WO2021243636A1

WO2021243636A1 - Inter-radio access technology reselection

Info

Publication number: WO2021243636A1
Application number: PCT/CN2020/094312
Authority: WO
Inventors: Yi Liu; Jinglin Zhang; Haojun WANG; Zhenqing CUI; Fojian ZHANG; Hao Zhang; Chaofeng HUI; Hong Wei
Original assignee: Qualcomm Incorporated
Priority date: 2020-06-04
Filing date: 2020-06-04
Publication date: 2021-12-09

Abstract

A user equipment is provided that may transition from a first radio access technology (RAT) to a second RAT without a reselection system information block (SIB). The UE may camp in idle mode on a first base station utilizing the first radio access technology, determine that the reselection SIB is not configured for the first base station, determine that a frequency for the second radio access technology is in the acquisition database for the UE, and search for a base station utilizing the second radio access technology.

Description

INTER-RADIO ACCESS TECHNOLOGY RESELECTION

BACKGROUND Technical Field

The present disclosure relates generally to communication systems, and more particularly, to a wireless communication system supporting transitioning between first and second radio access technologies.

Introduction

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

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

SUMMARY

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

In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a user equipment (UE) . The apparatus may camp in an idle mode on a first base station, the first base station utilizing a first radio access technology, determine that a reselection system information block is not configured for the first base station, the reselection system information block corresponding to a second radio access technology, determine that one or more base station utilizing the second radio access technology is present in an acquisition database of the UE, determine that a reference signal received power from the first base station is below a threshold, and search for a second base station utilizing the second radio access technology upon determining that one or more base station utilizing the second radio access technology is present in the acquisition database and that the reference signal received power from the first base station is below the threshold.

In some aspects, the apparatus may reselect from the first base station to a third base station utilizing the first radio access technology prior to finding the second base station, and terminate searching for the second base station.

In some aspects, the apparatus may determine that the second base station satisfies reselection criteria, and register to the second base station.

In some aspects, the second base station may not utilize the first radio access technology.

In some aspects, the one or more base station utilizing the second radio access technology may not utilize the first radio access technology.

In some aspects, the second radio access technology may be stand-alone 5GNR and the reselection system information block may be a SIB24.

In some aspects, the one or more base station utilizing the second radio access technology may include the second base station.

In some aspects, the one or more base station utilizing the second radio access technology may not include the second base station.

In some aspects, the apparatus may receive a frequency for the one or more base station utilizing the second radio access technology, and store the frequency for the one or more base station utilizing the second radio access technology in the acquisition database, wherein determining that the one or more base station utilizing the second radio access technology is present in the acquisition database is based on the frequency.

To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents.

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

FIG. 4 is a diagram showing a UE within the coverage areas of two base stations.

FIG. 5 is a flow chart illustrating a process of determining a serving base station for a UE.

FIG. 6 is a communication flow diagram illustrating a UE transitioning to a serving base station utilizing a new radio access technology.

FIG. 7 is a flowchart of a method of wireless communication.

DETAILED DESCRIPTION

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

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

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

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

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

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

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

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

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

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

A base station 102, whether a small cell 102'or a large cell (e.g., macro base station) , may include and/or be referred to as an eNB, gNodeB (gNB) , or another type of base station. Some base stations, such as gNB 180 may operate in a traditional sub 6 GHz spectrum, in millimeter wave (mmW) frequencies, and/or near mmW frequencies in communication with the UE 104. When the gNB 180 operates in mmW or near mmW frequencies, the gNB 180 may be referred to as an mmW base station. Extremely high frequency (EHF) is part of the RF in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in the band may be referred to as a millimeter wave. Near mmW may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Frequency range bands include frequency range 1 (FR1) , which includes frequency bands below 7.225 GHz, and frequency range 2 (FR2) , which includes frequency bands above 24.250 GHz. Communications using the mmW /near mmW radio frequency (RF) band (e.g., 3 GHz –300 GHz) has extremely high path loss and a short range. Base stations /UEs may operate within one or more frequency range bands. The mmW base station 180 may utilize beamforming 182 with the UE 104 to compensate for the extremely high path loss and short range. The base station 180 and the UE 104 may each include a plurality of antennas, such as antenna elements, antenna panels, and/or antenna arrays to facilitate the beamforming.

