IMS voice support in networks with 4G coverage holes using EPS fallback

Abstract

A method is provided. The method may be performed by a UE. The method includes attempting to attach to or perform a tracking area update in an EPS network to obtain a voice service a certain number of times. The method includes starting a modified timer based on failure to attach to or perform a tracking area update in the EPS network a certain number of times and based on a configuration parameter. The modified timer may be modified based on a default timer. The method includes maintaining an S1 mode enabled when starting the modified timer. The method includes attempting to obtain a voice service based on one or more access technologies other than EPS. The method includes attaching to or performing a tracking area update in the EPS network to obtain a voice service based on the modified timer.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Application No. 63 / 219,248, entitled "IMS VOICE SUPPORT IN NETWORK USING EPS FALLBACK AND HAVING 4G COVERAGE HOLES," filed on July 7, 2021, and U.S. Nonprovisional Patent Application No. 17 / 810,954, entitled "IMS VOICE SUPPORT IN NETWORK USING EPS FALLBACK AND HAVING 4G COVERAGE HOLES," filed on July 6, 2022, which are expressly incorporated by reference in their entireties into this specification.

[0002] FIELD OF THE DISCLOSURE

[0002] The present disclosure relates generally to communication systems, and more specifically to obtaining voice services via evolved packet system (EPS) fallback.

[0003] introduction

[0003] Wireless communication systems have been widely deployed to provide various telecommunication services, such as telephone, video, data, messaging, and broadcast. A typical wireless communication system may utilize multiple access technologies capable of supporting communication with multiple users by sharing available system resources. 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.

[0004]

[0004] These multiple access technologies are being adopted in various telecommunication standards to provide a common protocol that allows various wireless devices to communicate at city, national, regional, and even global levels. An exemplary telecommunication standard is 5G New Radio (NR). 5G NR is part of the continuing mobile broadband evolution promulgated by the 3rd Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with the Internet of Things (IoT)), and other requirements. 5G NR includes services related to enhanced mobile broadband (eMBB), massive machine-type communications (mMTC), and ultra-reliable low-latency communications (URLLC). Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. There is a need for further improvements in 5G NR technology. These improvements may also be applicable to other multiple access technologies and telecommunication standards that utilize these technologies. Summary of the Invention

[0005]

[0005] The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects. It is not intended to identify key or critical elements of all aspects, nor is it intended to delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later.

[0006] In an aspect of the present disclosure, a method is provided. The method may be executed by a user equipment (UE). The method includes starting a modified timer based on a number of failed attempts associated with a voice service for an Evolved Packet Service (EPS) network and based on a configuration parameter. The modified timer may be modified based on a default timer. The method includes attempting to acquire the voice service based on one or more access technologies other than EPS. The method includes attaching to the EPS network or performing a tracking area update in the EPS network to acquire the voice service based on the modified timer.

[0007]

[0007] In another aspect of the present disclosure, an apparatus is provided. The apparatus may be a UE. The apparatus includes a memory and at least one processor coupled to the memory, and the memory and the at least one processor are configured to: start a modified timer, which may be modified based on a default timer based on a number of failed attempts associated with a voice service for an EPS network and based on a configuration parameter; attempt to obtain the voice service based on one or more access technologies other than EPS; and attach to the EPS network or perform a tracking area update in the EPS network to obtain the voice service based on the modified timer.

[0008]

[0008] In another aspect of the present disclosure, an apparatus is provided. The apparatus may be a UE. The apparatus includes means for starting a modified timer based on a number of failed attempts associated with a voice service for an EPS network and based on a configuration parameter. The modified timer can be modified based on a default timer. The apparatus includes means for attempting to obtain the voice service based on one or more access technologies other than EPS. The apparatus includes means for attaching to the EPS network or performing a tracking area update in the EPS network to obtain the voice service based on the modified timer.

[0009]

[0009] In another aspect of the present disclosure, a computer-readable medium is provided, the computer-readable medium includes computer-executable code in a UE, which when executed by a processor, causes the processor to start a modified timer, which may be modified based on a default timer based on a number of failed attempts associated with a voice service for an EPS network and based on configuration parameters, to attempt to obtain a voice service based on one or more access technologies other than EPS, to attach to an EPS network to obtain the voice service based on the modified timer, or to perform a tracking area update in the EPS network.

[0010]

[0010] In an aspect of the present disclosure, a method is provided. The method may be performed by a base station. The method includes sending an indication of a duration associated with a modified timer to a voice-centric UE. The duration associated with the modified timer may be shorter than a duration associated with a default timer. The method includes initially failing to provide a voice service to the voice-centric UE through an EPS network. The method includes providing a voice service to the voice-centric UE through the EPS network based on the modified timer after an initial failure to provide the voice service to the voice-centric UE through the EPS network. The modified timer and the default timer may be associated with a retry to attach to the EPS network or perform a tracking area update in the EPS network. The voice service is not available through a 5th generation (5G) system (5GS) or a circuit-switched system.

[0011]

[0011] In another aspect of the present disclosure, an apparatus is provided. The apparatus may be a base station. The apparatus includes a memory and at least one processor coupled to the memory, where the memory and the at least one processor are configured to: send to the voice-centric UE an indication of a duration associated with a modified timer that is shorter than a duration associated with a default timer; initially fail to provide voice service to the voice-centric UE through the EPS network; and provide voice service to the voice-centric UE through the EPS network based on the modified timer after an initial failure to provide voice service to the voice-centric UE through the EPS network. The modified timer and the default timer may be associated with a retry to attach to the EPS network or perform a tracking area update in the EPS network. The voice service is not available through the 5GS or circuit-switched system.

[0012]

[0012] In another aspect of the present disclosure, an apparatus is provided. The apparatus may be a base station. The apparatus includes means for sending an indication of a duration associated with a modified timer to a voice-centric UE. The duration associated with the modified timer may be shorter than a duration associated with a default timer. The apparatus includes means for initially failing to provide a voice service to the voice-centric UE via the EPS network. The apparatus includes means for providing a voice service to the voice-centric UE via the EPS network based on the modified timer after an initial failure to provide a voice service to the voice-centric UE via the EPS network. The modified timer and the default timer may be associated with a retry to attach to the EPS network or perform a tracking area update in the EPS network. The voice service is not available via the 5GS or circuit-switched system.

[0013]

[0013] In another aspect of the present disclosure, a computer-readable medium is provided. The computer-readable medium includes computer-executable code in a base station, which, when executed by a processor, causes the processor to send to the voice-centric UE an indication of a duration associated with a modified timer that is shorter than a duration associated with a default timer, to initially fail to provide voice service to the voice-centric UE through the EPS network, and to provide voice service to the voice-centric UE through the EPS network based on the modified timer after an initial failure to provide voice service to the voice-centric UE through the EPS network. The modified timer and the default timer may be associated with a retry to attach to the EPS network or perform a tracking area update in the EPS network. The voice service is not available through the 5GS or circuit-switched system.

[0014]

[0014] To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of the various aspects may be employed. [Brief description of the drawings]

[0015] [Figure 1]

[0015] FIG. 1 illustrates an example of a wireless communication system and access network. [Figure 2A]

[0016] FIG. 2 illustrates an example of a first frame in accordance with various aspects of the present disclosure. [Figure 2B]

[0017] FIG. 1 illustrates an example of a downlink (DL) channel in a subframe, in accordance with various aspects of the present disclosure. [Figure 2C]

[0018] FIG. 2 illustrates an example of a second frame, according to various aspects of the present disclosure. [Figure 2D]

[0019] FIG. 1 illustrates an example of an uplink (UL) channel in a subframe, in accordance with various aspects of the present disclosure. [Diagram 3]

[0020] FIG. 1 illustrates an example of a base station and user equipment (UE) in an access network. [Figure 4]

[0021] FIG. 13 illustrates an unmodified timer T3402. [Diagram 5]

[0022] 1 is a communication flow diagram of a method of wireless communication. [Figure 6]

[0023] 1 is a communication flow diagram of a method of wireless communication. [Figure 7]

[0024] 1 is a communication flow diagram of a method of wireless communication. [Figure 8]

[0025] 1 is a communication flow diagram of a method of wireless communication. [Figure 9]

[0026] 1 is a flow chart of a method of wireless communication. [Figure 10]

[0027] 1 is a flow chart of a method of wireless communication. [Figure 11]

[0028] 1 is a flow chart of a method of wireless communication. [Figure 12]

[0029] 1 is a flow chart of a method of wireless communication. [Figure 13]

[0030] 1 is a flow chart of a method of wireless communication. [Figure 14]

[0031] 1 is a flow chart of a method of wireless communication. [Figure 15]

[0032] FIG. 2 illustrates an example of a hardware implementation for an exemplary device and / or network entity. [Figure 16]

[0033] FIG. 2 illustrates an example of a hardware implementation for an exemplary network entity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016]

[0034] In a fifth generation (5G) system (5GS), voice services over internet protocol (IP) multimedia subsystem (IMS) can be supported either natively (i.e., voice over new radio (VoNR)) or via EPS fallback. Support for VoNR can refer to support for packet-switched based voice services over NR. With EPS fallback, a UE can be handed over or redirected to EPS (e.g., in a 4th generation (4G) system) for either mobile originated (MO) or mobile terminated (MT) calls. An MO call can refer to a call that is initiated at the UE, and an MT call can refer to a call that is received at the UE. In this specification, EPS fallback can refer to a handover or redirection from 5GS to EPS for connecting MO or MT voice calls. A UE can be configured to be either voice-centric or data-centric. For example, a smartphone can be configured to be a voice-centric UE, and a sensor can be configured to be a data-centric UE. A voice-centric UE can prioritize voice services over data services. If a network cannot provide voice services to a voice-centric UE, the UE can turn to or search for other networks or access technologies (e.g., by lowering the priority of networks that cannot provide voice services or disabling access technologies that cannot obtain voice services). A network, such as a 5G network, can use a UE radio capability matching request procedure to determine whether it can provide voice services to a UE.The UE radio capability match request procedure may refer to a procedure in which a 5GS Access and Mobility Management Function (AMF) determines whether IMS voice service is supported for the UE, for example, as described in 3GPP TS 23.501 v16.9.0 subclause 5.4.4.2a. In one aspect, the network (e.g., 5GS AMF) may compare the UE's radio capability with the way voice is supported in the network (e.g., access technology). The network may indicate to the UE whether IMS voice is supported for the UE in a registration accept message. The registration accept message may be a message that the 5GS AMF sends to the UE to indicate that the AMF has accepted the UE's registration request, for example, as described in 3GPP TS 24.501 v16.9.0 subclause 5.5.1.3.4. In one embodiment, if IMS voice is supported, the registration accept message may not specify whether IMS voice is supported over VoNR or over EPS fallback.

[0017]

[0035] In one or more aspects, a voice-centric UE may experience long periods without access to voice services due to voice services being provided via EPS fallback in a 5GS network and the UE having difficulty attaching to or performing a tracking area update in the EPS network. Attaching to a network may refer to sending an attach request message, e.g., as described in 3GPP TS 24.301 v16.8.0 subclause 5.5.1.2.2, to obtain services from the network (e.g., the EPS network). Performing a tracking area update may refer to sending a tracking area update request message, e.g., as described in 3GPP TS 24.301 v16.8.0 subclause 5.5.3.2.2, to inform the network (e.g., the EPS network) that a registered UE has moved to a tracking area that is not included in the current tracking area identification list. In one embodiment, the UE may be voice-centric and VoNR may not be supported in the 5GS network (i.e., voice may only be supported via EPS fallback). Furthermore, because spectrum may be reused for other radio access technologies, voice services over older circuit-switched technologies (e.g., second generation ("2G") / third generation ("3G")) may not be available. Due to difficulties in attaching to an EPS network or performing tracking area updates in an EPS network, a UE may experience long periods without access to voice services.

