WO2021226926A1

WO2021226926A1 - Methods and systems to restore pocket data network connectivity in non-standalone mode

Info

Publication number: WO2021226926A1
Application number: PCT/CN2020/090220
Authority: WO
Inventors: Hao Zhang; Chaofeng HUI; Fojian ZHANG; Jian Li
Original assignee: Qualcomm Incorporated
Priority date: 2020-05-14
Filing date: 2020-05-14
Publication date: 2021-11-18

Abstract

Wireless communications systems and methods related to mechanisms for restoring pocket data network connectivity (PDN) in a non-standalone mode are disclosed. A user equipment (UE) may connect with a LTE base station (BS) and may request for a handover to a neighboring LTE BS. The UE may discover from a message sent by the neighboring LTE BS that a default bearer of the connection between the UE and the neighboring LTE BS has been removed. The UE then adds the neighboring LTE BS and attempt to connect with another LTE BS to restore PDN connectivity. If successful, then the UE may use this new LTE BS to establish dual connectivity with the LTE BS and a 5G BS as well as to access pocket switched data via the new LTE BS.

Description

METHODS AND SYSTEMS TO RESTORE POCKET DATA NETWORK CONNECTIVITY IN NON-STANDALONE MODE

INTRODUCTION

To meet the growing demands for expanded mobile broadband connectivity, wireless communication technologies are advancing from the long term evolution (LTE) technology to a next generation new radio (NR) technology, which may be referred to as 5 ^th Generation (5G) . In a wireless communication network implementing such wireless communication technologies, wireless multiple-access communications system may include a number of base stations (BSs) , each simultaneously supporting communications for multiple communication devices, which may be otherwise known as user equipment (UE) .

BRIEF SUMMARY OF SOME EXAMPLES

The following summarizes some aspects of the present disclosure to provide a basic understanding of the discussed technology. This summary is not an extensive overview of all contemplated features of the disclosure and is intended neither to identify key or critical elements of all aspects of the disclosure nor to delineate the scope of any or all aspects of the disclosure. Its sole purpose is to present some concepts of one or more aspects of the disclosure in summary form as a prelude to the more detailed description that is presented later.

For example, in an aspect of the disclosure, a method of wireless communication performed by a UE comprises transmitting, to a first LTE BS, a service request via a plurality of evolved packet system (EPS) bearers. The method further comprises receiving, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS. The method further comprises adding the second LTE BS to a barred cell list based on the received message indicating that the EPS bearer is removed. The method further comprises transmitting a PDN connectivity request to a third LTE BS in response to adding the second LTE BS to the barred cell list. In some aspects, the third LTE BS can be same as the first LTE BS. In yet other aspects, the third LTE BS can be different from the first LTE BS.

In an additional aspect of the disclosure, a method of wireless communication performed by a UE comprises transmitting, to a first LTE BS, a service request via a plurality of EPS bearers. The method further comprises receiving, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS. The method further comprises transmitting, to the second LTE BS, a first PDN connectivity request in response to receiving the message indicating that the EPS bearer is removed. The method further comprises adding the second LTE BS to a barred cell list in response to an expiration of a timer without the UE connecting to the second LTE BS. The method further comprises transmitting, to a third LTE BS, a second PDN connectivity request in response to the second LTE BS being added to the barred cell list. In some aspects, the third LTE BS can be same as the first LTE BS.In yet other aspects, the third LTE BS can be different from the first LTE BS.

In an additional aspect of the disclosure, a UE comprises a transceiver configured to transmit a service request to a first LTE BS via a plurality of EPS bearers and receive, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS. The UE further comprises a processor configured to add the second LTE BS to a barred cell list based on the received message indicating that the EPS bearer is removed. The transceiver is further configured to transmit a PDN connectivity request to a third LTE BS in response to the second LTE BS being added to the barred cell list. In some aspects, the third LTE BS can be same as the first LTE BS. In yet other aspects, the third LTE BS can be different from the first LTE BS.

In an additional aspect of the disclosure, a UE comprises a transceiver configured to transmit a service request to a first LTE BS via a plurality of EPS bearers; receive, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS and transmit a first PDN connectivity request to connect to the second LTE BS in response to receiving the message indicating that the EPS bearer is removed. The UE further comprises a processor configured to add the second LTE BS to a barred cell list in response to an expiration of a timer without the UE connecting to the second LTE BS. The transceiver is further configured to transmit a second PDN connectivity request to connect to a third LTE BS in response to the second LTE BS being added to the barred cell list. In some aspects, the third LTE BS can be same as the first LTE BS. In yet other aspects, the third LTE BS can be different from the first LTE BS.

In an additional aspect of the disclosure, a non-transitory computer-readable medium has program code recorded thereon, the program code comprising code for causing a UE to transmit a service request to a first LTE BS via a plurality of EPS bearers. The program code further comprises code for causing the UE to receive, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS. The program code further comprises code for causing the UE to add the second LTE BS to a barred cell list based on the received message indicating that the EPS bearer is removed. The program code further comprises code for causing the UE to transmit a PDN connectivity request to a third LTE BS in response to the second LTE BS being added to the barred cell list. In some aspects, the third LTE BS can be same as the first LTE BS. In yet other aspects, the third LTE BS can be different from the first LTE BS.

In an additional aspect of the disclosure, a UE comprises a means for transmitting to a first LTE BS a service request via a plurality of EPS bearers. The UE further comprises means for receiving from a second LTE BS a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS. The UE further comprises means for adding the second LTE BS to a barred cell list based on the received message indicating that the EPS bearer is removed. The UE further comprises means for transmitting a PDN connectivity request to a third LTE BS in response to adding the second LTE BS to the barred cell list. In some aspects, the third LTE BS can be same as the first LTE BS. In yet other aspects, the third LTE BS can be different from the first LTE BS.

Other aspects, features, and embodiments of the present invention will become apparent to those of ordinary skill in the art, upon reviewing the following description of specific, exemplary embodiments of the present invention in conjunction with the accompanying figures. While features of the present invention may be discussed relative to certain embodiments and figures below, all embodiments of the present invention can include one or more of the advantageous features discussed herein. In other words, while one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used in accordance with the various embodiments of the invention discussed herein. In similar fashion, while exemplary embodiments may be discussed below as device, system, or method embodiments it should be understood that such exemplary embodiments can be implemented in various devices, systems, and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication network according to some aspects of the present disclosure.

FIG. 2 illustrates an exemplary wireless communication network configured for non-standalone (NSA) mode according to some aspects of the present disclosure.

FIG. 3 is a block diagram of an exemplary UE according to some aspects of the present disclosure.

FIG. 4 is a block diagram of an exemplary BS according to some aspects of the present disclosure.

FIG. 5 illustrates a protocol diagram of a scheme for recovering PDN connectivity of a UE according to some aspects of the present disclosure.

FIG. 6 illustrates a flow diagram of a wireless communication method according to some aspects of the present disclosure.

DETAILED DESCRIPTION

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

This disclosure relates generally to wireless communications systems, also referred to as wireless communications networks. In various aspects, the techniques and apparatus may be used for wireless communication networks such as code division multiple access (CDMA) networks, time division multiple access (TDMA) networks, frequency division multiple access (FDMA) networks, orthogonal FDMA (OFDMA) networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, Global System for Mobile Communications (GSM) networks, 5 ^th Generation (5G) or new radio (NR) networks, as well as other communications networks. As described herein, the terms “networks” and “systems” may be used interchangeably.

An OFDMA network may implement a radio technology such as evolved UTRA (E-UTRA) , Institute of Electrical and Electronics Engineers (IEEE) 802.11, IEEE 802.16, IEEE 802.20, flash-OFDM and the like. UTRA, E-UTRA, and GSM are part of universal mobile telecommunication system (UMTS) . In particular, long term evolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA, GSM, UMTS and LTE are described in documents provided from an organization named “3rd Generation Partnership Project” (3GPP) , and cdma2000 is described in documents from an organization named “3rd Generation Partnership Project 2” (3GPP2) . These various radio technologies and standards are known or are being developed. For example, the 3rd Generation Partnership Project (3GPP) is a collaboration between groups of telecommunications associations that aims to define a globally applicable third generation (3G) mobile phone specification. 3GPP long term evolution (LTE) is a 3GPP project which was aimed at improving the UMTS mobile phone standard. The 3GPP may define specifications for the next generation of mobile networks, mobile systems, and mobile devices. The present disclosure is concerned with the evolution of wireless technologies from LTE, 4G, 5G, NR, and beyond with shared access to wireless spectrum between networks using a collection of new and different radio access technologies or radio air interfaces.

In particular, 5G networks contemplate diverse deployments, diverse spectrum, and diverse services and devices that may be implemented using an OFDM-based unified, air interface. In order to achieve these goals, further enhancements to LTE and LTE-Aare considered in addition to development of the new radio technology for 5G NR networks. The 5G NR will be capable of scaling to provide coverage (1) to a massive Internet of things (IoTs) with a ultra-high density (e.g., ～1M nodes/km ²) , ultra-low complexity (e.g., ～10s of bits/sec) , ultra-low energy (e.g., ～10+ years of battery life) , and deep coverage with the capability to reach challenging locations; (2) including mission-critical control with strong security to safeguard sensitive personal, financial, or classified information, ultra-high reliability (e.g., ～99.9999%reliability) , ultra-low latency (e.g., ～ 1 ms) , and users with wide ranges of mobility or lack thereof; and (3) with enhanced mobile broadband including extreme high capacity (e.g., ～ 10 Tbps/km ²) , extreme data rates (e.g., multi-Gbps rate, 100+ Mbps user experienced rates) , and deep awareness with advanced discovery and optimizations.

