WO2022056763A1

WO2022056763A1 - Optimization for internet protocol multimedia subsystem evolved packet system fallback

Info

Publication number: WO2022056763A1
Application number: PCT/CN2020/115809
Authority: WO
Inventors: Hao Zhang; Xiuqiu XIA; Haibo Liu
Original assignee: Qualcomm Inc
Current assignee: Qualcomm Inc
Priority date: 2020-09-17
Filing date: 2020-09-17
Publication date: 2022-03-24
Anticipated expiration: 2023-03-17

Abstract

Methods, systems, and devices for wireless communications are described. A user equipment (UE) may receive, during a call session and from a first base station associated with a first radio access technology (RAT), a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT (e.g., a different RAT). The UE may transmit, during the call session and to the second base station, a first tracking area update (TAU) request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based at least in part on the handover procedure. The UE may transmit, based at least in part on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT.

Description

OPTIMIZATION FOR INTERNET PROTOCOL MULTIMEDIA SUBSYSTEM EVOLVED PACKET SYSTEM FALLBACK

FIELD OF TECHNOLOGY

The following relates to wireless communications, including optimization for internet protocol multimedia subsystem evolved packet system fallback.

BACKGROUND

Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be capable of supporting communication with multiple users by sharing the available system resources (e.g., time, frequency, and power) . Examples of such multiple-access systems include fourth generation (4G) systems such as Long Term Evolution (LTE) systems, LTE-Advanced (LTE-A) systems, or LTE-A Pro systems, and fifth generation (5G) systems which may be referred to as New Radio (NR) systems. These systems may employ technologies such as code division multiple access (CDMA) , time division multiple access (TDMA) , frequency division multiple access (FDMA) , orthogonal frequency division multiple access (OFDMA) , or discrete Fourier transform spread orthogonal frequency division multiplexing (DFT-S-OFDM) . A wireless multiple-access communications system may include one or more base stations or one or more network access nodes, each simultaneously supporting communication for multiple communication devices, which may be otherwise known as user equipment (UE) .

SUMMARY

The described techniques relate to improved methods, systems, devices, and apparatuses that support optimization for internet protocol multimedia subsystem (IMS) evolved packet system (EPS) fallback. Generally, the described techniques provide for various techniques for a user equipment (UE) to temporarily disable N1 support (e.g., support for new radio (NR) communications during an IMS call session with a long term evolution (LTE) bases station to avoid call drop. For example, a UE may be handed over from an NR base station (e.g., a first base station associated with a first radio access technology (RAT) , such as an NR RAT) to an LTE base station (e.g., a second base station associated with a second RAT, such as an LTE RAT) during an IMS call session. To avoid dropping of the IMS call should the UE be handed over to another (or back to the same) NR base station, the UE may signal that it does not support NR communications to the LTE base station (e.g., the UE may temporarily suspend or disable support for NR communications during the IMS call session) . The UE may use a tracking area update (TAU) request to signal that it does not support NR communications. Accordingly, the UE may complete the IMS call session on the LTE base station and then, upon termination of the IMS call session, signal that it does support NR communications to the LTE base station (e.g., using another TAU request) . Accordingly, after the IMS call session ends on the LTE base station, the UE may resume support for NR communications, inter-RAT channel measurements, and the like.

A method of wireless communication at a UE is described. The method may include receiving, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT, transmitting, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure, and transmitting, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT.

An apparatus for wireless communication at a UE is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to receive, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT, transmit, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure, and transmit, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT.

Another apparatus for wireless communication at a UE is described. The apparatus may include means for receiving, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT, transmitting, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure, and transmitting, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT.

A non-transitory computer-readable medium storing code for wireless communication at a UE is described. The code may include instructions executable by a processor to receive, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT, transmit, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure, and transmit, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for refraining, based on transmitting the first TAU request indicating that the UE does not support communications on the first RAT, from performing channel performance measurements of one or more base stations associated with the first RAT.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for receiving, based on transmitting the second TAU request indicating that the UE does support communications on the first RAT, a signal triggering channel performance measurements of one or more base stations associated with the first RAT, and performing, based on the signal, channel performance measurements of the one or more base stations associated with the first RAT.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the call session includes an IMS call session.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the first RAT includes a NR RAT and the second RAT includes a LTE RAT.

A method of wireless communication at a first base station is described. The method may include performing, during a call session, a handover procedure of a UE to the first base station associated with a first RAT from a second base station associated with a second RAT that is different from the first RAT, receiving, during the call session and from the UE, a first TAU request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based on the handover procedure, and receiving, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the second RAT.

An apparatus for wireless communication at a first base station is described. The apparatus may include a processor, memory coupled with the processor, and instructions stored in the memory. The instructions may be executable by the processor to cause the apparatus to perform, during a call session, a handover procedure of a UE to the first base station associated with a first RAT from a second base station associated with a second RAT that is different from the first RAT, receive, during the call session and from the UE, a first TAU request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based on the handover procedure, and receive, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the second RAT.

Another apparatus for wireless communication at a first base station is described. The apparatus may include means for performing, during a call session, a handover procedure of a UE to the first base station associated with a first RAT from a second base station associated with a second RAT that is different from the first RAT, receiving, during the call session and from the UE, a first TAU request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based on the handover procedure, and receiving, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the second RAT.

A non-transitory computer-readable medium storing code for wireless communication at a first base station is described. The code may include instructions executable by a processor to perform, during a call session, a handover procedure of a UE to the first base station associated with a first RAT from a second base station associated with a second RAT that is different from the first RAT, receive, during the call session and from the UE, a first TAU request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based on the handover procedure, and receive, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the second RAT.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for refraining, based on receiving the first TAU request indicating that the UE does not support communications on the second RAT, from transmitting a signal triggering channel performance measurements by the UE of one or more base stations associated with the first RAT.

Some examples of the method, apparatuses, and non-transitory computer-readable medium described herein may further include operations, features, means, or instructions for transmitting, based on receiving the second TAU request indicating that the UE does support communications on the second RAT, a signal triggering channel performance measurements of one or more base stations associated with the second RAT, and receiving a channel performance feedback message from the UE based on a result of the channel performance measurements.

In some examples of the method, apparatuses, and non-transitory computer-readable medium described herein, the first RAT includes a LTE RAT and the second RAT includes a NR RAT.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a system for wireless communications that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

FIG. 2 illustrates an example of a wireless communication system that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

FIG. 3 illustrates an example of a process that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

FIG. 4 illustrates an example of a process that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

FIGs. 5 and 6 show block diagrams of devices that support optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

FIG. 7 shows a block diagram of a communications manager that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

FIG. 8 shows a diagram of a system including a device that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

FIGs. 9 and 10 show block diagrams of devices that support optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

FIG. 11 shows a block diagram of a communications manager that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

FIG. 12 shows a diagram of a system including a device that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

FIGs. 13 through 16 show flowcharts illustrating methods that support optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure.

DETAILED DESCRIPTION

Some wireless communication systems may not support the transfer of an internet protocol (IP) multimedia subsystem (IMS) call from a long term evolution (LTE) network to a new radio (NR) network. For example, a user equipment (UE) connected to an NR and/or LTE network may establish an IMS call session. If connected to the NR network first, the UE may perform a handover to the LTE network, e.g., due to UE mobility. Due to such UE mobility (or other factors) , the UE may perform another handover procedure from the LTE network back to the NR network. In this situation, the IMS call session would be dropped, thus disrupting communications.

Aspects of the disclosure are initially described in the context of wireless communication systems. Generally, the described techniques provide for various techniques for a UE to temporarily disable N1 support (e.g., support for NR communications during an IMS call session with a LTE bases station to avoid call drop. For example, a UE may be handed over from an NR base station (e.g., a first base station associated with a first radio access technology (RAT) , such as an NR RAT) to an LTE base station (e.g., a second base station associated with a second RAT, such as an LTE RAT) during an IMS call session. To avoid dropping of the IMS call should the UE be handed over to another (or back to the same) NR base station, the UE may signal that it does not support NR communications to the LTE base station (e.g., the UE may temporarily suspend or disable support for NR communications during the IMS call session) . The UE may use a tracking area update (TAU) request to signal that it does not support NR communications. Accordingly, the UE may complete the IMS call session on the LTE base station and then, upon termination of the IMS call session, signal that it does support NR communications to the LTE base station (e.g., using another TAU request) . Accordingly, after the IMS call session ends on the LTE base station, the UE may resume support for NR communications, inter-RAT channel measurements, and the like.

Aspects of the disclosure are further illustrated by and described with reference to apparatus diagrams, system diagrams, and flowcharts that relate to optimization for internet protocol multimedia subsystem evolved packet system fallback.

FIG. 1 illustrates an example of a wireless communication system 100 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The wireless communication system 100 may include one or more base stations 105, one or more UEs 115, and a core network 130. In some examples, the wireless communication system 100 may be a Long Term Evolution (LTE) network, an LTE-Advanced (LTE-A) network, an LTE-A Pro network, or a New Radio (NR) network. In some examples, the wireless communication system 100 may support enhanced broadband communications, ultra-reliable (e.g., mission critical) communications, low latency communications, communications with low-cost and low-complexity devices, or any combination thereof.

The base stations 105 may be dispersed throughout a geographic area to form the wireless communication system 100 and may be devices in different forms or having different capabilities. The base stations 105 and the UEs 115 may wirelessly communicate via one or more communication links 125. Each base station 105 may provide a coverage area 110 over which the UEs 115 and the base station 105 may establish one or more communication links 125. The coverage area 110 may be an example of a geographic area over which a base station 105 and a UE 115 may support the communication of signals according to one or more radio access technologies.