[0018]

[0036] In one embodiment, the long period without access to voice services may occur as follows: First, due to insufficient EPS coverage, the UE may fail to attach to or perform a tracking area update in the EPS network a certain number of consecutive times (e.g., 5 times), which may cause the UE to disable S1 mode (i.e., a mode related to the UE's 4G / EPS capabilities) and start timer T3402 (whose default duration may be 12 minutes). The number of times may be predetermined. According to one or more aspects, the S1 mode may refer to an operation mode in which the UE communicates with an EPS Mobility Management Entity (MME), e.g., as described in TS 24.301 v16.8.0 subclause 3.1, etc. Timer T3402 may be an EPS mobility management timer. Timer T3402 may be associated with a retry to attach to or perform a tracking area update in the EPS network. By default, the UE may not retry to attach to or perform a tracking area update in the EPS network before timer T3402 expires. The UE may then attempt to attach to or perform a tracking area update in the 5GS network and may indicate to the 5GS network that S1 mode is disabled in the registration request message. Since the network may support voice services via EPS fallback and EPS fallback may be unavailable when S1 mode is disabled, the network may indicate "IMS voice over 3GPP access is not supported" in the registration accept message. Since the UE is voice-centric, receiving an indication of "IMS voice over 3GPP access is not supported" in the registration accept message may cause the UE to disable N1 mode (i.e., a mode related to the UE's 5G capabilities).According to one or more aspects, N1 mode may refer to an operating mode in which the UE communicates with the AMF of 5GS, for example as described in TS 24.501 v16.9.0 subclause 3.1. With both S1 mode and N1 mode disabled, the UE may search 2G / 3G networks for voice services and may find none. Finally, the UE may re-enable N1 mode and camp on the 5GS network. The UE may not be able to obtain voice services via EPS fallback until timer T3402 expires. As a result, the user may experience noticeable periods without access to voice services.

[0019]

[0037] Aspects presented herein provide mechanisms for a UE to improve wireless communication between the UE and a network and enable the UE to access the network in reduced time when performing EPS fallback. In some aspects, the UE may skip disabling S1 mode when the T3402 timer is started. Thus, the UE may not receive an indication that "IMS voice over 3GPP access is not supported" in the registration accept message because the S1 mode remains enabled. As a result, the UE may not have to disable N1 mode and may not waste time attempting to obtain voice services over a legacy 2G / 3G network.

[0020]

[0038] In some aspects, the UE may use a shorter T3402 timer value than the unmodified or default T3402 timer value based on a UE configuration parameter indicating that the UE uses a shorter T3402 timer value. In some aspects, the UE may receive a configuration of a shorter T3402 timer value. In some aspects, when the N1 mode is re-enabled, the UE may also re-enable the S1 mode. In some aspects, if the T3402 timer is running and the S1 mode is disabled, the UE may periodically check the quality of a 4G cell. The 4G cell may refer to a radio cell of an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (E-UTRAN) network, for example, as described in 3GPP TS 38.300 v16.6.0 subclause 3.2. If the cell quality is above a certain threshold for longer than the threshold time, the UE may re-enable the S1 mode and stop the T3402 timer. The cell quality may be based on or may refer to the signal to noise ratio (SNR) of an E-UTRAN cell, as described, for example, in 3GPP TS 38.300 v16.6.0 subclause 9.2.4, etc. Thus, the period during which a voice-centric UE does not have any access to voice services may be reduced, improving the user experience.

[0021]

[0039] The detailed description set forth below with respect to the drawings describes various configurations and does not 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 the various concepts. However, these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form to avoid obscuring such concepts.

[0022]

[0040] Several aspects of a telecommunications system are presented with reference to various apparatus and methods that are described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, 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 on the particular application and design constraints imposed on the overall system.

[0023]

[0041] As an example, an element or any portion of an element or any combination of elements may be implemented as a "processing system" including one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on a chip (SoCs), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gate logic, discrete hardware circuits, and other suitable hardware configured to perform various functionality described throughout this disclosure. One or more processors in a processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, or any combination thereof, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

[0024]

[0042] Thus, in one or more example aspects, implementations, and / or use cases, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on a computer-readable medium or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. A storage medium may be any available medium that can be accessed by a computer. By way of example, such computer-readable media may include random-access memory (RAM), read-only memory (ROM), electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of types of computer-readable media, or any other medium that can be used to store computer-executable code in the form of instructions or data structures that can be accessed by a computer.

[0025]

[0043] Although aspects, implementations, and / or use cases are described herein by way of example to some embodiments, additional or different aspects, implementations, and / or use cases may arise in many different configurations and scenarios. The aspects, implementations, and / or use cases described herein may be implemented across many different platform types, devices, systems, shapes, sizes, and packaging configurations. For example, the aspects, implementations, and / or use cases may arise with integrated chip implementations and other non-modular component-based devices (e.g., end-user devices, vehicles, communication devices, computing devices, industrial equipment, retail / purchasing devices, medical devices, artificial intelligence (AI)-enabled devices, etc.). Some embodiments may or may not be specifically targeted to a use case or application, but a wide variety of applicability of the described embodiments may arise. The aspects, implementations, and / or use cases may range from chip-level or modular components to non-modular, non-chip-level implementations, and even aggregated, distributed, or original equipment manufacturer (OEM) devices or systems incorporating one or more of the techniques herein. In some practical settings, devices incorporating the described aspects and features may also include additional components and features for the implementation and practice of the claimed and described aspects. For example, the transmission and reception of wireless signals necessarily includes several components (e.g., hardware components including antennas, RF chains, power amplifiers, modulators, buffers, processors, interleavers, adders / summers, etc.) for analog and digital purposes. The techniques described herein can be practiced in a wide variety of devices, chip-level components, systems, distributed configurations, aggregated or non-aggregated components, end-user devices, etc. of various sizes, shapes, and configurations.

[0026]

[0044] The deployment of a communication system such as a 5G NR system (5GS) can be configured in multiple ways with various components or parts. In a 5G NR system or network, a network node, a network entity, a mobility element of the network, a radio access network (RAN) node, a core network node, a network element, or a network equipment such as a base station (BS), or one or more units (or one or more components) performing a base station function can be implemented in an aggregated or disaggregated architecture. For example, a BS (such as a Node B (NB), evolved NB (eNB), NR BS, 5G NB, access point (AP), transmit receive point (TRP), or cell) can be implemented as an aggregated base station (also known as a standalone BS or monolithic BS) or a disaggregated base station.

[0027]

[0045] An aggregated base station may be configured to utilize a radio protocol stack that is physically or logically integrated within a single RAN node. A non-aggregated base station may be configured to utilize a protocol stack that is physically or logically distributed between two or more units (e.g., one or more centralized units (CU), one or more distributed units (DU), or one or more radio units (RU)). In some aspects, a CU may be implemented within a RAN node, and one or more DUs may be co-located with the CU, or alternatively may be geographically or virtually distributed across one or more other RAN nodes. A DU may be implemented to communicate with one or more RUs. Each of the CU, DU, and RU may be implemented as a virtual unit, i.e., a virtual central unit (VCU), a virtual distributed unit (VDU), or a virtual radio unit (VRU).

[0028]

[0046] Base station operation or network design can take into account the aggregation characteristics of base station functions. For example, disaggregated base stations can be utilized in integrated access backhaul (IAB) networks, open radio access networks (O-RAN, such as the network configuration initiated by the O-RAN alliance), or virtualized radio access networks (vRAN, also known as cloud radio access networks (C-RAN)). Disaggregation can include distributing functions across two or more units in different physical locations as well as distributing functions virtually for at least one unit, which can allow flexibility in network design. Various units of a disaggregated base station or disaggregated RAN architecture can be configured for wired or wireless communication with at least one other unit.

[0029]

[0047] 1 illustrates an embodiment of a wireless communication system and access network 100. The wireless communication system (also referred to as a wireless wide area network (WWAN)) includes a base station 102, a UE 104, an evolved packet core (EPC) 160, and another core network 190 (e.g., 5G core (5GC)). The base station 102 may include a macro cell (high power cellular base station) and / or a small cell (low power cellular base station). The macro cell includes a base station. The small cell includes a femto cell, a pico cell, and a micro cell.

[0030]

[0048] A base station 102 configured for 4G LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) may interface with the EPC 160 through a first backhaul link 132 (e.g., an S1 interface). A base station 102 configured for 5G NR (collectively referred to as Next Generation RAN (NG-RAN)) may interface with the core network 190 through a second backhaul link 184. In addition to other functions, the base station 102 may perform one or more of the following functions: forwarding of user data, encryption and decryption of radio channels, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, delivery for non-access stratum (NAS) messages, NAS node selection, synchronization, Radio Access Network (RAN) sharing, Multimedia Broadcast Multicast Service (MBMS), subscriber and equipment tracking, RAN Information Management (RIM), paging, positioning, and delivery of alert messages. The base stations 102 may communicate with each other directly or indirectly (e.g., through the EPC 160 or the core network 190) via a third backhaul link 134 (e.g., an X2 interface). The first backhaul link 132, the second backhaul link 184, and the third backhaul link 134 may be wired or wireless.

[0031]

[0049] The base stations 102 may wirelessly communicate with the UEs 104. Each of the base stations 102 may provide communication coverage to a respective geographic coverage area 110. There may be overlapping geographic coverage areas 110. For example, a small cell 102' may have a coverage area 110' that overlaps with the coverage area 110 of one or more macro base stations 102. A network that includes both small cells and macro cells may be known as a heterogeneous network. A heterogeneous network may also include a Home Evolved Node B (eNB) (HeNB) that may provide service to closed groups known as closed subscriber groups (CSGs). The communication link 120 between the base station 102 and the UE 104 may include uplink (UL) (also referred to as reverse link) transmissions from the UE 104 to the base station 102, and / or downlink (DL) (also referred to as forward link) transmissions from the base station 102 to the UE 104. The communication link 120 may use multiple-input multiple-output (MIMO) antenna technologies, including spatial multiplexing, beamforming, and / or transmit diversity. The communication link may be through one or more carriers. The base station 102 / UE 104 may use spectrum with a bandwidth of up to Y MHz (e.g., 5, 10, 15, 20, 100, 400 MHz, etc.) per carrier, allocated in carrier aggregation with up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. The allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or fewer carriers may be allocated for DL ​​than for UL). The component carriers may include a primary component carrier, sometimes referred to as a primary cell (PCell), and one or more secondary component carriers, sometimes referred to as a secondary cell (SCell).

[0032]

[0050] Several UEs 104 may communicate with each other using device-to-device (D2D) communication links 158. The D2D communication links 158 may use DL / UL WWAN spectrum. The D2D communication links 158 may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH), a physical sidelink discovery channel (PSDCH), a physical sidelink shared channel (PSSCH), and a physical sidelink control channel (PSCCH). The D2D communication may be through various wireless D2D communication systems, such as, for example, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, LTE, or NR.

[0033]

[0051] The wireless communication system may further include a Wi-Fi access point (AP) 150 in communication with a Wi-Fi station (STA) 152 via a communication link 154, such as in the 5 GHz unlicensed frequency spectrum. When communicating in the unlicensed frequency spectrum, the STA 152 / AP 150 may perform a clear channel assessment (CCA) prior to communicating to determine if a channel is available.

[0034]

[0052] The small cell 102' may operate in a licensed and / or unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell 102' may employ NR and use the same unlicensed frequency spectrum (e.g., 5 GHz, etc.) used by the Wi-Fi AP 150. A small cell 102' utilizing NR in an unlicensed frequency spectrum may provide increased coverage to and / or increase the capacity of an access network.

[0035]

[0053] The electromagnetic spectrum is often subdivided into various classes, bands, channels, etc., based on frequency / wavelength. For 5G NR, two initial operating bands have been identified with frequency range designations FR1 (410 MHz-7.125 GHz) and FR2 (24.25 GHz-52.6 GHz). Although a portion of FR1 is higher than 6 GHz, FR1 is often referred to (interchangeably) as the "sub-6 GHz" band in various documents and papers. Similar nomenclature issues may arise with respect to FR2, which is often referred to (interchangeably) as the "millimeter wave" band in documents and papers, even though it is different from the extremely high frequency (EHF) band (30 GHz-300 GHz) identified as the "millimeter wave" band by the International Telecommunications Union (ITU).

[0036]

[0054] Frequencies between FR1 and FR2 are often referred to as mid-band frequencies. Recent 5G NR studies have identified operating bands for these mid-band frequencies as frequency range designation FR3 (7.125 GHz to 24.25 GHz). Frequency bands that fall within FR3 may inherit FR1 and / or FR2 characteristics, and thus may in effect extend the features of FR1 and / or FR2 to the mid-band frequencies. Additionally, higher frequency bands are currently being explored to extend 5G NR operation beyond 52.6 GHz. For example, three higher operating bands have been identified as frequency range designations FR4a or FR4-1 (52.6 GHz to 71 GHz), FR4 (52.6 GHz to 114.25 GHz), and FR5 (114.25 GHz to 300 GHz). Each of these higher frequency bands falls within the EHF band.

