Patent Publication Number: US-2022225183-A1

Title: Fast scell activation

Description:
CROSS REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of and priority to U.S. Provisional Application Ser. No. 63/135,472, entitled “METHOD AND APPARATUS FOR FAST SCELL ACTIVATION” and filed on Jan. 8, 2021, which is expressly incorporated by reference herein in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to communication systems, and more particularly, to a method of wireless communication including a fast secondary cell (SCell) activation using temporary reference signal (RS). 
     INTRODUCTION 
     Wireless communication systems are widely deployed to provide various telecommunication services such as telephony, video, data, messaging, and broadcasts. Typical wireless communication systems may employ multiple-access technologies capable of supporting communication with multiple users by sharing available system resources. Examples of such multiple-access technologies include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, orthogonal frequency division multiple access (OFDMA) systems, single-carrier frequency division multiple access (SC-FDMA) systems, and time division synchronous code division multiple access (TD-SCDMA) systems. 
     These multiple access technologies have been adopted in various telecommunication standards to provide a common protocol that enables different wireless devices to communicate on a municipal, national, regional, and even global level. An example telecommunication standard is 5G New Radio (NR). 5G NR is part of a continuous mobile broadband evolution promulgated by Third Generation Partnership Project (3GPP) to meet new requirements associated with latency, reliability, security, scalability (e.g., with Internet of Things (IoT)), and other requirements. 5G NR includes services associated with enhanced mobile broadband (eMBB), massive machine type communications (mMTC), and ultra-reliable low latency communications (URLLC). Some aspects of 5G NR may be based on the 4G Long Term Evolution (LTE) standard. There exists a need for further improvements in 5G NR technology. These improvements may also be applicable to other multi-access technologies and the telecommunication standards that employ these technologies. 
     BRIEF SUMMARY 
     The following presents a simplified summary of one or more aspects in order to provide a basic understanding of such aspects. This summary is not an extensive overview of all contemplated aspects, and is intended to neither identify key or critical elements of all aspects nor delineate the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form as a prelude to the more detailed description that is presented later. 
     In an aspect of the disclosure, a method, a computer-readable medium, and an apparatus are provided. The apparatus may be user equipment (UE) may receive, from a serving cell, an activation indication for a SCell, receiving a first reference signal from the SCell, the first reference signal including at least one temporary reference signal, identify whether a second reference signal is received after processing the activation indication and before an expiration of an SCell activation time, and activate, upon identifying that the second reference signal is received, the SCell based on one or more reference signals including at least one of the first reference signal or the second reference signal. The UE may activate the SCell no later than in slot n+K, and K may be determined based on at least in part the SCell activation time. 
     The UE may transmit, to the serving cell, an acknowledgment (ACK) of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell. The UE may transmit a channel state information (CSI) report of one of the first reference signal or the second reference signal on which the UE based the activation of the SCell. 
     The UE may activate the SCell no later than in slot n+K, and K may be determined based on at least in part the SCell activation time. In one aspect, the activation indication may be received via one of a medium access control (MAC) control element (CE) (MAC-CE) or downlink control information (DCI), and the at least one temporary reference signal includes an aperiodic tracking reference signal, and the activation indication indicates the aperiodic tracking reference signal transmitted by the SCell. The SCell activation time may be the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving the at least one temporary reference signal. 
     In another aspect, the activation indication may be received via radio resource control (RRC) signaling, and the at least one temporary reference signal includes a periodic tracking reference signal, and the activation indication indicates the periodic tracking reference signal transmitted by the SCell. The SCell activation time may be the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving a last of one or more reference signals on which the UE based the activation of the SCell. The activation indication may indicate activating multiple SCells simultaneously, and the multiple SCells may be in the same frequency band, in contiguous carriers in the same frequency band, or in a frequency range. 
     The UE may receive, from a serving cell, an activation indication for the SCell based on a first reference signal, the activation indication indicating a transmission of the first reference signal for activating the SCell, identify whether the first reference signal is transmitted as indicated, and activating, upon identifying that the first reference signal is transmitted as indicated, the SCell based on one or more reference signals including the first reference signal or a second reference signal. The UE may transmit, to the serving cell, the ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell. 
     The first reference signal may include at least one of a periodic tracking reference signal or an aperiodic tracking reference signal. The UE may identify whether the first reference signal is transmitted as indicated by performing a clear channel assessment to determine whether a channel measurement is greater than a threshold value, and identifying that the first reference signal is not transmitted as indicated by the activation indication in response to determining that the channel measurement is greater than the threshold value. 
     The UE may receive, from the serving cell, an instruction to cancel the transmission of the first reference signal where the UE identifies that the first reference signal is not transmitted in response to receiving the instruction to cancel the transmitted first reference signal, and where the instruction to cancel the activation indication for the SCell based on the first reference signal is indicated by one of a MAC-CE or DCI. 
     The UE may receive, upon identifying that the first reference signal is not transmitted as indicated, a second reference signal from the SCell, and activate, upon identifying that the first reference signal is not transmitted as indicated, the SCell based on the second reference signal received from the SCell. The SCell activation time may be the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal. 
     The UE may receive a new activation indication indicating a transmission of a second reference signal for activating the SCell, where, upon receiving the new activation indication, the UE identifies that the first reference signal is not transmitted as indicated. 
     The activation indication may indicate activating multiple SCells simultaneously, and the multiple SCells may be in the same frequency band, in contiguous carriers in the same frequency band, or in a frequency range. 
     To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of various aspects may be employed, and this description is intended to include all such aspects and their equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating an example of a wireless communications system and an access network. 
         FIG. 2A  is a diagram illustrating an example of a first frame, in accordance with various aspects of the present disclosure. 
         FIG. 2B  is a diagram illustrating an example of DL channels within a subframe, in accordance with various aspects of the present disclosure. 
         FIG. 2C  is a diagram illustrating an example of a second frame, in accordance with various aspects of the present disclosure. 
         FIG. 2D  is a diagram illustrating an example of UL channels within a subframe, in accordance with various aspects of the present disclosure. 
         FIG. 3  is a diagram illustrating an example of a base station and user equipment (UE) in an access network. 
         FIG. 4  illustrates an example of SCell activation of wireless communication. 
         FIG. 5  illustrates an example of SCell activation of wireless communication. 
         FIG. 6  illustrates an example of SCell activation of wireless communication. 
         FIG. 7  illustrates a call-flow diagram of wireless communication. 
         FIG. 8  is a flowchart of a method of wireless communication. 
         FIG. 9  is a flowchart of a method of wireless communication. 
         FIG. 10  illustrates an example of SCell activation of wireless communication. 
         FIG. 11  illustrates an example of SCell activation of wireless communication. 
         FIG. 12  illustrates a call-flow diagram of wireless communication. 
         FIG. 13  is a flowchart of a method of wireless communication. 
         FIG. 14  is a flowchart of a method of wireless communication. 
         FIG. 15  is a diagram illustrating an example of a hardware implementation for an example apparatus. 
     
    
    
