CN108377573B

CN108377573B - Method and apparatus for cluster-based multi-connection wireless communication system

Info

Publication number: CN108377573B
Application number: CN201610899524.8A
Authority: CN
Inventors: 温萍萍
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2016-10-14
Filing date: 2016-10-14
Publication date: 2020-06-19
Anticipated expiration: 2036-10-14
Also published as: CN108377573A

Abstract

Embodiments of the present disclosure relate to methods and apparatus for a cluster-based multi-connection wireless communication system. For example, a method on the terminal device side is proposed. The terminal device is served by a cluster including a plurality of network devices including a serving network device for performing data communication with the terminal device and a backup network device for switching the data communication. The method includes maintaining a first Radio Resource Control (RRC) state and a second RRC state for a link of the terminal device with the serving network device and a link of the terminal device with the backup network device, respectively. The embodiment of the disclosure also provides a corresponding method implemented at the network equipment, the network equipment capable of implementing the method and a device in the terminal equipment.

Description

Method and apparatus for cluster-based multi-connection wireless communication system

Technical Field

Embodiments of the present disclosure relate generally to wireless communication systems and, in particular, relate to methods, apparatuses and computer program products for managing connections between a network device and a terminal device in a cluster-based multi-connection wireless communication system architecture.

Background

Increasing network capacity and data rates have been an evolving goal of wireless communication networks. In order to achieve data rates in the gigabits per second for next generation mobile cellular communication standards (e.g., fifth generation or 5G), one solution is to communicate using the millimeter wave (mmWave or MMW) frequency band. Millimeter wave band communications provide higher communication bandwidth than current cellular band communication systems. For example, a new research project on a new Radio Access Technology (RAT) was approved at Radio Access Network (RAN) 71 th conference of the third generation partnership project (3 GPP). This new RAT (or NR) allows for the use of a frequency range of up to 100 GHz. Thus, millimeter wave communication has great potential for providing higher data rates. However, communication in the millimeter wave band has its own challenges.

In the high frequency band, the wireless link between the serving cell and the terminal device may be disturbed or blocked by many factors, such as fixed or moving obstacles, rotation of pedestrians and user equipment. Furthermore, communication links on high band have higher path loss the high band network requires a higher density of network devices, e.g. Base Stations (BS), than the BS density of the low band network, and therefore a terminal device in motion will require more frequent handovers in the high band than in the current cellular communication band, e.g. the Long Term Evolution (LTE) band.

Disclosure of Invention

The following presents a simplified summary of various embodiments in order to provide a basic understanding of some aspects of various embodiments. This summary is not intended to identify key elements or to delineate the scope of the various embodiments. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later.

A first aspect of the present disclosure provides a method of a terminal device in a wireless communication system, the terminal device being served by a cluster including a plurality of network devices including a serving network device for performing data communication with the terminal device and a backup network device for switching the data communication, the method comprising: maintaining first and second Radio Resource Control (RRC) states, respectively, for: a link between the terminal device and the serving network device, and a link between the terminal device and the backup network device.

In one embodiment, maintaining the first and second RRC states separately may include: setting both the first RRC state and the second RRC state to an idle state if the terminal device does not have a need to communicate with the cluster, and transitioning the first RRC state to a connected state in response to the terminal device establishing a connection with the serving network device; and in response to the terminal device establishing a connection with the backup network device, transitioning the state of the second RRC state to a third state different from the idle state and the connected state, the third state having lower energy consumption than the connected state and enabling fast communication of the terminal device with the backup network device.

In another embodiment, maintaining the first and second RRC states separately may further include at least one of: transitioning an RRC state for a link of the terminal device with the first network device to the third state in response to the first network device transitioning from a serving network device for the terminal device to a backup network device for the terminal device; responsive to a second network device transitioning from a backup network device for the terminal device to a serving network device for the terminal device, transitioning an RRC state for a link of the terminal device with the second network device to the connected state; and in response to a new network device joining the cluster: if the first RRC state of the terminal equipment is in the idle state, setting the RRC state of a link aiming at the terminal equipment and newly accessed network equipment into the idle state, and if the first RRC state of the terminal equipment is in the connection state, taking the newly added network equipment as backup network equipment of the terminal equipment; establishing a connection with the newly joined network device and setting the RRC state for the link of the terminal device with the newly joined network device to the third state.

In yet another embodiment, the third state may be an inactive state. In another embodiment, in the third state, the connection of the terminal device with the radio access network and the core network is established and maintained.

In further embodiments, maintaining the first and second RRC states separately may include at least one of: the first RRC state is maintained for the link between the terminal device and each of the serving network devices, and the second RRC state is maintained for the link between the terminal device and each of the backup network devices.

In some embodiments, maintaining the first and second RRC states separately may include at least one of: maintaining the first RRC state for a set of links of the terminal device and all of the serving network devices in the serving network devices, and maintaining the second RRC state for a set of links of the terminal device and all of the backup network devices in the backup network devices.

In one embodiment, the network device may be a base station or a transmission receiving node (TRP).

In another embodiment, the method may further comprise: and sending the information of the capability of the terminal equipment to the network equipment in the plurality of network equipment.

A second aspect of the present disclosure provides a method of a first network device in a wireless communication system, where the first network device and a second network device belong to a same cluster and serve a terminal device as a serving network device and a backup network device, respectively, where the serving network device is configured to perform data communication with the terminal device, and the backup network device is configured to switch the data communication, the method including: in response to the terminal device establishing a connection with the first network device, setting an RRC state for the connection to a connected state; and in response to the first network device transitioning from a serving network device for the terminal device to a backup network device for the terminal device, transitioning the RRC state from the connected state to a third state different from the idle state and the connected state, the third state having lower energy consumption than the connected state and enabling fast communication of the terminal device with the backup network device.

In one embodiment, the third state may be an inactive state. In another embodiment, in the third state, the connection of the terminal device to the radio access network and the core network is established and maintained.

In another embodiment, the first network device may be a base station or a TRP.

In yet another embodiment, the method may further comprise at least one of: receiving information of capabilities of the terminal device from a further network device; receiving information of the capability of the terminal device from the terminal device, and transmitting the capability information of the terminal device to another network device in the cluster; and coordinating RRC configuration with further network devices in the cluster.

