNB 106 may also be referred to as a base station, a Node B, an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), or some other suitable terminology. The eNB 106 provides an access point to the EPC 110 for a UE 102. Examples of UEs 102 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, or any other similar functioning device. The UE 102 may also be referred to by those skilled in the art as a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

[0033] The eNB 106 is connected to the EPC 110. The EPC 110 includes a Mobility

Management Entity (MME) 112, other MMEs 114, a Serving Gateway 116, a Multimedia Broadcast Multicast Service (MBMS) Gateway 124, a Broadcast Multicast Service Center (BM-SC) 126, and a Packet Data Network (PDN) Gateway 118. The MME 112 is the control node that processes the signaling between the UE 102 and the EPC 110. Generally, the MME 112 provides bearer and connection management. All user IP packets are transferred through the Serving Gateway 116, which itself is connected to the PDN Gateway 118. The PDN Gateway 118 provides UE IP address allocation as well as other functions. The PDN Gateway 118 is connected to the Operator's IP Services 122. The Operator's IP Services 122 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), and a PS Streaming Service (PSS). The BM-SC 126 may provide functions for MBMS user service provisioning and delivery. The BM-SC 126 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a PLMN, and may be used to schedule and deliver MBMS transmissions. The MBMS Gateway 124 may be used to distribute MBMS traffic to the eNBs (e.g., 106, 108) belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information.

[0034] FIG. 2 is a diagram illustrating an example of an access network 200 in an LTE network architecture. In this example, the access network 200 is divided into a number of cellular regions (cells) 202. One or more lower power class eNBs 208 may have cellular regions 210 that overlap with one or more of the cells 202. The lower power class eNB 208 may be a femto cell (e.g., home eNB (HeNB)), pico cell, micro cell, or remote radio head (RRH). The macro eNBs 204 are each assigned to a respective cell 202 and are configured to provide an access point to the EPC 110 for all the UEs 206 in the cells 202. There is no centralized controller in this example of an access network 200, but a centralized controller may be used in alternative configurations. The eNBs 204 are responsible for all radio related functions including radio bearer control, admission control, mobility control, scheduling, security, and connectivity to the serving gateway 116.

[0035] The modulation and multiple access scheme employed by the access network

200 may vary depending on the particular telecommunications standard being deployed. In LTE applications, OFDM is used on the DL and SC-FDMA is used on the UL to support both frequency division duplex (FDD) and time division duplex (TDD). As those skilled in the art will readily appreciate from the detailed description to follow, the various concepts presented herein are well suited for LTE applications. However, these concepts may be readily extended to other telecommunication standards employing other modulation and multiple access techniques. By way of example, these concepts may be extended to Evolution-Data Optimized (EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interface standards promulgated by the 3rd Generation Partnership Project 2 (3GPP2) as part of the CDMA2000 family of standards and employs CDMA to provide broadband Internet access to mobile stations. These concepts may also be extended to Universal Terrestrial Radio Access (UTRA) employing Wideband-CDMA (W- CDMA) and other variants of CDMA, such as TD-SCDMA; Global System for Mobile Communications (GSM) employing TDMA; and Evolved UTRA (E-UTRA), IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, and Flash-OFDM employing OFDM A. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents from the 3 GPP organization. CDMA2000 and UMB are described in documents from the 3GPP2 organization. The actual wireless communication standard and the multiple access technology employed will depend on the specific application and the overall design constraints imposed on the system.

[0036] The eNBs 204 may have multiple antennas supporting MIMO technology. The use of MIMO technology enables the eNBs 204 to exploit the spatial domain to support spatial multiplexing, beamforming, and transmit diversity. Spatial multiplexing may be used to transmit different streams of data simultaneously on the same frequency. The data steams may be transmitted to a single UE 206 to increase the data rate or to multiple UEs 206 to increase the overall system capacity. This is achieved by spatially precoding each data stream (i.e., applying a scaling of an amplitude and a phase) and then transmitting each spatially precoded stream through multiple transmit antennas on the DL. The spatially precoded data streams arrive at the UE(s) 206 with different spatial signatures, which enables each of the UE(s) 206 to recover the one or more data streams destined for that UE 206. On the UL, each UE 206 transmits a spatially precoded data stream, which enables the eNB 204 to identify the source of each spatially precoded data stream.

[0037] Spatial multiplexing is generally used when channel conditions are good. When channel conditions are less favorable, beamforming may be used to focus the transmission energy in one or more directions. This may be achieved by spatially precoding the data for transmission through multiple antennas. To achieve good coverage at the edges of the cell, a single stream beamforming transmission may be used in combination with transmit diversity.

[0038] In the detailed description that follows, various aspects of an access network will be described with reference to a MIMO system supporting OFDM on the DL. OFDM is a spread-spectrum technique that modulates data over a number of subcarriers within an OFDM symbol. The subcarriers are spaced apart at precise frequencies. The spacing provides "orthogonality" that enables a receiver to recover the data from the subcarriers. In the time domain, a guard interval (e.g., cyclic prefix) may be added to each OFDM symbol to combat inter-OFDM-symbol interference. The UL may use SC-FDMA in the form of a DFT-spread OFDM signal to compensate for high peak-to-average power ratio (PAPR).

[0039] FIG. 3 is a diagram 300 illustrating an example of a DL frame structure in LTE.

A frame (10 ms) may be divided into 10 equally sized sub-frames. Each sub-frame may include two consecutive time slots. A resource grid may be used to represent two time slots, each time slot including a resource block. The resource grid is divided into multiple resource elements. In LTE, a resource block contains 12 consecutive subcarriers in the frequency domain and, for a normal cyclic prefix in each OFDM symbol, 7 consecutive OFDM symbols in the time domain, or 84 resource elements. For an extended cyclic prefix, a resource block contains 6 consecutive OFDM symbols in the time domain and has 72 resource elements. Some of the resource elements, indicated as R 302, 304, include DL reference signals (DL-RS). The DL-RS include Cell-specific RS (CRS) (also sometimes called common RS) 302 and UE-specific RS (UE-RS) 304. UE-RS 304 are transmitted only on the resource blocks upon which the corresponding physical DL shared channel (PDSCH) is mapped. The number of bits carried by each resource element depends on the modulation scheme. Thus, the more resource blocks that a UE receives and the higher the modulation scheme, the higher the data rate for the UE.

[0040] FIG. 4 is a diagram 400 illustrating an example of an UL frame structure in

LTE. The available resource blocks for the UL may be partitioned into a data section and a control section. The control section may be formed at the two edges of the system bandwidth and may have a configurable size. The resource blocks in the control section may be assigned to UEs for transmission of control information. The data section may include all resource blocks not included in the control section. The UL frame structure results in the data section including contiguous subcarriers, which may allow a single UE to be assigned all of the contiguous subcarriers in the data section.

[0041] A UE may be assigned resource blocks 410a, 410b in the control section to transmit control information to an eNB. The UE may also be assigned resource blocks 420a, 420b in the data section to transmit data to the eNB. The UE may transmit control information in a physical UL control channel (PUCCH) on the assigned resource blocks in the control section. The UE may transmit only data or both data and control information in a physical UL shared channel (PUSCH) on the assigned resource blocks in the data section. A UL transmission may span both slots of a subframe and may hop across frequency.

[0042] A set of resource blocks may be used to perform initial system access and achieve UL synchronization in a physical random access channel (PRACH) 430. The PRACH 430 carries a random sequence and cannot carry any UL data/signaling. Each random access preamble occupies a bandwidth corresponding to six consecutive resource blocks. The starting frequency is specified by the network. That is, the transmission of the random access preamble is restricted to certain time and frequency resources. There is no frequency hopping for the PRACH. The PRACH attempt is carried in a single subframe (1 ms) or in a sequence of few contiguous subframes and a UE can make only a single PRACH attempt per frame (10 ms). FIG. 5 is a diagram 500 illustrating an example of a radio protocol architecture for the user and control planes in LTE. The radio protocol architecture for the UE and the eNB is shown with three layers: Layer 1, Layer 2, and Layer 3. Layer 1 (LI layer) is the lowest layer and implements various physical layer signal processing functions. The LI layer will be referred to herein as the physical layer 506. Layer 2 (L2 layer) 508 is above the physical layer 506 and is responsible for the link between the UE and eNB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control (MAC) sublayer 510, a radio link control (RLC) sublayer 512, and a packet data convergence protocol (PDCP) 514 sublayer, which are terminated at the eNB on the network side. Although not shown, the UE may have several upper layers above the L2 layer 508 including a network layer (e.g., IP layer) that is terminated at the PDN gateway 118 on the network side, and an application layer that is terminated at the other end of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radio bearers and logical channels. The PDCP sublayer 514 also provides header compression for upper layer data packets to reduce radio transmission overhead, security by ciphering the data packets, and handover support for UEs between eNBs. The RLC sublayer 512 provides segmentation and reassembly of upper layer data packets, retransmission of lost data packets, and reordering of data packets to compensate for out-of-order reception due to hybrid automatic repeat request (HARQ). The MAC sublayer 510 provides multiplexing between logical and transport channels. The MAC sublayer 510 is also responsible for allocating the various radio resources (e.g., resource blocks) in one cell among the UEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNB is substantially the same for the physical layer 506 and the L2 layer 508 with the exception that there is no header compression function for the control plane. The control plane also includes a radio resource control (RRC) sublayer 516 in Layer 3 (L3 layer). The RRC sublayer 516 is responsible for obtaining radio resources (e.g., radio bearers) and for configuring the lower layers using RRC signaling between the eNB and the UE.

