WO2022000470A1

WO2022000470A1 - Method and apparatus for managing inter-rat cell handover

Info

Publication number: WO2022000470A1
Application number: PCT/CN2020/100139
Authority: WO
Inventors: Chaofeng HUI; Bing LENG; Liang Xue; Tong Wu; Huawen CHEN
Original assignee: Qualcomm Incorporated
Priority date: 2020-07-03
Filing date: 2020-07-03
Publication date: 2022-01-06

Abstract

The apparatus of wireless communication includes UE and LTE cells that may block a handover from the LTE cell to a 5G NR Cell while an IMS call service is provided via the LTE cell. The UE may block the handover process to the 5G NR cell by blocking a transmission of a measurement report of neighboring cells to the LTE cell or filtering out the measurements of neighboring 5G NR cells in the measurement report of the neighboring cells. The LTE cell may block the initiation of the handover process to the 5G NR cell by excluding a measurement control to trigger a handover to the 5G NR cell in an instruction to modify the RRC connection, or ignoring the handover to the 5G NR cell indicated in the measurement report received from the UE.

Description

METHOD AND APPARATUS FOR MANAGING INTER-RAT CELL HANDOVER

BACKGROUND Technical Field

The present disclosure relates generally to communication systems, and more particularly, to method and apparatus for managing handover between different radio access technologies (RAT) , particularly between 4G Long Term Evolution (LTE) cells and 5G New Radio (NR) cells while voice over internet protocol (IP) (VoIP) call.

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 user equipment (UE) and LTE cells that may block a handover from the LTE cell to a 5G NR Cell while an internet protocol (IP) multimedia subsystem (IMS) call service is provided via the LTE cell. The LTE cell may transmit an instruction to modify a radio resource control (RRC) connection, and the instruction to modify the RRC connection may include a measurement control to trigger a handover to a 5G New Radio (NR) cell if the UE measures that a reference signal of the 5G NR cell is above a threshold value. However, if the LTE cell is providing the IMS call service to the UE, handing over UE to the 5G NR cell may terminate the IMS call service when the 5G NR cell does not support the IMS call service. The UE may block the handover process to the 5G NR cell by blocking a transmission of a measurement report of neighboring cells to the LTE cell or filtering out the measurements of neighboring 5G NR cells in the measurement report of the neighboring cells. The LTE cell may block the initiation of the handover process to the 5G NR cell by excluding a measurement control to trigger a handover to the 5G NR cell in an instruction to modify the RRC connection, or ignoring the handover to the 5G NR cell indicated in the measurement report received from the UE.

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.

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

FIG. 2B is a diagram illustrating an example of DL channels within a subframe, in accordance with various aspects of the present disclosure.

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

FIG. 2D is a diagram illustrating an example of UL channels within a subframe, in accordance with various aspects of the present disclosure.

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

FIG. 4 is a call flow diagram of a method of wireless communication.

FIG. 5 is a flowchart of a method of wireless communication.

FIG. 6 is a flowchart of a method of wireless communication.

FIG. 7 is a diagram illustrating an example of a hardware implementation for an example apparatus.

FIG. 8 is a diagram illustrating an example of a hardware implementation for an example apparatus.

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, e.g., in a 5 GHz unlicensed frequency spectrum or the like. 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 unlicensed frequency spectrum (e.g., 5 GHz, or the like) 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.

The electromagnetic spectrum is often subdivided, based on frequency/wavelength, into various classes, bands, channels, etc. In 5G NR, two initial operating bands have been identified as frequency range designations FR1 (410 MHz –7.125 GHz) and FR2 (24.25 GHz –52.6 GHz) . The frequencies between FR1 and FR2 are often referred to as mid-band frequencies. Although a portion of FR1 is greater than 6 GHz, FR1 is often referred to (interchangeably) as a “sub-6 GHz” band in various documents and articles. A similar nomenclature issue sometimes occurs with regard to FR2, which is often referred to (interchangeably) as a “millimeter wave” band in documents and articles, despite being different from the extremely high frequency (EHF) band (30 GHz –300 GHz) which is identified by the International Telecommunications Union (ITU) as a “millimeter wave” band.

With the above aspects in mind, unless specifically stated otherwise, it should be understood that the term “sub-6 GHz” or the like if used herein may broadly represent frequencies that may be less than 6 GHz, may be within FR1, or may include mid-band frequencies. Further, unless specifically stated otherwise, it should be understood that the term “millimeter wave” or the like if used herein may broadly represent frequencies that may include mid-band frequencies, may be within FR2, or may be within the EHF band.

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 frequencies, and/or near millimeter wave frequencies in communication with the UE 104. When the gNB 180 operates in millimeter wave or near millimeter wave frequencies, the gNB 180 may be referred to as a millimeter wave base station. The millimeter wave base station 180 may utilize beamforming 182 with the UE 104 to compensate for the 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 quality of service (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 and/or the base station 180 may be configured to manage cell handover between different RATs, particularly, between LTE cells and 5G NR cells while the UE is on a VoIP call (198) . Although the following description may be focused on LTE cells and 5G NR cells, the concepts described herein may be applicable to other similar areas, such as LTE-A, CDMA, GSM, and other wireless technologies.

