Tracking reference signal based synchronization signal block-less secondary cell activation

Abstract

Various example embodiments relate to methods and apparatuses for enabling TRS based SSB-less SCell activation. An apparatus may be configured to receive from a network device, configuration information of a plurality of TRSs for a SCell operating in SSB-less mode, the plurality of TRSs having QCL relation with at least one SSB configured in a reference cell; receive from the network device, a command of activation of the SCell; and determine a TRS from the plurality of TRSs to monitor during the activation of the SCell.

Description

TECHNICAL FIELD

[0001] Various example embodiments described herein generally relate to communication technologies, and more particularly, to methods and apparatuses for synchronization signal block (SSB)-less secondary cell (SCell) activation based on tracking reference signal (TRS). BACKGROUND

[0002] Reducing the power consumption is important for a wireless communication system. For example, in scenario when inter-band or intra-band carrier aggregation (CA) is deployed, the wireless communication system may provide time and frequency synchronization information in a reference cell (e.g., primary cell), and refrain from transmitting synchronization signal blocks (SSBs) for a secondary cell (SCell). The principle is to reuse the coarse timing and coarse automatic gain control (AGC) from the reference cell and the user equipment (UE) will keep monitoring maximum two TRSs for fine time tracking and fine AGC. Thus, signaling overhead between the network device and the UE can be reduced, and network energy savings can be achieved. SUMMARY

[0003] A brief summary of exemplary embodiments is provided below to provide basic understanding of some aspects of various embodiments. It should be noted that this summary is not intended to identify key features of essential elements or define scopes of the embodiments, and its sole purpose is to introduce some concepts in a simplified form as a preamble for a more detailed description provided below.

[0004] In a first aspect, an example embodiment of an apparatus for a terminal device is provided. The apparatus may comprise at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive from a network device, configuration information of a plurality of tracking reference signals, TRSs, for a secondary cell, SCell, operating in synchronization signal block-less, SSB-less, mode, the plurality of TRSs having quasi co-location, QCL, relation with at least one synchronization signal block, SSB, configured in a reference cell; receive from the network device, a command of activation of the SCell; and determine a TRS from the plurality of TRSs to monitor during the activation of the SCell.

[0005] In a second aspect, an example embodiment of an apparatus for a network device is provided. The apparatus may comprise at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: transmit to a terminal device, configuration information of a plurality of tracking reference signals, TRSs, for a secondary cell, SCell, operating in synchronization signal block-less, SSB-less, mode, the plurality of TRSs having quasi co-location, QCL, relation with at least one synchronization signal block, SSB, configured in a reference cell; transmit to the terminal device, a command of activation of the SCell; and determine a TRS from the plurality of TRSs for the activation of the SCell.

[0006] In a third aspect, an example embodiment of a method performed by an apparatus for a terminal device is provided. The method may comprise: receiving from a network device, configuration information of a plurality of tracking reference signals, TRSs, for a secondary cell, SCell, operating in synchronization signal block-less, SSB-less, mode, the plurality of TRSs having quasi co-location, QCL, relation with at least one synchronization signal block, SSB, configured in a reference cell; receiving from the network device, a command of activation of the SCell; and determining a TRS from the plurality of TRSs to monitor during the activation of the SCell.

[0007] In a fourth aspect, an example embodiment of a method performed by an apparatus for a network device is provided. The method may comprise: transmitting to a terminal device, configuration information of a plurality of tracking reference signals, TRSs, for a secondary cell, SCell, operating in synchronization signal block-less, SSB-less, mode, the plurality of TRSs having quasi co-location, QCL, relation with at least one synchronization signal block, SSB, configured in a reference cell; transmitting to the terminal device, a command of activation of the SCell; and determining a TRS from the plurality of TRSs for the activation of the SCell.

[0008] In a fifth aspect, an example embodiment of an apparatus for a terminal device is provided. The apparatus for the terminal device may comprise: means for performing the method of the third aspect.

[0009] In a sixth aspect, an example embodiment of an apparatus for a network device is provided. The apparatus for the network device may comprise: means for performing the method of the fourth aspect.

[0010] In a seventh aspect, an example embodiment of a computer readable medium is provided. The computer readable medium may comprise program instructions that, when executed by an apparatus, cause the apparatus to at least perform the method of the third or fourth aspect.

[0011] In an eighth aspect, an example embodiment of a computer program product is provided. The computer program product may comprise program instructions that, when executed by an apparatus, cause the apparatus to at least perform the method of the third or fourth aspect.

[0012] Other features and advantages of the example embodiments of the present disclosure will also be apparent from the following description of specific embodiments when read in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of example embodiments of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Some example embodiments will now be described, by way of non-limiting examples, with reference to the accompanying drawings.

[0014] Figs. 1A and IB illustrate example SCell configuration to which the present disclosure may apply.

[0015] Fig. 2 is an exemplary sequence diagram illustrating example operations for performing SSB-less SCell activation according to example embodiments of the present disclosure.

[0016] Figs. 3 through 7 illustrate example diagrams or operation flowcharts for selecting the TRS according to one or more example embodiments of the present disclosure.

[0017] Figs. 8 through 11 illustrate TRS selection operation sequences according to example embodiments of the present disclosure.

[0018] Fig. 12 is a flowchart illustrating operations for determining a TRS for activation of a SSB-less SCell at a terminal device according to an example embodiment of the present disclosure.

[0019] Fig. 13 is a flowchart illustrating operations for determining a TRS for activation of a SSB-less SCell implemented at a network device according to an example embodiment of the present disclosure.

[0020] Fig. 14 is a block diagram illustrating an apparatus in accordance with an example embodiment of the present disclosure.

[0021] Fig. 15 is a block diagram illustrating an apparatus in accordance with an example embodiment of the present disclosure.

[0022] Fig. 16 is a block diagram illustrating devices in a communication system in accordance with an example embodiment of the present disclosure.

[0023] Throughout the drawings, same or similar reference numbers indicate same or similar elements. A repetitive description on the same elements would be omitted. DETAILED DESCRIPTION

[0024] Herein below, some example embodiments are described in detail with reference to the accompanying drawings. The following description includes specific details for the purpose of providing a thorough understanding of various concepts. However, it will be apparent to those skilled in the art that these concepts may be practiced without these specific details. In some instances, well known circuits, techniques and components are shown in block diagram form to avoid obscuring the described concepts and features.

