WO2018057076A1 - Splitting signal radio bearer enhancements for standalone 5g new rat multi-connectivity - Google Patents

Splitting signal radio bearer enhancements for standalone 5g new rat multi-connectivity Download PDF

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Publication number
WO2018057076A1
WO2018057076A1 PCT/US2017/037985 US2017037985W WO2018057076A1 WO 2018057076 A1 WO2018057076 A1 WO 2018057076A1 US 2017037985 W US2017037985 W US 2017037985W WO 2018057076 A1 WO2018057076 A1 WO 2018057076A1
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WO
WIPO (PCT)
Prior art keywords
ue
menb
senb
srb
split
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PCT/US2017/037985
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French (fr)
Inventor
Jing Zhu
Candy YIU
Sudeep K. PALET
Yujian Zhang
Richard C. Burbidge
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Intel Corporation
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Priority to US201662399880P priority Critical
Priority to US62/399,880 priority
Priority to US201662402937P priority
Priority to US62/402,937 priority
Application filed by Intel Corporation filed Critical Intel Corporation
Publication of WO2018057076A1 publication Critical patent/WO2018057076A1/en

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W36/00Hand-off or reselection arrangements
    • H04W36/0005Control or signalling for completing the hand-off
    • H04W36/0055Transmission and use of information for re-establishing the radio link
    • H04W36/0069Transmission and use of information for re-establishing the radio link in case of dual connectivity, e.g. CoMP, decoupled uplink/downlink or carrier aggregation
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W88/00Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/08Access point devices

Abstract

Systems and methods of a Split SRB are generally described. The protocol stack is split either at the PDCP or the RLC layer. After acceptance of the Split SRB at a SeNB, RRC messaging is sent to the UE to indicate the Split SRB, after which the UE undertakes a Random Access Procedure to get connected with the SeNB. Subsequent RRC messages related to modifications of the E-RAB, or MeNB change, or handover are transmitted directly to the UE from the MeNB and/or through the SeNB. The UE maintains communications with the EPC when the communication path is changed at the EPC from MeNB to the SeNB due to handover or MeNB change.

Description

SPLITTING SIGNAL RADIO BEARER ENHANCEMENTS FOR STANDALONE 5G NEW RAT MULTI-CONNECTIVITY

PRIORITY CLAIM

[0001] This application claims the benefit of priority to United States

Provisional Patent Application Serial No. 62/399,880, filed September 26, 2016, and entitled, "SPLITTING SIGNAL RADIO BEARER ENHANCEMENTS FOR STANDALONE 5G NEW RAT (NR) MULTI-CONNECTIVITY," and Provisional Patent Application Serial No. 62/402,937, filed September 30, 2016, and entitled, "MOBILITY SUPPORT FOR NR IN HIGH FREQUENCY," each of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

[0002] Embodiments pertain to radio access networks. Some embodiments relate to reference signal measurement in various cellular and wireless local area network (WLAN) networks, including Third Generation Partnership Project Long Term Evolution (3GPP LTE) 5lh generation (5G) networks. Some embodiments relate to network connections with different radio access technologies.

BACKGROUND

[0003] The use of communication devices, especially mobile communication devices, has continued to increase, in large part due to the increase in available applications and content such as gaming and video streaming. As a result, networks continue to develop, with the next generation wireless communication systems, such as the 4lh and 5lh generation (4G, 5G) systems, striving to improve access to information and data sharing. 5G in particular looks to provide a unified network/system that is able to meet vastly different and sometime conflicting performance dimensions and services driven by disparate services and applications while maintaining compatibility with legacy communication devices and applications.

[0004] The increased flexibility inherent in the 5G network, including the combination of multiple evolved Node B (eNB) connections for a user equipment (UE) over multiple radio access technologies (RATs) may result in connection issues. This may be particularly problematic with the addition of mmWave communications, in which sudden, temporary changes in signal characteristics may result in one or more undesired handovers. It would be desirable to reduce undesirable in 5G systems.

BRIEF DESCRIPTION OF THE FIGURES

[0005] In the figures, which are not necessarily drawn to scale, like numerals may describe similar components in different views. Like numerals having different letter suffixes may represent different instances of similar components. The figures illustrate generally, by way of example, but not by way of limitation, various embodiments discussed in the present document.

[0006] FIG. 1 shows an example of a portion of an end-to-end network architecture of a LTE network in accordance with some embodiments.

[0007] FIG. 2 illustrates components of a communication device in accordance with some embodiments.

[0008] FIG. 3 illustrates a block diagram of a communication device in accordance with some embodiments.

[0009] FIG. 4 illustrates another block diagram of a communication device in accordance with some embodiments.

[00101 FIG. 5A illustrates a Packet Data Convergence Protocol (PDCP)- based Split SRB protocol stack in accordance with some embodiments; FIG. 5B illustrates a Radio Link Control (RLC)-based Split Signal Radio Bearer (SRB) protocol stack in accordance with some embodiments.

[0011] FIG. 6 illustrates a Secondary eNB (SeNB) addition procedure in accordance with some embodiments.

[0012] FIG. 7 illustrates a SeNB modification procedure in accordance with some embodiments.

[0013] FIG. 8 illustrates a Master eNB (MeNB) changing procedure in accordance with some embodiments.

[0014] FIG. 9 illustrates dual beam scenarios in accordance with some embodiments. [0015] FIG. 10 illustrates a dual beam procedure in accordance with some embodiments.

[0016] FIG. 1 1 illustrates a dual beam handover procedure in accordance with some embodiments.

[0017] FIG. 12 illustrates another dual beam handover procedure in accordance with some embodiments.

DETAILED DESCRIPTION

[0018] The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims.

[0019] FIG. 1 shows an example of a portion of an end-to-end network architecture of a LTE network in accordance with some embodiments. As used herein, an LTE network refers to both LTE and LTE Advanced (LTE-A) networks as well as other versions of LTE networks to be developed. The network 100 may comprise a radio access network (RAN) (e.g., as depicted, the evolved universal terrestrial radio access network (E-UTRAN), or the 5G New RAN) 101 and core network 120 (CN) coupled together through an SI interface 115. For convenience and brevity, only a portion of the CN 120, as well as the RAN 101, is shown in the example. The CN 120 may be an evolved packet core (EPC) or a 5G CN, for example. The network shown in FIG. 1 may include a non-standalone scenario in which 5G network co-exists with LTE/5G macro network and/or a standalone scenario in which the 5G network and LTE networks are isolated.

[0020] The CN 120 may include a mobility management entity (MME)

122, serving gateway (serving GW or SGW) 124, and packet data network gateway (PDN GW) 126. The RAN 101 may include evolved node Bs (eNBs) 104 for communicating with user equipment (UE) 102. The eNBs 104 may include macro eNBs 104A and low power (LP) eNBs 104B, the latter of which may also be referred to as small cells. Other elements, such as a Home Location Register (HLR)/Home Subscriber Server (HSS), a database including subscriber information of a 3GPP network that may perform configuration storage, identity management and user state storage, and a Policy and Charging Rule Function (PCRF) that performs policy decision for dynamically applying Quality of Service (QoS) and charging policy per service flow, are not shown for convenience. Note that in 5G networks, the eNBs 104 may be referred to as gNBs. Although the procedures may refer to only eNBs or gNBs, unless otherwise noted, the various procedures may apply to both eNBs and gNBs, which may be referred to simply as base stations.

[0021] The MME 122 may be similar in function to the control plane of legacy Serving GPRS Support Nodes (SGSN). The MME 122 may manage mobility aspects in access such as gateway selection and tracking area list management, performing both mobility management (MM) and session management (SM). The Non-Access Stratum (NAS) is a part of the control plane between a UE 102 and the MME 122. The NAS is used for signaling between the UE 102 and the CN in the LTE/UMTS protocol stack. The NAS supports UE mobility and session management for establishing and maintaining an IP connection between the UE 102 and PDN GW 126.

[0022] The serving GW 124 may terminate the user plane interface toward the RAN 101 , and route data packets between the RAN 101 and the core network 120. In addition, the serving GW 124 may be a local mobility anchor point for inter-eNB handovers and also may provide an anchor for inter-3GPP mobility. Other responsibilities may include lawful intercept, charging, and policy enforcement, packet routing, idle mode packet buffering, and triggering an MME to page a UE. The serving GW 124 and the MME 122 may be implemented in one physical node or separate physical nodes.

[0023] The PDN GW 126 may terminate a SGi interface toward the packet data network (PDN). The PDN GW 126 may route data packets between the CN 120 and the external PDN, and may perform policy enforcement and charging data collection UE ΓΡ address assignment, packet screening and filtering. The PDN GW 126 may also provide an anchor point for mobility devices with a non-LTE access. The external PDN can be any kind of IP network, as well as an IP Multimedia Subsystem (EMS) domain. The PDN GW 126 and the serving GW 124 may be implemented in a single physical node or separate physical nodes.

[0024] The eNBs 104 (macro and micro) may terminate the air interface protocol and may be the first point of contact for a UE 102. In some embodiments, an eNB 104 may fulfill various logical functions for the RAN 101 including, but not limited to, RNC (radio network controller functions) such as radio bearer management, uplink and downlink dynamic radio resource management and data packet scheduling, and mobility management. In accordance with embodiments, UEs 102 may be configured to communicate orthogonal frequency division multiplexed (OFDM) communication signals with an eNB 104 over a multicarrier communication channel in accordance with an OFDMA communication technique. The OFDM signals may comprise a plurality of orthogonal subcarriers.

[0025] The SI interface 115 may be the interface that separates the RAN 101 and the CN 120. It may be split into two parts: the Sl-U, which may carry traffic data between the eNBs 104 and the serving GW 124, and the Sl-MME, which may be a signaling interface between the eNBs 104 and the MME 122. The X2 interface may be the interface between eNBs 104. The X2 interface may comprise two parts, the X2-C and X2-U. The X2-C may be the control plane interface between the eNBs 104, while the X2-U may be the user plane interface between the eNBs 104.

[0026] With cellular networks, LP cells 104B may be typically used to extend coverage to indoor areas where outdoor signals do not reach well, or to add network capacity in areas with dense usage. In particular, it may be desirable to enhance the coverage of a wireless communication system using cells of different sizes, macrocells, microcells, picocells, and femtocells, to boost system performance. The cells of different sizes may operate on the same frequency band, or may operate on different frequency bands with each cell operating in a different frequency band or only cells of different sizes operating on different frequency bands. As used herein, the term LP eNB refers to any suitable relatively LP eNB for implementing a smaller cell (smaller than a macro cell) such as a femtocell, a picocell, or a microcell. Femtocell eNBs may be typically provided by a mobile network operator to its residential or enterprise customers. A femtocell may be typically the size of a residential gateway or smaller and generally connect to a broadband line. The femtocell may connect to the mobile operator's mobile network and provide extra coverage in a range of typically 30 to 50 meters. Thus, a LP eNB 104B might be a femtocell eNB. Similarly, a picocell may be a wireless communication system typically covering a small area, such as in-building (offices, shopping malls, train stations, etc.), or more recently in-aircraft. A picocell eNB may generally connect through the X2 link to another eNB such as a macro eNB through its base station controller (BSC) functionality and/or connect via an SI interface to an MME/Service Gateway. Thus, the LP eNB may be implemented with a picocell eNB since it may be coupled to a macro eNB 104A via an X2 interface. Picocell eNBs or other LP eNBs LP eNB 104B may incorporate some or all functionality of a macro eNB LP eNB 1 4 A.

[0027] LTE dual-connectivity (DC) framework allows the UE 102 to be connected simultaneously a master eNB (MeNB) and a secondary eNB (SeNB), e.g., communicating through an interface for transmission (generated by processing circuitry) to or reception (to the processing circuitry where the transmission is decoded) from the MeNB or SeNB. Interfaces in the MeNB and SeNB may similarly be used for communication with the UE and MeNB/SeNB. In some embodiments, the macro eNB 104A may be the MeNB and the LP eNB 104B may be the SeNB. The UE 102 may be connected to each of the MeNB 104 A and SeNB 104B through a Uu interface. Although the UE 102 is shown to be connected with both a macro eNB 104A and LP eNB 104B, in other embodiments, the UE 102 may be connected with multiple macro eNBs 104A and/or multiple LP eNBs 104B. Connection with multiple eNBs may increase UE throughput, in particular for cell edge UEs, as well as enhance mobility robustness and reduce signaling overhead towards the CN 120 due to frequent handover for SeNB changes.

