Move to WIFI voice preemption for single-radio voice call continuity to improve voice / video call quality

Abstract

A configuration is disclosed that enables a UE to preempt SRVCC by triggering a handover to a Wi-Fi network. The apparatus determines whether it is feasible for a Wi-Fi cell to be a first target cell among a plurality of target cells that serves the UE to continue active transmission on the Wi-Fi cell. The apparatus extends the TTT timer length at least in part based on the determination that it is feasible for the Wi-Fi cell to be a target cell that serves the UE to continue active transmission on the Wi-Fi cell. The apparatus initiates a handover from a first network to the Wi-Fi cell before the TTT timer expires and before the first network initiates a handover to a second target cell among the plurality of target cells on a second network.

Description

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of U.S. Patent Application No. 16 / 870,686, filed on May 8, 2020, entitled "Moving to Wi - Fi Voice to Pre - empt Single - Radio Voice Call Continuity (SRVCC) for Improving Voice / Video Call Quality", the entire content of which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure generally relates to communication systems, and more particularly, to configurations for pre - empting Single - Radio Voice Call Continuity (SRVCC) by moving to Wi - Fi voice. Background Art

[0004] Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasting. A typical wireless communication system may employ a multiple access technology 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.

[0005] These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate at the urban, national, regional, and even global levels. An example telecommunication standard is 5G New Radio (NR). 5G NR is part of the ongoing evolution of mobile broadband promulgated by the Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., related to the Internet of Things (IoT)), and other requirements. 5G NR includes services associated with Enhanced Mobile Broadband (eMBB), Massive Machine - Type Communication (mMTC), and Ultra - Reliable Low - Latency Communication (URLLC). Some aspects of 5G NR may be based on the 4G Long - Term Evolution (LTE) standard. There is a need for further improvement in 5G NR technology. These improvements may also be applicable to other multiple access technologies and telecommunication standards that employ these technologies. Summary of the Invention

[0006] A brief summary of one or more aspects is presented below to provide a basic understanding of these aspects. This summary is not an extensive overview of all contemplated aspects, and is neither intended to identify key or critical elements of all aspects nor to 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.

[0007] In one aspect of the present disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a device at a UE. The device may be a processor and / or a modem at the UE or the UE itself. The device determines whether it is feasible for a Wi-Fi cell to be a first target cell serving the UE from among a plurality of target cells to continue active transmission on the Wi-Fi cell. The device extends the length of a trigger time (TTT) timer at least partially based on the determination that it is feasible for the Wi-Fi cell to be a target cell serving the UE to continue active transmission on the Wi-Fi cell. The device initiates a handover from a first network to the Wi-Fi cell before the TTT timer expires and before the first network initiates a handover to a second target cell from among the plurality of target cells to a second network.

[0008] In some aspects, the device may receive a handover threshold for a handover between the first network and the second network from a base station of the first network.

[0009] In some aspects, based at least on the signal strength of the Wi-Fi cell, it is feasible for the Wi-Fi cell to be a target cell serving the UE to continue active transmission on the Wi-Fi cell.

[0010] In some aspects, the device may determine whether it is feasible for the Wi-Fi cell to be a target cell before the second target cell on the second network meets the handover threshold.

[0011] In some aspects, a handover from the first network to the Wi-Fi cell is initiated if the signal strength of the Wi-Fi cell is greater than the signal strength of the first network.

[0012] In some aspects, extending the length of the TTT timer delays the transmission of a measurement report from the UE to the base station, where the measurement report includes the signal strengths of the first network and the second network in the preparation for a handover from the first network to the second network.

[0013] In some aspects, the delay in the transmission of the measurement report allows the initiation of a handover from the first network to the Wi-Fi cell.

[0014] In some aspects, if the handover to the Wi-Fi cell is completed, the measurement report is not sent when the TTT timer expires.

[0015] In some aspects, if there is no active transmission on the first network, the measurement report is not sent when the TTT time expires.

[0016] In some aspects, the device may determine whether the signal strength of the second target cell is greater than the signal strength of the active transmission on the first network such that the first network is ready to initiate a handover to the second target cell.

[0017] In another aspect of the present disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be a device at a base station. The device may be a processor and / or a modem at the base station or the base station itself. The apparatus communicates with a user equipment (UE) on a first network, where an active transmission occurs between the base station and the UE. The apparatus receives an indication from the UE to perform a handover of the active transmission to a Wi-Fi cell, where the Wi-Fi cell is a first target cell from a plurality of target cells. The apparatus performs the handover of the active transmission to the Wi-Fi cell in response to the indication received from the UE.

[0018] In some aspects, the apparatus sends a handover threshold for handover between the first network and a second network to the UE.

[0019] In some aspects, at least based on the signal strength of the Wi-Fi cell, it is feasible for the Wi-Fi cell to be a target cell serving the UE to continue the active transmission on the Wi-Fi cell.

[0020] In some aspects, the base station receives an indication to perform a handover of the active transmission to the Wi-Fi cell before the trigger time (TTT) timer expires and before the first network initiates a handover to a second target cell from a plurality of target cells on the second network.

[0021] In some aspects, if the signal strength of the Wi-Fi cell is greater than the signal strength of the first network, the base station receives an indication to perform a handover of the active transmission to the Wi-Fi cell.

[0022] To achieve the foregoing and related purposes, one or more aspects include features that are fully described hereinafter and particularly pointed out in the claims. The following description and the drawings set forth in detail certain illustrative features of one or more aspects. However, these features merely indicate some of the various ways in which the principles of the various aspects may be employed, and this description is intended to include all such aspects and their equivalents. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a diagram illustrating an example of a wireless communication system and an access network.

[0024] Figure 2A 、 Figure 2B 、 Figure 2C and Figure 2D are diagrams respectively illustrating examples of a first 5G / NR frame, a DL channel within a 5G / NR subframe, a second 5G / NR frame, and a UL channel within a 5G / NR subframe.

[0025] Figure 3 is a diagram illustrating an example of a base station and a user equipment (UE) in an access network.

[0026] Figure 4 is a diagram showing an example of a wireless communication system.

[0027] Figure 5 is a diagram showing the handover to a Wi-Fi network.

[0028] Figure 6 is a call flow diagram of signaling between a UE and a base station according to certain aspects of the present disclosure.

[0029] Figure 7 is a flowchart of a method of wireless communication.

[0030] Figure 8 is a conceptual data flow diagram showing the data flow between different components / assemblies in an example device.

[0031] Figure 9 is a diagram showing an example of a hardware implementation of a device employing a processing system.

[0032] Figure 10 is a flowchart of a method of wireless communication.

[0033] Figure 11 is a conceptual data flow diagram showing the data flow between different components / assemblies in an example device.

[0034] Figure 12 is a diagram showing an example of a hardware implementation of a device employing a processing system. Detailed Description

[0035] The following detailed description presented in conjunction with the accompanying drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough understanding of the various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well-known structures and components are shown in block diagram form to avoid obscuring the concepts.

[0036] Several aspects of a telecommunications system will now be presented with reference to various devices and methods. These devices and methods will be described in the following detailed description and are illustrated in the drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as "elements"). These elements can be implemented using electronic hardware, computer software, or any combination thereof. Whether these elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

[0037] For example, an element or any portion of an element or any combination of elements can be implemented as a "processing system" that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, system on a chip (SoC), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functions described throughout this disclosure. One or more processors in the processing system can run software. Software should 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, executable programs, execution threads, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

[0038] Thus, in one or more example embodiments, the described functions 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. A computer-readable medium includes a computer storage medium. The storage medium can be any available medium that can be accessed by a computer. By way of example and not limitation, such computer-readable media can include random access memory (RAM), read only memory (ROM), electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of 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.

[0039] Figure 1 is a diagram illustrating an example of a wireless communication system and an access network 100. The wireless communication 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 can include macro cells (high-power cellular base stations) and / or small cells (low-power cellular base stations). Macro cells include base stations. Small cells include femtocells, picocells, and microcells.

