WO2024093370A1

WO2024093370A1 - Obtaining random access report for secondary node

Info

Publication number: WO2024093370A1
Application number: PCT/CN2023/108268
Authority: WO
Inventors: Le Yan; Lianhai WU; Congchi ZHANG
Original assignee: Lenovo (Beijing) Limited
Priority date: 2023-07-19
Filing date: 2023-07-19
Publication date: 2024-05-10

Abstract

Various aspects of the present disclosure relate to network entities and methods for supporting obtaining of at least one RA report for at least one SN. In one aspect, a first base station receives an indication indicating that at least one RA report for at least one SN is available at a UE. The UE is connected to a second base station and a first SN among the at least one SN. In turn, the first base station obtains the at least one RA report from the UE.

Description

OBTAINING RANDOM ACCESS REPORT FOR SECONDARY NODE

TECHNICAL FIELD

The present disclosure relates to wireless communications, and more specifically to an apparatus and a method for obtaining at least one random access (RA) report for at least one secondary node (SN) .

BACKGROUND

A wireless communications system may include one or multiple network communication devices, such as base stations, which may be otherwise known as an eNodeB (eNB) , a next-generation NodeB (gNB) , or other suitable terminology. Each network communication devices, such as a base station may support wireless communications for one or multiple user communication devices, which may be otherwise known as user equipment (UE) , or other suitable terminology. The wireless communications system may support wireless communications with one or multiple user communication devices by utilizing resources of the wireless communication system (e.g., time resources (e.g., symbols, slots, subframes, frames, or the like) or frequency resources (e.g., subcarriers, carriers) . Additionally, the wireless communications system may support wireless communications across various radio access technologies including third generation (3G) radio access technology, fourth generation (4G) radio access technology, fifth generation (5G) radio access technology, among other suitable radio access technologies beyond 5G (e.g., sixth generation (6G) ) .

At least one RA report for at least one SN is supported in EUTRA-NR dual connection (EN-DC) scenario, NGEN-DC scenario and NR-DC scenario, for example, for EN-DC and NG EN-DC, the UE collects SN RA report container (e.g. the container is encoded in NR format) and reports to a master node (MN) . The existing RA-ReportList IE can be used to provide the list of one or more RA reports that is stored by the UE for the past successful random access procedures occurring in one or more SNs, which means that a list of SN RA report entries can be stored or reported in a single container (i.e. RA-ReportList can be represented as the single container, e.g. SN RA report container) . At least one RA report for at least one SN is also referred to as an SN RA report for brevity. In Release 18, it has agreed to define a new class-2 message (i.e., random access channel (RACH) INDICATION) over X2 or Xn interface so that a secondary next-generation radio access network (S-NG-RAN) can inform a master next-generation radio access network (M-NG-RAN) that one or more RA reports are available at a UE. In this way, SN where a RACH procedure occurs can indicate the potential availability of one or more RA reports to a MN. Then, the MN can fetch the one or more RA reports from the UE.

SUMMARY

The present disclosure relates to base stations and methods that support obtaining of at least one RA report for at least one SN. In this way, a target MN can obtain at least one RA report for at least one SN. In addition, the RACH optimization may be achieved.

Some implementations of a first base station described herein may include: receiving an indication indicating that at least one RA report for at least one SN is available at a UE, the UE being connected to a second base station and a first SN among the at least one SN; and obtaining the at least one RA report from the UE.

In some implementations, a handover from the second base station to the first base station is triggered, and the first base station is configured to receive the indication by receiving the indication from the second base station.

In some implementations, the first base station is configured to receive the indication from the second base station by receiving, from the second base station, a handover request message comprising the indication.

In some implementations, the first base station is configured to receive the indication from the second base station by receiving, from the second base station, a message which indicates that the at least one RA report for the at least one SN is available at the UE.

In some implementations, the message comprises a gNodeB (gNB) UE XnAP identity (ID) or an eNodeB (eNB) UE X2AP ID allocated at the first base station.

In some implementations, a handover from the second base station to the first base station is triggered, and the first base station is configured to receive the indication by receiving the indication from the first SN.

In some implementations, the first base station is configured to receive the indication from the first SN by receiving, from the first SN, one of the following comprising the indication: a secondary gNodeB (SgNB) addition request acknowledge message, or an SN addition request acknowledge message.

In some implementations, the first base station is configured to obtain the at least one RA report from the UE by: transmitting, to the UE, a UE information request message; receiving, via the transceiver from the UE, a UE information response message comprising the at least one RA report.

In some implementations, each of the at least one RA report comprises an identity of a primary secondary cell (PSCell) associated with one of the at least one SN; and the first base station is further configured to obtain, from the second base station, at least one identity of at least one primary cell (PCell) associated with the PSCell.

In some implementations, the first base station is configured to obtain the at least one identity of the at least one PCell by: transmitting, to the second base station, a request for latest UE history information (UHI) ; and receiving, via the transceiver from the second base station, the latest UHI which at least comprises the at least one identity of the at least one PCell.

In some implementations, the first base station is configured to transmit the request for the latest UHI by transmitting, to the second base station, one of the following comprising the request: a UE context release message, a dedicated X2 message, or a dedicated Xn message.

In some implementations, the first base station is configured to obtain the at least one identity of the at least one PCell by: transmitting, to the second base station, a subscription request for latest UE history information (UHI) ; and receiving, from the second base station, a subscription notification comprising the at least one identity of the at least one PCell or the latest UHI comprising the at least one identity of the at least one PCell.

In some implementations, the first base station is configured to transmit the subscription request by transmitting, to the second base station, a handover request acknowledge message comprising an indication for the subscription request.

In some implementations, the first base station is configured to obtain the at least one identity of the at least one PCell by: transmitting, to the second base station, a request for an identity of a latest PCell; and receiving, from the second base station, a response comprising the identity of the latest PCell.

In some implementations, the first base station is configured to transmit the request for the identity of the latest PCell by transmitting, to the second base station, one of the following comprising the request: a UE context release message, a dedicated X2 message, or a dedicated Xn message.

In some implementations, the first base station is further configured to transmit one of the at least one RA report to at least one third base station associated with the at least one PCell.

Some implementations of a second base station described herein may include: receiving, from a first SN, an indication indicating that at least one RA report for at least one SN is available at a UE, the UE being connected to the second base station and the first SN, the at least one SN comprising the first SN; and transmitting the indication to a first base station.

In some implementations, a handover from the second base station to the first base station is triggered, and the second base station is configured to transmit the indication by transmitting, to the first base station, a handover request message comprising the indication.

In some implementations, a handover from the second base station to the first base station is triggered, and the second base station is configured to transmit the indication to the first base station by transmitting, to the first base station, a message which indicates that the at least one RA report for the at least one SN is available at the UE.

In some implementations, the message comprises a gNB UE XnAP ID or an eNB UE X2AP ID allocated at the first base station.

In some implementations, each of the at least one RA report comprises an identity of a PSCell associated with one of the at least one SN; and the second base station is further configured to transmit, to the first base station, at least one identity of at least one PCell associated with the PSCell.

In some implementations, the second base station is configured to transmit the at least one identity of the at least one PCell by: receiving, from the first base station, a request for latest UHI; and transmitting, to the first base station, the latest UHI which at least comprises at least one identity of the at least one PCell.

In some implementations, the second base station is configured to receive the request for the latest UHI by receiving, from the first base station, one of the following comprising the request: a UE context release message, a dedicated X2 message, or a dedicated Xn message.

In some implementations, the second base station is configured to transmit at least one identity of the at least one PCell by: receiving, from the first base station, a subscription request for latest UHI; and based on determining PCell change or UHI change, transmitting, to the first base station, a subscription notification comprising the at least one identity of the at least one PCell or the latest UHI comprising the at least one identity of the at least one PCell.

In some implementations, the second base station is configured to receive the subscription request by receiving, from the first base station, a handover request acknowledge message comprising an indication for the subscription request.

In some implementations, the second base station is configured to transmit the at least one identity of the at least one PCell by: receiving, from the first base station, a request for an identity of a latest PCell; and transmitting, to the first base station, a response comprising the identity of the latest PCell.

In some implementations, the second base station is configured to receive the request for the identity of the latest PCell by receiving, from the first base station, one of the following comprising the request: a UE context release message, a dedicated X2 message, or a dedicated Xn message.

It is to be understood that the summary section is not intended to identity key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1A and 1B illustrate an example of a wireless communications system that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure, respectively;

Fig. 2 illustrates a signaling chart illustrating an example process that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure;

Figs. 3 to 7 illustrate an example implementation of the example process in Fig. 2 in accordance with some implementations of the present disclosure, respectively;

Figs. 8 to 12 illustrate a signaling chart illustrating an example process that supports obtaining of at least one identity of at least one PCell in accordance with some implementations of the present disclosure, respectively;

Fig. 13 illustrates an example of a device that supports obtaining of at least one RA report for at least one SN in accordance with some aspects of the present disclosure;

Fig. 14 illustrates an example of a device that supports obtaining of at least one RA report for at least one SN in accordance with some aspects of the present disclosure;

Fig. 15 illustrates a flowchart of a method that supports obtaining of at least one RA report for at least one SN in accordance with some aspects of the present disclosure; and

Fig. 16 illustrates a flowchart of a method that supports indication of unused TOs in accordance with other aspects of the present disclosure.