A third aspect of the present disclosure provides a method of a second network device in a wireless communication system, where the second network device and a first network device belong to a same cluster and serve a terminal device as a backup network device and a serving network device of the terminal device, respectively, where the serving network device is configured to perform data communication with the terminal device, and the backup network device is configured to switch the data communication, the method including: in response to the terminal device establishing a connection with the second network device, setting an RRC state for the connection to a third state different from an idle state and a connected state; and changing the state value of the RRC state from the third state to the connected state in response to the second network device transitioning from the backup network device for the terminal device to the serving network device for the terminal device; the third state has a lower energy consumption than the connected state and enables fast communication of the terminal device with the backup network device.

In one embodiment, the third state may be an inactive state. In another embodiment, in the third state, the connection of the terminal device with the radio access network and the core network is maintained.

In another embodiment, the second network device may be a base station or a TRP.

In yet another embodiment, the method may further comprise at least one of: receiving information of capabilities of the terminal device from a further network device; and coordinating RRC configuration with further network devices in the cluster.

A fourth aspect of the present disclosure provides an apparatus in a terminal device, the terminal device being served by a cluster including a plurality of network devices including a serving network device for performing data communication with the terminal device and a backup network device for switching the data communication, the apparatus comprising: a processor, and a memory containing instructions for execution by the processor whereby the apparatus is operative to: maintaining first and second Radio Resource Control (RRC) states, respectively, for: a link between the terminal device and the serving network device, and a link between the terminal device and the backup network device.

A fifth aspect of the present disclosure provides an apparatus in a first network device, where the first network device and a second network device belong to a same cluster and serve as a serving network device and a backup network device of a terminal device, respectively, for the terminal device, where the serving network device is configured to perform data communication with the terminal device, and the backup network device is configured to switch the data communication, where the apparatus includes: a processor, and a memory containing instructions for execution by the processor whereby the apparatus is operative to: in response to the terminal device establishing a connection with the first network device, setting an RRC state for the connection to a connected state; and in response to the first network device transitioning from a serving network device for the terminal device to a backup network device for the terminal device, transitioning the RRC state from the connected state to a third state different from the idle state and the connected state, the third state having lower energy consumption than the connected state and enabling fast communication of the terminal device with the backup network device.

A sixth aspect of the present disclosure provides an apparatus in a second network device, where the second network device and a first network device belong to a same cluster, and serve as a backup network device and a serving network device of a terminal device to serve the terminal device, respectively, where the serving network device is configured to perform data communication with the terminal device, and the backup network device is configured to switch the data communication, where the apparatus includes: a processor, and a memory containing instructions for execution by the processor whereby the apparatus is operative to: in response to the terminal device establishing a connection with the second network device, setting an RRC state for the connection to a third state different from an idle state and a connected state; and changing the state value of the RRC state from the third state to the connected state in response to the second network device transitioning from the backup network device for the terminal device to the serving network device for the terminal device; the third state has a lower energy consumption than the connected state and enables fast communication of the terminal device with the backup network device.

As will be understood from the following description, according to embodiments of the present disclosure, a terminal device is able to maintain a connection with a network device with lower complexity, power consumption and signaling overhead. In some embodiments, the terminal device is able to quickly switch data transmission when the serving cell changes, thereby improving system performance and user experience.

It should be understood that the statements herein reciting aspects are not intended to limit the critical or essential features of the embodiments of the present disclosure, nor are they intended to limit the scope of the present disclosure. Other features of the present disclosure will become apparent from the following description.

Drawings

The objects, advantages and other features of the present invention will become more fully apparent from the following disclosure and appended claims. A non-limiting description of the preferred embodiments is given herein, by way of example only, with reference to the accompanying drawings, in which:

fig. 1 shows a schematic diagram of an example wireless communication system in which methods of embodiments of the present disclosure can be implemented;

fig. 2A illustrates a flow diagram of a method implemented at a terminal device of a wireless communication network in accordance with an embodiment of the present disclosure;

fig. 2B shows a schematic diagram of a connection of a terminal device to a network device according to an embodiment of the present disclosure;

fig. 3A illustrates an example of a terminal device maintaining a first RRC state and a second RRC state, respectively, in accordance with an embodiment of the present disclosure;

fig. 3B illustrates another example of a terminal device maintaining a first RRC state and a second RRC state, respectively, in accordance with an embodiment of the present disclosure;

4A-4B illustrate RRC state transition diagrams at a terminal device, according to embodiments of the present disclosure;

FIG. 5A illustrates another scenario of a network deployment in which embodiments of the present disclosure may be implemented;

FIG. 5B shows a schematic diagram of the connection of a terminal device and a network device in the scenario of FIG. 5A;

fig. 6 shows a flow diagram of a method implemented at a serving device of a wireless communication network, in accordance with an embodiment of the present disclosure;

fig. 7 shows a flow diagram of a method implemented at a backup device of a wireless communication network, in accordance with an embodiment of the present disclosure;

FIG. 8 shows a block diagram of an apparatus implemented at a terminal device, according to an embodiment of the present disclosure;

FIG. 9 shows a block diagram of an apparatus implemented at a service device, according to an embodiment of the present disclosure;

FIG. 10 illustrates a block diagram of an apparatus implemented at a backup device, according to an embodiment of the present disclosure; and

fig. 11 illustrates a block diagram of an apparatus in accordance with certain embodiments of the present disclosure.

Detailed Description

In the following description, numerous details are set forth for the purpose of explanation. However, one of ordinary skill in the art will realize that the invention may be practiced without the use of these specific details. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features described herein.

It will be understood that the terms "first," "second," and the like, are used merely to distinguish one element from another. And in fact, a first element can also be referred to as a second element and vice versa. It will be further understood that the terms "comprises" and "comprising," when used in this specification, specify the presence of stated features, elements, functions, or components, but do not preclude the presence or addition of one or more other features, elements, functions, or components.

For ease of explanation, some embodiments of the present invention will be described herein in the context of millimeter wave communication and using terminology such as in 3GPP specified long term evolution/long term evolution-advanced (LTE/LTE-a), however, as will be appreciated by those skilled in the art, embodiments of the present invention are in no way limited to wireless communication systems that follow 3GPP specified wireless communication protocols, nor to millimeter wave communication, but may be applied in any wireless communication system where similar problems exist, such as WLANs, or other communication systems developed in the future, etc.