The 5G NR may be implemented to use optimized OFDM-based waveforms with scalable numerology and transmission time interval (TTI) ; having a common, flexible framework to efficiently multiplex services and features with a dynamic, low-latency time division duplex (TDD) /frequency division duplex (FDD) design; and with advanced wireless technologies, such as massive multiple input, multiple output (MIMO) , robust millimeter wave (mmWave) transmissions, advanced channel coding, and device-centric mobility. Scalability of the numerology in 5G NR, with scaling of subcarrier spacing, may efficiently address operating diverse services across diverse spectrum and diverse deployments. For example, in various outdoor and macro coverage deployments of less than 3GHz FDD/TDD implementations, subcarrier spacing may occur with 15 kHz, for example over 5, 10, 20 MHz, and the like bandwidth (BW) . For other various outdoor and small cell coverage deployments of TDD greater than 3 GHz, subcarrier spacing may occur with 30 kHz over 80/100 MHz BW. For other various indoor wideband implementations, using a TDD over the unlicensed portion of the 5 GHz band, the subcarrier spacing may occur with 60 kHz over a 160 MHz BW. Finally, for various deployments transmitting with mmWave components at a TDD of 28 GHz, subcarrier spacing may occur with 120 kHz over a 500 MHz BW.

The scalable numerology of the 5G NR facilitates scalable TTI for diverse latency and quality of service (QoS) requirements. For example, shorter TTI may be used for low latency and high reliability, while longer TTI may be used for higher spectral efficiency. The efficient multiplexing of long and short TTIs to allow transmissions to start on symbol boundaries. 5G NR also contemplates a self-contained integrated subframe design with UL/downlink scheduling information, data, and acknowledgement in the same subframe. The self-contained integrated subframe supports communications in unlicensed or contention-based shared spectrum, adaptive UL/downlink that may be flexibly configured on a per-cell basis to dynamically switch between UL and downlink to meet the current traffic needs.

Various other aspects and features of the disclosure are further described below. It should be apparent that the teachings herein may be embodied in a wide variety of forms and that any specific structure, function, or both being disclosed herein is merely representative and not limiting. Based on the teachings herein one of an ordinary level of skill in the art should appreciate that an aspect disclosed herein may be implemented independently of any other aspects and that two or more of these aspects may be combined in various ways. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, such an apparatus may be implemented or such a method may be practiced using other structure, functionality, or structure and functionality in addition to or other than one or more of the aspects set forth herein. For example, a method may be implemented as part of a system, device, apparatus, and/or as instructions stored on a computer readable medium for execution on a processor or computer. Furthermore, an aspect may comprise at least one element of a claim.

Leveraging existing LTE infrastructure for control plane functions has proven useful to speed up networks’ transition to 5G. To that end, some providers support a non-standalone (NSA) mode for UEs equipped with the capability for dual connectivity. In NSA mode, a properly equipped UE connects to both LTE BSs (e.g., for the control plane) and 5G BSs (for the data plane) . After a UE attaches to an LTE BS that supports NSA mode, the UE sends a service request to the LTE BS that includes a request for UE handover to a neighboring LTE BS. Sometimes, after the handover of the UE, the neighboring LTE BS may remove or cause the removal of the default evolved packet system (EPS) bearer of the connection between the UER and the neighboring LTE BS, incapacitating the UE from accessing pocket switched (PS) data via the neighboring LTE BS by sending a pocket data network (PDN) connectivity request. Thus, there is a need to provide a way to ensure network functionality in the event that the neighboring LTE BS removes the default EPS bearer after handover of the UE.

The present application describes mechanisms for responding to a failure of a wireless communication device when attempting to take advantage of non-standalone (NSA) mode in a network. For example, a UE may run in NSA mode. In NSA mode, the UE communicates to both a LTE BS and a 5G NR BS. The UE may use the LTE BS for control plane functionality, and the 5G NR BS for data plane communication. Where service providers have enabled the network to function with NSA operation, the core network utilizes aspect of each BS to facilitate communication with the UE. In order to initiate NSA operation, the UE attaches to the LTE BS and signals that it supports dual connectivity (DC) operation. The LTE and 5G BSs then communicate to set up the bearer on the 5G BS. During this process, the UE and the LTE BS establish connection with each other by activating a default EPS bearer, and in some cases, additional dedicated bearers. Once the connection is established between the UE and the LTE BS (also referred to herein as LTE cells, corresponding to the LTE BS) , the UE may determine that a neighboring LTE cell has superior signal quality compared to the LTE cell to which the UE is connected (i.e., the serving LTE cell) and may send a service request message including a signal quality measurement report requesting the LTE BS to handover the UE to the neighboring LTE cell. The UE may generate and transmit to the serving LTE cell such signal quality measurement reports in response to a triggering event (e.g., signal quality of the neighboring LTE cell being better than that of the serving cell) or periodically.

After the handover of the UE to the neighboring LTE cell, however, the UE may discover that the connection between the UE and the neighboring LTE cell (which has become the serving LTE cell after the handover of the UE) has failed in that the connection is missing the default EPS bearer, and in some cases, additional dedicated EPS bearers. For example, the LTE BS may transmit a radio resource control (RRC) connection reconfiguration message listing the EPS bearers that connect the UE to the LTE BS, and the list may exclude the default EPS bearer. The neighboring LTE cell or BS may have removed or caused the removal of the default EPS bearer and/or the dedicated EPS bearers. According to aspects of the present invention, the UE may keep track of LTE BSs or cells with such issues, while also providing a mechanism to trigger LTE cell reselection so that the UE may attempt NSA service via a different LTE cell.

For example, upon receiving an RRC connection reconfiguration message after sending a service request with a measurement report, the UE can determine that the handover of the UE to the neighboring LTE cell has failed, in that the default EPS bearer of the connection (and in some cases, one or more dedicated EPS bearers) between the UE and the neighboring cell have been removed (e.g., by the neighboring LTE cell) . In some instances, the UE repeatedly transmits a pocket data network (PDN) connectivity request to properly reconnect with the neighboring LTE cell and access pocket switched (PS) data, and abandons the reconnection attempt when a timer expires without response from the neighboring LTE cell (e.g., after the fifth expiration of a T3482 timer) . According to aspects of the present invention, the UE may add the LTE cell to a barred cell list (e.g., by adding an identifier of the neighboring LTE BS to the barred cell list) without sending the PDN connectivity requests. The barred cell list can be a dynamic list maintained by the UE of any LTE cells that are not functioning properly (e.g., such as removing the default EPS bearer after handover of a UE and sending RRC connection reconfiguration messages indicating the removal to the UE) . In some aspects of the present invention, the UE may transmit the PDN connectivity requests, and wait for the expiration of a timer (e.g., one of the first expiration, the second expiration, the third expiration, the fourth expiration or the fifth expiration of the T3482 timer or other timer) without response from the neighboring LTE cell before adding the neighboring LTE BS to the barred cell list. Once the neighboring LTE cell is added to the barred cell list, the UE may not attempt to establish service using the barred cell again until a predetermined amount of time has elapsed.

After adding the neighboring (i.e., failed) LTE cell to the barred cell list, the UE may seek to establish a connection with a different LTE BS. If the connection to the new LTE cell functions correctly (e.g., a functioning default EPS is activated as part of the connection) , then the UE can continue to use this new LTE cell in the process of establishing an active EPS bearer with the 5G cell (e.g., by using the new LTE cell for control plane packets) . The 5G cell may also be referred to herein as the 5G BS, since it is the 5G BS that serves the 5G cell. Further, in some instances the UE can use this new LTE cell to access PS data by transmitting PDN connectivity requests to the new LTE cell. Once the predetermined amount of time has elapsed (and, in some aspects, independent from whether the UE succeeds with connecting to the new LTE cell properly) , the UE may remove the neighboring LTE cell from the barred cell list (e.g., after a timer expires and/or after a predetermined amount of time) . As a result, the UE may attempt (if needed) to establish NSA service by attaching to the LTE cell removed from the barred cell list again (if the cell supports NSA mode) , including sending a service request to begin the process again.

Aspects of the present disclosure can provide several benefits. For example, with a failed connection that lacks at least the default EPS bearer connecting the UE to a LTE BS after handover of the UE to the LTE BS, the UE could continually attempt to properly establish connection with, and access PS data via, the LTE BS without success. Implementing aspects of the present invention provide for a more robust reliable and properly functioning network. This is because the UE may place the LTE cell into the barred cell list after the UE discovers the removal of the default EPS bearer to the LTE BS or after the UE transmits PDN connectivity request (s) to the LTE BS and a timer expires with no response from the LTE BS to the PDN connectivity request (s) . Thus, by attempting to establish a connection with a new LTE BS instead of repeatedly attempting to establish functioning connection with a non-responsive LTE BS, the UE avoids or at least reduces wasting time, power, and resources. Removing a failed LTE cell from the barred cell list after a time has passed allows for the system to function more optimally by allowing the UE to try NSA mode with the LTE cell again once the issue has been resolved. Additionally, by responding to the failure (i.e., failure to establish proper connection due to removal of a default EPS bearer) in a way that maintains the ability to utilize NSA mode, the network is able to communicate at much higher data rates than would be possible if the UE stopped using NSA mode in response to a failure.

FIG. 1 illustrates a wireless communication network 100 according to some aspects of the present disclosure. The network 100 may be a 5G network. The network 100 includes a number of base stations (BSs) 105 (individually labeled as 105a, 105b, 105c, 105d, 105e, and 105f) and other network entities. A BS 105 may be a station that communicates with UEs 115 and may also be referred to as an evolved node B (eNB) , an LTE NB or LTE BS, a next generation eNB (gNB) or 5G BS, an access point, and the like. Each BS 105 may provide communication coverage for a particular geographic area. In 3GPP, the term “cell” can refer to this particular geographic coverage area of a BS 105 and/or a BS subsystem serving the coverage area, depending on the context in which the term is used. Thus, an LTE BS may provide an LTE cell that the LTE BS serves, and a 5G BS may provide a 5G cell that the 5G BS serves.

