WO2022067474A1

WO2022067474A1 - Enhanced recovery from radio link failure

Info

Publication number: WO2022067474A1
Application number: PCT/CN2020/118727
Authority: WO
Inventors: Rishika TINDOLA; Muralidharan Murugan; Jun Deng; Anupam Gupta; Kuo-Chun Lee
Original assignee: Qualcomm Incorporated
Priority date: 2020-09-29
Filing date: 2020-09-29
Publication date: 2022-04-07

Abstract

Techniques to establish a radio link when a radio link establish trigger (e.g., user equipment (UE) power on, radio link failure (RLF), out-of-sync (OOS) ) occurs are disclosed. For example, when a UE experiences an RLF, it is conventional to establish a radio link with a cell with highest signal energy in recovery. But in one or more aspects, it is proposed that the UE prioritize cells of one type over cells of another type in establishing the radio link. For example, in a multiple radio access technology (RAT) scenario, a UE may establish link with a Long Term Evolution (LTE) anchor cell rather than with an LTE only cell, even though the signal from the LTE only cell may have more energy.

Description

ENHANCED RECOVERY FROM RADIO LINK FAILURE

TECHNICAL FIELD

Various aspects described herein generally relate to wireless communication systems, and more particularly, to enhanced radio link establishment, such as when recovering from a radio link failure (RLF) .

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 Worldwide Interoperability for Microwave Access (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) 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, upon an occurrence of a radio link establish trigger, a first signal from a first cell and a second signal from a second cell. The processor, the memory, and/or the transceiver may also be configured to perform a biased selection to select the first cell or the second cell based on the first signal and/or the second signal. The first signal and/or the second signal may be weighted to bias the selection towards the first cell over the second cell. The first cell may be capable of enabling the UE to establish connections with at least one cell of one radio access technology (RAT) and with at least one cell of another RAT contemporaneously. The processor, the memory, and/or the transceiver may further be configured to establish a radio link with the selected cell.

An exemplary method performed by a user equipment (UE) is disclosed. The method may comprise determining, upon an occurrence of a radio link establish trigger, a first signal from a first cell and a second signal from a second cell. The method may also comprise performing a biased selection to select the first cell or the second cell based on the first signal and/or the second signal. The first signal and/or the second signal may be weighted to bias the selection towards the first cell over the second cell. The first cell may be capable of enabling the UE to establish connections with at least one cell of one radio access technology (RAT) and with at least one cell of another RAT contemporaneously. The method may further comprise establishing a radio link with the selected cell.

Another exemplary user equipment (UE) is disclosed. The UE may comprise means for determining, upon an occurrence of a radio link establish trigger, a first signal from a first cell and a second signal from a second cell. The UE may comprise also means for performing a biased selection to select the first cell or the second cell based on the first signal and/or the second signal. The first signal and/or the second signal may be weighted to bias the selection towards the first cell over the second cell. The first cell may be capable of enabling the UE to establish connections with at least one cell of one radio access technology (RAT) and with at least one cell of another RAT contemporaneously. The UE may further comprise means for establishing a radio link with the selected cell.

A non-transitory computer-readable medium storing computer-executable instructions for a user equipment (UE) is disclosed. The executable instructions may comprise one or more instructions instructing the UE to determine, upon an occurrence of a radio link establish trigger, a first signal from a first cell and a second signal from a second cell. The executable instructions may also comprise one or more instructions instructing the UE to perform a biased selection to select the first cell or the second cell based on the first signal and/or the second signal. The first signal and/or the second signal may be weighted to bias the selection towards the first cell over the second cell. The first cell may be capable of enabling the UE to establish connections with at least one cell of one radio access technology (RAT) and with at least one cell of another RAT contemporaneously. The executable instructions may further comprise one or more instructions instructing the UE to establish a radio link with the selected cell.

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 a flow of an example scenario in which a user equipment recovers from a radio link failure in accordance with one or more aspects of the disclosure;

FIGS. 4-11 illustrate flow charts of an exemplary method performed by a user equipment to establish a radio link in accordance with one or more aspects of the disclosure;

FIG. 12 illustrates a simplified block diagram of several sample aspects of an apparatus configured for recovery from radio link failure 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, Wireless Fidelity (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 (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 Evolved NodeBs (eNBs) where the wireless communications system 100 corresponds to an Long-Term Evolution (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 eNBs (HeNBs) 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 (corresponding to, for example, a UE and a base station (e.g., eNB, gNB) , respectively, 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 gNB and/or an eNB. 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 the communication devices 208 and 214) for communicating with other nodes via at least one designated RAT (e.g., LTE, New Radio (NR) ) . Each communication device 208 may include at least one transmitter (represented by the transmitter 210) for transmitting and encoding signals (e.g., messages, indications, information, and so on) and at least one receiver (represented by the 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 the transmitter 216) for transmitting signals (e.g., messages, indications, information, pilots, and so on) and at least one receiver (represented by the 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 the 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 a transmitter 222 and a 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, memory 238 can comprise a computer-readable medium storing one or more computer-executable instructions for a user equipment (UE) where the one or more instructions instruct 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 discussed 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 and a counter258. The timer 256 may be configured to measure or otherwise determine one or more time durations. The counter 258 may be configured to count or otherwise determine occurrences of one or more events.

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 functionalities represented by

blocks

208, 232, 238, and 244 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 functionalities represented by

blocks

214, 220, 234, 240, and 246 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) .

In an aspect, the apparatus 204 may correspond to a “small cell” or a Home gNodeB. 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. ) .

Also, a UE may be capable of operating in multiple RATs at the same time. For example, a UE that can operate in both LTE and NR simultaneously is an E-UTRA-NR Dual Connectivity (ENDC) capable UE. Note that ENDC is an example of Multi-RAT DC (MRDC) capability. In general, when an MRDC capable UE is operating in two RATs, it may be communicating with a base station (e.g., eNB) of a first RAT (e.g., LTE) and with a base station (e.g., gNB) of a second RAT (e.g., NR) . When the UE operates in the first RAT, it may communicate with a network node (e.g., base station, eNB, etc. ) of the first RAT. Similarly, when the UE operates in the second RAT, it may communicate with a network node (e.g., base station, gNB, etc. ) of the second RAT.

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 can exchange both control and data plane (also referred to as user plane) information with the network node and/or the core network of the given RAT (e.g., NR) . When operating in the NSA mode, the UE is 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 one of the RATS, such as the first RAT (e.g., LTE) .

A UE working in NSA mode initially can attach to a network to an anchor cell of a first RAT (e.g., LTE) , and also add a cell of a second RAT (e.g., NR) as a cell of a secondary cell group (SCG) . That is, the UE can be initially configured by the network with correct split bearer parameters. At this point, there is an LTE radio link established for communication between the UE and the LTE anchor cell, and an NR radio link established for communication between the UE and the NR cell.

Thereafter, the LTE radio link may fail for one reason or another. If the UE detects a radio link failure (RLF) in the LTE radio link (i.e., detects LTE RLF) , the scans for signals from cells. Conventionally, the UE attempts to establish a radio link with a cell whose transmitted signal is the strongest as measured at the UE. However, for ENDC capable UEs, or more generally MRDC capable UEs, this is not necessarily desirable. For example, in one scenario, a UE with dual subscriber identity modules (SIMs) may be configured with corresponding dual subscriptions SUB1 (e.g., default data subscription (DDS) ) and SUB2 (non-DDS) . Assume that SUB1 is in connected mode and camped on ENDC anchor cell-1 while SUB2 is camped on cell2. A registration trigger on SUB2 may cause a tune away leading to the radio frequency (RF) chain of the UE not being available for SUB1. If the RF is unavailable for a long time, e.g., because a long call is going on SUB2, RLF may happen for SUB1. Under conventional recovery from RLF, SUB1 may reestablish radio link with an LTE only cell (i.e., non-anchor) when its signal is stronger instead with the ENDC anchor cell-1 even if the signal from cell-1 is sufficiently strong.

To address such issues, it is proposed to incorporate recovery mechanism in which the radio link establishment mechanism is biased to favor linking to one type of cells (e.g., ENDC anchor cells) over another type of cells (e.g., LTE only cells) . In other words, in some circumstances, even if a signal from a preferred cell is weaker than a signal from a non-preferred cell, the preferred cell may be selected to establish a radio link with the UE. For example, if the signal from the preferred cell is “good enough” , the preferred cell may be selected over the non-preferred cell. As another example, the preferred cell may be selected if its signal is only “marginally worse” than the signal from the non-preferred cell. The non-preferred cell may be selected if its signal is significantly better than the signal from the preferred cell, which is also not good enough.

