WO2021243691A1

WO2021243691A1 - Fast switching between radio access technologies in wireless communication

Info

Publication number: WO2021243691A1
Application number: PCT/CN2020/094598
Authority: WO
Inventors: Yi Liu; Jinglin Zhang; Haojun WANG; Zhenqing CUI; Yuankun ZHU; Fojian ZHANG; Hao Zhang; Jian Li; Hong Wei
Original assignee: Qualcomm Inc
Current assignee: Qualcomm Inc
Priority date: 2020-06-05
Filing date: 2020-06-05
Publication date: 2021-12-09
Anticipated expiration: 2022-12-05

Abstract

Techniques to perform fast switching between radio access technologies (RATs) are disclosed. A user equipment (UE) may be capable of operating in first and second RATs (e.g., 4G LTE, 5G NR). When a UE in standalone (SA) mode is in a first RAT connected mode (e.g., LTE connected mode) with a first network node (eNB) of the first RAT, it may remain there even when there are higher performing second network nodes (gNB) of the second RAT. To address this issue, techniques to perform fast switching between RATS, e.g., from being connected with the first network node to a second network node, are disclosed.

Description

FAST SWITCHING BETWEEN RADIO ACCESS TECHNOLOGIES IN WIRELESS COMMUNICATION

TECHNICAL FIELD

Various aspects described herein generally relate to wireless communication systems, and more particularly, to fast switching between radio access technologies (RATs) in wireless communication, e.g., from 4G LTE to 5G NR.

BACKGROUND

Wireless communication systems have developed through various generations, including a first-generation analog wireless phone service (1G) , a second-generation (2G) digital wireless phone service (including interim 2.5G and 2.75G networks) , a third-generation (3G) high speed data, Internet-capable wireless service and a fourth-generation (4G) service (e.g., Long Term Evolution (LTE) or WiMax) . There are presently many different types of wireless communication systems in use, including Cellular and Personal Communications Service (PCS) systems. Examples of known cellular systems include the cellular Analog Advanced Mobile Phone System (AMPS) , and digital cellular systems based on Code Division Multiple Access (CDMA) , Frequency Division Multiple Access (FDMA) , Time Division Multiple Access (TDMA) , the Global System for Mobile access (GSM) variation of TDMA, etc.

A fifth generation (5G) mobile standard calls for higher data transfer speeds, greater numbers of connections, and better coverage, among other improvements. The 5G standard, according to the Next Generation Mobile Networks Alliance, is designed to provide data rates of several tens of megabits per second to each of tens of thousands of users, with 1 gigabit per second to tens of workers on an office floor. Several hundreds of thousands of simultaneous connections should be supported in order to support large sensor deployments. Consequently, the spectral efficiency of 5G mobile communications should be significantly enhanced compared to the current 4G standard. Furthermore, signaling efficiencies should be enhanced and latency should be substantially reduced compared to current standards.

5G New Radio (NR) connectivity, or simply NR connectivity, has gained significant commercial traction in recent time. Thus, to attract more users to their network, network operators would like to show NR connectivity to users most of the time on the user interface (UI) of the mobile device such as the user equipment (UE) .

SUMMARY

This summary identifies features of some example aspects, and is not an exclusive or exhaustive description of the disclosed subject matter. Whether features or aspects are included in, or omitted from this summary is not intended as indicative of relative importance of such features. Additional features and aspects are described, and will become apparent to persons skilled in the art upon reading the following detailed description and viewing the drawings that form a part thereof.

An exemplary user equipment (UE) configured to operate in first and second radio access technologies (RATs) is disclosed. The UE may comprise a processor, a memory, and a transceiver. The processor, the memory, and/or the transceiver may be configured to determine, while the UE is in a first RAT connected mode with a first network node of the first RAT, whether a RAT switch condition is satisfied. The first RAT connected mode may be a mode in which the UE receives data services from the first network node. The RAT switch condition may be such that when satisfied, the UE is triggered to search for one or more candidate second network nodes of the second RAT. The processor, the memory, and/or the transceiver may also be configured to determine, when it is determined that the RAT switch condition is satisfied, whether a candidate second network node of the second RAT is found based on a first RAT system information block (SIB) . The first RAT SIB may indicate one or more second network nodes of the second RAT neighboring the first network node. The processor, the memory, and/or the transceiver may further be configured to switch, when it is determined that the candidate second network node is found, connection from the first network node to the candidate second network node such that the UE receives data services from the candidate second network node after the switch takes place.

An exemplary method performed by a user equipment (UE) configured to operate in first and second radio access technologies (RATs) is disclosed. The method may comprise determining, while the UE is in a first RAT connected mode with a first network node of the first RAT, whether a RAT switch condition is satisfied. The first RAT connected mode may be a mode in which the UE receives data services from the first network node. The RAT switch condition may be such that when satisfied, the UE is triggered to search for one or more candidate second network nodes of the second RAT. The method may also comprise determining, when it is determined that the RAT switch condition is satisfied, whether a candidate second network node of the second RAT is found based on a first RAT system information block (SIB) . The first RAT SIB may indicate one or more second network nodes of the second RAT neighboring the first network node. The method may further comprise switching, when it is determined that the candidate second network node is found, connection from the first network node to the candidate second network node such that the UE receives data services from the candidate second network node after the switch takes place.

Another exemplary user equipment (UE) configured to operate in first and second radio access technologies (RATs) is disclosed. The UE may comprise means for determining, while the UE is in a first RAT connected mode with a first network node of the first RAT, whether a RAT switch condition is satisfied. The first RAT connected mode may be a mode in which the UE receives data services from the first network node. The RAT switch condition may be such that when satisfied, the UE is triggered to search for one or more candidate second network nodes of the second RAT. The UE may also comprise means for determining, when it is determined that the RAT switch condition is satisfied, whether a candidate second network node of the second RAT is found based on a first RAT system information block (SIB) . The first RAT SIB may indicate one or more second network nodes of the second RAT neighboring the first network node. The UE may further comprise means for switching, when it is determined that the candidate second network node is found, connection from the first network node to the candidate second network node such that the UE receives data services from the candidate second network node after the switch takes place.

A non-transitory computer-readable medium storing computer-executable instructions for a user equipment (UE) configured to operate in first and second radio access technologies (RATs) is disclosed. The executable instructions may comprise one or more instructions instructing the UE to determine, while the UE is in a first RAT connected mode with a first network node of the first RAT, whether a RAT switch condition is satisfied. The first RAT connected mode may be a mode in which the UE receives data services from the first network node. The RAT switch condition may be such that when satisfied, the UE is triggered to search for one or more candidate second network nodes of the second RAT. The executable instructions may also comprise one or more instructions instructing the UE to determine, when it is determined that the RAT switch condition is satisfied, whether a candidate second network node of the second RAT is found based on a first RAT system information block (SIB) . The first RAT SIB may indicate one or more second network nodes of the second RAT neighboring the first network node. The executable instructions may further comprise one or more instructions instructing the UE to switch, when it is determined that the candidate second network node is found, connection from the first network node to the candidate second network node such that the UE receives data services from the candidate second network node after the switch takes place.