FIG. 6 is a block diagram of an eNB 610 in communication with a UE 650 in an access network. In the DL, upper layer packets from the core network are provided to a controller/processor 675. The controller/processor 675 implements the functionality of the L2 layer. In the DL, the controller/processor 675 provides header compression, ciphering, packet segmentation and reordering, multiplexing between logical and transport channels, and radio resource allocations to the UE 650 based on various priority metrics. The controller/processor 675 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the UE 650.

[0048] The transmit (TX) processor 616 implements various signal processing functions for the LI layer (i.e., physical layer). The signal processing functions include coding and interleaving to facilitate forward error correction (FEC) at the UE 650 and mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase- shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols are then split into parallel streams. Each stream is then mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 674 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 650. Each spatial stream is then provided to a different antenna 620 via a separate transmitter 618TX. Each transmitter 618TX modulates an RF carrier with a respective spatial stream for transmission.

[0049] At the UE 650, each receiver 654RX receives a signal through its respective antenna 652. Each receiver 654RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor 656. The RX processor 656 implements various signal processing functions of the LI layer. The RX processor 656 performs spatial processing on the information to recover any spatial streams destined for the UE 650. If multiple spatial streams are destined for the UE 650, they may be combined by the RX processor 656 into a single OFDM symbol stream. The RX processor 656 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the eNB 610. These soft decisions may be based on channel estimates computed by the channel estimator 658. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the eNB 610 on the physical channel. The data and control signals are then provided to the controller/processor 659.

[0050] The controller/processor 659 implements the L2 layer. The controller/processor can be associated with a memory 660 that stores program codes and data. The memory 660 may be referred to as a computer-readable medium. In the UL, the controller/processor 659 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the core network. The upper layer packets are then provided to a data sink 662, which represents all the protocol layers above the L2 layer. Various control signals may also be provided to the data sink 662 for L3 processing. The controller/processor 659 is also responsible for error detection using an acknowledgement (ACK) and/or negative acknowledgement (NACK) protocol to support HARQ operations.

[0051] In the UL, a data source 667 is used to provide upper layer packets to the controller/processor 659. The data source 667 represents all protocol layers above the L2 layer. Similar to the functionality described in connection with the DL transmission by the eNB 610, the controller/processor 659 implements the L2 layer for the user plane and the control plane by providing header compression, ciphering, packet segmentation and reordering, and multiplexing between logical and transport channels based on radio resource allocations by the eNB 610. The controller/processor 659 is also responsible for HARQ operations, retransmission of lost packets, and signaling to the eNB 610.

[0052] Channel estimates derived by a channel estimator 658 from a reference signal or feedback transmitted by the eNB 610 may be used by the TX processor 668 to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor 668 are provided to different antenna 652 via separate transmitters 654TX. Each transmitter 654TX modulates an RF carrier with a respective spatial stream for transmission.

[0053] The UL transmission is processed at the eNB 610 in a manner similar to that described in connection with the receiver function at the UE 650. Each receiver 618RX receives a signal through its respective antenna 620. Each receiver 618RX recovers information modulated onto an RF carrier and provides the information to a RX processor 670. The RX processor 670 may implement the LI layer.

The controller/processor 675 implements the L2 layer. The controller/processor 675 can be associated with a memory 676 that stores program codes and data. The memory 676 may be referred to as a computer-readable medium. In the UL, the control/processor 675 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover upper layer packets from the UE 650. Upper layer packets from the controller/processor 675 may be provided to the core network. The controller/processor 675 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

FIG. 7 depicts a simplified wireless network environment in which a UE 702 is located within the coverage of multiple cells that use different frequencies and/or different radio access technologies (RATs) in a radio access network (RAN) to access a core network that provides mobility management, session management, transport for Internet Protocol packet services (e.g. through packet data network gateway 712 which is coupled to an IP network 714), and other services. A RAN may comprise ground-based infrastructure required for delivery of communication between UE 702 and the core network. In LTE, the RAN may comprise one or more eNBs 704. RATs may be based on UMTS, TD-SCDMA, GSM, CDMA2000 and WiMAX.

UE 702 may perform a mobility procedure that results in the UE 702 moving from a source cell to a target cell. The mobility procedure may include leaving the source cell to camp on the target cell, identifying characteristics of the target cell, establishing a connection on the target cell, receiving a grant on the target cell, and initiating a location update.

In one example, UE 702 may be able to receive packet-switched (PS) data services, including VoIP, from an LTE network and may initiate a circuit-switched fallback (CSFB) to initiate or receive voice calls. CSFB may be accomplished by IRAT redirection or handover executed by UE 702. For example, UE 702 may reselect a RAT that supports voice service, such as IxRTT, W-CDMA, GSM, or other RAT. UE 702 may transfer from an LTE network to another network if LTE service is lost, particularly when UE 702 physically moves through a coverage area of a communication system.

[0058] Mobility management (MM) functions may be provided to support UE 702 mobility, including for example non-access stratum (NAS) signaling and security, signaling between core network nodes for mobility between 3GPP access networks, packet data network gateway (P-GW) and serving gateway (S-GW) selection, and SGSN selection for handovers, and roaming and authentication. An EPS mobility management (EMM) process identifies and maintains communication connections to mobile devices that can move throughout or connect to different EPS networks. In one example, the EMM process sets an NAS state which reflects whether a UE 702 is registered with MME 706. UE 702 may have valid MM parameters from both an SGSN 722 and a MME 706, and/or another control node which processes the signaling between the UE 702 and the core network. MME 706 may provide a visitor location register (VLR) for an EPS. For example, a "Temporary Identity used in Next update" (TIN) may be a parameter of an MM context of UE 702, which can identify the identity of the UE 702 used in a next RAU request, a tracking area update (TAU) request or attach request message.

[0059] A TAU may be performed for a number of reasons and the TAU is a procedure by which the UE 702 updates the network when the UE 702 changes location and it moves out of its current tracking area (TA). TAU is typically performed when UE 702 enters a new cell outside the current tracking area (TA). A TAU procedure may be relatively prolonged, and can last for periods of 15 seconds or more, particularly where the TAU process fails and is retried. When UE 702 initiates a TAU process for any reason, it may enter an EMM-TRACKING- AREA-UPDATING- INITIATED state. During TAU procedures, the EMM may buffer high level requests, such as extended service requests (ESRs), until the TAU procedure has completed. The ESR request may comprise a request by UE 702 to perform circuit- CSFB to initiate or receive voice calls. For example, the UE 702 may request CSFB for an emergency call.

[0060] Certain radio access networks (RANs) may support one or more packet switched

(PS) service, such as Internet protocol (IP) service and IMS. A RAN may support voice over PS (VoPS) calls including voice over IP (VoIP). A UE may also be able to access a circuit switched RAN for voice service. Single radio voice call continuity (SRVCC) handles continuity between PS and CS voice calls that are anchored in IMS when the UE is capable of transmitting/receiving on only one of those RANs at a time. SRVCC capabilities may be identified and tracked at the access stratum (AS) and the non-access stratum (NAS). The AS comprises functions and protocols used to transfer information across a specific radio access technology (RAT), while the NAS comprises protocols which operate between the UE and a core network (CN) and NAS protocols are not specific to a particular RAT. In the EPS, the NAS protocols typically comprise protocols for mobility management and session management between the UE and the MME.

[0061] FIG. 8 is a diagram 800 of a 3 GPP circuit-switched fallback (CSFB) architecture.

