WO2020103152A1

WO2020103152A1 - Link switch in joint network deployments

Info

Publication number: WO2020103152A1
Application number: PCT/CN2018/117281
Authority: WO
Inventors: Tao Yang
Original assignee: Nokia Shanghai Bell Co., Ltd.
Priority date: 2018-11-23
Filing date: 2018-11-23
Publication date: 2020-05-28
Also published as: CN113170361A; CN113170361B

Abstract

Embodiments of the present disclosure relate to link switch in joint network deployment. A terminal device receives an uplink switch indication from a first network device, the first network device serving a first cell with a first frequency band. The terminal device switches, based on the uplink switch indication, from a first uplink with the first network device to a second uplink with a second network device while maintaining a first downlink with the first network device, the second network device serving a second cell with a second frequency band. The link switch as provided in the present disclosure is more flexible.

Description

LINK SWITCH IN JOINT NETWORK DEPLOYMENTS

FIELD

Embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to link switch in joint network deployments.

BACKGROUND

In the communications arena, there is a constant evolution ongoing in order to provide efficient and reliable solutions for utilizing wireless communication networks. Each new generation has it owns technical challenges for handling the different situations and processes that are needed to connect and serve devices connected to the wireless network. To meet the demand for wireless data traffic having increased since deployment of 4th generation (4G) communication systems, efforts have been made to develop an improved 5th generation (5G) or pre-5G communication system. The new communication systems can support various types of service applications for terminal devices.

In recent communication technologies, it has been proposed to deploy different types of cells jointly within a certain geographical area. The different types of cells may be overlapped with each other and are generally served by non-collocated network devices with respective frequency bands. Terminal devices located in the certain geographical areas may be connected to a network device and communicated therewith. Efficient communication solutions are still needed in such deployment.

SUMMARY

In general, example embodiments of the present disclosure provide a solution for link switch in joint network deployments.

In a first aspect, there is provided a device. The device comprises at least one processor; and at least one memory including computer program codes; the at least one memory and the computer program codes are configured to, with the at least one processor, cause the device to receive, at the terminal device, an uplink switch indication from a first network device, the first network device serving a first cell with a first frequency band; and switch, based on the uplink switch indication, from a first uplink with the first network device to a second uplink with a second network device while maintaining a frst downlink with the first network device, the second network device serving a second cell with a second frequency band.

In a second aspect, there is provided a device. The device comprises at least one processor; and at least one memory including computer program codes; the at least one memory and the computer program codes are configured to, with the at least one processor, cause the device to determine, at a network device, whether a first uplink of a terminal device with the network device is to be switched, the network device serving a first cell with a first frequency band; and in response to determining that the first uplink is to be switched, transmit 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 while maintaining a first downlink with the network device, the further network device serving a second cell with a second frequency band.

In a third aspect, there is provided a device. The device comprises at least one processor; and at least one memory including computer program codes; the at least one memory and the computer program codes are configured to, with the at least one processor, cause the device to receive, at a network device and 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; in response to determining that the switch is accepted, transmit a confirmation on the request to the further network device; and establish the second uplink with the terminal device, the terminal device maintaining a first downlink with the further network device.

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

In a fifth aspect, there is provided a method implemented at a network device. The method comprises determining whether a first uplink of a terminal device with the network device is to be switched, the network device serving a first cell with a first frequency band; and in response to determining that the first uplink is to be switched, transmitting 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 while maintaining a first downlink with the network device, the further network device serving a second cell with a second frequency band.

In a sixth aspect, there is provided a method implemented at a network device. The method comprises 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; in response to determining that the switch is accepted, transmitting a confirmation on the request to the further network device; and establishing the second uplink with the terminal device, the terminal device maintaining a first downlink with the further network device.

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

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

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

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

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

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

Fig. 2 illustrates a flowchart illustrating a process for link switch according to some embodiments of the present disclosure;

Fig. 3 illustrates a flowchart of a method implemented at a terminal device according to some embodiments of the present disclosure;

Fig. 4 illustrates a flowchart of a method implemented at a network device according to some embodiments of the present disclosure;

Fig. 5 illustrates a flowchart of a method implemented at a network device according to some other embodiments of the present disclosure; and

Fig. 6 illustrates a simplified block diagram of an apparatus that is suitable for implementing embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

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

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

References in the present disclosure to “one embodiment, ” “an embodiment, ” “an example embodiment, ” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases 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 other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “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” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.

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

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) :

(i) a combination of analog and/or digital hardware circuit (s) with software/firmware and

(ii) any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and memory (ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

As used herein, the term “communication network” refers to a network following any suitable communication standards, such as Long Term Evolution (LTE) , LTE-Advanced (LTE-A) , Wideband Code Division Multiple Access (WCDMA) , High-Speed Packet Access (HSPA) , Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the future fifth generation (5G) communication protocols, and/or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

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. The network device may refer to a base station (BS) or an access point (AP) , for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a NR NB (also referred to 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 a femto, a pico, and so forth, depending on the applied terminology and technology.

The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE) , a Subscriber Station (SS) , a Portable Subscriber Station, a Mobile Station (MS) , or an Access Terminal (AT) . The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA) , portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , USB dongles, smart devices, wireless customer-premises equipment (CPE) , an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD) , a vehicle, a drone, a medical device and applications (e.g., remote surgery) , an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts) , a consumer electronics device, a device 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 communication networks where a number of network devices are jointly deployed in a geographical area to serve respective cells, a terminal device may have an active connection with a network device when being located within the corresponding cell. In the active connection, the terminal device may communicate with that network device on the frequency band in both an uplink (UL) and a downlink (DL) . The terminal device may need to switch a link in one direction such as the UL to a further network device due to various reasons such as quality degradation in the UL.

Conventionally, the operating frequency band change or switch is realized by a handover (HO) procedure. The HO procedure will trigger the switch of both the UL and DL of a terminal device from a source network device to a target network device. However, in some use scenarios, it is more desirable to maintain the DL with the source network device due to a high DL quality and/or high DL thought with the source network device, a worse DL quality with the target network device, and/or the like.