[0040] The base station 102 configured for 4G LTE (collectively referred to as the evolved universal mobile telecommunication system (UMTS) terrestrial radio access network (E-UTRAN)) can interface with the EPC 160 via a first backhaul link 132 (e.g., the S1 interface). The base station 102 configured for 5G NR (collectively referred to as the next-generation RAN (NG-RAN)) can interface with the core network 190 via a second backhaul link 184. In addition to other functions, the base station 102 can perform one or more of the following functions: transfer of user data, radio channel encryption and decryption, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection establishment and release, load balancing, distribution of non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), user and equipment tracking, radio access network information management (RIM), paging, positioning, and transfer of warning messages. The base stations 102 can communicate with each other directly or indirectly (e.g., via the EPC 160 or the core network 190) via a third backhaul link 134 (e.g., the X2 interface). The third backhaul link 134 can be wired or wireless.

[0041] Base station 102 can communicate wirelessly with UE 104. Each of the base stations 102 can provide communication coverage for its respective geographical coverage area 110. There may be overlapping geographical coverage areas 110. For example, small cell 102’ may have a coverage area 110’ that overlaps with the coverage areas 110 of one or more macro base stations 102. A network including both small cells and macro cells can be referred to as a heterogeneous network. The heterogeneous network may also include a Home evolved Node B (eNB) (HeNB) that can provide services to a restricted group called a Closed Subscriber Group (CSG). The communication link 120 between the base station 102 and the UE 104 can include an uplink (UL) (also referred to as a reverse link) transmission from the UE 104 to the base station 102 and / or a downlink (DL) (also referred to as a forward link) transmission from the base station 102 to the UE 104. The communication link 120 can use multiple-input multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and / or transmit diversity. The communication link can be over one or more carriers. The base station 102 / UE 104 can use a spectrum with a bandwidth of up to Y MHz (e.g., 5, 10, 15, 20, 100, 400, etc. MHz) per carrier allocated in carrier aggregation with a total of up to Yx MHz (x component carriers) for transmission in each direction. These carriers can be adjacent to each other or may not be adjacent to each other. The allocation of carriers can be asymmetric with respect to the DL and UL (e.g., more or fewer carriers can be allocated for the DL than for the UL). The component carriers can include a primary component carrier and one or more secondary component carriers. The primary component carrier can be referred to as the Primary Cell (PCell), while the secondary component carriers can be referred to as Secondary Cells (SCells).

[0042] Some UEs 104 can communicate with each other using device-to-device (D2D) communication links 158. The D2D communication links 158 can use DL / UL WWAN spectrum. The D2D communication links 158 can use one or more sidelink channels, such as the Physical Sidelink Broadcast Channel (PSBCH), the Physical Sidelink Discovery Channel (PSDCH), the Physical Sidelink Shared Channel (PSSCH), and the Physical Sidelink Control Channel (PSCCH). D2D communication can be through various wireless D2D communication systems, such as FlashLinQ, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the IEEE 802.11 standard, LTE, or NR.

[0043] The wireless communication system may also include a Wi-Fi Access Point (AP) 150 that communicates with a Wi-Fi Station (STA) 152 via a communication link 154 in the 5 GHz unlicensed spectrum. When communicating in the unlicensed spectrum, the STA 152 / AP 150 can perform a Clear Channel Assessment (CCA) before communication to determine whether the channel is available.

[0044] The small cell 102' can operate in licensed and / or unlicensed spectrum. When operating in unlicensed spectrum, the small cell 102' can adopt NR and use the same 5 GHz unlicensed spectrum as that used by the Wi-Fi AP 150. The small cell 102' using NR in unlicensed spectrum can expand the coverage of the access network and / or increase the capacity of the access network.

[0045] The base station 102, whether it is a small cell 102' or a large cell (e.g., a macro base station), can include and / or be referred to as an eNB, a gNodeB (gNB), or another type of base station. Some base stations (such as gNB 180) can communicate with the UE 104 by operating in the traditional sub-6 GHz spectrum, millimeter wave (mmW) frequencies, and / or near mmW frequencies. When the gNB 180 operates at mmW or near mmW frequencies, the gNB 180 can be referred to as a mmW base station. The extremely high frequency (EHF) is a part of the RF in the electromagnetic spectrum. The range of EHF is from 30 GHz to 300 GHz, and the wavelength is between 1 millimeter and 10 millimeters. The radio waves in this frequency band can be called millimeter waves. Near mmW can 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 and is also called centimeter waves. Communications using the mmW / near mmW radio frequency (RF) band (e.g., 3 GHz - 300 GHz) have extremely high path loss and short distances. The mmW base station 180 can utilize beamforming 182 with the UE 104 to compensate for the extremely high path loss and short distances. The base station 180 and the UE 104 can each include multiple antennas, such as antenna elements, antenna panels, and / or antenna arrays, to facilitate beamforming.

[0046] The base station 180 can send beamformed signals to the UE 104 in one or more transmission directions 182'. The UE 104 can receive the beamformed signals from the base station 180 in one or more reception directions 182". The UE 104 can also send beamformed signals to the base station 180 in one or more transmission directions. The base station 180 can receive the beamformed signals from the UE 104 in one or more reception directions. The base station 180 / UE 104 can perform beam training to determine the optimal reception and transmission directions for each base station 180 / UE 104. The transmission and reception directions of the base station 180 can be the same or can be different. The transmission and reception directions of the UE 104 can be the same or can be different.

[0047] 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 communicate with a Home Subscriber Server (HSS) 174. The MME 162 is a control node that processes signaling between the UE 104 and the EPC 160. Generally, the MME 162 provides bearer and connection management. All user Internet Protocol (IP) packets are transported through the Serving Gateway 166, which itself is connected to the PDN Gateway 172. The PDN Gateway 172 provides UE IP address allocation and other functions. The PDN Gateway 172 and the BM-SC 170 are connected to an IP service 176. The IP service 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 transmissions, may be used to authorize and initiate MBMS bearer services within a Public Land Mobile Network (PLMN), and may be used to schedule MBMS transmissions. The MBMS Gateway 168 may be used to distribute MBMS services to base stations 102 belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area for a particular broadcast service, and may be responsible for session management (start / stop) and collecting charging information related to eMBMS.

[0048] The core network 190 may include an 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 communicate with a Unified Data Management (UDM) 196. The AMF 192 is a control node that processes signaling between the UE 104 and the core network 190. Generally, the AMF 192 provides QoS flow and session management. All user Internet Protocol (IP) packets are transported through the UPF 195. The UPF 195 provides UE IP address allocation and other functions. The UPF 195 is connected to an IP service 197. The IP service 197 may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a Packet Switched (PS) Streaming (PSS) service, and / or other IP services.

[0049] The base station may include and / or be referred to as a gNB, Node B, eNB, access point, base station transceiver station, radio base station, radio transceiver, transceiver function, basic service set (BSS), extended service set (ESS), transmission reception point (TRP), or some other suitable term. The base station 102 provides an access point for the UE 104 to the EPC 160 or the core network 190. Examples of the UE 104 include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop computer, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., an MP3 player), a camera, a game console, a tablet computer, a smart device, a wearable device, a vehicle, a power meter, a gas pump, a large or small kitchen appliance, a health device, an implant, a sensor / actuator, a display, or any other similar functional device. Some UEs 104 may be referred to as IoT devices (e.g., parking meters, gas pumps, toasters, vehicles, heart monitors, etc.). The UE 104 may also be referred to as a station, a mobile station, a user station, a mobile unit, a user unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communication device, a remote device, a mobile user station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a cell phone, a user agent, a mobile client, a client, or some other suitable term.

[0050] Referring again to Figure 1 , in some aspects, the UE 104 may be configured to extend the TTT timer to preempt an SRVCC handover and trigger a handover to a Wi-Fi network. For example, Figure 1 the UE 104 may include an extension component 198 that is configured to extend the TTT timer length based on a determination that a handover from the first network to the Wi-Fi cell is acceptable. The UE 104 determines whether it is feasible to hand over to a Wi-Fi cell that is the first target cell serving the UE from among multiple target cells to continue active transmission on the Wi-Fi cell. The UE 104 extends the TTT time length based at least in part on a determination that it is feasible for the Wi-Fi cell to be the target cell serving the UE to continue active transmission on the Wi-Fi cell. Before the TTT timer expires and before the first network initiates a handover to a second target cell from among multiple target cells on a second network, the UE104 initiates a handover from the first network to the Wi-Fi cell.

