CN113170361A

CN113170361A - Link switching in federated network deployments

Info

Publication number: CN113170361A
Application number: CN201880099680.3A
Authority: CN
Inventors: 杨涛
Original assignee: Nokia Shanghai Bell Co Ltd
Current assignee: Nokia Shanghai Bell Co Ltd
Priority date: 2018-11-23
Filing date: 2018-11-23
Publication date: 2021-07-23
Anticipated expiration: 2038-11-23
Also published as: CN113170361B; WO2020103152A1

Abstract

Embodiments of the present disclosure relate to link switching in federated network deployments. The terminal device receives an uplink handover indication from a first network device, the first network device serving a first cell using a first frequency band. The terminal device switches from a first uplink with the first network device to a second uplink with a second network device using a second frequency band to serve the second cell based on the uplink switch indication while maintaining the first downlink with the first network device. The link switching provided in the present disclosure is more flexible.

Description

Link switching in federated network deployments

Technical Field

Embodiments of the present disclosure relate generally to the field of telecommunications, and in particular to link switching in federated network deployments.

Background

In the field of communications, there is a continuing evolution towards providing efficient and reliable solutions for exploiting wireless communication networks. Each new generation faces technical challenges in dealing with the different scenarios and procedures required to connect and service devices connected to a wireless network. In order to meet the increasing demand for wireless data services since the deployment of fourth generation (4G) communication systems, efforts have been made to develop improved fifth generation (5G) or 5G pre-communication systems. The new communication system may support various types of service applications for the terminal device.

In recent communication technologies, it has been proposed to jointly deploy different types of cells within a particular geographic area. Different types of cells may overlap each other and are typically served by non-collocated network devices with corresponding frequency bands. Terminal devices located in certain geographic areas may connect to and communicate with network devices. In such deployments, there is still a need for an efficient communication scheme.

Disclosure of Invention

In general, example embodiments of the present disclosure provide a scheme for link switching in a federated network deployment.

In a first aspect, an apparatus is provided. The apparatus includes at least one processor and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: receiving, at a terminal device, an uplink handover indication from a first network device, the first network device serving a first cell using a first frequency band; and switching from a first uplink with the first network device to a second uplink with the second network device while maintaining the first downlink with the first network device based on the uplink switching indication, the second network device serving the second cell using the second frequency band.

In a second aspect, an apparatus is provided. The apparatus includes at least one processor and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: determining, at a network device, whether a first uplink of a terminal device and the network device is to be handed over, the network device serving a first cell using a first frequency band; and in response to determining that the first uplink is to be switched, transmitting an uplink switching indication to the terminal device to trigger the terminal device to switch from the first uplink to a second uplink with a further network device while maintaining the first downlink with the network device, the further network device serving a second cell using a second frequency band.

In a third aspect, an apparatus is provided. The apparatus includes at least one processor and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to: receiving, at the network device, a request from a further network device to switch the terminal device from a first uplink with the further network device to a second uplink with the network device, the further network device serving the first cell using the first frequency band, the network device serving the second cell using the second frequency band; transmitting an acknowledgement to the further network device regarding the request in response to determining that the handover is accepted; and establishing a second uplink with the terminal device, the terminal device maintaining the first downlink with the further network device.

In a fourth aspect, a method implemented at a terminal device is provided. The method comprises the following steps: receiving an uplink handover indication from a first network device, the first network device serving a first cell using a first frequency band; and switching from a first uplink with the first network device to a second uplink with the second network device while maintaining the first downlink with the first network device based on the uplink switching indication, the second network device serving the second cell using the second frequency band.

In a fifth aspect, a method implemented at a network device is provided. The method comprises the following steps: determining whether a first uplink of the terminal device and a network device is to be handed over, the network device serving a first cell using a first frequency band; and in response to determining that the first uplink is to be switched, transmitting an uplink switching indication to the terminal device to trigger the terminal device to switch from the first uplink to a second uplink with a further network device while maintaining the first downlink with the network device, the further network device serving a second cell using a second frequency band.

In a sixth aspect, a method implemented at a network device is provided. The method comprises the following steps: receiving, from a further network device, a request to switch a terminal device from a first uplink with the further network device to a second uplink with the network device, the further network device serving a first cell using a first frequency band, the network device serving a second cell using a second frequency band; transmitting an acknowledgement to the further network device regarding the request in response to determining that the handover is accepted; and establishing a second uplink with the terminal device, the terminal device maintaining the first downlink with the further network device.

In a seventh aspect, there is provided an apparatus comprising means for performing the steps of the method according to the fourth aspect above.

In an eighth aspect, there is provided an apparatus comprising means for performing the steps of the method according to the fifth aspect above.

In a ninth aspect, there is provided an apparatus comprising means for performing the steps of the method according to the sixth aspect above.

In a tenth aspect, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least a method according to any of the fourth to sixth aspects described above.

It should be understood that this summary is not intended to identify key or essential features of the embodiments of the disclosure, nor is it intended to be used to limit the scope of the disclosure. Other features of the present disclosure will become readily apparent from the following description.

Drawings

Some example embodiments will now be described with reference to the accompanying drawings, in which:

FIG. 1 illustrates an example communication network in which embodiments of the present disclosure may be implemented;

fig. 2 shows a flow diagram illustrating a process for link handover in accordance with some embodiments of the present disclosure;

FIG. 3 illustrates a flow diagram of a method implemented at a terminal device in accordance with some embodiments of the present disclosure;

FIG. 4 illustrates a flow diagram of a method implemented at a network device in accordance with some embodiments of the present disclosure;

fig. 5 illustrates a flow diagram of a method implemented at a network device in accordance with some other embodiments of the present disclosure; and

fig. 6 shows a simplified block diagram of an apparatus suitable for implementing embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numbers refer to the same or similar elements.

Detailed Description

The principles of the present disclosure will now be described with reference to a few exemplary embodiments. It is to be understood that these embodiments are described for illustrative purposes only and are intended to aid those skilled in the art in understanding and enabling the present disclosure without giving any limitation to the scope of the present disclosure. The disclosure described herein may be implemented in various other ways besides those described below.

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

References in the present disclosure to "one embodiment," "an example embodiment," etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with an embodiment whether or not explicitly described.

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

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

As used in this application, the term "circuitry" may refer to one or more or all of the following:

(a) a purely hardware circuit implementation (such as an implementation in analog and/or digital circuitry only); and

(b) a combination of hardware circuitry and software, such as (where applicable):

(i) combinations of analog and/or digital hardware circuitry and software/firmware, and

(ii) any portion of a hardware processor with software (including a digital signal processor), software, and memory that work in conjunction to cause a device such as a mobile phone or server to perform various functions; and

(c) hardware circuitry and/or a processor, such as a microprocessor or a portion of a microprocessor, that requires software (e.g., firmware) to operate, but this software may not be present when operation is not required.

Such definitions of circuitry apply to all uses of that term in this application, including in any claims. As another example, as used in this application, the term circuitry also encompasses an implementation as pure hardware circuitry or processor (or multiple processors), or an implementation of a portion of a hardware circuitry or processor and its (or their) accompanying software and/or firmware. By way of example, and where applicable to particular claim elements, the term circuitry also encompasses baseband integrated circuits or processor integrated circuits for mobile devices, or similar integrated circuits in servers, cellular network devices, or other computing or network devices.

As used herein, the term "communication network" refers to a network that conforms to any suitable communication standard, such as Long Term Evolution (LTE), LTE-advanced (LTE-a), Wideband Code Division Multiple Access (WCDMA), High Speed Packet Access (HSPA), narrowband internet of things (NB-IoT), and so forth. Further, communication between the terminal device and the network devices in the communication network may be performed according to any suitable generation communication protocol, including, but not limited to, first generation (1G), second generation (2G), 2.5G, 2.75G, third generation (3G), fourth generation (4G), 4.5G, future fifth generation (5G) communication protocols, and/or any other protocol currently known or developed in the future. Embodiments of the present disclosure may be applied to various communication systems. Given the rapid development of communications, there will of course also be future types of communication techniques and systems that may embody the present disclosure. The scope of the present disclosure should not be limited to only the above-described systems.

As used herein, the term "network device" refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. A network device may refer to a Base Station (BS) or an Access Point (AP), e.g., a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also known as a gNB), a Remote Radio Unit (RRU), a Radio Header (RH), a Remote Radio Head (RRH), a relay, a low power node (such as femto, pico, etc.), depending on the terminology and technology applied.

