CN117561743A - IMS voice support in networks using EPS fallback and having 4G coverage holes - Google Patents

Abstract

A method is provided. The method may be performed by a UE. The method comprises the following steps: attempting to attach to the EPS network or performing tracking area update in the EPS network for a number of times to obtain voice service. The method comprises the following steps: the modified timer is started based on failing to attach to the EPS network or performing tracking area updates in the EPS network the number of times and based on the configuration parameters. The modified timer may be modified based on a default timer. The method comprises the following steps: the S1 mode enable is maintained while the modified timer is started. The method comprises the following steps: attempts to obtain voice services based on one or more access technologies other than EPS. The method comprises the following steps: attach to the EPS network or perform tracking area update in the EPS network based on the modified timer to obtain voice service.

Description

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

Cross Reference to Related Applications

The present application claims the benefit and priority of U.S. provisional application Ser. No.63/219,248, filed 7 at 2021 and entitled "IMS VOICE SUPPORT IN NETWORK USING EPS FALLBACK AND HAVING G COVERAGE HOLES", and U.S. non-provisional patent application Ser. No.17/810,954, filed 7 at 2022 and entitled "IMS VOICE SUPPORT IN NETWORK USING EPS FALLBACK AND HAVING G COVERAGE HOLES", the entire contents of which are expressly incorporated herein by reference.

Technical Field

The present disclosure relates generally to communication systems, and more particularly to obtaining voice services over Evolved Packet System (EPS) fallback.

Background

Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcast. A typical wireless communication system may employ multiple-access techniques capable of supporting communication with multiple users by sharing the available system resources. Examples of such multiple-access techniques 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.

These multiple access techniques have been employed in various telecommunications standards to provide a common protocol that enables different wireless devices to communicate at the urban, national, regional, and even global levels. An example telecommunications standard is 5G New Radio (NR). The 5G NR is part of the continuous mobile broadband evolution promulgated by the third generation partnership project (3 GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with the internet of things (IoT)), and other requirements. The 5G NR includes services associated with: enhanced mobile broadband (emmbb), large-scale machine type communication (mctc), and Ultra Reliable Low Latency Communication (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 techniques and telecommunication standards employing these techniques.

Disclosure of Invention

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. This summary does not identify key or critical elements of all aspects nor 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.

In one aspect of the disclosure, a method is provided. The method may be performed by a User Equipment (UE). The method comprises the following steps: the modified timer is started 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 comprises the following steps: attempts to obtain the voice service based on one or more access technologies other than EPS. The method comprises the following steps: attaching to the EPS network or performing tracking area update in the EPS network based on the modified timer to obtain voice service.

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, the memory and the at least one processor configured to: starting a modified timer based on a number of failed attempts associated with a voice service for the EPS network and based on a configuration parameter, wherein the modified timer may be modified based on a default timer; attempting to obtain the voice service based on one or more access technologies other than EPS; and attaching to the EPS network or performing tracking area update in the EPS network to obtain voice service based on the modified timer.

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

In another aspect of the disclosure, a computer-readable medium is provided. The computer-readable medium includes computer executable code at a UE, which when executed by a processor causes the processor to: starting a modified timer based on a number of failed attempts associated with a voice service for the EPS network and based on a configuration parameter, wherein the modified timer may be modified based on a default timer; attempting to obtain the voice service based on one or more access technologies other than EPS; and attaching to the EPS network or performing tracking area update in the EPS network to obtain voice service based on the modified timer.

In one aspect of the disclosure, a method is provided. The method may be performed by a base station. The method comprises the following steps: an indication of a duration associated with the modified timer is sent to the voice-centric UE. The duration associated with the modified timer may be shorter than a duration associated with a default timer. The method comprises the following steps: the voice-centric UE is initially not provided with voice services via the EPS network. The method comprises the following steps: after the initial failure to provide voice service to the voice-centric UE via the EPS network, voice service is provided to the voice-centric UE via the EPS network based on the modified timer. The modified timer and the default timer may be associated with reattempting to attach to the EPS network or performing tracking area updates in the EPS network. Voice services are not available on the fifth generation (5G) system (5 GS) or circuit switched system.

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, the memory and the at least one processor configured to: transmitting an indication of a duration associated with a modified timer to a voice-centric UE, the duration associated with the modified timer being shorter than a duration associated with a default timer; initially failing to provide voice services to the voice-centric UE via an EPS network; and after the initial failure to provide voice services to the voice-centric UE via the EPS network, providing voice services to the voice-centric UE via the EPS network based on the modified timer. The modified timer and the default timer may be associated with reattempting to attach to the EPS network or performing tracking area updates in the EPS network. Voice services are not available on 5GS or circuit switched systems.

In another aspect of the present disclosure, an apparatus is provided. The apparatus may be a base station. The device comprises: the processor is configured to send an indication of a duration associated with the modified timer to the voice-centric UE. The duration associated with the modified timer may be shorter than a duration associated with a default timer. The device comprises: the apparatus includes means for initially failing to provide voice services to the voice-centric UE via an EPS network. The device comprises: 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. The modified timer and the default timer may be associated with reattempting to attach to the EPS network or performing tracking area updates in the EPS network. Voice services are not available on 5GS or circuit switched systems.

In another aspect of the disclosure, a computer-readable medium is provided. The computer readable medium includes computer executable code at a base station, which when executed by a processor causes the processor to: transmitting an indication of a duration associated with a modified timer to a voice-centric UE, the duration associated with the modified timer being shorter than a duration associated with a default timer; initially failing to provide voice services to the voice-centric UE via an EPS network; and after the initial failure to provide voice services to the voice-centric UE via the EPS network, providing voice services to the voice-centric UE via the EPS network based on the modified timer. The modified timer and the default timer may be associated with reattempting to attach to the EPS network or performing tracking area updates in the EPS network. Voice services are not available on 5GS or circuit switched systems.

To the accomplishment of the foregoing and related ends, one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed 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 various aspects may be employed.

Drawings

Fig. 1 is a diagram showing an example of a wireless communication system and an access network.

Fig. 2A is a diagram illustrating an example of a first frame in accordance with aspects of the present disclosure.

Fig. 2B is a diagram illustrating an example of a Downlink (DL) channel within a subframe in accordance with various aspects of the present disclosure.

Fig. 2C is a diagram illustrating an example of a second frame in accordance with aspects of the present disclosure.

Fig. 2D is a diagram illustrating an example of an Uplink (UL) channel within a subframe in accordance with various aspects of the present disclosure.

Fig. 3 is a diagram showing an example of a base station and a User Equipment (UE) in an access network.

Fig. 4 is a diagram showing an unmodified timer T3402.

Fig. 5 is a diagram of a communication flow of a method of wireless communication.

Fig. 6 is a diagram of a communication flow of a method of wireless communication.

Fig. 7 is a diagram of a communication flow of a method of wireless communication.

Fig. 8 is a diagram of a communication flow of a method of wireless communication.

Fig. 9 is a flow chart of a method of wireless communication.

Fig. 10 is a flow chart of a method of wireless communication.

Fig. 11 is a flow chart of a method of wireless communication.

Fig. 12 is a flow chart of a method of wireless communication.

Fig. 13 is a flow chart of a method of wireless communication.

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

Fig. 15 is a diagram illustrating an example of a hardware implementation for an example apparatus and/or network entity.

Fig. 16 is a diagram illustrating an example of a hardware implementation for an example network entity.

Detailed Description

In the fifth generation (5G) system (5 GS), voice services over Internet Protocol (IP) multimedia subsystem (IMS) may be supported locally (i.e., voice over new radio "NR," VoNR ") or via EPS fallback. Support for VoNR may refer to support for packet-switched based voice services over NR. In case of EPS fallback, the UE may be handed over or redirected to EPS (e.g., in a fourth generation "4G" system) in case of mobile originated (mobile originated) (MO) or mobile called (mobile terminated) (MT) call. MO calls may refer to calls initiated at a UE, and MT calls may refer to calls received at a UE. Here, EPS fallback may refer to a handover or redirection from 5GS to EPS to connect an MO or MT voice call. The UE may be configured to be voice-centric or data-centric. For example, a smart phone may be configured as a voice-centric UE, and a sensor may be configured as a data-centric UE. Voice-centric UEs may prioritize voice service over data service. If the network is unable to provide voice services to the voice-centric UE, the UE may be transferred to or search for other networks or access technologies (e.g., by de-prioritizing the network that is unable to provide voice services or disabling the access technology via which voice services are not available). A network, such as a 5G network, may determine whether a UE wireless capability matching request procedure may be used to provide voice services to the UE. The UE radio capability matching request procedure may refer to a procedure by which an access and mobility management function (AMF) of 5GS determines whether IMS voice services are supported for the UE, e.g., as described in clause 3GPP TS23.501v16.9.0, clause 5.4.4.2a. In one aspect, a network (e.g., an AMF of 5 GS) may compare the wireless capabilities of a UE with a method (e.g., access technology) via which voice is supported in the network. The network may indicate to the UE in a registration accept message whether IMS voice is supported for the UE. The registration accept message may be a message sent to the UE by the AMF of 5GS indicating that the AMF has accepted the registration request of the UE, e.g., as described in clause 3GPP TS24.501v16.9.0 5.5.1.3.4. In one example, if IMS voice is supported, the registration accept message may not specify whether IMS voice is supported via VoNR or EPS fallback.

In one or more aspects, since voice service is provided via EPS fallback in a 5GS network and it is difficult for a UE to attach to the EPS network or perform tracking area update in the EPS network, voice-centric UEs may experience long periods of inability to access voice service. Attaching to a network may refer to sending an attach request message (e.g., as described in clause 5.5.1.2.2 of 3GPP TS24.301v16.8.0) to obtain service from the network (e.g., EPS network). Performing tracking area update may refer to sending a tracking area update request message (e.g., as described in clause 5.5.3.2.2 of 3GPP TS24.301v16.8.0) to inform a network (e.g., EPS network) that a registered UE has moved to a tracking area that is not included in the current tracking area identity list. In one example, the UE may be voice-centric and may not support VoNR in the 5GS network (i.e., voice may only be supported via EPS fallback). Furthermore, voice services via early circuit-switched technologies (e.g., second generation "2G"/third generation "3G") may not be available because the spectrum may have been reused for other radio access technologies. The UE may not be able to access the voice service for a long time due to difficulty in attaching to the EPS network or performing tracking area update in the EPS network.