DETAILED DESCRIPTION

Principles of the present disclosure will now be described with reference to some embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein may be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

References in the present disclosure to “one embodiment, ” “an example embodiment, ” “an embodiment, ” “some embodiments, ” and the like indicate that the embodiment (s) described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment (s) . Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” or the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, a first element could also be termed as a second element, and similarly, a second element could also be termed as a first element, without departing from the scope of embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” , “comprising” , “has” , “having” , “includes” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.

Currently in Release 18, an SN RA report is being discussed, but there are some issues left to be considered. For example, if an inter-MN handover (HO) happens, how does a target MN know when and how to obtain the SN RA report from a UE needs to be considered. For another example, in case inter-MN HO happens, or the MN that obtains the SN RA report is not connected to any SN related to the primary secondary cell (PSCell) associated with the SN RA report, or the node that obtains the SN RA report does not have an X2 or Xn interface with the PSCells indicated by the UE in the SN RA report, how to forward the SN RA report needs to be considered.

In view of the above, the present disclosure provides a solution that supports obtaining of at least one RA report for at least one SN. In this solution, a first base station receives an indication indicating that at least one RA report for at least one SN is available at a UE. The UE is connected to a second base station and a first SN among the at least one SN. In turn, the first base station obtains the at least one RA report from the UE. In this way, a target MN can obtain at least one RA report for at least one SN.

Aspects of the present disclosure are described in the context of a wireless communications system.

Fig. 1A illustrates an example of a wireless communications system 100 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. The wireless communications system 100 may include one at least one of network entities 102-1 and 102-2 (also referred to as network equipment (NE) ) , one or more terminal devices or UEs 104, a core network 106, and a packet data network 108. The wireless communications system 100 may support various radio access technologies. In some implementations, the wireless communications system 100 may be a 4G network, such as an LTE network or an LTE-advanced (LTE-A) network. In some other implementations, the wireless communications system 100 may be a 5G network, such as an NR network. In other implementations, the wireless communications system 100 may be a combination of a 4G network and a 5G network, or other suitable radio access technology including institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20. The wireless communications system 100 may support radio access technologies beyond 5G. Additionally, the wireless communications system 100 may support technologies, such as time division multiple access (TDMA) , frequency division multiple access (FDMA) , or code division multiple access (CDMA) , etc.

The network entities 102-1 and 102-2 may be collectively referred to as network entities 102 or individually referred to as a network entity 102. Alternatively, the network entities 102-1 and 102-2 may be referred to as a first network entity 102-1 and a second network entity 102-2, respectively.

The network entities 102 may be dispersed throughout a geographic region to form the wireless communications system 100. One or more of the network entities 102 described herein may be or include or may be referred to as a network node, a base station (BS) , a network element, a radio access network (RAN) node, a base transceiver station, an access point, a NodeB, an eNodeB (eNB) , a next-generation NodeB (gNB) , or other suitable terminology. A network entity 102 and a UE 104 may communicate via a communication link 110, which may be a wireless or wired connection. For example, a network entity 102 and a UE 104 may perform wireless communication (e.g., receive signaling, transmit signaling) over a Uu interface.

A network entity 102 may provide a geographic coverage area 112 for which the network entity 102 may support services (e.g., voice, video, packet data, messaging, broadcast, etc. ) for one or more UEs 104 within the geographic coverage area 112. For example, a network entity 102 and a UE 104 may support wireless communication of signals related to services (e.g., voice, video, packet data, messaging, broadcast, etc. ) according to one or multiple radio access technologies. In some implementations, a network entity 102 may be moveable, for example, a satellite associated with a non-terrestrial network. In some implementations, different geographic coverage areas 112 associated with the same or different radio access technologies may overlap, but the different geographic coverage areas 112 may be associated with different network entities 102. Information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

The one or more UEs 104 may be dispersed throughout a geographic region of the wireless communications system 100. A UE 104 may include or may be referred to as a mobile device, a wireless device, a remote device, a remote unit, a handheld device, or a subscriber device, or some other suitable terminology. In some implementations, the UE 104 may be referred to as a unit, a station, a terminal, or a client, among other examples. Additionally, or alternatively, the UE 104 may be referred to as an internet-of-things (IoT) device, an internet-of-everything (IoE) device, or machine-type communication (MTC) device, among other examples. In some implementations, a UE 104 may be stationary in the wireless communications system 100. In some other implementations, a UE 104 may be mobile in the wireless communications system 100.

The one or more UEs 104 may be devices in different forms or having different capabilities. Some examples of UEs 104 are illustrated in Fig. 1A. A UE 104 may be capable of communicating with various types of devices, such as the network entities 102, other UEs 104, or network equipment (e.g., the core network 106, the packet data network 108, a relay device, an integrated access and backhaul (IAB) node, or another network equipment) , as shown in Fig. 1A. Additionally, or alternatively, a UE 104 may support communication with other network entities 102 or UEs 104, which may act as relays in the wireless communications system 100.

A UE 104 may also be able to support wireless communication directly with other UEs 104 over a communication link 114. For example, a UE 104 may support wireless communication directly with another UE 104 over a device-to-device (D2D) communication link. In some implementations, such as vehicle-to-vehicle (V2V) deployments, vehicle-to-everything (V2X) deployments, or cellular-V2X deployments, the communication link 114 may be referred to as a sidelink. For example, a UE 104 may support wireless communication directly with another UE 104 over a PC5 interface.

A network entity 102 may support communications with the core network 106, or with another network entity 102, or both. For example, a network entity 102 may interface with the core network 106 through one or more backhaul links 116 (e.g., via an S1, N2, N2, or another network interface) . The network entities 102 may communicate with each other over the backhaul links 116 (e.g., via an X2, Xn, or another network interface) . In some implementations, the network entities 102 may communicate with each other directly (e.g., between the network entities 102) . In some other implementations, the network entities 102 may communicate with each other or indirectly (e.g., via the core network 106) . In some implementations, one or more network entities 102 may include subcomponents, such as an access network entity, which may be an example of an access node controller (ANC) . An ANC may communicate with the one or more UEs 104 through one or more other access network transmission entities, which may be referred to as a radio heads, smart radio heads, or transmission-reception points (TRPs) .

In some implementations, a network entity 102 may be configured in a disaggregated architecture, which may be configured to utilize a protocol stack physically or logically distributed among two or more network entities 102, such as an integrated access backhaul (IAB) network, an open radio access network (O-RAN) (e.g., a network configuration sponsored by the O-RAN Alliance) , or a virtualized RAN (vRAN) (e.g., a cloud RAN (C-RAN) ) . For example, a network entity 102 may include one or more of a central unit (CU) , a distributed unit (DU) , a radio unit (RU) , a RAN intelligent controller (RIC) (e.g., a near-real time RIC (Near-RT RIC) , a non-real time RIC (Non-RT RIC) ) , a service management and orchestration (SMO) system, or any combination thereof.

An RU may also be referred to as a radio head, a smart radio head, a remote radio head (RRH) , a remote radio unit (RRU) , or a transmission reception point (TRP) . One or more components of the network entities 102 in a disaggregated RAN architecture may be co-located, or one or more components of the network entities 102 may be located in distributed locations (e.g., separate physical locations) . In some implementations, one or more network entities 102 of a disaggregated RAN architecture may be implemented as virtual units (e.g., a virtual CU (VCU) , a virtual DU (VDU) , a virtual RU (VRU) ) .

Split of functionality between a CU, a DU, and an RU may be flexible and may support different functionalities depending upon which functions (e.g., network layer functions, protocol layer functions, baseband functions, radio frequency functions, and any combinations thereof) are performed at a CU, a DU, or an RU. For example, a functional split of a protocol stack may be employed between a CU and a DU such that the CU may support one or more layers of the protocol stack and the DU may support one or more different layers of the protocol stack. In some implementations, the CU may host upper protocol layer (e.g., a layer 3 (L3) , a layer 2 (L2) ) functionality and signaling (e.g., radio resource control (RRC) , service data adaption protocol (SDAP) , packet data convergence protocol (PDCP) ) . The CU may be connected to one or more DUs or RUs, and the one or more DUs or RUs may host lower protocol layers, such as a layer 1 (L1) (e.g., physical (PHY) layer) or an L2 (e.g., radio link control (RLC) layer, medium access control (MAC) layer) functionality and signaling, and may each be at least partially controlled by the CU 160.

Additionally, or alternatively, a functional split of the protocol stack may be employed between a DU and an RU such that the DU may support one or more layers of the protocol stack and the RU may support one or more different layers of the protocol stack. The DU may support one or multiple different cells (e.g., via one or more RUs) . In some implementations, a functional split between a CU and a DU, or between a DU and an RU may be within a protocol layer (e.g., some functions for a protocol layer may be performed by one of a CU, a DU, or an RU, while other functions of the protocol layer are performed by a different one of the CU, the DU, or the RU) .

A CU may be functionally split further into CU control plane (CU-CP) and CU user plane (CU-UP) functions. A CU may be connected to one or more DUs via a midhaul communication link (e.g., F1, F1-c, F1-u) , and a DU may be connected to one or more RUs via a fronthaul communication link (e.g., open fronthaul (FH) interface) . In some implementations, a midhaul communication link or a fronthaul communication link may be implemented in accordance with an interface (e.g., a channel) between layers of a protocol stack supported by respective network entities 102 that are in communication via such communication links.