     DETAILED DESCRIPTION 
     The detailed description set forth below in connection with the appended drawings is intended as a description of various configurations and is not intended to represent the only configurations in which the concepts described herein may be practiced. The detailed 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 structures and components are shown in block diagram form in order to avoid obscuring such concepts. 
     Several aspects of telecommunication systems will now be presented with reference to various apparatus and methods. These apparatus and methods will be described in the following detailed description and illustrated in the accompanying drawings by various blocks, components, circuits, processes, algorithms, etc. (collectively referred to as “elements”). These elements may be implemented using electronic hardware, computer software, or any combination thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. 
     By way of example, an element, or any portion of an element, or any combination of elements may be implemented as a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on a chip (SoC), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. 
     Accordingly, in one or more example embodiments, the functions described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer. 
     While aspects and implementations are described in this application by illustration to some examples, those skilled in the art will understand that additional implementations and use cases may come about in many different arrangements and scenarios. Innovations described herein may be implemented across many differing platform types, devices, systems, shapes, sizes, and packaging arrangements. For example, implementations and/or uses may come about via integrated chip implementations and other non-module-component based devices (e.g., end-user devices, vehicles, communication devices, computing devices, industrial equipment, retail/purchasing devices, medical devices, artificial intelligence (AI)-enabled devices, etc.). While some examples may or may not be specifically directed to use cases or applications, a wide assortment of applicability of described innovations may occur. Implementations may range a spectrum from chip-level or modular components to non-modular, non-chip-level implementations and further to aggregate, distributed, or original equipment manufacturer (OEM) devices or systems incorporating one or more aspects of the described innovations. In some practical settings, devices incorporating described aspects and features may also include additional components and features for implementation and practice of claimed and described aspect. For example, transmission and reception of wireless signals necessarily includes a number of components for analog and digital purposes (e.g., hardware components including antenna, RF-chains, power amplifiers, modulators, buffer, processor(s), interleaver, adders/summers, etc.). It is intended that innovations described herein may be practiced in a wide variety of devices, chip-level components, systems, distributed arrangements, aggregated or disaggregated components, end-user devices, etc. of varying sizes, shapes, and constitution. 
       FIG. 1  is a diagram illustrating an example of a wireless communications system and an access network  100 . The wireless communications system (also referred to as a wireless wide area network (WWAN)) includes base stations  102 , UEs  104 , an Evolved Packet Core (EPC)  160 , and another core network  190  (e.g., a 5G Core (5GC)). The base stations  102  may include macrocells (high power cellular base station) and/or small cells (low power cellular base station). The macrocells include base stations. The small cells include femtocells, picocells, and microcells. 
     The base stations  102  configured for 4G LTE (collectively referred to as Evolved 
     Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN)) may interface with the EPC  160  through first backhaul links  132  (e.g., S1 interface). The base stations  102  configured for 5G NR (collectively referred to as Next Generation RAN (NG-RAN)) may interface with core network  190  through second backhaul links  184 . In addition to other functions, the base stations  102  may perform one or more of the following functions: transfer of user data, radio channel ciphering and deciphering, integrity protection, header compression, mobility control functions (e.g., handover, dual connectivity), inter-cell interference coordination, connection setup and release, load balancing, distribution for non-access stratum (NAS) messages, NAS node selection, synchronization, radio access network (RAN) sharing, multimedia broadcast multicast service (MBMS), subscriber and equipment trace, RAN information management (RIM), paging, positioning, and delivery of warning messages. The base stations  102  may communicate directly or indirectly (e.g., through the EPC  160  or core network  190 ) with each other over third backhaul links  134  (e.g., X2 interface). The first backhaul links  132 , the second backhaul links  184 , and the third backhaul links  134  may be wired or wireless. 
     The base stations  102  may wirelessly communicate with the UEs  104 . Each of the base stations  102  may provide communication coverage for a respective geographic coverage area  110 . There may be overlapping geographic coverage areas  110 . For example, the small cell  102 ′ may have a coverage area  110 ′ that overlaps the coverage area  110  of one or more macro base stations  102 . A network that includes both small cell and macrocells may be known as a heterogeneous network. A heterogeneous network may also include Home Evolved Node Bs (eNBs) (HeNBs), which may provide service to a restricted group known as a closed subscriber group (CSG). The communication links  120  between the base stations  102  and the UEs  104  may include uplink (UL) (also referred to as reverse link) transmissions from a UE  104  to a base station  102  and/or downlink (DL) (also referred to as forward link) transmissions from a base station  102  to a UE  104 . The communication links  120  may use multiple-input and multiple-output (MIMO) antenna technology, including spatial multiplexing, beamforming, and/or transmit diversity. The communication links may be through one or more carriers. The base stations  102 /UEs  104  may use spectrum up to Y MHz (e.g., 5, 10, 15, 20, 100, 400, etc. MHz) bandwidth per carrier allocated in a carrier aggregation of up to a total of Yx MHz (x component carriers) used for transmission in each direction. The carriers may or may not be adjacent to each other. Allocation of carriers may be asymmetric with respect to DL and UL (e.g., more or fewer carriers may be allocated for DL than for UL). The component carriers may include a primary component carrier and one or more secondary component carriers. A primary component carrier may be referred to as a primary cell (PCell) and a secondary component carrier may be referred to as a secondary cell (SCell). 
     Certain UEs  104  may communicate with each other using device-to-device (D2D) communication link  158 . The D2D communication link  158  may use the DL/UL WWAN spectrum. The D2D communication link  158  may use one or more sidelink channels, such as a physical sidelink broadcast channel (PSBCH), a physical sidelink discovery channel (PSDCH), a physical sidelink shared channel (PSSCH), and a physical sidelink control channel (PSCCH). D2D communication may be through a variety of wireless D2D communications systems, such as for example, WiMedia, Bluetooth, ZigBee, Wi-Fi based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standard, LTE, or NR. 
     The wireless communications system may further include a Wi-Fi access point (AP)  150  in communication with Wi-Fi stations (STAs)  152  via communication links  154 , e.g., in a 5 GHz unlicensed frequency spectrum or the like. When communicating in an unlicensed frequency spectrum, the STAs  152 /AP  150  may perform a clear channel assessment (CCA) prior to communicating in order to determine whether the channel is available. 
     The small cell  102 ′ may operate in a licensed and/or an unlicensed frequency spectrum. When operating in an unlicensed frequency spectrum, the small cell  102 ′ may employ NR and use the same unlicensed frequency spectrum (e.g., 5 GHz, or the like) as used by the Wi-Fi AP  150 . The small cell  102 ′, employing NR in an unlicensed frequency spectrum, may boost coverage to and/or increase capacity of the access network. 
     The electromagnetic spectrum is often subdivided, based on frequency/wavelength, into various classes, bands, channels, etc. In 5G NR, two initial operating bands have been identified as frequency range designations FR1 (410 MHz-7.125 GHz) and FR2 (24.25 GHz-52.6 GHz). Although a portion of FR1 is greater than 6 GHz, FR1 is often referred to (interchangeably) as a “sub-6 GHz” band in various documents and articles. A similar nomenclature issue sometimes occurs with regard to FR2, which is often referred to (interchangeably) as a “millimeter wave” band in documents and articles, despite being different from the extremely high frequency (EHF) band (30 GHz-300 GHz) which is identified by the International Telecommunications Union (ITU) as a “millimeter wave” band. 
     The frequencies between FR1 and FR2 are often referred to as mid-band frequencies. Recent 5G NR studies have identified an operating band for these mid-band frequencies as frequency range designation FR3 (7.125 GHz-24.25 GHz). Frequency bands falling within FR3 may inherit FR1 characteristics and/or FR2 characteristics, and thus may effectively extend features of FR1 and/or FR2 into mid-band frequencies. In addition, higher frequency bands are currently being explored to extend 5G NR operation beyond 52.6 GHz. For example, three higher operating bands have been identified as frequency range designations FR2-2 (52.6 GHz-71 GHz), FR4 (71 GHz-114.25 GHz), and FR5 (114.25 GHz-300 GHz). Each of these higher frequency bands falls within the EHF band. 
     With the above aspects in mind, unless specifically stated otherwise, it should be understood that the term “sub-6 GHz” or the like if used herein may broadly represent frequencies that may be less than 6 GHz, may be within FR1, or may include mid-band frequencies. Further, unless specifically stated otherwise, it should be understood that the term “millimeter wave” or the like if used herein may broadly represent frequencies that may include mid-band frequencies, may be within FR2, FR4, FR2-2, and/or FR5, or may be within the EHF band. 
     A base station  102 , whether a small cell  102 ′ or a large cell (e.g., macro base station), may include and/or be referred to as an eNB, gNodeB (gNB), or another type of base station. Some base stations, such as gNB  180  may operate in a traditional sub 6 GHz spectrum, in millimeter wave frequencies, and/or near millimeter wave frequencies in communication with the UE  104 . When the gNB  180  operates in millimeter wave or near millimeter wave frequencies, the gNB  180  may be referred to as a millimeter wave base station. The millimeter wave base station  180  may utilize beamforming  182  with the UE  104  to compensate for the path loss and short range. The base station  180  and the UE  104  may each include a plurality of antennas, such as antenna elements, antenna panels, and/or antenna arrays to facilitate the beamforming. 
     The base station  180  may transmit a beamformed signal to the UE  104  in one or more transmit directions  182 ′. The UE  104  may receive the beamformed signal from the base station  180  in one or more receive directions  182 ″. The UE  104  may also transmit a beamformed signal to the base station  180  in one or more transmit directions . The base station  180  may receive the beamformed signal from the UE  104  in one or more receive directions. The base station  180 /UE  104  may perform beam training to determine the best receive and transmit directions for each of the base station  180 / UE  104 . The transmit and receive directions for the base station  180  may or may not be the same. The transmit and receive directions for the UE  104  may or may not be the same. 
     The EPC  160  may include a Mobility Management Entity (MME)  162 , other MMEs  164 , a Serving Gateway  166 , a Multimedia Broadcast Multicast Service (MBMS) Gateway  168 , a Broadcast Multicast Service Center (BM-SC)  170 , and a Packet Data Network (PDN) Gateway  172 . The MME  162  may be in communication with a Home Subscriber Server (HSS)  174 . The MME  162  is the control node that processes the signaling between the UEs  104  and the EPC  160 . Generally, the MME  162  provides bearer and connection management. All user Internet protocol (IP) packets are transferred through the Serving Gateway  166 , which itself is connected to the PDN Gateway  172 . The PDN Gateway  172  provides UE IP address allocation as well as other functions. The PDN Gateway  172  and the BM-SC  170  are connected to the IP Services  176 . The IP Services  176  may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a PS Streaming Service, and/or other IP services. The BM-SC  170  may provide functions for MBMS user service provisioning and delivery. The BM-SC  170  may serve as an entry point for content provider MBMS transmission, may be used to authorize and initiate MBMS Bearer Services within a public land mobile network (PLMN), and may be used to schedule MBMS transmissions. The MBMS Gateway  168  may be used to distribute MBMS traffic to the base stations  102  belonging to a Multicast Broadcast Single Frequency Network (MBSFN) area broadcasting a particular service, and may be responsible for session management (start/stop) and for collecting eMBMS related charging information. 
     The core network  190  may include an Access and Mobility Management Function (AMF)  192 , other AMFs  193 , a Session Management Function (SMF)  194 , and a User Plane Function (UPF)  195 . The AMF  192  may be in communication with a Unified Data Management (UDM)  196 . The AMF  192  is the control node that processes the signaling between the UEs  104  and the core network  190 . Generally, the AMF  192  provides QoS flow and session management. All user Internet protocol (IP) packets are transferred through the UPF  195 . The UPF  195  provides UE IP address allocation as well as other functions. The UPF  195  is connected to the IP Services  197 . The IP Services  197  may include the Internet, an intranet, an IP Multimedia Subsystem (IMS), a Packet Switch (PS) Streaming (PSS) Service, and/or other IP services. 
     The base station may include and/or be referred to as a gNB, Node B, eNB, an access point, a base transceiver station, a radio base station, a radio transceiver, a transceiver function, a basic service set (BSS), an extended service set (ESS), a transmit reception point (TRP), or some other suitable terminology. The base station  102  provides an access point to the EPC  160  or core network  190  for a UE  104 . Examples of UEs  104  include a cellular phone, a smart phone, a session initiation protocol (SIP) phone, a laptop, a personal digital assistant (PDA), a satellite radio, a global positioning system, a multimedia device, a video device, a digital audio player (e.g., MP3 player), a camera, a game console, a tablet, a smart device, a wearable device, a vehicle, an electric meter, a gas pump, a large or small kitchen appliance, a healthcare device, an implant, a sensor/actuator, a display, or any other similar functioning device. Some of the UEs  104  may be referred to as IoT devices (e.g., parking meter, gas pump, toaster, vehicles, heart monitor, etc.). The UE  104  may also be referred to as a station, a mobile station, a subscriber station, a mobile unit, a subscriber unit, a wireless unit, a remote unit, a mobile device, a wireless device, a wireless communications device, a remote device, a mobile subscriber station, an access terminal, a mobile terminal, a wireless terminal, a remote terminal, a handset, a user agent, a mobile client, a client, or some other suitable terminology. In some scenarios, the term UE may also apply to one or more companion devices such as in a device constellation arrangement. One or more of these devices may collectively access the network and/or individually access the network. 
     Referring again to  FIG. 1 , in certain aspects, the UE  104  may include an SCell activation component  198  configured to receive, from a serving cell, an activation indication for an SCell, receive a first reference signal from the SCell, the first reference signal including at least one temporary reference signal, identify whether a second reference signal is received after processing the activation indication and before an expiration of an SCell activation time, and activate, upon identifying that the second reference signal is received, the SCell based on one or more reference signals including at least one of the first reference signal or the second reference signal. Although the following description may be focused on 5G NR, the concepts described herein may be applicable to other similar areas, such as LTE, LTE-A, CDMA, GSM, and other wireless technologies. 
       FIG. 2A  is a diagram  200  illustrating an example of a first subframe within a 5G NR frame structure.  FIG. 2B  is a diagram  230  illustrating an example of DL channels within a 5G NR subframe.  FIG. 2C  is a diagram  250  illustrating an example of a second subframe within a 5G NR frame structure.  FIG. 2D  is a diagram  280  illustrating an example of UL channels within a 5G NR subframe. The 5G NR frame structure may be frequency division duplexed (FDD) in which for a particular set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated for either DL or UL, or may be time division duplexed (TDD) in which for a particular set of subcarriers (carrier system bandwidth), subframes within the set of subcarriers are dedicated for both DL and UL. In the examples provided by  FIGS. 2A ,  2 C, the 5G NR frame structure is assumed to be TDD, with subframe 4 being configured with slot format 28 (with mostly DL), where D is DL, U is UL, and F is flexible for use between DL/UL, and subframe 3 being configured with slot format 1 (with all UL). While subframes 3, 4 are shown with slot formats 1, 28, respectively, any particular subframe may be configured with any of the various available slot formats 0-61. Slot formats 0, 1 are all DL, UL, respectively. Other slot formats 2-61 include a mix of DL, UL, and flexible symbols. UEs are configured with the slot format (dynamically through DL control information (DCI), or semi-statically/statically through radio resource control (RRC) signaling) through a received slot format indicator (SFI). Note that the description infra applies also to a 5G NR frame structure that is TDD. 
       FIGS. 2A-2D  illustrate a frame structure, and the aspects of the present disclosure may be applicable to other wireless communication technologies, which may have a different frame structure and/or different channels. A frame (10 ms) may be divided into 10 equally sized subframes (1 ms). Each subframe may include one or more time slots. Subframes may also include mini-slots, which may include 7, 4, or 2 symbols. Each slot may include 14 or 12 symbols, depending on whether the cyclic prefix (CP) is normal or extended. For normal CP, each slot may include 14 symbols, and for extended CP, each slot may include 12 symbols. The symbols on DL may be CP orthogonal frequency division multiplexing (OFDM) (CP-OFDM) symbols. The symbols on UL may be CP-OFDM symbols (for high throughput scenarios) or discrete Fourier transform (DFT) spread OFDM (DFT-s-OFDM) symbols (also referred to as single carrier frequency-division multiple access (SC-FDMA) symbols) (for power limited scenarios; limited to a single stream transmission). The number of slots within a subframe is based on the CP and the numerology. The numerology defines the subcarrier spacing (SCS) and, effectively, the symbol length/duration, which is equal to 1/SCS. 
     
       
         
           
               
               
               
             
               
                   
               
               
                   
                 SCS 
                   
               
               
                   
                 Δƒ = 2 μ  · 
                   
               
               
                 μ 
                 15 [kHz] 
                 Cyclic prefix 
               
               
                   
               
             
            
               
                 0 
                  15 
                 Normal 
               
               
                 1 
                  30 
                 Normal 
               
               
                 2 
                  60 
                 Normal, Extended 
               
               
                 3 
                 120 
                 Normal 
               
               
                 4 
                 240 
                 Normal 
               
               
                   
               
            
           
         
       
     