[0051] Referring again to Figure 1, in some aspects, the base station 180 can be configured to switch the active transmission to a Wi-Fi network in response to the UE 104 triggering a handover. For example, the base station 180 can include an indication component 199, which can receive an indication from the UE to perform a handover of the active transmission to a Wi-Fi cell. The base station 180 can communicate with the UE 104 on a first network, where an active transmission occurs between the base station 180 and the UE 104. The base station 180 can receive an indication from the UE to perform a handover of the active transmission to a Wi-Fi cell, where the Wi-Fi cell is the first target cell from a plurality of target cells. In response to the indication received from the UE, the base station 180 can perform a handover of the active transmission to the Wi-Fi cell.

[0052] The concepts described herein can be applicable to other similar fields, such as LTE, LTE-A, 5G NR, CDMA, GSM, and other wireless technologies.

[0053] Figure 2A FIG. 200 is an example showing a first subframe within the 5G / NR frame structure. Figure 2B FIG. 230 is an example showing DL channels within a 5G / NR subframe. Figure 2C FIG. 250 is an example showing a second subframe within the 5G / NR frame structure. Figure 2D FIG. 280 is an example showing UL channels within a 5G / NR subframe. The 5G / NR frame structure can be FDD, where for a specific set of subcarriers (carrier system bandwidth), the subframes within the set of subcarriers are dedicated to DL or UL; or it can be TDD, where for a specific set of subcarriers (carrier system bandwidth), the subframes within the set of subcarriers are dedicated to DL and UL. In Figure 2A 、 Figure 2C the example provided, the 5G / NR frame structure is assumed to be TDD, subframe 4 is configured with slot format 28 (mostly DL), where D is DL, U is UL, and X is flexibly used between DL / UL; subframe 3 is configured with slot format 34 (mostly UL). Although subframes 3 and 4 are shown as having slot formats 34 and 28 respectively, any specific subframe can be configured with any one of the various available slot formats 0 - 61. Slot formats 0 and 1 are DL and UL respectively. The other slot formats 2 - 61 include a mixture of DL, UL, and flexible symbols. The UE is configured with a slot format (dynamically via DL control information (DCI), or semi-statically / statically via radio resource control (RRC) signaling) by the received slot format indicator (SFI). Note that the following description also applies to the 5G / NR frame structure as TDD.

[0054] Other wireless communication technologies may have different frame structures and / or different channels. A frame (10 ms) can be divided into 10 equally sized sub-frames (1 ms). Each sub-frame can include one or more time slots. A sub-frame can also include mini-slots, which can include 7, 4, or 2 symbols. Depending on the time slot configuration, each time slot can include 7 or 14 symbols. For time slot configuration 0, each time slot can include 14 symbols, while for time slot configuration 1, each time slot can include 7 symbols. Symbols on the DL can be cyclic prefix (CP) OFDM (CP-OFDM) symbols. Symbols on the UL can be CP-OFDM symbols (for high throughput cases) or discrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) symbols (also known as single carrier frequency division multiple access (SC-FDMA) symbols) (for power-constrained cases; limited to single stream transmission). The number of time slots within a sub-frame is based on the time slot configuration and numerology. For time slot configuration 0, different numerologies μ0 to 5 allow 1, 2, 4, 8, 16, and 32 time slots per sub-frame respectively. For time slot configuration 1, different numerologies 0 to 2 allow 2, 4, and 8 time slots per sub-frame respectively. Thus, for time slot configuration 0 and numerology μ, there are 14 symbols / slot and 2 μ time slots / sub-frame. The subcarrier spacing and symbol length / duration are functions of the numerology. The subcarrier spacing may be equal to 2 μ * 15 kHz, where μ is the numerology from 0 to 5. Thus, the subcarrier spacing for numerology μ = 0 is 15 kHz, while the subcarrier spacing for numerology μ = 5 is 480 kHz. The symbol length / duration is inversely proportional to the subcarrier spacing. Figures 2A to 2D An example is provided with time slot configuration 0 having 14 symbols per time slot and numerology μ = 2 having 4 time slots per sub-frame. The time slot duration is 0.25 ms, the subcarrier spacing is 60 kHz, and the symbol duration is approximately 16.67 μs.

[0055] A resource grid can be used to represent the frame structure. Each time slot includes a resource block (RB) (also known as a physical RB (PRB)) that spans 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.

[0056] As Figure 2A shown, some REs carry the reference (pilot) signals (RS) of the UE. The RS can include demodulation RS (DM-RS) (represented as R for a specific configuration x, where 100x is the port number, but other DM-RS configurations are also 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).

[0057] Figure 2B FIG. 4 shows an example of various DL channels within a subframe of a frame. The physical downlink control channel (PDCCH) carries DCI within one or more control channel elements (CCEs), each CCE including nine resource element groups (REGs), each REG including four consecutive resource elements (REs) in an OFDM symbol. The primary synchronization signal (PSS) may be in symbol 2 of a specific subframe of the frame. UE 104 uses the PSS to determine subframe / symbol timing and the physical layer identity. The secondary synchronization signal (SSS) may be in symbol 4 of a specific subframe of the frame. The UE uses the SSS to determine the physical layer cell identity group number and the radio frame timing. Based on the physical layer identity and the physical layer cell identity group number, the UE can determine the physical cell identifier (PCI). Based on the PCI, the UE can determine the location of the aforementioned DM-RS. The physical broadcast channel (PBCH) carrying the master information block (MIB) may be logically grouped with the PSS and SSS to form a synchronization signal (SS) / PBCH block. The MIB provides the number of resource blocks (RBs) in the system bandwidth and the system frame number (SFN). The physical downlink shared channel (PDSCH) carries user data, broadcast system information (such as system information blocks (SIBs)) not transmitted through the PBCH, and paging messages.

[0058] As Figure 2C shown, some resource elements carry DM-RS (denoted as R for one particular configuration, but other DM-RS configurations are also 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 previous one or two symbols of the PUSCH. The PUCCH DM-RS may be transmitted in different configurations, depending on whether a short PUCCH or a long PUCCH is being 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 the subframe. The SRS may have a comb structure, and the UE may transmit the SRS on one of the combs. The base station may use the SRS for channel quality estimation to enable frequency-dependent scheduling on the UL.

[0059] Figure 2DShows an example of various UL channels within a subframe of a frame. As indicated in one configuration, the PUCCH can be located. The PUCCH carries uplink control information (UCI), such as a scheduling request, a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), and HARQ ACK / NACK feedback. The PUSCH carries data and can additionally be used to carry a buffer status report (BSR), a power headroom report (PHR), and / or UCI.

[0060] Figure 3 Is a block diagram of a base station 310 communicating with a UE 350 in an access network. In the DL, IP packets from the EPC 160 can be provided to a controller / processor 375. The controller / processor 375 implements layer 3 and layer 2 functions. Layer 3 includes the radio resource control (RRC) layer, and layer 2 includes the service data adaptation protocol (SDAP) layer, the packet data convergence protocol (PDCP) layer, the radio link control (RLC) layer, and the media access control (MAC) layer. The controller / processor 375 provides RRC layer functions associated with the broadcast of system information (e.g., MIB, SIB), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter-radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functions associated with header compression / decompression, security (encryption, decryption, integrity protection, integrity verification), and handover support functions; RLC layer functions associated with the transfer of upper layer packet data units (PDUs), error correction via ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs), re-segmentation of RLC data PDUs, and re-ordering of RLC data PDUs; and MAC layer functions associated with the 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 via HARQ, priority handling, and logical channel prioritization.

[0061] The transmit (TX) processor 316 and the receive (RX) processor 370 implement layer 1 functions associated with various signal processing functions. Layer 1, which includes the physical (PHY) layer, may include error detection on the transport channel, forward error correction (FEC) encoding / decoding of the transport channel, interleaving, rate matching, mapping to the physical channel, modulation / demodulation of the physical channel, and MIMO antenna processing. The TX processor 316 processes the mapping to the signal constellation 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 OFDM subcarriers, multiplexed with reference signals (e.g., pilots) in the time domain and / or frequency domain, and then combined together using an inverse fast Fourier transform (IFFT) to generate a physical channel carrying a stream of time-domain OFDM symbols. The OFDM stream is space precoded to generate multiple spatial streams. Channel estimates from the channel estimator 374 may be used to determine the coding and modulation schemes, as well as for spatial processing. The channel estimates may be derived from reference signals transmitted by the UE 350 and / or channel condition feedback. 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 its respective spatial stream for transmission.