[0028] FIG. 2 illustrates components of a communication device in accordance with some embodiments. The communication device 200 may be a UE, eNB or other network component as described herein. The communication device 200 may be a stationary, non-mobile device or may be a mobile device. In some embodiments, the UE 200 may include application circuitry 202, baseband circuitry 204, Radio Frequency (RF) circuitry 206, front-end module (FEM) circuitry 208 and one or more antennas 210, coupled together at least as shown. At least some of the baseband circuitry 204, RF circuitry 206, and FEM circuitry 208 may form a transceiver. In some embodiments, other network elements, such as the MME may contain some or all of the components shown in FIG. 2.

[0029] The application or processing circuitry 202 may include one or more application processors. For example, the application circuitry 202 may include circuitry such as, but not limited to, one or more single-core or multi- core processors. The processor(s) may include any combination of general- purpose processors and dedicated processors (e.g., graphics processors, application processors, etc.). The processors may be coupled with and/or may include memory/storage and may be configured to execute instructions stored in the memory/storage to enable various applications and/or operating systems to run on the system.

[0030] The baseband circuitry 204 may include circuitry such as, but not limited to, one or more single-core or multi-core processors. The baseband circuitry 204 may include one or more baseband processors and/or control logic to process baseband signals received from a receive signal path of the RF circuitry 206 and to generate baseband signals for a transmit signal path of the RF circuitry 206. Baseband processing circuity 204 may interface with the application circuitry 202 for generation and processing of the baseband signals and for controlling operations of the RF circuitry 206. For example, in some embodiments, the baseband circuitry 204 may include a second generation (2G) baseband processor 204a, third generation (3G) baseband processor 204b, fourth generation (4G) baseband processor 204c, and/or other baseband processor(s) 204d for other existing generations, generations in development or to be developed in the future (e.g., fifth generation (5G), 5G, etc.). The baseband circuitry 204 (e.g., one or more of baseband processors 204a-d) may handle various radio control functions that enable communication with one or more radio networks via the RF circuitry 206. The radio control functions may include, but are not limited to, signal modulation/demodulation,

encoding/decoding, radio frequency shifting, etc. In some embodiments, modulation/demodulation circuitry of the baseband circuitry 204 may include FFT, precoding, and/or constellation mapping/demapping functionality. In some embodiments, encoding/decoding circuitry of the baseband circuitry 204 may include convolution, tail-biting convolution, turbo, Viterbi, and/or Low Density Parity Check (LDPC) encoder/decoder functionality. Embodiments of modulation/demodulation and encoder/decoder functionality are not limited to these examples and may include other suitable functionality in other embodiments.

[0031] In some embodiments, the baseband circuitry 204 may include elements of a protocol stack such as, for example, elements of an Evolved UTRON (EUTRAN) protocol including, for example, physical (PHY), media access control (MAC), radio link control (RLC), packet data convergence protocol (PDCP), radio resource control (RRC) elements, and/or Non-Access Stratum (NAS) elements. A central processing unit (CPU) 204e of the baseband circuitry 204 may be configured to run elements of the protocol stack for signaling of the PHY, MAC, RLC, PDCP and/or RRC layers, and/or NAS. In some embodiments, the baseband circuitry may include one or more audio digital signal processor(s) (DSP) 204f. The audio DSP(s) 204f may be include elements for compression/decompression and echo cancellation and may include other suitable processing elements in other embodiments. Components of the baseband circuitry may be suitably combined in a single chip, a single chipset, or disposed on a same circuit board in some embodiments. In some embodiments, some or all of the constituent components of the baseband circuitry 204 and the application circuitry 202 may be implemented together such as, for example, on a system on a chip (SOC).

[0032] In some embodiments, the baseband circuitry 204 may provide for communication compatible with one or more radio technologies. For example, in some embodiments, the baseband circuitry 204 may support communication with an EUTRAN and/or other wireless metropolitan area networks (WMAN), a wireless local area network (WLAN), a wireless personal area network (WPAN). Embodiments in which the baseband circuitry 204 is configured to support radio communications of more than one wireless protocol may be referred to as multi-mode baseband circuitry. In some embodiments, the device can be configured to operate in accordance with communication standards or other protocols or standards, including Institute of Electrical and Electronic Engineers (IEEE) 802.16 wireless technology (WiMax), IEEE 802.11 wireless technology (WiFi) including IEEE 802.11 ad, which operates in the 60 GHz millimeter wave spectrum, various other wireless technologies such as global system for mobile communications (GSM), enhanced data rates for GSM evolution (EDGE), GSM EDGE radio access network (GERAN), universal mobile telecommunications system (UMTS), UMTS terrestrial radio access network (UTRAN), or other 2G, 3G, 4G, 5G, etc. technologies either already developed or to be developed.

[0033] RF circuitry 206 may enable communication with wireless networks using modulated electromagnetic radiation through a non-solid medium. In various embodiments, the RF circuitry 206 may include switches, filters, amplifiers, etc. to facilitate the communication with the wireless network. RF circuitry 206 may include a receive signal path which may include circuitry to down-convert RF signals received from the FEM circuitry 208 and provide baseband signals to the baseband circuitry 204. RF circuitry 206 may also include a transmit signal path which may include circuitry to up-convert baseband signals provided by the baseband circuitry 204 and provide RF output signals to the FEM circuitry 208 for transmission.

[0034] In some embodiments, the RF circuitry 206 may include a receive signal path and a transmit signal path. The receive signal path of the RF circuitry 206 may include mixer circuitry 206a, amplifier circuitry 206b and filter circuitry 206c. The transmit signal path of the RF circuitry 206 may include filter circuitry 206c and mixer circuitry 206a. RF circuitry 206 may also include synthesizer circuitry 206d for synthesizing a frequency for use by the mixer circuitry 206a of the receive signal path and the transmit signal path. In some embodiments, the mixer circuitry 206a of the receive signal path may be configured to down-convert RF signals received from the FEM circuitry 208 based on the synthesized frequency provided by synthesizer circuitry 206d. The amplifier circuitry 206b may be configured to amplify the down-converted signals and the filter circuitry 206c may be a low-pass filter (LPF) or band-pass filter (BPF) configured to remove unwanted signals from the down-converted signals to generate output baseband signals. Output baseband signals may be provided to the baseband circuitry 204 for further processing. In some embodiments, the output baseband signals may be zero-frequency baseband signals, although this is not a requirement. In some embodiments, mixer circuitry 206a of the receive signal path may comprise passive mixers, although the scope of the embodiments is not limited in this respect.

[0035] In some embodiments, the mixer circuitry 206a of the transmit signal path may be configured to up-convert input baseband signals based on the synthesized frequency provided by the synthesizer circuitry 206d to generate RF output signals for the FEM circuitry 208. The baseband signals may be provided by the baseband circuitry 204 and may be filtered by filter circuitry 206c. The filter circuitry 206c may include a low-pass filter (LPF), although the scope of the embodiments is not limited in this respect.

[0036] In some embodiments, the mixer circuitry 206a of the receive signal path and the mixer circuitry 206a of the transmit signal path may include two or more mixers and may be arranged for quadrature downconversion and/or upconversion respectively. In some embodiments, the mixer circuitry 206a of the receive signal path and the mixer circuitry 206a of the transmit signal path may include two or more mixers and may be arranged for image rejection (e.g., Hartley image rejection). In some embodiments, the mixer circuitry 206a of the receive signal path and the mixer circuitry 206a may be arranged for direct downconversion and/or direct upconversion, respectively. In some embodiments, the mixer circuitry 206a of the receive signal path and the mixer circuitry 206a of the transmit signal path may be configured for super-heterodyne operation.

[0037] In some embodiments, the output baseband signals and the input baseband signals may be analog baseband signals, although the scope of the embodiments is not limited in this respect. In some alternate embodiments, the output baseband signals and the input baseband signals may be digital baseband signals. In these alternate embodiments, the RF circuitry 206 may include analog-to-digital converter (ADC) and digital-to-analog converter (DAC) circuitry and the baseband circuitry 204 may include a digital baseband interface to communicate with the RF circuitry 206. [0038] In some dual-mode embodiments, a separate radio IC circuitry may be provided for processing signals for each spectrum, although the scope of the embodiments is not limited in this respect.

[0039] In some embodiments, the synthesizer circuitry 206d may be a fractional-N synthesizer or a fractional N/N+1 synthesizer, although the scope of the embodiments is not limited in this respect as other types of frequency synthesizers may be suitable. For example, synthesizer circuitry 206d may be a delta-sigma synthesizer, a frequency multiplier, or a synthesizer comprising a phase-locked loop with a frequency divider.

[0040] The synthesizer circuitry 206d may be configured to synthesize an output frequency for use by the mixer circuitry 206a of the RF circuitry 206 based on a frequency input and a divider control input. In some embodiments, the synthesizer circuitry 206d may be a fractional N/N+1 synthesizer.

[0041] In some embodiments, frequency input may be provided by a voltage controlled oscillator (VCO), although that is not a requirement. Divider control input may be provided by either the baseband circuitry 204 or the applications processor 202 depending on the desired output frequency. In some embodiments, a divider control input (e.g., N) may be determined from a lookup table based on a channel indicated by the applications processor 202.

[0042] Synthesizer circuitry 206d of the RF circuitry 206 may include a divider, a delay-locked loop (DLL), a multiplexer and a phase accumulator. In some embodiments, the divider may be a dual modulus divider (DMD) and the phase accumulator may be a digital phase accumulator (DP A). In some embodiments, the DMD may be configured to divide the input signal by either N or N+l (e.g., based on a carry out) to provide a fractional division ratio. In some example embodiments, the DLL may include a set of cascaded, tunable, delay elements, a phase detector, a charge pump and a D-type flip-flop. In these embodiments, the delay elements may be configured to break a VCO period up into Nd equal packets of phase, where Nd is the number of delay elements in the delay line. In this way, the DLL provides negative feedback to help ensure that the total delay through the delay line is one VCO cycle.

[0043] In some embodiments, synthesizer circuitry 206d may be configured to generate a carrier frequency as the output frequency, while in other embodiments, the output frequency may be a multiple of the carrier frequency (e.g., twice the carrier frequency, four times the carrier frequency) and used in conjunction with quadrature generator and divider circuitry to generate multiple signals at the carrier frequency with multiple different phases with respect to each other. In some embodiments, the output frequency may be a LO frequency (fi-o). In some embodiments, the RF circuitry 206 may include an IQ/polar converter.

[0044] FEM circuitry 208 may include a receive signal path which may include circuitry configured to operate on RF signals received from one or more antennas 210, amplify the received signals and provide the amplified versions of the received signals to the RF circuitry 206 for further processing. FEM circuitry 208 may also include a transmit signal path which may include circuitry configured to amplify signals for transmission provided by the RF circuitry 206 for transmission by one or more of the one or more antennas 210.

[0045] In some embodiments, the FEM circuitry 208 may include a

TX RX switch to switch between transmit mode and receive mode operation. The FEM circuitry may include a receive signal path and a transmit signal path. The receive signal path of the FEM circuitry may include a low-noise amplifier (LNA) to amplify received RF signals and provide the amplified received RF signals as an output (e.g., to the RF circuitry 206). The transmit signal path of the FEM circuitry 208 may include a power amplifier (PA) to amplify input RF signals (e.g., provided by RF circuitry 206), and one or more filters to generate RF signals for subsequent transmission (e.g., by one or more of the one or more antennas 210.