Likewise, a terminal device in the present disclosure may be a User Equipment (UE), but may also be any terminal with wireless communication capabilities, including but not limited to, cell phones, computers, personal digital assistants, game consoles, wearable devices, in-vehicle communication devices, machine-to-machine communication devices, sensors, and the like. The term terminal device can be used interchangeably with UE, mobile station, subscriber station, mobile terminal, user terminal, or wireless device. In addition, the network device may be a network Node, such as a Node B (or NB), a Base Transceiver Station (BTS), a Base Station (BS), or a base station subsystem (BSs), a relay, a remote radio head (RRF), AN Access Node (AN), AN Access Point (AP), and so on.

A schematic diagram of an example wireless communication system 100 in which the methods of embodiments of the present disclosure can be implemented is shown in fig. 1. The wireless communication system 100 may include one or

more network devices

101 and 105. For example, in this example,

network device

101 and 105 may be embodied as a base station, such as an evolved node B (eNodeB or eNB). It should be understood that the network devices 101-105 may also be embodied in other forms, such as node-BS, Base Transceiver Stations (BTSs), Base Stations (BSs), or Base Station Subsystems (BSSs), repeaters, etc. And each network device may be embodied in a different form. Network devices 101-105 may each provide wireless connectivity to a plurality of terminal devices 111-112 within their coverage area.

To increase network capacity and data rates, some of the

network devices

101 and 105 may operate in a high frequency band, such as the millimeter wave (MMW) band. As previously mentioned, wireless links in the high frequency band are more susceptible to blocking, and to support high frequency band network coverage, a high density deployment of the network is typically required. Based at least on the above considerations, a cluster-based multi-connection network architecture is proposed. The architecture defines a flexible network architecture and a fast and reliable mobility scheme to serve users.

Specifically, the cluster-based network architecture is a multi-connection architecture in which a plurality of base stations/transmission points (e.g.,

network devices

101 and 102, 104, or 103, 105 in fig. 1) form a cluster. The base station/transmission node may operate in a high frequency band, such as a millimeter wave band, or may operate in a low frequency band (such as an LTE band) and a high frequency band, respectively. The cluster may be UE-specific, cell-specific, or beam-specific. And a terminal device (e.g., UE111 or 112 in fig. 1) will establish multiple connections with multiple (e.g., all) BSs/transmission points within the same cluster. At least one BS in the cluster may be selected as a serving BS, which is responsible for transmitting/receiving data. While other BSs in the cluster may be used as backup BSs providing backup links for fast data transfer handover. The UE will perform measurements on the connected links with cells in the cluster, and on links with neighboring cells outside the cluster. Based on the measurements, serving cell selection/change and cluster formation/update may be performed. In general, the selection/change of serving cell may occur among cells in a cluster, since the link may be blocked by an obstacle. In addition, a cluster change may result, for example, due to a user's movement. When a cluster is changed/updated, the connection with the BS that no longer belongs to the new cluster will be released. In addition, the UE may also establish a connection with a new cell in the new cluster.

As described above, to support fast link switching between BSs within a cluster (e.g.,

cluster

121 or 122 in fig. 1), a UE should have connections with these BSs. For multi-connectivity in NR systems, there is currently no discussion nor decision on how to implement a control plane with Radio Resource Control (RRC) functionality.

As an alternative to the multi-connection control plane for NR systems, one solution is similar to that for dual-connection in LTE. Wherein the RRC entity in the master base station (MeNB) assumes all control of all RRC procedures, such as radio configuration, measurements and mobility control. In this solution, there is no RRC entity in the secondary base station (SeNB). Therefore, if the serving link is handed over to the SeNB, an RRC entity needs to be established in the SeNB first, which is not appropriate for fast link switching.

In another alternative solution, the primary NR node and the secondary NR node can be allowed to control their radio resources in a completely independent or semi-independent manner. A terminal device (e.g., UE) will have more than 1 RRC connection at the same time. But with this solution the cost of maintaining multiple RRC connections is increased complexity. Especially for cluster-based network architectures. With this solution, it is also necessary for the backup links in the cluster to be maintained as well as the data communication links, although the backup links are only used for backup for fast link switching and not for data transmission before link switching.

In order to solve at least part of the above-mentioned technical problems, a new method and apparatus are proposed in the present disclosure. Some embodiments of the method and apparatus provide a control plane solution with lower complexity and power consumption and enable fast data link switching and transmission. Some embodiments of the present disclosure provide a control plane solution for a cluster-based multi-connection network architecture. In some embodiments, utilizing a new RRC state (e.g., referred to as an RRC inactive state) for the backup link for the terminal device in the cluster enables the control plane to operate more efficiently, not only with lower complexity, power consumption, and signaling overhead for the backup link, but also with the ability for fast data transfer upon a serving cell change.

An example method according to an embodiment of the present disclosure is now described with reference to fig. 2A. Fig. 2A illustrates a flow diagram of a method 200 implemented at a terminal device in a wireless communication network (e.g., network 100 in fig. 1) according to an embodiment of the disclosure. The method 200 may be performed by, for example, UE111 or 112 in fig. 1. For ease of description, the method 200 is described below in conjunction with FIG. 1.

The terminal device implementing the method 200 is served by a cluster comprising a plurality of network devices, which may be, for example, the

network device

101 and 104 or 103 and 105 in fig. 1, and correspondingly the cluster may be the

cluster

121 or 122 in fig. 1. The plurality of network devices include a serving network device (e.g., one or more of 101-104 in fig. 1 or one or more of 103-105 in fig. 1) for performing data communication with the terminal device (e.g., UE111 or 112), and a backup network device (e.g., one or more of 101-104 in fig. 1 or one or more of 103-105 in fig. 1) for switching the data communication.

As shown in fig. 2A, at

blocks

210 and 220, the terminal device maintains a first RRC state and a second RRC state for a link of the terminal device with the serving network device and for a link of the terminal device with the backup network device, respectively.

The method 200 is further described below by taking the UE111 in fig. 1 as an example. The UE111 in fig. 1 is served by a cluster 121 and it may have connections to multiple Base Stations (BSs). In the example of fig. 1, the plurality of BSs includes BS 101-104. Wherein BS101 may operate, for example, in a legacy cellular communications band (e.g., an LTE band, in which example BS101 may be an LTE BS). While other BSs 102-104 may operate in higher frequency bands (e.g., MMW bands) than the conventional cellular communication bands.

As shown in fig. 1, to avoid disconnecting the high band link due to being blocked, the UE may establish multiple connections (e.g., when there is a communication demand) with multiple (e.g., all) high band cells included in the cluster (e.g., 121). In this example, the UE111 may establish a connection with a low band BS (LTE BS 111 in the figure) and high band (e.g., MMW band) BSs 102-104.