[0037]

[0055] With the above aspects in mind, it should be understood that unless otherwise specified, terms such as "sub-6 GHz" as used herein may broadly refer to frequencies that may be below 6 GHz, may be within FR1, or may include mid-band frequencies. Additionally, it should be understood that unless otherwise specified, terms such as "mmWave" as used herein may broadly refer to frequencies that may include mid-band frequencies, may be within FR2, FR4, FR4-a or FR4-1, and / or FR5, or may be within the EHF band.

[0038]

[0056] The base station 102, whether a small cell 102′ or a large cell (e.g., a macro base station), may include and / or be referred to as an eNB, gNodeB (gNB), or another type of base station. Some base stations, such as the gNB 180, may operate at millimeter wave and / or quasi-millimeter wave frequencies in the conventional sub-6 GHz spectrum in communication with the UE 104. When the gNB 180 operates at millimeter wave or quasi-millimeter wave frequencies, the gNB 180 may be referred to as a millimeter wave base station. The millimeter wave base station 180 may utilize beamforming 182 for the UE 104 to compensate for path loss and short distances. The base station 180 and the UE 104 may each include multiple antennas, such as antenna elements, antenna panels, and / or antenna arrays, to facilitate beamforming.

[0039]

[0057] The base station 180 may transmit a beamformed signal to the UE 104 in one or more transmit directions 182′. The UE 104 may receive the beamformed signal from the base station 180 in one or more receive directions 182″. The UE 104 may also transmit a beamformed signal to the base station 180 in one or more transmit directions. The base station 180 may receive the beamformed signal from the UE 104 in one or more receive directions. The base station 180 / UE 104 may perform beam training to determine the best receive direction and transmit direction for each of the base station 180 / UE 104. The transmit direction and receive direction for the base station 180 may be the same or different. The transmit direction and receive direction for the UE 104 may be the same or different.

[0040]

[0058] The EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Mobility Management Entity (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be in communication with a Home Subscriber Server (HSS) 174. The MME 162 is a control node that handles signaling between the UE 104 and the EPC 160. In general, the MME 162 provides bearer and connection management. All user Internet Protocol (IP) packets are forwarded through the Serving Gateway 166, which is itself connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation as well as other functions. The PDN Gateway 172 and the BM-SC 170 are connected to an IP service 176. The IP services 176 may include the Internet, an intranet, an IP multimedia subsystem (IMS) 176a, PS streaming services, and / or other IP services. The BM-SC 170 may provide functionality for MBMS user service provisioning and delivery. The BM-SC 170 may act as an entry point for content provider MBMS transmissions, may be used to authorize and initiate MBMS bearer services in a public land mobile network (PLMN), and may be used to schedule MBMS transmissions.The MBMS gateway 168 may be used to deliver MBMS traffic to base stations 102 that belong to a Multicast Broadcast Single Frequency Network (MBSFN) area that broadcasts a particular service, and may be responsible for session management (start / stop) and collecting eMBMS-related charging information.

[0041]

[0059] The core network 190 may include an Access and Mobility Management Function (AMF) 192, other AMFs 193, a Session Management Function (SMF) 194, and a User Plane Function (UPF) 195. The AMF 192 may be in communication with a Unified Data Management (UDM) 196. The AMF 192 is a control node that handles signaling between the UE 104 and the core network 190. In general, the AMF 192 provides QoS flow and session management. All user Internet Protocol (IP) packets are forwarded through the UPF 195. The UPF 195 provides IP address allocation for the UE as well as other functions. The UPF 195 is connected to IP services 197. The IP services 197 may include Internet, intranet, IP Multimedia Subsystem (IMS) 197a, Packet Switch (PS) Streaming (PSS) services, and / or other IP services.

[0042]

[0060] A base station may include and / or be referred to as a gNB, Node B, eNB, access point, base transceiver station, radio base station, radio transceiver, transceiver function, basic service set (BSS), extended service set (ESS), transmit reception point (TRP), or some other suitable terminology. The base station 102 provides an access point to the EPC 160 or core network 190 for the UE 104. Examples of the UE 104 include a cellular phone, a smartphone, 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, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small cooking appliance, a healthcare device, an implant, a sensor / actuator, a display, or any other similarly functional device. Some of the UEs 104 may be referred to as IoT devices (e.g., a parking meter, a gas pump, a toaster, a vehicle, a heart monitor, etc.). The UE 104 may also be referred to as a station, mobile station, subscriber station, mobile unit, subscriber unit, wireless unit, remote unit, mobile device, wireless device, wireless communication device, remote device, mobile subscriber station, access terminal, mobile terminal, wireless terminal, remote terminal, handset, user agent, mobile client, client, or any other suitable terminology. In some scenarios, the term UE may also apply to one or more companion devices, such as in a device constellation configuration. One or more of these devices may collectively access the network and / or individually access the network.

[0043]

[0061] Referring again to FIG. 1, in some aspects, the UE 104 may include a voice component 198 that may be configured to attempt to attach to or perform a tracking area update in an EPS network to obtain voice services for a certain number of times. The voice component 198 may be configured to start a modified timer based on failure to attach to or perform a tracking area update in an EPS network for the number of times and based on configuration parameters. The modified timer may be modified based on a default timer. The number of times may be a predetermined or defined number in some aspects. The voice component 198 may be configured to attempt to obtain voice services based on one or more access technologies other than EPS. The voice component 198 may be configured to attach to or perform a tracking area update in an EPS network to obtain voice services based on the modified timer (e.g., based on stopping the modified timer or based on expiration of the modified timer). In some aspects, the base station 180 may include a voice component 199 that may be configured to send an indication of a duration associated with the modified timer to the voice centric UE. A duration associated with the modified timer may be shorter than a duration associated with the default timer. The voice component 199 may be configured to initially fail to provide voice service to the voice-centric UE over the EPS network. The voice component 199 may be configured to provide voice service to the voice-centric UE over the EPS network based on the modified timer after an initial failure to provide voice service to the voice-centric UE over the EPS network. The modified timer and the default timer may be associated with retries to attach to the EPS network or perform a tracking area update in the EPS network. Voice services may not be available over the 5GS or circuit-switched system.The following description may focus on 5G NR, however, the concepts described herein may be applicable to other similar domains, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies.

[0044]

[0062] As used herein, a network node may be implemented as an aggregated base station, a disaggregated base station, an integrated access backhaul (IAB) node, a relay node, a sidelink node, etc. The network node / entity may be implemented in an aggregated or monolithic base station architecture, or alternatively in a disaggregated base station architecture, and may include one or more of a central unit (CU), a distributed unit (DU), a radio unit (RU), a Near-Real Time (Near-RT) RAN Intelligent Controller (RIC), or a Non-Real Time (Non-RT) RIC.

[0045]

[0063] FIG. 2A is a diagram 200 illustrating an example of a first subframe in a 5G NR frame structure. FIG. 2B is a diagram 230 illustrating an example of a DL channel in a 5G NR subframe. FIG. 2C is a diagram 250 illustrating an example of a second subframe in a 5G NR frame structure. FIG. 2D is a diagram 280 illustrating an example of a UL channel in a 5G NR subframe. The 5G NR frame structure may be frequency division duplex (FDD) where for a particular set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated to either DL or UL, or time division duplex (TDD) where for a particular set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated to both DL and UL. In the example provided by Figures 2A, 2C, the 5G NR frame structure is assumed to be TDD, subframe 4 is configured with slot format 28 (mostly DL), where D is DL, U is UL, and F is flexible for DL / UL use, and subframe 3 is configured with slot format 1 (all UL). Subframes 3 and 4 are shown with slot formats 1 and 28, respectively, although any particular subframe may be configured with any of the various available slot formats 0-61. Slot formats 0 and 1 are all DL and UL, respectively. The other slot formats 2-61 include a mix of DL, UL, and flexible symbols. The UE is configured with the slot format through a received slot format indicator (SFI) (dynamically through DL control information (DCI) or semi-statically / statically through radio resource control (RRC) signaling). Note that the following description also applies to the 5G NR frame structure, which is TDD.

[0046]

[0064] 2A-2D show a frame structure, aspects of the present disclosure may be applicable to other wireless communication techniques that may have different frame structures and / or different channels. A frame (10 ms) may be divided into 10 subframes (1 ms) of equal size. Each subframe may include one or more time slots. A subframe may also include a minislot that may include 7, 4, or 2 symbols. Each slot may include 14 or 12 symbols depending on whether the cyclic prefix (CP) is normal or extended. With a normal CP, each slot may include 14 symbols, and with an extended CP, each slot may include 12 symbols. The symbols on the DL may be CP Orthogonal Frequency Division Multiplexing (OFDM) (CP-OFDM) symbols. Symbols on the UL may be CP-OFDM symbols (for high throughput scenarios) or discrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) symbols (also called single carrier frequency-division multiple access (SC-FDMA) symbols) (for power limited scenarios, restricted to single stream transmission). The number of slots in a subframe is based on the CP and numerology. The numerology defines the subcarrier spacing (SCS), which effectively defines the symbol length / duration equal to 1 / SCS.

[0047] [Table 1]

[0048]

[0065] For the normal CP (14 symbols / slot), the different numerologies μ0-4 allow 1, 2, 4, 8, and 16 slots per subframe, respectively. For the extended CP, numerology 2 allows 4 slots per subframe. Thus, for the normal CP and numerology μ, 14 symbols / slot and 2 μThere are slots / subframes. The subcarrier spacing is 2 μ * may be equal to 15 kHz, where μ is the numerology 0 to 4. Thus, numerology μ=0 has a subcarrier spacing of 15 kHz, and numerology μ=4 has a subcarrier spacing of 240 kHz. The symbol length / duration is inversely proportional to the subcarrier spacing. Figures 2A to 2D provide an example of a normal CP with 14 symbols per slot and a numerology μ=2 with 4 slots per subframe. The slot duration is 0.25 ms, the subcarrier spacing is 60 kHz, and the symbol duration is approximately 16.67 μs. Within a set of frames, there may be one or more different bandwidth parts (BWPs) (see Figure 2B) that are frequency division multiplexed. Each BWP may have a specific numerology and CP (normal or extended).

[0049]

[0066] A resource grid may be used to represent the frame structure. Each time slot contains a resource block (RB), also called physical RB (PRB), spanning 12 consecutive subcarriers. The resource grid is divided into resource elements (RE). The number of bits carried by each RE depends on the modulation scheme.

[0050]

[0067] As shown in Figure 2A, some of the REs carry reference (pilot) signals (RS) for the UE. The RS may include demodulation RS (DM-RS) (denoted as R for one particular configuration, but other DM-RS configurations are possible) and channel state information reference signals (CSI-RS) for channel estimation at the UE. The RS may also include beam measurement RS (BRS), beam improvement RS (BRRS), and phase tracking RS (PT-RS).

[0051]

[0068] FIG. 2B illustrates an example of various DL channels in a subframe of a frame. A physical downlink control channel (PDCCH) carries DCI in one or more control channel elements (CCEs) (e.g., 1, 2, 4, 8, or 16 CCEs), where each CCE includes 6 RE groups (REGs), and each REG includes 12 consecutive REs in an OFDM symbol of an RB. The PDCCHs in one BWP may be referred to as a control resource set (CORESET). A UE is configured to monitor PDCCH candidates in a PDCCH search space (e.g., common search space, UE-specific search space) during a PDCCH monitoring opportunity on the CORESET, where the PDCCH candidates have different DCI formats and different aggregation levels. Additional BWPs may be located at higher and / or lower frequencies across the channel bandwidth. A primary synchronization signal (PSS) may be in symbol 2 of a particular subframe of a frame. The PSS is used by the UE 104 to determine subframe / symbol timing and physical layer identity. The secondary synchronization signal (SSS) may be in symbol 4 of a particular subframe of a frame. The SSS is used by the UE to determine the physical layer cell identity group number and radio frame timing. Based on the physical layer identity and the physical layer cell identity group number, the UE can determine the physical cell identifier (PCI). Based on the PCI, the UE can determine the location of the DM-RS. The physical broadcast channel (PBCH), which carries the master information block (MIB), may be logically grouped with the PSS and SSS to form a synchronization signal (SS) / PBCH block (also called SS block (SSB)). The MIB provides the number of RBs in the system bandwidth and the system frame number (SFN). The physical downlink shared channel (PDSCH) carries user data, broadcast system information not transmitted over the PBCH, such as system information blocks (SIBs), and paging messages.