According to embodiments of the present disclosure, there is providing a solution for link switch in joint network deployments. In the joint network deployments, different network devices services different cells with respective frequency bands. A terminal device has an UL and a DL with a first one of the different network devices. The first network device transmits an 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 the UL link switch indication in response to receiving a confirmation on such switch in UL. Upon receiving the UL link switch indication, the terminal device switches from the UL with the first network device to an UL with a second one of the different network devices while maintaining a DL with the first network device. The link switch as provided in the present disclosure is more flexible. As such, it is possible to maintain the DL with a good quality and change the UL with a deteriorated.

Principle and embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Reference is first made to Fig. 1, which illustrates an example communication system 100 in which embodiments of the present disclosure may be implemented. The system 100 includes a plurality of network devices, such as a network device 111 and a network device 112. The

network devices

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

The system 100 also includes one or more terminal devices, such as

terminal devices

120, 121, 122. The

terminal devices

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

network devices

111, 112 as long as the terminal devices located within the corresponding cells. In communication systems, an UL refers to a link in a direction from a terminal device to a network device, and a DL refers to a link in a direction from the network device to the terminal device. In addition to communicating the

terminal devices

120, 121, 122, the

network devices

111, 112 may also communicate with each other, for example, via a backhaul link.

It is to be understood that the number of network devices and terminal devices is only for the purpose of illustration without suggesting any limitations. The system 100 may include any suitable number of network devices and terminal devices adapted for implementing embodiments of the present disclosure. Although not shown, it would be appreciated that one or more terminal devices may be located in the

cell

101 or 102.

Communications in the communication system 100 may be implemented according to any proper communication protocol (s) , comprising, but not limited to, cellular communication protocols of the first generation (1G) , the second generation (2G) , the third generation (3G) , the fourth generation (4G) and the fifth generation (5G) and on the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Divided Multiple Address (CDMA) , Frequency Divided Multiple Address (FDMA) , Time Divided Multiple Address (TDMA) , Frequency Divided Duplexer (FDD) , Time Divided Duplexer (TDD) , Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Divided Multiple Access (OFDMA) and/or any other technologies currently known or to be developed in the future.

The coverage ranges of the cells 102, 104 of the network devices 111 is tightly related to the operating frequency bands of the

network devices

111, 112. Fig. 1 shows an example where the operating frequency bands of the network devices 111, 113 are different, with the operating frequency band of the network device 111 higher than the operating frequency band of the network device 112. It is very possible that the coverage range of the cell 101 is smaller than that of the cell 102, due to a more serious path-loss situation in the high frequency band system. In the shown example, the cell 101 is overlapped with the 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 small cell 101 may sometimes be referred to as a small cell and the network device 111 may be referred to as a small base station. As a specific example, the network device 111 may be operating at sub6GHz, such as 3.5 GHz, while the network device 112 may be operating at a millimetre-wave (mmW) frequency band, such as at 28 GHz. It is to be understood that other operating frequency bands are also possible for the

network devices

111, 112.

In some scenarios, the cell 101 and/or the cell 102 may have an asymmetric UL and DL budget. Such asymmetric budget easily happens in a cell with a high frequency band. For example, in a case of operating at the mmW frequency band, the different budget between the UL and DL may be up to 25 dB. Fig. 1 shows that the asymmetric UL and DL in the cell 101. For example, the cell 101 includes an UL coverage area 103 and a DL coverage area that is the same as the range of the cell 101. The UL coverage area 103 is smaller than the DL coverage area. For example, up to 25 dB budget difference may lead to a situation where the UL coverage area is only about 1/4 of the DL coverage area. The main reasons are the small UL transmission power of terminal devices and/or smaller UL transmission beamforming gain, as compared with the DL case.

Due to the UL/DL coverage asymmetry in the cell 101, there may be a situation where a terminal device is still communicating with the network device 101 in a DL with a high quality while the UL from that terminal device to the network device 101 is worse. For example, the terminal device 120 was previously in the coverage area 103 and had both UL and DL connections with the network device 111. After movement, the terminal device 120 is still in the cell 101 of the network device 111 and can work in the DL with the network device 111. However, at this time, the UL quality from the terminal device 120 to the network device 111 is decreased. For the terminal device 121 within the coverage area 103, the UL and DL with the network device 111 both works well. For the terminal device 122 outside the cell 101 but within the cell 102, it may establish a connection with the network device 112 in both UL and DL. To enable UL communication of the terminal device 120, as mentioned above, in embodiments of the present disclosure, the terminal device 120 is allowed to switch only its UL to the network device 112 and still maintain its DL with the network device 111.

It would be appreciated that although the frequency band of the network device 111 has been described as being higher than that of the network device 112, in some other cases, the frequency band of the network device 112 may be higher than or equal to that of the network device 111. In these cases, there may also occur when a terminal device has a good DL and a worse UL with one of the

network devices

111, 112 and may thus switch the UL to the other one of the

network devices

111, 112.

Reference is now made to Fig. 2, which shows a process 200 for link switch according to an embodiment of the present disclosure. For the purpose of discussion, the process 200 will be described with reference to Fig. 1. The process 200 may involve the terminal device 120 and the

network devices

111, 112 as illustrated in Fig. 1. It would be appreciated that although the process 200 for link has been described in the communication system 100 of Fig. 1, this process may be likewise applied to other communication scenarios where different network devices are jointly deployed to provide respective serving cells. It would also be appreciated that although the UL link switch of the terminal device 200 is discussed, a similar process can be applied for any other terminal devices in the

cell

101 or 102 to switch their links.

In the process 200, the network device 111 determines 205 whether an UL of the terminal device 120 with the network device 111 is to be switched. The terminal device 120 has established a connection with the network device 111 and thus the cell 101 is a serving cell of the terminal device 120 in both UL and DL. For purpose of discussion, the UL from the terminal device 120 to the network device 111 is referred to as a first UL, and the DL from the network device 111 to the terminal device 120 is referred to as a second UL. According to embodiments of the present disclosure, the network device 111, as the current serving cell of the terminal device 120 in both the UL and DL, controls the link switch of the terminal device 120.

