WO2020263051A1

WO2020263051A1 - Method and apparatus for managing mobility in dual connectivity in wireless communication system

Info

Publication number: WO2020263051A1
Application number: PCT/KR2020/008441
Authority: WO
Inventors: Jian Xu; Daewook BYUN; Seokjung KIM
Original assignee: Lg Electronics Inc.
Priority date: 2019-06-27
Filing date: 2020-06-29
Publication date: 2020-12-30

Abstract

The present disclosure relates to method and apparatus for managing a mobility in a dual connectivity (DC) in a wireless communication system. According to an embodiment of the present disclosure, a method performed by a secondary node (SN) serving a wireless device with a master node (MN) in a dual connectivity (DC) in a wireless communication system comprises: receiving a first message comprising information related to a random access (RA) avoidance for the SN; determining that a RA is not needed for the SN after a handover based on the information; and transmitting a second message comprising RA avoidance information for the SN based on the determination.

Description

METHOD AND APPARATUS FOR MANAGING MOBILITY IN DUAL CONNECTIVITY IN WIRELESS COMMUNICATION SYSTEM

The present disclosure relates to method and apparatus for managing a mobility in a dual connectivity (DC) in a wireless communication system.

3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

Work has started in international telecommunication union (ITU) and 3GPP to develop requirements and specifications for new radio (NR) systems. 3GPP has to identify and develop the technology components needed for successfully standardizing the new RAT timely satisfying both the urgent market needs, and the more long-term requirements set forth by the ITU radio communication sector (ITU-R) international mobile telecommunications (IMT)-2020 process. Further, the NR should be able to use any spectrum band ranging at least up to 100 GHz that may be made available for wireless communications even in a more distant future.

The NR targets a single technical framework addressing all usage scenarios, requirements and deployment scenarios including enhanced mobile broadband (eMBB), massive machine-type-communications (mMTC), ultra-reliable and low latency communications (URLLC), etc. The NR shall be inherently forward compatible.

In a wireless communication system, a wireless device and/or user equipment (UE) may move along cells/base stations deployed in a wide range of areas. To provide proper services to the wireless device, the network should manage a mobility of the wireless device. For example, the network may control a handover of the wireless device from a source cell to a target cell.

Also, a wireless device (e.g., user equipment (UE)) may be connected to two or more radio access network (RAN) nodes and utilize radio resources provided by the RAN nodes. This situation may be called a dual connectivity (DC), in which the wireless device can maintain a connectivity to the dual RAN nodes. Mobility management may also be required in such a DC situation.

An aspect of the present disclosure is to provide method and apparatus for a mobility management in a wireless communication system.

Another aspect of the present disclosure is to provide method and apparatus for managing a mobility in a DC in a wireless communication system.

Another aspect of the present disclosure is to provide method and apparatus for performing a handover to a secondary node (SN) in DC in a wireless communication system.

Another aspect of the present disclosure is to provide method and apparatus for performing a handover to another master node (MN) in DC while maintaining a SN in a wireless communication system.

According to an embodiment of the present disclosure, a method performed by a secondary node (SN) serving a wireless device with a master node (MN) in a dual connectivity (DC) in a wireless communication system comprises: receiving a first message comprising information related to a random access (RA) avoidance for the SN; determining that a RA is not needed for the SN after a handover based on the information; and transmitting a second message comprising RA avoidance information for the SN based on the determination.

According to an embodiment of the present disclosure, a secondary node (SN) serving a wireless device with a master node (MN) in a dual connectivity (DC) in a wireless communication system comprises: a transceiver; a memory; and at least one processor operatively coupled to the memory and the transceiver. The at least one processor is configured to receive a first message comprising information related to a random access (RA) avoidance for the SN, determine that a RA is not needed for the SN after a handover based on the information, and transmit a second message comprising RA avoidance information for the SN based on the determination.

The present disclosure can have various advantageous effects.

For example, various embodiments of the present disclosure may provide solutions to make the UE's experience better by sufficiently using a SN, thereby the service may be better provided during a handover or while radio link failure happens in MN.

For example, various embodiments of the present disclosure may provide solutions to reduce signalling overhead by keeping a link of SN while performing a MN handover.

For example, various embodiments of the present disclosure may provide solutions to provide a service of SN seamlessly to a UE as much as possible during a mobility, thereby the UE's experience can be enhanced.

Advantageous effects which can be obtained through specific embodiments of the present disclosure are not limited to the advantageous effects listed above. For example, there may be a variety of technical effects that a person having ordinary skill in the related art can understand and/or derive from the present disclosure. Accordingly, the specific effects of the present disclosure are not limited to those explicitly described herein, but may include various effects that may be understood or derived from the technical features of the present disclosure.

FIG. 1 shows examples of 5G usage scenarios to which the technical features of the present disclosure can be applied.

FIG. 2 shows an example of a wireless communication system to which the technical features of the present disclosure can be applied.

FIG. 3 shows an example of a wireless communication system to which the technical features of the present disclosure can be applied.

FIG. 4 shows another example of a wireless communication system to which the technical features of the present disclosure can be applied.

FIG. 5 shows a block diagram of a user plane protocol stack to which the technical features of the present disclosure can be applied.

FIG. 6 shows a block diagram of a control plane protocol stack to which the technical features of the present disclosure can be applied.

FIG. 7 shows an example of a dual connectivity (DC) architecture to which technical features of the present disclosure can be applied.

FIGs. 8A-8B show an example of network controlled handover procedure to which technical features of the present disclosure can be applied.

FIG. 9 shows an example of MN handover procedure without SN change to which technical features of the present disclosure can be applied.

FIG. 10 shows an example of a method for random access (RA) avoidance in handover according to an embodiment of the present disclosure.

FIGs. 11A-11B show an example of RA avoidance in handover to SN according to an embodiment of the present disclosure.

FIGs. 12A-12B show an example of RA avoidance in handover to another RAN node according to an embodiment of the present disclosure.

FIG. 13 shows an example of an AI device to which the technical features of the present disclosure can be applied.

FIG. 14 shows an example of an AI system to which the technical features of the present disclosure can be applied.

FIG. 15 shows a UE to implement an embodiment of the present disclosure.

The technical features described below may be used by a communication standard by the 3rd generation partnership project (3GPP) standardization organization, a communication standard by the institute of electrical and electronics engineers (IEEE), etc. For example, the communication standards by the 3GPP standardization organization include long-term evolution (LTE) and/or evolution of LTE systems. The evolution of LTE systems includes LTE-advanced (LTE-A), LTE-A Pro, and/or 5G new radio (NR). The communication standard by the IEEE standardization organization includes a wireless local area network (WLAN) system such as IEEE 802.11a/b/g/n/ac/ax. The above system uses various multiple access technologies such as orthogonal frequency division multiple access (OFDMA) and/or single carrier frequency division multiple access (SC-FDMA) for downlink (DL) and/or uplink (UL). For example, only OFDMA may be used for DL and only SC-FDMA may be used for UL. Alternatively, OFDMA and SC-FDMA may be used for DL and/or UL.

In the present disclosure, “A or B” may mean “only A”, “only B”, or “both A and B”. In other words, “A or B” in the present disclosure may be interpreted as “A and/or B”. For example, “A, B or C” in the present disclosure may mean “only A”, “only B”, “only C”, or “any combination of A, B and C”.

In the present disclosure, slash (/) or comma (,) may mean “and/or". For example, “A/B” may mean “A and/or B”. Accordingly, “A/B” may mean “only A”, “only B”, or “both A and B”. For example, “A, B, C” may mean “A, B or C”.

In the present disclosure, “at least one of A and B” may mean “only A”, “only B” or “both A and B”. In addition, the expression “at least one of A or B” or “at least one of A and/or B” in the present disclosure may be interpreted as same as “at least one of A and B”.

In addition, in the present disclosure, “at least one of A, B and C” may mean “only A”, “only B”, “only C”, or “any combination of A, B and C”. In addition, “at least one of A, B or C” or “at least one of A, B and/or C” may mean “at least one of A, B and C”.

Also, parentheses used in the present disclosure may mean “for example”. In detail, when it is shown as “control information (PDCCH)”, "PDCCH" may be proposed as an example of “control information”. In other words, “control information” in the present disclosure is not limited to “PDCCH”, and "PDDCH" may be proposed as an example of “control information”. In addition, even when shown as “control information (i.e., PDCCH)”, “PDCCH” may be proposed as an example of “control information”.

Technical features that are separately described in one drawing in the present disclosure may be implemented separately or simultaneously.

The following drawings are created to explain specific embodiments of the present disclosure. The names of the specific devices or the names of the specific signals/messages/fields shown in the drawings are provided by way of example, and thus the technical features of the present disclosure are not limited to the specific names used in the following drawings.

The 5G usage scenarios shown in FIG. 1 are only exemplary, and the technical features of the present disclosure can be applied to other 5G usage scenarios which are not shown in FIG. 1.

Referring to FIG. 1, the three main requirements areas of 5G include (1) enhanced mobile broadband (eMBB) domain, (2) massive machine type communication (mMTC) area, and (3) ultra-reliable and low latency communications (URLLC) area. Some use cases may require multiple areas for optimization and, other use cases may only focus on only one key performance indicator (KPI). 5G is to support these various use cases in a flexible and reliable way.

eMBB focuses on across-the-board enhancements to the data rate, latency, user density, capacity and coverage of mobile broadband access. The eMBB aims ~10 Gbps of throughput. eMBB far surpasses basic mobile Internet access and covers rich interactive work and media and entertainment applications in cloud and/or augmented reality. Data is one of the key drivers of 5G and may not be able to see dedicated voice services for the first time in the 5G era. In 5G, the voice is expected to be processed as an application simply using the data connection provided by the communication system. The main reason for the increased volume of traffic is an increase in the size of the content and an increase in the number of applications requiring high data rates. Streaming services (audio and video), interactive video and mobile Internet connectivity will become more common as more devices connect to the Internet. Many of these applications require always-on connectivity to push real-time information and notifications to the user. Cloud storage and applications are growing rapidly in mobile communication platforms, which can be applied to both work and entertainment. Cloud storage is a special use case that drives growth of uplink data rate. 5G is also used for remote tasks on the cloud and requires much lower end-to-end delay to maintain a good user experience when the tactile interface is used. In entertainment, for example, cloud games and video streaming are another key factor that increases the demand for mobile broadband capabilities. Entertainment is essential in smartphones and tablets anywhere, including high mobility environments such as trains, cars and airplanes. Another use case is augmented reality and information retrieval for entertainment. Here, augmented reality requires very low latency and instantaneous data amount.

mMTC is designed to enable communication between devices that are low-cost, massive in number and battery-driven, intended to support applications such as smart metering, logistics, and field and body sensors. mMTC aims ~10 years on battery and/or ~1 million devices/km2. mMTC allows seamless integration of embedded sensors in all areas and is one of the most widely used 5G applications. Potentially by 2020, internet-of-things (IoT) devices are expected to reach 20.4 billion. Industrial IoT is one of the areas where 5G plays a key role in enabling smart cities, asset tracking, smart utilities, agriculture and security infrastructures.