In one example, the inability to access voice services for a long period of time may occur as follows. First, due to poor EPS coverage, the UE may fail to attach to the EPS network or perform tracking area updates in the EPS network multiple times in succession (e.g., 5 times), which may cause the UE to disable the S1 mode (i.e., the mode related to the UE' S4G/EPS capability) and start a timer T3402 (the 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 a UE communicates with a Mobility Management Entity (MME) of an EPS, e.g., as described in ts24.301v16.8.0 sub-clause 3.1, etc. The timer T3402 may be an EPS mobility management timer. The timer T3402 may be associated with retrying attachment to the EPS network or performing tracking area update in the EPS network. By default, the UE may not reattempt to attach to the EPS network or perform tracking area update in the EPS network before the timer T3402 expires. The UE may then attempt to attach to the 5GS network or perform tracking area update in the 5GS network, and may indicate to the 5GS network that the S1 mode is disabled in the registration request message. Since the network may support voice services via EPS fallback and EPS fallback may not be available when S1 mode is disabled, the network may indicate "IMS voice access over 3GPP is not supported" in the registration accept message. Since the UE is voice-centric, receipt of the "do not support IMS voice access over 3 GPP" indication in the registration accept message may cause the UE to disable the N1 mode (i.e., the mode related to the UE's 5G capability). According to one or more aspects, the N1 mode may refer to an operational mode in which the UE communicates with the AMF of 5GS, e.g., as described in ts24.501v16.9.0 sub-clause 3.1, etc. With both the S1 mode and the N1 mode disabled, the UE may search for a 2G/3G network for voice services and may not find the 2G/3G network. Finally, the UE may re-enable the N1 mode and may camp in the 5GS network. The UE may not be able to obtain voice service via EPS backoff until timer T3402 expires. Thus, the user may experience significant periods of time when voice services are not accessible.

Aspects presented herein provide mechanisms for a UE to improve wireless communication between the UE and the network and enable the UE to access the network in a reduced amount of time when performing EPS backoff. In some aspects, the UE may skip disabling the S1 mode when starting the T3402 timer. Thus, since the S1 mode remains enabled, the UE may not receive an "IMS voice access over 3GPP not supported" indication in the registration accept message. Thus, the UE may not disable the N1 mode and may not waste time attempting to obtain voice services via the legacy 2G/3G network.

In some aspects, based on the UE configuration parameters indicating that the UE uses a shorter T3402 timer value, the UE may use a T3402 timer value that is shorter than the T3402 timer of the unmodified or default T3402 timer. In some aspects, the UE may receive a configuration of a shorter T3402 timer value. In some aspects, the UE may also re-enable the S1 mode when the N1 mode is re-enabled. In some aspects, if the T3402 timer is running and the S1 mode is disabled, the UE may periodically check the quality of the 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, e.g., as described in clause 3GPP TS 38.300v16.6.0, clause 3.2, etc. If the cell quality is above a certain threshold for more than a threshold amount of 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 the E-UTRAN cell, e.g., as described in clause 3GPP TS 38.300v16.6.0, clause 9.2.4, etc. Accordingly, a period during which a voice-centric UE cannot access voice services may be reduced, and user experience may be improved.

The various configurations are described below in connection with the detailed description set forth in the drawings and do 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, the concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Several aspects of a telecommunications system are presented with reference to various apparatus and methods. These apparatus and methods are described in the following detailed description and are illustrated in the figures 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 upon the particular application and design constraints imposed on the overall system.

For example, an element, or any portion of an element, or any combination of elements, may be implemented as a "processing system" that includes 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, system on a chip (SoC), baseband processors, field Programmable Gate Arrays (FPGAs), programmable Logic Devices (PLDs), state machines, gating logic, discrete hardware circuits, and other suitable hardware configured to perform the various functions described throughout this disclosure. One or more processors in the processing system may execute the software. Software should be construed broadly to mean instructions, instruction sets, code segments, program code, programs, subroutines, software components, 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.

Accordingly, in one or more example aspects, implementations, and/or use cases, the described functionality may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored or encoded on a computer-readable medium as one or more instructions or code. Computer readable media includes computer storage media. A storage media may be any available media that can be accessed by a computer. By way of example, such computer-readable media can comprise 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.

Although aspects, implementations, and/or use cases have been described herein by way of illustration of some examples, additional or different aspects, implementations, and/or use cases may be produced in many different arrangements and scenarios. Aspects, implementations, and/or use cases described herein may be implemented across many different platform types, devices, systems, shapes, sizes, package arrangements. For example, aspects, implementations, and/or use cases may result via integrated chip implementations and other non-module component based devices (e.g., end user equipment, vehicles, communication devices, computing devices, industrial devices, retail/purchasing devices, medical devices, artificial Intelligence (AI) enabled devices, etc.). While some examples may or may not be specific to use cases or applications, there may be a wide range of applicability of the described examples. Aspects, implementations, and/or use cases may range from chip-level or modular components to non-modular, non-chip-level implementations, and further to aggregate, distributed, or Original Equipment Manufacturer (OEM) devices or systems incorporating one or more of the techniques herein. In some practical arrangements, devices incorporating the described aspects and features may also include additional components and features for implementation and practice of the claimed and described aspects. For example, the transmission and reception of wireless signals necessarily includes a plurality of components for analog and digital purposes (e.g., hardware components including antennas, RF chains, power amplifiers, modulators, buffers, processors, interleavers, adders/accumulators, etc.). The techniques described herein may be practiced in a wide variety of devices, chip-level components, systems, distributed arrangements, aggregated or disassembled components, end-user devices, and the like, having different sizes, shapes, and configurations.

Deployment of a communication system, such as a 5G NR system (5 GS), may be arranged in a variety of ways using individual components or parts. In a 5G NR system or network, network nodes, network entities, mobile elements of a network, radio Access Network (RAN) nodes, core network nodes, network elements, or network devices, such as a Base Station (BS) or one or more units (or one or more components) performing base station functions, may be implemented in an aggregated or decomposed architecture. For example, BSs, such as Node BS (NB), evolved NB (eNB), NR BS, 5G NB, access Points (APs), transmission and Reception Points (TRP), cells, or the like, may be implemented as an aggregated base station (also referred to as a standalone BS or a monolithic BS) or a decomposed base station.

The aggregated base station may be configured to utilize a radio protocol stack that is physically or logically integrated within a single RAN node. An decomposed base station may be configured to utilize a protocol stack that is physically or logically distributed among two or more units, such as one or more central or Centralized Units (CUs), one or more Distributed Units (DUs), or one or more wireless units (RUs). 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 distributed geographically or virtually throughout one or more other RAN nodes. A DU may be implemented to communicate with one or more RUs. Each of the CUs, DUs, and RUs may be implemented as virtual units, i.e., virtual Central Units (VCUs), virtual Distributed Units (VDUs), or virtual wireless units (VRUs).

The base station operation or network design may take into account the aggregate nature of the base station functions. For example, the decomposed base stations may be utilized in an Integrated Access Backhaul (IAB) network, an open radio access network (O-RAN, such as a network configuration sponsored by the O-RAN alliance), or a virtual radio access network (vRAN, also known as a cloud radio access network (C-RAN)). The decomposition may include distributing functionality across two or more units at various physical locations, as well as virtually distributing functionality for at least one unit, which may enable flexibility in network design. The individual units of the split base station or the split RAN architecture may be configured for wired or wireless communication with at least one other unit.

Fig. 1 is a diagram illustrating an example of a wireless communication system and an access network 100. A 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., a 5G core (5 GC)). Base station 102 may include a macrocell (high power cellular base station) and/or a small cell (low power cellular base station). The macrocell includes a base station. Small cells include femto cells, pico cells, and micro cells.

A base station 102 configured for 4G LTE, commonly referred to as evolved Universal Mobile Telecommunications System (UMTS) terrestrial radio access network (E-UTRAN), may interface with the EPC 160 over a first backhaul link 132 (e.g., an S1 interface). A base station 102 configured for 5G NR, collectively referred to as a next generation RAN (NG-RAN), may interface with a core network 190 over a second backhaul link 184. Base station 102 may perform, among other functions, one or more of the following functions: transmission of user data, radio channel encryption and decryption, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection establishment and release, load balancing, distribution of non-access stratum (NAS) messages, NAS node selection, synchronization, radio Access Network (RAN) sharing, multimedia Broadcast Multicast Services (MBMS), user and device tracking, RAN Information Management (RIM), paging, positioning, and delivery of warning messages. The base stations 102 may communicate directly or indirectly (e.g., through the EPC 160 or the core network 190) with each other over 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.

The base station 102 may communicate wirelessly with the UE 104. Each of the base stations 102 may provide communication coverage for a respective geographic coverage area 110. There may be overlapping geographic coverage areas 110. For example, the 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 comprising both small cells and macro cells may be referred to as a heterogeneous network. The heterogeneous network may also include home evolved node B (eNB) (HeNB) and the HeNB may provide services to a restricted group called a Closed Subscriber Group (CSG). The communication link 120 between the base station 102 and the UE 104 may include Uplink (UL) (also referred to as a reverse link) transmissions from the UE 104 to the base station 102 and/or Downlink (DL) (also referred to as a forward link) transmissions from the base station 102 to the UE 104. Communication link 120 may use multiple-input multiple-output (MIMO) antenna techniques 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 a spectrum of up to Y MHz (e.g., 5, 10, 15, 20, 100, 400, etc.) bandwidth per carrier allocated in carrier aggregation for up to yxmhz (x component carriers) total 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 UL). The component carriers may include a primary component carrier and one or more secondary component carriers. The primary component carrier may be referred to as a primary cell (PCell), and the secondary component carrier may be referred to as a secondary cell (SCell).

Some UEs 104 may communicate with each other using a device-to-device (D2D) communication link 158. The D2D communication link 158 may use the DL/UL WWAN spectrum. The D2D communication link 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 over a variety of wireless D2D communication systems, such as, for example, wiMedia, bluetooth, zigBee, wi-Fi, LTE or NR based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard.

The wireless communication system may also include a Wi-Fi Access Point (AP) 150 that communicates with Wi-Fi Stations (STAs) 152 via a communication link 154, for example, in a 5GHz unlicensed spectrum or the like. When communicating in the unlicensed spectrum, STA 152/AP 150 may perform Clear Channel Assessment (CCA) prior to communication to determine whether a channel is available.

The small cell 102' may operate in licensed and/or unlicensed spectrum. When operating in unlicensed spectrum, the small cell 102' may employ NR and use the same unlicensed spectrum (e.g., 5GHz, etc.) as used by the Wi-Fi AP 150. The use of NR small cells 102' in unlicensed spectrum may improve coverage of the access network and/or increase capacity of the access network.

The electromagnetic spectrum is generally subdivided into various categories, bands, channels, etc., based on frequency/wavelength. In 5G NR, two initial operating bands have been identified as frequency range names FR1 (410 MHz-7.125 GHz) and FR2 (24.25 GHz-52.6 GHz). Although a portion of FR1 is greater than 6GHz, FR1 is often (interchangeably) referred to as the "below 6GHz" band in various documents and articles. Similar naming problems sometimes occur with respect to FR2, which is often (interchangeably) referred to in documents and articles as the "millimeter wave" band, although it is different from the Extremely High Frequency (EHF) band (30 GHz-300 GHz), identified by the International Telecommunications Union (ITU) as the "millimeter wave" band.

The frequency between FR1 and FR2 is commonly referred to as the mid-band frequency. Recent 5G NR studies have identified the operating band of these mid-band frequencies as frequency range designation FR3 (7.125 GHz-24.25 GHz). The frequency band falling within FR3 may inherit FR1 characteristics and/or FR2 characteristics, and thus may effectively extend the characteristics of FR1 and/or FR2 to mid-band frequencies. In addition, higher frequency bands are currently being explored to extend 5G NR operation above 52.6GHz. For example, three higher operating bands have been identified as frequency range names FR4a or FR4-1 (52.6 GHz-71 GHz), FR4 (52.6 GHz-114.25 GHz) and FR5 (114.25 GHz-300 GHz). Each of these higher frequency bands falls within the EHF frequency band.