The core network 106 may support user authentication, access authorization, tracking, connectivity, and other access, routing, or mobility functions. The core network 106 may be an evolved packet core (EPC) , or a 5G core (5GC) , which may include a control plane entity that manages access and mobility (e.g., a mobility management entity (MME) , an access and mobility management functions (AMF) ) and a user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW) , a packet data network (PDN) gateway (P-GW) , or a user plane function (UPF) ) . In some implementations, the control plane entity may manage non-access stratum (NAS) functions, such as mobility, authentication, and bearer management (e.g., data bearers, signal bearers, etc. ) for the one or more UEs 104 served by the one or more network entities 102 associated with the core network 106.

The core network 106 may communicate with the packet data network 108 over one or more backhaul links 116 (e.g., via an S1, N2, N2, or another network interface) . The packet data network 108 may include an application server 118. In some implementations, one or more UEs 104 may communicate with the application server 118. A UE 104 may establish a session (e.g., a protocol data unit (PDU) session, or the like) with the core network 106 via a network entity 102. The core network 106 may route traffic (e.g., control information, data, and the like) between the UE 104 and the application server 118 using the established session (e.g., the established PDU session) . The PDU session may be an example of a logical connection between the UE 104 and the core network 106 (e.g., one or more network functions of the core network 106) .

In the wireless communications system 100, the network entities 102 and the UEs 104 may use resources of the wireless communications system 100 (e.g., time resources (e.g., symbols, slots, subframes, frames, or the like) or frequency resources (e.g., subcarriers, carriers) ) to perform various operations (e.g., wireless communications) . In some implementations, the network entities 102 and the UEs 104 may support different resource structures. For example, the network entities 102 and the UEs 104 may support different frame structures. In some implementations, such as in 4G, the network entities 102 and the UEs 104 may support a single frame structure. In some other implementations, such as in 5G and among other suitable radio access technologies, the network entities 102 and the UEs 104 may support various frame structures (i.e., multiple frame structures) . The network entities 102 and the UEs 104 may support various frame structures based on one or more numerologies.

One or more numerologies may be supported in the wireless communications system 100, and a numerology may include a subcarrier spacing and a cyclic prefix. A first numerology (e.g., μ=0) may be associated with a first subcarrier spacing (e.g., 15 kHz) and a normal cyclic prefix. In some implementations, the first numerology (e.g., μ=0) associated with the first subcarrier spacing (e.g., 15 kHz) may utilize one slot per subframe. A second numerology (e.g., μ=1) may be associated with a second subcarrier spacing (e.g., 30 kHz) and a normal cyclic prefix. A third numerology (e.g., μ=2) may be associated with a third subcarrier spacing (e.g., 60 kHz) and a normal cyclic prefix or an extended cyclic prefix. A fourth numerology (e.g., μ=3) may be associated with a fourth subcarrier spacing (e.g., 120 kHz) and a normal cyclic prefix. A fifth numerology (e.g., μ=4) may be associated with a fifth subcarrier spacing (e.g., 240 kHz) and a normal cyclic prefix.

A time interval of a resource (e.g., a communication resource) may be organized according to frames (also referred to as radio frames) . Each frame may have a duration, for example, a 10 millisecond (ms) duration. In some implementations, each frame may include multiple subframes. For example, each frame may include 10 subframes, and each subframe may have a duration, for example, a 1 ms duration. In some implementations, each frame may have the same duration. In some implementations, each subframe of a frame may have the same duration.

Additionally or alternatively, a time interval of a resource (e.g., a communication resource) may be organized according to slots. For example, a subframe may include a number (e.g., quantity) of slots. The number of slots in each subframe may also depend on the one or more numerologies supported in the wireless communications system 100. For instance, the first, second, third, fourth, and fifth numerologies (i.e., μ=0, μ=1, μ=2, μ=3, μ=4) associated with respective subcarrier spacings of 15 kHz, 30 kHz, 60 kHz, 120 kHz, and 240 kHz may utilize a single slot per subframe, two slots per subframe, four slots per subframe, eight slots per subframe, and 16 slots per subframe, respectively. Each slot may include a number (e.g., quantity) of symbols (e.g., OFDM symbols) . In some implementations, the number (e.g., quantity) of slots for a subframe may depend on a numerology. For a normal cyclic prefix, a slot may include 14 symbols. For an extended cyclic prefix (e.g., applicable for 60 kHz subcarrier spacing) , a slot may include 12 symbols. The relationship between the number of symbols per slot, the number of slots per subframe, and the number of slots per frame for a normal cyclic prefix and an extended cyclic prefix may depend on a numerology. It should be understood that reference to a first numerology (e.g., μ=0) associated with a first subcarrier spacing (e.g., 15 kHz) may be used interchangeably between subframes and slots.

In the wireless communications system 100, an electromagnetic (EM) spectrum may be split, based on frequency or wavelength, into various classes, frequency bands, frequency channels, etc. By way of example, the wireless communications system 100 may support one or multiple operating frequency bands, such as frequency range designations FR1 (410 MHz –7.125 GHz) , FR2 (24.25 GHz –52.6 GHz) , FR3 (7.125 GHz –24.25 GHz) , FR4 (52.6 GHz –114.25 GHz) , FR4a or FR4-1 (52.6 GHz –71 GHz) , and FR5 (114.25 GHz –300 GHz) . In some implementations, the network entities 102 and the UEs 104 may perform wireless communications over one or more of the operating frequency bands. In some implementations, FR1 may be used by the network entities 102 and the UEs 104, among other equipment or devices for cellular communications traffic (e.g., control information, data) . In some implementations, FR2 may be used by the network entities 102 and the UEs 104, among other equipment or devices for short-range, high data rate capabilities.

FR1 may be associated with one or multiple numerologies (e.g., at least three numerologies) . For example, FR1 may be associated with a first numerology (e.g., μ=0) , which includes 15 kHz subcarrier spacing; a second numerology (e.g., μ=1) , which includes 30 kHz subcarrier spacing; and a third numerology (e.g., μ=2) , which includes 60 kHz subcarrier spacing. FR2 may be associated with one or multiple numerologies (e.g., at least 2 numerologies) . For example, FR2 may be associated with a third numerology (e.g., μ=2) , which includes 60 kHz subcarrier spacing; and a fourth numerology (e.g., μ=3) , which includes 120 kHz subcarrier spacing.

Hereinafter, some implementations of the present disclosure will be described by taking each of the network entities 102 as a base station. In this regard, the first network entity 102-1 and the second network entity 102-2 may be referred to as a first base station 102-1 and a second base station 102-2, respectively.

Fig. 1B illustrates an example of a wireless communications system 100B that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure.

Similar to the wireless communications system 100A, the wireless communications system 100B comprises the first base station 102-1, the second base station 102-2 and the UE 104. The wireless communications system 100B is different from the wireless communications system 100A in that the wireless communications system 100B further comprises a first SN 103. The UE 104 may be dually connected to the second base station 102-2 and the first SN 103. The second base station 102-2 may act as an MN. Due to mobility of the UE 104, a HO of the UE 104 from the second base station 102-2 to the first base station 102-1 may be triggered. For example, the HO may be an inter-MN HO. In this regard, the second base station 102-2 and the first base station 102-1 may be referred to as a source MN and a target MN, respectively.

Fig. 2 illustrates a signaling chart illustrating an example process 200 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. For the purpose of discussion, the process 200 will be described with reference to Fig. 1A or 1B. The process 200 may involve the first base station 102-1 and the UE 104 in Fig. 1A or 1B.

As shown in Fig. 2, the first base station 102-1 receives an indication indicating that at least one RA report for at least one SN is available at the UE 104. Hereinafter, at least one RA report for at least one SN is also referred to as at least one SN RA report for brevity. Alternatively, the indication may indicate one or more performed random access procedures at the at least one SN. Alternatively, the indication may indicate existence of the at least one RA report for at least one SN at the UE 104. The UE 104 is connected to the second base station 102-2 and the first SN 103, wherein the first SN 103 is among the at least one SN.

In turn, the first base station 102-1 obtains the at least one RA report for at least one SN from the UE 104.

With the process 200, a target MN can obtain at least one RA report for at least one SN.

In some implementations, in order to obtain the at least one RA report for at least one SN, the first base station 102-1 may transmit a UE information request message to the UE 104. For example, the UE information request message may comprise a flag for RA-Report request.

Upon receiving the UE information request message, the UE 104 may transmit a UE information response message to the first base station 102-1.

In some implementations, the UE information response message may comprise an RA report container. The RA report container may comprise an RA-ReportList. The RA-ReportList may comprise the at least one RA report that is stored by the UE for the past successful random access procedures occurring in one or more SNs. Each of the at least one RA report may be associated with a PSCell. For example, each of the at least one RA report may comprise an identity of the PSCell and RA related information (e.g. which can be represented by the RA-InformationCommon IE in TS38.331) . The identity of the PSCell may be a cellGlobalId or physical cell identifier (PCI) of the PSCell.

In some implementations, the UE information response message may further comprise a list of PSCell identities outside the RA report container. The PSCell identities comprise unique PSCell identities. That is, if an identity of the PSCell occurs more than once in the RA-ReportList, the identity of the PSCell is recorded only once in the list of PSCell identities.