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

The EPC 160 may include a Mobility Management Entity (MME) 162, other MMEs 164, a Serving Gateway 166, a Multimedia Broadcast Multicast Service (MBMS) Gateway 168, a Broadcast Multicast Service Center (BM-SC) 170, and a Packet Data Network (PDN) Gateway 172. The MME 162 may be in communication with a Home Subscriber Server (HSS) 174. The MME 162 is the control node that processes the signaling between the UEs 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the Serving Gateway 166, which itself is connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation as well as other functions. The PDN Gateway 172 and the BM-SC 170 are connected to the IP Services 176. The IP Services 176 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS) , a PS Streaming Service, and/or other IP services. The BM-SC 170 may provide functions for MBMS user service provisioning and delivery. The BM-SC 170 may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a public land mobile network (PLMN) , and may be used to schedule MBMS transmissions. The MBMS Gateway 168 may be used to distribute MBMS traffic to the base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information.

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

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

Referring again to FIG. 1, in certain aspects, the UE 104 may be configured to reselect from a first base station using a first radio access technology to a second base station using a second radio access technology when the first base station is not configured with a SIB that supports the reselection (198) . Although the following description may be focused on inter-RAT reselection from LTE to 5G NR, the concepts described herein may be applicable to resection between other wireless technologies, such as LTE-A, CDMA, and GSM.

FIG. 2A is a diagram 200 illustrating an example of a first subframe within a 5G/NR frame structure. FIG. 2B is a diagram 230 illustrating an example of DL channels within a 5G/NR subframe. FIG. 2C is a diagram 250 illustrating an example of a second subframe within a 5G/NR frame structure. FIG. 2D is a diagram 280 illustrating an example of UL channels within a 5G/NR subframe. The 5G/NR frame structure may be frequency division duplexed (FDD) in which for a particular set of subcarriers (carrier system bandwidth) , subframes within the set of subcarriers are dedicated for either DL or UL, or may be time division duplexed (TDD) in which for a particular set of subcarriers (carrier system bandwidth) , subframes within the set of subcarriers are dedicated for both DL and UL. In the examples provided by FIGs. 2A, 2C, the 5G/NR frame structure is assumed to be TDD, with subframe 4 being configured with slot format 28 (with mostly DL) , where D is DL, U is UL, and F is flexible for use between DL/UL, and subframe 3 being configured with slot format 34 (with mostly UL) . While

subframes

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

Other wireless communication technologies may have a different frame structure and/or different channels. A frame (10 ms) may be divided into 10 equally sized subframes (1 ms) . Each subframe may include one or more time slots. Subframes may also include mini-slots, which may include 7, 4, or 2 symbols. Each slot may include 7 or 14 symbols, depending on the slot configuration. For slot configuration 0, each slot may include 14 symbols, and for slot configuration 1, each slot may include 7 symbols. The symbols on DL may be cyclic prefix (CP) OFDM (CP-OFDM) symbols. The symbols on UL may be CP-OFDM symbols (for high throughput scenarios) or discrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) symbols (also referred to as single carrier frequency-division multiple access (SC-FDMA) symbols) (for power limited scenarios; limited to a single stream transmission) . The number of slots within a subframe is based on the slot configuration and the numerology. For slot configuration 0, different numerologies μ 0 to 4 allow for 1, 2, 4, 8, and 16 slots, respectively, per subframe. For slot configuration 1, different numerologies 0 to 2 allow for 2, 4, and 8 slots, respectively, per subframe. Accordingly, for slot configuration 0 and numerology μ, there are 14 symbols/slot and 2 ^μ slots/subframe. The subcarrier spacing and symbol length/duration are a function of the numerology. The subcarrier spacing may be equal to 2 ^μ*15 kHz, where μ is the numerology 0 to 4. As such, the numerology μ=0 has a subcarrier spacing of 15 kHz and the numerology μ=4 has a subcarrier spacing of 240 kHz. The symbol length/duration is inversely related to the subcarrier spacing. FIGs. 2A-2D provide an example of slot configuration 0 with 14 symbols per slot and numerology μ=2 with 4 slots per subframe. The slot duration is 0.25 ms, the subcarrier spacing is 60 kHz, and the symbol duration is approximately 16.67 μs. Within a set of frames, there may be one or more different bandwidth parts (BWPs) (see FIG. 2B) that are frequency division multiplexed. Each BWP may have a particular numerology.