[0046] In some embodiments, the communication device 200 may include additional elements such as, for example, memory/storage, display, camera, sensor, and/or input/output (I/O) interface as described in more detail below. In some embodiments, the communication device 200 described herein may be part of a portable wireless communication device, such as a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a web tablet, a wireless telephone, a smartphone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a medical device (e.g., a heart rate monitor, a blood pressure monitor, etc.), or other device that may receive and/or transmit information wirelessly. In some embodiments, the communication device 200 may include one or more user interfaces designed to enable user interaction with the system and/or peripheral component interfaces designed to enable peripheral component interaction with the system. For example, the communication device 200 may include one or more of a keyboard, a keypad, a touchpad, a display, a sensor, a non-volatile memory port, a universal serial bus (USB) port, an audio jack, a power supply interface, one or more antennas, a graphics processor, an application processor, a speaker, a microphone, and other I O components. The display may be an LCD or LED screen including a touch screen. The sensor may include a gyro sensor, an accelerometer, a proximity sensor, an ambient light sensor, and a positioning unit. The positioning unit may communicate with components of a positioning network, e.g., a global positioning system (GPS) satellite.

[0047] The antennas 210 may comprise one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other types of antennas suitable for transmission of RF signals. In some multiple-input multiple-output (MIMO) embodiments, the antennas 210 may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result.

[0048] Although the communication device 200 is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, field-programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements may refer to one or more processes operating on one or more processing elements. [0049] Embodiments may be implemented in one or a combination of hardware, firmware and software. Embodiments may also be implemented as instructions stored on a computer-readable storage device, which may be read and executed by at least one processor to perform the operations described herein. A computer-readable storage device may include any non-transitory mechanism for storing information in a form readable by a machine (e.g., a computer). For example, a computer-readable storage device may include readonly memory (ROM), random-access memory (RAM), magnetic disk storage media, optical storage media, flash-memory devices, and other storage devices and media. Some embodiments may include one or more processors and may be configured with instructions stored on a computer-readable storage device.

[0050] FIG. 3 is a block diagram of a communication device in accordance with some embodiments. The device may be a UE, for example, such as the UE shown in FIG. 1. The physical layer circuitry 302 may perform various encoding and decoding functions that may include formation of baseband signals for transmission and decoding of received signals. The communication device 300 may also include medium access control layer (MAC) circuitry 304 for controlling access to the wireless medium. The communication device 300 may also include processing circuitry 306, such as one or more single-core or multi-core processors, and memory 308 arranged to perform the operations described herein. The physical layer circuitry 302, MAC circuitry 304 and processing circuitry 306 may handle various radio control functions that enable communication with one or more radio networks compatible with one or more radio technologies. The radio control functions may include signal modulation, encoding, decoding, radio frequency shifting, etc. For example, similar to the device shown in FIG. 2, in some embodiments, communication may be enabled with one or more of a WMAN, a WLAN, and a WPAN. In some embodiments, the communication device 300 can be configured to operate in accordance with 3 GPP standards or other protocols or standards, including WiMax, WiFi, WiGig, GSM, EDGE, GERAN, UMTS,

UTRAN, or other 3G, 3G, 4G, 5G, etc. technologies either already developed or to be developed. The communication device 300 may include transceiver circuitry 312 to enable communication with other external devices wirelessly and interfaces 314 to enable wired communication with other external devices. As another example, the transceiver circuitry 312 may perform various transmission and reception functions such as conversion of signals between a baseband range and a Radio Frequency (RF) range.

[0051] The antennas 301 may comprise one or more directional or omnidirectional antennas, including, for example, dipole antennas, monopole antennas, patch antennas, loop antennas, microstrip antennas or other types of antennas suitable for transmission of RF signals. In some ΜΓΜΟ embodiments, the antennas 301 may be effectively separated to take advantage of spatial diversity and the different channel characteristics that may result.

[0052] Although the communication device 300 is illustrated as having several separate functional elements, one or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including DSPs, and/or other hardware elements. For example, some elements may comprise one or more

microprocessors, DSPs, FPGAs, ASICs, RFICs and combinations of various hardware and logic circuitry for performing at least the functions described herein. In some embodiments, the functional elements may refer to one or more processes operating on one or more processing elements. Embodiments may be implemented in one or a combination of hardware, firmware and software. Embodiments may also be implemented as instructions stored on a computer- readable storage device, which may be read and executed by at least one processor to perform the operations described herein.

[0053] FIG. 4 illustrates another block diagram of a communication device in accordance with some embodiments. In alternative embodiments, the communication device 400 may operate as a standalone device or may be connected (e.g., networked) to other communication devices. In a networked deployment, the communication device 400 may operate in the capacity of a server communication device, a client communication device, or both in server- client network environments. In an example, the communication device 400 may act as a peer communication device in peer-to-peer (P2P) (or other distributed) network environment. The communication device 400 may be a UE, eNB, PC, a tablet PC, a STB, a PDA, a mobile telephone, a smart phone, a web appliance, a network router, switch or bridge, or any communication device capable of executing instructions (sequential or otherwise) that specify actions to be taken by that communication device. Further, while only a single communication device is illustrated, the term "communication device" shall also be taken to include any collection of communication devices that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein, such as cloud computing, software as a service (SaaS), other computer cluster configurations.

[0054] Examples, as described herein, may include, or may operate on, logic or a number of components, modules, or mechanisms. Modules are tangible entities (e.g., hardware) capable of performing specified operations and may be configured or arranged in a certain manner. In an example, circuits may be arranged (e.g., internally or with respect to external entities such as other circuits) in a specified manner as a module. In an example, the whole or part of one or more computer systems (e.g., a standalone, client or server computer system) or one or more hardware processors may be configured by firmware or software (e.g., instructions, an application portion, or an application) as a module that operates to perform specified operations. In an example, the software may reside on a communication device readable medium. In an example, the software, when executed by the underlying hardware of the module, causes the hardware to perform the specified operations.

[0055] Accordingly, the term "module" is understood to encompass a tangible entity, be that an entity that is physically constructed, specifically configured (e.g., hardwired), or temporarily (e.g., transitorily) configured (e.g., programmed) to operate in a specified manner or to perform part or all of any operation described herein. Considering examples in which modules are temporarily configured, each of the modules need not be instantiated at any one moment in time. For example, where the modules comprise a general-purpose hardware processor configured using software, the general-purpose hardware processor may be configured as respective different modules at different times. Software may accordingly configure a hardware processor, for example, to constitute a particular module at one instance of time and to constitute a different module at a different instance of time. [0056] Communication device (e.g., computer system) 400 may include a hardware processor 402 (e.g., a central processing unit (CPU), a graphics processing unit (GPU), a hardware processor core, or any combination thereof), a main memory 404 and a static memory 406, some or all of which may communicate with each other via an interlink (e.g., bus) 408. The

communication device 400 may further include a display unit 410, an alphanumeric input device 412 (e.g., a keyboard), and a user interface (UI) navigation device 414 (e.g., a mouse). In an example, the display unit 410, input device 412 and UI navigation device 414 may be a touch screen display. The communication device 400 may additionally include a storage device (e.g., drive unit) 416, a signal generation device 418 (e.g., a speaker), a network interface device 420, and one or more sensors 421 , such as a global positioning system (GPS) sensor, compass, accelerometer, or other sensor. The communication device 400 may include an output controller 428, such as a serial (e.g., universal serial bus (USB), parallel, or other wired or wireless (e.g., infrared (IR), near field communication (NFC), etc.) connection to communicate or control one or more peripheral devices (e.g., a printer, card reader, etc.).

[0057] The storage device 416 may include a communication device readable medium 422 on which is stored one or more sets of data structures or instructions 424 (e.g., software) embodying or utilized by any one or more of the techniques or functions described herein. The instructions 424 may also reside, completely or at least partially, within the main memory 404, within static memory 406, or within the hardware processor 402 during execution thereof by the communication device 400. In an example, one or any combination of the hardware processor 402, the main memory 404, the static memory 406, or the storage device 416 may constitute communication device readable media.

[0058] While the communication device readable medium 422 is illustrated as a single medium, the term "communication device readable medium" may include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) configured to store the one or more instructions 424.

[0059] The term "communication device readable medium" may include any medium that is capable of storing, encoding, or carrying instructions for execution by the communication device 400 and that cause the communication device 400 to perform any one or more of the techniques of the present disclosure, or that is capable of storing, encoding or carrying data structures used by or associated with such instructions. Non-limiting communication device readable medium examples may include solid-state memories, and optical and magnetic media. Specific examples of communication device readable media may include: non-volatile memory, such as semiconductor memory devices (e.g., Electrically Programmable Read-Only Memory (EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM)) and flash memory devices; magnetic disks, such as internal hard disks and removable disks;

magneto-optical disks; Random Access Memory (RAM); and CD-ROM and DVD-ROM disks. In some examples, communication device readable media may include non-transitory communication device readable media. In some examples, communication device readable media may include communication device readable media that is not a transitory propagating signal.

[0060] The instructions 424 may further be transmitted or received over a communications network 426 using a transmission medium via the network interface device 420 utilizing any one of a number of transfer protocols (e.g., frame relay, internet protocol (IP), transmission control protocol (TCP), user datagram protocol (UDP), hypertext transfer protocol (HTTP), etc.). Example communication networks may include a local area network (LAN), a wide area network (WAN), a packet data network (e.g., the Internet), mobile telephone networks (e.g., cellular networks), Plain Old Telephone (POTS) networks, and wireless data networks (e.g., IEEE 802.11 family of standards known as WiFi®, IEEE 802.16 family of standards known as WiMax®), IEEE 802.15.4 family of standards, a LTE family of standards, a UMTS family of standards, peer-to-peer (P2P) networks, among others. In an example, the network interface device 420 may include one or more physical jacks (e.g., Ethernet, coaxial, or phone jacks) or one or more antennas to connect to the communications network 426. In an example, the network interface device 420 may include a plurality of antennas to wirelessly communicate using at least one of single-input multiple-output (SIMO), ΜΓΜΟ, or multiple-input single-output (MISO) techniques. In some examples, the network interface device 420 may wirelessly communicate using Multiple User MIMO techniques. The term "transmission medium" shall be taken to include any intangible medium that is capable of storing, encoding or carrying instructions for execution by the communication device 400, and includes digital or analog communications signals or other intangible medium to facilitate communication of such software.

[0061] As above, connection with multiple eNBs may increase UE throughput, in particular for cell edge UEs, as well as enhance mobility robustness and reduce signaling overhead towards the CN due to frequent handover for SeNB changes. In particular, in some embodiments, only one Sl- MME connection may be used per UE. This SI -MME connection may be terminated at the MeNB to reduce signaling overhead towards the CN in case of SeNB change. The RRC connection of the UE may be terminated only at the MeNB to reduce radio resource management (RRM) and signaling complexity. Thus, in some embodiments, the SeNB may lack an RRC entity. SeNB-related RRC configurations may thus be transmitted to the MeNB in an RRC container and sent to the UE. The MeNB may make a final decision, construct the eventual RRC configuration message and transmits the RRC configuration message to the UE. The UE may maintain an RRC connection with the MeNB as long it is under the macro cell coverage.

[0062] This direct current (DC) architecture can be extended to multi- connectivity, in which the UE connects to the MeNB and SeNB with multiple secondary cell groups (SCGs). To extend this, 5G New RAT (NR) may be deployed using the mmWave band, in which a UE may simultaneously connect to multiple 5G NR small-cells with similar coverage. Unfortunately, the use of the mm Wave band may engender additional issues; in particular, the UE may lose the link to the MeNB (i.e. RLF) temporarily due to mobility of the UE or blockage by various physical objects within the environment. This may result in handovers that are more frequent than those that occur when lower frequencies are used, and are undesirable in particular due to the temporary nature of the RLF. Although 5G devices and the use of mm Wave bands may encounter such issues to a greater extent, it may be desirable to perform the various procedures described herein with 4G/LTE devices and when lower frequency bands are used. [0063] Accordingly, various embodiments may be directed to avoid or defer handover when the UE loses the RLF link to the MeNB. The

embodiments may be applied to networks that use LTE and 4G communications, in addition to those that use 5G communications. In some embodiments, a Split Signal Radio Bearer (SRB) may be introduced. The Split SRB may allow some or all control packets of the UE to be sent over the MeNB or/and SeNB. The control packets may include RRC packets or packet data convergence protocol (PDCP) packets.