The UEs 115 may be dispersed throughout a coverage area 110 of the wireless communication system 100, and each UE 115 may be stationary, or mobile, or both at different times. The UEs 115 may be devices in different forms or having different capabilities. Some example UEs 115 are illustrated in FIG. 1. The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115, the base stations 105, or network equipment (e.g., core network nodes, relay devices, integrated access and backhaul (IAB) nodes, or other network equipment) , as shown in FIG. 1.

The base stations 105 may communicate with the core network 130, or with one another, or both. For example, the base stations 105 may interface with the core network 130 through one or more backhaul links 120 (e.g., via an S1, N2, N3, or other interface) . The base stations 105 may communicate with one another over the backhaul links 120 (e.g., via an X2, Xn, or other interface) either directly (e.g., directly between base stations 105) , or indirectly (e.g., via core network 130) , or both. In some examples, the backhaul links 120 may be or include one or more wireless links.

One or more of the base stations 105 described herein may include or may be referred to by a person having ordinary skill in the art as a base transceiver station, a radio base station, an access point, a radio transceiver, a NodeB, an eNodeB (eNB) , a next-generation NodeB or a giga-NodeB (either of which may be referred to as a gNB) , a Home NodeB, a Home eNodeB, or other suitable terminology.

A UE 115 may include or may be referred to as a mobile device, a wireless device, a remote device, a handheld device, or a subscriber device, or some other suitable terminology, where the “device” may also be referred to as a unit, a station, a terminal, or a client, among other examples. A UE 115 may also include or may be referred to as a personal electronic device such as a cellular phone, a personal digital assistant (PDA) , a tablet computer, a laptop computer, or a personal computer. In some examples, a UE 115 may include or be referred to as a wireless local loop (WLL) station, an Internet of Things (IoT) device, an Internet of Everything (IoE) device, or a machine type communications (MTC) device, among other examples, which may be implemented in various objects such as appliances, or vehicles, meters, among other examples.

The UEs 115 described herein may be able to communicate with various types of devices, such as other UEs 115 that may sometimes act as relays as well as the base stations 105 and the network equipment including macro eNBs or gNBs, small cell eNBs or gNBs, or relay base stations, among other examples, as shown in FIG. 1.

The UEs 115 and the base stations 105 may wirelessly communicate with one another via one or more communication links 125 over one or more carriers. The term “carrier” may refer to a set of radio frequency spectrum resources having a defined physical layer structure for supporting the communication links 125. For example, a carrier used for a communication link 125 may include a portion of a radio frequency spectrum band (e.g., a bandwidth part (BWP) ) that is operated according to one or more physical layer channels for a given radio access technology (e.g., LTE, LTE-A, LTE-A Pro, NR) . Each physical layer channel may carry acquisition signaling (e.g., synchronization signals, system information) , control signaling that coordinates operation for the carrier, user data, or other signaling. The wireless communication system 100 may support communication with a UE 115 using carrier aggregation or multi-carrier operation. A UE 115 may be configured with multiple downlink component carriers and one or more uplink component carriers according to a carrier aggregation configuration. Carrier aggregation may be used with both frequency division duplexing (FDD) and time division duplexing (TDD) component carriers.

In some examples (e.g., in a carrier aggregation configuration) , a carrier may also have acquisition signaling or control signaling that coordinates operations for other carriers. A carrier may be associated with a frequency channel (e.g., an evolved universal mobile telecommunication system terrestrial radio access (E-UTRA) absolute radio frequency channel number (EARFCN) ) and may be positioned according to a channel raster for discovery by the UEs 115. A carrier may be operated in a standalone mode where initial acquisition and connection may be conducted by the UEs 115 via the carrier, or the carrier may be operated in a non-standalone mode where a connection is anchored using a different carrier (e.g., of the same or a different radio access technology) .

The communication links 125 shown in the wireless communication system 100 may include uplink transmissions from a UE 115 to a base station 105, or downlink transmissions from a base station 105 to a UE 115. Carriers may carry downlink or uplink communications (e.g., in an FDD mode) or may be configured to carry downlink and uplink communications (e.g., in a TDD mode) .

A carrier may be associated with a particular bandwidth of the radio frequency spectrum, and in some examples the carrier bandwidth may be referred to as a “system bandwidth” of the carrier or the wireless communication system 100. For example, the carrier bandwidth may be one of a number of determined bandwidths for carriers of a particular radio access technology (e.g., 1.4, 3, 5, 10, 15, 20, 40, or 80 megahertz (MHz) ) . Devices of the wireless communication system 100 (e.g., the base stations 105, the UEs 115, or both) may have hardware configurations that support communications over a particular carrier bandwidth or may be configurable to support communications over one of a set of carrier bandwidths. In some examples, the wireless communication system 100 may include base stations 105 or UEs 115 that support simultaneous communications via carriers associated with multiple carrier bandwidths. In some examples, each served UE 115 may be configured for operating over portions (e.g., a sub-band, a BWP) or all of a carrier bandwidth.

Signal waveforms transmitted over a carrier may be made up of multiple subcarriers (e.g., using multi-carrier modulation (MCM) techniques such as orthogonal frequency division multiplexing (OFDM) or discrete Fourier transform spread OFDM (DFT-S-OFDM) ) . In a system employing MCM techniques, a resource element may consist of one symbol period (e.g., a duration of one modulation symbol) and one subcarrier, where the symbol period and subcarrier spacing are inversely related. The number of bits carried by each resource element may depend on the modulation scheme (e.g., the order of the modulation scheme, the coding rate of the modulation scheme, or both) . Thus, the more resource elements that a UE 115 receives and the higher the order of the modulation scheme, the higher the data rate may be for the UE 115. A wireless communications resource may refer to a combination of a radio frequency spectrum resource, a time resource, and a spatial resource (e.g., spatial layers or beams) , and the use of multiple spatial layers may further increase the data rate or data integrity for communications with a UE 115.

One or more numerologies for a carrier may be supported, where a numerology may include a subcarrier spacing (Δf) and a cyclic prefix. A carrier may be divided into one or more BWPs having the same or different numerologies. In some examples, a UE 115 may be configured with multiple BWPs. In some examples, a single BWP for a carrier may be active at a given time and communications for the UE 115 may be restricted to one or more active BWPs.

The time intervals for the base stations 105 or the UEs 115 may be expressed in multiples of a basic time unit which may, for example, refer to a sampling period of T _s= 1/ (Δf _max·N _f) seconds, where Δf _max may represent the maximum supported subcarrier spacing, and N _f may represent the maximum supported discrete Fourier transform (DFT) size. Time intervals of a communications resource may be organized according to radio frames each having a specified duration (e.g., 10 milliseconds (ms) ) . Each radio frame may be identified by a system frame number (SFN) (e.g., ranging from 0 to 1023) .

Each frame may include multiple consecutively numbered subframes or slots, and each subframe or slot may have the same duration. In some examples, a frame may be divided (e.g., in the time domain) into subframes, and each subframe may be further divided into a number of slots. Alternatively, each frame may include a variable number of slots, and the number of slots may depend on subcarrier spacing. Each slot may include a number of symbol periods (e.g., depending on the length of the cyclic prefix prepended to each symbol period) . In some wireless communication systems 100, a slot may further be divided into multiple mini-slots containing one or more symbols. Excluding the cyclic prefix, each symbol period may contain one or more (e.g., N _f) sampling periods. The duration of a symbol period may depend on the subcarrier spacing or frequency band of operation.

A subframe, a slot, a mini-slot, or a symbol may be the smallest scheduling unit (e.g., in the time domain) of the wireless communication system 100 and may be referred to as a transmission time interval (TTI) . In some examples, the TTI duration (e.g., the number of symbol periods in a TTI) may be variable. Additionally or alternatively, the smallest scheduling unit of the wireless communication system 100 may be dynamically selected (e.g., in bursts of shortened TTIs (sTTIs) ) .

Physical channels may be multiplexed on a carrier according to various techniques. A physical control channel and a physical data channel may be multiplexed on a downlink carrier, for example, using one or more of time division multiplexing (TDM) techniques, frequency division multiplexing (FDM) techniques, or hybrid TDM-FDM techniques. A control region (e.g., a control resource set (CORESET) ) for a physical control channel may be defined by a number of symbol periods and may extend across the system bandwidth or a subset of the system bandwidth of the carrier. One or more control regions (e.g., CORESETs) may be configured for a set of the UEs 115. For example, one or more of the UEs 115 may monitor or search control regions for control information according to one or more search space sets, and each search space set may include one or multiple control channel candidates in one or more aggregation levels arranged in a cascaded manner. An aggregation level for a control channel candidate may refer to a number of control channel resources (e.g., control channel elements (CCEs) ) associated with encoded information for a control information format having a given payload size. Search space sets may include common search space sets configured for sending control information to multiple UEs 115 and UE-specific search space sets for sending control information to a specific UE 115.

Each base station 105 may provide communication coverage via one or more cells, for example a macro cell, a small cell, a hot spot, or other types of cells, or any combination thereof. The term “cell” may refer to a logical communication entity used for communication with a base station 105 (e.g., over a carrier) and may be associated with an identifier for distinguishing neighboring cells (e.g., a physical cell identifier (PCID) , a virtual cell identifier (VCID) , or others) . In some examples, a cell may also refer to a geographic coverage area 110 or a portion of a geographic coverage area 110 (e.g., a sector) over which the logical communication entity operates. Such cells may range from smaller areas (e.g., a structure, a subset of structure) to larger areas depending on various factors such as the capabilities of the base station 105. For example, a cell may be or include a building, a subset of a building, or exterior spaces between or overlapping with geographic coverage areas 110, among other examples.

A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by the UEs 115 with service subscriptions with the network provider supporting the macro cell. A small cell may be associated with a lower-powered base station 105, as compared with a macro cell, and a small cell may operate in the same or different (e.g., licensed, unlicensed) frequency bands as macro cells. Small cells may provide unrestricted access to the UEs 115 with service subscriptions with the network provider or may provide restricted access to the UEs 115 having an association with the small cell (e.g., the UEs 115 in a closed subscriber group (CSG) , the UEs 115 associated with users in a home or office) . A base station 105 may support one or multiple cells and may also support communications over the one or more cells using one or multiple component carriers.