Other objects and advantages associated with the aspects disclosed herein will be apparent to those skilled in the art based on the accompanying drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are presented to aid in the description of examples of one or more aspects of the disclosed subject matter and are provided solely for illustration of the examples and not limitation thereof:

FIG. 1 illustrates an exemplary wireless communications system in accordance with one or more aspects of the disclosure;

FIG. 2 is a simplified block diagram of several sample aspects of components that may be employed in wireless communication nodes and configured to support communication in accordance with one or more aspects of the disclosure;

FIG. 3 illustrates examples of search parameters to enable fast switching from one radio access technology to another radio access technology in accordance with one or more aspects of the disclosure;

FIG. 4 illustrates a flow of an example scenario that can occur in which a user equipment conducts a fast switch from from one radio access technology to another radio access technology in accordance with one or more aspects of the disclosure;

FIGS. 5-8 illustrate flow charts of an exemplary method performed by a user equipment capable of communicating in multiple radio access technologies to perform fast switching between radio access technologies in accordance with one or more aspects of the disclosure;

FIG. 9 illustrates a simplified block diagram of several sample aspects of an apparatus configured to operate in multiple radio access technologies in accordance with one or more aspects of the disclosure.

DETAILED DESCRIPTION

Aspects of the subject matter are provided in the following description and related drawings directed to specific examples of the disclosed subject matter. Alternates may be devised without departing from the scope of the disclosed subject matter. Additionally, well-known elements will not be described in detail or will be omitted so as not to obscure the relevant details.

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration. ” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Likewise, the term “aspects” does not require that all aspects include the discussed feature, advantage, or mode of operation.

The terminology used herein describes particular aspects only and should not be construed to limit any aspects disclosed herein. As used herein, the singular forms “a, ” “an, ” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Those skilled in the art will further understand that the terms “comprises, ” “comprising, ” “includes, ” and/or “including, ” as used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Further, various aspects may be described in terms of sequences of actions to be performed by, for example, elements of a computing device. Those skilled in the art will recognize that various actions described herein can be performed by specific circuits (e.g., an application specific integrated circuit (ASIC) ) , by program instructions being executed by one or more processors, or by a combination of both. Additionally, these sequences of actions described herein can be considered to be embodied entirely within any form of non-transitory computer-readable medium having stored thereon a corresponding set of computer instructions that upon execution would cause an associated processor to perform the functionality described herein. Thus, the various aspects described herein may be embodied in a number of different forms, all of which have been contemplated to be within the scope of the claimed subject matter. In addition, for each of the aspects described herein, the corresponding form of any such aspects may be described herein as, for example, “logic configured to” and/or other structural components configured to perform the described action.

As used herein, the terms “user equipment” (UE) and “base station” are not intended to be specific or otherwise limited to any particular Radio Access Technology (RAT) , unless otherwise noted. In general, such UEs may be any wireless communication device (e.g., a mobile phone, router, tablet computer, laptop computer, tracking device, Internet of Things (IoT) device, etc. ) used by a user to communicate over a wireless communications network. A UE may be mobile or may (e.g., at certain times) be stationary, and may communicate with a Radio Access Network (RAN) . As used herein, the term “UE” may be referred to interchangeably as an “access terminal” or “AT, ” a “client device, ” a “wireless device, ” a “subscriber device, ” a “subscriber terminal, ” a “subscriber station, ” a “user terminal” or UT, a “mobile terminal, ” a “mobile station, ” or variations thereof. Generally, UEs can communicate with a core network via a RAN, and through the core network the UEs can be connected with external networks such as the Internet and with other UEs. Of course, other mechanisms of connecting to the core network and/or the Internet are also possible for the UEs, such as over wired access networks, WiFi networks (e.g., based on Institute of Electrical and Electronics Engineers (IEEE) 802.11, etc. ) and so on.

A base station may operate according to one of several RATs in communication with UEs depending on the network in which it is deployed, and may be alternatively referred to as an Access Point (AP) , a Network Node, a NodeB, an evolved NodeB (eNodeB, eNB) , a general Node B (gNodeB, gNB) , etc. In addition, in some systems a base station may provide edge node signaling functions while in other systems it may provide additional control and/or network management functions.

UEs can be embodied by any of a number of types of devices including but not limited to printed circuit (PC) cards, compact flash devices, external or internal modems, wireless or wireline phones, smartphones, tablets, tracking devices, asset tags, and so on. A communication link through which UEs can send signals to a RAN is called an uplink channel (e.g., a reverse traffic channel, a reverse control channel, an access channel, etc. ) . A communication link through which the RAN can send signals to UEs is called a downlink or forward link channel (e.g., a paging channel, a control channel, a broadcast channel, a forward traffic channel, etc. ) . As used herein the term traffic channel (TCH) can refer to either an uplink /reverse or downlink /forward traffic channel.

FIG. 1 illustrates an exemplary wireless communications system 100 according to one or more aspects. The wireless communications system 100, which may also be referred to as a wireless wide area network (WWAN) , may include various base stations 102 and various UEs 104. The base stations 102 may include macro cells (high power cellular base stations) and/or small cells (low power cellular base stations) . The macro cells may include eNodeBs (eNBs) where the wireless communications system 100 corresponds to an LTE network, gNodeBs (gNBs) where the wireless communications system 100 corresponds to a 5G network, and/or a combination thereof, and the small cells may include femtocells, picocells, microcells, etc.

The base stations 102 may collectively form a Radio Access Network (RAN) and interface with an Evolved Packet Core (EPC) or Next Generation Core (NGC) through backhaul links. In addition to other functions, the base stations 102 may perform functions that relate to one or more of transferring user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity) , inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, RAN sharing, multimedia broadcast multicast service (MBMS) , subscriber and equipment trace, RAN information management (RIM) , paging, positioning, and delivery of warning messages. The base stations 102 may communicate with each other directly or indirectly (e.g., through the EPC /NGC) over backhaul links 134, which may be wired or wireless.

The base stations 102 may wirelessly communicate with the UEs 104. Each of the base stations 102 may provide communication coverage for a respective geographic coverage area 110. In an aspect, although not shown in FIG. 1, coverage areas 110 may be subdivided into a plurality of cells (e.g., three) , or sectors, each cell corresponding to a single antenna or array of antennas of a base station 102. As used herein, the term “cell” or “sector” may correspond to one of a plurality of cells of a base station 102, or to the base station 102 itself, depending on the context.

While neighbor macro cell geographic coverage areas 110 may partially overlap (e.g., in a handover region) , some of the geographic coverage areas 110 may be substantially overlapped by a larger geographic coverage area 110. For example, a small cell base station 102' may have a coverage area 110' that substantially overlaps with the coverage area 110 of one or more macro cell base stations 102. A network that includes both small cell and macro cells may be known as a heterogeneous network. A heterogeneous network may also include Home eNodeBs (HeNodeBs) and/or Home gNodeBs, which may provide service to a restricted group known as a closed subscriber group (CSG) . The communication links 120 between the base stations 102 and the UEs 104 may include uplink (UL) (also referred to as reverse link) transmissions from a UE 104 to a base station 102 and/or downlink (DL) (also referred to as forward link) transmissions from a base station 102 to a UE 104. The communication links 120 may use multiple input multiple output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links may be through one or more carriers. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or less carriers may be allocated for DL than for UL) .

The wireless communications system 100 may further include a wireless local area network (WLAN) access point (AP) 150 in communication with WLAN stations (STAs) 152 via communication links 154 in an unlicensed frequency spectrum (e.g., 5 GHz) . When communicating in an unlicensed frequency spectrum, the WLAN STAs 152 and/or the WLAN AP 150 may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available.