[0064] FIG. 5A illustrates a PDCP-based Split SRB protocol stack in accordance with some embodiments; FIG. 5B illustrates a Radio Link Control (RLC)-based Split SRB protocol stack in accordance with some embodiments. As shown, the network 500 may include a MeNB 510 and one or more SeNBs 520A, 520B, 520C. The MeNB 510 may contain functionality associated with each of the protocol layers of the Radio Protocol Stack. The functionality may include, as shown, a RRC layer 518, a PDCP layer 516 on the RRC layer 518, an RLC layer 514 on the PDCP layer 516 and a MAC layer 512 on the RLC layer 514. The functionality of the individual layers shown may be described in the 3GPP specification and will not be described here for brevity. The SeNBs 520A, 520B, 520 may have limited control functionality; the MeNB 510 may provide the missing control functionality.

[0065] FIGS. 5 A and 5B show different embodiments of the Split SRB protocol stack. A dedicated logical channel may be established at the SeNB 520A, 520B, 520C to deliver PDCP or RLC packets for the SRB/RRC messages of the UE. Specifically, in FIG. 5 A, the RRC layer 518 and PDCP layer 516 may be located in the MeNB 510, while the MAC layer 512 and RLC layer 14 may be located in both the MeNB 510 and the SeNBs 520A, 520B, 520C.

Packets for/from the UE may be provided between the PDCP layer 516 in the MeNB 510 and the appropriate RLC layer 514 in one of the SeNBs 520A, 520B, 520C. In FIG. 5B, on the other hand, the RRC layer 518, PDCP layer 516 and RLC layer 514 may be located in the MeNB 510, while the MAC layer 512 may be located in both the MeNB 510 and the SeNBs 520A, 520B, 520C. Thus, packets for/from the UE may be provided between the RLC layer 514 in the MeNB 510 and the appropriate MAC layer 512 in one of the SeNBs 520 A, 520B, 520C.

[0066] The functionality in the SeNBs 520A, 520B, 520C may be limited dependent on, for example, the processing ability or size of the SeNBs 520A, 520B, 520C, or the amount of centralization of the control signals desired. In some embodiments, the SeNBs 520A, 520B, 520C may retain the same functionality as the MeNB 510, but may only activate a portion of the functionality due to the Split SRB. Independent of which Split SRB

embodiment shown in FIG. 5A or 5B is used, as a result of the Split SRB, the UE may send or receive RRC messages to/from MeNB via SeNB even in the event that the UE loses the link to the MeNB 510 temporarily. Thus, handover may be avoided or deferred.

[0067] FIG. 6 illustrates a SeNB addition procedure in accordance with some embodiments. The operations shown in FIG. 6 are exemplary, other operations may be present but are not described for convenience. The various devices shown in FIG. 6, the UE 612, MeNB 614 and SeNB 616 may be shown in any of FIGS. 1-4. In FIG. 6, an E-UTRAN Radio Access Bearer (E-RAB) for the UE 612 is added.

[0068] At operation 1 , the MeNB 614 may request the SeNB 616 to allocate radio resources for a specific E-RAB. The MeNB 614 may determine the E-RAB characteristics, such as E-RAB parameters and Transport Network Layer (TNL) address information corresponding to the bearer type of the E- RAB. In addition, the MeNB 614 may indicate, within the Secondary Cell Group (SCG)-Configlnfo, the Master Cell Group (MCG) configuration and the UE capabilities for UE capability coordination to be used as basis for the reconfiguration by the SeNB 616, but may not include SCG configuration. The MeNB 614 can provide the latest measurement results for the SCG cells requested to be added.

[0069] The SeNB 616 may accept or reject the request. The MeNB 614 may indicate that the MeNB 614 requests to activate Split SRB functionality at the SeNB 616. This request may be provided, for example, if the Split SRB functionality has not yet been activated at the SeNB 616. The indication of the Split SRB functionality may be provided in different embodiments within SCG- Configlnfo or within a new Information Element.

[0070] The SeNB 616 may allocate respective radio resources at operation 2 in response to the RRM entity in the SeNB 616 being able to admit the resource request. In addition, dependent on the bearer option, the SeNB 616 may allocate respective transport network resources. The SeNB 616 may trigger a Random Access procedure so that synchronization of the SeNB radio resource configuration can be performed. The SeNB 616 may provide the new radio resource of SCG in SCG-Config to the MeNB 614. For SCG bearers, the SeNB 616 may provide the new radio resource of the SCG together with SI DL TNL address information for the respective E-RAB and security algorithm, for split bearers together with X2 DL TNL address information.

[0071] The SeNB 616 may instead reject the Split SRB activation request. The rejection may be due to one or more reasons determined by the SeNB 616, for example limited radio resources. As a result, the MeNB 614 may return to the default mode in which SRB is only active at MeNB 614.

[0072] In response to reception of the acceptance of the SRB from the

SeNB 616, at operation 3, the MeNB 614 may endorse the new configuration. In response to the MeNB 614 may endorsing the new configuration, the MeNB 614 may send a RRCConnectionReconfiguration message to the UE 612. The RRCConnectionReconfiguration message may include the new radio resource configuration of the SCG based on the SCG-Config. If the SeNB 616 accepts the request, the MeNB 614 may indicate, in the RRCConnectionReconfiguration message, the UE 612 to activate the Split SRB (has been accepted by the SeNB 616).

[0073] In response to reception of the RRCConnectionReconfiguration message that indicates activation of the Split SRB, at operation 4 the UE 612 may apply the new configuration. The UE 612 may subsequently reply with RRCConnectionReconfigurationComplete message. If the UE 612 is unable to comply with part of the configuration included in the

RRCConnectionReconfiguration message, the UE 612 may perform a reconfiguration failure procedure. [0074] After reception of the RRCConnectionReconfigurationComplete message, at operation 5 the MeNB 614 may inform the SeNB 616 that the UE 612 has completed the reconfiguration procedure successfully via a

ReconfigureComplete message. The MeNB 614 may also indicate in the ReconfigureComplete message whether or not the Split SRB has been successfully activated.

[0075] The UE 612 at operation 6 may perform synchronization towards the SCell of the SeNB 616. The order of operations 4-6 may be different from that shown. This is to say that the order between performance of the Random Access procedure towards the SCG by the UE 612 and transmission of the RRCConnectionReconfigurationComplete message by the UE 612 may vary.

[0076] After Split SRB is activated at the SeNB 616, the MeNB 614 may send subsequent RRC messages (which may include the

RRCConnectionReconfiguration message) to UE 612 via one or more different paths. This is to say that the RRCConnectionReconfiguration message may be transmitted in various embodiments: directly from the MeNB 614 to the UE 612 (i.e., no SeNB is used), from the MeNB 614 to the UE 612 via one or multiple SeNB 616s, or from the MeNB 614 to the UE 612 via both MeNB 614 and SeNB 616 simultaneously. The various messages described herein may first be generated and then encoded before being transmitted, and subsequently received and decoded.

[0077] In addition to addition of a SeNB path, the SeNB path may be modified. FIG. 7 illustrates a SeNB modification procedure in accordance with some embodiments. The operations shown in FIG. 7 are exemplary, other operations may be present but are not described for convenience.

[0078] At operation 1, the MeNB 714 may request the SeNB 716 to modify radio resources for a specific E-RAB. The MeNB 714 may determine the E-RAB characteristics that are to be modified. The MeNB 714 may indicate the modification within the SCG-Configlnfo or within a new Information Element. The MeNB 714 can provide the latest measurement results for the SCG cells requested to be modified. The SeNB 716 may accept or reject the request. [0079] The SeNB 716 may modify the radio resources at operation 2 in response to the RRM entity in the SeNB 716 accepting the modification of the resource request. The SeNB 716 may acknowledge the request and indicate acceptance or rejection of the request within the SCG-Config or within a new Information Element.

[0080] In response to reception of the acceptance of modification of the

SRB from the SeNB 716, at operation 3a, the MeNB 714 may send a

RRCConnectionReconfiguration message to the UE 712. The

RRCConnectionReconfiguration message may include the modified radio resource configuration of the SCG based on the SCG-Config.

[0081] In response to reception of the RRCConnectionReconfiguration message that indicates modification, at operation 4a the UE 712 may apply the modified configuration. The UE 712 may subsequently reply with

RRCConnectionReconfigurationComplete message. If the UE 712 is unable to comply with part of the configuration included in the

RRCConnectionReconfiguration message, the UE 712 may perform a reconfiguration failure procedure.

[0082] However, as an indirect path exists between the MeNB 714 and the UE 712, during temporary MeNB link outage, the RRC message exchange between the UE 712 and the MeNB 714 may be delivered via the SeNB

716. Thus, when the MeNB 714 initiates the RRC connection reconfiguration procedure, if the link between the MeNB 714 and the UE 712 is temporarily unavailable, the MeNB 714 may forward the RRCConnectionReconfiguration message over the X2-AP interface to the SeNB 716 at operation 3b. The SeNB 716 may relay the RRCConnectionReconfiguration message over the air to the UE 712.

[0083] In response to reception via the SeNB 716, the UE 712 may apply the new configuration. The UE 712 may then at operation 4b reply, sending the RRCConnectionReconfigurationComplete message to the SeNB 716 rather than directly to the MeNB 714. The SeNB 716 may, in response, relay the

RRCConnectionReconfigurationComplete message over the X2-AP interface back to the MeNB 714. If the UE 712 is unable to comply with some or all of the configuration included in the RRCConnectionReconfiguration message, the UE 712 may perform the reconfiguration failure procedure.

[0084] After reception of the RRCConnectionReconfigurationComplete message, at operation 5 the MeNB 714 may inform the SeNB 716 that the UE 712 has completed the reconfiguration procedure successfully via a

ReconfigureComplete message. The MeNB 714 may also indicate in the ReconfigureComplete message whether or not the Split SRB has been successfully modified.

[0085] After creation or modification of the Split SRB, the UE may lose direct connection temporarily with the MeNB. Rather than initiate an immediate handover however, the Split SRB may provide an indirect connection with the MeNB, which may be used until handover is desired. FIG. 8 illustrates a MeNB changing procedure in accordance with some embodiments. The operations shown in FIG. 8 are exemplary, other operations may be present but are not described for convenience. The various devices shown in FIG. 8, the UE 812, MeNB 814, SeNB 816, MME 818 and SQW 822 may be shown in any of FIGS. 1-4.

[0086] In general, handover may be initiated after the UE 812 may transmit a measurement report to the source eNB (MeNB 814). The measurement report may comprise a measurement of reference signals to the UE 812 from the MeNB 814 (or the source eNB in the handover procedure). The measurement report may include, for example, the signal-to-noise ratio (SNR), the signal-to-interference plus noise ratio (SINR) of the reference signals, the received signal strength (RSS), the bit-error-rate (BER) before or after the channel decoder or a Channel Quality Indication (CQI) report carried by the PUCCH, among others.

[0087] The MeNB 814 may, in response to receiving the measurement report, determine that handover of the UE 812 to the target eNB (SeNB 816) is to occur. For example, for an Intra-LTE (Intra-MME/SGW 822) handover using the X2 interface, the MeNB 814 may transmit a resource status request message to the SeNB 816 to determine the load on the SeNB 816. Based on a resource status response message received from the SeNB 816 in response to the resource status request message, the MeNB 814 may decide to continue the handover procedure to the SeNB 816 using the X2 interface. The MeNB 814 may transmit a handover request message to the SeNB 816, passing information to prepare the handover at the target side. This information may include UE 812 Context, which includes the Security Context, and RB Context, including E- RAB to RB Mapping, and the target cell info as well as the TMGI list. The SeNB 816 may check for resource availability and, if available, reserve the resources and transmit to the MeNB 814 a handover request ACK message including a transparent container to be sent to the UE 812 as an RRC message to perform the handover and the MBMS information of the SeNB 816. The container may include a new C-RNTI, SeNB 816 security algorithm identifiers for selected security algorithms, a dedicated RACH preamble, and other parameters such as access parameters, SIBs, etc.