More generally, a BS 105 may provide communication coverage for a macro cell or a small cell, such as a pico cell or a femto cell, and/or other types of cell. A macro cell generally covers a relatively large geographic area (e.g., several kilometers in radius) and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a pico cell, would generally cover a relatively smaller geographic area and may allow unrestricted access by UEs with service subscriptions with the network provider. A small cell, such as a femto cell, would also generally cover a relatively small geographic area (e.g., a home) and, in addition to unrestricted access, may also provide restricted access by UEs having an association with the femto cell (e.g., UEs in a closed subscriber group (CSG) , UEs for users in the home, and the like) . A BS for a macro cell may be referred to as a macro BS. A BS for a small cell may be referred to as a small cell BS, a pico BS, a femto BS or a home BS. In the example shown in FIG. 1, the

BSs

105d and 105e may be regular macro BSs, while the BSs 105a-105c may be macro BSs enabled with one of three dimension (3D) , full dimension (FD) , or massive MIMO. The BSs 105a-105c may take advantage of their higher dimension MIMO capabilities to exploit 3D beamforming in both elevation and azimuth beamforming to increase coverage and capacity. The BS 105f may be a small cell BS which may be a home node or portable access point. A BS 105 may support one or multiple (e.g., two, three, four, and the like) cells.

The network 100 may support synchronous or asynchronous operation. For synchronous operation, the BSs may have similar frame timing, and transmissions from different BSs may be approximately aligned in time. For asynchronous operation, the BSs may have different frame timing, and transmissions from different BSs may not be aligned in time.

The UEs 115 are dispersed throughout the wireless network 100, and each UE 115 may be stationary or mobile. A UE 115 may also be referred to as a terminal, a mobile station, a subscriber unit, a station, or the like. A UE 115 may be a cellular phone, a personal digital assistant (PDA) , a wireless modem, a wireless communication device, a handheld device, a tablet computer, a laptop computer, a cordless phone, a wireless local loop (WLL) station, or the like. In one aspect, a UE 115 may be a device that includes a Universal Integrated Circuit Card (UICC) . In another aspect, a UE may be a device that does not include a UICC. In some aspects, the UEs 115 that do not include UICCs may also be referred to as IoT devices or internet of everything (IoE) devices. The UEs 115a-115d are examples of mobile smart phone-type devices accessing network 100. A UE 115 may also be a machine specifically configured for connected communication, including machine type communication (MTC) , enhanced MTC (eMTC) , narrowband IoT (NB-IoT) and the like. The UEs 115e-115h are examples of various machines configured for communication that access the network 100. The UEs 115i-115k are examples of vehicles equipped with wireless communication devices configured for communication that access the network 100. A UE 115 may be able to communicate with any type of the BSs, whether macro BS, small cell, or the like. In FIG. 1, a lightning bolt (e.g., communication links) indicates wireless transmissions between a UE 115 and a serving BS 105, which is a BS designated to serve the UE 115 on the downlink (DL) and/or uplink (UL) , desired transmission between BSs 105, backhaul transmissions between BSs, or sidelink transmissions between UEs 115.

In operation, the BSs 105a-105c may serve the

UEs

115a and 115b using 3D beamforming and coordinated spatial techniques, such as coordinated multipoint (CoMP) or multi-connectivity. The macro BS 105d may perform backhaul communications with the BSs 105a-105c, as well as small cell, the BS 105f. The macro BS 105d may also transmit multicast services which are subscribed to and received by the

UEs

115c and 115d. Such multicast services may include mobile television or stream video, or may include other services for providing community information, such as weather emergencies or alerts, such as Amber alerts or gray alerts.

The BSs 105 may also communicate with a core network. The core network may provide user authentication, access authorization, tracking, Internet Protocol (IP) connectivity, and other access, routing, or mobility functions. At least some of the BSs 105 (e.g., which may be an example of a gNB or an access node controller (ANC) ) may interface with the core network through backhaul links (e.g., NG-C, NG-U, etc. ) and may perform radio configuration and scheduling for communication with the UEs 115. In various examples, the BSs 105 may communicate, either directly or indirectly (e.g., through core network) , with each other over backhaul links (e.g., X1, X2, etc. ) , which may be wired or wireless communication links.

The network 100 may also support mission critical communications with ultra-reliable and redundant links for mission critical devices, such as the UE 115e, which may be a drone. Redundant communication links with the UE 115e may include links from the

macro BSs

105d and 105e, as well as links from the small cell BS 105f. Other machine type devices, such as the UE 115f (e.g., a thermometer) , the UE 115g (e.g., smart meter) , and UE 115h (e.g., wearable device) may communicate through the network 100 either directly with BSs, such as the small cell BS 105f, and the macro BS 105e, or in multi-step-size configurations by communicating with another user device which relays its information to the network, such as the UE 115f communicating temperature measurement information to the smart meter, the UE 115g, which is then reported to the network through the small cell BS 105f. The network 100 may also provide additional network efficiency through dynamic, low-latency TDD/FDD communications, such asV2V, V2X, C-V2X communications between a

UE

115i, 115j, or 115k and other UEs 115, and/or vehicle-to-infrastructure (V2I) communications between a

UE

115i, 115j, or 115k and a BS 105.

In some implementations, the network 100 utilizes OFDM-based waveforms for communications. An OFDM-based system may partition the system BW into multiple (K) orthogonal subcarriers, which are also commonly referred to as subcarriers, tones, bins, or the like. Each subcarrier may be modulated with data. In some instances, the subcarrier spacing between adjacent subcarriers may be fixed, and the total number of subcarriers (K) may be dependent on the system BW. The system BW may also be partitioned into subbands. In other instances, the subcarrier spacing and/or the duration of TTIs may be scalable.

In some aspects, the BSs 105 can assign or schedule transmission resources (e.g., in the form of time-frequency resource blocks (RB) ) for downlink (DL) and uplink (UL) transmissions in the network 100. DL refers to the transmission direction from a BS 105 to a UE 115, whereas UL refers to the transmission direction from a UE 115 to a BS 105. The communication can be in the form of radio frames. A radio frame may be divided into a plurality of subframes or slots, for example, about 10. Each slot may be further divided into mini-slots. In a FDD mode, simultaneous UL and DL transmissions may occur in different frequency bands. For example, each subframe includes a UL subframe in a UL frequency band and a DL subframe in a DL frequency band. In a TDD mode, UL and DL transmissions occur at different time periods using the same frequency band. For example, a subset of the subframes (e.g., DL subframes) in a radio frame may be used for DL transmissions and another subset of the subframes (e.g., UL subframes) in the radio frame may be used for UL transmissions.

The DL subframes and the UL subframes can be further divided into several regions. For example, each DL or UL subframe may have pre-defined regions for transmissions of reference signals, control information, and data. Reference signals are predetermined signals that facilitate the communications between the BSs 105 and the UEs 115. For example, a reference signal can have a particular pilot pattern or structure, where pilot tones may span across an operational BW or frequency band, each positioned at a pre-defined time and a pre-defined frequency. For example, a BS 105 may transmit cell specific reference signals (CRSs) and/or channel state information –reference signals (CSI-RSs) to enable a UE 115 to estimate a DL channel. Similarly, a UE 115 may transmit sounding reference signals (SRSs) to enable a BS 105 to estimate a UL channel. Control information may include resource assignments and protocol controls. Data may include protocol data and/or operational data. In some aspects, the BSs 105 and the UEs 115 may communicate using self-contained subframes. A self-contained subframe may include a portion for DL communication and a portion for UL communication. A self-contained subframe can be DL-centric or UL-centric. A DL-centric subframe may include a longer duration for DL communication than for UL communication. A UL-centric subframe may include a longer duration for UL communication than for UL communication.

In some aspects, the network 100 may be an NR network deployed over a licensed spectrum. The BSs 105 can transmit synchronization signals (e.g., including a primary synchronization signal (PSS) and a secondary synchronization signal (SSS) ) in the network 100 to facilitate synchronization. The BSs 105 can broadcast system information associated with the network 100 (e.g., including a master information block (MIB) , remaining system information (RMSI) , and other system information (OSI) ) to facilitate initial network access. In some instances, the BSs 105 may broadcast the PSS, the SSS, and/or the MIB in the form of synchronization signal block (SSBs) over a physical broadcast channel (PBCH) and may broadcast the RMSI and/or the OSI over a physical downlink shared channel (PDSCH) .

In some aspects, a UE 115 attempting to access the network 100 may perform an initial cell search by detecting a PSS from a BS 105. The PSS may enable synchronization of period timing and may indicate a physical layer identity value. The UE 115 may then receive a SSS. The SSS may enable radio frame synchronization, and may provide a cell identity value, which may be combined with the physical layer identity value to identify the cell. The PSS and the SSS may be located in a central portion of a carrier or any suitable frequencies within the carrier.

After receiving the PSS and SSS, the UE 115 may receive a MIB. The MIB may include system information for initial network access and scheduling information for RMSI and/or OSI. After decoding the MIB, the UE 115 may receive RMSI and/or OSI. The RMSI and/or OSI may include radio resource control (RRC) information related to random access channel (RACH) procedures, paging, control resource set (CORESET) for physical downlink control channel (PDCCH) monitoring, physical UL control channel (PUCCH) , physical UL shared channel (PUSCH) , power control, and SRS.

After obtaining the MIB, the RMSI and/or the OSI, the UE 115 can perform a random access procedure to establish a connection with the BS 105. In some examples, the random access procedure may be a four-step random access procedure. For example, the UE 115 may transmit a random access preamble and the BS 105 may respond with a random access response. The random access response (RAR) may include a detected random access preamble identifier (ID) corresponding to the random access preamble, timing advance (TA) information, a UL grant, a temporary cell-radio network temporary identifier (C-RNTI) , and/or a backoff indicator. Upon receiving the random access response, the UE 115 may transmit a connection request to the BS 105 and the BS 105 may respond with a connection response. The connection response may indicate a contention resolution. In some examples, the random access preamble, the RAR, the connection request, and the connection response can be referred to as message 1 (MSG1) , message 2 (MSG2) , message 3 (MSG3) , and message 4 (MSG4) , respectively. In some examples, the random access procedure may be a two-step random access procedure, where the UE 115 may transmit a random access preamble and a connection request in a single transmission and the BS 105 may respond by transmitting a random access response and a connection response in a single transmission.