The small cell base station 102' may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell base station 102' may employ LTE or 5G technology and use the same 5 GHz unlicensed frequency spectrum as used by the WLAN AP 150. The small cell base station 102', employing LTE/5G in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network. LTE in an unlicensed spectrum may be referred to as LTE-unlicensed (LTE-U) , licensed assisted access (LAA) , or MulteFire.

The wireless communications system 100 may further include a mmW base station 180 that may operate in mmW frequencies and/or near mmW frequencies in communication with a UE 182. Extremely high frequency (EHF) is part of the radio frequency (RF) range in the electromagnetic spectrum. EHF has a range of 30 GHz to 300 GHz and a wavelength between 1 millimeter and 10 millimeters. Radio waves in this band may be referred to as a millimeter wave. Near mmW may extend down to a frequency of 3 GHz with a wavelength of 100 millimeters. The super high frequency (SHF) band extends between 3 GHz and 30 GHz, also referred to as centimeter wave. Communications using the mmW/near mmW radio frequency band have high path loss and a relatively short range. The mmW base station 180 may utilize beamforming 184 with the UE 182 to compensate for the extremely high path loss and short range. Further, it will be appreciated that in alternative configurations, one or more base stations 102 may also transmit using mmW or near mmW and beamforming. Accordingly, it will be appreciated that the foregoing illustrations are merely examples and should not be construed to limit the various aspects disclosed herein.

The wireless communications system 100 may further include one or more UEs, such as UE 190, that connects indirectly to one or more communication networks via one or more device-to-device (D2D) peer-to-peer (P2P) links. In the embodiment of FIG. 1, UE 190 has a D2D P2P link 192 with one of the UEs 104 connected to one of the base stations 102 (e.g., through which UE 190 may indirectly obtain cellular connectivity) and a D2D P2P link 194 with WLAN STA 152 connected to the WLAN AP 150 (through which UE 190 may indirectly obtain WLAN-based Internet connectivity) . In an example, the D2D P2P links 192-194 may be supported with any well-known D2D radio access technology (RAT) , such as LTE Direct (LTE-D) , WiFi Direct (WiFi-D) , Bluetooth, and so on. Any of the

base stations

102, 102’, 180 may send measurement requests (e.g., measurement control order (MCO) ) to the

UEs

104, 182, 190, and the UE’s 104, 182, 190 may respond with measurement reports accordingly.

FIG. 2 illustrates several sample components (represented by corresponding blocks) that may be incorporated into an apparatus 202 and an apparatus 204 to support the operations as disclosed herein. As an example, the apparatus 202 may correspond to a UE, and the apparatus 204 may correspond to a network node such as a gNodeB and/or an eNodeB. It will be appreciated that the components may be implemented in different types of apparatuses in different implementations (e.g., in an ASIC, in a System-on-Chip (SoC) , etc. ) . The illustrated components may also be incorporated into other apparatuses in a communication system. For example, other apparatuses in a system may include components similar to those described to provide similar functionality. Also, a given apparatus may contain one or more of the components. For example, an apparatus may include multiple transceiver components that enable the apparatus to operate on multiple carriers and/or communicate via different technologies.

The apparatus 202 and the apparatus 204 each may include at least one wireless communication device (represented by communication devices 208 and 214) for communicating with other nodes via at least one designated RAT (e.g., LTE, NR) . Each communication device 208 may include at least one transmitter (represented by transmitter 210) for transmitting and encoding signals (e.g., messages, indications, information, and so on) and at least one receiver (represented by receiver 212) for receiving and decoding signals (e.g., messages, indications, information, pilots, and so on) . Each communication device 214 may include at least one transmitter (represented by transmitter 216) for transmitting signals (e.g., messages, indications, information, pilots, and so on) and at least one receiver (represented by receiver 218) for receiving signals (e.g., messages, indications, information, and so on) .

A transmitter and a receiver may comprise an integrated device (e.g., embodied as a transmitter circuit and a receiver circuit of a single communication device) in some implementations, may comprise a separate transmitter device and a separate receiver device in some implementations, or may be embodied in other ways in other implementations. In an aspect, a transmitter may include a plurality of antennas, such as an antenna array, that permits the respective apparatus to perform transmit “beamforming, ” as described further herein. Similarly, a receiver may include a plurality of antennas, such as an antenna array, that permits the respective apparatus to perform receive beamforming, as described further herein. In an aspect, the transmitter and receiver may share the same plurality of antennas, such that the respective apparatus can only receive or transmit at a given time, not both at the same time. A wireless communication device (e.g., one of multiple wireless communication devices) of the apparatus 204 may also comprise a Network Listen Module (NLM) or the like for performing various measurements.

The apparatus 204 may include at least one communication device (represented by communication device 220) for communicating with other nodes. For example, the communication device 220 may comprise a network interface (e.g., one or more network access ports) configured to communicate with one or more network entities via a wire-based or wireless backhaul connection. In some aspects, the communication device 220 may be implemented as a transceiver configured to support wire-based or wireless signal communication. This communication may involve, for example, sending and receiving messages, parameters, or other types of information. Accordingly, in the example of FIG. 2, the communication device 220 is shown as comprising transmitter 222 and receiver 224 (e.g., network access ports for transmitting and receiving) .

The

apparatuses

202 and 204 may also include other components used in conjunction with the operations as disclosed herein. The apparatus 202 may include a processing system 232 for providing functionality relating to, for example, communication with the network. The apparatus 204 may include a processing system 234 for providing functionality relating to, for example, communication with the UEs. In an aspect, the

processing systems

232 and 234 may include, for example, one or more general purpose processors, multi-core processors, ASICs, digital signal processors (DSPs) , field programmable gate arrays (FPGA) , or other programmable logic devices or processing circuitry.

The

apparatuses

202 and 204 may include

measurement components

252 and 254 that may be used to obtain channel related measurements. The measurement component 252 may measure one or more downlink (DL) signals such as channel state information reference signal (CSI-RS) , phase tracking reference signal (PTRS) , primary synchronization signal (PSS) , secondary synchronization signal (SSS) , demodulation reference signal (DMRS) , etc. The measurement component 254 may measure one or more uplink (UL) signals such as DMRS, sounding reference signal (SRS) , etc.

The

apparatuses

202 and 204 may include memory components 238 and 240 (e.g., each including a memory device) , respectively, for maintaining information (e.g., information indicative of reserved resources, thresholds, parameters, and so on) . In various implementations, the memory component 238 may comprise a computer-readable medium storing one or more computer-executable instructions for a user equipment (UE) where the one or more instructions instruct the apparatus 202 (e.g., processing system 232 in combination with communications device 208 and/or other aspects of apparatus 202) to perform any of the functions to support operations as described herein. In addition, the

apparatuses

202 and 204 may include

user interface devices

244 and 246, respectively, for providing indications (e.g., audible and/or visual indications) to a user and/or for receiving user input (e.g., upon user actuation of a sensing device such a keypad, a touch screen, a microphone, and so on) . The apparatus 202 may include a timer 256, which may be configured to measure or otherwise determine one or more time durations.

For convenience, the

apparatuses

202 and 204 are shown in FIG. 2 as including various components that may be configured according to the various examples described herein. It will be appreciated, however, that the illustrated blocks may have different functionality in different designs.

