WO2021142820A1

WO2021142820A1 - Timer based nr 5g service search

Info

Publication number: WO2021142820A1
Application number: PCT/CN2020/072945
Authority: WO
Inventors: Hao Zhang; Jian Li; Tianya LIN; Xiuqiu XIA; Hong Wei; Quanling ZHANG
Original assignee: Qualcomm Incorporated
Priority date: 2020-01-19
Filing date: 2020-01-19
Publication date: 2021-07-22

Abstract

A UE is configured to determine that the UE has lost service to a first RAT. The UE is configured to connect to a second RAT different than the first RAT. The UE is configured to start a timer to trigger a search for cells associated with the first RAT upon determining that the UE has lost service to the first RAT or upon connecting to the second RAT. The UE is configured to search for available cells associated with the first RAT upon expiration of the timer. The UE is configured to switch service from the second RAT to the first RAT upon a successful search for available cells associated with the first RAT.

Description

TIMER BASED NR 5G SERVICE SEARCH

BACKGROUND Technical Field

The present disclosure relates generally to communication systems, and more particularly, to a timer based search for service in a New Radio (NR) 5G when service has been lost from a Radio Access Technology (RAT) in a standalone mode (SA) .

Introduction

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

These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is 5G NR. 5G NR is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with Internet of Things (IoT) ) , and other requirements. 5G NR includes services associated with enhanced mobile broadband (eMBB) , massive machine type communications (mMTC) , and ultra-reliable low latency communications (URLLC) . Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. There exists a need for further improvements in 5G NR technology. These improvements may also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies.

SUMMARY

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, and is intended to neither 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.

Upon loss of service from a first RAT such as 5G NR, a User Equipment (UE) may switch service to a second RAT such as 4G LTE. The UE may continue service with the second RAT and may not search for availability of service from the first RAT. In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a device at the UE. The device may be a processor, a modem and/or a network chip at the UE or the UE itself. The device is configured to determine that the UE has lost service to a first RAT. The device connects to a second RAT different than the first RAT. In addition, the device starts a timer to trigger a search for cells associated with the first RAT upon determining that the UE has lost service to the first RAT or upon connecting to the second RAT. The device searches for available cells associated with the first RAT upon expiration of the timer. The device switches service from the second RAT to the first RAT upon a successful search for available cells associated with the first RAT.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and 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, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network.

FIGs. 2A, 2B, 2C, and 2D are diagrams illustrating examples of a first 5G/NR frame, DL channels within a 5G/NR subframe, a second 5G/NR frame, and UL channels within a 5G/NR subframe, respectively.

FIG. 3 is a diagram illustrating an example of a base station and user equipment (UE) in an access network.

FIG. 4 is a call flow diagram illustrating switching service at a UE from a second RAT to a first RAT based on a timer.

FIG. 5 is a call flow diagram illustrating maintaining service with a second RAT upon an unsuccessful search for available cells associated with the first RAT.

FIG. 6 is a diagram illustrating processes at a UE for switching service from a second RAT to a first RAT based on a timer.

FIG. 7 is a diagram illustrating message exchanges between a UE and a Radio Resource Control (RRC) of a first RAT and between the UE and a RRC of a second RAT for switching service from the second RAT to the first RAT based on a timer.

FIG. 8 is a diagram illustrating the mobility of a UE from a cell associated with a first RAT to a cell associated with a second RAT and vice-versa.

FIG. 9 is a flowchart of a method of switching service from a second RAT to a first RAT based on a timer.

DETAILED DESCRIPTION

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

Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, 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.

By way of 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, systems on a chip (SoC) , baseband processors, field programmable gate arrays (FPGAs) , programmable logic devices (PLDs) , state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more example embodiments, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM) , a read-only memory (ROM) , an electrically erasable programmable ROM (EEPROM) , optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the aforementioned 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.

FIG. 1 is a diagram illustrating an example of a wireless communications system and an access network 100. The wireless communications system (also referred to as a wireless wide area network (WWAN) ) includes base stations 102, UEs 104, an Evolved Packet Core (EPC) 160, and another core network 190 (e.g., a 5G Core (5GC) ) . The base stations 102 may include macrocells (high power cellular base station) and/or small cells (low power cellular base station) . The macrocells include base stations. The small cells include femtocells, picocells, and microcells.

The base stations 102 configured for 4G LTE (collectively referred to as Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN) ) may interface with the EPC 160 through first backhaul links 132 (e.g., S1 interface) . The base stations 102 configured for 5G NR (collectively referred to as Next Generation RAN (NG-RAN) ) may interface with core network 190 through second backhaul links 184. In addition to other functions, the base stations 102 may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity) , inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS) , subscriber and equipment trace, 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 core network 190) with each other over third backhaul links 134 (e.g., X2 interface) . The third backhaul links 134 may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 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 the coverage area 110 of one or more macro base stations 102. A network that includes both small cell and macrocells may be known as a heterogeneous network. A heterogeneous network may also include Home Evolved Node Bs (eNBs) (HeNBs) , which may provide service to a restricted group known as a closed subscriber group (CSG) . The communication links 120 between the base stations 102 and the UEs 104 may include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a base station 102 and/or downlink (DL) (also referred to as forward link) transmissions from a base station 102 to a UE 104. The communication links 120 may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links may be through one or more carriers. The base stations 102 /UEs 104 may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100, 400, etc. MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or fewer carriers may be allocated for DL than for UL) . The component carriers may include a primary component carrier and one or more secondary component carriers. A primary component carrier may be referred to as a primary cell (PCell) and a secondary component carrier may be referred to as a secondary cell (SCell) .