[0088] The MeNB 814 may then transmit an

RRCConnectionReconfiguration message to the UE 812 to initiate handover of the UE 812 to the SeNB 816. The RRCConnectionReconfiguration message may comprise eMBMS specific parameters that may normally be obtained by the UE 812 from the SeNB 816 after the UE 812 has attached to the SeNB 816. The MeNB 814 may transmit an eNB status transfer message to the SeNB 816 to convey the PDCP and HFN status of the E-RABs. The MeNB 814 may start forwarding the downlink data packets to the SeNB 816 for all the data bearers established in the SeNB 816 during processing of the handover request message. The UE 812 may attempt to access the SeNB 816 using the non-contention- based Random Access Procedure.

[0089] If the UE 812 succeeds in accessing the SeNB 816, the UE 812 may transmit an RRCConnectionReconfigurationComplete message to the SeNB 816. The SeNB 816 may transmit a path switch request message to the MME 818 to inform the MME 818 that the UE 812 has changed cells, including the TAI+ECGI of the target. The MME 818 may determine whether or not the SGW 822 can continue to serve the UE 812. The MME 818 may transmit to the SGW 822 a modify bearer request message that includes the eNodeB address and TEEDs for downlink user plane for the accepted EPS bearers to the SGW 822. If the PDN GW requested the UE 812 location info, the MME 818 may also include a User Location Information IE in the modify bearer request message. The SGW 822 may transmit downlink packets to the SeNB 816 using the newly received addresses and TEIDs, as well as sending a modify bearer response to the MME 818. The SGW 822 may transmit one or more packets on the old path to the MeNB 814 and then can release user plane resources toward the MeNB 814. The MME 818 may respond to the SeNB 816 with a path switch request ACK message to notify the completion of the handover. The SeNB 816 may now request the MeNB 814 to release the resources using an X2 UE 812 context release message.

[0090] In addition to the above procedures, a new timer - the MeNB Link Outage Timer, may be implemented. The MeNB Link Outage Timer may indicate, when the Split SRB has been established, the amount of time that the link between the UE 812 and the MeNB 814 may be out before the MeNB 814 triggers handover. The MeNB Link Outage Timer may be a timer different from other known timers, such as T33xx or T34xx series. In some embodiments, the handover-related RRC message exchange between the UE 812 and the MeNB 814 may be delivered via the SeNB 812 using the Split SRB during the temporary MeNB link outage. The messages may include measurement control, measurement reports and RRCConnectionReconfiguration.

[0091] As shown in FIG. 8, a link outage between the UE 812 and the MeNB 814 may occur. The link outage may occur due to an issue at the MeNB 814 or may be temporary in nature due to the bearer, e.g., caused by the mmWave connection between the UE 812 and the MeNB 814 being blocked or losing significant signal strength when the UE 812 moves to a particular location. However, the UE 812 may continue to be connected with the SeNB 816. Thus, during the MeNB change procedure the UE 812 may already be connected with the eventual new MeNB (SeNB 816), and therefore may avoid communication interruption.

[0092] When the link is lost but the MeNB 814 continues to operate, the

MeNB 814 may still be in communication with the SGW 822 as well as the SeNB 816. After determination that the UE-MeNB link is non-functional, the MeNB 814 may start the MeNB Link Outage Timer. The MeNB Link Outage Timer may have a constant initial value or, in some embodiments, the initial value may be variable. In the latter case, the initial value may depend, for example, on characteristics of the UE 812 (e.g., priority) or data for the UE 812. In addition, the MeNB 814 may continue to transmit stored packet data of the UE to the SGW 822 for transmission to the appropriate destination. As handover has not yet occurred, the SGW 822 may similarly continue to transmit packet data for the UE 812 to the MeNB 814.

[0093] The MeNB 814, upon receiving the data from the SGW 822, and with knowledge of the alternate path(s), may forward the data to SeNB 816. In some embodiments, the data may be forwarded by the MeNB 814 to a single SeNB 816 independent of the number of SeNBs connected with the UE 812. In other embodiments, the data path may depend on one or more of the type of data (e.g., user/control, application), the load of the SeNBs (e.g., the least loaded SeNB may be used), data and/or UE priority (e.g., high/medium/low) or the amount of data or time that a particular SeNB has been used to forward data to the UE 812, among others. Similarly, the UE 812 may provide data for the MeNB 814 to the same or different SeNB, depending on the embodiment.

[0094] Data communication with the UE 812 may continue in this manner until the MeNB Link Outage Timer has expired. The MeNB 814 may determine whether the MeNB Link Outage Timer has expired, as well as whether the direct UE-MeNB link has been reestablished. If the direct UE- MeNB link has been reestablished, the MeNB Link Outage Timer may be reset and deactivated. In response to a determination that the MeNB Link Outage Timer has expired and the direct UE-MeNB link has not been reestablished, the MeNB 814 may transmit to the UE 812 a MeNB change request message, along with corresponding configuration, via SeNB 816. The MeNB change request message, although different from a handover request, may carry similar information (e.g. UE context, etc.) as the handover request message above.

[0095] In response to reception of the MeNB change request message, the SeNB 816 may set up the related protocol stack for the UE 812. The SeNB 816 still be able to reject the MeNB change, however.

[0096] In response to acceptance of the MeNB change, the SeNB 816 may subsequently send a MeNB change ACK message to the MeNB 814. The MeNB change ACK may be similar to the handover request ACK message above. [0097] The SeNB 816 may also transmit messages to the MME 818 and the UE 812. In particular, the SeNB 816 may transmit a path switch request to the MME 818, and MeNB 814 may transmit a MeNB change message (RRC message) via SeNB 816 using the split SRB to the UE 812, the latter of which is shown as a dashed line from the MeNB 814 to the SeNB 816 and then from the SeNB 816 to the UE 812. The MeNB change message may contain the new configuration to establish or modify the SeNB bearers at the UE 812 and include the MeNB information as the RRC message originates at the MeNB 814. The MeNB change ACK, path switch request and MeNB change message may be transmitted in any order.

[0098] Each of the UE 812 and MME 818 may transmit further messages in response to reception of the MeNB change message and the path switch request, respectively. The UE 812 may, in response to the MeNB change message, transmit a MeNB change message ACK to the SeNB 816. In response to the path switch request, the MME 818 may send a modify bearer request to the SGW 822.

[0099] The SGW 822 may, in response to reception of the path switch request, initiate the DL path switch procedure. The DL path switch procedure, similar to the handover procedure, may include transmission of an end marker to the MeNB 814. The end marker may indicate the last packet associated with the MeNB 814 for communication with the UE 812 (or the first packet for the SeNB 816 to use as the new MeNB). The MeNB 814 may then forward the end marker to the SeNB 816.

[00100] The SGW 822 may also reply to the MME 818 with a Modify bearer response message. In response to reception of the Modify bearer response message, the MME 818 may send a path switch ACK back to the SeNB 816. The SeNB 816 may, in response to reception of the path switch ACK, transmit a UE context release message to the MeNB 814. The MeNB 814 in response to reception of the UE context release message may release the UE bearers, severing the UE-MeNB link, and complete the MeNB

change procedure.

[00101] In some embodiments, the RRC message exchange between the UE 812 and the MeNB 814 can be delivered via the SeNB 816 using the Split SRB even if the UE-MeNB link remains intact or is restored. This may occur, for example, when handover is to occur due to the measurement report or the load on the MeNB 814 become excessive. In other embodiment, the UE 812 may send the same RRC/PDCP packet to both the MeNB 814 and the SeNB 816. Similarly, the MeNB 814 may send the same RRC/PDCP packet to the UE 812 directly, and via the SeNB 816. This can improve the reliability of the RRC message.

[00102] Handover may occur in multiple types of networks. As above, the network deployment shown in FIG. 1 may include 5G standalone or non- standalone scenarios. In general, mobility can be considered based on the different scenarios: standalone and non-standalone. Different mobility supports may be used in 5G networks and LTE networks due to UE capability, transmit- receive point (TRP)-beamforming element at high frequency (e.g., the mm Wave bands), and multiple types of 5G nodes, among others. Accordingly, handover may be adjusted due to the change in mobility support. In particular, LTE-based handover with TRP, dual and multiple beam handover and dual/multi- connectivity handover may be used. The TRP may be a LP eNB or gNB (e.g., AP, micro/pico/femto).

[00103] As described above, one of the differences between the LTE inter-cell mobility handover procedure (between source and target eNB) and the NR mobility handover procedure (between source and target gNB) is the TRP beamforming aspect. The final signaling flow may also depend on the functional split between the TRP and the gNB shown in FIGS 5A and 5B. Different split options may result in the signaling differently. After a handover request is sent by the source gNB to the target gNB, it is assumed that the target gNB can make the decision whether or not to admit the UE. After the decision, the target gNB may inform the TRP using a handover indication (assuming the measurement report contains TRP and beam information). Similarly, after the UE sends the RRCConnectionReconfigurationComplete message to the target gNB via the target TRP to indicate that the handover is completed, the target gNB can start sending data to the UE.

[00104] LTE may be used as a baseline for the inter-cell handover procedure for NR. Note that measurements may take relatively longer time in a beam-based environment, especially in the high frequency bands due to the beam sweep process in comparison to legacy PUCCH measurements. Handover performance and the impact of measurements for NR networks may be impacted due to the beam sweep delay. The impact of a beam-based environment on NR measurement and handover may also be taken into account. Various embodiments, for example, RACH-less handover and Make-Before-Break connections, may be used for NR networks to reduce handover interruption time and to improve handover performance for NR.

[00105] In both intra-cell and inter-cell mobility, the UE may also support multiple beams. In dual/multiple beam operation, the UE may have the capability to support dual/multiple transmit and receive beams simultaneously. In this case, the UE can connect to a dual/multiple TRP associated with the same NR cell or different NR cells.

[00106] FIG. 9 illustrates dual beam scenarios in accordance with some embodiments. The scenarios may include UEs 902, TRPs 912 and gNBs 920 in different NR cells 910. The dual beam scenarios may include (1) intra-cell dual beams and (2) inter-cell dual beams. In intra-cell dual beams, the UE 902 may form 2 beams and connects to the same serving TRP 904, as indicated by UEl, or different TRPs 904 within the same NR cell 910, as indicated by UE2. Such an arrangement can be used for data boosting. In inter-cell dual beams, the UE 902 may form 2 beams but may be able to connect to 2 different NR cells, as shown by UE3 and UE4. The latter case can also be used for handover purposes.

[00107] If the UE 902 is capable of dual/multiple beam operation in NR networks, the UE 902 may be used for handover purposes. The UE 902 can, in this case, handover to a target gNB by connecting to target gNB 920 before releasing the source gNB 920, as discussed above. There are two architecture considerations: (1) DC like for intra-frequency NR and (2) dual protocol stacks. In the first architecture, DC like architecture for intra-frequency NR, as above the source gNB may be considered a MeNB and the target gNB may be considered a SeNB. Once the target gNB is added to the UE as a SeNB, a MeNB-SeNB switch may allow the target to become the MeNB. Then the source eNB can be released. In the second architecture, dual protocol stacks may be used for the UE to maintain connections to both the source and target gNB.

[00108] Thus, the DC like architecture with intra-frequency NR MCG and SCG, in some embodiments only the source gNB may have RRC functionality while the target gNB may not have RRC functionality. FIG. 10 illustrates a dual beam procedure in accordance with some embodiments. The dual beam procedure may be an inter-cell handover that may involve the UE 1002, multiple source TRP 1004 and target TRP 1006, a source gNB 1012 and a target gNB 1014. The TRP 1004, 1006 may be NR TRP. The UE 1002, multiple source TRPs 1004 and target TRPs 1006 (at least one of which is in communication with the UE 1002), a source gNB 1012 and a target gNB 1014 may be shown in FIGs. 2-4. Unlike the procedure shown in FIG. 8, the modification shown in FIG. 10 (and handover in FIG. 11) may be made without a connection between the UE 1002 and the target gNB 1014 (or SeNB) existing prior to the modification or handover.