The term "terminal device" refers to any terminal device that may be capable of wireless communication. By way of example, and not limitation, a terminal device may also be referred to as a communication device, User Equipment (UE), Subscriber Station (SS), portable subscriber station, Mobile Station (MS), or Access Terminal (AT). Terminal devices may include, but are not limited to, mobile phones, cellular phones, smart phones, voice over IP (VoIP) phones, wireless local loop phones, tablets, wearable terminals, Personal Digital Assistants (PDAs), portable computers, desktop computers, image capture terminals such as digital cameras, gaming terminals, music storage and playback devices, in-vehicle wireless terminals, wireless endpoints, mobile stations, laptop embedded devices (LEEs), laptop installation devices (LMEs), USB dongle, smart devices, wireless Customer Premises Equipment (CPE), internet of things (loT) devices, watches or other wearable devices, Head Mounted Displays (HMDs), vehicles, drones, medical devices and applications (e.g., tele-surgery), industrial devices and applications (e.g., robots and/or other wireless devices operating in industrial and/or automated processing chain environments), Consumer electronics devices, devices operating on commercial and/or industrial wireless networks, and the like. In the following description, the terms "terminal device", "communication device", "terminal", "user equipment" and "UE" may be used interchangeably.

In a communication network, a plurality of network devices are co-deployed in a geographical area to serve respective cells, with which a terminal device may have an active connection when the terminal device is located within a corresponding cell. In an active connection, a terminal device may communicate with the network device on both Uplink (UL) and Downlink (DL) frequency bands. Due to various reasons, such as quality degradation in the UL, the terminal device may need to switch the link to another network device in one direction, such as the UL.

Typically, the change or handover of the operating frequency band is achieved through a Handover (HO) procedure. The HO procedure will trigger a handover of both UL and DL of the terminal device from the source network device to the target network device. However, in some usage scenarios, it may be more desirable to maintain DL with the source network device due to high DL quality and/or high DL throughput with the source network device, poor DL quality with the target network device, and so on.

According to an embodiment of the present disclosure, a scheme for link switching in a federated network deployment is provided. In a joint network deployment, different network devices serve different cells with corresponding frequency bands. The terminal device has UL and DL with a first network device of the different network devices. The first network device transmits a UL link switch indication to the terminal device if the UL with the terminal device is to be switched. In some cases, the first network device may transmit an UL link switch indication in response to receiving an acknowledgement in the UL regarding such a switch. Upon receiving the UL link switch indication, the terminal device switches from UL with the first network device to UL with a second network device of the different network devices while maintaining DL with the first network device. The link switching provided in the present disclosure is more flexible. In this way, it is possible to maintain high quality DL and change UL with degraded quality.

The principles and embodiments of the present disclosure will be described in detail below with reference to the drawings. Referring initially to fig. 1, fig. 1 illustrates an example communication system 100 in which embodiments of the present disclosure may be implemented. System 100 includes a plurality of network devices, such as network device 111 and network device 112.

Network devices

111, 112 serve respective areas 101 and 102 (also referred to as cells 101 and 102) using different frequency bands in both the DL and UL. Such a frequency band may also be referred to as an operating frequency band of the corresponding network device.

System 100 also includes one or more terminal devices, such as

terminal devices

120, 121, 122.

Terminal devices

120, 121, 122 are capable of connecting and communicating in UL and DL with one or both of

network devices

111, 112 as long as the terminal device is located within the corresponding cell. In the communication system, UL refers to a link in a direction from a terminal device to a network device, and DL refers to a link in a direction from a network device to a terminal device. In addition to communicating with

terminal devices

120, 121, 122,

network devices

111, 112 may also communicate with each other, e.g., via backhaul links.

It should be understood that the number of network devices and terminal devices is for illustration purposes only and is not given any limitation. System 100 may include any suitable number of network devices and terminal devices suitable for implementing embodiments of the present disclosure. Although not shown, it is to be understood that one or more terminal devices may be located in a

cell

101 or 102.

Communications in communication system 100 may be implemented in accordance with any suitable communication protocol, including, but not limited to, first-generation (1G), second-generation (2G), third-generation (3G), fourth-generation (4G), and fifth-generation (5G), etc. cellular communication protocols, wireless local area network communication protocols such as Institute of Electrical and Electronics Engineers (IEEE)802.11, etc., and/or any other protocol currently known or developed in the future. Moreover, the communication may utilize any suitable wireless communication technology, including but not limited to: code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple Input Multiple Output (MIMO), Orthogonal Frequency Division Multiple Access (OFDMA), and/or any currently known or later developed technique.

The coverage of the cells 102, 104 of the network device 111 is closely related to the operating frequency band of the

network device

111, 112. Fig. 1 shows an example in which the operating frequency bands of network devices 111, 113 are different, the operating frequency band of network device 111 being higher than the operating frequency band of network device 112. Due to the more severe path loss situation in the high band system, the coverage of cell 101 is likely to be smaller than the coverage of cell 102. In the example shown, cell 101 overlaps with cell 102. The large cell 102 may sometimes be referred to as a macro cell and the network device 112 may be referred to as a macro base station, while the relatively smaller cell 101 may be referred to as a small cell and the network device 111 may be referred to as a small base station. As a particular example, network device 111 may operate in a frequency band below 6GHz, such as 3.5GHz, while network device 112 may operate in a millimeter wave (mmW) frequency band, such as 28 GHz. It should be understood that the

network devices

111, 112 may have other operating frequency bands.

In some cases, cell 101 and/or cell 102 may have asymmetric UL and DL budgets. Such an asymmetric budget easily occurs in cells with high frequency bands. For example, in the case of operation in the mmW band, the different budget between UL and DL may be up to 25 dB. Fig. 1 shows asymmetric UL and DL in a cell 101. For example, cell 101 includes UL coverage area 103 and DL coverage area that is the same range as cell 101. The UL coverage area 103 is smaller than the DL coverage area. For example, a budget difference of up to 25dB may result in a case where the UL coverage area is only about 1/4 of the DL coverage area. The main reason is that the UL transmission power of the terminal device is smaller and/or the UL transmission beamforming gain is smaller compared to the DL case.

Due to UL/DL coverage asymmetry in cell 101, there may be the following: the terminal device still communicates with network device 101 in DL with high quality, while the UL from the terminal device to network device 101 is poor. For example, terminal device 120 was previously located in coverage area 103 and had both UL and DL connections with network device 111. After moving, terminal device 120 is still located in cell 101 of network device 111 and can work in the DL with network device 111. However, at this time, the UL quality from terminal device 120 to network device 111 degrades. Both UL and DL with network device 111 work well for terminal device 121 within coverage area 103. For terminal device 122 outside cell 101 but within cell 102, it may establish a connection with network device 112 in both UL and DL. To support UL communication for terminal device 120, as described above, in embodiments of the present disclosure, terminal device 120 is allowed to switch its UL only to network device 112 and still maintain its DL with network device 111.

It should be understood that although the frequency band of network device 111 is described as being higher than the frequency band of network device 112, in some other cases, the frequency band of network device 112 may be higher than or equal to the frequency band of network device 111. In such a case, the following may also occur: the terminal device has a good DL and a poor UL with one of the

network devices

111, 112 and can therefore switch the UL to the other of the

network devices

111, 112.

Referring now to fig. 2, fig. 2 illustrates a process 200 for link switching according to an embodiment of the disclosure. For purposes of discussion, the process 200 will be described with reference to fig. 1. Process 200 may involve terminal device 120 and

network devices

111, 112 as shown in fig. 1. It should be appreciated that although process 200 for a link has been described in communication system 100 of fig. 1, the process may be similarly applied to other communication scenarios in which different network devices are co-deployed to provide respective serving cells. It should also be understood that although UL link switching for terminal device 120 is discussed, a similar procedure may be applied for any other terminal device in

cell

101 or 102 to switch its link.

In process 200, network device 111 determines 205 whether the UL of terminal device 120 and network device 111 is to be switched. Terminal device 120 has established a connection with network device 111, so cell 101 is the serving cell for terminal device 120 in both UL and DL. For purposes of discussion, the UL from terminal device 120 to network device 111 is referred to as the first UL, and the DL from network device 111 to terminal device 120 is referred to as the first DL. According to an embodiment of the present disclosure, network device 111 controls link switching of terminal device 120 as a current serving cell in both UL and DL of terminal device 120.

Whether to switch the first UL but maintain the first DL for the terminal device 120 depends on various factors. One possible factor is that the terminal device 120 is in a link asymmetric state where the first DL meets the first DL requirement and the first UL with the first network device cannot meet the UL requirement. This indicates that terminal device 120 is still within a good DL coverage area, but will leave the UL coverage area served by network device 111, resulting in asymmetric quality in the UL and DL. The determination of the link asymmetry status will be discussed in detail below. Other factors that cause an uplink-only handover may be due to different UL/DL access control at network device 111, UL/DL load allocation among network devices, and/or other reasons.