Whether to switch the first UL but maintain the first DL of the terminal device 120 depends on various factors. One possible factor is that the terminal device 120 is in a link asymmetric status in which the first DL satisfies a first DL requirement and the first UL with the first network device fails to satisfy an UL requirement. This indicates that the terminal device 120 is still within a good DL coverage area but is to be out of an UL coverage area served by the network device 111, leading to asymmetry in qualities in the UL and DL. The determination of the link asymmetric status will be discussed in detail below. Other factors causing the only uplink switch may due to different UL/DL access controls at the network device 111, UL/DL load distribution between network devices, and/or other reasons.

In some embodiments, if the network device 111 intends to switch the terminal device 120 from the first UL to an UL with the network device 112 (referred to as a second UL for purpose of discussion) , it may request whether the network device 112 accepts such switch. The network device 111 may send to the network device 112 a request to switch the 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. The network device 112 may determine whether such UL link switch is accepted, for example, based on some normal activities such as UL access control. If the switch is accepted, the network device 112 may transmit a confirmation on the request to the network device 111, for example, via the backhaul link therebetween. Upon receipt of the confirmation, the network device 111 makes a decision on the only UL link switch of the terminal device 120.

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

Upon receipt of 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 a result, the terminal device 120 establishes the second UL with the network device 112 and thus can transmit UL data and/or other UL information to the network device 112 via the second UL using the UL frequency band of the network device 112. In addition, the terminal device 120 can still work on the DL frequency band of the network device 111 and receive DL data and/or other DL information from the network device 111, such as DL control information (DCI) , DL measurement, acknowledgement information on the UL transmission, and/or the like. In the only UL link switch, the terminal device 120 may have some pending UL and/or DL data transmissions. Specific handling on those pending transmissions will be needed, as will be discussed below.

As mentioned above, one possible situation that will trigger the only UL link switch of the terminal device 120 is to identify whether the terminal device 120 is in a status with asymmetric link qualities in the first UL and DL. There are some events and/or triggers in the traditional HO procedure to identify whether a terminal device is in a good or worse connection of the current serving cell and/or the neighbor cell, but all these events and/or triggers can measure and indicate a good or worse quality of the connection in both the UL and DL. The events in the traditional HO procedure are defined to measure the DL RS of the serving cell and/or the neighbor cell. In all the events that are defined to trigger a HO procedure, it is only needed 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 the neighbor cell. If a HO procedure is triggered, the serving cell of the terminal device switches to the neighbor cell in both the UL and DL. The reason is that in legacy systems such as those operating at frequencies lower than 6 GHz, the UL and the DL always have similar coverage. The terminal device only needs to measure the RS in one direction (such as DL RS) to identify whether it is in or out of the coverage of the serving cell and trigger the HO procedure accordingly.

In some use cases, such as in the 5G network systems, it is desirable to well leverage high frequency band with wide bandwidth so as to achieve big throughput to satisfy service requirement such as the Enhanced Mobile Broadband (eMBB) service, especially for DL. However, based on current defined HO related events, regardless how the corresponding thresholds defined in HO related events are configured, either early or late HO will be resulted which are both not optimal for communications at the high frequency band. For example, a big-threshold configuration to guarantee the UL quality will lead to too early HO to a new network device with a low frequency band although the terminal device is still in good DL coverage at the high frequency band. On the other hand, late HO will occur if a small threshold is configured to wait for the terminal device to be out of DL coverage, which will seriously impact UL performance because the terminal device is already out of UL coverage long before this event is triggered.

Thus, the events and/or triggers used in the traditional HO procedures may thus not be applicable directly to trigger the only UL link switch as proposed herein, more specifically, to determine whether the terminal device 120 is to be in the link asymmetric status with the satisfied DL and unsatisfied UL. The terminal device 120 may enter the link asymmetric status usually in the network deployment with asymmetric UL/DL coverage, such as in the cell of the network device operating at a high frequency band such as the mmW frequency band. Due to the asymmetry, the good DL coverage does not always refer to good UL coverage. Accordingly, in some embodiments of the present disclosure, there is proposed a new event (s) and/or procedure (s) to evaluate both the UL and DL qualities.

In an embodiment, the determination of the link asymmetric status is based on measurement on a DL reference signal by the terminal device 120. Specifically, the terminal device 120 may determine a quality of the first DL (referred to as a first DL quality for purpose of discussion) by measuring a DL reference signal (RS) received from the network device 111. The DL RS may be of any types, such as a Channel Status Indication-Reference signal (CSI-RS) , and the like. The DL reference signal may be transmitted by the network device 111 either periodically or by an event trigger. Various methods for link quality estimation may be applied, either currently existing or to be developed in the future. As some examples, the terminal device 120 may measure Reference Signal Received Power (RSRP) , a Received Signal Strength Indicator (RSRI) , or a Reference Signal Received Quality (RSRQ) of the DL RS, and/or the like.

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, which means that the terminal device 120 is still within good DL coverage and the network device 111 can continue to serve the terminal device 120 with its operating frequency band in the first DL and obtain good or acceptable DL performance. If the first DL quality is determined to be below the second quality, it means that the terminal device 120 is leaving the UL coverage area of the network device 111, such as the UL coverage area 103, and thus no acceptable UL service can be provided on the frequency band of the network device 111 in near future.

The first and second thresholds may be configured by the network device 111 to the terminal device 120 in advance. The first threshold may be configured depending on the DL requirement and depending on what aspect of the DL RS is measured. The second threshold may be configured based on the UL requirement so as 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 and second thresholds may be determined according to actual implementations and the scope of the present disclosure is not limited in this regard.

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 while the second UL is unsatisfied and identifies that it is in the link asymmetric status. In some embodiments, the terminal device 120 may monitor whether the first DL quality is above the first threshold for a first predetermined time period, and/or whether the first DL quality is below the second threshold for a second predetermined time period, so as to avoid instantaneous movement, possible inaccurate quality estimation, and/or other reasons. The first and second predetermined time period may be preconfigured as the same or different depending on the DL and UL requirements.

The terminal device 120 may transmit to the network device 111 a status indication indicating that the terminal device 120 is in the link asymmetric status. Upon receipt of such status indication, the network device 111 can determine that the terminal device 120 is in the link asymmetric status. In some embodiments, the terminal device 120 may report the first DL quality of the first DL to the network device 111 and the network device 111 determines whether the terminal device 120 is in the link asymmetric status by comparing the received first DL quality with the first and second thresholds in a similar way as the terminal device 120.