After establishing a connection, the UE 115 and the BS 105 can enter a normal operation stage, where operational data may be exchanged. For example, the BS 105 may schedule the UE 115 for UL and/or DL communications. The BS 105 may transmit UL and/or DL scheduling grants to the UE 115 via a PDCCH. The scheduling grants may be transmitted in the form of DL control information (DCI) . The BS 105 may transmit a DL communication signal (e.g., carrying data) to the UE 115 via a PDSCH according to a DL scheduling grant. The UE 115 may transmit a UL communication signal to the BS 105 via a PUSCH and/or PUCCH according to a UL scheduling grant.

In some aspects, the BS 105 may communicate with a UE 115 using HARQ techniques to improve communication reliability, for example, to provide a URLLC service. The BS 105 may schedule a UE 115 for a PDSCH communication by transmitting a DL grant in a PDCCH. The BS 105 may transmit a DL data packet to the UE 115 according to the schedule in the PDSCH. The DL data packet may be transmitted in the form of a transport block (TB) . If the UE 115 receives the DL data packet successfully, the UE 115 may transmit a HARQ ACK to the BS 105. Conversely, if the UE 115 fails to receive the DL transmission successfully, the UE 115 may transmit a HARQ NACK to the BS 105. Upon receiving a HARQ NACK from the UE 115, the BS 105 may retransmit the DL data packet to the UE 115. The retransmission may include the same coded version of DL data as the initial transmission. Alternatively, the retransmission may include a different coded version of the DL data than the initial transmission. The UE 115 may apply soft-combining to combine the encoded data received from the initial transmission and the retransmission for decoding. The BS 105 and the UE 115 may also apply HARQ for UL communications using substantially similar mechanisms as the DL HARQ.

In some aspects, the network 100 may operate over a system BW or a component carrier (CC) BW. The network 100 may partition the system BW into multiple BWPs (e.g., portions) . A BS 105 may dynamically assign a UE 115 to operate over a certain BWP (e.g., a certain portion of the system BW) . The assigned BWP may be referred to as the active BWP. The UE 115 may monitor the active BWP for signaling information from the BS 105. The BS 105 may schedule the UE 115 for UL or DL communications in the active BWP. In some aspects, a BS 105 may assign a pair of BWPs within the CC to a UE 115 for UL and DL communications. For example, the BWP pair may include one BWP for UL communications and one BWP for DL communications.

In some aspects, the network 100 may operate over a shared channel, which may include shared frequency bands or unlicensed frequency bands. For example, the network 100 may be an NR-unlicensed (NR-U) network operating over an unlicensed frequency band. In such an aspect, the BSs 105 and the UEs 115 may be operated by multiple network operating entities. To avoid collisions, the BSs 105 and the UEs 115 may employ a listen-before-talk (LBT) procedure to monitor for transmission opportunities (TXOPs) in the shared channel. For example, a transmitting node (e.g., a BS 105 or a UE 115) may perform an LBT prior to transmitting in the channel. When the LBT passes, the transmitting node may proceed with the transmission. When the LBT fails, the transmitting node may refrain from transmitting in the channel. In an example, the LBT may be based on energy detection. For example, the LBT results in a pass when signal energy measured from the channel is below a threshold. Conversely, the LBT results in a failure when signal energy measured from the channel exceeds the threshold. In another example, the LBT may be based on signal detection. For example, the LBT results in a pass when a channel reservation signal (e.g., a predetermined preamble signal) is not detected in the channel. A TXOP may also be referred to as channel occupancy time (COT) .

In some aspects, the network 100 may provision for sidelink communications to allow a UE 115 to communicate with another UE 115 without tunneling through a BS 105 and/or the core network. The BS 105 may configure certain resources in a licensed band and/or an unlicensed band for sidelink communications between the UE 115 and the other UE 115. A UE 115 may transmit, during sidelink communications, physical sidelink shared channel (PSSCH) data, physical sidelink shared control channel (PSCCH) sidelink control information (SCI) , sidelink COT sharing SCI, sidelink scheduling SCI, and/or physical sidelink feedback channel (PSFCH) ACK/NACK feedbacks (e.g., HARQ for sidelink) to another UE and/or receive PSSCH data, PSCCH SCI, sidelink COT sharing SCI, sidelink scheduling SCI, and/or PSFCH ACK/NACK feedbacks from another UE 115.

In addition to, or as an alternative to, the aspects of communication described above, a UE 115 may operate (or seek to operate) in dual connectivity NSA mode. For example, the UE 115 may use one of the LTE BS 105 (e.g., LTE BS 105a) for control plane packet transmission, and the 5G BS 105 for data plane packet transmission. The UE may determine that LTE BS 105b has superior signal quality compared to the serving LTE BS 105a and may request a UE handover to LTE BS 105b. After handover, however, the LTE BS 105b may remove the default EPS bearer of the connection between the UE 115 and the LTE BS 105b. According to aspects of the present disclosure, the UE 115 may add LTE BS 105b to a barred cell list (e.g., by adding an identifier of LTE BS 105b) . The UE 115 may add LTE BS 105b to the barred cell list either after transmitting one or more PDN connectivity requests to LTE BS 105b and not receiving any response before a timer (e.g., T3482 timer) expires or without sending any PDN connectivity request to LTE BS 105b.

Once LTE BS 105b is added to the barred cell list, the UE 115 may not attempt to establish NSA service using the barred cell again until a predetermined amount of time has elapsed. Instead, the UE 115 may seek to attach to a different LTE BS 105 (e.g., LTE BS 105c) and attempt to establish NSA service with this new LTE BS 105. In some cases, this new LTE BS may have priority over the initial LTE cell that undertook the UE handover process (i.e., LTE BS 105a) . In such cases, once LTE BS 105b is added to the barred cell list, the UE 115 may attempt to establish a connection with the higher priority LTE cell (i.e., LTE BS 105c) instead of or prior to attempting to establish connection with the LTE cell (i.e., LTE BS 105a) that handed over the UE 115 to the barred LTE BS. If the new LTE BS 105c functions correctly (i.e., it does not remove the default bearer of the connection between itself and the UE 115) , then the UE 115 can continue to use this new LTE BS 105c in the process of establishing an active EPS bearer that can facilitate the UE 115 communicating data plane packets via a 5G BS 105’s cell.

An example of dual connectivity (e.g., NSA) operation according to aspects of the present disclosure is illustrated with respect to the network 200 in FIG. 2. UE 202 may be an example of a UE 115 which is able to operate in NSA mode. The UE 200 may support NSA mode operation by supporting dual connectivity, i.e., the UE 200 includes the capability to connect to multiple radio access technologies (RATs) at the same time. For example, the UE 200 can include a single transceiver implementing multiple RATs and/or various components, where different combinations of components can implement different RATs. As illustrated in FIG. 2, the

BSs

204 and 208 are examples of LTE BSs 105. BS 206 is an example of a 5G BS 105.

The UE 202 may be in wireless communication via wireless connection 210 with the LTE BS 204. When UE 202 attaches to LTE BS 204, it may indicate that it is capable of using dual connectivity in order to communicate (e.g., via a dual connectivity bit or bits in an attach request/tracking area update request message) . After UE 202 attaches to LTE BS 204, the UE 202 may send a service request (e.g., an RRC service connection establishment request) to the LTE BS 204 via the wireless connection 210. Under normal operation the UE 202 would activate an EPS bearer on the 5G BS 206 via the LTE BS 204. For example, once the LTE BS 204 receives the service request, the LTE BS 204 may check the EPC 210 (e.g., via a connection 216 with the EPC 210, where the connection 216 may be, for example, an S1 interface) to determine if the UE 202 is authorized for dual connectivity with the LTE and 5G networks. If authorized, the LTE BS 204 may communicate with the 5G BS 206 via the link 212 (e.g., a wired and/or wireless link such as an X2 interface) . With the active EPS bearer, the UE 202 may use the LTE BS 204 (via wireless connection 210) for control plane communication, and the 5G BS 206 (via wireless connection 212) for data plane communication (e.g., using the most of the same, or all of the same, EPC 210 by connection 218, which may be for example the S1-U interface) .

In some cases, the UE 202 may discover that the signal quality of a neighboring LTE BS (e.g., LTE BS 208) may be superior the signal quality of the serving LTE BS 204, and may send a service request to the serving LTE BS 204 for a UE handover to LTE BS 208. The service request may include measurement reports including information about the signal qualities of LTE BS 204 and LTE BS 208. After the handover of the UE 202 to LTE BS 208, however, the UE 202 may discover that the connection between the UE 202 and LTE BS 208 is defective in that the LTE BS 208 has removed the default EPS bearer between UE 202 and LTE BS 208. For example, LTE BS 208 may transmit a connection reconfiguration message (e.g., an RRC connection reconfiguration message) to the UE 202 that lists the EPS bearers available between UE 202 and LTE BS 208 while excluding the default EPS bearer from the list. This network issue can prevent the UE 202 from not only accessing PS data via LTE BS 208 (by sending PDN connectivity requests) but also from completing active EPS bearer establishment with the 5G BS 206, and thus from transferring any data via the 5G BS 206 in NSA mode. According to aspects of the present disclosure, when the UE 202 discovers the removal of the default EPS bearer by the LTE BS 208 (e.g., from the RRC message) , the UE 202 may add LTE BS 204 to a barred cell list at the UE 202. This may be after failed PDN connectivity attempt or without transmitting any PDN connectivity requests to LTE BS 208) . Adding the LTE BS 204 to the barred cell list may involve the UE 202 adding an identifier of the LTE BS 204 to the barred cell list.