[0062] At the UE 350, each receiver 354RX receives signals via its respective antenna 352. Each receiver 354RX recovers the information modulated onto the RF carrier and provides the information to the receive (RX) processor 356. The TX processor 368 and the RX processor 356 implement layer 1 functions 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 uses a fast Fourier transform (FFT) to convert the OFDM symbol stream from the time domain to the frequency domain. The frequency domain signal includes a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols and reference signals on each subcarrier 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 the channel estimates computed by the channel estimator 358. The soft decisions are then decoded and deinterleaved to recover the data and control signals 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 functions.

[0063] The controller / processor 359 may be associated with a memory 360 that stores program code 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, decryption, 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 the ACK and / or NACK protocols to support HARQ operations.

[0064] Similar to the functions described in connection with the DL transmission of the base station 310, the controller / processor 359 provides RRC layer functions associated with system information (e.g., MIB, SIB) acquisition, RRC connection, and measurement reporting; PDCP layer functions associated with header compression / decompression and security (encryption, decryption, integrity protection, integrity verification); RLC layer functions associated with the transfer of upper layer PDUs, error correction via ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and re-ordering of RLC data PDUs; and MAC layer functions associated with the mapping between logical and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction via HARQ, priority handling, and logical channel prioritization.

[0065] The TX processor 368 may select an appropriate coding and modulation scheme using channel estimates derived from reference signals or feedback sent from the base station 310 by the channel estimator 358 and facilitate spatial processing. The spatial streams generated by the TX processor 368 may be provided to different antennas 352 via separate transmitters 354TX. Each transmitter 354TX may modulate an RF carrier with its respective spatial stream for transmission.

[0066] 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 signals via its respective antenna 320. Each receiver 318RX recovers the information modulated onto the RF carrier and provides the information to the RX processor 370.

[0067] The controller / processor 375 may be associated with a memory 376 that stores program code 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, decryption, header decompression, control signal processing, to recover IP packets from the UE 350. The 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 the ACK and / or NACK protocols to support HARQ operations.

[0068] At least one of TX processor 368, RX processor 356, and controller / processor 359 may be configured to perform aspects related to Figure 1 198.

[0069] At least one of TX processor 316, RX processor 370, and controller / processor 375 may be configured to perform aspects related to Figure 1 199.

[0070] In some wireless communications, a user may make an active transmission on a base station. The active transmission may be a video or voice call, such as an Internet Protocol (IP) Multimedia Subsystem (IMS) Multimedia Telephony Service (MMTel) call. An IMS MMTel voice call may use a stronger audio codec on an LTE and / or Wi-Fi network than on a circuit-switched (CS) network (e.g., 2G, 3G, WCDMA, GSM, or other traditional non-LTE network). IMS MMTel video calls may be supported on LTE and Wi-Fi networks, but not on CS networks. The SRVCC handover threshold may be configured by the network, and the SRVCC handover command from the network takes precedence, such that the UE honors the SRVCC handover command. The handover from the LTE network to the Wi-Fi network may be controlled by the UE. As long as the call quality is acceptable on the LTE network, the UE will not trigger a handover to the Wi-Fi network even if the Wi-Fi network can accept the call. Thus, when the UE moves to the LTE cell edge during an IMS MMTel voice / video call, if both the CS and Wi-Fi networks are available and the call quality is acceptable on the LTE network, the UE sends a measurement report to the LTE network once the SRVCC handover threshold is met. This may result in the IMS MMTel call being handed over to the CS network in response to the SRVCC handover command from the network, which may lead to a loss of call quality and a loss of video call capacity due to the CS network using a lower-quality codec. Therefore, it is desirable to improve the way the UE operates to allow the UE to preempt SRVCC and trigger a handover to the Wi-Fi network.

[0071] Figure 4FIG. 400 is an example showing a wireless communication system. FIG. 400 includes a base station 402, which can provide coverage for a first network (e.g., LTE or NR) 406 and a second network (e.g., CS) 404. The Wi-Fi network 408 can also provide overlapping coverage with the LTE network 406 and / or the CS network 404. As described above, a UE (not shown) can have an IMS MMTel call on the LTE network 406, and when the UE approaches the LTE cell edge, it may cause the call to be switched to the CS network when the HO threshold 410 is met. The HO threshold 410 can be configured by the first network. In the case where the UE approaches the LTE cell edge, the call will be switched to the CS network without allowing the call to be switched to the Wi-Fi network 408. As Figure 4 shown, when the SRVCC threshold is met, the call is switched to the CS network, causing the UE to miss the opportunity to switch the call to the Wi-Fi network 408, which can maintain the call quality of the IMS MMTel call.

[0072] Figure 5 FIG. 500 is a diagram showing a handover to a Wi-Fi network. FIG. 500 includes a base station 502 similar to the base station 402, and the base station 502 can provide coverage for the LTE network 506 and the CS network 504. Similar to the Wi-Fi network 408, the Wi-Fi network 508 can also provide overlapping coverage with the LTE network 506 and / or the CS network 504.

[0073] In Figure 5 aspect, before the SRVCC HO threshold 510 is met, a UE (not shown) can measure the signal strengths of the LTE network 506 and the CS network 504, and if the Wi-Fi network 508 can serve the UE (e.g., continue the call on the Wi-Fi network 508), the UE triggers a handover 512 to the Wi-Fi network 508. The handover 512 to the Wi-Fi network can allow the call to continue as an IMS MMTell call on the Wi-Fi network 508. The handover to the Wi-Fi network 508 can allow the same codec used on the LTE network 506 to be used on the Wi-Fi network 508. This also eliminates the need to downgrade a video call to a voice call if the call is switched to the CS network 504.

[0074] When there is an active call on the LTE network 506, the UE can determine whether it is possible to handover the call to the Wi-Fi network 508. After determining that it is possible to handover the call to the Wi-Fi network 508, the UE can extend the TTT timer length so that the UE can delay sending a measurement report of the signal strengths of the LTE network 506 and the CS network 504 to the first network. In some aspects, the UE can measure the signal strengths of the LTE network 506 and the CS network 504 to determine whether it is approaching the SRVCC HO threshold based on a delta 514, in order to determine whether the signal strength of the CS network meets or exceeds the SRVCC HO threshold 510. For example, the UE can consider the delta 514 to measure the signal strength of the LTE network 506, and also consider the delta 514 to measure the signal strength of the CS network 504, to determine whether the LTE network 506 is ready to initiate a handover to the CS network 504. The UE can be configured to initiate a handover 512 to the Wi-Fi network 508 before the CS network 504 meets the HO threshold 510 (e.g., SRVCC). Based on the delta 514, the handover 512 to the Wi-Fi network 508 can occur before the CS network 504 meets the HO threshold 510, where the delta 514 is the separation of the signal strengths between the handover 512 to the Wi-Fi network 508 and the HO threshold 510 for the LTE network 506 to handover to the CS network 504. The SRVCC HO threshold 510 can be configured by the LTE network 506. In some aspects, the delta 514 can be an internal parameter of the UE to control the size of the SRVCC region, where the SRVCC region is the region when the UE is approaching the LTE cell edge and approaching the HO threshold 510 for handover to the CS network. The SRVCC region can be based on the signal strength separation between the HO threshold 510 and the handover 512 to the Wi-Fi network, based on the delta 514.

[0075] Figure 6 is a call flow diagram 600 of signaling between a UE 602 and a base station 604 according to certain aspects of the present disclosure. Optional aspects are shown with dashed lines. The base station 604 can provide a cell serving the UE 602. For example, in Figure 1 the context of, the base station 604 can correspond to the base station 102 / 180, and thus, the cell can include a geographic coverage area 110 providing communication coverage and / or a small cell 102' having a coverage area 110'. Additionally, the UE 602 can at least correspond to the UE 104. In another example, in Figure 3 the context of, the base station 604 can correspond to the base station 310, and the UE 602 can correspond to the UE 350.