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

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

FIG. 2B illustrates an example of various DL channels within a subframe of a frame. The physical downlink control channel (PDCCH) carries DCI within one or more control channel elements (CCEs) , each CCE including nine RE groups (REGs) , each REG including four consecutive REs in an OFDM symbol. A PDCCH within one BWP may be referred to as a control resource set (CORESET) . Additional BWPs may be located at greater and/or lower frequencies across the channel bandwidth. A primary synchronization signal (PSS) may be within symbol 2 of particular subframes of a frame. The PSS is used by a UE 104 to determine subframe/symbol timing and a physical layer identity. A secondary synchronization signal (SSS) may be within symbol 4 of particular subframes of a frame. The SSS is used by a UE to determine a physical layer cell identity group number and radio frame timing. Based on the physical layer identity and the physical layer cell identity group number, the UE can determine a physical cell identifier (PCI) . Based on the PCI, the UE can determine the locations of the aforementioned DM-RS. The physical broadcast channel (PBCH) , which carries a master information block (MIB) , may be logically grouped with the PSS and SSS to form a synchronization signal (SS) /PBCH block (also referred to as SS block (SSB) ) . The MIB provides a number of RBs in the system bandwidth and a system frame number (SFN) . The physical downlink shared channel (PDSCH) carries user data, broadcast system information not transmitted through the PBCH such as system information blocks (SIBs) , and paging messages.

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

FIG. 2D illustrates an example of various UL channels within a subframe of a frame. The PUCCH may be located as indicated in one configuration. The PUCCH carries uplink control information (UCI) , such as scheduling requests, a channel quality indicator (CQI) , a precoding matrix indicator (PMI) , a rank indicator (RI) , and hybrid automatic repeat request (HARQ) ACK/NACK feedback. The PUSCH carries data, and may additionally be used to carry a buffer status report (BSR) , a power headroom report (PHR) , and/or UCI.

FIG. 3 is a block diagram of a base station 310 in communication with a UE 350 in an access network. In the DL, IP packets from the EPC 160 may be provided to a controller/processor 375. The controller/processor 375 implements layer 3 and layer 2 functionality. Layer 3 includes a radio resource control (RRC) layer, and layer 2 includes a service data adaptation protocol (SDAP) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller/processor 375 provides RRC layer functionality associated with broadcasting of system information (e.g., MIB, SIBs) , RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release) , inter radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression /decompression, security (ciphering, deciphering, integrity protection, integrity verification) , and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs) , error correction through ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs) , re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs) , demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

The transmit (TX) processor 316 and the receive (RX) processor 370 implement layer 1 functionality associated with various signal processing functions. Layer 1, which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The TX processor 316 handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK) , quadrature phase-shift keying (QPSK) , M-phase-shift keying (M-PSK) , M-quadrature amplitude modulation (M-QAM) ) . The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator 374 may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE 350. Each spatial stream may then be provided to a different antenna 320 via a separate transmitter 318TX. Each transmitter 318TX may modulate an RF carrier with a respective spatial stream for transmission.

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

The controller/processor 359 can be associated with a memory 360 that stores program codes and data. The memory 360 may be referred to as a computer-readable medium. In the UL, the controller/processor 359 provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC 160. The controller/processor 359 is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations.

Similar to the functionality described in connection with the DL transmission by the base station 310, the controller/processor 359 provides RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression /decompression, and security (ciphering, deciphering, integrity protection, integrity verification) ; RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization.

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

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

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

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

FIG. 4 is a diagram 400 showing a UE 402 within the coverage areas of two base stations. A first base station 404 may operate using a first radio access technology, such as 4G LTE. A second base station 406 may operate using a second radio access technology, such as stand-alone 5G. The UE 402 may be within the coverage area of the first base station 404 and the coverage area of the second base station 406, and the first base station 404 may be the serving cell for the UE 402.

A base station may be configured with a reselection system information block (SIB) . A reselection SIB may contain reselection information which allows a UE being served by the base station configured with the reselection SIB to search for and reselect to another base station utilizing a different radio access technology than the serving base station, such as during RRC idle mode. For example, a reselection SIB may be a SIB24 and may contain reselection information which allows a UE being served by a LTE base station to reselect to a stand-alone 5G base station. A reselection SIB may include information about neighboring cells using a different radio access technology, such as the frequency, the band, or the SSB information of the neighboring cells. A reselection SIB may additionally or alternatively include cell reselection related parameters for reselecting to a base station using the different radio access technology, such as the threshold, the priority, or the timer information.