In some implementations, a HO from the second base station 102-2 to the first base station 102-1 is triggered, and the first base station 102-1 may receive the indication from the second base station 102-2. In such implementations, the first base station 102-1 may receive, from the second base station 102-2, a HO request message comprising the indication. This will be described with reference to Fig. 3.

Fig. 3 illustrates a signaling chart illustrating an example process 300 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. The example process 300 may be considered as an example implementation of the process 200. For the purpose of discussion, the process 300 will be described with reference to Fig. 1B. The process 300 may involve the UE 104, the first base station 102-1, the second base station 102-2 and the first SN 103 in Fig. 1B.

Generally, in the process 300, a HO from the second base station 102-2 to the first base station 102-1 is triggered, and the HO comprises an inter-MN HO. The inter-MN HO may be triggered after a RACH INDICATION message is transmitted from the first SN 103 to the second base station 102-2 and before the at least one RA report for at least one SN is requested by the second base station 102-2 in Uu interface.

Specifically, as shown in Fig. 3, the first SN 103 transmits 310 a RACH INDICATION message to the second base station 102-2. The RACH INDICATION message may indicate that the at least one RA report for at least one SN is available at the UE 104. Alternatively, the RACH INDICATION message may indicate one or more random access procedures performed at the at least one SN. Alternatively, the RACH INDICATION message may indicate existence of the at least one RA report for at least one SN at the UE 104.

Then, the inter-MN HO is triggered. Thus, the second base station 102-2 transmits 320 a HO request message to the first base station 102-1. The HO request message comprises the indication. The indication indicates that at least one RA report for at least one SN is available at the UE 104. Alternatively, the indication may indicate one or more random access procedures performed at the at least one SN. Alternatively, the indication may indicate existence of the at least one RA report for at least one SN at the UE 104.

Upon receiving the HO request, the first base station 102-1 transmits 330 an SN addition request message or a secondary gNodeB (SgNB) addition request message to the first SN 103.

Upon receiving the SN addition request message or the SgNB addition request message, the first SN 103 transmits 340 an SN addition request acknowledge (ACK) message or an SgNB addition request ACK message to the first base station 102-1.

In turn, the first base station 102-1 transmits 350 a HO request ACK message to the second base station 102-2.

Upon receiving the HO request ACK message, the second base station 102-2 transmits 360 a HO command to the UE 104. The HO command is a RRC reconfiguration message or a RRC connection reconfiguration message.

Then, in order to obtain the at least one RA report for at least one SN, the first base station 102-1 transmits 370 a UE information request message to the UE 104.

Upon receiving the UE information request message, the UE 104 transmits 380 a UE information response message to the first base station 102-1. The UE information response message comprises the at least one RA report for at least one SN.

In some implementations, a HO from the second base station 102-2 to the first base station 102-1 is triggered, and the first base station 102-1 may receive the indication from the first SN 103. In such implementations, the first base station 102-1 may receive, from the first SN 103, a secondary gNodeB (SgNB) addition request ACK message or an SN addition request ACK message. The SgNB addition request ACK message or the SN addition request ACK message may comprise the indication. This will be described with reference to Fig. 4.

Fig. 4 illustrates a signaling chart illustrating an example process 400 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. The example process 400 may be considered as an example implementation of the process 200. For the purpose of discussion, the process 400 will be described with reference to Fig. 1B. The process 400 may involve the UE 104, the first base station 102-1, the second base station 102-2 and the first SN 103 in Fig. 1B.

Actions 310, 330, 350, 360, 370 and 380 in the process 400 are similar to those in the process 300. Details of these actions are omitted for brevity.

The process 400 is different from the process 300 in actions 420 and 440.

Specifically, after the RACH INDICATION message is transmitted from the first SN 103 to the second base station 102-2, the inter-MN HO is triggered. Thus, the second base station 102-2 transmits 420 a HO request message to the first base station 102-1. The HO request message does not comprise the indication.

Upon receiving the SgNB addition request message or SN addition request message from the first base station 102-1, the first SN 103 transmits 440 an SgNB addition request ACK message or an SN addition request ACK message to the first base station 102-1. The SgNB addition request ACK message or the SN addition request ACK message may comprise the indication. The indication indicates that at least one RA report for at least one SN is available at the UE 104. Alternatively, the indication may indicate one or more random access procedures performed at the at least one SN. Alternatively, the indication may indicate existence of the at least one RA report for at least one SN at the UE 104.

It shall be understood that in the process 400, even if the first SN 103 has transmitted the RACH INDICATION message to the second base station 102-2 before the HO is triggered, the first SN 103 still keeps the context that there is at least one RA report for at least one SN stored at the UE 104 or occurrences of successful RA procedures at the at least one SN. Thus, the first SN 103 can inform the first base station 102-1 that the at least one RA report for at least one SN is available at the UE 104.

In some implementations, a HO from the second base station 102-2 to the first base station 102-1 is triggered, and the first base station 102-1 may receive the indication from the second base station 102-2. In such implementations, the first base station 102-1 may receive, from the second base station 102-2, a message which indicates that the at least one RA report for at least one SNis available at the UE 104. This will be described with reference to Fig. 5.

Fig. 5 illustrates a signaling chart illustrating an example process 500 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. The example process 500 may be considered as an example implementation of the process 200. For the purpose of discussion, the process 500 will be described with reference to Fig. 1B. The process 500 may involve the UE 104, the first base station 102-1, the second base station 102-2 and the first SN 103 in Fig. 1B.

Generally, in the process 500, a HO from the second base station 102-2 to the first base station 102-1 is triggered, and the HO comprises an inter-MN HO. The inter-MN HO may be triggered before a RACH INDICATION message is transmitted from the first SN 103 to the second base station 102-2.

Specifically, as shown in Fig. 5, the second base station 102-2 triggers the inter-MN HO by transmitting 510 a HO request message to the first base station 102-1.

After the inter-MN HO is triggered, the first SN 103 transmits 520 a RACH INDICATION message to the second base station 102-2. The RACH INDICATION message may indicate that the at least one RA report for at least one SN is available at the UE 104. Alternatively, the RACH INDICATION message may indicate one or more random access procedures performed at the at least one SN. Alternatively, the RACH INDICATION message may indicate existence of the at least one RA report for at least one SN at the UE 104.

Upon receiving the RACH INDICATION message, the second base station 102-2 transmits 530 a message to the first base station 102-1. The message indicates that the at least one RA report for at least one SN is available at the UE 104. Alternatively, the message may indicate one or more random access procedures performed at the at least one SN. Alternatively, the message may indicate existence of the at least one RA report for at least one SN at the UE 104.

In some implementations, the message may be a RACH INDICATION message. Alternatively, the message may be a message which is different from the RACH INDICATION message. The scope of the present disclosure is not limited in this regard.

In some implementations, the message itself can be used to indicate the availability of the at least one RA report for at least one SN at the UE 104, one or more random access procedures performed at the at least one SN or existence of the at least one RA report for at least one SN at the UE 104.

In some implementations, the message may comprise information concerning the availability of the at least one RA report for at least one SN at the UE 104, one or more random access procedures performed at the at least one SN or existence of the at least one RA report for at least one SN at the UE 104. For example, the information may comprise a gNB UE XnAP ID or eNB UE X2AP ID allocated at the first base station 102-1. For another example, the information may comprise an indication, the indication indicates that at least one RA report for at least one SN is available at the UE 104, or the indication may indicate one or more random access procedures performed at the at least one SN, or the indication may indicate existence of the at least one RA report for at least one SN at the UE 104.

Then, the first base station 102-1 transmits 540 an SgNB addition request message or SN addition request message to the first SN 103.

Upon receiving the SN addition request message, the first SN 103 transmits 550 an SgNB addition request ACK message or an SN addition request ACK message to the first base station 102-1.

In turn, the first base station 102-1 transmits 560 a HO request ACK message to the second base station 102-2.

Upon receiving the HO request ACK message, the second base station 102-2 transmits 570 a HO command to the UE 104. The HO command is a RRC reconfiguration message or a RRC connection reconfiguration message.

Then, in order to obtain the at least one RA report for at least one SN, the first base station 102-1 transmits 580 a UE information request message to the UE 104.

Upon receiving the UE information request message, the UE 104 transmits 590 a UE information response message to the first base station 102-1. The UE information response message comprises the at least one RA report for at least one SN.

In some implementations, a HO from the second base station 102-2 to the first base station 102-1 is triggered, and the second base station 102-2 may receive the indication from the first SN 103. In such implementations, the first base station 102-1 may receive, from the first SN 103, an SgNB addition request ACK message or an SN addition request ACK message. The SgNB addition request ACK message or the SN addition request ACK message may comprise the indication. This will be described with reference to Fig. 6.

Fig. 6 illustrates a signaling chart illustrating an example process 600 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. The example process 600 may be considered as an example implementation of the process 200. For the purpose of discussion, the process 600 will be described with reference to Fig. 1B. The process 600 may involve the UE 104, the first base station 102-1, the second base station 102-2 and the first SN 103 in Fig. 1B.

Actions 510, 520, 540, 560, 570, 580 and 590 in the process 600 are similar to those in the process 500. Details of these actions are omitted for brevity.

The process 600 is different from the process 500 in that the action 530 is not performed and an action 650 is performed.