In view of the above, unless specifically stated otherwise, it should be understood that the term "below 6GHz" and the like, if used herein, may broadly represent frequencies that may be less than 6GHz, may be within FR1, or may include mid-band frequencies. Furthermore, unless specifically stated otherwise, it should be understood that the term "millimeter wave" or the like, if used herein, may broadly represent frequencies that may include mid-band frequencies, may be within FR2, FR4-a or FR4-1 and/or FR5, or may be within the EHF band.

Base station 102, whether small cell 102' or a large cell (e.g., macro base station), may include and/or be referred to as an eNB, a gndeb (gNB), or another type of base station. Some base stations (such as the gNB 180) may operate in the conventional below 6GHz spectrum, in millimeter wave frequencies, and/or near millimeter wave frequencies to communicate with the UE 104. When the gNB 180 operates in millimeter wave or near millimeter wave frequencies, the gNB 180 may be referred to as a millimeter wave base station. Millimeter-wave base station 180 may utilize beamforming 182 with UE 104 to compensate for path loss and short distance. 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.

The base station 180 may transmit the beamformed signals to the UEs 104 in one or more transmit directions 182'. The UE 104 may receive the beamformed signals from the base station 180 in one or more receive directions 182 ". The UE 104 may also transmit the beamformed signals in one or more transmit directions to the base station 180. The base station 180 may receive the beamformed signals from the UEs 104 in one or more directions. The base stations 180/UEs 104 may perform beam training to determine the best reception and transmission direction for each of the base stations 180/UEs 104. The transmit direction and the receive direction for the base station 180 may be the same or may be different. The transmit direction and the receive direction for the UE 104 may be the same or may be different.

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 service center (BM-SC) 170, and a Packet Data Network (PDN) gateway 172.MME 162 may communicate 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, MME 162 provides bearer and connection management. All user Internet Protocol (IP) packets are communicated through the serving gateway 166, which itself is 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 BM-SC 170 are connected to an IP service 176.IP services 176 may include the internet, intranets, 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 serve as an entry point for content provider MBMS transmissions, may be used to authorize and initiate MBMS bearer services within a Public Land Mobile Network (PLMN), and may be used to schedule MBMS transmissions. The MBMS gateway 168 may be used to distribute MBMS traffic to base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting charging information related to eMBMS.

The core network 190 may include access and mobility management functions (AMFs) 192, other AMFs 193, session Management Functions (SMFs) 194, and User Plane Functions (UPFs) 195. The AMF192 may communicate with a Universal data management Unit (UDM) 196. The AMF192 is a control node that handles signaling between the UE 104 and the core network 190. In general, AMF192 provides QoS flows and session management. All user Internet Protocol (IP) packets are transmitted through UPF 195. The UPF 195 provides UE IP address assignment as well as other functions. The UPF 195 is connected to an IP service 197. The IP services 197 may include the internet, intranets, IP Multimedia Subsystem (IMS) 197a, packet Switched (PS) streaming (PSs) services, and/or other IP services.

A base station may also include and/or be referred to as a gNB, a node B, eNB, an access point, a base station transceiver, a wireless base station, a wireless transceiver, a transceiver functional unit, a Basic Service Set (BSS), an Extended Service Set (ESS), a transmit-receive point (TRP), or some other suitable terminology. The base station 102 provides an access point for the UE 104 to the EPC 160 or core network 190. Examples of UEs 104 include a cellular telephone, a smart phone, a Session Initiation Protocol (SIP) phone, a laptop, a Personal Digital Assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electricity meter, an air pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor/actuator, a display, or any other similarly functioning device. Some of the UEs 104 may be referred to as IoT devices (e.g., parking meters, air pumps, ovens, vehicles, cardiac monitors, 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 communication device, remote device, mobile subscriber station, access terminal, mobile terminal, wireless terminal, remote terminal, handheld device, user agent, mobile client, or some other suitable terminology. In some scenarios, the term UE may also apply to one or more partner devices, such as in a device constellation arrangement. One or more of these devices may access the network in common and/or individually.

Referring again to fig. 1, in some aspects, the UE 104 may include a voice component 198, which voice component 198 may be configured to attempt to attach to the EPS network or perform tracking area updates in the EPS network a number of times to obtain voice services. The voice component 198 may be configured to start a modified timer based on failing to attach to or perform tracking area updates in the EPS network for a number of times and based on configuration parameters. The modified timer may be modified based on a default timer. In some aspects, the number of times may be a predetermined or defined number of times. 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 the EPS network or perform tracking area updates 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). In certain aspects, the base station 180 may include a voice component 199, which voice component 199 may be configured to send an indication of the duration associated with the modified timer to the voice-centric UE. The duration associated with the modified timer may be shorter than the duration associated with the default timer. The voice component 199 may be configured to initially fail to provide voice services to voice-centric UEs via the EPS network. The voice component 199 may be configured to provide voice services to the voice-centric UE via the EPS network based on the modified timer after initially failing to provide voice services to the voice-centric UE via the EPS network. The modified timer and the default timer may be associated with reattempting to attach to the EPS network or performing tracking area updates in the EPS network. Voice services may not be available on 5GS or circuit switched systems. Although the following description may focus on 5G NR, the concepts described herein may be applicable to other similar fields, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies.

Herein, a network node may be implemented as an aggregated base station, a decomposed base station, an Integrated Access and Backhaul (IAB) node, a relay node, a sidelink node, and the like. The network nodes/entities may be implemented in an aggregated or monolithic (monolithic) base station architecture, or alternatively, in an exploded base station architecture, and may include one or more of a Central Unit (CU), a Distributed Unit (DU), a wireless unit (RU), a near real-time (near RT) RAN Intelligent Controller (RIC), or a non-real-time (non-RT) RIC.

Fig. 2A is a diagram 200 illustrating an example of a first subframe within a 5G NR frame structure. Fig. 2B is a diagram 230 illustrating an example of DL channels within a 5G NR subframe. Fig. 2C is a diagram 250 illustrating an example of a second subframe within a 5G NR frame structure. Fig. 2D is a diagram 280 illustrating an example of UL channels within a 5G NR subframe. The 5G NR frame structure may be Frequency Division Duplex (FDD) in which subframes within a subcarrier set are dedicated to DL or UL for a particular subcarrier set (carrier system bandwidth), or Time Division Duplex (TDD) in which subframes within a subcarrier set are dedicated to both DL and UL for a particular subcarrier set (carrier system bandwidth). In the example provided by fig. 2A, 2C, the 5G NR frame structure is assumed to be TDD, where subframe 4 is configured with slot format 28 (most of which are DL), where D is DL, U is UL, and F is flexibly usable between DL/UL, and subframe 3 is configured with slot format 1 (all of which are UL). Although subframes 3, 4 are shown as having slot formats 1, 28, respectively, any particular subframe may be configured with any of the various available slot formats 0-61. The slot formats 0, 1 are full DL, full UL, respectively. Other slot formats 2-61 include a mix of DL, UL and flexible symbols. The UE is configured with a slot format (dynamically configured by DL Control Information (DCI) or semi-statically/statically configured by Radio Resource Control (RRC) signaling) through a received Slot Format Indicator (SFI). Note that the following description also applies to a 5G NR frame structure as TDD.

Fig. 2A-2D illustrate frame structures, and aspects of the present disclosure may be applicable to other wireless communication technologies, which may have different frame structures and/or different channels. A frame (10 ms) may be divided into 10 equally sized subframes (1 ms). Each subframe may include one or more slots. The subframe may also include a minislot, which 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. For a normal CP, each slot may include 14 symbols, and for an extended CP, each slot may include 12 symbols. The symbols on DL may be CP Orthogonal Frequency Division Multiplexing (OFDM) (CP-OFDM) symbols. The 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 referred to as single carrier frequency division multiple access (SC-FDMA) symbols) (for power limited scenarios; limited to single stream transmission). The number of slots within a subframe is based on CP and digital scheme (numerology). The digital scheme defines a subcarrier spacing (SCS) and in practice defines a symbol length/duration (which may be equal to 1/SCS).

For a normal CP (14 symbols/slot), different digital schemes μ0 to 4 allow 1, 2, 4, 8 and 16 slots per subframe, respectively. For extended CP, digital scheme 2 allows 4 slots per subframe. Accordingly, for the normal CP and digital scheme μ, there are 14 symbols/slot and 2 ^μ Each slot/subframe. The subcarrier spacing may be equal to 2 μ 15kHz, where μ is a digital scheme 0 through 4. Thus, the digital scheme μ=0 has a subcarrier spacing of 15kHz, and the digital scheme μ=4 has a subcarrier spacing of 240 kHz. The symbol length/duration is inversely related to the subcarrier spacing. Fig. 2A-2D provide examples of a normal CP (with 14 symbols per slot) and a digital scheme μ=2 (with 4 slots per subframe). The slot duration is 0.25ms, the subcarrier spacing is 60kHz and the symbol duration is approximately 16.67 mus. Within the frame set, there may be one or more different bandwidth portions (BWP) of the frequency division multiplexing (see fig. 2B). Each BWP may have a specific digital scheme and CP (normal or extended).

The resource grid may be used to represent a frame structure. Each slot includes Resource Blocks (RBs) (also referred to as Physical RBs (PRBs)) that extend for 12 consecutive subcarriers. The resource grid is divided into a plurality of Resource Elements (REs). The number of bits carried by each RE depends on the modulation scheme.

As shown in fig. 2A, some of the REs carry a reference (pilot) signal (RS) for the UE. The RSs may include demodulation RSs (DM-RSs) for channel estimation at the UE (indicated as R for one particular configuration, but other DM-RS configurations are possible) and channel state information reference signals (CSI-RSs). The RSs may also include beam measurement RSs (BRSs), beam Refinement RSs (BRRSs), and phase tracking RSs (PT-RSs).

Fig. 2B shows an example of various DL channels within a subframe of a frame. The Physical Downlink Control Channel (PDCCH) carries DCI within one or more Control Channel Elements (CCEs) (e.g., 1, 2, 4, 8, or 16 CCEs), each CCE including six RE groups (REGs), each REG including 12 consecutive REs in an OFDM symbol of an RB. The PDCCH within one BWP may be referred to as a control resource set (CORESET). The 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 occasion on CORESET, wherein the PDCCH candidates have different DCI formats and different aggregation levels. Additional BWP may be located at a larger and/or lower frequency across the channel bandwidth. The Primary Synchronization Signal (PSS) may be within symbol 2 of a particular subframe of a frame. PSS is used by the UE 104 to determine subframe/symbol timing and physical layer identity. The Secondary Synchronization Signal (SSS) may be within symbol 4 of a particular subframe of a frame. SSS is used by the UE to determine the physical layer cell identification group number and radio frame timing. Based on the physical layer identity and the physical layer cell identity group number, the UE may determine a Physical Cell Identifier (PCI). Based on the PCI, the UE can determine the location of the DM-RS. A Physical Broadcast Channel (PBCH) carrying a Master Information Block (MIB) may be logically grouped with PSS and SSS to form a Synchronization Signal (SS)/PBCH block (also referred to as an SS block (SSB)). The MIB provides the number of RBs in the system bandwidth and a System Frame Number (SFN). The Physical Downlink Shared Channel (PDSCH) carries user data, broadcast system information such as System Information Blocks (SIBs) that are not transmitted over the PBCH, and paging messages.