URLLC will make it possible for devices and machines to communicate with ultra-reliability, very low latency and high availability, making it ideal for vehicular communication, industrial control, factory automation, remote surgery, smart grids and public safety applications.　URLLC aims ~1ms of latency. URLLC includes new services that will change the industry through links with ultra-reliability / low latency, such as remote control of key infrastructure and self-driving vehicles. The level of reliability and latency is essential for smart grid control, industrial automation, robotics, drones control and coordination.

Next, a plurality of use cases included in the triangle of FIG. 1 will be described in more detail.

5G can complement fiber-to-the-home (FTTH) and cable-based broadband (or DOCSIS) as a means of delivering streams rated from hundreds of megabits per second to gigabits per second. This high speed can be required to deliver TVs with resolutions of 4K or more (6K, 8K and above) as well as virtual reality (VR) and augmented reality (AR). VR and AR applications include mostly immersive sporting events. Certain applications may require special network settings. For example, in the case of a VR game, a game company may need to integrate a core server with an edge network server of a network operator to minimize delay.

Automotive is expected to become an important new driver for 5G, with many use cases for mobile communications to vehicles. For example, entertainment for passengers demands high capacity and high mobile broadband at the same time. This is because future users will continue to expect high-quality connections regardless of their location and speed. Another use case in the automotive sector is an augmented reality dashboard. The driver can identify an object in the dark on top of what is being viewed through the front window through the augmented reality dashboard. The augmented reality dashboard displays information that will inform the driver about the object's distance and movement. In the future, the wireless module enables communication between vehicles, information exchange between the vehicle and the supporting infrastructure, and information exchange between the vehicle and other connected devices (e.g. devices accompanied by a pedestrian). The safety system allows the driver to guide the alternative course of action so that he can drive more safely, thereby reducing the risk of accidents. The next step will be a remotely controlled vehicle or self-driving vehicle. This requires a very reliable and very fast communication between different self-driving vehicles and between vehicles and infrastructure. In the future, a self-driving vehicle will perform all driving activities, and the driver will focus only on traffic that the vehicle itself cannot identify. The technical requirements of self-driving vehicles require ultra-low latency and high-speed reliability to increase traffic safety to a level not achievable by humans.

Smart cities and smart homes, which are referred to as smart societies, will be embedded in high density wireless sensor networks. The distributed network of intelligent sensors will identify conditions for cost and energy-efficient maintenance of a city or house. A similar setting can be performed for each home. Temperature sensors, windows and heating controllers, burglar alarms and appliances are all wirelessly connected. Many of these sensors typically require low data rate, low power and low cost. However, for example, real-time high-definition (HD) video may be required for certain types of devices for monitoring.

The consumption and distribution of energy, including heat or gas, is highly dispersed, requiring automated control of distributed sensor networks. The smart grid interconnects these sensors using digital information and communication technologies to collect and act on information. This information can include supplier and consumer behavior, allowing the smart grid to improve the distribution of fuel, such as electricity, in terms of efficiency, reliability, economy, production sustainability, and automated methods. The smart grid can be viewed as another sensor network with low latency.

The health sector has many applications that can benefit from mobile communications. Communication systems can support telemedicine to provide clinical care in remote locations. This can help to reduce barriers to distance and improve access to health services that are not continuously available in distant rural areas. It is also used to save lives in critical care and emergency situations. Mobile communication based wireless sensor networks can provide remote monitoring and sensors for parameters such as heart rate and blood pressure.

Wireless and mobile communications are becoming increasingly important in industrial applications. Wiring costs are high for installation and maintenance. Thus, the possibility of replacing a cable with a wireless link that can be reconfigured is an attractive opportunity in many industries. However, achieving this requires that wireless connections operate with similar delay, reliability, and capacity as cables and that their management is simplified. Low latency and very low error probabilities are new requirements that need to be connected to 5G.

Logistics and freight tracking are important use cases of mobile communications that enable tracking of inventory and packages anywhere using location based information systems. Use cases of logistics and freight tracking typically require low data rates, but require a large range and reliable location information.

NR supports multiple numerology (or, subcarrier spacing (SCS)) to support various 5G services. For example, when the SCS is 15 kHz, wide area in traditional cellular bands may be supported. When the SCS is 30 kHz/60 kHz, dense-urban, lower latency and wider carrier bandwidth may be supported. When the SCS is 60 kHz or higher, a bandwidth greater than 24.25 GHz may be supported to overcome phase noise.

The NR frequency band may be defined as two types of frequency range, i.e., FR1 and FR2. The numerical value of the frequency range may be changed. For example, the frequency ranges of the two types (FR1 and FR2) may be as shown in Table 1 below. For ease of explanation, in the frequency ranges used in the NR system, FR1 may mean "sub 6 GHz range", FR2 may mean "above 6 GHz range," and may be referred to as millimeter wave (mmW).

Frequency Range designation	Corresponding frequency range	Subcarrier Spacing
FR1	450MHz - 6000MHz	15, 30, 60kHz
FR2	24250MHz - 52600MHz	60, 120, 240kHz

As mentioned above, the numerical value of the frequency range of the NR system may be changed. For example, FR1 may include a frequency band of 410MHz to 7125MHz as shown in Table 2 below. That is, FR1 may include a frequency band of 6GHz (or 5850, 5900, 5925 MHz, etc.) or more. For example, a frequency band of 6 GHz (or 5850, 5900, 5925 MHz, etc.) or more included in FR1 may include an unlicensed band. Unlicensed bands may be used for a variety of purposes, for example for communication for vehicles (e.g., autonomous driving).

Frequency Range designation	Corresponding frequency range	Subcarrier Spacing
FR1	410MHz - 7125MHz	15, 30, 60kHz
FR2	24250MHz - 52600MHz	60, 120, 240kHz

FIG. 2 shows an example of a wireless communication system to which the technical features of the present disclosure can be applied.Referring to FIG. 2, the wireless communication system may include a first device 210 and a second device 220.

The first device 210 includes a base station, a network node, a transmitting UE, a receiving UE, a wireless device, a wireless communication device, a vehicle, a vehicle equipped with an autonomous driving function, a connected car, a drone, an unmanned aerial vehicle (UAV), an artificial intelligence (AI) module, a robot, an AR device, a VR device, a mixed reality (MR) device, a hologram device, a public safety device, an MTC device, an IoT device, a medical device, a fin-tech device (or, a financial device), a security device, a climate/environmental device, a device related to 5G services, or a device related to the fourth industrial revolution.

The second device 220 includes a base station, a network node, a transmitting UE, a receiving UE, a wireless device, a wireless communication device, a vehicle, a vehicle equipped with an autonomous driving function, a connected car, a drone, a UAV, an AI module, a robot, an AR device, a VR device, an MR device, a hologram device, a public safety device, an MTC device, an IoT device, a medical device, a fin-tech device (or, a financial device), a security device, a climate/environmental device, a device related to 5G services, or a device related to the fourth industrial revolution.

For example, the UE may include a mobile phone, a smart phone, a laptop computer, a digital broadcasting terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation device, a slate personal computer (PC), a tablet PC, an ultrabook, a wearable device (e.g. a smartwatch, a smart glass, a head mounted display (HMD)) . For example, the HMD may be a display device worn on the head. For example, the HMD may be used to implement AR, VR and/or MR.

For example, the drone may be a flying object that is flying by a radio control signal without a person boarding it. For example, the VR device may include a device that implements an object or background in the virtual world. For example, the AR device may include a device that implements connection of an object and/or a background of a virtual world to an object and/or a background of the real world. For example, the MR device may include a device that implements fusion of an object and/or a background of a virtual world to an object and/or a background of the real world. For example, the hologram device may include a device that implements a 360-degree stereoscopic image by recording and playing stereoscopic information by utilizing a phenomenon of interference of light generated by the two laser lights meeting with each other, called holography. For example, the public safety device may include a video relay device or a video device that can be worn by the user's body. For example, the MTC device and the IoT device may be a device that do not require direct human intervention or manipulation. For example, the MTC device and the IoT device may include a smart meter, a vending machine, a thermometer, a smart bulb, a door lock and/or various sensors. For example, the medical device may be a device used for the purpose of diagnosing, treating, alleviating, handling, or preventing a disease. For example, the medical device may be a device used for the purpose of diagnosing, treating, alleviating, or correcting an injury or disorder. For example, the medical device may be a device used for the purpose of inspecting, replacing or modifying a structure or function. For example, the medical device may be a device used for the purpose of controlling pregnancy. For example, the medical device may include a treatment device, a surgical device, an (in vitro) diagnostic device, a hearing aid and/or a procedural device, etc. For example, a security device may be a device installed to prevent the risk that may occur and to maintain safety. For example, the security device may include a camera, a closed-circuit TV (CCTV), a recorder, or a black box. For example, the fin-tech device may be a device capable of providing financial services such as mobile payment. For example, the fin-tech device may include a payment device or a point of sales (POS). For example, the climate/environmental device may include a device for monitoring or predicting the climate/environment.

The first device 210 may include at least one or more processors, such as a processor 211, at least one memory, such as a memory 212, and at least one transceiver, such as a transceiver 213. The processor 211 may perform the functions, procedures, and/or methods of the present disclosure described below. The processor 211 may perform one or more protocols. For example, the processor 211 may perform one or more layers of the air interface protocol. The memory 212 is connected to the processor 211 and may store various types of information and/or instructions. The transceiver 213 is connected to the processor 211 and may be controlled to transmit and receive wireless signals.