In some examples, a carrier may support multiple cells, and different cells may be configured according to different protocol types (e.g., MTC, narrowband IoT (NB-IoT) , enhanced mobile broadband (eMBB) ) that may provide access for different types of devices.

In some examples, a base station 105 may be movable and therefore provide communication coverage for a moving geographic coverage area 110. In some examples, different geographic coverage areas 110 associated with different technologies may overlap, but the different geographic coverage areas 110 may be supported by the same base station 105. In other examples, the overlapping geographic coverage areas 110 associated with different technologies may be supported by different base stations 105. The wireless communication system 100 may include, for example, a heterogeneous network in which different types of the base stations 105 provide coverage for various geographic coverage areas 110 using the same or different radio access technologies.

The wireless communication system 100 may support synchronous or asynchronous operation. For synchronous operation, the base stations 105 may have similar frame timings, and transmissions from different base stations 105 may be approximately aligned in time. For asynchronous operation, the base stations 105 may have different frame timings, and transmissions from different base stations 105 may, in some examples, not be aligned in time. The techniques described herein may be used for either synchronous or asynchronous operations.

Some UEs 115, such as MTC or IoT devices, may be low cost or low complexity devices and may provide for automated communication between machines (e.g., via Machine-to-Machine (M2M) communication) . M2M communication or MTC may refer to data communication technologies that allow devices to communicate with one another or a base station 105 without human intervention. In some examples, M2M communication or MTC may include communications from devices that integrate sensors or meters to measure or capture information and relay such information to a central server or application program that makes use of the information or presents the information to humans interacting with the application program. Some UEs 115 may be designed to collect information or enable automated behavior of machines or other devices. Examples of applications for MTC devices include smart metering, inventory monitoring, water level monitoring, equipment monitoring, healthcare monitoring, wildlife monitoring, weather and geological event monitoring, fleet management and tracking, remote security sensing, physical access control, and transaction-based business charging.

Some UEs 115 may be configured to employ operating modes that reduce power consumption, such as half-duplex communications (e.g., a mode that supports one-way communication via transmission or reception, but not transmission and reception simultaneously) . In some examples, half-duplex communications may be performed at a reduced peak rate. Other power conservation techniques for the UEs 115 include entering a power saving deep sleep mode when not engaging in active communications, operating over a limited bandwidth (e.g., according to narrowband communications) , or a combination of these techniques. For example, some UEs 115 may be configured for operation using a narrowband protocol type that is associated with a defined portion or range (e.g., set of subcarriers or resource blocks (RBs) ) within a carrier, within a guard-band of a carrier, or outside of a carrier.

The wireless communication system 100 may be configured to support ultra-reliable communications or low-latency communications, or various combinations thereof. For example, the wireless communication system 100 may be configured to support ultra-reliable low-latency communications (URLLC) or mission critical communications. The UEs 115 may be designed to support ultra-reliable, low-latency, or critical functions (e.g., mission critical functions) . Ultra-reliable communications may include private communication or group communication and may be supported by one or more mission critical services such as mission critical push-to-talk (MCPTT) , mission critical video (MCVideo) , or mission critical data (MCData) . Support for mission critical functions may include prioritization of services, and mission critical services may be used for public safety or general commercial applications. The terms ultra-reliable, low-latency, mission critical, and ultra-reliable low-latency may be used interchangeably herein.

In some examples, a UE 115 may also be able to communicate directly with other UEs 115 over a device-to-device (D2D) communication link 135 (e.g., using a peer-to-peer (P2P) or D2D protocol) . One or more UEs 115 utilizing D2D communications may be within the geographic coverage area 110 of a base station 105. Other UEs 115 in such a group may be outside the geographic coverage area 110 of a base station 105 or be otherwise unable to receive transmissions from a base station 105. In some examples, groups of the UEs 115 communicating via D2D communications may utilize a one-to-many (1: M) system in which each UE 115 transmits to every other UE 115 in the group. In some examples, a base station 105 facilitates the scheduling of resources for D2D communications. In other cases, D2D communications are carried out between the UEs 115 without the involvement of a base station 105.

In some systems, the D2D communication link 135 may be an example of a communication channel, such as a sidelink communication channel, between vehicles (e.g., UEs 115) . In some examples, vehicles may communicate using vehicle-to-everything (V2X) communications, vehicle-to-vehicle (V2V) communications, or some combination of these. A vehicle may signal information related to traffic conditions, signal scheduling, weather, safety, emergencies, or any other information relevant to a V2X system. In some examples, vehicles in a V2X system may communicate with roadside infrastructure, such as roadside units, or with the network via one or more network nodes (e.g., base stations 105) using vehicle-to-network (V2N) communications, or with both.

The core network 130 may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. The core network 130 may be an evolved packet core (EPC) or 5G core (5GC) , which may include at least one control plane entity that manages access and mobility (e.g., a mobility management entity (MME) , an access and mobility management function (AMF) ) and at least one user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW) , a Packet Data Network (PDN) gateway (P-GW) , or a user plane function (UPF) ) . The control plane entity may manage non-access stratum (NAS) functions such as mobility, authentication, and bearer management for the UEs 115 served by the base stations 105 associated with the core network 130. User IP packets may be transferred through the user plane entity, which may provide IP address allocation as well as other functions. The user plane entity may be connected to IP services 150 for one or more network operators. The IP services 150 may include access to the Internet, Intranet (s) , an IP Multimedia Subsystem (IMS) , or a Packet-Switched Streaming Service.

Some of the network devices, such as a base station 105, may include subcomponents such as an access network entity 140, which may be an example of an access node controller (ANC) . Each access network entity 140 may communicate with the UEs 115 through one or more other access network transmission entities 145, which may be referred to as radio heads, smart radio heads, or transmission/reception points (TRPs) . Each access network transmission entity 145 may include one or more antenna panels. In some configurations, various functions of each access network entity 140 or base station 105 may be distributed across various network devices (e.g., radio heads and ANCs) or consolidated into a single network device (e.g., a base station 105) .

The wireless communication system 100 may operate using one or more frequency bands, typically in the range of 300 megahertz (MHz) to 300 gigahertz (GHz) . Generally, the region from 300 MHz to 3 GHz is known as the ultra-high frequency (UHF) region or decimeter band because the wavelengths range from approximately one decimeter to one meter in length. The UHF waves may be blocked or redirected by buildings and environmental features, but the waves may penetrate structures sufficiently for a macro cell to provide service to the UEs 115 located indoors. The transmission of UHF waves may be associated with smaller antennas and shorter ranges (e.g., less than 100 kilometers) compared to transmission using the smaller frequencies and longer waves of the high frequency (HF) or very high frequency (VHF) portion of the spectrum below 300 MHz.

The wireless communication system 100 may also operate in a super high frequency (SHF) region using frequency bands from 3 GHz to 30 GHz, also known as the centimeter band, or in an extremely high frequency (EHF) region of the spectrum (e.g., from 30 GHz to 300 GHz) , also known as the millimeter band. In some examples, the wireless communication system 100 may support millimeter wave (mmW) communications between the UEs 115 and the base stations 105, and EHF antennas of the respective devices may be smaller and more closely spaced than UHF antennas. In some examples, this may facilitate use of antenna arrays within a device. The propagation of EHF transmissions, however, may be subject to even greater atmospheric attenuation and shorter range than SHF or UHF transmissions. The techniques disclosed herein may be employed across transmissions that use one or more different frequency regions, and designated use of bands across these frequency regions may differ by country or regulating body.

The wireless communication system 100 may utilize both licensed and unlicensed radio frequency spectrum bands. For example, the wireless communication system 100 may employ License Assisted Access (LAA) , LTE-Unlicensed (LTE-U) radio access technology, or NR technology in an unlicensed band such as the 5 GHz industrial, scientific, and medical (ISM) band. When operating in unlicensed radio frequency spectrum bands, devices such as the base stations 105 and the UEs 115 may employ carrier sensing for collision detection and avoidance. In some examples, operations in unlicensed bands may be based on a carrier aggregation configuration in conjunction with component carriers operating in a licensed band (e.g., LAA) . Operations in unlicensed spectrum may include downlink transmissions, uplink transmissions, P2P transmissions, or D2D transmissions, among other examples.

A base station 105 or a UE 115 may be equipped with multiple antennas, which may be used to employ techniques such as transmit diversity, receive diversity, multiple-input multiple-output (MIMO) communications, or beamforming. The antennas of a base station 105 or a UE 115 may be located within one or more antenna arrays or antenna panels, which may support MIMO operations or transmit or receive beamforming. For example, one or more base station antennas or antenna arrays may be co-located at an antenna assembly, such as an antenna tower. In some examples, antennas or antenna arrays associated with a base station 105 may be located in diverse geographic locations. A base station 105 may have an antenna array with a number of rows and columns of antenna ports that the base station 105 may use to support beamforming of communications with a UE 115. Likewise, a UE 115 may have one or more antenna arrays that may support various MIMO or beamforming operations. Additionally or alternatively, an antenna panel may support radio frequency beamforming for a signal transmitted via an antenna port.

The base stations 105 or the UEs 115 may use MIMO communications to exploit multipath signal propagation and increase the spectral efficiency by transmitting or receiving multiple signals via different spatial layers. Such techniques may be referred to as spatial multiplexing. The multiple signals may, for example, be transmitted by the transmitting device via different antennas or different combinations of antennas. Likewise, the multiple signals may be received by the receiving device via different antennas or different combinations of antennas. Each of the multiple signals may be referred to as a separate spatial stream and may carry bits associated with the same data stream (e.g., the same codeword) or different data streams (e.g., different codewords) . Different spatial layers may be associated with different antenna ports used for channel measurement and reporting. MIMO techniques include single-user MIMO (SU-MIMO) , where multiple spatial layers are transmitted to the same receiving device, and multiple-user MIMO (MU-MIMO) , where multiple spatial layers are transmitted to multiple devices.