[0076] As Figure 6As shown, the UE 602 may include a handover (HO) module 606 and an access stratum (AS) module 608. The UE 602 may have an active transmission 610 with the base station 604. In some aspects, the active transmission may include a video or voice call, such as but not limited to IMS MMTel. The active transmission may be on a first network (e.g., LTE or NR).

[0077] In some aspects, for example, at 612, the base station 604 may send a handover threshold for handover between the first network and the second network. The UE 602 may receive the handover threshold for handover between the first network and the second network from the base station 604. In some aspects, the first network may include an LTE network or an NR network. In some aspects, the second network may include a CS network (e.g., 2G, 3G, WCDMA, GSM, or other traditional non-LTE networks).

[0078] At 614, the UE 602 may evaluate the possibility of handover to a Wi-Fi network. The UE 602 may determine whether a Wi-Fi cell is feasible as a first target cell serving the UE 602. The UE 602 may determine whether a Wi-Fi cell is feasible as a first target cell serving the UE to continue the active transmission on the Wi-Fi cell. The Wi-Fi cell may be a target cell from among multiple target cells. In some aspects, at least based on the signal strength of the Wi-Fi cell, it is feasible for the Wi-Fi network to be a target cell serving the UE to continue the active transmission on the Wi-Fi cell. In some aspects, the UE 602 may determine whether a Wi-Fi cell is feasible as a target cell before a second cell among multiple target cells meets the handover threshold for handover between the first network and the second target cell.

[0079] In some aspects, the handover (HO) module 606 of the UE 602 may send an indication 616 to the access stratum (AS) module 608 of the UE that a handover to a Wi-Fi network is possible. For example, if there is an active call on the first network and it is possible to switch the call from the first network to a Wi-Fi cell, the HO module 606 may send a mobility_to_wifi_possible indication 616 to the AS module 608. Based on the determination that the Wi-Fi cell is feasible as a target cell, the indication 616 may be sent to the AS module 608.

[0080] At 618, the UE 602 may measure the signal strength of the active transmissions on the first network and the second target cell of the second network. The UE 602 may measure the signal strength of the active transmissions on the first network and the second target cell on the second network to determine whether the signal strengths of the first network and the second network are close to the handover threshold. In some aspects, the AS module 608 may be configured to measure the signal strengths of the first network and the second network.

[0081] At 620, the UE 602 may generate a measurement report of the signal strength of the active transmissions on the first network and the second target cell. The UE 602 may generate a measurement report of the signal strengths of the first network and the second target cell to prepare for a handover between the first network and the second network. The measurement report may be based on the signal strength of the active transmissions and the second target cell. In some aspects, the AS module 608 of the UE 602 may generate the measurement report.

[0082] In some aspects, the AS module 608 may provide an indication 622 of entering the SRVCC area to the HO module 606 of the UE 602. The SRVCC area may include the cell edge of the first network such that the coverage or signal strength of the first network is decreasing and the first network may be ready to initiate a handover to the second network. The SRVCC area may be based on the SRVCC HO threshold 510 and delta 514. For example, if the UE 602 enters the SRVCC area, the AS module 608 may send an SRVCC_region_enter indication 622 to the HO module 606 indicating that a handover from the first network to the second network (e.g., a CS-based network) may occur. In some aspects, if the RSRP of the first network is less than the HO threshold 510 plus delta 514 and the RSSI of the second network is greater than the HO threshold 510 minus delta 514, the AS module 608 may send the indication 622. In some aspects, if the RSSI of the second network is greater than the HO threshold 510 minus delta 514, the AS module 608 may send the indication 622. The delta may be an internal parameter of the UE, which may be configured to control the size of the SRVCC area such that changing the value of delta may change the size of the SRVCC area. For example, if the TTT is large (e.g., 1.28 seconds), the delta may be a small value, e.g., 2 dB. In some aspects, if the TTT is small (e.g., 128 ms or 256 ms), the delta may include a value of approximately 5 dB. The values provided for the TTT and delta are examples and the present disclosure is not intended to be limited to the examples disclosed herein. In some aspects, the TTT may be less than or greater than 1.28 seconds. In some aspects, the delta may be less than or greater than 2 dB.

[0083] At 624, the UE 602 may extend the length of the time-to-trigger (TTT) timer. The UE 602 may extend the TTT timer length at least in part based on a determination that it is feasible to continue active transmission on the Wi-Fi cell as the target cell serving the UE. In some aspects, extending the TTT timer length may delay the transmission of the measurement report 620 from the UE 602 to the base station 604. The delay in the transmission of the measurement report may allow for the initiation of a handover from the first network to the Wi-Fi cell. In some aspects, if the handover to the Wi-Fi cell has been completed, the measurement report may not be sent when the TTT timer expires. In some aspects, if there is no active transmission on the first network, the measurement report may not be sent when the TTT timer expires. In some aspects, when receiving the indication 616 from the HO module 606, if the SRVCC threshold is met, the AS module 608 may extend the TTT timer length.

[0084] In some aspects, such as at 626, the HO module 606 may evaluate the handover conditions. If the AS module 608 sends an indication 622 that the UE 602 has entered the handover area (e.g., the SRVCC area), the HO module 606 may evaluate the signal strength of the Wi-Fi cell. In some aspects, the UE 602 may determine whether the signal strength of the second target cell is greater than the signal strength of the active transmission on the first network. The UE 602 may determine whether the signal strength of the second target cell is greater than the signal strength of the active transmission on the first network such that the first network is ready to initiate a handover of the active transmission to the second target cell.

[0085] At 628, the UE 602 may initiate a handover from the first network to the Wi-Fi cell. The UE 602 may initiate a handover from the first network to the Wi-Fi cell before the TTT timer expires. The UE may initiate a handover from the first network to the Wi-Fi cell before the first network initiates a handover to the second target cell from among multiple target cells on the second network. In some aspects, if the signal strength of the Wi-Fi cell is greater than the signal strength of the first network, the UE may initiate a handover from the first network to the Wi-Fi cell. In some aspects, the HO module 606 of the UE 602 may initiate a handover from the first network to the Wi-Fi network. For example, if the signal strength of the Wi-Fi cell is acceptable for active transmission, the HO module 606 may initiate a handover to the Wi-Fi network.

[0086] In some aspects, the HO module 606 may send an indication 630 to initiate a handover to a Wi-Fi network. For example, if a trigger occurs to switch an active transmission from a first network to a Wi-Fi cell, the HO module 606 may send a mobility_to_wifi_start indication 630 to the AS module 608.

[0087] At 632, the active transmission is switched to the Wi-Fi cell such that the active transmission from the first network (e.g., IMS MM Tel) is maintained on the Wi-Fi cell. When the TTT timer expires, if there is no longer an active transmission between the UE and the first network, the UE 602 does not send a measurement report to the base station 604. In some aspects, at the expiration of the TTT timer, the measurement report is not sent to the base station 604 because the active transmission has been switched to the Wi-Fi cell. In some aspects, if there is no active transmission between the UE 602 and the base station 604, no measurement report is sent to the base station at the expiration of the TTT timer.

[0088] Figure 7 It is a flowchart 700 of a method of wireless communication. The method may be performed by a UE or a component of the UE (e.g., UE 104, 350, 602; device 802 / 802'; processing system 914, which may include a memory 360 and may be the entire UE 350 or a component of the UE 350, such as a TX processor 368, an RX processor 356, and / or a controller / processor 359). According to various aspects, one or more of the illustrated operations of method 700 may be omitted, reordered, and / or performed simultaneously. Optional aspects are shown in dashed lines. The method may enable the UE to preempt SRVCC by triggering a handover to a Wi-Fi network.

[0089] In some aspects, for example, at 702, the UE may receive a handover threshold for a handover between a first network and a second network. For example, 702 may be performed by a threshold component 806 of the device 802. The UE may receive a handover threshold for a handover between a first network and a second network from a base station. In some aspects, the first network may include an LTE network or an NR network. In some aspects, the second network may include a CS network (e.g., 2G, 3G, WCDMA, GSM, or other traditional non-LTE network).

