WO2022056718A1

WO2022056718A1 - Priority-based radio access technology reselection handling

Info

Publication number: WO2022056718A1
Application number: PCT/CN2020/115560
Authority: WO
Inventors: Jinglin Zhang; Haojun WANG; Jiangang JIAO; Hao Zhang; Yi Liu; Xiaomeng Lu; Zhenqing CUI
Original assignee: Qualcomm Incorporated
Priority date: 2020-09-16
Filing date: 2020-09-16
Publication date: 2022-03-24

Abstract

Systems and methods for wireless communication in a network with multiple radio access technologies (RATs) are provided. In one aspect, a method includes performing an inter-RAT scan for a first RAT associated with a first priority. The method further includes selecting a first cell associated with the first RAT, and reselecting to a second cell associated with a second RAT, wherein the second RAT is associated with a second priority higher than the first priority. The method further includes refraining, based on the reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority.

Description

PRIORITY-BASED RADIO ACCESS TECHNOLOGY RESELECTION HANDLING

Jinglin ZHANG, Haojun WANG, Jiangang JIAO, Hao ZHANG, Yi LIU, Xiaomeng LU, Zhenqing CUI

TECHNICAL FIELD

This application relates to wireless communication systems, and more particularly to improving user equipment (UE) mobility performance and coverage in a wireless communication network.

INTRODUCTION

Wireless communications systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power) . A wireless multiple-access communications system may include a number of base stations (BSs) , each simultaneously supporting communications for multiple communication devices, which may be otherwise known as user equipment (UE) .

To meet the growing demands for expanded mobile broadband connectivity, wireless communication technologies are advancing from the LTE technology to a next generation new radio (NR) technology. For example, NR is designed to provide a lower latency, a higher bandwidth and throughput, and a higher reliability than LTE. NR is designed to operate over a wide array of spectrum bands, for example, from low-frequency bands below about 1 gigahertz (GHz) and mid-frequency bands from about 1 GHz to about 6 GHz, to high-frequency bands such as millimeter wave (mmWave) bands. NR is also designed to operate across different spectrum types, from licensed spectrum to unlicensed and shared spectrum. Spectrum sharing enables operators to opportunistically aggregate spectrums to dynamically support high-bandwidth services. Spectrum sharing can extend the benefit of NR technologies to operating entities that may not have access to a licensed spectrum.

Maintaining mobility is important in a wireless communication network, where a UE may travel from one coverage area or cell to another coverage area or cell. In general, a UE may be in an idle state or a connected state with respect to a network. An idle mode UE is not attached to any BS and there are no network and/or radio resources allocated to the UE. The UE’s location is known to the network, for example, within a group of cells referred to as a tracking area. While a UE is not attached to any BS, the UE is required to select a suitable cell to camp on. The procedure of a UE selecting and camping on a cell is referred to as cell selection. While camping on a cell, the UE continues to monitor other cells, which may include cells associated with other radio access technologies (RATs) . In this regard, a UE may support multiple RATs, where each RAT is associated with a different priority. The priority of a RAT may be based on the connection capabilities and properties, such as uplink/downlink throughputs. The UE may periodically initiate an inter-RAT scan or search to detect cells associated with different RATs for camping. Formally speaking, the procedure of evaluating and reselecting another cell while the UE is currently camped on a serving cell is referred to as cell reselection. However, it is understood that the procedure formally referred to as cell reselection may be referred to informally as cell selection for ease of reference. Hence, when it is understood from the context that the UE is currently camped on a serving cell and is evaluating other cells for camping, terms like “UE selects” or “selecting” or “selection” of another cell may be used. As such, in such situations, cell selection and cell reselection may be used interchangeably.

BRIEF SUMMARY OF SOME EXAMPLES

The following summarizes some aspects of the present disclosure to provide a basic understanding of the discussed technology. This summary is not an extensive overview of all contemplated features of the disclosure, and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in summary form as a prelude to the more detailed description that is presented later.

For example, in an aspect of the disclosure, a method of wireless communication includes a user equipment (UE) initiating an inter-radio access technology (inter-RAT) scan, which may involve successively searching for cells associated with RATs of different priorities. The selection or reselection of a RAT may be based on the priority of the RAT being searched. If the UE detects a first RAT having a first priority (e.g., NR) while searching for a second RAT of a different second priority (e.g., LTE) , the UE can reselect to the RAT of the first priority, and cause the inter-RAT scan to terminate so that the UE stays camped on the first RAT.

According to one aspect of the present disclosure, a method of wireless communication performed by a user equipment (UE) includes: performing an inter-radio access technology (RAT) scan for a first RAT associated with a first priority; selecting a first cell associated with the first RAT; reselecting to a second cell associated with a second RAT, wherein the second RAT is associated with a second priority higher than the first priority; and refraining, based on the reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority.

According to another aspect of the present disclosure, a UE includes a processor configured to:perform an inter-RAT scan for a first RAT associated with a first priority; select a first cell associated with the first RAT; reselect to a second cell associated with a second RAT, wherein the second RAT is associated with a second priority higher than the first priority; and refrain, based on the reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority.

According to another aspect of the present disclosure, non-transitory computer-readable medium having program code recorded thereon, the program code comprising: code for causing a UE to perform an inter-RAT scan for a first RAT associated with a first priority; code for causing the UE to select a first cell associated with the first RAT; code for causing the UE to reselect to a second cell associated with a second RAT, wherein the second RAT is associated with a second priority higher than the first priority; and code for causing the UE to refrain, based on the reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority.

According to another aspect of the present disclosure, a UE includes: means for performing an inter-RAT scan for a first RAT associated with a first priority; means for selecting a first cell associated with the first RAT; means for reselecting to a second cell associated with a second RAT, wherein the second RAT is associated with a second priority higher than the first priority; and means for refraining, based on the reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority.

Other aspects, features, and embodiments of the present invention will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary aspects of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain aspects and figures below, all aspects of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more aspects may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various aspects of the invention discussed herein. In similar fashion, while exemplary aspects may be discussed below as device, system, or method aspects it should be understood that such exemplary aspects can be implemented in various devices, systems, and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication network according to some aspects of the present disclosure.

FIG. 2 illustrates a wireless communication network according to some aspects of the present disclosure.

FIG. 3 is a signaling diagram illustrating a cell reselection method according to aspects of the present disclosure.

FIG. 4 is a block diagram of a user equipment (UE) according to some aspects of the present disclosure.

FIG. 5 is a block diagram of an exemplary base station (BS) according to some aspects of the present disclosure.

FIG. 6 is a flow diagram of an inter-radio access technology (inter-RAT) cell reselection method according to some aspects of the present disclosure.

FIG. 7 is a signaling diagram of a priority-based inter-RAT cell reselection method according to some aspects of the present disclosure.

FIG. 8 is a flow diagram of a priority-based inter-RAT cell reselection method according to some aspects of the present disclosure.

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 the 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.

This disclosure relates generally to wireless communications systems, also referred to as wireless communications networks. In various aspects, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, global system for mobile communications (GSM) networks, 5 ^th Generation (5G) or new radio (NR) networks, as well as other communications networks. As described herein, the terms “networks” and “systems” may be used interchangeably.

An OFDMA network may implement a radio technology such as evolved UTRA (E-UTRA) , Institute of Electrical and Electronics Engineers (IEEE) 802.11, IEEE 802.16, IEEE 802.20, flash-OFDM and the like. UTRA, E-UTRA, and GSM are part of universal mobile telecommunication system (UMTS) . In particular, long term evolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents provided from an organization named “3rd Generation Partnership Project” (3GPP) , and cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2) . These various radio technologies and standards are known or are being developed. For example, the 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations that aims to define a globally applicable third generation (3G) mobile phone specification. 3GPP long term evolution (LTE) is a 3GPP project which was aimed at improving the universal mobile telecommunications system (UMTS) mobile phone standard. The 3GPP may define specifications for the next generation of mobile networks, mobile systems, and mobile devices. The present disclosure is concerned with the evolution of wireless technologies from LTE, 4G, 5G, NR, and beyond with shared access to wireless spectrum between networks using a collection of new and different radio access technologies or radio air interfaces.

In particular, 5G networks contemplate diverse deployments, diverse spectrum, and diverse services and devices that may be implemented using an OFDM-based unified, air interface. In order to achieve these goals, further enhancements to LTE and LTE-A are considered in addition to development of the new radio technology for 5G NR networks. The 5G NR will be capable of scaling to provide coverage (1) to a massive Internet of things (IoTs) with an ultra-high density (e.g., ～1M nodes/km ²) , ultra-low complexity (e.g., ～10s of bits/sec) , ultra-low energy (e.g., ～10+years of battery life) , and deep coverage with the capability to reach challenging locations; (2) including mission-critical control with strong security to safeguard sensitive personal, financial, or classified information, ultra-high reliability (e.g., ～99.9999%reliability) , ultra-low latency (e.g., ～ 1 ms) , and users with wide ranges of mobility or lack thereof; and (3) with enhanced mobile broadband including extreme high capacity (e.g., ～ 10 Tbps/km ²) , extreme data rates (e.g., multi-Gbps rate, 100+ Mbps user experienced rates) , and deep awareness with advanced discovery and optimizations.