Beamforming, which may also be referred to as spatial filtering, directional transmission, or directional reception, is a signal processing technique that may be used at a transmitting device or a receiving device (e.g., a base station 105, a UE 115) to shape or steer an antenna beam (e.g., a transmit beam, a receive beam) along a spatial path between the transmitting device and the receiving device. Beamforming may be achieved by combining the signals communicated via antenna elements of an antenna array such that some signals propagating at particular orientations with respect to an antenna array experience constructive interference while others experience destructive interference. The adjustment of signals communicated via the antenna elements may include a transmitting device or a receiving device applying amplitude offsets, phase offsets, or both to signals carried via the antenna elements associated with the device. The adjustments associated with each of the antenna elements may be defined by a beamforming weight set associated with a particular orientation (e.g., with respect to the antenna array of the transmitting device or receiving device, or with respect to some other orientation) .

A base station 105 or a UE 115 may use beam sweeping techniques as part of beam forming operations. For example, a base station 105 may use multiple antennas or antenna arrays (e.g., antenna panels) to conduct beamforming operations for directional communications with a UE 115. Some signals (e.g., synchronization signals, reference signals, beam selection signals, or other control signals) may be transmitted by a base station 105 multiple times in different directions. For example, the base station 105 may transmit a signal according to different beamforming weight sets associated with different directions of transmission. Transmissions in different beam directions may be used to identify (e.g., by a transmitting device, such as a base station 105, or by a receiving device, such as a UE 115) a beam direction for later transmission or reception by the base station 105.

Some signals, such as data signals associated with a particular receiving device, may be transmitted by a base station 105 in a single beam direction (e.g., a direction associated with the receiving device, such as a UE 115) . In some examples, the beam direction associated with transmissions along a single beam direction may be determined based on a signal that was transmitted in one or more beam directions. For example, a UE 115 may receive one or more of the signals transmitted by the base station 105 in different directions and may report to the base station 105 an indication of the signal that the UE 115 received with a highest signal quality or an otherwise acceptable signal quality.

In some examples, transmissions by a device (e.g., by a base station 105 or a UE 115) may be performed using multiple beam directions, and the device may use a combination of digital precoding or radio frequency beamforming to generate a combined beam for transmission (e.g., from a base station 105 to a UE 115) . The UE 115 may report feedback that indicates precoding weights for one or more beam directions, and the feedback may correspond to a configured number of beams across a system bandwidth or one or more sub-bands. The base station 105 may transmit a reference signal (e.g., a cell-specific reference signal (CRS) , a channel state information reference signal (CSI-RS) ) , which may be precoded or unprecoded. The UE 115 may provide feedback for beam selection, which may be a precoding matrix indicator (PMI) or codebook-based feedback (e.g., a multi-panel type codebook, a linear combination type codebook, a port selection type codebook) . Although these techniques are described with reference to signals transmitted in one or more directions by a base station 105, a UE 115 may employ similar techniques for transmitting signals multiple times in different directions (e.g., for identifying a beam direction for subsequent transmission or reception by the UE 115) or for transmitting a signal in a single direction (e.g., for transmitting data to a receiving device) .

A receiving device (e.g., a UE 115) may try multiple receive configurations (e.g., directional listening) when receiving various signals from the base station 105, such as synchronization signals, reference signals, beam selection signals, or other control signals. For example, a receiving device may try multiple receive directions by receiving via different antenna subarrays, by processing received signals according to different antenna subarrays, by receiving according to different receive beamforming weight sets (e.g., different directional listening weight sets) applied to signals received at multiple antenna elements of an antenna array, or by processing received signals according to different receive beamforming weight sets applied to signals received at multiple antenna elements of an antenna array, any of which may be referred to as “listening” according to different receive configurations or receive directions. In some examples, a receiving device may use a single receive configuration to receive along a single beam direction (e.g., when receiving a data signal) . The single receive configuration may be aligned in a beam direction determined based on listening according to different receive configuration directions (e.g., a beam direction determined to have a highest signal strength, highest signal-to-noise ratio (SNR) , or otherwise acceptable signal quality based on listening according to multiple beam directions) .

The wireless communication system 100 may be a packet-based network that operates according to a layered protocol stack. In the user plane, communications at the bearer or Packet Data Convergence Protocol (PDCP) layer may be IP-based. A Radio Link Control (RLC) layer may perform packet segmentation and reassembly to communicate over logical channels. A Medium Access Control (MAC) layer may perform priority handling and multiplexing of logical channels into transport channels. The MAC layer may also use error detection techniques, error correction techniques, or both to support retransmissions at the MAC layer to improve link efficiency. In the control plane, the Radio Resource Control (RRC) protocol layer may provide establishment, configuration, and maintenance of an RRC connection between a UE 115 and a base station 105 or a core network 130 supporting radio bearers for user plane data. At the physical layer, transport channels may be mapped to physical channels.

The UEs 115 and the base stations 105 may support retransmissions of data to increase the likelihood that data is received successfully. Hybrid automatic repeat request (HARQ) feedback is one technique for increasing the likelihood that data is received correctly over a communication link 125. HARQ may include a combination of error detection (e.g., using a cyclic redundancy check (CRC) ) , forward error correction (FEC) , and retransmission (e.g., automatic repeat request (ARQ) ) . HARQ may improve throughput at the MAC layer in poor radio conditions (e.g., low signal-to-noise conditions) . In some examples, a device may support same-slot HARQ feedback, where the device may provide HARQ feedback in a specific slot for data received in a previous symbol in the slot. In other cases, the device may provide HARQ feedback in a subsequent slot, or according to some other time interval.

A UE 115 may receive, during a call session and from a first base station associated with a first RAT (e.g., an LTE base station) , a configuration signal indicating for the UE 115 to handover from the first base station to a second base station associated with a second RAT (e.g., an NR RAT) that is different from the first RAT. The UE 115 may transmit, during the call session and to the second base station, a first TAU request indicating that the UE 115 does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based at least in part on the handover procedure. The UE 115 may transmit, based at least in part on a termination of the call session, a second TAU request indicating that the UE 115 does support communications on the first RAT.

A base station 105 (e.g., the base station associated with the LTE RAT in this example) may perform, during a call session, a handover procedure of a UE 115 to the first base station associated with a first RAT from a second base station associated with a second RAT that is different from the first RAT. The base station 105 may receive, during the call session and from the UE 115, a first TAU request indicating that the UE 115 does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based at least in part on the handover procedure. The base station1 105 may receive, based at least in part on a termination of the call session, a second TAU request indicating that the UE 115 does support communications on the second RAT.

FIG. 2 illustrates an example of a wireless communication system 200 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. In some examples, wireless communication system 200 may implement aspects of wireless communication system 100. Wireless communication system 200 may include base station 205, base station 210, and UE 215, which may be examples of the corresponding devices described herein.

In some examples, base station 205 may be considered a first base station associated with a first RAT (e.g., a NR RAT or NR base station) and base station 210 may be considered a second base station associated with a second RAT (e.g., an LTE RAT or LTE base station) . In other examples, base station 210 may be considered the first base station associated with the first RAT (e.g., the LTE RAT or LTE base station) and base station 205 may be considered the second base station associated with the second RAT (e.g., the NR RAT or NR base station) . Accordingly and for simplicity, base station 205 may be referred to simply as the NR base station and base station 210 may be referred to simply as the LTE base station.

Some wireless communication systems may not support an IMS call over an NR RAT. Accordingly, when an IMS call has been triggered, the network may redirect the call to an LTE base station. For example, when UE 215 is connected to the NR base station and the IMS call session begins, UE 215 may transmit or otherwise convey an IMS_SIP_INVITE indication to the NR base station for the IMS call session. In response, the NR base station may transmit or otherwise convey an RRC connection release (e.g., RRC_CONN_REL) indication to UE 215 in order for UE 215 to perform a handover procedure from the NR base station to the LTE base station for the IMS call session. For example, during the IMS call session (e.g., in response to the IMS_SIP_INVITE indication) , the NR base station may transmit or otherwise convey a configuration signal indicating for UE 215 to handover from the NR base station to the LTE base station, e.g., to handover to a different RAT. Typically, this would result in UE 215 for performing a handover procedure to handover to the LTE base station to continue/perform the IMS call session. This is typically called IMS-to-EPS fallback (or more generally as IMS EPS fallback) for the IMS call session (e.g., IMS call over NR5G fallback to EPS as an IMS call session over the LTE RAT) .

However, this may result in dropping the IMS call if UE 215, during the IMS call session, were to perform a handover procedure back to the NR base station or any other NR base station. This is because some wireless communication systems may not support an IMS call session over an NR network. UE 215 may, during the IMS call session, be redirected to handover to an NR base station due to UE mobility, load balancing with the network, and the like. That is, during the IMS call session UE 215 may perform inter-RAT channel performance measurements and, based on the results, be handed over to an NR base station based on the channel performance failing to satisfy a threshold. As the IMS call session is not supported over the NR RAT, this would result in the IMS call session being dropped (e.g., call failure) .

Accordingly, aspects of the described techniques provide various mechanisms for UE 215 may temporarily disable NR support during the IMS call session on the LTE base station to avoid such LTE-to-NR handover. For example, UE 215 may perform the handover procedure to be handed over from the NR base station to the LTE base station for the IMS call session. The handover procedure may include TAU exchanges, EPS bearer context set up, and the like. In some aspects, this may include UE 215 transmitting or otherwise conveying a first TAU request to the LTE base station indicating that UE 215 does not support communications on the first RAT (e.g., on the NR RAT) . For example, UE 215 may disable an N1 mode (e.g., NR support) in the first TAU request. In some aspects, UE 215 may disable NR support during the IMS call session to avoid a handover procedure back to an NR base station.