In some embodiments, if network device 111 intends to switch terminal device 120 from a first UL to an UL with network device 112 (referred to as a second UL for discussion purposes), it may request whether network device 112 accepts such a switch. Network device 111 may send a request to network device 112 to switch terminal device 120 from the first UL to the second UL. The request may be transmitted via a backhaul link between the

network devices

111, 112. For example, network device 112 may determine whether such UL link switch is accepted based on some normal activity, such as UL access control. If the handover is accepted, network device 112 may transmit an acknowledgement to network device 111 regarding the request, e.g., via a backhaul link therebetween. Upon receiving the acknowledgement, network device 111 makes a decision regarding UL-only link handover for terminal device 120.

If it is determined that the first UL of terminal device 120 is to be switched, network device 111 transmits 210 a UL link switch indication to terminal device 120. The UL link switch indication is used to trigger the terminal device to switch from a first UL with network device 111 to a second UL with network device 112. Some examples of UL link switch indications are described in detail below.

Upon receiving the UL link switch indication, the terminal device 120 switches 215 from the first UL to the second UL while maintaining the first DL with the network device 112. As such, terminal device 120 establishes a second UL with network device 112, and thus may transmit UL data and/or other UL information to network device 112 via the second UL using the UL frequency band of network device 112. Furthermore, terminal device 120 may still operate on the DL band of network device 111 and receive DL data and/or other DL information from network device 111, such as DL Control Information (DCI), DL measurements, acknowledgement information regarding UL transmissions, and the like. In a UL-only link handover, the terminal device 120 may have some pending UL and/or DL data transmissions. As will be discussed below, specific processing of these pending transmissions will be required.

As described above, one possible scenario that would trigger a UL-only link handover for a terminal device 120 is to identify whether the terminal device 120 is in a state with asymmetric link quality in the first UL and DL. There are some events and/or triggers in the conventional HO procedure to identify whether the terminal device is in good connection or poor connection of the current serving cell and/or neighboring cells, but all of these events and/or triggers can measure and indicate the quality of the connection in both UL and DL. Events in the conventional HO procedure are defined to measure DL RS of a serving cell and/or a neighbor cell. In all events defined to trigger the HO procedure, it is only necessary to identify whether the terminal device is in good or bad DL coverage of the serving cell, or whether the terminal device is in good DL coverage of a neighboring cell. If the HO procedure is triggered, the serving cell of the terminal device is handed over to a neighboring cell in both UL and DL. The reason is that in legacy systems, such as operating at frequencies below 6GHz, the UL and DL always have similar coverage. The terminal device need only measure the RS (such as DL RS) in one direction to identify whether it is in or out of coverage of the serving cell and trigger the HO procedure accordingly.

In certain use cases, such as in 5G network systems, it is desirable to leverage the high frequency band with wide bandwidth to achieve large throughput to meet service requirements, such as enhanced mobile broadband (eMBB) services, especially for DL. However, based on the currently defined HO-related event, configuring the corresponding threshold defined in the HO-related event anyway will result in an earlier HO or a later HO, both of which are not optimal for high frequency band communication. For example, a high threshold configuration to ensure UL quality will result in premature HO to a new network device with a low frequency band, although the terminal device is still in good DL coverage on the high frequency band. On the other hand, if a smaller threshold is configured to wait for the terminal device to exceed DL coverage, a later HO can occur, which will severely impact UL performance because the terminal device has exceeded UL coverage long before the event is triggered.

Thus, the events and/or triggers used in conventional HO procedures may therefore not be directly applicable for triggering the UL-only link handover proposed herein, and more particularly for determining whether the terminal device 120 is in a link asymmetric state with DL-met and UL-not-met. The terminal device 120 may typically enter a link asymmetric state in a network deployment with asymmetric UL/DL coverage, such as in a cell of a network device operating in a high frequency band, such as the mmW band. Due to asymmetry, good DL coverage does not always refer to good UL coverage. Thus, in some embodiments of the present disclosure, a new event and/or procedure is proposed to evaluate UL and DL quality.

In one embodiment, the determination of the link asymmetry status is based on terminal device 120 measurements of DL reference signals. Specifically, terminal device 120 may determine the quality of the first DL (referred to as the first DL quality for purposes of discussion) by measuring DL Reference Signals (RSs) received from network device 111. The DL RS may be of any type, such as a channel state indication reference signal (CSI-RS) or the like. The DL reference signal may be transmitted by network device 111 periodically or by event triggering. Various methods for link quality estimation that currently exist or will be developed in the future may be applied. As some examples, the terminal device 120 may measure Reference Signal Received Power (RSRP), received signal strength indicator (RSRI), or Reference Signal Received Quality (RSRQ), etc., of the DL RS.

The terminal device 120 may then compare the first DL quality with a first threshold and a second threshold, respectively. The second threshold may be higher than the first threshold. If the first DL quality is above the first threshold, it indicates that terminal device 120 is still within good DL coverage and network device 111 may continue to utilize its operating frequency band in the first DL to serve terminal device 120 and obtain good or acceptable DL performance. If it is determined that the first DL quality is below the second threshold, this indicates that terminal device 120 is leaving the UL coverage area of network device 111, such as UL coverage area 103, and therefore cannot provide acceptable UL service on the frequency band of network device 111 in the near future.

The first threshold and the second threshold may be preconfigured by network device 111 to terminal device 120. The first threshold may be configured according to DL requirements and according to which aspect of DL RS is measured. The second threshold may be configured based on UL requirements to reflect the UL situation of the terminal device 120 by means of the first DL quality of the first DL. The specific values of the first threshold and the second threshold may be determined according to actual implementations, and the scope of the present disclosure is not limited in this respect.

If the first DL quality is determined to be above the first threshold and below the second threshold, the terminal device 120 determines that the first DL is satisfied and the second DL is not, and identifies that it is in a link asymmetry state. In some embodiments, the terminal device 120 may monitor whether the first DL quality is above a first threshold for a first predetermined time period and/or whether the first DL quality is below a second threshold for a second predetermined time period in order to avoid momentary movement, possibly inaccurate quality estimates, and/or other reasons. The first predetermined time period and the second predetermined time period may be preconfigured to be the same or different, depending on DL and UL requirements.

End device 120 may transmit a status indication to network device 111 indicating that end device 120 is in a link asymmetric state. Upon receiving such a status indication, network device 111 may determine that end device 120 is in a link asymmetric state. In some embodiments, terminal device 120 may report a first DL quality of the first DL to network device 111, and network device 111 determines whether terminal device 120 is in a link asymmetry state by comparing the received first DL quality to a first threshold and a second threshold in a similar manner as terminal device 120.

Alternatively or additionally, the determination of the link asymmetry status is based on terminal device 120 measurements of DL RS and network device 111 measurements of UL RS. Network device 111 may determine the UL quality of the first UL (referred to as the first UL quality for discussion purposes) by measuring the UL RS transmitted from terminal device 120. The UL RS may be of any type, such as Sounding Reference Signal (SRS), and the like. The UL reference signal may be transmitted by the terminal device 120 periodically or by event triggering. Various methods for link quality estimation that currently exist or will be developed in the future may be applied. As some examples, network device 111 may measure Reference Signal Received Power (RSRP), received signal strength indicator (RSRI), or Reference Signal Received Quality (RSRQ) of the UL RS, among others.

Network device 111 may then compare the first UL quality to a third threshold. The third threshold may be set to any value depending on UL requirements and actual implementation. The scope of the present disclosure is not limited in this respect. The third threshold may be the same as or different from the second threshold as described above. If the first UL quality is below the third threshold, e.g., for a predetermined period of time, network device 111 identifies that its UL frequency band cannot continue to provide good service to terminal device 120. Thus, network device 111 will make a coarse decision regarding UL link switching for terminal device 120.

In response, in some embodiments, network device 111 may request terminal device 120 to measure a first DL quality of the first DL in order to further confirm that terminal device 120 is within good DL coverage. The measurement of the first DL quality is similar to that discussed above. In other cases, terminal device 120 may always measure and report the first DL quality in case of low UL quality without any request from network device 111. After determining the first DL quality, the terminal device 120 may compare the first DL quality to a fourth threshold and transmit a quality indication (referred to as a first quality indication) to the first network device.