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. At least one of the TX processor 316, the RX processor 370, and the controller/processor 375 may be configured to perform aspects in connection with 198 of FIG. 1.

There are reports of evolved packet system (EPS) fallback IMS call failure issues in field tests because the LTE cells redirect the UE back to NR cell due to measurement report during an LTE tracking area update (TAU) procedure. That is, according to the mobile network with the LTE RAT and the 5G NR RAT configuration, initiating an IMS call on the UE registered to the 5G NR cell may initiate the handover to the LTE cell since the 5G NR cell does not support the VoIP call. After the successful handover to the LTE cell, the UE may transmit a request for tracking area update, and the LTE cell may send a RRC connection reconfiguration instruction with a measurement control to the UE. The UE may prepare and transmit a measurement report, which may indicate the LTE cell to initiate a handover to the 5G NR cell.

This would cause VoIP call fail since NR cell may not support a voice over NR (VoNR) at current stage. Particularly, for initial standalone (SA) NR network deployment, only a packet switched handover (PSHO) may be supported for SA voice call solution. Therefore, during the VoIP call setup or active phase, a handover back to the SA NR cell based on the UE indication in the measurement report to handover to the NR cell would cause the VoIP call failure since the SA NR cell may not have the VoNR capabilities. Accordingly, when the UE is handed over to the LTE cells and performs the TAU, we may block the handover of the UE back to the 5G NR order if the UE and the LTE cell are providing an IMS call.

FIG. 4 is a call flow diagram 400 of a method of wireless communication.

Consider that the initial 5G core network does not support full VoNR functionalities at current stage, redirecting the UE 402 to 5G NR cell 404 is not reasonable when LTE cell 406 is in critical voice call setup procedure. That is, not all 5G NR core network support the VoNR functions, redirecting the UE 402, that is provided with VoIP call via LTE cell 406, to the 5G NR cell 404 is not reasonable because the UE 402 may lose the critical VoIP call service that was provided via the LTE cell 406. According to the first aspects of disclosure, which provides that when UE 402 handover to LTE and doing TAU, let UE 402 block report B1 event until the call ends. For the PSHO, a dedicate bearer could be only assigned in LTE network, and the 5G NR network could not modify PDU session to add QoS flow for the PDU session. In the call, there is also no need to be back to SA 5G NR network since the voice /video real-time transport protocol (RTP) packet could be sent through LTE network.

At 408, the UE 402 is connected and registered to a 5G NR cell 404, which is a SA 5G NR cell 404, and also registered to the IMS service via the 5G NR cell 404. At 410, the user of the UE 402 initiates an VoIP call via the UE 402.

At 412, the UE 402 transmits a request for VoIP call to the 5G NR cell 404, in response to the user of the UE 402 initiating the VoIP call. For example, the UE 402 may receive a mobile originated (MO) call, and initiate a VoIP call. The UE 402 may follow certain session initiation protocol (SIP) , and transmit an IMS_SIP_INVITE request to the 5G NR cell 404, indicating that the UE 402 is being invited to participate in a call session.

At 414, upon receiving the request for VoIP call, the 5G NR cell 404 may instruct the UE 402 to initiate a handover to an LTE cell 406, since the 5G NR cell 404 does not support the VoIP call. For example, the 5G NR cell 404 may transmit a Mobility From NR Command message to the UE 402, initiating a handover procedure to move the UE 402 to a cell using other RAT, such as the LTE. The Mobility From NR Command message may include the radio resources that have been allocated for the UE 402 in the target LTE cell 406, based on previous measurement reports.

At 416, the UE 402 and the LTE cell 406 may reconfigure the RRC connection and complete the handover process. For example, the LTE cell 406 may transmit an RRC Connection Reconfiguration message to the UE 402 to handover the UE 402 to the LTE cell 406 by modifying the RRC connection. In response, the UE 402 may transmit an RRC Connection Reconfiguration complete message to the LTE cell 406, indicating that the handover is completed.

Upon handing over the UE 402 to the LTE cell 406, at 418, the UE 402 may transmit a TAU request to update the tracking area. At 420, upon receiving the TAU request from the UE 402, the LTE cell 406 may transmit an RRC Connection Reconfiguration message including a measurement control. The measurement control may indicate and/or configure a set of handover events to other RAT. For example, the set of handover events may include an A1 event, an A2 event, and a B1 event. First, the A1 event may be triggered when the serving cell becomes better than a threshold. When the A1 event is triggered, the UE may stop measuring for the other RAT. Second, the A2 event may be triggered when the serving cell becomes worse than a threshold. When the A2 event is triggered, the UE may start measuring for the other RAT. Finally, the B1 event may be triggered when a neighboring cell becomes better than a threshold. Then the B1 event is triggered, the UE may initiate the inter-RAT handover to the other RAT.