The components of FIG. 2 may be implemented in various ways. In some implementations, the components of FIG. 2 may be implemented in one or more circuits such as, for example, one or more processors and/or one or more ASICs (which may include one or more processors) . Here, each circuit may use and/or incorporate at least one memory component for storing information or executable code used by the circuit to provide this functionality. For example, some or all of the functionality represented by

blocks

208, 232, 238, 244, 252 and 256 may be implemented by processor and memory component (s) of the apparatus 202 (e.g., by execution of appropriate code and/or by appropriate configuration of processor components) . Similarly, some or all of the functionality represented by

blocks

214, 220, 234, 240, 246 and 254 may be implemented by processor and memory component (s) of the apparatus 204 (e.g., by execution of appropriate code and/or by appropriate configuration of processor components) .

The apparatus 202 may transmit and receive messages via a wireless link 260 with the apparatus 204, the messages including information related to various types of communication (e.g., voice, data, multimedia services, associated control signaling, etc. ) . The wireless link 260 may operate over a communication medium of interest, shown by way of example in FIG. 2 as the medium 262, which may be shared with other communications as well as other RATs. A medium of this type may be composed of one or more frequency, time, and/or space communication resources (e.g., encompassing one or more channels across one or more carriers) associated with communication between one or more transmitter /receiver pairs, such as the apparatus 204 and the apparatus 202 for the medium 262.

In general, the apparatus 202 and the apparatus 204 may operate via the wireless link 260 according to one or more radio access types, such as LTE, LTE-U, or NR, depending on the network in which they are deployed. These networks may include, for example, different variants of CDMA networks (e.g., LTE networks, NR networks, etc. ) , TDMA networks, FDMA networks, Orthogonal FDMA (OFDMA) networks, Single-Carrier FDMA (SC-FDMA) networks, and so on.

A UE may be capable of operating in multiple radio access technologies (RATs) . For example, a UE may be capable of operating in a first RAT (e.g., LTE) and in a second RAT (e.g., NR) . These are merely examples, and first and second RATs may be any of the RATs currently known (e.g., WiMax, CDMA, WCDMA, UTRA, Evolved Universal Terrestrial Radio Access (E-UTRA) , GSM, FDMA, GSM, TDMA, etc. ) .

The UE may be capable of operating in a standalone (SA) or in a non-standalone (NSA) mode within a given RAT. When operating in the SA mode, the UE may be able to exchange both control and data plane information with the network node and/or the core network of the given RAT (e.g., LTE, NR) . When operating in the NSA mode, the UE may be communicating with network nodes of the first and second RATs. In the NSA mode, the UE can exchange data plane information with the network nodes of both the first RAT (e.g., LTE) and the second RAT (e.g., NR) . However, the control plane information is exchanged only with the network node of the first RAT (e.g., LTE) .

A UE in SA mode may be connected to either an LTE cell or an NR cell. For performance reasons, it can be preferable to be connected to the NR cell over the LTE cell when possible. Nonetheless, in some circumstances, the UE may be in LTE connected mode for data service. For example, the UE may physically move from an area of reliable NR service to an area where NR service is unreliable or even not available. In this instance, the UE may connect to LTE to receive data services. Unfortunately, it is often the case that the UE does not switch back to being connected to NR for a long time even when the UE moves back to an area where NR service is available.

One of the reasons that the UE does not switch to NR from the LTE connected mode is that the network side does not instruct the UE to measure for NR cells. That is, the network side does not configure a measurement control message. As a result, the UE does not make NR measurements, e.g., for cell reselection, and thus remains in the LTE connected mode.

To address such issues, it is proposed to have the UE to register or otherwise attach directly to an NR cell under certain circumstances when the UE is in the LTE connected mode. The proposed technique takes advantage of the fact that even when the UE is in the LTE connected mode, the LTE network still provides system information block (SIB) information including SIB24, which includes information about neighboring cells including NR cells neighboring the LTE cell. In the proposed technique, even though the UE is in the LTE connected mode, the UE may register directly with one or more of the neighboring NR cells when the circumstances permit.

In general, the proposed technique may be summarized as follows. When the UE is in the LTE connected mode, the UE may determine whether the LTE signal is good enough. For example, the UE may determine whether LTE_RSRP (reference signal received power) ) meets a minimum quality threshold (e.g., LTE_RSRP_Threshold) . If the LTE signal does not meet the minimum LTE quality threshold (e.g., if LTE_RSRP < LTE_RSRP_Threshold) and there is no measurement control for NR from the network side, the UE may determine whether any of the neighboring NR cells indicated in the SIB24 are candidate NR cells. A candidate NR cell may be a cell whose NR signal (e.g., NR_RSRP) meets a minimum NR quality threshold (NR_RSRP_Threshold) . IF a candidate NR cell is found (e.g., if NR_RSRP ≥ NR_RSRP_Threshold) , then the UE may perform LTE local release (to detach from the LTE cell) , and register to the candidate NR cell directly. One benefit (of which there can be several) is that the proposed technique can enable a faster attachment to the NR cell than performing a conventional cell reselection.

The parameter threshold values may be preset within the UE. For example, the LTE_RSRP_Threshold and the NR_RSRP_Threshold may be set to default values of -90dbm and -110dbm, respectively. Alternatively or in addition there to, one or both threshold values may be configured by the network. If the threshold parameter values are configured by the network, then the configured values may override the previous settings within the UE, whether preset or previously configured.

When operating in one RAT, it is often the case that a UE is unable to measure in a different RAT simultaneously. If it is decided to search for candidate NR cells (e.g., if UE in LTE connected mode and LTE_RSRP < LTE_RSRP_Threshold) , then the UE may proceed to making measurements. However, since the UE is still in the LTE connected mode, there may be data to be exchanged with the LTE cell when it is decided to search for the candidate NR cells. Assuming that the UE cannot exchange data with the LTE cell and make NR measurements simultaneously, it would be desirable to make the NR measurements while still providing opportunities for the UE to exchange data with–i.e., transfer data to and/or receive data from –the LTE cell in a timely fashion. To state it another way, it would be desirable to prevent starving of the LTE data exchange.

To enable sufficient opportunities for data transfer to take place even when the search for candidate NR cells is performed, the following search parameters may be defined:

● Meas_Gap = default value ‘SSB period from SIB24’ + 1ms, configurable,

● Meas_Cycle = default value 80ms, configurable,

● Meas_Max_Timer = default value 5 sec, configurable, and

● Meas_Forbid_Timer = default value 30 sec, configurable.

The NR search parameters may be preset within the UE. Alternatively or in addition thereto, one or more of the NR search parameters may be configured by the network. Again, if the search parameter values are configured by the network, then the configured values may override the previous settings within the UE, whether preset or previously configured.

FIG. 3 illustrates relationships of the NR search parameters. Within Meas_Cycle, the UE may make NR measurements during Meas_Gap. Note that Meas_Cycle is longer than Meas_Gap. For convenience, the remainder of the Meas_Cycle may be referred to as Non_Meas_Gap. This may represent a duration within each Meas_Cycle in which the UE may exchange data with the LTE cell, i.e., receive data services from the LTE cell.

Note that in an aspect, Meas_Gap can be set to ‘SSB period from SIB24’ + 1ms. This is merely an example. Generally, Meas_Gap may be set to any value longer than the SSB period defined in SIB24, i.e., longer than the SSB period of the NR. This is to account for the fact that measurement gap offset that would be configured in a measurement control is unlikely to be known to the UE since the UE has not received the measurement control configuration from the network. By so setting the Meas_Gap, the UE should be able to detect a synchronization signal block (SSB) of an NR cell.