The 5G NR may be implemented to use optimized OFDM-based waveforms with scalable numerology and transmission time interval (TTI) ; having a common, flexible framework to efficiently multiplex services and features with a dynamic, low-latency time division duplex (TDD) /frequency division duplex (FDD) design; and with advanced wireless technologies, such as massive multiple input, multiple output (MIMO) , robust millimeter wave (mmWave) transmissions, advanced channel coding, and device-centric mobility. Scalability of the numerology in 5G NR, with scaling of subcarrier spacing, may efficiently address operating diverse services across diverse spectrum and diverse deployments. For example, in various outdoor and macro coverage deployments of less than 3GHz FDD/TDD implementations, subcarrier spacing may occur with 15 kHz, for example over 1, 5, 10, 20 MHz, and the like BW. For other various outdoor and small cell coverage deployments of TDD greater than 3 GHz, subcarrier spacing may occur with 30 kHz over 80/100 MHz BW. For other various indoor wideband implementations, using a TDD over the unlicensed portion of the 5 GHz band, the subcarrier spacing may occur with 60 kHz over a 160 MHz BW. Finally, for various deployments transmitting with mmWave components at a TDD of 28 GHz, subcarrier spacing may occur with 120 kHz over a 500MHz BW.

The scalable numerology of the 5G NR facilitates scalable TTI for diverse latency and quality of service (QoS) requirements. For example, shorter TTI may be used for low latency and high reliability, while longer TTI may be used for higher spectral efficiency. The efficient multiplexing of long and short TTIs to allow transmissions to start on symbol boundaries. 5G NR also contemplates a self-contained integrated subframe design with uplink/downlink scheduling information, data, and acknowledgement in the same subframe. The self-contained integrated subframe supports communications in unlicensed or contention-based shared spectrum, adaptive uplink/downlink that may be flexibly configured on a per-cell basis to dynamically switch between uplink and downlink to meet the current traffic needs.

Various other aspects and features of the disclosure are further described below. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative and not limiting. Based on the teachings herein one of an ordinary level of skill in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. For example, a method may be implemented as part of a system, device, apparatus, and/or as instructions stored on a computer readable medium for execution on a processor or computer. Furthermore, an aspect may comprise at least one element of a claim.

In a wireless communication network, a BS serving a cell may broadcast system information, for example, in the form of master information block (MIB) and system information blocks (SIBs) to facilitate communications with UEs in the cell. The system information may include neighboring cell information, for example, indicating one or more intra-frequency neighboring cells, one or more inter-frequency neighboring cells, and/or one or more inter-frequency neighboring cells to the serving cell. Each cell may operate over a carrier frequency. In some instances, multiple cells may operate over the same carrier frequency. The system information may indicate cell reselection priorities for the carrier frequency of the serving cell and carrier frequencies of the neighboring cells. Thus, each neighboring cell may be associated with a cell reselection priority based on the operating carrier frequency of the cell. The system information may further indicate cell reselection criteria for each candidate cell to guide a UE in selecting a suitable cell for camping. The cell reselection criteria may include a signal threshold and/or a cell reselection timeout value. In some examples, the network or the BS may configure the UE to reselect to a high priority layer (e.g., a neighboring cell of a higher priority than the serving cell) .

Many UEs support multiple different radio access technologies (RATs) , such as 5G NR, LTE, wideband code division multiplexing access (W-CDMA) , and GSM. In many instances, more than one RAT may be available to a UE for selection and camping. A UE may periodically initiate an inter-RAT scan to identify and select a suitable cell or RAT for camping. The inter-RAT scan may be priority-based such that a higher priority RAT (e.g., 5G NR) are selected when multiple RATs of different priorities are detected. The inter-RAT scan may be triggered or initiated by a higher layer of the UE, such as the non-access stratum (NAS) layer, while some or all of the procedures of the inter-RAT scan may be performed by one or more lower layers of the UE, such as an access stratum (AS) layer, a radio resource control (RRC) layer, a media access control (MAC) layer, a physical (PHY) layer, or any other suitable layer. The inter-RAT scan procedure may involve a series of conditional scanning protocols whereby a first RAT (e.g., NR) having a first priority is searched, and if not detected, a second RAT (e.g., LTE) having a lower second priority is searched, and so on. If the RAT being scanned or searched is not detected, the higher layer (e.g., NAS layer) triggers a scan of the next-highest priority RAT until a suitable RAT is detected, or until a timeout condition is met. When a suitable RAT is detected, the UE camps on the detected RAT, and signals the successful camping to the higher layer, which may in-turn terminate the inter-RAT scan.

In some instances, the UE may be configured with a certain RAT priority order. For instance, the UE may perform cell search in the order of NR, LTE, W-CDMA, and GSM or any other suitable RAT scanning order. In some instances, the UE may detect and reselect to a higher priority RAT while searching/scanning for a lower priority RAT. For example, while scanning for an LTE cell, the UE may detect an NR cell. Because NR has a higher priority, the lower layer of the UE reselects to the NR cell. However, because the inter-RAT scan for the LTE cell did not result in camping on the LTE cell, the higher layer (e.g., NAS layer) determines that the UE failed to detect or camp on the LTE cell, and triggers a scan of the next-highest priority RAT (e.g., W-CDMA) , which causes the UE to deactivate the NR connection and possibly camp on the lower-priority RAT with reduced connection capabilities (e.g., UL/DL throughputs) , such as W-CDMA or GSM. These undesirable cell reselections to lower priority RATs can cause unnecessary power consumption of the UE and degrade user experience.

The present disclosure describes mechanisms for a UE to prevent unnecessary cell reselection to lower priority RATs by terminating or preventing further inter-RAT scans when a higher priority RAT is reselected. For example, a UE may initiate or trigger an inter-RAT scan, which includes searching for cells associated with different RATs, and camping on a cell detected during the RAT scan. The RAT scan may be initiated in a higher layer (e.g., NAS layer) , and performed in a lower layer (e.g., RRC layer) . During the RAT scan, the UE may search for a first RAT of a first priority, but detect a second RAT of a different second (e.g., higher) priority. For example, while performing a search for an LTE cell, the UE may detect an NR cell. The UE camps on the NR cell, which has a higher priority and improved connection capabilities. In response, the UE refrains from triggering or initiating an inter-RAT scan for a next-highest priority RAT (e.g., W-CDMA) , allowing the UE to remain camped on the NR cell. The UE may cause the inter-RAT scan to terminate by indicating to the higher layer (e.g., NAS layer) that the UE has camped on the NR cell. Accordingly, this mechanism prevents or reduces unnecessary cell reselections to lower priority RATs, thus increasing the chance that the UE camps on a higher priority RAT with improved connection capabilities. This provides enhanced mobility support and improved user experience.

FIG. 1 illustrates a wireless communication network 100 according to some aspects of the present disclosure. The network 100 may be a 5G network. The network 100 includes a number of base stations (BSs) 105 (individually labeled as 105a, 105b, 105c, 105d, 105e, and 105f) and other network entities. A BS 105 may be a station that communicates with UEs 115 and may also be referred to as an evolved node B (eNB) , a next generation eNB (gNB) , an access point, and the like. Each BS 105 may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of a BS 105 and/or a BS subsystem serving the coverage area, depending on the context in which the term is used.

A BS 105 may provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a pico cell, would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a femto cell, would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG) , UEs for users in the home, and the like) . A BS for a macro cell may be referred to as a macro BS. A BS for a small cell may be referred to as a small cell BS, a pico BS, a femto BS or a home BS. In the example shown in FIG. 1, the

BSs

105d and 105e may be regular macro BSs, while the BSs 105a-105c may be macro BSs enabled with one of the following configurations: three dimension (3D) , full dimension (FD) , or massive MIMO. The BSs 105a-105c may take advantage of their higher dimension MIMO capabilities to exploit 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. The BS 105f may be a small cell BS which may be a home node or portable access point. A BS 105 may support one or multiple (e.g., two, three, four, and the like) cells.

The network 100 may support synchronous or asynchronous operation. For synchronous operation, the BSs may have similar frame timing, and transmissions from different BSs may be approximately aligned in time. For asynchronous operation, the BSs may have different frame timing, and transmissions from different BSs may not be aligned in time.

The UEs 115 are dispersed throughout the wireless network 100, and each UE 115 may be stationary or mobile. A UE 115 may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE 115 may be a cellular phone, a personal digital assistant (PDA) , a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. In one aspect, a UE 115 may be a device that includes a Universal Integrated Circuit Card (UICC) . In another aspect, a UE may be a device that does not include a UICC. In some aspects, the UEs 115 that do not include UICCs may also be referred to as IoT devices or internet of everything (IoE) devices. The UEs 115a-115d are examples of mobile smart phone-type devices accessing network 100. A UE 115 may also be a machine specifically configured for connected communication, including machine type communication (MTC) , enhanced MTC (eMTC) , narrowband IoT (NB-IoT) and the like. The UEs 115e-115k are examples of various machines configured for communication that access the network 100. A UE 115 may be able to communicate with any type of the BSs, whether macro BS, small cell, or the like. In FIG. 1, a lightning bolt (e.g., communication links) indicates wireless transmissions between a UE 115 and a serving BS 105, which is a BS designated to serve the UE 115 on the downlink and/or uplink, or desired transmission between BSs, and backhaul transmissions between BSs.

In operation, the BSs 105a-105c may serve the

UEs

115a and 115b using 3D beamforming and coordinated spatial techniques, such as coordinated multipoint (CoMP) or multi-connectivity. The macro BS 105d may perform backhaul communications with the BSs 105a-105c, as well as small cell, the BS 105f. The macro BS 105d may also transmits multicast services which are subscribed to and received by the

UEs

115c and 115d. Such multicast services may include mobile television or stream video, or may include other services for providing community information, such as weather emergencies or alerts, such as Amber alerts or gray alerts.

The BSs 105 may also communicate with a core network. The core network may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. At least some of the BSs 105 (e.g., which may be an example of a gNB or an access node controller (ANC) ) may interface with the core network through backhaul links (e.g., NG-C, NG-U, etc. ) and may perform radio configuration and scheduling for communication with the UEs 115. In various examples, the BSs 105 may communicate, either directly or indirectly (e.g., through core network) , with each other over backhaul links (e.g., X1, X2, etc. ) , which may be wired or wireless communication links.