Specifically, upon receiving the SgNB addition request message or SN addition request message from the first base station 102-1, the first SN 103 transmits 650 an SgNB addition request ACK message or an SN addition request ACK message to the first base station 102-1. The SgNB addition request ACK message or the SN addition request ACK message may comprise the indication. The indication indicates that at least one RA report for at least one SN is available at the UE 104. Alternatively, the indication may indicate one or more random access procedures performed at the at least one SN. Alternatively, the indication may indicate existence of the at least one RA report for at least one SN at the UE 104.

It shall be understood that in the process 600, even if the first SN 103 has transmitted the RACH INDICATION message to the second base station 102-2, the first SN 103 still keeps the context that there is at least one RA report for at least one SN stored at the UE 104 or occurrences of one or more successful RA procedures at the at least one SN . Thus, the first SN 103 can inform the first base station 102-1 that the at least one RA report for at least one SN is available at the UE 104.

In some implementations, a HO from the second base station 102-2 to the first base station 102-1 is triggered, and the first base station 102-1 may receive, from the UE 104, a radio resource control (RRC) reconfiguration complete message or RRC connection reconfiguration complete message. The RRC reconfiguration complete message or RRC connection reconfiguration complete message may comprise the at least one RA report for at least one SN. This will be described with reference to Fig. 7.

Fig. 7 illustrates a signaling chart illustrating an example process 700 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. The example process 700 may be considered as an example implementation of the process 200. For the purpose of discussion, the process 700 will be described with reference to Fig. 1B. The process 700 may involve the UE 104, the first base station 102-1, the second base station 102-2 and the first SN 103 in Fig. 1B.

Generally, in the process 700, a HO from the second base station 102-2 to the first base station 102-1 is triggered, and the HO comprises an inter-MN HO. The inter-MN HO may be triggered after the at least one RA report for at least one SN is requested by the second base station 102-2 in Uu interface.

Specifically, as shown in Fig. 7, the first SN 103 transmits 710 a RACH INDICATION message to the second base station 102-2. The RACH INDICATION message may indicate that the at least one RA report for at least one SN is available at the UE 104. Alternatively, the RACH INDICATION message may indicate one or more random access procedures performed at the at least one SN. Alternatively, the RACH INDICATION message may indicate existence of the at least one RA report for at least one SN at the UE 104.

Upon receiving the RACH INDICATION message, the second base station 102-2 transmits 720, to the UE 104, a UE information request message to request the at least one RA report for at least one SN.

Then, the inter-MN HO is triggered. Thus, the second base station 102-2 transmits 730 a HO request message to the first base station 102-1.

Upon receiving the HO request message, the first base station 102-1 transmits 740 a HO request ACK message to the second base station 102-2.

Upon receiving the HO request ACK message, the second base station 102-2 transmits 750 a HO command to the UE 104, the HO command is a RRC reconfiguration message or a RRC connection reconfiguration message.

Then, the UE 104 transmits 760, to the first base station 102-1, an RRC reconfiguration complete message or RRC connection reconfiguration complete message. The RRC reconfiguration complete message or RRC connection reconfiguration complete message may comprise the at least one RA report for at least one SN.

In some implementations, the RRC reconfiguration complete message or RRC connection reconfiguration complete message may comprise an RA-ReportList. The RA-ReportList may comprise the at least one RA report for at least one SN. Each of the at least one RA report for at least one SN may be associated with a PSCell. For example, each of the at least one RA report for at least one SN may comprise an identity of the PSCell and RA related information (e.g. which can be represented by the RA-InformationCommon IE in TS38.331) . The identity of the PSCell may be a cellGlobalId or PCI of the PSCell.

In some implementations, the RRC reconfiguration complete message or RRC connection reconfiguration complete message may further comprise a list of PSCell identities. The PSCell identities comprise unique PSCell identities. That is, if an identity of the PSCell occurs more than once in the RA-ReportList, the identity of the PSCell is recorded only once in the list of PSCell identities.

It shall be understood that in the process 700, even if the UE information request message for the at least one RA report for at least one SN is received by the UE 104 from the second base station 102-2, the UE 104 cannot transmit the stored SN RA report to the second base station 102-2 due to the HO is initiated.

As described above, when the first base station 102-1 is aware of that there is at least one RA report for at least one SN stored at the UE 104 or occurrences of successful RA procedures in the at least one SN, the first base station 102-1 can obtain the at least one RA report for at least one SN from the UE 104 via UE Information request/UE Information response procedure, or via the RRC reconfiguration complete message or RRC connection reconfiguration complete message.

In some implementations, each of the at least one RA report comprises an identity of a PSCell associated with one of the at least one SN. If the first base station 102-1 obtaining the SN RA report does not have a direct X2/Xn connectivity with the at least one SN, the first base station 102-1 cannot forward the received SN RA report to the right SN for RACH optimization.

To address this issue, in some implementations, for one PSCell associated with one of the at least one SN that included in the at least one RA report, the first base station 102-1 may obtain, from the second base station 102-2, at least one identity of at least one primary cell (PCell) associated with the PSCell. In turn, the first base station 102-1 may transmit one of the at least one RA report to at least one third base station associated with the at least one PCell. For example, the at least one third base station may comprise the second base station 102-2. Alternatively, the at least one third base station may comprise other base station than the second base station 102-2. Then, the at least one third base station may forward the SN RA report to the right SN for RACH optimization.

Hereinafter, some implementations of obtaining at least one identity of at least one PCell will be described with reference to Figs. 8 to 12. Hereinafter, at least one identity of at least one PCell is also referred to as at least one PCell identity for brevity.

Fig. 8 illustrates a signaling chart illustrating an example process 800 that supports obtaining of at least one PCell identity in accordance with aspects of the present disclosure. The example process 800 may be considered as an example implementation of the process 200. For the purpose of discussion, the process 800 will be described with reference to Fig. 1B. The process 800 may involve the UE 104, the first base station 102-1, the second base station 102-2 and the first SN 103 in Fig. 1B.

As shown in Fig. 8, the first base station 102-1 obtains 810 the at least one RA report for at least one SN from the UE 104. For example, the first base station 102-1 may obtain the at least one RA report for at least one SN by performing one of the processes 200 to 700 as described above.

In turn, in order to obtain at least one PCell identity, the first base station 102-1 transmits 820, to the second base station 102-2, a request for latest UE history information (UHI) .

Upon receiving the request, the second base station 102-2 transmits 830, to the first base station 102-1, the latest UHI which at least comprises the at least one PCell identity. Also, the latest UHI may comprise at least one PSCell identity.

In some implementations, the first base station 102-1 may transmit, to the second base station 102-2, one of the following comprising the request: a UE context release message, a dedicated X2 message, or a dedicated Xn message.

In some implementations, the UE context release message, the dedicated X2 message or the dedicated Xn message may comprise an indication for obtaining the latest UHI.

For example, an UE History Information Retrieve Information Element (IE) may be included in the UE context release message, the dedicated X2 message or the dedicated Xn message to indicate that the latest UHI is requested. Then, the second base station 102-2 may transmit the latest UHI to the first base station 102-1. For example, the second base station 102-2 may transmit the latest UHI via a further dedicated X2 message or a further dedicated Xn message. Alternatively, for example, the second base station 102-2 may transmit the latest UHI via an existing X2 message or an existing Xn message.

In some implementations, the latest UHI may comprise correlated master cell group (MCG) UHI and secondary cell group (SCG) UHI. Based on the correlated MCG UHI and SCG UHI, the first base station 102-1 may determine relationship between PCell (s) and PSCell (s) . For example, the relationship between PCell (s) and PSCell (s) may comprise relationship between PCell#1 and PSCell#1, relationship between PCell#2 and PSCell#1, relationship between PCell#3 and PSCell#2, and so on.

Based on the relationship between PCell (s) and PSCell (s) , the first base station 102-1 may determine which PCell (s) is associated with a PSCell that is included in the at least one RA report for at least one SN. For example, the first base station 102-1 may determine PCell#1 and PCell#2 are associated with PSCell#1. PCell#1 and PCell#2 are associated with the second base station 102-2, and PSCell#1 is associated with the first SN 103. For another example, the first base station 102-1 may determine PCell#3 is associated with PSCell#2. PCell#3 is associated with a third base station, and PSCell#2 is associated with a second SN.

Then, the first base station 102-1 may determine at least one third base station associated with the at least one PCell, or the first base station 102-1 may determine at least one third base station manages the at least one PCell. The at least one third base station may comprise the second base station 102-2. Alternatively, the at least one third base station may comprise other base station than the second base station 102-2.

For example, the first base station 102-1 may determine the second base station 102-2 associated with PCell#1 and PCell#2, or the first base station 102-1 may determine the second base station 102-2 manages PCell#1 and PCell#2. In turn, the first base station 102-1 may transmit the at least one RA report for at least one SN or a first SN RA report among the at least one RA report for at least one SN to the second base station 102-2. Upon receiving the at least one RA report for at least one SN or the first SN RA report, the second base station 102-2 may forward the at least one RA report for at least one SN or the first SN RA report to the first SN 103 for RACH optimization.

For example, the first base station 102-1 may determine the third base station associated with PCell#3, or the first base station 102-1 may determine the third base station manages PCell#3. In turn, the first base station 102-1 may transmit the at least one RA report for at least one SN or a second SN RA report among the at least one RA report for at least one SN to the third base station. Upon receiving the at least one RA report for at least one SN or the second SN RA report, the third base station may forward the at least one RA report for at least one SN or the second SN RA report to the second SN for RACH optimization.