FIG. 3 illustrates an example of a scenario 300 in which a UE recovers from an RLF. maintains a stable SCG connection with a network. In FIG. 3 the UE may be multi-RAT capable. For example, the UE may be an ENDC UE capable of operating in 4G LTE and in 5G NR. Thus, for the UE, ENDC capable cells may be preferred over LTE only capable cells. In FIG. 3, it may be assumed that the UE is currently connected with a current cell (e.g., an ENDC anchor cell, which may be same or different from the ENDC anchor cell illustrated in FIG. 3) . The sequence in scenario 300 may be as follows:

A. RLF occurrence with current cell;

B. UE determines, from one or more databases (further described below) , signals of cells for scanning:

· UE scans for candidate preferred signals from one or more candidate preferred cells (e.g., ENDC anchor cells) including a preferred signal from a preferred cell, which is the candidate preferred cell whose candidate preferred signal is the best (e.g., highest energy and/or highest quality) as detected at the UE among the scanned candidate preferred signals from all candidate preferred cells;

· UE scans for candidate non-preferred signals from one or more candidate non-preferred cells (e.g., LTE only cells) including a non-preferred signal from a non-preferred cell, which is the candidate non-preferred cell whose candidate non-preferred signal is the best (e.g., highest energy and/or highest quality) as detected at the UE among the scanned candidate non-preferred signals from all candidate non-preferred cells;

C. UE determines if connection-establishment-duration (further described below) has passed:

· If not, UE selects a cell –candidate preferred cell or candidate non-preferred cell –with bias toward candidate preferred cell;

· If so, UE selects a cell –candidate preferred cell or candidate non-preferred cell –without bias;

D. UE establish radio link with selected cell:

· If preferred cell selected, establish radio link with preferred cell;

· If non-preferred cell selected, establish radio link with non-preferred cell.

FIG. 4 illustrates a flow chart of an exemplary RLF recovery method performed by a UE in accordance with one or more aspects of the disclosure. FIG. 4 may be viewed as a generalization of the flow of FIG. 3. Here, the UE (such as the UE 202) may be capable of operating in multiple radio access technologies (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.

It is noted that FIG. 3 is in the context of recovering from RLF. However, it should be noted that the radio link establishment techniques illustrated and described may also be applicable to other situations where radio link establishing is triggered such as when the UE is first powered on, in out-of-sync (OOS) scenarios, etc. But for descriptive purposes, RLF context will be assumed to be the trigger to establish the radio link with the recognition that the description may apply to other radio link establish triggers.

In block 405 of FIG. 4, the UE may maintain (i.e., generate and/or update) the databases of preferred and non-preferred cells (referred to as first and second candidate cells databases) . The databases maintained in block 405 may be used by the UE to recover from RLF (or when radio link needs to be established for other reasons) described with respect to blocks 410-450. Note that block 405 may be performed somewhat independently of block 410-450. That is, performing block 405 may not necessarily trigger performing block 410-450, and performing block 410-450 may not necessarily trigger performing block 405. Details of block 405 will be provided further below with respect to FIGS. 9-11.

In block 410, the UE may determine, upon an occurrence of a radio link establish trigger, a first signal from a first cell and a second signal from a second cell. As noted, radio link establishment may be triggered upon a power on of the UE, an RLF with a current cell, an out-of-sync (OOS) link with the current cell, etc. The first cell may be capable of enabling the UE to establish connections with at least one cell of one RAT (e.g., LTE) and with at least one cell of another RAT (e.g., NR) contemporaneously. For example, the first cell may be an ENDC anchor cell. The second cell may not be capable of enabling the UE to establish connections with cells of different RATs contemporaneously. For example, the second cell may be an LTE only cell.

The current cell may be any cell of the network. That is, the current cell may or may not be capable of enabling the UE to establish connections cell with different RATs contemporaneously. Also, the current cell may be the same as one of the first cell or the second cell, or different from both the first and second cells.

The first and second signals may be reference signals respectively transmitted from the first and second cells. Examples of reference signals include a channel state information reference signal (CSI-RS) , a cell specific reference signal (CRS) , a phase tracking reference signal (PTRS) , a primary synchronization signal (PSS) , a secondary synchronization signal (SSS) , a demodulation reference signal (DMRS) , a positioning reference signal (PRS) , etc.

Optionally, the UE may also determine a third signal from a third cell. The third cell may or may not be similar to the first cell. That is, the third cell may or may not be capable of enabling the UE to establish connections with cells of different RATs contemporaneously. The third signal may also be a reference signal transmitted from the third cell. The optional third signal and cell will be elaborated further below.

FIG. 5 illustrates a flow chart of an example process that may be performed by the UE to implement block 410. A first candidate cells database (DB) (discussed further below with respect to FIGS. 9-11) may be configured by the UE and/or by the network (e.g., through configuration messages) . The first candidate cells database may identify one or more first candidate cells and identify one or more first candidate signals transmitted from the one or more first candidate cells. Each first candidate cell may be a cell capable of enabling a UE to establish connections with cells of different RATs (e.g., first and second RATs) contemporaneously or even simultaneously. For example, each first candidate cell may be an ENDC anchor cell.

In block 510, the UE may scan for the one or more first candidate signals transmitted from the one or more first candidate cells based on the first candidate cells database. That is, the UE may scan for the one or more first candidate signals of the one or more first candidate cells identified in the first candidate cells database. The first candidate signals may be reference signals.

In an aspect, scanning may be performed to obtain an energy and/or a quality –referred to as “energy-quality” for ease of reference –for each of the one or more first candidate signals. In an aspect, the energy-quality of each first candidate signal may be determined as any combination of a reference signal received power (RSRP) , a reference signal received quality (RSRQ) , a reference signal strength indicator (RSSI) , a signal-to-noise and interference ratio (SINR) , etc.

In block 520, the UE may determine the first candidate signal with the highest energy-quality among the scanned first candidate signals as the first signal and may also determine the first candidate cell that transmitted the first signal as the first cell. The energy-quality of the first signal may be referred to as the first energy-quality, which may be any combination of a first RSRP, a first RSRQ, a first RSSI, a first SINR, etc.

Also, a second candidate cells database (discussed further below with respect to FIGS. 9-11) may be configured by the UE and/or by the network (e.g., through configuration messages) . The second candidate cells database may identify one or more second candidate cells and identify one or more second candidate signals transmitted from the one or more second candidate cells. In an example, the second candidate cells may be LTE only cells.

In block 530, the UE may scan for the one or more second candidate signals transmitted from the one or more second candidate cells based on the second candidate cells database, i.e., the UE may scan for the one or more second candidate signals of the one or more second candidate cells identified in the second candidate cells database. The second candidate signals may be reference signals. In an aspect, scanning may be performed to obtain energy-quality of each second candidate signal (e.g., any combination of RSRP, RSRQ, RSSI, SINR, etc. ) .

In block 540, the UE may determine the second candidate signal with the highest energy-quality among the scanned second candidate signals as the second signal and may also determine the second candidate cell that transmitted the second signal as the second cell. The energy-quality of the second signal may be referred to as the second energy-quality, which may be any combination of a second RSRP, a second RSRQ, a second RSSI, a second SINR, etc.

Optionally in the UE, a third candidate cells database may be configured. The third candidate cells database may be a customized database, e.g., configured by the user or customer. The third candidate cells database may identify one or more third candidate cells and identify one or more third candidate signals transmitted from the one or more third candidate cells. The third candidate cells may be any mix of cell types. That is, some, none or all third candidate cells may be similar to the first cells (capable of enabling a UE to establish connections with cells of different RATs contemporaneously or even simultaneously. Also, some, none or all third candidate cells may be similar to the second cells. In an aspect, the third cells may represent cells that are particularly favored, even over the first cells.

When the third candidate cells database is configured, the UE may perform

blocks

550 and 560. Note that even when the third candidate cells database is configured, performing

blocks

550 and 560 may nonetheless remain optional. In block 550, the UE may scan for the one or more third candidate signals transmitted from the one or more third candidate cells based on the third candidate cells database, i.e., the UE may scan for the one or more third candidate signals of the one or more third candidate cells identified in the third candidate cells database. The third candidate signals may be reference signals. In an aspect, scanning may be performed to obtain energy-quality of each third candidate signal (e.g., any combination of RSRP, RSRQ, RSSI, SINR, etc. ) .