A schematic diagram of the UE connection with the BS 101-104 is shown in fig. 2B. One or more of the BSs, e.g., LTE BS101 (low band BS) and high band BS102, may be selected as the serving BS. In this case, as shown in fig. 2B, the LTE BS101 and the MMW BS102 are used as serving cells, which may be used to support conventional multi-connectivity (e.g., a function like dual connectivity in LTE). Data transmission may be performed through two serving BSs, the LTE BS101 and the MMW BS 102. The control plane of the LTE BS101 and the MMW BS102 may follow any existing or later developed mechanism for tight inter-working between LTE and NR, e.g. according to the discussion and final agreement in 3GPP on tight inter-working between LTE and NR. Embodiments of the present disclosure are not limited to any particular manner of implementing the control

plane serving BSs

101 and 102. The other BSs (103-104) are backup BSs, and the corresponding links may be referred to as backup links. If the UE111 link with the MMW BS102 is blocked, the UE111 will quickly hand over its transmission/reception by the BS102 to other BSs in the cluster, e.g., the MMW BS 103. Furthermore, as the UE moves, a new cluster may be formed, for example, the cluster 122 composed of the MMW BS103 and 105 shown in fig. 1 may be formed, and the connection of the UE111 with the MMW BS102 will be disconnected.

With the method 200, the UE111 can maintain RRC states for the serving BS (101-102) and the backup BS (103-104), respectively. This means that the second RRC state between the UE111 and the backup BS may be different from the first RRC state between the UE and the serving BS. This provides greater flexibility in the management of connections between the UE and the BSs in the cluster, enabling savings in radio resources (including power and signaling) as needed, and since in this state the user has established a connection with the radio network and the core network, fast data transmission is enabled, thus enabling fast handover from the serving BS to the backup BS.

An example of the UE111 maintaining the first and second RRC states at block 210-220, respectively, is shown in FIG. 3A. As shown in fig. 3A, if the UE111 has no need to communicate with the cluster, the UE111 may set state values of a first RRC state with the serving BS and a second RRC state with the backup BS to an idle state at block 310.

At block 320, responsive to the UE111 establishing a connection with a serving network device (e.g., 101 and/or 102 in fig. 1), transitioning a state value of the first RRC state to a connected state; and, at block 330, in response to the UE111 establishing a connection with a backup network device (e.g., 103-104 in fig. 1), transitioning the state value of the second RRC state to a third state different from the idle state and the connected state, the third state having lower energy consumption than the connected state. For example, the third state can achieve power efficiency comparable to the idle state of LTE.

By setting the second RRC state with the backup BS to the third state, the UE can achieve the purpose of saving radio resources (e.g., energy consumption and signaling) and has the capability of fast data transmission. Note that embodiments of the present disclosure are not limited to any particular definition and design of this third state. This third state enables, for example only, fast communication of the terminal device with the backup network device. As another example, the third state may be other states besides idle and connected states (which may be referred to, for example and without limitation, as "inactive state", "RRC inactive state", or as "RRC inactive-connected" state) discussed in 3GPP or defined in the future, and following the provisions in 3GPP for the third state. For example, in this third state, a connection of UE111 with a Radio Access Network (RAN) and a core network may be established and/or maintained. In addition, the third RRC state may be designed to meet NR control plane latency requirements. In addition, it may also be required that for a UE in this third RRC state, the RAN should know whether the UE moves from one "RAN-based notification area" to another.

By keeping the connection with the backup cell in the RRC third state, the UE111 is able to obtain low power consumption and signaling overhead on the one hand and fast data transfer handover on the other hand, since in this new RRC state the connection between RAN and CN, whether User Plane (UP) or Control Plane (CP), is maintained. With this embodiment, it is possible to keep up with the requirements regarding the backup link, i.e. the UE should be able to have a fast link switch (data transmission) and also have a minimum resource consumption (including power/signaling).

Note that in embodiments of the present disclosure, the state transition operations in blocks 320-330 of FIG. 3A may be implemented in different ways. State transition diagrams for two example embodiments are given in fig. 4A and 4B.

As shown in fig. 4A, UE111 may set the RRC states of all links (including part of the links and serving links) to RRC idle state 410 upon power up or without a communication traffic demand (460, 461). This may correspond to block 310 in fig. 3A, for example. When the UE111 establishes a connection with the serving BS and the backup BS (as shown in 420-430 of fig. 4A), the connection with the serving BS may be transitioned from the RRC idle state to the RRC connected state 440 (corresponding to block 320 of fig. 3A) and the connection with the backup BS may be transitioned from the RRC idle state to the third RRC state (e.g., referred to as the inactive state) 450 (corresponding to block 330 of fig. 3A). That is, in block 320 of fig. 3A, transitioning the state value of the second RRC state to the third state includes changing the state value of the second RRC state directly from the RRC idle state to the third state.

As another example, in fig. 4B, all links may be set to RRC idle state 410 upon power up of UE111 or without a communication traffic demand (460, 461). When the UE111 establishes a connection of BSs (including the serving BS and the backup BS) (421), the connection with the serving BS and the connection with the backup BS may both be transitioned from the RRC idle state to the RRC connected state 440, and then transitioned (462) from the RRC connected state to a third RRC state (e.g., referred to as an inactive state) 450 (corresponding to block 330 in fig. 3A). That is, in block 320 of fig. 3A, the operation of transitioning the state value of the second RRC state to the third state may include: and changing the state value of the second RRC state into the RRC connected state firstly and then into the third state.

Referring now to fig. 3B, another example is shown in which the UE111 maintains the first RRC state and the second RRC state at block 210-220 of fig. 2, respectively. As shown in FIG. 3B, maintaining the first RRC state and the second RRC state separately can further include at least one of block 340-360 to transition the RRC states accordingly for updates to the serving network device and/or cluster. For example, at block 340, in response to a first network device (e.g., BS 102) transitioning from a serving network device for the terminal device (e.g., UE 111) to a backup network device for the terminal device, the terminal device transitions a state value for an RRC state of a link of the terminal device with the first network device to a third state. At block 350, the terminal device transitions a state value for an RRC state of a link of the terminal device with a second network device (e.g., BS103) to a connected state in response to the second network device transitioning from a backup network device for the terminal device to a serving network device for the terminal device.