In some implementations, in order to obtain the at least one PCell identity, the first base station 102-1 may transmit, to the second base station 102-2, a subscription request for latest UHI. Then, the first base station 102-1 may receive, from the second base station 102-2, a subscription notification comprising the at least one PCell identity or the latest UHI comprising the at least one PCell identity. This will be described with reference to Fig. 9.

Fig. 9 illustrates a signaling chart illustrating an example process 900 that supports obtaining of at least one PCell identity in accordance with aspects of the present disclosure. The example process 900 may be considered as an example implementation of the process 200. For the purpose of discussion, the process 900 will be described with reference to Fig. 1B. The process 900 may involve the UE 104, the first base station 102-1, the second base station 102-2 and the first SN 103 in Fig. 1B.

As shown in Fig. 9, when a HO from the second base station 102-2 to the first base station 102-1 is triggered, the second base station 102-2 transmits 910 a HO request message to the first base station 102-1.

Upon receiving the HO request message, the first base station 102-1 transmits 920 a HO request ACK message to the second base station 102-2. The HO request ACK message comprises an indication for a subscription request for latest UHI.

For example, the HO request ACK message comprises may comprises an indicator indicating that the latest UHI is request.

For another example, an UE History Information IE which is set to “reporting full UE history” may be included in the HO request ACK message.

Upon receiving the HO request ACK message, the second base station 102-2 transmits 930 a HO command to the UE 104. The HO command is a RRC reconfiguration message or a RRC connection reconfiguration message.

Then, the UE 104 transmits 940 the at least one RA report for at least one SN to the first base station 102-1. For example, the first base station 102-1 may obtain the at least one RA report for at least one SN by performing one of the processes 200 to 700 as described above.

If the second base station 102-2 supports the subscription request, every time UHI changes, PCell change and/or PSCell change, the second base station 102-2 transmits 950 a subscription notification to the first base station 102-1. The subscription notification comprises the at least one PCell identity or the latest UHI comprising the at least one PCell identity. Also, the latest UHI may comprise at least one PSCell identity.

For example, the second base station 102-2 may transmit the subscription notification via a dedicated X2 message or a dedicated Xn message. Alternatively, for example, the second base station 102-2 may transmit the subscription notification via an existing X2 message or an existing Xn message.

For example, the first base station 102-1 may determine the second base station 102-2 associated with PCell#1 and PCell#2, or the first base station 102-1 may determine the second base station 102-2 manages PCell#1 and PCell#2. In turn, the first base station 102-1 may transmit the at least one RA report for at least one SN or a first SN RA report among the at least one RA report for at least one SN to the second base station 102-2. Upon receiving the at least one RA report for at least one SN or the first SN RA report, the second base station 102-2 may forward the least one RA report for at least one SN or the first SN RA report to the first SN 103 for RACH optimization.

In some implementations, if MCG UHI and SCG UHI is included in a HO request message, the first base station 102-1 may only request an identity of a latest PCell from the second base station 102-2 since the MCG UHI and SCG UHI would be updated after HO is initiated. This will be described with reference to Fig. 10.

Fig. 10 illustrates a signaling chart illustrating an example process 1000 that supports obtaining of at least one PCell identity in accordance with aspects of the present disclosure. The example process 1000 may be considered as an example implementation of the process 200. For the purpose of discussion, the process 1000 will be described with reference to Fig. 1B. The process 1000 may involve the UE 104, the first base station 102-1, the second base station 102-2 and the first SN 103 in Fig. 1B.

As shown in Fig. 10, when a HO from the second base station 102-2 to the first base station 102-1 is triggered, the second base station 102-2 transmits 1010 a HO request message to the first base station 102-1. The HO request message comprises latest UHI, i.e., the HO request message comprises MCG UHI and SCG UHI.

Upon receiving the HO request message, the first base station 102-1 transmits 1020 a HO request ACK message to the second base station 102-2.

Upon receiving the HO request ACK message, the second base station 102-2 transmits 1030 a HO command to the UE 104. The HO command is a RRC reconfiguration message or a RRC connection reconfiguration message.

Upon receiving the HO command, the UE 104 performs a HO from the second base station 102-2 to the first base station 102-1. For example, the UE 104 performs a HO from PCell #1 associated with the second base station 102-2 to PCell #2 associated with the first base station 102-1. In this example, PCell #1 is a latest PCell to serve the UE 104 before HO is triggered, PCell #2 is a latest PCell to serve the UE 104 after HO is successful (e.g. after the UE 104 access to PCell #2 successfully) .

After the UE 104 performs the HO from the second base station 102-2 to the first base station 102-1 successfully, the second base station 102-2 may update the MCG UHI by recording information concerning the latest PCell in the MCG UHI. For example, the information concerning the latest PCell may comprise an identity of the latest PCell. For example, after the UE 104 performs the HO from PCell #1 associated with the second base station 102-2 to PCell #2 associated with the first base station 102-1 successfully, the information concerning the latest PCell may comprise an identity of the PCell #2.

Alternatively, the second base station 102-2 may update the MCG UHI and SCG UHI by recording information concerning the latest PCell in the MCG UHI and recording information concerning at least one PSCell associated with the latest PCell in the SCG UHI. For example, the information concerning the at least one PSCell may comprise at least one identity of the at least one PSCell. For example, the information concerning the at least one PSCell may comprise an identity of the PSCell #1 which is associated with PCell #2.

Then, upon receiving 1040 a UE information request message from the first base station 102-1, the UE 104 transmits 1050 a UE information response message to the first base station 102-1. The UE information response message comprises the at least one RA report for at least one SN.

In turn, the first base station 102-1 transmits 1060, to the second base station 102-2, a request for an identity of a latest PCell.

For example, the UE context release message, the dedicated X2 message, or the dedicated Xn message may comprise an indication for obtaining the identity of the latest PCell. Alternatively, the UE context release message, the dedicated X2 message, or the dedicated Xn message may comprise an indication for obtaining the identity of the latest PCell and at least one identity of at least one PSCell. The at least one PSCell is associated with the latest PCell.

Upon receiving the request, the second base station 102-2 transmits 1070 a response to the first base station 102-1. For example, the response comprises the identity of the latest PCell. Alternatively, the response comprises the identity of the latest PCell and at least one identity of at least one PSCell associated with the latest PCell.

For example, the second base station 102-2 may transmit the response via a further dedicated X2 message or a further dedicated Xn message. Alternatively, for example, the second base station 102-2 may transmit the response via an existing X2 message or an existing Xn message.

Then, the first base station 102-1 may determine the second base station 102-2 associated with the latest PCell (e.g. PCell #2) . In turn, the first base station 102-1 may transmit the at least one RA report for at least one SN or a first SN RA report among the at least one RA report for at least one SN t to the second base station 102-2. Upon receiving the at least one RA report for at least one SN or the first SN RA report, the second base station 102-2 may forward the at least one RA report for at least one SN or the first SN RA report to the first SN 103 (e.g. which manages PSCell#1) for RACH optimization.

In the process 700, each of the at least one RA report comprises an identity of a PSCell associated with one of the at least one SN. If the first base station 102-1 obtaining the SN RA report does not have a direct X2/Xn connectivity with the at least one SN, the first base station 102-1 cannot forward the received SN RA report to the right SN for RACH optimization. Two solutions for this issue will be described with reference to Figs. 11 and 12.

Fig. 11 illustrates a signaling chart illustrating an example process 1100 that supports obtaining of at least one PCell identity in accordance with aspects of the present disclosure. The example process 1100 may be considered as an example implementation of the process 200. For the purpose of discussion, the process 1100 will be described with reference to Fig. 1B. The process 1100 may involve the UE 104, the first base station 102-1, the second base station 102-2 and the first SN 103 in Fig. 1B.

Actions 710, 720, 730, 740 and 750 in the process 1100 are similar to those in the process 700. Details of these actions are omitted for brevity.

The process 1100 is different from the process 700 in an action 1160.

As shown in Fig. 11, besides the unique PSCell identities (i.e. if an identity of a PSCell occurs more than once in the SN RA report or in the at least one RA report for at least one SN (e.g. RA-ReportList) , the identity of the PSCell is recorded only once in the list of PSCell identities) and the SN RA report or the at least one RA report for at least one SN (e.g. RA-ReportList) , the UE 104 may also include PCell related information in an RRC reconfiguration complete message or RRC connection reconfiguration complete message to the first base station 102-1. Alternatively, the UE 104 may also include PCell related information and PSCell related information in the RRC reconfiguration complete message or RRC connection reconfiguration complete message.

In some implementations, the at least one RA report comprises at least one identity of at least one PSCell associated with the at least one SN. Each of the at least one RA report comprises an identity of a PSCell associated with one of the at least one SN. In such implementations, the PCell related information may comprise a list of identity of PCells associated with each of the at least one PSCell, and the PSCell related information may comprise a list of identity of the at least one PCells.

Fig. 12 illustrates a signaling chart illustrating an example process 1200 that supports obtaining of at least one PCell identity in accordance with aspects of the present disclosure. The example process 1200 may be considered as an example implementation of the process 200. For the purpose of discussion, the process 1200 will be described with reference to Fig. 1B. The process 1200 may involve the UE 104, the first base station 102-1, the second base station 102-2 and the first SN 103 in Fig. 1B.