[0052]

[0069] As shown in FIG. 2C, some of the REs carry DM-RS (denoted as R for one particular configuration, but other DM-RS configurations are possible) for channel estimation at the base station. The UE may transmit DM-RS for the physical uplink control channel (PUCCH) and DM-RS for the physical uplink shared channel (PUSCH). The PUSCH DM-RS may be transmitted in the first one or two symbols of the PUSCH. The PUCCH DM-RS may be transmitted in different configurations depending on whether a short or long PUCCH is transmitted and depending on the particular PUCCH format used. The UE may transmit a sounding reference signal (SRS). The SRS may be transmitted in the last symbol of a subframe. The SRS may have a comb structure, and the UE may transmit the SRS on one of the combs. The SRS may be used by the base station for channel quality estimation to enable frequency-dependent scheduling on the UL.

[0053]

[0070] 2D shows an example of various UL channels within a subframe of a frame. The PUCCH, in one configuration, may be located as shown. The PUCCH carries uplink control information (UCI) such as scheduling requests, channel quality indicators (CQI), precoding matrix indicators (PMI), rank indicators (RI), and hybrid automatic repeat request (HARQ) acknowledgment (ACK) (HARQ-ACK) feedback (i.e., one or more HARQ ACK bits indicating one or more ACKs and / or negative ACKs (NACKs)). The PUSCH carries data and may additionally be used to carry buffer status reports (BSRs), power headroom reports (PHRs), and / or UCIs.

[0054]

[0071] 3 is a block diagram of a base station 310 communicating with a UE 350 in an access network. In the DL, Internet Protocol (IP) packets can be provided to a controller / processor 375. The controller / processor 375 implements Layer 3 and Layer 2 functions. Layer 3 includes a Radio Resource Control (RRC) layer, and Layer 2 includes a Service Data Adaptation Protocol (SDAP) layer, a Packet Data Convergence Protocol (PDCP) layer, a Radio Link Control (RLC) layer, and a Medium Access Control (MAC) layer. The controller / processor 375 provides RRC layer functions associated with system information (e.g., MIBs, SIBs), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter-radio access technology (RAT) mobility, and broadcast of measurement configurations for UE measurement reporting; PDCP layer functions associated with header compression / decompression, security (encryption, decryption, integrity protection, integrity verification), and handover support functions; RLC layer functions associated with forwarding of upper layer packet data units (PDUs), error correction via ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs), resegmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functions associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction via HARQ, priority handling, and logical channel prioritization.

[0055]

[0072] The transmit (TX) processor 316 and receive (RX) processor 370 implement Layer 1 functions associated with various signal processing functions. Layer 1, including the physical (PHY) layer, may include error detection on transport channels, forward error correction (FEC) coding / decoding of transport channels, interleaving, rate matching, mapping onto physical channels, modulation / demodulation of physical channels, and MIMO antenna processing. The TX processor 316 handles 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 may then be split into parallel streams. Each stream may then be 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 generate a physical channel carrying a time-domain OFDM symbol stream. The OFDM streams may be spatially precoded to generate multiple spatial streams. Channel estimates from a channel estimator 374 may be used to determine the coding and modulation schemes as well as for spatial processing. The channel estimates may be derived from a reference signal and / or channel condition feedback transmitted by the UE 350. Each spatial stream may then be provided to a different antenna 320 via a separate transmitter 318Tx. Each transmitter 318Tx may modulate a radio frequency (RF) carrier with the respective spatial stream for transmission.

[0056]

[0073] At the UE 350, each receiver 354Rx receives a signal via its respective antenna 352. Each receiver 354Rx recovers the information modulated onto an RF carrier and provides the information to a receive (RX) processor 356. The TX processor 368 and the RX processor 356 implement Layer 1 functionality related to various signal processing functions. The RX processor 356 may perform spatial processing on the information to recover any spatial streams destined for the UE 350. Multiple spatial streams may be combined into a single OFDM symbol stream by the RX processor 356 if they are destined for the UE 350. The RX processor 356 then converts the OFDM symbol stream from the time domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal includes a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, as well as the reference signal, are recovered and demodulated by determining the most likely signal constellation point transmitted by the base station 310. These soft decisions may be based on channel estimates calculated by a channel estimator 358. The soft decisions are then decoded and deinterleaved to recover the data and control signals originally transmitted by the base station 310 on the physical channel. The data and control signals are then provided to a controller / processor 359, which implements Layer 3 and Layer 2 functions.

[0057]

[0074] The controller / processor 359 may be associated with a memory 360 that stores program codes and data. The memory 360 may be referred to as a computer-readable medium. In the UL, the controller / processor 359 performs demultiplexing between transport and logical channels, packet reassembly, decryption, header decompression, and control signal processing to recover IP packets. The controller / processor 359 is also responsible for error detection using an ACK and / or NACK protocol to support HARQ operations.

[0058]

[0075] Similar to the functionality described in connection with DL transmissions by the base station 310, the controller / processor 359 provides RRC layer functions associated with system information (e.g., MIBs, SIBs) acquisition, RRC connection, and measurement reporting; PDCP layer functions associated with header compression / decompression and security (encryption, decryption, integrity protection, integrity verification); RLC layer functions associated with forwarding of upper layer PDUs, error correction via ARQ, concatenation, segmentation, and reassembly of RLC SDUs, resegmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functions associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto the TB, demultiplexing of MAC SDUs from the TB, scheduling information reporting, error correction via HARQ, priority handling, and logical channel prioritization.

[0059]

[0076] Channel estimates derived by the channel estimator 358 from a reference signal or feedback transmitted by the base station 310 may be used by the TX processor 368 to select an appropriate coding and modulation scheme as well as to facilitate spatial processing. The spatial streams generated by the TX processor 368 may be provided to different antennas 352 via separate transmitters 354Tx. Each transmitter 354Tx may modulate an RF carrier with a respective spatial stream for transmission.

[0060]

[0077] The UL transmission is processed at the base station 310 in a manner similar to that described for the receiver functions at the UE 350. Each receiver 318Rx receives a signal via its respective antenna 320. Each receiver 318Rx recovers the information modulated onto an RF carrier and provides the information to the RX processor 370.

[0061]

[0078] The controller / processor 375 may be associated with a memory 376 that stores program codes and data. The memory 376 may be referred to as a computer-readable medium. In the UL, the controller / processor 375 performs demultiplexing between transport and logical channels, packet reassembly, decryption, header decompression, and control signal processing to recover IP packets. The controller / processor 375 is also responsible for error detection using an ACK and / or NACK protocol to support HARQ operations.

[0062]

[0079] At least one of the TX processor 368, the RX processor 356, and the controller / processor 359 may be configured to perform aspects associated with the audio component 198 of FIG.

[0063]

[0080] At least one of the TX processor 316, the RX processor 370, and the controller / processor 375 may be configured to perform aspects associated with the audio component 199 of FIG.

[0064]

[0081] 4 is a diagram 400 illustrating an unmodified (or default) timer T3 402. The UE 402 may attempt to attach to or perform a tracking area update in the EPS network 404. If the attach attempt fails repeatedly a predetermined number of times (e.g., N times), the UE 402 may start the timer T3 402. The UE 402 may not retry attaching to or performing a tracking area update in the EPS network 404 before the timer T3 402 expires.

[0065]

[0082] In one or more aspects, a voice-centric UE may experience long periods without access to voice services due to the voice services being provided via EPS fallback in a 5GS network and the UE having difficulty attaching to the EPS network or performing a tracking area update in the EPS network. In one embodiment, the UE may be voice-centric and VoNR may not be supported in the 5GS network (i.e., voice may only be supported via EPS fallback). Furthermore, voice services via previous circuit-switched technologies (e.g., 2G / 3G) may not be available because the spectrum may be reused for other radio access technologies. The UE may experience long periods without access to voice services due to the difficulties attaching to the EPS network or performing a tracking area update in the EPS network.

[0066]

[0083] In one embodiment, the long period without access to voice services may occur as follows: First, due to insufficient EPS coverage, the UE may fail to attach to or perform a tracking area update in the EPS network five consecutive times, which may cause the UE to disable S1 mode (i.e., a mode related to the UE's 4G / EPS capabilities) and start timer T3402 (whose default duration is 12 minutes). Timer T3402 may be associated with retries to attach to or perform a tracking area update in the EPS network. By default, the UE may not retry to attach to or perform a tracking area update in the EPS network before timer T3402 expires. The UE may then attempt to attach to or perform a tracking area update in the 5GS network and may indicate to the 5GS network that S1 mode is disabled in a registration request message. Since the network can support voice services via EPS fallback and EPS fallback may be unavailable when S1 mode is disabled, the network can indicate "IMS voice over 3GPP access is not supported" in the registration accept message. Since the UE is voice-centric, receiving the indication "IMS voice over 3GPP access is not supported" in the registration accept message can cause the UE to disable N1 mode (i.e., the mode related to the UE's 5G capabilities). With both S1 mode and N1 mode disabled, the UE can search 2G / 3G networks for voice services and may find none. Finally, the UE can re-enable N1 mode and camp on the 5GS network. The UE may not be able to obtain voice services via EPS fallback until timer T3402 expires. As a result, the user may experience noticeable periods without access to voice services.

[0067]

[0084] FIG. 5 is a diagram of a communication flow 500 of a method of wireless communication. VoNR may not be available from a base station 504. At 510, the UE 502 may attempt to attach to or perform a tracking area update in an EPS network to obtain voice services for a certain number of times. The number of times may be a predetermined or defined number of times in some aspects. At 512, the UE 502 may start a modified timer based on failure to attach to or perform a tracking area update in an EPS network for the number of times and based on a configuration parameter. The modified timer may be modified based on a default timer. In one or more configurations, the configuration parameter may be stored in a mobile equipment (ME) or a universal subscriber identify module (USIM) of the UE 502. At 514, the UE 502 may disable S1 mode upon starting the modified timer. At 516, the UE 502 may skip retrying to attach to the EPS network or performing a tracking area update in the EPS network before stopping (e.g., if the cell quality is above a threshold for longer than the threshold time, the modified timer may be stopped early) or expiry of the modified timer. At 518, the UE 502 may attempt to acquire voice services based on one or more access technologies other than EPS. In some aspects, the UE may attempt to acquire voice services from each of the one or more access technologies. The attempt at 518 may also fail.

[0068]

[0085] In one aspect, the modified timer may be associated with a shorter duration (e.g., 3 minutes, 4 minutes, etc.) than the unmodified / default timer T3402. The modified timer may be used at 512 based on the value of a configuration parameter (e.g., a "UseReducedT3402" parameter). The shorter duration of the modified timer may be stored in the ME or USIM of the UE 502. It should be appreciated that the UE 502 may use the modified timer associated with the shorter duration regardless of the quality of EPS coverage. The UE 502 may still not have voice service for the duration of the modified timer.

[0069]

[0086] In one aspect, the modified timer with the shorter duration may be used a first predetermined number of times (e.g., two times) after the UE 502 is last powered up, otherwise the unmodified timer T3402 will be used. After the modified timer has been used a predetermined number of times, the unmodified timer T3402 with the default duration may be used the next and further occasions when the timer T3402 is started. In other words, at 524, the UE 502 may start the unmodified timer based on a failure to attach to or perform a tracking area update in the EPS network after the modified timer has been used a threshold number of times after the UE is last powered up. By limiting the number of times the modified timer is used, the UE 502 may revert to using the unmodified timer T3402 with the default duration if the UE 502 is truly outside the 4G / EPS coverage area and not temporarily in a coverage hole. As a result, energy may not be wasted on an excessive number of failed attempts to attach to or perform tracking area updates in an EPS network.

[0070]

[0087] In one aspect, the shorter duration associated with the modified timer may be pre-configured.

[0071]

[0088] In one aspect, the shorter duration associated with the modified timer can be based on an indication that the UE 502 receives from the base station 504. In other words, the UE 502 can receive an indication of the shorter duration associated with the modified timer from the base station 504. Thus, a network operator can tailor the modified timer duration to a particular deployment.