That is, even though UE 215 may support NR communications, UE 215 may support temporary N1 mode disablement in the first TAU request during the IMS call session in order to temporarily avoid handover to the NR base station, or any other NR base station. Based on UE 215 indicating no N1 mode capability (e.g., the N1 mode bit set to “N1 mode not supported” ) , the network will not trigger inter-RAT channel performance measurements by UE 215. Accordingly, while NR support is disabled during the IMS call session, UE 215 will refrain from performing channel performance measurements on NR base stations. As UE 215 refrains from performing channel performance measurements, this avoids the situation where UE 215 may be triggered to perform a handover procedure from the LTE base station to an NR base station when there is an NR base station that might otherwise be a more suitable serving cell for UE 215.

When the IMS call session ends or is otherwise terminated, UE 215 may transmit a second TAU request to the LTE base station indicating that UE 215 supports NR communications (e.g., indicating that UE does support communications on the first RAT, which is the NR RAT in this example) . That is, upon termination of the IMS call session, UE 215 may transmit or otherwise convey a second TAU request that enables the N1 mode for UE 215 (e.g., the N1 mode bit set to “N1 mode supported” ) . Based on UE 215 indicating N1 mode capability, the network may now trigger inter-RAT channel performance measurements by UE 215. Accordingly, once NR support is enabled after the IMS call session, UE 215 may perform channel performance measurements on NR base station (s) . As UE 215 performs channel performance measurements on the NR base station (s) , UE 215 may be triggered to perform a handover procedure from the LTE base station to an NR base station when there is an NR base station that might otherwise be a more suitable serving cell for UE 215. Accordingly, these techniques permit UE 215 to temporarily turn NR support on and off during an IMS call session to avoid an LTE-to-NR handover being performed.

Although the techniques discussed above are generally described in terms of IMS EPS fallback, such techniques are not limited to the fallback scenario. Instead, UE 215 may initiate and perform the IMS call session with the LTE base station, but temporarily disable NR communication support depending on whether or not UE 215 knows if the NR network supports a voice-over-NR (VONR) call session. This example is illustrated below with respect to process 300 where the IMS call session is initiated on the LTE base station.

FIG. 3 illustrates an example of a process 300 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. In some examples, process 300 may implement aspects of wireless communication systems 100 and/or 200. Aspects of process 300 may be implemented by or implemented at LTE base station 305 and/or UE 310, which may be examples of the corresponding devices described herein.

Generally, the techniques described herein are discussed with reference to UE 310 initiating an IMS call session on an NR base station and then performing an IMS EPS fallback to handover UE 315 to an LTE base station (such as LTE base station 305) to transfer and perform the IMS call session. However, in some scenarios the IMS call session may be initiated while UE 310 is connected to the LTE base station 305. Accordingly, at 315 LTE base station 305 and UE 310 may establish and perform an IMS call session. For example, UE 310 may transmit or otherwise convey an IMS_SIP_INVITE indication to LTE base station 305, which may initiate the IMS call session.

At 320, UE 310 may determine whether the NR network (e.g., the NR RAT) supports a VONR call session. For example, UE 310 may have been previously connected to an NR base station and received a configuration signal indicating whether the NR network supports a VONR call session. In another example, base station 305 may transmit or otherwise convey a configuration signal to UE 310 indicating whether a proximate NR network supports a VONR call session. Accordingly, UE 310 may determine whether NR base station (s) nearby may be used for an IMS call session. If the NR base stations can be used for the IMS call session, then UE 310 may continue the IMS call session on LTE base station 305 and, should a handover to an NR base station be warranted, perform the handover procedure to transfer the IMS call session to the NR base station as a VONR call session. However, in the example illustrated in process 300, at 320 UE 310 may determine that the NR network does not support a VONR call session.

Accordingly and at 325, UE 310 may transmit a first TAU request to LTE base station 305 indicating that UE 310 does not support communications on the NR RAT. For example, the first TAU request may include or otherwise convey an indication that an N1 mode is not supported by UE 310 (e.g., the N1 bit is set to “N1 mode not supported” ) . This may avoid the situation where UE 310 could be triggered for inter-RAT channel performance measurements, which could potentially lead to the LTE-to-NR handover scenario.

At 330, the IMS call session may end or otherwise be terminated. For example, UE 310 may end the IMS call session and/or the distant end may terminate the IMS call session. In response and at 335, UE 310 may transmit or otherwise convey a second TAU request to the LTE base station 305 indicating that UE 310 does support communications on the NR RAT. For example, the second TAU request may include or otherwise convey an indication that an N1 mode is supported by UE 310 (e.g., the N1 mode bit is set to “N1 mode supported” ) . This may enable UE 310 to be triggered for inter-RAT channel performance measurements, which could lead to an LTE-to-NR handover scenario.

Accordingly, the described techniques where UE 310 temporarily disables NR support during an IMS call session on LTE base station 305 may be implemented in an IMS EPS fallback scenario (e.g., as generally discussed with reference to FIGs. 2 and 4) and/or in an IMS call session originally established on LTE base station 305 where UE 310 knows whether the NR network supports VONR.

FIG. 4 illustrates an example of a process 400 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. In some examples, process 400 may implement aspects of wireless communication systems 100 and/or 200 and/or process 300. Aspects of process 400 may be implemented at or implemented by NR base station 405, UE 410, and/or LTE base station 415, which may be examples of the corresponding devices described herein. In some aspects, NR base station 405 may be associated with a first RAT (e.g., an NR RAT) and LTE base station 415 may be associated with a second RAT (e.g., an LTE RAT) .

At 420, NR base station 405 and UE 10 may establish an IMS call session. For example, UE 410 may transmit or otherwise convey an IMS_SIP_INVITE indication to NR base station 405 indicating that the IMS call is to be established.

Accordingly and at 425, NR base station 405 may transmit or otherwise convey (and UE 410 may receive or otherwise obtain) a configuration signal indicating for UE 410 to handover from NR base station 405 (the first base station associated with the first RAT in this example) to LTE base station 415 (the second base station associated with the second RAT in this example) . For example, NR base station 405 may transmit or otherwise convey an RRC connection release (RRC_CONN_REL) indication to UE 410 that redirects UE 410 to LTE base station 415.

At 430, NR base station 405, UE 410, and/or LTE base station 415 may perform the handover procedure to handover UE 410 from NR base station 405 to LTE base station 415. The IMS call session may be transferred to LTE base station 415 based on the handover procedure. The handover procedure may include UE 410 and LTE base station 415 establishing one or more bearers. For example, UE 410 may transmit an activated dedicated EPS bearer context request message to LTE base station 415, which may respond by transmitting an activated dedicated EPS bearer context accept to UE 410.

Typically, the handover procedure may include UE 410 transmitting a TAU request to LTE base station 415, which responds with a TAU accept indication to UE 410. UE 410 may respond with a TAU complete indication transmitted to LTE base station 415. However and in accordance with the techniques described herein, at 435 UE 410 may transmit or otherwise convey (and LTE base station 415 may receive or otherwise obtain) a first TAU request indicating that UE 410 does not support NR wireless communications. For example, UE 410 may configure an N1 mode indication in the first TAU request to indicate that the N1 mode is disabled. This may trigger the network to refrain from configuring UE 410 to perform inter-RAT channel performance measurements, which could lead to a handover procedure of UE 410 from LTE base station 415 to NR base station 405. Accordingly, UE 410 may refrain from performing channel performance measurements for NR base stations, such as NR base station 405, during the IMS call session.

At 440, the IMS call session may end. For example, the IMS call session may end at UE 410 and/or at the distant end.

Based on the IMS call session terminating, at 445 UE 410 may transmit or otherwise convey (and LTE base station 415 may receive or otherwise obtain) a second TAU request indicating that UE 410 does support NR wireless communications. For example, UE 410 may configure the N1 mode indication to indicate that the N1 mode is enabled. Accordingly, the network may now trigger UE 410 to perform inter-RAT channel performance measurements. For example, LTE base station 415 may transmit a trigger signal to UE 410 indicating for UE 410 to perform inter-RAT channel performance measurements. Accordingly, UE 410 may perform the inter-RAT channel performance measurements and report the results to LTE base station 415.

Accordingly, process 400 illustrates an example process where UE 410 temporarily disables NR wireless communication support during an IMS call session on LTE base station 415. This may avoid UE 410 being handed over to NR base station 405 during the IMS call session, which may result in call drop. After the IMS call session has ended, UE 410 may resume NR support and begin to perform inter-RAT channel performance measurements.

FIG. 5 shows a block diagram 500 of a device 505 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The device 505 may be an example of aspects of a UE 115 as described herein. The device 505 may include a receiver 510, a communications manager 515, and a transmitter 520. The device 505 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 510 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to optimization for internet protocol multimedia subsystem evolved packet system fallback, etc. ) . Information may be passed on to other components of the device 505. The receiver 510 may be an example of aspects of the transceiver 820 described with reference to FIG. 8. The receiver 510 may utilize a single antenna or a set of antennas.

The communications manager 515 may receive, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT, transmit, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure, and transmit, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT. The communications manager 515 may be an example of aspects of the communications manager 810 described herein.

The communications manager 515, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communications manager 515, or its sub-components may be executed by a general-purpose processor, a digital signal processor (DSP) , an application-specific integrated circuit (ASIC) , a field-programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

The communications manager 515, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communications manager 515, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communications manager 515, or its sub-components, may be combined with one or more other hardware components, including but not limited to an input/output (I/O) component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

The transmitter 520 may transmit signals generated by other components of the device 505. In some examples, the transmitter 520 may be collocated with a receiver 510 in a transceiver module. For example, the transmitter 520 may be an example of aspects of the transceiver 820 described with reference to FIG. 8. The transmitter 520 may utilize a single antenna or a set of antennas.