The first base station 404 may not be configured with a reselection SIB. The UE 402 may be camped on the first base station 404 and may be in idle mode, but may have a better signal from the second base station 406 than from the first base station 404. Because the first base station 404 uses a different radio access technology than the second base station 406 and is not configured with a reselection SIB, the UE 402 may not reselect to the second base station 406. For example, the UE 402 may not have the information (e.g., a list of neighboring cells using the second radio access technology from a reselection SIB) to determine to measure the signal from the second base station 406 to evaluate the second base station 406 for reselection.

FIG. 5 is a flow chart 500 illustrating a process of determining a serving base station for a UE. The UE may be camped on a first base station utilizing a first radio access technology. The first base station may be part of a network utilizing the first radio access technology The UE may be configured for both the first radio access technology (e.g., 4G LTE) and a second radio access technology (e.g., 5GNR, stand-alone 5GNR) .

At 502, the UE may be in idle mode on the first radio access technology network (e.g., camped on the first base station) .

At 504, while the UE is in idle mode of the first radio access technology network, the UE may determine whether a reselection SIB is configured for the first base station. If the first base station is configured with a reselection SIB, at 506, the UE may perform an inter-RAT cell reselection search based on the information in the reselection SIB. For example, if the first base station utilizes 4G LTE and is configured with a SIB24, the UE may perform a L2NR cell reselection to evaluate options for reselecting to a 5GNR or stand-alone 5GNR base station.

If the first base station is not configured with a reselection SIB, at 508, the UE may determine whether an acquisition database (ACQ DB) of the UE includes one or more frequency for the second radio access technology. The ACQ DB may be associated with the second radio access technology, and may include information about base stations which the UE has previously connected to using the second radio access technology. By determining that the ACQ DB includes a frequency for the second radio access technology, the UE may infer that coverage for the second radio access technology may be available in the area.

At 508, the UE may also determine whether the reference signal received power (RSRP) for the first radio access technology network (e.g., the RSRP of reference signals from the first base station) is below a threshold value. For example, the UE may determine whether the RSRP is below -100 dBm. In some aspects, the threshold value may be configurable. For example, the threshold may be configured on the UE. In some aspects, the threshold may be configured on a modem side of the UE. In some aspects, the threshold may be configured on a AP side of the UE and transmitted to the modem side of the UE.

If the UE determines that the ACQ DB does not include one or more frequency for the second radio access technology or determines that the RSRP for the first radio access technology network is not below the threshold value, then at 510, the UE may remain in the first radio access technology network (e.g., may remain camped on the first base station) .

If the UE determines that the ACQ DB does include one or more frequency for the second radio access technology and determines that the RSRP for the first radio access technology network is below the threshold value, then at 512 the UE may start a background search for a base station belonging to a second radio access technology network. For example, in some aspects, the UE may search the frequencies for the second radio access technology contained in the ACQ DB for a base station belonging to the second radio access technology network. In some aspects, if the UE does not find a suitable base station belonging to the second radio access technology at a frequency contained in the ACQ DB, the UE may do a full band search for a suitable base station belonging to the second radio access technology. In some aspects, the UE may only scan the frequencies contained in the ACQ DB, and in some aspects, the UE may initiate a full band search without scanning the frequencies in the ACQ DB first.

At 514, while the UE is performing the background search for a base station belonging to the second radio access technology network, the UE may determine whether the current cell serving the UE on the first radio access technology network has changed. For example, the UE may be handed off from the first base station to another base station in the first radio access technology network. If the UE determines that the serving cell has changed, then at 516, the UE may stop the background search. The UE may remain in idle mode on the first radio access technology network, camping on the new serving cell.

If the UE has not determined that the serving cell has changed during the background search, at 518, the UE may determine whether it has found a suitable second radio access technology base station to serve as a new serving cell during the background search. For example, the UE may evaluate the RSRP of base stations using the second radio access technology during the background search and may determine whether a base station using the second radio access technology has a RSRP over a reselection threshold or has a RSRP higher than the RSRP of the current serving cell. The UE may additionally or alternatively evaluate whether the PMI of the base station using the second radio access technology is compatible with the UE or other cell reselection criteria. For example, the UE may determine whether it has found a suitable second radio access technology based on a reselection procedure specified in 5GNR.

Upon determining that a suitable base station using the second radio access technology has been found, at 520, the UE may register to the second RAT network (e.g., may register to the found suitable base station) . If the UE does not find a suitable base station using the second radio access technology during the background search, then at 510, the UE may remain in the first radio access technology network (e.g., may remain camped on the first base station) .