In block 560, the UE may determine the third candidate signal with the highest energy-quality among the scanned third candidate signals as the third signal and may also determine the third candidate cell that transmitted the third signal as the third cell. The energy-quality of the third signal may be referred to as the third energy-quality, which may be any combination of a third RSRP, a third RSRQ, a third RSSI, a third SINR, etc.

In an aspect, the UE may comprise a plurality of subscriber identity modules (SIMs) configured with a corresponding plurality of subscriptions. For example, in a dual SIM UE, one SIM may correspond with SUB1 configured as a default data subscription (DDS) and another SIM may correspond SUB2 configured as a non-DDS. The subscription that is currently attempting to recover from the RLF (or is attempting to establish the radio link for other reasons) , may be referred to as the current subscription for ease of reference. In this scenario, any one or more of the first candidate cells database, the second candidate cells database, and the third candidate cells database, may be databases associated with the subscriptions other than the current subscription. For example, any of the first, second, and/or the third databases may have been configured by other subscriptions.

In a perspective, blocks 510 –540 (and 550 –560) may be viewed as representing an example algorithm to choose candidate cells for RLF (or more generally, for radio link establishment) .

Input:

· ENDC anchor DB with N signals: ef (1) , ef (2) , …ef (N) –example of first candidate cells database;

· Acquisition (ACQ) DB with M signals: lf (1) , lf (2) , …lf (M) –example of second candidate cells database;

· Customer DB with P signals: cf (1) , cf (2) , …cf (P) –example of third candidate cells database;

Algorithm:

· Perform scan to obtain energy-quality Q (ef (i) ) for each signal ef (i) , i=1…N (corresponding to block 510) and obtain energy-quality Q (ef (j) ) for each signal lf (j) , j=1…M (corresponding to block 530) and optionally obtain energy-quality Q (cf (k) ) for each signal cf (k) , k=1…P (corresponding to block 560) ;

· Choose the best among the N ef (i) signals (e.g., highest energy and/or quality) and the best among the M lf (j) signals (e.g., highest energy and/or quality) :

· ef_max = argmax (Q (ef (i) ) , i=1…N (corresponding to block 520) ;

· lf_max = argmax (Q (lf (j) ) , j=1…M (corresponding to block 540) ;

· cf_max = argmax (Q (cf (k) ) , k=1…P (corresponding to block 560) .

Referring back to FIG. 4, in block 415, the UE may optionally determine whether a connection-reestablish-duration-portion threshold has passed. For context, when the UE starts a procedure to establish the radio link (e.g., recover from the RLF) , the UE may start a connection-reestablish timer (e.g., one of the timers 256) . The connection-reestablish timer may stop when the UE establishes a radio link with a cell, i.e., when the UE completes the recovery. On the other hand, if the connection-reestablish timer expires without completing the recovery, the UE may enter an idle state. T311 timer may be an example of the connection-reestablish timer. In this context, the connection-reestablish-duration-portion threshold may represent a portion of a duration between a start and expiration of the connection-reestablish timer. For example, connection-reestablish-duration-portion threshold may be half, third, fourth, two fifths, etc.

In an aspect, the connection-reestablish-duration-portion threshold may be set within the UE (e.g., factory setting, by a user, etc. ) and/or configured by the network. As indicated, block 415 may be optional. Thus, in an aspect, a flag may be configured (e.g., set within the UE and/or configured by the network) to indicate whether or not block 415 is to be performed.

If it indicated that the connection-reestablish-duration-portion threshold has not yet passed (N branch from block 415) , then in block 420, the UE may perform a biased selection to select between the first cell and the second cell. Note that the UE may proceed from block 410 to block 420 if block 415 is not performed. In block 420, the first and/or the second signal may be weighted so as to favor the selection of the first cell over the second cell. Optionally, if the third signal is determined, the biasing may favor the third cell over the first cell.

FIG. 6 illustrates a flow chart of an example process that may be performed by the UE to implement block 420. Continuing with the algorithmic perspective, as between the first and second signals, the following cases may be considered:

a) If ef_max > lf_max, select first cell;

b) If ef_max + energy-quality-bias-threshold > lf_max, select first cell;

c) If ef_max > sufficient-energy-quality-threshold, select first cell;

d) If none of a) , b) , c) is satisfied, select second cell.

Cases a) –d) may be described as follows. Case a) may reflect a situation in which the first signal is strictly better (higher energy and/or quality) than the second signal. Case b) may reflect a situation in which the second signal may be better than the first signal, but “not by much” , which may be quantified with the energy-quality-bias threshold. For example, the energy-quality-bias threshold may be set to 5 dbm. Case c) may reflect a situation in which the first signal is “good enough” , which may be quantified with the sufficient-energy-quality threshold. For example, the sufficient-energy-quality threshold may be set to -90 dbm. Case d) may reflect a situation in which the first signal is not good enough and the second signal is significantly better than the first signal. The energy-quality-bias threshold and/or the sufficient-energy-quality threshold may be set within the UE and/or configured by the network.

In block 615, the UE may determine whether the first energy-quality (i.e., energy and/or quality of the first signal) is greater than the second energy-quality (i.e., energy and/or quality of the second signal) . Block 615 may correspond to case a) described above. If so (Y branch from block 615) , then in block 640, the UE may select the first cell as the selected cell. If not (N branch from block 615) , the UE may proceed to block 625.

In block 625, the UE may determine whether the first energy-quality plus the energy-quality-bias threshold is greater than the second energy-quality. Block 625 may correspond to case b) described above. If so (Y branch from block 625) , then in block 640, the UE may select the first cell as the selected cell. If not (N branch from block 625) , the UE may proceed to block 635.

In block 635, the UE may determine whether the first energy-quality is greater than the sufficient-energy-quality threshold. Block 635 may correspond to case c) described above. If so (Y branch from block 635) , then in block 640, the UE may select the first cell as the selected cell. If not (N branch from block 635) , then in block 650, the UE may select the second cell as the selected cell. Block 650 may correspond to case d) described above.

Note that the block 615 may be viewed as optional in the context of performing a biased selection. In block 615, the UE may make a strict comparison, which may be considered as making an unbiased comparison. Note that if the first and second signals are such that block 615 evaluates to be true, then block 625 will also evaluate to be true. Thus, in an aspect, the UE may perform block 625 without performing block 615. In this aspect, if block 625 evaluates to be false, then the UE may proceed to block 635.

FIG. 6 represents a situation in which the UE may evaluate case a) or case b) first and then proceeding to evaluate case c) . However, it is also possible that the UE may initially evaluate case c) . This is shown in FIG. 7, which illustrates a flow chart of another example process that may be performed by the UE to implement block 420.

In block 715, the UE may determine whether the first energy-quality is greater than the sufficient-energy-quality threshold. Block 715 may correspond to case c) described above. That is, the UE may initially determine whether the first signal is “good enough” . If so, (Y branch from block 715) , then in block 740, the UE may select the first cell as the selected cell. If not (N branch from block 715) , then the UE may proceed to block 725 or to block 735.

In block 725, the UE may determine whether the first energy-quality is greater than the second energy-quality. Block 725 may correspond to case a) described above. If so (Y branch from block 725) , then in block 740, the UE may select the first cell as the selected cell. If not (N branch from block 725) , the UE may proceed to block 735. For reasons similar to block 615, block 725 may be considered as optional. That is, if block 715 evaluates to be false, then the UE may proceed to block 735.

In block 735, the UE may determine whether the first energy-quality plus the energy-quality-bias threshold is greater than the second energy-quality. Block 735 may correspond to case b) described above. If so (Y branch from block 735) , then in block 740, the UE may select the first cell as the selected cell. If not (N branch from block 735) , then in block 750, the UE may select the second cell as the selected cell. Block 750 may correspond to case d) described above.

While not specifically shown, it is relatively straight forward to modify FIGs. 6 and 7 to bias the selection of the third cell over the first cell, which is biased to be selected over the second cell. For example, FIGs. 6 and 7 may be modified to consider the following cases:

e) Select third signal if it is strictly the best, i.e., cf_max > ef_max and cf_max> lf_max;

f) Select third signal if it is within energy-quality-bias threshold of the better of the first and second signals, i.e., cf_max + energy-quality-bias-threshold> max (ef_max, lf_max) ;

g) Select third signal if it is good enough, i.e., cf_max > sufficient-energy-quality-threshold, choose the first cell;

h) If none of e) , f) , g) is satisfied, choose according to cases a) , b) , c) , and d) .

Referring back to FIG. 4, if it indicated that the connection-reestablish-duration-portion threshold has passed (Y branch from block 415) , then in block 430, the UE may perform an unbiased selection to select between the first cell and the second cell. Optionally, if the third signal is determined, the third cell may be included in the selection.