CSFB is a mainstream voice solution for LTE. CSFB enables the support of voice service without deploying an IP multimedia subsystem (IMS) infrastructure. CSFB and IMS may also be deployed simultaneously, meaning that an operator can gradually roll out an IMS system while still supporting a fallback mechanism where necessary. A UE may indicate to the network that it wants to perform a "Combined Attached" during initial registration with the MME. In practice, this means that the UE requests from the network to also register its presence in the 2G/3G circuit switched network.

[0062] A mobile terminated call for a subscriber arrives at the MSC, which then signals the incoming call to the MME. The UE is paged in LTE if in idle mode or notified of the call if in active mode. It responds requesting CS fallback for the call to proceed. For Mobile Originated (MO) calls, the UE establishes an RRC Connection (if idle) and then notifies the MME that a CS fallback call is required. The CSFB mechanism itself may include either of a PS Handover to another radio access technology (RAT) or an RRC Connection Release with redirection to the other RAT.

[0063] Referring to FIG. 8, the CSFB architecture provides an SGs interface between the MSC server and the MME. The interface is based on Gs protocols and is utilized to enable mobility management and paging procedures between the CS Domain and EPC. As a result of a combined attached procedure, a terminating voice call arriving at the MSC will cause a paging notification to be sent to the MME. The MME will then be responsible for paging (or notifying) the UE of the incoming voice call.

[0064] Additionally, an S3 interface between the MME and SGSN is also shown and enables Idle Mode Signaling Reduction (ISR). ISR enables a UE to be simultaneously registered in a Tracking Area and UTRAN/GERAN Routing Area (RA). Tracking and Routing Area Updates are not required as the UE reselects between technologies unless the TA/RA has changed. Pages for downlink data (or CSFB calls) will be sent on both technologies as enabled by the S3 interface.

In an aspect, CSFB may not always be available to the UE, particularly when the UE is roaming. In such a situation, a voice-centric UE will disable the E-UTRAN (i.e., disable an LTE connection) according to 3GPP standard specifications. The UE disables the LTE connection so that: 1) the UE stays connected to 2G/3G for a CS voice service; 2) the UE does not reselect/select LTE; and 3) the UE is not handed over or redirected to LTE. Hence, a legacy UE camps only on 2G/3G (e.g., GSM) and gives up packet-switched services (e.g., LTE) when CSFB is not available.

In an aspect, the UE may initiate a single radio LTE (SR-LTE) operating mode as an alternative solution when neither CSFB nor voice over IMS (VoIMS) is available. As described herein, with SR-LTE, the UE does not disable LTE when CSFB or VoIMS is not supported. This allows the UE to participate in an LTE packet-switched (PS) service when the UE is not performing a CS operation (e.g., voice call). SR-LTE also allows the UE to dually standby on both LTE and 2G. An SR-LTE UE may use the same hardware as a normal CSFB UE, and may use a simple universal subscriber identity module (USIM). The SR-LTE UE includes a single transmitter (Tx) and a single receiver (Rx) with tune-away capability for dual camping on a GSM/UMTS CS network and a LTE PS network.

FIG. 9 is a diagram 900 illustrating a call flow for a power-on registration procedure. At step 1, the UE establishes an RRC connection with an eNB. At step 2, the UE initiates combined registration by sending a request to the MME for a combined EPS/IMSI Attach. The combined EPS/IMS Attach request may include a CS/PS mode 1 signal. At step 3, the eNB performs an EPS Attach procedure with the home subscriber server (HSS).

If the network MME supports CSFB (e.g., SGs interface exists), then the MME may accept the combined registration and enable normal CSFB operation. However, if the network MME does not support CSFB (e.g., SGs interface does not exist), then the UE enables an SR-LTE operation instead of disabling LTE. For example, at step 4, when the MME rejects the IMSI Attach request in an Attach Accept message including EMM Cause #18 (CS not available), the UE receives an RRC connection release message from the eNB (step 5) and tunes to GSM to register with a GSM CS network (step 6).

In another example, at step 4, the MME may respond to the combined Attach request with certain conditions. The conditions may include: 1) combined registration available for a short message service (SMS) only; or 2) CSFB not preferred. In that case, the full combined Attach request was not accepted and CSFB operation is not available to the UE. In response, the UE enables SR-LTE operation, maintains it registration with the PS network, and also camps on the CS network. Unlike CSFB procedures, the SR-LTE behavior enables the UE to maintain access to the packet-switched network even when it has been designated for voice-centric operation. The UE may also initiate an IMSI detach procedure with the MME. The UE then tunes to GSM to register with a GSM CS network (step 6).

The above-described procedures of FIG. 9 may also be applicable to a tracking area update (TAU) procedure.

In an SR-LTE operation, the UE camps on both LTE and 2G (e.g., GSM) in parallel. The UE may camp via a one-on-one-off approach. For example, because the SR-LTE UE utilizes one transmitter and one receiver, the receiver may tune to LTE for a period of time (e.g., a first DRX cycle), then tune to GSM for another period of time (e.g., a second DRX cycle).

The SR-LTE UE in EPS connection management idle mode (ECM-Idle) and GSM idle mode (GSM-Idle) knows the paging occasions for both LTE and GSM. Accordingly, the UE may intermittently tune between LTE and GSM to perform certain operations. For example, the UE may intermittently tune between LTE and GSM to perform: 1) paging reception; 2) cell reselection/selection and measurement; 3) system information reading; or 4) location registration.

When the SR-LTE UE needs to enter a GSM dedicated mode for a CS operation (e.g., CS call, SMS, location update, etc.), the UE may tune to GSM when the UE is in ECM connected mode (ECM-Connected) and GSM-Idle. In a first example, the UE may act as if it is out of service (00 S) (outside of LTE coverage) or a radio link failure (RLF) has occurred by locally suspending a PS operation on the LTE network and tuning to GSM to perform the CS operation without notifying the LTE network. An advantage of such operation is that the UE not dependent on network behavior. In a second example, the UE may request the LTE network to suspend a PS operation and release an RRC connection.

[0074] FIG. 10 is a diagram 1000 illustrating a call flow of a UE requesting suspension of a PS operation. At step 1, the UE in LTE initiates a mobile originated (MO) CSFB (e.g., service type = "0000") by sending an extended service request (ESR) to the MME. The UE sends the ESR when the UE needs to transmit anything in GSM, e.g., MO call, mobile terminated (MT) call, or MT-SMS. In an aspect, a dedicated LTE PS suspending procedure can be defined. For example, a new service type may be defined for the UE to request the suspension of the LTE PS operation by ESR. In another example, the MME may suspend a PS operation and release SI without indicating CSFB to the eNB.

[0075] At step 2, the MME sends a request (UE context modification request) to the eNB to perform CSFB. For example, the MME may direct the eNB to perform CSFB when CSFB operation is not available in order to accommodate SR-LTE operation of the UE. At step 3, the eNB sends a response (UE context modification response) to the MME. At step 4, the eNB sends an RRC connection release message to the UE. If the UE receives a message redirecting the UE to GSM, the UE ignores the redirection message. At step 5, the eNB sends a UE context release request to the MME. The UE context release request informs the MME that the UE is not available for a PS service. At step 6, the MME suspends a PS operation which may include the MME sending a suspending notification to SGW. SGW then sends a suspending request to PGW, whereupon the SGW/PGW marks the UE as suspended. Afterward, when downlink data arrives for the UE, the SGW/PGW does not send any of the data to the MME or eNB. At step 7, the UE tunes to GSM to perform CS activities. In an aspect, if the UE does not receive the RRC connection release message from the eNB after a predetermined time period from when the ESR is sent to the MME, then the UE may locally suspend the PS operation on the LTE network and tune to GSM to perform a CS operation without notifying the LTE network.

[0076] In an aspect, SMS may be transmitted between the MME and SMS-SC directly

(UE^MME^SMS-SC). Notably, "SMS over SGs" uses the MSC to transmit SMS (UE<→MME<→MSC<→SMS-SC). This operation may be used when an operator does not have a CS network to transmit SMS, a UE does not have a CS subscription, or for an MTC device. SMS transmitted via the MME is transparent to the UE. With SR-LTE, the UE may utilize a similar procedure as "SMS over SGs." However, the UE needs combined EPS/IMSI registration.