As shown in fig. 2C, some of the REs carry DM-RS for channel estimation at the base station (indicated as R for one particular configuration, but other DM-RS configurations are possible). The UE may transmit DM-RS for a Physical Uplink Control Channel (PUCCH) and DM-RS for a Physical Uplink Shared Channel (PUSCH). PUSCH DM-RS may be transmitted in the previous or two symbols of PUSCH. The PUCCH DM-RS may be transmitted in different configurations according to whether a short PUCCH or a long PUCCH is transmitted and according to a specific PUCCH format used. The UE may transmit a Sounding Reference Signal (SRS). The SRS may be transmitted in the last symbol of the 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.

Fig. 2D shows examples of various UL channels within a subframe of a frame. The PUCCH may be located as indicated in one configuration. The PUCCH carries Uplink Control Information (UCI) such as a scheduling request, a Channel Quality Indicator (CQI), a Precoding Matrix Indicator (PMI), a Rank Indicator (RI), and hybrid automatic repeat request (HARQ) Acknowledgement (ACK) (HARQ-ACK) feedback (i.e., one or more HARQ ACK bits indicating one or more ACKs and/or Negative ACKs (NACKs)). PUSCH carries data and may additionally be used to carry Buffer Status Reports (BSR), power Headroom Reports (PHR), and/or UCI.

Fig. 3 is a block diagram illustrating a base station 310 in an access network in communication with a UE 350. In DL, internet Protocol (IP) packets may be provided to controller/processor 375. Controller/processor 375 implements layer 3 and layer 2 functionality. 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. Controller/processor 375 provides: RRC layer functions associated with: broadcast of system information (e.g., MIB, SIB), 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 measurement configuration 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: transmission of upper layer Packet Data Units (PDUs), error correction by ARQ, concatenation, segmentation and reassembly of RLC Service Data Units (SDUs), re-segmentation of RLC data PDUs and re-ordering of RLC data PDUs; and a MAC layer function 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 by HARQ, priority handling and logical channel prioritization.

The Transmit (TX) processor 316 and the Receive (RX) processor 370 implement layer 1 functions associated with various signal processing functions. Layer 1, which includes a Physical (PHY) layer, may include error detection of a transmission channel, forward Error Correction (FEC) encoding/decoding of the transmission channel, interleaving, rate matching, mapping onto a physical channel, modulation/demodulation of the physical channel, and MIMO antenna processing. TX processor 316 processes the 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 encoded and modulated symbols may then be separated into parallel streams. Each stream may then be mapped to OFDM subcarriers, multiplexed with reference signals (e.g., pilots) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying the time domain OFDM symbol stream. The OFDM streams are spatially precoded to produce a plurality of spatial streams. The channel estimates from the channel estimator 374 may be used to determine the coding and modulation scheme and for spatial processing. The channel estimate may be derived from reference signals and/or channel condition feedback transmitted by the UE 350. Each spatial stream is then provided to a different antenna 320 via a separate transmitter 318 Tx. Each transmitter 318Tx may modulate a Radio Frequency (RF) carrier with a respective spatial stream for transmission.

At the UE 350, each receiver 354Rx receives a signal through its respective antenna 352. Each receiver 354Rx recovers information modulated onto an RF carrier and provides the information to the receive (Rx) processor 356.TX processor 368 and RX processor 356 implement layer 1 functions associated with various signal processing functions. RX processor 356 can perform spatial processing on the information to recover any spatial streams destined for UE 350. If multiple spatial streams are destined for UE 350, RX processor 356 may combine them into a single OFDM symbol stream. An RX processor 356 then uses a Fast Fourier Transform (FFT) to convert the OFDM symbol stream from the time domain to the frequency domain. The frequency domain signal comprises 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 points transmitted by the base station 310. These soft decisions may be based on channel estimates computed by channel estimator 358. The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station 310 on the physical channel. The data and control signals are then provided to a controller/processor 359, the controller/processor 359 implementing layer 3 and layer 2 functions.

The controller/processor 359 can be associated with a memory 360 that stores program codes and data. Memory 360 may be referred to as a computer-readable medium. In the UL, the controller/processor 359 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, 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.

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., MIB, SIB) acquisition, RRC connection and measurement report; PDCP layer functions associated with: header compression/decompression and security (encryption, decryption, integrity protection, integrity verification); RLC layer functions associated with: transmission of upper layer PDUs, error correction by ARQ, concatenation, segmentation and reassembly of RLC SDUs, re-segmentation of RLC data PDUs and re-ordering of RLC data PDUs; and a MAC layer function associated with: mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction by HARQ, priority handling and logical channel prioritization.

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

At the base station 310, UL transmissions are processed in a manner similar to that described in connection with the receiver functionality at the UE 350. Each receiver 318Rx receives a signal through its corresponding antenna 320. Each receiver 318Rx recovers information modulated onto an RF carrier and provides the information to the Rx processor 370.

The controller/processor 375 may be associated with a memory 376 that stores program codes and data. Memory 376 may be referred to as a computer-readable medium. In the UL, controller/processor 375 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets. Controller/processor 375 is also responsible for supporting HARQ operations using error detection of ACK and/or NACK protocols.

At least one of TX processor 368, RX processor 356, and controller/processor 359 may be configured to perform aspects in conjunction with voice component 198 of fig. 1.

At least one of TX processor 316, RX processor 370, and controller/processor 375 may be configured to perform various aspects in conjunction with voice component 199 of fig. 1.

Fig. 4 is a diagram 400 showing an unmodified (or default) timer T3402. The UE 402 may attempt to attach to the EPS network 404 or perform tracking area updates 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 a timer T3402. Until the timer T3402 expires, the UE 402 may not reattempt to attach to the EPS network 404 or perform tracking area update in the EPS network 404.

In one or more aspects, since voice service is provided via EPS fallback in a 5GS network and it is difficult for a UE to attach to the EPS network or perform tracking area update in the EPS network, voice-centric UEs may experience long periods of inability to access voice service. In one example, the UE may be voice-centric and may not support VoNR in the 5GS network (i.e., voice may only be supported via EPS fallback). Furthermore, voice services via early circuit switched technologies (e.g., 2G/3G) may not be available because the spectrum may have been reused for other radio access technologies. The UE may not be able to access the voice service for a long time due to difficulty in attaching to the EPS network or performing tracking area update in the EPS network.

In one example, the inability to access voice services for a long period of time may occur as follows. First, due to poor EPS coverage, the UE may fail to attach to the EPS network or perform tracking area update in the EPS network 5 consecutive times, which may cause the UE to disable the S1 mode (i.e., the mode related to the 4G/EPS capability of the UE) and start the timer T3402 (default duration is 12 minutes). The timer T3402 may be associated with retrying attachment to the EPS network or performing tracking area update in the EPS network. By default, the UE may not reattempt to attach to the EPS network or perform tracking area update in the EPS network before the timer T3402 expires. The UE may then attempt to attach to the 5GS network or perform tracking area update in the 5GS network, and may indicate to the 5GS network that the S1 mode is disabled in the registration request message. Since the network may support voice services via EPS fallback and EPS fallback may not be available when S1 mode is disabled, the network may indicate "IMS voice access over 3GPP is not supported" in the registration accept message. Since the UE is voice-centric, receipt of the "do not support IMS voice access over 3 GPP" indication in the registration accept message may cause the UE to disable the N1 mode (i.e., the mode related to the UE's 5G capability). With both the S1 mode and the N1 mode disabled, the UE may search for a 2G/3G network for voice services and may not find the 2G/3G network. Finally, the UE may re-enable the N1 mode and may camp in the 5GS network. The UE may not be able to obtain voice service via EPS backoff until timer T3402 expires. Thus, the user may experience significant periods of time when voice services are not accessible.

Fig. 5 is a diagram of a communication flow 500 of a method of wireless communication. The VoNR from base station 504 may not be available. At 510, the UE 502 may attempt to attach to the EPS network or perform tracking area updates in the EPS network for a number of times to obtain voice services. In some aspects, the number of times may be a predetermined or defined number of times. At 512, the UE 502 may start a modified timer based on failing to attach to the EPS network or performing tracking area updates in the EPS network for the number of times and based on the configuration parameters. The modified timer may be modified based on a default timer. In one or more configurations, the configuration parameters may be stored in a Universal Subscriber Identity Module (USIM) of the Mobile Equipment (ME) or UE 502. At 514, the UE 502 may disable the S1 mode when starting the modified timer. At 516, the UE 502 may skip retrying attachment to the EPS network or performing tracking area updates in the EPS network before stopping the modified timer (e.g., the modified timer may be stopped early if the cell quality is above a certain threshold for more than a threshold amount of time) or expiration of the modified timer. At 518, UE 502 may attempt to obtain voice services based on one or more access technologies other than EPS. In some aspects, the UE may attempt to obtain voice services from each of one or more access technologies. The attempt at 518 may also fail.

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., the "usereduce 3402" 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 a modified timer associated with a shorter duration regardless of the quality of EPS coverage. During the duration of the modified timer, the UE 502 may still not have voice service.

In one aspect, the modified timer having a shorter duration may be used a first predetermined number of times (e.g., 2 times) after the UE 502 has been recently powered on, with the unmodified timer T3402 to be used in other cases. After the modified timer has been used a predetermined number of times, on the next occasion and on another occasion when the timer T3402 is started, the unmodified timer T3402 with the default duration may be used. In other words, at 524, the UE 502 may start an unmodified timer based on failing to attach to the EPS network or performing a tracking area update in the EPS network after the modified timer has been used a threshold number of times after the last power-on of the UE. By limiting the number of times the modified timer is used, if the UE 502 is indeed outside the 4G/EPS coverage area and temporarily not in a coverage hole, the UE 502 may revert to using the unmodified timer T3402 with the default duration. Thus, energy may not be wasted on too many failed attempts to attach to the EPS network or perform tracking area updates in the EPS network.

In one aspect, the shorter duration associated with the modified timer may be preconfigured.

In one aspect, the shorter duration associated with the modified timer may be based on an indication received by the UE 502 from the base station 504. In other words, the UE 502 may receive an indication of the shorter duration associated with the modified timer from the base station 504. Thus, the network operator can customize the duration of the modified timer for a particular deployment.

At 520, the UE 502 may re-enable the S1 mode upon expiration or cessation of the modified timer. At 522, the UE 502 may attach to the EPS network or perform tracking area updates 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).