The second device 220 may include at least one or more processors, such as a processor 221, at least one memory, such as a memory 222, and at least one transceiver, such as a transceiver 223. The processor 221 may perform the functions, procedures, and/or methods of the present disclosure described below. The processor 221 may perform one or more protocols. For example, the processor 221 may perform one or more layers of the air interface protocol. The memory 222 is connected to the processor 221 and may store various types of information and/or instructions. The transceiver 223 is connected to the processor 221 and may be controlled to transmit and receive wireless signals.

The

memory

212, 222 may be connected internally or externally to the

processor

211, 212, or may be connected to other processors via a variety of technologies such as wired or wireless connections.

The first device 210 and/or the second device 220 may have more than one antenna. For example, antenna 214 and/or antenna 224 may be configured to transmit and receive wireless signals.

According to various embodiments, some components of the first device 210 and/or the second device 220 may be omitted, and the first device 210 and/or the second device 220 may further comprise one or more other components not illustrated in FIG. 2. For example, the first device 210 (or the second device 220) may further comprise a communication interface which is connected to the processor 211 (or processor 221) and may be controlled to transmit and receive signals through wired backhaul or wireless backhaul.

According to various embodiments, the processor 211 (or the processor 221) may be configured to, or configured to control the transceiver (e.g., transceiver 213 and/or transceiver 223) and/or the communication interface to implement steps performed by the RAN node (or, gNB, eNB, base station, cell, CU, DU, CU-CP, CU-UP) as illustrated throughout the disclosure.

Specifically, FIG. 3 shows a system architecture based on an evolved-UMTS terrestrial radio access network (E-UTRAN). The aforementioned LTE is a part of an evolved-UTMS (e-UMTS) using the E-UTRAN.

Referring to FIG. 3, the wireless communication system includes one or more user equipment (UE) 310, an E-UTRAN and an evolved packet core (EPC). The UE 310 refers to a communication equipment carried by a user. The UE 310 may be fixed or mobile. The UE 310 may be referred to as another terminology, such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, etc.

The E-UTRAN consists of one or more evolved NodeB (eNB) 320. The eNB 320 provides the E-UTRA user plane and control plane protocol terminations towards the UE 10. The eNB 320 is generally a fixed station that communicates with the UE 310. The eNB 320 hosts the functions, such as inter-cell radio resource management (RRM), radio bearer (RB) control, connection mobility control, radio admission control, measurement configuration/provision, dynamic resource allocation (scheduler), etc. The eNB 320 may be referred to as another terminology, such as a base station (BS), a base transceiver system (BTS), an access point (AP), etc.

A downlink (DL) denotes communication from the eNB 320 to the UE 310. An uplink (UL) denotes communication from the UE 310 to the eNB 320. A sidelink (SL) denotes communication between the UEs 310. In the DL, a transmitter may be a part of the eNB 320, and a receiver may be a part of the UE 310. In the UL, the transmitter may be a part of the UE 310, and the receiver may be a part of the eNB 320. In the SL, the transmitter and receiver may be a part of the UE 310.

The EPC includes a mobility management entity (MME), a serving gateway (S-GW) and a packet data network (PDN) gateway (P-GW). The MME hosts the functions, such as non-access stratum (NAS) security, idle state mobility handling, evolved packet system (EPS) bearer control, etc. The S-GW hosts the functions, such as mobility anchoring, etc. The S-GW is a gateway having an E-UTRAN as an endpoint. For convenience, MME/S-GW 330 will be referred to herein simply as a “gateway,” but it is understood that this entity includes both the MME and S-GW. The P-GW hosts the functions, such as UE Internet protocol (IP) address allocation, packet filtering, etc. The P-GW is a gateway having a PDN as an endpoint. The P-GW is connected to an external network.

The UE 310 is connected to the eNB 320 by means of the Uu interface. The UEs 310 are interconnected with each other by means of the PC5 interface. The eNBs 320 are interconnected with each other by means of the X2 interface. The eNBs 320 are also connected by means of the S1 interface to the EPC, more specifically to the MME by means of the S1-MME interface and to the S-GW by means of the S1-U interface. The S1 interface supports a many-to-many relation between MMEs / S-GWs and eNBs.

Specifically, FIG. 4 shows a system architecture based on a 5G NR. The entity used in the 5G NR (hereinafter, simply referred to as "NR") may absorb some or all of the functions of the entities introduced in FIG. 3 (e.g. eNB, MME, S-GW). The entity used in the NR may be identified by the name “NG” for distinction from the LTE/LTE-A.

Referring to FIG. 4, the wireless communication system includes one or more UE 410, a next-generation RAN (NG-RAN) and a 5th generation core network (5GC). The NG-RAN consists of at least one NG-RAN node. The NG-RAN node is an entity corresponding to the eNB 320 shown in FIG. 3. The NG-RAN node consists of at least one gNB 421 and/or at least one ng-eNB 422. The gNB 421 provides NR user plane and control plane protocol terminations towards the UE 410. The ng-eNB 422 provides E-UTRA user plane and control plane protocol terminations towards the UE 410.

The 5GC includes an access and mobility management function (AMF), a user plane function (UPF) and a session management function (SMF). The AMF hosts the functions, such as NAS security, idle state mobility handling, etc. The AMF is an entity including the functions of the conventional MME. The UPF hosts the functions, such as mobility anchoring, protocol data unit (PDU) handling. The UPF an entity including the functions of the conventional S-GW. The SMF hosts the functions, such as UE IP address allocation, PDU session control.

The gNBs 421 and ng-eNBs 422 are interconnected with each other by means of the Xn interface. The gNBs 421 and ng-eNBs 422 are also connected by means of the NG interfaces to the 5GC, more specifically to the AMF by means of the NG-C interface and to the UPF by means of the NG-U interface.

A protocol structure between network entities described above is described. On the system of FIG. 3 and/or FIG. 4, layers of a radio interface protocol between the UE and the network (e.g. NG-RAN and/or E-UTRAN) may be classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of the open system interconnection (OSI) model that is well-known in the communication system.

FIG. 5 shows a block diagram of a user plane protocol stack to which the technical features of the present disclosure can be applied. FIG. 6 shows a block diagram of a control plane protocol stack to which the technical features of the present disclosure can be applied.

The user/control plane protocol stacks shown in FIG. 5 and FIG. 6 are used in NR. However, user/control plane protocol stacks shown in FIG. 5 and FIG. 6 may be used in LTE/LTE-A without loss of generality, by replacing gNB/AMF with eNB/MME.

Referring to FIG. 5 and FIG. 6, a physical (PHY) layer belonging to L1. The PHY layer offers information transfer services to media access control (MAC) sublayer and higher layers. The PHY layer offers to the MAC sublayer transport channels. Data between the MAC sublayer and the PHY layer is transferred via the transport channels. Between different PHY layers, i.e., between a PHY layer of a transmission side and a PHY layer of a reception side, data is transferred via the physical channels.

The MAC sublayer belongs to L2. The main services and functions of the MAC sublayer include mapping between logical channels and transport channels, multiplexing/de-multiplexing of MAC service data units (SDUs) belonging to one or different logical channels into/from transport blocks (TB) delivered to/from the physical layer on transport channels, scheduling information reporting, error correction through hybrid automatic repeat request (HARQ), priority handling between UEs by means of dynamic scheduling, priority handling between logical channels of one UE by means of logical channel prioritization (LCP), etc. The MAC sublayer offers to the radio link control (RLC) sublayer logical channels.

The RLC sublayer belong to L2. The RLC sublayer supports three transmission modes, i.e. transparent mode (TM), unacknowledged mode (UM), and acknowledged mode (AM), in order to guarantee various quality of services (QoS) required by radio bearers. The main services and functions of the RLC sublayer depend on the transmission mode. For example, the RLC sublayer provides transfer of upper layer PDUs for all three modes, but provides error correction through ARQ for AM only. In LTE/LTE-A, the RLC sublayer provides concatenation, segmentation and reassembly of RLC SDUs (only for UM and AM data transfer) and re-segmentation of RLC data PDUs (only for AM data transfer). In NR, the RLC sublayer provides segmentation (only for AM and UM) and re-segmentation (only for AM) of RLC SDUs and reassembly of SDU (only for AM and UM). That is, the NR does not support concatenation of RLC SDUs. The RLC sublayer offers to the packet data convergence protocol (PDCP) sublayer RLC channels.

The PDCP sublayer belong to L2. The main services and functions of the PDCP sublayer for the user plane include header compression and decompression, transfer of user data, duplicate detection, PDCP PDU routing, retransmission of PDCP SDUs, ciphering and deciphering, etc. The main services and functions of the PDCP sublayer for the control plane include ciphering and integrity protection, transfer of control plane data, etc.

The service data adaptation protocol (SDAP) sublayer belong to L2. The SDAP sublayer is only defined in the user plane. The SDAP sublayer is only defined for NR. The main services and functions of SDAP include, mapping between a QoS flow and a data radio bearer (DRB), and marking QoS flow ID (QFI) in both DL and UL packets. The SDAP sublayer offers to 5GC QoS flows.

A radio resource control (RRC) layer belongs to L3. The RRC layer is only defined in the control plane. The RRC layer controls radio resources between the UE and the network. To this end, the RRC layer exchanges RRC messages between the UE and the BS. The main services and functions of the RRC layer include broadcast of system information related to AS and NAS, paging, establishment, maintenance and release of an RRC connection between the UE and the network, security functions including key management, establishment, configuration, maintenance and release of radio bearers, mobility functions, QoS management functions, UE measurement reporting and control of the reporting, NAS message transfer to/from NAS from/to UE.

In other words, the RRC layer controls logical channels, transport channels, and physical channels in relation to the configuration, reconfiguration, and release of radio bearers. A radio bearer refers to a logical path provided by L1 (PHY layer) and L2 (MAC/RLC/PDCP/SDAP sublayer) for data transmission between a UE and a network. Setting the radio bearer means defining the characteristics of the radio protocol layer and the channel for providing a specific service, and setting each specific parameter and operation method. Radio bearer may be divided into signaling RB (SRB) and data RB (DRB). The SRB is used as a path for transmitting RRC messages in the control plane, and the DRB is used as a path for transmitting user data in the user plane.