Actions 710, 720, 730, 740 and 750 in the process 1200 are similar to those in the process 700. Details of these actions are omitted for brevity.

The process 1200 is different from the process 700 in an action 1260.

As shown in Fig. 12, besides the unique PSCell identities (i.e. if an identity of a PSCell occurs more than once in the SN RA report or in the at least one RA report for at least one SN (e.g. RA-ReportList) , the identity of the PSCell is recorded only once in the list of PSCell identities) and the SN RA report or the at least one RA report for at least one SN (e.g. RA-ReportList) , the UE 104 may also include the latest UHI in an RRC reconfiguration complete message or RRC connection reconfiguration complete message to the first base station 102-1.

In some implementations, the latest UHI may comprise correlated MCG UHI and SCG UHI. Based on the correlated MCG UHI and SCG UHI, the first base station 102-1 may determine relationship between PCell (s) and PSCell (s) .

Based on the relationship between PCell (s) and PSCell (s) , the first base station 102-1 may determine which PCell (s) is associated with a PSCell that is included in the at least one RA report for at least one SN.

In turn, the first base station 102-1 may transmit the at least one RA report for at least one SN to the at least one third base station. Upon receiving the at least one RA report for at least one SN, each of the at least one third base station may forward full or partial of the at least one RA report for at least one SN to the right SN for RACH optimization.

Fig. 13 illustrates an example of a device 1300 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. The device 1300 may be an example of the first base station 102-1 as described herein. The device 1300 may support wireless communication with one or more network entities 102, UEs 104, or any combination thereof. The device 1300 may include components for bi-directional communications including components for transmitting and receiving communications, such as a processor 1302, a memory 1304, a transceiver 1306, and, optionally, an I/O controller 1308. These components may be in electronic communication or otherwise coupled (e.g., operatively, communicatively, functionally, electronically, electrically) via one or more interfaces (e.g., buses) .

The processor 1302, the memory 1304, the transceiver 1306, or various combinations thereof or various components thereof may be examples of means for performing various aspects of the present disclosure as described herein. For example, the processor 1302, the memory 1304, the transceiver 1306, or various combinations or components thereof may support a method for performing one or more of the operations described herein.

In some implementations, the processor 1302, the memory 1304, the transceiver 1306, or various combinations or components thereof may be implemented in hardware (e.g., in communications management circuitry) . The hardware may include a processor, a digital signal processor (DSP) , an application-specific integrated circuit (ASIC) , a field-programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic, discrete hardware components, or any combination thereof configured as or otherwise supporting a means for performing the functions described in the present disclosure. In some implementations, the processor 1302 and the memory 1304 coupled with the processor 1302 may be configured to perform one or more of the functions described herein (e.g., executing, by the processor 1302, instructions stored in the memory 1304) .

For example, the processor 1302 may support wireless communication at the device 1300 in accordance with examples as disclosed herein. The processor 1302 may be configured to operable to support a means for performing the following: receiving an indication indicating that at least one RA report for at least one SN is available at a UE, the UE being connected to a second base station and a first SN among the at least one SN; and obtaining the at least one RA report from the UE.

The processor 1302 may include an intelligent hardware device (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some implementations, the processor 1302 may be configured to operate a memory array using a memory controller. In some other implementations, a memory controller may be integrated into the processor 1302. The processor 1302 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1304) to cause the device 1300 to perform various functions of the present disclosure.

The memory 1304 may include random access memory (RAM) and read-only memory (ROM) . The memory 1304 may store computer-readable, computer-executable code including instructions that, when executed by the processor 1302 cause the device 1300 to perform various functions described herein. The code may be stored in a non-transitory computer-readable medium such as system memory or another type of memory. In some implementations, the code may not be directly executable by the processor 1302 but may cause a computer (e.g., when compiled and executed) to perform functions described herein. In some implementations, the memory 1304 may include, among other things, a basic I/O system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The I/O controller 1308 may manage input and output signals for the device 1300. The I/O controller 1308 may also manage peripherals not integrated into the device M02. In some implementations, the I/O controller 1308 may represent a physical connection or port to an external peripheral. In some implementations, the I/O controller 1308 may utilize an operating system such as or another known operating system. In some implementations, the I/O controller 1308 may be implemented as part of a processor, such as the processor 1306. In some implementations, a user may interact with the device 1300 via the I/O controller 1308 or via hardware components controlled by the I/O controller 1308.

In some implementations, the device 1300 may include a single antenna 1310. However, in some other implementations, the device 1300 may have more than one antenna 1310 (i.e., multiple antennas) , including multiple antenna panels or antenna arrays, which may be capable of concurrently transmitting or receiving multiple wireless transmissions. The transceiver 1306 may communicate bi-directionally, via the one or more antennas 1310, wired, or wireless links as described herein. For example, the transceiver 1306 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1306 may also include a modem to modulate the packets, to provide the modulated packets to one or more antennas 1310 for transmission, and to demodulate packets received from the one or more antennas 1310. The transceiver 1306 may include one or more transmit chains, one or more receive chains, or a combination thereof.

A transmit chain may be configured to generate and transmit signals (e.g., control information, data, packets) . The transmit chain may include at least one modulator for modulating data onto a carrier signal, preparing the signal for transmission over a wireless medium. The at least one modulator may be configured to support one or more techniques such as amplitude modulation (AM) , frequency modulation (FM) , or digital modulation schemes like phase-shift keying (PSK) or quadrature amplitude modulation (QAM) . The transmit chain may also include at least one power amplifier configured to amplify the modulated signal to an appropriate power level suitable for transmission over the wireless medium. The transmit chain may also include one or more antennas 1310 for transmitting the amplified signal into the air or wireless medium.

A receive chain may be configured to receive signals (e.g., control information, data, packets) over a wireless medium. For example, the receive chain may include one or more antennas 1310 for receive the signal over the air or wireless medium. The receive chain may include at least one amplifier (e.g., a low-noise amplifier (LNA) ) configured to amplify the received signal. The receive chain may include at least one demodulator configured to demodulate the receive signal and obtain the transmitted data by reversing the modulation technique applied during transmission of the signal. The receive chain may include at least one decoder for decoding the processing the demodulated signal to receive the transmitted data.

Fig. 14 illustrates an example of a device 1400 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. The device 1400 may be an example of the second base station 102-2 as described herein. The device 1400 may support wireless communication with one or more network entities 102, UEs 104, or any combination thereof. The device 1400 may include components for bi-directional communications including components for transmitting and receiving communications, such as a processor 1402, a memory 1404, a transceiver 1406, and, optionally, an I/O controller 1408. These components may be in electronic communication or otherwise coupled (e.g., operatively, communicatively, functionally, electronically, electrically) via one or more interfaces (e.g., buses) .

The processor 1402, the memory 1404, the transceiver 1406, or various combinations thereof or various components thereof may be examples of means for performing various aspects of the present disclosure as described herein. For example, the processor 1402, the memory 1404, the transceiver 1406, or various combinations or components thereof may support a method for performing one or more of the operations described herein.

In some implementations, the processor 1402, the memory 1404, the transceiver 1406, or various combinations or components thereof may be implemented in hardware (e.g., in communications management circuitry) . The hardware may include a processor, a digital signal processor (DSP) , an application-specific integrated circuit (ASIC) , a field-programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic, discrete hardware components, or any combination thereof configured as or otherwise supporting a means for performing the functions described in the present disclosure. In some implementations, the processor 1402 and the memory 1404 coupled with the processor 1402 may be configured to perform one or more of the functions described herein (e.g., executing, by the processor 1402, instructions stored in the memory 1404) .

For example, the processor 1402 may support wireless communication at the device 1400 in accordance with examples as disclosed herein. The processor 1402 may be configured to operable to support a means for performing the following: receiving, from a first SN, an indication indicating that at least one RA report for at least one SN is available at a UE, the UE being connected to the second base station and the first SN, the at least one SN comprising the first SN; and transmitting the indication to a first base station.

The processor 1402 may include an intelligent hardware device (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some implementations, the processor 1402 may be configured to operate a memory array using a memory controller. In some other implementations, a memory controller may be integrated into the processor 1402. The processor 1402 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1404) to cause the device 1400 to perform various functions of the present disclosure.

The memory 1404 may include random access memory (RAM) and read-only memory (ROM) . The memory 1404 may store computer-readable, computer-executable code including instructions that, when executed by the processor 1402 cause the device 1400 to perform various functions described herein. The code may be stored in a non-transitory computer-readable medium such as system memory or another type of memory. In some implementations, the code may not be directly executable by the processor 1402 but may cause a computer (e.g., when compiled and executed) to perform functions described herein. In some implementations, the memory 1404 may include, among other things, a basic I/O system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The I/O controller 1408 may manage input and output signals for the device 1400. The I/O controller 1408 may also manage peripherals not integrated into the device M02. In some implementations, the I/O controller 1408 may represent a physical connection or port to an external peripheral. In some implementations, the I/O controller 1408 may utilize an operating system such as or another known operating system. In some implementations, the I/O controller 1408 may be implemented as part of a processor, such as the processor 1406. In some implementations, a user may interact with the device 1400 via the I/O controller 1408 or via hardware components controlled by the I/O controller 1408.