     For normal CP (14 symbols/slot), different numerologies μ 0 to 4 allow for 1, 2, 4, 8, and 16 slots, respectively, per subframe. For extended CP, the numerology 2 allows for 4 slots per subframe. Accordingly, for normal CP and numerology μ, there are 14 symbols/slot and 2 μ  slots/subframe. The subcarrier spacing may be equal to 2 μ *15 kHz, where μ is the numerology 0 to 4. As such, the numerology μ=0 has a subcarrier spacing of 15 kHz and the numerology μ=4 has a subcarrier spacing of 240 kHz. The symbol length/duration is inversely related to the subcarrier spacing.  FIGS. 2A-2D  provide an example of normal CP with 14 symbols per slot and numerology μ=2 with 4 slots per subframe. The slot duration is 0.25 ms, the subcarrier spacing is 60 kHz, and the symbol duration is approximately 16.67 μs. Within a set of frames, there may be one or more different bandwidth parts (BWPs) (see  FIG. 2B ) that are frequency division multiplexed. Each BWP may have a particular numerology and CP (normal or extended). 
     A resource grid may be used to represent the frame structure. Each time slot includes a resource block (RB) (also referred to as physical RBs (PRBs)) that extends 12 consecutive subcarriers. The resource grid is divided into multiple resource elements (REs). The number of bits carried by each RE depends on the modulation scheme. 
     As illustrated in  FIG. 2A , some of the REs carry reference (pilot) signals (RS) for the UE. The RS may include demodulation RS (DM-RS) (indicated as R for one particular configuration, but other DM-RS configurations are possible) and channel state information reference signals (CSI-RS) for channel estimation at the UE. The RS may also include beam measurement RS (BRS), beam refinement RS (BRRS), and phase tracking RS (PT-RS). 
       FIG. 2B  illustrates an example of various DL channels within a subframe of a frame. The physical downlink control channel (PDCCH) carries DCI within one or more control channel elements (CCEs) (e.g., 1, 2, 4, 8, or 16 CCEs), each CCE including six RE groups (REGs), each REG including 12 consecutive REs in an OFDM symbol of an RB. A PDCCH within one BWP may be referred to as a control resource set (CORESET). A UE is configured to monitor PDCCH candidates in a PDCCH search space (e.g., common search space, UE-specific search space) during PDCCH monitoring occasions on the CORESET, where the PDCCH candidates have different DCI formats and different aggregation levels. Additional BWPs may be located at greater and/or lower frequencies across the channel bandwidth. A primary synchronization signal (PSS) may be within symbol 2 of particular subframes of a frame. The PSS is used by a UE  104  to determine subframe/symbol timing and a physical layer identity. A secondary synchronization signal (SSS) may be within symbol 4 of particular subframes of a frame. The SSS is used by a UE to determine a physical layer cell identity group number and radio frame timing. Based on the physical layer identity and the physical layer cell identity group number, the UE can determine a physical cell identifier (PCI). Based on the PCI, the UE can determine the locations of the DM-RS. The physical broadcast channel (PBCH), which carries a master information block (MIB), may be logically grouped with the PSS and SSS to form a synchronization signal (SS)/PBCH block (also referred to as SS block (SSB)). The MIB provides a number of RBs in the system bandwidth and a system frame number (SFN). The physical downlink shared channel (PDSCH) carries user data, broadcast system information not transmitted through the PBCH such as system information blocks (SIBs), and paging messages. 
     As illustrated in  FIG. 2C , some of the REs carry DM-RS (indicated as R for one particular configuration, but other DM-RS configurations are possible) for channel estimation at the base station. The UE may transmit DM-RS for the physical uplink control channel (PUCCH) and DM-RS for the physical uplink shared channel (PUSCH). The PUSCH DM-RS may be transmitted in the first one or two symbols of the PUSCH. The PUCCH DM-RS may be transmitted in different configurations depending on whether short or long PUCCHs are transmitted and depending on the particular PUCCH format used. The UE may transmit sounding reference signals (SRS). The SRS may be transmitted in the last symbol of a subframe. The SRS may have a comb structure, and a UE may transmit SRS on one of the combs. The SRS may be used by a base station for channel quality estimation to enable frequency-dependent scheduling on the UL. 
       FIG. 2D  illustrates an example of various UL channels within a subframe of a frame. The PUCCH may be located as indicated in one configuration. The PUCCH carries uplink control information (UCI), such as scheduling requests, a channel quality indicator (CQI), a precoding matrix indicator (PMI), a rank indicator (RI), and hybrid automatic repeat request (HARQ) acknowledgment (ACK) (HARQ-ACK) feedback (i.e., one or more HARQ ACK bits indicating one or more ACK and/or negative ACK (NACK)). The PUSCH carries data, and may additionally be used to carry a buffer status report (BSR), a power headroom report (PHR), and/or UCI. 
       FIG. 3  is a block diagram of a base station  310  in communication with a UE  350  in an access network. In the DL, IP packets from the EPC  160  may be provided to a controller/processor  375 . The controller/processor  375  implements layer 3 and layer 2 functionality. Layer 3 includes a radio resource control (RRC) layer, and layer 2 includes a service data adaptation protocol (SDAP) layer, a packet data convergence protocol (PDCP) layer, a radio link control (RLC) layer, and a medium access control (MAC) layer. The controller/processor  375  provides RRC layer functionality associated with broadcasting of system information (e.g., MIB, SIBs), RRC connection control (e.g., RRC connection paging, RRC connection establishment, RRC connection modification, and RRC connection release), inter radio access technology (RAT) mobility, and measurement configuration for UE measurement reporting; PDCP layer functionality associated with header compression/decompression, security (ciphering, deciphering, integrity protection, integrity verification), and handover support functions; RLC layer functionality associated with the transfer of upper layer packet data units (PDUs), error correction through ARQ, concatenation, segmentation, and reassembly of RLC service data units (SDUs), re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto transport blocks (TBs), demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization. 
     The transmit (TX) processor  316  and the receive (RX) processor  370  implement layer 1 functionality associated with various signal processing functions. Layer 1, which includes a physical (PHY) layer, may include error detection on the transport channels, forward error correction (FEC) coding/decoding of the transport channels, interleaving, rate matching, mapping onto physical channels, modulation/demodulation of physical channels, and MIMO antenna processing. The TX processor  316  handles mapping to signal constellations based on various modulation schemes (e.g., binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK), M-quadrature amplitude modulation (M-QAM)). The coded and modulated symbols may then be split into parallel streams. Each stream may then be mapped to an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot) in the time and/or frequency domain, and then combined together using an Inverse Fast Fourier Transform (IFFT) to produce a physical channel carrying a time domain OFDM symbol stream. The OFDM stream is spatially precoded to produce multiple spatial streams. Channel estimates from a channel estimator  374  may be used to determine the coding and modulation scheme, as well as for spatial processing. The channel estimate may be derived from a reference signal and/or channel condition feedback transmitted by the UE  350 . Each spatial stream may then be provided to a different antenna  320  via a separate transmitter  318  TX. Each transmitter  318  TX may modulate a radio frequency (RF) carrier with a respective spatial stream for transmission. 
     At the UE  350 , each receiver  354  RX receives a signal through its respective antenna  352 . Each receiver  354  RX recovers information modulated onto an RF carrier and provides the information to the receive (RX) processor  356 . The TX processor  368  and the RX processor  356  implement layer 1 functionality associated with various signal processing functions. The RX processor  356  may perform spatial processing on the information to recover any spatial streams destined for the UE  350 . If multiple spatial streams are destined for the UE  350 , they may be combined by the RX processor  356  into a single OFDM symbol stream. The RX processor  356  then converts the OFDM symbol stream from the time-domain to the frequency domain using a Fast Fourier Transform (FFT). The frequency domain signal comprises a separate OFDM symbol stream for each subcarrier of the OFDM signal. The symbols on each subcarrier, and the reference signal, are recovered and demodulated by determining the most likely signal constellation points transmitted by the base station  310 . These soft decisions may be based on channel estimates computed by the channel estimator  358 . The soft decisions are then decoded and deinterleaved to recover the data and control signals that were originally transmitted by the base station  310  on the physical channel. The data and control signals are then provided to the controller/processor  359 , which implements layer 3 and layer 2 functionality. 
     The controller/processor  359  can be associated with a memory  360  that stores program codes and data. The memory  360  may be referred to as a computer-readable medium. In the UL, the controller/processor  359  provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, and control signal processing to recover IP packets from the EPC  160 . The controller/processor  359  is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations. 
     Similar to the functionality described in connection with the DL transmission by the base station  310 , the controller/processor  359  provides RRC layer functionality associated with system information (e.g., MIB, SIBs) acquisition, RRC connections, and measurement reporting; PDCP layer functionality associated with header compression/decompression, and security (ciphering, deciphering, integrity protection, integrity verification); RLC layer functionality associated with the transfer of upper layer PDUs, error correction through ARQ, concatenation, segmentation, and reassembly of RLC SDUs, re-segmentation of RLC data PDUs, and reordering of RLC data PDUs; and MAC layer functionality associated with mapping between logical channels and transport channels, multiplexing of MAC SDUs onto TBs, demultiplexing of MAC SDUs from TBs, scheduling information reporting, error correction through HARQ, priority handling, and logical channel prioritization. 
     Channel estimates derived by a channel estimator  358  from a reference signal or feedback transmitted by the base station  310  may be used by the TX processor  368  to select the appropriate coding and modulation schemes, and to facilitate spatial processing. The spatial streams generated by the TX processor  368  may be provided to different antenna  352  via separate transmitters  354 TX. Each transmitter  354 TX may modulate an RF carrier with a respective spatial stream for transmission. 
     The UL transmission is processed at the base station  310  in a manner similar to that described in connection with the receiver function at the UE  350 . Each receiver  318 RX receives a signal through its respective antenna  320 . Each receiver  318 RX recovers information modulated onto an RF carrier and provides the information to a RX processor  370 . 
     The controller/processor  375  can be associated with a memory  376  that stores program codes and data. The memory  376  may be referred to as a computer-readable medium. In the UL, the controller/processor  375  provides demultiplexing between transport and logical channels, packet reassembly, deciphering, header decompression, control signal processing to recover IP packets from the UE  350 . IP packets from the controller/processor  375  may be provided to the EPC  160 . The controller/processor  375  is also responsible for error detection using an ACK and/or NACK protocol to support HARQ operations. 
     At least one of the TX processor  368 , the RX processor  356 , and the controller/processor  359  may be configured to perform aspects in connection with  198  of  FIG. 1 . 
     In some aspects of wireless communication, one or more active serving cells may instruct a UE to activate a deactivated SCell for carrier aggregation. The one or more active serving cells may include the PCell or another active serving SCell connected to the UE. The UE may receive an SCell activation command or indication from the one or more active serving cells, and upon receiving the SCell activation indication, the UE may receive a synchronization signal block (SSB) from the deactivated SCell, and activate the deactivated SCell. To activate the deactivated SCell, the UE may perform at least one procedure including an SSB detection, a fine time/frequency tracking, or an automatic gain control (AGC) setting to activate the SCell. 
     Upon receiving an SCell activation indication in a slot n, the UE may transmit a valid CSI report and apply actions related to the activation indication for the SCell being activated no later than in slot 
     
       
         
           
             
               n 
               + 
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
                       ⁢ 
                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     T 
                     
                       a 
                       ⁢ 
                       c 
                       ⁢ 
                       t 
                       ⁢ 
                       i 
                       ⁢ 
                       v 
                       ⁢ 
                       a 
                       ⁢ 
                       tion 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       time 
                     
                   
                   + 
                   
                     T 
                     
                       CSI 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Reporting 
                     
                   
                 
                 
                   NR 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
             
             , 
           
         
       
     
     where T HARQ  in milliseconds (ms) is a time period between DL data transmission of the SCell activation indication and transmitting an acknowledgment (ACK) of the activation indication, T activation_time  is the SCell activation delay in ms, and T CSI_reporting  is a delay uncertainty in acquiring one or more first available CSI reporting resources. For example, the ACK may be a hybrid automatic repeat request (HARQ) ACK  424 . 
     In some aspects, the T activation_time  may be determined based on the slot in which the SSB is received from the SCell and the at least one procedure that the UE performs to activate the SCell. In one aspect when the SCell is known to the UE and the SCell measurement cycle is less than or equal to 160 ms, the UE may perform the fine time/frequency tracking to activate the SCell. That is, if the SCell is known to the UE and the SCell measurement cycle is less than or equal to 160 ms, the UE may use one (1) SSB to perform the fine time/frequency tracking to activate the SCell. 
     Accordingly, the T activation_time  may be T FirstSSB +T FirstDelay +T SecondDelay , where T FirstDelay  may be the processing time of the received SCell activation indication after transmitting the ACK of the activation indication, T FirstSSB  may be the time between processing the activation indication and transmission of the first complete SSB burst, and T SecondDelay  may be the processing time of the received first complete SSB burst after the transmission of the first complete SSB burst. For example, the T FirstDelay  may be 3 ms and the T SecondDelay  may be 2 ms. In such a case, the T activation_time  may be T FirstSSB +5 ms, and the T FirstSSB  may be the time to the end of the first complete SSB burst after slot 
     
       
         
           
             n 
             + 
             
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
                       ⁢ 
                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     3 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ms 
                   
                 
                 
                   NR 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
               . 
             
           
         
       
     
     In one aspect when the SCell is known to the UE and the SCell measurement cycle is greater than 160 ms, the UE may perform the fine time/frequency tracking and the AGC setting to activate the SCell. That is, if the SCell is known to the UE and the SCell measurement cycle is greater than 160 ms, the UE may use two (2) SSBs to perform the fine time/frequency tracking and the AGC setting to activate the SCell. Accordingly, the T activation_time  may be T FirstSSB_MAX +T rs +T FirstDelay +T SecondDelay , where T FirstDelay  is the processing time of the received SCell activation indication after transmitting the ACK of the activation indication, T FirstSSB_MAX  is the time between processing the activation indication and transmission of the first complete SSB burst, T rs  is a SSB based RRM measurement timing configuration (SMTC) periodicity or a measurement object periodicity or the SSB frequency, and T SecondDelay  is the processing time of the received first complete SSB burst after the transmission of the first complete SSB burst. For example, the T FirstDelay  may be 3 ms and the T SecondDelay  may be 2 ms. In such a case, the T activation_time  may be T FirstSSB_MAX +T rs +5 ms and the T FirstSSB_MAX  may be the time to the end of the first complete SSB burst after slot 
     
       
         
           
             n 
             + 
             
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
                       ⁢ 
                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     3 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ms 
                   
                 
                 
                   NR 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
               . 
             
           
         
       
     
     In one aspect when the SCell is unknown to the UE the UE may perform the fine time/frequency tracking, the AGC setting, and the SSB detection to activate the SCell. That is, if the SCell is unknown to the UE, the UE may use four (4) SSBs to perform the fine time/frequency tracking, the AGC setting, and the SSB detection to activate the SCell. Accordingly, the T activation_time  may be T FirstSSB_MAX +T SMTC_MAX +2T rs +T FirstDelay +T SecondDelay , where T FirstDelay  is the processing time of the received SCell activation indication after transmitting the ACK of the activation indication, T FirstSSB_MAX  is the time between processing the activation indication and transmission of the first complete SSB burst, T rs  is the SMTC periodicity or the measurement object periodicity or the SSB frequency, the T SMTC_MAX  is the longer SMTC periodicity between active serving cells and SCell being activated, and T SecondDelay  is the processing time of the received first complete SSB burst after the transmission of the first complete SSB burst. For example, the T FirstDelay  may be 3 ms and the T SecondDelay  may be 2 ms. In such a case, the T activation_time  may be T firstSSB_MAX +T SMTC_MAX +2T rs +5 ms and the T firstSSB_MAX  may be the time to the end of the first complete SSB burst after slot 
     
       
         
           
             n 
             + 
             
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
                       ⁢ 
                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     3 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ms 
                   
                 
                 
                   NR 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
               . 
             
           
         
       
     
     In some aspects, one or more temporary RS may be provided to expedite the SCell activation process. Particularly, the PCell may configure the one or more temporary RS for the SCell and the UE, and the SCell may transmit the temporary RS to the UE. The UE may reduce a latency in activating an SCell for carrier aggregation by activating the SCell based on the one or more temporary RS and therefore, expedite the SCell activation procedure for efficient SCell activation for both FR1 and FR2. The UE may perform an AGC setting and time/frequency tracking during the SCell activation procedure based on the temporary RS received from the SCell. The UE may measure the temporary RS received from the SCell and generate and transmit a CSI report. The UE may also perform a cell search for the SCell based on the received temporary RS. That is, the UE may reduce the T activation_Time  by activating the SCell based at least in part on the one or more temporary RS. 
     The temporary RS may include one or more aperiodic tracking RS and/or periodic tracking RS including, but not limited to, aperiodic CSI-RS, periodic/semi-persistent CSI-RS, SRS and RS based on the PSS or the SSS. The aperiodic tracking RS may be triggered by DCI or a MAC-CE, and the periodic tracking RS may be triggered by an RRC signal. The aspects of the present disclosure may be applicable to FR1 and may be extended to FR2. 
       FIG. 4  illustrates an example of SCell activation  400  of wireless communication. The example of SCell activation  400  includes an SCell  410  and a PCell  420 . Here, the PCell  420  is the one or more active serving cells from which the UE and the SCell  410  may receive an SCell activation indication  422 . The SCell may transmit the SSB s  412  at an SSB periodicity, and the SCell may transmit the temporary RS  418  based on the SCell activation indication  422  received from the PCell  420 .  FIG. 4  illustrates that the temporary RS  418  is an aperiodic tracking RS, but the aspects of the disclosure are not limited thereto, and the temporary RS  418  may be a periodic tracking RS. 
     The UE may receive the SCell activation indication  422  from the PCell  420  instructing the UE to activate the deactivated SCell  410  based on the temporary RS  418  received from the SCell  410 . Upon receiving the SCell activation indication  422 , the UE may transmit an ACK and process the received SCell activation indication  422 . For example, the ACK may be a HARQ ACK  424  transmitted in response to the received SCell activation indication. The UE may receive the temporary RS  418  from the SCell  410 , and activate the SCell  410  based on the temporary RS  418 . To activate the SCell  410 , the UE may perform at least one procedure including an SSB detection, a fine time/frequency tracking, or an AGC setting to activate the SCell based on the temporary RS  418  received from the PCell  420 . 
     Upon receiving SCell activation indication  422  in a slot n, the UE may transmit valid CSI report and apply actions related to the activation indication  422  for the SCell being activated no later than in slot 
     