Fig. 6 is a diagram of a communication flow 600 of a method of wireless communication. The VoNR from base station 604 may not be available. At 608, the UE 602 may attempt to attach to the EPS network or perform tracking area updates in the EPS network for a number of times to obtain voice services. In some aspects, the number of times may be a predetermined or defined number of times. At 610, the UE 602 may start a modified timer based on failing to attach to the EPS network or performing tracking area updates in the EPS network for the number of times and based on the configuration parameters. The modified timer may be modified based on a default timer. At 612, the UE 602 may disable the S1 mode when starting the modified timer. At 614, the UE 602 may skip retrying attachment to the EPS network or performing tracking area updates in the EPS network before stopping the modified timer (e.g., the modified timer may be stopped early if the cell quality is above a certain threshold for more than a threshold amount of time) or expiration of 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 an indication that packet-switched voice services are not supported. At 622, the UE 602 may attempt to obtain voice services based on one or more access technologies (e.g., 2G/3G access technologies) other than EPS. The attempt at 622 may also fail. At 624, the UE 602 may re-enable the N1 mode when it fails to obtain circuit switched voice service in an access technology other than 5 GS. While aspects are described for the purpose of illustrating this concept for examples of 5GS networks and other access technologies, these aspects may be similarly applied to other access technologies, including future access technologies. For example, the UE may send an indication to the base station of the first access technology that the 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 the mode of operation associated with the first access technology upon receiving an indication that packet-switched voice service is not supported, and may re-enable the mode of operation associated with the first access technology upon failure to obtain voice service in one or more access technologies (e.g., a first access technology other than the base station).

In one aspect, the UE 602 may re-enable the S1 mode when re-enabling the N1 mode at 624. Further, the UE may stop the modified timer when the N1 mode and the S1 mode are re-enabled. The use of the modified timer at 610 may be based on the value of a configuration parameter (e.g., an "EnableT3402EarlyStop" parameter). In other words, at 626, the UE 602 may re-enable the S1 mode when re-enabling the N1 mode. At 628, the UE 602 may stop the modified timer when the S1 mode is re-enabled. Thus, the UE 602 may again obtain voice service before the natural expiration of the unmodified timer T3402. However, it should be appreciated that when the modified timer is stopped, EPS coverage may still be poor, in which case attempting to obtain voice service via EPS backoff may again fail.

In one aspect, the UE 602 may re-enable the S1 mode when re-enabling the N1 mode at 624. Further, the UE may stop the modified timer when one of the following occurs: the reselection to the EPS network by the UE, or the network handover or redirection 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 "EnableT3402EarlyStop" parameter). In other words, at 626, the UE 602 may re-enable the S1 mode when re-enabling the N1 mode. At 628, the UE 602 may stop the modified timer when one of the following occurs: the reselection to the EPS network by the UE, or the network handover or redirection to the EPS network. Thus, the UE 602 may again obtain voice service before the natural expiration of the unmodified timer T3402. However, it should be appreciated that after disabling the S1 mode at 612, the N1 mode may still be disabled at 620, and before the UE may return to the 5GS network at 624 and again obtain voice service at 630, an attempt may still be made to obtain voice service over the 2G/3G access technology at 622. In other words, the user may still experience periods of no voice service.

At 630, the UE 602 may attach to the EPS network or perform tracking area updates 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).

Fig. 7 is a diagram of a communication flow 700 of a method of wireless communication. The VoNR from base station 704 may not be available. At 708, the UE 702 may attempt to attach to the EPS network or perform tracking area updates in the EPS network for a number of times to obtain voice services. At 710, the UE 702 may start a modified timer based on failing to attach to or perform tracking area updates in the EPS network for the number of times and based on the configuration parameters. The modified timer may be modified based on a default timer. At 712, the UE 702 may disable the S1 mode when starting the modified timer. At 714, the UE 602 may skip retrying to attach to the EPS network or performing tracking area updates in the EPS network before stopping the modified timer (e.g., the modified timer may be stopped early if the cell quality is above a certain threshold for more than a threshold amount of time) or expiration of the modified timer. At 716, the UE 702 may attempt to obtain voice services based on one or more access technologies other than EPS. Attempts at 716 may also fail.

In one aspect, when the modified timer runs 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 more 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 "EnableT3402EarlyStop" parameter). In other words, at 718, the UE 702 may monitor the quality of cells associated with the EPS network. 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 722, the UE 702 may re-enable the S1 mode based on the expiration of the modified timer. Thus, the UE 702 may again obtain voice service before the unmodified timer T3402 expires naturally. Further, the UE 702 may re-enable the S1 mode and stop the modified timer when the EPS coverage is good enough. However, it should be appreciated that stopping the NAS timer based on the AS trigger may be considered a layer violation (layer operation).

At 724, the UE 702 may attach to the EPS network or perform tracking area updates 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).

Fig. 8 is a diagram of a communication flow 800 of a method of wireless communication. The VoNR from base station 804 may not be available. At 808, the UE 802 may attempt to attach to the EPS network or perform tracking area updates in the EPS network for a number of times to obtain voice services. In some aspects, the number of times may be a predetermined or defined number of times. At 810, the UE 802 may start a modified timer based on failing to attach to the EPS network or performing tracking area updates in the EPS network for the number of times and based on the 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.

The UE 802 may not disable the S1 mode when the modified timer is started at 810. When the modified timer runs after 810 and before stopping the modified timer (e.g., the modified timer may be stopped early if the cell quality is above a certain threshold for more than a threshold amount of time) or before expiration of the modified timer, the UE 802 may de-prioritize the EPS network (regardless of the priority indicated by the network), or may not reattempt to attach to the EPS network or perform tracking area updates 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 "EnableT3402EarlyStop" parameter). Since the S1 mode remains enabled, the UE may not receive an "IMS voice access over 3GPP not supported" indication in the registration accept message. Thus, the UE may not disable the N1 mode and may not waste time attempting to obtain voice services via the legacy 2G/3G network (i.e., in some configurations 816 may not be performed). Thus, at 812, the UE 802 may maintain S1 mode enablement when starting the modified timer. At 814, the UE 802 may de-prioritize or not reattempt to attach to the EPS network or perform tracking area updates in the EPS network before the expiration or expiration of the modified timer.

In one aspect, the UE 802 may not reattempt to attach to the EPS network or perform a tracking area update in the EPS network before the expiration or expiration of the modified timer. The UE 802 may stop the modified timer when one of the following occurs: the reselection to the EPS network, the handover to the EPS network, or the redirection to the EPS network by the network is performed by the UE. In other words, at 818, the UE 802 may stop the modified timer when one of the following occurs: the reselection to the EPS network, the handover to the EPS network, or the redirection to the EPS network by the network is performed by the UE. Thus, the UE 802 may again obtain voice service before the natural expiration of the unmodified timer T3402.

In one aspect, the UE 802 may de-prioritize one or more cells associated with the EPS network for cell reselection prior to the expiration or expiration of the modified timer regardless of the priority indicated by the network. The UE 802 may stop the modified timer when one of the following occurs: switch to the EPS network, or be redirected by the network to the EPS network. In other words, at 818, the UE 802 may stop the modified timer when one of the following occurs: switch to the EPS network, or be redirected by the network to the EPS network. Thus, the UE 802 may again obtain voice service before the natural expiration of the unmodified timer T3402. However, it should be appreciated that the UE 802 may override the normal cell reselection rules.

At 820, the UE 802 may attach to the EPS network or perform tracking area updates 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).

Fig. 9 is a flow chart 900 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104/350/502/602/702/802; apparatus 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 a configuration parameter. The modified timer may be modified based on a default timer. For example, 902 may be performed by component 198 in fig. 15. Referring to fig. 5-8, 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 a configuration parameter.

At 904, the ue may attempt to obtain voice services based on one or more access technologies other than EPS. For example, 904 may be performed by component 198 in fig. 15. Referring to fig. 5-8, at 518, 622, 716, 816, the UE 502, 602, 702, 802 may attempt to obtain voice services based on one or more access technologies other than EPS.

At 906, the UE may attach to the EPS network or perform tracking area updates 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 in fig. 15. Referring to fig. 5-8, at 522, 630, 724, 820, the UE 502, 602, 702, 802 may attach to the EPS network or perform tracking area updates in the EPS network to obtain voice services based on the modified timer.

Fig. 10 is a flow chart 1000 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104/350/502; apparatus 1502). At 1004, the UE may attempt to attach to the EPS network or perform tracking area update in the EPS network for a number of times to obtain voice service. In some aspects, the number of times may be a predetermined or defined number of times. For example, 1004 may be performed by component 198 in fig. 15. Referring to fig. 5, at 510, the UE 502 may attempt to attach to the EPS network or perform tracking area updates in the EPS network for a number of times to obtain voice services.

At 1006, the UE may start a modified timer based on failing to attach to the EPS network or performing tracking area updates in the EPS network for the number of times 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 in fig. 15. Referring to fig. 5, at 512, the UE 502 may start a modified timer based on failing to attach to or perform tracking area updates in the EPS network for the number of times and based on the configuration parameters.

At 1012, the UE may attempt to obtain voice services based on one or more access technologies other than EPS. For example, 1012 may be performed by component 198 in fig. 15. Referring to fig. 5, at 518, UE 502 may attempt to obtain voice services based on one or more access technologies other than EPS.

At 1016, the UE may attach to the EPS network or perform tracking area updates 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 in fig. 15. Referring to fig. 5, at 522, the UE 502 may attach to the EPS network or perform tracking area update in the EPS network to obtain voice services based on the modified timer.

In one configuration, at 1008, the UE may disable the S1 mode when starting the modified timer. For example, 1008 may be performed by component 198 in fig. 15. Referring to fig. 5, at 514, the UE 502 may disable the S1 mode when starting the modified timer. At 1010, the UE may skip retrying to attach to the EPS network or perform tracking area updates in the EPS network before the expiration or expiration of the modified timer. For example, 1010 may be performed by component 198 in fig. 15. Referring to fig. 5, at 516, the UE 502 may skip retrying to attach to the EPS network or perform tracking area updates in the EPS network before the expiration or expiration of the modified timer.

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 in FIG. 15. Referring to fig. 5, at 520, the UE 502 may re-enable the S1 mode upon expiration of the modified timer.

In one configuration, at 1018, the UE may start an unmodified/default timer based on failing to attach to the EPS network or performing a tracking area update in the EPS network after the modified timer has been used a threshold number of times after the last power-on of the UE. For example, 1018 may be performed by component 198 in fig. 15. Referring to fig. 5, at 524, the UE 502 may start an unmodified/default timer based on failing to attach to the EPS network or performing a tracking area update in the EPS network after the modified timer has been used a threshold number of times after the last power-on of the UE 502.

In one configuration, the shorter duration associated with the modified timer may be preconfigured.

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

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, the UE may be a voice-centric UE.

Fig. 11 is a flow chart 1100 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104/350/602; apparatus 1502). At 1102, the UE may attempt to attach to the EPS network or perform tracking area updates in the EPS network for a number of times to obtain voice services. For example, 1102 may be performed by component 198 in fig. 15. In some aspects, the number of times may be a predetermined or defined number of times. Referring to fig. 6, at 608, the UE 602 may attempt to attach to the EPS network or perform tracking area updates in the EPS network for a number of times to obtain voice services.

At 1104, the UE may start a modified timer based on failing to attach to the EPS network or performing tracking area updates in the EPS network for the number of times 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 in fig. 15. Referring to fig. 6, at 610, the UE 602 may start a modified timer based on failing to attach to or perform tracking area updates in the EPS network for the number of times and based on configuration parameters.