FIG. 6 shows a block diagram 600 of a device 605 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The device 605 may be an example of aspects of a device 505, or a UE 115 as described herein. The device 605 may include a receiver 610, a communications manager 615, and a transmitter 630. The device 605 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 610 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to optimization for internet protocol multimedia subsystem evolved packet system fallback, etc. ) . Information may be passed on to other components of the device 605. The receiver 610 may be an example of aspects of the transceiver 820 described with reference to FIG. 8. The receiver 610 may utilize a single antenna or a set of antennas.

The communications manager 615 may be an example of aspects of the communications manager 515 as described herein. The communications manager 615 may include an IMS session manager 620 and a TAU request manager 625. The communications manager 615 may be an example of aspects of the communications manager 810 described herein.

The IMS session manager 620 may receive, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT.

The TAU request manager 625 may transmit, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure and transmit, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT.

The transmitter 630 may transmit signals generated by other components of the device 605. In some examples, the transmitter 630 may be collocated with a receiver 610 in a transceiver module. For example, the transmitter 630 may be an example of aspects of the transceiver 820 described with reference to FIG. 8. The transmitter 630 may utilize a single antenna or a set of antennas.

FIG. 7 shows a block diagram 700 of a communications manager 705 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The communications manager 705 may be an example of aspects of a communications manager 515, a communications manager 615, or a communications manager 810 described herein. The communications manager 705 may include an IMS session manager 710, a TAU request manager 715, and a channel measurement manager 720. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The IMS session manager 710 may receive, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT. In some cases, the call session includes an IMS call session. In some cases, the first RAT includes a NR RAT and the second RAT includes a LTE RAT.

The TAU request manager 715 may transmit, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure. In some examples, the TAU request manager 715 may transmit, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT.

The channel measurement manager 720 may refrain, based on transmitting the first TAU request indicating that the UE does not support communications on the first RAT, from performing channel performance measurements of one or more base stations associated with the first RAT. In some examples, the channel measurement manager 720 may receive, based on transmitting the second TAU request indicating that the UE does support communications on the first RAT, a signal triggering channel performance measurements of one or more base stations associated with the first RAT. In some examples, the channel measurement manager 720 may perform, based on the signal, channel performance measurements of the one or more base stations associated with the first RAT.

FIG. 8 shows a diagram of a system 800 including a device 805 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The device 805 may be an example of or include the components of device 505, device 605, or a UE 115 as described herein. The device 805 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 810, an I/O controller 815, a transceiver 820, an antenna 825, memory 830, and a processor 840. These components may be in electronic communication via one or more buses (e.g., bus 845) .

The communications manager 810 may receive, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT, transmit, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure, and transmit, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT.

The I/O controller 815 may manage input and output signals for the device 805. The I/O controller 815 may also manage peripherals not integrated into the device 805. In some cases, the I/O controller 815 may represent a physical connection or port to an external peripheral. In some cases, the I/O controller 815 may utilize an operating system such as

or another known operating system. In other cases, the I/O controller 815 may represent or interact with a modem, a keyboard, a mouse, a touchscreen, or a similar device. In some cases, the I/O controller 815 may be implemented as part of a processor. In some cases, a user may interact with the device 805 via the I/O controller 815 or via hardware components controlled by the I/O controller 815.

The transceiver 820 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 820 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 820 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 825. However, in some cases the device may have more than one antenna 825, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 830 may include random access memory (RAM) and read-only memory (ROM) . The memory 830 may store computer-readable, computer-executable code 835 including instructions that, when executed, cause the processor to perform various functions described herein. In some cases, the memory 830 may contain, among other things, a basic input/output system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 840 may include an intelligent hardware device, (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some cases, the processor 840 may be configured to operate a memory array using a memory controller. In other cases, a memory controller may be integrated into the processor 840. The processor 840 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 830) to cause the device 805 to perform various functions (e.g., functions or tasks supporting optimization for internet protocol multimedia subsystem evolved packet system fallback) .

The code 835 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 835 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 835 may not be directly executable by the processor 840 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG. 9 shows a block diagram 900 of a device 905 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The device 905 may be an example of aspects of a base station 105 as described herein. The device 905 may include a receiver 910, a communications manager 915, and a transmitter 920. The device 905 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 910 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to optimization for internet protocol multimedia subsystem evolved packet system fallback, etc. ) . Information may be passed on to other components of the device 905. The receiver 910 may be an example of aspects of the transceiver 1220 described with reference to FIG. 12. The receiver 910 may utilize a single antenna or a set of antennas.

The communications manager 915 may perform, during a call session, a handover procedure of a UE to the first base station associated with a first RAT from a second base station associated with a second RAT that is different from the first RAT, receive, during the call session and from the UE, a first TAU request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based on the handover procedure, and receive, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the second RAT. The communications manager 915 may be an example of aspects of the communications manager 1210 described herein.

The communications manager 915, or its sub-components, may be implemented in hardware, code (e.g., software or firmware) executed by a processor, or any combination thereof. If implemented in code executed by a processor, the functions of the communications manager 915, or its sub-components may be executed by a general-purpose processor, a DSP, an ASIC, a FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described in the present disclosure.

The communications manager 915, or its sub-components, may be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations by one or more physical components. In some examples, the communications manager 915, or its sub-components, may be a separate and distinct component in accordance with various aspects of the present disclosure. In some examples, the communications manager 915, or its sub-components, may be combined with one or more other hardware components, including but not limited to an I/O component, a transceiver, a network server, another computing device, one or more other components described in the present disclosure, or a combination thereof in accordance with various aspects of the present disclosure.

The transmitter 920 may transmit signals generated by other components of the device 905. In some examples, the transmitter 920 may be collocated with a receiver 910 in a transceiver module. For example, the transmitter 920 may be an example of aspects of the transceiver 1220 described with reference to FIG. 12. The transmitter 920 may utilize a single antenna or a set of antennas.

FIG. 10 shows a block diagram 1000 of a device 1005 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The device 1005 may be an example of aspects of a device 905, or a base station 105 as described herein. The device 1005 may include a receiver 1010, a communications manager 1015, and a transmitter 1030. The device 1005 may also include a processor. Each of these components may be in communication with one another (e.g., via one or more buses) .

The receiver 1010 may receive information such as packets, user data, or control information associated with various information channels (e.g., control channels, data channels, and information related to optimization for internet protocol multimedia subsystem evolved packet system fallback, etc. ) . Information may be passed on to other components of the device 1005. The receiver 1010 may be an example of aspects of the transceiver 1220 described with reference to FIG. 12. The receiver 1010 may utilize a single antenna or a set of antennas.

The communications manager 1015 may be an example of aspects of the communications manager 915 as described herein. The communications manager 1015 may include an IMS session manager 1020 and a TAU request manager 1025. The communications manager 1015 may be an example of aspects of the communications manager 1210 described herein.

The IMS session manager 1020 may perform, during a call session, a handover procedure of a UE to the first base station associated with a first RAT from a second base station associated with a second RAT that is different from the first RAT.

The TAU request manager 1025 may receive, during the call session and from the UE, a first TAU request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based on the handover procedure and receive, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the second RAT.

The transmitter 1030 may transmit signals generated by other components of the device 1005. In some examples, the transmitter 1030 may be collocated with a receiver 1010 in a transceiver module. For example, the transmitter 1030 may be an example of aspects of the transceiver 1220 described with reference to FIG. 12. The transmitter 1030 may utilize a single antenna or a set of antennas.

FIG. 11 shows a block diagram 1100 of a communications manager 1105 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The communications manager 1105 may be an example of aspects of a communications manager 915, a communications manager 1015, or a communications manager 1210 described herein. The communications manager 1105 may include an IMS session manager 1110, a TAU request manager 1115, and a channel measurement manager 1120. Each of these modules may communicate, directly or indirectly, with one another (e.g., via one or more buses) .

The IMS session manager 1110 may perform, during a call session, a handover procedure of a UE to the first base station associated with a first RAT from a second base station associated with a second RAT that is different from the first RAT. In some cases, the call session includes an IMS call session. In some cases, the first RAT includes a LTE RAT and the second RAT includes a NR RAT.

The TAU request manager 1115 may receive, during the call session and from the UE, a first TAU request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based on the handover procedure. In some examples, the TAU request manager 1115 may receive, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the second RAT.

The channel measurement manager 1120 may refrain, based on receiving the first TAU request indicating that the UE does not support communications on the second RAT, from transmitting a signal triggering channel performance measurements by the UE of one or more base stations associated with the first RAT. In some examples, the channel measurement manager 1120 may transmit, based on receiving the second TAU request indicating that the UE does support communications on the second RAT, a signal triggering channel performance measurements of one or more base stations associated with the second RAT. In some examples, the channel measurement manager 1120 may receive a channel performance feedback message from the UE based on a result of the channel performance measurements.

FIG. 12 shows a diagram of a system 1200 including a device 1205 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The device 1205 may be an example of or include the components of device 905, device 1005, or a base station 105 as described herein. The device 1205 may include components for bi-directional voice and data communications including components for transmitting and receiving communications, including a communications manager 1210, a network communications manager 1215, a transceiver 1220, an antenna 1225, memory 1230, a processor 1240, and an inter-station communications manager 1245. These components may be in electronic communication via one or more buses (e.g., bus 1250) .

The communications manager 1210 may perform, during a call session, a handover procedure of a UE to the first base station associated with a first RAT from a second base station associated with a second RAT that is different from the first RAT, receive, during the call session and from the UE, a first TAU request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based on the handover procedure, and receive, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the second RAT.

The network communications manager 1215 may manage communications with the core network (e.g., via one or more wired backhaul links) . For example, the network communications manager 1215 may manage the transfer of data communications for client devices, such as one or more UEs 115.