[0077] A number of issues may arise when performing SMS in MME. For example, a first issue (Issue 1) may arise when a dual receiver CSFB UE is not combined EPS/IMSI registered. A second issue (Issue 2) may arise when the MME does not know that the UE needs to "SMS in MME." A third issue (Issue 3) may arise when there is a conflict in CS registration. In one example of Issue 3, registering the MME (as MSC) for MT-SMS may trigger the HSS to cancel CS registration for a voice service. In another example of Issue 3, CS registration from GSM may cancel MME registration for MT-SMS.

[0078] To resolve Issues 1 and 2, a first option may be for the UE to request "SMS in

MME" via a tracking area update (TAU) with an "SMS only" flag, when IMSI registration is rejected by the MME in an Attach Accept message. A TAU accept message may include an "SMS Only" flag confirming that "SMS in MME" is enabled by the network. A second option is to use a reserved bit in an "additional update type" in a combined EPS/IMSI Attach message to: 1) indicate that "SMS in MME" is requested; and 2) implicitly indicate that the UE is a dual Rx CSFB UE.

[0079] To resolve Issue 3 (CS registration confliction), a first option may be to register an address of the MME as an SGSN for receiving MT-SMS. A second option may be to register the MME as the MME. A third option may be to isolate CS registration for SMS and voice. In the third option, the HSS maintains two MSC addresses for a UE, one MSC for MT-SMS and another MSC for another CS service.

[0080] FIG. 11 is a diagram 1100 illustrating a call flow for registering an address of the MME as an SGSN for receiving MT-SMS with SR-LTE operation. Previously, the MME could only request registering itself as an MSC in the HSS for receiving MT-SMS. However, according to the present disclosure, the MME may utilize a cause value such as "SMS REGISTRATION AS SGSN REQUIRED" to request the HSS to register the MME as an SGSN for receiving MT-SMS. Referring to FIG. 11, at step 1, the UE requests "SMS in MME" by indicating "SMS Only" in an EPS TAU Request message. This is performed after the UE learns that CSFB operation is not available. At step 2, the MME sends to the HSS a request to update a location (SMS REGISTRATION AS SGSN REQUIRED). This may be facilitated by adding a new enum value "SMS REGISTRATION AS SGSN REQUIRED" to an "SMS-Register-Request" of a ULA message. At step 3, if the HSS supports "SMS in MME" and understands "SMS REGISTRATION AS SGSN REQUIRED", the HSS replies with an update location acknowledgement (ACK) (SMS in MME Support). At step 4, the MME replies to the UE with TAU Accept ("SMS Only") to confirm that "SMS in MME" is enabled.

[0081] FIG. 12 is a diagram 1200 illustrating a call flow for MT-SMS delivery. For

MT-SMS (step 1), the SMS-SC queries the HSS for serving nodes for SMS (step 2). The HSS replies with both an MSC address and an SGSN address (step 3). The SMS-SC configures SMS over SGSN to have a higher priority than SMS over MSC (step 4). In an aspect, in case where two addresses (SGSN and MSC) are received from the HLR, the SMS-GMSC may choose (operator dependant) via which nodes (SGSN or MSC) the SMS is first to be sent. The SMS delivery via the SGSN is typically more radio resource efficient than the SMS delivery via the MSC. The SMS-SC sends the SMS to the MME (step 4). If PS operation is suspended for the UE (e.g., due to the UE being in a GSM dedicated mode), the MME rejects the SMS and the SMS-SC resends the SMS via the MSC. Otherwise, the MME sends the SMS to the UE via a non-access stratum (NAS) (step 5).

[0082] FIG. 13 is a diagram 1300 illustrating a call flow for PS mobility to SGSN.

Referring to FIG. 13, when the UE goes out of LTE coverage, the UE sends a routing area update (RAU) to the SGSN. Thereafter, SGSN (MME) registration for MT-SMS is replaced with a new SGSN address, if "SMS in SGSN" is supported. Otherwise, the HSS deletes the SGSN registration for MT-SMS

[0083] FIG. 14 is a flow chart 1400 of a method of wireless communication. The method may be performed by a UE supporting multiple radio access technologies (RATs). The UE may have a single radio to provide circuit-switched (CS) and packet- switched (PS) connectivity. At step 1402, the UE sends a request to a first network entity of a first RAT for combined registration to detect whether circuit- switched fallback (CSFB) or voice over LTE (VoLTE) is available at the first network entity. The request for combined registration may include a request for concurrent registration with a PS network of the first RAT and a CS network of a second RAT. The first RAT may be a Long Term Evolution (LTE) system. The second RAT may be a Global System for Mobile Communications (GSM) or a Universal Mobile Telecommunications System (UMTS).

[0084] At step 1404, the UE determines that the requested combined registration is not accepted at the first network entity. Determining that the request for combined registration is not accepted by the first network entity may include: 1) receiving an indication that registration with the CS network is not available; 2) receiving an indication that registration with the CS network is only supported for a short message service (SMS); and/or 3) receiving an indication that registration with the CS network is not preferred.

[0085] At step 1406, the UE enables a single radio LTE (SR-LTE) operation, instead of disabling a registration with the PS network of the first RAT, when it is determined that the requested combined registration is not accepted at the first network entity. The SR-LTE operation facilitates the CS service without utilizing a CSFB or VoLTE service. The enabling the SR-LTE operation includes maintaining the registration with the PS network of the first RAT in response to determining that the request for combined registration is not accepted and registering with the CS network of the second RAT via a second network entity of the second RAT while the PS network registration is maintained.

[0086] In an aspect, when the UE is in an idle mode, the enabling the SR-LTE operation further includes camping on the first RAT and the second RAT in parallel and intermittently tuning between the first RAT and the second RAT to perform at least one of: paging reception, cell reselection/selection and measurement, system information reading, or location registration. The intermittent tuning may include tuning to the first RAT and not the second RAT for a period of time, and tuning to the second RAT and not the first RAT for another period of time.

[0087] In a further aspect, when the UE is in a connected mode of the first RAT, the enabling the SR-LTE operation further includes tuning to the second RAT to perform the CS service without notifying the first RAT and locally suspending a PS operation on the first RAT.

[0088] In another aspect, when the UE is in a connected mode of the first RAT and is triggered to perform the CS service on the second RAT, the enabling the SR-LTE operation further includes sending an extended service request to the first network entity of the first RAT and waiting to receive a radio resource control (RRC) connection release message from the first RAT. When the RRC connection release message is received from a base station, the UE tunes to the second RAT to perform the CS service based on information about the second RAT included in the RRC connection release message. When the RRC connection release message is not received from the base station within a predefined time period, the UE tunes to the second RAT to perform the CS service without notifying the first RAT and locally suspends a PS operation on the first RAT.

At step 1408, when the first network entity is a mobility management entity (MME), the UE may send a message to the MME via a tracking area update. The message may be a request for a short message service (SMS) in the MME. Upon the MME receiving the request from the UE, the MME sends a request to a home subscriber server (HSS) to register an address of the MME as a serving GPRS support node (SGSN) for receiving a mobile terminated short message service (MT- SMS). When the HSS supports the SMS in the MME, the MME receives from the HSS an acknowledgment that the SMS is supported in the MME in response to the request from the MME. At step 1410, the UE receives from the MME confirmation that the SMS in the MME is enabled.

FIG. 15 is a data flow diagram 1500 illustrating the data flow between different modules/means/components in an exemplary apparatus 1502. The apparatus may be a UE supporting multiple radio access technologies (RATs). The UE may have a single radio to provide circuit-switched (CS) and packet-switched (PS) connectivity. The apparatus includes a receiving module 1504, a combined registration module 1506, an SR-LTE module 1508, an SMS module 1510, and a transmission module 1512.

The combined registration module 1506 sends (via transmission module 1512) a request to a first network entity 1550 of a first RAT for combined registration to detect whether circuit-switched fallback (CSFB) or voice over LTE (VoLTE) is available at the first network entity 1550. The request for combined registration may include a request for concurrent registration with a PS network of the first RAT and a CS network of a second RAT. The first RAT may be a Long Term Evolution (LTE) system. The second RAT may be a Global System for Mobile Communications (GSM) or a Universal Mobile Telecommunications System (UMTS).

Thereafter, the combined registration module 1506 determines that the requested combined registration is not accepted at the first network entity 1550. Determining that the request for combined registration is not accepted by the first network entity 1550 may include: 1) receiving an indication that registration with the CS network is not available; 2) receiving an indication that registration with the CS network is only supported for a short message service (SMS); and/or 3) receiving an indication that registration with the CS network is not preferred.