       
         
           
             
               n 
               + 
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
                       ⁢ 
                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     T 
                     
                       a 
                       ⁢ 
                       c 
                       ⁢ 
                       t 
                       ⁢ 
                       i 
                       ⁢ 
                       v 
                       ⁢ 
                       a 
                       ⁢ 
                       tion 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       time 
                     
                   
                   + 
                   
                     T 
                     
                       CSI 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Reporting 
                     
                   
                 
                 
                   NR 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
             
             , 
           
         
       
     
     where T HARQ  in milliseconds (ms) is a time period between DL data transmission of the SCell activation indication  422  and transmitting the HARQ ACK  424  of the activation indication, T activation_time  is the SCell activation delay in ms, and T CSI_reporting  is a delay uncertainty in acquiring one or more first available CSI reporting resources. 
     In some aspects, the T activation_time  may be determined based on the slot that the temporary RS is received from the SCell  410  and the at least one procedure that the UE performs to activate the SCell  410 . In one aspect when the SCell  410  is known to the UE and the SCell measurement cycle is less than or equal to 160 ms, the UE may perform the fine time/frequency tracking to activate the SCell  410 . That is, if the SCell  410  is known to the UE and the SCell measurement cycle is less than or equal to 160 ms, the UE may use one (1) RS including the temporary RS to perform the fine time/frequency tracking to activate the SCell  410 . Accordingly, the T activation_time  may be T Temp_RS +T firstDelay +T SecondDelay , where T firstDelay  is the processing time of the received SCell activation indication  422  after transmitting the HARQ ACK  424  of the SCell activation indication  422 , and T SecondDelay  is the processing time of the received first temporary RS  418  after the transmission of the first temporary RS  418 . The T temp RS  may be the time between processing the activation indication and transmission of the first temporary RS  418 , between T firstDelay  after transmission of the HARQ ACK  424  and transmission of the first temporary RS  418 . For example, the T FirstDelay  may be 3 ms and the T SecondDelay  may be 2 ms. In such case, the T activation_time  may be T Temp_RS +5 ms, and the T Temp_RS  may be the time to the end of the first complete RS burst after slot 
     
       
         
           
             n 
             + 
             
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
                       ⁢ 
                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     3 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ms 
                   
                 
                 
                   NR 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
               . 
             
           
         
       
     
       FIG. 4  illustrates that the first temporary RS  418  may meet the T activation_time , and the UE may activate the SCell  410  based on the first temporary RS  418 . However, aspects of the disclosure are not limited thereto, and the UE may use any RS that may meet the T activation_time . The SCell activation indication may be transmitted via a MAC-CE, DCI, or an RRC signal. That is, the RRC-based direct SCell activation at SCell addition/handover/RRC-resume may be possible. Furthermore, on a to-be-activated SCell, the SSB and/or the periodic tracking RS configured by RRC signaling may not be triggered/canceled by the MAC-CE/DCI. That is, an RRC signal may configure a periodic tracking RS for the SCell and the UE directly upon SCell addition/handover/RRC-resume, and the periodic tracking RS may not be triggered or canceled by the MAC-CE or the DCI. The MAC-CE of the DCI may also configure the aperiodic tracking RS. 
     The UE may use one or more RSs from a set of RSs for SCell activation in the same or different serving cell(s), whichever may meet the SCell activation delay. That is, the deactivated SCell or other SCell may transmit one or more RSs for SCell activation, and as long as the SCell activation delay may be met, the UE may use any RS of a set of RSs including all or a subset of the SSB, the periodic tracking RS, or the aperiodic tracking RS. That is, as long as the one or more RSs for SCell activation may meet the T activation_time , the UE may use at least one of the one or more RSs for the SCell activation. 
       FIG. 5  illustrates an example of SCell activation  500  of wireless communication. The example of SCell activation  500  includes an SCell  510  and a PCell  520 . The example of SCell activation  500  of wireless communication illustrates that the SCell  510  may be activated using a first temporary RS  518 , and an SSB  512  may be received between T firstDelay  after transmission of the HARQ ACK  524  and before expiration of the T activation_time . The first temporary RS  518  may be an aperiodic tracking RS triggered by DCI or a MAC-CE. 
     Referring to  FIG. 5 , the SSB  512  received after ‘t=ACK timing+3 ms’ may be usable if the UE processes the SCell activation indication  522  received via DCI or a MAC-CE is completed earlier than ‘t=ACK timing+3 ms.’ Therefore, the UE may use the SSB  512  to activate the SCell  510 . The UE may use one or more RS including the SSBs, periodic tracking RS s, and/or the indicated aperiodic tracking RS for the AGC setting, or fine time/frequency tracking for the SCell activation. That is, the window for T activation time  may be determined based on the timing of the triggered first temporary RS  518 , and the UE can utilize any RS including the SSB/the periodic tracking RS/the aperiodic tracking RS as long as the necessary procedure can be performed within the window. 
     Upon receiving SCell activation indication  522  in a slot n, the UE may transmit a valid CSI report and apply actions related to the SCell activation indication  522  for the SCell being activated no later than in slot 
     
       
         
           
             
               n 
               + 
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
                       ⁢ 
                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     T 
                     
                       a 
                       ⁢ 
                       c 
                       ⁢ 
                       t 
                       ⁢ 
                       i 
                       ⁢ 
                       v 
                       ⁢ 
                       a 
                       ⁢ 
                       tion 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       time 
                     
                   
                   + 
                   
                     T 
                     
                       CSI 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Reporting 
                     
                   
                 
                 
                   NR 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
             
             , 
           
         
       
     
     where T HARQ  in milliseconds (ms) is a time period between DL data transmission of the SCell activation indication  522  and transmitting the HARQ ACK  524  of the activation indication, T activation_time  is the SCell activation delay in ms, and T CSI_reporting  is a delay uncertainty in acquiring one or more first available CSI reporting resources. 
     In some aspects, the T activation_time  may be determined based on the slot in which the temporary RS is received from the SCell  510  and the at least one procedure that the UE performs to activate the SCell  510 . In one aspect when the SCell  510  is known to the UE and the SCell measurement cycle is less than or equal to 160 ms, the UE may perform the fine time/frequency tracking to activate the SCell  510 . That is, if the SCell  510  is known to the UE and the SCell measurement cycle is less than or equal to 160 ms, the UE may use one (1) temporary RS to perform the fine time/frequency tracking to activate the SCell  510 . Accordingly, the T activation_time  may be T Temp_RS +T FirstDelay +T SecondDelay , where T FirstDelay  is the processing time of the received SCell activation indication  522  after transmitting the HARQ ACK  524  of the SCell activation indication  522 , and T SecondDelay  is the processing time of the received first temporary RS  518  after the transmission of the first temporary RS  518 . The T temp RS  may be a time duration starting from ‘T HARQ +3 ms’ to the end of the last OFDM symbol or the last slot of the first temporary RS, if the first temporary RS is triggered for the SCell activation, no matter whether the UE actually uses the first temporary RS to activate the SCell. That is, the T Temp_RS  may be the time between processing the activation indication and transmission of the first temporary RS  518 , between T firstDelay  after transmission of the HARQ ACK  524  and transmission of the first temporary RS  518 . For example, the T FirstDelay  may be 3 ms, and the T SecondDelay  may be 2 ms. In such a case, the T activation_time  may be T Temp_RS +5 ms, and the T Temp_RS  may be the time to the end of the first complete RS burst after slot 
     
       
         
           
             n 
             + 
             
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
                       ⁢ 
                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     3 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     ms 
                   
                 
                 
                   NR 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
               . 
             
           
         
       
     
     For other conditions (e.g., unknown cell), the value of T activation time  may be different but the principle may be the same. In one aspect when the SCell is known to the UE and the SCell measurement cycle is greater than 160 ms, the UE may perform the fine time/frequency tracking and the AGC setting to activate the SCell  510 . That is, if the SCell is known to the UE and the SCell measurement cycle is greater than 160 ms, the UE may use two (2) RS including the first temporary RS  518  to perform the fine time/frequency tracking and the AGC setting to activate the SCell  510 . Here, the UE may use the SSB  512  and the first temporary RS  518  as the two (2) RS including the first temporary RS  518  to activate the SCell  510 . Accordingly, referring to  FIG. 4 , the T activation_time  may be reduced to T Temp_RS +T FirstDelay +T SecondDelay , where T FirstDelay  is the processing time of the received SCell activation indication  522  after transmitting the HARQ ACK  524  of the SCell activation indication  522 , and T SecondDelay  is the processing time of the received first temporary RS  518  after the transmission of the first temporary RS  518 . The T Temp_RS  may be the time between processing the activation indication and transmission of the first temporary RS  518 , between T firstDelay  after transmission of the HARQ ACK  524  and transmission of the first temporary RS  518 . For example, the T FirstDelay  may be 3 ms, and the T SecondDelay  may be 2 ms. In such a case, the T activation_time  may be T Temp_RS +5 ms, and the T Temp_RS  may be the time to the end of the first complete RS burst after slot 
     
       
         
           
             n 
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     In one aspect when the SCell is unknown to the UE and belongs to FR1, the UE may perform the fine time/frequency tracking, the AGC setting, and the SSB detection to activate the SCell. That is, if the SCell is unknown to the UE, the UE may use four (4) RSs including the first temporary RS  518  to perform the fine time/frequency tracking, the AGC setting, and the SSB detection to activate the SCell. Here, the UE may use the SSBs  512 ,  514 , and  516 , and the first temporary RS  518 . Accordingly, referring to  FIG. 4 , the T activation_time  may be reduced to T FirstSSB +2T rs +T FirstDelay +T SecondDelay , where T FirstDelay  is the processing time of the received SCell activation indication after transmitting the ACK of the activation indication, T FirstSSB  is the time between processing the activation indication and transmission of the first complete SSB burst, T rs  is the SSB frequency, and T SecondDelay  is the processing time of the received first complete SSB burst after the transmission of the first complete SSB burst. For example, the T FirstDelay  may be 3 ms, and the T SecondDelay  may be 2 ms. In such a case, the T activation_time  may be T FirstSSB +2T rs +5 ms, and the T FirstSSB_MAX  may be the time to the end of the first complete SSB burst after slot 
     
       
         
           
             n 
             + 
             
               
                 