Once LTE BS 204 is on the barred cell list, UE 202 may attempt to communicate via another LTE BS where already attached (e.g., where both LTE BS have the same tracking area code (TAC) and a default bearer can be set up) , or seek to attach to another LTE BS (e.g., where the LTE BSs have different TACs from each other) in order to establish dual connectivity. Once attached to the third LTE BS (not shown) , UE 202 may send the service request to the third LTE BS via wireless connection (not shown) in order to attempt to set up an active EPS bearer with the 5G BS 206 via the third LTE BS (in view of, for example, the 5G BS 206 communicating with the third LTE BS via another wired and/or wireless connection which may be, for example, an X2 interface as well) . The third LTE BS may check the EPC 210 (e.g., via a connection (not shown) with the EPC 210, where the connection 220 may also be, for example, an S1 interface) to determine if the UE 202 is authorized for dual connectivity with the LTE and 5G networks. If authorized, the third LTE BS may communicate with the 5G BS 206 via a wired and/or wireless link (not shown) such as an X2 interface. UE 202 may also access PS data via the third LTE BS (e.g., by transmitting PDN connectivity requests) .

With the active EPS bearer, the UE 202 may use the third LTE BS (via wireless connection 210) for control plane communication, and the 5G BS 206 (via wireless connection 212) for data plane communication (e.g., using the most of the same, or all of the same, EPC 210 by connection 218, which may be for example the S1-U interface) . With the active EPS bearer set up for the 5G BS 206 via the third LTE BS, the UE 202 may communicate in NSA mode using the combination of the 5G BS 206 and the third LTE BS. After a predetermined time elapses (e.g., from the time of adding LTE BS 204 to the barred cell list) , UE 202 may remove LTE BS 204 from the barred cell list. At that point, UE 202 may again attempt to establish NSA mode communication using LTE BS 204 as appropriate/needed.

FIG. 3 is a block diagram of an exemplary UE 300 according to some aspects of the present disclosure. The UE 300 may be a UE 115 discussed above in FIG. 1, and/or a UE 202 as discussed above in FIG. 2. As shown, the UE 300 may include a processor 302, a memory 304, an NSA mode recovery module 308, a transceiver 310 including a modem subsystem 312 and a radio frequency (RF) unit 314, and one or more antennas 316. These elements may be in direct or indirect communication with each other, for example via one or more buses.

The processor 302 may include a central processing unit (CPU) , a digital signal processor (DSP) , an application specific integrated circuit (ASIC) , a controller, a field programmable gate array (FPGA) device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor 302 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 memory 304 may include a cache memory (e.g., a cache memory of the processor 302) , random access memory (RAM) , magnetoresistive RAM (MRAM) , read-only memory (ROM) , programmable read-only memory (PROM) , erasable programmable read only memory (EPROM) , electrically erasable programmable read only memory (EEPROM) , flash memory, solid state memory device, hard disk drives, other forms of volatile and non-volatile memory, or a combination of different types of memory. In an aspect, the memory 304 includes a non-transitory computer-readable medium. The memory 304 may store, or have recorded thereon, instructions 306. The instructions 306 may include instructions that, when executed by the processor 302, cause the processor 302 to perform the operations described herein with reference to the UEs 115 in connection with aspects of the present disclosure, for example, aspects of FIGS. 5-6. Instructions 306 may also be referred to as program code. The program code may be for causing a wireless communication device to perform these operations, for example by causing one or more processors (such as processor 302) to control or command the wireless communication device to do so. The terms “instructions” and “code” should be interpreted broadly to include any type of computer-readable statement (s) . For example, the terms “instructions” and “code” may refer to one or more programs, routines, sub-routines, functions, procedures, etc. “Instructions” and “code” may include a single computer-readable statement or many computer-readable statements.

The PDN connectivity recovery module 308 may be implemented via hardware, software, or combinations thereof. For example, the PDN connectivity recovery module 308 may be implemented as a processor, circuit, and/or instructions 306 stored in the memory 304 and executed by the processor 302. In some instances, the PDN connectivity recovery module 308 can be integrated within the modem subsystem 312. Moreover, the PDN connectivity recovery module 308 can be implemented by a combination of software components (e.g., executed by a DSP or a general processor) and hardware components (e.g., logic gates and circuitry) within the modem subsystem 312 alone or in combination with, or solely by, an application processor such as processor 302.

The PDN connectivity recovery module 308 may be used for various aspects of the present disclosure, for example, aspects of FIGS. 1-2 and 5-6. For example, the PDN connectivity recovery module 308 is configured to determine when a connection established between a UE 300 and an LTE BS 105 after the handover of the UE 300 to the LTE BS 105 by another neighboring LTE BS 105 is missing a default EPS bearer. For example, upon receiving a connection reconfiguration message from LTE BS 105 after the establishment of a connection between UE 300 and LTE BS 105 following handover of the UE 300 to LTE BS 105, the PDN connectivity recovery module 308 may determine whether the default EPS bearer of the connection between the UE 300 to LTE BS 105 has been removed (e.g., by the LTE BS 105) . In such cases, the PDN connectivity recovery module 308 may add the LTE BS 105 to a barred cell list (e.g., by adding an identifier of the LTE BS 105) maintained by the PDN connectivity recovery module 308 (and, e.g., stored in memory 304) . In some cases, UE 300 may send PDN connectivity requests to LTE BS 105 instead of immediately adding LTE BS 105 to the barred list, and in such instances, the PDN connectivity recovery module 308 may keep track via a counter (e.g., stored in memory 304 or some other storage) to determine if the LTE BS 105 has responded to the PDN connectivity requests. If the counter expires without a response from LTE BS 105, the PDN connectivity recovery module 308 may then proceed with adding the LTE BS 105 to the barred cell list. The counter can be a T3482 timer, and the PDN connectivity recovery module 308 can wait for the expiration of the timer (e.g., one of the first expiration, the second expiration, the third expiration, the fourth expiration or the fifth expiration of the T3482 timer) before adding the LTE BS 105 to the barred cell list. The barred cell list may be a dynamic list maintained by the UE of any LTE cells that are not functioning properly (e.g., LTE cells that have removed the default EPS bearer of their connections with the UE 300) . Once the LTE BS 105 is added to the barred cell list, the PDN connectivity recovery module 308 may cause the UE 300 to stop attempting to establish connection with the LTE BS 105 again until a predetermined amount of time has elapsed.

Instead, with the LTE BS 105 added to the barred cell list, the PDN connectivity recovery module 308 may cause the UE 300 to seek to attach to a different LTE BS 105 and attempt to establish the active EPS bearer with a 5G BS 105 via the different LTE BS 105 (by sending a service request to the different LTE BS 105, for example) . If the new LTE BS 105 functions correctly (e.g., the default EPS bearer is not removed by the new LTE BS 105) , then the UE 300 can continue to use this new LTE BS 105 in the process of establishing an active EPS bearer with the 5G BS 105. Further, the UE 300 can also use the LTE BS 105 to access PS data (e.g., by transmitting PDN connectivity requests to the new LTE BS 105) .

The PDN connectivity recovery module 308 may track the amount of time that the LTE BS 105 has been in the barred cell list. Once the predetermined amount of time has elapsed (and, in some aspects, independent from whether the UE 300 succeeds with connecting with the new LTE BS 105) , the PDN connectivity recovery module 308 may remove the barred LTE BS 105 from the barred cell list. As a result, the UE 300 may be free to attempt (if needed) to access PS data through the removed LTE BS 105 or to establish NSA service by attaching to the removed LTE BS 105 again and sending a service request to begin the process again.

As shown, the transceiver 310 may include the modem subsystem 312 and the RF unit 314. The transceiver 310 can be configured to communicate bi-directionally with other devices, such as the BSs 105 and other UEs 115. The modem subsystem 312 may be configured to modulate and/or encode the data from the memory 304 and/or the NSA mode recovery module 308 (whether implemented by the processor 302 or otherwise) according to a modulation and coding scheme (MCS) , e.g., a low-density parity check (LDPC) coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc.

The RF unit 314 may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc. ) modulated/encoded data from the modem subsystem 312 (on outbound transmissions) or of transmissions originating from another source such as a UE 115 or a BS 105. The RF unit 314 may be further configured to perform analog beamforming in conjunction with the digital beamforming. Although shown as integrated together in transceiver 310, the modem subsystem 312 and the RF unit 314 may be separate devices that are coupled together at the UE 115 to enable the UE 115 to communicate with other devices.

The RF unit 314 may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information) , to the antennas 316 for transmission to one or more other devices. The antennas 316 may further receive data messages transmitted from other devices. The antennas 316 may provide the received data messages for processing and/or demodulation at the transceiver 310. The antennas 316 may include multiple antennas of similar or different designs in order to sustain multiple transmission links. The RF unit 314 may configure the antennas 316.

In an aspect, the UE 300 can include multiple transceivers 310 implementing different RATs (e.g., 5G NR and LTE) . In an aspect, the UE 300 can include a single transceiver 310 implementing multiple RATs (e.g., 5G NR and LTE) . In an aspect, the transceiver 310 can include various components, where different combinations of components can implement different RATs.

FIG. 4 is a block diagram of an exemplary BS 400 according to some aspects of the present disclosure. The BS 400 may be a BS 105 in the network 100 as discussed above in FIG. 1, a LTE BS 204/208 or 5G BS 206 as discussed above in FIG. 2. A shown, the BS 400 may include a processor 402, a memory 404, a transceiver 408 including a modem subsystem 412 and a RF unit 414, and one or more antennas 416. These elements may be in direct or indirect communication with each other, for example via one or more buses.

The processor 402 may have various features as a specific-type processor. For example, these may include a CPU, a DSP, an ASIC, a controller, a FPGA device, another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor 402 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 memory 404 may include a cache memory (e.g., a cache memory of the processor 402) , RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, a solid-state memory device, one or more hard disk drives, memristor-based arrays, other forms of volatile and non-volatile memory, or a combination of different types of memory. In some aspects, the memory 404 may include a non-transitory computer-readable medium. The memory 404 may store instructions 406. The instructions 406 may include instructions that, when executed by the processor 402, cause the processor 402 to perform operations described herein. Instructions 406 may also be referred to as code, which may be interpreted broadly to include any type of computer-readable statement (s) as discussed above with respect to FIG. 3.