[0093] The SR-LTE module 1508 enables a single radio LTE (SR-LTE) operation, instead of disabling a registration with the PS network of the first RAT, when it is determined that the requested combined registration is not accepted at the first network entity 1550. The SR-LTE operation facilitates the CS service without utilizing a CSFB or VoLTE service. The enabling the SR-LTE operation includes the SR-LTE module 1508 maintaining the registration with the PS network of the first RAT in response to determining that the request for combined registration is not accepted and registering with the CS network of the second RAT via a second network entity 1570 of the second RAT while the PS network registration is maintained.

[0094] In an aspect, when the apparatus 1502 is in an idle mode, the enabling the SR-

LTE operation further includes the SR-LTE module 1508 camping on the first RAT and the second RAT in parallel and intermittently tuning between the first RAT and the second RAT to perform at least one of: paging reception, cell reselection/selection and measurement, system information reading, or location registration. The intermittent tuning may include tuning to the first RAT and not the second RAT for a period of time, and tuning to the second RAT and not the first RAT for another period of time.

[0095] In a further aspect, when the apparatus 1502 is in a connected mode of the first

RAT, the enabling the SR-LTE operation further includes the SR-LTE module 1508 tuning to the second RAT to perform the CS service without notifying the first RAT and locally suspending a PS operation on the first RAT.

[0096] In another aspect, when the UE is in a connected mode of the first RAT and is triggered to perform the CS service on the second RAT, the enabling the SR-LTE operation further includes the SR-LTE module 1508 sending (via transmission module 1512) an extended service request to the first network entity 1550 of the first RAT and waiting to receive a radio resource control (RRC) connection release message from the first RAT. When the RRC connection release message is received (via receiving module 1504) from a base station, the SR-LTE module 1508 tunes to the second RAT to perform the CS service based on information about the second RAT included in the RRC connection release message. When the RRC connection release message is not received from the base station within a predefined time period, the SR-LTE module 1508 tunes to the second RAT to perform the CS service without notifying the first RAT and locally suspends a PS operation on the first RAT.

[0097] In an aspect, when the first network entity 1550 is a mobility management entity

(MME), the SMS module 1510 may send (via transmission module 1512) a message to the MME via a tracking area update. The message may be a request for a short message service (SMS) in the MME. Upon the MME receiving the request from the UE, the MME sends a request to a home subscriber server (HSS) to register an address of the MME as a serving GPRS support node (SGSN) for receiving a mobile terminated short message service (MT-SMS). When the HSS supports the SMS in the MME, the MME receives from the HSS an acknowledgment that the SMS is supported in the MME in response to the request from the MME. Thereafter, the SMS module 1510 receives (via receiving module 1504) from the MME confirmation that the SMS in the MME is enabled.

[0098] The apparatus may include additional modules that perform each of the steps of the algorithm in the aforementioned flow chart of FIG. 14. As such, each step in the aforementioned flow chart of FIG. 14 may be performed by a module and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

[0099] FIG. 16 is a diagram 1600 illustrating an example of a hardware implementation for an apparatus 1602' employing a processing system 1614. The processing system 1614 may be implemented with a bus architecture, represented generally by the bus 1624. The bus 1624 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 1614 and the overall design constraints. The bus 1624 links together various circuits including one or more processors and/or hardware modules, represented by the processor 1604, the modules 1504, 1506, 1508, 1510, 1512 and the computer-readable medium 1606. The bus 1624 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further. [00100] The processing system 1614 may be coupled to a transceiver 1610. The transceiver 1610 is coupled to one or more antennas 1620. The transceiver 1610 provides a means for communicating with various other apparatus over a transmission medium. The transceiver 1610 receives a signal from the one or more antennas 1620, extracts information from the received signal, and provides the extracted information to the processing system 1614, specifically the receiving module 1504. In addition, the transceiver 1610 receives information from the processing system 1614, specifically the transmission module 1512, and based on the received information, generates a signal to be applied to the one or more antennas 1620. The processing system 1614 includes a processor 1604 coupled to a computer-readable medium 1606. The processor 1604 is responsible for general processing, including the execution of software stored on the computer-readable medium 1606. The software, when executed by the processor 1604, causes the processing system 1614 to perform the various functions described supra for any particular apparatus. The computer-readable medium 1606 may also be used for storing data that is manipulated by the processor 1604 when executing software. The processing system further includes at least one of the modules 1504, 1506, 1508, 1510, and 1512. The modules may be software modules running in the processor 1604, resident/stored in the computer readable medium 1606, one or more hardware modules coupled to the processor 1604, or some combination thereof. The processing system 1614 may be a component of the UE 650 and may include the memory 660 and/or at least one of the TX processor 668, the RX processor 656, and the controller/processor 659.

[00101] In one configuration, the apparatus 1502/1502' for wireless communication includes means for means for sending a request to a first network entity of a first RAT for combined registration to detect whether CSFB or VoLTE is supported at the first network entity, the request for combined registration comprising a request for concurrent registration with a packet switched (PS) network of the first RAT and a CS network of a second RAT, means for enabling a single radio LTE (SR-LTE) operation, instead of disabling a registration with the PS network of the first RAT, when CSFB or VoLTE is not supported at the first network entity, the SR-LTE operation facilitating the CS service without CSFB or VoLTE support, means for determining that CSFB or VoLTE is not supported at the first network entity upon receiving an indication that the first network entity does not support the combined registration, means for sending a request from the UE to the MME via a tracking area update, the request requesting a short message service (SMS) in the MME, and means for receiving at the UE from the MME confirmation that the SMS in the MME is enabled.

The aforementioned means may be one or more of the aforementioned modules of the apparatus 1502 and/or the processing system 1614 of the apparatus 1502' configured to perform the functions recited by the aforementioned means. As described supra, the processing system 1614 may include the TX Processor 668, the RX Processor 656, and the controller/processor 659. As such, in one configuration, the aforementioned means may be the TX Processor 668, the RX Processor 656, and the controller/processor 659 configured to perform the functions recited by the aforementioned means.

FIG. 17 is a flow chart 1700 of a method of wireless communication. The method may be performed by a mobility management entity (MME) communicating with a user equipment (UE). The UE may support communication on multiple radio access technologies (RATs) using a single radio.

At step 1702, the MME receives from the UE a request for combined registration. The request for combined registration may include a request for concurrent registration with a packet-switched (PS) network of a first RAT and a circuit-switched (CS) network of a second RAT.

At step 1704, the MME indicates to the UE that the request for combined registration is not accepted when circuit-switched fallback (CSFB) is not available. At step 1706, the MME receives an extended service request from the UE relating to the UE's registration with the PS network after indicating that the request for combined registration is not accepted.

In an aspect, the extended service request may be a request for mobile originated (MO) CSFB. Accordingly, at step 1708, the MME informs a base station to perform MO CSFB with the UE. At step 1710, the MME receives from the base station an indication that the UE is unavailable for PS service. Thereafter, at step 1712, the MME suspends a PS operation on the first RAT for the UE in response to the indication that the UE is unavailable for PS service.

In a further aspect, the extended service request may be a request to suspend a PS operation on the first RAT. Accordingly, the MME proceeds directly to step 1712 and suspends the PS operation on the first RAT for the UE in response to the request.

FIG. 18 is a flow chart 1800 of a method of wireless communication. The method may be performed by a mobility management entity (MME) communicating with a user equipment (UE), the UE supporting communication on a circuit- switched (CS) and a packet-switched (PS) radio access network using a single radio.

At step 1802, the MME receives a request from the UE via a tracking area update, the request requesting a short message service (SMS) in the MME. At step 1804, the MME sends a request to a home subscriber server (HSS) to register an address of the MME as a serving GPRS support node (SGSN) for receiving a mobile terminated short message service (MT-SMS).

At step 1806, the MME receives from the HSS an acknowledgment that the SMS is supported in the MME in response to the request from the MME when the HSS supports the SMS in the MME. At step 1808, the MME sends to the UE confirmation that the SMS in the MME is enabled.

In an aspect, the UE requests the SMS in the MME via the tracking area update using an SMS-only flag when IMSI registration is rejected by the MME in an Attach Accept message. In a further aspect, the UE requests the SMS in the MME via the tracking area update using a reserved bit in a combined EPS/IMSI Attach message. The reserved bit in the combined EPS/IMSI Attach message may implicitly indicate that the UE is a dual receiver circuit-switched fallback (CSFB) UE.