In some implementations, the device 1400 may include a single antenna 1410. However, in some other implementations, the device 1400 may have more than one antenna 1410 (i.e., multiple antennas) , including multiple antenna panels or antenna arrays, which may be capable of concurrently transmitting or receiving multiple wireless transmissions. The transceiver 1406 may communicate bi-directionally, via the one or more antennas 1410, wired, or wireless links as described herein. For example, the transceiver 1406 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1406 may also include a modem to modulate the packets, to provide the modulated packets to one or more antennas 1410 for transmission, and to demodulate packets received from the one or more antennas 1410. The transceiver 1406 may include one or more transmit chains, one or more receive chains, or a combination thereof.

A transmit chain may be configured to generate and transmit signals (e.g., control information, data, packets) . The transmit chain may include at least one modulator for modulating data onto a carrier signal, preparing the signal for transmission over a wireless medium. The at least one modulator may be configured to support one or more techniques such as amplitude modulation (AM) , frequency modulation (FM) , or digital modulation schemes like phase-shift keying (PSK) or quadrature amplitude modulation (QAM) . The transmit chain may also include at least one power amplifier configured to amplify the modulated signal to an appropriate power level suitable for transmission over the wireless medium. The transmit chain may also include one or more antennas 1410 for transmitting the amplified signal into the air or wireless medium.

A receive chain may be configured to receive signals (e.g., control information, data, packets) over a wireless medium. For example, the receive chain may include one or more antennas 1410 for receive the signal over the air or wireless medium. The receive chain may include at least one amplifier (e.g., a low-noise amplifier (LNA) ) configured to amplify the received signal. The receive chain may include at least one demodulator configured to demodulate the receive signal and obtain the transmitted data by reversing the modulation technique applied during transmission of the signal. The receive chain may include at least one decoder for decoding the processing the demodulated signal to receive the transmitted data.

Fig. 15 illustrates a flowchart of a method 1500 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. The operations of the method 1500 may be implemented by a device or its components as described herein. For example, the operations of the method 1500 may be performed by the first base station 102-1 as described herein. In some implementations, the device may execute a set of instructions to control the function elements of the device to perform the described functions. Additionally, or alternatively, the device may perform aspects of the described functions using special-purpose hardware.

At 1510, the method may include receiving an indication indicating that at least one RA report for at least one SN is available at a UE. The UE is connected to a second base station and a first SN among the at least one SN. The operations of 1510 may be performed in accordance with examples as described herein. In some implementations, aspects of the operations of 1510 may be performed by a device as described with reference to Fig. 1A or 1B.

At 1520, the method may include obtaining the at least one RA report from the UE. The operations of 1520 may be performed in accordance with examples as described herein. In some implementations, aspects of the operations of 1520 may be performed by a device as described with reference to Fig. 1A or 1B.

Fig. 16 illustrates a flowchart of a method 1600 that supports obtaining of at least one RA report for at least one SN in accordance with aspects of the present disclosure. The operations of the method 1600 may be implemented by a device or its components as described herein. For example, the operations of the method 1600 may be performed by the second base station 102-2 as described herein. In some implementations, the device may execute a set of instructions to control the function elements of the device to perform the described functions. Additionally, or alternatively, the device may perform aspects of the described functions using special-purpose hardware.

At 1610, the method may includereceiving, from a first SN, an indication indicating that at least one RA report for at least one SN is available at a UE. The UE is connected to the second base station and the first SN, the at least one SN comprising the first SN. The operations of 1610 may be performed in accordance with examples as described herein. In some implementations, aspects of the operations of 1610 may be performed by a device as described with reference to Fig. 1A or 1B.

At 1620, the method may include transmitting the indication to a first base station. The operations of 1620 may be performed in accordance with examples as described herein. In some implementations, aspects of the operations of 1620 may be performed by a device as described with reference to Fig. 1A or 1B.

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

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

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

Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that may be accessed by a general-purpose or special-purpose computer. By way of example, non-transitory computer-readable media may include RAM, ROM, electrically erasable programmable ROM (EEPROM) , flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that may be used to carry or store desired program code means in the form of instructions or data structures and that may be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor.

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

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

Claims

A first base station, comprising:

a processor; and

a transceiver coupled to the processor,

wherein the processor is configured to:

receive, via the transceiver, an indication indicating that at least one random access (RA) report for at least one secondary node (SN) is available at a user equipment (UE) , the UE being connected to a second base station and a first SN among the at least one SN; and

obtain, via the transceiver, the at least one RA report from the UE.
The first base station of claim 1, wherein a handover from the second base station to the first base station is triggered, and the processor is configured to receive the indication by:

receiving the indication via the transceiver from the second base station.
The first base station of claim 2, wherein the processor is configured to receive the indication from the second base station by:

receiving, via the transceiver from the second base station, a handover request message comprising the indication.
The first base station of claim 2, wherein the processor is configured to receive the indication from the second base station by:

receiving, via the transceiver from the second base station, a message which indicates that the at least one RA report for the at least one SN is available at the UE.
The first base station of claim 4, wherein the message comprises a gNodeB

(gNB) UE XnAP identity (ID) or an eNodeB (eNB) UE X2AP ID allocated at the first base station.
The first base station of claim 1, wherein a handover from the second base station to the first base station is triggered, and the processor is configured to receive the indication by:

receiving the indication via the transceiver from the first SN.
The first base station of claim 6, wherein the processor is configured to receive the indication from the first SN by:

receiving, via the transceiver from the first SN, one of the following comprising the indication:

a secondary gNodeB (SgNB) addition request acknowledge message, or

an SN addition request acknowledge message.
The first base station of claim 1, wherein each of the at least one RA report comprises an identity of a primary secondary cell (PSCell) associated with one of the at least one SN; and

the processor is further configured to:

obtain, via the transceiver from the second base station, at least one identity of at least one primary cell (PCell) associated with the PSCell.
The first base station of claim 8, wherein the processor is configured to obtain the at least one identity of the at least one PCell by:

transmitting, via the transceiver to the second base station, a request for latest UE history information (UHI) ; and

receiving, via the transceiver from the second base station, the latest UHI which at least comprises the at least one identity of the at least one PCell.
The first base station of claim 8, wherein the processor is configured to obtain the at least one identity of the at least one PCell by:

transmitting, via the transceiver to the second base station, a subscription request for latest UE history information (UHI) ; and

receiving, via the transceiver from the second base station, a subscription notification comprising the at least one identity of the at least one PCell or the latest UHI comprising the at least one identity of the at least one PCell.
The first base station of claim 8, wherein the processor is configured to obtain the at least one identity of the at least one PCell by:

transmitting, via the transceiver to the second base station, a request for an identity of a latest PCell; and

receiving, via the transceiver from the second base station, a response comprising the identity of the latest PCell.
A second base station, comprising:

a processor; and

a transceiver coupled to the processor,

wherein the processor is configured to:

receive, via the transceiver from a first secondary node (SN) , an indication indicating that at least one random access (RA) report for at least one SN is available at a user equipment (UE) , the UE being connected to the second base station and the first SN, the at least one SN comprising the first SN; and

transmit the indication via the transceiver to a first base station.
The second base station of claim 12, wherein a handover from the second base station to the first base station is triggered, and the processor is configured to transmit the indication by:

transmitting, via the transceiver to the first base station, a handover request message comprising the indication.
The second base station of claim 12, wherein a handover from the second base station to the first base station is triggered, and the processor is configured to transmit the indication to the first base station by:

transmitting, via the transceiver to the first base station, a message which indicates that the at least one RA report for the at least one SN is available at the UE.
The second base station of claim 12, wherein each of the at least one RA report comprises an identity of a primary secondary cell (PSCell) associated with one of the at least one SN; and

the processor is further configured to:

transmit, via the transceiver to the first base station, at least one identity of at least one primary cell (PCell) associated with the PSCell.
The second base station of claim 15, wherein the processor is configured to transmit the at least one identity of the at least one PCell by:

receiving, via the transceiver from the first base station, a request for latest UE history information (UHI) ; and

transmitting, via the transceiver to the first base station, the latest UHI which at least comprises at least one identity of the at least one PCell.
The second base station of claim 15, wherein the processor is configured to transmit at least one identity of the at least one PCell by:

receiving, via the transceiver from the first base station, a subscription request for latest UE history information (UHI) ; and

based on determining PCell change or UHI change, transmitting, via the transceiver to the first base station, a subscription notification comprising the at least one identity of the at least one PCell or the latest UHI comprising the at least one identity of the at least one PCell.
The second base station of claim 15, wherein the processor is configured to transmit the at least one identity of the at least one PCell by:

receiving, via the transceiver from the first base station, a request for an identity of a latest PCell; and

transmitting, via the transceiver to the first base station, a response comprising the identity of the latest PCell.
A method performed by a first base station, the method comprising:

receiving an indication indicating that at least one random access (RA) report for at least one secondary node (SN) is available at a user equipment (UE) , the UE being connected to a second base station and a first SN among the at least one SN; and

obtaining the at least one RA report from the UE.
A method performed by a second base station, the method comprising:

receiving, from a first secondary node (SN) , an indication indicating that at least one random access (RA) report for at least one SN is available at a user equipment (UE) , the UE being connected to the second base station and the first SN, the at least one SN comprising the first SN; and transmitting the indication to a first base station.