As shown, the transceiver 408 may include the modem subsystem 412 and the RF unit 414. The transceiver 408 can be configured to communicate bi-directionally with other devices, such as the UEs 115 and/or 300 and/or another core network element. The modem subsystem 412 may be configured to modulate and/or encode data according to a MCS, e.g., a LDPC coding scheme, a turbo coding scheme, a convolutional coding scheme, a digital beamforming scheme, etc. The modem subsystem 412 may include storage (e.g., memory 404) to store antenna configuration information. The RF unit 414 may be configured to process (e.g., perform analog to digital conversion or digital to analog conversion, etc. ) modulated/encoded data from the modem subsystem 412 (on outbound transmissions) or of transmissions originating from another source such as a UE 115 and/or UE 300. The RF unit 414 may be further configured to perform analog beamforming in conjunction with the digital beamforming, for example after processing a codeword including channel state information (with its dimensionality reduced using the neural network at the transmitting side) to estimate the channel. Although shown as integrated together in transceiver 408, the modem subsystem 412 and/or the RF unit 414 may be separate devices that are coupled together at the BS 400 to enable the BS 400 to communicate with other devices.

The RF unit 414 may provide the modulated and/or processed data, e.g. data packets (or, more generally, data messages that may contain one or more data packets and other information) , to the antennas 416 for transmission to one or more other devices. The antennas 416 may further receive data messages transmitted from other devices and provide the received data messages for processing and/or demodulation at the transceiver 408. The antennas 416 may include multiple antennas of similar or different designs in order to sustain multiple transmission links. In an aspect, the BS 400 can include multiple transceivers 408 implementing different RATs (e.g., NR and LTE) . In an aspect, the BS 400 can include a single transceiver 408 implementing multiple RATs (e.g., NR and LTE) . In an aspect, the transceiver 408 can include various components, where different combinations of components can implement different RATs.

According to aspects of the present disclosure, BS 400 may be an example of an LTE BS 204 that supports NSA mode operation for a UE 300 capable of dual connectivity. When a UE 300 attaches to BS 400 (when an LTE BS 204) and sends a service request to the BS 400, the BS 400 may operate to establish an active EPS bearer between the UE 300 and a 5G BS 206 (which BS 400 may also or alternatively be an example of) . For example, the LTE BS 400 may check with the EPC 210 to check if the UE 300 is authorized for NSA mode operation. If so, the LTE BS 400 may communicate with a 5G BS 400 to activate an EPS bearer on the 5G BS 400. With the active EPS bearer, the UE 300 may use the LTE BS 400 for control plane communication, and the 5G BS 400 for data plane communication.

Turning now to FIG. 5, illustrated is a protocol diagram of a scheme 500 for responding to a removal of an EPS bearer during handover of a device, according to some aspects of the present disclosure. Communication may be between a UE 502, an LTE BS 504, an LTE BS 506, and/or an LTE BS 508. For example, the UE 502 may be an example of a UE 115/202/300, and each of LTE BS 504, LTE BS 506 or LTE BS 508 may be an example of a BS 105/LTE BS 204 or LTE BS 208, or BS 400.

At action 510, the UE 502 and the LTE BS 504 establish connection with each other by activating a default EPS bearer context, and optionally one or more dedicated EPS bearers. The UE 502 may, according to aspects of the present disclosure, also signal to the LTE BS 504 that it is able to utilize NSA mode (e.g., as part of the initial establishment of connection) . LTE BS 504 may be configured to support NSA mode operation for a UE 502 that is NR ready and capable of dual connectivity.

At action 512, the UE 502 transmits a service request to the LTE BS 504. The service request may include, for example, a measurement report on the signal quality of LTE BS 504 and a request for handover of the UE 52 to a neighboring LTE BS (e.g., LTE BS 506) .

At action 514, in response to receiving the service request from UE 502, the LTE BS 504 transfers its connection with UE 502 to LTE BS 506 (i.e., a handover process connecting UE 502 to LTE BS 506 may be executed by LTE BS 504) . LTE BS 506 may be configured to support NSA mode operation.

At action 516, the LTE BS 504 responds to the service request by transmitting a service request response to UE 502 (e.g., an RRC Connection Reconfiguration message) .

At action 518, after the handover of UE 502 to LTE BS 506, the default EPS bearer of the connection between UE 502 and LTE BS 506 is removed. For example, the LTE BS 506 may remove or cause the removal of the default EPS bearer.

At action 520, the LTE BS 506 transmits, in response to the handover of UE 502 to LTE BS 506, a message including information about the removed default EPS bearer to UE 502 (e.g., an RRC Connection Reconfiguration message) .

In some aspects of the present disclosure, the UE 502 does not execute action 522 and action 524, instead proceeding to action 526 after action 520, while in other aspects, the UE 502 executes action 522 and action 524 prior to proceeding to action 528. This is illustrated in dashed lines in FIG. 5.At action 522, in response to receiving the message from LTE BS 506 with the information about the removed default EPS bearer, the UE 502 may generate and transmit to LTE BS 506 a PDN connectivity request and set a timer to track the time since the PDN connectivity request was transmitted. In some instances, the timer can be the so-called T3482 timer which expires every eight (8) seconds, after which the PDN connectivity request is retransmitted to the LTE BS 506, before no more PDN connectivity request could be retransmitted after the fifth expiration. At action 524, the UE may make the determination that no response would be received from LTE BS 506 to the UE’s PDN connectivity request after expiration of the timer. For example, in some implementations, the UE 502 may wait until the fifth expiration of the T3482 timer before making the determination that no response would be received from LTE BS 506 to the UE’s PDN connectivity request. In some implementations, the UE 502 may wait only until the first expiration, only until the second expiration, only until the third expiration or only until the fourth expiration of the T3482 timer before making the determination that no response would be received from LTE BS 506 to the UE’s PDN connectivity request. After making such determination, the UE 502 may then proceed to action 526.

At action 526, the UE 502 adds an identification of the LTE BS 506 to a barred cell list. As discussed above, this action could occur after action 520 (i.e., without executing action 522 and action 524) . That is, the UE 502 may detect or determine that the default EPS bearer has been removed from the connection between UE 502 and LTE BS 506, and the UE 52 may add the identification of the LTE BS 506 to the barred cell list in response to the detection or determination. For example, the UE 502 may determine that the default EPS bearer has been removed based on an RRC Connection Reconfiguration message sent by LTE BS 506 at action 506. Action 526 may also occur after the execution of

action

522 and 524. In such cases, the UE 502 may add the identification of the LTE BS 506 to the barred cell list after determining that that no response would be received from LTE BS 506 to the UE’s PDN connectivity request, as discussed with reference to Action 524. The identification of the LTE BS 506 may be provided to the UE 502 by the LTE BS 506 (e.g., as part of the RRC Connection Reconfiguration message) or may be an identifier generated by the UE 502 that may be mapped to an identifier used by the LTE BS 506 in communication with the UE 502, for example.

At action 528, the UE 502 starts a timer in response to adding the LTE BS 506 to the barred cell list at action 522. This timer may be used to keep track of and limit how long the LTE BS 506 has been on the list. For example, the LTE BS 506 may be removed from the barred cell list by the UE 502 after the timer expires.

At action 530, after the LTE BS 506 is on the barred cell list, the UE 502 searches for another LTE BS to communicate with and select LTE BS 508 as a result. LTE BS 508 may be configured to support NSA mode operation and may have priority over LTE BS 504. That is, after the handover of UE 502 by LTE BS 504, UE 502 may choose to attempt to connect to LTE BS 508 before attempting to do the same with LTE BS 504. In some cases, the LTE BS 502 that performed the handover operation may have priority over other base stations (e.g., because signal quality of LTE BS 504 exceeds that of other base stations such as LTE BS 508) . In such cases, UE 502 may choose to attempt to connect to LTE BS 508 before attempting to so the same with LTE BS 508.

At action 532, the UE 502 transmits a PDN connectivity request to the LTE BS 508. Instead of, or in addition to, transmitting a PDN connectivity request to the LTE BS 508, the UE 502 can also transmit a PDN connectivity request to the LTE BS 504.

At action 530, the UE 502 and the LTE BS 508 may establish communication with each other via the activation of a default EPS bearer context.

By connecting with an alternate BS that is configured to support NSA mode operation when an initial connection with another BS fails after a device handover (e.g., the removal of a default EPS bearer connecting UE 502 to LTE BS 506 after the handover of UE 502 from LTE BS 504 to LTE BS 506) , this allows the UE 502 to still take advantage of the benefits of NSA mode operation, including the increased speeds of 5G data transfer. Having this switch occur automatically increases the reliability of the network.

FIG. 6 illustrates a flow diagram of a wireless communication method 600 according to some aspects of the present disclosure. Aspects of the method 600 may be executed by a wireless communication device, such as the UEs 115, 202, 300, and/or UE 502 utilizing one or more components, such as the processor 302, the memory 304, the PDN Connectivity Restorative Module 308, the transceiver 310, the modem 312, the one or more antennas 316, and various combinations thereof. As illustrated, the method 600 includes a number of enumerated steps, but aspects of the method 600 may include additional steps before, during, after, and in between the enumerated steps. For example, in some instances one or more aspects of protocol diagram 500 may be implemented as part of method 600. Further, in some aspects, one or more of the enumerated steps may be omitted or performed in a different order.

At block 602, a UE that is capable of operating in an NSA mode establishes connection with a first LTE BS that is configured to support NSA mode operation, for example as discussed above with respect to action 510 of FIG. 5. The connection may be established via the activation of one or more EPS bearers, including a default EPS bearer, between the UE and the first LTE BS.

At block 604, the UE sends a service request to the first LTE BS via an EPS bearer, for example as discussed above with respect to action 512 of FIG. 5. This service request may be an RRC message including a measurement report and a request for a device handover of the UE to a neighboring LTE BS that the UE has identified as having better quality signals. The measurement report may include results of signal quality measurements of the first LTE BS and the neighboring LTE BS performed by the UE. The UE may send the measurement report to its serving cell (i.e., the first LTE BS) in response to an event (e.g., when the signal quality of the first LTE BS exceeds a threshold signal quality measure) or periodically.