[0072]

[0089] At 520, the UE 502 may re-enable S1 mode upon expiration or stopping of the modified timer. At 522, the UE 502 may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer (e.g., based on stopping the modified timer or based on expiration of the modified timer).

[0073]

[0090] FIG. 6 is a diagram of a communication flow 600 of a method of wireless communication. VoNR may not be available from a base station 604. At 608, the UE 602 may attempt to attach to or perform a tracking area update in an EPS network to obtain voice services a certain number of times. The number may be a predetermined or defined number in some aspects. At 610, the UE 602 may start a modified timer based on failure to attach to or perform a tracking area update in an EPS network the number of times and based on configuration parameters. The modified timer may be modified based on a default timer. At 612, the UE 602 may disable S1 mode upon starting the modified timer. At 614, the UE 602 may skip retrying to attach to or perform a tracking area update in an EPS network before stopping (e.g., if the cell quality is above a certain threshold for longer than the threshold time, the modified timer may be stopped early) or expiring the modified timer. At 616, the UE 602 may send an indication to the 5GS base station 604 that the S1 mode is disabled. At 618, the UE 602 may receive an indication from the 5GS base station 604 that packet-switched voice services are not supported. At 620, the UE 602 may disable the N1 mode upon receiving the indication that packet-switched voice services are not supported. At 622, the UE 602 may attempt to acquire voice services based on one or more access technologies other than EPS (e.g., 2G / 3G access technologies). The attempt at 622 may also fail. At 624, the UE 602 may re-enable the N1 mode upon failing to acquire circuit-switched voice services on an access technology other than 5GS.To illustrate the concepts, aspects are described with respect to examples of 5GS networks and other access technologies, but aspects may be similarly applied to other access technologies, including future access technologies. For example, the UE may send an indication to a base station of a first access technology that S1 mode is disabled and may receive an indication from the base station that packet-switched voice services are not supported. The UE may disable an operating mode associated with the first access technology upon receiving an indication that packet-switched voice services are not supported, and may re-enable an operating mode associated with the first access technology upon failure to acquire voice services in one or more access technologies (e.g., different from the first access technology of the base station).

[0074]

[0091] In one aspect, the UE 602 may re-enable the S1 mode upon re-enabling the N1 mode at 624. Furthermore, the UE may stop the modified timer upon re-enabling the N1 and S1 modes. The use of the modified timer at 610 may be based on the value of a configuration parameter (e.g., the "Enable T3402 Early Stop" parameter). In other words, the UE 602 may re-enable the S1 mode upon re-enabling the N1 mode at 626. The UE 602 may stop the modified timer upon re-enabling the S1 mode at 628. Thus, the UE 602 may regain voice services before the natural expiration of the unmodified timer T3402. However, it should be appreciated that when the modified timer is stopped, the EPS coverage may still be insufficient, in which case an attempt to obtain voice services via EPS fallback may fail again.

[0075]

[0092] In one aspect, the UE 602 may re-enable the S1 mode upon re-enabling the N1 mode at 624. Furthermore, the UE may stop the modified timer in response to one of a reselection by the UE to the EPS network or a handover or redirection by the network to the EPS network. The use of the modified timer at 610 may be based on the value of a configuration parameter (e.g., an "Enable T3402 Early Stop" parameter). In other words, the UE 602 may re-enable the S1 mode at 626 upon re-enabling the N1 mode. The UE 602 may stop the modified timer in response to one of a reselection by the UE to the EPS network or a handover or redirection by the network to the EPS network at 628. Thus, the UE 602 may regain voice services before the natural expiration of the unmodified timer T3402. However, it should be appreciated that after disabling S1 mode at 612, N1 mode may still be disabled at 620 and attempts may still be made to obtain voice service via 2G / 3G access technologies at 622 before the UE can return to the 5GS network at 624 and regain voice service at 630. In other words, the user may still experience periods without voice service.

[0076]

[0093] At 630, the UE 602 can attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer (e.g., based on stopping the modified timer or based on expiration of the modified timer).

[0077]

[0094] FIG. 7 is a diagram of a communication flow 700 of a method of wireless communication. VoNR may not be available from a base station 704. At 708, the UE 702 may attempt to attach to or perform a tracking area update in an EPS network to obtain voice services a certain number of times. At 710, the UE 702 may start a modified timer based on failure to attach to or perform a tracking area update in an EPS network a certain number of times and based on configuration parameters. The modified timer may be modified based on a default timer. At 712, the UE 702 may disable S1 mode upon starting the modified timer. At 714, the UE 702 may skip retrying to attach to or perform a tracking area update in an EPS network before stopping (e.g., if the cell quality is above a certain threshold for longer than the threshold time, the modified timer may be stopped early) or expiring the modified timer. At 716, the UE 702 may attempt to acquire voice services based on one or more access technologies other than EPS. The attempt at 716 may also fail.

[0078]

[0095] In one aspect, when the modified timer is running after 710 and the S1 mode is disabled after 712, the access stratum (AS) at the UE 702 may periodically check the quality of the 4G / EPS cell. If the cell quality is above a predetermined threshold for longer than a predetermined duration, the UE 702 may re-enable the S1 mode and stop the modified timer. The use of the modified timer at 710 may be based on the value of a configuration parameter (e.g., an "Enable T3402 Early Stop" parameter). In other words, at 718, the UE 702 may monitor the quality of a cell associated with the EPS network. At 720, the UE 702 may stop the modified timer when the cell quality is above a predetermined threshold for a predetermined period of time. At 722, the UE 702 may re-enable the S1 mode based on the stopping of the modified timer. Thus, the UE 702 may regain voice services before the natural expiration of the unmodified timer T3402. Further, the UE 702 may re-enable the S1 mode and stop the modified timer when the EPS coverage is sufficiently good. However, it should be understood that stopping the NAS timer based on an AS trigger may be considered a layer violation.

[0079]

[0096] At 724, the UE 702 can attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer (e.g., based on stopping the modified timer or based on expiration of the modified timer).

[0080]

[0097] FIG. 8 is a diagram of a communication flow 800 of a method of wireless communication. VoNR may not be available from a base station 804. At 808, the UE 802 may attempt to attach to or perform a tracking area update in an EPS network to obtain voice services a certain number of times. The number may be a predetermined or defined number in some aspects. At 810, the UE 802 may start a modified timer based on failure to attach to or perform a tracking area update in an EPS network the number of times and based on configuration parameters. The modified timer may be modified based on a default timer. At 816, the UE 802 may attempt to obtain voice services based on one or more access technologies other than EPS. The attempt at 816 may also fail.

[0081]

[0098] The UE 802 may not disable S1 mode when the modified timer is started at 810. After 810 and before the stopping of the modified timer (e.g., the modified timer may be stopped early if the cell quality is above a threshold for longer than the threshold time) or expiration, when the modified timer is running, the UE 802 may either deprioritize the EPS network (regardless of the priority indicated by the network) or not retry attaching to or performing a tracking area update in the EPS network. The use of the modified timer at 810 may be based on the value of a configuration parameter (e.g., an "Enable T3402 Early Stop" parameter). Because the S1 mode remains enabled, the UE may not receive an indication that "IMS voice over 3GPP access is not supported" in the registration accept message. As a result, the UE may not disable N1 mode and may not waste time trying to obtain voice services over the legacy 2G / 3G network (i.e., in some configurations, 816 may not be performed). Thus, the UE 802 may maintain the S1 mode in effect when starting the modified timer at 812. At 814, the UE 802 may deprioritize the EPS network or not retry attaching to or performing a tracking area update in the EPS network prior to the stopping or expiration of the modified timer.

[0082]

[0099] In one aspect, the UE 802 may not retry attaching to the EPS network or performing a tracking area update in the EPS network before the stop or expiration of the modified timer. The UE 802 may stop the modified timer in response to one of a reselection by the UE to the EPS network, a handover to the EPS network, or a redirection by the network to the EPS network. In other words, at 818, the UE 802 may stop the modified timer in response to one of a reselection by the UE to the EPS network, a handover to the EPS network, or a redirection by the network to the EPS network. Thus, the UE 802 may regain voice services before the natural expiration of the unmodified timer T3402.

[0083]

[0100] In one aspect, the UE 802 may deprioritize one or more cells associated with the EPS network for cell reselection prior to the stop or expiration of the modified timer, regardless of the priority indicated by the network. The UE 802 may stop the modified timer in response to one of a handover to the EPS network or a redirection by the network to the EPS network. In other words, at 818, the UE 802 may stop the modified timer in response to one of a handover to the EPS network or a redirection by the network to the EPS network. Thus, the UE 802 may regain voice service prior to the natural expiration of the unmodified timer T3402. However, it should be understood that the UE 802 may override the normal cell reselection rules.

[0084]

[0101] At 820, the UE 802 can attach to the EPS network or perform a tracking area update in the EPS network to obtain voice services based on the modified timer (e.g., based on stopping the modified timer or based on expiration of the modified timer).

[0085]

[0102] FIG. 9 is a flowchart 900 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104 / 350 / 502 / 602 / 702 / 802, device 1502). At 902, the UE may start a modified timer based on a number of failed attempts associated with a voice service for the EPS network and based on configuration parameters. The modified timer may be modified based on a default timer. For example, 902 may be performed by component 198 of FIG. 15. Referring to FIG. 5-FIG. 8, at 512, 610, 710, 810, the UE 502, 602, 702, 802 may start a modified timer based on a number of failed attempts associated with a voice service for the EPS network and based on configuration parameters.

[0086]

[0103] At 904, the UE may attempt to acquire voice services based on one or more access technologies other than EPS. For example, 904 may be performed by component 198 of Figure 15. With reference to Figures 5-8, at 518, 622, 716, 816, the UE 502, 602, 702, 802 may attempt to acquire voice services based on one or more access technologies other than EPS.

[0087]

[0104] At 906, the UE may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer (e.g., based on stopping the modified timer or based on expiration of the modified timer). For example, 906 may be performed by component 198 of FIG. 15. With reference to FIGs. 5-8, at 522, 630, 724, 820, the UE 502, 602, 702, 802 may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer.

[0088]

[0105] FIG. 10 is a flowchart 1000 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104 / 350 / 502, device 1502). At 1004, the UE may attempt to attach to an EPS network or perform a tracking area update in the EPS network to obtain voice services a certain number of times. The number of times may be a predetermined or defined number in some aspects. For example, 1004 may be performed by component 198 of FIG. 15. Referring to FIG. 5, at 510, the UE 502 may attempt to attach to an EPS network or perform a tracking area update in the EPS network to obtain voice services a certain number of times.

[0089]

[0106] At 1006, the UE may start a modified timer based on the number of failures to attach to or perform a tracking area update in the EPS network and based on the configuration parameters. The modified timer may be modified based on a default timer. For example, 1006 may be performed by component 198 of FIG. 15. Referring to FIG. 5, at 512, the UE 502 may start a modified timer based on the number of failures to attach to or perform a tracking area update in the EPS network and based on the configuration parameters.

[0090]

[0107] At 1012, the UE may attempt to acquire voice services based on one or more access technologies other than EPS. For example, 1012 may be performed by component 198 of Figure 15. Referring to Figure 5, at 518, the UE 502 may attempt to acquire voice services based on one or more access technologies other than EPS.

[0091]

[0108] At 1016, the UE may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer (e.g., based on stopping the modified timer or based on expiration of the modified timer). For example, 1016 may be performed by component 198 of Figure 15. Referring to Figure 5, at 522, the UE 502 may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer.

[0092]

[0109] In one configuration, at 1008, the UE may disable S1 mode upon starting the modified timer. For example, 1008 may be performed by component 198 of FIG. 15. Referring to FIG. 5, at 514, the UE 502 may disable S1 mode upon starting the modified timer. At 1010, the UE may skip retrying to attach to the EPS network or performing a tracking area update in the EPS network before the stopping or expiration of the modified timer. For example, 1010 may be performed by component 198 of FIG. 15. Referring to FIG. 5, at 516, the UE 502 may skip retrying to attach to the EPS network or performing a tracking area update in the EPS network before the stopping or expiration of the modified timer.