[00109] The UE 1002 may be in communication with the source gNB 1012 through the multiple source TRP 1004 as well as directly, and after handover with the target gNB 1014 through the target TRP 1006 as well as directly. As above, the source gNB 1012 may add the target gNB 1014 as a SeNB, with the target gNB 1014 communicating the addition to the target TRP 1006. The UE 1002 may perform a random access procedure with the target TRP 1006 after the RRCConnectionReconfiguration message is received from the source gNB 1012 and the RRCConnectionReconfigurationComplete message is sent to the target gNB 1014. The target TRP 1006 may then communicate with the target gNB 1014 to indicate that the UE 1002 has successfully completed addition.

[00110] Once the target gNB 1014 is successfully added, a MeNB-SeNB switch may be performed after communication of the successful addition. The MeNB-SeNB switch indication may be provided to both the UE 1002 and the target gNB 1014. The source gNB 1012 may be subsequently released. In this architecture, there may be only one RRC entity at the MeNB at any given time. Moreover, it may be beneficial to allow the MeNB (source) to forward not only data but also RRC messages (e.g. the RRC Connection Reconfiguration) to the UE via the SeNB (target) especially when the link between the UE and the MeNB (source) is lost or blocked during handover.

[00111] In the second architecture the UE may maintain short term dual protocol stacks. The stacks may be a full protocol or part protocol stack. The UE may maintain dual protocol stacks with both the source gNB and target gNB until the handover is completed. In embodiments in which only one RRC entity may be present, there may be a switching point during the handover procedure. The location of the switching point may be variable, for example dependent on the implementation.

[00112] FIG. 11 illustrates a dual beam handover procedure in accordance with some embodiments. The signaling flow, as with FIG. 10, may involve the UE 1102, multiple source TRPs 1104 and target TRPs 1106, a source gNB 1112 and a target gNB 1 1 14.

[00113] The handover procedure shown in FIG. 11 may be similar to a standalone inter-cell handover procedure. However, the target gNB 1114 may have prior knowledge that the source gNB 1112 is performing a handover with dual beam operation. Thus, an indication of dual beam operation may be provided in the handover request between the source gNB 1112 and the target gNB 1 1 14.

[00114] As shown in operation 1, the UE 1102 may send a measurement report to the source TRP 1 104. The measurement report may be triggered by a network-configured event, such as the RSRP or RSRQ decreasing below a threshold. The TRP 1104 may at operation 2 forward the measurement report to the source gNB 1112.

[00115] At operation 3, the source gNB 1112 may determine that handover to the target TRP 1 106 is appropriate. In this case, the source gNB 11 12 may send a handover request with a dual beam indicator (if configured by the source gNB 1112) to the target gNB 1114.

[00116] The target gNB 1114 may decide whether to accept or decline the handover request. At operation 4, the target gNB 1 114 may send the handover indication to the target TRP 1106 if the target gNB 1114 decides to accept the handover request. The target gNB 1 114 may also reply to the handover request at operation 5 by sending a handover request ACK to the source gNB 1112. [00117] In response to receiving the handover request ACK, the source gNB 1112 may send a RRC reconfiguration message to the UE 1102 at operation 6. The transmission, unlike data transmission (which may be through the source TRP 1104) may be transmitted directly to the UE 1102. In some embodiments, both paths may be used. The RRCConnectionReconfiguration message transmitted may contain mobility information.

[00118] At operation 7, the UE 1102 may continue to communicate with the source TRP 1104 while performing a random access procedure with the target TRP 1106. The target TRP ID may be indicated in the

' RRCConnectionReconfiguration message.

[00119] Once the random access procedure is completed, the UE 1102 may communicate with the source gNB 11 12. In particular, the UE 1102 may send a RRCConnectionReconfigurationComplete message to the target TRP 1106 to complete the handover. As shown, the UE 1102 may continue to communicate with the source TRP 1104.

[00120] When handover is complete, the target TRP 1106 may notify the target gNB 1114 of successful handover. Thus, at operation 9, in response to reception of the RRCConnectionReconfigurationComplete message, the target TRP 1 106 may send an indication of handover success to the target gNB 1114. The indication may be provided in a single bit, for example.

[00121] The target gNB 1114, in response to reception of the handover success indication, may at operation 10 confirm the success with the source gNB 1 112. As shown, the target gNB 1114 may send a handover success message to source gNB 11 12. The handover success message may automatically request data transfer to the target gNB 1114.

[00122] The source gNB 11 12 may take multiple actions in response to reception of the handover success message from the target gNB 1114. At operation 11, the source gNB 1112 may send a handover complete indicator to the source TRP 1104 to prepare to stop data transmission. At operation 12, the source gNB 1112 may also send a SN status transfer to the target gNB 11 14 to start data forwarding from the source gNB 1112 to the target gNB 1114.

[00123] The target gNB 114 may send a release the source cell to the UE 1102. The UE 1102 may thus remain connected to the source gNB 1112 and data transfer between the two may continue until the target gNB 1114 notifies the source gNB 1112 of the completion of handover. The source gNB 11 12 can then stop data transmission to the UE 1102 through the source TRP 1104 and start forwarding data to the target gNB 1114. The data from the target gNB 1 114 may be sent to the UE 1102 through the target TRP 1106. The target TRP 1106 can release the UE 1102 any time after receiving handover complete indicator. In some embodiments, a switch message can be sent by the target to the UE 1102 to indicate when the UE 1102 should switch to the target completely.

[00124] FIG. 12 illustrates another dual beam handover procedure in accordance with some embodiments. The signaling flow, as with FIG. 11, may involve the UE 1202, multiple source TRPs 1204 and target TRPs 1206, a source gNB 1212 and a target gNB 1214. In addition, signaling with the MME 1220 and the SOW 1230 is shown in FIG. 12

[00125] As shown in operation 1, the UE 1202 may send a measurement report to the source TRP 1204. The measurement report may be triggered by a network-configured event, such as the RSRP or RSRQ decreasing below a threshold. The TRP 1204 may at operation 2 forward the measurement report to the source gNB 1212.

[00126] At operation 3, the source gNB 1212 may determine that handover to the target TRP 1206 is appropriate. In this case, the source gNB 1212 may send a handover request with a dual beam indicator (if configured by the source gNB 1212) to the target gNB 1214.

[00127] The target gNB 1214 may decide whether to accept or decline the handover request. At operation 4, the target gNB 1214 may send the handover indication to the target TRP 1206 if the target gNB 1214 decides to accept the handover request. The target gNB 1214 may also reply to the handover request at operation 5 by sending a handover request ACK to the source gNB 1212.

[00128] In response to receiving the handover request ACK, the source gNB 1212 may send a handover request ACK to the source TRP 1204 at operation 8. The handover request ACK may contain the dual beam indicator to the source TRP 1204. [00129] At operation 9, the source TRP 1204 may transmit a RRC reconfiguration message to the UE 1202. As in FIG. 11, the

RRCConnection econfiguration message may contain mobility information. This differs from the signal flow shown in FIG. 11 in which the source gNB may send the RRCConnectionReconfiguration message directly to the UE.

[00130] At operation 12, the UE 1202 may continue to communicate with the source TRP 1204 while performing a random access procedure with the target TRP 1206. The target TRP ID may be indicated in the

RRCConnectionReconfiguration message.

[00131] Once the random access procedure is completed, the UE 1202 may communicate with the source gNB 1212. In particular, the UE 1202 may send a RRCConnectionReconfigurationComplete message to the target TRP 1206 at operation 13 to complete the handover. As shown, the UE 1202 may continue to communicate with the source TRP 1204.

[00132] When handover is complete, the target TRP 1206 may notify the target gNB 1214 of successful handover. Thus, at operation 14, in response to reception of the RRCConnectionReconfigurationComplete message, the target TRP 1206 may send an indication of handover success to the target gNB 1214.

[00133] The target gNB 1214, in response to reception of the handover success indication, may request the communication path to be switched. As shown, the target gNB 1214 may send a path switch request to the MME 1220 at operation 15.

[00134] The MME 1220, in response to reception of the path switch request, may request the bearer to be modified. As shown, the MME 1220 may send a Modify bearer request to the SGW 1230 at operation 16.

[00135] The SGW 1230 may transmit an end maker to the source gNB 1212 to switch the path. The end marker may be forwarded by the source gNB 1212 to the UE 1202. After transmission of the end marker, the SGW 1230 may send a Modify bearer response to the MME 1220 at operation 17.

[00136] The MME 1220, in response to reception of the Modify bearer response may indicate that the communication path has been switched. As shown, the MME 1220 may send a path switch request ACK to the target gNB 1214 at operation 18. [00137] The target gNB 124 may indicate to the source gNB 1212 that the path has been modified. In particular, the target gNB 124 may send a UE context release to the source gNB 1212 at operation 19.

[00138] The source gNB 1212 may determine when a packet indicated by the end marker has been reached. At that point, the source gNB 1212 may indicate at operation 20 to the source TRP 1204 to terminate DL data transmission to the UE 1202. The source TRP 1204 may then stop DL data transmission at operation 21. The target TRP 1206 can subsequently release the UE 1202.

[00139] Dual or multiple beam-capable UEs can thus enhance inter-cell handover through the use of simultaneous transmission and reception with both the source and target cell. Moreover, as above, the data communicated between the UE and the source and target gNB may be different. In some embodiments, bi-casting may be used; the same data may be communicated from the source and target gNB. This may increase the reliability of data reception by the UE during handover. Alternatively, uni-casting may be used; different data may be communicated from the source and target gNB. In this case, re-ordering may be used above the PDCP layer to re-order data sent by the source and target gNB. This may reduce reliability but increase throughout.

[00140] Examples

[00141] Example 1 is an apparatus of a master eNodeB (MeNB), the apparatus comprising: at least one interface through which the MeNB is configured to communicate with a user equipment (UE) and a secondary eNodeB (SeNB); and processing circuitry in communication with the at least one interface and arranged to: encode, for transmission to the SeNB, a request to allocate radio resources for an evolved Universal Terrestrial Radio Access Network (E-UTRAN) Radio Access Bearer (E-RAB), the request comprising a Split Signal Radio Bearer (SRB) activation request to activate a Split SRB; in response to reception of an indication of acceptance of the SRB activation request from the SeNB, encode, for transmission to the UE, a Radio Resource Control (RRC) ConnectionReconfiguration message for activation of the Split SRB at the UE; and in response to reception of an indication of whether the Split SRB has been applied at the UE, encode, for transmission to the SeNB, an indication whether the Split SRB is successfully activated.

[00142] In Example 2, the subject matter of Example 1 optionally includes wherein: the Split SRB activation request is provided within a secondary cell group (SCG)-Configlnfo information element.

[00143] In Example 3, the subject matter of any one or more of Examples 1-2 optionally include wherein the processing circuitry is further configured to: in response to reception of an indication of rejection of the SRB activation request from the SeNB, use a default mode in which a SRB to be the Split SRB is active at the MeNB and is free from being active at the SeNB.

[00144] In Example 4, the subject matter of any one or more of Examples 1-3 optionally include wherein: the indication of whether application of the Split SRB has been applied at the UE comprises: an

RRCConnectionReconfigurationComplete message in response to the application of the Split SRB being applied at the UE, and a reconfiguration failure indication in response to the application of the Split SRB being applied at the UE.

[00145] In Example 5, the subject matter of any one or more of Examples 1-4 optionally include wherein: the RRCConnectionReconfiguration message is provided to the UE from the MeNB through the SeNB.

[00146] In Example 6, the subject matter of Example 5 optionally includes wherein: the RRCConnectionReconfiguration message is additionally provided to the UE directly from the MeNB.

[00147] In Example 7, the subject matter of any one or more of Examples 1-6 optionally include wherein: after the Split SRB is successfully activated, the processing circuitry is further configured to: encode, for transmission to the SeNB, a SeNB Modification Request, after reception of an acknowledgement to the SeNB Modification Request and in response to a link between the MeNB and the UE being temporarily unavailable, encode, for transmission to the UE through the SeNB, another RRC ConnectionReconfiguration message related to the SeNB Modification Request, and after transmission of the other RRC ConnectionReconfiguration message, decode a RRC ConnectionReconfigurationComplete message from the UE received through the SeNB.