An RRC state indicates whether an RRC layer of the UE is logically connected to an RRC layer of the E-UTRAN. In LTE/LTE-A, when the RRC connection is established between the RRC layer of the UE and the RRC layer of the E-UTRAN, the UE is in the RRC connected state (RRC_CONNECTED). Otherwise, the UE is in the RRC idle state (RRC_IDLE). In NR, the RRC inactive state (RRC_INACTIVE) is additionally introduced. RRC_INACTIVE may be used for various purposes. For example, the massive machine type communications (MMTC) UEs can be efficiently managed in RRC_INACTIVE. When a specific condition is satisfied, transition is made from one of the above three states to the other.

A predetermined operation may be performed according to the RRC state. In RRC_IDLE, public land mobile network (PLMN) selection, broadcast of system information (SI), cell re-selection mobility, core network (CN) paging and discontinuous reception (DRX) configured by NAS may be performed. The UE shall have been allocated an identifier (ID) which uniquely identifies the UE in a tracking area. No RRC context stored in the BS.

In RRC_CONNECTED, the UE has an RRC connection with the network (i.e. E-UTRAN/NG-RAN). Network-CN connection (both C/U-planes) is also established for UE. The UE AS context is stored in the network and the UE. The RAN knows the cell which the UE belongs to. The network can transmit and/or receive data to/from UE. Network controlled mobility including measurement is also performed.

Most of operations performed in RRC_IDLE may be performed in RRC_INACTIVE. But, instead of CN paging in RRC_IDLE, RAN paging is performed in RRC_INACTIVE. In other words, in RRC_IDLE, paging for mobile terminated (MT) data is initiated by core network and paging area is managed by core network. In RRC_INACTIVE, paging is initiated by NG-RAN, and RAN-based notification area (RNA) is managed by NG-RAN. Further, instead of DRX for CN paging configured by NAS in RRC_IDLE, DRX for RAN paging is configured by NG-RAN in RRC_INACTIVE. Meanwhile, in RRC_INACTIVE, 5GC-NG-RAN connection (both C/U-planes) is established for UE, and the UE AS context is stored in NG-RAN and the UE. NG-RAN knows the RNA which the UE belongs to.

NAS layer is located at the top of the RRC layer. The NAS control protocol performs the functions, such as authentication, mobility management, security control.

The physical channels may be modulated according to OFDM processing and utilizes time and frequency as radio resources. The physical channels consist of a plurality of orthogonal frequency division multiplexing (OFDM) symbols in time domain and a plurality of subcarriers in frequency domain. One subframe consists of a plurality of OFDM symbols in the time domain. A resource block is a resource allocation unit, and consists of a plurality of OFDM symbols and a plurality of subcarriers. In addition, each subframe may use specific subcarriers of specific OFDM symbols (e.g. first OFDM symbol) of the corresponding subframe for a physical downlink control channel (PDCCH), i.e. L1/L2 control channel. A transmission time interval (TTI) is a basic unit of time used by a scheduler for resource allocation. The TTI may be defined in units of one or a plurality of slots, or may be defined in units of mini-slots.

The transport channels are classified according to how and with what characteristics data are transferred over the radio interface. DL transport channels include a broadcast channel (BCH) used for transmitting system information, a downlink shared channel (DL-SCH) used for transmitting user traffic or control signals, and a paging channel (PCH) used for paging a UE. UL transport channels include an uplink shared channel (UL-SCH) for transmitting user traffic or control signals and a random access channel (RACH) normally used for initial access to a cell.

Different kinds of data transfer services are offered by MAC sublayer. Each logical channel type is defined by what type of information is transferred. Logical channels are classified into two groups: control channels and traffic channels.

Control channels are used for the transfer of control plane information only. The control channels include a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH) and a dedicated control channel (DCCH). The BCCH is a DL channel for broadcasting system control information. The PCCH is DL channel that transfers paging information, system information change notifications. The CCCH is a channel for transmitting control information between UEs and network. This channel is used for UEs having no RRC connection with the network. The DCCH is a point-to-point bi-directional channel that transmits dedicated control information between a UE and the network. This channel is used by UEs having an RRC connection.

Traffic channels are used for the transfer of user plane information only. The traffic channels include a dedicated traffic channel (DTCH). The DTCH is a point-to-point channel, dedicated to one UE, for the transfer of user information. The DTCH can exist in both UL and DL.

Regarding mapping between the logical channels and transport channels, in DL, BCCH can be mapped to BCH, BCCH can be mapped to DL-SCH, PCCH can be mapped to PCH, CCCH can be mapped to DL-SCH, DCCH can be mapped to DL-SCH, and DTCH can be mapped to DL-SCH. In UL, CCCH can be mapped to UL-SCH, DCCH can be mapped to UL- SCH, and DTCH can be mapped to UL-SCH.

FIG. 7 shows an example of a dual connectivity (DC) architecture to which technical features of the present disclosure can be applied. In FIG. 7 and throughout the disclosure, 'radio access network (RAN) node' refers to a network entity to which a wireless device can access through a radio channel. Examples of the RAN node may comprise gNB, eNB, base station, and/or cell.

Referring to FIG. 7, MN 711, SN 721, and a UE 730 communicating with both the MN 711 and the SN 721 are illustrated. As illustrated in FIG. 7, DC refers to a scheme in which a UE (e.g., UE 730) utilizes radio resources provided by at least two RAN nodes comprising a MN (e.g., MN 711) and one or more SNs (e.g., SN 721). In other words, DC refers to a scheme in which a UE is connected to both the MN and the one or more SNs, and communicates with both the MN and the one or more SNs. Since the MN and the SN may be in different sites, a backhaul between the MN and the SN may be construed as non-ideal backhaul (e.g., relatively large delay between nodes).

MN (e.g., MN 711) refers to a main RAN node providing services to a UE in DC situation. SN (e.g., SN 721) refers to an additional RAN node providing services to the UE with the MN in the DC situation. If one RAN node provides services to a UE, the RAN node may be a MN. SN can exist if MN exists.

For example, the MN may be associated with macro cell whose coverage is relatively larger than that of a small cell. However, the MN does not have to be associated with macro cell - that is, the MN may be associated with a small cell. Throughout the disclosure, a RAN node that is associated with a macro cell may be referred to as 'macro cell node'. MN may comprise macro cell node.

For example, the SN may be associated with small cell (e.g., micro cell, pico cell, femto cell) whose coverage is relatively smaller than that of a macro cell. However, the SN does not have to be associated with small cell - that is, the SN may be associated with a macro cell. Throughout the disclosure, a RAN node that is associated with a small cell may be referred to as 'small cell node'. SN may comprise small cell node.

The MN may be associated with a master cell group (MCG). MCG may refer to a group of serving cells associated with the MN, and may comprise a primary cell (PCell) and optionally one or more secondary cells (SCells). User plane data and/or control plane data may be transported from a core network to the MN through a MCG bearer. MCG bearer refers to a bearer whose radio protocols are located in the MN to use MN resources. As shown in FIG. 7, the radio protocols of the MCG bearer may comprise PDCP, RLC, MAC and/or PHY.

The SN may be associated with a secondary cell group (SCG). SCG may refer to a group of serving cells associated with the SN, and may comprise a primary secondary cell (PSCell) and optionally one or more SCells. User plane data may be transported from a core network to the SN through a SCG bearer. SCG bearer refers to a bearer whose radio protocols are located in the SN to use SN resources. As shown in FIG. 7, the radio protocols of the SCG bearer may comprise PDCP, RLC, MAC and PHY.

User plane data and/or control plane data may be transported from a core network to the MN and split up/duplicated in the MN, and at least part of the split/duplicated data may be forwarded to the SN through a split bearer. Split bearer refers to a bearer whose radio protocols are located in both the MN and the SN to use both MN resources and SN resources. As shown in FIG. 7, the radio protocols of the split bearer located in the MN may comprise PDCP, RLC, MAC and PHY. The radio protocols of the split bearer located in the SN may comprise RLC, MAC and PHY.

According to various embodiments, PDCP anchor/PDCP anchor point/PDCP anchor node refers to a RAN node comprising a PDCP entity which splits up and/or duplicates data and forwards at least part of the split/duplicated data over X2/Xn interface to another RAN node. In the example of FIG. 7, PDCP anchor node may be MN.

According to various embodiments, the MN for the UE may be changed. This may be referred to as handover, or a MN handover.

According to various embodiments, a SN may newly start providing radio resources to the UE, establishing a connection with the UE, and/or communicating with the UE (i.e., SN for the UE may be newly added). This may be referred to as a SN addition.

According to various embodiments, a SN for the UE may be changed while the MN for the UE is maintained. This may be referred to as a SN change.

According to various embodiments, DC may comprise E-UTRAN NR - DC (EN-DC), and/or multi-radio access technology (RAT) - DC (MR-DC). EN-DC refers to a DC situation in which a UE utilizes radio resources provided by E-UTRAN node and NR RAN node. MR-DC refers to a DC situation in which a UE utilizes radio resources provided by RAN nodes with different RATs.

In some mobility situations, UE may receive a handover command comprising a single target cell from a network and perform a handover (or, handover attempt) to the target cell indicated by the network. This handover may be referred to as 'network controlled handover'. The handover command related to the network controlled handover may be referred to as 'network controlled handover command'. Detailed network controlled handover procedure is illustrated in FIGs. 8A-8B.

FIGs. 8A-8B show an example of network controlled handover procedure to which technical features of the present disclosure can be applied. Throughout the disclosure, the gNB can be substituted for eNB, cell, RAN node or base station, and both the access and mobility management function (AMF) and user plane function(s) (UPF(s)) can be substituted for a mobility management entity (MME) - that is, steps associated with the AMF and/or the UPF can be associated with the MME.

Referring to FIG. 8A, in step 0, the UE context within the source gNB may contain information regarding roaming and access restrictions which were provided either at connection establishment or at the last tracking area (TA) update.

In step 1, the source gNB may configure the UE measurement procedures and the UE reports according to the measurement configuration.