Certain UEs 104 may communicate with each other using 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) . D2D communication may be through a variety of wireless D2D communications systems, such as for example, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, LTE, or NR.

The wireless communications system may further include a Wi-Fi access point (AP) 150 in communication with Wi-Fi stations (STAs) 152 via communication links 154 in a 5 GHz unlicensed frequency spectrum. When communicating in an unlicensed frequency spectrum, the STAs 152 /AP 150 may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available.

The small cell 102' may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell 102' may employ NR and use the same 5 GHz unlicensed frequency spectrum as used by the Wi-Fi AP 150. The small cell 102', employing NR in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network.

A base station 102, whether a small cell 102' or a large cell (e.g., macro base station) , may include and/or be referred to as an eNB, gNodeB (gNB) , or another type of base station. Some base stations, such as gNB 180 may operate in a traditional sub 6 GHz spectrum, in millimeter wave (mmW) frequencies, and/or near mmW frequencies in communication with the UE 104. When the gNB 180 operates in mmW or near mmW frequencies, the gNB 180 may be referred to as an mmW base station. Extremely high frequency (EHF) is part of the RF in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in the band may be referred to as a millimeter wave. Near mmW may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Communications using the mmW /near mmW radio frequency (RF) band (e.g., 3 GHz –300 GHz) has extremely high path loss and a short range. The mmW base station 180 may utilize beamforming 182 with the UE 104 to compensate for the extremely high path loss and short range. The base station 180 and the UE 104 may each include a plurality of antennas, such as antenna elements, antenna panels, and/or antenna arrays to facilitate the beamforming.

The base station 180 may transmit a beamformed signal to the UE 104 in one or more transmit directions 182'. The UE 104 may receive the beamformed signal from the base station 180 in one or more receive directions 182” . The UE 104 may also transmit a beamformed signal to the base station 180 in one or more transmit directions. The base station 180 may receive the beamformed signal from the UE 104 in one or more receive directions. The base station 180 /UE 104 may perform beam training to determine the best receive and transmit directions for each of the base station 180 /UE 104. The transmit and receive directions for the base station 180 may or may not be the same. The transmit and receive directions for the UE 104 may or may not be the same.

The EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be in communication with a Home Subscriber Server (HSS) 174. The MME 162 is the control node that processes the signaling between the UEs 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet protocol (IP) packets are transferred 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 the BM-SC 170 are connected to the IP Services 176. The IP Services 176 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS) , a PS Streaming Service, and/or other IP services. The BM-SC 170 may provide functions for MBMS user service provisioning and delivery. The BM-SC 170 may serve as an entry point for content provider MBMS transmission, 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 the 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 eMBMS related charging information.

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

The base station may include and/or be referred to as a gNB, Node B, eNB, an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS) , an extended service set (ESS) , a transmit reception point (TRP) , or some other suitable terminology. The base station 102 provides an access point to the EPC 160 or core network 190 for a UE 104. Examples of UEs 104 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA) , a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player) , a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor/actuator, a display, or any other similar functioning device. Some of the UEs 104 may be referred to as IoT devices (e.g., parking meter, gas pump, toaster, vehicles, heart monitor, etc. ) . The UE 104 may also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology.

Referring again to FIG. 1, in certain aspects, the UE 104 may be configured to switch service from a second RAT to a first RAT based on a timer as discussed below in relation to FIGs. 4, 5, 6, 7, 8 and 9 (198) . Although the following description may be focused on switching service from a second RAT to a first RAT where the first RAT is 5G NR, the concepts described herein may be applicable to RATs such as LTE, LTE-A, CDMA, GSM, being the first RAT.

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 duplexed (FDD) in which for a particular set of subcarriers (carrier system bandwidth) , subframes within the set of subcarriers are dedicated for either DL or UL, or may be time division duplexed (TDD) in which for a particular set of subcarriers (carrier system bandwidth) , subframes within the set of subcarriers are dedicated for both DL and UL. In the examples provided by FIGs. 2A, 2C, the 5G/NR frame structure is assumed to be TDD, with subframe 4 being configured with slot format 28 (with mostly DL) , where D is DL, U is UL, and X is flexible for use between DL/UL, and subframe 3 being configured with slot format 34 (with mostly UL) . While

subframes

3, 4 are shown with slot formats 34, 28, respectively, any particular subframe may be configured with any of the various available slot formats 0-61. Slot formats 0, 1 are all DL, UL, respectively. Other slot formats 2-61 include a mix of DL, UL, and flexible symbols. UEs are configured with the slot format (dynamically through DL control information (DCI) , or semi-statically/statically through radio resource control (RRC) signaling) through a received slot format indicator (SFI) . Note that the description infra applies also to a 5G/NR frame structure that is TDD.