FIG. 8 illustrates a flow chart of an example process that may be performed by the UE to implement block 430. In block 815, the UE may determine whether the first energy-quality is greater than the second energy-quality. If so (Y branch from block 815) , then in block 820, the UE may select the first cell as the selected cell. If not (N branch from block 815) , then in block 830, the UE may select the second cell as the selected cell.

While not specifically shown, it is relatively straight forward to modify FIG. 8 to include the third cell in the unbiased selection. For example, FIG. 8 may be modified to select the cell with the best signal (highest energy and/or quality) among the first, second, and third signals.

Referring back to FIG. 4, in block 440, the UE may establish a radio link with the selected cell, i.e., with the cell selected in

block

420 or 430.

In block 445, the UE may determine whether or not the radio link is successfully established with the selected cell, e.g., whether or not the RLF recovery is successful. In one aspect, the UE may determine whether or not the connection-reestablish timer has expired without the link being established.

If not (N branch from block 445) , then in block 450, the UE may modify the databases such that a signal associated with the selected cell is removed from further consideration. For example, if the first cell was selected in

block

420 or 430, the first signal may be removed from further evaluation from the first candidate cells database. Note that this does not necessarily mean that the entry corresponding to the first signal itself is removed from the database. In an aspect, a flag may be set to indicate whether that signal will be considered next time block 410 is performed. Similarly, if the second cell (or the third cell) was selected in

block

420 or 430, the second signal (or the third signal) may be removed from further evaluation from the second (or the third) cells database. Again, the entry itself need not be removed.

Also, while not specifically illustrated, in addition to updating the candidate cells database, the UE may proceed back to block 410.

Recall from above that in block 405, the UE may maintain (e.g., generate and/or update) first and second candidate cells databases. The candidate cells databases may be particular to a UE. That is, the first and second candidate cells databases for one UE need not be the same as the first and second candidate cells databases for another UE, even if the two UEs are currently attached to a same cell (e.g., same neighbor cells) . For example, assume that there are first and second UEs. Also assume that a network allows dual-connectivity for the first UE within a tracking area (TA) but does not allow dual-connectivity to the second UE within the same tracking area. If there is an ENDC capable cell within the tracking area, the ENDC capable cell can enable the first UE to establish connections with cells of different RATs, but the same ENDC capable cell will not enable the second UE to do the same. In this instance, first UE may include the ENDC capable cell in its first candidate cells database. However, the second UE will likely include the same ENDC capable cell it its second candidate cells database, not in its first candidate cells database.

Thus, for a UE, the first candidate cells database –the database of preferred candidate cells –may include cells that enable the UE to establish links with cells of multiple RATs contemporaneously. For example, the first candidate cells database may comprise cells that are MRDC capable (e.g., ENDC capable) and allow multi-RAT connectivity (e.g., dual connectivity) to the UE.

The second candidate cells database –the database of non-preferred cells –may include cells that cannot or will not allow the UE to establish links with cells of multiple RATs simultaneously. For example, the second candidate cells database may comprise single RAT cells (e.g., LTE only cells) or cells that are MRDC capable but will not allow the UE to establish multi-RAT connectivity.

In one aspect, the first and second candidate cells databases may be maintained in two stages. In the first stage, the UE may generate/update TA-to-MRDC map, and may also generate/update a cell-to-TA map. The TA-to-MRDC may indicate whether the UE is allow to have multi-RAT connectivity within a tracking area, and the cell-to-TA map may indicate association of cells to tracking areas. In the second stage, the TA-to-MRDC map and the cell-to-TA map may be used to generate/update the first and second candidate cells database.

FIG. 9A illustrates an example of a scenario 900A in which a UE may generate/update the TA-to-MRDC map and/or generate/update the cell-to-TA map. In general, whenever the UE sends an Attach Request or a tracking area update (TAU) Request, the UE may indicate that it is capable of supporting MRDC (e.g., capable of supporting DCNR capable) . The mobility management entity (MME) may respond back with whether MRDC is allowed or not (e.g., DCNR allowed/restricted) in corresponding Attach Accept or TAU Accept. The UE may generate/update the TR-to-MRDC map accordingly. Contemporaneously, the UE may also generate/update associations between the cells and tracking areas, e.g., may generate/update the cell-to-TA map.

In FIG. 9A, the UE may be assumed to be multi-RAT capable (e.g., ENDC capable UE) . The UE may also be assumed to be initially camped and attached to a MRDC capable cell-1 (e.g., ENDC capable eNodeB) . As seen, the UE (in particular the non-access stratum (NAS) layer of the UE) may send an Attach Request to MME-1 with DCNR=true (indicating that the UE is capable of supporting dual connectivity) . In this instance, MME-1 may respond with DCNR=false (indicating that dual connectivity is restricted for the UE) back to the NAS layer of the UE in an Attach Accept. The restriction may correspond to tracking areas identified with tracking area indicators (TAIs) corresponding to cell-1 (e.g., TAI-1, TAI-2) . The UE’s NAS layer may generate the initial TA-to-MRDC map (referred to as ENDC TAI DB in FIG. 9A) , and the UE’s access stratum (AS) /RRC layer may generate the initial cell-to-TA map (referred to as ENDC FP DB) . Tables 1 and 2 illustrate the initial TA-to-MRDC and cell-to-TA maps, respectively.

TAI-1	DCNR–FALSE
TAI-2	DCNR–FALSE

Table 1 (TA-to-MRDC map–initial)

cell-1

TAI-1, TAI-2

Table 2 (cell-to-TA map–initial)

Then the UE may be handed over to cell-2 which may also be assumed to be MRDC capable. In this instance, the UE’s NAS layer may send a tracking area update (TAU) request to MME-2 (e.g., of different network) with DCNR=true (again indicating that the UE is capable of supporting dual connectivity) . But this time, MME-2 may respond with DCNR=true (indicating that dual connectivity is allowed for the UE) back to the NAS layer of the UE in a TAU Accept. The allowance may correspond to tracking areas identified with tracking area indicators (TAIs) corresponding to cell-2 (e.g., TAI-3, TAI-4) . The UE’s NAS layer may update the TA-to-MRDC map (i.e., update ENDC TAI DB) , and the UE’s AS/RRC layer may update the cell-to-TA map (i.e., update ENDC FP DB) . Tables 3 and 4 illustrate the updated TA-to-MRDC and cell-to-TA maps, respectively.

TAI-1	DCNR–FALSE
TAI-2	DCNR–FALSE
TAI-3	DCNR–TRUE
TAI-4	DCNR–TRUE

Table 3 (TA-to-MRDC map–updated)

cell-1	TAI-1, TAI-2
cell-2	TAI-3, TAI-4

Table 4 (cell-to-TA map–updated)

In an aspect, the TA-to-MRDC map may be retained across power on/off cycles. Also, the maximum size of the TA-to-MRDC map may be set within the UE (e.g., factory setting, by a user, etc. ) and/or configured by the network. The UE’s NAS layer may share the TA-to-MRDC map with the UE’s AS/RRC layer, which in turn may generate the cells databases to help the UE to camp on the preferred cells –MRDC capable cells where multi-RAT connectivity is allowed (e.g., by the MME of the network) –as much as possible.

FIG. 9B illustrates an example of a scenario 900B in which a UE may generate/update the preferred and non-preferred (e.g., first and second) candidate cell databases from the TA-to-MRDC map shared by the UE’s NAS layer along with the cell-to-TA map maintained by the UE’s AS/RRC layer. After the TA-to-MRDC map sharing, the UE’s AS/RRC layer is assumed to have the mapping information as illustrated in tables 5 and 6. Note that in some instances, whether DCNR is allowed or not may not be known to the UE. Tables 5 and 6 illustrates this.

TAI-1	DCNR–FALSE
TAI-2	DCNR–FALSE
TAI-3	DCNR–TRUE
TAI-4	DCNR–TRUE
TAI-5	DCNR–unknown

Table 5 (TA-to-MRDC map–for candidate cells database generation)

cell-1	TAI-1, TAI-2
cell-2	TAI-3, TAI-4
cell-3	TAI-5

Table 6 (cell-to-TA map–for candidate cells database generation)

An example technique to generate the first/preferred candidate cells database maybe as follows:

· The AS/RRC layer may pick a MRDC capable cell from its cell-to-TA map;

· Check the cell’s TAI multi-RAT connectivity (e.g., DCNR) support from the TA-to-MRDC map shared by the NAS layer;

· If the TAI DCNR support is TRUE or unknown, then include the cell in the first/preferred candidate cells database;

· If the TAI DCNR support is false, then include the cell in the second/non-preferred candidate cells database;

As a result, cell-2 and cell-3 may be included in the first/preferred candidate cells database, while cell-1 may be included in the second/non-preferred candidate cells database. Note that the example technique includes the cell whose TAI’s multi-RAT connectivity is unknown to the preferred cells database. But in an alternative, a more conservative approach may be implemented. That is, the multi-RAT connectivity being unknown may be treated if the multi-RAT connectivity not allowed for the UE (e.g., DCNR= FALSE in the TA-to-MRDC map.