At 422, upon receiving the RRC Connection Reconfiguration message from the LTE cell 406, the UE 402 may determine whether the IMS call is provided via the LTE cell 406. If the UE 402 determines that the IMS call is provided via the LTE cell 406, the UE 402 may determine to block an initiation of a handover process from the LTE cell 406 to 5G NR cell 404 at 423.

At 424, the UE 402 may block transmitting a B1 event to the LTE cell 406, which may initiate the LTE cell 406 to handover UE 402 to the 5G NR cell 404, based on determining that the IMS call is provided via the LTE cell 406. For example, the UE 402 may block transmitting the B1 event to the LTE cell 406 by two different approaches. First, the UE 402 may simply block transmitting the measurement report with the B1 event. That is, the UE 402 may generate the measurement report and when the measurement report triggers the B1 event, the UE 402 may determine not to transmit the measurement report with the B1 event. At 425, the UE 402 may generate a measurement report with reference signals received from neighboring 5G NR cells filtered out. That is, UE 402 may filter out the measurements of the reference signals received from the neighboring 5G NR cells, and the measurement report would not trigger a B1 event.

At 426, the UE 402 may transmit a measurement report without the B1 event to the LTE cell 406. Accordingly, the LTE cell 406 may receive the measurement report without the B1 event from the UE 402, and therefore, the LTE cell 406 may not instruct the UE 402 to handover to the 5G NR cell 404.

At 428, the UE 402 and the LTE cell 406 may complete the TAU and successfully setup the VoIP call. Accordingly the UE 402 may be able to successfully set up the VoIP call with the LTE cell 406 without handing over UE 402 to the 5G NR cell 404.

In an aspect of the disclosure, the LTE cell 406 shall not trigger sending a measurement control with B1 event for NR cell 404 to UE 402 when found there is an ongoing IMS call for the UE 402. In another aspect, the LTE cell 406 may configure measurement control with B1 event for 5G NR cell 404 during the IMS call procedure, by receiving the measurement report containing the 5G NR cell 404 from the UE 402, the LTE cell 406 may ignore the B1 event and not trigger the inter-RAT handover to 5G NR cell 404 if there is an ongoing IMS call.

The LTE cell 406 may also take certain steps to block the handover process of the UE 402 to the 5G NR cell 404. At 430, the LTE cell 406 may determine whether the IMS call is provided via the LTE cell 406 to the UE 402. Here, the LTE cell 406 may receive IMS call information from the corresponding IMS core network.

First, upon determining that the IMS call is provided via the LTE cell 406 to the UE 402, the LTE cell 406 may, at 420, transmit the measurement control without the B1 event. Accordingly, the UE 402 may generate measurement report without the B1 event, and therefore, the UE 402 may transmit the measurement report without the B1 event (426) .

Second, upon determining that the IMS call is provided via the LTE cell 406 to the UE 402, the LTE cell 406 may, at 420, transmit the measurement control with the B1 event, and when, at 432, the UE 402 transmits a measurement report with the B1 event to the LTE cell 406, the LTE cell 406 may determine, at 434, to ignore the B1 event in the measurement report received from the UE 402. Accordingly, the UE 402 and the LTE cell 406 may complete the TAU and successfully setup the VoIP call at 428. Accordingly, the UE 402 may be able to successfully set up the VoIP call with the LTE cell 406 without handing over UE 402 to the 5G NR cell 404.

Accordingly, in live network, the UE may have a good NR cell coverage area and a little weaker LTE cell coverage area from a neighboring compared to the NR cell. When the UE registers to the 5G NR SA network and make a voice call, the UE may successfully setup the voice call over LTE despite the better cell coverage area of the NR cell. The OTA messages captured from the UE may also show that 1) the measurement control is not received from the LTE cell, 2) the measurement report does not include the B1 event, or 3) the LTE cell ignores the measurement control with B1 received from the UE.

FIG. 5 is a flowchart 500 of a method of wireless communication. The method may be performed by a UE (e.g., the UE 104; the apparatus 702) . At 502, the UE may receive, from LTE cell, an RRC connection reconfiguration instruction including measurement control to trigger a handover (420) . For example, 502 may be performed by a RRC and handover component 742.

At 504, the UE may determine whether an IMS call service is provided via the LTE cell. For example, 504 may be performed by an IMS component 740.

At 506, based on the determination that the IMS call service is not provided via the LTE cell, the UE may generate and transmit a measurement report of reference signals received from neighboring cells including 5G NR cells. For example, 506 may be performed by an RS measurement component 744.

At 508, based on the determination that the IMS call service is provided via the LTE cell, the UE may block an initiation of the handover process from the LTE cell to the 5G NR cell (423) . For example, 508 may be performed by the RRC and handover component 742.