In block 360, the terminal device operates according to its current RRC state in response to a new network device joining the cluster. For example, if the first RRC state of the terminal device is in the idle state, the RRC state for the link of the terminal device with the newly accessed network device is set to the idle state. On the other hand, if the first RRC state of the terminal device is in the connected state, the newly joined network device is used as a backup network device of the terminal device. At this time, it is also possible to establish a connection with the newly joined network device and set the RRC state for the link of the terminal device with the newly joined network device to the third state.

The embodiment can adaptively adjust the RRC state for the corresponding network device according to the change/update of the cluster and/or serving network device, achieving saving of radio resources while maintaining the capability of fast data link switching.

The RRC state transitions in

blocks

340 and 350 of fig. 3B are also embodied in the examples of fig. 4A and 4B, illustrated by

state transitions

470 and 480, respectively.

In one embodiment, the UE may have more than one serving network device. For example, UE111 may have two serving network devices, BS101 and BS 102. In this embodiment, the UE111 may maintain the RRC state for the link with BS 101-102 at block 310 in a different manner. For example, at block 310, the UE111 can maintain a first RRC state for each of the BSs 101-102, respectively. In this embodiment, there will be multiple first RRC states. The plurality of first RRC states are synchronous, i.e., have the same state value. In another example, the UE may maintain the first RRC state for the set of links with BS 101-102, i.e., a single first RRC state for all serving BSs.

Similarly, in another embodiment, the UE may have more than one backup network device. For example, UE111 may have two backup network devices, BS103 and BS 104. In this embodiment, the UE111 may maintain the RRC state for the link with BS 103-104 at block 320 in a different manner. For example, at block 320, the UE111 may maintain a second RRC state for each of the BSs 103-104, respectively. In this embodiment, there will be a plurality of second RRC states. Also, the plurality of second RRC states have the same state value. In another alternative example, the UE may maintain the second RRC state for the set of links with BS 103-104. That is, a single second RRC state is maintained for all backup BSs.

Another network deployment scenario in which embodiments of the present disclosure may be implemented is shown in fig. 5A. There may be no base station of legacy LTE in this scenario. As shown in fig. 5A, a BS501, a BS 502, and a BS 503 operating in a high frequency band (e.g., MMW band) form a cluster 510, the BS 502, the BS 503, and the BS504 form a cluster 520, and the BS 503, the BS504, and the BS505 form a cluster 530. UE511 will establish a connection with BS501, BS 502 and BS 503. BS501 may be selected as the serving BS for UE 511. When the service link of the UE511 (i.e., the link with the serving BS 501) is blocked by a car or the like, the UE511 may perform a fast transmission handover, for example, handover of data transmission/reception from the BS501 to the BS 502.

Since the link of BS501 and UE511 has better quality, UE511 can re-perform fast transmission handover to handover transmission/reception from BS 502 to BS501 when the service link with BS501 is restored. As the UE501 moves, for example, to the location of UE 512 in fig. 5A, the cluster for that UE501 may be updated. For example, BS504 may be added to a new cluster and BS501 removed from the new cluster. The UE501 will then establish a new connection with BS504 and release the connection with BS 501.

A schematic diagram of the connection of the UE511 with the BS 501-503 is shown in fig. 5B. As shown in fig. 5B, the UE111 establishes multiple RRC connections with three BSs (e.g., MMWBS) 501-503. The BS501 serves as a serving cell for data transmission/reception, and the other BSs, i.e.,

BS

502 and 503, are used as backup BSs. The UE will also establish connections with these backup BSs.

In one embodiment, the methods of RRC state maintenance described above in connection with fig. 1-4 and method 200 apply equally to the example scenarios of fig. 5A-5B. For example, in response to the BS504 joining a new cluster, the UE511 may set an RRC state with the BS, e.g., according to the operation of 350 in fig. 3.

For convenience of discussion, a network deployment scenario including the LTE BS in fig. 1 may be referred to as scenario 1, and a network deployment scenario not including the LTE BS in fig. 5A may be referred to as scenario 2. For scenario 1, the UE will maintain RRC idle state for all connections when there is no need for Uplink (UL)/Downlink (DL) data transmission. For example, the UE may be kept in an RRC idle state for the link of the serving BSs (LTE BS and BS 101) according to the currently agreed resolution in 3GPP regarding achieving tight interworking of LTE and NR (i.e., the UE has a single primary cell based RRC state machine). Here, it is assumed that the LTE BS is a primary base station (or primary cell), the MMW BS101 is a secondary base station (or secondary cell), and the RRC state is based on a link for the primary base station (i.e., LTE BS). Further, in this scenario 1, the UE also maintains the RRC idle state with respect to the MMW BS102 and the MMW BS 10. For scenario 2, the UE will maintain RRC idle state with respect to all serving BSs (BS 501) and backup BSs (502-503).

If the UE has data transmission for UL/DL, the UE will establish multiple connections with multiple cells. For scenario 1, the UE will establish multiple RRC connections with the LTE BS101 and multiple MMW BSs. The LTE BS101 and the MMW BS102 are tightly interconnected serving cells for supporting LTE and NR, and data can be transmitted through the two BSs. In this scenario, the RRC connected state may be maintained for the links of the LTE BS101 and the MMW BS102 in accordance with the current resolution in 3GPP that the UE has a single RRC state machine based on the primary base station. For the backup cells in the cluster, e.g., MMW BS 103-104, the UE will remain in the third RRC state, e.g., inactive state. The same principles apply to scenario 2. For example, the UE will maintain the RRC connected state for the serving cell MMW BS501 and the RRC inactive state for the backup cell MMW BS 502-503.

By maintaining the connection with the backup cell in the RRC third state (e.g., inactive state), the UE can achieve low power consumption and low signaling overhead on the one hand, and can perform fast data transmission handover between the serving cell and the backup cell on the other hand. Since in this third state (e.g. the new inactive state) the connection of RAN and radio network and core network can be maintained (both in terms of UP and CP). This is consistent with the requirements for backup links: the UE should be capable of fast link switching for data transmission and have minimal resource consumption, including power and signaling consumption.

Further, optionally, for either scenario 1 or scenario 2, the UE may send information regarding the capabilities of the terminal device to one or more network devices in the cluster. This operation may be performed, for example, in block 230 of fig. 2. Information on the capabilities of the terminal device may be shared among multiple BSs and, for example, RRC messages generated by coordination may be directed to RRC entities within different BSs.