[0093]

[0110] In one configuration, the modified timer may be associated with a shorter duration than the unmodified / default timer. At 1014, the UE may re-enable the S1 mode upon expiration of the modified timer. For example, 1014 may be performed by component 198 of FIG. 15. Referring to FIG. 5, at 520, the UE 502 may re-enable the S1 mode upon expiration of the modified timer.

[0094]

[0111] In one configuration, at 1018, the UE may start the unmodified / default timer based on a failure to attach to or perform a tracking area update in the EPS network after the modified timer has been used a threshold number of times since the UE was last powered up. For example, 1018 may be performed by component 198 of FIG. 15. Referring to FIG. 5, at 524, the UE 502 may start the unmodified / default timer based on a failure to attach to or perform a tracking area update in the EPS network after the modified timer has been used a threshold number of times since the UE 502 was last powered up.

[0095]

[0112] In one configuration, the shorter duration associated with the modified timer may be pre-configured.

[0096]

[0113] In one configuration, the UE may receive, from a base station, an indication of a shorter duration associated with a modified timer, at 1002. For example, 1002 may be performed by component 198 of FIG. 15. Referring to FIG. 5, the UE 502 may receive, at 508, from the base station 504, an indication of a shorter duration associated with a modified timer.

[0097]

[0114] In one configuration, an indication of the shorter duration associated with the modified timer may be stored in the ME or USIM of the UE.

[0098]

[0115] In one configuration, the UE may be a voice-centric UE.

[0099]

[0116] FIG. 11 is a flowchart 1100 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104 / 350 / 602, device 1502). At 1102, the UE may attempt to attach to an EPS network or perform a tracking area update in the EPS network to obtain voice services a certain number of times. For example, 1102 may be performed by component 198 of FIG. 15. The number of times may be a predetermined or defined number in some aspects. Referring to FIG. 6, at 608, the UE 602 may attempt to attach to an EPS network or perform a tracking area update in the EPS network to obtain voice services a certain number of times.

[0100]

[0117] At 1104, the UE may start a modified timer based on the number of failures to attach to or perform a tracking area update in the EPS network and based on the configuration parameters. The modified timer may be modified based on a default timer. For example, 1104 may be performed by component 198 of FIG. 15. Referring to FIG. 6, at 610, the UE 602 may start a modified timer based on the number of failures to attach to or perform a tracking area update in the EPS network and based on the configuration parameters.

[0101]

[0118] At 1116, the UE may attempt to acquire voice services based on one or more access technologies other than EPS. For example, 1116 may be performed by component 198 of Figure 15. Referring to Figure 6, at 622, the UE 602 may attempt to acquire voice services based on one or more access technologies other than EPS.

[0102]

[0119] At 1124, the UE may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer (e.g., based on stopping the modified timer or based on expiration of the modified timer). For example, 1124 may be performed by component 198 of FIG. 15. Referring to FIG. 6, at 630, the UE 602 may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer.

[0103]

[0120] In one configuration, at 1106, the UE may disable S1 mode upon starting the modified timer. For example, 1106 may be performed by component 198 of FIG. 15. With reference to FIG. 6, at 612, the UE 602 may disable S1 mode upon starting the modified timer. At 1108, the UE may skip retrying to attach to the EPS network or perform a tracking area update in the EPS network before the stopping or expiration of the modified timer. For example, 1108 may be performed by component 198 of FIG. 15. With reference to FIG. 6, at 614, the UE may skip retrying to attach to the EPS network or perform a tracking area update in the EPS network before the stopping or expiration of the modified timer.

[0104]

[0121] In one configuration, in response to failing to acquire voice services based on the EPS, at 1110, the UE may send an indication to the 5GS base station that the S1 mode is disabled. For example, 1110 may be performed by component 198 of FIG. 15. With reference to FIG. 6, at 616, the UE 602 may send an indication to the 5GS base station 604 that the S1 mode is disabled. At 1112, the UE may receive an indication from the 5GS base station that packet switched voice services are not supported. For example, 1112 may be performed by component 198 of FIG. 15. With reference to FIG. 6, at 618, the UE 602 may receive an indication from the 5GS base station 604 that packet switched voice services are not supported. At 1114, the UE may disable the N1 mode upon receiving the indication that packet switched voice services are not supported. For example, 1114 may be performed by component 198 of FIG. 15. With reference to FIG. 6, at 620, the UE 602 may disable the N1 mode upon receiving an indication that packet switched voice services are not supported. At 1118, the UE may re-enable the N1 mode upon failure to acquire circuit switched voice services in an access technology other than 5GS. For example, 1118 may be performed by component 198 of FIG. 15. With reference to FIG. 6, at 624, the UE 602 may re-enable the N1 mode upon failure to acquire circuit switched voice services in an access technology other than 5GS.

[0105]

[0122] In one configuration, at 1120, the UE may re-enable the S1 mode upon re-enabling the N1 mode. For example, 1120 may be performed by component 198 of FIG. 15. With reference to FIG. 6, at 626, the UE 602 may re-enable the S1 mode upon re-enabling the N1 mode. At 1122, the UE may stop the modified timer upon re-enabling the S1 mode. For example, 1122 may be performed by component 198 of FIG. 15. With reference to FIG. 6, at 628, the UE 602 may stop the modified timer upon re-enabling the S1 mode.

[0106]

[0123] In one configuration, at 1120, the UE may re-enable the S1 mode upon re-enabling the N1 mode. For example, 1120 may be performed by component 198 of FIG. 15. With reference to FIG. 6, at 626, the UE 602 may re-enable the S1 mode upon re-enabling the N1 mode. At 1122, the UE may stop the modified timer in response to one of a reselection by the UE to the EPS network or a handover or redirection by the network to the EPS network. For example, 1122 may be performed by component 198 of FIG. 15. With reference to FIG. 6, at 628, the UE 602 may stop the modified timer in response to one of a reselection by the UE to the EPS network or a handover or redirection by the network to the EPS network.

[0107]

[0124] In one configuration, the UE may be a voice-centric UE.

[0108]

[0125] FIG. 12 is a flowchart 1200 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104 / 350 / 702, device 1502). At 1202, the UE may attempt to attach to an EPS network or perform a tracking area update in the EPS network to obtain voice services a certain number of times. The number of times may be a predetermined or defined number in some aspects. For example, 1202 may be performed by component 198 of FIG. 15. Referring to FIG. 7, at 708, the UE 702 may attempt to attach to an EPS network or perform a tracking area update in the EPS network to obtain voice services a certain number of times.

[0109]

[0126] At 1204, the UE may start a modified timer based on the number of failures to attach to or perform a tracking area update in the EPS network and based on the configuration parameters. The modified timer may be modified based on a default timer. For example, 1204 may be performed by component 198 of FIG. 15. Referring to FIG. 7, at 710, the UE 702 may start a modified timer based on the number of failures to attach to or perform a tracking area update in the EPS network and based on the configuration parameters.

[0110]

[0127] At 1210, the UE may attempt to acquire voice services based on one or more access technologies other than EPS. For example, 1210 may be performed by component 198 of Figure 15. Referring to Figure 7, at 716, the UE 702 may attempt to acquire voice services based on one or more access technologies other than EPS.

[0111]

[0128] At 1218, the UE may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer (e.g., based on stopping the modified timer or based on expiration of the modified timer). For example, 1218 may be performed by component 198 of FIG. 15. Referring to FIG. 7, at 724, the UE 702 may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer.

[0112]

[0129] In one configuration, at 1206, the UE may disable S1 mode upon starting the modified timer. For example, 1206 may be performed by component 198 of FIG. 15. With reference to FIG. 7, at 712, the UE 702 may disable S1 mode upon starting the modified timer. At 1208, the UE may skip retrying to attach to the EPS network or perform a tracking area update in the EPS network before the stopping or expiration of the modified timer. For example, 1208 may be performed by component 198 of FIG. 15. With reference to FIG. 7, at 714, the UE 702 may skip retrying to attach to the EPS network or perform a tracking area update in the EPS network before the stopping or expiration of the modified timer.

[0113]

[0130] In one configuration, at 1212, the UE may monitor a quality of a cell associated with the EPS network. For example, 1212 may be performed by component 198 of FIG. 15. With reference to FIG. 7, at 718, the UE 702 may monitor a quality of a cell associated with the EPS network. At 1214, the UE may stop the modified timer when the quality of the cell is above a predetermined threshold for a predetermined period of time. For example, 1214 may be performed by component 198 of FIG. 15. With reference to FIG. 7, at 720, the UE 702 may stop the modified timer when the quality of the cell is above a predetermined threshold for a predetermined period of time. At 1216, the UE may re-enable S1 mode based on the stopping of the modified timer. For example, 1216 may be performed by component 198 of FIG. 15. With reference to FIG. 7, at 722, the UE 702 may re-enable S1 mode based on the stopping of the modified timer.

[0114]

[0131] In one configuration, the UE may be a voice-centric UE.

[0115]

[0132] FIG. 13 is a flowchart 1300 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104 / 350 / 802, device 1502). At 1302, the UE may attempt to attach to an EPS network or perform a tracking area update in the EPS network to obtain voice services a certain number of times. The number of times may be a predetermined or defined number in some aspects. For example, 1302 may be performed by component 198 of FIG. 15. Referring to FIG. 8, at 808, the UE 802 may attempt to attach to an EPS network or perform a tracking area update in the EPS network to obtain voice services a certain number of times.

[0116]

[0133] At 1304, the UE may start a modified timer based on the number of failures to attach to or perform a tracking area update in the EPS network and based on the configuration parameters. The modified timer may be modified based on a default timer. For example, 1304 may be performed by component 198 of FIG. 15. Referring to FIG. 8, at 810, the UE 802 may start a modified timer based on the number of failures to attach to or perform a tracking area update in the EPS network and based on the configuration parameters.

[0117]

[0134] At 1310, the UE may attempt to acquire voice services based on one or more access technologies other than EPS. For example, 1310 may be performed by component 198 of Figure 15. Referring to Figure 8, at 816, the UE 802 may attempt to acquire voice services based on one or more access technologies other than EPS.

[0118]

[0135] At 1314, the UE may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer. For example, 1314 may be performed by component 198 of Figure 15. Referring to Figure 8, at 820, the UE 802 may attach to or perform a tracking area update in the EPS network to obtain voice services based on the modified timer.

[0119]

[0136] In one configuration, at 1306, the UE may keep the S1 mode active when starting the modified timer. For example, 1306 may be performed by component 198 of FIG. 15. Referring to FIG. 8, at 812, the UE 802 may keep the S1 mode active when starting the modified timer. At 1308, the UE may de-prioritize the EPS network or not retry attaching to or performing a tracking area update in the EPS network before the stopping or expiration of the modified timer. For example, 1308 may be performed by component 198 of FIG. 15. Referring to FIG. 8, at 814, the UE 802 may de-prioritize the EPS network or not retry attaching to or performing a tracking area update in the EPS network before the stopping or expiration of the modified timer.

[0120]

[0137] In one configuration, at 1312, the UE may stop the modified timer in response to one of a reselection by the UE to the EPS network, a handover to the EPS network, or a redirection by the network to the EPS network. For example, 1312 may be performed by component 198 of Figure 15. Referring to Figure 8, at 818, the UE 802 may stop the modified timer in response to one of a reselection by the UE to the EPS network, a handover to the EPS network, or a redirection by the network to the EPS network.

[0121]

[0138] In one configuration, the UE may deprioritize one or more cells associated with the EPS network for cell reselection prior to stopping or expiration of the modified timer.

[0122]

[0139] In one configuration, the UE may be a voice-centric UE.

[0123]

[0140] FIG. 14 is a flowchart 1400 of a method of wireless communication. The method may be performed by a base station (e.g., base station 102 / 310 / 504, network entity 1602). At 1402, the base station may send to a voice centric UE an indication of a duration associated with a modified timer. The duration associated with the modified timer may be shorter than a duration associated with a default timer. For example, 1402 may be performed by component 199 of FIG. 16. Referring to FIG. 5, at 508, the base station 504 may send to the voice centric UE 502 an indication of a duration associated with the modified timer.

[0124]

[0141] At 1404, the base station may initially fail to provide voice service to the voice centric UE over the EPS network. For example, 1404 may be performed by component 199 of Figure 16. Referring to Figure 5, at 510, the base station 504 may initially fail to provide voice service to the voice centric UE 502 over the EPS network.