                   
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     Accordingly, by using the first temporary RS  518 , the T activation_time  may be reduced, and the SCell  510  activation may be expedited. Furthermore, if a periodic tracking RS is configured on the carrier that can be used for AGC or fine time/frequency tracking and the periodic tracking RS falls into the time period, the periodic tracking RS may be used as one or more RS for the UE to use instead of or together with the triggered first temporary RS. Referring to  FIG. 5 , for example, if the first temporary RS  518  is a non-zero-power (NZP) CSI-RS (NZP-CSI-RS) with trs-Info’ with l ∈ {4,8} for FR1, the T temp RS  can be a time duration of 1 slot+9 OFDM symbols (if the duration ends at the last OFDM symbol) and can be a time duration of 2 slots (if the duration ends at the last slot). 
       FIG. 6  illustrates an example of SCell activation  600  of wireless communication. The example of SCell activation  600  includes an SCell  610  and a PCell  620 . The example of SCell activation  500  of wireless communication illustrates that the SCell  610  may be activated using a second temporary RS  619  received between T firstDelay  after transmission of the HARQ ACK  624  and before expiration of the T activation_time . The second temporary RS  619  may be a periodic tracking RS and may not be triggered by DCI or a MAC-CE, and the example of SCell activation  600  may be an RRC-based direct SCell activation. That is, the SCell activation indication  622  may be the RRC signal. The UE may use one or more RS including the SSBs and/or the periodic tracking RS for the AGC setting and/or the fine time/frequency tracking for the SCell activation. Here, the T activation time  may be T RS +5 ms, where T RS  is the timing of transmission of the SSB or the periodic tracking RS, whichever may be received first for the known cell with SCell measurement cycle less than or equal to 160 ms. That is, referring to  FIG. 6 , if the second temporary RS  619  is received after T firstDelay  past the transmission of the HARQ ACK  524 , the T activation_time  may expire T SecondDelay  after the transmission of the second temporary RS  619 . If the SSB  612  is received after T firstDelay  past the transmission of the HARQ ACK  624  prior to the second temporary RS  619 , the T activation_time  may expire T SecondDelay  after the transmission of the SSB  612 . 
     For other conditions (e.g., unknown cell), the value of T activation time  may be different but the principle may be the same. The window for T activation time  may be determined based on the timing where the SSB or the periodic tracking RS, whichever is received first, and the UE can utilize the SSB and/or P-TRS as long as the necessary procedure can be performed within the window for T activation time . Accordingly, the T activation_time  may be T FirstDelay +T RS +T SecondDelay , where the T RS  is a time duration starting from ‘T HARQ +3 ms’ to the end of the last OFDM symbol or the last slot of the one or more RS that the UE determines to use for SCell activation. 
     The one or more RS may be the SSB or the periodic tracking RS, whichever is received earlier after T HARQ +3 ms. In one aspect when the SCell  610  is known to the UE and the SCell measurement cycle is greater than 160 ms, the UE may perform the fine time/frequency tracking and the AGC setting to activate the SCell  610 . That is, if the SCell is known to the UE and the SCell measurement cycle is greater than 160 ms, the UE may use two (2) RS including the SSB  612  and/or the second temporary RS  619  to perform the fine time/frequency tracking and the AGC setting to activate the SCell  610 . Accordingly, the T activation_time  may be T FirstDelay +T RS +T SecondDelay , where the T RS  is a time duration starting from ‘T HARQ +3 ms’ to the end of the last OFDM symbol or the last slot of the second RS in which the UE determines to use for the SCell activation. 
     In one aspect when the SCell  610  is unknown to the UE and belongs to FR1, the UE may perform the fine time/frequency tracking, the AGC setting, and the SSB detection to activate the SCell. That is, if the SCell is unknown to the UE, the UE may use four (4) RSs including the second temporary RS  619  to perform the fine time/frequency tracking, the AGC setting, and the SSB detection to activate the SCell  610 . Accordingly, the T activation_time  may be T FirstDelay +T RS +T SecondDelay , where the TRS is a time duration starting from ‘T HARQ +3 ms’ to the end of the last OFDM symbol or the last slot of the fourth RS that the UE determines to use for the SCell activation. 
     In some aspects, referring again to  FIGS. 5 and 6 , multiple SCells can be activated simultaneously. The UE may activate the multiple SCells using the SSB and/or the temporary RS including the periodic tracking RS or the aperiodic tracking RS transmitted in a serving cell different from the SCell to-be-activated. For example, if there is an active serving cell in the same band as the one for the to-be-activated SCell, the temporary RSs in the active serving cell can be used for activation of the SCell. That is, in one aspect when the SCell activation indication provides a plurality of SCells to be activated simultaneously, the active serving cell may transmit the temporary RS on one of the plurality of SCells to be activated, and the UE may use the temporary RS transmitted on one of the plurality of SCells to activate the plurality of the SCells based on the SCell activation indication received from the active serving cell. 
     In some aspects, referring again to  FIGS. 5 and 6 , multiple RSs including SSBs or temporary RSs including the periodic tracking RS and/or the aperiodic tracking RS s associated with different TCI-states/QCL assumptions may be present. That is, in case of a beam-sweeping operation, multiple RSs provided on different beams may be associated with different TCI-state/QCL assumptions. Accordingly, the UE may use one or more RSs from the SSB or the temporary RS including the periodic tracking RS or the aperiodic tracking RS that are associated with the same TCI-state or QCL assumption. That is, the UE may use the one or more RSs that are transmitted on the same beams and associated with the same TCI-state/QCL assumptions. Accordingly, the UE may assume that the SSB and/or the temporary RS including the periodic tracking RS and the aperiodic tracking RS that may be used for the AGC setting and/or the fine time/frequency tracking may be quasi-co-located. The network may also configure the TCI-states of the RSs so that they are supposed to be quasi-co-located from the UE&#39;s point of view. 
     In some aspects, various configurations of the multiple SCells may be activated using the temporary RS. In one aspect, the to-be-activated multiple SCells may be in the same frequency band. In another aspect, the to-be-activated multiple SCells may be contiguous carriers in the same frequency band. In another aspect, the to-be-activated multiple SCells may be in FR2. 
     In some aspects, various configurations of the temporary RS may be used to activate the SCells. In one aspect, the UE may use the earliest received RSs of the SSB, or the temporary RS including the periodic tracking RS or the aperiodic tracking RS, received from the SCell amongst the to-be-activated multiple SCells. In another aspect, the UE may use the earliest timing that received RSs of the SSB, or the temporary RS including the periodic tracking RS or the aperiodic tracking RS transmitted over all the to-be-activated multiple SCells. In another aspect, the UE may use the latest received RSs of the SSB, or the temporary RS including the periodic tracking RS or the aperiodic tracking RS, transmitted on a SCell amongst the to-be-activated multiple SCells. 
     As indicated in  FIGS. 5 and 6 , the UE may perform procedures other than the fine time/frequency tracking to activate the one or more SCells. For example, the SCells may be unknown or the SCells may be known with the measurement cycle greater than 160 ms. The temporary RS including the periodic tracking RS and/or the aperiodic tracking RS may refer to one or more sets of temporary RS including the periodic tracking RSs and/or the aperiodic tracking RSs. Accordingly, the one or more sets of temporary RS including the periodic tracking RSs and/or the aperiodic tracking RSs received after the first SSB or SSB burst from to-be-activated SCells can be considered a valid RS, and the UE may perform at least one procedure including an SSB detection, a fine time/frequency tracking, or an automatic gain control (AGC) setting to activate the SCell based on the SSB and/or the one or more sets of temporary RS including the periodic tracking RSs and/or the aperiodic tracking RSs. The structures of the periodic/aperiodic tracking RS, including the symbol position, the number of slots, and/or the number of resource sets, may be dynamically indicated and/or determined depending on the state of to-be-activated SCell(s). For example, the SCell may be a known or unknown SCell, and the SCell measurement cycle may be less than or equal to 160 ms or greater than 160 ms, and the structures of the temporary RS including the periodic tracking RS or the aperiodic tracking RS for activating the SCell may be dynamically configured to reduce the latency in activating the SCell for carrier aggregation. 
       FIG. 7  illustrates a call-flow diagram  700  of wireless communication. The call-flow diagram  700  may include a UE  702 , a serving cell  704 , and an SCell  706  to be activated by the UE  702 . The UE  702  may receive an SCell activation command or indication from the one or more active serving cells, e.g., the serving cell  704 . One or more temporary RSs may be provided to expedite the SCell activation procedure, and the UE  702  may expedite the SCell activation procedure using the one or more temporary RS received from the SCell  706 . The UE  702  may activate the SCell  706  no later than in slot n+K, and K may be determined based on at least in part the SCell activation time. 
     At  710 , the UE  702  may receive, from the serving cell  704 , an activation indication for activating an SCell  706 . The activation indication may be received via one of a MAC-CE, DCI, or an RRC signal. The activation indication may indicate activating multiple SCells  706  simultaneously, the multiple SCells  706  including a first SCell and a second SCell. The first SCell and the second SCell may be in the same frequency band, in contiguous carriers in the same frequency band, or in a frequency range. At  711 , the serving cell  704  may configure the SCell  706  to transmit one or more RS, including a first reference signal and/or a second reference signal. 
     At  712 , the UE  702  may transmit, to the serving cell  704 , an ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell  704 . 
     At  714 , the UE  702  may process the activation indication received from the serving cell  704 . The UE  702  may receive the first reference signal and/or the second reference signal based on the processed activation indication. 
     At  716 , the UE  702  may receive the first reference signal from the SCell  706 , the first reference signal including at least one temporary reference signal. The first reference signal may be a temporary RS, including an aperiodic tracking RS instructed by the MAC-CE or the DCI or a periodic tracking RS instructed by the RRC signal. Here, the first reference signal may be received from the active serving cell  704 . 
     At  718 , the UE  702  may receive the second reference signal from the SCell  706 , the second reference signal including at least one temporary reference signal. The second reference signal may be an SSB or a temporary RS, including an aperiodic tracking RS instructed by a MAC-CE or DCI or a periodic tracking RS instructed by the RRC signal. Here, the second reference signal may be received from the active serving cell  704 . The first reference signal and the second reference signal may be assumed to be quasi-co-located with each other. 
     At  720 , the UE  702  may identify whether a second reference signal is received after processing the activation indication and before the expiration of an SCell activation time. 
     At  722 , the UE  702  may generate a CSI report of one of the first reference signal or the second reference signal on which the UE  702  based the activation of the SCell  706 . 
     At  724 , the UE  702  may transmit the CSI report of one of the first reference signal or the second reference signal on which the UE  702  based the activation of the SCell  706 . 
     At  726 , the UE  702  may activate the SCell  706  based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal. The UE  702  may activate, upon identifying that the second reference signal is received, the SCell  706  based on one or more reference signals, including at least one of the first reference signal or the second reference signal. The UE  702  may receive the activation indication in slot n, and may activate the SCell  706  no later than in slot n+K, where K is determined based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, the SCell activation time, and a delay uncertainty in acquiring one or more first available CSI reporting resources. For example, the UE  702  may receive the activation indication in slot n, and may activate the SCell  706  no later than in in slot 
     
       
         
           
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     The T activation_time  may be the SCell activation time, and be determined based on one or more reference signals, including at least one of the first reference signal or the second reference signal. In one aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving the at least one temporary reference signal. In another aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving a last of the one or more reference signals on which the UE based the activation of the SCell. In another aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving two or four reference signals including one of the first reference signal or the second reference signal. 
     The UE  702  may activate multiple SCells  706  simultaneously, based on one or more reference signals including at least one temporary reference signal including the aperiodic tracking reference signal or the periodic tracking reference signal, whichever is received earliest from the multiple S Cells  706 . The UE  702  may activate the multiple SCells  706  based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received within an earliest activation time for the multiple SCells  706 . The UE  702  may activate the multiple SCells  706  based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received latest from the multiple SCells  706 . 
       FIG. 8  is a flowchart  800  of a method of wireless communication. The method may be performed by a UE (e.g., the UE  104 ,  702 ; the apparatus  1502 ). The UE may receive an SCell activation command or indication from the one or more active serving cells, e.g., a serving cell. One or more temporary RS may be provided to expedite a SCell activation procedure, and the UE may expedite the SCell activation procedure using the one or more temporary RS received from the SCell. The UE may activate the SCell no later than in slot n+K, and K may be determined based on at least in part the SCell activation time. 
     At  802 , the UE may receive, from a serving cell, an activation indication for activating an SCell. The activation indication may be received via one of a MAC-CE, DCI, or an RRC signal. The activation indication may indicate activating multiple SCells simultaneously, the multiple SCells including a first SCell and a second SCell. For example, at  710 , the UE  702  may receive, from the serving cell  704 , an activation indication for activating an SCell  706 . Furthermore,  802  may be performed by an SCell activation component  1540 . 
     At  804 , the UE may transmit, to the serving cell, an ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell. For example, at  712 , the UE  702  may transmit, to the serving cell  704 , an ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell  704 . Furthermore,  804  may be performed by an ACK component  1542 . 
     At  806 , the UE may process the activation indication received from the serving cell. 
     The UE may receive the first reference signal and/or the second reference signal based on the processed activation indication. For example, at  714 , the UE  702  may process the activation indication received from the serving cell  704 . Furthermore,  806  may be performed by the SCell activation component  1540 . 
     At  808 , the UE may receive the first reference signal from the SCell, the first reference signal including at least one temporary reference signal (i.e., as at  716 ). The first reference signal may be a temporary RS, including an aperiodic tracking RS instructed by the MAC-CE or the DCI or a periodic tracking RS instructed by the RRC signal. Here, the first reference signal may be received from the active serving cell. For example, at  716 , the UE  702  may receive the first reference signal from the SCell  706 , the first reference signal including at least one temporary reference signal. Furthermore,  808  may be performed by the SCell activation component  1540 . 
     At  810 , the UE may receive the second reference signal from the SCell, the second reference signal including at least one temporary reference signal (i.e., as at  718 ). The second reference signal may be an SSB or a temporary RS, including an aperiodic tracking RS instructed by the MAC-CE or the DCI or a periodic tracking RS instructed by the RRC signal. Here, the second reference signal may be received from the active serving cell. The first reference signal and the second reference signal may be assumed to be quasi-co-located with each other. For example, at  718 , the UE  702  may receive the second reference signal from the SCell  706 , the second reference signal including at least one temporary reference signal. Furthermore,  810  may be performed by the SCell activation component  1540 . 
     At  812 , the UE may identify whether a second reference signal is received after processing the activation indication and before the expiration of an SCell activation time (i.e., as at  720 ). For example, at  720 , the UE  702  may identify whether a second reference signal is received after processing the activation indication and before the expiration of an SCell activation time. Furthermore,  812  may be performed by the SCell activation component  1540 . 
     At  814 , the UE may generate a CSI report of one of the first reference signal or the second reference signal on which the UE based the activation of the SCell (i.e., as at  722 ). For example, at  722 , the UE  702  may generate a CSI report of one of the first reference signal or the second reference signal on which the UE  702  based the activation of the SCell  706 . Furthermore,  814  may be performed by a CSI component  1544 . 
     At  816 , the UE may transmit the CSI report of one of the first reference signal or the second reference signal on which the UE based the activation of the SCell (i.e., as at  724 ). For example, at  724 , the UE  702  may transmit the CSI report of one of the first reference signal or the second reference signal on which the UE  702  based the activation of the SCell  706 . Furthermore,  816  may be performed by the CSI component  1544 . 
     At  818 , the UE may activate the SCell based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal (i.e., as at  726 ). The UE may activate, upon identifying that the second reference signal is received, the SCell based on one or more reference signals, including at least one of the first reference signal or the second reference signal. The UE may receive the activation indication in slot n, and may activate the SCell no later than in slot n+K, where K is determined based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, the SCell activation time, and a delay uncertainty in acquiring one or more first available CSI reporting resources. For example, the UE may receive the activation indication in slot n, and may activate the SCell no later than in in slot 
     
       
         
           
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     The T activation_time  may be determined based on one or more reference signals, including at least one of the first reference signal or the second reference signal. In one aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving the at least one temporary reference signal. In another aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving a last of the one or more reference signals on which the UE based the activation of the SCell. In another aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving two or four reference signals including one of the first reference signal or the second reference signal. The UE may activate multiple SCells simultaneously, based on one or more reference signals including at least one temporary reference signal including the aperiodic tracking reference signal or the periodic tracking reference signal, whichever is received earliest from the multiple SCells. The UE may activate the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received within an earliest activation time for the multiple SCells. The UE may activate the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received latest from the multiple SCells. For example, at  726 , the UE  702  may activate the SCell  706  based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal. Furthermore,  818  may be performed by the SCell activation component  1540 . 
       FIG. 9  is a flowchart  900  of a method of wireless communication. The method may be performed by a UE (e.g., the UE  104 ,  702 ; the apparatus  1502 ). The UE may receive an SCell activation command or indication from the one or more active serving cells, e.g., a serving cell. One or more temporary RS may be provided to expedite a SCell activation procedure, and the UE may expedite the SCell activation procedure using the one or more temporary RS received from the SCell. The UE may activate the SCell no later than in slot n+K, and K may be determined based on at least in part the SCell activation time. 
     At  902 , the UE may receive, from a serving cell, an activation indication for activating an SCell. The activation indication may be received via one of a MAC-CE, DCI, or an RRC signal. The activation indication may indicate activating multiple SCells simultaneously, the multiple SCells including a first SCell and a second SCell. For example, at  710 , the UE  702  may receive, from the serving cell  704 , an activation indication for activating an SCell  706 . Furthermore,  902  may be performed by an SCell activation component  1540 . 
     At  908 , the UE may receive the first reference signal from the SCell, the first reference signal including at least one temporary reference signal (i.e., as at  716 ). The first reference signal may be a temporary RS, including an aperiodic tracking RS instructed by the MAC-CE or the DCI or a periodic tracking RS instructed by the RRC signal. Here, the first reference signal may be received from the active serving cell. For example, at  716 , the UE  702  may receive the first reference signal from the SCell  706 , the first reference signal including at least one temporary reference signal. Furthermore,  908  may be performed by the SCell activation component  1540 . 
     At  912 , the UE may identify whether a second reference signal is received after processing the activation indication and before the expiration of an SCell activation time (i.e., as at  720 ). For example, at  720 , the UE  702  may identify whether a second reference signal is received after processing the activation indication and before the expiration of an SCell activation time. Furthermore,  912  may be performed by the SCell activation component  1540 . 
     At  918 , the UE may activate the SCell based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal (i.e., as at  726 ). The UE may activate, upon identifying that the second reference signal is received, the SCell based on one or more reference signals, including at least one of the first reference signal or the second reference signal. The UE may receive the activation indication in slot n, and may activate the SCell no later than in slot n+K, where K is determined based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, the SCell activation time, and a delay uncertainty in acquiring one or more first available CSI reporting resources. For example, the UE may receive the activation indication in slot n, and may activate the SCell no later than in slot 
     