Other wireless communication technologies may have a different frame structure 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 time slots. Subframes may also include mini-slots, which may include 7, 4, or 2 symbols. Each slot may include 7 or 14 symbols, depending on the slot configuration. For slot configuration 0, each slot may include 14 symbols, and for slot configuration 1, each slot may include 7 symbols. The symbols on DL may be cyclic prefix (CP) OFDM (CP-OFDM) symbols. The symbols on 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 a single stream transmission) . The number of slots within a subframe is based on the slot configuration and the numerology. For slot configuration 0, different numerologies μ 0 to 5 allow for 1, 2, 4, 8, 16, and 32 slots, respectively, per subframe. For slot configuration 1, different numerologies 0 to 2 allow for 2, 4, and 8 slots, respectively, per subframe. Accordingly, for slot configuration 0 and numerology μ, there are 14 symbols/slot and 2 ^μ slots/subframe. The subcarrier spacing and symbol length/duration are a function of the numerology. The subcarrier spacing may be equal to 2 ^μ*15 kHz, where μ is the numerology 0 to 5. As such, the numerology μ=0 has a subcarrier spacing of 15 kHz and the numerology μ=5 has a subcarrier spacing of 480 kHz. The symbol length/duration is inversely related to the subcarrier spacing. FIGs. 2A-2D provide an example of slot configuration 0 with 14 symbols per slot and numerology μ=2 with 4 slots per subframe. The slot duration is 0.25 ms, the subcarrier spacing is 60 kHz, and the symbol duration is approximately 16.67 μs.

A resource grid may be used to represent the frame structure. Each time slot includes a resource block (RB) (also referred to as physical RBs (PRBs) ) that extends 12 consecutive subcarriers. The resource grid is divided into multiple resource elements (REs) . The number of bits carried by each RE depends on the modulation scheme.

As illustrated in FIG. 2A, some of the REs carry reference (pilot) signals (RS) for the UE. The RS may include demodulation RS (DM-RS) (indicated as R _x for one particular configuration, where 100x is the port number, but other DM-RS configurations are possible) and channel state information reference signals (CSI-RS) for channel estimation at the UE. The RS may also include beam measurement RS (BRS) , beam refinement RS (BRRS) , and phase tracking RS (PT-RS) .

FIG. 2B illustrates 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) , each CCE including nine RE groups (REGs) , each REG including four consecutive REs in an OFDM symbol. A primary synchronization signal (PSS) may be within symbol 2 of particular subframes of a frame. The PSS is used by a UE 104 to determine subframe/symbol timing and a physical layer identity. A secondary synchronization signal (SSS) may be within symbol 4 of particular subframes of a frame. The SSS is used by a UE to determine a physical layer cell identity group number and radio frame timing. Based on the physical layer identity and the physical layer cell identity group number, the UE can determine a physical cell identifier (PCI) . Based on the PCI, the UE can determine the locations of the aforementioned DM-RS. The physical broadcast channel (PBCH) , which carries a master information block (MIB) , may be logically grouped with the PSS and SSS to form a synchronization signal (SS) /PBCH block. The MIB provides a 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 not transmitted through the PBCH such as system information blocks (SIBs) , and paging messages.

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

FIG. 2D illustrates an example 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 scheduling requests, a channel quality indicator (CQI) , a precoding matrix indicator (PMI) , a rank indicator (RI) , and hybrid automatic repeat request (HARQ) ACK/NACK feedback. The PUSCH carries data, and may additionally be used to carry a buffer status report (BSR) , a power headroom report (PHR) , and/or UCI.

FIG. 3 is a block diagram of a base station 310 in communication with a UE 350 in an access network. In the DL, IP packets from the EPC 160 may be provided to a controller/processor 375. The 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. The controller/processor 375 provides RRC layer functionality associated with broadcasting of system information (e.g., MIB, SIBs) , RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release) , inter radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression /decompression, security (ciphering, deciphering, integrity protection, integrity verification) , and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs) , error correction through ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs) , re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality 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 through HARQ, priority handling, and logical channel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370 implement layer 1 functionality associated with various signal processing functions. Layer 1, which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The TX processor 316 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK) , quadrature phase-shift keying (QPSK) , M-phase-shift keying (M-PSK) , M-quadrature amplitude modulation (M-QAM) ) . The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 374 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 350. Each spatial stream may then be provided to a different antenna 320 via a separate transmitter 318TX. Each transmitter 318TX may modulate an 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. The TX processor 368 and the RX processor 356 implement layer 1 functionality associated with various signal processing functions. The RX processor 356 may perform spatial processing on the information to recover any spatial streams destined for the UE 350. If multiple spatial streams are destined for the UE 350, they may be combined by the RX processor 356 into a single OFDM symbol stream. The RX processor 356 then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT) . The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station 310. These soft decisions may be based on channel estimates computed by the 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 the controller/processor 359, which implements layer 3 and layer 2 functionality.

The controller/processor 359 can be associated with a memory 360 that stores program codes and data. The memory 360 may be referred to as a computer-readable medium. In the UL, the controller/processor 359 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC 160. 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 the DL transmission by the base station 310, the controller/processor 359 provides RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression /decompression, and security (ciphering, deciphering, integrity protection, integrity verification) ; RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality 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 through HARQ, priority handling, and logical channel prioritization.