[0025] As used herein, the term “network device” may refer to a radio access network (RAN) device. The RAN device may include for example a base station that can provide cells or coverage, through which terminal devices can access the network or receive services. The base station may be implemented as an evolved node B (eNB), a next generation eNB (ng-eNB), a next generation node B (gNB), or a beyond 5G base station. The base station may be embodied as a macro base station, a relay node, or a low power node such as a pico base station or a femto base station. The base station may consist of several distributed network units, such as a central unit (CU), one or more distributed units (DUs), one or more remote radio heads (RRHs) or remote radio units (RRUs). The number and functions of these distributed units depend on the selected split RAN architecture. The base station may be deployed on the ground or in the sky, for example on a satellite, a high altitude platform station, an unmanned aircraft system, a balloon, an airplane, and / or the like.

[0026] As used herein, the term “terminal device” or “user equipment” (UE) may refer to any entities or devices that can wirelessly communicate with the network devices or with each other. Examples of the terminal device can include a mobile phone, a mobile terminal (MT), a mobile station (MS), a subscriber station (SS), a portable subscriber station (PSS), an access terminal (AT), a computer, a wearable device, an on-vehicle communication device, a machine type communication (MTC) device, a D2D communication device, a V2X communication device, a sensor and the like. The term “terminal device” can be used interchangeably with a UE, a user terminal, a mobile terminal, a mobile station, or a wireless device.

[0027] As briefly mentioned above, in order to improve network energy savings, a wireless communication system or a UE may support some carriers (e.g., secondaiy cells, or SCell) without SSBs, herein also briefly referred to as “SSB-less SCell”. For example, in inter-band CA operating in FR1, an SSB of a reference cell can be a source of timing and / or frequency synchronization for the SSB-less SCell. The SSB-less SCell may be configured with TRS(s) for activation of the SSB-less SCell. The reference cell and SSB-less SCell may be collocated. In some aspects, the TRS(s) of the SSB-less SCell being activated may be quasi-collocation (e.g., QCL-typeC) with SSB(s) of the reference cell such that the coarse timing and AGC based on the SSB of the reference cell can be reused.

[0028] The reference cell is considered as the cell which has QCL relation with the TRSs on the SSB-less SCell in case there is only one active QCL source cell configured. Otherwise, if more than one active QCL source cell is configured, it is up to the network to indicate the reference cell to be used for the SSB-less SCell, for example, during the SCell activation. In other words, the network generally knows the number of QCL source cells that have been configured, and hence is able to indicate explicitly the exact reference cell if there are more than one potential QCL source cell to the TRS.

[0029] However, there are various issues about SSB-less SCell that remain unsolved. For example, it is unclear how UEs should select the TRS for activation of the SCell when two or more TRSs are configured for the SSB-less SCell.

[0030] For example, Figs. 1A and IB illustrate example SCell configuration to which the present disclosure may apply. As shown in Fig. 1A, an SSB-less SCell is configured with two TRSs, labelled as TRS 1 and TRS 2, for example. For instance, one TRS is considered as a series of CSI-RS resource set which are periodically or aperiodically transmitted in the SSB-less SCell, wherein one CSI-RS resource cell includes one set of CSI-RS resources (i.e. one TRS burst) with trs-info set to “true”. In present disclosure, TRS is used to indicate periodic TRS i.e. P-TRS for simplicity. The reference cell may transmit SSB that may be used by the SSB-less SCell for coarse synchronization. Herein, the SSB may also refer to synchronous signal and physical broadcast channel (PBCH) block. The two TRSs of the SSB-less SCell have QCL-typeC relation (or can be described as being “QCLed”) with two SSBs in the same reference cell, i.e., the QCL source cell. For example, TRS 1 is QCLed with the SSB 1, and TRS 2 is QCLed with the SSB 2, respectively.

[0031] In this case, the network device (e.g., gNB) does not indicate which TRS the UE shall assume to be used, so it is unclear which TRS burst is to be monitored by the UE and used for the SSB-less SCell activation. That is, the UE is not able to determine if TRS 1 or TRS 2 is to be monitored in the SSB-less SCell. In some aspects, when the TRS 1 and TRS 2 are periodic TRSs, since the UE is not able to measure the TRSs before SCell activation, the UE cannot know which P-TRS to monitor when activating the SSB-less SCell.

[0032] A similar issue exists for the case when one SSB is configured in the QCL source cell or multiple TRSs are QCLed with the same SSB in the reference cell. Referring to Fig. IB, both TRS 1 and TRS 2 are QCLed with the SSB 1 in the reference cell. In this case, the UE may also have no idea which TRS is to be used for the SSB-less SCell activation.

[0033] Example embodiments of the present disclosure provide solutions for this problem. The example embodiments enable the UE to determine the exact TRS to be monitored for activating the SSB-less SCell based on deterministic criteria or rules if there are more than one TRS configured for the SSB-less SCell. Thus the network device will be able to schedule the UE after the SCell is activated. The criteria or rules are known by both the network device and the UE such that the UE and the network device may align understanding on the TRS to be used in the SSB-SCell activation. Since no dedicated signaling is needed for the UE to be indicated which TRS is to be used, the signaling overhead between the UE and the network device can be alleviated.

[0034] Fig. 2 is an exemplary sequence diagram illustrating example operations for performing SSB-less SCell activation according to example embodiments of the present disclosure. In some implementations, the operations shown in the Fig. 2 may be performed by a terminal device 110 and a network device 120. The terminal device 110 may represent any terminal device in a wireless communication system, and the network device 120 may function as the network side serving the terminal device 110, such that they may communicate via a bidirectional link, which includes an uplink and a downlink.

[0035] In some cases, inter-band CA may be configured for the terminal device 110. For example, the network device 120 may configure CA for the terminal device 110 via a higher layer (e.g., RRC) signaling, DCI, a MAC-CE or other signaling messages. In this case, a set of aggregated carriers (or cells) configured for the terminal device 110 may include a plurality of carriers or cells operating in different frequency bands. The plurality of cells may include at least one a primary cell that transmits SSBs, and one or more SSB-less SCells that do not include SSBs. The primary cell may function as a reference cell for the SSB-less SCells. Additionally or alternatively, a QCL source cell of TRS in the SSB-less SCell may be identified by the network device 120 and the terminal device 110 as the reference cell. Or the reference cell may be indicated by the network device 120.