If the UE does not find a candidate NR cell in one Meas_Cycle, the UE can repeat measurements for candidate NR cells in more Meas_Cycles until Meas_Max_Timer expires. If Meas_Max_Timer expires and the UE still has not found any suitable candidate NR cells, then the UE may refrain from making NR measurements until expiration of Meas_Forbid_Timer, which may also be referred to as Meas_Forbid_duration for convenience. After Meas_Forbid_duration expires, the UE may start again in search for candidate NR cells. Also for convenience, Meas_Period may be defined as a sum of Meas_Max_Timer and Meas_Forbid_Timer.

FIG. 4 illustrates a flow of an example scenario 400 that can occur in which a UE switches from being connected to a cell of one RAT to a cell of another RAT. In this instance, it is assumed that the switch is from a 4G LTE cell to a 5G NR cell. In the scenario 400, it may be assumed that the UE is currently in LTE connected mode, i.e., is currently connected to an LTE cell for data services.

In block 410, while there are no NR measurement control configuration messages from the network, the UE may determine whether the signal from the LTE cell is of sufficient quality. For example, the UE may determine whether LTE_RSRP (reference signal received power) is less than LTE_RSRP_Threshold. If it is determined that the LTE_RSRP is not less than LTE_RSRP_Threshold (N branch from block 410) , then in block 415, the UE may operate conventionally. For example, the UE may remain in the LTE connected mode to exchange data with the LTE cell. To state it another way, if the UE determines that the LTE signal is of sufficient quality, the UE may operate conventionally and remain connected with the LTE cell to receive data services.

However, if the UE determines that the LTE signal is not of sufficient quality, this may trigger the UE the search for candidate NR cells for switching purposes. That is, if it is determined that LTE_RSRP is less than LTE_RSRP_Threshold (Y branch from block 410) , then in block 420, the UE may start a measurement timer. Then in block 430, the UE may measure one or more NR cells according to SIB24. That is, the UE may make measurements of one or more NR cells that are neighbors of the current LTE cell. Also, during each Meas_Cycle, the UE may make measurements during Meas_Gap.

In block 440, the UE may determine whether a signal of a neighboring NR cell is of sufficient quality. For example, the UE may determine whether NR_RSRP of the NR cell is greater than or equal to NR_RSRP_Threshold. If so (Y branch from block 440) , the UE in block 450 may switch to the NR cell by performing LTE local release (to detach from the LTE cell) , and register to the NR cell directly.

On the other hand, if it is determined that the NR signal is not of sufficient quality (e.g., NR_RSRP is less than NR_RSRP_Threshold) , then in block 460, the UE may determine whether the measurement timer is greater than Meas_Max_Timer. That is, the UE may determine whether the maximum time for conducting NR measurements has passed since deciding to switch for candidate NR cells.

If the measurement time is not greater than Meas_Max_Timer (N branch from block 460) , the UE may proceed back to block 430 and continue measuring for candidate NR cells. If measurement time is greater than Meas_Max_Timer (Y branch from block 460) , the UE may proceed to block 465 to start a measurement forbid timer. While the measurement forbid time is less than Meas_Forbid_Timer, the UE may refrain from making NR measurements as seen in

blocks

475 and 485.

FIG. 5 illustrates a flow chart of an example method 500 performed by a UE for fast switching between RATs. FIG. 5 may be viewed as a generalization of the flow of FIG. 4. Here, the UE (such as the UE 202) may be capable of operating in multiple RATs including first (e.g., 4G LTE) and second (e.g., 5G NR) RATs. The memory component 238 may be viewed as an example of a non-transitory computer-readable medium that stores computer-executable instructions to operate components of the UE 202 such as the transceiver 208 (including transmitter 210 and receiver 212) , the processing system 232 (including one or more processors) , memory component 238, etc.

In FIG. 5, it may be assumed that the UE is operating in the standalone (SA) mode, and has established communication with a first network node (e.g., eNodeB) of the first RAT. That is, the UE may be assumed to be in first RAT connected mode (e.g., LTE connected mode) such that it can receive data services from (i.e., exchange data with) the first network node. It may also be assumed that during the method 500, the network (e.g., the core network) does not initiate cell reselection to attach to a second network node (e.g., gNodeB) of the second RAT, e.g., by sending a measurement control configuration message to the UE.

In block 510, the UE may determine whether a RAT switch condition is satisfied. The RAT switch condition may be such that when satisfied, the UE is triggered to search for one or more candidate second network nodes of the second RAT. As indicated, the UE may be in the first RAT connected mode with the first network node when it performs block 510. That is, the UE may be in a mode in which it receives data services from the first network node when it determines whether or not the RAT switch condition is satisfied. Means for performing block 510 may include the processing system 232, the memory component 238, the transceiver 208 and/or the measurement component 252 of the UE 202.

FIG. 6 illustrates a flow chart of an example process the UE may perform to implement block 510. In block 610, the UE may measure a quality of a signal from the first network node. For ease of description, “first signal” may be used to refer to the signal from the first network node, and “first signal quality” may be used to refer to the quality of the first signal. Then it may be said that in block 610, the UE may measure the first signal quality. Means for performing block 610 may include the processing system 232, the memory component 238, the transceiver 208 and/or the measurement component 252 of the UE 202.

In block 620, the UE may determine whether the first signal quality is below a certain minimum threshold. For ease of description, “first-signal-quality-min-threshold” may be used to refer to the minimum threshold. Then it may be said that in block 620, the UE may determine whether the first signal quality is less than the first-signal-quality-min-threshold. Means for performing block 620 may include the processing system 232 and/or the memory component 238 of the UE 202.

In an aspect, the first signal may be one or more reference signals of first RAT. These may include cell specific reference signal (CRS) , synchronization signal (SS) , channel state information RS (CSI-RS) , demodulation RS (DMRS) , phase tracking RS (PTRS) , and so on. The first signal quality may be measured in a variety of ways. For example, if the first signal is a reference signal (RS) , then the first signal quality may be any one or more of the following: first reference signal received power (first RSRP) , first reference signal received quality (first RSRQ) , first received signal strength indicator (first RSSI) , first signal-to-noise-and-interference-ratio (first SINR) , and so on. Then correspondingly, the first-signal-quality-min-threshold may be any combination of first-RSRP-min-threshold, first-RSRQ-min-threshold, first-RSSI-min-threshold, first-SINR-min-threshold, and so on. The first-signal-quality-min-threshold may be preset within the UE. Alternatively or in addition thereto, the first-signal-quality-min-threshold may be configured by the network.

When it is determined that the first signal quality is less than the first-signal-quality-min-threshold (Y branch from block 620) , then in block 630, the UE may determine that the RAT switch condition is satisfied. Means for performing block 620 may include the processing system 232 and/or the memory component 238 of the UE 202.

On the other hand, if it is determined that the first signal quality is not less than the first-signal-quality-min-threshold (N branch from block 620) , then in block 640, the UE may determine that the RAT switch condition is not satisfied. Means for performing block 630 may include the processing system 232 and/or the memory component 238 of the UE 202.

Referring back to FIG. 5, when it is determined that the RAT switch condition is not satisfied (N branch from block 510) , then the method 500 may proceed back to block 510. While not explicitly shown, since the UE is in the first RAT connected mode, the UE may continue to receive data services from (e.g., exchange data with) the first network node when is determined that the RAT switch condition is not satisfied.