A method 600 corresponding to the method 200 performed by the terminal device, as performed at the serving network device, is described below in conjunction with fig. 6.

For simplicity, the method 600 is described with the BS102 in fig. 1 as an example of a serving network device. BS102 may be referred to herein as a first network device that belongs to the same cluster (e.g., 121) as a second network device (e.g., BS103 in fig. 1) and serves UE111 as a terminal device, e.g., a serving network device of UE111 and a backup network device, respectively, where the serving network device 102 is used for data communication with UE111, the backup network device 103 is used for handing over data communication, i.e., handing over data communication from BS102 to BS103 when needed, and there is no data communication on the link between BS103 and UE111 prior to the handing over

As shown in fig. 6, in response to UE111 establishing a connection with BS102, BS102 sets an RRC state for the connection to a connected state at block 610. In block 620, in response to the BS102 transitioning from the serving network device for the UE111 to the backup network device for the UE, the BS102 transitions the RRC state from the connected state to a third state different from the idle state and the connected state, the third state having lower energy consumption than the connected state and enabling fast communication of the UE111 with the backup network device.

The method 600 enables a network device to update the RRC state of the connection with the UE depending on whether it is serving or backup, resulting in saving of radio resources. In particular, in one embodiment, the description regarding the third state described above in connection with method 200 applies equally here and is not repeated.

In another embodiment, the BS102 may optionally also receive information regarding the capabilities of the UE111 from another network device (e.g., BS101 or 104 in fig. 1) at block 630. Alternatively or additionally, in yet another embodiment, the BS102 may also perform at least one of blocks 640-660. For example, at block 640, BS102 may receive information from UE111 regarding the capabilities of the UE; at block 650, BS102 may transmit capability information about UE111 to another network device (e.g., BS103) in the cluster; and at block 660 BS102 may coordinate RRC configuration with additional network devices in the cluster.

A method 700, corresponding to the method 200 performed by the terminal device, performed at the backup network device is described below in conjunction with fig. 7. For simplicity, method 700 is described with BS103 in fig. 1 as an example of a backup network device. BS103 may be referred to herein as a second network device that belongs to the same cluster (e.g., 121) as a first network device (e.g., BS102 in fig. 1) and that is a serving network device for a terminal device, e.g., UE 111.

As shown in fig. 7, in response to the UE111 establishing a connection with the BS103, the BS103 sets an RRC state for the connection to a third state different from the idle state and the connected state at block 710; and at block 720, in response to the BS103 transitioning from the backup network device for the UE to the serving network device for the UE, changing the state value of the RRC state from a third state to a connected state, wherein the third state has lower energy consumption than the connected state and enables fast communication of the UE with the backup network device BS103 when needed.

The method 700 enables the BS103 to update the RRC state of the connection with the UE according to whether it is a serving network device or a backup network device, resulting in saving of radio resources.

In one embodiment, the description regarding the third state described above in connection with method 200 applies equally here and is not repeated.

In one embodiment, the backup network device BS103 may optionally receive information of the capabilities of the terminal device from the further network device at block 730 and/or coordinate the RRC configuration with the further network device in the cluster at block 740.

Fig. 8 illustrates a block diagram of an apparatus 800 according to certain embodiments of the present disclosure. The apparatus 800 may be implemented, for example, on the side of the

terminal device

111 or 112 shown in fig. 1. The apparatus 800 is described below with the UE111 as an example.

As shown in fig. 8, the apparatus 800 includes: a first RRC state control unit 801 and a second RRC state control unit 802. The first RRC state control unit 801 and the second RRC state control unit 802 are configured to maintain a first RRC state for the link of the UE111 with the serving network device and a second RRC state for the link of the UE111 with the backup network device, respectively.

In one embodiment, the first RRC state control unit 801 and the second RRC state control unit 802 may maintain RRC states for the serving network device and the backup network device, respectively, according to the method of any of the embodiments described in connection with the method 200 and fig. 2-5B. Therefore, specific details thereof will not be repeated.

Optionally, in an embodiment, the apparatus 800 may further include a sending unit 803 for sending information about the capability of the UE 112 to one or more network devices in a cluster in which the UE is located.

Fig. 9 illustrates a block diagram of an apparatus 900 according to certain embodiments of the present disclosure. The apparatus 900 may be implemented at any one of the

network devices

101 and 105 shown in fig. 1, for example. The apparatus 900 is described below by taking the BS102 as an example. The BS102 and another network device (e.g., BS103) serve the UE111 as a serving network device and a backup network device, respectively. It will be appreciated that in some embodiments, the terminal device may also have other serving network devices and backup network devices.

As shown in fig. 9, the apparatus 900 includes an RRC state control unit 901 and an RRC state update unit 902. The RRC state control unit 901 is configured to set an RRC state for a connection to a connected state in response to the UE111 establishing the connection with the BS 102; the RRC state updating unit 902 is configured to, in response to a transition of the BS102 from a serving network device for the UE to a backup network device for the UE, transition the RRC state from the connected state to a third state different from the idle state and the connected state, the third state having lower energy consumption than the connected state and being capable of enabling fast communication of the UE111 with the backup network device BS103 when needed, i.e. when data communication needs to be handed over from BS102 to BS 103.

In one embodiment, the RRC state control unit 901 and the RRC state update unit 902 may implement the operations of

blocks

610 and 620 of method 600, respectively.

Optionally, in an embodiment, the apparatus 900 may further include a first receiving unit 903 configured to receive information about the capability of the UE111 from another network device. The further network device may be, for example, BS101 or BS 103.

Alternatively or additionally, in another embodiment, the apparatus 900 may further comprise at least one of the following. A second receiving unit 904 configured to receive information of the capability of the terminal device from the UE; a transmitting unit 905 configured to transmit capability information about the UE to the further network devices in the cluster; and a coordinating unit 906 configured to coordinate the RRC configuration with the further network devices in the cluster.

In one embodiment, blocks 903-906 may perform the functions of blocks 630-660 of method 600, respectively.

Fig. 10 illustrates a block diagram of an apparatus 1000 in accordance with certain embodiments of the present disclosure. The apparatus 1000 may be implemented at any one of the

network devices

101 and 105 shown in fig. 1, for example. The apparatus 1000 is described below with reference to the BS103 as an example. The BS103 serves the UE111 as a backup network device, which is in the same cluster as another serving network device (e.g., BS 102). It is understood that in some embodiments, the terminal device UE111 may also have other serving network devices and backup network devices.