Alternatively, or in addition, the determination of the link asymmetric status is based on both measurement of a DL RS by the terminal device 120 and measurement of an UL RS by the network device 111. The network device 111 may determine a first UL quality of the first UL (referred to as a first UL quality for purpose of discussion) by measuring an UL RS transmitted from the terminal device 120. The UL RS may be of any types, such as Sounding Reference Signal (SRS) , and the like. The UL reference signal may be transmitted by the terminal device 120 either periodically or by an event trigger. Various methods for link quality estimation may be applied, either currently existing or to be developed in the future. As some examples, the network device 111 may measure Reference Signal Received Power (RSRP) , a Received Signal Strength Indicator (RSRI) , or a Reference Signal Received Quality (RSRQ) of the UL RS, and/or the like.

The network device 111 may then compare the first UL quality with a third threshold. The third threshold may be set as any value depending on the UL requirement and actual implementations. The scope of the present disclosure is not limited in this regard. The third threshold may be the same as or different from the second threshold as mentioned above. If the first UL quality is below the third threshold, for example, for a predetermine time period, the network device 111 identifies that its UL frequency band cannot continue to provide a good service to the terminal device 120. Thus, the network device 111 will reach a rough decision on UL link switch for the terminal device 120.

As a response, the network device 111 may request the terminal device 120 to measure the first DL quality of the first DL in some embodiments so as to further confirm that the terminal device 120 is in good DL coverage. The measurement of the first DL quality is similar as discussed above. In other cases, the terminal device 120 may always measure and report the first DL quality without any request from the network device 111 in the case of the low UL quality. Upon determining the first DL quality, the terminal device 120 may compare the first DL quality with 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 the explicit first DL quality or specifically indicate that the first DL quality is below the fourth threshold. The fourth threshold may be configured based on the UL requirement and may be the same as or different from the second threshold as mentioned above. The specific value of the fourth threshold may be determined according to actual implementations and the scope of the present disclosure is not limited in this regard. In the case that the explicit first DL quality is indicated to the network device 111, it may compare the first DL quality with the fourth threshold to determine whether the first DL quality exceeds or is below that threshold.

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

In some embodiments of determining that the terminal device 120 is in the link asymmetric status, the network device 111 may determine to transmit the UL link switch indication to trigger the only UL link switch for the terminal device 120, assuming that the terminal device 120 is always in good UL coverage of the network device 112. In some embodiments, in addition to the link asymmetric status, a UL quality of the second UL may also be evaluated. The network device 111 determines that the terminal device 120 can switch from the first UL to the second UL if the UL quality of the second UL is satisfied.

In some embodiments, if the UL and DL qualities in the coverage of the cell 101 are symmetric, the network device 111 may request the terminal device 120 to measure a DL from the network device 112 to the terminal device 120 (referred to as a second DL for purpose of discussion) and evaluate whether the second DL is satisfied to allow the only UL link switch based on the quality of the second DL. More specifically, the network device 111 may transmit synchronization information and related information on 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 to the network device 112 at least in a DL direction so as to benefit measurement of a DL RS transmitted from the network device 112.

The synchronization information may include, for example, DL synchronization related signaling, a measurement gap, the DL control channel of the network device 112, and the like. In some embodiments, the related information on the second DL may include one or more of the DL RS to be transmitted by the network device 112, such as a CSI-RS, a Primary Synchronization Signal (PSS) , a Secondary Synchronization Signal (SSS) , information on a measurement gap, and the like. The synchronization and related information may be preconfigured and sent to the terminal device 120 after the terminal device 120 accessed to the network device 111 system immediately, or by an event trigger, for example, after identifying that the terminal device 120 is in the link asymmetric status.

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

Upon receipt of the second quality indication, the network device 111 may determine that the terminal device 120 is in good UL coverage of the network device 112 due to the DL and UL symmetry in the cell 101. As such, the network device 111 may then decide to trigger the only UL link switch of the terminal device 120.

The trigger of determination of the only UL link switch has been described above. It is to be understood that during the measurement of the UL/DL qualities, if it is determined that both the first UL and first DL fail to satisfy the corresponding requirement (below the corresponding thresholds) , which means that the network device 111 cannot provide either satisfied UL coverage or satisfied DL coverage, a normal HO procedure may be triggered to switch both UL and DL of the terminal device 120 to a further network device, such as the network device 112.

In the following, some embodiments on how to implement the only UL link switch from the network device 111 to the network device 112 are provided. As mentioned above, after the network device 111 decides on the only UL link switch of the terminal device 120, it transmits the UL link switch indication to trigger such UL link switch. In some embodiments, the only UL link switch may be implemented by configuring a virtual serving cell based on the frequency band of the network device 112.

Particularly, the network device 111 may configure the terminal device 120 with a virtual serving cell (referred to as a first virtual serving cell) . The first virtual serving cell has its operating frequency band the frequency band (for example, the UL operating frequency band) paired to the frequency band of the network device 112 (more specifically, the UL frequency band) . Thus, the (UL) frequency 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 the network device 111. An identity (ID) of the first virtual serving cell may be assigned to identify this virtual cell, for example, via a virtual carrier indication field (CIF) . The network device 111 may transmit configuration information (referred to as first configuration information) to the terminal device 120 to configure the first virtual cell, for example, via Radio Resource Control (RRC) signaling.

The first configuration information may include at least the operating frequency band and/or ID of the first virtual serving cell, and/or the like. The first configuration information may be transmitted, for example, after the terminal device 120 accessed to the network device 111. In some embodiments, the first configuration information or further configuration information to be sent to the terminal device 120 to convey information related to the frequency band of the network device 112 for UL transmission, such as information on UL Physical Random Access Channel (PRACH) , configuration on UL Physical Uplink Control Channel (PUCCH) , UL synchronization information, and the like.

After the network device 111 decides to allow the terminal device 120 to switch only the first UL and maintain the first DL, for example, after obtaining the confirmation on the request for the UL link switch from the network device 112, the network device 111 may transmit the UL link switch indication to the terminal device 120. In some embodiments, Layer 2 (L2) signaling may be transmitted as the UL link switch indication to the terminal device 120 to activate the first virtual serving cell. At this time, the previous serving cell of the terminal device 120 (i.e., the cell 101) may be deactivated. As an example, the network device 111 may transmit a L2 Medium 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 this virtual cell.