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

The UL transmission is processed at the base station 310 in a manner similar to that described in connection with the receiver function at the UE 350. Each receiver 318RX receives a signal through its respective antenna 320. Each receiver 318RX recovers information modulated onto an RF carrier and provides the information to a RX processor 370.

The controller/processor 375 can be associated with a memory 376 that stores program codes and data. The memory 376 may be referred to as a computer-readable medium. In the UL, the controller/processor 375 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE 350. IP packets from the controller/processor 375 may be provided to the EPC 160. The controller/processor 375 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

At least one of the TX processor 368, the RX processor 356, and the controller/processor 359 may be configured to perform aspects in connection with 198 of FIG. 1.

5G NR as a RAT may have coverage limitations during deployment. For example, there may be several areas that may not be covered by 5G NR RAT and a UE operating in a standalone (SA) mode may lose service from 5G NR RAT, and may switch to one of the other RATs (e.g., 2G, 3G, 4G, etc. ) . However, upon return to an area with 5G NR RAT coverage, the UE may not automatically search for availability of service from a 5G NR RAT. For example, the RAT from which the UE is receiving service may lack 5G NR neighbor cell information, and therefore the UE may not be aware of the availability 5G NR RAT.

FIG. 4 is a call flow diagram 400 illustrating switching service at a UE from a second RAT to a first RAT based on a timer. As illustrated in Fig. 4, at 412, a UE 402 may lose service from a first RAT 408. The first RAT 408 may be 5G NR RAT and may include a base station 404 and a base station 406. For example, the UE 402 may detect a loss of service from the base station 404. Upon loss of service from the first RAT 408, the UE 402 may establish a connection with a second RAT 410 at 414. The second RAT 410 may be 4G LTE, 3G Wideband Code Division Multiple Access (W-CDMA) , 3G Time Division Synchronous Code Division Multiple Access (TD-SCDMA) , 2G Global System for Mobile Communications (GSM) , etc. At 416, the UE 402 starts a timer with a timer length 418 to trigger a search for cells associated with the first RAT 408. The timer may be a modem timer, an application processor (AP) timer, or some other timer at the UE 402. The timer length 418 may be based on one or more parameters, such as whether the UE 402 is in a mobile state or a stationary state, power consumption at the UE 402, etc. In one configuration, the UE 402 may determine the speed of the UE 402 and based on the speed the UE 402 may determine the timer length 418. For example, when the UE 402 is moving at a speed above a first threshold, the timer length 418 may be a few seconds. Further, when the UE 402 is moving at a speed below a second threshold, the timer length 418 may be up to a few minutes. In one configuration, the timer length 418 may be configurable by a user. In another configuration, the timer length 418 may be set to a default value, for example 10 minutes. Further, in one configuration the UE 402 may start the timer after the loss of service from the first RAT 408 at 412, and before establishing the connection with the second RAT 410 at 414.

Upon expiration of the timer, i.e., after waiting for a duration equivalent to the timer length 418, the UE 402 may search 420 for available cells associated with the first RAT 408. When the search 420 for available cells associated with the first RAT 408 is successful, the UE 402 may deactivate connection with the second RAT 410 at 422. At 424, the UE 402 activates a connection with the first RAT 408. The UE 402 may activate connection with the first RAT 408 by establishing a connection with the base station 404 (for example, when the UE 402 moves back to an area which is covered by the base station 404) . Alternately, when the UE 402 moves to an area where the service on the first RAT 408 is provided by the base station 406, the UE 402 may activate connection with the first RAT 408 by establishing a connection with the base station 406 at 426.

FIG. 5 is a call flow diagram 500 illustrating maintaining service with a second RAT upon an unsuccessful search for available cells associated with the first RAT. As illustrated in Fig. 5, at 512, a UE 502 may lose service from a first RAT 508. For example, the UE 502 may detect a loss of service from the base station 504. The first RAT 508 may be 5G NR RAT and may include a base station 504 and a base station 506. Upon loss of service from the first RAT 508, the UE 502 may establish connection with a second RAT 510 at 514. The second RAT 510 may be 4G LTE, 3G W-CDMA, 3G TD-SCDMA, 2G GSM, etc. At 516, the UE 502 starts a timer with a timer length 518 to trigger search for cells associated with the first RAT 508. In one configuration the UE 502 may start the timer after the loss of service from the first RAT 508 at 512, and before establishing the connection with the second RAT 510 at 514.

Upon expiration of the timer, i.e., after waiting for a duration equivalent to the timer length 518, the UE 502 may search for available cells associated with the first RAT 508. When the search for available cells associated with the first RAT 508 is unsuccessful, the UE 502 may maintain connection with the second RAT 510 at 522. At 524, the UE 502 may restart the timer to trigger search for cells associated with the first RAT 508. In one configuration, the timer length 518 may be modified upon an unsuccessful search. For example, in a second iteration of the timer after an unsuccessful search, the timer length 518 may be increased to be greater than the first iteration of the timer. Similarly, in a third iteration of the timer, the timer length 518 may be greater than the second iteration, and so on.