The transceiver 1220 may communicate bi-directionally, via one or more antennas, wired, or wireless links as described above. For example, the transceiver 1220 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1220 may also include a modem to modulate the packets and provide the modulated packets to the antennas for transmission, and to demodulate packets received from the antennas.

In some cases, the wireless device may include a single antenna 1225. However, in some cases the device may have more than one antenna 1225, which may be capable of concurrently transmitting or receiving multiple wireless transmissions.

The memory 1230 may include RAM, ROM, or a combination thereof. The memory 1230 may store computer-readable code 1235 including instructions that, when executed by a processor (e.g., the processor 1240) cause the device to perform various functions described herein. In some cases, the memory 1230 may contain, among other things, a BIOS which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The processor 1240 may include an intelligent hardware device, (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some cases, the processor 1240 may be configured to operate a memory array using a memory controller. In some cases, a memory controller may be integrated into processor 1240. The processor 1240 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1230) to cause the device 1205 to perform various functions (e.g., functions or tasks supporting optimization for internet protocol multimedia subsystem evolved packet system fallback) .

The inter-station communications manager 1245 may manage communications with other base station 105, and may include a controller or scheduler for controlling communications with UEs 115 in cooperation with other base stations 105. For example, the inter-station communications manager 1245 may coordinate scheduling for transmissions to UEs 115 for various interference mitigation techniques such as beamforming or joint transmission. In some examples, the inter-station communications manager 1245 may provide an X2 interface within an LTE/LTE-A wireless communication network technology to provide communication between base stations 105.

The code 1235 may include instructions to implement aspects of the present disclosure, including instructions to support wireless communications. The code 1235 may be stored in a non-transitory computer-readable medium such as system memory or other type of memory. In some cases, the code 1235 may not be directly executable by the processor 1240 but may cause a computer (e.g., when compiled and executed) to perform functions described herein.

FIG. 13 shows a flowchart illustrating a method 1300 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The operations of method 1300 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1300 may be performed by a communications manager as described with reference to FIGs. 5 through 8. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At 1305, the UE may receive, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT. The operations of 1305 may be performed according to the methods described herein. In some examples, aspects of the operations of 1305 may be performed by an IMS session manager as described with reference to FIGs. 5 through 8.

At 1310, the UE may transmit, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure. The operations of 1310 may be performed according to the methods described herein. In some examples, aspects of the operations of 1310 may be performed by a TAU request manager as described with reference to FIGs. 5 through 8.

At 1315, the UE may transmit, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT. The operations of 1315 may be performed according to the methods described herein. In some examples, aspects of the operations of 1315 may be performed by a TAU request manager as described with reference to FIGs. 5 through 8.

FIG. 14 shows a flowchart illustrating a method 1400 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The operations of method 1400 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1400 may be performed by a communications manager as described with reference to FIGs. 5 through 8. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At 1405, the UE may receive, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT. The operations of 1405 may be performed according to the methods described herein. In some examples, aspects of the operations of 1405 may be performed by an IMS session manager as described with reference to FIGs. 5 through 8.

At 1410, the UE may transmit, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure. The operations of 1410 may be performed according to the methods described herein. In some examples, aspects of the operations of 1410 may be performed by a TAU request manager as described with reference to FIGs. 5 through 8.

At 1415, the UE may refrain, based on transmitting the first TAU request indicating that the UE does not support communications on the first RAT, from performing channel performance measurements of one or more base stations associated with the first RAT. The operations of 1415 may be performed according to the methods described herein. In some examples, aspects of the operations of 1415 may be performed by a channel measurement manager as described with reference to FIGs. 5 through 8.

At 1420, the UE may transmit, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT. The operations of 1420 may be performed according to the methods described herein. In some examples, aspects of the operations of 1420 may be performed by a TAU request manager as described with reference to FIGs. 5 through 8.

FIG. 15 shows a flowchart illustrating a method 1500 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The operations of method 1500 may be implemented by a UE 115 or its components as described herein. For example, the operations of method 1500 may be performed by a communications manager as described with reference to FIGs. 5 through 8. In some examples, a UE may execute a set of instructions to control the functional elements of the UE to perform the functions described below. Additionally or alternatively, a UE may perform aspects of the functions described below using special-purpose hardware.

At 1505, the UE may receive, during a call session and from a first base station associated with a first RAT, a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT. The operations of 1505 may be performed according to the methods described herein. In some examples, aspects of the operations of 1505 may be performed by an IMS session manager as described with reference to FIGs. 5 through 8.

At 1510, the UE may transmit, during the call session and to the second base station, a first TAU request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based on the handover procedure. The operations of 1510 may be performed according to the methods described herein. In some examples, aspects of the operations of 1510 may be performed by a TAU request manager as described with reference to FIGs. 5 through 8.

At 1515, the UE may transmit, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the first RAT. The operations of 1515 may be performed according to the methods described herein. In some examples, aspects of the operations of 1515 may be performed by a TAU request manager as described with reference to FIGs. 5 through 8.

At 1520, the UE may receive, based on transmitting the second TAU request indicating that the UE does support communications on the first RAT, a signal triggering channel performance measurements of one or more base stations associated with the first RAT. The operations of 1520 may be performed according to the methods described herein. In some examples, aspects of the operations of 1520 may be performed by a channel measurement manager as described with reference to FIGs. 5 through 8.

At 1525, the UE may perform, based on the signal, channel performance measurements of the one or more base stations associated with the first RAT. The operations of 1525 may be performed according to the methods described herein. In some examples, aspects of the operations of 1525 may be performed by a channel measurement manager as described with reference to FIGs. 5 through 8.

FIG. 16 shows a flowchart illustrating a method 1600 that supports optimization for internet protocol multimedia subsystem evolved packet system fallback in accordance with aspects of the present disclosure. The operations of method 1600 may be implemented by a base station 105 or its components as described herein. For example, the operations of method 1600 may be performed by a communications manager as described with reference to FIGs. 9 through 12. In some examples, a base station may execute a set of instructions to control the functional elements of the base station to perform the functions described below. Additionally or alternatively, a base station may perform aspects of the functions described below using special-purpose hardware.

At 1605, the base station may perform, during a call session, a handover procedure of a UE to the first base station associated with a first RAT from a second base station associated with a second RAT that is different from the first RAT. The operations of 1605 may be performed according to the methods described herein. In some examples, aspects of the operations of 1605 may be performed by an IMS session manager as described with reference to FIGs. 9 through 12.

At 1610, the base station may receive, during the call session and from the UE, a first TAU request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based on the handover procedure. The operations of 1610 may be performed according to the methods described herein. In some examples, aspects of the operations of 1610 may be performed by a TAU request manager as described with reference to FIGs. 9 through 12.

At 1615, the base station may receive, based on a termination of the call session, a second TAU request indicating that the UE does support communications on the second RAT. The operations of 1615 may be performed according to the methods described herein. In some examples, aspects of the operations of 1615 may be performed by a TAU request manager as described with reference to FIGs. 9 through 12.

It should be noted that the methods described herein describe possible implementations, and that the operations and the steps may be rearranged or otherwise modified and that other implementations are possible. Further, aspects from two or more of the methods may be combined.

Although aspects of an LTE, LTE-A, LTE-A Pro, or NR system may be described for purposes of example, and LTE, LTE-A, LTE-A Pro, or NR terminology may be used in much of the description, the techniques described herein are applicable beyond LTE, LTE-A, LTE-A Pro, or NR networks. For example, the described techniques may be applicable to various other wireless communication systems such as Ultra Mobile Broadband (UMB) , Institute of Electrical and Electronics Engineers (IEEE) 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20, Flash-OFDM, as well as other systems and radio technologies not explicitly mentioned herein.

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

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

The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described herein may be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.

Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that may be accessed by a general-purpose or special-purpose computer. By way of example, and not limitation, non-transitory computer-readable media may include random-access memory (RAM) , read-only memory (ROM) , electrically erasable programmable ROM (EEPROM) , flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that may be used to carry or store desired program code means in the form of instructions or data structures and that may be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL) , or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of computer-readable medium. Disk and disc, as used herein, include CD, laser disc, optical disc, digital versatile disc (DVD) , floppy disk and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above are also included within the scope of computer-readable media.

As used herein, including in the claims, “or” as used in a list of items (e.g., a list of items prefaced by a phrase such as “at least one of” or “one or more of” ) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C) . Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an example step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on. ”

In the appended figures, similar components or features may have the same reference label. Further, various components of the same type may be distinguished by following the reference label by a dash and a second label that distinguishes among the similar components. If just the first reference label is used in the specification, the description is applicable to any one of the similar components having the same first reference label irrespective of the second reference label, or other subsequent reference label.

The description set forth herein, in connection with the appended drawings, describes example configurations and does not represent all the examples that may be implemented or that are within the scope of the claims. The term “example” used herein means “serving as an example, instance, or illustration, ” and not “preferred” or “advantageous over other examples. ” The detailed description includes specific details for the purpose of providing an understanding of the described techniques. These techniques, however, may be practiced without these specific details. In some instances, known structures and devices are shown in block diagram form in order to avoid obscuring the concepts of the described examples.