       
         
           
             n 
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                       time 
                     
                   
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                       Reporting 
                     
                   
                 
                 
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     The T activation_time  may be determined based on one or more reference signals, including at least one of the first reference signal or the second reference signal. In one aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving the at least one temporary reference signal. In another aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving a last of the one or more reference signals on which the UE based the activation of the SCell. In another aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving two or four reference signals including one of the first reference signal or the second reference signal. The UE may activate multiple SCells simultaneously, based on one or more reference signals including at least one temporary reference signal including the aperiodic tracking reference signal or the periodic tracking reference signal, whichever is received earliest from the multiple SCells. The UE may activate the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received within an earliest activation time for the multiple SCells. The UE may activate the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received latest from the multiple SCells. For example, at  726 , the UE  702  may activate the SCell  706  based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal. Furthermore,  918  may be performed by the SCell activation component  1540 . 
       FIG. 10  illustrates an example of SCell activation  1000  of wireless communication. 
     The example of SCell activation  1000  includes an SCell  1010  and a PCell  1020 . The example of SCell activation  1000  of wireless communication illustrates that the SCell  1010  may transmit a first temporary RS  1018 , a second temporary RS  1019 , and an SSB  1012 . The first temporary RS  1018  may be an aperiodic tracking RS triggered by DCI or a MAC-CE, and the second temporary RS  1019  may be a periodic tracking RS triggered by an RRC signal. The UE may generate and transmit the ACK  1024  to the PCell  1020 . For the SCell in the unlicensed band (or in the shared spectrum), the one or more RS  1018  and  1019  (an SSB or a temporary RS including a periodic tracking RS or an aperiodic tracking RS) may not be transmitted due to an LBT failure. That is, the UE may determine whether the SCell activation indication  1022  is implicitly canceled based on the transmission of the temporary RS including the first temporary RS  1018  or the second temporary RS  1019 . The UE may perform a clear channel assessment to determine whether a channel measurement of the received power is greater than a threshold value. If the UE determines that the channel measurement of the received power is greater than the threshold value, the UE may determine that the window for T activation_time  based on the one or more RS  1018  and  1019  is actually used for data transmission and the temporary RS including the first temporary RS  1018  or the second temporary RS  1019  are not transmitted as indicated by the SCell activation indication  1022 . 
     Aspects of the disclosure are not limited to the SCell  1010  in the unlicensed band (or in the shared spectrum) in the LBT failure. In some aspects, the same procedure may be applied when/if one or more RS  1018  and  1019  are not transmitted due to an overlapping UL transmission or DL reception of the other signal/channel a cancellation/preemption of DL reception. That is, the UE may receive DCI or a MAC-CE that may instruct the UL transmission, DL reception, cancellation, or preemption, which may instruct the UE not to use the one or more RS  1018  and  1019  may not be transmitted as indicated by the SCell activation indication. 
       FIG. 11  illustrates an example of SCell activation  1100  of wireless communication. The example of SCell activation  1100  includes an SCell  1110  and a PCell  1120 . The example of SCell activation  1100  of wireless communication illustrates that the SCell  1110  may transmit a first temporary RS  1118 , a second temporary RS  1119 , and an SSB  1112 . The first temporary RS  1118  and the second temporary RS  1119  may be aperiodic tracking RSs triggered by DCI or a MAC-CE. The UE may generate and transmit the ACK  1124  to the PCell  1120 . The network may update the temporary RS resource, and eventually cancel/preempt the temporary RS. For such a case, the network or BS may indicate a new temporary RS resource by DCI or MAC-CE. That is, the UE may receive a new SCell activation indication  1122  instructing the UE to activate the SCell  1110  using a new temporary RS  1119 . In response to determining that the RS resource is updated from the first temporary RS  1118  to the second temporary RS  1119 , the UE may determine that the original SCell activation indication is no longer valid, and the first temporary RS  1118  may not be transmitted as indicated in the original SCell activation indication. Accordingly, the window for T activation_time  may be based on the new RS resource associated with the second temporary RS  1119 . The network may indicate the cancellation/preemption via DCI or a MAC-CE. The DCI may be DCI sent to trigger a cancellation or offset of the temporary RS, or may be the same as the scheduling DCI for the UL/DL Tx/Rx overlapping with the initial A-TRS. The MAC-CE may directly trigger cancellation or offset of the temporary RS, or may be the same as the MAC-CE used to trigger another temporary RS on this carrier or other carriers. The MAC-CE may also be used to trigger SCell activation on other carriers. 
     In some aspects, the to-be-activated SCell for a wideband operation in the unlicensed band (or in the shared spectrum may include multiple LBT sub-bands, for example, every 20 MHz, and the temporary RS and/or the periodic tracking RS may be subject to LBT per the multiple LBT sub-bands. That is, a partial transmission of the temporary RS and/or the periodic tracking RS for the activation of the SCell in the frequency domain due to LBT failure in at least one part of the LBT sub-bands may not be accounted for valid transmission of the temporary RS for the purpose of the activation procedure. 
       FIG. 12  illustrates a call-flow diagram  1200  of wireless communication. The call-flow diagram  1200  may include a UE  1202 , a serving cell  1204 , and an SCell  1206  to be activated by the UE  1202 . The UE  1202  may receive an SCell activation command or indication from the one or more active serving cells, e.g., the serving cell  1204 . One or more temporary RS may be provided to expedite the SCell activation procedure, and the UE  1202  may expedite the SCell activation procedure using the one or more temporary RS received from the SCell  1206 . The UE  1202  may activate the SCell  1206  no later than in slot n+K, and K may be determined based on at least in part the SCell activation time. 
     At  1210 , the UE  1202  may receive, from the serving cell  1204 , an activation indication for activating an SCell  1206 . The activation indication may be received via one of a MAC-CE, DCI, or an RRC signal. The activation indication may indicate activating multiple SCells  1206  simultaneously, the multiple SCells  1206  including a first SCell and a second SCell. The first SCell and the second SCell may be in the same frequency band, in contiguous carriers in the same frequency band, or in a frequency range. At  1211 , the serving cell  1204  may configure the SCell  1206  to transmit one or more RS, including a first reference signal and/or a second reference signal. 
     At  1212 , the UE  1202  may transmit, to the serving cell  1204 , an ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell  1204 . 
     At  1214 , the UE  1202  may process the activation indication received from the serving cell  1204 . The UE  1202  may receive the first reference signal and/or the second reference signal based on the processed activation indication. 
     At  1216 , the UE  1202  may receive the first reference signal from the SCell  1206 , the first reference signal including at least one temporary reference signal as indicated by the activation indication at  1210 . The first reference signal may be a temporary RS, including an aperiodic tracking RS instructed by the MAC-CE or the DCI or a periodic tracking RS instructed by the RRC signal. Here, the first reference signal may be received from the active serving cell  1204 . 
     At  1218 , the UE  1202  may receive, from the serving cell  1204 , a new activation indication for activating an SCell  1206 . The activation indication may be received via one of the MAC-CE or the DCI. The activation indication may indicate activating multiple SCells  1206  simultaneously, the multiple SCells  1206  including a first SCell and a second SCell. The first SCell and the second SCell may be in the same frequency band, in contiguous carriers in the same frequency band, or in a frequency range. At  1219 , the serving cell  1204  may configure the SCell  1206  to transmit one or more RS, including a first reference signal and/or a second reference signal. 
     At  1220 , the UE  1202  may transmit, to the serving cell  1204 , an ACK of receiving the new activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell  1204 . 
     At  1222 , the UE  1202  may perform a clear channel assessment to determine whether a channel measurement is greater than a threshold value. 
     At  1224 , the UE  1202  may identify whether the first reference signal is transmitted as indicated by the activation indication at  1210 . The UE  1202  may identify that the first reference signal is not transmitted as indicated by the activation indication in response to determining that the channel measurement is greater than the threshold value at  1222 . The UE  1202  may also receive, from the serving cell, an instruction to cancel the transmission of the first reference signal where the UE identifies that the first reference signal is not transmitted in response to receiving the instruction to cancel the transmitted first reference signal, the instruction to cancel the activation indication for the SCell based on the first reference signal being indicated by one of the MAC-CE or the DCI. The SCell may include multiple sub-bands, and the UE  1202  may perform a clear channel assessment to determine whether channel measurements are greater than a threshold value for at least one of the multiple sub-bands and identify that the first reference signal is not transmitted as indicated upon determining that the channel measurements of at least one of the multiple sub-bands are greater than a threshold value. 
     At  1226 , the UE  1202  may receive the second reference signal from the SCell  1206 , the first reference signal including at least one temporary reference signal as indicated by the new activation indication at  1218 . The first reference signal may be a temporary RS, including an aperiodic tracking RS instructed by the MAC-CE or the DCI or a periodic tracking RS instructed by the RRC signal. Here, the first reference signal may be received from the active serving cell  1204 . 
     At  1228 , the UE  1202  may generate a CSI report of one of the first reference signal or the second reference signal on which the UE  1202  based the activation of the SCell  1206 . 
     At  1230 , the UE  1202  may transmit the CSI report of one of the first reference signal or the second reference signal on which the UE  1202  based the activation of the SCell  1206 . 
     At  1232 , the UE  1202  may activate the SCell  1206  based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal. The UE  1202  may activate, upon identifying that the first reference signal is transmitted as indicated, the SCell based on one or more reference signals including the first reference signal or a second reference signal. The UE  1202  may receive the activation indication in slot n, and may activate the SCell  1206  no later than in slot n+K, where K is determined based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, the SCell activation time, and a delay uncertainty in acquiring one or more first available CSI reporting resources. For example, the UE  1202  may receive the activation indication in slot n, and may activate the SCell  1206  no later than in in slot 
     
       
         
           
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     The T activation_time  may be the SCell activation time, and be determined based on one or more reference signals, including at least one of the first reference signal or the second reference signal. In one aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal. In another aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal. 
     The UE  1202  may activate multiple SCells  1206  simultaneously, based on one or more reference signals including at least one temporary reference signal including the aperiodic tracking reference signal or the periodic tracking reference signal, whichever is received earliest from the multiple SCells  1206 . The UE  1202  may activate the multiple SCells  1206  based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received within an earliest activation time for the multiple SCells  1206 . The UE  1202  may activate the multiple SCells  1206  based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received latest from the multiple SCells  1206 . 
       FIG. 13  is a flowchart  1300  of a method of wireless communication. The method may be performed by a UE (e.g., the UE  104 ,  1202 ; the apparatus  1502 ). The UE may receive an SCell activation command or indication from the one or more active serving cells, e.g., the serving cell. One or more temporary RS may be provided to expedite the SCell activation procedure, and the UE may expedite the SCell activation procedure using the one or more temporary RS received from the SCell. The UE may activate the SCell no later than in slot n+K, and K may be determined based on at least in part the SCell activation time. 
     At  1302 , the UE may receive, from the serving cell, an activation indication for activating an SCell. The activation indication may be received via one of a MAC-CE, DCI, or RRC signal. The activation indication may indicate activating multiple SCells simultaneously, the multiple SCells including a first SCell and a second SCell. The first SCell and the second SCell may be in the same frequency band, in contiguous carriers in the same frequency band, or in a frequency range. For example, at  1210 , the UE  1202  may receive, from the serving cell  1204 , an activation indication for activating an SCell  1206 . Furthermore,  1302  may be performed by the SCell activation component  1540 . 
     At  1304 , the UE may transmit, to the serving cell, an ACK of receiving the activation indication, wherein the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell. For example, at  1212 , the UE  1202  may transmit, to the serving cell  1204 , an ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell  1204 . Furthermore,  1304  may be performed by the ACK component  1542 . 
     At  1306 , the UE may process the activation indication received from the serving cell. The UE may receive the first reference signal and/or the second reference signal based on the processed activation indication. For example, at  1214 , the UE  1202  may process the activation indication received from the serving cell  1204 . Furthermore,  1306  may be performed by the SCell activation component  1540 . 
     At  1308 , the UE may receive the first reference signal from the SCell, the first reference signal including at least one temporary reference signal as indicated by the activation indication at  1302 . The first reference signal may be a temporary RS, including an aperiodic tracking RS instructed by the MAC-CE or the DCI or a periodic tracking RS instructed by the RRC signal. Here, the first reference signal may be received from the active serving cell. For example, at  1216 , the UE  1202  may receive the first reference signal from the SCell  1206 , the first reference signal including at least one temporary reference signal as indicated by the activation indication at  1210 . Furthermore,  1308  may be performed by the SCell activation component  1540 . 
     At  1310 , the UE may receive, from the serving cell, a new activation indication for activating an SCell (i.e., as at  1118 ). The activation indication may be received via one of the MAC-CE or the DCI. The activation indication may indicate activating multiple SCells simultaneously, the multiple SCells including a first SCell and a second SCell. The first SCell and the second SCell may be in the same frequency band, in contiguous carriers in the same frequency band, or in a frequency range. For example, at  1218 , the UE  1202  may receive, from the serving cell  1204 , a new activation indication for activating an SCell  1206 . Furthermore,  1310  may be performed by the SCell activation component  1540 . 
     At  1312 , the UE may transmit, to the serving cell, an ACK of receiving the new activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell. For example, at  1220 , the UE  1202  may transmit, to the serving cell  1204 , an ACK of receiving the new activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell  1204 . Furthermore,  1312  may be performed by the ACK component  1542 . 
     At  1314 , the UE may perform a clear channel assessment to determine whether a channel measurement is greater than a threshold value. For example, at  1222 , the UE  1202  may perform a clear channel assessment to determine whether a channel measurement is greater than a threshold value. Furthermore,  1314  may be performed by a LBT component  1546 . 
     At  1316 , the UE may identify whether the first reference signal is transmitted as indicated by the activation indication at  1302 . The UE may identify that the first reference signal is not transmitted as indicated by the activation indication in response to determining that the channel measurement is greater than the threshold value at  1314 . The UE may also receive, from the serving cell, an instruction to cancel the transmission of the first reference signal where the UE identifies that the first reference signal is not transmitted in response to receiving the instruction to cancel the transmitted first reference signal, the instruction to cancel the activation indication for the SCell based on the first reference signal being indicated by one of the MAC-CE or the DCI. The SCell may include multiple sub-bands, and the UE may perform a clear channel assessment to determine whether channel measurements are greater than a threshold value for at least one of the multiple sub-bands and identify that the first reference signal is not transmitted as indicated upon determining that the channel measurements of at least one of the multiple sub-bands are greater than a threshold value. For example, at  1224 , the UE  1202  may identify whether the first reference signal is transmitted as indicated by the activation indication at  1210 . Furthermore,  1316  may be performed by the SCell activation component  1540 . 
     At  1318 , the UE may receive the second reference signal from the SCell  1206 , the second reference signal including at least one temporary reference signal as indicated by the new activation indication received at  1312 . The second reference signal may be a temporary RS including an aperiodic tracking RS instructed by the MAC-CE or the DCI. Here, the second reference signal may be received from the active serving cell. For example, at  1226 , the UE  1202  may receive the second reference signal from the SCell  1206 , the first reference signal including at least one temporary reference signal as indicated by the new activation indication at  1218 . Furthermore,  1318  may be performed by the SCell activation component  1540 . 
     At  1320 , the UE may generate a CSI report of one of the first reference signal or the second reference signal on which the UE based the activation of the SCell. For example, at  1228 , the UE  1202  may generate a CSI report of one of the first reference signal or the second reference signal on which the UE  1202  based the activation of the SCell  1206 . Furthermore,  1320  may be performed by the CSI component  1544 . 
     At  1322 , the UE may transmit the CSI report of one of the first reference signal or the second reference signal on which the UE based the activation of the SCell. For example, at  1230 , the UE  1202  may transmit the CSI report of one of the first reference signal or the second reference signal on which the UE  1202  based the activation of the SCell  1206 . Furthermore,  1322  may be performed by the CSI component  1544 . 
     At  1324 , the UE may activate the SCell based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal. The UE may activate, upon identifying that the first reference signal is transmitted as indicated, the SCell based on one or more reference signals including the first reference signal or a second reference signal. The UE may receive the activation indication in slot n, and may activate the SCell no later than in slot n+K, where K is determined based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, the SCell activation time, and a delay uncertainty in acquiring one or more first available CSI reporting resources. For example, the UE may receive the activation indication in slot n, and may activate the SCell no later than in in slot 
     