[0036] Referring to Fig. 2, at an operation 210, the network device 120 may transmit to the terminal device 110, configuration information of a plurality of TRSs for a SCell of the terminal device 110. For example, the SCell may be operated in an SSB-less mode, and may be activated by using one of the plurality of TRSs.

[0037] In some embodiments, the network device 120 may transmit the configuration information to the terminal device 110 on a carrier or cell that transmits the SSBs. For example, the configuration information may be transmitted on the primary cell, via an RRC message, a MAC-CE, or DCI. In an example, the configuration information may indicate various characteristics of the TRSs on the SSB-less SCell, e.g., the location of symbol in which the plurality of TRSs are transmitted, the periodicity of the plurality of TRSs, and the like. In an example, the TRS may include at least one of periodic TRS (P-TRS), or aperiodic TRS (A-TRS).

[0038] In some embodiments, the plurality of TRSs may have a QCL relation or be QCLed with at least one SSB configured in the reference cell. For example, the TRSs of the SCell may be configured to have a QCL-TypeC relation with the SSB(s) of the reference cell.

[0039] In an example, the QCL relation may be configured between an antenna port for transmitting the one or more SSBs and an antenna port for transmitting the plurality of TRSs. In an example, the QCL relation may be configured by a high layer signaling, e.g., indicated through one or more transmission configuration indication (TCI) states. In an example, the configuration of the QCL relation between the TRSs and the associated SSB(s) may be indicated as pairs of the TRSs and the associated SSBs, such that when a particular SSB is identified, the corresponding TRS may accordingly be determined or selected by the terminal device 110.

[0040] At an operation 220, the network device 120 may transmit, and the terminal device 110 may receive, a command of activation of the SSB-less SCell. The SCell activation command may indicate that the SSB-less SCell is to be activated for the terminal device. In an example, the network device 120 may transmit the command of SCell activation on a carrier or cell that transmits the SSBs. For example, the command of SCell activation may be transmitted via a higher layer (RRC) message, a MAC-CE, or DCI, on the primary cell. In an example, the command of SCell activation may be transmitted to the teiminal device 110 together with other configuration or message for the terminal device 110. For example, the configuration information of the plurality of TRSs and the command of SCell activation may be transmitted via a same message. Alternatively, they may be transmitted to the terminal device 110 via separate messages.

[0041] In response to the command of SCell activation received from the network device 120, at an operation 230, the terminal device 110 may determine a TRS from the plurality of TRSs to monitor during the activation of the SSB-less SCell. Meanwhile, at an operation 240, the network device 120 may also determine the TRS from the plurality of TRSs for the activation of the SSB-less SCell.

[0042] In some embodiments, the terminal device 110 and the network device 120 may determine implicitly which TRS from the configured plurality of TRSs to be used for the SCell activation based on a predetermined rule or set of rules. For example, the rule(s) may be defined in a wireless communication standard, e.g., a 3GPP communication standard. In this way, no explicit signaling is needed to be transmitted from the network device 120 to the terminal device 110, and accordingly the signaling overhead can be reduced.

[0043] In some embodiments, the terminal device 110 and the network device 120 may follow a same rule or set of rules to determine the TRS, so that the terminal device 110 and the network device 120 may align understanding of the TRS to be used for the SCell activation.

[0044] For example, the terminal device 110 and the network device 120 may determine the TRS from the configured plurality of TRSs based on at least one of the following criteria: the TRS which has the QCL relation with the SSB in an active TCI state of the reference cell; the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel (PDCCH) monitoring of the reference cell; the TRS which has a shortest periodicity of the plurality of TRSs which have the QCL relation with the SSB configured in the reference cell; the TRS which has the QCL relation with the SSB corresponding to the highest result of layer 1 (LI) or layer 3 (L3) measurement of the reference cell at the terminal device 110, or the TRS which has the QCL relation with the SSB corresponding to the highest result of LI or L3 measurement reporting of the reference cell reported to the network device 120; the TRS which has the QCL relation with the SSB corresponding to the shortest receive timing difference (RTD) between the TRS and the SSB configured in the reference cell, measured at the terminal device 110, or the TRS which has the QCL relation with the SSB corresponding to a shortest RTD between the TRS and the SSB, reported to the network device 120; the TRS which has the QCL relation with the SSB of the reference cell corresponding to a lowest SSB index; or the TRS which has a lowest index among the plurality of TRSs. More details of applying any one or combination of the criteria will be described later.

[0045] Then, at an operation 250, the terminal device 110 may activate the SSB- less SCell based on the determined TRS. For example, the terminal device 110 may active the SCell using the determined TRS starting from the first TRS burst after the SCell activation command. The determined TRS may further be used by the terminal device 110 for fine time / frequency tracking and fine AGC settling.

[0046] Based on the selection of the TRS, the SCell activation delay will be determined by the configuration information corresponding to the determined or selected TRS. In an example, the activation of the SSB-less SCell may be done with an activation delay, which may be within an activation delay requirement. Thus, the efficiency of SCell activation may be guaranteed.

[0047] In some embodiments, the terminal device 110 may, at an operation 260, transmit a notification message for informing the network device 120 that the SSB-less SCell has been activated or in an active state. In one example, the notification message may be a valid CSI report. Then, the network device 120 may perform inter- or intra- band CA through multiple cells including the activated SSB-less SCell.

[0048] As described above, when the network device 120 does not indicate which TRS to be used by the terminal device 110, the terminal device 110 should have some mechanism to select one TRS from the plurality of TRSs based on certain evaluation criteria. Figs. 3 through 7 illustrate example diagrams or operation flowcharts for selecting the TRS according to one or more example embodiments of the present disclosure.