At 1116, the UE may attempt to obtain voice services based on one or more access technologies other than EPS. For example, 1116 may be performed by component 198 in fig. 15. Referring to fig. 6, at 622, the UE 602 may attempt to obtain voice services based on one or more access technologies other than EPS.

At 1124, the UE may attach to the EPS network or perform tracking area updates 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 in fig. 15. Referring to fig. 6, at 630, the UE 602 may attach to the EPS network or perform tracking area update in the EPS network to obtain voice services based on the modified timer.

In one configuration, at 1106, the UE may disable the S1 mode when starting the modified timer. For example, 1106 may be performed by component 198 in fig. 15. Referring to fig. 6, at 612, the UE 602 may disable the S1 mode when starting the modified timer. At 1108, the UE may skip retrying to attach to the EPS network or perform tracking area updates in the EPS network before the modified timer expires or expires. For example, 1108 may be performed by component 198 in fig. 15. Referring to fig. 6, at 614, the UE may skip retrying to attach to the EPS network or perform tracking area update in the EPS network before the modified timer expires or expires.

In one configuration, in response to failing to obtain voice service based on EPS, the UE may send an indication to the 5GS base station that S1 mode is disabled at 1110. For example, 1110 may be performed by component 198 in fig. 15. Referring 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 in fig. 15. Referring 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 an indication that packet-switched voice services are not supported. For example, 1114 may be performed by component 198 in fig. 15. Referring 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 when it fails to obtain circuit switched voice service in an access technology other than 5 GS. For example, 1118 may be performed by component 198 in fig. 15. Referring to fig. 6, at 624, the UE 602 may re-enable the N1 mode upon failure to obtain circuit switched voice service in an access technology other than 5 GS.

In one configuration, at 1120, the UE may re-enable the S1 mode when re-enabling the N1 mode. For example, 1120 may be performed by component 198 in fig. 15. Referring to fig. 6, at 626, the UE 602 may re-enable the S1 mode when re-enabling the N1 mode. At 1122, the UE may stop the modified timer when the S1 mode is re-enabled. 1122 may be performed, for example, by component 198 in fig. 15. Referring to fig. 6, at 628, the UE 602 may stop the modified timer when the S1 mode is re-enabled.

In one configuration, at 1120, the UE may re-enable the S1 mode when re-enabling the N1 mode. For example, 1120 may be performed by component 198 in fig. 15. Referring to fig. 6, at 626, the UE 602 may re-enable the S1 mode when re-enabling the N1 mode. At 1122, the UE may stop the modified timer when one of the following occurs: the reselection to the EPS network by the UE, or the network handover or redirection to the EPS network. 1122 may be performed, for example, by component 198 in fig. 15. Referring to fig. 6, at 628, the UE 602 may stop the modified timer when one of the following occurs: the reselection to the EPS network by the UE, or the network handover or redirection to the EPS network.

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

Fig. 12 is a flow chart 1200 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104/350/702; apparatus 1502). At 1202, the UE may attempt to attach to the EPS network or perform tracking area update in the EPS network for a number of times to obtain voice service. In some aspects, the number of times may be a predetermined or defined number of times. 1202 may be performed, for example, by component 198 in fig. 15. Referring to fig. 7, at 708, the UE 702 may attempt to attach to the EPS network or perform tracking area updates in the EPS network for a number of times to obtain voice services.

At 1204, the UE may start a modified timer based on failing to attach to the EPS network or performing tracking area updates in the EPS network for the number of times 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 in fig. 15. Referring to fig. 7, at 710, the UE 702 may start a modified timer based on failing to attach to or perform tracking area updates in the EPS network for the number of times and based on configuration parameters.

At 1210, the UE may attempt to obtain voice services based on one or more access technologies other than EPS. For example, 1210 may be performed by component 198 in fig. 15. Referring to fig. 7, at 716, the UE 702 may attempt to obtain voice services based on one or more access technologies other than EPS.

At 1218, the UE may attach to the EPS network or perform tracking area updates in the EPS network to obtain the voice service 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 the component 198 of fig. 15. Referring to fig. 7, at 724, the UE 702 may attach to the EPS network or perform tracking area update in the EPS network to obtain voice services based on the modified timer.

In one configuration, at 1206, the UE may disable the S1 mode when starting the modified timer. For example, 1206 may be performed by component 198 in fig. 15. Referring to fig. 7, at 712, the UE 702 may disable the S1 mode when starting the modified timer. At 1208, the UE may skip retrying to attach to the EPS network or perform tracking area updates in the EPS network before the modified timer expires or expires. For example, 1208 may be performed by component 198 in fig. 15. Referring to fig. 7, at 714, the UE 702 may skip retrying to attach to the EPS network or perform tracking area updates in the EPS network before the expiration or expiration of the modified timer.

In one configuration, at 1212, the UE may monitor the quality of a cell associated with the EPS network. 1212 may be performed by component 198 in fig. 15, for example. Referring to fig. 7, at 718, the UE 702 may monitor quality of a cell associated with an 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 executed by component 198 in fig. 15. Referring 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 the S1 mode based on the expiration of the modified timer. For example, 1216 may be performed by component 198 in fig. 15. Referring to fig. 7, at 722, the UE 702 may re-enable the S1 mode based on the stop of the modified timer.

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

Fig. 13 is a flow chart 1300 of a method of wireless communication. The method may be performed by a UE (e.g., UE 104/350/802; apparatus 1502). At 1302, the UE may attempt to attach to the EPS network or perform tracking area updates in the EPS network for a number of times to obtain voice services. In some aspects, the number of times may be a predetermined or defined number of times. For example, 1302 may be performed by component 198 in fig. 15. Referring to fig. 8, at 808, the UE 802 may attempt to attach to the EPS network or perform tracking area update in the EPS network for a number of times to obtain voice services.

At 1304, the UE may start a modified timer based on failing to attach to the EPS network or performing tracking area updates in the EPS network for the number of times 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 in fig. 15. Referring to fig. 8, at 810, the UE 802 may start a modified timer based on failing to attach to or perform tracking area updates in the EPS network for the number of times and based on configuration parameters.

At 1310, the UE may attempt to obtain voice services based on one or more access technologies other than EPS. For example, 1310 may be performed by component 198 in fig. 15. Referring to fig. 8, at 816, the UE 802 may attempt to obtain voice services based on one or more access technologies other than EPS.

At 1314, the UE may attach to the EPS network or perform tracking area updates in the EPS network to obtain voice services based on the modified timer. 1314 may be performed by component 198 in fig. 15, for example. Referring to fig. 8, at 820, the UE 802 may attach to the EPS network or perform tracking area update in the EPS network to obtain voice services based on the modified timer.

In one configuration, at 1306, the UE may maintain S1 mode enablement when starting the modified timer. For example, 1306 may be performed by component 198 in fig. 15. Referring to fig. 8, at 812, the UE 802 may maintain S1 mode enablement when starting the modified timer. At 1308, the UE may de-prioritize the EPS network or not reattempt to attach to the EPS network or perform a tracking area update in the EPS network before the stop or expiration of the modified timer. For example, 1308 may be performed by component 198 in FIG. 15. Referring to fig. 8, at 814, the UE 802 may de-prioritize or not reattempt to attach to the EPS network or perform tracking area updates in the EPS network prior to the expiration or expiration of the modified timer.

In one configuration, at 1312, the UE may stop the modified timer when one of the following occurs: the reselection to the EPS network, the handover to the EPS network, or the redirection to the EPS network by the network is performed by the UE. For example, 1312 may be performed by component 198 in fig. 15. Referring to fig. 8, at 818, the UE 802 may stop the modified timer when one of the following occurs: the reselection to the EPS network, the handover to the EPS network, or the redirection to the EPS network by the network is performed by the UE.

In one configuration, the UE may de-prioritize one or more cells associated with the EPS network for cell reselection prior to the expiration or expiration of the modified timer.

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

Fig. 14 is a flow chart 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 can transmit an indication of a duration associated with the modified timer to the voice-centric UE. The duration associated with the modified timer may be shorter than the duration associated with the default timer. 1402 may be performed, for example, by component 199 in fig. 16. Referring to fig. 5, at 508, the base station 504 may send an indication of the duration associated with the modified timer to the voice-centric UE 502.

At 1404, the base station initially fails to provide voice services to the voice-centric UE via the EPS network. For example, 1404 may be performed by component 199 in fig. 16. Referring to fig. 5, at 510, the base station 504 initially fails to provide voice services to the voice-centric UE 502 via the EPS network.

At 1406, the base station may provide voice services to the voice-centric UE via the EPS network based on the modified timer after initially failing to provide voice services to the voice-centric UE via the EPS network. 1406 may be performed, for example, by component 199 in fig. 16. Referring to fig. 5, at 522, the base station 504 may provide voice services to the voice-centric UE 502 via the EPS network based on the modified timer after initially failing to provide voice services to the voice-centric UE 502 via the EPS network.

The modified timer and the default timer may be associated with reattempting to attach to the EPS network or performing tracking area updates in the EPS network. Voice services may not be available on 5GS or circuit switched systems.

Fig. 15 is a diagram 1500 illustrating an example of a hardware implementation for an apparatus 1502. The apparatus 1502 may be a UE, a component of a UE, or may implement UE functionality. In some aspects, the apparatus 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 apparatus 1502 may also 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 supply 1518. The cellular baseband processor 1504 communicates with the UE 104 and/or BS102/180 via a cellular RF transceiver 1522. The cellular baseband processor 1504 may include a computer readable medium/memory. The computer readable medium/memory may be non-transitory. The cellular baseband processor 1504 is responsible for general processing, including the execution of software stored on a computer-readable medium/memory. The software, when executed by the cellular baseband processor 1504, causes the cellular baseband processor 1504 to perform the various functions described supra. The computer readable medium/memory can also be used for storing data that is manipulated by the cellular baseband processor 1504 when executing software. The cellular baseband processor 1504 also includes a receive component 1530, a communication manager 1532, and a transmit component 1534. The communication manager 1532 includes one or more of the components shown. The components within the communication manager 1532 may be stored in a computer readable medium/memory and/or configured as hardware within 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 apparatus 1502 may be a modem chip and include only the baseband processor 1504, and in another configuration, the apparatus 1502 may be an entire UE (see, e.g., 350 of fig. 3) and include additional modules of the apparatus 1502.

The communication manager 1532 includes a first attempt component 1540 configured to attempt to attach to or perform tracking area updates in the EPS network a number of times to obtain voice services, e.g., as described in connection with 1004 in fig. 10, 1102 in fig. 11, 1202 in fig. 12, and 1302 in fig. 13. The communication manager 1532 also includes a timer component 1542 configured to start a modified timer based on failing to attach to or perform tracking area updates in the EPS network for the number of times and based on configuration parameters, e.g., as described in connection with 902 in fig. 9, 1006 in fig. 10, 1104 in fig. 11, 1204 in fig. 12, and 1304 in fig. 13. The communication manager 1532 also includes a second attempt component 1544 configured to attempt to obtain voice services based on one or more access technologies other than EPS, e.g., as described in connection with 904 in fig. 9, 1012 in fig. 10, 1116 in fig. 11, 1210 in fig. 12, and 1310 in fig. 13. The communication manager 1532 also includes a service component 1546 configured to attach to or perform tracking area updates in the EPS network based on the modified timer to obtain voice services, e.g., as described in connection with 906 in fig. 9, 1016 in fig. 10, 1124 in fig. 11, 1218 in fig. 12, and 1314 in fig. 13.