FIG. 6 is a diagram 600 illustrating processes at a UE for switching service from a second RAT to a first RAT based on a timer. As illustrated in Fig. 6, a UE 602 is in a powered on state and may operate in SA mode. A first RAT callbox 604 at the UE 602 may be responsible for enabling or disabling service with a first RAT (e.g., 5G NR RAT) . A second RAT callbox 606 at the UE 602 may be responsible for enabling or disabling service with a second RAT (e.g., 4G (LTE) , 3G W-CDMA, 3G TD-SCDMA, 2G GSM, etc. At 603, the first RAT callbox 604 is in an enabled mode to register service with the first RAT. At 605, the second RAT callbox 606 is in an enabled mode to register service with the second RAT. At 608, the UE 602 sends a registration request to the first RAT callbox 604 to register with the first RAT. One or more components in the UE 602 may send the registration request to the first RAT callbox 604 or the second RAT callbox 606, however the description refers to the UE 602 performing such operations. At 605, the first RAT callbox 604 sends an acceptance of registration on the first RAT to the UE 602. At 612, the UE 602 operates with the service from the first RAT. At 614, the first RAT callbox 604 switches to a disabled mode. For example, the first RAT callbox 604 determines that service from the first RAT is no longer available and upon such determination, switches operation to a disabled mode.

At 616, the UE 602 sends a registration request to the second RAT callbox 606. For example, when the first RAT callbox 604 disables service availability from the first RAT, the UE 602 sends a registration request to the second RAT callbox 606 to register with the second RAT. At 618, the second RAT callbox 606 sends an acceptance of registration to the UE 602. At 620, the UE 602 deactivates service on the first RAT and activates service on the second RAT upon receiving the acceptance of registration with the second RAT. Further, at 622 the UE 602 starts a timer for search of cells associated with the first RAT. In one configuration, the UE 602 may start the timer after deactivating service on the first RAT and before activating service on the second RAT. The timer started by the UE 602 may be similar to the timer with timer length 418/518 as described above with reference to FIGs. 4 and 5. At 624, the UE 602 detects that the timer has expired. Upon expiration of the timer, the first RAT callbox 604 may switch to enable mode. In one configuration, upon expiration of the timer, one or more components of the UE 602 may search for the availability of cells associated with the first RAT, and upon availability of compatible cells (e.g., the cells with which the UE 602 is capable of registering successfully) , the first RAT callbox 604 may switch to enable mode.

At 628, the UE 602 sends a registration request to the first RAT callbox 604 to register with the first RAT. At 630, the first RAT callbox 604 sends an acceptance of registration on the first RAT to the UE 602. At 632, the UE 602 operates with the service from the first RAT.

FIG. 7 is a diagram 700 illustrating message exchanges between a UE and Radio Resource Control (RRC) of a first RAT and between the UE and RRC of a second RAT for switching service from the second RAT to the first RAT based on a timer. As illustrated in FIG. 7, a UE includes components associated with a timer 702 (which may be similar to the timer as described above with reference to FIGs. 4-6) , an NAS 706, a first RAT RRC 708 and a second RAT RRC 710. At 712, the second RAT RRC sends a message to the NAS 706 to activate service from the second RAT. At 714, the NAS 706 may send a message to the first RAT RRC 708 about deactivation of service from the first RAT. At 716, the NAS 706 determines to keep the service on the second RAT. At 718, the NAS 706 sends a message to the timer 702 to start the timer for search of cells associated with the first RAT. The timer 702 may have a predefined timer length (for example, the timer length 418/518 as described above with reference to FIGs. 4-6) . In one configuration, the NAS 706 may send a message to the timer 702 to start the timer for search of cells associated with the first RAT before 716. Upon expiration of the timer length, at 720, the timer 702 updates the NAS 706 that the timer 702 has expired.

At 722, the NAS 706 sends a PLMN search request for the first RAT to the second RAT RRC 710. For example, the NAS 706 may request the second RAT RRC 710 to identify any cells associated with the first RAT that may be available. The request may include information about one or more RF bands (for example, the bands supported by the UE) and one or more PLMN identifiers of the UE for which cells associated with the first RAT are to be searched. At 724, the second RAT RRC 710 performs a search for the cells associated with the first RAT based on the request at 722. At 726, the second RAT RRC 710 determines whether the discovered cells associated with the first RAT 708 are not in an FPLMN (Forbidden Public Land Mobile Network) list or an FTAC (Forbidden Tracking Area Code) list of the UE. When at least one cell associated with the first RAT is discovered which is not in the FPLMN list or the FTAC list, at 728 the second RAT RRC 710 sends a PLMN list of cells associated with the first RAT to the NAS 706. The PLMN list may include one or more identifiers of the network and/or identifiers of the cells associated with the first RAT.