[0049] In some example embodiments, the TRS used for SSB-less SCell activation may be determined based on the QCL relation between the TRS(s) of the SSB-less SCell and the SSB(s) of the reference cell. For explanation of this principle, reference is made to Fig. 3, which shows an example communication scenario in which example embodiments of the present disclosure may be implemented. Referring to Fig. 3, the communication network may include a terminal device (e.g., UE) 110, and a network device 120 implemented as a gNB. The gNB 120 may transmit SSBs, e.g., SSB 1 and SSB 2, in a QCL source cell (i.e., the reference cell). The gNB 120 may configure, for the UE 110, an SSB-less SCell which transmits one or more TRSs, each TRS including a series of TRS bursts, according to the TRS configuration information. Each TRS burst may include 4 symbols e.g. CSL RS resources. Not all the SSBs have QCL-typeC relation with the TRS bursts. Further, the two TRSs may be QCLed with two different SSBs of the QCL source cell. For brief explanation, the TRS 1 and the TRS 2 is shown as having QCL-typeC relation with the SSB 1, and SSB 2, respectively.

[0050] The UE 110 may receive from the gNB 120 an active TCI state 310 of the QCL source cell. Based on the active TCI state, there may be an SSB transmission in the QCL source cell. In an example, the UE 110 may select the TRS in the SSB-less SCell which has the QCL-typeC relation with the SSB in the active TCI state list. For example, if the SSB 1 is included in the active TCI state, the UE 110 will select TRS burst 1 to be monitored during the activation of the S SB-less SCell. By using the QCL relation between the TRS and the SSB, the SCell activation can be implemented in a relatively efficient manner.

[0051] In some instances, if there are multiple SSBs in the active TCI state of the reference cell, the UE 110 may select the TRS which has the QCL-typeC relation with the SSB in the active TCI state used for PDCCH monitoring of the reference cell, rather than the SSB in the TCI state used for, e.g., PDSCH.

[0052] In some example embodiments, the TRS used for SSB-less SCell activation may be determined based on the periodicity of the plurality of TRSs. In some cases, the network device (e.g., gNB) 120 may not necessarily need to configure to transmit the plurality of TRS bursts with the same periodicity. As an illustration, Fig. 4 shows an example that multiple P-TRSs may be configured with different periodicities. In Fig. 4, the reference cell may transmit an SSB burst of four SSBs (SSB 0, SSB 1, SSB 2, SSB 4) in an SSB period. The UE may be configured with two TRSs in the SSB-less SCell, i.e., including TRS burst 1, and TRS burst 2 respectively. The TRS burst 1 may be QCLed with SSB 0, and have a periodicity 410. The TRS burst 2 may be QCLed with SSB 2, and have a periodicity 420.

[0053] In such a scenario, the UE 110 may select the TRS which has the shortest periodicity of the plurality of TRSs which have the QCL relation with the SSB, e.g., in the active TCI state of the reference cell. For example, the TRS burst 1 will be selected in the case of Fig. 4. In this way, a fast activation of the SSB-less SCell can be achieved.

[0054] In some example embodiments, the TRS used for SSB-less SCell activation may be determined based on a measurement of the plurality of SSBs of the reference cell. Fig. 5 illustrates the TRS selection operation according to an example embodiment. Referring to Fig. 5, the operation starts at step 510, where the UE 110 may measure a signal strength of the SSBs transmitted by the QCL source cell and may send the measurement report to the network. For example, the measurement may include a L1 / L3 reference signal received power (RSRP) measurement, a L1 / L3 reference signal received quality (RSRQ) measurement, a L1 / L3 SINR measurement or any other suitable parameter based measurement, of the SSBs, may be performed by the UE 110.

[0055] At step 520, the UE 110 may identify the SSB corresponding to the latest highest measurement result or the latest highest measurement report. Having measured the received signal strength for all the SSBs, the UE 110 knows which SSB has the highest measurement value. In an example, the UE 110 may report to the gNB 120, the SSB measurement or the SSB index corresponding to the highest measurement result, such that the gNB 120 will be aware of the TRS to be used by the UE 110 for SSB-less SCell activation.

[0056] Then, at step 530, the UE 110 may select from the plurality of configured TRSs, the TRS which has QCL-typeC relation with the identified SSB as the TRS to be monitored during the SSB-less SCell activation. At the network side, the gNB 120 may also determine the same TRS as selected by the UE 110, based on the measurement reporting of the QCL source cell.

[0057] In some example embodiments, the TRS used for SSB-less SCell activation may be determined based on a receive timing difference (RTD) between the SSBs and the TRSs. Fig. 6 shows a diagram that SSB transmissions and TRS bursts are transmitted from the QCL source cell 610 and the SSB-less SCell 620 respectively. In Fig. 6, the QCL source cell 610 and the SSB-less SCell 620 are co-located cells, and the QCL relation between the TRS bursts and the associated SSBs may be indicated as pairs of the TRSs and the associated SSBs. For example, the TRS burst 1 is paired with SSB 1, and TRS burst 2 is paired with SSB 2. The UE 110 may measure, detect or otherwise determine the RTD for the SSB-TRS pairs. In an example, the UE 110 may report the RTD to the gNB 120 such that the gNB 120 will be aware of the TRS to be used by the UE 110 for SSB-less SCell activation.

[0058] In some cases, the RTD between the SSBs transmitted from the QCL source cell 610 and the TRSs from the SSB-less SCell 620 may not be equal. As shown in Fig. 6, the RTD between SSB 1 and TRS 1 (denoted as RTD1) is not equal to the RTD between SSB 2 and TRS 2 (denoted as RTD2). In this case, the UE 110 may select the TRS of the SSB-TRS pair which has the shortest RTD value. For example, TRS burst 1 will be selected if RTD 1 is less than RTD2. In this way, a reliable and efficient activation of the SSB-less SCell can be achieved.

[0059] In some example embodiments, the TRS used for SSB-less SCell activation may be determined based on the SSB index. For explanation of this approach, reference is made to Fig. 7, which shows example TRS configurations of the SSB-less SCell in connection with the QCL source cell. A first TRS configuration 700a shows two configured TRSs, e.g., TRS1 and TRS2, are QCLed to SSB 1 and SSB2 in the QCL source cell, respectively. In this case, the UE may select the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index configured by the gNB, i.e., TRS 1, to be used for SSB-less SCell activation. A second TRS configuration 700b shows TRS1 and TRS2 are QCLed to SSB 2 and SSB1 in the QCL source cell, respectively. In this case, TRS 2 will be selected to be used for the SSB-less SCell activation.