The network 100 may also support mission critical communications with ultra-reliable and redundant links for mission critical devices, such as the UE 115e, which may be a drone. Redundant communication links with the UE 115e may include links from the

macro BSs

105d and 105e, as well as links from the small cell BS 105f. Other machine type devices, such as the UE 115f (e.g., a thermometer) , the UE 115g (e.g., smart meter) , and UE 115h (e.g., wearable device) may communicate through the network 100 either directly with BSs, such as the small cell BS 105f, and the macro BS 105e, or in multi-hop configurations by communicating with another user device which relays its information to the network, such as the UE 115f communicating temperature measurement information to the smart meter, the UE 115g, which is then reported to the network through the small cell BS 105f. The network 100 may also provide additional network efficiency through dynamic, low-latency TDD/FDD communications, such as in a vehicle-to-vehicle (V2V)

In some implementations, the network 100 utilizes OFDM-based waveforms for communications. An OFDM-based system may partition the system BW into multiple (K) orthogonal subcarriers, which are also commonly referred to as subcarriers, tones, bins, or the like. Each subcarrier may be modulated with data. In some instances, the subcarrier spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system BW. The system BW may also be partitioned into subbands. In other instances, the subcarrier spacing and/or the duration of TTIs may be scalable.

In some aspects, the BSs 105 can assign or schedule transmission resources (e.g., in the form of time-frequency resource blocks (RB) ) for downlink (DL) and uplink (UL) transmissions in the network 100. DL refers to the transmission direction from a BS 105 to a UE 115, whereas UL refers to the transmission direction from a UE 115 to a BS 105. The communication can be in the form of radio frames. A radio frame may be divided into a plurality of subframes, for example, about 10. Each subframe can be divided into slots, for example, about 2. Each slot may be further divided into mini-slots. In a frequency-division duplexing (FDD) mode, simultaneous UL and DL transmissions may occur in different frequency bands. For example, each subframe includes a UL subframe in a UL frequency band and a DL subframe in a DL frequency band. In a time-division duplexing (TDD) mode, UL and DL transmissions occur at different time periods using the same frequency band. For example, a subset of the subframes (e.g., DL subframes) in a radio frame may be used for DL transmissions and another subset of the subframes (e.g., UL subframes) in the radio frame may be used for UL transmissions.

The DL subframes and the UL subframes can be further divided into several regions. For example, each DL or UL subframe may have pre-defined regions for transmissions of reference signals, control information, and data. Reference signals are predetermined signals that facilitate the communications between the BSs 105 and the UEs 115. For example, a reference signal can have a particular pilot pattern or structure, where pilot tones may span across an operational BW or frequency band, each positioned at a pre-defined time and a pre-defined frequency. For example, a BS 105 may transmit cell specific reference signals (CRSs) and/or channel state information –reference signals (CSI-RSs) to enable a UE 115 to estimate a DL channel. Similarly, a UE 115 may transmit sounding reference signals (SRSs) to enable a BS 105 to estimate a UL channel. Control information may include resource assignments and protocol controls. Data may include protocol data and/or operational data. In some aspects, the BSs 105 and the UEs 115 may communicate using self-contained subframes. A self-contained subframe may include a portion for DL communication and a portion for UL communication. A self-contained subframe can be DL-centric or UL-centric. A DL-centric subframe may include a longer duration for DL communication than for UL communication. A UL-centric subframe may include a longer duration for UL communication than for UL communication.

In some aspects, the network 100 may be an NR network deployed over a licensed spectrum. The BSs 105 can transmit synchronization signals (e.g., including a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) ) in the network 100 to facilitate synchronization. The BSs 105 can broadcast system information associated with the network 100 (e.g., including a MIB, remaining minimum system information (RMSI) , and other system information (OSI) ) to facilitate initial network access. In some instances, the BSs 105 may broadcast the PSS, the SSS, and/or the MIB in the form of synchronization signal blocks (SSBs) over a physical broadcast channel (PBCH) and may broadcast the RMSI and/or the OSI over a physical downlink shared channel (PDSCH) .

In some aspects, a UE 115 attempting to access the network 100 may perform an initial cell search by detecting a PSS from a BS 105. The PSS may enable synchronization of period timing and may indicate a physical layer identity value. The UE 115 may then receive a SSS. The SSS may enable radio frame synchronization, and may provide a cell identity value, which may be combined with the physical layer identity value to identify the cell. The PSS and the SSS may be located in a central portion of a carrier or any suitable frequencies within the carrier.

After receiving the PSS and SSS, the UE 115 may receive a MIB. The MIB may include system information for initial network access and scheduling information for RMSI and/or OSI. After decoding the MIB, the UE 115 may receive RMSI and/or OSI. The RMSI and/or OSI may include radio resource control (RRC) information related to random access channel (RACH) procedures, paging, control resource set (CORESET) for physical downlink control channel (PDCCH) monitoring, physical uplink control channel (PUCCH) , physical uplink shared channel (PUSCH) , power control, and SRS.

After obtaining the MIB, the RMSI and/or the OSI, the UE 115 can perform a random access procedure to establish a connection with the BS 105. For the random access procedure, the UE 115 may transmit a random access preamble and the BS 105 may respond with a random access response. Upon receiving the random access response, the UE 115 may transmit a connection request to the BS 105 and the BS 105 may respond with a connection response (e.g., contention resolution message) .

After establishing a connection, the UE 115 and the BS 105 can enter a normal operation stage, where operational data may be exchanged. For example, the BS 105 may schedule the UE 115 for UL and/or DL communications. The BS 105 may transmit UL and/or DL scheduling grants to the UE 115 via a PDCCH. The BS 105 may transmit a DL communication signal to the UE 115 via a PDSCH according to a DL scheduling grant. The UE 115 may transmit a UL communication signal to the BS 105 via a PUSCH and/or PUCCH according to a UL scheduling grant. The connection may be referred to as an RRC connection. When the UE 115 is actively exchanging data with the BS 105, the UE 115 is in an RRC connected state.

In an example, after establishing a connection with the BS 105, the UE 115 may initiate an initial network attachment procedure with the network 100. The BS 105 may coordinate with various network entities or fifth generation core (5GC) entities, such as a access and mobility function (AMF) , a serving gateway (SGW) , and/or a packet data network gateway (PGW) , to complete the network attachment procedure. For example, the BS 105 may coordinate with the network entities in the 5GC to identify the UE, authenticate the UE, and/or authorize the UE for sending and/or receiving data in the network 100. In addition, the AMF may assign the UE with a group of tracking areas (TAs) . Once the network attach procedure succeeds, a context is established for the UE 115 in the AMF. After a successful attach to the network, the UE 115 can move around the current TA. For tracking area update (TAU) , the BS 105 may request the UE 115 to update the network 100 with the UE 115’s location periodically. Alternatively, the UE 115 may only report the UE 115’s location to the network 100 when entering a new TA. The TAU allows the network 100 to quickly locate the UE 115 and page the UE 115 upon receiving an incoming data packet or call for the UE 115.

When the UE 115 has no active data communication with the BS 105 after the network attachment, the UE 115 may return to RRC idle state by releasing the RRC connection. In some examples, the UE 115 may enter transition from an RRC connected state to an inactive state or RRC inactive state while maintaining an RRC connection with the BS 105. The or RRC inactive state allows the UE 115 to quickly return to the RRC connected state, which may be suitable for ultra-reliable low-latency communication (URLLC) type traffic. During an idle state or an inactive state, the UE 115 may perform channel measurements, perform cell reselection, update TA location, and/or monitor a paging channel. Mechanisms for performing mobility or cell reselection are described in greater detail herein.

FIGS. 2 and 3 illustrate a cell reselection scenario. FIG. 2 illustrates a wireless communication network 200 according to some aspects of the present disclosure. The network 200 may correspond to a portion of the network 100. FIG. 2 illustrates three BSs 205 (individually labeled as 205a, 205b, and 205c) , three cells 210 (individually labeled as 210a, 210b, and 210c) , and one UE 215 for purposes of simplicity of discussion, though it will be recognized that aspects of the present disclosure may scale to many more UEs 215 and/or BSs 205. The BSs 205 are similar to the BSs 105. The UE 215 is similar to the UEs 115.

The BS 205a provides service in a coverage area or cell 210a. The BS 205b provides service in a coverage area or cell 210b. The BS 205c provides service in a coverage area or cell 210c. In some examples, the

BSs

205a, 205b, and 205c serve the

cells

210a, 210b, and 210c, respectively, over different carrier frequencies. In some examples, the

BSs

205a, 205b, and 205c serve the

cells

210a, 210b, and 210c, respectively, over the same carrier frequency. In some examples, the

BSs

205a, 205b, and 205c serve the

cells

210a, 210b, and 210c, respectively, using different RATs. In some examples, the

BSs

205a, 205b, and 205c serve the

cells

210a, 210b, and 210c, respectively, using different RATs.

As an example, at time T1, the UE 215 is activated when the UE 215 is in the coverage of the cell 210a. The UE 215 performs an initial cell selection procedure and camp on the cell 210a based channel measurements and certain selection criteria. While camping on the cell 210a, the UE 215 may search for a better cell 210 to camp on, for example, due to mobility of the UE 215 (at time T2) as shown by the dashed arrow. Mechanisms for performing cell reselection or mobility are described in greater detail herein.

FIG. 3 is a signaling diagram illustrating a cell reselection method 300 according to aspects of the present disclosure. The method 300 is employed by the network 200. The method 300 is implemented by the UE 215 and the

BSs

205a, 205b, and 205c. For example, the UE 215 is camped on the cell 210a. Steps of the method 300 can be executed by computing devices (e.g., a processor, processing circuit, and/or other suitable component) of the

BS

205a, 205b, and 205c and the UE 215. As illustrated, the method 300 includes a number of enumerated steps, but aspects of the method 300 may include additional steps before, after, and in between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

At step 310, the BS 205a transmits system information A associated with BS 205a and/or the cell 210a. The BS 205a may transmit the system information A in a broadcast mode periodically to enable a UE desiring to join the network 200 to perform cell selection and initial network access. In addition, the system information A enables a UE camped on the cell 210a to perform channel measurements and/or cell reselection.