The first quality indication may indicate an explicit first DL quality, or specifically indicate that the first DL quality is below a fourth threshold. The fourth threshold may be configured based on UL requirements and may be the same as or different from the second threshold as described above. The specific value of the fourth threshold may be determined according to actual implementation, and the scope of the present disclosure is not limited in this respect. In the event that an explicit first DL quality is indicated to network device 111, network device 111 may compare the first DL quality to a fourth threshold to determine whether the first DL quality exceeds or falls below the threshold.

The first quality indication may be used to support network device 111 in determining the link asymmetry status of terminal device 120. For example, network device 111 may determine that terminal device 120 is in the link asymmetry state if the first UL quality is determined to be below a third threshold and the first DL quality is determined to be above a fourth threshold.

In some embodiments where terminal device 120 is determined to be in a link asymmetric state, network device 111 may determine to transmit a UL link switch indication to trigger a UL-only link switch for terminal device 120, assuming terminal device 120 is always within good UL coverage of network device 112. In some embodiments, the UL quality of the second UL may be evaluated in addition to the link asymmetry status. If the UL quality of the second UL is met, network device 111 determines that terminal device 120 can switch from the first UL to the second UL.

In some embodiments, if the UL and DL quality in the coverage of cell 101 is symmetric, network device 111 may request terminal device 120 to measure the DL (referred to as the second DL for discussion purposes) from network device 112 to terminal device 120 and evaluate whether the second DL is sufficient to allow only UL link handover based on the quality of the second DL. More specifically, the network device 111 may transmit synchronization information and related information about the second DL to the terminal device 120 to support quality measurement of the second DL. The synchronization information is used to synchronize the terminal device 120 with the network device 112 at least in the DL direction in order to benefit the measurement of DL RS transmitted from the network device 112.

The synchronization information may include, for example, DL synchronization related signaling, measurement gaps, DL control channels of the network device 112, and so on. In some embodiments, the related information about the second DL may include one or more of: DL RS (such as CSI-RS), Primary Synchronization Signal (PSS), Secondary Synchronization Signal (SSS), information about measurement gaps, etc., to be transmitted by network device 112. The synchronization related information may be pre-configured and sent to the terminal device 120 immediately after the terminal device 120 accesses the network device 111 system, or triggered by an event, for example, after identifying that the terminal device 120 is in a link asymmetric state.

Based on the received information, terminal device 120 may perform DL synchronization with network device 112 in the DL direction. The terminal device 120 may determine the second DL quality of the second DL by measuring the DL RS transmitted from the network device 112 (referred to as the second DL RS). If the terminal device 120 determines that the second quality is above the fifth threshold, it is an indication that the terminal device 120 is in good DL coverage. Terminal device 120 may transmit a second quality indication to network device 111 indicating a second DL quality. The second quality indication may indicate an explicit second DL quality or specifically indicate that the second DL quality is below a fifth threshold. The fifth threshold may be configured based on DL/UL requirements in the cell 102. The specific value of the fifth threshold may be determined according to actual implementation, and the scope of the present disclosure is not limited in this respect. In the case where an explicit second DL quality is indicated to network device 111, it may compare the second DL quality to a fifth threshold to determine whether the second DL quality exceeds or falls below the threshold.

Upon receiving the second quality indication, network device 111 may determine that terminal device 120 is within good UL coverage of network device 112 due to DL and UL symmetry in cell 101. In this way, network device 111 may then decide to trigger an UL-only link handover for terminal device 120.

The determination of the triggering of the UL-only link handover has been described above. It is to be appreciated that in the process of measuring UL/DL quality, if it is determined that neither the first UL nor the first DL meets the corresponding requirements (below the corresponding thresholds), which indicates that network device 111 cannot provide either satisfactory UL coverage or satisfactory DL coverage, then a normal HO procedure may be triggered to handover both the UL and DL of terminal device 120 to another network device, such as network device 112.

In the following, some embodiments are provided regarding how to implement an UL-only link handover from network device 111 to network device 112. As described above, after network device 111 decides on UL-only link handover for terminal device 120, network device 111 transmits a UL link handover indication to trigger such UL link handover. In some embodiments, UL-only link switching may be achieved by configuring a virtual serving cell based on the frequency band of network device 112.

In particular, network device 111 may configure a virtual serving cell (referred to as a first virtual serving cell) for terminal device 120. The operating frequency band of the first virtual serving cell is a frequency band (e.g., UL operating frequency band) that is paired with the frequency band (more specifically, UL frequency band) of the network device 112. Thus, the (UL) band of the network device 112 may be configured as a virtual UL carrier in the first virtual serving cell. In addition, the operating frequency band of the first serving cell may be configured as the DL frequency band of network device 111. An Identification (ID) of the first virtual serving cell may be assigned to identify the virtual cell, e.g., via a virtual Carrier Indication Field (CIF). Network device 111 may transmit configuration information, referred to as first configuration information, to terminal device 120 to configure the first virtual cell, e.g., via Radio Resource Control (RRC) signaling.

The first configuration information may include at least an operating frequency band and/or an ID of the first virtual serving cell, and the like. For example, the first configuration information may be transmitted after terminal device 120 accesses network device 111. In some embodiments, the first configuration information or additional configuration information will be sent to terminal device 120 to convey information related to the frequency band used by network device 112 for UL transmissions, such as information about the UL Physical Random Access Channel (PRACH), configuration about the UL Physical Uplink Control Channel (PUCCH), UL synchronization information, and so forth.

After network device 111 decides to allow terminal device 120 to switch only the first UL and maintain the first DL, for example, after acquiring an acknowledgement from network device 112 regarding the request for UL link switching, network device 111 may transmit an UL link switch indication to terminal device 120. In some embodiments, layer 2(L2) signaling may be transmitted as a UL link switch indication to the terminal device 120 to activate the first virtual serving cell. At this time, the previous serving cell (i.e., cell 101) of the terminal device 120 may be deactivated. As an example, network device 111 may transmit an L2 Media Access Control (MAC) Control Element (CE) to activate the first virtual serving cell. Other specific elements in L2 may also be used. The ID of the first virtual serving cell may be included in the L2 signaling to identify the virtual cell.

Upon receiving a UL link switch indication, such as L2 signaling, the terminal device 120 determines that the first virtual serving cell to activate is a previously configured cell. In this way, terminal device 120 identifies that the current first UL with network device 111 is to be switched to the second UL without affecting the current first DL. Thus, terminal device 120 will operate in the frequency band of network device 112 in the UL direction and in the frequency band of network device 111 in the DL direction.

Alternatively, network device 111 may perform cross-network device virtual bandwidth part (BWP) configuration. Network device 111 may configure terminal device 120 with a virtual serving cell (referred to as a second virtual serving cell). The operating band of the second virtual serving cell may include the band (e.g., UL band) of

network devices

111, 112 as two different BWPs of the second virtual serving cell, referred to as a first BWP and a second BWP, corresponding to the band of

network devices

111, 112, respectively. These two BWPs may be used for UL transmission in the second virtual serving cell. A corresponding virtual ID may be assigned to the BWP. With such second configuration information, for terminal device 120 that is within normal DL and UL coverage of cell 101, the first BWP corresponding to the band of network device 111 is activated so that terminal device 120 can communicate with network device 111 in both UL and DL.

Network device 111 may transmit configuration information, referred to as second configuration information, to terminal device 120, e.g., via Radio Resource Control (RRC) signaling, to configure the second virtual cell. The second configuration information may include at least two BWPs of the second virtual serving cell and/or their respective IDs, etc. For example, the second configuration information may be transmitted after terminal device 120 accesses network device 111. For example, the second configuration information may be transmitted after terminal device 120 accesses network device 111. In some embodiments, the second configuration information or additional configuration information will be sent to terminal device 120 to convey information about the frequency band used by network device 112 for UL transmissions, such as information about UL PRACH, configuration about UL PUCCH, UL synchronization information, and so forth.

If network device 111 determines to allow terminal device 120 to switch only the first UL and maintain the first DL, network device 111 may transmit an UL link switch indication to terminal device 120, e.g., after obtaining an acknowledgement from network device 112 regarding the request for UL link switch. In some embodiments, layer 1(L1) signaling may be transmitted as a UL link switch indication to terminal device 120 to activate a second BWP for a second virtual serving cell corresponding to the band of network device 112. The L1 signaling may include Downlink Control Information (DCI) for BWP handover. Upon receiving the L1 signaling, terminal device 120 determines that the current first UL with network device 111 is to be switched to the second UL without affecting the current first DL. Thus, terminal device 120 will operate in the frequency band of network device 112 in the UL direction and in the frequency band of network device 111 in the DL direction.