As shown in fig. 10, the apparatus 1000 includes an RRC state control unit 1001 and an RRC state update unit 1002. The RRC state control unit 1001 is configured to set, in response to the UE111 establishing a connection with the BS103, an RRC state for the connection to a third state different from the idle state and the connected state; the RRC state updating unit 1002 is configured to change the state value of the RRC state from the third state to the connected state in response to the BS103 transitioning from the backup network device for the UE to the serving network device. Wherein the third state has a lower energy consumption than the connected state and enables fast communication of the UE111 with the backup network device BS103 when needed.

In one embodiment, RRC state control unit 1001 and RRC state update unit 1002 may implement the operations of

blocks

710 and 720, respectively, of method 700.

Optionally, in an embodiment, the apparatus 1000 may further include a receiving unit 1003 configured to receive information about the capability of the UE111 from another network device; and/or a coordinating unit 1004 configured to coordinate the RRC configuration with further network devices in the cluster. In one embodiment, blocks 1003-1004 may perform the operations of blocks 730-740 of method 700, respectively.

It should be noted that in some embodiments, other units not shown in the figures may also be included in the apparatus 800-1000. Additionally, the elements included in 800-1000 may be implemented in a variety of ways including software, hardware, firmware, or any combination thereof. In one embodiment, one or more of the units may be implemented using software and/or firmware, such as machine executable instructions stored on a storage medium. In addition to or in the alternative to machine-executable instructions, some or all of the elements in apparatus 800-1000 may be implemented at least in part by one or more hardware logic components. By way of example, and not limitation, exemplary types of hardware logic components that may be used include Field Programmable Gate Arrays (FPGAs), Application Specific Integrated Circuits (ASICs), Application Specific Standards (ASSPs), systems on a chip (SOCs), Complex Programmable Logic Devices (CPLDs), and so forth.

As described above, in some embodiments, the above-described flows, methods or processes may be implemented by hardware in a network device or a terminal device. For example, the network device or the terminal device may utilize its transmitter, receiver, transceiver and/or processor or controller to implement the

methods

200, 600, and 700. Fig. 11 illustrates a block diagram of a device 1100 suitable for implementing embodiments of the present disclosure. The device 1100 may be used to implement a network device, such as the

network device

101 and 105 shown in fig. 1, 501 and 505 in fig. 5A; and/or to implement a terminal device, such as the first

terminal device

111 or 112 shown in fig. 1.

As shown in the example of fig. 11, device 1100 includes a processor 1110. Processor 1110 controls the operation and functions of device 1100. For example, in certain embodiments, processor 1110 may perform various operations by way of instructions 1130 stored in memory 1120 coupled thereto. The memory 1120 may be of any suitable type suitable to the local technical environment and may be implemented using any suitable data storage technology, including but not limited to semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems. Although only one memory unit is shown in FIG. 11, there may be multiple physically distinct memory units within device 1100.

The processors 1110 may be of any suitable type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microcontrollers, digital signal controllers (DSPs), and controller-based multi-core controller architectures, but are not limited to. The device 1100 may also include a plurality of processors 1110. The processor 1110 may also be coupled with a transceiver 1140, which transceiver 1140 may enable the reception and transmission of information via one or more antennas 1150 and/or other components.

When device 1100 is acting as a terminal device, e.g., UE111, processor 1110 and memory 1120 may operate in conjunction to implement method 200 described above with reference to fig. 2.

When the device 1100 is acting as the network device 102, the processor 1110 and the memory 1120 may operate in conjunction to implement the

methods

600 or 700 described above with reference to fig. 6 or 7.

All of the features described above with reference to fig. 2 and fig. 6 and 7 apply to the apparatus 1100 and are not described in detail here.

In general, the various example embodiments of this disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Certain aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While aspects of embodiments of the disclosure have been illustrated or described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

By way of example, embodiments of the disclosure may also be described in the context of machine-executable instructions, such as those included in program modules, being executed in devices on target real or virtual processors. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, etc. that perform particular tasks or implement particular abstract data types. In various embodiments, the functionality of the program modules may be combined or divided between program modules as described. Machine-executable instructions for program modules may be executed within local or distributed devices. In a distributed facility, program modules may be located in both local and remote memory storage media.

Computer program code for implementing the methods of the present disclosure may be written in one or more programming languages. These computer program codes may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the computer or other programmable data processing apparatus, cause the functions/acts specified in the flowchart and/or block diagram block or blocks to be performed. The program code may execute entirely on the computer, partly on the computer, as a stand-alone software package, partly on the computer and partly on a remote computer or entirely on the remote computer or server.

In the context of this disclosure, a machine-readable medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination thereof. More detailed examples of a machine-readable storage medium include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical storage device, a magnetic storage device, or any suitable combination thereof.

Additionally, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In some cases, multitasking or parallel processing may be beneficial. Likewise, while the above discussion contains certain specific implementation details, this should not be construed as limiting the scope of any invention or claims, but rather as describing particular embodiments that may be directed to particular inventions. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. A method of a terminal device in a wireless communication system, the terminal device being served by a cluster of network devices, the cluster comprising a plurality of network devices including a serving network device for data communication with the terminal device and a backup network device for switching the data communication, the method comprising:

maintaining a first radio resource control, RRC, state and a second RRC state, respectively, for:

the link of the terminal device with the serving network device, and

a link between the terminal device and the backup network device.

2. The method of claim 1, wherein maintaining the first and second RRC states, respectively, comprises:

setting both the first RRC state and the second RRC state to an idle state if the terminal device does not have a need to communicate with the cluster, an

Responsive to the terminal device establishing a connection with the serving network device, transitioning the first RRC state to a connected state;

and in response to the terminal device establishing a connection with the backup network device, transitioning the state of the second RRC state to a third state different from the idle state and the connected state, the third state having lower energy consumption than the connected state and enabling fast communication of the terminal device with the backup network device.