In step 2, the source gNB may decide to handover the UE, based on MeasurementReport and RRM information.

In step 3, the source gNB may issue a Handover Request message to the target gNB passing a transparent RRC container with necessary information to prepare the handover at the target side. The information may include at least the target cell ID, KgNB*, the C-RNTI of the UE in the source gNB, RRM-configuration including UE inactive time, basic AS-configuration including antenna Info and DL Carrier Frequency, the current QoS flow to DRB mapping rules applied to the UE, the SIB1 from source gNB, the UE capabilities for different RATs, PDU session related information, and can include the UE reported measurement information including beam-related information if available. The PDU session related information may include the slice information and QoS flow level QoS profile(s). After issuing a Handover Request, the source gNB may not reconfigure the UE, including performing Reflective QoS flow to DRB mapping.

In step 4, admission control may be performed by the target gNB. Slice-aware admission control shall be performed if the slice information is sent to the target gNB. If the PDU sessions are associated with non-supported slices the target gNB shall reject such PDU Sessions.

In step 5, the target gNB may prepare the handover with L1/L2 and send the HANDOVER REQUEST ACKNOWLEDGE to the source gNB, which may include a transparent container to be sent to the UE as an RRC message to perform the handover.

In step 6, the source gNB may trigger the Uu handover by sending an RRCReconfiguration message to the UE, containing the information required to access the target cell: at least the target cell ID, the new C-RNTI, the target gNB security algorithm identifiers for the selected security algorithms. It can also include a set of dedicated RACH resources, the association between RACH resources and SSB(s), the association between RACH resources and UE-specific CSI-RS configuration(s), common RACH resources, and system information of the target cell.

In step 7, the source gNB may send the SN STATUS TRANSFER message to the target gNB.

In step 8, the UE may synchronize to the target cell and complete the RRC handover procedure by sending RRCReconfigurationComplete message to target gNB.

FIG. 8B illustrates steps which continue from the steps illustrated in FIG. 8A.

Referring to FIG. 8B, in step 9, the target gNB may send a PATH SWITCH REQUEST message to AMF to trigger 5GC to switch the DL data path towards the target gNB and to establish an NG-C interface instance towards the target gNB.

In step 10, core network entity(ies)(e.g., AMF, UPF(s) and/or MME) may switch the DL data path towards the target gNB. The UPF may send one or more "end marker" packets on the old path to the source gNB per PDU session/tunnel and then can release any U-plane/transport network layer (TNL) resources towards the source gNB.

In step 11, the AMF may confirm the PATH SWITCH REQUEST message with the PATH SWITCH REQUEST ACKNOWLEDGE message.

In step 12, upon reception of the PATH SWITCH REQUEST ACKNOWLEDGE message from the AMF, the target gNB may send the UE CONTEXT RELEASE to inform the source gNB about the success of the handover. The source gNB can then release radio and C-plane related resources associated to the UE context. Any ongoing data forwarding may continue.

In a wireless communication system (e.g., 5G NR), the mobility enhancement and DC/carrier aggregation (CA) enhancement may be important items for enhancing communication services (e.g., 5G services). To provide seamless services for UE as much as possible, the current DC/mobility procedure may need to be enhanced. For example, if the link of SN is good enough, a method to keep the SN in case that MN should be handed over or MN suffers from radio link failure may need to be enhanced.

In a wireless communication system such as NR, small interruption is one of the requirements to provide good UE experience in handover. Mobility performance is one of the most important performance metrics for a wireless communication system (e.g., NR). Therefore, it is important to identify handover solution to achieve high handover performance with almost 0ms interruption, low latency and high reliability.

For example, handover may happen while trying to keep the secondary node, as illustrated in FIG. 9.

FIG. 9 shows an example of MN handover procedure without SN change to which technical features of the present disclosure can be applied. That is, according to examples illustrated in FIG. 9, SN may be maintained while MN handover is performed from a source MN (e.g., source master eNB (MeNB)) to a target MN (e.g., target MeNB).

Referring to FIG. 9, in step 1, the source MeNB may start the handover procedure by initiating the X2 Handover Preparation procedure. The source MeNB may include the SCG configuration in the HandoverPreparationInformation. The source MeNB may include the SeNB UE X2AP ID and SeNB ID as a reference to the UE context in the SeNB that was established by the source MeNB in the Handover Request message.

In step 2, if the target MeNB decides to keep the SeNB, the target MeNB may send SeNB Addition Request to the SeNB including the SeNB UE X2AP ID as a reference to the UE context in the SeNB that was established by the source MeNB.

In step 3, the SeNB may reply with SeNB Addition Request Acknowledge.

In step 4, the target MeNB may include within the Handover Request Acknowledge message a transparent container to be sent to the UE as an RRC message to perform the handover which also includes the SCG configuration, and may also provide forwarding addresses to the source MeNB. The target MeNB may indicate to the source MeNB that the UE context in the SeNB is kept if the target MeNB and the SeNB decided to keep the UE context in the SeNB in step 2 and step 3.

In step 5, the source MeNB may send SeNB Release Request to the SeNB. The source MeNB may indicate to the SeNB that the UE context in SeNB is kept. If the indication as the UE context kept in SeNB is included, the SeNB may keep the UE context.

In step 6, the source MeNB may trigger the UE to apply the new configuration.

In

step

7 and 8, the UE may synchronize to the target MeNB and reply with RRCConnectionReconfigurationComplete message.

In step 9, the UE may synchronize to the SeNB.

In step 10, if the RRC connection reconfiguration procedure was successful, the target MeNB may inform the SeNB.

In

step

11 and 12, data forwarding from the source MeNB may take place. Data forwarding may be omitted for SCG bearers. Direct data forwarding from the source MeNB to the SeNB may not be possible for split bearers. Direct data forwarding may occur only for bearer type change.

In step 13 to 16, the target MeNB may initiate the S1 Path Switch procedure. If new UL TEIDs of the S-GW are included, the target MeNB may perform MeNB initiated SeNB Modification procedure to provide them to the SeNB.

In step 17, the target MeNB may initiate the UE Context Release procedure towards the source MeNB.

In step 18, upon reception of the UE Context Release message, the SeNB can release C-plane related resource associated to the UE context towards the source MeNB. Any ongoing data forwarding may continue. The SeNB shall not release the UE context associated with the target MeNB if the indication was included in the SeNB Release Request in step 5.

The procedure illustrated in FIG. 9 may be realized almost from a network point of view - that is, data forwarding/path switch can be skipped. However, from radio point of view, the procedure may hard to be realized.

For another example, in a DC of MN and SN, handover procedure may be performed for a handover from the MN to the SN. The handover procedure may also need to be realized from radio point of view.

With regard to DC/CA enhancements, one of the objectives on DC/CA enhancements is to enhance the situation of MCG link failure. Basically, even though MCG link failure happens, there might be a case that SN is still good to provide the service. Thus, in this case, it may be desirable that the SN continues to provide the services as good as possible. Therefore, enhancements may be needed to realize the case in which the SN continues to provide the services as good as possible even though the MCG link failure happens.

Various embodiments of the present disclosure may provide solutions to solve problems from both network and radio points of view. Various embodiments of the present disclosure may also provide solutions to enhance UE's experience on DC in a wireless communication system (e.g., NR), especially considering challenges in high/medium frequency. Various embodiments may be applied to a case that one link suffers from radio link failure or significantly reduced radio quality while the other link can be used as normal as possible in DC.

FIG. 10 shows an example of a method for random access (RA) avoidance in handover according to an embodiment of the present disclosure. The method may be performed by a SN serving a wireless device with a MN in DC.

Referring to FIG. 10, in step S1001, the SN may receive a first message comprising information related to a RA avoidance for the SN. The information related to a RA avoidance for the SN may comprise information that can be a basis for determining whether a RA is needed for the SN after a handover or not. For example, the information related to a RA avoidance for the SN may comprise information informing that a signal quality for the SN exceeds a threshold value. That is, the information related to a RA avoidance for the SN may comprise information informing that a signal quality for the SN is good enough. The threshold value may be preset and/or predetermined, or be configured by higher layer signalling/dynamic signalling form a network. The threshold value may be a criterion for determining that a signal quality for the SN is good enough to maintain a link of the SN. The information related to a RA avoidance for the SN may further comprise information for a radio link failure of the MN (i.e., MCG failure, MCG link failure).

In step S1003, the SN may determine that a RA is not needed for the SN after a handover based on the information related to a RA avoidance for the SN. For example, the information related to a RA avoidance for the SN may comprise information informing that a signal quality for the SN is good enough, and information for a radio link failure (RLF) of the MN. Therefore, the SN may determine that a handover from the MN will be performed based on the information for a RLF of the MN. However, since the SN is also informed that a signal quality for the SN is good enough, the SN may determine that a link of the SN may be maintained after the handover. Therefore, the SN may determine that a RA is not needed or RA is avoided for the SN after the handover based on the information related to a RA avoidance for the SN. For another example, the information related to a RA avoidance for the SN may comprise RA avoidance information for the SN. The SN may also determine that a RA is not needed or RA is avoided for the SN after the handover based on the RA avoidance information.

In step S1005, the SN may transmit a second message comprising RA avoidance information for the SN based on the determination. For example, if it is determined that a RA is not needed or RA is avoided for the SN after the handover, the SN may transmit a second message comprising RA avoidance information for the SN, to a target MN for the handover or the wireless device. The RA avoidance information may comprise information informing that a RA procedure for the SN is avoided to communicate with the SN after the handover. Therefore, the SN may communicate with the wireless device without performing a RA procedure with the wireless device after the handover based on the RA avoidance information for the SN.

According to various embodiments, the handover may comprise a handover of the wireless device from the MN to the SN.

According to various embodiments, the first message may be a handover request message or a SN modification request message received from the MN. The second message may be a handover request acknowledge (ACK) message or SN modification request ACK message transmitted to the MN.

According to various embodiments, the first message may further comprise at least one of: a request for the handover of the wireless device to the SN; RA avoidance information for the SN; information for a list of radio access bearers to be maintained in the SN after the handover; or information for a list of packet data unit (PDU) sessions to be maintained in the SN after the handover.