[0060] Alternatively, in some example embodiments, the TRS used for SSB-less SCell activation may be determined based on the TRS index. For example, the UE may determine the TRS which has a lowest index among the plurality of configured TRSs as the TRS for SSB-less SCell activation. Still referring to Fig. 7, the TRS 1 will be selected to be used for the SSB-less SCell activation, for both configuration 700a and 700b.

[0061] In the above example embodiments, two TRSs and SSBs are described as exemplary and not limiting. It shall be understood that the example embodiments according to the present disclosure may also apply in the case where more than two TRSs and SSBs are configured for the SSB-less SCell and the reference cell.

[0062] In some cases, a combination of the TRS selection criteria described above can be used to select the TRS for SSB-SCell activation. Figs. 8 through 11 illustrate TRS selection operation sequences in case a plurality of TRSs are configured for SSB-less SCell, in according to example embodiments of the present disclosure.

[0063] In some example embodiments, referring to Fig. 8, the operation may start at step 810, where the active TCI state of the reference cell is received. Then at step 820, a determination is made whether there are more than one SSB in the active TCI state, e.g., used for the PDCCH monitoring. If the determination is “No”, the UE 110 may select, at step 830, the TRS which has the QCL relation with the SSB in the active TCI state of the reference cell, or the TRS which has the QCL relation with the SSB in the active TCI state used for PDCCH monitoring of the reference cell. Otherwise, at step 840, the UE 110 may select the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index, or the TRS which has a lowest index among the plurality of TRSs.

[0064] In some example embodiments, referring to Fig. 9, the operation may start at step 910, where a determination is made whether there are more than one TRS having the shortest periodicity, based on the received configuration information for the plurality of TRSs. If the determination is “No”, the UE 110 may select, at step 920, the TRS with the minimum periodicity. Otherwise, at step 930, the UE 110 may select the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index, or the TRS which has a lowest index among the plurality of TRSs.

[0065] In some example embodiments, referring to Fig. 10, the operation may start at step 1010, where an SSB measurement (e.g., L1 / L3 RSRP) is performed. Then at step 1020, a determination is made whether there are more than one TRS having the same highest measurement value or the measurement report. If the determination is “No”, the UE 110 may select, at step 1030, the TRS which has the QCL relation with the SSB corresponding to the highest result of L1 / L3 measurement or the measurement report. Otherwise, at step 1040, the UE 110 may select the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index, or the TRS which has a lowest index among the plurality of TRSs.

[0066] In some example embodiments, referring to Fig. 11, the operation may start at step 1110, where a RTD measurement is performed. Then at step 1120, a determination is made whether there are more than one pair of the TRS and the SSB corresponding to the shortest RTD. If the determination is “No”, the UE 110 may select, at step 1130, the TRS which has the QCL relation with the SSB corresponding to the shortest RTD between the TRS and the SSB. Otherwise, at step 1140, the UE 110 may select the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index, or the TRS which has a lowest index among the plurality of TRSs

[0067] According to example embodiments of the present disclosure, in case multiple TRSs are configured for a SSB-less SCell, and more than one TRS is QCL-ed with the SSBs in single reference cell, an exact TRS for activation of the SSB-less SCell can be determined by the terminal device and the network device without the need of dedicated signaling. Thus, a technical advantage provided by some example embodiments is that the signaling overhead between the terminal device and the network device can be alleviated, and network energy saving can be increased.

[0068] Fig. 12 shows a flowchart of an example method 1200 for determining a TRS for activation of a SSB-less SCell according to an example embodiment of the present disclosure. The method 1200 can be implemented at a terminal device e.g. the UE 110 discussed above. In some example embodiments, the method 1200 may further include one or more steps that are performed at the UE 110 as described above with respect to Figs. 2-11. It would also be understood that details of some steps in the procedure 1200 have been discussed above with respect to Figs. 2-11 and the procedure 1200 will be described here in a simple manner.

[0069] At block 1210, the terminal device may receive from a network device, configuration information of a plurality of TRSs for a SCell operating in SSB-less mode, wherein the plurality of TRSs may have QCL relation with at least one SSB configured in a reference cell.

[0070] In some example embodiments, the QCL relation may be QCL-TypeC relation.

[0071] In some example embodiments, the tracking reference signal may be a periodic TRS, or an aperiodic TRS.

[0072] At block 1220, the terminal device may receive from the network device, a command of activation of the SCell.

[0073] At block 1230, the terminal device may determine a TRS from the plurality of TRSs to monitor during the activation of the SCell.

[0074] In some example embodiments, the terminal device may determine the TRS based on at least one of the following criteria: the TRS which has the QCL relation with the SSB in an active transmission configuration indication, TCI, state of the reference cell; the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell; the TRS which has a shortest periodicity of the plurality of TRSs which have the QCL relation with the SSB configured in the reference cell; the TRS which has the QCL relation with the SSB corresponding to the highest result of layer 1 or layer 3 measurement of the reference cell at the terminal device; the TRS which has the QCL relation with the SSB corresponding to the highest result of layer 1 or layer 3 measurement reporting of the reference cell at the terminal device; the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB configured in the reference cell; the TRS which has the QCL relation with the SSB of the reference cell corresponding to a lowest SSB index; or the TRS which has a lowest index among the plurality of TRSs.

[0075] In some example embodiments, determining the TRS may comprise: determining the TRS which has the QCL relation with the SSB in the active TCI state of the reference cell or determining the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell; and determining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB in the active TCI state.

[0076] In some example embodiments, determining the TRS may comprise: determining the TRS which has a shortest periodicity of the plurality of TRSs; and determining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one TRS having the shortest periodicity.

[0077] In some example embodiments, determining the TRS may comprise: determining the TRS which has the QCL relation with the SSB corresponding to a highest result of layer 1 or layer 3 measurement or a highest result of layer 1 or layer 3 measurement reporting of the reference cell at the terminal device; and determining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB having the highest result of layer 1 or layer 3 measurement.

[0078] In some example embodiments, determining the TRS may comprise: determining the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB; and determining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one pair of the TRS and the SSB corresponding to the shortest RTD.

[0079] At block 1240, the terminal device may activate the SCell based on the determined TRS.

[0080] In some example embodiments, the activation of the SCell is done with an activation delay.