FIG. 6 is a communication flow diagram 600 illustrating a UE 602 transitioning to a serving base station utilizing a new radio access technology. The UE 602 may be configured to utilize a first radio access technology (e.g., 4G LTE) and a second radio access technology (e.g., 5GNR, stand-alone 5GNR) .

As illustrated at 620, the UE 602 may store a frequency corresponding to a second base station 606 in an ACQ DB of the UE 602. The second base station 606 may be configured to utilize a second radio access technology (e.g., 5GNR, stand-alone 5GNR) . For example, the UE 602 may detect the second base station 606 during a scan while utilizing the second radio access technology or may register to the second base station 606 while utilizing the second radio access technology, and may store the frequency of the second base station 606 in the ACQ DB upon scanning the second base station 606 or registering to the second base station 606.

Later, the UE 602 may be camped on a first base station 604. The first base station 604 may utilize a first radio access technology (e.g., 4G LTE) , and the UE 602 may have transitioned from using the second radio access technology at 620 to using the firs ratio access technology at 610. The first base station 604 may not be configured with a reselection SIB for reselecting to the second radio access technology (e.g., SIB24) . As illustrated at 610, the UE 602 may be in an RRC idle state with respect to the first base station 604.

As illustrated at 630, the UE 602 may determine that the first base station 604 is not configured with a reselection SIB, that the ACQ DB includes a frequency corresponding to the second radio access technology, and that the RSRP for the first base station 604 is below a threshold value, for example, as described above with respect to 504 and 508.

As illustrated at 632, the UE 602 may perform a background search for base stations utilizing the second radio access technology. As illustrated at 634, during the background search, the UE 602 may detect a third base station 608 and may determine that the third base station 608, which uses the second radio access technology, meets reselection criteria. In some aspects, the frequency stored in the ACQ DB may be the frequency for the third base station 608 (e.g, the third base station 608 may be the second base station 606, and the background search may have been triggered based on the frequency of the third base station being in the ACQ DB) . In some aspects, the frequency of the third base station 608 may not be stored in the ACQ DB, and the background search may have been triggered based on the frequency of another base station utilizing the second radio access technology (e.g., the background search may have been triggered based on the frequency of the second base station 606 being in the ACQ DB, and the third base station 608 may have been detected in a full band scan) .

The UE 602 may transmit at registration message 636 to the third base station 608 to register to the third base station 608. For example, the registration message 636 may be a RRC connection setup message.

FIG. 7 is a flowchart 700 of a method of wireless communication. The method may be performed by a UE (e.g., the

UE

104, 350, 602) .

At 702, the UE may camp in an idle mode on a first base station. The first base station may utilize a first radio access technology.

At 704, the UE may determine that a reselection system information block is not configured for the first base station. The reselection system information block may correspond to a second radio access technology. The second radio access technology may be stand-alone 5GNR and the reselection system information block may be a SIB24.

At 706, the UE may determine that one or more base station utilizing the second radio access technology is present in an acquisition database of the UE. The one or more base station utilizing the second radio access technology may not utilize the first radio access technology. The one or more base station utilizing the second radio access technology may include the second base station. The one or more base station utilizing the second radio access technology may not include the second base station.

In some aspects, the UE may receive a frequency for the one or more base station utilizing the second radio access technology, and may store the frequency for the one or more base station utilizing the second radio access technology in the acquisition database, and determining that the one or more base station utilizing the second radio access technology is present in the acquisition database may be based on the frequency. For example, the UE may receive the frequency for the one or more base station in the process of registering to the one or more base station or scanning the one or more base station.

At 708, the UE may determine that a reference signal received power from the first base station is below a threshold.

At 710, the UE may search for a second base station utilizing the second radio access technology. The UE may search for the second base station upon determining that one or more base station utilizing the second radio access technology is present in the acquisition database and that the reference signal received power from the first base station is below the threshold. The second base station may not utilize the first radio access technology.

In some aspects, at 720, the UE may reselect from the first base station to a third base station utilizing the first radio access technology prior to finding the second base station.

At 722, the UE may terminate searching for the second base station.

In some aspects, at 720, the UE may determining that the second base station satisfies reselection criteria.

At 732, the UE may register to the second base station.