When no cells associated with the first RAT are discovered, or the discovered cells associated with the first RAT are associated with a PLMN present in either the FPLMN list or the FTAC list, the second RAT RRC 710 sends a message to the NAS 706 to keep service on the second RAT at 742. At 730, the NAS 706 determines whether the UE can get service from one of the PLMNs in the PLMN list received from the second RAT RRC 710 at 728. On determining that the UE cannot get service from a first RAT PLMN, the NAS 706 keeps service on the second RAT at 742. On determining that the UE can get service on a first RAT PLMN, at 732 the NAS 706 sends a request to deactivate service from the second RAT to the second RAT RRC 710. At 734, the UE receives a deactivation acknowledgement from the second RAT RRC 710 for deactivation of the service from the second RAT. At 736, the NAS 706 sends a request for service from the first RAT to the first RAT RRC 708. At 740, the first RAT RRC 708 sends a confirmation regarding the service from the first RAT to the NAS 706.

FIG. 8 is a diagram illustrating the mobility of a UE from a cell associated with a first RAT to a cell associated with a second RAT and vice-versa. FIG. 8 illustrates two scenarios of a UE 802 moving from the cell associated with the first RAT to the cell associated with the second RAT and vice-versa. The first RAT may be a 5G NR RAT and the second RAT may be a RAT such as 4G LTE, 3G W-CDMA, 3G TD-SCDMA, 2G GSM, etc.

A first scenario 800 includes the UE 802, a cell 804 associated with the first RAT and a cell 806 associated with the second RAT. In the first scenario 800, the UE 802 moves from an area of the cell 804 to an area of the cell 806 (as indicated by the solid arrow in the first scenario 800) . On moving from the area of the cell 804 to the area of the cell 806, the UE 802 may lose service from the first RAT, and upon determining that the UE 802 has lost service from the first RAT, the UE 802 may start a timer (similar to the timer as described above with reference to FIGs. 4-7) for a search of cells associated with the first RAT. Upon expiration of the timer, the UE 802 may perform the search for cells associated with the first RAT. For example, in a state of mobility, the UE 802 may travel from an area of the cell 806 to an area of the cell 804 (as indicated by a dashed line in the first scenario 800) . When the UE 802 has moved to the area of the cell 804 and the timer expires, the UE 802 may perform the search for cells associated with the first RAT (as described above with reference to FIGs. 4-7) and may resume service from the cell 804 associated with the first RAT.

A second scenario 801 includes the UE 802, the cell 804 associated with the first RAT, another cell 805 associated with the first RAT, and the cell 806 associated with the second RAT. In the second scenario 801, the UE 802 moves from an area of the cell 804 to an area of the cell 806 (as indicated by the solid arrow in the second scenario 801) . On moving from the area of the cell 804 to the area of the cell 806, the UE 802 may lose service from the first RAT, and upon determining that the UE 802 has lost service from the first RAT, the UE 802 may start a timer (similar to the timer as described above with reference to FIGs. 4-7) for the search of cells associated with the first RAT. Upon expiration of the timer, the UE 802 may perform the search of cells associated with the first RAT. For example, in a state of mobility, the UE 802 may travel from an area of the cell 806 to an area of the cell 805 (as indicated by a dashed line in the second scenario 801) . When the UE 802 has moved to the area of the cell 805, and the timer expires, the UE 802 may perform a search for cells associated with the first RAT (as described above with reference to FIGs. 4-7) and may resume service from the cell 805 associated with the first RAT.

FIG. 9 is a flowchart of a method 900 of switching service from a second RAT to a first RAT based on a timer. The method may be performed by a device at a UE (for example the UE 402/502/602/702/802 as described above with reference to FIGs. 4-8) . The device may be a timer related switch for RAT in the UE (for example the timer related switch for RAT 198 as described above with reference to FIG. 1) , any other component of the UE or the UE itself. The device is herein referred to as the UE. At 902, the UE determines that the UE has lost service to a first RAT. For example, the UE may detect a loss of service from a cell associated with the first RAT, or a no-signal indication from a cell associated with the first RAT. In one example, referring to FIGs. 4, 5, the

UE

402, 502 may determine at 412, 512 that the

UE

402, 502 has lost service to a

first RAT

408, 508. After determining that the UE has lost service to the first RAT, the UE may perform the operations at 904 or 922.

In one configuration, at 904, the UE connects to a second RAT different than the first RAT. The second RAT may be a RAT such as 4G LTE, 3G W-CDMA, 3G TD-SCDMA, 2G GSM, etc. The UE may connect to the second RAT through one or more components of the UE (e.g., the second RAT callbox 606 as described above with reference to FIG. 6) . After the UE connects to the second RAT, the UE may perform operations at 906 or 922 (the UE may perform operations at 922 if the UE had not performed operations at 922 after 902) .

At, 922, the UE deactivates service with the first RAT upon determining that the UE has lost service to the first RAT (after 902) or upon connecting to the second RAT (after 904) . For example, the UE may deactivate service with the first RAT through one or more components (e.g., the first RAT callbox 604, as described above with reference to FIG. 6) .

At 906, the UE starts a timer to trigger a search for cells associated with the first RAT upon connecting to the second RAT. For example, the UE may start a timer with a timer length 418/518 (as described above with reference to FIGs. 4 and 5) . As described above in FIGs. 4 and 5, the length of the timer may be based on mobility of the UE, power consumption at the UE, etc. Upon expiration of the timer, the UE performs operations at 908.