In response to receiving the service request, the first LTE BS may handover the UE to the neighboring LTE BS (i.e., a second LTE BS) that the UE has identified as having better signal quality. Further, the first LTE BE may generate and send an RRC message to the UE about the handover of the UE to the second LTE BS. The RRC message can be, for example, an RRC Connection Reconfiguration message indicating that the one or more EPS bearers connecting the UE to the first LTE BS have been modified to connect the UE to the second LTE BS.

At block 606, in response to the handover of the UE to the second LTE BS, the second LTE BS may generate and send to the UE a message (e.g., an RRC Connection Reconfiguration message) listing the available EPS bearers connecting the UE to the second LTE BS. In some cases, the available EPS bearers between the UE and the second LTE BS may not include the default EPS bearer. That is, the second LTE BS may remove or cause the removal of the default EPS bearer from the one or more EPS bearers that connect the UE to the second LTE BS. In some instances, the second LTE BS may also remove or cause the removal of dedicated EPS bearers from the one or more EPS bearers connecting the UE to the second LTE BS. In other words, compared to the one or more EPS bearers that connected the UE to the first LTE BS, the one or more EPS bearers modified to connect the UE to the second LTE BS may be missing the default EPS bearer, and in some instances additional (i.e., dedicated) EPS bearers. With the removal of the default EPS bearer, the UE may become unable to recover data from the second LTE BS via a PDN connectivity request.

In some aspects of the present disclosure, the wireless communication method 600 may not include the steps in block 608 and block 610, instead proceeding to block 612 after block 606, while in other aspects, the wireless communication method 600 may include the steps in block 608 and block 610 prior to proceeding to block 612. This is similar to the discussion above with reference to action 522 and action 524 in FIG. 5 and is illustrated in FIG. 6 in dashed lines. At block 608, in response to receiving the message from the second LTE BS with the information about the removed default EPS bearer, the UE may generate and transmit to the second LTE BS a PDN connectivity request and set a timer to track the time since the PDN connectivity request was transmitted. In some instances, the timer can be the so-called T3482 timer which expires every eight (8) seconds, after which the PDN connectivity request is re-transmitted to the second LTE BS, before no more PDN connectivity request could be re-transmitted after the fifth expiration. At action 524, the UE may make the determination that no response would be received from the second LTE BS to the UE’s PDN connectivity request after expiration of the timer. For example, in some implementations, the UE may wait until the fifth expiration of the T3482 timer before making the determination that no response would be received from the second LTE BS to the UE’s PDN connectivity request. In some implementations, the UE may wait only until the first expiration, only until the second expiration, only until the third expiration or only until the fourth expiration of the T3482 timer before making the determination that no response would be received from the second LTE BS to the UE’s PDN connectivity request. After making such determination, the UE may then proceed to execute the method step at block 612.

At block 612, the UE adds the second LTE BS to a barred cell list configured to include a list of LTE base stations to which the UE is barred from connecting (e.g., by adding an identifier of the second LTE BS into the barred cell list) . As discussed above, block 612 of the wireless communications method 600 may occur after block 606 (i.e., without execution of the method steps in block 608 and block 610) . In other words, the UE adds the second LTE BS to the barred cell list in response to receiving the message from the second LTE BS indicating the removal of the default EPS bearer (and in some cases, additional dedicated EPS bearers) between the UE and the second LTE BS. Block 612 can also occur after block 610, in which case the UE adds the second LTE BS to the barred cell list in response making the afore-mentioned determination no response is forthcoming from the second LTE BS in response to the PDN connectivity request from the UE. The UE may add and remove LTE base stations from the barred cell list in response to triggering events as discussed herein. The barred cell list may be visible to the user of the first device, or may be hidden. In some aspects, a user may be able to override the barred cell list, while in others they may not.

In some implementations, the UE may also start a barred cell timer for the second LTE BS to keep track of the amount of time that the second LTE BS remains in the barred cell list. The UE may remove the second LTE BS from the list of the barred cell list after the expiration of the timer or after a threshold duration has passed since the start of the timer. The time that a LTE BS remains on the barred cell list may be configurable by the user of the UE and/or some other party. For example, the timer may be on the order of minutes, hours, or some other time period. Once the second LTE BS has been removed from the list, the UE can send a PDN connectivity request to the second LTE BS to establish connection with the second LTE BS (e.g., establish NSA mode communications) .

Multiple timers may be running simultaneously each associated with a LTE BS in the list. Alternatively, a single timer may be used to keep track of a global time, and a timestamp is kept for each barred LTE BS indicating the time when that LTE BS was added to the barred cell list. As yet another alternative, in addition to or instead of having a timer to keep track of the amount of time a barred LTE BS is included in the list, the barred LTE BS may be removed from the list in response to another barred LTE BS being added to the list. In yet another alternative, a barred device may be removed from the list in response to a notification that a network associated with the barred device has been repaired or otherwise updated.

At block 614, after placing the second LTE BS in the barred cell list, the UE searches for a new LTE BS to which to form a connection, identify a third LTE BS as a candidate for such an LTE BS and transmit a PDN connectivity request to the third LTE BS to request for the connection. In some cases, the third LTE BS can be different from the first LTE BS (e.g., the third LTE BS may have higher priority than the first LTE BS case as the third LTE BS may have better signal quality than the first LTE BS case) . In yet other cases, the third LTE BS can be the same as the first LTE BS. In other words, the UE may return to the LTE BS that performed the handover operation after placing the second LTE BS in the barred cell list. Following the transmission of the PDN connectivity request, the UE and the third LTE BS may establish communication with each other via the activation of a default EPS bearer context. For example, after receiving the PDN connectivity request, the third LTE BS may transmit a request to activate a default EPS bearer context request and the UE may transmit an acceptance of the request, resulting in the establishment of the connection between the UE and third LTE BS as a result of the activation of the default EPS bearer. The request and/or the acceptance can be in the form of RRC messages.

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.

The various illustrative blocks and modules described in connection with the disclosure 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, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration) .

The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer- readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described above can be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations. Also, as used herein, including in the claims, “or” as used in a list of items (for example, a list of items prefaced by a phrase such as “at least one of” or “one or more of” ) indicates an inclusive list such that, for example, a list of [at least one of A, B, or C] means A or B or C or AB or AC or BC or ABC (i.e., A and B and C) .

As those of some skill in this art will by now appreciate and depending on the particular application at hand, many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the devices of the present disclosure without departing from the spirit and scope thereof. In light of this, the scope of the present disclosure should not be limited to that of the particular aspects or embodiments illustrated and described herein, as they are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.

Claims

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

transmitting, to a first LTE base station (BS) , a service request via a plurality of evolved packet system (EPS) bearers;

receiving, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS;

adding the second LTE BS to a barred cell list based on the received message indicating that the EPS bearer is removed; and

transmitting a pocket data network (PDN) connectivity request to a third LTE BS in response to adding the second LTE BS to the barred cell list.
The method of claim 1, further comprising:

removing the second LTE BS from the barred cell list after a timer expires.
The method of claim 2, further comprising:

starting the timer in response to adding the second LTE BS to the barred cell list.
The method of claim 1, wherein one or more of the first LTE BS, the second LTE BS, or the third LTE BS are configured to support a non-standalone mode.
The method of claim 1, wherein the UE is configured to operate in a non-standalone mode.
The method of claim 1, wherein the message is a Radio Resource Control connection reconfiguration message excluding the removed EPS bearer from a list of active EPS bearers between the UE and the second LTE BS.
The method of claim 1, wherein the removed EPS bearer is a default EPS bearer of the plurality of EPS bearers.
The method of claim 1, further comprising:

determining the third LTE BS has priority over the first LTE BS prior to transmitting the PDN connectivity request to the third LTE BS.
The method of claim 1, wherein the third LTE BS is same as the first LTE BS.
A method of wireless communication performed by a user equipment (UE) , the method comprising:

transmitting, to a first LTE base station (BS) , a service request via a plurality of evolved packet system (EPS) bearers;

receiving, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS;

transmitting, to the second LTE BS, a first pocket data network (PDN) connectivity request in response to receiving the message indicating that the EPS bearer is removed;

adding the second LTE BS to a barred cell list in response to an expiration of a timer without the UE connecting to the second LTE BS; and

transmitting, to a third LTE BS, a second PDN connectivity request in response to the second LTE BS being added to the barred cell list.
The method of claim 10, wherein the timer is a T3482 timer.
The method of claim 10, wherein the expiration of the timer is one of a first expiration, a second expiration, a third expiration, a fourth expiration, or a fifth expiration of the timer after the transmitting of the second PDN connectivity request.
The method of claim 10, wherein the timer is a first timer, the method further comprising:

removing, by the UE, the second LTE BS from the barred cell list after a second timer expires.
The method of claim 13, further comprising:

starting the second timer in response to the second LTE BS being added to the barred cell list.
The method of claim 10, wherein one or more of the first LTE BS, the second LTE BS, or the third LTE BS are configured to support a non-standalone mode.
The method of claim 10, wherein the UE is configured to operate in non-standalone mode.
The method of claim 10, wherein the message is a Radio Resource Control connection reconfiguration message excluding the removed EPS bearer from a list of active EPS bearers between the UE and the second LTE BS.
The method of claim 10, wherein the removed EPS bearer is a default EPS bearer of the plurality of EPS bearers.
The method of claim 10, further comprising:

determining the third LTE BS has priority over the first LTE BS prior to transmitting the PDN connectivity request to the third LTE BS.
The method of claim 10, wherein the third LTE BS is same as the first LTE BS.
A User Equipment (UE) , comprising:

a transceiver configured to:

transmit a service request to a first base station (BS) via a plurality of evolved packet system (EPS) bearers; and