It is understood that the specific order or hierarchy of blocks in the processes /flowcharts disclosed is an illustration of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes /flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more. ” Terms such as “if, ” “when, ” and “while” should be interpreted to mean “under the condition that” rather than imply an immediate temporal relationship or reaction. That is, these phrases, e.g., “when, ” do not imply an immediate action in response to or during the occurrence of an action, but simply imply that if a condition is met then an action will occur, but without requiring a specific or immediate time constraint for the action to occur. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C, ” “one or more of A, B, or C, ” “at least one of A, B, and C, ” “one or more of A, B, and C, ” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module, ” “mechanism, ” “element, ” “device, ” and the like may not be a substitute for the word “means. ” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ”

The following examples are illustrative only and may be combined with aspects of other embodiments or teachings described herein, without limitation.

Claims

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

camping in an idle mode on a first base station, the first base station utilizing a first radio access technology;

determining that a reselection system information block is not configured for the first base station, the reselection system information block corresponding to a second radio access technology;

determining that one or more base station utilizing the second radio access technology is present in an acquisition database of the UE;

determining that a reference signal received power from the first base station is below a threshold; and

searching for a second base station utilizing the second radio access technology upon determining that one or more base station utilizing the second radio access technology is present in the acquisition database and that the reference signal received power from the first base station is below the threshold.
The method of claim 1, further comprising:

reselecting from the first base station to a third base station utilizing the first radio access technology prior to finding the second base station; and

terminating searching for the second base station.
The method of claim 1, further comprising:

determining that the second base station satisfies reselection criteria; and

registering to the second base station.
The method of claim 1, wherein the second base station does not utilize the first radio access technology.
The method of claim 1, wherein the one or more base station utilizing the second radio access technology does not utilize the first radio access technology.
The method of claim 1, wherein the second radio access technology is stand-alone 5GNR and the reselection system information block is a SIB24.
The method of claim 1, wherein the one or more base station utilizing the second radio access technology comprises the second base station.
The method of claim 1, wherein the one or more base station utilizing the second radio access technology does not comprise the second base station.
The method of claim 1, further comprising:

receiving a frequency for the one or more base station utilizing the second radio access technology; and

storing the frequency for the one or more base station utilizing the second radio access technology in the acquisition database, wherein determining that the one or more base station utilizing the second radio access technology is present in the acquisition database is based on the frequency.
An apparatus for wireless communication at a user equipment (UE) , comprising:

means for camping in an idle mode on a first base station, the first base station utilizing a first radio access technology;

means for determining that a reselection system information block is not configured for the first base station, the reselection system information block corresponding to a second radio access technology;

means for determining that one or more base station utilizing the second radio access technology is present in an acquisition database of the UE;

means for determining that a reference signal received power from the first base station is below a threshold; and

means for searching for a second base station utilizing the second radio access technology upon determining that one or more base station utilizing the second radio access technology is present in the acquisition database and that the reference signal received power from the first base station is below the threshold.
An apparatus for wireless communication at a user equipment (UE) comprising:

a memory; and

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

camp in an idle mode on a first base station, the first base station utilizing a first radio access technology;

determine that a reselection system information block is not configured for the first base station, the reselection system information block corresponding to a second radio access technology;

determine that one or more base station utilizing the second radio access technology is present in an acquisition database of the UE;

determine that a reference signal received power from the first base station is below a threshold; and

search for a second base station utilizing the second radio access technology upon determining that one or more base station utilizing the second radio access technology is present in the acquisition database and that the reference signal received power from the first base station is below the threshold.
The apparatus of claim 11, wherein the processor is further configured to:

reselect from the first base station to a third base station utilizing the first radio access technology prior to finding the second base station; and

terminate searching for the second base station.
The apparatus of claim 11, wherein the processor is further configured to:

determine that the second base station satisfies reselection criteria; and

register to the second base station.
The apparatus of claim 11, wherein the second base station does not utilize the first radio access technology.
The apparatus of claim 11, wherein the one or more base station utilizing the second radio access technology does not utilize the first radio access technology.
The apparatus of claim 11, wherein the second radio access technology is stand-alone 5GNR and the reselection system information block is a SIB24.
The apparatus of claim 11, wherein the one or more base station utilizing the second radio access technology comprises the second base station.
The apparatus of claim 11, wherein the one or more base station utilizing the second radio access technology does not comprise the second base station.
The apparatus of claim 11, wherein the processor is further configured to:

receive a frequency for the one or more base station utilizing the second radio access technology; and

store the frequency for the one or more base station utilizing the second radio access technology in the acquisition database, wherein determining that the one or more base station utilizing the second radio access technology is present in the acquisition database is based on the frequency.
A non-transitory computer-readable medium storing computer executable code for wireless communication at a user equipment the code when executed by a processor cause the processor to perform the method of any of claims 1-9.