In the above embodiment, since L1 and L2 signaling cannot carry much information, the configuration information related to the virtual serving cell may be previously provided in advance. In some embodiments, if network device 111 determines to allow terminal device 120 to switch only the first UL and maintain the first DL, network device 111 may transmit RRC signaling as the UL link switch indication. Upon receiving RRC signaling, terminal device 120 may switch to the second UL for UL transmission and continue to maintain DL transmission in the first DL.

The RRC signaling may indicate to the terminal device 120 a handover of the first UL to the second UL while maintaining the first DL. In some embodiments, the RRC signaling may also include configuration information about the frequency band of the network device 112, such as UL information about the UL PRACH, configuration about the UL PUCCH, UL synchronization information, and so on. In this manner, network device 111 may not need to pre-configure information regarding the frequency band of network device 112 in advance. RRC signaling may be included in the RRC message to trigger UL link switching. This is because the UL link switch command is based on an RRC message with an opportunity to include the necessary configuration information along with the message.

For the link switching procedure, one of the tasks is how to handle ongoing/pending DL/UL data transmission activities. In normal HO procedures, all pending UL and DL data transmission activities will be released, e.g., buffers for DL and UL retransmission procedures are flushed, DL and UL retransmission procedures may be released, etc. This is because in normal HO procedures the security key used for data processing can be changed and therefore all pending transmissions have to be released. Therefore, previously buffered packets such as L2 packets cannot be processed in the new serving cell. After the normal HO procedure, unacknowledged data packets, such as Internet Protocol (IP) packets, will be forwarded to the HO target cell for retransmission.

In an embodiment of the present disclosure, terminal device 120 only switches the UL to network device 112 and maintains its DL in the previous network device 111. The conventionally defined HARQ release behavior may not be optimal for UL link handover only scenarios, at least not for DL performance improvement. Therefore, different processing methods may be applied.

In some embodiments, for DL transmission by terminal device 120, the DL transmission and reception points (network device 111 and terminal device 120) remain the same since there is no DL link handover. The security keys used for data processing in DL transmission may not change. Thus, if there is a pending DL retransmission process, such as a hybrid automatic repeat request (HARQ) process, the terminal device 120 may maintain a buffer for that process with the security key unchanged. In some embodiments, after the UL link switch is complete, network device 111 may have an opportunity to retransmit the data in the pending DL retransmission process. In this way, better efficiency in DL transmission may be provided compared to normal HO procedures. Network device 111 may also instruct terminal device 120 to release the pending DL retransmission procedure by a new transmission indication.

The handling of UL transmissions depends on whether the security key used for data handling is changed during UL retransmissions. For a better understanding of the UL/DL transmission process after UL-only link handover, reference is again made to fig. 2.

As shown, network device 111 transmits 220 a key-related indication to terminal device 120. The key-related indication indicates to the terminal device 120 whether the security key of the data processing is to be changed after the handover. Here, the security key is a key applied during a pending uplink retransmission of the terminal device 120. The key related indication may be transmitted to the terminal device 120, for example, via RRC signaling. Although shown separately, in some embodiments, the key related indication may be signaled to the terminal device 120 along with the UL handover indication. For example, if the UL handover indication is transmitted as RRC signaling, the key related indication may also be combined in RRC signaling. In some other examples, the key-related indication may be included in configuration information (such as the configuration information first or second configuration information described above) for terminal device 120.

Whether to change the security key depends on various factors and may be determined by network device 111, network device 112, or a negotiation between them. The scope of the present disclosure is not limited in this respect. The terminal device 120 may determine how to perform UL transmissions, in particular how to handle pending UL retransmission procedures, based on whether the security key has changed.

In some embodiments, the security key for UL transmissions may be indicated as having changed due to the terminal device 120 switching to a new UL. The security keys used for UL/DL transmission/reception may then be different from the point of view of the terminal device 120. In such a case, the terminal device 120 may release the buffer for the pending UL retransmission process, e.g., after switching to the second UL. The reason is that buffered UL packets to be used for retransmission are handled by a security key that is different from the security key used in the first UL. All higher layer entities for the pending process may be released and a new higher layer entity may be established according to the schedule from the network device 112. As such, if transmitted in the second UL, none of the buffered data can be processed by the network device 112, such as a Packet Data Convergence Protocol (PDCP) entity for the terminal device 120, even if the data is decoded correctly at L1. By releasing the buffer, unacknowledged UL packets can be retransmitted at higher layers after the UL link switch is completed.

Yet another possibility is that even if the terminal device 120 switches to the second UL, the previous security key used in the first UL remains unchanged and can continue to be used for UL transmissions. Therefore, in both UL/DL transmission/reception of the terminal device 120, the same security key as in the first UL and DL of the network device 111 is used. In such a case, the current UL retransmission activity need not be released. The terminal device 120 may maintain a buffer for pending UL retransmission processes with the security key unchanged. Thus, after only the UL link switch is complete, the network device 112 may be able to immediately schedule UL retransmissions. In this way, UL transmission efficiency can be improved.

Network device 112 may obtain the security key from network device 111, e.g., via a backhaul link, if the security key for the UL transmission of terminal device 120 has not changed. Network device 111 may send the same key-related indication to network device 112 to indicate whether the security key used in the UL transmission of terminal device 120 changed. In the event that the security key is unchanged, network device 112 may use different security keys to process UL data received from two different types of terminal devices. The first type is a terminal device served by network device 112 in both UL and DL using UL and DL frequency bands, respectively. For such types of terminal devices, UL data may be processed by network device 112 using a security key generated by network device 112. The second type is a terminal device that only switches its UL to the network device 112 and whose security key remains unchanged.

In an embodiment, network device 111 indicates that the security key has not changed after a UL-only link handover. Network device 111 may forward configuration information related to pending UL retransmission processes for terminal device 120 to assist network device 112 in scheduling and processing UL transmissions from terminal device 120. The configuration information may include one or more of the following: unchanged security keys, process ID, packet size of pending uplink retransmission processes, any other information related to the process and/or buffer, etc. With the configuration information, network device 112 may be able to properly schedule UL transmissions for terminal device 120.

As shown in fig. 2, in an UL transmission from the terminal device 120 to the network device 112, the network device 112 transmits 225 the scheduling information to the terminal device 120 with or without a change in the security key. The scheduling information may be transmitted as, for example, DCI, and may be used to indicate to terminal device 120 the resources, transmission mode, and/or other information needed for UL transmission. In the event of a security key change, network device 112 may schedule UL transmissions for terminal device 120 in the normal manner. The terminal device 120 transmits 230UL data to the network device 112 based on the scheduling information. To perform UL transmissions, terminal device 120 may synchronize with network device 112 in the UL direction. The synchronization information in the UL may be preconfigured by network device 111.

In case the security key does not change, the scheduling information may indicate to the terminal device 120 that a self-decodable data retransmission is to be scheduled on the pending UL retransmission process. The terminal device 120 can transmit a self-decodable version of the UL data to the network device 112 using the unchanged security key. In some embodiments, the self-decodable data retransmission may be scheduled in the first retransmission of a pending UL retransmission process. As such, after an UL-only link switch, the network device 112 may successfully decode the self-decodable version of the UL data without any prior information that facilitates the combining of the UL data. If the scheduled first retransmission is not self-decodable without any prior information about the pending UL retransmission process, then the network device 112 may not be able to successfully decode the retransmitted UL data even if the second UL with the network device 112 is good for the terminal device 120.

In some embodiments, if the scheduling information indicates a non-self-decodable retransmission to be scheduled in a pending UL retransmission, in particular if the non-self-decodable retransmission is the first scheduled retransmission on the pending process, the terminal device 120 may discard the scheduling information and wait for a later scheduling. In some embodiments, if the scheduling information indicates a new UL retransmission process from the terminal device 120 to the network device 112, the terminal device 120 may release the buffer for the pending UL retransmission process.

Fig. 3 illustrates a flowchart of an example method 300 implemented at a terminal device, in accordance with some embodiments of the present disclosure. For purposes of discussion, the method 300 will be described with reference to fig. 1 from the perspective of the terminal device 120.

At block 310, terminal device 120 receives an uplink handover indication from a first network device, the first network device serving a first cell using a first frequency band. At block 320, terminal device 120 switches from a first uplink with a first network device to a second uplink with a second network device using a second frequency band to serve a second cell based on the uplink switch indication while maintaining a first downlink with the first network device.

In some embodiments, the first frequency band is higher than the second frequency band. In some embodiments, the first cell includes a downlink coverage area and an uplink coverage area, the uplink coverage area being smaller than the downlink coverage area.