On the other hand, when it is determined that the RAT switch condition is satisfied (Y block from block 510) , then in block 520, the UE may determine whether there is a candidate second network node of the second RAT based on a first RAT system information block (SIB) received from the first network node. The first RAT SIB may indicate one or more second network nodes of the second RAT that neighbor the first network node. The LTE SIB24 may be an example of the first RAT SIB. The first RAT SIB may be received from the first network node. Means for performing block 520 may include the processing system 232, the memory component 238, the transceiver 208, the measurement component 252 and/or the timer 256 of the UE 202.

FIG. 7 illustrates a flow chart of an example process the UE may perform to implement block 520. In block 710, the UE may start a measurement timer. Means for performing block 710 may include the processing system 232, the memory component 238, the transceiver 208 and/or the timer 256 of the UE 202.

In block 720, the UE may measure a quality of a signal from a second network node indicated in the first SIB to neighbor the first network node. For ease of description, “second signal” may be used to refer to the signal from the neighboring second network node, and “second signal quality” may be used to refer to the quality of the second signal. Then it may be said that in block 720, the UE may measure the second signal quality. Means for performing block 720 may include the processing system 232, the memory component 238, the transceiver 208 and/or the measurement component 252 of the UE 202.

In block 730, the UE may determine whether the second signal quality is at least a certain minimum threshold. For ease of description, “second-signal-quality-min-threshold” may be used to refer to the minimum threshold. Then it may be said that in block 730, the UE may determine whether the second signal quality is greater than or equal to the second-signal-quality-min-threshold. Means for performing block 720 may include the processing system 232 and/or the memory component 238 of the UE 202.

In an aspect, the second signal may be one or more reference signals of second RAT. These may include SS, CSI-RS, DMRS, PTRS, and so on. The second signal quality may be measured in a variety of ways. For example, if the first signal is a reference signal (RS) , then the second signal quality may be any one or more of the following: second RSRP, second RSRQ, second RSSI, second SINR, and so on. Then correspondingly, the second-signal-quality-min-threshold may be any combination of second-RSRP-min-threshold, second-RSRQ-min-threshold, second-RSSI-min-threshold, second-SINR-min-threshold, and so on. The second-signal-quality-min-threshold may be preset within the UE. Alternatively or in addition thereto, the second-signal-quality-min-threshold may be configured by the network.

When it is determined that the second signal quality is greater than or equal to the second-signal-quality-min-threshold (Y branch from block 730) , then in block 740, the UE may determine that the candidate second network node is found. In this instance, the candidate second network node may be the neighboring second network node that corresponds to the measured second signal quality, i.e., corresponds to the neighboring network whose second signal quality measured in block 720 is greater than or equal to the second-signal-quality-min-threshold. Means for performing block 740 may include the processing system 232 and/or the memory component 238 of the UE 202.

On the other hand, if it is determined that the second signal quality is not greater than or equal to the second-signal-quality-min-threshold (N branch from block 730) , then in block 750, the UE may determine whether a max-measurement-duration has expired since the of the measurement timer in block 710. For example, the UE may compare and determine whether the measurement timer is greater than the max-measurement-duration. Means for performing block 750 may include the processing system 232, the memory component 238 and/or the timer 256 of the UE 202.

The Meas_Max_Timer (see FIG. 3) may be an example of the max-measurement-duration. The max-measurement-duration may be preset within the UE. Alternatively or in addition thereto, the max-measurement-duration may be configured by the network.

If it is determined that the max-measurement-duration has expired since the start of the measurement time (Y branch from block 750) , then in block 760, the UE may determine that no candidate second network node is found. Means for performing block 760 may include the processing system 232 and/or the memory component 238 of the UE 202.

On the other hand, if it is determined that the max-measurement-duration has not expired since the start of the measurement time (N branch from block 750) , then the method may proceed to block 720 in which the UE repeats measuring the second signal quality. It is thus seen that within a max-measurement-duration duration, block 720 may be repeated one or more times.

In an aspect, the max-measurement-duration may comprise one or more measurement cycles. For example, FIG. 3 indicates that there can be multiple Meas_Cycles (examples of measurement cycles) in one Meas_Max_Timer (example of max-measurement-duration) . Within each measurement cycle, there may be a measurement gap (e.g., Meas_Gap in FIG. 3) . In an aspect, when the UE measures the second signal quality measurement in block 720, the UE may perform the measurement during the measurement gap of each measurement cycle. On the other hand, the UE may refrain from measuring the second signal quality during a non-measurement gap of each measurement cycle. In this context, the non-measurement gap may be a portion of the measurement cycle other than the measurement gap. During any non-measurement gap, the UE may receive data services from the first network node. That is, the UE may send data to and/or receive data from the first network node.

Also, when the first RAT SIB indicates that there are multiple neighboring second network nodes, the UE may perform the second signal quality measurement of the second signal of different neighboring second network node when it repeats block 720 of measuring the second signal quality.

Referring back to FIG. 5, when it is determined that the candidate second network node is found (Y branch from block 520) , then in block 530, the UE may switch connection from the first network node to the candidate second network node. After the switch occurs, the UE may receive data services from the candidate second network node instead of from the first network node. Means for performing block 540 may include the processing system 232, the memory component 238 and/or the transceiver 208 of the UE 202.

FIG. 8 illustrates a flow chart of an example process the UE may perform to implement block 530. In block 810, the UE may perform a first RAT local release from the first network node. As a result, the UE may no longer be in the first RAT connected mode with the first network node. Means for performing block 810 may include the processing system 232, the memory component 238 and/or the transceiver 208 of the UE 202.

In block 820, the UE may register with the candidate second network node. Thereafter, the UE may receive data services from the second network node. In an aspect, the registration with the candidate second network node may be a direct registration. Means for performing block 820 may include the processing system 232, the memory component 238 and/or the transceiver 208 of the UE 202.

Referring back to FIG. 5, when it is determined that the candidate second network node is not found (Y branch from block 520) , then in block 540, the UE may refrain from making second RAT measurements for a measurement-forbid-duration. Means for performing block 540 may include the processing system 232, the memory component 238, the transceiver 208, the measurement component 252 and/or the timer 256 of the UE 202.

The Meas_Forbid_Timer may be an example of the measurement-forbid-duration. The measurement-forbid-duration may be preset within the UE. Note that during at least a part of the measurement-forbid-duration, the UE may receive data services from the first network node.

FIG. 9 illustrates an example user equipment apparatus 900 represented as a series of interrelated functional modules connected by a common bus. Each of the modules may be implemented in hardware or as a combination of hardware and software. For example, the modules may be implemented as any combination of the components of the apparatus 202 of FIG. 2. A module for determining whether the RAT switch condition is satisfied 910 may correspond at least in some aspects to a communication device (e.g., communication device 208) , a processing system (e.g., processing system 232) , a memory component (e.g., memory component 238) , and/or a measurement component (e.g., measurement component 252) . A module for determining whether candidate second network node is found 920 may correspond at least in some aspects to a communication device (e.g., communication device 208) , a processing system (e.g., processing system 232) , a memory component (e.g., memory component 238) , a measurement component (e.g., measurement component 252) and/or a timer (e.g., timer 256) . A module for switching connection from the first network node to the candidate network node 920 may correspond at least in some aspects to a communication device (e.g., communication device 208) , a processing system (e.g., processing system 232) , and/or a memory component (e.g., memory component 238) . A module for refraining from making the second RAT measurement may correspond at least in some aspects to a processing system (e.g., processing system 232) and/or a memory component (e.g., memory component 238) .