[0081] Fig. 13 shows a flowchart of an example method 1300 for determining a TRS for activation of a SSB-less SCell according to an example embodiment of the present disclosure. The method 1300 may be performed at a network device like the network device e.g. the gNB 120 discussed above. In some example embodiments, the method 1300 may further include one or more steps that are performed at the network device 120 as described above with respect to Figs. 2-11. It would also be understood that details of some steps in the procedure 1300 have been discussed above with respect to Figs. 2-11 and the procedure 1300 will be described here in a simple manner.

[0082] At block 1310, the network device may transmit to a terminal device, configuration information of a plurality of TRSs for a SCell operating in SSB-less mode, wherein the plurality of TRSs may have QCL relation with at least one SSB configured in a reference cell.

[0083] In some example embodiments, the QCL relation may be QCL-TypeC relation.

[0084] In some example embodiments, the tracking reference signal may be a periodic TRS, or an aperiodic TRS.

[0085] At block 1320, the network device may transmit to the terminal device, a command of activation of the SCell.

[0086] At block 1330, the network device may determine a TRS from the plurality of TRSs for the activation of the SCell.

[0087] In some example embodiments, the network device may determine the TRS based on at least one of the following criteria: the TRS which has the QCL relation with the SSB in an active transmission configuration indication, TCI, state of the reference cell; the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell; the TRS which has a shortest periodicity of the plurality of TRSs which have the QCL relation with the SSB configured in the reference cell; the TRS which has the QCL relation with the SSB corresponding to the highest result of layer 1 or layer 3 measurement reporting of the reference cell reported to the network device; the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB configured in the reference cell, reported to the network device; the TRS which has the QCL relation with the SSB of the reference cell corresponding to a lowest SSB index; or the TRS which has a lowest index among the plurality of TRSs.

[0088] In some example embodiments, determining the TRS may comprise: determining the TRS which has the QCL relation with the SSB in the active TCI state of the reference cell or determining the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell; and determining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB in the active TCI state.

[0089] In some example embodiments, determining the TRS may comprise: determining the TRS which has a shortest periodicity of the plurality of TRSs; and determining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one TRS having the shortest periodicity.

[0090] In some example embodiments, determining the TRS may comprise: determining the TRS which has the QCL relation with the SSB corresponding to a highest result of layer 1 or layer 3 measurement reporting of the reference cell reported to the network device; and determining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB having the highest result of layer 1 or layer 3 measurement.

[0091] In some example embodiments, determining the TRS may comprise: determining the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB, reported to the network device; and determining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one pair of the TRS and the SSB corresponding to the shortest RTD.

[0092] Fig. 14 is a block diagram illustrating an apparatus 1400 according to an example embodiment of the present disclosure. The apparatus 1400 may be implemented at a terminal device like the UE 110 to perform operations relating to the UE 110 as discussed above. Since the operations relating to the UE 110 have been discussed in detail with reference to Figs. 2-11, the blocks of the apparatus 1400 will be described briefly here and details thereof may refer to the above description.

[0093] Referring to Fig. 14, the apparatus 1400 may include a first means 1410 for receiving from a network device, configuration information of a plurality of TRSs for a SCell operating in SSB-less mode, wherein the plurality of TRSs may have QCL relation with at least one SSB configured in a reference cell.

[0094] In some example embodiments, the apparatus 1400 may further include a second means 1420 for receiving from the network device a command of activation of the SCell.

[0095] In some example embodiments, the apparatus 1400 may further include a third means 1430 for determining a TRS from the plurality of TRSs to monitor during the activation of the SCell.

[0096] In some example embodiments, the apparatus 1400 may further include a fourth means 1440 for activating the SCell based on the determined TRS.

[0097] Fig. 15 is a block diagram illustrating an apparatus 1500 according to an example embodiment of the present disclosure. The apparatus 1500 may be implemented to comprise or to form at least part of the network device like gNB 120 discussed above to perform at least part of operations related to the gNB 120. Since the operations related to the gNB 120 have been discussed above with reference to Figs. 2-11, the blocks of the apparatus 1500 will be described briefly here and details thereof may refer to the above description.

[0098] Referring to Fig. 15, the apparatus 1500 may include a first means 1510 for transmitting to a terminal device, configuration information of a plurality of TRSs for a SCell operating in SSB-less mode, wherein the plurality of TRSs may have QCL relation with at least one SSB configured in a reference cell.

[0099] In some example embodiments, the apparatus 1500 may further include a second means 1520 for transmitting to the terminal device, a command of activation of the SCell.

[00100] In some example embodiments, the apparatus 1500 may further include a third means 1530 for determining a TRS from the plurality of TRSs for the activation of the SCell.

[00101] Fig. 16 is a block diagram illustrating devices in a communication system 1600 in accordance with an example embodiment of the present disclosure. As shown in Fig. 16, the communication system 1600 may comprise a terminal device 1610 which may be implemented as the UE 110 discussed above and a network device 1620 which may be implemented as the gNB 120 discussed above.

[00102] Referring to Fig. 16, the terminal device 1610 may comprise one or more processors 1611, one or more memories 1612 and one or more transceivers 1613 interconnected through one or more buses 1614. The one or more buses 1614 may be address, data, or control buses, and may include any interconnection mechanism such as series of lines on a motherboard or integrated circuit, fiber, optics or other optical communication equipment, and the like. Each of the one or more transceivers 1613 may comprise a receiver and a transmitter, which are connected to one or more antennas 1616. The terminal device 1610 may wirelessly communicate with the radio access network device 1620 through the one or more antennas 1616. The one or more memories 1612 may include instructions 1615 which, when executed by the one or more processors 1611, may cause the terminal device 1610 to perform operations and procedures relating to the UE 110 as described above.

[00103] The network device 1620 may comprise one or more processors 1621, one or more memories 1622, one or more transceivers 1623 and one or more network interfaces 1627 interconnected through one or more buses 1624. The one or more buses 1624 may be address, data, or control buses, and may include any interconnection mechanism such as a series of lines on a motherboard or integrated circuit, fiber, optics or other optical communication equipment, and the like. Each of the one or more transceivers 1623 may comprise a receiver and a transmitter, which are connected to one or more antennas 1626. The network device 1620 may operate as a base station for the terminal device 1610 and wirelessly communicate with terminal device 1610 through the one or more antennas 1626. The one or more network interfaces 1627 may provide wired or wireless communication links through which the network device 1620 may communicate with other network devices, entities, elements or functions. For example, the network device 1620 may communicate with a core network device (not shown) via backhaul connections. The one or more memories 1622 may include instructions 1625 which, when executed by the one or more processors 1621, may cause the network device 1620 to perform operations and procedures relating to the gNB 120.