In some embodiments, when the uplink handover indication is received, the terminal device is in a link asymmetric state in which the first downlink meets the first downlink requirements and the first uplink does not meet the uplink requirements.

In some embodiments, the method 300 further comprises: determining a first downlink quality of the first downlink by measuring a downlink reference signal received from the first network device; comparing the first downlink quality with a first threshold and a second threshold, respectively, the second threshold being higher than the first threshold and the second threshold being based on the uplink requirement; and in response to the first downlink quality being above the first threshold and below the second threshold, transmitting a status indication to the first network device indicating that the terminal device is in a link asymmetry state.

In some embodiments, the method 300 further comprises: determining a first downlink quality of the first downlink by measuring a first downlink reference signal received from the first network device; and in response to the first downlink quality being above the fourth threshold, transmitting a first quality indication indicative of the first downlink quality to the first network device to support the first network device in determining the link asymmetry status of the terminal device.

In some embodiments, the method 300 further comprises: receiving, from the first network device, synchronization related information related to a second downlink from the second network device to the terminal device; determining a second downlink quality of the second downlink by measuring a second downlink reference signal received from the second network device based on the synchronization related information; and in response to determining that the second downlink quality is above the fifth threshold, transmitting a second quality indication indicative of the second downlink quality to the first network device to support the first network device determining the handover of the first uplink.

In some embodiments, the method 300 further comprises: first configuration information is received from the first network device to configure a first virtual serving cell for the terminal device, the first virtual serving cell having the second frequency band as an operating frequency band of the first virtual serving cell. In some embodiments, terminal device 120 receives layer 2(L2) signaling as an uplink handover indication to activate the virtual serving cell.

In some embodiments, the method 300 further comprises: second configuration information is received from the first network device to configure a second virtual serving cell for the terminal device, the second virtual serving cell having the first frequency band and the second frequency band as a first bandwidth part (BWP) and a second BWP, respectively, of an operating frequency band of the second virtual serving cell. In some embodiments, end device 120 receives layer 1(L1) signaling as an uplink handover indication to activate the second BWP.

In some embodiments, receiving the uplink handover indication comprises: radio Resource Control (RRC) signaling is received as an uplink handover indication, the RRC signaling indicating a handover of a first uplink to a second uplink while maintaining a first downlink.

In some embodiments, the method 300 further comprises: receiving a key-related indication from the first network device, the key-related indication indicating whether a security key of the data processing is to be changed after the handover, the security key being applied during a pending uplink retransmission of the terminal device; and releasing the buffer for pending uplink retransmission procedures in response to the key-related indication indicating that the security key is to be changed.

In some embodiments, the method 300 further comprises: releasing a buffer for pending uplink retransmission procedures in response to the key-related indication indicating that the security key is to be changed; transmitting a self-decodable version of the uplink data to the second network device using the security key in response to the scheduling information indicating a self-decodable data retransmission to be scheduled in a pending uplink retransmission process; discarding the scheduling information in response to the scheduling information indicating a non-self-decodable retransmission to be scheduled during a pending uplink retransmission; and releasing the buffer for pending uplink retransmission processes in response to the scheduling information indicating a new uplink retransmission process from the terminal device to the second network device.

In some embodiments, the method 300 further comprises: a buffer for pending downlink retransmission processes for the terminal device is maintained, and the security keys for data processing during pending downlink retransmission processes are maintained unchanged.

Fig. 4 illustrates a flow diagram of an example method 400 implemented at a network device in accordance with some embodiments of the present disclosure. For purposes of discussion, method 400 will be described with reference to fig. 1 from the perspective of network device 111.

At block 410, network device 111 determines whether a first uplink of the terminal device and the network device is to be handed over, the network device serving a first cell using a first frequency band. In response to determining that the first uplink is to be switched, network device 111 transmits an uplink switch indication to the terminal device to trigger the terminal device to switch from the first uplink to a second uplink with a further network device (e.g., network device 112) serving a second cell using a second frequency band while maintaining the first downlink with the network device at block 420.

In some embodiments, determining whether the first uplink is to be switched comprises: determining whether the terminal device is in a link asymmetric state in which the first downlink meets first downlink requirements and the first uplink does not meet uplink requirements; and in response to determining that the terminal device is in the link asymmetry state, determining that the first uplink is to be switched.

In some embodiments, determining whether the first uplink is to be switched comprises: receiving a status indication from the terminal device indicating that the terminal device is in a link asymmetry state, the status indication being based on a first downlink quality of the first downlink being above a first threshold and below a second threshold, the second threshold being above the first threshold.

In some embodiments, determining whether the terminal device is in the link asymmetric state comprises: determining a first uplink quality of a first uplink by measuring uplink reference signals transmitted from a terminal device; requesting the terminal device to measure a first downlink quality of the first downlink in response to the first uplink quality being below a third threshold; and determining that the terminal device is in the link asymmetry state in response to the first quality indication received from the terminal device indicating that the first downlink quality is above the fourth threshold.

In some embodiments, determining whether the first uplink is to be switched comprises: transmitting a request to the further network device to switch the terminal device from the first uplink to the second uplink; and determining that the first uplink is to be switched in response to receiving an acknowledgement of the request from the further network device.

In some embodiments, transmitting the uplink handover indication comprises: transmitting synchronization related information to the terminal device on a second downlink from the further network device to the terminal device; receiving a second quality indication from the terminal device indicating a third quality of the second downlink; and transmitting the uplink handover indication further based on the determination that the third quality is above the third threshold.

In some embodiments, the method 400 further comprises: the first configuration information is transmitted from the first network device to configure a first virtual serving cell for the terminal device, the first virtual serving cell having the second frequency band as an operating frequency band of the first virtual serving cell. In some embodiments, network device 111 transmits layer 2(L2) signaling as an uplink handover indication to trigger the terminal device to activate the virtual serving cell.

In some embodiments, the method 400 further comprises: and transmitting second configuration information to the terminal device to configure a second virtual serving cell for the terminal device, wherein the second virtual serving cell takes the first frequency band and the second frequency band as a first bandwidth part and a second bandwidth part of an operating frequency band of the second virtual serving cell respectively. In some embodiments, network device 111 transmits layer 1(L1) signaling as an uplink handover indication to trigger the end device to activate the second BWP.

In some embodiments, transmitting the uplink switching indication comprises transmitting the uplink switching indication as Radio Resource Control (RRC) signaling indicating a switch from the first uplink to the second uplink while maintaining the first downlink.

In some embodiments, the method 400 further comprises: transmitting a key-related indication to the terminal device and the further network device, the key-related indication indicating whether a security key of the data processing is to be changed after the handover, the security key being applied during a pending uplink retransmission of the terminal device; and transmitting configuration information relating to the pending uplink retransmission process to the further network device, the configuration information comprising at least one of: security keys, process identification and packet size of pending uplink retransmission processes.

Fig. 5 illustrates a flow diagram of an example method 500 implemented at a network device in accordance with some embodiments of the present disclosure. For purposes of discussion, the method 500 will be described with reference to fig. 1 from the perspective of the network device 112.

At block 510, network device 112 receives a request from a further network device (e.g., network device 111) to switch a terminal device from a first uplink with the further network device to a second uplink with the network device, the further network device serving a first cell with a first frequency band and the network device serving a second cell with a second frequency band. At block 520, the network device 112 determines whether the handover is accepted. At block 530, in response to determining that the handover is accepted, the network device 112 transmits an acknowledgement to the further network device regarding the request. At block 540, the network device 112 establishes a second uplink with the terminal device, which maintains the first downlink with the further network device.

In some embodiments, the method 500 further comprises: receiving a key-related indication from the further network device, the key-related indication indicating whether a security key for data processing of the terminal device is to be changed after the handover, the security key being applied during a pending uplink retransmission of the terminal device. In some embodiments, the method 500 further comprises: receiving configuration information relating to a pending uplink retransmission process from a further network device, the configuration information comprising at least one of: security keys, process identification and packet size of pending uplink retransmission processes.

In some embodiments, the method 500 further comprises: transmitting scheduling information to the terminal device in response to the key-related indication indicating that the security key remains unchanged, the scheduling information indicating a self-decodable data retransmission to be performed on a pending uplink retransmission process; and decoding a self-decodable version of the uplink data received from the terminal device using the security key.

In some embodiments, an apparatus (e.g., terminal device 120) capable of performing any of method 300 may include means for performing the respective steps of method 300. The module may be implemented in any suitable form. For example, the module may be implemented in circuitry or a software module.