FIG. 19 is a data flow diagram 1900 illustrating the data flow between different modules/means/components in an exemplary apparatus 1902. The apparatus 1902 may be a mobility management entity (MME) communicating with a user equipment (UE) 1950. The UE 1950 may support communication on multiple radio access technologies (RATs) using a single radio. The UE 1950 may also support communication on a circuit-switched (CS) and a packet-switched (PS) radio access network using a single radio. The apparatus 1902 includes a receiving module 1904, a combined registration module 1906, an extended service request module 1908, an SMS module 1910, and a transmission module 1912.

The combined registration module 1906 receives from the UE 1950 (via receiving module 1904) a request for combined registration. The request for combined registration may include a request for concurrent registration with a packet-switched (PS) network of a first RAT and a circuit-switched (CS) network of a second RAT.

The combined registration module 1906 indicates to the UE 1950 (via transmission module 1912) that the request for combined registration is not accepted when circuit-switched fallback (CSFB) is not available. Thereafter, the extended service request module 1908 receives an extended service request from the UE 1950 relating to the UE 1950's registration with the PS network after indicating that the request for combined registration is not accepted.

In an aspect, the extended service request may be a request for mobile originated (MO) CSFB. Accordingly, the extended service request module 1908 informs a base station (e.g., entity 1970) to perform MO CSFB with the UE 1950. The extended service request module 1908 then receives from the base station 1970 an indication that the UE 1950 is unavailable for PS service. Thereafter, the extended service request module 1908 suspends a PS operation on the first RAT for the UE 1950 in response to the indication that the UE 1950 is unavailable for PS service.

In a further aspect, the extended service request may be a request to suspend a PS operation on the first RAT. Accordingly, the extended service request module 1908 suspends the PS operation on the first RAT for the UE 1950 in response to the request.

The SMS module 1910 receives a request from the UE 1950 via a tracking area update, the request requesting a short message service (SMS) in the apparatus 1902. The SMS module 1910 sends a request to a home subscriber server (HSS) to register an address of the apparatus 1902 as a serving GPRS support node (SGSN) for receiving a mobile terminated short message service (MT-SMS).

The SMS module 1910 receives from the HSS an acknowledgment that the SMS is supported in the apparatus 1902 in response to the request from the SMS module 1910 when the HSS supports the SMS in the apparatus 1902. Thereafter, the SMS module 1910 sends to the UE 1950 confirmation that the SMS in the apparatus 1902 is enabled.

In an aspect, the UE 1950 requests the SMS in the apparatus 1902 via the tracking area update using an SMS-only flag when IMSI registration is rejected by the apparatus 1902 in an Attach Accept message. In a further aspect, the UE 1950 requests the SMS in the apparatus 1902 via the tracking area update using a reserved bit in a combined EPS/IMSI Attach message. The reserved bit in the combined EPS/IMSI Attach message may implicitly indicate that the UE 1950 is a dual receiver circuit-switched fallback (CSFB) UE.

[00120] The apparatus may include additional modules that perform each of the steps of the algorithm in the aforementioned flow charts of FIGs. 17 and 18. As such, each step in the aforementioned flow charts of FIGs. 17 and 18 may be performed by a module and the apparatus may include one or more of those modules. The modules may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

[00121] FIG. 20 is a diagram 2000 illustrating an example of a hardware implementation for an apparatus 1902' employing a processing system 2014. The processing system 2014 may be implemented with a bus architecture, represented generally by the bus 2024. The bus 2024 may include any number of interconnecting buses and bridges depending on the specific application of the processing system 2014 and the overall design constraints. The bus 2024 links together various circuits including one or more processors and/or hardware modules, represented by the processor 2004, the modules 1904, 1906, 1908, 1910, 1912 and the computer-readable medium 2006. The bus 2024 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art, and therefore, will not be described any further.

[00122] The processing system 2014 may be coupled to a transceiver 2010. The transceiver 2010 is coupled to one or more antennas 2020. The transceiver 2010 provides a means for communicating with various other apparatus over a transmission medium. The transceiver 2010 receives a signal from the one or more antennas 2020, extracts information from the received signal, and provides the extracted information to the processing system 2014, specifically the receiving module 1904. In addition, the transceiver 2010 receives information from the processing system 2014, specifically the transmission module 1912, and based on the received information, generates a signal to be applied to the one or more antennas 2020. The processing system 2014 includes a processor 2004 coupled to a computer-readable medium 2006. The processor 2004 is responsible for general processing, including the execution of software stored on the computer-readable medium 2006. The software, when executed by the processor 2004, causes the processing system 2014 to perform the various functions described supra for any particular apparatus. The computer-readable medium 2006 may also be used for storing data that is manipulated by the processor 2004 when executing software. The processing system further includes at least one of the modules 1904, 1906, 1908, 1910, and 1912. The modules may be software modules running in the processor 2004, resident/stored in the computer readable medium 2006, one or more hardware modules coupled to the processor 2004, or some combination thereof.

[00123] In one configuration, the apparatus 1902/1902' for wireless communication includes means for receiving from the UE a request for combined registration comprising a request for concurrent registration with a packet-switched (PS) network of a first RAT and a circuit-switched (CS) network of a second RAT, means for indicating to the UE that the request for combined registration is not accepted when circuit-switched fallback (CSFB) is not available, means for receiving an extended service request from the UE relating to the UE's registration with the PS network after indicating that the request for combined registration is not accepted, wherein the extended service request is a request for mobile originated (MO) CSFB, means for informing a base station to perform MO CSFB with the UE, means for receiving from the base station an indication that the UE is unavailable for PS service, means for suspending a PS operation on the first RAT for the UE in response to the indication that the UE is unavailable for PS service, wherein the extended service request is a request to suspend a PS operation on the first RAT, means for suspending the PS operation on the first RAT for the UE in response to the request, means for receiving a request from the UE via a tracking area update, the request requesting a short message service (SMS) in the MME, means for sending a request to a home subscriber server (HSS) to register an address of the MME as a serving GPRS support node (SGSN) for receiving a mobile terminated short message service (MT-SMS), means for receiving from the HSS an acknowledgment that the SMS is supported in the MME in response to the request from the MME when the HSS supports the SMS in the MME, and means for sending to the UE from the MME confirmation that the SMS in the MME is enabled.

[00124] The aforementioned means may be one or more of the aforementioned modules of the apparatus 1902 and/or the processing system 2014 of the apparatus 1902' configured to perform the functions recited by the aforementioned means. [00125] It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Further, some steps may be combined or omitted. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

[00126] The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean "one and only one" unless specifically so stated, but rather "one or more." Unless specifically stated otherwise, the term "some" refers to one or more. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed as a means plus function unless the element is expressly recited using the phrase "means for."

WHAT IS CLAIMED IS:

Claims

1. A method of wireless communication performed by a user equipment (UE) supporting multiple radio access technologies (RATs), the UE having a single radio configured to provide circuit-switched (CS) and packet-switched (PS) connectivity, the method comprising:

sending a request for combined registration to a first network entity with a first RAT to detect whether circuit- switched fallback (CSFB) service is available in the first network, the request for combined registration comprising a request for concurrent registration for PS service in the first network and CS service in a second network with a second RAT; and

enabling a single radio LTE (SR-LTE) operation of the UE to maintain the availability of PS service in the first network when the requested combined registration is not accepted by the first network entity, the SR-LTE operation facilitating the CS service without utilizing a CSFB or VoLTE service.

2. The method of claim 1, wherein the enabling the SR-LTE operation comprises:

maintaining the registration for PS service in response to determining that the request for combined registration is not accepted; and

registering for CS service with the second network via a second network entity while the PS service registration is maintained.

3. The method of claim 2, further comprising determining that the request for combined registration is not accepted by the first network entity based on at least one of:

receiving an indication that registration with the CS network is not available; receiving an indication that registration with the CS network is supported for a short message service (SMS); or

receiving an indication that registration with the CS network is not preferred.

4. The method of claim 1, wherein the first RAT is a Long Term Evolution (LTE) system and the second RAT is a Global System for Mobile Communications (GSM) or a Universal Mobile Telecommunications System (UMTS).

5. The method of claim 2, wherein the UE is in an idle mode, the enabling the SR-LTE operation further comprising:

camping on the first network and the second network in parallel; and intermittently tuning between the first RAT and the second RAT to perform at least one of:

paging reception,

cell reselection/selection and measurement,

system information reading, or

location registration.

6. The method of claim 5, wherein the intermittent tuning comprises: tuning to the first RAT and not the second RAT for a period of time; and tuning to the second RAT and not the first RAT for another period of time.