Upon receipt of the UL link switch indication, such as the L2 signaling, the terminal device 120 determines that the first virtual serving cell to be activated is the one that is previously configured. As such, the terminal device 120 identifies that the current first UL with the network device 111 is to be switched to the second UL with no impact to the current first DL. Thus, the terminal device 120 will work at the frequency band of the network device 112 in the UL direction and at the frequency band of the network device 111 in the DL direction.

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

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 frequency bands of the

network devices

111, 112, respectively. The two BWPs are available for UL transmissions in the second virtual serving cell. Respective virtual IDs may be assigned to the BWPs. With such second configuration information, for the terminal device 120 in normal DL and UL coverage of the cell 101, the first BWP corresponding to the frequency band of the network device 111 is activated so that the terminal device 120 may communicate with the network device 111 in both UL and DL.

The network device 111 may transmit configuration information (referred to as second configuration information) to the terminal device 120 to configure the second virtual cell, for example, via Radio Resource Control (RRC) signaling. The second configuration information may include at least the two BWPs and/or their respective IDs of the second virtual serving cell, and/or the like. The second configuration information may be transmitted, for example, after the terminal device 120 accessed to the network device 111. The second configuration information may be transmitted, for example, after the terminal device 120 accessed to the network device 111. In some embodiments, the second configuration information or further configuration information to be sent to the terminal device 120 to convey information related to the frequency band of the network device 112 for UL transmission, such as information on UL PRACH, configuration on UL PUCCH, UL synchronization information, and the like.

If the network device 111 determines to allow the terminal device 120 to switch only the first UL and maintain the first DL, for example, after obtaining the confirmation on the request for the UL link switch from the network device 112, the network device 111 may transmit the UL link switch indication to the terminal device 120. In some embodiments, Layer 1 (L1) signaling may be transmitted as the UL link switch indication to the terminal device 120 to activate the second BWP of the second virtual serving cell that is corresponding to the frequency band of the network device 112. The L1 signaling may include downlink control information (DCI) for BWP switching. Upon receipt of the L1 signaling, the terminal device 120 determines that the current first UL with the network device 111 is to be switched to the second UL with no impact to the current first DL. Thus, the terminal device 120 will work at the frequency band of the network device 112 in the UL direction and at the frequency band of the network device 111 in the DL direction.

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

The RRC signaling may indicate to the terminal device 120 a switch of the first UL to the second UL while maintaining the first DL. In some embodiments, the RRC signaling may also include configuration information on the frequency band of the network device 112, such as the UL information on UL PRACH, configuration on UL PUCCH, UL synchronization information, and/or the like. In this way, the network device 111 may not need to preconfigure information on the frequency band of the network device 112 in advance. The RRC signaling may be included in a RRC message to trigger the UL link switch. This reason is that the UL link switch command is based on the RRC message, which has the chance to include the necessary configuration information along this message.

For the link switch procedure, one of the tasks that is how to handle the ongoing/pending DL/UL data transmission activities. In the normal HO procedure, all pending UL and DL data transmission activities will be released, for example, the buffers for DL and UL retransmission procedures are flushed, the DL and UL retransmission procedures may be released, and the like. This is because in the normal HO procedure, the security key for data processing may be changed so all the pending transmissions have to be released. Thus, the previous buffered packets such as the L2 packets cannot be handled in the new serving cell. After the normal HO procedure, the unacknowledged data packet, such as an Internet Protocol (IP) packet, will be forwarded to the HO target cell for retransmission.

In the embodiments of the present disclosure, the terminal device 120 switches only the UL to the network device 112 and maintains its DL in the previous network device 111. The legacy defined HARQ release behavior may not be optimal for the only UL link switch case, at least not good for DL performance improvement. Thus, different processing methods can be applied.

In some embodiments, for DL transmission of the terminal device 120, since no DL link switch, the DL transmission and reception points (the network device 111 and the terminal device 120) remain the same. There may not be change on a security key for data processing in the DL transmission. Thus, if there is a pending DL retransmission procedure, such as a Hybrid Automatic Repeat reQuest (HARQ) procedure, the terminal device 120 may maintain a buffer for this procedure, with the security key unchanged. In some embodiments, after the UL link switch is completed, the network device 111 may have a chance to retransmit data in the pending DL retransmission procedure. In this way, it is possible to provide better efficiency in the DL transmission as compared with the normal HO procedure. The network device 111 may also possibly command the terminal device 120 to release the pending DL retransmission procedure by a new transmission indication.

The processing on the UL transmission is depending on whether a security key for data processing in the UL retransmission procedure is changed or not. To better understand the processing on the UL/DL transmission after the only UL link switch, reference is made back to Fig. 2.

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

Whether the security key is changed is depending on various factors and may be determined by the network device 111, the network device 112, or the negotiation therebetween. The scope of the present disclosure is not limited in this regard. The terminal device 120 may determine how to perform UL transmission, especially how to handle a pending UL retransmission procedure based on whether the security key is changed or not.

In some embodiments, the security key for UL transmission may be indicated as being changed since the terminal device 120 switches to a new UL. Then the security keys for UL/DL transmission/reception may be different from the perspective of the terminal device 120. In this situation, the terminal device 120 may release a buffer for the pending UL retransmission procedure, for example, after switching to the second UL. The reason is that a buffered UL packet (s) pending for retransmission is processed by the security key which is different to the one that was used in the first UL. All the high layer entities for the pending procedure may be released and new ones may be set up upon the scheduling from the network device 112. As such, ifbeing transmitted in the second UL, all the buffered data cannot be processed by the network device 112, such as the Packet Data Convergence Protocol (PDCP) entity for the terminal device 120 even it is correctly decoded at L1. By releasing the buffer, the unacknowledged UL packet may be retransmitted at a high layer after the UL link switch is finished.

There is another possibility that the previous security key used in the first UL remains unchanged and can continue to be used for the UL transmission even the terminal device 120 switches to the second UL. Thus, in both the UL/DL transmission/reception of the terminal device 120, the same security key as in the first UL and DL with the network device 111 is used. In this case, there is no need to release current UL retransmission activities. The terminal device 120 may maintain the buffer for the pending UL retransmission procedure with the security key unchanged. Thus, the network device 112 may be able to schedule UL retransmission immediately after the only UL link switch is finished. As such, the UL transmission efficiency can be improved.