[0125]

[0142] At 1406, the base station may provide the voice service to the voice-centric UE via the EPS network based on the modified timer after an initial failure to provide the voice service to the voice-centric UE via the EPS network. For example, 1406 may be performed by component 199 of FIG. 16. Referring to FIG. 5, at 522, the base station 504 may provide the voice service to the voice-centric UE 502 via the EPS network based on the modified timer after an initial failure to provide the voice service to the voice-centric UE 502 via the EPS network.

[0126]

[0143] The modified and default timers may be associated with retries to attach to or perform a tracking area update in an EPS network. Voice services may not be available over 5GS or circuit-switched systems.

[0127]

[0144] 15 is a diagram 1500 illustrating an example of a hardware implementation for a device 1502. The device 1502 may be a UE, may be a component of a UE, or may implement UE functionality. In some aspects, the device 1502 may include a cellular baseband processor 1504 (also referred to as a modem) coupled to a cellular RF transceiver 1522. In some aspects, the device 1502 may further include one or more subscriber identity module (SIM) cards 1520, an application processor 1506 coupled to a secure digital (SD) card 1508 and a screen 1510, a Bluetooth module 1512, a wireless local area network (WLAN) module 1514, a global positioning system (GPS) module 1516, or a power source 1518. The cellular baseband processor 1504 communicates with the UE 104 and / or the BS 102 / 180 through the cellular RF transceiver 1522. The cellular baseband processor 1504 may include computer readable media / memory. The computer readable media / memory may be non-transitory. The cellular baseband processor 1504 is responsible for general processing, including the execution of software stored on the computer readable media / memory. The software, when executed by the cellular baseband processor 1504, causes the cellular baseband processor 1504 to perform the various functions described above. The computer readable media / memory may also be used to store data that is manipulated by the cellular baseband processor 1504 when executing the software. The cellular baseband processor 1504 further includes a receiving component 1530, a communications manager 1532, and a transmitting component 1534. The communications manager 1532 includes one or more of the illustrated components. The components in the communications manager 1532 may be stored in a computer readable medium / memory and / or configured as hardware in the cellular baseband processor 1504. The cellular baseband processor 1504 may be a component of the UE 350 and may include the memory 360 and / or at least one of the TX processor 368, the RX processor 356, and the controller / processor 359.In one configuration, the device 1502 may be a modem chip and may include only a baseband processor 1504, while in another configuration, the device 1502 may be an entire UE (e.g., see 350 in FIG. 3) and may include additional modules of the device 1502.

[0128]

[0145] The communications manager 1532 includes a first attempt component 1540 configured to attempt to attach to or perform a tracking area update on the EPS network to obtain voice services a certain number of times, for example, as described with respect to 1004 of Figure 10, 1102 of Figure 11, 1202 of Figure 12, and 1302 of Figure 13. The communications manager 1532 further includes a timer component 1542 configured to start a modified timer based on failure to attach to or perform a tracking area update on the EPS network a certain number of times, for example, as described with respect to 902 of Figure 9, 1006 of Figure 10, 1104 of Figure 11, 1204 of Figure 12, and 1304 of Figure 13, and based on configuration parameters. The communications manager 1532 further includes a second attempt component 1544 configured to attempt to obtain voice services based on one or more access technologies other than EPS, as described, for example, with respect to 904 of Figure 9, 1012 of Figure 10, 1116 of Figure 11, 1210 of Figure 12, and 1310 of Figure 13. The communications manager 1532 further includes a service component 1546 configured to attach to an EPS network or perform a tracking area update in the EPS network to obtain voice services based on the modified timer, as described, for example, with respect to 906 of Figure 9, 1016 of Figure 10, 1124 of Figure 11, 1218 of Figure 12, and 1314 of Figure 13.

[0129]

[0146] The communications manager 1532 further includes a service component 1546 configured to disable the S1 mode upon starting the modified timer, e.g., as described with respect to 1008 of Figure 10, 1106 of Figure 11, and 1206 of Figure 12. The service component 1546 can be further configured to skip retrying to attach to the EPS network or to perform a tracking area update in the EPS network prior to stopping or expiry of the modified timer, e.g., as described with respect to 1010 of Figure 10, 1108 of Figure 11, and 1208 of Figure 12. The service component 1546 can be further configured to re-enable the S1 mode upon expiry of the modified timer, e.g., as described with respect to 1014 of Figure 10. The service component 1546 may be further configured to start the unmodified timer based on failure to attach to or perform a tracking area update in the EPS network after the modified timer has been used a threshold number of times since the most recent power-up of the UE, e.g., as described with respect to 1018 of FIG. 10. The service component 1546 may be further configured to receive an indication of a shorter duration associated with the modified timer from the base station, e.g., as described with respect to 1002 of FIG. 10. The service component 1546 may be further configured to send an indication to the 5GS base station that the S1 mode is disabled, e.g., as described with respect to 1110 of FIG. 11. The service component 1546 may be further configured to receive an indication from the 5GS base station that packet switched voice services are not supported, e.g., as described with respect to 1112 of FIG. 11. The service component 1546 may be further configured to disable the N1 mode upon receiving an indication that packet switched voice services are not supported, e.g., as described with respect to 1114 of FIG. 11.The service component 1546 can be further configured to re-enable the N1 mode upon failure to obtain circuit switched voice service on an access technology other than 5GS, e.g., as described with respect to 1118 of FIG. 11. The service component 1546 can be further configured to re-enable the S1 mode upon re-enabling the N1 mode, e.g., as described with respect to 1120 of FIG. 11. The service component 1546 can be further configured to stop the modified timer, e.g., as described with respect to 1122 of FIG. 11. The service component 1546 can be further configured to monitor the quality of a cell associated with the EPS network, e.g., as described with respect to 1212 of FIG. 12. The service component 1546 can be further configured to stop the modified timer when the quality of the cell is above a predetermined threshold for a predetermined period of time, e.g., as described with respect to 1214 of FIG. 12. The service component 1546 can be further configured to re-enable the S1 mode based on stopping the modified timer, e.g., as described with respect to 1216 of FIG. 12. The service component 1546 can be further configured to keep the S1 mode valid when starting the modified timer, e.g., as described with respect to 1306 of FIG. 13. The service component 1546 can be further configured to deprioritize the EPS network or not retry attaching to or performing a tracking area update in the EPS network before stopping or expiry of the modified timer, e.g., as described with respect to 1308 of FIG. 13. The service component 1546 can be further configured to stop the modified timer in response to one of a reselection by the UE to the EPS network, a handover to the EPS network, or a redirection by the network to the EPS network, e.g., as described with respect to 1312 of FIG. 13.

[0130]

[0147] The apparatus may include additional components that perform each of the blocks of the algorithms in the flowcharts of Figures 5-13. Thus, each block in the flowcharts of Figures 5-13 may be performed by a component, and the apparatus may include one or more of those components. The components may be one or more hardware components specifically configured to perform the described process / algorithm, implemented by a processor configured to perform the described process / algorithm, stored in a computer-readable medium for implementation by a processor, or some combination thereof.

[0131]

[0148] As shown, the apparatus 1502 may include various components configured for various functions. In one configuration, the apparatus 1502, specifically the cellular baseband processor 1504, includes means for attempting to attach to or perform a tracking area update in an EPS network to obtain voice services a certain number of times. The apparatus 1502 may include means for initiating a modified timer based on failure to attach to or perform a tracking area update in an EPS network a certain number of times and based on configuration parameters. The modified timer may be modified based on a default timer. The apparatus 1502 may include means for attempting to obtain voice services based on one or more access technologies other than EPS. The apparatus 1502 may include means for attaching to or performing a tracking area update in an EPS network to obtain voice services based on the modified timer.

[0132]

[0149] In one configuration, the apparatus 1502 may include means for disabling the S1 mode upon starting the modified timer. The apparatus 1502 may include means for skipping retrying to attach to or perform a tracking area update in the EPS network prior to stopping or expiry of the modified timer. In one configuration, the modified timer may be associated with a shorter duration than the unmodified / default timer. The apparatus 1502 may include means for re-enabling the S1 mode upon expiry of the modified timer. In one configuration, the apparatus 1502 may include means for starting the unmodified / default timer based on failure to attach to or perform a tracking area update in the EPS network after the modified timer has been used a threshold number of times since the most recent power-up of the UE. In one configuration, the shorter duration associated with the modified timer may be pre-configured. In one configuration, the apparatus 1502 may include means for receiving an indication of the shorter duration associated with the modified timer from a base station. In one configuration, the indication of the shorter duration associated with the modified timer may be stored in the ME or USIM of the UE. In one configuration, in response to a failure to acquire voice service based on the EPS, the apparatus 1502 can include means for sending an indication to the 5GS base station that the S1 mode is disabled. The apparatus 1502 can include means for receiving an indication from the 5GS base station that packet switched voice service is not supported. The apparatus 1502 can include means for disabling the N1 mode upon receiving the indication that the packet switched voice service is not supported. The apparatus 1502 can include means for re-enabling the N1 mode upon a failure to acquire circuit switched voice service in an access technology other than 5GS. In one configuration, the apparatus 1502 can include means for re-enabling the S1 mode upon re-enabling the N1 mode. The apparatus 1502 can include means for stopping the modified timer upon re-enabling the S1 mode.In one configuration, the apparatus 1502 can include means for re-enabling the S1 mode upon re-enabling the N1 mode. The apparatus 1502 can include means for stopping the modified timer in response to one of a reselection by the UE to the EPS network or a handover or redirection by the network to the EPS network. In one configuration, the apparatus 1502 can include means for monitoring a quality of a cell associated with the EPS network. The apparatus 1502 can include means for stopping the modified timer when the quality of the cell is above a predetermined threshold for a predetermined period of time. The apparatus 1502 can include means for re-enabling the S1 mode based on the stopping of the modified timer. In one configuration, the apparatus 1502 can include means for maintaining the S1 mode in effect when starting the modified timer. The apparatus 1502 can include means for de-prioritizing the EPS network or not retrying to attach to or perform a tracking area update in the EPS network prior to the stopping or expiration of the modified timer. In one configuration, the apparatus 1502 may include means for stopping the modified timer in response to one of a reselection by the UE to the EPS network, a handover to the EPS network, or a redirection by the network to the EPS network. In one configuration, the apparatus 1502 may include means for deprioritizing one or more cells associated with the EPS network for cell reselection prior to stopping or expiration of the modified timer. In one configuration, the UE may be a voice-centric UE.

[0133]

[0150] The means may be one or more of the components of the apparatus 1502 configured to perform the functions recited by the means. As described above, the apparatus 1502 may include the TX processor 368, the RX processor 356, and the controller / processor 359. Thus, in one configuration, the means may be the TX processor 368, the RX processor 356, and the controller / processor 359 configured to perform the functions recited by the means.

[0134]

[0151] FIG. 16 is a diagram 1600 illustrating an example of a hardware implementation for an apparatus 1602. The apparatus 1602 may be a base station, a component of a base station, or may implement base station functionality. In some aspects, the apparatus 1602 may include a baseband unit 1604. The baseband unit 1604 may communicate with the UE 104 via a cellular RF transceiver 1622. The baseband unit 1604 may include a computer-readable medium / memory. The baseband unit 1604 is responsible for general processing, including the execution of software stored in the computer-readable medium / memory. The software, when executed by the baseband unit 1604, causes the baseband unit 1604 to perform various functions described above. The computer-readable medium / memory may also be used to store data that is manipulated by the baseband unit 1604 when executing the software. The baseband unit 1604 further includes a receiving component 1630, a communication manager 1632, and a transmitting component 1634. The communications manager 1632 includes one or more of the illustrated components. The components in the communications manager 1632 may be stored in a computer readable medium / memory and / or configured as hardware in the baseband unit 1604. The baseband unit 1604 may be a component of the base station 310 and may include the memory 376 and / or at least one of the TX processor 316, the RX processor 370, and the controller / processor 375.

[0135]

[0152] The communications manager 1632 includes an indication component 1640 configured to send an indication of the duration associated with the modified timer to the voice-centric UE, e.g., as described with respect to 1402 of FIG. 14. The communications manager 1632 further includes a first service component 1642 configured to initially fail to provide voice service to the voice-centric UE via the EPS network, e.g., as described with respect to 1404 of FIG. 14. The communications manager 1632 further includes a second service component 1644 configured to provide voice service to the voice-centric UE via the EPS network based on the modified timer after an initial failure to provide voice service to the voice-centric UE via the EPS network, e.g., as described with respect to 1406 of FIG. 14.