The system information A may include SSBs, PSS, SSS, PBCH signals, MIBs, and/or various types of system information blocks (SIBs) . For example, a SIB type one (SIB1) provides scheduling information and/or availability of other SIB types and/or information (e.g., public land mobile network (PLMN) information and/or cell barring information) that can guide a UE in performing cell selection. Some examples for the other SIB types may include a SIB type two (SIB2) , a SIB type three (SIB3) , a SIB type four (SIB4) , and a SIB type five (SIB5) . A SIB2 provides information for cell reselection that are common for inter-frequency cell reselection, intra-frequency cell reselection, and inter-radio access technology (RAT) cell reselection. For example, a SIB2 may include measurement thresholds for a UE to determine when to start searching for another cell, cell priorities for cell reselection, and/or various cell reselection criteria and/or thresholds. A SIB3 provides neighboring cell related information for intra-frequency cell reselection. For example, the SIB3 includes physical cell identifier (ID) information associated with an intra-frequency neighboring cell and/or corresponding criteria for cell reselection. A SIB4 provides neighboring cell related information for inter-frequency cell reselection. For example, the SIB4 includes physical cell ID, frequency carrier, frequency band, and/or beam information associated with an inter-frequency neighboring cell and/or corresponding criteria for cell reselection. A SIB5 provides neighboring cell related information for inter-RAT cell reselection. For example, the SIB5 includes RAT, frequency carrier, frequency band, and/or beam information associated with an inter-RAT neighboring cell and/or corresponding criteria for cell reselection. An example of an inter-RAT cell reselection may include a UE camped on an NR cell and reselecting to camp on an LTE cell or camping. Alternatively, a UE camped on an LTE cell may reselect to camp on an NR cell. In some instances, an inter-RAT cell reselection may be based on UE’s preferences.

In an example, when the cell 210b is an inter-frequency neighboring cell of the cell 210a, the SIB4 may include information to guide a UE 215 to reselect to the cell 210b. Alternatively, when the cell 210b is an intra-frequency neighboring cell of the cell 210a, the SIB3 may include information to guide a UE 215 to reselect to the cell 210b. Yet alternatively, when the cell 210b is an inter-RAT neighboring cell of the cell 210a, the SIB5 may include information to guide a UE 215 to reselect to the cell 210b.

At step 320, while camping on the cell 210a, the UE 215 performs channel measurements. For example, the UE 215 tunes to a channel frequency or carrier frequency of the camped cell 210a, receives a signal from the camped cell 210a on the channel frequency, and measures a receive signal quality or a received signal power of the signal (e.g., the periodic system information A) received from the BS 205a. The received signal may be a reference signal associated with the periodic system information A.

In an example, the received signal power may be a reference signal received power (RSRP) and the received signal quality may be a reference signal received quality (RSRQ) . A reference signal may refer to a predetermined signal with pilot symbols located at certain frequency subcarriers or resource elements. RSRP is an average signal power of a single reference signal resource element. RSRQ is defined as N× (RSRP/RSSI) , where RSSI is an average of total power measured across OFDM symbols that carry a reference signal and N is the number of resource blocks over which RSSI is measured, where each resource block includes a group of consecutive resource elements or subcarriers (e.g., about 12) .

At step 330, the UE 215 performs a cell reselection. The UE 215 may autonomously make the cell camping decision. However, the list of cells that are qualified for reselection, the thresholds for beginning a cell search, and/or the cell evaluation parameters and/or the criteria for selecting a candidate cell are configured by the BS 205a through the system information A (e.g., including SIB2, SIB3, SIB4, and/or SIB5) .

The UE 215 may start to search for another cell for camping when the measured received signal power and/or the received signal quality from the currently camped cell 210a falls below a certain threshold. In an example, SIB2 can include an S _IntraSearchP threshold, an S _IntraSearchQ threshold, an S _{NonIntraSearchP} threshold, and/or an S _{NonIntraSearchQ} threshold for beginning a cell search. When the received signal power of the currently camped cell falls below the S _IntraSearchP threshold and/or when the received signal quality of the currently camped cell falls below the S _IntraSearchQ threshold, the UE 215 may search and/or monitor for an intra-frequency candidate cell. Alternatively, when the received signal power of the currently camped cell falls below the S _{NonIntraSearchP} threshold and/or when the received signal quality of the currently camped cell falls below the S _{NonIntraSearchQ} threshold, the UE 215 may optionally search and/or monitor for an inter-frequency candidate cell with an equal or lower reselection priority than a priority of the serving frequency or an inter-RAT candidate cell with an equal or lower cell reselection priority than the serving frequency priority. In general, the UE 215 may search and/or monitor neighboring frequencies with a higher reselection priority than the serving frequency priority for cell reselection as described in greater detail herein.

During the search, the UE 215 may measure received signal power and/or received signal quality from the currently camped cell 210a and candidate cells (e.g., the

cells

210b and 210c) . For example, at step 340, the BS 205b transmits reference signals at certain intervals to facilitate signal measurements for cell selection and/or cell reselection. Similarly, at step 350, the BS 205c transmits reference signal at certain intervals to facilitate signal measurements for cell selection and/or cell reselection. The UE 215 may identify the candidate cells based on the signal measurements. For intra-frequency cell reselection, the UE 215 may identify an intra-frequency neighboring cell as a candidate when the intra-frequency neighboring cell has a receive signal strength better than the currently camped cell 210a by a certain amount (e.g., based on hysteresis and/or a ranking parameter) . When the receive signal strength (e.g., the received signal power and/or the received signal quality) of a candidate cell remains better than the currently camped cell 210a by the certain amount for a reference time duration, the UE 215 selects to camp on the candidate cell. In an example, SIB2 can include a t-Reselection (e.g., T _reselection) timer parameter specifying the reference time duration and a Q _hyst parameter for the determining that a candidate cell has a better receive signal strength than the currently camped cell. SIB3 can include Q _Offset parameters for ranking intra-frequency cells.

For inter-frequency cell reselection and/or inter-RAT cell reselection, the UE 215 may select to camp on a cell with a higher reselection priority than the currently camped cell. The UE 215 may identify an inter-frequency neighboring cell or an inter-RAT neighboring cell as a candidate when the inter-frequency neighboring cell or the inter-RAT neighboring cell has a receive signal strength satisfying a threshold. When the receive signal strength (e.g., the received signal power and/or the received signal quality) of a candidate cell satisfy a threshold for a reference time duration, the UE 215 selects to camp on the candidate cell. In an example, SIB4 can include a set of cell reselection parameters for each carrier frequency. The set of cell reselection parameters can include a Thresh _X, _LowQ threshold, a Thresh _X, LowP threshold, a Thresh _X, HighQ threshold, and/or a Thresh _X, HighP threshold for triggering a new inter-frequency cell to be reselected, a T _{ReselectionRAT} timer parameter for the reference time duration, and/or a cell reselection priority (e.g., an absolute priority) for a corresponding carrier frequency. In an example, SIB5 can include a set of cell reselection parameters for each RAT (e.g., NR or LTE) . The set of cell reselection parameters can include a Thresh _X, LowQ threshold, a Thresh _X, LowP threshold, a Thresh _X, HighQ threshold, and/or a Thresh _X, HighP threshold for triggering a new inter-RAT cell to be reselected, a Q _Hyst parameter for the hysteresis, a t-Reselection timer parameter for the reference time duration, and/or a cell reselection priority (e.g., an absolute priority) for a corresponding RAT.

In some examples, the cell reselection parameters can be arranged in SIB2, SIB3, SIB4, and/or SIB5 as described in the 3GPP document TS 38.331 Release 15, titled “3 ^rd Generation Partnership Project; Technical Specification Group Radio Access Network; NR; Radio Resource Control (RRC) protocol specification, ” September 26, 2018, which is incorporated herein by reference. In general, the cell reselection parameters can be organized in any suitable arrangement and/or format for system information broadcast.

In an example, when the UE 215 identifies a candidate cell for cell reselection evaluation, the UE 215 may start a cell reselection timer. The UE 215 may configure an evaluation duration for timer based on a reference duration (e.g., t-Reselection time parameter) configured by the system information A. While the timer is running, the UE 215 may continue to monitor and/or evaluate signal measurements of the candidate cell. When the UE 215 detects that a signal measurement of the candidate cell falls below a threshold, the UE 215 stops the timer and aborts the evaluation for the candidate cell. Otherwise, when the timer expires, the UE 215 may select the candidate cell for camping.

FIG. 4 is a block diagram of an exemplary UE 400 according to aspects of the present disclosure. The UE 400 may be a UE 115 in the network 100 or a UE 215 in the network 200 as discussed above. As shown, the UE 400 may include a processor 402, a memory 404, an inter-RAT reselection module 408, a transceiver 410 including a modem subsystem 412 and a radio frequency (RF) unit 414, and one or more antennas 416. These elements may be in direct or indirect communication with each other, for example via one or more buses.