[00148] In Example 8, the subject matter of any one or more of Examples 1-7 optionally include wherein: after the Split SRB is successfully activated, the processing circuitry is further configured to initiate one of a Me B change or a handover from the MeNB to the SeNB in response to a link between the MeNB and the UE being unavailable for a MeNB Link Outage Timer.

[00149] In Example 9, the subject matter of any one or more of Examples 1-8 optionally include wherein: after the Split SRB is successfully activated, the processing circuitry is further configured to encode, for transmission to the UE via the SeNB, another RRC message independent of whether a link between the MeNB and the UE is available.

[00150] In Example 10, the subject matter of any one or more of Examples 1-9 optionally include wherein: a protocol stack of the Split SRB is a packet data convergence protocol (PDCP)-based Split SRB protocol split.

[00151] In Example 11 , the subject matter of any one or more of Examples 1-10 optionally include wherein: a protocol stack of the Split SRB is a Radio Link Control (RLC)-based Split SRB protocol stack.

[00152] In Example 12, the subject matter of any one or more of Examples 1-1 1 optionally include wherein: the processing circuitry comprises a baseband processor configured to operate on signals at baseband frequencies, and the apparatus further comprises an antenna through which communications with the SeNB and UE occur.

[00153] Example 13 is an apparatus of a secondary eNodeB (SeNB), the apparatus comprising: at least one interface through which the SeNB is configured to communicate with a user equipment (UE) and a master eNodeB (MeNB); and processing circuitry in communication with the at least one interface and arranged to: decode, from the MeNB, a request to allocate radio resources for an evolved Universal Terrestrial Radio Access Network (E- UTRAN) Radio Access Bearer (E-RAB), the request comprising a Split Signal Radio Bearer (SRB) activation request to activate a Split SRB; encode, for transmission to the MeNB, an indication of acceptance of the SRB activation request; and after the Split SRB is successfully activated, forward messages between the UE and the MeNB independent of whether a link between the MeNB and the UE is available.

[00154] In Example 14, the subject matter of Example 13 optionally includes wherein: the Split SRB activation request is provided within a secondary cell group (SCG)-Configlnfo information element.

[00155] In Example 15, the subject matter of any one or more of

Examples 13-14 optionally include wherein: in response to acceptance of an MeNB change request from the MeNB, the processing circuitry is further configured to: set up a protocol stack for the UE, encode, for transmission to a Mobility Management Entity (MME), a path switch request to switch a communication path from between a signal gateway (SGW) and the MeNB to between the SGW and the SeNB, and in response to an indication of acknowledgment to the path switch request, encode, for transmission to the MeNB, a UE context release message to the MeNB.

[00156] In Example 16, the subject matter of any one or more of Examples 13-15 optionally include wherein: the indication of whether application of the Split SRB has been applied at the UE comprises: an

RRCConnectionReconfigurationComplete message in response to the application of the Split SRB being applied at the UE, and a reconfiguration failure indication in response to the application of the Split SRB being applied at the UE.

[00157] In Example 17, the subject matter of any one or more of Examples 13-16 optionally include wherein: a RRCConnectionReconfiguration message for activation of the Split SRB at the UE is provided to the UE from the MeNB through the SeNB.

[00158] In Example 18, the subject matter of any one or more of

Examples 13-17 optionally include wherein: after the Split SRB is successfully activated, the processing circuitry is further configured to: decode, a SeNB Modification Request from the MeNB in response to a link between the MeNB and the UE being temporarily unavailable, forward, from the MeNB to the UE, a RRC ConnectionReconfiguration message related to the SeNB Modification Request after transmission of an acknowledgment of the SeNB Modification Request, and forward, from the UE to the MeNB, a RRC Connection econfigurationComplete message in response to transmission of the RRC ConnectionReconfiguration message to the UE.

[00159] In Example 19, the subject matter of any one or more of Examples 13-18 optionally include wherein: after the Split SRB is successfully activated, the processing circuitry is further configured to initiate one of a MeNB change or a handover from the MeNB to the SeNB in response to a link between the MeNB and the UE being unavailable for a MeNB Link Outage Timer.

[00160] In Example 20, the subject matter of any one or more of Examples 13-19 optionally include wherein: a protocol stack of the Split SRB is a packet data convergence protocol (PDCP)-based Split SRB protocol split.

[00161] In Example 21, the subject matter of any one or more of Examples 13-20 optionally include wherein: a protocol stack of the Split SRB is a Radio Link Control (RLC)-based Split SRB protocol stack.

[00162] Example 22 is a computer-readable storage medium that stores instructions for execution by one or more processors of a master eNodeB

(MeNB), the one or more processors to: encode, for transmission to a secondary eNodeB (SeNB), a request to allocate radio resources for an evolved Universal Terrestrial Radio Access Network (E-UTRAN) Radio Access Bearer (E-RAB), the request comprising a Split Signal Radio Bearer (SRB) activation request to activate a Split SRB, a protocol stack of the Split SRB comprising one of a packet data convergence protocol (PDCP)-based Split SRB protocol split or a Radio Link Control (RLC)-based Split SRB protocol stack; in response to reception of an indication of acceptance of the SRB activation request from the SeNB, encode, for transmission to a User Equipment (UE), a Radio Resource Control (RRC) ConnectionReconfiguration message for activation of the Split SRB at the UE; and in response to reception of an indication of whether the Split SRB has been applied at the UE, encode, for transmission to the SeNB, an indication whether the Split SRB is successfully activated.

[00163] In Example 23, the subject matter of Example 22 optionally includes wherein the instructions further configure the one or more processors to: in response to reception of an indication of rejection of the SRB activation request from the SeNB, use a default mode in which a SRB to be the Split SRB is active at the MeNB and is free from being active at the SeNB. [00164] In Example 24, the subject matter of any one or more of Examples 22-23 optionally include wherein: the indication of whether application of the Split SRB has been applied at the UE comprises: an

RRCConnectionReconfigurationComplete message in response to the application of the Split SRB being applied at the UE, and a reconfiguration failure indication in response to the application of the Split SRB being applied at the UE.

[00165] In Example 25, the subject matter of any one or more of Examples 22-24 optionally include wherein: the

RRCConnectionReconfiguration message is provided to the UE from the MeNB through the SeNB.

[00166] In Example 26, the subject matter of any one or more of Examples 22-25 optionally include wherein: the

RRCConnectionReconfiguration message is additionally provided to the UE directly from the MeNB.

[00167] In Example 27, the subject matter of any one or more of Examples 22-26 optionally include wherein: after the Split SRB is successfully activated, the instructions further configure the one or more processors to: encode, for transmission to the SeNB, a SeNB Modification Request, after reception of an acknowledgement to the SeNB Modification Request and in response to a link between the MeNB and the UE being temporarily unavailable, encode, for transmission to the UE through the SeNB, another RRC

ConnectionReconfiguration message related to the SeNB Modification Request, and after transmission of the other RRC ConnectionReconfiguration message, decode a RRC ConnectionReconfigurationComplete message from the UE received through the SeNB.

[00168] In Example 28, the subject matter of any one or more of Examples 22-27 optionally include wherein: after the Split SRB is successfully activated, the instructions further configure the one or more processors to initiate one of a MeNB change or a handover from the MeNB to the SeNB in response to a link between the MeNB and the UE being unavailable for a MeNB Link Outage Timer. [00169] In Example 29, the subject matter of any one or more of Examples 22-28 optionally include wherein: after the Split SRB is successfully activated, the instructions further configure the one or more processors to encode, for transmission to the UE via the SeNB, another RRC message independent of whether a link between the MeNB and the UE is available.

[00170] Example 30 is a method of using a Split Signal Radio Bearer (SRB) in a master eNodeB (MeNB), the method comprising: encoding, for transmission to a secondary eNodeB (SeNB), a request to allocate radio resources for an evolved Universal Terrestrial Radio Access Network (E- UTRAN) Radio Access Bearer (E-RAB), the request comprising a SRB activation request to activate a Split SRB, a protocol stack of the Split SRB comprising one of a packet data convergence protocol (PDCP)-based Split SRB protocol split or a Radio Link Control (RLC)-based Split SRB protocol stack; in response to reception of an indication of acceptance of the SRB activation request from the SeNB, encoding, for transmission to a User Equipment (UE), a Radio Resource Control (RRC) ConnectionReconfiguration message for activation of the Split SRB at the UE; and in response to reception of an indication of whether the Split SRB has been applied at the UE, encoding, for transmission to the SeNB, an indication whether the Split SRB is successfully activated.

[00171] In Example 31, the subject matter of Example 30 optionally includes in response to reception of an indication of rejection of the SRB activation request from the SeNB, using a default mode in which a SRB to be the Split SRB is active at the MeNB and is free from being active at the SeNB.

[00172] In Example 32, the subject matter of any one or more of Examples 30-31 optionally include wherein: the indication of whether application of the Split SRB has been applied at the UE comprises: an

RRCConnectionReconfigurationComplete message in response to the application of the Split SRB being applied at the UE, and a reconfiguration failure indication in response to the application of the Split SRB being applied at the UE.

[00173] In Example 33, the subject matter of any one or more of Examples 30-32 optionally include wherein: the RRCConnectionReconfiguration message is provided to the UE from the MeNB through the SeNB.

[00174] In Example 34, the subject matter of any one or more of Examples 30-33 optionally include wherein: the

RRCConnectionReconfiguration message is additionally provided to the UE directly from the MeNB.

[00175] In Example 35, the subject matter of any one or more of Examples 30-34 optionally include after the Split SRB is successfully activated: encoding, for transmission to the SeNB, a SeNB Modification Request, after reception of an acknowledgement to the SeNB Modification Request and in response to a link between the MeNB and the UE being temporarily unavailable, encoding, for transmission to the UE through the SeNB, another RRC

ConnectionReconfiguration message related to the SeNB Modification Request, and after transmission of the other RRC ConnectionReconfiguration message, decoding a RRC ConnectionReconfigurationComplete message from the UE received through the SeNB.

[00176] In Example 36, the subject matter of any one or more of Examples 30-35 optionally include after the Split SRB is successfully activated, initiating one of a MeNB change or a handover from the MeNB to the SeNB in response to a link between the MeNB and the UE being unavailable for a MeNB Link Outage Timer.

[00177] In Example 37, the subject matter of any one or more of Examples 30-36 optionally include after the Split SRB is successfully activated, encoding, for transmission to the UE via the SeNB, another RRC message independent of whether a link between the MeNB and the UE is available.

[00178] Example 38 is an apparatus of a master eNodeB (MeNB), the apparatus comprising: means for encoding, for transmission to a secondary eNodeB (SeNB), a request to allocate radio resources for an evolved Universal Terrestrial Radio Access Network (E-UTRAN) Radio Access Bearer (E-RAB), the request comprising a Split Signal Radio Bearer (SRB) activation request to activate a Split SRB, a protocol stack of the Split SRB comprising one of a packet data convergence protocol (PDCP)-based Split SRB protocol split or a Radio Link Control (RLC)-based Split SRB protocol stack; in response to reception of an indication of acceptance of the SRB activation request from the SeNB, means for encoding, for transmission to a User Equipment (UE), a Radio Resource Control (RRC) ConnectionReconfiguration message for activation of the Split SRB at the UE; and in response to reception of an indication of whether the Split SRB has been applied at the UE, means for encoding, for transmission to the SeNB, an indication whether the Split SRB is successfully activated.

[00179] In Example 39, the subject matter of Example 38 optionally includes in response to reception of an indication of rejection of the SRB activation request from the SeNB, means for using a default mode in which a SRB to be the Split SRB is active at the MeNB and is free from being active at the SeNB.

[001801 In Example 40, the subject matter of any one or more of Examples 38-39 optionally include wherein: the indication of whether application of the Split SRB has been applied at the UE comprises: an

RRCConnectionReconfigurationComplete message in response to the application of the Split SRB being applied at the UE, and a reconfiguration failure indication in response to the application of the Split SRB being applied at the UE.

[00181] In Example 41 , the subject matter of any one or more of Examples 38-40 optionally include wherein: the

RRCConnectionReconfiguration message is provided to the UE from the MeNB through the SeNB.