At 510, to block the initiation of the handover process from the LTE cell to the 5G NR cell, the UE may block transmission of the measurement report of neighboring cells’ reference signals that triggers B1 event to the LTE cell (424) . For example, 510 may be performed by the RS measurement component 744.

At 512, to block the initiation of the handover process from the LTE cell to the 5G NR cell, the UE may generate a measurement report with reference signals received from neighboring 5G NR cells filtered out (425) . For example, 510 may be performed by the RS measurement component 744.

At 514, the UE may transmit measurement report without B1 event to the LTE cell (426) . For example, 512 may be performed by the RS measurement component 744.

Finally at 516, the UE may successfully setup the VoIP call with the LTE cell (428) . For example, 516 may be performed by the RS measurement component 744.

FIG. 6 is a flowchart 600 of a method of wireless communication. The method may be performed by a base station (e.g., the base station 102/180; the apparatus 802. At 602, the base station may transmit, to the UE, the RRC connection reconfiguration instruction including measurement control to trigger a handover (420) . For example, 602 may be performed by an RRC and handover component 842.

At 604, the base station may receive, from the UE, the measurement report from the UE indicating a handover to a 5G NR cell (432) . For example, 604 may be performed by the RRC and handover component 842.

At 606, the base station may determine whether the IMS call service is provided via the LTE cell (430) . For example, 606 may be performed by an IMS component 840.

At 608, the base station may ignore the handover to the 5G NR cell indicated in the measurement report received from the UE (434) . For example, 608 may be performed by the RRC and handover component 842.

At 609, the base station may successfully setup the VoIP call with the UE (428) . For example, 609 may be performed by the IMS component 840.

At 610, the base station may initiate the handover to the 5G NR cell as indicated in the measurement report received from the UE. For example, 610 may be performed by the RRC and handover component 842.

At 612, the base station may determine whether the IMS call service is provided via the LTE cell (430) . For example, 612 may be performed by the IMS component 840.

At 614, the base station may transmit, to the UE, the RRC connection reconfiguration instruction without a measurement control to trigger a handover (420) . For example, 614 may be performed by the RRC and handover component 842.

Finally, at 616, the base station may receive, from the UE, the measurement report from the UE without the handover to the 5G NR cell (426) . For example, 616 may be performed by the RRC and handover component 842.

FIG. 7 is a diagram 700 illustrating an example of a hardware implementation for an apparatus 702. The apparatus 702 is a UE and includes a cellular baseband processor 704 (also referred to as a modem) coupled to a cellular RF transceiver 722 and one or more subscriber identity modules (SIM) cards 720, an application processor 706 coupled to a secure digital (SD) card 708 and a screen 710, a Bluetooth module 712, a wireless local area network (WLAN) module 714, a Global Positioning System (GPS) module 716, and a power supply 718. The cellular baseband processor 704 communicates through the cellular RF transceiver 722 with the UE 104 and/or BS 102/180. The cellular baseband processor 704 may include a computer-readable medium /memory. The computer-readable medium /memory may be non-transitory. The cellular baseband processor 704 is responsible for general processing, including the execution of software stored on the computer-readable medium /memory. The software, when executed by the cellular baseband processor 704, causes the cellular baseband processor 704 to perform the various functions described supra. The computer-readable medium /memory may also be used for storing data that is manipulated by the cellular baseband processor 704 when executing software. The cellular baseband processor 704 further includes a reception component 730, a communication manager 732, and a transmission component 734. The communication manager 732 includes the one or more illustrated components. The components within the communication manager 732 may be stored in the computer-readable medium /memory and/or configured as hardware within the cellular baseband processor 704. The cellular baseband processor 704 may be a component of the UE 350 and may include the memory 360 and/or at least one of the TX processor 368, the RX processor 356, and the controller/processor 359. In one configuration, the apparatus 702 may be a modem chip and include just the baseband processor 704, and in another configuration, the apparatus 702 may be the entire UE (e.g., see 350 of FIG. 3) and include the aforediscussed additional modules of the apparatus 702.

The communication manager 732 includes an IMS component 740 that is configured to determine whether an IMS call service is provided via the LTE cell and successfully setup the VoIP call with the LTE cell, e.g., as described in connection with 504 and 516. The communication manager 732 further includes an RRC and handover component 742 that is configured to receive, from LTE cell, RRC connection reconfiguration instruction including measurement control to trigger a handover and block an initiation of the handover process from the LTE cell to the 5G NR cell, e.g., as described in connection with 502 and 508. The communication manager 732 further includes an RS measurement component 744 that is configured to generate and transmit a measurement report of reference signals received from neighboring cells including 5G NR cells, block transmission of the measurement report of neighboring cells’ reference signals that triggers B1 event to the LTE cell, and generate a measurement report with reference signals received from neighboring 5G NR cells filtered out and transmit the measurement report without B1 event to the LTE cell, e.g., as described in connection with 506, 510, 512, and 514.