The communication manager 1532 also includes a service component 1546 configured to disable the S1 mode when the modified timer is started, e.g., as described in connection with 1008 in fig. 10, 1106 in fig. 11, and 1206 in fig. 12. The service component 1546 may also be configured to skip reattempting to attach to the EPS network or perform tracking area updates in the EPS network prior to the expiration or expiration of the modified timer, e.g., as described in connection with 1010 in fig. 10, 1108 in fig. 11, and 1208 in fig. 12. The service component 1546 may also be configured to re-enable the S1 mode upon expiration of the modified timer, e.g., as described in connection with 1014 in fig. 10. The service component 1546 may also be configured to start the unmodified timer based on failing to attach to the EPS network or performing a tracking area update in the EPS network after the modified timer has been used a threshold number of times after the last power-on of the UE, e.g., as described in connection with 1018 in fig. 10. The service component 1546 may also be configured to receive an indication of a shorter duration associated with the modified timer from the base station, e.g., as described in connection with 1002 in fig. 10. The service component 1546 may also be configured to send an indication to the 5GS base station that the S1 mode is disabled, e.g., as described in connection with 1110 in fig. 11. The service component 1546 may also be configured to receive an indication from the 5GS base station that packet switched voice services are not supported, e.g., as described in connection with 1112 in fig. 11. Service component 1546 may also be configured to disable the N1 mode upon receiving an indication that packet-switched voice services are not supported, e.g., as described in connection with 1114 in fig. 11. Service component 1546 may also be configured to re-enable the N1 mode upon failure to obtain circuit-switched voice service in an access technology other than 5GS, e.g., as described in connection with 1118 of fig. 11. Service component 1546 may also be configured to re-enable the S1 mode when re-enabling the N1 mode, e.g., as described in connection with 1120 in fig. 11. Service component 1546 may also be configured to stop the modified timer, for example, as described in connection with 1122 in fig. 11. Service component 1546 may also be configured to monitor the quality of cells associated with the EPS network, e.g., as described in connection with 1212 in fig. 12. The service component 1546 may also be 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 in connection with 1214 in fig. 12. Service component 1546 may also be configured to re-enable S1 mode based on the expiration of the modified timer, e.g., as described in connection with 1216 in fig. 12. Service component 1546 may also be configured to maintain S1 mode enablement when starting the modified timer, e.g., as described in connection with 1306 in fig. 13. The service component 1546 may also be configured to de-prioritize or not re-attempt to attach to the EPS network or perform tracking area updates in the EPS network prior to the expiration or expiration of the modified timer, e.g., as described in connection with 1308 in fig. 13. Service component 1546 may also be configured to stop the modified timer when one of the following occurs: reselection to the EPS network, handover to the EPS network, or redirection to the EPS network by the network is performed by the UE, e.g., as described in connection with 1312 in fig. 13.

The apparatus may include additional components to perform each of the blocks of the algorithm in the flowcharts of fig. 5-13. Accordingly, each block in the flowcharts of fig. 5-13 may be performed by components, and the apparatus may include one or more of those components. A component may be one or more hardware components specifically configured to perform the process/algorithm, implemented by a processor configured to perform the process/algorithm, stored within a computer readable medium for implementation by a processor, or some combination thereof.

As shown, the apparatus 1502 may include various components configured for various functions. In one configuration, the apparatus 1502 (in particular, the cellular baseband processor 1504) includes means for attempting to attach to an EPS network or performing tracking area updates in the EPS network a number of times to obtain voice services. The apparatus 1502 may include means for starting a modified timer based on failing to attach to or perform tracking area updates 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 apparatus 1502 may include means for attempting to obtain a voice service based on one or more access technologies other than EPS. The apparatus 1502 may include means for attaching to an EPS network or performing tracking area updates in the EPS network to obtain voice services based on the modified timer.

In one configuration, apparatus 1502 may include means for disabling the S1 mode when a modified timer is started. The apparatus 1502 may include means for skipping a retry of attaching to the EPS network or performing a tracking area update in the EPS network before a stop or expiration 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 expiration of the modified timer. In one configuration, the apparatus 1502 may include means for starting an unmodified/default timer based on failing to attach to the EPS network or performing a tracking area update in the EPS network after the modified timer has been used a threshold number of times after a last power-on of the UE. In one configuration, the shorter duration associated with the modified timer may be preconfigured. In one configuration, an apparatus 1502 may include means for receiving an indication of a shorter duration associated with a 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 failing to obtain voice service based on EPS, the apparatus 1502 may include means for sending an indication to the 5GS base station that S1 mode is disabled. The apparatus 1502 may include means for receiving an indication from a 5GS base station that packet switched voice services are not supported. The apparatus 1502 may include means for disabling the N1 mode upon receiving an indication that packet-switched voice services are not supported. The apparatus 1502 may include means for re-enabling the N1 mode when a circuit switched voice service is not available in an access technology other than 5 GS. In one configuration, apparatus 1502 may include means for re-enabling the S1 mode when re-enabling the N1 mode. The apparatus 1502 may include means for stopping the modified timer when the S1 mode is re-enabled. In one configuration, apparatus 1502 may include means for re-enabling the S1 mode when re-enabling the N1 mode. The apparatus 1502 may include means for stopping the modified timer when one of the following occurs: the reselection to the EPS network by the UE, or the network handover or redirection to the EPS network. In one configuration, the apparatus 1502 may include means for monitoring quality of a cell associated with an EPS network. The apparatus 1502 may 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 may include means for re-enabling the S1 mode based on a stop of the modified timer. In one configuration, apparatus 1502 may include means for maintaining S1 mode enablement when starting a modified timer. The apparatus 1502 may include means for de-prioritizing or not re-attempting to attach to or perform tracking area update in an EPS network prior to a stop or expiration of a modified timer. In one configuration, the apparatus 1502 may include means for stopping the modified timer when one of the following occurs: the reselection to the EPS network, the handover to the EPS network, or the redirection to the EPS network by the network is performed by the UE. In one configuration, the apparatus 1502 may include means for de-prioritizing one or more cells associated with an EPS network for cell reselection prior to a stop or expiration of a modified timer. In one configuration, the UE may be a voice-centric UE.

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

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 a 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. 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 on a computer-readable medium/memory. The software, when executed by the baseband unit 1604, causes the baseband unit 1604 to perform the various functions described supra. The computer readable medium/memory can also be used for storing data that is manipulated by the baseband unit 1604 when executing software. The baseband unit 1604 also includes a receiving component 1630, a communication manager 1632, and a transmitting component 1634. The communications manager 1632 includes one or more components as shown. Components within the communication manager 1632 may be stored in a computer-readable medium/memory and/or configured as hardware within the baseband unit 1604. Baseband unit 1604 may be a component of base station 310 and may include memory 376 and/or at least one of TX processor 316, RX processor 370, and controller/processor 375.

The communication manager 1632 includes an indication component 1640 that is configured to send an indication of the duration associated with the modified timer to the voice-centric UE, e.g., as described in connection with 1402 in fig. 14. The communication manager 1632 also includes a first service component 1642 that is configured to initially fail to provide voice services to voice-centric UEs via the EPS network, e.g., as described in connection with 1404 in fig. 14. The communication manager 1632 also includes a second service component 1644 that is configured to provide voice services to the voice-centric UE via the EPS network based on the modified timer after initially failing to provide voice services to the voice-centric UE via the EPS network, e.g., as described in connection with 1406 in fig. 14.

The apparatus may include additional components to perform each of the blocks of the algorithms in the flowcharts of fig. 5-8 and 14. Accordingly, each block in the flowcharts of fig. 5-8 and 14 may be performed by components, and the apparatus may include one or more of those components. A component may be one or more hardware components specifically configured to perform the process/algorithm, implemented by a processor configured to perform the process/algorithm, stored within a computer readable medium for implementation by a processor, or some combination thereof.

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 the modified timer to the voice-centric UE. The apparatus 1602 may include means for initially failing to provide voice services to a voice-centric UE via an EPS network. The apparatus 1602 may include means for providing voice services to a voice-centric UE via an EPS network based on a modified timer after initially failing to provide voice services to the voice-centric UE via the EPS network. The modified timer and the default timer may be associated with reattempting to attach to the EPS network or performing tracking area updates in the EPS network. Voice services may not be available on 5GS or circuit switched systems.

The unit may be one or more of the components of the apparatus 1602 configured to perform the functions recited by the unit. 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 elements may be TX processor 316, RX processor 370, and controller/processor 375 configured to perform the functions recited by the elements.

According to aspects described herein, a UE may attempt to attach to an EPS network or perform tracking area updates in the EPS network for a number of times to obtain voice services. The UE may start the modified timer based on failing to attach to the EPS network or performing tracking area updates in the EPS network for the number of times and based on the configuration parameters. The modified timer is modified based on the 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 the EPS network or perform tracking area update in the EPS network based on the modified timer. In some aspects, the UE may not disable the S1 mode when the modified timer is started or run, and thus the UE may not waste time attempting to obtain voice services via the legacy 2G/3G network. Thus, the period during which the voice-centric UE does not have any voice service access may be reduced, and the user experience may be improved.

It should be understood that the specific order or hierarchy of blocks in the processes/flowcharts disclosed is an illustration of example approaches. It should be appreciated that the particular order or hierarchy of blocks in the process/flow diagram may be rearranged based on design preferences. Furthermore, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not limited to the aspects described herein, but are to be accorded the full scope consistent with the language claims, unless specifically so stated, reference to an element in the singular is not intended to mean "one and only one", but rather "one or more". Terms such as "if," "when … …," and "contemporaneously with … …" do not imply a direct temporal relationship or reaction. That is, these phrases (e.g., "when … …") do not mean that an action occurs in response to or during the occurrence of the action, but rather merely that the action will occur if a condition is met, but do not require a particular 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. The term "some" refers to one or more unless specifically stated otherwise. 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 may include multiple a, multiple B, or multiple C. Specifically, a combination such as "at least one of A, B or C", "A, B, or one or more of 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", may be a alone, B alone, C, A and B, A and C, B and C, or a and B and C, wherein any such combination may comprise one or more members or several members of A, B or C. A collection should be interpreted as a collection of elements, where the number of elements is one or more. Thus, for a collection of X, X will include one or more elements. If 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 indirectly between the first device and the second device through a set of devices. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Furthermore, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words "module," mechanism, "" element, "" device, "and the like may not be a substitute for the word" unit. Thus, no claim element is to be construed as a functional module element unless the element is explicitly recited using the phrase "means for … …".

As used herein, the phrase "based on" should not be construed as a reference to a closed information set, one or more conditions, one or more factors, etc. In other words, unless explicitly stated otherwise, the phrase "based on a" (where "a" may be information, conditions, factors, etc.) should be construed as "based at least on a".