FIG. 10 illustrates a flow chart of an example process that may be performed by the UE to implement block 405. FIG. 10 may be viewed as a generalization of the flow of FIGS. 9A, 9B. In block 1010, the UE may send a request to a mobility management entity (MME) associated with a cell when the UE is attached to the cell and/or is handed over to the cell. The request may indicate that the UE is capable of supporting multi-RAT connectivity (e.g., DCNR support) . In an aspect, the NAS layer of the UE may send the request.

In block 1020, the UE may receive a response to the request from the MME. The response may indicate whether multi-RAT connectivity (e.g., dual connectivity) is allowed for the UE for one or more tracking areas corresponding to the cell. The response may be an Attach Response when the request is an Attach Request, and may be a TAU response when the request is a TAU request. In an aspect, the NAS layer of the UE may receive the response from the MME.

In block 1030, the UE may generate/update the cell-to-TA map and the TA-to-MRDC map based on the response received from the MME. That is if the cells-to-TA map and/or the TA-to-MRDC map do not yet exist, the UE may generate the missing maps or maps. On the other hand, if the cells-to-TA map and/or the TA-to-MRDC map do yet exist, then the UE may update the existing map or maps. In an aspect, the AS/RRC layer of the UE may generate/update the cell-to-TA map and/or the NAS layer of the UE may generate/update the TA-to-MRDC map.

In block 1040, the UE may generate/update the first and second candidate cells databases based on the cell-to-TA map and the TA-to-MRDC map. FIG. 11 illustrates a flow chart of an example process that may be performed by the UE to implement block 1040.

In block 1110, the UE may, for each cell in the cells-to-TA map, include the cell in the first candidate cells database when the TA-to-MRDC map indicates that the multi-RAT connectivity is allowed or unknown for any of the one or more tracking areas corresponding to the cell.

In block 1120, the UE may, for each cell in the cells-to-TA map, include the cell in the second candidate cells database when the TA-to-MRDC map indicates that the multi-RAT connectivity is not allowed for all of the tracking areas corresponding to the cell.

While not shown, a more conservative approach may be taken in an alternative. In this alternative, the unknown multi-RAT connectivity may be treated like not-allowed multi-RAT connectivity.

FIG. 12 illustrates an example user equipment apparatus 1200 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 modules of the apparatus 202 of FIG. 2. A module for generating/updating candidate cells database 1205 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 detecting a first signal, a second signal, and/or a third signal 1210 may correspond at least in some aspects to a measurement component (e.g., measurement component 252) , 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 determining whether connection-reestablish-duration has passed 1215 may correspond at least in some aspects to a timer (e.g., timer 256) , a processing system (e.g., processing system 232) and/or a memory component (e.g., memory component 238) . A module for performing a biased selection 1220 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) . A module for performing an unbiased selection 1230 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) . A module for establishing a radio link 1240 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 determining whether the radio link successfully established 1245 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) . A module for modifying the candidate cells database 1250 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. 12 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. 12, 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. 12 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.

The following provides an overview of examples of the present disclosure:

Example 1: A method of a user equipment (UE) , comprising: determining, upon an occurrence of a radio link establish trigger, a first signal from a first cell and a second signal from a second cell; performing a biased selection to select the first cell or the second cell based on the first signal and/or the second signal, the first signal and/or the second signal being weighted to bias the selection towards the first cell over the second cell, the first cell being capable of enabling the UE to establish connections with at least one cell of one radio access technology (RAT) and with at least one cell of another RAT contemporaneously; and establishing a radio link with the selected cell.

Example 2: The method of example 1, wherein the one RAT is 4G Long Term Evolution (LTE) and the another RAT is 5G New Radio (NR) , and wherein the first cell is an E-UTRAN New Radio dual connectivity (ENDC) cell.

Example 3: The method of any of examples 1-2, wherein the first signal is a reference signal from the first cell, and the second signal is a reference signal from the second cell.

Example 4: The method of any of examples 1-3, wherein the first signal is a first candidate signal with a highest energy and/or quality as measured at the UE among one or more first candidate signals transmitted from one or more first candidate cells, each first candidate cell being capable of enabling the UE to establish connections with at least one cell of the one radio access technology (RAT) and with at least one cell of the another RAT contemporaneously, the first cell being the first candidate cell that transmitted the first signal, and the energy and/or the quality of the first signal being a first energy-quality, and wherein the second signal is a second candidate signal with a highest energy and/or quality as measured at the UE among one or more second candidate signals transmitted from one or more second candidate cells, the second cell being the second candidate cell that transmitted the second signal, and the energy and/or the quality of the second signal being a second energy-quality.

Example 5: The method of example 4, wherein the first energy-quality comprises any combination of a first reference signal received power (RSRP) , a first reference signal received quality (RSRQ) , a first reference strength indicator (RSSI) , and a first signal-to-noise and interference ratio (SINR) , and wherein the second energy-quality comprises any combination of a second RSRP, a second RSRQ, a second RSSI, and a second SINR.

Example 6: The method of any of examples 4-5, wherein determining the first signal from the first cell and the second signal from the second cell comprises: scanning for the one or more first candidate signals transmitted from the one or more first candidate cells based on a first candidate cells database identifying the one or more first candidate cells and their corresponding one or more first candidate signals; determining the first candidate signal with the highest energy and/or quality among the scanned one or more first candidate signals as the first signal and the first candidate cell that transmitted the first signal as the first cell; scanning for the one or more second candidate signals transmitted from the one or more second candidate cells based on a second candidate cells database identifying the one or more second candidate cells and their corresponding one or more second candidate signals; and determining the second candidate signal with the highest energy and/or quality among the scanned one or more second candidate signals as the second signal and the second candidate cell that transmitted second first signal as the second cell.

Example 7: The method of example 6, wherein the first candidate cells database and/or the second candidate cells database is configured by the UE and/or the network.

Example 8: The method of any of examples 6-7, wherein the UE comprises a plurality of subscriber identity modules (SIMs) configured with a corresponding plurality of subscriptions, a current subscription of the plurality of subscriptions being currently active in the UE, and wherein the first candidate cells database and/or the second candidate cells database are associated with a subscription of the plurality of subscriptions other than the current subscription.

Example 9: The method of any of examples 4-8, wherein performing the biased selection comprises: determining whether the first energy-quality plus an energy-quality-bias threshold is greater than the second energy-quality; and selecting the first cell when it is determined that the first energy-quality plus the energy-quality-bias threshold is greater than the second energy-quality.

Example 10: The method of example 9, wherein performing the biased selection further comprises: determining whether the first energy-quality is greater than a sufficient-energy-quality threshold when it is determined that the first energy-quality plus the energy-quality-bias threshold is not greater than the second energy-quality; selecting the first cell when it is determined that the first energy-quality is greater than the sufficient- energy-quality threshold; and selecting the second cell when it is determined that the first energy-quality is not greater than the sufficient-energy-quality threshold.

Example 11: The method of any of examples 9-10, wherein the energy-quality-bias threshold is set within the UE and/or configured by the network.

Example 12: The method of any of examples 4-8, wherein performing the biased selection comprises: determining whether the first energy-quality is greater than a sufficient-energy-quality threshold; and selecting the first cell when it is determined that the first energy-quality is greater than the sufficient-energy-quality threshold.

Example 13: The method of example 12, wherein performing the biased selection further comprises: determining whether the first energy-quality plus an energy-quality-bias threshold is greater than the second energy-quality when it is determined that the first energy-quality is not greater than the sufficient-energy-quality threshold; selecting the first cell when it is determined that the first energy-quality plus the energy-quality-bias threshold is greater than the second energy-quality; and selecting the second cell when it is determined that the first energy-quality plus the energy-quality-bias threshold is not greater than the second energy-quality.

Example 14: The method of any of examples 12-13, wherein the energy-quality-bias threshold is set within the UE and/or configured by the network.

Example 15: The method of any of examples 1-14, further comprising: prior to performing the biased selection to select the first cell or the second cell, determining whether a connection-reestablishment timer has passed a connection-reestablish-duration-portion threshold, wherein the biased selection is performed when it is determined that the connection-reestablishment timer has not passed the connection-reestablish-duration-portion threshold.