3. The method of claim 2, wherein maintaining the first and second RRC states, respectively, further comprises at least one of:

transitioning an RRC state for a link of the terminal device with the first network device to the third state in response to the first network device transitioning from a serving network device for the terminal device to a backup network device for the terminal device,

responsive to a second network device transitioning from a backup network device for the terminal device to a serving network device for the terminal device, transitioning an RRC state for a link of the terminal device with the second network device to the connected state; and

in response to a new network device joining the cluster:

setting an RRC state for a link of the terminal device with a newly accessed network device to an idle state if the first RRC state of the terminal device is in the idle state,

if the first RRC state of the terminal equipment is in the connection state, taking the newly added network equipment as backup network equipment of the terminal equipment; establishing a connection with the newly joined network device and setting the RRC state for the link of the terminal device with the newly joined network device to the third state.

4. The method of claim 2, wherein the third state is an inactive state.

5. A method according to claim 2, wherein in the third state, a connection is established and maintained between the terminal device and the radio access network and core network.

6. The method of any of claims 1-5, wherein maintaining the first and second RRC states, respectively, comprises at least one of:

maintaining the first RRC state separately for links of the terminal device and each of the serving network devices, an

And respectively maintaining the second RRC state aiming at the link between the terminal equipment and each backup network equipment in the backup network equipment.

7. The method of any of claims 1-5, wherein maintaining the first and second RRC states, respectively, comprises at least one of:

maintaining the first RRC state for a set of links of the terminal device with all of the serving network devices, an

And maintaining the second RRC state aiming at the set of the links of the terminal equipment and all the backup network equipment in the backup network equipment.

8. The method according to any of claims 1-5, wherein the network device is a base station or a transmission receiving node, TRP.

9. The method of any of claims 1-5, further comprising:

and sending the information of the capability of the terminal equipment to the network equipment in the plurality of network equipment.

10. A method of a first network device in a wireless communication system, the first network device and a second network device belonging to a same cluster and serving a terminal device as a serving network device and a backup network device, respectively, of the terminal device, wherein the serving network device is configured to perform data communication with the terminal device, and the backup network device is configured to switch the data communication, the method comprising:

in response to the terminal device establishing a connection with the first network device, setting a radio resource control, RRC, state for the connection to a connected state; and

transitioning the RRC state from the connected state to a third state different from the idle state and the connected state in response to the first network device transitioning from a serving network device for the terminal device to a backup network device for the terminal device, the third state having lower energy consumption than the connected state and enabling fast communication of the terminal device with the backup network device.

11. The method of claim 10, wherein the third state is an inactive state.

12. A method according to claim 10, wherein in the third state the connection of the terminal device to the radio access network and the core network is established and maintained.

13. The method according to claim 10, wherein the first network device is a base station or a transmission receiving node, TRP.

14. The method of any of claims 10-13, further comprising at least one of:

receiving information of capabilities of the terminal device from a further network device;

receiving information of capabilities of the terminal device from the terminal device,

sending the capability information of the terminal device to another network device in the cluster; and

coordinating RRC configuration with further network devices in the cluster.

15. A method of a second network device in a wireless communication system, the second network device and a first network device belonging to a same cluster and serving a terminal device as a backup network device and a serving network device of the terminal device, respectively, wherein the serving network device is configured to perform data communication with the terminal device, and the backup network device is configured to switch the data communication, the method comprising:

in response to the terminal device establishing a connection with the second network device, setting a radio resource control, RRC, state for the connection to a third state different from the idle state and the connected state; and

changing the state value of the RRC state from the third state to the connected state in response to the second network device transitioning from a backup network device for the terminal device to a serving network device for the terminal device;

the third state has a lower energy consumption than the connected state and enables fast communication of the terminal device with the backup network device.

16. The method of claim 15, wherein the third state is an inactive state.

17. The method of claim 15, wherein in the third state, the connection of the terminal device and a core network is maintained.

18. The method according to claim 15, wherein the second network device is a base station or a transmission receiving node TRP.

19. The method of any of claims 15-18, further comprising at least one of:

receiving information of capabilities of the terminal device from a further network device; and

coordinating RRC configuration with further network devices in the cluster.

20. An apparatus in a terminal device in a wireless communication network, the terminal device being served by a cluster of network devices, the cluster comprising a plurality of network devices including a serving network device for data communication with the terminal device and a backup network device for switching the data communication, the apparatus comprising:

a processor, and

a memory containing instructions executed by the processor whereby the device is operative to:

the link of the terminal device with the serving network device, and

a link between the terminal device and the backup network device.

21. The apparatus of claim 20, further operative to maintain the first and second RRC states, respectively, by:

22. The apparatus of claim 21, further operative to maintain the first and second RRC states, respectively, by at least one of:

in response to a new network device joining the cluster:

23. The device of claim 21, wherein the third state is an inactive state.

24. The apparatus of claim 21, wherein in the third state, connections of the terminal device with a radio access network and a core network are established and maintained.

25. The apparatus of any of claims 20-24, further operative to maintain the first and second RRC states, respectively, by at least one of:

26. The apparatus of any of claims 20-24, further operative to maintain the first and second RRC states, respectively, by at least one of:

27. The apparatus according to any of claims 20-24, wherein the network device is a base station or a transmission receiving node, TRP.

28. The apparatus of any of claims 20-24, wherein the apparatus is further operative to:

29. An apparatus in a first network device in a wireless communication network, the first network device and a second network device belonging to a same cluster and serving a terminal device as a serving network device and a backup network device, respectively, of the terminal device, wherein the serving network device is configured to perform data communication with the terminal device, and the backup network device is configured to switch the data communication, wherein the apparatus comprises:

a processor, and

30. The device of claim 29, wherein the third state is an inactive state.

31. The apparatus of claim 29, wherein in the third state, the connection of the terminal device with a radio access network and a core network is established and maintained.

32. The apparatus according to claim 29, wherein the first network device is a base station or a transmission receiving node, TRP.

33. The apparatus of any of claims 29-32, further operative to perform at least one of:

coordinating RRC configuration with further network devices in the cluster.

34. An apparatus in a second network device in a wireless communication network, the second network device and a first network device belonging to a same cluster and serving a terminal device as a backup network device and a serving network device, respectively, of the terminal device, wherein the serving network device is configured to perform data communication with the terminal device, and the backup network device is configured to switch the data communication, wherein the apparatus comprises:

a processor, and

35. The device of claim 34, wherein the third state is an inactive state.

36. The apparatus of claim 34, wherein in the third state, the connection of the terminal device and a core network is maintained.

37. The apparatus of claim 34, wherein the second network device is a base station or a transmit receive node, TRP.

38. The apparatus of any of claims 34-37, further operative to perform at least one of:

coordinating RRC configuration with further network devices in the cluster.