The following aspects are merely illustrative and may be combined with other aspects or teachings described herein, but are not limited thereto.

Aspect 1 is a method for wireless communication at a UE, comprising: starting a modified timer based on a number of failed attempts associated with a voice service for the EPS network and based on a configuration parameter, wherein the modified timer is modified based on a default timer; attempting to obtain the voice service based on one or more access technologies other than EPS; and attaching to the EPS network or performing tracking area update in the EPS network to obtain voice service based on the modified timer.

Aspect 2 is the method of aspect 1, further comprising: the S1 mode enable is maintained while the modified timer is started.

Aspect 3 is the method of aspect 2, further comprising: de-prioritizing or not re-attempting to attach to the EPS network or performing the tracking area update in the EPS network before a stop or expiration of the modified timer; and stopping the modified timer when one of the following occurs: reselecting to the EPS network, switching to the EPS network, or redirecting to the EPS network by a network by the UE.

Aspect 4 is the method of aspect 3, further comprising: one or more cells associated with the EPS network are de-prioritized for cell reselection prior to the expiration or the expiration of the modified timer.

Aspect 5 is the method of any one of aspects 1 to 4, wherein the UE is a voice-centric UE.

Aspect 6 is the method of any one of aspects 1 to 5, wherein each of the number of failed attempts associated with a voice service for the EPS network includes failing to attach to the EPS network or performing a tracking area update in the EPS network to obtain a voice service.

Aspect 7 is the method of aspect 1, further comprising: disabling S1 mode upon starting the modified timer; and skipping reattempting to attach to the EPS network or performing the tracking area update in the EPS network before the modified timer expires or expires.

Aspect 8 is the method of aspect 7, wherein the modified timer is associated with a shorter duration than the default timer, and the at least one processor is further configured to: the S1 mode is re-enabled upon the expiration of the modified timer.

Aspect 9 is the method of aspect 8, further comprising: the default timer is started based on a failure to attach to the EPS network or to perform the tracking area update in the EPS network after the modified timer has been used a threshold number of times after a latest power-on of the UE.

Aspect 10 is the method of any one of aspects 8 and 9, wherein the shorter duration associated with the modified timer is preconfigured.

Aspect 11 is the method of any one of aspects 8 and 9, further comprising: an indication of the shorter duration associated with the modified timer is received from a base station.

Aspect 12 is the method of any one of aspects 8 to 11, wherein the indication of the shorter duration associated with the modified timer is stored in an ME or USIM of the UE.

Aspect 13 is the method of aspect 7, wherein, in response to failing to obtain voice services based on the EPS, the method further comprises: transmitting an indication to the 5GS base station that the S1 mode is disabled; receiving an indication from the 5GS base station that packet switched voice services are not supported; disabling the N1 mode upon receiving the indication that packet switched voice services are not supported; and re-enabling the N1 mode when circuit switched voice service is not available in an access technology other than 5 GS.

Aspect 14 is the method of aspect 13, further comprising: re-enabling the S1 mode when the N1 mode is re-enabled; and stopping the modified timer when the S1 mode is re-enabled.

Aspect 15 is the method of aspect 13, further comprising: re-enabling the S1 mode when the N1 mode is re-enabled; and stopping the modified timer when one of the following occurs: reselecting to the EPS network by the UE or switching or redirecting to the EPS network by a network.

Aspect 16 is the method of aspect 7, further comprising: monitoring a quality of a cell associated with the EPS network; stopping the modified timer when the quality of the cell is above a predetermined threshold for a predetermined period of time; and re-enabling the S1 mode based on the stopping of the modified timer.

Aspect 17 is a method for wireless communication at a network node, comprising: transmitting an indication of a duration associated with a modified timer to a voice-centric UE, the duration associated with the modified timer being shorter than a duration associated with a default timer; initially failing to provide voice services to the voice-centric UE via an 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 retrying attachment to the EPS network or performing tracking area updates in the EPS network and voice service is not available on a 5GS or circuit switched system.

Aspect 18 is an apparatus for wireless communication, comprising at least one processor coupled to a memory, and based at least in part on information stored in the memory, the at least one processor configured to implement the method of any one of aspects 1-17.

Aspect 19 may be combined with aspect 18 and further comprising a transceiver coupled to the at least one processor.

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

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

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

Claims (30)

1. An apparatus for wireless communication at a User Equipment (UE), comprising:

a memory; and

at least one processor coupled to the memory and configured to, based at least in part on information stored in the memory:

starting a modified timer based on a number of failed attempts associated with a voice service for an Evolved Packet System (EPS) network and based on a configuration parameter, wherein the modified timer is modified based on a default timer;

attempting to obtain the voice service based on one or more access technologies other than EPS; and

Attaching to the EPS network or performing tracking area updates in the EPS network based on the modified timer to obtain the voice service.

2. The apparatus of claim 1, the at least one processor further configured to:

the S1 mode enable is maintained while the modified timer is started.

3. The apparatus of claim 2, the at least one processor further configured to:

de-prioritizing or not re-attempting to attach to the EPS network or performing the tracking area update in the EPS network before a stop or expiration of the modified timer; and

stopping the modified timer when one of the following occurs:

reselecting to the EPS network by the UE,

switching to the EPS network, or

Is redirected by a network to the EPS network.

4. The apparatus of claim 3, the at least one processor further configured to:

one or more cells associated with the EPS network are de-prioritized for cell reselection prior to the expiration or the expiration of the modified timer.

5. The apparatus of claim 1, wherein the UE is a voice-centric UE.

6. The apparatus of claim 1, wherein each of the number of failed attempts associated with the voice service for the EPS network comprises failing to attach to the EPS network or performing the tracking area update in the EPS network to obtain the voice service.

7. The apparatus of claim 1, the at least one processor further configured to:

disabling S1 mode upon starting the modified timer; and

the reattempting to attach to the EPS network or performing the tracking area update in the EPS network is skipped before the modified timer expires or expires.

8. The apparatus of claim 7, wherein the modified timer is associated with a shorter duration than the default timer, and the at least one processor is further configured to:

the S1 mode is re-enabled upon the expiration of the modified timer.

9. The apparatus of claim 8, the at least one processor further configured to:

the default timer is started based on a failure to attach to the EPS network or to perform the tracking area update in the EPS network after the modified timer has been used a threshold number of times after a latest power-on of the UE.

10. The apparatus of claim 8, wherein the shorter duration associated with the modified timer is preconfigured.

11. The apparatus of claim 8, the at least one processor further configured to:

an indication of the shorter duration associated with the modified timer is received from a base station.

12. The apparatus of claim 8, wherein the indication of the shorter duration associated with the modified timer is stored in a Mobile Equipment (ME) or a Universal Subscriber Identity Module (USIM) of the UE.

13. The apparatus of claim 7, wherein, in response to failing to obtain the voice service based on the EPS, the at least one processor is further configured to:

transmitting a first indication to a fifth generation (5G) system (5 GS) base station that the S1 mode is disabled;

receiving a second indication from the 5GS base station that packet switched voice services are not supported;

disabling N1 mode upon receiving the second indication that the packet-switched voice service is not supported; and

the N1 mode is re-enabled when circuit switched voice service is not available in an access technology other than 5 GS.

14. The apparatus of claim 13, the at least one processor further configured to:

re-enabling the S1 mode when re-enabling the N1 mode; and

the modified timer is stopped when the S1 mode is re-enabled.

15. The apparatus of claim 13, the at least one processor further configured to:

re-enabling the S1 mode when the N1 mode is re-enabled; and

stopping the modified timer when one of the following occurs: reselecting to the EPS network by the UE or switching or redirecting to the EPS network by a network.

16. The apparatus of claim 7, the at least one processor further configured to:

monitoring a quality of a cell associated with the EPS network;

stopping the modified timer when the quality of the cell is above a predetermined threshold for a predetermined period of time; and

the S1 mode is re-enabled based on the stopping of the modified timer.

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

18. A method of wireless communication at a User Equipment (UE), comprising:

starting a modified timer based on a number of failed attempts associated with a voice service for an Evolved Packet System (EPS) network and based on a configuration parameter, wherein the modified timer is modified based on a default timer;

attempting to obtain the voice service based on one or more access technologies other than EPS; and

attaching to the EPS network or performing tracking area updates in the EPS network based on the modified timer to obtain the voice service.

19. The method of claim 18, further comprising:

the S1 mode enable is maintained while the modified timer is started.

20. The method of claim 19, further comprising:

de-prioritizing or not re-attempting to attach to the EPS network or performing the tracking area update in the EPS network before a stop or expiration of the modified timer; and

stopping the modified timer when one of the following occurs:

reselecting to the EPS network by the UE,

switching to the EPS network, or

Is redirected by a network to the EPS network.

21. The method of claim 20, further comprising:

one or more cells associated with the EPS network are de-prioritized for cell reselection prior to the expiration or the expiration of the modified timer.

22. The method of claim 18, wherein the UE is a voice-centric UE.

23. The method of claim 18, wherein each of the number of failed attempts associated with the voice service for the EPS network comprises failing to attach to the EPS network or performing the tracking area update in the EPS network to obtain the voice service.

24. The method of claim 18, further comprising:

disabling S1 mode upon starting the modified timer; and

the reattempting to attach to the EPS network or performing the tracking area update in the EPS network is skipped before the modified timer expires or expires.

25. The method of claim 24, wherein the modified timer is associated with a shorter duration than the default timer, and the method further comprises:

The S1 mode is re-enabled upon the expiration of the modified timer.

26. The method of claim 25, further comprising:

the default timer is started based on a failure to attach to the EPS network or to perform the tracking area update in the EPS network after the modified timer has been used a threshold number of times after a latest power-on of the UE.

27. The method of claim 25, wherein the shorter duration associated with the modified timer is preconfigured.

28. An apparatus for wireless communication at a network node, comprising:

a memory; and

at least one processor coupled to the memory and configured to, based at least in part on information stored in the memory:

transmitting an indication of a duration associated with a modified timer to a voice-centric User Equipment (UE), the duration associated with the modified timer being shorter than a duration associated with a default timer;

initially failing to provide voice services to the voice-centric UE via an Evolved Packet System (EPS) network; and

After the initial failure to provide the voice service to the voice-centric UE via the EPS network, providing the 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 reattempting to attach to the EPS network or performing tracking area updates in the EPS network, and the voice service is not available on a fifth generation (5G) system (5 GS) or circuit switched system.

29. The apparatus of claim 28, further comprising a transceiver coupled to the memory and the at least one processor.

30. A method of wireless communication at a network node, comprising:

transmitting an indication of a duration associated with a modified timer to a voice-centric User Equipment (UE), the duration associated with the modified timer being shorter than a duration associated with a default timer;

initially failing to provide voice services to the voice-centric UE via an Evolved Packet System (EPS) network; and

after the initial failure to provide the voice service to the voice-centric UE via the EPS network, providing the 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 reattempting to attach to the EPS network or performing tracking area updates in the EPS network, and the voice service is not available on a fifth generation (5G) system (5 GS) or circuit switched system.