At 908, the UE searches for available cells associated with the first RAT upon expiration of the timer. For example, the UE may search for available cells associated with the first RAT by performing one or more operations as described at 724 (FIG. 7) .

At 910, the UE determines whether a search for available cells associated with the first RAT was successful. If the search was successful, the UE switches service from the second RAT to the first RAT at 912. For example, the search may be successful when the UE finds cells in at least one PLMN of the UE that are associated with the first RAT and are unassociated with an FPLMN list and an FTAC list (as described at 726, 728 and 730, FIG. 7) . If the search was unsuccessful, the UE maintains service with the second RAT at 918. For example, the search may be unsuccessful when the UE finds cells in at least one PLMN of the UE that are associated with the first RAT, and are also associated with an FPLMN list or an FTAC list, or upon an inability to find cells in at least one PLMN of the UE that are associated with the first RAT.

At 912, the UE switches service from the second RAT to the first RAT upon a successful search for available cells associated with the first RAT. For example, the UE may switch service from the second RAT to the first RAT by performing operations as described above at 732, 734, 736 and 740 (FIG. 7) . In one configuration, the UE may perform operations at 914 and 916 to switch service from the second RAT to the first RAT.

At 914, the UE deactivates service with the second RAT. For example, the UE may deactivate service with the second RAT by performing operations described at 732 and 734 (FIG. 7) .

At 916, the UE activates service with the first RAT through one cell of the searched available cells. For example, the UE may activate service with the first RAT by performing operations as described above at 736 and 740 (FIG. 7) .

At 918, the UE maintains service with the second RAT upon an unsuccessful search for available cells associated with the first RAT. For example, the UE maintains service with the second RAT by performing operations as described above at 742 (FIG. 7) .

At 920, the UE re-starts the timer. In one configuration, the UE may reset the timer to re-start the timer with a similar timer length as in the previous iteration of the timer. In another configuration, the UE may re-start the timer with a different timer length. For example, the timer length in a successive iteration of the timer may be increased from the timer length in the previous iteration of the timer (as described above in FIG. 5) . After re-starting the timer, the UE may wait for the expiration of the timer and perform operations at 908 (i.e., search for available cells associated with the first RAT upon expiration of the timer) .

The steps of the method described by the in the flowchart in FIG. 9 are not limited to necessarily being performed in the order described above. For example, in one configuration, the UE may start the timer to trigger the search for cells associated with the first RAT at 706 upon determining that the UE has lost service to the first RAT at 902 and before connecting to the second RAT at 904.

Referring again to FIGs. 4-8 as discussed above, a UE 402 when operating in SA mode may lose service from a first RAT (e.g., 5G NR) , and the UE 402 may switch service to a second RAT (e.g., 4G LTE, etc. ) . However, upon return to an area with the first RAT coverage, the UE 402 may not automatically search for availability of service from the first RAT. For example, the UE 402 when receiving service from the second RAT may not be able to get neighbor cell information of the cells associated with the first RAT, and therefore the UE 402 may not be aware of the availability of the first RAT. As a result, the UE 402 may continue service from the second RAT even when service from the first RAT may be available. In order to improve the discovery of the first RAT and switch service to the first RAT when it becomes available, the UE 402 may utilize the timer having the timer length 418. Upon the expiration of the timer, the UE 402 may perform search for cells associated with the first RAT, and upon finding a suitable cell associated with the first RAT, the UE 402 may switch service from the second RAT to the first RAT without delay.

It is understood that the specific order or hierarchy of blocks in the processes /flowcharts disclosed is an illustration of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes /flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be 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 intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module, ” “mechanism, ” “element, ” “device, ” and the like may not be a substitute for the word “means. ” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

Claims

A method of wireless communication of a device at a user equipment (UE) , comprising:

determining that the UE has lost service to a first radio access technology (RAT) ;

connecting to a second RAT different than the first RAT;

starting a timer to trigger a search for cells associated with the first RAT upon determining that the UE has lost service to the first RAT or upon connecting to the second RAT;

searching for available cells associated with the first RAT upon expiration of the timer; and

switching service from the second RAT to the first RAT upon a successful search for available cells associated with the first RAT.
The method of claim 1, further comprising deactivating service with the first RAT upon determining that the UE has lost service to the first RAT or upon connecting to the second RAT.
The method of claim 1, wherein the switching service from the second RAT to the first RAT comprises:

deactivating service with the second RAT; and

activating service with the first RAT through one cell of the searched available cells.
The method of claim 1, wherein the search is successful upon finding cells in at least one public land mobile network (PLMN) of the UE that are associated with the first RAT, and are unassociated with a forbidden PLMN (FPLMN) and a forbidden tracking area code (FTAC) list.
The method of claim 1, further comprising:

determining a mobility of the UE; and

setting a time length of the timer based at least on the determined mobility.
The method of claim 1, further comprising:

maintaining service with the second RAT upon an unsuccessful search for available cells associated with the first RAT; and