[0090] At 704, the UE may determine whether a Wi-Fi cell is feasible as a first target cell. For example, 704 may be performed by the determination component 808 of the device 802. The UE may determine whether a Wi-Fi cell is feasible as a first target cell serving the UE to continue active transmission on the Wi-Fi cell. The Wi-Fi cell may be the first target cell from among multiple target cells. In some aspects, at least based on the signal strength of the Wi-Fi cell, it is feasible for the Wi-Fi network to be a target cell serving the UE to continue active transmission on the Wi-Fi cell. In some aspects, the UE may determine whether the Wi-Fi cell is feasible as a target cell before a second target cell from among multiple target cells meets a handover threshold for handover between the first network and the second target cell.

[0091] In some aspects, the UE may measure the signal strength of the active transmission on the first network and the second target cell on the second network. The UE may measure the signal strength of the active transmission on the first network and the second target cell on the second network to determine whether the signal strengths of the first network and the second network are close to the handover threshold.

[0092] In some aspects, the UE may generate a measurement report of the signal strength of the active transmission and the second target cell. The UE may generate a measurement report of the signal strength of the active transmission and the second target cell to prepare for handover between the first network and the second network. The measurement report may be based on the signal strength of the active transmission and the second target cell.

[0093] At 706, the UE may extend the TTT timer length. For example, 706 may be performed by the extension component 810 of the device 802. The UE may extend the TTT timer length at least in part based on the determination that a Wi-Fi cell is feasible as a target cell serving the UE to continue active transmission on the Wi-Fi cell. In some aspects, extending the TTT timer length delays the transmission of the measurement report from the UE to the base station. The measurement report may include the signal strengths of the first network and the second network to prepare for handover from the first network to the second network. The delay in the transmission of the measurement report may allow the initiation of a handover from the first network to the Wi-Fi cell. For example, the delay in the transmission of the measurement report may allow the UE to trigger or initiate a handover to the Wi-Fi cell. In some aspects, if the handover to the Wi-Fi cell has been completed, the measurement report may not be sent when the TTT timer expires. In some aspects, if there is no active transmission on the first network, the measurement report may not be sent when the TTT timer expires. Since the UE triggers a handover to the Wi-Fi cell, the first network may no longer have an active transmission. Thus, no measurement report will be sent from the UE to the base station because once the active transmission has been switched to the Wi-Fi cell, there will no longer be a need to prepare for handover from the first network to the second network.

[0094] In some aspects, such as at 708, the UE can determine whether the signal strength of the second target cell is greater than the signal strength of the active transmission on the first network. For example, 708 can be performed by the signal component 812 of the device 802. The UE can determine whether the signal strength of the second target cell is greater than the signal strength of the active transmission on the first network such that the first network is ready to initiate a handover to the second target cell for active transmission.

[0095] At 710, the UE can initiate a handover from the first network to a Wi-Fi cell. For example, 710 can be performed by the handover component 814 of the device 802. The UE can initiate a handover from the first network to a Wi-Fi cell before the TTT timer expires. The UE can initiate a handover from the first network to a Wi-Fi cell before the first network initiates a handover to the second target cell from among multiple target cells on the second network. In some aspects, if the signal strength of the Wi-Fi cell is greater than the signal strength of the first network, the UE can initiate a handover from the first network to the Wi-Fi cell.

[0096] Figure 8 FIG. 800 is a conceptual data flow diagram showing the data flow between different components / elements in an example device 802. The device can be a UE or a component of a UE. The device includes a receiving component 804, which can be configured to receive various types of signals / messages and / or other information from other devices including, for example, a base station 750. The device includes a threshold component 806, which can be configured to receive a handover threshold for a handover between the first network and the second network from a base station of the first network, for example, as described in 702 in connection with Figure 7 The device includes a determination component 808, which can be configured to determine whether it is feasible for a Wi-Fi cell to be the first target cell serving the UE from among multiple target cells to continue an active transmission on the Wi-Fi cell, for example, as described in 704 in connection with Figure 7 The device includes an extension component 810, which can be configured to extend the TTT timer length at least in part based on the determination that it is feasible for a Wi-Fi cell to be a target cell serving the UE to continue an active transmission on the Wi-Fi cell, for example, as described in 706 in connection with Figure 7 The device includes a signal component 812, which can be configured to determine whether the signal strength of the second target cell is greater than the signal strength of the active transmission on the first network such that the first network is ready to initiate a handover to the second target cell, for example, as described in 708 in connection with Figure 7as described in 708. The apparatus includes a switching component 814, which may be configured to initiate a handover from the first network to a Wi-Fi cell before the TTT timer expires and before the first network initiates a handover to a second target cell of a plurality of target cells on a second network, e.g., as described in conjunction with Figure 7 as described in 710. The apparatus includes a transmission component 816, which may be configured to send various types of signals / messages and / or other information to other devices including, e.g., a base station 750.

[0097] The apparatus may include additional components that perform each of the blocks of the algorithms in the foregoing Figure 7 flowchart. Thus, each block in the foregoing Figure 7 flowchart may be performed by a component, and the apparatus may include one or more of these components. The components may be one or more hardware components that are specifically configured to perform the processes / algorithms, implemented by a processor configured to perform the processes / algorithms, stored in a computer-readable medium for implementation by a processor, or some combination thereof.

[0098] Figure 9 FIG. 900 is an example of a hardware implementation of an apparatus 802’ employing a processing system 914. The processing system 914 may be implemented with a bus architecture (generally represented by bus 924). Depending on the particular application and overall design constraints of the processing system 914, bus 924 may include any number of interconnecting buses and bridges. Bus 924 links together various circuits including one or more processors and / or hardware components (represented by processor 904, components 804, 806, 808, 810, 812, 814, 816, and computer-readable medium / memory 906). Bus 924 may also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art and will not be described further herein.

[0099] The processing system 914 can be coupled to the transceiver 910. The transceiver 910 is coupled to one or more antennas 920. The transceiver 910 provides components for communicating with various other devices via a transmission medium. The transceiver 910 receives signals from one or more antennas 920, extracts information from the received signals, and provides the extracted information to the processing system 914 (specifically, the receiving component 804). Additionally, the transceiver 910 receives information from the processing system 914 (specifically, the transmitting component 816) and generates signals to be applied to one or more antennas 920 based on the received information. The processing system 914 includes a processor 904 coupled to a computer-readable medium / memory 906. The processor 904 is responsible for general processing, including running software stored on the computer-readable medium / memory 906. When run by the processor 904, the software causes the processing system 914 to perform the various functions described above for any particular device. The computer-readable medium / memory 906 can also be used to store data manipulated by the processor 904 when running the software. The processing system 914 also includes at least one of the components 804, 806, 808, 810, 812, 814, 816. These components can be software components running in the processor 904, hardware components resident / stored in the computer-readable medium / memory 906, coupled to the processor 904, or some combination thereof. The processing system 914 can be a component of the UE 350 and can include at least one of the memory 360 and / or the TX processor 368, the RX processor 356, and the controller / processor 359. Alternatively, the processing system 914 can be the entire UE (e.g., see Figure 3 of 350).

[0100] In one configuration, the apparatus 802 / 802' for wireless communication includes components for determining whether it is feasible for a Wi-Fi cell to be a first target cell from among a plurality of target cells that serves the UE to continue active transmission on the Wi-Fi cell. The apparatus includes components for extending the length of a TTT timer based at least in part on the determination that it is feasible for the Wi-Fi cell to be a target cell that serves the UE to continue active transmission on the Wi-Fi cell. The apparatus includes components for initiating a handover from a first network to the Wi-Fi cell before the TTT timer expires and before a first network initiates a handover to a second target cell from among the plurality of target cells onto a second network. The apparatus further includes components for receiving, from a base station of the first network, a handover threshold for a handover between the first network and the second network. The apparatus further includes components for determining whether the signal strength of the second target cell is greater than the signal strength of an active transmission on the first network such that the first network is ready to initiate a handover to the second target cell. The foregoing components may be one or more of the foregoing components of the apparatus 802 and / or the processing system 914 of the apparatus 802', which is configured to perform the functions described for the foregoing components. As described above, the processing system 914 may include a TX processor 368, an RX processor 356, and a controller / processor 359. Thus, in one configuration, the foregoing components may be the TX processor 368, the RX processor 356, and the controller / processor 359, which are configured to perform the functions recited for the foregoing modules.