The apparatus may include additional components that perform each of the blocks of the algorithm in the aforementioned flowcharts of FIGs. 4 and 5. As such, each block in the aforementioned flowcharts of FIGs. 4 and 5 may be performed by a component and the apparatus may include one or more of those components. The components may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

In one configuration, the apparatus 702, and in particular the cellular baseband processor 704, includes means for receiving an instruction to modify an RRC connection from an LTE cell, the instruction including a measurement control to trigger a handover to a 5G NR cell, means for determining whether an IMS call service is provided via the LTE cell, and means for blocking an initiation of a handover process from the LTE cell to the 5G NR cell based on the determination that the IMS call is provided via the LTE cell. The aforementioned means may be one or more of the aforementioned components of the apparatus 702 configured to perform the functions recited by the aforementioned means. As described supra, the apparatus 702 may include the TX Processor 368, the RX Processor 356, and the controller/processor 359. As such, in one configuration, the aforementioned means may be the TX Processor 368, the RX Processor 356, and the controller/processor 359 configured to perform the functions recited by the aforementioned means.

FIG. 8 is a diagram 800 illustrating an example of a hardware implementation for an apparatus 802. The apparatus 802 is a BS and includes a baseband unit 804. The baseband unit 804 may communicate through a cellular RF transceiver with the UE 104. The baseband unit 804 may include a computer-readable medium /memory. The baseband unit 804 is responsible for general processing, including the execution of software stored on the computer-readable medium /memory. The software, when executed by the baseband unit 804, causes the baseband unit 804 to perform the various functions described supra. The computer-readable medium /memory may also be used for storing data that is manipulated by the baseband unit 804 when executing software. The baseband unit 804 further includes a reception component 830, a communication manager 832, and a transmission component 834. The communication manager 832 includes the one or more illustrated components. The components within the communication manager 832 may be stored in the computer-readable medium /memory and/or configured as hardware within the baseband unit 804. The baseband unit 804 may be a component of the BS 310 and may include the memory 376 and/or at least one of the TX processor 316, the RX processor 370, and the controller/processor 375.

The communication manager 832 includes an IMS component 840 that is configured to determine whether the IMS call service is provided via the LTE cell and setup the VoIP call with the UE, e.g., as described in connection with 606, 609, and 612. The communication manager 832 further includes an RRC and handover component 842 that is configured to transmit, to the UE, the RRC connection reconfiguration instruction with or without the measurement control to trigger a handover, receive, from the UE, the measurement report from the UE with or without a handover to the 5G NR cell, ignore the handover to the 5G NR cell indicated in the measurement report received from the UE, and initiate the handover to the 5G NR cell as indicated in the measurement report received from the UE, e.g., as described in connection with 602, 604, 608, 610, 612, 614, and 616.

The apparatus may include additional components that perform each of the blocks of the algorithm in the aforementioned flowcharts of FIGs. 4 and 6. As such, each block in the aforementioned flowcharts of FIGs. 4 and 6 may be performed by a component and the apparatus may include one or more of those components. The components may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof.

In one configuration, the apparatus 802, and in particular the baseband unit 804, includes means for determining whether an IMS call service is provided to a UE via the LTE cell, means for blocking an initiation of a handover process from the LTE cell to a 5G NR cell based on the determination that the IMS call is provided to the UE via the LTE cell, and means for transmitting an instruction to modify an RRC connection from the LTE cell, the instruction including a measurement control to trigger a handover to the 5G NR cell based on the determination that the IMS call is not provided to the UE via the LTE cell. The aforementioned means may be one or more of the aforementioned components of the apparatus 802 configured to perform the functions recited by the aforementioned means. As described supra, the apparatus 802 may include the TX Processor 316, the RX Processor 370, and the controller/processor 375. As such, in one configuration, the aforementioned means may be the TX Processor 316, the RX Processor 370, and the controller/processor 375 configured to perform the functions recited by the aforementioned means.

Referring again to FIGs. 4, 5, 6, 7, and 8, user equipment (UE) and LTE cells that may block a handover from the LTE cell to a 5G NR Cell while an internet protocol (IP) multimedia subsystem (IMS) call service is provided via the LTE cell. The LTE cell may transmit an instruction to modify a radio resource control (RRC) connection, and the instruction to modify the RRC connection may include a measurement control to trigger a handover to a 5G New Radio (NR) cell if the UE measures that a reference signal of the 5G NR cell is above a threshold value. However, if the LTE cell is providing the IMS call service to the UE, handing over UE to the 5G NR cell may terminate the IMS call service when the 5G NR cell does not support the IMS call service. The UE may block the handover process to the 5G NR cell by blocking a transmission of a measurement report of neighboring cells to the LTE cell or filtering out the measurements of neighboring 5G NR cells in the measurement report of the neighboring cells. The LTE cell may block the initiation of the handover process to the 5G NR cell by excluding a measurement control to trigger a handover to the 5G NR cell in an instruction to modify the RRC connection, or ignoring the handover to the 5G NR cell indicated in the measurement report received from the UE.