The processor 402 may include a central processing unit (CPU) , a digital signal processor (DSP) , an application specific integrated circuit (ASIC) , a controller, a field programmable gate array (FPGA) device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor 402 may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The memory 404 may include a cache memory (e.g., a cache memory of the processor 402) , random access memory (RAM) , magnetoresistive RAM (MRAM) , read-only memory (ROM) , programmable read-only memory (PROM) , erasable programmable read only memory (EPROM) , electrically erasable programmable read only memory (EEPROM) , flash memory, solid state memory device, hard disk drives, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some aspects, the memory 404 includes a non-transitory computer-readable medium. The memory 404 may store instructions 406. The instructions 406 may include instructions that, when executed by the processor 402, cause the processor 402 to perform the operations described herein with reference to the UEs 115 in connection with aspects of the present disclosure, for example, aspects of FIGS. 3 and 6-8. Instructions 406 may also be referred to as code. The terms “instructions” and “code” should be interpreted broadly to include any type of computer-readable statement (s) . For example, the terms “instructions” and “code” may refer to one or more programs, routines, sub-routines, functions, procedures, etc. “Instructions” and “code” may include a single computer-readable statement or many computer-readable statements.

The cell selection module 408 may be implemented via hardware, software, or combinations thereof. For example, the inter-RAT reselection module 408 may be implemented as a processor, circuit, and/or instructions 406 stored in the memory 404 and executed by the processor 402. In some examples, the inter-RAT reselection module 408 can be integrated within the modem subsystem 412. In some examples, the inter-RAT reselection module 408 may be implemented by a DSP within the modem subsystem 412. The inter-RAT reselection module 408 may be used for various aspects of the present disclosure, for example, aspects of FIGS. 3, 6, 7, and/or 8. The inter-RAT reselection module 408 is configured to select an initial cell (e.g., the cell 210a) for camping, acquire system information (MIB, SIBs, RMSI, OSI) from a BS (e.g., the BS 105 or 205) serving the selected cell, and/or perform cell reselection during an RRC idle mode and/or an RRC inactive mode. The system information may indicate one or more intra-frequency neighboring cells operating over the same carrier frequency as the selected cell, one or more inter-frequency neighboring carrier frequencies and neighboring cells operating over carrier frequencies different from the serving frequency, and/or one or more inter-RAT neighboring cells operating over carrier frequencies different from the serving frequency or on the same carrier frequency as the serving frequency. The system information may indicate a cell reselection priority for the selected cell and each neighboring carrier frequency. The system information may indicate cell reselection criteria (e.g., RSRP threshold, RSRQ threshold, and/or cell reselection evaluation timeout values) for each neighboring frequency and/or neighboring cell.

In some aspects, the inter-RAT reselection module 408 is configured to monitor and evaluate signal strengths (e.g., RSRPs and RSRQs) of inter-frequency candidate cells and/or inter-RAT candidate cells for cell reselections, determine relative priorities among candidate cells, and/or configure timers and/or adjust timer configurations for evaluating the candidate cells based on the relative priorities to give priority to selection of a highest priority candidate cell. In some aspects, the inter-RAT reselection module 408 is configured to perform an inter-radio access technology (RAT) scan for a first RAT associated with a first priority, select a first cell associated with the first RAT, reselect to a second cell associated with a second RAT having a second priority higher than the first priority, and refrain, based on the reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority.

The inter-RAT reselection module 408 may be further configured to initiate, at a first layer, the inter-RAT scan for the first RAT, and perform the inter-RAT scan at a second layer different than the first layer. For example, the first layer may be a non-access stratum (NAS) layer, and the second layer may be a radio resource control (RRC) layer. The inter-RAT reselection module 408 may be further configured to provide, to the first layer, an indication based on an indication based on the reselecting to the second cell, and refrain from initiating the inter-RAT scan for the third rat by removing, in the first layer based on the indication, a trigger associated with the inter-RAT scan for the third RAT. In some aspects, the inter-RAT reselection module 408 is configured to reselect to the second cell at the second layer. In another aspect, the inter-RAT reselection module 408 is configured to perform the inter-RAT scan for the first cell by obtaining signal measurements of the first cell and comparing the signal measurements to a threshold. The inter-RAT reselection module 408 may be configured to select the first cell by camping on the first cell. The inter-RAT reselection module 408 may be further configured to send, based on reselecting to the second cell, a registration request to the second cell. Mechanisms for performing inter-RAT cell reselections during an idle more or an inactive mode with a reduction in unnecessary cell reselections are described in greater detail herein.

As shown, the transceiver 410 may include the modem subsystem 412 and the RF unit 414. The transceiver 410 can be configured to communicate bi-directionally with other devices, such as the BSs 105. The modem subsystem 412 may be configured to modulate and/or encode the data from the memory 404, the inter-RAT reselection module 408 according to a modulation and coding scheme (MCS) , e.g., a low-density parity check (LDPC) coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit 414 may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc. ) modulated/encoded data from the modem subsystem 412 (on outbound transmissions) or of transmissions originating from another source such as a UE 115 or a BS 105. The RF unit 414 may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver 410, the modem subsystem 412 and the RF unit 414 may be separate devices that are coupled together at the UE 115 to enable the UE 115 to communicate with other devices.

The RF unit 414 may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information) , to the antennas 416 for transmission to one or more other devices. The antennas 416 may further receive data messages transmitted from other devices. The antennas 416 may provide the received data messages for processing and/or demodulation at the transceiver 410. The antennas 416 may include multiple antennas of similar or different designs in order to sustain multiple transmission links. The RF unit 414 may configure the antennas 416.

In some aspects, the UE 400 can include multiple transceivers 410 implementing different RATs (e.g., NR and LTE) . In some aspects, the UE 400 can include a single transceiver 410 implementing multiple RATs (e.g., NR and LTE) . In some aspects, the transceiver 410 can include various components, where different combinations of components can implement RATs.

FIG. 5 is a block diagram of an exemplary BS 500 according to aspects of the present disclosure. The BS 500 may be a BS 105 in the network 100 or a BS 205 in the network 200 as discussed above. A shown, the BS 500 may include a processor 502, a memory 504, a system information module 508, a transceiver 510 including a modem subsystem 512 and a RF unit 514, and one or more antennas 516. These elements may be in direct or indirect communication with each other, for example via one or more buses.

The processor 502 may have various features as a specific-type processor. For example, these may include a CPU, a DSP, an ASIC, a controller, a FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor 502 may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The memory 504 may include a cache memory (e.g., a cache memory of the processor 502) , RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, a solid state memory device, one or more hard disk drives, memristor-based arrays, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some aspects, the memory 504 may include a non-transitory computer-readable medium. The memory 504 may store instructions 506. The instructions 506 may include instructions that, when executed by the processor 502, cause the processor 502 to perform operations described herein, for example, aspects of FIG. 6-13. Instructions 506 may also be referred to as code, which may be interpreted broadly to include any type of computer-readable statement (s) as discussed above with respect to FIG. 4.

The system information module 508 may be implemented via hardware, software, or combinations thereof. For example, the system information module 508 may be implemented as a processor, circuit, and/or instructions 506 stored in the memory 504 and executed by the processor 502. In some examples, the system information module 508 may be implemented by a DSP within the modem subsystem 512. The system information module 508 may be used for various aspects of the present disclosure, for example, aspects of FIGS. 3, 6, 7, and/or 8. The system information module 508 is configured to transmit broadcast system information periodically according to certain schedules to enable a UE (e.g., the UEs 115, 215, and 400) to perform initial network access, cell selection, and/or reselection, as described in greater detail herein. The system information may indicate one or more intra-frequency neighboring cells operating over the same carrier frequency as the selected cell, one or more inter-frequency neighboring carrier frequencies and neighboring cells operating over carrier frequencies different from the serving frequency, and/or one or more inter-RAT neighboring cells operating over carrier frequencies different from the serving frequency or on the same carrier frequency as the serving frequency. The system information may indicate a cell reselection priority for the selected cell and each neighboring carrier frequency. The system information may indicate cell reselection criteria (e.g., RSRP threshold, RSRQ threshold, and/or cell reselection evaluation timeout values) for each neighboring frequency and/or neighboring cell.

As shown, the transceiver 510 may include the modem subsystem 512 and the RF unit 514. The transceiver 510 can be configured to communicate bi-directionally with other devices, such as the UEs 115 and/or another core network element. The modem subsystem 512 may be configured to modulate and/or encode data according to a MCS, e.g., a LDPC coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The RF unit 514 may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc. ) modulated/encoded data from the modem subsystem 512 (on outbound transmissions) or of transmissions originating from another source such as a UE 115, 215, or 400. The RF unit 514 may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver 510, the modem subsystem 512 and/or the RF unit 514 may be separate devices that are coupled together at the BS 105 to enable the BS 105 to communicate with other devices.

The RF unit 514 may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information) , to the antennas 516 for transmission to one or more other devices. This may include, for example, transmission of information to complete attachment to a network and communication with a camped UE 115 or 500 according to aspects of the present disclosure. The antennas 516 may further receive data messages transmitted from other devices and provide the received data messages for processing and/or demodulation at the transceiver 510. The antennas 516 may include multiple antennas of similar or different designs in order to sustain multiple transmission links.

In some aspects, the BS 500 can include multiple transceivers 510 implementing different RATs (e.g., NR and LTE) . In some aspects, the BS 500 can include a single transceiver 510 implementing multiple RATs (e.g., NR and LTE) . In some aspects, the transceiver 510 can include various components, where different combinations of components can implement RATs.

FIG. 6 illustrates a method 600 for inter-RAT cell reselection in a network (e.g., the networks 100 and 200) when multiple inter-RAT candidate cells (e.g., the cells 110 and 210) are available for selection according to some aspects of the present disclosure. Steps of the method 600 can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device or other suitable means for performing the steps. For example, a wireless communication device, such as the UE 115, UE 215, or UE 400, may utilize one or more components, such as the processor 402, the memory 404, the inter-RAT reselection module 408, the transceiver 410, the modem 412, and the one or more antennas 416, to execute the steps of method 600. As illustrated, the method 600 includes a number of enumerated steps, but aspects of the method 600 may include additional steps before, after, and in between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

At block 610, the method 600 includes camping on a serving cell associated with a first RAT. The serving cell may operate over a certain carrier frequency. The network may assign an absolute cell reselection priority for the serving carrier frequency, an absolute cell reselection priority for each inter-frequency carrier frequency, and an absolute cell reselection priority for each inter-RAT carrier frequency. The cell reselection priorities may also be referred to as frequency priorities or simply priorities. In some examples, an inter-frequency carrier frequency may have the same priority as the serving carrier frequency or a different priority than the serving carrier frequency, while an inter-RAT carrier frequency may always have a different priority than the serving carrier frequency. The serving cell may broadcast system information including cell reselection parameters as described above in the method 300 with respect to FIG. 3.