If the security key for the UL transmission of the terminal device 120 is not changed, the network device 112 may obtain the security key, for example, from the network device 111 via the backhaul link. The network device 111 may send the same key related indication to the network device 112 to indicate whether the security key used in the UL transmission of the terminal device 120 is changed or not. In the case of the unchanged security key, the network device 112 may use different security keys to handle the received UL data from two different types of terminal devices. A first type is a terminal device (s) that are served by the network device 112 in both UL and DL with the UL and DL frequency bands respectively. For this type of terminal devices, the UL data may be processed by the network device 112 using a security key generated by the network device 112. A second type is a terminal device (s) having only its UL switched to the network device 112 and having their security key unchanged.

In the embodiments where the network device 111 indicates no security key change after the only UL link switch. The network device 111 may forward configuration information related to the pending UL retransmission procedure of the terminal device 120 to assist the network device 112 in scheduling and processing the UL transmission from the terminal device 120. The configuration information may include one or more of the unchanged security key, a procedure ID, a packet size of the pending uplink retransmission procedure, any other information related to the procedure and/or the buffer, and/or the like. With the configuration information, the network device 112 may be able to schedule the UL transmission correctly for the terminal device 120.

In the UL transmission from the terminal device 120 to the network device 112, the network device 112 transmits 225 scheduling information to the terminal device 120 in the case of the security key is either changed or not, as shown in Fig. 2. The scheduling information may be transmitted as, for example, DCI, and may be used to indicate to the terminal device 120 the resources, the transmission manner, and/or other information that is necessary for the UL transmission. In the case of the security key is changed, the network device 112 may schedule the UL transmission of the terminal device 120 in a normal manner. The terminal device 120 transmits 230 UL data to the network device 112 based on the scheduling information. To perform the UL transmission, the terminal device 120 may synchronize with the network device 112 in the UL direction. The synchronization information in UL may be configured by the network device 111 in advance.

In the case where the security key is unchanged, 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 procedure. The terminal device 120 may transmit to the network device 112 a self-decodable version of UL data using the unchanged security key. In some embodiments, the self-decodable data retransmission may be scheduled in the first retransmission in the pending UL retransmission procedure. As such, without any previous information to facilitate the combination of the UL data after the only UL link switch, the network device 112 can successfully decode the self-decodable version of UL data. If the first scheduled retransmission is non-self-decodable, without any previous information on the pending UL retransmission procedure, it is impossible for the network device 112 to successfully decode the retransmitted UL data, even the second UL with the network device 112 is good for the the terminal device 120.

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

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

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

In some embodiments, the first frequency band is higher than the second frequency band. In some embodiments, the first cell comprises 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 switch indication is received, the terminal device is in a link asymmetric status where the first downlink satisfies a first downlink requirement and the first uplink fails to satisfy an uplink requirement.

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 being based on the uplink requirement; and in response to the first downlink quality being above the first threshold and being below the second threshold, transmitting to the first network device a status indication indicating that the terminal device is in the link asymmetric status.

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 a fourth threshold, transmitting a first quality indication indicating the first downlink quality to the first network device to support the first network device to determine the link asymmetric status of the terminal device.

In some embodiments, the method 300 further comprises receiving, from the first network device, synchronization and related information on 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 being above a fifth threshold, transmitting a second quality indication indicating the second downlink quality to the first network device so as to support the first network device to determine the switching of the first uplink.

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

In some embodiments, the method 300 further comprises receiving second configuration information from the first network device to configure the terminal device with a second virtual serving cell, the second virtual serving cell having the first and second frequency bands as first and second bandwidth parts (BWPs) of an operating frequency band of the second virtual serving cell, respectively. In some embodiments, the terminal device 120 receives Layer 1 (L1) signaling as the uplink switch indication to activate the second BWP.

In some embodiments, receiving the uplink switch indication comprises receiving radio resource control (RRC) signaling as the uplink switch indication, the RRC signaling indicating a switch of the first uplink to the second uplink while maintaining the 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 data processing is to be changed after the switching, the security key being applied in a pending uplink retransmission procedure of the terminal device; and in response to the key related indication indicating that the security key is to be changed, releasing a buffer for the pending uplink retransmission procedure.

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

In some embodiments, the method 300 further comprises maintaining a buffer for a pending downlink retransmission procedure of the terminal device, a security key of data processing in the pending downlink retransmission procedure remaining unchanged.

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

At block 410, the network device 111 determines whether a first uplink of a terminal device with the network device is to be switched, the network device serving a first cell with a first frequency band. In response to determining that the first uplink is to be switched, at block 420, the 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 (for example, the network device 112) while maintaining a first downlink with the network device, the further network device serving a second cell with a second frequency band.

In some embodiments, determining whether the first uplink is to be switched comprises determining whether the terminal device is in a link asymmetric status in which the first downlink satisfies a first downlink requirement and the first uplink fails to satisfy an uplink requirement; and in response to determining that the terminal device is in the link asymmetric status, determining that the first uplink is to be switched.

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

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

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

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

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

In some embodiments, the method 400 further comprises transmitting second configuration information to the terminal device to configure the terminal device with a second virtual serving cell, the second virtual serving cell having the first and second frequency bands as first and second bandwidth parts of an operating frequency band of the second virtual serving cell, respectively. In some embodiments, the network device 111 transmits Layer 1 (L1) signaling as the uplink switch indication to trigger the terminal device to activate the second BWP.

In some embodiments, transmitting the uplink switch indication comprises transmitting the uplink switch 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 data processing is to be changed after the switching, the security key being applied in a pending uplink retransmission procedure of the terminal device, and transmitting, to the further network device, configuration information related to the pending uplink retransmission procedure, the configuration information including at least one of the security key, a procedure identity, and a packet size of the pending uplink retransmission procedure.