According to the aspects of disclosure, the UE may have a good NR cell coverage area and a little weaker LTE cell coverage area compared to the neighboring NR cell. The UE registered to the 5G NR SA network may make a voice call, and the UE may be handed over to the LTE cell and successfully setup the voice call over LTE cell despite the better cell coverage area of the NR cell. The over the air (OTA) messages captured from the UE may also show that 1) the measurement control is not received from the LTE cell, 2) the measurement report does not include the B1 event, or 3) the LTE cell ignores the measurement control with B1 received from the UE.

Further disclosure is included in the Appendix.

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.

Priority EPS fallback over inter radio access technology (RAT) redirection procedure for VoIP call

Inter RAT handover on VoIP call:

There are reports of EPS fallback IMS call failure issues in field tests.

UE redirection to NR cell again due to report B1 event in measurement report during LTE TAU procedure is the reason for IMS call failure.

This would cause VoIP call fail since NR cell does not support VoNR at current stage.

For initial SA NR network deployment, only PSHO is supported for SA voice solution.

Therefore, during VoIP call setup or active phase, the handover back to SA NR network even when UE meets the B1 event threshold would cause VoIP call failure.

Inter-RAT handover on VoIP and call drop:

FIRST ASPECT OF THE DISCLOSURE: UE side

Consider initial 5G core network does not support full Voice over NR functionalities at current stage, redirect to NR is not reasonable when LTE rat is in critical voice call setup procedure. Accordingly, the aspects of disclosure provide that when UE handover to LTE and doing TAU, let UE block report B1 event until call end. For PSHO, dedicate bearer could be only assigned in LTE network. NR network could not modify PDU session to add QoS flow for it. In the call, it is also no need to be back to NR SA network since voice/video RTP packet could be sent through LTE network.

Flow chart:

SECOND ASPECT OF THE DISCLOSURE: Network side

LTE network shall not trigger send measurement control with B1 event for NR to UE when found there is an ongoing IMS call for this UE.

Flow Chart:

THIRD ASPECT OF THE DISCLOSURE: Network side:

LTE network configure measurement control with B1 event for NR during IMS call procedure, by receiving measurement report contains NR rat from UE, it shall ignore the B1 event and not trigger inter-RAT handover to NR if there is an ongoing IMS call

Flow Chart:

Example:

In live network, the UE may have a good NR cell coverage area and a little weaker LTE cell coverage area compared to the neighboring NR cell. When the UE registers to the 5G NR SA network and make a voice call, the UE may successfully setup the voice call over LTE despite the better cell coverage area of the NR cell. The OTA messages captured from the UE may also show that 1) the measurement control is not received from the LTE cell, 2) the measurement report does not include the B1 event, or 3) the LTE cell ignores the measurement control with B1 received from the UE.

Claims

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

receiving an instruction to modify a radio resource control (RRC) connection from a 4G Long Term Evolution (LTE) cell, the instruction including a measurement control to trigger a handover to a 5G New Radio (NR) cell;

determining whether an internet protocol (IP) multimedia subsystem (IMS) call service is provided via the LTE cell; and

blocking an initiation of a handover process from the LTE cell to the 5G NR cell based on the determination that the IMS call is provided via the LTE cell.
The method of claim 1, wherein the blocking the initiation of the handover process comprises:

blocking a transmission of a measurement report of reference signals received from neighboring cells to the LTE cell.
The method of claim 2, further comprising:

transmitting the measurement report without a B1 event to the LTE cell.
The method of claim 3, further comprising:

establishing a voice over IP (VoIP) with the LTE cell in response to transmitting the measurement report without the B1 event to the LTE cell.
The method of claim 1, wherein the blocking the initiation of the handover process comprises:

generating a measurement report of reference signals received from neighboring cells by filtering out measurements of reference signals received from neighboring 5G NR cells; and

transmitting the generated measurement report to the LTE cell.
The method of claim 1, further comprising:

generating a measurement report of reference signals received from neighboring cells including 5G NR cells based on the determination that the IMS call is not provided via the LTE cell; and

transmitting the generated measurement report to the LTE cell.
An apparatus for wireless communication of a user equipment (UE) , comprising:

means for receiving an instruction to modify a radio resource control (RRC) connection from a 4G Long Term Evolution (LTE) cell, the instruction including a measurement control to trigger a handover to a 5G New Radio (NR) cell;

means for determining whether an internet protocol (IP) multimedia subsystem (IMS) call service is provided via the LTE cell; and

means for blocking an initiation of a handover process from the LTE cell to the 5G NR cell based on the determination that the IMS call is provided via the LTE cell.
The apparatus of claim 7, wherein the initiation of the handover process is blocked by blocking a transmission of a measurement report of reference signals received from neighboring cells to the LTE cell.
The apparatus of claim 8, further comprising:

means for transmitting the measurement report without a B1 event to the LTE cell.
The apparatus of claim 9, further comprising:

means for establishing a voice over IP (VoIP) with the LTE cell in response to transmitting the measurement report without the B1 event to the LTE cell.
The apparatus of claim 7, wherein the initiation of the handover process is blocked by:

generating a measurement report of reference signals received from neighboring cells by filtering out measurements of reference signals received from neighboring 5G NR cells; and

transmitting the generated measurement report to the LTE cell.
The apparatus of claim 7, further comprising:

means for generating a measurement report of reference signals received from neighboring cells including 5G NR cells based on the determination that the IMS call is not provided via the LTE cell; and

means for transmitting the generated measurement report to the LTE cell.
An apparatus for wireless communication of a user equipment (UE) , comprising:

a memory; and

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

receive an instruction to modify a radio resource control (RRC) connection from a 4G Long Term Evolution (LTE) cell, the instruction including a measurement control to trigger a handover to a 5G New Radio (NR) cell;

determine whether an internet protocol (IP) multimedia subsystem (IMS) call service is provided via the LTE cell; and

block an initiation of a handover process from the LTE cell to the 5G NR cell based on the determination that the IMS call is provided via the LTE cell.
The apparatus of claim 13, wherein the at least one processor is configured to block the initiation of the handover process by blocking a transmission of a measurement report of reference signals received from neighboring cells to the LTE cell.
The apparatus of claim 14, wherein the at least one processor is configured to:

transmit the measurement report without a B1 event to the LTE cell.
The apparatus of claim 15, wherein the at least one processor is configured to:

establish a voice over IP (VoIP) with the LTE cell in response to transmitting the measurement report without the B1 event to the LTE cell.
The apparatus of claim 13, wherein the at least one processor is configured to block the initiation of the handover process by:

generating a measurement report of reference signals received from neighboring cells by filtering out measurements of reference signals received from neighboring 5G NR cell, and

transmitting the generated measurement report to the LTE cell.
The apparatus of claim 13, wherein the at least one processor is configured to:

generate a measurement report of reference signals received from neighboring cells including 5G NR cells based on the determination that the IMS call is not provided via the LTE cell; and

transmit the generated measurement report to the LTE cell.
A computer-readable medium storing computer executable code, the code when executed by a processor of a user equipment (UE) cause the processor to:

receive an instruction to modify a radio resource control (RRC) connection from a 4G Long Term Evolution (LTE) cell, the instruction including a measurement control to trigger a handover to a 5G New Radio (NR) cell;

determine whether an internet protocol (IP) multimedia subsystem (IMS) call service is provided via the LTE cell; and

block an initiation of a handover process from the LTE cell to the 5G NR cell based on the determination that the IMS call is provided via the LTE cell.
A method of wireless communication of a 4G Long Term Evolution (LTE) cell, comprising:

determining whether an internet protocol (IP) multimedia subsystem (IMS) call service is provided to a user equipment (UE) via the LTE cell; and

blocking an initiation of a handover process from the LTE cell to a 5G New Radio (NR) cell based on the determination that the IMS call is provided to the UE via the LTE cell.
The method of claim 20, wherein the blocking the initiation of the handover process comprises:

determining to exclude a measurement control to trigger a handover to a 5G New Radio (NR) cell in an instruction transmitted to the UE to modify a radio resource control (RRC) , based on the determination that the IMS call is provided to the UE via the LTE cell; and

transmitting the instruction to modify the RRC connection without the measurement control to trigger the handover to the 5G NR cell based on the determination that the IMS call is provided to the UE via the LTE cell.
The method of claim 21, further comprising:

receiving, from the UE, a measurement report without the handover to the 5G NR cell in response to transmitting the instruction to modify the RRC connection without the measurement control.
The method of claim 22, further comprising:

establishing a voice over IP (VoIP) with the UE in response to receiving the measurement report without the handover to the 5G NR cell.
The method of claim 20, wherein the blocking the initiation of the handover process comprises:

transmitting an instruction to modify a radio resource control (RRC) connection from the LTE cell, the instruction including a measurement control to trigger a handover to the 5G NR cell; and

receiving, from the UE, a measurement report of reference signals received by the UE from neighboring cells, the measurement report indicating a handover to the 5G NR cell.
The method of claim 21, further comprising:

ignoring the handover to the 5G NR cell indicated in the measurement report received from the UE based on the determination that the IMS call is provided to the UE via the LTE cell.
The method of claim 25, further comprising:

establishing a voice over IP (VoIP) with the UE in response to ignoring the handover to the 5G NR cell indicated in the measurement report.
The method of claim 20, further comprising:

transmitting an instruction to modify a radio resource control (RRC) connection from the LTE cell, the instruction including a measurement control to trigger a handover to the NR cell based on the determination that the IMS call is not provided to the UE via the LTE cell.
An apparatus for wireless communication of a 4G Long Term Evolution (LTE) cell, comprising:

means for determining whether an internet protocol (IP) multimedia subsystem (IMS) call service is provided to a user equipment (UE) via the LTE cell; and

means for blocking an initiation of a handover process from the LTE cell to a 5G New Radio (NR) cell based on the determination that the IMS call is provided to the UE via the LTE cell.
The apparatus of claim 28, wherein the initiation of the handover process is blocked by:

means for determining to exclude a measurement control to trigger a handover to a 5G New Radio (NR) cell in an instruction transmitted to the UE to modify a radio resource control (RRC) , based on the determination that the IMS call is provided to the UE via the LTE cell; and

means for transmitting the instruction to modify the RRC connection without the measurement control to trigger the handover to the 5G NR cell based on the determination that the IMS call is provided to the UE via the LTE cell.
The apparatus of claim 29, further comprising:

means for receiving, from the UE, a measurement report without the handover to the 5G NR cell in response to transmitting the instruction to modify the RRC connection without the measurement control.
The apparatus of claim 30, further comprising:

means for establishing a voice over IP (VoIP) with the UE in response to receiving the measurement report without the handover to the 5G NR cell.
The apparatus of claim 28, wherein the initiation of the handover process is blocked by:

means for transmitting an instruction to modify a radio resource control (RRC) connection from the LTE cell, the instruction including a measurement control to trigger a handover to the 5G NR cell; and

means for receiving, from the UE, a measurement report of reference signals received by the UE from neighboring cells, the measurement report indicating a handover to the 5G NR cell.
The apparatus of claim 32, further comprising:

means for ignoring the handover to the 5G NR cell indicated in the measurement report received from the UE based on the determination that the IMS call is provided to the UE via the LTE cell.
The apparatus of claim 33, further comprising:

means for establishing a voice over IP (VoIP) with the UE in response to ignoring the handover to the 5G NR cell indicated in the measurement report.
The apparatus of claim 28, further comprising:

means for transmitting an instruction to modify a radio resource control (RRC) connection from the LTE cell, the instruction including a measurement control to trigger a handover to the 5G NR cell based on the determination that the IMS call is not provided to the UE via the LTE cell.
An apparatus for wireless communication of a 4G Long Term Evolution (LTE) cell, comprising:

a memory; and

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

determine whether an internet protocol (IP) multimedia subsystem (IMS) call service is provided to a user equipment (UE) via the LTE cell; and

block an initiation of a handover process from the LTE cell to a 5G New Radio (NR) cell based on the determination that the IMS call is provided to the UE via the LTE cell.
The apparatus of claim 36, wherein the at least one processor is configured to block the initiation of the handover process by:

determining to exclude a measurement control to trigger a handover to a 5G New Radio (NR) cell in an instruction transmitted to the UE to modify a radio resource control (RRC) , based on the determination that the IMS call is provided to the UE via the LTE cell; and

transmitting the instruction to modify the RRC connection without the measurement control to trigger the handover to the 5G NR cell based on the determination that the IMS call is provided to the UE via the LTE cell.
The apparatus of claim 37, wherein the at least one processor is configured to:

receive, from the UE, a measurement report without the handover to the 5G NR cell in response to transmitting the instruction to modify the RRC connection without the measurement control.
The apparatus of claim 38, wherein the at least one processor is configured to:

establish a voice over IP (VoIP) with the UE in response to receiving the measurement report without the handover to the 5G NR cell.
The apparatus of claim 36, wherein the at least one processor is configured to block the initiation of the handover process by:

transmitting an instruction to modify a radio resource control (RRC) connection from the LTE cell, the instruction including a measurement control to trigger a handover to the 5G NR cell; and

receiving, from the UE, a measurement report of reference signals received by the UE from neighboring cells, the measurement report indicating a handover to the 5G NR cell.
The apparatus of claim 40, wherein the at least one processor is configured to:

ignore the handover to the 5G NR cell indicated in the measurement report received from the UE based on the determination that the IMS call is provided to the UE via the LTE cell.
The apparatus of claim 41, wherein the at least one processor is configured to:

establish a voice over IP (VoIP) with the UE in response to ignoring the handover to the 5G NR cell indicated in the measurement report.
The apparatus of claim 36, wherein the at least one processor is further configured to:

transmit an instruction to modify a radio resource control (RRC) connection from the LTE cell, the instruction including a measurement control to trigger a handover to the 5G NR cell based on the determination that the IMS call is not provided to the UE via the LTE cell.
A computer-readable medium storing computer executable code, the code when executed by a processor of a 4G Long Term Evolution (LTE) cell cause the processor to:

determine whether an internet protocol (IP) multimedia subsystem (IMS) call service is provided to a user equipment (UE) via the LTE cell; and

block an initiation of a handover process from the LTE cell to a 5G New Radio (NR) cell based on the determination that the IMS call is provided to the UE via the LTE cell.