7. The method of claim 2, wherein the UE is in a connected mode of the first RAT, the enabling the SR-LTE operation further comprising:

tuning to the second RAT to perform the CS service without notifying the first RAT; and

locally suspending a PS operation on the first RAT.

8. The method of claim 2, wherein the UE is in a connected mode of the first RAT and is triggered to perform the CS service on the second RAT, the enabling the SR-LTE operation further comprising:

sending an extended service request to the first network entity;

waiting to receive a radio resource control (RRC) connection release message from the first network entity; when the RRC connection release message is received from a base station, tuning to the second RAT to perform the CS service based on information about the second RAT included in the RRC connection release message; and

when the RRC connection release message is not received from the base station within a predefined time period, tuning to the second RAT to perform the CS service without notifying the first RAT and locally suspending a PS operation on the first RAT.

9. A method of wireless communication performed by a mobility management entity (MME) communicating with a user equipment (UE), the UE supporting communication on multiple radio access technologies (RATs) using a single radio, the method comprising:

receiving from the UE a request for combined registration, the request for combined registration comprising a request for concurrent registration with a packet- switched (PS) service in a first RAT and a circuit-switched (CS) service in a second RAT;

indicating that the request for combined registration is not accepted when circuit-switched fallback (CSFB) operation is not available to the UE; and

receiving an extended service request from the UE relating to the UE's registration with the PS service after indicating that the request for combined registration is not accepted.

10. The method of claim 9, wherein the extended service request is a request for mobile originated (MO) CSFB, the method further comprising:

informing a base station to perform MO CSFB with the UE;

receiving from the base station an indication that the UE is unavailable for PS service; and

suspending a PS operation on the first RAT for the UE in response to the indication that the UE is unavailable for PS service.

11. The method of claim 9, wherein the extended service request is a request to suspend a PS operation on the first RAT, the method further comprising: suspending the PS operation on the first RAT for the UE in response to the request.

12. A method of wireless communication performed by a mobility management entity (MME) communicating with a user equipment (UE), the UE supporting communication on a circuit-switched (CS) and a packet-switched (PS) radio access network using a single radio, the method comprising:

receiving a request from the UE via a tracking area update, the request requesting a short message service (SMS) in the MME;

sending a request to a home subscriber server (HSS) to register an address of the MME as a serving GPRS support node (SGSN) for receiving a mobile terminated short message service (MT-SMS);

receiving from the HSS an acknowledgment that the SMS is supported in the MME in response to the request from the MME when the HSS supports the SMS in the MME; and

sending to the UE from the MME confirmation that the SMS in the MME is enabled.

13. The method of claim 12, wherein the UE requests the SMS in the MME via the tracking area update using an SMS-only flag when IMSI registration is rejected by the MME in an Attach Accept message.

14. The method of claim 12, wherein the UE requests the SMS in the MME via the tracking area update using a reserved bit in a combined EPS/IMSI Attach message.

15. The method of claim 14, wherein the reserved bit in the combined EPS/IMSI Attach message indicates that the UE is a dual receiver circuit-switched fallback (CSFB) UE.

16. A user equipment (UE) apparatus for wireless communication supporting multiple radio access technologies (RATs), the UE having a single radio configured to provide circuit-switched (CS) and packet-switched (PS) connectivity, the UE comprising:

means for sending a request for combined registration to a first network entity with a first RAT to detect whether circuit-switched fallback (CSFB) is available in the first network, the request for combined registration comprising a request for concurrent registration with PS service in the first network and CS service in a second network with a second RAT; and

means for enabling a single radio LTE (SR-LTE) operation of the UE to maintain the availability of the PS service in the first network when the request for combined registration is not accepted by the first network entity, the SR-LTE operation facilitating the CS service without utilizing a CSFB or VoLTE service.

17. The apparatus of claim 16, wherein the means for enabling the SR-LTE operation is configured to:

maintain the registration for PS service in response to determining that the request for combined registration is not accepted; and

register for CS service with the second network via a second network entity while the PS service registration is maintained.

18. The apparatus of claim 17, further comprising means for determining that the request for combined registration is not accepted by the first network entity based on at least one of:

receiving an indication that registration with the CS network is not available; receiving an indication that registration with the CS network is only supported for a short message service (SMS); or

receiving an indication that registration with the CS network is not preferred.

19. The apparatus of claim 16, wherein the first RAT is a Long Term Evolution (LTE) system and the second RAT is a Global System for Mobile

Communications (GSM) or a Universal Mobile Telecommunications System (UMTS).

20. The apparatus of claim 17, wherein the UE is in an idle mode, the means for enabling the SR-LTE operation further configured to:

camp on the first network and the second network in parallel; and

intermittently tune between the first RAT and the second RAT to perform at least one of:

paging reception,

cell reselection/selection and measurement,

system information reading, or

location registration.

21. The apparatus of claim 20, wherein the intermittent tuning comprises: tuning to the first RAT and not the second RAT for a period of time; and tuning to the second RAT and not the first RAT for another period of time.

22. The apparatus of claim 17, wherein the UE is in a connected mode of the first RAT, the means for enabling the SR-LTE operation further configured to:

tune to the second RAT to perform the CS service without notifying the first RAT; and

locally suspend a PS operation on the first RAT.

23. The apparatus of claim 17, wherein the UE is in a connected mode of the first RAT and is triggered to perform the CS service on the second RAT, the means for enabling the SR-LTE operation further configured to:

send an extended service request to the first network entity;

wait to receive a radio resource control (RRC) connection release message from the first network entity;

when the RRC connection release message is received from a base station, tune to the second RAT to perform the CS service based on information about the second RAT included in the RRC connection release message; and when the RRC connection release message is not received from the base station within a predefined time period, tune to the second RAT to perform the CS service without notifying the first RAT and locally suspend a PS operation on the first RAT.

24. An apparatus for wireless communication for a mobility management entity (MME) communicating with a user equipment (UE), the UE supporting communication on multiple radio access technologies (RATs) using a single radio, the apparatus comprising:

means for receiving from the UE a request for combined registration, the request for combined registration comprising a request for concurrent registration with a packet- switched (PS) service of the first network and a circuit-switched (CS) service of a second network with a second RAT;

means for indicating that the request for combined registration is not accepted when circuit-switched fallback (CSFB) operation is not available to the UE; and

means for receiving an extended service request from the UE relating to the UE's registration for PS service after indicating that the request for combined registration is not accepted.

25. The apparatus of claim 24, wherein the extended service request is a request for mobile originated (MO) CSFB, the apparatus further comprising:

means for informing a base station to perform MO CSFB with the UE;

means for receiving from the base station an indication that the UE is unavailable for PS service; and

means for suspending a PS operation on the first RAT for the UE in response to the indication that the UE is unavailable for PS service.

26. The apparatus of claim 24, wherein the extended service request is a request to suspend a PS operation on the first RAT, the apparatus further comprising: means for suspending the PS operation on the first RAT for the UE in response to the request.

27. An apparatus for wireless communication for a mobility management entity (MME) communicating with a user equipment (UE), the UE supporting communication on a circuit-switched (CS) and a packet-switched (PS) radio access network using a single radio, the apparatus comprising:

means for receiving a request from the UE via a tracking area update, the request requesting a short message service (SMS) in the MME;

means for sending a request to a home subscriber server (HSS) to register an address of the MME as a serving GPRS support node (SGSN) for receiving a mobile terminated short message service (MT-SMS);

means for receiving from the HSS an acknowledgment that the SMS is supported in the MME in response to the request from the MME when the HSS supports the SMS in the MME; and

means for sending to the UE from the MME confirmation that the SMS in the MME is enabled.

28. The apparatus of claim 27, wherein the UE requests the SMS in the MME via the tracking area update using an SMS-only flag when IMSI registration is rejected by the MME in an Attach Accept message.

29. The apparatus of claim 27, wherein the UE requests the SMS in the MME via the tracking area update using a reserved bit in a combined EPS/IMSI Attach message.

30. The apparatus of claim 29, wherein the reserved bit in the combined EPS/IMSI Attach message indicates that the UE is a dual receiver circuit-switched fallback (CSFB) UE.

31. A user equipment apparatus for wireless communication supporting multiple radio access technologies (RATs), the UE having a single radio configured to provide circuit- switched (CS) and packet- switched (PS) connectivity, the apparatus comprising:

a processing system configured to: send a request for combined registration to a first network entity with a first RAT to detect whether circuit- switched fallback (CSFB) service is available in the first network, the request for combined registration comprising a request for concurrent registration for PS service in the first network and CS service in a second network with a second RAT; and

enable a single radio LTE (SR-LTE) operation of the UE to maintain the availability of PS service in the first network when the requested combined registration is not accepted by the first network entity, the SR-LTE operation facilitating the CS service without utilizing a CSFB or VoLTE service.