According to various embodiments, to determine that a RA is not needed for the SN after a handover, the SN may determine to maintain one or more parameters for the wireless device after the handover based on the information related to a RA avoidance for the SN. The one or more parameters may comprise at least one of a timing advance value for an uplink (UL) transmission, UL grant for the wireless device, or parameters related to an UL power control for the wireless device.

According to various embodiments, the second message may comprise at least one of: information instructing to maintain one or more parameters for the wireless device after the handover; information informing that a secondary cell group (SCG) configuration for the SN is maintained after the handover; information for a list of radio access bearers to be maintained in the SN after the handover; or information for a list of packet data unit (PDU) sessions to be maintained in the SN after the handover. The one or more parameters may comprise at least one of a timing advance value for an uplink (UL) transmission, UL grant for the wireless device, or parameters related to an UL power control for the wireless device.

According to various embodiments, the SN may transmit, to the wireless device, a third message comprising at least one of: the RA avoidance information for the SN; information instructing to maintain at least one of a timing advance value for an uplink (UL) transmission, UL grant for the wireless device, or parameters related to an UL power control for the wireless device after the handover; or information informing that a secondary cell group (SCG) configuration for the SN is maintained after the handover.

According to various embodiments, the handover may comprise a MN handover of the wireless device from the MN to target radio access network (RAN) node. The target RAN node becomes a MN for a DC after the MN handover. The SN is maintained as a SN for a DC after the MN handover.

According to various embodiments, the first message may be a SN addition request message received from a target radio access network (RAN) node for the handover. The second message may be a SN addition request acknowledge (ACK) message transmitted to the target RAN node.

According to various embodiments, the SN may receive, from the MN, a SN release request message comprising information instructing to maintain context information of the wireless device related to a target radio access network (RAN) node for the handover after the handover.

According to various embodiments, the SN may receive, from the MN, a context release message comprising information instructing to release context information of the wireless device related to the MN. The SN may release the context information of the wireless device related to the MN based on the context release message while maintaining context information of the wireless device related to a target radio access network (RAN) node for the handover.

FIGs. 11A-11B show an example of RA avoidance in handover to SN according to an embodiment of the present disclosure. In FIGs. 11A-11B, it is assumed that a DC of the MN and the SN has been established initially.

Referring to FIG. 11A, in step 1, the UE may detect MCG failure. Upon the detection, the UE may transmit MCG failure report to source MN through SN since the link for the SN is good enough. The transmission of the MCG failure report can be transparent to the SN, or may not be decoded by the SN. The MCG failure report may comprise at least one of:

- The measurement report of MCG, SCG and/or neighbor cells; or

- The reason of the MCG failure e.g., physical layer failure, random access failure, and/or RLC failure.

In step 2, When the source MN gets the MAC failure report on the MCG failure, the source MN may judge whether the MCG failure can be recovered or not. If the MCG failure cannot be recovered, the MN may decide to handover the UE to the SN based on the measurement report the MN has received. The MN can know that the current SN's status is good (i.e., signal quality for the SN exceeds a threshold value) based on or not based on the measurement report the MN has received. Even though the MCG failure does not happen, the MN can also decide the handover based on the measurement report of the UE comprising measurement on the current serving MCG and/or the current serving SCG. The MN can judge whether to trigger the handover to the SN or not.

In step 3, the MN may initiate Handover Preparation procedure and/or SN Modification procedure to SN, by transmitting a handover request message and/or SN modification request message to the SN. The message may comprise an indication that the MCG failure happened while SN status is good, and also the message may include an indication that the MN has intention to handover the UE to SN. The message may also include the indication on avoiding RACH procedure for the SN (i.e., RA avoidance information) since the SN is still providing service to UE. The message may also include at least one of:

- E-UTRAN radio access bearers (E-RABs) not to be modified list in the SN (e.g., E-RAB ID, E-RAB Level QoS Parameters, DL TNL Address, DL general packet radio service (GTRS) tunneling protocol (GTP) ID), i.e., services still be served in the SN; or

- PDU Sessions not to be modified list in the SN (PDU Session ID and the corresponding QoS Flow ID/flow level QoS Parameters, DL TNL Address, DL GTP ID), i.e., services still be served in SN.

In step 4, SN may make a decision on whether to accept the handover on top of the SN's existing services or not. The SN can also judge, based on the SN's NG-C/S1-C connection availability, whether to accept the handover on top of the SN's existing services or not. If the handover is not available, the SN may reject the handover.

If the handover is accepted, based on the indication(s) in the handover request message and/or the SN modification request message, the SN may not re-allocate the parameters (e.g., Timing Advance value, UL grant, UL power control) for the UE. An indication of keeping using the old parameters can also be included.

In step 5, if the SN decides to accept the handover, the SN may send Handover Request ACK message or SN Modification ACK message to the MN. The message may comprise an indication on avoiding RACH procedure for the SN (i.e., RA avoidance information), and also include an indication of keeping using the old parameters on RACH for the UE and/or an indication of successfully keeping the services in the SN). The indication can be explicit in X2/Xn or implicit in the RRC container.

The SN also gives a response by the message comprising the status of E-RABs not to be Modified List in SN and/or PDU Sessions not to be Modified List in SN - that is, whether E-RABs and/or PDU sessions are successfully not modified or not. The indication of modification can be Boolean parameter (i.e., yes or no), or with some modifications of the SN. The exact E-RAB/PDU Session should be clearly notified to the MN. The corresponding SCG configuration may also take the list into account and not be modified as possible. If the SCG Configuration is not changed, the indication that the SCG configuration is not changed can be clearly indicated to MN. The indication may be finally passed to the UE.

In step 6, in case that radio link failure did not happen in the MN, the MN send the RRC connection Reconfiguration message to UE. The RRC connection Reconfiguration message can include the indication that RACH is not needed to SN (i.e., RA avoidance information), indication of keeping using the old parameters on RACH for the UE, indication of successfully keeping the SN and/or indication that avoiding RACH is possible. An indication on SCG configuration not changed on the SCG services before handover is also included in the message.

On the other hand, in case that radio link failure happened in the MN, the SN should send the RRC connection Reconfiguration message to UE. The RRC connection Reconfiguration message can include the indication that RACH is not needed to SN (i.e., RA avoidance information), indication of keeping using the old parameters on RACH for the UE, indication of successfully keeping the SN and/or indication that avoiding RACH is possible. An indication on SCG configuration not changed on the SCG services before handover is also included in the message.

FIG. 11B illustrates steps which continue from the steps illustrated in FIG. 11A.

Referring to FIG. 11B, in step 7, the UE may skip the RACH procedure i.e., skip to synchronize to SN. Based on the indication(s), UE may not change the configurations on SCG bearer/flow.

In step 8, in case that radio link failure did not happen in the MN, the UE may send RRC Connection Reconfiguration Complete message to the MN, which is forwarded by the MN to the SN.

On the other hand, in case that radio link failure happened in the MN, the UE sends RRC Connection Reconfiguration Complete message to the SN directly.

In step 9, SN status transfer may start and data forwarding is performed.

In step 10, path switch request message may be sent to AMF or MME. The path switch request message may comprise at least one of:

- E-RABs not to be Modified List in the SN (E-RAB ID, DL TNL Address, DL GTP ID), i.e., E-RABs to be kept list; or

- PDU Sessions not to be Modified List in the SN (PDU Session ID and the corresponding QoS Flow ID, DL TNL Address, DL GTP ID), i.e., PDU sessions to be kept list.

In step 11, bearer/PDU Session modification happens in a core network i.e., between UPF/S-GW and AMF/MME.

In step 12, AMF/MME may give a response through path switch response message. The path switch response message may comprise at least one of:

- E-RABs not to be Modified List in SN, whether the E-RABs are successfully modified or not; or

- PDU Sessions not to be Modified List in SN, whether the PDU sessions are successfully modified or not.

In step 13, the SN may initiate the UE Context Release procedure towards the MN.

The messages used in steps of the FIG. 11 are exemplary. Other messages and/or new message may be defined to realize the same purpose.

FIGs. 12A-12B show an example of RA avoidance in handover to another RAN node according to an embodiment of the present disclosure. In FIGs. 12A-12B, it is assumed that a DC of the MN and the SN has been established initially.

Referring to FIG. 12A, in step 1, the UE may detect MCG failure. Upon the detection, the UE may transmit MCG failure report to source MN through SN since the link for the SN is good enough. The transmission of the MCG failure report can be transparent to the SN, or may not be decoded by the SN. The MCG failure report may comprise at least one of:

- The measurement report of MCG, SCG and/or neighbor cells; or

In step 2, When the source MN gets the MAC failure report on the MCG failure, the source MN may judge whether the MCG failure can be recovered or not. If the MCG failure cannot be recovered, the MN may decide to handover the UE to neighbor cells based on the measurement report the MN has received. The MN can also know that the current SN's status is good (i.e., signal quality for the SN exceeds a threshold value) based on or not based on the measurement report the MN has received. Even though the MCG failure does not happen, the MN can also decide the handover based on the measurement report of the UE comprising measurement on neighbor cells of the MN and/or the current serving MCG/SCG. The MN can judge whether to keep the SN or not.

In step 3, the source MN may start the handover procedure by initiating the X2/Xn Handover Preparation procedure. To initiate the X2/Xn handover preparation procedure, the source MN may transmit a handover request message to a target MN. The handover request message may comprise handover preparation information including the SCG configuration. The handover request message may include the indication that MCG failure happened while SN status is good, and also include an indication on keeping the SN and/or avoiding RACH procedure in the SN (i.e., RA avoidance information for the SN) since the status of SN is still good. The handover request message may further comprise at least one of:

- E-UTRAN radio access bearers (E-RABs) not to be modified list in the SN (e.g., E-RAB ID, E-RAB Level QoS Parameters, DL TNL Address, DL general packet radio service (GTRS) tunneling protocol (GTP) ID), E-RABs to be kept for the SN; or

- PDU Sessions not to be modified list in the SN (PDU Session ID and the corresponding QoS Flow ID/flow level QoS Parameters, DL TNL Address, DL GTP ID), i.e., PDU sessions to be kept for the SN.