receive, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS; and

a processor configured to add the second LTE BS to a barred cell list based on the received message indicating that the EPS bearer is removed,

the transceiver further configured to transmit a pocket data network (PDN) connectivity request to a third LTE BS in response to the second LTE BS being added to the barred cell list.
The UE of claim 21, wherein the processor is further configured to remove the second LTE BS from the barred cell list after a timer expires.
The UE of claim 22, wherein

the processor is further configured to start the timer in response to adding the second LTE BS to the barred cell list.
The UE of claim 21, wherein one or more of the first LTE BS, the second LTE BS or the third LTE BS are configured to support a non-standalone mode.
The UE of claim 21, wherein the UE is configured to operate in a non-standalone mode.
The UE of claim 21, wherein the message is a Radio Resource Control connection reconfiguration message excluding the removed EPS bearer from a list of active EPS bearers between the UE and the second LTE BS.
The UE of claim 21, wherein the removed EPS bearer is the default EPS bearer of the plurality of EPS bearers.
The UE of claim 21, wherein the processor is further configured to determine that the third LTE BS has priority over the first LTE BS prior to transmitting the PDN connectivity request to the third LTE BS.
The UE of claim 21, wherein the third LTE BS is same as the first LTE BS.
A User Equipment (UE) , comprising:

a transceiver configured to:

transmit a service request to a first LTE base station (BS) via a plurality of evolved packet system (EPS) bearers;

receive, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS; and

transmit a first pocket data network (PDN) connectivity request to connect to the second LTE BS in response to receiving the message indicating that the EPS bearer is removed; and

a processor configured to add the second LTE BS to a barred cell list in response to an expiration of a timer without the UE connecting to the second LTE BS,

the transceiver further configured to transmit a second PDN connectivity request to connect to a third LTE BS in response to the second LTE BS being added to the barred cell list.
The UE of claim 30, wherein the timer is a T3482 timer.
The UE of claim 30, wherein the expiration of the timer is one of a first expiration, a second expiration, a third expiration, a fourth expiration or a fifth expiration of the timer after the second PDN connectivity request is transmitted to the second LTE BS.
The UE of claim 30, wherein the timer is a first timer, the processor further configured to remove the second LTE BS from the barred cell list after a second timer expires.
The UE of claim 33, wherein the processor is configured to start the second timer in response to the second LTE BS being added to the barred cell list.
The UE of claim 30, wherein one or more of the first LTE BS, the second LTE BS or the third LTE BS are configured to support a non-standalone mode.
The UE of claim 30, wherein the UE is configured to operate in a non-standalone mode.
The UE of claim 30, wherein the message is a Radio Resource Control connection reconfiguration message excluding the removed EPS bearer from a list of active EPS bearers between the UE and the second LTE BS.
The UE of claim 30, wherein the removed EPS bearer is the default EPS bearer of the plurality of EPS bearers.
The UE of claim 30, wherein the processor is configured to transmit the second PDN connectivity request to the third LTE BS occurs after determining that the third LTE BS has priority over the first LTE BS.
The UE of claim 30, wherein the third LTE BS is same as the first LTE BS.
A non-transitory computer-readable medium (CRM) having program code recorded thereon, the program code comprising:

code for causing a user equipment (UE) to transmit a service request to a first LTE base station (BS) via a plurality of evolved packet system (EPS) bearers;

code for causing the UE to receive, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS;

code for causing the UE to add the second LTE BS to a barred cell list based on the received message indicating that the EPS bearer is removed; and

code for causing the UE to transmit a pocket data network (PDN) connectivity request to a third LTE BS in response to the second LTE BS being added to the barred cell list.
The non-transitory CRM of claim 41, further comprising code for causing the UE to remove the second LTE BS from the barred cell list after a timer expires.
The non-transitory CRM of claim 42, further comprising code for causing the UE start the timer in response to adding the second LTE BS to the barred cell list.
The non-transitory CRM of claim 41, wherein one or more of the first LTE BS, the second LTE BS or the third LTE BS are configured to support a non-standalone mode.
The non-transitory CRM of claim 41, wherein the UE is configured to operate in a non-standalone mode.
The non-transitory CRM of claim 41, wherein the message is a Radio Resource Control connection reconfiguration message excluding the removed EPS bearer from a list of active EPS bearers between the UE and the second LTE BS.
The non-transitory CRM of claim 41, wherein the removed EPS bearer is the default EPS bearer of the plurality of EPS bearers.
The non-transitory CRM of claim 41, further comprising code for causing the UE to determine that the third LTE BS has priority over the first LTE BS prior to transmitting the PDN connectivity request to the third LTE BS.
The non-transitory CRM of claim 41, wherein the third LTE BS is same as the first LTE BS.
A non-transitory computer-readable medium (CRM) having program code recorded thereon, the program code comprising:

code for causing a user equipment (UE) to transmit a service request to a first LTE base station (BS) via a plurality of evolved packet system (EPS) bearers;

code for causing the UE to receive, from a second LTE BS, a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS;

code for causing the UE to transmit a first pocket data network (PDN) connectivity request to connect to the second LTE BS in response to receiving the message indicating that the EPS bearer is removed;

code for causing the UE to add the second LTE BS to a barred cell list in response to an expiration of a timer without the UE connecting to the second LTE BS; and

code for causing the UE to transmit a second PDN connectivity request to connect to a third LTE BS in response to the second LTE BS being added to the barred cell list.
The non-transitory CRM of claim 50, wherein the timer is a T3482 timer.
The non-transitory CRM of claim 50, wherein the expiration of the timer is one of a first expiration, a second expiration, a third expiration, a fourth expiration or a fifth expiration of the timer after the second PDN connectivity request is transmitted to the second LTE BS.
The non-transitory CRM of claim 50, wherein the timer is a first timer, further comprising code for causing the UE to remove the second LTE BS from the barred cell list after a second timer expires.
The non-transitory CRM of claim 53, further comprising code for causing the UE to start the second timer in response to the second LTE BS being added to the barred cell list.
The non-transitory CRM of claim 50, wherein one or more of the first LTE BS, the second LTE BS or the third LTE BS are configured to support a non-standalone mode.
The non-transitory CRM of claim 50, wherein the UE is configured to operate in a non-standalone mode.
The non-transitory CRM of claim 50, wherein the message is a Radio Resource Control connection reconfiguration message excluding the removed EPS bearer from a list of active EPS bearers between the UE and the second LTE BS.
The non-transitory CRM of claim 50, wherein the removed EPS bearer is the default EPS bearer of the plurality of EPS bearers.
The non-transitory CRM of claim 50, further comprising code for causing the UE to determine that the third LTE BS has priority over the first LTE BS prior to transmitting the second PDN connectivity request to the third LTE BS.
The non-transitory CRM of claim 50, wherein the third LTE BS is same as the first LTE BS.
A user equipment (UE) , comprising:

means for transmitting to a first LTE base station (BS) a service request via a plurality of evolved packet system (EPS) bearers;

means for receiving from a second base station a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS;

means for adding the second LTE BS to a barred cell list based on the received message indicating that the EPS bearer is removed; and

means for transmitting a pocket data network (PDN) connectivity request to a third LTE BS in response to adding the second LTE BS to the barred cell list.
The UE of claim 61, further comprising means for removing the second LTE BS from the barred cell list after a timer expires.
The UE of claim 62, further comprising means for starting the timer in response to adding the second LTE BS to the barred cell list.
The UE of claim 61, wherein one or more of the first LTE BS, the second LTE BS or the third LTE BS are configured to support a non-standalone mode.
The UE of claim 61, wherein the UE is configured to operate in a non-standalone mode.
The UE of claim 61, wherein the message is a Radio Resource Control connection reconfiguration message excluding the removed EPS bearer from a list of active EPS bearers between the UE and the second LTE BS.
The UE of claim 61, wherein the removed EPS bearer is the default EPS bearer of the plurality of EPS bearers.
The UE of claim 61, further comprising means for determining that the third LTE BS has priority over the first LTE BS prior to transmitting the PDN connectivity request to the third LTE BS.
The UE of claim 61, wherein the third LTE BS is same as the first LTE BS.
A user equipment (UE) , comprising:

means for transmitting to a first LTE base station (BS) a service request via a plurality of evolved packet system (EPS) bearers;

means for receiving from a second LTE BS a message indicating that an EPS bearer of the plurality of EPS bearers is removed after handover of the UE from the first LTE BS to the second LTE BS;

means for transmitting a first pocket data network (PDN) connectivity request to connect to the second LTE BS in response to receiving the message indicating that the EPS bearer is removed;

means for adding the second LTE BS to a barred cell list in response to an expiration of a timer without the UE connecting to the second LTE BS; and

means for transmitting a second PDN connectivity request to connect to a third LTE BS in response to the second LTE BS being added to the barred cell list.
The UE of claim 70, wherein the timer is a T3482 timer.
The UE of claim 70, wherein the expiration of the timer is one of a first expiration, a second expiration, a third expiration, a fourth expiration or a fifth expiration of the timer after the transmitting of the second PDN connectivity request to the second LTE BS.
The UE of claim 70, wherein the timer is a first timer, further comprising:

means for removing the second LTE BS from the barred cell list after a second timer expires.
The UE of claim 73, further comprising:

means for starting the second timer in response to the second LTE BS being added to the barred cell list.
The UE of claim 70, wherein one or more of the first LTE BS, the second LTE BS or the third LTE BS are configured to support a non-standalone mode.
The UE of claim 70, wherein the UE is configured to operate in a non-standalone mode.
The UE of claim 70, wherein the message is a Radio Resource Control connection reconfiguration message excluding the removed EPS bearer from a list of active EPS bearers between the UE and the second LTE BS.
The UE of claim 70, wherein the removed EPS bearer is the default EPS bearer of the plurality of EPS bearers.
The UE of claim 70, further comprising means to determine that the third LTE BS has priority over the first LTE BS prior to transmitting the second PDN connectivity request to the third LTE BS.
The UE of claim 70, wherein the third LTE BS is same as the first LTE BS.