[00104] The one or more processors 1611, 1621 discussed above may be of any appropriate type that is suitable for the local technical network, and may include one or more of general purpose processors, special purpose processor, microprocessors, a digital signal processor (DSP), one or more processors in a processor based multi-core processor architecture, as well as dedicated processors such as those developed based on Field Programmable Gate Array (FPGA) and Application Specific Integrated Circuit (ASIC). The one or more processors 1611, 1621 may be configured to control other elements of the UE / radio access network device / core network device and operate in cooperation with them to implement the procedures discussed above.

[00105] The one or more memories 1612, 1622 may include at least one storage medium in various forms, such as a transitory memory and / or a non-transitory memory. The transitory memory may include, but not limited to, for example, a random access memory (RAM) or a cache. The non-transitory memory may include, but not limited to, for example, a read only memory (ROM), a hard disk, a flash memory, and the like. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM). Further, the one or more memories 1612, 1622 may include but not limited to an electric, a magnetic, an optical, an electromagnetic, an infrared, or a semiconductor system, apparatus, or device or any combination of the above.

[00106] It would be understood that blocks in the drawings may be implemented in various manners, including software, hardware, firmware, or any combination thereof. In some embodiments, one or more blocks may be implemented using software and / or firmware, for example, machine-executable instructions stored in the storage medium. In addition to or instead of machine-executable instructions, parts or all of the blocks in the drawings may be implemented, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include Field-Programmable Gate Arrays (FPGAs), Application-Specific Integrated Circuits (ASICs), Application-Specific Standard Products (ASSPs), System-on-Chip systems (SOCs), Complex Programmable Logic Devices (CPLDs), etc.

[00107] Some exemplary embodiments further provide program instruction or instructions which, when executed by one or more processors, may cause a device or apparatus to perform the procedures described above. The program instruction for carrying out procedures of the exemplary embodiments may be written in any combination of one or more programming languages. The program instruction may be provided to one or more processors or controllers of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program instruction, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program instruction 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.

[00108] Some exemplary embodiments further provide a computer program product or a computer readable medium having the program instruction or instructions stored therein. The computer readable medium may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but is not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine 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.

[00109] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[00110] 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.

[00111] Although the subject matter has been described in a language that is specific to structural features and / or method actions, it is to be understood the subject matter defined in the appended claims is not limited to the specific features or actions described above. On the contrary, the above-described specific features and actions are disclosed as an example of implementing the claims.

[00112] Certain abbreviations that may be found in the description and / or in the figures are herewith defined as follows: QCL quasi co-location RTD receive timing difference SSB synchronization signal block TCI transmission configuration indication TRS tracking reference signal UE user equipment

Claims

1. An apparatus for a terminal device, comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:receive from a network device, configuration information of a plurality of tracking reference signals, TRSs, for a secondary cell, SCell, operating in synchronization signal block-less, SSB-less, mode, the plurality of TRSs having quasi co-location, QCL, relation with at least one synchronization signal block, SSB, configured in a reference cell;receive from the network device, a command of activation of the SCell; anddetermine a TRS from the plurality of TRSs to monitor during the activation of the SCell.

2. The apparatus of claim 1, wherein the apparatus is configured to:determine the TRS based on at least one of the following criteria:the TRS which has the QCL relation with the SSB in an active transmission configuration indication, TCI, state of the reference cell;the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell;the TRS which has a shortest periodicity of the plurality of TRSs which havethe QCL relation with the SSB configured in the reference cell;the TRS which has the QCL relation with the SSB corresponding to the highest result of layer 1 or layer 3 measurement of the reference cell at the terminal device;the TRS which has the QCL relation with the SSB corresponding to the highest result of layer 1 or layer 3 measurement reporting of the reference cell at the terminal device;the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB configured in the reference cell;the TRS which has the QCL relation with the SSB of the reference cell corresponding to a lowest SSB index; orthe TRS which has a lowest index among the plurality of TRSs.

3. The apparatus of claim 2, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB in the active TCI state of the reference cell or determining the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB in the active TCI state.

4. The apparatus of claim 2, wherein determining the TRS comprises:determining the TRS which has a shortest periodicity of the plurality of TRSs; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one TRS having the shortest periodicity.

5. The apparatus of claim 2, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB corresponding to a highest result of layer 1 or layer 3 measurement or a highest result of layer 1 or layer 3 measurement reporting of the reference cell at the terminal device; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB having the highest result of layer 1 or layer 3 measurement.

6. The apparatus of claim 2, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality ofTRSs, in case there are more than one pair of the TRS and the SSB corresponding to the shortest RTD.

7. The apparatus of any of claims 1-6, wherein the apparatus is configured to:activate the SCell based on the determined TRS.

8. The apparatus of claim 7, wherein the activation of the SCell is done with an activation delay.

9. The apparatus of any of claims 1-8, wherein the QCL relation is QCL-TypeC relation.

10. The apparatus of any of claims 1-9, wherein the tracking reference signal is a periodic TRS, or an aperiodic TRS.

11. An apparatus for a network device, comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:transmit to a terminal device, configuration information of a plurality of tracking reference signals, TRSs, for a secondary cell, SCell, operating in synchronization signal block-less, SSB-less, mode, the plurality of TRSs havingquasi co-location, QCL, relation with at least one synchronization signal block, SSB, configured in a reference cell;transmit to the terminal device, a command of activation of the SCell; and determine a TRS from the plurality of TRSs for the activation of the SCell.

12. The apparatus of claim 11, wherein the apparatus is configured to:determine the TRS based on at least one of the following criteria:the TRS which has the QCL relation with the SSB in an active transmission configuration indication, TCI, state of the reference cell;the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell;the TRS which has a shortest periodicity of the plurality of TRSs which have the QCL relation with the SSB configured in the reference cell;the TRS which has the QCL relation with the SSB corresponding to the highest result of layer 1 or layer 3 measurement reporting of the reference cell reported to the network device;the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB configured in the reference cell, reported to the network device;the TRS which has the QCL relation with the SSB of the reference cell corresponding to a lowest SSB index; orthe TRS which has a lowest index among the plurality of TRSs.