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

At block 510, the network device 112 receives, from a further network device (for example, the network device 111) , 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. At block 520, the network device 112 determines whether the switch is accepted. At block 530, in response to determining that the switch is accepted, the network device 112 transmits a confirmation on the request to the further network device. At block 540, the network device 112 establishes the second uplink with the terminal device, the terminal device maintaining a 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 of data processing for the terminal device is to be changed after the switching, the security key being applied in a pending uplink retransmission procedure of the terminal device. In some embodiments, the method 500 further comprises receiving, from the further network device, configuration information related to the pending uplink retransmission procedure, the configuration information including at least one of the security key, a procedure identity, and a packet size of the pending uplink retransmission procedure.

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

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

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

In some embodiments, the apparatus further comprises 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 computer program code configured to, with the at least one processor, cause the performance of the apparatus.

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

In some embodiments, the apparatus comprises: means for determining, at a network device, whether a first uplink of a terminal device with the network device is to be switched, the network device serving a first cell with a first frequency band; and means for transmitting, in response to determining that the first uplink is to be switched, 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 while maintaining a first downlink with the network device, the further network device serving a second cell with a second frequency band.

In some embodiments, the apparatus further comprises 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 computer program code configured to, with the at least one processor, cause the performance of the apparatus.

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

In some embodiments, the apparatus comprises: means for receiving, at a network device and 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; means for transmitting a confirmation on the request to the further network device in response to determining that the switch 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.

In some embodiments, the apparatus further comprises 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 computer program code configured to, with the at least one processor, cause the performance of the apparatus.

Fig. 6 illustrates a simplified block diagram of an apparatus 600 that can be embodied as or comprised in the terminal device 120, the network device 111, or the network device 112 shown in Fig. 1, to implement embodiments of the present disclosure.

The apparatus 600 comprises 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 69 may further include a transmitter TX and receiver RX 613 coupled to the processor 611, which may be operable to communicatively connect to other apparatuses. The MEM 612 stores a 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 in accordance with embodiments of the present disclosure, for example the

method

300, 400, or 500.

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

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

The MEM 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 multicore processor architecture, as non-limiting examples.

Although some of the above descriptions on the GD based signal detection and staged signal detection are made in the context of a wireless communication system shown in Fig. 1, it should not be construed as limiting the spirit and scope of the present disclosure. The principle and concept of the present disclosure may be more generally applicable to other scenarios.

In addition, the present disclosure may also provide a carrier containing the computer program as mentioned above (e.g., computer instructions/grogram code 614 in Fig. 6) . The carrier includes a computer readable storage medium and a transmission medium. The computer readable storage medium may include, for example, an optical compact disk or an electronic memory device like a RAM (random access memory) , a ROM (read only memory) , Flash memory, magnetic tape, CD-ROM, DVD, Blue-ray disc and the like. The transmission medium may include, for example, electrical, optical, radio, acoustical or other form of propagated signals, such as carrier waves, infrared signals, and the like.

Generally, various embodiments of the present 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 embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that block, apparatus, system, technique or method 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, being executed in a device on a target real or virtual processor, to carry out the

method

300, 400, or 500 as described above with reference to Figs. 3 and 4. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like 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 a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out 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 flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a 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, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable media.

The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but 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 the computer readable storage medium would 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 of the foregoing.

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

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

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

- method steps and/or devices, units or means likely to be implemented as hardware components at the above-defined apparatuses, or any module (s) thereof, (e.g., devices carrying out the functions of the apparatuses according to the embodiments as described above, eNode-B etc. as described above) are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS (Metal Oxide Semiconductor) , CMOS (Complementary MOS) , BiMOS (Bipolar MOS) , BiCMOS (Bipolar CMOS) , ECL (Emitter Coupled Logic) , TTL (Transistor-Transistor Logic) , etc., using for example ASIC (Application Specific IC (Integrated Circuit) ) components, FPGA (Field-programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components;

- devices, units or means (e.g. the above-defined apparatuses, or any one of their respective means) can be implemented as individual devices, units or means, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device, unit or means is preserved;

- an apparatus may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of an apparatus or module, instead of being hardware implemented, be implemented as software in a (software) module such as a computer program or a computer program product comprising executable software code portions for execution/being run on a processor;

- a device may be regarded as an apparatus or as an assembly of more than one apparatus, whether functionally in cooperation with each other or functionally independently of each other but in a same device housing, for example.

It is noted that the embodiments and examples described above are provided for illustrative purposes only and are in no way intended that the present disclosure is restricted thereto. Rather, it is the intention that all variations and modifications be included which 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 certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present 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 may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present 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 as an alternative to the above, the following examples are described. The features described in any of the following examples may be utilized with any of the other examples described herein.

Claims

A device, comprising:

at least one processor; and

at least one memory including computer program codes;

the at least one memory and the computer program codes are configured to, with the at least one processor, cause the device to:

receive, at the terminal device, an uplink switch indication from a first network device, the first network device serving a first cell with a first frequency band, and

switch, based on the uplink switch indication, from a first uplink with the first network device to a second uplink with a second network device while maintaining a first downlink with the first network device, the second network device serving a second cell with a second frequency band.
The device of claim 1, wherein the first frequency band is higher than the second frequency band, and

wherein the first cell comprises a downlink coverage area and an uplink coverage area, the uplink coverage area being smaller than the downlink coverage area.
The device of claim 1, wherein when the uplink switch indication is received, the terminal device is in a link asymmetric status where the first downlink satisfies a first downlink requirement and the first uplink fails to satisfy an uplink requirement.
The device of claim 3, wherein the device is further caused to:

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

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

in response to the first downlink quality being above the first threshold and being below the second threshold, transmit to the first network device a status indication indicating that the terminal device is in the link asymmetric status.
The device of claim 3, wherein the device is further caused to:

determine 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, transmit a first quality indication indicating the first downlink quality to the first network device to support the first network device to determine the link asymmetric status of the terminal device.
The device of claim 1, wherein the device is further caused to:

receive, from the first network device, synchronization and related information on a second downlink from the second network device to the terminal device;

determine 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 being above a fifth threshold, transmit a second quality indication indicating the second downlink quality to the first network device so as to support the first network device to determine the switching of the first uplink.
The device of claim 1, wherein the device is further caused to:

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

wherein the device is caused to receive Layer 2 (L2) signaling as the uplink switch indication to activate the virtual serving cell.
The device of claim 1, wherein the device is further caused to:

receive second configuration information from the first network device to configure the terminal device with a second virtual serving cell, the second virtual serving cell having the first and second frequency bands as first and second bandwidth parts (BWPs) of an operating frequency band of the second virtual serving cell, respectively,

wherein the device is caused to receive Layer 1 (L1) signaling as the uplink switch indication to activate the second BWP.
The device of claim 1, wherein the device is caused to:

receive radio resource control (RRC) signaling as the uplink switch indication, the RRC signaling indicating a switch of the first uplink to the second uplink while maintaining the first downlink.
The device of claim 1, wherein the device is further caused to:

receive a key related indication from the first network device, the key related indication indicating whether a security key of data processing is to be changed after the switching, the security key being applied in a pending uplink retransmission procedure of the terminal device; and

in response to the key related indication indicating that the security key is to be changed, release a buffer for the pending uplink retransmission procedure.
The device of claim 10, wherein the device is further caused to:

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

in response to the scheduling information indicating a self-decodable data retransmission to be scheduled in the pending uplink retransmission procedure, transmit to the second network device a self-decodable version ofuplink data using the security key;

in response to the scheduling information indicating a non-self-decodable retransmission to be scheduled in the pending uplink retransmission procedure, discard the scheduling information; and

in response to the scheduling information indicating a new uplink retransmission procedure from the terminal device to the second network device, release the buffer for the pending uplink retransmission procedure.
The device of claim 1, wherein the device is further caused to:

maintain a buffer for a pending downlink retransmission procedure of the terminal device, a security key of data processing in the pending downlink retransmission procedure remaining unchanged.
A device, comprising:

at least one processor; and

at least one memory including computer program codes;

the at least one memory and the computer program codes are configured to, with the at least one processor, cause the device to:

determine, at a network device, whether a first uplink of a terminal device with the network device is to be switched, the network device serving a first cell with a first frequency band, and

in response to determining that the first uplink is to be switched, transmit 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 while maintaining a first downlink with the network device, the further network device serving a second cell with a second frequency band.
The device of claim 13, wherein the first frequency band is higher than the second frequency band, and

wherein the first cell comprises a downlink coverage area and an uplink coverage area, the uplink coverage area being smaller than the downlink coverage area.
The device of claim 13, wherein the device is caused to:

determine whether the terminal device is in a link asymmetric status in which the first downlink satisfies a first downlink requirement and the first uplink fails to satisfy an uplink requirement; and

in response to determining that the terminal device is in the link asymmetric status, determine that the first uplink is to be switched.
The device of claim 15, wherein the device is caused to:

receive, from the terminal device, a status indication indicating that the terminal device is in the link asymmetric status, the status indication being based on a first downlink quality of the first downlink being above a first threshold and being below a second threshold higher than the first threshold.
The device of claim 15, wherein the device is caused to:

determine a first uplink quality of the first uplink by measuring an uplink reference signal transmitted from the terminal device;

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

in response to a first quality indication received from the terminal device indicating the first downlink quality being above a fourth threshold, determine that the terminal device is in the link asymmetric status.
The device of claim 13, wherein the device is caused to:

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

in response to receiving a confirmation on the request from the further network device, determine that the first uplink is to be switched.
The device of claim 13, wherein the device is caused to:

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

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

transmit the uplink switch indication further based on a determination of the third quality being above a third threshold.
The device of claim 13, wherein the device is further caused to:

transmit first configuration information from the first network device to configure the terminal device with a first virtual serving cell, 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 switch indication to trigger the terminal device to activate the virtual serving cell.
The device of claim 13, wherein the device is further caused to:

transmit second configuration information to the terminal device to configure the terminal device with a second virtual serving cell, the second virtual serving cell having the first and second frequency bands as first and second bandwidth parts 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 switch indication to trigger the terminal device to activate the second BWP.
The device of claim 13, wherein the device is caused to:

transmit the uplink switch indication as radio resource control (RRC) signaling indicating a switch from the first uplink to the second uplink while maintaining the first downlink.
The device of claim 13, wherein the device is further caused to perform at least one of the following:

transmit a key related indication to the terminal device and the further network device, the key related indication indicating whether a security key of data processing is to be changed after the switching, the security key being applied in a pending uplink retransmission procedure of the terminal device, and

transmit, to the further network device, configuration information related to the pending uplink retransmission procedure, the configuration information including at least one of the security key, a procedure identity, and a packet size of the pending uplink retransmission procedure.
A device, comprising:

at least one processor; and

at least one memory including computer program codes;

the at least one memory and the computer program codes are configured to, with the at least one processor, cause the device to:

receive, at a network device and 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;

in response to determining that the switch is accepted, transmit a confirmation on the request to the further network device; and

establish the second uplink with the terminal device, the terminal device maintaining a first downlink with the further network device.
The device of claim 24, wherein the device is further caused to perform at least one of the following:

receive a key related indication from the further network device, the key related indication indicating whether a security key of data processing for the terminal device is to be changed after the switching, the security key being applied in a pending uplink retransmission procedure of the terminal device; and

receive, from the further network device, configuration information related to the pending uplink retransmission procedure, the configuration information including at least one of the security key, a procedure identity, and a packet size of the pending uplink retransmission procedure.
The device of claim 24, wherein the device is further caused to:

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

decode a self-decodable version of uplink data received from the terminal device using the security key.
A method implemented at a terminal device comprising:

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

switching, based on the uplink switch indication, from a first uplink with the first network device to a second uplink with a second network device while maintaining a first downlink with the first network device, the second network device serving a second cell with a second frequency band.
A method implemented at a network device, comprising:

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

in response to determining that the first uplink is to be switched, transmitting 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 while maintaining a first downlink with the network device, the further network device serving a second cell with a second frequency band.
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;

in response to determining that the switch is accepted, transmitting a confirmation on the request to the further network device; and

establishing the second uplink with the terminal device, the terminal device maintaining a first downlink with the further network device.
An apparatus, comprising:

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

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

means for transmitting, in response to determining that the first uplink is to be switched, 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 while maintaining a first downlink with the network device, the further network device serving a second cell with a second frequency band.
An apparatus, comprising:

means for receiving, at a network device and 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;

means for transmitting a confirmation on the request to the further network device in response to determining that the switch 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.
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.