The functionality of the modules of FIG. 9 may be implemented in various ways consistent with the teachings herein. In some designs, the functionality of these modules may be implemented as one or more electrical components. In some designs, the functionality of these blocks may be implemented as a processing system including one or more processor components. In some designs, the functionality of these modules may be implemented using, for example, at least a portion of one or more integrated circuits (e.g., an ASIC) . As discussed herein, an integrated circuit may include a processor, software, other related components, or some combination thereof. Thus, the functionality of different modules may be implemented, for example, as different subsets of an integrated circuit, as different subsets of a set of software modules, or a combination thereof. Also, it will be appreciated that a given subset (e.g., of an integrated circuit and/or of a set of software modules) may provide at least a portion of the functionality for more than one module.

In addition, the components and functions represented by FIG. 9, as well as other components and functions described herein, may be implemented using any suitable means. Such means also may be implemented, at least in part, using corresponding structure as taught herein. For example, the components described above in conjunction with the “module for” components of FIG. 9 also may correspond to similarly designated “means for” functionality. Thus, in some aspects one or more of such means may be implemented using one or more of processor components, integrated circuits, or other suitable structure as taught herein.

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

Further, those of skill in the art will appreciate that the various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the aspects disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present disclosure.

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

The methods, sequences and/or algorithms described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in random access memory (RAM) , flash memory, read-only memory (ROM) , erasable programmable ROM (EPROM) , electrically erasable programmable ROM (EEPROM) , registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal (e.g., UE) . In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

In one or more exemplary aspects, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. 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 medium. Disk and disc, as used herein, includes compact disc (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 should also be included within the scope of computer-readable media.

While the foregoing disclosure shows illustrative aspects of the disclosure, it should be noted that various changes and modifications could be made herein without departing from the scope of the disclosure as defined by the appended claims. The functions, steps and/or actions of the method claims in accordance with the aspects of the disclosure described herein need not be performed in any particular order. Furthermore, although elements of the disclosure may be described or claimed in the singular, the plural is contemplated unless limitation to the singular is explicitly stated.

Claims

A user equipment (UE) configured to operate in first and second radio access technologies (RATs) , comprising:

a processor;

a memory; and

a transceiver,

wherein the processor, the memory, and/or the transceiver are configured to:

determine, while the UE is in a first RAT connected mode with a first network node of the first RAT, whether a RAT switch condition is satisfied, the first RAT connected mode being a mode in which the UE receives data services from the first network node, the RAT switch condition being such that when satisfied, the UE is triggered to search for one or more candidate second network nodes of the second RAT;

determine, when it is determined that the RAT switch condition is satisfied, whether a candidate second network node of the second RAT is found based on a first RAT system information block (SIB) indicating one or more second network nodes of the second RAT neighboring the first network node; and

switch, when it is determined that the candidate second network node is found, connection from the first network node to the candidate second network node such that the UE receives data services from the candidate second network node after the switch takes place.
The UE of claim 1, wherein the first RAT is 4G Long Term Evolution (LTE) and the second RAT is 5G New Radio (NR) .
The UE of claim 1, wherein in determining whether the RAT switch condition is satisfied, the processor, the memory, and/or the transceiver are configured to:

measure a first signal quality, the first signal quality being a quality of one or more signals from the first network node;

determine whether the first signal quality is less than a first-signal-quality-min-threshold;

determine that the RAT switch condition is satisfied when it is determined that the first signal quality is less than the first-signal-quality-min-threshold; and

determine that the RAT switch condition is not satisfied when it is determined that the first signal quality is not less than the first-signal-quality-min-threshold.
The UE of claim 3,

wherein the first signal quality is any one or more of a first reference signal received power (first RSRP) , a first reference signal received quality (first RSRQ) , a first received signal strength indicator (first RSSI) , and a first signal-to-noise-and-interference-ratio (first SINR) , and

wherein the first-signal-quality-min-threshold is a corresponding any one or more of a first-RSRP-min-threshold, a first-RSRQ-min-threshold, a first-RSSI-min-threshold, and a first-SINR-min-threshold.
The UE of claim 3, wherein the first-signal-quality-min-threshold is preset within the UE and/or is configured when the UE is connected to a network.
The UE of claim 1, wherein the first RAT SIB is received from the first network node.
The UE of claim 6, wherein the first RAT SIB is a 4G LTE SIB24.
The UE of claim 1, wherein in determining whether the candidate second network node of the second RAT is found based on the first RAT SIB, the processor, the memory, and/or the transceiver are configured to:

start a measurement timer;

measure a second signal quality, the second signal quality being a quality of one or more signals from a second network node indicated in the first RAT SIB as being a neighboring node of the first network node;

determine whether the second signal quality is greater than or equal to a second-signal-quality-min-threshold;

determine that the candidate second network node has been found when it is determined that the second signal quality is greater than or equal to the second-signal- quality-min-threshold, the candidate second network node being the neighboring second network node corresponding to the measured second signal quality;

determine whether a max-measurement-duration has expired since the start of the measurement timer when it is determined that the second signal quality is not greater than or equal to the second-signal-quality-min-threshold;

determine that no candidate second network node is found when it is determined that the max-measurement-duration has expired since the start of the measurement timer; and

repeat measuring the second signal quality when it is determined that the max-measurement-duration has not expired since the start of the measurement timer.
The UE of claim 8,

wherein the second signal quality is any one or more of a second reference signal received power (second RSRP) , a second reference signal received quality (second RSRQ) , a second received signal strength indicator (second RSSI) , and a second signal-to-noise-and-interference-ratio (second SINR) , and

wherein the second-signal-quality-min-threshold is a corresponding any one or more of a second-RSRP-min-threshold, a second-RSRQ-min-threshold, a second-RSSI-min-threshold, and a second-SINR-min-threshold.
The UE of claim 8, wherein the second-signal-quality-min-threshold is preset within the UE and/or is configured when the UE is connected to a network.
The UE of claim 8, wherein the max-measurement-duration is preset within the UE and/or is configured when the UE is connected to a network.
The UE of claim 8,

wherein the max-measurement-duration comprises one or more measurement cycles, and

wherein in measuring the second signal quality, the processor, the memory, and/or the transceiver are configured to perform the second signal quality measurement within a measurement gap of each measurement cycle.
The UE of claim 12, wherein the processor, the memory, and/or the transceiver are configured to refrain from measuring the second signal quality during a non-measurement gap of each measurement cycle, the non-measurement gap being a portion of the measurement cycle other than the measurement cap.
The UE of claim 12,

wherein the measurement gap is preset within the UE and/or is configured when the UE is connected to a network, and/or

wherein the measurement cycle is preset within the UE and/or is configured when the UE is connected to a network.
The UE of claim 12, wherein the measurement gap is longer than a period of a synchronization signal block (SSB) of the second RAT.
The UE of claim 8, wherein when the first RAT SIB indicates multiple neighboring second network nodes, the processor, the memory, and/or the transceiver are configured to perform the second signal quality measurement of the second signal of different neighboring second network node when repeating the measuring the second signal quality.
The UE of claim 1, wherein in switching the connection from the first network node to the candidate second network node, the processor, the memory, and/or the transceiver are configured to:

perform a first RAT local release from the first network node; and

register with the candidate second network node.
The UE of claim 1, wherein the processor, the memory, and/or the transceiver are further configured to:

refrain, when it is determined that the candidate second network node is not found, from making second RAT measurements for a measurement-forbid-duration; and

repeat determining whether the RAT switch condition is satisfied after expiration of the measurement-forbid-duration.
The UE of claim 18, wherein the measurement-forbid-duration is preset within the UE and/or is configured when the UE is connected to a network.
The UE of claim 18, wherein the UE receives data services from the first network node during at least a part of the measurement-forbid-duration.
A method of a user equipment (UE) configured to operate in first and second radio access technologies (RATs) , the method comprising:

determining, while the UE is in a first RAT connected mode with a first network node of the first RAT, whether a RAT switch condition is satisfied, the first RAT connected mode being a mode in which the UE receives data services from the first network node, the RAT switch condition being such that when satisfied, the UE is triggered to search for one or more candidate second network nodes of the second RAT;

determining, when it is determined that the RAT switch condition is satisfied, whether a candidate second network node of the second RAT is found based on a first RAT system information block (SIB) indicating one or more second network nodes of the second RAT neighboring the first network node; and

switching, when it is determined that the candidate second network node is found, connection from the first network node to the candidate second network node such that the UE receives data services from the candidate second network node after the switch takes place.
The method of claim 21, wherein the first RAT is 4G Long Term Evolution (LTE) and the second RAT is 5G New Radio (NR) .
The method of claim 21, wherein determining whether the RAT switch condition is satisfied comprises:

measuring a first signal quality, the first signal quality being a quality of one or more signals from the first network node;

determining whether the first signal quality is less than a first-signal-quality-min-threshold;

determining that the RAT switch condition is satisfied when it is determined that the first signal quality is less than the first-signal-quality-min-threshold; and

determining that the RAT switch condition is not satisfied when it is determined that the first signal quality is not less than the first-signal-quality-min-threshold.
The method of claim 23,

wherein the first signal quality is any one or more of a first reference signal received power (first RSRP) , a first reference signal received quality (first RSRQ) , a first received signal strength indicator (first RSSI) , and a first signal-to-noise-and-interference-ratio (first SINR) , and

wherein the first-signal-quality-min-threshold is a corresponding any one or more of a first-RSRP-min-threshold, a first-RSRQ-min-threshold, a first-RSSI-min-threshold, and a first-SINR-min-threshold.
The method of claim 23, wherein the first-signal-quality-min-threshold is preset within the UE and/or is configured when the UE is connected to a network.
The method of claim 21, wherein the first RAT SIB is received from the first network node.
The method of claim 26, wherein the first RAT SIB is a 4G LTE SIB24.
The method of claim 21, wherein determining whether the candidate second network node of the second RAT is found based on the first RAT SIB comprises:

starting a measurement timer;

measuring a second signal quality, the second signal quality being a quality of one or more signals from a second network node indicated in the first RAT SIB as being a neighboring node of the first network node;

determining whether the second signal quality is greater than or equal to a second-signal-quality-min-threshold;

determining that the candidate second network node has been found when it is determined that the second signal quality is greater than or equal to the second-signal-quality-min-threshold, the candidate second network node being the neighboring second network node corresponding to the measured second signal quality;

determining whether a max-measurement-duration has expired since the start of the measurement timer when it is determined that the second signal quality is not greater than or equal to the second-signal-quality-min-threshold;

determining that no candidate second network node is found when it is determined that the max-measurement-duration has expired since the start of the measurement timer; and

repeating measuring the second signal quality when it is determined that the max-measurement-duration has not expired since the start of the measurement timer.
The method of claim 28,

wherein the second signal quality is any one or more of a second reference signal received power (second RSRP) , a second reference signal received quality (second RSRQ) , a second received signal strength indicator (second RSSI) , and a second signal-to-noise-and-interference-ratio (second SINR) , and

wherein the second-signal-quality-min-threshold is a corresponding any one or more of a second-RSRP-min-threshold, a second-RSRQ-min-threshold, a second-RSSI-min-threshold, and a second-SINR-min-threshold.
The method of claim 28, wherein the second-signal-quality-min-threshold is preset within the UE and/or is configured when the UE is connected to a network.
The method of claim 28, wherein the max-measurement-duration is preset within the UE and/or is configured when the UE is connected to a network.
The method of claim 28,

wherein the max-measurement-duration comprises one or more measurement cycles, and

wherein measuring the second signal quality comprises performing the second signal quality measurement within a measurement gap of each measurement cycle.
The method of claim 32, further comprising refraining from measuring the second signal quality during a non-measurement gap of each measurement cycle, the non-measurement gap being a portion of the measurement cycle other than the measurement cap.
The method of claim 32,

wherein the measurement gap is preset within the UE and/or is configured when the UE is connected to a network, and/or

wherein the measurement cycle is preset within the UE and/or is configured when the UE is connected to a network.
The method of claim 32, wherein the measurement gap is longer than a period of a synchronization signal block (SSB) of the second RAT.
The method of claim 28, wherein when the first RAT SIB indicates multiple neighboring second network nodes, the second signal quality measurement of the second signal of different neighboring second network node are performed when repeating the measuring the second signal quality.
The method of claim 21, wherein switching the connection from the first network node to the candidate second network node comprises:

performing a first RAT local release from the first network node; and

registering with the candidate second network node.
The method of claim 21, further comprising:

refraining, when it is determined that the candidate second network node is not found, from making second RAT measurements for a measurement-forbid-duration; and

repeating determining whether the RAT switch condition is satisfied after expiration of the measurement-forbid-duration.
The method of claim 38, wherein the measurement-forbid-duration is preset within the UE and/or is configured when the UE is connected to a network.
The method of claim 38, wherein the UE receives data services from the first network node during at least a part of the measurement-forbid-duration.
A user equipment (UE) configured to operate in first and second radio access technologies (RATs) , comprising:

means for determining, while the UE is in a first RAT connected mode with a first network node of the first RAT, whether a RAT switch condition is satisfied, the first RAT connected mode being a mode in which the UE receives data services from the first network node, the RAT switch condition being such that when satisfied, the UE is triggered to search for one or more candidate second network nodes of the second RAT;

means for determining, when it is determined that the RAT switch condition is satisfied, whether a candidate second network node of the second RAT is found based on a first RAT system information block (SIB) indicating one or more second network nodes of the second RAT neighboring the first network node; and

means for switching, when it is determined that the candidate second network node is found, connection from the first network node to the candidate second network node such that the UE receives data services from the candidate second network node after the switch takes place.
A non-transitory computer-readable medium storing computer-executable instructions for a user equipment (UE) , the computer-executable instructions comprising:

one or more instructions causing the UE to determine, while the UE is in a first RAT connected mode with a first network node of the first RAT, whether a RAT switch condition is satisfied, the first RAT connected mode being a mode in which the UE receives data services from the first network node, the RAT switch condition being such that when satisfied, the UE is triggered to search for one or more candidate second network nodes of the second RAT;

one or more instructions causing the UE to determine, when it is determined that the RAT switch condition is satisfied, whether a candidate second network node of the second RAT is found based on a first RAT system information block (SIB) indicating one or more second network nodes of the second RAT neighboring the first network node; and

one or more instructions causing the UE to switch, when it is determined that the candidate second network node is found, connection from the first network node to the candidate second network node such that the UE receives data services from the candidate second network node after the switch takes place.