[0101] Figure 10 is a flow chart 1000 of a method of wireless communication. The method may be performed by a base station or a component of a base station (e.g., base stations 102, 180, 402, 502, 604, 850; apparatus 1102 / 1102'; processing system 1214, which may include a memory 376 and may be the entire base station 310 or a component of the base station 310, such as a TX processor 316, an RX processor 370, and / or a controller / processor 375). In accordance with various aspects, one or more of the illustrated operations of method 1000 may be omitted, reordered, and / or performed simultaneously. Optional aspects are shown in dashed lines. The method may enable the base station to switch an active transmission to a Wi-Fi network in response to an indication from the UE triggering a handover to the Wi-Fi network.

[0102] In some aspects, such as at 1002, the base station may send a handover threshold to the UE. For example, 1002 may be performed by a threshold component 1106 of the apparatus 1102. The handover threshold sent to the UE may be a handover threshold for a handover between the first network and the second network. In some aspects, the first network may include an LTE network or an NR network. In some aspects, the second network may include a CS network (e.g., 2G, 3G, WCDMA, GSM, or other traditional non-LTE network).

[0103] At 1004, the base station may communicate with a UE on a first network. For example, 1004 may be performed by the communication component 1108 of the device 1102. The base station may communicate with the UE on the first network such that an active transmission occurs between the base station and the UE.

[0104] At 1006, the base station may receive an indication to perform a handover of the active transmission to a Wi-Fi cell. For example, 1006 may be performed by the indication component 1110 of the device 1102. The base station may receive an indication from the UE to perform a handover of the active transmission to a Wi-Fi cell. The Wi-Fi cell may be a first target cell from among a plurality of target cells. In some aspects, at least based on the signal strength of the Wi-Fi cell, it is feasible for the Wi-Fi cell to be the first target cell serving the UE to continue the active transmission on the Wi-Fi cell. In some aspects, the base station may receive an indication to perform a handover of the active transmission to a Wi-Fi cell before the TTT timer expires. In some aspects, before the first network initiates a handover to a second target cell on a second network, the base station may receive an indication to perform a handover of the active transmission to a Wi-Fi cell. The second target cell may be from among a plurality of target cells. In some aspects, if the signal strength of the Wi-Fi cell is greater than the signal strength of the first network, the base station may receive an indication to perform a handover of the active transmission to a Wi-Fi cell.

[0105] At 1008, the base station may perform a handover of the active transmission to a Wi-Fi cell. For example, 1008 may be performed by the handover component 1112 of the device 1102. In response to an indication received from the UE, the base station may perform a handover of the active transmission to a Wi-Fi cell.

[0106] Figure 11 FIG. 1100 is a conceptual data flow diagram showing the data flow between different components of an exemplary device 1102. The device may be a base station or a component of a base station. The device includes a receiving component 1104, which may be configured to receive various types of signals / messages and / or other information from other devices including, for example, a UE 1150. The device includes a threshold component 1106, which may be configured to send a handover threshold for a handover between a first network and a second network to the UE, for example, as described in 1002 in connection with Figure 10 The device includes a communication component 1108, which may be configured to communicate with a UE on a first network, for example, as described in 1004 in connection with Figure 10 The device includes an indication component 1110, which may be configured to receive an indication from the UE to perform a handover of the active transmission to a Wi-Fi cell, for example, as described in 1006 in connection with Figure 10as described in 1006. The apparatus includes a switching component 1112 that can be configured to perform a handover of an active transmission to a Wi-Fi cell in response to an indication received from a UE, e.g., as described in conjunction with Figure 10 as described in 1008. The apparatus includes a transmission component 1114 that can be configured to send various types of signals / messages and / or other information to other devices including, e.g., UE 1150.

[0107] The apparatus may include additional components that perform each of the blocks of the algorithms in the foregoing Figure 10 flowcharts. Thus, each block in the foregoing Figure 10 flowcharts can be performed by a component, and the apparatus may include one or more of these components. The components can be one or more hardware components that are specifically configured to perform the processes / algorithms, implemented by a processor configured to perform the processes / algorithms, stored in a computer-readable medium for implementation by a processor, or some combination thereof.

[0108] Figure 12 FIG. 1200 is an example showing a hardware implementation of an apparatus 1102' employing a processing system 1214. The processing system 1214 can be implemented with a bus architecture (generally represented by bus 1224). Depending on the specific application and overall design constraints of the processing system 1214, bus 1224 can include any number of interconnecting buses and bridges. Bus 1224 links together various circuits including one or more processors and / or hardware components (represented by processor 1204, components 1104, 1106, 1108, 1110, 1112, 1114, and computer-readable medium / memory 1206). Bus 1224 can also link various other circuits such as timing sources, peripherals, voltage regulators, and power management circuits, which are well known in the art and thus will not be described further.

[0109] The processing system 1214 can be coupled to the transceiver 1210. The transceiver 1210 is coupled to one or more antennas 1220. The transceiver 1210 provides components for communicating with various other devices via a transmission medium. The transceiver 1210 receives signals from one or more antennas 1220, extracts information from the received signals, and provides the extracted information to the processing system 1214 (specifically, the receiving component 1104). Additionally, the transceiver 1210 receives information from the processing system 1214 (specifically, the transmitting component 1114) and generates signals to be applied to one or more antennas 1220 based on the received information. The processing system 1214 includes a processor 1204 coupled to a computer-readable medium / memory 1206. The processor 1204 is responsible for general processing, including running software stored on the computer-readable medium / memory 1206. When run by the processor 1204, the software causes the processing system 1214 to perform the various functions described above for any particular device. The computer-readable medium / memory 1206 can also be used to store data manipulated by the processor 1204 when running the software. The processing system 1214 also includes at least one of the components 1104, 1106, 1108, 1110, 1112, 1114. These components can be software components running in the processor 1204, resident / stored in the computer-readable medium / memory 1206, one or more hardware components coupled to the processor 1204, or some combination thereof. The processing system 1214 can be a component of the base station 310 and can include at least one of the memory 376 and / or the TX processor 316, the RX processor 370, and the controller / processor 375. Alternatively, the processing system 1214 can be the entire base station (e.g., see Figure 3 of 310).

[0110] In one configuration, the apparatus 1102 / 1102’ for wireless communication includes components for communicating with a UE on a first network. An active transmission occurs between the base station and the UE. The apparatus includes components for receiving an indication from the UE to perform a handover of the active transmission to a Wi-Fi cell. The Wi-Fi cell is a first target cell from a plurality of target cells. The apparatus includes components for performing, in response to the indication received from the UE, a handover of the active transmission to the Wi-Fi cell. The apparatus further includes components for sending to the UE a handover threshold for a handover between the first network and a second network. The foregoing components may be one or more of the foregoing components of the apparatus 1102 and / or the processing system 1214 of the apparatus 1102’, which is configured to perform the functions described for the foregoing components. As described above, the processing system 1214 may include a TX processor 316, an RX processor 370, and a controller / processor 375. Thus, in one configuration, the foregoing components may be the TX processor 316, the RX processor 370, and the controller / processor 375, which are configured to perform the functions recited for the foregoing components.

[0111] The present disclosure allows a UE to initiate a handover from a first network (e.g., LTE) to a Wi-Fi network before meeting the SRVCC threshold. The UE may have an active transmission (e.g., a video or voice call) on the first network and may be configured to trigger a handover to the Wi-Fi network when the UE moves to the cell edge of LTE. At least one advantage of the present disclosure is that the active transmission can continue on the Wi-Fi network without a degradation or loss in the quality of the active transmission (e.g., a video or voice call). The quality of the active transmission on the Wi-Fi network may not experience a degradation or loss in quality because the same codec can be used on the Wi-Fi network as is used on the first network (e.g., LTE).