While camped on the serving cell, the UE may receive reselection criteria from the serving cell for determining whether to reselect to a cell associated with a different RAT. The reselection criteria may be received in system information from a BS, such as BS 105, BS 205, or BS 500. For example, the reselection criteria may be received as a system information block (SIB) , such as SIB2, SIB4, SIB5, and/or SIB24. The cell reselection criteria may include signal thresholds and/or timer values. For example, the cell reselection criteria may include parameters such as an S _IntraSearchP threshold, an S _IntraSearchQ threshold, an S _{NonIntraSearchP} threshold, S _{NonIntraSearchQ}, Thresh _X, LowQ threshold, a Thresh _X, LowP threshold, a Thresh _X, HighQ threshold, a Thresh _{Serving, LowP} threshold, a Thresh _{Serving, LowQ} threshold, and/or a Thresh _X, HighP threshold for triggering a new inter-frequency cell to be reselected, a T _{ReselectionRAT} timer parameter for the reference time duration, and/or a cell reselection priority (e.g., an absolute priority) for a corresponding carrier frequency. The cell reselection criteria may further indicate the priorities associated with each of the RATs in a cell/network. In some aspects, the priorities of the RATs are configured as (0-GSM, 1-W-CDMA, 2-LTE, 3-TDS, 4-NR5G) , where 4 is the highest priority and 0 is the lowest priority. However, other priority configurations may be used.

Further, the camped UE may monitor the signal strength of the serving cell and neighboring cells, including neighboring cells associated with RATs different from the RAT of the serving cell. The monitoring can include measuring received signal power and/or quality of signals of the serving cell and/or neighboring cells. When the signal strength or measurements of the serving cell fall below a certain threshold, the UE may start to search for an inter-frequency candidate cell or an inter-RAT candidate cell. The threshold for starting an inter-RAT candidate cell search may be provided by the system information (e.g., S _{NonIntraSearchQ}, S _{NonIntraSearchP}) or any suitable threshold. The UE can start monitoring signal strengths (e.g., received signal power and/or received signal quality) of neighboring cells provided by the broadcast system information.

At block 615, the method 600 includes determining whether a new candidate cell is identified based on the monitoring. The UE may identify a neighboring cell as a candidate cell when a signal measurement of the neighboring cell satisfies a certain threshold, which may be provided by the system information (e.g., Thresh _X, HighQ and/or a Thresh _X, HighP) or any suitable threshold. When no candidate cell is identified, the method 600 returns to step 610 and stays camped on the first RAT while continuing to monitor. Otherwise, the method 600 proceeds to block 620.

In block 620, the UE may determine whether a RAT of the new candidate cell, or target cell, has a higher priority than the priority of the serving cell’s RAT (i.e., ReselPrio _NonServ >ReselP _rioServCell) . For example, if the UE is camped on an LTE cell and the system information indicates that an NR cell is available, the UE may determine that the priority of the NR cell is greater than the priority of the LTE cell. As explained above, the respective priorities of the RATs may be indicated in system information providing by the serving cell.

If the priority of other cell is greater that the priority of the serving cell, the UE performs cell measurements at block 625. Performing the cell measurements may include determining a suitability of the other cell, or target cell (S _NonServ) . The suitability may be based on a plurality of parameters, including signal strength (e.g., in dB) , signal quality, or any other suitable parameter. In some aspects, S _NonServ may correspond to an srxlev parameter for the other RAT, which is a cell selection RX level value measured for the other RAT.

At block 630, the UE determines whether the suitability of the target cell (S _NonServ) is greater than a system-configured threshold (Thresh _X, HighP) for the duration of T _ReselRAT. Thresh _X, High P may specify a threshold cell level for the target cell used by the UE when reselecting towards a higher priority RAT than the current serving cell. This threshold may be obtained from system information, for example, in SIB4. The time period of T _ReselRAT may also be obtained in SIB4.

If the condition of block 630 is satisfied and more than a certain duration (e.g., about 1 second) has elapsed since the UE camped on the 1 ^st RAT, the UE reselects to the higher priority RAT at block 635. The UE is then camped on the cell of the higher priority RAT.

Returning to block 620, if the target cell does not have a higher priority than the serving cell, the UE determines whether the suitability of the serving cell (S _ServCell) is greater than a system-configured threshold (S _{NonIntraSearchP}) at block 640. If the suitability of the serving cell is greater than the threshold, the UE remains camped on the serving cell.

If the suitability of the serving cell is not greater than the threshold, the UE performs cell measurements at block 645. The measurements obtained in block 645 may be used to determine a suitability of the serving cell (S _ServCell) , and a suitability of the target cell (S _NonServ) . In some aspects, the suitability of the serving cell and the target cell may correspond to a cell selection RX level value (e.g., srxlev) , and may be determined in units of decibels (dB) .

At block 650, the UE determines if the suitability of the serving cell is lower than a system-configured threshold value for the serving cell, Thresh _Serv, LowP. The value Thresh _Serv, LowP may specify the suitability threshold for the serving cell when determining whether to reselect to a lower priority cell. The threshold Thresh _Serv, LowP may be obtained in SIB2. If the suitability of the serving cell is not less than the system-configured threshold, the UE stays camped on the serving cell.

If the suitability of the serving cell (S _ServCell) is lower than the system-configured threshold (Thresh _Serv, LowP) , the UE proceeds to block 655, at which the UE determines whether the suitability of the non-serving cell (S _NonServ) is greater than a system-configured threshold (Thresh _X, LowP) for the duration of T _ReselRAT. The value Thresh _X, LowP may specify the suitability threshold for the non-serving cell RAT when determining whether to reselect to a lower priority RAT, and may be obtained in SIB4. If the suitability of the target cell (S _NonServ) is not greater than the threshold (Thres _X, LowP) for T _ReselRAT, the UE stays camped on the serving cell. If the suitability of the target cell (S _NonServ) is greater than the threshold (Thresh _X, LowP) for T _ReselRAT, the UE reselects to the cell of the lower priority RAT at block 635.

It will be understood that the aspects of the method 600 are not limited to the blocks illustrated in FIG. 6, and one or more blocks or aspects of the method 600 may be modified without departing from the scope of the present disclosure. For example, in some aspects, additional criteria may be used instead of or in addition to the criteria described with respect to FIG. 6. For example, in some aspects, the UE determines a cell selection quality value (squal) for the serving cell and/or the target cell. The UE may compare the cell selection quality value to a quality threshold value Thresh _X, HighQ of the target cell to determine whether to reselect to a target cell having a higher priority RAT compared to the serving cell. In other aspects, UE may compare the cell selection quality value of the serving cell to a quality threshold value Thresh _{Serv, Low Q} of the serving cell, and the cell selection quality value of the target cell to a quality threshold value Thresh _X, LowQ of the target cell to determine whether to reselect to a target cell having a lower priority RAT compared to the serving cell. In some aspects, if the RAT of the target cell has the same priority as the serving cell RAT, the UE may use cell ranking rules for intra-frequency cell reselection.

The method 600 described above may be performed periodically, or in response to a condition being satisfied. For example, if the serving cell does not satisfy the condition: S _ServCell >S _IntraSearchP, the UE may perform measurements to detect other cells as described above. However, other mechanisms or conditions may be configured by the UE to determine when to perform an inter-RAT scan, including initiation by an upper layer such as an application layer, an RRC layer, an operator configuration, and/or user selection.

In some aspects, a higher layer (e.g., a NAS layer) of the UE may initiate an inter-RAT scan, which may include triggering the UE to perform some or all of the steps of the method 600 for each of a plurality of RATs. In an example, the NAS layer of the UE may initiate an inter-RAT scan in a certain order, for example, in an order of NR, LTE, W-CDMA, and GSM. A lower layer (e.g., an RRC layer) of the UE may coordinate with a MAC layer and/or a PHY layer of the UE to perform the inter-RAT scan. If the UE detected an NR cell and successfully camped on the NR cell, the NAS layer may send a registration request message to the network. If the network accepted the registration, the NAS layer may terminate the inter-RAT scan and/or remove remaining RATs of lower priorities for the scan. However, if UE fails to detect an NR cell or detected an NR cell, but the registration with the NR cell fails (registration rejected, for example, after multiple retries) , the NAS layer may trigger the RRC layer to scan a next-highest priority RAT.

In some instances, when the UE is performing the scan of a given RAT, the UE may detect a higher priority RAT available for reselection. The UE may choose to reselect and camp on a cell of the higher priority RAT based on the priority criteria provided in the system information. For example, while searching for an LTE cell, the UE may detect and reselect to an NR cell, which has a higher priority than the LTE cell. However, since the inter-RAT scan triggered by the higher layer of the UE ultimately resulted in camping on the NR cell, and not the LTE cell, the higher layer assumes that the inter-RAT scan for the LTE cell failed, and triggers a scan of the next-highest priority RAT (e.g., W-CDMA) . In some aspects, the higher layer of the UE may trigger the next RAT scan if no registration accept message is received from the LTE cell after a period of time. This causes the UE to no longer be camped on the NR cell, and may result in the UE being camped on a lower-priority RAT, such as W-CDMA or GSM. This reselection results in unnecessary power consumption by the UE and degraded user experience since the lower priority RATs may have reduced connection capabilities.