Example 16: The method of example 15, further comprising: performing an unbiased selection to select the first cell or the second cell based on the first signal and/or the second signal when it is determined that the connection-reestablishment timer has passed the connection-reestablish-duration-portion threshold, wherein the radio link is established with the selected cell from performing the unbiased selection.

Example 17: The method of example 16, wherein performing the unbiased selection comprises: determining whether the first energy-quality is greater than the second energy-quality; selecting the first cell when it is determined that the first energy-quality is greater than the second energy-quality; and selecting the second cell when it is determined that the first energy-quality is not greater than the second energy-quality.

Example 18: The method of example 17, wherein the connection-reestablish-duration-portion threshold is set within the UE and/or configured by the network.

Example 19: The method of any of examples 1-18, wherein a third signal from a third cell is also determined upon the occurrence of the RLF, the third signal being a third candidate signal with a highest energy and/or quality as measured at the UE among one or more third candidate signals transmitted from one or more third candidate cells, wherein when the biased selection is performed, the first signal, the second signal, and/or the third signal is weighted to bias the selection of the third cell over the first cell, and wherein when determining the third candidate signal, the one or more third candidate signals transmitted from the one or more third candidate cells are scanned based on a third candidate cells database identifying the one or more first candidate cells and their corresponding one or more first candidate signals, the third candidate cells database being configurable by a user.

Example 20: The method of any of examples 1-19, further comprising: determining whether the radio link is successfully established with the selected cell; updating one or more candidate cell databases to remove a signal associated with the selected cell from further evaluation.

Example 21: The method of any of examples 1-20, further comprising: maintaining first and second candidate cells databases, the first candidate cells database identifying one or more first candidate cells and their corresponding one or more first candidate signals, the second candidate cells database identifying the one or more second candidate cells and their corresponding one or more second candidate signals, wherein the first cell is one of the first candidate cells and the second cell is one of the second candidate cells.

Example 22: The method of example 21, wherein in maintaining the plurality of candidate cells databases comprises: sending a request to a mobility management entity (MME) associated with a cell when the UE is attached to the cell and/or is handed over to the cell, the request indicating that the UE is capable of supporting multi-RAT connectivity; receiving a response to the request from the MME, the response indicating whether multi-RAT connectivity is allowed for the UE for one or more tracking areas corresponding to the cell; generating/updating a cell-to-TA (tracking area) map and a TA-to-MRDC (multi-RAT dual connectivity) map based on the response received from the MME, the cell-to-TA map comprising a mapping of the cell to its corresponding one or more tracking areas, and the TA-to-MRDC map comprising a mapping, for each of the one or more tracking areas corresponding to the cell, of whether multi-RAT connectivity is allowed for the UE through that tracking area; and generating/updating the first and second candidate cells databases based on the cell-to-TA map and the TA-to-MRDC map.

Example 23: The method of example 22, wherein the request sent to the MME is an Attach Request or a tracking area update (TAU) request, the Attach Request being sent when the UE is camped and attached to the cell, and the TAU request being sent when the UE is handed over to the cell, and wherein the response is an Attach Response or a TAU response, the Attach Response being received when the Attach Request is sent, and the TAU response being received when the TAU request is sent.

Example 24: The method of any of examples 22-23, wherein generating/updating the first and second candidate cells database comprises: including, for each cell in the cells-to-TA map, the cell in the first candidate cells database when the TA-to-MRDC map indicates that the multi-RAT connectivity is allowed or unknown for any of the one or more tracking areas corresponding to the cell; and including, for each cell in the cells-to-TA map, the cell in the second candidate cells database when the TA-to-MRDC map indicates that the multi-RAT connectivity is not allowed for all of the tracking areas corresponding to the cell.

Example 25: The method of any of examples 22-24, wherein the cell-to-TA (tracking area) map is generated/updated by an access stratum/radio resource control (AS/RRC) layer of the UE, and/or wherein the TA-to-MRDC map is generated/updated by a non-access stratum (NAS) layer of the UE.

Example 26: The method of example 25, wherein the (NAS) layer of the UE shares the TA-to-MRDC map with the AS/RRC layer of the UE, and wherein the AS/RRC layer of the UE generates/updates the first and second candidate cells databases.

Example 27: The method of any of examples 22-26, wherein the TA-to-MRDC map is maintained across power on/off cycles of the UE.

Example 28: The method of any of examples 22-27, wherein a maximum size of the TA-to-MRDC is configured within the UE.

Example 29: The method of any of examples 1-28, wherein the radio link establish trigger is any one or more of a UE power on, a radio link failure (RLF) with a current cell, and an out-of-sync (OOS) link with the current cell.

Example 30: A user equipment comprising at least one means for performing a method of any of examples 1-29.

Example 31: A user equipment comprising a processor, memory coupled with the processor, the processor and memory configured perform a method of examples 1-29.

Example 32: A non-transitory computer-readable medium storing code for a user equipment comprising a processor, memory coupled with the processor, and instructions stored in the memory and executable by the processor to cause the user equipment to perform a method of any of examples 1-29.

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) , comprising:

a processor;

a memory; and

a transceiver,

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

determine, upon an occurrence of a radio link establish trigger, a first signal from a first cell and a second signal from a second cell;

perform a biased selection to select the first cell or the second cell based on the first signal and/or the second signal, the first signal and/or the second signal being weighted to bias the selection towards the first cell over the second cell, the first cell being capable of enabling the UE to establish connections with at least one cell of one radio access technology (RAT) and with at least one cell of another RAT contemporaneously; and

establish a radio link with the selected cell.
The UE of claim 1,

wherein the one RAT is 4G Long Term Evolution (LTE) and the another RAT is 5G New Radio (NR) , and

wherein the first cell is an E-UTRAN New Radio dual connectivity (ENDC) cell.
The UE of claim 1, wherein the first signal is a reference signal from the first cell, and the second signal is a reference signal from the second cell.
The UE of claim 1,

wherein the first signal is a first candidate signal with a highest energy and/or quality as measured at the UE among one or more first candidate signals transmitted from one or more first candidate cells, each first candidate cell being capable of enabling the UE to establish connections with at least one cell of the one RAT and with at least one cell of the another RAT contemporaneously, the first cell being the first candidate cell that transmitted the first signal, and the energy and/or the quality of the first signal being a first energy-quality, and

wherein the second signal is a second candidate signal with a highest energy and/or quality as measured at the UE among one or more second candidate signals transmitted from one or more second candidate cells, the second cell being the second candidate cell that transmitted the second signal, and the energy and/or the quality of the second signal being a second energy-quality.
The UE of claim 4,

wherein the first energy-quality comprises any combination of a first reference signal received power (RSRP) , a first reference signal received quality (RSRQ) , a first reference strength indicator (RSSI) , and a first signal-to-noise and interference ratio (SINR) , and

wherein the second energy-quality comprises any combination of a second RSRP, a second RSRQ, a second RSSI, and a second SINR.
The UE of claim 4, wherein when determining the first signal from the first cell and the second signal from the second cell, the processor, the memory, and/or the transceiver are configured to:

scan for the one or more first candidate signals transmitted from the one or more first candidate cells based on a first candidate cells database identifying the one or more first candidate cells and their corresponding one or more first candidate signals;

determine the first candidate signal with the highest energy and/or quality among the scanned one or more first candidate signals as the first signal and the first candidate cell that transmitted the first signal as the first cell;

scan for the one or more second candidate signals transmitted from the one or more second candidate cells based on a second candidate cells database identifying the one or more second candidate cells and their corresponding one or more second candidate signals; and

determine the second candidate signal with the highest energy and/or quality among the scanned one or more second candidate signals as the second signal and the second candidate cell that transmitted second first signal as the second cell.
The UE of claim 6, wherein the first candidate cells database and/or the second candidate cells database is configured by the UE and/or the network.
The UE of claim 6,

wherein the UE comprises a plurality of subscriber identity modules (SIMs) configured with a corresponding plurality of subscriptions, a current subscription of the plurality of subscriptions being currently active in the UE, and

wherein the first candidate cells database and/or the second candidate cells database are associated with a subscription of the plurality of subscriptions other than the current subscription.
The UE of claim 4, wherein when performing the biased selection, the processor, the memory, and/or the transceiver are configured to:

determine whether the first energy-quality plus an energy-quality-bias threshold is greater than the second energy-quality; and