re-starting the timer.
The method of claim 6, wherein the search is unsuccessful upon finding cells in at least one PLMN of the UE that are associated with the first RAT, and are also associated with a forbidden PLMN (FPLMN) or a forbidden tracking area code (FTAC) list, or upon an inability to find cells in at least one public land mobile network (PLMN) of the UE that are associated with the first RAT.
The method of claim 1, wherein the first RAT is a 5G New Radio (5G NR) , and the second RAT is one of 4G Long Term Evolution (LTE) , 3G Wideband Code Division Multiple Access (W-CDMA) , 3G Time Division Synchronous Code Division Multiple Access (TD-SCDMA) , or 2G Global System for Mobile Communications (GSM) .
An apparatus for wireless communication, the apparatus being a user equipment (UE) , comprising:

means for determining that the UE has lost service to a first radio access technology (RAT) ;

means for connecting to a second RAT different than the first RAT;

means for starting a timer to trigger a search for cells associated with the first RAT upon determining that the UE has lost service to the first RAT or upon connecting to the second RAT;

means for searching for available cells associated with the first RAT upon expiration of the timer; and

means for switching service from the second RAT to the first RAT upon a successful search for available cells associated with the first RAT.
The apparatus of claim 9, further comprising means for deactivating service with the first RAT upon determining that the UE has lost service to the first RAT or upon connecting to the second RAT.
The apparatus of claim 9, wherein the means for switching service from the second RAT to the first RAT is configured to:

deactivate service with the second RAT; and

activate service with the first RAT through one cell of the searched available cells.
The apparatus of claim 9, wherein the search is successful upon finding cells in at least one public land mobile network (PLMN) of the UE that are associated with the first RAT, and are unassociated with a forbidden PLMN (FPLMN) and a forbidden tracking area code (FTAC) list.
The apparatus of claim 9, further comprising:

means for determining a mobility of the UE; and

means for setting a time length of the timer based at least on the determined mobility.
The apparatus of claim 9, further comprising:

means for maintaining service with the second RAT upon an unsuccessful search for available cells associated with the first RAT; and

means for re-starting the timer.
The apparatus of claim 14, wherein the search is unsuccessful upon finding cells in at least one PLMN of the UE that are associated with the first RAT, and are also associated with a forbidden PLMN (FPLMN) or a forbidden tracking area code (FTAC) list, or upon an inability to find cells in at least one public land mobile network (PLMN) of the UE that are associated with the first RAT.
The apparatus of claim 9, wherein the first RAT is a 5G New Radio (5G NR) , and the second RAT is one of 4G Long Term Evolution (LTE) , 3G Wideband Code Division Multiple Access (W-CDMA) , 3G Time Division Synchronous Code Division Multiple Access (TD-SCDMA) , or 2G Global System for Mobile Communications (GSM) .
An apparatus for wireless communication, the apparatus being a user equipment (UE) , comprising:

a memory; and

at least one processor coupled to the memory and configured to:

determine that the UE has lost service to a first radio access technology (RAT) ;

connect to a second RAT different than the first RAT;

start a timer to trigger a search for cells associated with the first RAT upon determining that the UE has lost service to the first RAT or upon connecting to the second RAT ;

search for available cells associated with the first RAT upon expiration of the timer; and

switch service from the second RAT to the first RAT upon a successful search for available cells associated with the first RAT.
The apparatus of claim 17, wherein the at least one processor is further configured to deactivate service with the first RAT upon determining that the UE has lost service to the first RAT or upon connecting to the second RAT.
The apparatus of claim 17, wherein to switch service from the second RAT to the first RAT, the at least one processor is configured to:

deactivate service with the second RAT; and

activate service with the first RAT through one cell of the searched available cells.
The apparatus of claim 17, wherein the search is successful upon finding cells in at least one public land mobile network (PLMN) of the UE that are associated with the first RAT, and are unassociated with a forbidden PLMN (FPLMN) and a forbidden tracking area code (FTAC) list.
The apparatus of claim 17, wherein the at least one processor is further configured to:

determine a mobility of the UE; and

set a time length of the timer based at least on the determined mobility.
The apparatus of claim 17, wherein the at least one processor is further configured to:

maintain service with the second RAT upon an unsuccessful search for available cells associated with the first RAT; and

re-start the timer.
The apparatus of claim 22, wherein the search is unsuccessful upon finding cells in at least one PLMN of the UE that are associated with the first RAT, and are also associated with a forbidden PLMN (FPLMN) or a forbidden tracking area code (FTAC) list, or upon an inability to find cells in at least one public land mobile network (PLMN) of the UE that are associated with the first RAT.
The apparatus of claim 17, wherein the first RAT is a 5G New Radio (5G NR) , and the second RAT is one of 4G Long Term Evolution (LTE) , 3G Wideband Code Division Multiple Access (W-CDMA) , 3G Time Division Synchronous Code Division Multiple Access (TD-SCDMA) , or 2G Global System for Mobile Communications (GSM) .
A computer-readable medium storing computer executable code, the code when executed by a processor at a user equipment (UE) causes the processor to:

determine that the UE has lost service to a first radio access technology (RAT) ;

connect to a second RAT different than the first RAT;

starting a timer to trigger a search for cells associated with the first RAT upon determining that the UE has lost service to the first RAT or upon connecting to the second RAT;

search for available cells associated with the first RAT upon expiration of the timer; and

switch service from the second RAT to the first RAT upon a successful search for available cells associated with the first RAT.