In step 4, if target MN decides to keep the SN based on the indications the target MN has received, the target MN may SN Addition Request message to the SN including an indication on keeping the SN and/or avoiding RACH procedure for the SN (i.e., RA avoidance information for the SN). The target MN may also take the list the target MN has received as a reference for deciding the target MN's E-RABs/PDU sessions. The SN addition request message may further comprise at least one of:

In step 5, based on the indication(s) in the SN addition request message, the SN may not re-allocate the parameters (e.g., Timing Advance value, UL grant, UL power control) for the UE. An indication of keeping using the old parameters can also be included. The SN may reply with SN Addition Request Acknowledge message comprising indication(s) (e.g., RACH is not needed to SN, keeping using the old parameters on RACH for the UE, and/or successfully keeping the SN and avoiding RACH are possible). The indication(s) can be explicit in X2/Xn or implicit in the RRC container.

The SN also gives a response by the message comprising the status of E-RABs not to be Modified List in SN and/or PDU Sessions not to be Modified List in SN - that is, whether E-RABs and/or PDU sessions are successfully not modified or not. The indication of modification can be Boolean parameter (i.e., yes or no), or with some modifications of the SN. The exact E-RAB/PDU Session should be clearly notified to the target MN. The corresponding SCG configuration may also take the list into account and not be modified as possible. If the SCG Configuration is not changed, the indication that the SCG configuration is not changed can be clearly indicated to MN. The indication may be finally passed to the source MN in step 6.

FIG. 12B illustrates steps which continue from the steps illustrated in FIG. 12A.

Referring to FIG. 12B, in step 6, the target MN may transmit, to the source MN, a handover request acknowledge message comprising a transparent container to be sent to the UE as an RRC message to perform the handover. The transparent container may comprise the SCG configuration, and may also provide forwarding addresses to the source MN. The target MN may indicate to the source MN that the UE context in the SN is kept. An indication (e.g., RACH is not needed to SN, keeping using the old parameters on RACH for the UE, successfully keeping the SN and avoiding RACH are possible) may be included in the handover request ACK message. The indication can be explicit in X2/Xn or implicit in the RRC container. The target MN may also give the exact E-RAB/PDU Session IDs that are successfully kept (i.e., not modified) to the source MN.

In step 7, the source MN may send SN Release Request message to the SN. The source MN may indicate to the SN that the UE context in SN is kept. That is, the SN release request message may comprise information instructing to maintain context information of the UE related to the target MN after the handover. If the indication that the UE context is kept in the SN is included in the SN release request message, the SN may keep the UE context in the SN. It can be also indicated that RACH is not needed to for the SN for the UE (i.e., RA avoidance information for the SN can also be included). The source MN may also give the exact E-RAB/PDU Session IDs that are successfully kept (i.e., not modified) to the SN.

In step 8, the source MN may trigger the UE to apply the new configuration by transmitting RRC connection reconfiguration message to the UE. Also, the RRC connection reconfiguration message can include indications (e.g., indication that RACH is not needed to the SN, indication of keeping using the old parameters on RACH for the UE, indication that successfully keeping the SN and avoiding RACH are possible). An indication that SCG configuration is not changed may also be included in the RRC connection reconfiguration message.

In step 9 to 11, the UE may synchronize to the target MN, and may not synchronize to the SN based on the RA avoidance information for the SN in the RRC connection reconfiguration message. The UE may reply with RRC Connection Reconfiguration Complete message. UE does not need to synchronize to the SN. Also UE does not need modify the configuration on SCG (i.e., SCG configuration).

In step 12, if the RRC connection reconfiguration procedure was successful, the target MN may inform the SN of SN reconfiguration complete.

In

step

13 and 14, data forwarding from the source MN may take place. Data forwarding may be omitted for SCG bearers.

In step 15 to 18, the target MN may initiate the Path Switch procedure.

In step 19, the target MN may initiate the UE Context Release procedure towards the source MN by transmitting a UE context release message to the source MN. The UE context release message may comprise information instructing to release context information of the UE related to the source MN. The UE context release message may be forwarded from the source MN to the SN.

In step 20, upon reception of the UE Context Release message, the SN can release C-plane related resource associated to the UE context towards the source MN. That is, the SN may release the context information of the UE related to the source MN based on the UE context release message while maintaining context information of the UE related to the target MN. Any ongoing data forwarding may continue. The SN shall not release the UE context associated with the target MN if the indication was included in the SN Release Request message in step 7. That is, the SN may not release the context information of the UE related to the target MN based on an indication in the SN release request message.

The messages used in steps of the FIG. 12 are exemplary. Other messages and/or new message may be defined to realize the same purpose.

The present disclosure may be applied to various future technologies, such as AI, robots, autonomous-driving/self-driving vehicles, and/or extended reality (XR).

<AI>

AI refers to artificial intelligence and/or the field of studying methodology for making it. Machine learning is a field of studying methodologies that define and solve various problems dealt with in AI. Machine learning may be defined as an algorithm that enhances the performance of a task through a steady experience with any task.

An artificial neural network (ANN) is a model used in machine learning. It can mean a whole model of problem-solving ability, consisting of artificial neurons (nodes) that form a network of synapses. An ANN can be defined by a connection pattern between neurons in different layers, a learning process for updating model parameters, and/or an activation function for generating an output value. An ANN may include an input layer, an output layer, and optionally one or more hidden layers. Each layer may contain one or more neurons, and an ANN may include a synapse that links neurons to neurons. In an ANN, each neuron can output a summation of the activation function for input signals, weights, and deflections input through the synapse. Model parameters are parameters determined through learning, including deflection of neurons and/or weights of synaptic connections. The hyper-parameter means a parameter to be set in the machine learning algorithm before learning, and includes a learning rate, a repetition number, a mini batch size, an initialization function, etc. The objective of the ANN learning can be seen as determining the model parameters that minimize the loss function. The loss function can be used as an index to determine optimal model parameters in learning process of ANN.

Machine learning can be divided into supervised learning, unsupervised learning, and reinforcement learning, depending on the learning method. Supervised learning is a method of learning ANN with labels given to learning data. Labels are the answers (or result values) that ANN must infer when learning data is input to ANN. Unsupervised learning can mean a method of learning ANN without labels given to learning data. Reinforcement learning can mean a learning method in which an agent defined in an environment learns to select a behavior and/or sequence of actions that maximizes cumulative compensation in each state.

Machine learning, which is implemented as a deep neural network (DNN) that includes multiple hidden layers among ANN, is also called deep learning. Deep learning is part of machine learning. In the following, machine learning is used to mean deep learning.

The AI device 1300 may be implemented as a stationary device or a mobile device, such as a TV, a projector, a mobile phone, a smartphone, a desktop computer, a notebook, a digital broadcasting terminal, a PDA, a PMP, a navigation device, a tablet PC, a wearable device, a set-top box (STB), a digital multimedia broadcasting (DMB) receiver, a radio, a washing machine, a refrigerator, a digital signage, a robot, a vehicle, etc.

Referring to FIG. 13, the AI device 1300 may include a communication part 1310, an input part 1320, a learning processor 1330, a sensing part 1340, an output part 1350, a memory 1360, and a processor 1370.

The communication part 1310 can transmit and/or receive data to and/or from external devices such as the AI devices and the AI server using wire and/or wireless communication technology. For example, the communication part 1310 can transmit and/or receive sensor information, a user input, a learning model, and a control signal with external devices. The communication technology used by the communication part 1310 may include a global system for mobile communication (GSM), a code division multiple access (CDMA), an LTE/LTE-A, a 5G, a WLAN, a Wi-Fi, Bluetooth^TM, radio frequency identification (RFID), infrared data association (IrDA), ZigBee, and/or near field communication (NFC).

The input part 1320 can acquire various kinds of data. The input part 1320 may include a camera for inputting a video signal, a microphone for receiving an audio signal, and a user input part for receiving information from a user. A camera and/or a microphone may be treated as a sensor, and a signal obtained from a camera and/or a microphone may be referred to as sensing data and/or sensor information. The input part 1320 can acquire input data to be used when acquiring an output using learning data and a learning model for model learning. The input part 1320 may obtain raw input data, in which case the processor 1370 or the learning processor 1330 may extract input features by preprocessing the input data.

The learning processor 1330 may learn a model composed of an ANN using learning data. The learned ANN can be referred to as a learning model. The learning model can be used to infer result values for new input data rather than learning data, and the inferred values can be used as a basis for determining which actions to perform. The learning processor 1330 may perform AI processing together with the learning processor of the AI server. The learning processor 1330 may include a memory integrated and/or implemented in the AI device 1300. Alternatively, the learning processor 1330 may be implemented using the memory 1360, an external memory directly coupled to the AI device 1300, and/or a memory maintained in an external device.

The sensing part 1340 may acquire at least one of internal information of the AI device 1300, environment information of the AI device 1300, and/or the user information using various sensors. The sensors included in the sensing part 1340 may include a proximity sensor, an illuminance sensor, an acceleration sensor, a magnetic sensor, a gyro sensor, an inertial sensor, an RGB sensor, an IR sensor, a fingerprint recognition sensor, an ultrasonic sensor, an optical sensor, a microphone, a light detection and ranging (LIDAR), and/or a radar.

The output part 1350 may generate an output related to visual, auditory, tactile, etc. The output part 1350 may include a display unit for outputting visual information, a speaker for outputting auditory information, and/or a haptic module for outputting tactile information.

The memory 1360 may store data that supports various functions of the AI device 1300. For example, the memory 1360 may store input data acquired by the input part 1320, learning data, a learning model, a learning history, etc.

The processor 1370 may determine at least one executable operation of the AI device 1300 based on information determined and/or generated using a data analysis algorithm and/or a machine learning algorithm. The processor 1370 may then control the components of the AI device 1300 to perform the determined operation. The processor 1370 may request, retrieve, receive, and/or utilize data in the learning processor 1330 and/or the memory 1360, and may control the components of the AI device 1300 to execute the predicted operation and/or the operation determined to be desirable among the at least one executable operation. The processor 1370 may generate a control signal for controlling the external device, and may transmit the generated control signal to the external device, when the external device needs to be linked to perform the determined operation. The processor 1370 may obtain the intention information for the user input and determine the user's requirements based on the obtained intention information. The processor 1370 may use at least one of a speech-to-text (STT) engine for converting speech input into a text string and/or a natural language processing (NLP) engine for acquiring intention information of a natural language, to obtain the intention information corresponding to the user input. At least one of the STT engine and/or the NLP engine may be configured as an ANN, at least a part of which is learned according to a machine learning algorithm. At least one of the STT engine and/or the NLP engine may be learned by the learning processor 1330 and/or learned by the learning processor of the AI server, and/or learned by their distributed processing. The processor 1370 may collect history information including the operation contents of the AI device 1300 and/or the user's feedback on the operation, etc. The processor 1370 may store the collected history information in the memory 1360 and/or the learning processor 1330, and/or transmit to an external device such as the AI server. The collected history information can be used to update the learning model. The processor 1370 may control at least some of the components of AI device 1300 to drive an application program stored in memory 1360. Furthermore, the processor 1370 may operate two or more of the components included in the AI device 1300 in combination with each other for driving the application program.