Accordingly, the present disclosure provides techniques for a UE (e.g., at a NAS layer) to avoid triggering a scan for a lower priority RAT when a scan for a certain RAT results in a reselection to a higher priority RAT.

FIG. 7 is a signaling diagram illustrating a method 700 for optimizing inter-RAT cell reselection and reducing unnecessary inter-RAT cell reselections in a network (e.g., the networks 100 and 200) when multiple inter-frequency and/or inter-RAT candidate cells (e.g., the cells 110 and 210) are available. At a high level, a UE (e.g., the UE 115, 215, or 400) may configure preferences to reselect to a candidate cell having a relatively higher cell reselection priority than other candidate cells. When a higher layer of the UE triggers an inter-RAT scan (e.g., for a certain RAT with a certain scan priority) , one or more lower layers of the UE perform the inter-RAT scan based on triggers provided by the higher layer. If the lower layer indicates to the higher layer that a higher priority RAT (with a higher priority than the requested RAT) has been reselected, the higher layer removes a trigger to perform an inter-RAT scan for a lower priority RAT based on the indication provided by the lower layer. Accordingly, the inter-RAT scan duration may be reduced, and unnecessary cell reselections may be avoided.

Steps of the method 700 can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device or other suitable means for performing the steps. For example, a wireless communication device, such as the UE 115, UE 215, or UE 400, may utilize one or more components, such as the processor 402, the memory 404, the inter-RAT reselection module 408, the transceiver 410, the modem 412, and the one or more antennas 416, to execute the steps of method 700. As illustrated, the method 700 includes a number of enumerated steps, but aspects of the method 700 may include additional steps before, after, and in between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

At 705, a non-access stratum (NAS) layer of a UE provides a trigger to initiate an inter-RAT scan for a first cell having a first RAT (RAT 1) associated with a first priority. In one example, the first RAT may be long-term evolution (LTE) . As explained above with respect to the method 600, the UE may initiate the inter-RAT scan based on measurements of signal strength of the serving cell and neighboring cells, including neighboring cells associated with RATs different from the RAT of the serving cell. The monitoring can include measuring received signal power and/or quality of signals of the serving cell and/or neighboring cells. When the signal strength or measurements of the serving cell fall below a certain threshold, the UE may start to search for an inter-frequency candidate cell or an inter-RAT candidate cell. The threshold for starting an inter-RAT candidate cell search may be provided by the system information (e.g., S _{NonIntraSearchQ}, S _{NonIntraSearchP}) or any suitable threshold. The UE can start monitoring signal strengths (e.g., received signal power and/or received signal quality) of neighboring cells provided by the broadcast system information. It will be understood that the trigger to initiate the inter-RAT scan may occur while the UE is camped on a serving cell and/or at power up. In some aspects, the serving cell may provide system information indicating the cell frequencies and/or RATs available for reselection.

At 710, the NAS layer of the UE instructs a radio resource control (RRC) layer of the UE to perform the inter-RAT scan for the RAT 1 cell. In some aspects, the RRC layer may be an access stratum (AS) layer. In some aspects, performing the reselection to the RAT 1 cell may comprise performing some or all of the steps of the method 600. Accordingly, in some aspects, reselecting to the RAT 1 cell may include determining whether measurements of the RAT 1 cell meet the reselection criteria provided in system information (e.g., SIB2, SIB4, SIB5, SIB24) .

At 715, the RRC layer of the UE scans and camps on the RAT 1 cell. In other words, the RAT 1 cell becomes a current serving cell of the UE. In some aspects, operations at 715 may include obtaining measurements of the RAT 1 cell and comparing the measurements to a threshold to detect the first cell. In some aspects, operations at 715 may include monitoring for system information provided by the RAT 1 cell. In some aspects, when the RRC layer has successfully camped on the RAT 1 cell, the RRC layer changes notifies the NAS layer that the UE is camped on the RAT 1 cell.

At 720, in response to the UE camping on the RAT 1 cell, the NAS layer sends a registration request (e.g., via the RRC layer) to register the UE on the RAT 1 cell. In some aspects, the registration request may be referred to as an attachment request, particularly if RAT 1 is LTE. In some aspects, the registration request is a NAS layer message from the UE to a core network.

At 725, the RRC layer and the RAT 1 cell attempts to establish an RRC connection and a signaling radio bearer (SRB) . In some aspects, the RRC connection setup may include sending, to the RAT 1 cell, an RRC setup request message, receiving, from the RAT 1 cell, an RRC setup message, and sending, to the first cell, an RRC setup complete message. In some aspects, the registration request (the NAS message) may be included in a dedicated NAS message field within the RRC setup completion message. The NAS layer may request the RRC layer to perform the RRC connection setup and SRB establishment while the UE is in the idle state and has acquired essential system information. In some aspects, establishing the connection includes performing a random access procedure, such as a RACH, by a lower layer or sublayer of the UE, such as a media access control (MAC) layer.

At 730, the RRC of the UE makes a cell reselection to a different RAT (e.g., reselect to a RAT2 cell) . In an example, the RAT 2 cell may be an NR cell having a higher scan order than the RAT 1 cell (the LTE cell) . In some aspects, performing the reselection to the NR cell may comprise performing some or all of the steps of the method 600. Accordingly, in some aspects, reselecting to the RAT 2 cell may include determining whether measurements of the RAT 2 cell meet the reselection criteria provided in the system information (e.g., SIB2, SIB4, SIB5, SIB24) . In some aspects, the RRC layer aborts the RACH procedure for establishing the connection with the RAT 1 cell before triggering the reselection to the RAT 2 cell.

In some aspects, the UE may determine the inter-RAT reselection to the RAT 2 cell based on system information provided by the RAT 1 cell and/or signal measurements obtained from the RAT 1 cell and the RAT 2 cell. For example, an SIB of the RAT 1 cell, such as SIB2, SIB4, SIB5, and/or SIB24 may indicate cells associated with other RATs in the network, and provide information (e.g., reselection criteria) for performing the reselection.

At 735, the RRC layer of the UE indicates to the NAS layer that the RAT 2 cell has been reselected. In some aspects, the UE may include in the indication a first message field indicating the RAT 2 and a second message field indicating a successful reselection. In some other aspects, the UE may include a single message field indicating the successful reselection to RAT 2. In some aspects, the indication can be a software function call, for example, when the NAS layer and the RRC layer are implemented on the same processor core or hardware module. In some other aspects, the indication can be an inter-core signaling, for example, when the NAS layer and the RRC layer are implemented on different processing cores.

At 740, the NAS layer removes a trigger to perform a scan for a RAT 3 cell in response to receiving the indication in 735. In this regard, the NAS layer may maintain a list of RATs in a certain priority order for the inter-RAT scan. For instance, the list may include RAT 2 (e.g., NR) , RAT 1 (e.g., LTE) , RAT 3 (e.g., W-CDMA) from a highest priority to a lowest priority order. Thus, removing the scan for the RAT 3 results in the UE refraining from initiating an inter-RAT scan for RAT 3, which has a priority lower than the priority of RAT 2.

At 745, the NAS layer triggers a request to register the UE on the RAT 2 cell.

At 750, the NAS layer sends a registration request message to the RAT 2 cell. In some aspects, the registration request may be similar to the registration request sent in 720.

In this manner, when the UE performs a reselection to a higher priority RAT during a scan of a lower priority RAT, the higher layer is notified so that the inter-RAT scan can be terminated and the UE can remain camped on the higher priority cell. If the higher layer was not notified that the higher layer NR cell was reselected during the inter-RAT scan, the higher layer may assume that the inter-RAT scan failed and may proceed to trigger the next inter-RAT scan for a lower priority RAT (e.g., W-CDMA, GSM) . Thus, causing the lower layer to indicate or notify the higher layer (e.g., NAS layer) when a higher priority RAT reselection has occurred, unnecessary RAT reselections to lower priority RATs may be avoided, improving the user experience and reducing power consumption.

FIG. 8 illustrates a wireless communication method 800 according to some aspects of the present disclosure. Aspects of the method 800 can be executed by a computing device (e.g., a processor, processing circuit, and/or other suitable component) of a wireless communication device or other suitable means for performing the steps. For example, a wireless communication device, such as the UE 115, UE 215, or UE 400, may utilize one or more components, such as the processor 402, the memory 404, the inter-RAT reselection module 408, the transceiver 410, the modem 412, and the one or more antennas 416, to execute the steps of method 800. The method 800 may employ similar mechanisms as in the

schemes

300, 600, and 700 discussed above with respect to FIGS. 3 and 6-8. As illustrated, the method 800 includes a number of enumerated steps, but aspects of the method 800 may include additional steps before, after, and in between the enumerated steps. In some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

At 810, the UE performs an inter-RAT scan for a first RAT associated with a first priority. In one aspect, a higher layer, such as a non-access stratum (NAS) layer, triggers or initiates the inter-RAT scan for the first RAT, and one or more lower layers of the UE, such as a radio-resource control (RRC) layer, a media access control (MAC) layer, and/or a physical (PHY) layer may perform the inter-RAT scan. In one example, the first RAT is LTE. In some aspects, the priorities of different RATs may be configured by the network in system information. The priorities may be, from highest to lowest, NR, LTE, W-CDMA, and GSM. However, these priorities are not binding and can be modified without departing from the scope of the present disclosure. In some aspects, other RATS are prioritized other than those listed above. In one aspect, performing the inter-RAT scan includes: obtaining signal measurements of the first cell, and comparing the signal measurements to a threshold. The threshold may be configured in system information provided by the first cell. In some aspects the UE may utilize one or more components, such as the processor 402, the memory 404, the inter-RAT reselection module 408, the transceiver 410, the modem 412, and/or the one or more antennas 416, to perform the operations of 810.