       
         
           
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     The T activation_time  may be the SCell activation time, and be determined based on one or more reference signals, including at least one of the first reference signal or the second reference signal. In one aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal. In another aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal. The UE may activate multiple SCells simultaneously, based on one or more reference signals including at least one temporary reference signal including the aperiodic tracking reference signal or the periodic tracking reference signal, whichever is received earliest from the multiple SCells. The UE may activate the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received within an earliest activation time for the multiple SCells. The UE may activate the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received latest from the multiple SCells. For example, at  1232 , the UE  1202  may activate the SCell  1206  based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal. Furthermore,  1324  may be performed by the SCell activation component  1540 . 
       FIG. 14  is a flowchart  1400  of a method of wireless communication. The method may be performed by a UE (e.g., the UE  104 ,  1202 ; the apparatus  1502 ). The UE may receive an SCell activation command or indication from the one or more active serving cells, e.g., the serving cell. One or more temporary RS may be provided to expedite the SCell activation procedure, and the UE may expedite the SCell activation procedure using the one or more temporary RS received from the SCell. The UE may activate the SCell no later than in slot n+K, and K may be determined based on at least in part the SCell activation time. 
     At  1402 , the UE may receive, from the serving cell, an activation indication for activating an SCell. The activation indication may be received via one of a MAC-CE, DCI, or RRC signal. The activation indication may indicate activating multiple SCells simultaneously, the multiple SCells including a first SCell and a second SCell. The first SCell and the second SCell may be in the same frequency band, in contiguous carriers in the same frequency band, or in a frequency range. For example, at  1210 , the UE  1202  may receive, from the serving cell  1204 , an activation indication for activating an SCell  1206 . Furthermore,  1402  may be performed by the SCell activation component  1540 . 
     At  1416 , the UE may identify whether the first reference signal is transmitted as indicated by the activation indication at  1402 . The UE may identify that the first reference signal is not transmitted as indicated by the activation indication in response to determining that the channel measurement is greater than the threshold value. The UE may also receive, from the serving cell, an instruction to cancel the transmission of the first reference signal where the UE identifies that the first reference signal is not transmitted in response to receiving the instruction to cancel the transmitted first reference signal, the instruction to cancel the activation indication for the SCell based on the first reference signal being indicated by one of the MAC-CE or the DCI. The SCell may include multiple sub-bands, and the UE may perform a clear channel assessment to determine whether channel measurements are greater than a threshold value for at least one of the multiple sub-bands and determine that the first reference signal is not transmitted as indicated upon determining that the channel measurements of at least one of the multiple sub-bands are greater than a threshold value. For example, at  1224 , the UE  1202  may identify whether the first reference signal is transmitted as indicated by the activation indication at  1210 . Furthermore,  1416  may be performed by the SCell activation component  1540 . 
     At  1424 , the UE may activate the SCell based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal. The UE may activate, upon identifying that the first reference signal is transmitted as indicated, the SCell based on one or more reference signals including the first reference signal or a second reference signal. The UE may receive the activation indication in slot n, and may activate the SCell no later than in slot n+K, where K is determined based on at least one of a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, the SCell activation time, and a delay uncertainty in acquiring one or more first available CSI reporting resources. For example, the UE may receive the activation indication in slot n, and may activate the SCell no later than in in slot 
     
       
         
           
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     The T activation_time  may be the SCell activation time, and be determined based on one or more reference signals, including at least one of the first reference signal or the second reference signal. In one aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal. In another aspect, the SCell activation time may be between transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal. The UE may activate multiple SCells simultaneously, based on one or more reference signals including at least one temporary reference signal including the aperiodic tracking reference signal or the periodic tracking reference signal, whichever is received earliest from the multiple SCells. The UE may activate the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received within an earliest activation time for the multiple SCells. The UE may activate the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received latest from the multiple SCells. For example, at  1232 , the UE  1202  may activate the SCell  1206  based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal. Furthermore,  1424  may be performed by the SCell activation component  1540 . 
       FIG. 15  is a diagram  1500  illustrating an example of a hardware implementation for an apparatus  1502 . The apparatus  1502  may be a UE, a component of a UE, or may implement UE functionality. In some aspects, the apparatus 1502  may include a cellular baseband processor  1504  (also referred to as a modem) coupled to a cellular RF transceiver  1522 . In some aspects, the apparatus  1502  may further include one or more subscriber identity modules (SIM) cards  1520 , an application processor  1506  coupled to a secure digital (SD) card  1508  and a screen  1510 , a Bluetooth module  1512 , a wireless local area network (WLAN) module  1514 , a Global Positioning System (GPS) module  1516 , or a power supply  1518 . The cellular baseband processor  1504  communicates through the cellular RF transceiver  1522  with the UE  104  and/or BS  102 / 180 . The cellular baseband processor  1504  may include a computer-readable medium/memory. The computer-readable medium/memory may be non-transitory. The cellular baseband processor  1504  is responsible for general processing, including the execution of software stored on the computer-readable medium/memory. The software, when executed by the cellular baseband processor  1504 , causes the cellular baseband processor  1504  to perform the various functions described supra. The computer-readable medium/memory may also be used for storing data that is manipulated by the cellular baseband processor  1504  when executing software. The cellular baseband processor  1504  further includes a reception component  1530 , a communication manager  1532 , and a transmission component  1534 . The communication manager  1532  includes the one or more illustrated components. The components within the communication manager  1532  may be stored in the computer-readable medium/memory and/or configured as hardware within the cellular baseband processor  1504 . The cellular baseband processor  1504  may be a component of the UE  350  and may include the memory  360  and/or at least one of the TX processor  368 , the RX processor  356 , and the controller/processor  359 . In one configuration, the apparatus  1502  may be a modem chip and include just the baseband processor  1504 , and in another configuration, the apparatus  1502  may be the entire UE (e.g., see  350  of  FIG. 3 ) and include the additional modules of the apparatus  1502 . 
     The communication manager  1532  includes an SCell activation component  1540  that is configured to receive, from a serving cell, an activation indication for activating an SCell, process the received activation indication, receive a first reference signal and/or a second reference signal, identify whether the second reference signal is received after processing the activation indication and before the expiration of an SCell activation time, identify whether the first reference signal is transmitted as indicated by the activation indication, and activate the SCell based on one or more reference signals, including at least one of the received first reference signal and/or second reference signal, e.g., as described in connection with  802 ,  806 ,  808 ,  810 ,  812 ,  818 ,  902 ,  908 ,  912 ,  918 ,  1302 ,  1306 ,  1308 ,  1310 ,  1316 ,  1318 ,  1324 ,  1402 ,  1416 , and  1424 . The communication manager  1532  further includes an ACK component  1542  that is configured to transmit, to the serving cell, an ACK of receiving the activation indication, e.g., as described in connection with  804 ,  1304 , and  1312 . The communication manager  1532  further includes a CSI component  1544  that is configured to generate a CSI report of one of the first reference signal or the second reference signal on which the UE based the activation of the SCell and transmit the CSI, e.g., as described in connection with  814 ,  816 ,  1320 , and  1322 . The communication manager  1532  further includes an LBT component  1546  that is configured to perform a clear channel assessment to determine whether a channel measurement is greater than a threshold value, e.g., as described in connection with  1314 . 
     The apparatus may include additional components that perform each of the blocks of the algorithm in the flowcharts of  FIGS. 7, 8, 9, 12, 13, and 14 . As such, each block in the flowcharts of  FIGS. 7, 8, 9, 12, 13, and 14  may be performed by a component and the apparatus may include one or more of those components. The components may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by a processor configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by a processor, or some combination thereof. 
     As shown, the apparatus  1502  may include a variety of components configured for various functions. In one configuration, the apparatus  1502 , and in particular the cellular baseband processor  1504 , includes means for receiving, from a serving cell, an activation indication for a SCell, means for receiving a first reference signal from the SCell, the first reference signal including at least one temporary reference signal, means for identifying whether a second reference signal is received after processing the activation indication and before an expiration of an SCell activation time, and means for activating, upon identifying that the second reference signal is received, the SCell based on one or more reference signals including at least one of the first reference signal or the second reference signal. The apparatus  1502  includes means for transmitting, to the serving cell, an ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell and means for transmitting, a CSI report of one of the first reference signal or the second reference signal on which the UE based the activation of the SCell. The apparatus  1502  includes means for identifying whether the second reference signal is received from the active serving cell. The apparatus  1502  includes means for receiving, from a serving cell, an activation indication for a SCell based on a first reference signal, the activation indication indicating a transmission of the first reference signal for activating the SCell, means for identifying whether the first reference signal is transmitted as indicated, and means for activating, upon identifying that the first reference signal is transmitted as indicated, the SCell based on one or more reference signals including the first reference signal or a second reference signal. The apparatus  1502  includes means for transmitting, to the serving cell, an ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell, and means for receiving a new activation indication indicating a transmission of a second reference signal for activating the SCell. The apparatus  1502  includes means for performing a clear channel assessment to determine whether channel measurements are greater than a threshold value for at least one of the multiple sub-bands, and means for identifying that the first reference signal is not transmitted as indicated upon determining that the channel measurements of at least one of the multiple sub-bands are greater than a threshold value. The means may be one or more of the components of the apparatus  1502  configured to perform the functions recited by the means. As described supra, the apparatus  1502  may include the TX Processor  368 , the RX Processor  356 , and the controller/processor  359 . As such, in one configuration, the means may be the TX Processor  368 , the RX Processor  356 , and the controller/processor  359  configured to perform the functions recited by the means. 
     A UE may receive, from a serving cell, an activation indication for a SCell, receiving a first reference signal from the SCell, the first reference signal including at least one temporary reference signal, identify whether a second reference signal is received after processing the activation indication and before an expiration of an SCell activation time, and activate, upon identifying that the second reference signal is received, the SCell based on one or more reference signals including at least one of the first reference signal or the second reference signal. 
     The UE may transmit, to the serving cell, an ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell. The UE may transmit a CSI report of one of the first reference signal or the second reference signal on which the UE based the activation of the SCell. 
     The UE may activate the SCell no later than in slot n+K, and K may be determined based on at least in part the SCell activation time. In one aspect, the activation indication may be received via one of a MAC-CE or DCI, and the at least one temporary reference signal includes an aperiodic tracking reference signal, and the activation indication indicates the aperiodic tracking reference signal transmitted by the SCell. The SCell activation time may be the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving the at least one temporary reference signal, 
     In another aspect, the activation indication may be received via RRC signaling, and the at least one temporary reference signal includes a periodic tracking reference signal, and the activation indication indicates the periodic tracking reference signal transmitted by the SCell. The SCell activation time may be the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving a last of one or more reference signals on which the UE based the activation of the SCell. The activation indication may indicate activating multiple SCells simultaneously, and the multiple SCells may be in the same frequency band, in contiguous carriers in the same frequency band, or in a frequency range. 
     The UE may receive, from a serving cell, an activation indication for the SCell based on a first reference signal, the activation indication indicating a transmission of the first reference signal for activating the SCell, identify whether the first reference signal is transmitted as indicated, and activating, upon identifying that the first reference signal is transmitted as indicated, the SCell based on one or more reference signals including the first reference signal or a second reference signal. The UE may transmit, to the serving cell, the ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell. 
     The first reference signal may include at least one of a periodic tracking reference signal or an aperiodic tracking reference signal. The UE may identify whether the first reference signal is transmitted as indicated by performing a clear channel assessment to determine whether a channel measurement is greater than a threshold value, and identifying that the first reference signal is not transmitted as indicated by the activation indication in response to determining that the channel measurement is greater than the threshold value. 
     The UE may receive, from the serving cell, an instruction to cancel the transmission of the first reference signal where the UE identifies that the first reference signal is not transmitted in response to receiving the instruction to cancel the transmitted first reference signal, and where the instruction to cancel the activation indication for the SCell based on the first reference signal is indicated by one of a MAC-CE or DCI. 
     The UE may receive, upon identifying that the first reference signal is not transmitted as indicated, a second reference signal from the SCell, and activate, upon identifying that the first reference signal is not transmitted as indicated, the SCell based on the second reference signal received from the SCell. The SCell activation time may be the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal. 
     The UE may receive a new activation indication indicating a transmission of a second reference signal for activating the SCell, where, upon receiving the new activation indication, the UE identifies that the first reference signal is not transmitted as indicated. 
     It is understood that the specific order or hierarchy of blocks in the processes/flowcharts disclosed is an illustration of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes/flowcharts may be rearranged. Further, some blocks may be combined or omitted. The accompanying method claims present elements of the various blocks in a sample order, and are not meant to be limited to the specific order or hierarchy presented. 
     The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Terms such as “if,” “when,” and “while” should be interpreted to mean “under the condition that” rather than imply an immediate temporal relationship or reaction. That is, these phrases, e.g., “when,” do not imply an immediate action in response to or during the occurrence of an action, but simply imply that if a condition is met then an action will occur, but without requiring a specific or immediate time constraint for the action to occur. The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any aspect described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects. Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” include any combination of A, B, and/or C, and may include multiples of A, multiples of B, or multiples of C. Specifically, combinations such as “at least one of A, B, or C,” “one or more of A, B, or C,” “at least one of A, B, and C,” “one or more of A, B, and C,” and “A, B, C, or any combination thereof” may be A only, B only, C only, A and B, A and C, B and C, or A and B and C, where any such combinations may contain one or more member or members of A, B, or C. All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. The words “module,” “mechanism,” “element,” “device,” and the like may not be a substitute for the word “means.” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for.” 
     The following aspects are illustrative only and may be combined with other aspects or teachings described herein, without limitation. 
     Aspect 1 is a method of wireless communication of a UE, the method including: receiving, from a serving cell, an activation indication for an SCell, receiving a first reference signal from the SCell, the first reference signal including at least one temporary reference signal, identifying whether a second reference signal is received after processing the activation indication and before an expiration of an SCell activation time, and activating, upon identifying that the second reference signal is received, the SCell based on one or more reference signals including at least one of the first reference signal or the second reference signal. 
     Aspect 2 is the method of aspect 1, further including transmitting, to the serving cell, an ACK of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell. 
     Aspect 3 is the method of any of aspects 1 and 2, further includes transmitting, a CSI report of one of the first reference signal or the second reference signal on which the UE based the activation of the SCell. 
     Aspect 4 is the method of any of aspects 1 to 3, where the activation indication is received via one of a MAC-CE or DCI. 
     Aspect 5 is the method of aspect 4, where the at least one temporary reference signal includes an aperiodic tracking reference signal, and the activation indication indicates the aperiodic tracking reference signal transmitted by the SCell. 
     Aspect 6 is the method of aspect 5, where the UE activates the SCell no later than in slot 
     