32. The apparatus of claim 31 , wherein the processing system configured to enable the SR-LTE operation is further configured to:

maintain the registration with the PS network of the first RAT in response to determining that the request for combined registration is not accepted; and

33. The apparatus of claim 32, wherein the processing system is configured to determined that the request for combined registration is not accepted by the first network entity based on at least one of:

receiving an indication that registration with the CS network is not preferred.

34. The apparatus of claim 31 , wherein the first RAT is a Long Term Evolution (LTE) system and the second RAT is a Global System for Mobile

Communications (GSM) or a Universal Mobile Telecommunications System (UMTS).

35. The apparatus of claim 32, wherein the UE is in an idle mode, the processing system configured to enable the SR-LTE operation further configured to: camp on the first network and the second network in parallel; and

paging reception,

cell reselection/selection and measurement,

system information reading, or

location registration.

36. The apparatus of claim 35, wherein the processing system configured to intermittently tune is further configured to:

tune to the first RAT and not the second RAT for a period of time; and tune to the second RAT and not the first RAT for another period of time.

37. The apparatus of claim 32, wherein the UE is in a connected mode of the first RAT, the processing system configured to enable the SR-LTE operation further configured to:

locally suspend a PS operation on the first RAT.

38. The apparatus of claim 32, wherein the UE is in a connected mode of the first RAT and is triggered to perform the CS service on the second RAT, the processing system configured to enable the SR-LTE operation further configured to:

send an extended service request to the first network entity;

wait to receive a radio resource control (RRC) connection release message from the first network entity; when the RRC connection release message is received from a base station, tune to the second RAT to perform the CS service based on information about the second RAT included in the RRC connection release message; and when the RRC connection release message is not received from the base station within a predefined time period, tune to the second RAT to perform the CS service without notifying the first RAT and locally suspending a PS operation on the first RAT.

39. An apparatus for wireless communication for a mobility management entity (MME) communicating with a user equipment (UE) supporting communication on multiple radio access technologies (RATs) using a single radio, the apparatus comprising:

a processing system configured to:

receive from the UE a request for combined registration, the request for combined registration comprising a request for concurrent registration with a packet- switched (PS) service of a first network and a circuit-switched (CS) service of a second network with a second RAT;

indicate that the request for combined registration is not accepted when circuit- switched fallback (CSFB) operation is not available to the UE; and

receive an extended service request from the UE relating to the UE's registration for PS service after indicating that the request for combined registration is not accepted.

40. The apparatus of claim 39, wherein the extended service request is a request for mobile originated (MO) CSFB, the processing system further configured to: inform a base station to perform MO CSFB with the UE;

receive from the base station an indication that the UE is unavailable for PS service; and

suspend a PS operation on the first RAT for the UE in response to the indication that the UE is unavailable for PS service.

41. The apparatus of claim 39, wherein the extended service request is a request to suspend a PS operation on the first RAT, the processing system further configured to:

suspend the PS operation on the first RAT for the UE in response to the request.

42. An apparatus for wireless communication for a mobility management entity (MME) communicating with a user equipment (UE), the UE supporting communication on a circuit-switched (CS) and a packet-switched (PS) radio access network using a single radio, the apparatus comprising:

a processing system configured to:

receive a request from the UE via a tracking area update, the request requesting a short message service (SMS) in the MME;

send a request to a home subscriber server (HSS) to register an address of the MME as a serving GPRS support node (SGSN) for receiving a mobile terminated short message service (MT-SMS);

receive from the HSS an acknowledgment that the SMS is supported in the MME in response to the request from the MME when the HSS supports the SMS in the MME; and

send to the UE from the MME confirmation that the SMS in the MME is enabled.

43. The apparatus of claim 42, wherein the UE requests the SMS in the MME via the tracking area update using an SMS-only flag when IMSI registration is rejected by the MME in an Attach Accept message.

44. The apparatus of claim 42, wherein the UE requests the SMS in the MME via the tracking area update using a reserved bit in a combined EPS/IMSI Attach message.

45. The apparatus of claim 44, wherein the reserved bit in the combined EPS/IMSI Attach message indicates that the UE is a dual receiver circuit-switched fallback (CSFB) UE.

46. A computer program product for a user equipment (UE) supporting multiple radio access technologies (RATs), the UE having a single radio configured to provide circuit- switched (CS) and packet- switched (PS) connectivity, the computer program product comprising: a computer-readable storage medium comprising code for:

sending a request for combined registration to a first network entity with a first RAT to detect whether circuit- switched fallback (CSFB) service is available in the first network, the request for combined registration comprising a request for concurrent registration with a PS service of the first network and a CS service of a second network with a second RAT; and

47. The computer program product of claim 46, wherein the code for enabling the SR-LTE operation is configured to:

register for CS service with the second network via a second network entity while the PS network registration is maintained.

48. The computer program product of claim 47, further comprising code for determining that the request for combined registration is not accepted by the first network entity based on at least one of:

an indication that registration with the CS network is not available;

an indication that registration with the CS network is only supported for a short message service (SMS); or

an indication that registration with the CS network is not preferred.

49. The computer program product of claim 46, wherein the first RAT is a Long Term Evolution (LTE) system and the second RAT is a Global System for Mobile Communications (GSM) or a Universal Mobile Telecommunications System (UMTS).

50. The computer program product of claim 47, wherein the UE is in an idle mode, the code for enabling the SR-LTE operation further configured for:

paging reception,

cell reselection/selection and measurement,

system information reading, or

location registration.

51. The computer program product of claim 50, wherein the code for intermittently tuning is configured to:

52. The computer program product of claim 47, wherein when the UE is in a connected mode of the first RAT, the code for enabling the SR-LTE operation is further configured for:

locally suspending a PS operation on the first RAT.

53. The computer program product of claim 47, wherein when the UE is in a connected mode of the first RAT and is triggered to perform the CS service on the second RAT, the code for enabling the SR-LTE operation is further configured for: sending an extended service request to the first network entity of the first RAT; waiting to receive a radio resource control (RRC) connection release message from the first RAT;

when the RRC connection release message is received from a base station, tuning to the second RAT to perform the CS service based on information about the second RAT included in the RRC connection release message; and when the RRC connection release message is not received from the base station within a predefined time period, tuning to the second RAT to perform the CS service without notifying the first RAT and locally suspending a PS operation on the first RAT.

54. A computer program product for a mobility management entity (MME) communicating with a user equipment (UE), the UE supporting communication on multiple radio access technologies (RATs) using a single radio, the computer program product comprising:

a computer-readable storage medium comprising code for:

receiving from the UE a request for combined registration, the request for combined registration comprising a request for concurrent registration with a packet- switched (PS) service of a first network using a first RAT and a circuit-switched (CS) service of a second network with a second RAT;

indicating that the request for combined registration is not accepted when circuit-switched fallback (CSFB) is not available to the UE; and

receiving an extended service request from the UE relating to the UE's registration for PS service after indicating that the request for combined registration is not accepted.

55. The computer program product of claim 54, wherein the extended service request is a request for mobile originated (MO) CSFB, the computer-readable storage medium further comprising code for:

informing a base station to perform MO CSFB with the UE;

56. The computer program product of claim 54, wherein the extended service request is a request to suspend a PS operation on the first RAT, the computer-readable storage medium further comprising code for: suspending the PS operation on the first RAT for the UE in response to the request.

57. A computer program product for a mobility management entity (MME) communicating with a user equipment (UE), the UE supporting communication on a circuit-switched (CS) and a packet-switched (PS) radio access network using a single radio, the computer program product comprising:

a computer-readable storage medium comprising code for:

sending to the UE from the MME confirmation that the SMS in the MME is enabled.

58. The computer program product of claim 57, wherein the UE requests the SMS in the MME via the tracking area update using an SMS-only flag when IMSI registration is rejected by the MME in an Attach Accept message.

59. The computer program product of claim 57, wherein the UE requests the SMS in the MME via the tracking area update using a reserved bit in a combined EPS/IMSI Attach message.

60. The computer program product of claim 59, wherein the reserved bit in the combined EPS/IMSI Attach message indicates that the UE is a dual receiver circuit- switched fallback (CSFB) UE.