At 820, the UE selects the first cell associated with the first RAT. Selecting the first cell may include camping on the first cell. In one aspect, one or more lower layers of the UE, such as the RRC layer, the MAC layer, and/or the PHY layer, selects the first cell. In some aspects, selecting the first cell includes camping on the first cell. In some aspects the UE may utilize one or more components, such as the processor 402, the memory 404, the inter-RAT reselection module 408, the transceiver 410, the modem 412, and/or the one or more antennas 416, to perform the operations of 820.

At 830, the UE reselects, to a second cell associated with a second RAT, wherein the second RAT is associated with a second priority higher than a first priority. In one aspect, one or more lower layers of the UE, such as the RRC layer, the MAC layer, and/or the PHY layer reselects to the second cell. In one aspect, the second RAT may be NR. In one aspect, the lower layer of the UE provides an indication to the higher layer based on the reselecting to the second cell associated with the second RAT. In some aspects the UE may utilize one or more components, such as the processor 402, the memory 404, the inter-RAT reselection module 408, the transceiver 410, the modem 412, and/or the one or more antennas 416, to perform the operations of 830.

At 840, the UE refrains, based on reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority. In one example, the third RAT is W-CDMA. In another example, the third RAT is GSM. In one aspect a higher layer of the UE, such as the NAS layer, refrains from initiating the inter-RAT scan for the third RAT. In some aspects, refraining from performing the inter-RAT scan for the third RAT includes the higher layer (e.g., NAS layer) removing a trigger to perform the inter-RAT scan for the third RAT. In some aspects the UE may utilize one or more components, such as the processor 402, the memory 404, the inter-RAT reselection module 408, the transceiver 410, the modem 412, and/or the one or more antennas 416, to perform the operations of 840.

In some aspects, the UE may apply the method 800 to initiate a scan for a cell with a W-CDMA RAT and may terminate the scan when the UE reselects to an LTE cell or an NR cell instead of triggering a scan for a GSM cell. Similarly, the UE may apply the method 800 to initiate a scan for a cell with a GSM RAT and may terminate the scan when the UE reselects to a W-CDMA cell, an LTE cell, or an NR cell instead of triggering a new inter-RAT scan.

Information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration) .

The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items (for example, a list of items prefaced by a phrase such as “at least one of” or “one or more of” ) indicates an inclusive list such that, for example, a list of [at least one of A, B, or C] means A or B or C or AB or AC or BC or ABC (i.e., A and B and C) .

As those of some skill in this art will by now appreciate and depending on the particular application at hand, many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the spirit and scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular embodiments illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.

Claims

A method of wireless communication performed by a user equipment (UE) , the method comprising:

performing an inter-radio access technology (RAT) scan for a first RAT associated with a first priority;

selecting a first cell associated with the first RAT;

reselecting to a second cell associated with a second RAT, wherein the second RAT is associated with a second priority higher than the first priority; and

refraining, based on the reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority.
The method of claim 1, further comprising:

initiating, at a first layer, the inter-RAT scan for the first RAT,

wherein the performing the inter-RAT scan for the first RAT comprises:

performing the inter-RAT scan at a second layer different than the first layer.
The method of claim 2, further comprising:

providing, to the first layer, an indication based on the reselecting to the second cell,

wherein the refraining from initiating the inter-RAT scan for the third RAT comprises:

removing, in the first layer based on the indication, a trigger associated with the inter-RAT scan for the third RAT.
The method of claim 2, wherein the reselecting to the second cell comprises:

reselecting to the second cell at the second layer.
The method of claim 2, wherein the first layer is a non-access stratum (NAS) layer, and wherein the second layer is a radio resource control (RRC) layer.
The method of claim 1, wherein the performing the inter-RAT scan for the first cell comprises:

obtaining signal measurements of the first cell; and

comparing the signal measurements to a threshold.
The method of claim 1, wherein the selecting the first cell comprises:

camping on the first cell.
The method of claim 1, further comprising:

sending, based on the reselecting to the second cell, a registration request to the second cell.
The method of claim 1, wherein the first RAT is long-term evolution (LTE) .
The method of claim 1, wherein the second RAT is 5G new radio (NR) .
A user equipment (UE) , comprising:

a processor configured to:

perform an inter-radio access technology (RAT) scan for a first RAT associated with a first priority;

select a first cell associated with the first RAT;

reselect to a second cell associated with a second RAT, wherein the second RAT is associated with a second priority higher than the first priority; and

refrain, based on the reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority.
The UE of claim 11, wherein the processor is further configured to:

initiate, at a first layer, the inter-RAT scan for the first RAT,

wherein the processor configured to perform the inter-RAT scan for the first RAT comprises the processor configured to:

perform the inter-RAT scan for the first RAT at a second layer different than the first layer.
The UE of claim 12, wherein the processor is further configured to:

provide, to the first layer, an indication based on the reselecting to the second cell,

wherein the processor configured to refrain from initiating the inter-RAT scan for the third RAT comprises the processor configured to:

remove, in the first layer based on the indication, a trigger associated with the inter-RAT scan for the third RAT.
The UE of claim 12, wherein the processor configured to reselect to the second cell comprises the processor configured to:

reselect to the second cell at the second layer.
The UE of claim 12, wherein the first layer is a non-access stratum (NAS) layer, and wherein the second layer is a radio resource control (RRC) layer.
The UE of claim 11, wherein the processor configured to perform the inter-RAT scan for the first cell comprises the processor configured to:

obtain signal measurements of the first cell; and

compare the signal measurements to a threshold.
The UE of claim 11, wherein the processor configured to select the first cell comprises the processor configured to:

camp on the first cell.
The UE of claim 11, wherein the processor is further configured to:

send, based on the reselecting to the second cell, a registration request to the second cell.
The UE of claim 11, wherein the first RAT is long-term evolution (LTE) .
The UE of claim 11, wherein the second RAT is 5G new radio (NR) .
A non-transitory computer-readable medium having program code recorded thereon, the program code comprising:

code for causing a user equipment (UE) to perform an inter-radio access technology (RAT) scan for a first RAT associated with a first priority;

code for causing the UE to select a first cell associated with the first RAT;

code for causing the UE to reselect to a second cell associated with a second RAT, wherein the second RAT is associated with a second priority higher than the first priority; and

code for causing the UE to refrain, based on the reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority.
The non-transitory computer-readable medium of claim 21, wherein the non-transitory computer-readable medium further comprises:

code for causing the UE to initiate, at a first layer, the inter-RAT scan for the first RAT,

wherein the code for causing the UE to perform the inter-RAT scan for the first RAT is configured to:

perform the inter-RAT scan for the first RAT at a second layer different than the first layer.
The non-transitory computer-readable medium of claim 22, wherein the non-transitory computer-readable medium further comprises:

code for causing the UE to provide, to the first layer, an indication based on the reselecting to the second cell,

wherein the code for causing the UE to refrain from initiating the inter-RAT scan for the third RAT is configured to:

remove, in the first layer based on the indication, a trigger associated with the inter-RAT scan for the third RAT.
The non-transitory computer-readable medium of claim 22, wherein the code for causing the UE to reselect to the second cell is configured to:

reselect to the second cell at the second layer.
The non-transitory computer-readable medium of claim 22, wherein the first layer is a non-access stratum (NAS) layer, and wherein the second layer is a radio resource control (RRC) layer.
The non-transitory computer-readable medium of claim 21, wherein the code for causing the UE to perform the inter-RAT scan for the first cell is configured to:

obtain signal measurements of the first cell; and

compare the signal measurements to a threshold.
The non-transitory computer-readable medium of claim 21, wherein the code for causing the UE to select the first cell is configured to:

camp on the first cell.
The non-transitory computer-readable medium of claim 21, wherein the non-transitory computer-readable medium further comprises:

code for causing the UE to send, based on the reselecting to the second cell, a registration request to the second cell.
The non-transitory computer-readable medium of claim 21, wherein the first RAT is long-term evolution (LTE) .
The non-transitory computer-readable medium of claim 21, wherein the second RAT is 5G new radio (NR) .
A user equipment (UE) , comprising:

means for performing an inter-radio access technology (RAT) scan for a first RAT associated with a first priority;

means for selecting a first cell associated with the first RAT;

means for reselecting to a second cell associated with a second RAT, wherein the second RAT is associated with a second priority higher than the first priority; and

means for refraining, based on the reselecting to the second cell, from initiating an inter-RAT scan for a third RAT associated with a third priority lower than the first priority.
The UE of claim 31, further comprising:

means for initiating, at a first layer, the inter-RAT scan for the first RAT, wherein the means for performing the inter-RAT scan for the first RAT comprises:

means for performing the inter-RAT scan for the first RAT at a second layer different than the first layer.
The UE of claim 32, further comprising:

means for providing, to the first layer, an indication based on the reselecting to the second cell,

wherein the means for refraining from initiating the inter-RAT scan for the third RAT comprises:

means for removing, in the first layer based on the indication, a trigger associated with the inter-RAT scan for the third RAT.
The UE of claim 32, wherein the means for reselecting to the second cell comprises:

means for reselecting to the second cell at the second layer.
The UE of claim 32, wherein the first layer is a non-access stratum (NAS) layer, and wherein the second layer is a radio resource control (RRC) layer.
The UE of claim 31, wherein the means for performing the inter-RAT scan for the first cell comprises:

means for obtaining signal measurements of the first cell; and

means for comparing the signal measurements to a threshold.
The UE of claim 31, wherein the means for selecting the first cell comprises:

means for camping on the first cell.
The UE of claim 31, further comprising:

means for sending, based on the reselecting to the second cell, a registration request to the second cell.
The UE of claim 31, wherein the first RAT is long-term evolution (LTE) .
The UE of claim 31, wherein the second RAT is 5G new radio (NR) .