In some embodiments, the apparatus comprises: means for receiving, at a terminal device, an uplink handover indication from a first network device, the first network device serving a first cell using a first frequency band; and means for switching from a first uplink with the first network device to a second uplink with a second network device using a second frequency band while maintaining the first downlink with the first network device based on the uplink switch indication.

In some embodiments, the apparatus also includes means for performing other steps in some embodiments of the method 300. In some embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause execution of the apparatus.

In some embodiments, an apparatus (e.g., network device 111) capable of performing any of method 400 may include means for performing the respective steps of method 400. The module may be implemented in any suitable form. For example, the module may be implemented in circuitry or a software module.

In some embodiments, the apparatus comprises: means for determining, at a network device, whether a first uplink of a terminal device and the network device is to be handed over, the network device serving a first cell using a first frequency band; and means for transmitting an uplink handover indication to the terminal device to trigger the terminal device to switch from the first uplink to maintain the first downlink with the network device concurrently with a second uplink of a further network device that serves the second cell using the second frequency band in response to determining that the first uplink is to be switched.

In some embodiments, the apparatus also includes means for performing other steps in some embodiments of the method 400. In some embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause execution of the apparatus.

In some embodiments, an apparatus (e.g., network device 112) capable of performing any of method 500 may include means for performing the respective steps of method 500. The module may be implemented in any suitable form. For example, the module may be implemented in circuitry or a software module.

In some embodiments, the apparatus comprises: means for receiving, at a network device, a request from a further network device to switch a terminal device from a first uplink with the further network device to a second uplink with the network device, the further network device serving a first cell with a first frequency band, the network device serving a second cell with a second frequency band; means for transmitting an acknowledgement to the further network device regarding the request in response to determining that the handover is accepted; and means for establishing a second uplink with the terminal device, the terminal device maintaining the first downlink with the further network device.

In some embodiments, the apparatus also includes means for performing other steps in some embodiments of the method 500. In some embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause execution of the apparatus.

Fig. 6 shows a simplified block diagram of an apparatus 600, which apparatus 600 may be implemented as or included in terminal device 120, network device 111, or network device 112 shown in fig. 1 to implement embodiments of the present disclosure.

The apparatus 600 includes at least one processor 611, such as a Data Processor (DP), and at least one memory (MEM)612 coupled to the processor 611. The apparatus 600 may also include a transmitter TX and a receiver RX 613 coupled to the processor 611, which processor 611 may be operable to communicatively connect to other apparatuses. The MEM 612 stores program or computer program code 614. The at least one memory 612 and the computer program code 614 are configured to, with the at least one processor 611, cause the apparatus 500 at least to perform operations according to embodiments of the present disclosure, such as the

method

300, 400 or 500.

The combination of the at least one processor 611 and the at least one MEM 612 may form a processing apparatus 615 configured to implement various embodiments of the present disclosure.

Various embodiments of the disclosure may be implemented by computer programs, software, firmware, hardware, or a combination thereof executable by the processor 611.

The MEMs 612 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples.

The processor 611 may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, Digital Signal Processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples.

Although some of the above descriptions regarding GD-based signal detection and hierarchical signal detection are made in the context of the wireless communication system shown in fig. 1, they should not be construed as limiting the spirit and scope of the present disclosure. The principles and concepts of the present disclosure may be more generally applicable to other scenarios.

Additionally, the present disclosure may also provide a carrier containing a computer program (e.g., computer instructions/program code 614 in fig. 6) as described above. The carrier includes computer readable storage media and transmission media. The computer-readable storage medium may include, for example, an optical or electronic memory device, such as a RAM (random access memory), ROM (read only memory), flash memory, magnetic tape, CD-ROM, DVD, blu-ray disc, and so forth. Transmission media may include, for example, electrical, optical, radio, acoustic, or other forms of propagated signals, such as carrier waves, infrared signals, and the like.

In general, the various embodiments of the disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some 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 various aspects of the embodiments of the disclosure are illustrated and 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.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, that execute in the device on the target real or virtual processor to perform the

methods

300, 400 or 500 described above with reference to fig. 3 and 4. Generally, program modules include routines, programs, libraries, objects, classes, components, data types, etc. that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. 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.

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

In the context of the present disclosure, computer program code or related data may be carried by any suitable carrier to enable a device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium.

The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer 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 of the foregoing. More specific examples of a computer-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 fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination thereof.

For purposes of the present disclosure as described herein above, it should be noted,

method steps (as examples of devices, apparatuses and/or modules thereof, or as examples of entities including apparatuses and/or modules) that may be implemented as software code portions and run using a processor at a network element or terminal are independent of the software code and may be specified using any known or future developed programming language as long as the functionality defined by the method steps is preserved;

in general, any method step is suitable to be implemented as software or by hardware without changing the idea of the invention in terms of the functions implemented;

the method steps and/or the devices, units or components that may be implemented at the above-described apparatus as hardware components, or any module or modules thereof (e.g. a device performing the functionality of an apparatus according to embodiments described above, eNode-B, etc.) are hardware-independent and may be implemented using any known or future developed hardware technology or any mixture of these technologies (such as MOS (metal oxide semiconductor), CMOS (complementary MOS), BiMOS (bipolar MOS), BiCMOS (bipolar CMOS), ECL (emitter coupled logic), TTL (transistor-transistor logic), etc.), e.g. using ASIC (application specific IC (integrated circuit)) components, FPGA (field programmable gate array) components, CPLD (complex programmable logic device) components, or DSP (digital signal processor) components;

a device, unit or component (e.g. any of the means defined above or their respective modules) may be implemented as an individual device, unit or component, but this does not exclude that they are implemented in a distributed manner throughout the system, as long as the functionality of the device, unit or component is preserved; an apparatus may be represented by a semiconductor chip, a chip set or a (hardware) module comprising such a chip or chip set; however, this does not exclude the possibility of: the functionality of the apparatus or module is not implemented in hardware, but as software in a (software) module, such as a computer program or a computer program product comprising executable software code portions for execution/running on a processor;

an apparatus may be considered to be a device or an assembly of more than one device, whether functionally cooperating or functionally independent of each other, for example.

Note that the above embodiments and examples are provided for illustrative purposes only, and are in no way intended to limit the present disclosure thereto. On the contrary, it is intended to cover all alternatives and modifications as fall within the spirit and scope of the appended claims.

Further, 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 and parallel processing may be advantageous. Also, while the above discussion contains several specific implementation details, these should not be construed as limitations on the scope of the disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described 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 disclosure has been described in language specific to structural features and/or methodological acts, it is to be understood that the disclosure defined in the appended claims is not necessarily 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.

Various embodiments of the techniques have been described. In addition to or instead of the above, the following examples are described. The functionality described in any of the examples below may be used with other examples described herein.

Claims

1. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code;

the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus to:

receiving, at a terminal device, an uplink handover indication from a first network device, the first network device serving a first cell using a first frequency band, and

switching from a first uplink with the first network device to a second uplink with a second network device serving a second cell using a second frequency band based on the uplink switch indication while maintaining a first downlink with the first network device.

2. The apparatus of claim 1, wherein the first frequency band is higher than the second frequency band, and

wherein the first cell includes a downlink coverage area and an uplink coverage area, the uplink coverage area being smaller than the downlink coverage area.

3. The apparatus of claim 1, wherein when the uplink switching indication is received, the terminal device is in a link asymmetric state in which the first downlink meets first downlink requirements and the first uplink does not meet uplink requirements.

4. An apparatus of claim 3, wherein the apparatus is further caused to:

determining a first downlink quality of the first downlink by measuring a downlink reference signal received from the first network device;

comparing the first downlink quality to a first threshold and a second threshold, respectively, the second threshold being higher than the first threshold and the second threshold being based on the uplink requirement; and

transmitting, to the first network device, a status indication indicating that the terminal device is in the link asymmetry state in response to the first downlink quality being above the first threshold and below the second threshold.

5. An apparatus of claim 3, wherein the apparatus is further caused to:

determining a first downlink quality of the first downlink by measuring a first downlink reference signal received from the first network device; and

in response to the first downlink quality being above a fourth threshold, transmitting a first quality indication indicative of the first downlink quality to the first network device to support the first network device in determining the link asymmetry status of the terminal device.

6. An apparatus of claim 1, wherein the apparatus is further caused to:

receiving, from the first network device, synchronization related information related to a second downlink from the second network device to the terminal device;

determining a second downlink quality of the second downlink by measuring a second downlink reference signal received from the second network device based on the synchronization related information; and

in response to determining that the second downlink quality is above a fifth threshold, transmitting a second quality indication indicative of the second downlink quality to the first network device to support the first network device determining the handover of the first uplink.