13. The apparatus of claim 12, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB in the active TCI state of the reference cell or determining the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB in the active TCI state.

14. The apparatus of claim 12, wherein determining the TRS comprises:determining the TRS which has a shortest periodicity of the plurality of TRSs; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one TRS having the shortest periodicity.

15. The apparatus of claim 12, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB corresponding to a highest result of layer 1 or layer 3 measurement reporting of the reference cell reported to the network device; anddetermining the TRS which has the QCL relation with the SSB correspondingto a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB having the highest result of layer 1 or layer 3 measurement.

16. The apparatus of claim 12, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB, reported to the network device; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one pair of the TRS and the SSB corresponding to the shortest RTD.

17. The apparatus of any of claims 11-16, wherein the QCL relation is QCL-TypeC relation.

18. The apparatus of any of claims 11-17, wherein the tracking reference signal is a periodic TRS, or an aperiodic TRS.

19. A method performed by an apparatus for a terminal device, comprising:receiving from a network device, configuration information of a plurality of tracking reference signals, TRSs, for a secondary cell, SCell, operating insynchronization signal block-less, SSB-less, mode, the plurality of TRSs having quasi co-location, QCL, relation with at least one synchronization signal block, SSB, configured in a reference cell;receiving from the network device, a command of activation of the SCell; and determining a TRS from the plurality of TRSs to monitor during the activation of the SCell.

20. The method of claim 19, further comprising:determining the TRS based on at least one of the following criteria:the TRS which has the QCL relation with the SSB in an active transmission configuration indication, TCI, state of the reference cell;the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell;the TRS which has a shortest periodicity of the plurality of TRSs which have the QCL relation with the SSB configured in the reference cell;the TRS which has the QCL relation with the SSB corresponding to the highest result of layer 1 or layer 3 measurement of the reference cell at the terminal device;the TRS which has the QCL relation with the SSB corresponding to the highest result of layer 1 or layer 3 measurement reporting of the reference cell at the terminal device;the TRS which has the QCL relation with the SSB corresponding to a shortestreceive timing difference, RTD, between the TRS and the SSB configured in the reference cell;the TRS which has the QCL relation with the SSB of the reference cell corresponding to a lowest SSB index; orthe TRS which has a lowest index among the plurality of TRSs.

21. The method of claim 20, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB in the active TCI state of the reference cell or determining the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB in the active TCI state.

22. The method of claim 20, wherein determining the TRS comprises:determining the TRS which has a shortest periodicity of the plurality of TRSs; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one TRS having the shortest periodicity.

23. The method of claim 20, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB corresponding to a highest result of layer 1 or layer 3 measurement or a highest result of layer 1 or layer 3 measurement reporting of the reference cell at the terminal device; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB having the highest result of layer 1 or layer 3 measurement.

24. The method of claim 20, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one pair of the TRS and the SSB corresponding to the shortest RTD.

25. The method of any of claims 19-24, further comprising:activating the SCell based on the determined TRS.

26. The method of claim 25, wherein the activation of the SCell is done with an activation delay.

27. The method of any of claims 19-26, wherein the QCL relation is QCL-TypeC relation.

28. The method of any of claims 19-27, wherein the tracking reference signal is a periodic TRS, or an aperiodic TRS.

29. A method performed by an apparatus for a network device, comprising:transmitting to a terminal device, configuration information of a plurality of tracking reference signals, TRSs, for a secondary cell, SCell, operating in synchronization signal block-less, SSB-less, mode, the plurality of TRSs having quasi co-location, QCL, relation with at least one synchronization signal block, SSB, configured in a reference cell;transmitting to the terminal device, a command of activation of the SCell; and determining a TRS from the plurality of TRSs for the activation of the SCell.

30. The method of claim 29, further comprising:determining the TRS based on at least one of the following criteria:the TRS which has the QCL relation with the SSB in an active transmission configuration indication, TCI, state of the reference cell;the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell;the TRS which has a shortest periodicity of the plurality of TRSs which have the QCL relation with the SSB configured in the reference cell;the TRS which has the QCL relation with the SSB corresponding to the highest result of layer 1 or layer 3 measurement reporting of the reference cell reported to the network device;the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB configured in the reference cell, reported to the network device;the TRS which has the QCL relation with the SSB of the reference cell corresponding to a lowest SSB index; orthe TRS which has a lowest index among the plurality of TRSs.

31. The method of claim 30, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB in the active TCI state of the reference cell or determining the TRS which has the QCL relation with the SSB in the active TCI state used for physical downlink control channel, PDCCH, monitoring of the reference cell; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB in the active TCI state.

32. The method of claim 30, wherein determining the TRS comprises:determining the TRS which has a shortest periodicity of the plurality of TRSs; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one TRS having the shortest periodicity.

33. The method of claim 30, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB corresponding to a highest result of layer 1 or layer 3 measurement reporting of the reference cell reported to the network device; anddetermining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one SSB having the highest result of layer 1 or layer 3 measurement.

34. The method of claim 30, wherein determining the TRS comprises:determining the TRS which has the QCL relation with the SSB corresponding to a shortest receive timing difference, RTD, between the TRS and the SSB, reported to the network device;determining the TRS which has the QCL relation with the SSB corresponding to a lowest SSB index or the TRS which has a lowest index among the plurality of TRSs, in case there are more than one pair of the TRS and the SSB correspondingto the shortest RTD.

35. The method of any of claims 29-34, wherein the QCL relation is QCL-TypeC relation.

36. The method of any of claims 29-35, wherein the tracking reference signal is a periodic TRS, or an aperiodic TRS.

37. An apparatus for a terminal device, comprising means for performing the method of any of claims 19 to 28.

38. An apparatus for a network device, comprising means for performing the method of any of claims 29 to 36.

39. A computer readable medium comprising instructions which, when executed by an apparatus, cause the apparatus to at least perform the method of any of claims 19 to 36.

40. A computer program product comprising instructions which, when executed by an apparatus, cause the apparatus to at least perform the method of any of claims 19 to 36.

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