[0136]

[0153] The apparatus may include additional components that perform each of the blocks of the algorithms in the flowcharts of Figures 5-8 and 14. Thus, each block in the flowcharts of Figures 5-8 and 14 may be performed by a component, and the apparatus may include one or more of these components. The components may be one or more hardware components specifically configured to perform the described processes / algorithms, implemented by a processor configured to perform the described processes / algorithms, stored in a computer-readable medium for implementation by a processor, or some combination thereof.

[0137]

[0154] As shown, the apparatus 1602 may include various components configured for various functions. In one configuration, the apparatus 1602, specifically the baseband unit 1604, includes means for sending an indication of a duration associated with a modified timer to the voice-centric UE. The apparatus 1602 may include means for initially failing to provide voice service to the voice-centric UE via the EPS network. The apparatus 1602 may include means for providing voice service to the voice-centric UE via the EPS network based on the modified timer after an initial failure to provide voice service to the voice-centric UE via the EPS network. The modified timer and the default timer may be associated with retries to attach to the EPS network or perform a tracking area update in the EPS network. Voice service may not be available via the 5GS or circuit-switched system.

[0138]

[0155] The means may be one or more of the components of the apparatus 1602 configured to perform the functions recited by the means. As described above, the apparatus 1602 may include the TX processor 316, the RX processor 370, and the controller / processor 375. Thus, in one configuration, the means may be the TX processor 316, the RX processor 370, and the controller / processor 375 configured to perform the functions recited by the means.

[0139]

[0156] According to aspects described herein, a UE may attempt to attach to or perform a tracking area update in an EPS network to obtain voice services a certain number of times. The UE may start a modified timer based on failure to attach to or perform a tracking area update in an EPS network the number of times and based on configuration parameters. The modified timer may be modified based on a default timer. The UE may attempt to obtain voice services based on one or more access technologies other than EPS. The UE may attach to or perform a tracking area update in an EPS network to obtain voice services based on the modified timer. In some aspects, the UE may not disable S1 mode when the modified timer is started or running, so that the UE may not waste time attempting to obtain voice services via a legacy 2G / 3G network. Thus, the period during which a voice-centric UE does not have any access to voice services may be reduced, improving the user experience.

[0140]

[0157] It is understood that the particular order or hierarchy of the blocks in the disclosed processes / flowcharts is illustrative of example approaches. Based on design preferences, it is understood that the particular order or hierarchy of the blocks in the processes / flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in an example order, and are not limited to the particular order or hierarchy presented.

[0141]

[0158] The foregoing description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications of these aspects will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other aspects. Thus, the claims are not limited to the aspects described herein, but should be accorded the full scope consistent with the language of the claims. Reference to an element in the singular does not mean "one and only one," but rather "one or more," unless so expressly stated. Terms such as "if," "when," and "while" do not imply an immediate temporal relationship or reaction. That is, these phrases, e.g., "when," do not imply an immediate action in response to or during the occurrence of an action, but merely imply that an action will occur if a condition is met, but does not require a specific or immediate time constraint for the action to occur. The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other aspects. Unless otherwise specified, the term "some" refers to one or more. Combinations such as "at least one of A, B, or C," "one or more of A, B, or C," "at least one of A, B, and C," "one or more of A, B, and C," and "A, B, C, or any combination thereof" include any combination of A, B, and / or C and can include multiple A, multiple B, or multiple C. Specifically, combinations such as "at least one of A, B, or C," "one or more of A, B, or C," "at least one of A, B, and C," "one or more of A, B, and C," "A, B, C, or any combination thereof" can be A only, B only, C only, A and B, A and C, B and C, or A and B and C, and any such combination can include one or more member(s) of A, B, or C. A set should be interpreted as a set of elements, the number of which may be one or more.Thus, for a set of X, X will include one or more elements. When a first device receives data from or transmits data to a second device, the data may be received / transmitted directly between the first device and the second device, or may be received / transmitted indirectly between the first device and the second device via a set of devices. All structural and functional equivalents of the elements of the various embodiments described throughout this disclosure that are known or that later become known to those skilled in the art are expressly incorporated herein by reference and are encompassed by the claims. Moreover, nothing disclosed herein is made public, regardless of whether such disclosure is expressly recited in the claims. Words such as "module," "mechanism," "element," "device," and the like may not be substitutes for the word "means." Thus, no claim element should be construed as a means plus function unless the element is expressly recited using the phrase "means for."

[0142]

[0159] As used herein, the phrase "based on" should not be construed as a reference to a closed set of information, one or more conditions, one or more factors, etc. In other words, the phrase "based on A" (where "A" may be information, a condition, a factor, etc.) shall be construed as "based at least on A," unless expressly stated otherwise.

[0143]

[0160] The following aspects are exemplary only and can be combined with other aspects or teachings described herein without limitation.

[0144]

[0161] Aspect 1 is a method of wireless communication in a UE, the method including: starting a modified timer that is modified based on a default timer based on a number of failed attempts associated with a voice service for an EPS network and based on configuration parameters; attempting to acquire the voice service based on one or more access technologies other than EPS; and attaching to the EPS network or performing a tracking area update in the EPS network to acquire the voice service based on the modified timer.

[0145]

[0162] Example 2 is the method of example 1, further comprising maintaining the S1 mode in effect when starting the modified timer.

[0146]

[0163] Aspect 3 is the method of aspect 2, further including lowering the priority of the EPS network or not retrying to attach to or perform a tracking area update in the EPS network before stopping or expiration of the modified timer, and stopping the modified timer in response to one of a reselection by the UE to the EPS network, a handover to the EPS network, or a redirection by the network to the EPS network.

[0147]

[0164] Example 4 is the method of example 3, further comprising de-prioritizing one or more cells associated with the EPS network for cell reselection prior to stopping or expiry of the modified timer.

[0148]

[0165] Example 5 is the method of any one of Examples 1 to 4, wherein the UE is a voice-centric UE.

[0149]

[0166] Example 6 is a method of any one of examples 1 to 5, wherein each of a number of failed attempts associated with voice services for the EPS network includes a failure to attach to the EPS network to obtain voice services or to perform a tracking area update in the EPS network.

[0150]

[0167] Example 7 is the method of example 1, further including disabling S1 mode upon starting the modified timer, and skipping retrying to attach to the EPS network or performing a tracking area update in the EPS network prior to stopping or expiration of the modified timer.

[0151]

[0168] Example 8 is the method of example 7, wherein the modified timer is associated with a duration that is shorter than the default timer, and the at least one processor is further configured to re-enable the S1 mode upon expiration of the modified timer.

[0152]

[0169] Example 9 is the method of example 8, further comprising starting the default timer based on a failure to attach to the EPS network or perform a tracking area update in the EPS network after the modified timer has been used a threshold number of times since the UE was last powered on.

[0153]

[0170] Example 10 is the method of any one of Examples 8 and 9, wherein a shorter duration associated with the modified timer is preconfigured.

[0154]

[0171] Example 11 is the method of any one of Examples 8 and 9, further comprising receiving, from a base station, an indication of the shorter duration associated with the modified timer.

[0155]

[0172] Example 12 is the method of any one of Examples 8 to 11, wherein an indication of the shorter duration associated with the modified timer is stored in the ME or USIM of the UE.

[0156]

[0173] Example 13 is the method of example 7, wherein in response to a failure to acquire voice service based on the EPS, the method further includes sending an indication to the 5GS base station that S1 mode is disabled, receiving an indication from the 5GS base station that packet-switched voice service is not supported, disabling the N1 mode upon receiving the indication that packet-switched voice service is not supported, and re-enabling the N1 mode upon a failure to acquire circuit-switched voice service in an access technology other than 5GS.

[0157]

[0174] Example 14 is the method of example 13, further including: upon re-enabling the N1 mode, re-enabling the S1 mode; and upon re-enabling the S1 mode, stopping the modified timer.

[0158]

[0175] Example 15 is the method of example 13, further including, upon re-enabling the N1 mode, re-enabling the S1 mode and stopping the modified timer in response to one of reselection by the UE to the EPS network or handover or redirection by the network to the EPS network.

[0159]

[0176] Example 16 is the method of example 7, further including monitoring a quality of a cell associated with the EPS network, stopping the modified timer when the quality of the cell exceeds a predetermined threshold for a predetermined period of time, and re-enabling the S1 mode based on stopping the modified timer.

[0160]

[0177] Aspect 17 is a method of wireless communication in a network node, comprising: sending to a voice-centric UE an indication of a duration associated with a modified timer, the duration being shorter than a duration associated with a default timer; initially failing to provide voice service to the voice-centric UE via the EPS network; and after the initial failure to provide voice service to the voice-centric UE via the EPS network, providing voice service to the voice-centric UE via the EPS network based on the modified timer, wherein the modified timer and the default timer are associated with retries to attach to the EPS network or perform a tracking area update in the EPS network, and voice service is not available via a 5GS or circuit-switched system.

[0161]

[0178] Example 18 is an apparatus for wireless communication including at least one processor coupled to a memory, wherein the at least one processor is configured to perform a method according to any one of Examples 1 to 17 based at least in part on information stored in the memory.

[0162]

[0179] Example 19 may be combined with example 18 and further includes a transceiver coupled to the at least one processor.

[0163]

[0180] Aspect 20 is an apparatus for wireless communication, comprising means for implementing any one of aspects 1 to 17.

[0164]

[0181] Aspect 21 is a non-transitory computer-readable storage medium storing computer-executable code, which when executed by a processor causes the processor to perform any one of aspects 1 to 17.

[0165]

[0182] Various aspects have been described herein. These and other aspects are within the scope of the following claims.

Claims

1. An apparatus for wireless communication in a user equipment (UE), a memory, at least one processor coupled to the memory, comprising, based at least in part on information stored in the memory, the at least one processor starts a modified timer based on several failed attempts associated with a voice service for an evolved packet system (EPS) network and based on configuration parameters, wherein the modified timer is shorter than the duration associated with a default timer, when starting the modified timer, maintains the S1 mode enabled, attempts to obtain the voice service based on one or more access technologies other than EPS, attaches to the EPS network or performs a tracking area update in the EPS network to obtain the voice service based on the modified timer, is configured to be. device.

2. The at least one processor, before the stop or expiration of the modified timer, lowers the priority of the EPS network or does not retry attaching to the EPS network or performing the tracking area update in the EPS network, the modified timer, reselection by the UE to the EPS network, handover to the EPS network, or network - directed redirection to the EPS network, stops in response to one of. is further configured to be. The apparatus according to claim 1.

3. the at least one processor is further configured to lower the priority of one or more cells associated with the EPS network for cell reselection before the stop or expiration of the modified timer. The apparatus according to claim 2.

4. The apparatus according to claim 1, wherein the UE is a voice-centric UE.

5. Each of the several failed attempts associated with the voice service for the EPS network comprises a failure to attach to the EPS network or to perform a tracking area update in the EPS network in order to obtain the voice service. The apparatus according to claim 1.

6. The apparatus according to claim 1, further comprising a transceiver coupled to the memory and the at least one processor.

7. A method of wireless communication in a user equipment (UE), comprising: starting a modified timer based on several failed attempts associated with a voice service for an evolved packet system (EPS) network and based on configuration parameters, the modified timer being shorter than a duration associated with a default timer; maintaining the S1 mode active when starting the modified timer; attempting to obtain the voice service based on one or more access technologies other than EPS; attaching to the EPS network or performing a tracking area update in the EPS network to obtain the voice service based on the modified timer; A method comprising the steps of:

8. Before the stop or expiration of the modified timer, lowering the priority of the EPS network, or not retrying to attach to the EPS network or perform the tracking area update in the EPS network, the modified timer reselection by the UE to the EPS network, handover to the EPS network, or network - directed redirection to the EPS network, stops in response to one of them, further comprising The method according to claim 7.

9. Before the stop or expiration of the modified timer, lowering the priority of one or more cells associated with the EPS network for cell reselection, further comprising The method according to claim 8.

10. The method according to claim 7, wherein the UE is a voice - centric UE.

11. Each of the several failed attempts associated with the voice service for the EPS network comprises a failure to attach to the EPS network or perform the tracking area update in the EPS network to obtain the voice service. The method according to claim 7.

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