7. An apparatus of claim 1, wherein the apparatus is further caused to:

receiving first configuration information from the first network device to configure a first virtual serving cell for the terminal device, the first virtual serving cell having the second frequency band as an operating frequency band of the first virtual serving cell, and

wherein the apparatus is caused to receive layer 2(L2) signaling as the uplink handover indication to activate the virtual serving cell.

8. An apparatus of claim 1, wherein the apparatus is further caused to:

receiving second configuration information from the first network device to configure a second virtual serving cell for the terminal device, the second virtual serving cell having the first frequency band and the second frequency band as a first bandwidth part (BWP) and a second BWP, respectively, of an operating frequency band of the second virtual serving cell,

wherein the device is caused to receive layer 1(L1) signaling as the uplink handover indication to activate the second BWP.

9. The apparatus of claim 1, wherein the apparatus is caused to:

receiving Radio Resource Control (RRC) signaling as the uplink switching indication, the RRC signaling indicating a switching of the first uplink to the second uplink while maintaining the first downlink.

10. An apparatus of claim 1, wherein the apparatus is further caused to:

receiving a key-related indication from the first network device indicating whether a security key of data processing is to be changed after the handover, the security key being applied during a pending uplink retransmission process of the terminal device; and

releasing a buffer for the pending uplink retransmission process in response to the key-related indication indicating that the security key is to be changed.

11. An apparatus of claim 10, wherein the apparatus is further caused to:

receiving scheduling information from the second network device in response to the key-related indication indicating that the security key remains unchanged;

transmitting a self-decodable data retransmission to the second network device using the security key in response to the scheduling information indicating that a self-decodable data retransmission is to be scheduled in the pending uplink retransmission process;

discarding the scheduling information in response to the scheduling information indicating a non-self-decodable retransmission to be scheduled during the pending uplink retransmission; and

releasing the buffer for the pending uplink retransmission process in response to the scheduling information indicating a new uplink retransmission process from the terminal device to the second network device.

12. An apparatus of claim 1, wherein the apparatus is further caused to:

maintaining a buffer of pending downlink retransmission processes for the terminal device, security keys for data processing during the pending downlink retransmission processes being maintained unchanged.

13. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code;

at a network device, determining whether a first uplink of a terminal device and the network device is to be handed over, the network device serving a first cell using a first frequency band, an

In response to determining that the first uplink is to be switched, transmitting an uplink switching indication to the terminal device to trigger the terminal device to switch from the first uplink to a second uplink with a further network device serving a second cell using a second frequency band while maintaining the first downlink with the network device.

14. The apparatus of claim 13, wherein the first frequency band is higher than the second frequency band, and

15. An apparatus of claim 13, wherein the apparatus is caused to:

determining whether the terminal device is in a link asymmetric state in which the first downlink meets first downlink requirements and the first uplink does not meet uplink requirements; and

determining that the first uplink is to be switched in response to determining that the terminal device is in the link asymmetry state.

16. The apparatus of claim 15, wherein the apparatus is caused to:

receiving a status indication from the terminal device indicating that the terminal device is in the link asymmetry state, the status indication being based on a first downlink quality of the first downlink being above a first threshold and below a second threshold, the second threshold being above the first threshold.

17. The apparatus of claim 15, wherein the apparatus is caused to:

determining a first uplink quality of the first uplink by measuring uplink reference signals transmitted from the terminal device;

requesting the terminal device to measure a first downlink quality of the first downlink in response to the first uplink quality being below a third threshold; and

determining that the terminal device is in the link asymmetry state in response to the first quality indication received from the terminal device indicating that the first downlink quality is above a fourth threshold.

18. An apparatus of claim 13, wherein the apparatus is caused to:

transmitting a request to the further network device to switch the terminal device from the first uplink to the second uplink; and

determining that the first uplink is to be switched in response to receiving an acknowledgement from the further network device regarding the request.

19. An apparatus of claim 13, wherein the apparatus is caused to:

transmitting synchronization related information to the terminal device on a second downlink from the further network device to the terminal device;

receiving a second quality indication from the terminal device indicating a third quality of the second downlink; and

transmitting the uplink handover indication further based on a determination that the third quality is above a third threshold.

20. An apparatus of claim 13, wherein the apparatus is further caused to:

transmitting first configuration information from the first network device to configure a first virtual serving cell for the terminal device, the first virtual serving cell having the second frequency band as an operating frequency band of the first virtual serving cell,

wherein the device is caused to transmit layer 2(L2) signaling as the uplink handover indication to trigger the terminal device to activate the virtual serving cell.

21. An apparatus of claim 13, wherein the apparatus is further caused to:

transmitting second configuration information to the terminal device to configure a second virtual serving cell for the terminal device, the second virtual serving cell having the first frequency band and the second frequency band as a first bandwidth part and a second bandwidth part of an operating frequency band of the second virtual serving cell, respectively,

wherein the device is further caused to transmit layer 1(L1) signaling as the uplink handover indication to trigger the end device to activate the second BWP.

22. An apparatus of claim 13, wherein the apparatus is caused to:

transmitting the uplink switching indication as Radio Resource Control (RRC) signaling indicating a switching from the first uplink to the second uplink while maintaining the first downlink.

23. An apparatus of claim 13, wherein the apparatus is further caused to perform at least one of:

transmitting a key-related indication to the terminal device and the further network device, the key-related indication indicating whether a security key of the data processing is to be changed after the handover, the security key being applied during a pending uplink retransmission of the terminal device, and

transmitting configuration information relating to the pending uplink retransmission process to the further network device, the configuration information comprising at least one of: the security key, a process identification, and a packet size of the pending uplink retransmission process.

24. An apparatus, comprising:

at least one processor; and

at least one memory including computer program code;

receiving, at a network device, a request from a further network device to switch a terminal device from a first uplink with the further network device to a second uplink with the network device, the further network device serving a first cell with a first frequency band, the network device serving a second cell with a second frequency band;

transmitting an acknowledgement to the further network device regarding the request in response to determining that the handover is accepted; and

establishing the second uplink with the terminal device, the terminal device maintaining the first downlink with the further network device.

25. An apparatus of claim 24, wherein the apparatus is further caused to perform at least one of:

receiving a key-related indication from the further network device indicating whether a security key for data processing of the terminal device is to be changed after the handover, the security key being applied during a pending uplink retransmission of the terminal device; and

receiving configuration information relating to the pending uplink retransmission process from the further network device, the configuration information comprising at least one of: the security key, a process identification, and a packet size of the pending uplink retransmission process.

26. An apparatus of claim 24, wherein the apparatus is further caused to:

transmitting scheduling information to the terminal device in response to the key-related indication indicating that the security key remains unchanged, the scheduling information indicating a self-decodable data retransmission to be performed on the pending uplink retransmission process; and

decoding a self-decodable version of the uplink data received from the terminal device using the security key.

27. A method implemented at a terminal device, comprising:

receiving an uplink handover indication from a first network device, the first network device serving a first cell using a first frequency band; and

28. A method implemented at a network device, comprising:

determining whether a first uplink of a terminal device and the network device is to be handed over, the network device serving a first cell using a first frequency band; and

29. A method implemented at a network device, comprising:

receiving, from a further network device, a request to switch a terminal device from a first uplink with the further network device to a second uplink with the network device, the further network device serving a first cell with a first frequency band, the network device serving a second cell with a second frequency band;

30. An apparatus, comprising:

means for receiving, at a terminal device, an uplink handover indication from a first network device, the first network device serving a first cell using a first frequency band; and

means for switching from a first uplink with the first network device to a second uplink with a second network device serving a second cell with a second frequency band while maintaining a first downlink with the first network device based on the uplink switch indication.

31. An apparatus, comprising:

means for determining, at a network device, whether a first uplink of a terminal device with the network device is to be handed over, the network device serving a first cell using a first frequency band; and

means for transmitting an uplink handover indication to the terminal device to trigger the terminal device to handover from the first uplink to a second uplink with a further network device serving a second cell with a second frequency band while maintaining a first downlink with the network device in response to determining that the first uplink is to be handed over.

32. An apparatus, comprising:

means for receiving, at a network device from a further network device, a request to switch a terminal device from a first uplink with the further network device to a second uplink with the network device, the further network device serving a first cell using a first frequency band, the network device serving a second cell using a second frequency band;

means for transmitting an acknowledgement to the further network device regarding the request in response to determining that the handover is accepted; and

means for establishing the second uplink with the terminal device, the terminal device maintaining a first downlink with the further network device.

33. A non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method of claim 27, 28 or 29.