       
         
           
             
               n 
               + 
               
                 
                   
                     T 
                     
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                       ⁢ 
                       A 
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                       R 
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                       Q 
                     
                   
                   + 
                   
                     T 
                     
                       a 
                       ⁢ 
                       c 
                       ⁢ 
                       t 
                       ⁢ 
                       i 
                       ⁢ 
                       v 
                       ⁢ 
                       a 
                       ⁢ 
                       tion 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       time 
                     
                   
                   + 
                   
                     T 
                     
                       CSI 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
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                       ⁢ 
                       Reporting 
                     
                   
                 
                 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
             
             , 
           
         
       
     
     where the activation indication is received in slot n, T HARQ  is a time period between receiving the activation indication from the serving cell and transmitting an acknowledgment (ACK) of the activation indication to the serving cell, T activation_time  is the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving the at least one temporary reference signal, and T CSI_reporting  is a delay uncertainty in acquiring one or more first available CSI reporting resources. 
     Aspect 7 is the method of any of aspects 1 to 3, where the activation indication is received via RRC signaling. 
     Aspect 8 is the method of aspect 7, where the at least one temporary reference signal includes a periodic tracking reference signal, and the activation indication indicates the periodic tracking reference signal transmitted by the SCell. 
     Aspect 9 is the method of aspect 8, where the UE activates the SCell no later than in slot 
     
       
         
           
             
               n 
               + 
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
                       ⁢ 
                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     T 
                     
                       a 
                       ⁢ 
                       c 
                       ⁢ 
                       t 
                       ⁢ 
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                       ⁢ 
                       v 
                       ⁢ 
                       a 
                       ⁢ 
                       tion 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       time 
                     
                   
                   + 
                   
                     T 
                     
                       CSI 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Reporting 
                     
                   
                 
                 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
             
             , 
           
         
       
     
     where the activation indication is received in slot n, T HARQ  is a time period between receiving the activation indication from the serving cell and transmitting the ACK of the activation indication to the serving cell, T activation_time  is the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving a last of one or more reference signals on which the UE based the activation of the SCell, and T CSI_reporting  is a delay uncertainty in acquiring one or more first available CSI reporting resources. 
     Aspect 10 is the method of any of aspects 1 to 9, where the first reference signal is received from an active serving cell, and where the UE identifies whether the second reference signal is received from the active serving cell. 
     Aspect 11 is the method of any of aspects 1 to 10, where the first reference signal and the second reference signal are assumed to be quasi-co-located with each other. 
     Aspect 12 is the method of any of aspects 1 to 11, where the activation indication indicates activating multiple SCells simultaneously, the multiple SCells including a first SCell and a second SCell. 
     Aspect 13 is the method of aspect 12, where the first SCell and the second SCell are in a same frequency band, in contiguous carriers in the same frequency band, or in a frequency range. 
     Aspect 14 is the method of any of aspects 12 and 13, where the UE activates the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received earliest from the multiple SCells. 
     Aspect 15 is the method of any of aspects 12 to 14, where the UE activates the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received within an earliest activation time for the multiple SCells. 
     Aspect 16 is the method of any of aspects 12 to 15, where the UE activates the multiple SCells based on one or more reference signals including at least one temporary reference signal including an aperiodic tracking reference signal or a periodic tracking reference signal, whichever is received latest from the multiple SCells. 
     Aspect 17 is the method of any of aspects 1 to 5, 7, 8, 10 to 16, where the UE activates the SCell no later than in slot 
     
       
         
           
             
               n 
               + 
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
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                       R 
                       ⁢ 
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                   + 
                   
                     T 
                     
                       a 
                       ⁢ 
                       c 
                       ⁢ 
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                       ⁢ 
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                       ⁢ 
                       v 
                       ⁢ 
                       a 
                       ⁢ 
                       tion 
                       ⁢ 
                       
                           
                       
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                       _ 
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                       time 
                     
                   
                   + 
                   
                     T 
                     
                       CSI 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
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                       ⁢ 
                       Reporting 
                     
                   
                 
                 
                   slot 
                   ⁢ 
                   
                       
                   
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                   length 
                 
               
             
             , 
           
         
       
     
     where the activation indication is received in slot n, T HARQ  is a time period between receiving the activation indication from the serving cell and transmitting the ACK of the activation indication to the serving cell, T activation time  is the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving two reference signals including one of the first reference signal or the second reference signal, and T CSI_reporting  is a delay uncertainty in acquiring one or more first available CSI reporting resources. 
     Aspect 18 is the method of any of aspects 1 to 5, 7, 8, 10 to 16, where the UE activates the SCell no later than in slot 
     
       
         
           
             
               n 
               + 
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
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                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     T 
                     
                       a 
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                       ⁢ 
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                       ⁢ 
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                       v 
                       ⁢ 
                       a 
                       ⁢ 
                       tion 
                       ⁢ 
                       
                           
                       
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                       _ 
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                       time 
                     
                   
                   + 
                   
                     T 
                     
                       CSI 
                       ⁢ 
                       
                           
                       
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                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Reporting 
                     
                   
                 
                 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
             
             , 
           
         
       
     
     where the activation indication is received in slot n, T HARQ  is a time period between receiving the activation indication from the serving cell and transmitting the ACK of the activation indication to the serving cell, T activation_time  is the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving four reference signals including one of the first reference signal or the second reference signal, and T CSI_reporting  is a delay uncertainty in acquiring one or more first available CSI reporting resources. 
     Aspect 19 is an apparatus for wireless communication including at least one processor coupled to a memory and configured to implement a method as in any of aspects 1 to 18. 
     Aspect 20 is an apparatus for wireless communication including means for implementing a method as in any of aspects 1 to 18. 
     Aspect 21 is a computer-readable medium storing computer executable code, where the code when executed by a processor causes the processor to implement a method as in any of aspects 1 to 18. 
     Aspect 22 is a method of wireless communication of a UE, the method including: receiving, from a serving cell, an activation indication for a secondary cell (SCell) based on a first reference signal, the activation indication indicating a transmission of the first reference signal for activating the SCell, identifying whether the first reference signal is transmitted as indicated, and activating, upon identifying that the first reference signal is transmitted as indicated, the SCell based on one or more reference signals including the first reference signal or a second reference signal. 
     Aspect 23 is the method of aspect 22, further including transmitting, to the serving cell, an acknowledgment (ACK) of receiving the activation indication, where the activation indication is processed within a first time duration after the ACK is transmitted to the serving cell. 
     Aspect 24 is the method of any of aspects 22 and 23, where the first reference signal includes at least one of a periodic tracking reference signal or an aperiodic tracking reference signal. 
     Aspect 25 is the method of any of aspects 22 to 24, where identifying whether the first reference signal is transmitted as indicated includes performing a clear channel assessment to determine whether a channel measurement is greater than a threshold value, and identifying that the first reference signal is not transmitted as indicated by the activation indication in response to determining that the channel measurement is greater than the threshold value. 
     Aspect 26 is the method of any of aspects 22 to 25, further includes receiving, from the serving cell, an instruction to cancel the transmission of the first reference signal where the UE identifies that the first reference signal is not transmitted in response to receiving the instruction to cancel the transmitted first reference signal, and where the instruction to cancel the activation indication for the SCell based on the first reference signal is indicated by one of a MAC-CE or DCI. 
     Aspect 27 is the method of any of aspects 22 to 26, further including receiving, upon identifying that the first reference signal is not transmitted as indicated, a second reference signal from the SCell, and activating, upon identifying that the first reference signal is not transmitted as indicated, the SCell based on the second reference signal received from the SCell. 
     Aspect 28 is the method of aspect 27, where the UE activates the SCell no later than in slot 
     
       
         
           
             
               n 
               + 
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
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                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     T 
                     
                       a 
                       ⁢ 
                       c 
                       ⁢ 
                       t 
                       ⁢ 
                       i 
                       ⁢ 
                       v 
                       ⁢ 
                       a 
                       ⁢ 
                       tion 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       time 
                     
                   
                   + 
                   
                     T 
                     
                       CSI 
                       ⁢ 
                       
                           
                       
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                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Reporting 
                     
                   
                 
                 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
             
             , 
           
         
       
     
     where the activation indication is received in slot n, T HARQ  is a time period between receiving the activation indication from the serving cell transmitting an ACK of the activation indication to the serving cell, T activation_time  is the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal, and T CSI_reporting  is a delay uncertainty in acquiring one or more first available CSI reporting resources. 
     Aspect 29 is the method of any of aspects 22 to 26, further including receiving a new activation indication indicating a transmission of a second reference signal for activating the SCell, where, upon receiving the new activation indication, the UE identifies that the first reference signal is not transmitted as indicated. 
     Aspect 30 is the method of aspect 29, where the UE activates the SCell no later than in slot 
     
       
         
           
             
               n 
               + 
               
                 
                   
                     T 
                     
                       H 
                       ⁢ 
                       A 
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                       R 
                       ⁢ 
                       Q 
                     
                   
                   + 
                   
                     T 
                     
                       a 
                       ⁢ 
                       c 
                       ⁢ 
                       t 
                       ⁢ 
                       i 
                       ⁢ 
                       v 
                       ⁢ 
                       a 
                       ⁢ 
                       tion 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       time 
                     
                   
                   + 
                   
                     T 
                     
                       CSI 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       _ 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       Reporting 
                     
                   
                 
                 
                   slot 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   length 
                 
               
             
             , 
           
         
       
     
     where the activation indication is received in slot n, T HARQ  is a time period between receiving the activation indication from the serving cell and transmitting an ACK of the activation indication to the serving cell, T activation_time  is the SCell activation time between transmission of the ACK of the activation indication and a second time duration after receiving the second reference signal, and T CSI_reporting  is a delay uncertainty in acquiring one or more first available CSI reporting resources. 
     Aspect 31 is the method of any of aspects 22 to 30, where the SCell includes multiple sub-bands, and where identifying whether the first reference signal is transmitted as indicated includes performing a clear channel assessment to determine whether channel measurements are greater than a threshold value for at least one of the multiple sub-bands, and identifying, that the first reference signal is not transmitted as indicated upon determining that the channel measurements of at least one of the multiple sub-bands are greater than a threshold value. 
     Aspect 32 is an apparatus for wireless communication including at least one processor coupled to a memory and configured to implement a method as in any of aspects 22 to 31. 
     Aspect 33 is an apparatus for wireless communication including means for implementing a method as in any of aspects 22 to 31. 
     Aspect 34 is a computer-readable medium storing computer executable code, where the code when executed by a processor causes the processor to implement a method as in any of aspects 22 to 31.