[00182] In Example 42, the subject matter of any one or more of Examples 38—41 optionally include wherein: the

RRCConnectionReconfiguration message is additionally provided to the UE directly from the MeNB,

[00183] In Example 43, the subject matter of any one or more of Examples 38^2 optionally include after the Split SRB is successfully activated: means for encoding, for transmission to the SeNB, a SeNB Modification Request, after reception of an acknowledgement to the SeNB Modification Request and in response to a link between the MeNB and the UE being temporarily unavailable, means for encoding, for transmission to the UE through the SeNB, another RRC ConnectionReconfiguration message related to the SeNB Modification Request, and after transmission of the other RRC

ConnectionReconfiguration message, means for decoding a RRC

ConnectionReconfigurationComplete message from the UE received through the SeNB.

[00184] In Example 44, the subject matter of any one or more of

Examples 38^3 optionally include after the Split SRB is successfully activated, means for initiating one of a MeNB change or a handover from the MeNB to the SeNB in response to a link between the MeNB and the UE being unavailable for a MeNB Link Outage Timer.

[00185] In Example 45, the subject matter of any one or more of

Examples 38-44 optionally include after the Split SRB is successfully activated, means for encoding, for transmission to the UE via the SeNB, another RRC message independent of whether a link between the MeNB and the UE is available.

[00186] Although an embodiment has been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader scope of the present disclosure. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. The

accompanying drawings that form a part hereof show, by way of illustration, and not of limitation, specific embodiments in which the subject matter may be practiced. The embodiments illustrated are described in sufficient detail to enable those skilled in the art to practice the teachings disclosed herein. Other embodiments may be utilized and derived therefrom, such that structural and logical substitutions and changes may be made without departing from the scope of this disclosure. This Detailed Description, therefore, is not to be taken in a limiting sense, and the scope of various embodiments is defined only by the appended claims, along with the full range of equivalents to which such claims are entitled.

[00187] The subject matter may be referred to herein, individually and/or collectively, by the term "embodiment" merely for convenience and without intending to voluntarily limit the scope of this application to any single inventive concept if more than one is in fact disclosed. Thus, although specific embodiments have been illustrated and described herein, it should be appreciated that any arrangement calculated to achieve the same purpose may be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments. Combinations of the above embodiments, and other embodiments not specifically described herein, will be apparent to those of skill in the art upon reviewing the above description.

[00188] In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one, independent of any other instances or usages of "at least one" or "one or more." In this document, the term "or" is used to refer to a nonexclusive or, such that "A or B" includes "A but not B," "B but not A," and "A and B," unless otherwise indicated. In this document, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "wherein." Also, in the following claims, the terms "including" and "comprising" are open-ended, that is, a system, UE, article, composition, formulation, or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim. Moreover, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects.

[00189] The Abstract of the Disclosure is provided to comply with 37 C.F.R. § 1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the

Detailed Description, with each claim standing on its own as a separate embodiment.

Claims

CLAIMS What is claimed is:
1. An apparatus of a master eNodeB (MeNB), the apparatus comprising: at least one interface through which the MeNB is configured to communicate with a user equipment (UE) and a secondary eNodeB (SeNB); and processing circuitry in communication with the at least one interface and arranged to:
encode, for transmission to the SeNB, a request to allocate radio resources for an evolved Universal Terrestrial Radio Access Network (E-
UTRAN) Radio Access Bearer (E-RAB), the request comprising a Split Signal Radio Bearer (SRB) activation request to activate a Split SRB; in response to reception of an indication of acceptance of the SRB activation request from the SeNB, encode, for transmission to the UE, a Radio Resource Control (RRC) ConnectionReconfiguration message for activation of the Split SRB at the UE; and
in response to reception of an indication of whether the Split SRB has been applied at the UE, encode, for transmission to the SeNB, an indication whether the Split SRB is successfully activated.
2. The apparatus of claim 1, wherein:
the Split SRB activation request is provided within a secondary cell group (SCG)-Configlnfo information element.
3. The apparatus of claim 1 or 2, wherein the processing circuitry is further configured to:
in response to reception of an indication of rejection of the SRB activation request from the SeNB, use a default mode in which a SRB to be the Split SRB is active at the MeNB and is free from being active at the SeNB.
4. The apparatus of claim 1 or 2, wherein:
the indication of whether application of the Split SRB has been applied at the UE comprises: an R CConnectionReconfigurationComplete message in response to the application of the Split SRB being applied at the UE, and a reconfiguration failure indication in response to the application of the Split SRB being applied at the UE.
5. The apparatus of claim 1 or 2, wherein:
the RRCConnectionReconfiguration message is provided to the UE from the MeNB through the SeNB.
6. The apparatus of claim 5, wherein:
the RRCConnectionReconfiguration message is additionally provided to the UE directly from the MeNB.
7. The apparatus of claim 1 or 2, wherein:
after the Split SRB is successfully activated, the processing circuitry is further configured to:
encode, for transmission to the SeNB, a SeNB Modification
Request,
after reception of an acknowledgement to the SeNB Modification Request and in response to a link between the MeNB and the UE being temporarily unavailable, encode, for transmission to the UE through the SeNB, another RRC ConnectionReconfiguration message related to the SeNB Modification Request, and
after transmission of the other RRC ConnectionReconfiguration message, decode a RRC ConnectionReconfigurationComplete message from the UE received through the SeNB.
8. The apparatus of claim 1 or 2, wherein:
after the Split SRB is successfully activated, the processing circuitry is further configured to initiate one of a MeNB change or a handover from the MeNB to the SeNB in response to a link between the MeNB and the UE being unavailable for a MeNB Link Outage Timer.
9. The apparatus of claim 1 or 2, wherein:
after the Split SRB is successfully activated, the processing circuitry is further configured to encode, for transmission to the UE via the SeNB, another RRC message independent of whether a link between the MeNB and the UE is available.
10. The apparatus of claim 1 or 2, wherein:
a protocol stack of the Split SRB is a packet data convergence protocol (PDCP)-based Split SRB protocol split.
11. The apparatus of claim 1 or 2, wherein:
a protocol stack of the Split SRB is a Radio Link Control (RLC)-based Split SRB protocol stack.
12. The apparatus of claim 1 or 2, wherein:
the processing circuitry comprises a baseband processor configured to operate on signals at baseband frequencies, and
the apparatus further comprises an antenna through which
communications with the SeNB and UE occur.
13. An apparatus of a secondary eNodeB (SeNB), the apparatus comprising: at least one interface through which the SeNB is configured to communicate with a user equipment (UE) and a master eNodeB (MeNB); and processing circuitry in communication with the at least one interface and arranged to:
decode, from the MeNB, a request to allocate radio resources for an evolved Universal Terrestrial Radio Access Network (E-UTRAN) Radio Access Bearer (E-RAB), the request comprising a Split Signal Radio Bearer (SRB) activation request to activate a Split SRB;
encode, for transmission to the MeNB, an indication of acceptance of the SRB activation request; and after the Split SRB is successfully activated, forward messages between the UE and the MeNB independent of whether a link between the MeNB and the UE is available.
14. The apparatus of claim 13, wherein:
the Split SRB activation request is provided within a secondary cell group (SCG)-Configlnfo information element.
15. The apparatus of claim 13 or 14, wherein:
in response to acceptance of an MeNB change request from the MeNB, the processing circuitry is further configured to:
set up a protocol stack for the UE,
encode, for transmission to a Mobility Management Entity (MME), a path switch request to switch a communication path from between a signal gateway (SGW) and the MeNB to between the SGW and the SeNB, and
in response to an indication of acknowledgment to the path switch request, encode, for transmission to the MeNB, a UE context release message to the MeNB.
16. The apparatus of claim 13 or 14, wherein:
the indication of whether application of the Split SRB has been applied at the UE comprises:
an RRCConnectionReconfigurationComplete message in response to the application of the Split SRB being applied at the UE, and a reconfiguration failure indication in response to the application of the Split SRB being applied at the UE.
17. The apparatus of claim 13 or 14, wherein:
a RRCConnectionReconfiguration message for activation of the Split
SRB at the UE is provided to the UE from the MeNB through the SeNB.
18. The apparatus of claim 13 or 14, wherein: after the Split SRB is successfully activated, the processing circuitry is further configured to:
decode, a SeNB Modification Request from the MeNB in response to a link between the MeNB and the UE being temporarily unavailable,
forward, from the MeNB to the UE, a RRC
ConnectionReconfiguration message related to the SeNB Modification Request after transmission of an acknowledgment of the SeNB
Modification Request, and
forward, from the UE to the MeNB, a RRC
ConnectionReconfigurationComplete message in response to transmission of the RRC ConnectionReconfiguration message to the UE.
19. The apparatus of claim 13 or 14, wherein:
after the Split SRB is successfully activated, the processing circuitry is further configured to initiate one of a MeNB change or a handover from the MeNB to the SeNB in response to a link between the MeNB and the UE being unavailable for a MeNB Link Outage Timer.
20. The apparatus of claim 13 or 14, wherein:
a protocol stack of the Split SRB is a packet data convergence protocol (PDCP)-based Split SRB protocol split.
21. The apparatus of claim 13 or 14, wherein:
a protocol stack of the Split SRB is a Radio Link Control (RLC)-based Split SRB protocol stack.
22. A computer-readable storage medium that stores instructions for execution by one or more processors of a master eNodeB (MeNB), the one or more processors to:
encode, for transmission to a secondary eNodeB (SeNB), a request to allocate radio resources for an evolved Universal Terrestrial Radio Access Network (E-UTRAN) Radio Access Bearer (E-RAB), the request comprising a Split Signal Radio Bearer (SRB) activation request to activate a Split SRB, a protocol stack of the Split SRB comprising one of a packet data convergence protocol (PDCP)-based Split SRB protocol split or a Radio Link Control (RLC)- based Split SRB protocol stack;
in response to reception of an indication of acceptance of the SRB activation request from the SeNB, encode, for transmission to a User Equipment (UE), a Radio Resource Control (RRC) ConnectionReconfiguration message for activation of the Split SRB at the UE; and
in response to reception of an indication of whether the Split SRB has been applied at the UE, encode, for transmission to the SeNB, an indication whether the Split SRB is successfully activated.
23. The medium of claim 22, wherein the instructions further configure the one or more processors to:
in response to reception of an indication of rejection of the SRB activation request from the SeNB, use a default mode in which a SRB to be the Split SRB is active at the MeNB and is free from being active at the SeNB.
24. The medium of claim 22 or 23, wherein:
the indication of whether application of the Split SRB has been applied at the UE comprises:
an RRCConnectionReconfigurationComplete message in response to the application of the Split SRB being applied at the UE, and a reconfiguration failure indication in response to the application of the Split SRB being applied at the UE.
25. The medium of claim 22 or 23, wherein:
the RRCConnectionReconfiguration message is provided to the UE from the MeNB through the SeNB.
26. The medium of claim 22 or 23, wherein:
the RRCConnectionReconfiguration message is additionally provided to the UE directly from the MeNB.
27. The medium of claim 22 or 23, wherein:
after the Split SRB is successfully activated, the instructions further configure the one or more processors to:
encode, for transmission to the SeNB, a SeNB Modification
Request,
after reception of an acknowledgement to the SeNB Modification Request and in response to a link between the MeNB and the UE being temporarily unavailable, encode, for transmission to the UE through the SeNB, another RRC ConnectionReconfiguration message related to the
SeNB Modification Request, and
after transmission of the other RRC ConnectionReconfiguration message, decode a RRC ConnectionReconfigurationComplete message from the UE received through the SeNB.
28. The medium of claim 22 or 23, wherein:
after the Split SRB is successfully activated, the instructions further configure the one or more processors to initiate one of a MeNB change or a handover from the MeNB to the SeNB in response to a link between the MeNB and the UE being unavailable for a MeNB Link Outage Timer.
29. The medium of claim 22 or 23, wherein:
after the Split SRB is successfully activated, the instructions further configure the one or more processors to encode, for transmission to the UE via the SeNB, another RRC message independent of whether a link between the MeNB and the UE is available.
PCT/US2017/037985 2016-09-26 2017-06-16 Splitting signal radio bearer enhancements for standalone 5g new rat multi-connectivity WO2018057076A1 (en)

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