The description herein is provided to enable a person having ordinary skill in the art to make or use the disclosure. Various modifications to the disclosure will be apparent to a person having ordinary skill in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein, but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims

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

receiving, during a call session and from a first base station associated with a first radio access technology (RAT) , a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT;

transmitting, during the call session and to the second base station, a first tracking area update request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based at least in part on the handover; and

transmitting, based at least in part on a termination of the call session, a second tracking area update request indicating that the UE does support communications on the first RAT.
The method of claim 1, further comprising:

refraining, based at least in part on transmitting the first tracking area update request indicating that the UE does not support communications on the first RAT, from performing channel performance measurements of one or more base stations associated with the first RAT.
The method of claim 1, further comprising:

receiving, based at least in part on transmitting the second tracking area update request indicating that the UE does support communications on the first RAT, a signal triggering channel performance measurements of one or more base stations associated with the first RAT; and

performing, based at least in part on the signal, channel performance measurements of one or more base stations associated with the first RAT.
The method of claim 1, wherein the call session comprises an internet protocol (IP) multimedia subsystem (IMS) call session.
The method of claim 1, wherein the first RAT comprises a new radio (NR) RAT and the second RAT comprises a long term evolution (LTE) RAT.
A method for wireless communication at a first base station, comprising:

performing, during a call session, a handover procedure of a user equipment (UE) to the first base station associated with a first radio access technology (RAT) from a second base station associated with a second RAT that is different from the first RAT;

receiving, during the call session and from the UE, a first tracking area update request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based at least in part on the handover procedure; and

receiving, based at least in part on a termination of the call session, a second tracking area update request indicating that the UE does support communications on the second RAT.
The method of claim 6, further comprising:

refraining, based at least in part on receiving the first tracking area update request indicating that the UE does not support communications on the second RAT, from transmitting a signal triggering channel performance measurements by the UE of one or more base stations associated with the first RAT.
The method of claim 6, further comprising:

transmitting, based at least in part on receiving the second tracking area update request indicating that the UE does support communications on the second RAT, a signal triggering channel performance measurements of one or more base stations associated with the second RAT; and

receiving a channel performance feedback message from the UE based at least in part on a result of the channel performance measurements.
The method of claim 6, wherein the call session comprises an internet protocol (IP) multimedia subsystem (IMS) call session.
The method of claim 6, wherein the first RAT comprises a long term evolution (LTE) RAT and the second RAT comprises a new radio (NR) RAT.
An apparatus for wireless communication at a user equipment (UE) , comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

receive, during a call session and from a first base station associated with a first radio access technology (RAT) , a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT;

transmit, during the call session and to the second base station, a first tracking area update request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based at least in part on the handover; and

transmit, based at least in part on a termination of the call session, a second tracking area update request indicating that the UE does support communications on the first RAT.
The apparatus of claim 11, wherein the instructions are further executable by the processor to cause the apparatus to:

refrain, based at least in part on transmitting the first tracking area update request indicating that the UE does not support communications on the first RAT, from performing channel performance measurements of one or more base stations associated with the first RAT.
The apparatus of claim 11, wherein the instructions are further executable by the processor to cause the apparatus to:

receive, based at least in part on transmitting the second tracking area update request indicating that the UE does support communications on the first RAT, a signal triggering channel performance measurements of one or more base stations associated with the first RAT; and

perform, based at least in part on the signal, channel performance measurements of one or more base stations associated with the first RAT.
The apparatus of claim 11, wherein the call session comprises an internet protocol (IP) multimedia subsystem (IMS) call session.
The apparatus of claim 11, wherein the first RAT comprises a new radio (NR) RAT and the second RAT comprises a long term evolution (LTE) RAT.
An apparatus for wireless communication at a first base station, comprising:

a processor,

memory coupled with the processor; and

instructions stored in the memory and executable by the processor to cause the apparatus to:

perform, during a call session, a handover procedure of a user equipment (UE) to the first base station associated with a first radio access technology (RAT) from a second base station associated with a second RAT that is different from the first RAT;

receive, during the call session and from the UE, a first tracking area update request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based at least in part on the handover procedure; and

receive, based at least in part on a termination of the call session, a second tracking area update request indicating that the UE does support communications on the second RAT.
The apparatus of claim 16, wherein the instructions are further executable by the processor to cause the apparatus to:

refrain, based at least in part on receiving the first tracking area update request indicating that the UE does not support communications on the second RAT, from transmitting a signal triggering channel performance measurements by the UE of one or more base stations associated with the first RAT.
The apparatus of claim 16, wherein the instructions are further executable by the processor to cause the apparatus to:

transmit, based at least in part on receiving the second tracking area update request indicating that the UE does support communications on the second RAT, a signal triggering channel performance measurements of one or more base stations associated with the second RAT; and

receive a channel performance feedback message from the UE based at least in part on a result of the channel performance measurements.
The apparatus of claim 16, wherein the call session comprises an internet protocol (IP) multimedia subsystem (IMS) call session.
The apparatus of claim 16, wherein the first RAT comprises a long term evolution (LTE) RAT and the second RAT comprises a new radio (NR) RAT.
An apparatus for wireless communication at a user equipment (UE) , comprising:

means for receiving, during a call session and from a first base station associated with a first radio access technology (RAT) , a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT;

means for transmitting, during the call session and to the second base station, a first tracking area update request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based at least in part on the handover; and

means for transmitting, based at least in part on a termination of the call session, a second tracking area update request indicating that the UE does support communications on the first RAT.
The apparatus of claim 21, further comprising:

means for refraining, based at least in part on transmitting the first tracking area update request indicating that the UE does not support communications on the first RAT, from performing channel performance measurements of one or more base stations associated with the first RAT.
The apparatus of claim 21, further comprising:

means for receiving, based at least in part on transmitting the second tracking area update request indicating that the UE does support communications on the first RAT, a signal triggering channel performance measurements of one or more base stations associated with the first RAT; and

means for performing, based at least in part on the signal, channel performance measurements of one or more base stations associated with the first RAT.
The apparatus of claim 21, wherein the call session comprises an internet protocol (IP) multimedia subsystem (IMS) call session.
The apparatus of claim 21, wherein the first RAT comprises a new radio (NR) RAT and the second RAT comprises a long term evolution (LTE) RAT.
An apparatus for wireless communication at a first base station, comprising:

means for performing, during a call session, a handover procedure of a user equipment (UE) to the first base station associated with a first radio access technology (RAT) from a second base station associated with a second RAT that is different from the first RAT;

means for receiving, during the call session and from the UE, a first tracking area update request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based at least in part on the handover procedure; and

means for receiving, based at least in part on a termination of the call session, a second tracking area update request indicating that the UE does support communications on the second RAT.
The apparatus of claim 26, further comprising:

means for refraining, based at least in part on receiving the first tracking area update request indicating that the UE does not support communications on the second RAT, from transmitting a signal triggering channel performance measurements by the UE of one or more base stations associated with the first RAT.
The apparatus of claim 26, further comprising:

means for transmitting, based at least in part on receiving the second tracking area update request indicating that the UE does support communications on the second RAT, a signal triggering channel performance measurements of one or more base stations associated with the second RAT; and

means for receiving a channel performance feedback message from the UE based at least in part on a result of the channel performance measurements.
The apparatus of claim 26, wherein the call session comprises an internet protocol (IP) multimedia subsystem (IMS) call session.
The apparatus of claim 26, wherein the first RAT comprises a long term evolution (LTE) RAT and the second RAT comprises a new radio (NR) RAT.
A non-transitory computer-readable medium storing code for wireless communication at a user equipment (UE) , the code comprising instructions executable by a processor to:

receive, during a call session and from a first base station associated with a first radio access technology (RAT) , a configuration signal indicating for the UE to handover from the first base station to a second base station associated with a second RAT that is different from the first RAT;

transmit, during the call session and to the second base station, a first tracking area update request indicating that the UE does not support communications on the first RAT, the call session being transferred from the first base station to the second base station based at least in part on the handover; and

transmit, based at least in part on a termination of the call session, a second tracking area update request indicating that the UE does support communications on the first RAT.
The non-transitory computer-readable medium of claim 31, wherein the instructions are further executable to:

refrain, based at least in part on transmitting the first tracking area update request indicating that the UE does not support communications on the first RAT, from performing channel performance measurements of one or more base stations associated with the first RAT.
The non-transitory computer-readable medium of claim 31, wherein the instructions are further executable to:

receive, based at least in part on transmitting the second tracking area update request indicating that the UE does support communications on the first RAT, a signal triggering channel performance measurements of one or more base stations associated with the first RAT; and

perform, based at least in part on the signal, channel performance measurements of one or more base stations associated with the first RAT.
The non-transitory computer-readable medium of claim 31, wherein the call session comprises an internet protocol (IP) multimedia subsystem (IMS) call session.
The non-transitory computer-readable medium of claim 31, wherein the first RAT comprises a new radio (NR) RAT and the second RAT comprises a long term evolution (LTE) RAT.
A non-transitory computer-readable medium storing code for wireless communication at a first base station, the code comprising instructions executable by a processor to:

perform, during a call session, a handover procedure of a user equipment (UE) to the first base station associated with a first radio access technology (RAT) from a second base station associated with a second RAT that is different from the first RAT;

receive, during the call session and from the UE, a first tracking area update request indicating that the UE does not support communications on the second RAT, the call session being transferred to the first base station from the second base station based at least in part on the handover procedure; and

receive, based at least in part on a termination of the call session, a second tracking area update request indicating that the UE does support communications on the second RAT.
The non-transitory computer-readable medium of claim 36, wherein the instructions are further executable to:

refrain, based at least in part on receiving the first tracking area update request indicating that the UE does not support communications on the second RAT, from transmitting a signal triggering channel performance measurements by the UE of one or more base stations associated with the first RAT.
The non-transitory computer-readable medium of claim 36, wherein the instructions are further executable to:

transmit, based at least in part on receiving the second tracking area update request indicating that the UE does support communications on the second RAT, a signal triggering channel performance measurements of one or more base stations associated with the second RAT; and

receive a channel performance feedback message from the UE based at least in part on a result of the channel performance measurements.
The non-transitory computer-readable medium of claim 36, wherein the call session comprises an internet protocol (IP) multimedia subsystem (IMS) call session.
The non-transitory computer-readable medium of claim 36, wherein the first RAT comprises a long term evolution (LTE) RAT and the second RAT comprises a new radio (NR) RAT.