Referring to FIG. 14, in the AI system, at least one of an AI server 1420, a robot 1410a, an autonomous vehicle 1410b, an XR device 1410c, a smartphone 1410d and/or a home appliance 1410e is connected to a cloud network 1400. The robot 1410a, the autonomous vehicle 1410b, the XR device 1410c, the smartphone 1410d, and/or the home appliance 1410e to which the AI technology is applied may be referred to as AI devices 1410a to 1410e.

The cloud network 1400 may refer to a network that forms part of a cloud computing infrastructure and/or resides in a cloud computing infrastructure. The cloud network 1400 may be configured using a 3G network, a 4G or LTE network, and/or a 5G network. That is, each of the devices 1410a to 1410e and 1420 consisting the AI system may be connected to each other through the cloud network 1400. In particular, each of the devices 1410a to 1410e and 1420 may communicate with each other through a base station, but may directly communicate with each other without using a base station.

The AI server 1420 may include a server for performing AI processing and a server for performing operations on big data. The AI server 1420 is connected to at least one or more of AI devices constituting the AI system, i.e. the robot 1410a, the autonomous vehicle 1410b, the XR device 1410c, the smartphone 1410d and/or the home appliance 1410e through the cloud network 1400, and may assist at least some AI processing of the connected AI devices 1410a to 1410e. The AI server 1420 can learn the ANN according to the machine learning algorithm on behalf of the AI devices 1410a to 1410e, and can directly store the learning models and/or transmit them to the AI devices 1410a to 1410e. The AI server 1420 may receive the input data from the AI devices 1410a to 1410e, infer the result value with respect to the received input data using the learning model, generate a response and/or a control command based on the inferred result value, and transmit the generated data to the AI devices 1410a to 1410e. Alternatively, the AI devices 1410a to 1410e may directly infer a result value for the input data using a learning model, and generate a response and/or a control command based on the inferred result value.

Various embodiments of the AI devices 1410a to 1410e to which the technical features of the present disclosure can be applied will be described. The AI devices 1410a to 1410e shown in FIG. 14 can be seen as specific embodiments of the AI device 1300 shown in FIG 13.

FIG. 15 shows a UE to implement an embodiment of the present disclosure. The present disclosure described above for UE side may be applied to this embodiment.

A UE includes a processor 1510, a power management module 1511, a battery 1512, a display 1513, a keypad 1514, a subscriber identification module (SIM) card 1515, a memory 1520, a transceiver 1530, one or more antennas 1531, a speaker 1540, and a microphone 1541.

The processor 1510 may be configured to implement proposed functions, procedures and/or methods described in this description. Layers of the radio interface protocol may be implemented in the processor 1510. The processor 1510 may include application-specific integrated circuit (ASIC), other chipset, logic circuit and/or data processing device. The processor 1510 may be an application processor (AP). The processor 1510 may include at least one of a digital signal processor (DSP), a central processing unit (CPU), a graphics processing unit (GPU), a modem (modulator and demodulator). An example of the processor 1510 may be found in SNAPDRAGONTM series of processors made by Qualcomm®, EXYNOSTM series of processors made by Samsung®, A series of processors made by Apple®, HELIOTM series of processors made by MediaTek®, ATOMTM series of processors made by Intel® or a corresponding next generation processor.

According to various embodiments, the processor 1510 may be configured to, or configured to control the transceiver 1530 to implement steps performed by wireless device and/or UE throughout the disclosure.

The power management module 1511 manages power for the processor 1510 and/or the transceiver 1530. The battery 1512 supplies power to the power management module 1511. The display 1513 outputs results processed by the processor 1510. The keypad 1514 receives inputs to be used by the processor 1510. The keypad 1514 may be shown on the display 1513. The SIM card 1515 is an　integrated circuit　that is intended to　securely store the　international mobile subscriber identity　(IMSI) number and its related　key, which are used to identify and authenticate subscribers on　mobile telephony　devices (such as　mobile phones　and　computers). It is also possible to store contact information on many SIM cards.

The memory 1520 is operatively coupled with the processor 1510 and stores a variety of information to operate the processor 1510. The memory 1520 may include read-only memory (ROM), random access memory (RAM), flash memory, memory card, storage medium and/or other storage device. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The modules can be stored in the memory 1520 and executed by the processor 1510. The memory 1520 can be implemented within the processor 1510 or external to the processor 1510 in which case those can be communicatively coupled to the processor 1510 via various means as is known in the art.

The transceiver 1530 is operatively coupled with the processor 1510, and transmits and/or receives a radio signal. The transceiver 1530 includes a transmitter and a receiver. The transceiver 1530 may include baseband circuitry to process radio frequency signals. The transceiver 1530 controls the one or more antennas 1531 to transmit and/or receive a radio signal.

The speaker 1540 outputs sound-related results processed by the processor 1510. The microphone 1541 receives sound-related inputs to be used by the processor 1510.

The present disclosure can have various advantageous effects.

In view of the exemplary systems described herein, methodologies that may be implemented in accordance with the disclosed subject matter have been described with reference to several flow diagrams. While for purposed of simplicity, the methodologies are shown and described as a series of steps or blocks, it is to be understood and appreciated that the claimed subject matter is not limited by the order of the steps or blocks, as some steps may occur in different orders or concurrently with other steps from what is depicted and described herein. Moreover, one skilled in the art would understand that the steps illustrated in the flow diagram are not exclusive and other steps may be included or one or more of the steps in the example flow diagram may be deleted without affecting the scope of the present disclosure.

Claims in the present description can be combined in a various way. For instance, technical features in method claims of the present description can be combined to be implemented or performed in an apparatus, and technical features in apparatus claims can be combined to be implemented or performed in a method. Further, technical features in method claim(s) and apparatus claim(s) can be combined to be implemented or performed in an apparatus. Further, technical features in method claim(s) and apparatus claim(s) can be combined to be implemented or performed in a method. Other implementations are within the scope of the following claims.

Claims

A method performed by a secondary node (SN) serving a wireless device with a master node (MN) in a dual connectivity (DC) in a wireless communication system, the method comprising:

receiving a first message comprising information related to a random access (RA) avoidance for the SN;

determining that a RA is not needed for the SN after a handover based on the information; and

transmitting a second message comprising RA avoidance information for the SN based on the determination.
The method of claim 1, wherein the RA avoidance information comprises information informing that a RA procedure for the SN is avoided to communicate with the SN after the handover.
The method of claim 1, wherein the handover comprises a handover of the wireless device from the MN to the SN.
The method of claim 1, wherein the first message is a handover request message or a SN modification request message received from the MN, and

wherein the second message is a handover request acknowledge (ACK) message or SN modification request ACK message transmitted to the MN.
The method of claim 1, wherein the information related to the RA avoidance for the SN comprises information informing that a signal quality for the SN exceeds a threshold value.
The method of claim 5, wherein the information related to the RA avoidance for the SN further comprises information for a radio link failure of the MN.
The method of claim 1, wherein the first message further comprises at least one of:

a request for the handover of the wireless device to the SN;

RA avoidance information for the SN;

information for a list of radio access bearers to be maintained in the SN after the handover; or

information for a list of packet data unit (PDU) sessions to be maintained in the SN after the handover.
The method of claim 1, wherein the determining that a RA is not needed for the SN after a handover based on the information comprises:

determining to maintain one or more parameters for the wireless device after the handover based on the information,

wherein the one or more parameters comprise at least one of a timing advance value for an uplink (UL) transmission, UL grant for the wireless device, or parameters related to an UL power control for the wireless device.
The method of claim 1, wherein the second message comprises at least one of:

information instructing to maintain one or more parameters for the wireless device after the handover;

information informing that a secondary cell group (SCG) configuration for the SN is maintained after the handover;

information for a list of radio access bearers to be maintained in the SN after the handover; or

information for a list of packet data unit (PDU) sessions to be maintained in the SN after the handover,

wherein the one or more parameters comprise at least one of a timing advance value for an uplink (UL) transmission, UL grant for the wireless device, or parameters related to an UL power control for the wireless device.
The method of claim 1, further comprising:

transmitting, to the wireless device, a third message comprising at least one of:

the RA avoidance information for the SN;

information instructing to maintain at least one of a timing advance value for an uplink (UL) transmission, UL grant for the wireless device, or parameters related to an UL power control for the wireless device after the handover; or

information informing that a secondary cell group (SCG) configuration for the SN is maintained after the handover.
The method of claim 1, further comprising:

communicating with the wireless device without performing a RA procedure with the wireless device after the handover based on the RA avoidance information for the SN.
The method of claim 1, wherein the handover comprises a MN handover of the wireless device from the MN to target radio access network (RAN) node,

wherein the target RAN node becomes a MN for a DC after the MN handover, and

wherein the SN is maintained as a SN for a DC after the MN handover.
The method of claim 1, wherein the first message is a SN addition request message received from a target radio access network (RAN) node for the handover, and

wherein the second message is a SN addition request acknowledge (ACK) message transmitted to the target RAN node.
The method of claim 1, further comprising:

receiving, from the MN, a SN release request message comprising information instructing to maintain context information of the wireless device related to a target radio access network (RAN) node for the handover after the handover.
The method of claim 1, further comprising:

receiving, from the MN, a context release message comprising information instructing to release context information of the wireless device related to the MN; and

releasing the context information of the wireless device related to the MN based on the context release message while maintaining context information of the wireless device related to a target radio access network (RAN) node for the handover.