[0112] It should be understood that the specific order or hierarchy of the blocks in the disclosed process / flowchart is an illustration of an example method. Based on design preferences, it should be understood that the specific order or hierarchy of the blocks in the process / flowchart may be rearranged. Additionally, some blocks may be combined or omitted. The appended method claims present the elements of the various blocks in an example order, but are not meant to be limited to the specific order or hierarchy presented.

[0113] The foregoing description is provided to enable a person skilled in the art to practice the various aspects described herein. Those skilled in the art will readily appreciate various modifications to these aspects, and the general principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein but are to be accorded the full scope consistent with the language of the claims, where the reference to an element in the singular is not intended to mean "one and only one" but rather "one or more" unless specifically stated otherwise. The term "exemplary" as used herein means "serving as an example, instance, or illustration." Any aspect described herein as "exemplary" is not necessarily to be construed as preferred or more advantageous than 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 "any combination of A, B, C, or thereof" include any combination of A, B, and / or C and may include multiples of A, multiples of B, or multiples of C. Specifically, such combinations 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 "any combination of A, B, C, or thereof" can 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 combination can include one or more members of A, B, or C. All structural and functional equivalents of the elements of the various aspects described herein 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. Further, 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," etc. do not substitute for the word "component." Thus, no claim element is to be construed as a means-plus-function unless the element is expressly recited using the phrase "means for...".

Claims

1. A method for wireless communication at a user equipment (UE), comprising: Determining whether it is feasible to use a Wi-Fi cell as a first target cell from among a plurality of target cells that serves the UE to continue active transmission on the Wi-Fi cell; Extending a trigger time (TTT) timer length at least in part based on a determination that the Wi-Fi cell is a feasible target cell serving the UE to continue the active transmission on the Wi-Fi cell; And Before the TTT timer expires and before the first network initiates a handover to a second target cell from among the plurality of target cells on a second network, initiating a handover from the first network to the Wi-Fi cell.

2. The method according to claim 1, further comprising: Receiving, from a base station of the first network, a handover threshold for a handover between the first network and the second network.

3. The method according to claim 1, wherein, Based at least on a signal strength of the Wi-Fi cell, it is feasible for the Wi-Fi cell to be the first target cell serving the UE to continue the active transmission on the Wi-Fi cell.

4. The method according to claim 1, wherein, Determining whether the Wi-Fi cell is a feasible first target cell occurs before the second target cell on the second network meets the handover threshold.

5. The method according to claim 4, wherein If the signal strength of the Wi-Fi cell is greater than the signal strength of the first network, a handover from the first network to the Wi-Fi cell is initiated.

6. The method according to claim 1, wherein, Extending the TTT timer length delays transmission of a measurement report from the UE to the base station, where the measurement report includes signal strengths of the first network and the second network in preparation for a handover from the first network to the second network.

7. The method according to claim 6, wherein, The delay in transmission of the measurement report allows initiation of a handover from the first network to the Wi-Fi cell.

8. The method according to claim 7, wherein If the handover to the Wi-Fi cell is completed, the measurement report is not sent when the TTT timer expires.

9. The method according to claim 7, wherein If there is no active transmission on the first network, the measurement report is not sent when the TTT timer expires.

10. The method according to claim 1, further comprising: Determining whether the signal strength of the second target cell is greater than the signal strength of the active transmission on the first network such that the first network is ready to initiate a handover to the second target cell.

11. 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: Determine whether it is feasible to use a Wi-Fi cell as a first target cell from among a plurality of target cells that serves the UE to continue active transmission on the Wi-Fi cell; Extend a trigger time (TTT) timer length at least in part based on a determination that the Wi-Fi cell is a feasible target cell serving the UE to continue the active transmission on the Wi-Fi cell; And Before the TTT timer expires and before the first network initiates a handover to a second target cell among multiple target cells on the second network, initiate a handover from the first network to the Wi-Fi cell.

12. The device according to claim 11, wherein, The at least one processor is further configured to: Receive, from a base station of the first network, a handover threshold for handover between the first network and the second network.

13. The device according to claim 11, wherein, Based at least on the signal strength of the Wi-Fi cell, it is feasible for the Wi-Fi cell to continue the active transmission on the Wi-Fi cell as the first target cell serving the UE.

14. The apparatus according to claim 11, wherein, The at least one processor is configured to: Determine whether the Wi-Fi cell is feasible as the first target cell before the second target cell on the second network meets the handover threshold.

15. The apparatus according to claim 14, wherein, The at least one processor is configured to: If the signal strength of the Wi-Fi cell is greater than the signal strength of the first network, initiate a handover from the first network to the Wi-Fi cell.

16. The apparatus according to claim 11, wherein, The at least one processor is configured to: Extend the length of the TTT timer to delay the transmission of a measurement report from the UE to the base station, where the measurement report includes the signal strengths of the first network and the second network in the handover preparation from the first network to the second network.

17. The device according to claim 16, wherein, The delay in the transmission of the measurement report allows for the initiation of a handover from the first network to the Wi-Fi cell.

18. The apparatus according to claim 17, wherein, If the handover to the Wi-Fi cell is completed, do not send the measurement report when the TTT timer expires.

19. The device according to claim 17, wherein, If there is no active transmission on the first network, do not send the measurement report when the TTT timer expires.

20. The apparatus according to claim 11, wherein, The at least one processor is further configured to: Determine whether the signal strength of the second target cell is greater than the signal strength of the active transmission on the first network, such that the first network is ready to initiate a handover to the second target cell.

21. A method for wireless communication at a base station, comprising: Communicate with a user equipment UE on a first network, wherein, An active transmission occurs between the base station and the UE; Receive, from the UE, an indication to perform a handover of the active transmission to a Wi-Fi cell, where the Wi-Fi cell is the first target cell among multiple target cells; and In response to the indication received from the UE, perform a handover of the active transmission to the Wi-Fi cell, where the base station receives the indication to perform a handover of the active transmission to the Wi-Fi cell before the trigger time TTT timer expires and before the first network initiates a handover to a second target cell among the multiple target cells on the second network.

22. The method according to claim 21, further comprising: Send to the UE a handover threshold for handover between the first network and the second network.

23. The method according to claim 21, wherein, Based at least on the signal strength of the Wi-Fi cell, it is feasible for the Wi-Fi cell to continue the active transmission on the Wi-Fi cell as the first target cell serving the UE.

24. The method according to claim 21, wherein, If the signal strength of the Wi-Fi cell is greater than the signal strength of the first network, the base station receives an indication to perform a handover of the active transmission to the Wi-Fi cell.

25. An apparatus for wireless communication at a base station, comprising: a memory; and at least one processor, coupled to the memory and configured to: Communicate with a user equipment UE on a first network, wherein, perform an active transmission between the base station and the UE; receive from the UE an indication to perform a handover of the active transmission to a Wi-Fi cell, wherein the Wi-Fi cell is a first target cell from a plurality of target cells; and in response to the indication received from the UE, perform a handover of the active transmission to the Wi-Fi cell, wherein the at least one processor is configured to: receive an indication to perform a handover of the active transmission to the Wi-Fi cell before a trigger time TTT timer length expires and before the first network initiates a handover to a second target cell from the plurality of target cells on a second network.

26. The device according to claim 25, wherein, The at least one processor is further configured to: send to the UE a handover threshold for a handover between the first network and the second network.

27. The apparatus according to claim 25, wherein At least based on the signal strength of the Wi-Fi cell, it is feasible for the Wi-Fi cell, as the first target cell serving the UE, to continue the active transmission on the Wi-Fi cell.

28. The apparatus according to claim 25, wherein, The at least one processor is configured to: if the signal strength of the Wi-Fi cell is greater than the signal strength of the first network, receive an indication to perform a handover of the active transmission to the Wi-Fi cell.

29. An apparatus for wireless communication to be performed at a user equipment UE, the apparatus comprising components for performing the method according to any one of claims 1-10.

30. An apparatus for wireless communication to be performed at a base station BS, the apparatus comprising components for performing the method according to any one of claims 21-24.

31. A computer-readable medium having program code recorded thereon, wherein the program code is executable by one or more processors of a user equipment UE to cause the processors to perform the method according to any one of claims 1-10.

32. A computer-readable medium having program code recorded thereon, wherein the program code is executable by one or more processors of a base station BS to cause the processors to perform the method according to any one of claims 21-24.

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