select the first cell when it is determined that the first energy-quality plus the energy-quality-bias threshold is greater than the second energy-quality.
The UE of claim 9, wherein when performing the biased selection, the processor, the memory, and/or the transceiver are further configured to:

determine whether the first energy-quality is greater than a sufficient-energy-quality threshold when it is determined that the first energy-quality plus the energy-quality-bias threshold is not greater than the second energy-quality;

select the first cell when it is determined that the first energy-quality is greater than the sufficient-energy-quality threshold; and

select the second cell when it is determined that the first energy-quality is not greater than the sufficient-energy-quality threshold.
The UE of claim 9, wherein the energy-quality-bias threshold is set within the UE and/or configured by the network.
The UE of claim 4, wherein when performing the biased selection, the processor, the memory, and/or the transceiver are configured to:

determine whether the first energy-quality is greater than a sufficient-energy-quality threshold; and

select the first cell when it is determined that the first energy-quality is greater than the sufficient-energy-quality threshold.
The UE of claim 12, wherein when performing the biased selection, the processor, the memory, and/or the transceiver are further configured to:

determine whether the first energy-quality plus an energy-quality-bias threshold is greater than the second energy-quality when it is determined that the first energy-quality is not greater than the sufficient-energy-quality threshold;

select the first cell when it is determined that the first energy-quality plus the energy-quality-bias threshold is greater than the second energy-quality; and

select the second cell when it is determined that the first energy-quality plus the energy-quality-bias threshold is not greater than the second energy-quality.
The UE of claim 12, wherein the sufficient-energy-quality threshold is set within the UE and/or configured by the network.
The UE of claim 4, wherein the processor, the memory, and/or the transceiver are further configured to:

prior to performing the biased selection to select the first cell or the second cell, determine whether a connection-reestablishment timer has passed a connection-reestablish-duration-portion threshold,

wherein the biased selection is performed when it is determined that the connection-reestablishment timer has not passed the connection-reestablish-duration-portion threshold.
The UE of claim 15, wherein the processor, the memory, and/or the transceiver are further configured to:

perform an unbiased selection to select the first cell or the second cell based on the first signal and/or the second signal when it is determined that the connection-reestablishment timer has passed the connection-reestablish-duration-portion threshold,

wherein the radio link is established with the selected cell from performing the unbiased selection.
The UE of claim 16, wherein when performing the unbiased selection comprises, the processor, the memory, and/or the transceiver are configured to:

determine whether the first energy-quality is greater than the second energy-quality;

select the first cell when it is determined that the first energy-quality is greater than the second energy-quality; and

select the second cell when it is determined that the first energy-quality is not greater than the second energy-quality.
The UE of claim 15, wherein the connection-reestablish-duration-portion threshold is set within the UE and/or configured by the network.
The UE of claim 4,

wherein a third signal from a third cell is also determined upon the occurrence of the radio link establish trigger, the third signal being a third candidate signal with a highest energy and/or quality as measured at the UE among one or more third candidate signals transmitted from one or more third candidate cells,

wherein when the biased selection is performed, the processor, the memory, and/or the transceiver are configured to weigh the first signal, the second signal, and/or the third signal to bias the selection of the third cell over the first cell, and

wherein when determining the third candidate signal, the memory, and/or the transceiver are configured to scan the one or more third candidate signals transmitted from the one or more third candidate cells based on a third candidate cells database identifying the one or more first candidate cells and their corresponding one or more first candidate signals, the third candidate cells database being configurable by a user.
The UE of claim 1, wherein the processor, the memory, and/or the transceiver are further configured to:

determine whether the radio link is successfully established with the selected cell;

update one or more candidate cell databases to remove a signal associated with the selected cell from further evaluation.
The UE of claim 1, wherein the processor, the memory, and/or the transceiver are further configured to:

maintain first and second candidate cells databases, the first candidate cells database identifying one or more first candidate cells and their corresponding one or more first candidate signals, the second candidate cells database identifying the one or more second candidate cells and their corresponding one or more second candidate signals,

wherein the first cell is one of the first candidate cells and the second cell is one of the second candidate cells.
The UE of claim 21, wherein in maintaining the plurality of candidate cells databases, the processor, the memory, and/or the transceiver are further configured to:

send a request to a mobility management entity (MME) associated with a cell when the UE is attached to the cell and/or is handed over to the cell, the request indicating that the UE is capable of supporting multi-RAT connectivity;

receive a response to the request from the MME;

generate/update a cell-to-TA (tracking area) map and a TA-to-MRDC (multi-RAT dual connectivity) map based on the response received from the MME, the cell-to-TA map comprising a mapping of the cell to its corresponding one or more tracking areas, and the TA-to-MRDC map comprising a mapping, for each of the one or more tracking areas corresponding to the cell, of whether multi-RAT connectivity is allowed for the UE through that tracking area; and

generate/update the first and second candidate cells databases based on the cell-to-TA map and the TA-to-MRDC map.
The UE of claim 22,

wherein the request sent to the MME is an Attach Request or a tracking area update (TAU) request, the Attach Request being sent when the UE is camped and attached to the cell, and the TAU request being sent when the UE is handed over to the cell, and

wherein the response is an Attach Response or a TAU response, the Attach Response being received when the Attach Request is sent, and the TAU response being received when the TAU request is sent.
The UE of claim 22, wherein in generating/updating the first and second candidate cells database, the processor, the memory, and/or the transceiver are further configured to:

include, for each cell in the cells-to-TA map, the cell in the first candidate cells database when it is determined that the TA-to-MRDC map indicates that the multi-RAT connectivity is allowed or unknown for any of the tracking areas corresponding to the cell; and

include, for each cell in the cells-to-TA map, the cell in the second candidate cells database when it is determined that the TA-to-MRDC map indicates that the multi-RAT connectivity is not allowed for all of the tracking areas corresponding to the cell.
The UE of claim 22,

wherein the cell-to-TA (tracking area) map is generated/updated by an access stratum/radio resource control (AS/RRC) layer of the UE, and/or

wherein the TA-to-MRDC map is generated/updated by a non-access stratum (NAS) layer of the UE.
The UE of claim 25,

wherein the (NAS) layer of the UE shares the TA-to-MRDC map with the AS/RRC layer of the UE, and

wherein the AS/RRC layer of the UE generates/updates the first and second candidate cells databases.
The UE of claim 22, wherein the TA-to-MRDC map is maintained across power on/off cycles of the UE.
The UE of claim 22, wherein a maximum size of the TA-to-MRDC is configured within the UE.
The UE of claim 1, wherein the radio link establish trigger is any one or more of a UE power on, a radio link failure (RLF) with a current cell, and an out-of-sync (OOS) link with the current cell.
A method of a user equipment (UE) , the method comprising:

determining, upon an occurrence of a radio link establish trigger, a first signal from a first cell and a second signal from a second cell;

performing a biased selection to select the first cell or the second cell based on the first signal and/or the second signal, the first signal and/or the second signal being weighted to bias the selection towards the first cell over the second cell, the first cell being capable of enabling the UE to establish connections with at least one cell of one radio access technology (RAT) and with at least one cell of another RAT contemporaneously; and

establishing a radio link with the selected cell.
The method of claim 30,

wherein the one RAT is 4G Long Term Evolution (LTE) and the another RAT is 5G New Radio (NR) , and

wherein the first cell is an E-UTRAN New Radio dual connectivity (ENDC) cell.
The method of claim 30, wherein the first signal is a reference signal from the first cell, and the second signal is a reference signal from the second cell.
The method of claim 30,

wherein the first signal is a first candidate signal with a highest energy and/or quality as measured at the UE among one or more first candidate signals transmitted from one or more first candidate cells, each first candidate cell being capable of enabling the UE to establish connections with at least one cell of the one RAT and with at least one cell of the another RAT contemporaneously, the first cell being the first candidate cell that transmitted the first signal, and the energy and/or the quality of the first signal being a first energy-quality, and

wherein the second signal is a second candidate signal with a highest energy and/or quality as measured at the UE among one or more second candidate signals transmitted from one or more second candidate cells, the second cell being the second candidate cell that transmitted the second signal, and the energy and/or the quality of the second signal being a second energy-quality.
The method of claim 33,

wherein the first energy-quality comprises any combination of a first reference signal received power (RSRP) , a first reference signal received quality (RSRQ) , a first reference strength indicator (RSSI) , and a first signal-to-noise and interference ratio (SINR) , and

wherein the second energy-quality comprises any combination of a second RSRP, a second RSRQ, a second RSSI, and a second SINR.
The method of claim 33, wherein determining the first signal from the first cell and the second signal from the second cell comprises:

scanning for the one or more first candidate signals transmitted from the one or more first candidate cells based on a first candidate cells database identifying the one or more first candidate cells and their corresponding one or more first candidate signals;

determining the first candidate signal with the highest energy and/or quality among the scanned one or more first candidate signals as the first signal and the first candidate cell that transmitted the first signal as the first cell;

scanning for the one or more second candidate signals transmitted from the one or more second candidate cells based on a second candidate cells database identifying the one or more second candidate cells and their corresponding one or more second candidate signals; and

determining the second candidate signal with the highest energy and/or quality among the scanned one or more second candidate signals as the second signal and the second candidate cell that transmitted second first signal as the second cell.
The method of claim 35, wherein the first candidate cells database and/or the second candidate cells database is configured by the UE and/or the network.
The method of claim 35,

wherein the UE comprises a plurality of subscriber identity modules (SIMs) configured with a corresponding plurality of subscriptions, a current subscription of the plurality of subscriptions being currently active in the UE, and

wherein the first candidate cells database and/or the second candidate cells database are associated with a subscription of the plurality of subscriptions other than the current subscription.
The method of claim 33, wherein performing the biased selection comprises:

determining whether the first energy-quality plus an energy-quality-bias threshold is greater than the second energy-quality; and

selecting the first cell when it is determined that the first energy-quality plus the energy-quality-bias threshold is greater than the second energy-quality.
The method of claim 38, wherein performing the biased selection further comprises:

determining whether the first energy-quality is greater than a sufficient-energy-quality threshold when it is determined that the first energy-quality plus the energy-quality-bias threshold is not greater than the second energy-quality;

selecting the first cell when it is determined that the first energy-quality is greater than the sufficient-energy-quality threshold; and

selecting the second cell when it is determined that the first energy-quality is not greater than the sufficient-energy-quality threshold.
The method of claim 38, wherein the energy-quality-bias threshold is set within the UE and/or configured by the network.
The method of claim 33, wherein performing the biased selection comprises:

determining whether the first energy-quality is greater than a sufficient-energy-quality threshold; and

selecting the first cell when it is determined that the first energy-quality is greater than the sufficient-energy-quality threshold.
The method of claim 41, wherein performing the biased selection further comprises:

determining whether the first energy-quality plus an energy-quality-bias threshold is greater than the second energy-quality when it is determined that the first energy-quality is not greater than the sufficient-energy-quality threshold;

selecting the first cell when it is determined that the first energy-quality plus the energy-quality-bias threshold is greater than the second energy-quality; and

selecting the second cell when it is determined that the first energy-quality plus the energy-quality-bias threshold is not greater than the second energy-quality.
The method of claim 41, wherein the sufficient-energy-quality threshold is set within the UE and/or configured by the network.
The method of claim 33, further comprising:

prior to performing the biased selection to select the first cell or the second cell, determining whether a connection-reestablishment timer has passed a connection-reestablish-duration-portion threshold,

wherein the biased selection is performed when it is determined that the connection-reestablishment timer has not passed the connection-reestablish-duration-portion threshold.
The method of claim 44, further comprising:

performing an unbiased selection to select the first cell or the second cell based on the first signal and/or the second signal when it is determined that the connection-reestablishment timer has passed the connection-reestablish-duration-portion threshold,

wherein the radio link is established with the selected cell from performing the unbiased selection.
The method of claim 45, wherein performing the unbiased selection comprises:

determining whether the first energy-quality is greater than the second energy-quality;

selecting the first cell when it is determined that the first energy-quality is greater than the second energy-quality; and

selecting the second cell when it is determined that the first energy-quality is not greater than the second energy-quality.
The method of claim 44, wherein the connection-reestablish-duration-portion threshold is set within the UE and/or configured by the network.
The method of claim 33,

wherein a third signal from a third cell is also determined upon the occurrence of the radio link establish trigger, the third signal being a third candidate signal with a highest energy and/or quality as measured at the UE among one or more third candidate signals transmitted from one or more third candidate cells,

wherein when the biased selection is performed, the first signal, the second signal, and/or the third signal is weighted to bias the selection of the third cell over the first cell, and

wherein when determining the third candidate signal, the one or more third candidate signals transmitted from the one or more third candidate cells are scanned based on a third candidate cells database identifying the one or more first candidate cells and their corresponding one or more first candidate signals, the third candidate cells database being configurable by a user.
The method of claim 30, further comprising:

determining whether the radio link is successfully established with the selected cell;

updating one or more candidate cell databases to remove a signal associated with the selected cell from further evaluation.
The method of claim 30, further comprising:

maintaining first and second candidate cells databases, the first candidate cells database identifying one or more first candidate cells and their corresponding one or more first candidate signals, the second candidate cells database identifying the one or more second candidate cells and their corresponding one or more second candidate signals,

wherein the first cell is one of the first candidate cells and the second cell is one of the second candidate cells.
The method of claim 50, wherein in maintaining the plurality of candidate cells databases comprises:

sending a request to a mobility management entity (MME) associated with a cell when the UE is attached to the cell and/or is handed over to the cell, the request indicating that the UE is capable of supporting multi-RAT connectivity;

receiving a response to the request from the MME, the response indicating whether multi-RAT connectivity is allowed for the UE for one or more tracking areas corresponding to the cell;

generating/updating a cell-to-TA (tracking area) map and a TA-to-MRDC (multi-RAT dual connectivity) map based on the response received from the MME, the cell-to-TA map comprising a mapping of the cell to its corresponding one or more tracking areas, and the TA-to-MRDC map comprising a mapping, for each of the one or more tracking areas corresponding to the cell, of whether multi-RAT connectivity is allowed for the UE through that tracking area; and

generating/updating the first and second candidate cells databases based on the cell-to-TA map and the TA-to-MRDC map.
The method of claim 51,

wherein the request sent to the MME is an Attach Request or a tracking area update (TAU) request, the Attach Request being sent when the UE is camped and attached to the cell, and the TAU request being sent when the UE is handed over to the cell, and

wherein the response is an Attach Response or a TAU response, the Attach Response being received when the Attach Request is sent, and the TAU response being received when the TAU request is sent.
The method of claim 51, wherein generating/updating the first and second candidate cells database comprises:

including, for each cell in the cells-to-TA map, the cell in the first candidate cells database when the TA-to-MRDC map indicates that the multi-RAT connectivity is allowed or unknown for any of the one or more tracking areas corresponding to the cell; and

including, for each cell in the cells-to-TA map, the cell in the second candidate cells database when the TA-to-MRDC map indicates that the multi-RAT connectivity is not allowed for all of the tracking areas corresponding to the cell.
The method of claim 51,

wherein the cell-to-TA (tracking area) map is generated/updated by an access stratum/radio resource control (AS/RRC) layer of the UE, and/or

wherein the TA-to-MRDC map is generated/updated by a non-access stratum (NAS) layer of the UE.
The method of claim 54,

wherein the (NAS) layer of the UE shares the TA-to-MRDC map with the AS/RRC layer of the UE, and

wherein the AS/RRC layer of the UE generates/updates the first and second candidate cells databases.
The method of claim 51, wherein the TA-to-MRDC map is maintained across power on/off cycles of the UE.
The method of claim 51, wherein a maximum size of the TA-to-MRDC is configured within the UE.
The method of claim 30, wherein the radio link establish trigger is any one or more of a UE power on, a radio link failure (RLF) with a current cell, and an out-of-sync (OOS) link with the current cell.
A user equipment (UE) , comprising:

means for determining, upon an occurrence of a radio link establish trigger, a first signal from a first cell and a second signal from a second cell;

means for performing a biased selection to select the first cell or the second cell based on the first signal and/or the second signal, the first signal and/or the second signal being weighted to bias the selection towards the first cell over the second cell, the first cell being capable of enabling the UE to establish connections with at least one cell of one radio access technology (RAT) and with at least one cell of another RAT contemporaneously; and

means for establishing a radio link with the selected cell.
A non-transitory computer-readable medium storing computer-executable instructions for a user equipment (UE) , the computer-executable instructions comprising:

one or more instructions instructing the UE to determine, upon an occurrence of a radio link establish trigger, a first signal from a first cell and a second signal from a second cell;

one or more instructions instructing the UE to perform a biased selection to select the first cell or the second cell based on the first signal and/or the second signal, the first signal and/or the second signal being weighted to bias the selection towards the first cell over the second cell, the first cell being capable of enabling the UE to establish connections with at least one cell of one radio access technology (RAT) and with at least one cell of another RAT contemporaneously; and

one or more instructions instructing the UE to establish a radio link with the selected cell.