Patent Publication Number: US-2022225338-A1

Title: Method and apparatus for configuring and determining default beams in a wireless communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM OF PRIORITY 
     The present application claims priority to U.S. Provisional Patent Application No. 63/137,477, filed on Jan. 14, 2021. The content of the above-identified patent document is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to wireless communication systems and, more specifically, the present disclosure relates to configuration and determination of default beams in a wireless communication system. 
     BACKGROUND 
     5th generation (5G) or new radio (NR) mobile communications is recently gathering increased momentum with all the worldwide technical activities on the various candidate technologies from industry and academia. The candidate enablers for the 5G/NR mobile communications include massive antenna technologies, from legacy cellular frequency bands up to high frequencies, to provide beamforming gain and support increased capacity, new waveform (e.g., a new radio access technology (RAT)) to flexibly accommodate various services/applications with different requirements, new multiple access schemes to support massive connections, and so on. 
     SUMMARY 
     The present disclosure relates to wireless communication systems and, more specifically, the present disclosure relates to configuration and determination of default beams in a wireless communication system. 
     In one embodiment, a user equipment (UE) is provided. The UE includes a transceiver configured to receive: a first physical downlink control channel (PDCCH) including a first downlink control information (DCI) format indicating one or more first unified transmission configuration indication (TCI) states; a second PDCCH including a second DCI format indicating one or more second unified TCI states; and information on a beam application time. The UE further includes a processor operably coupled to the transceiver. The processor is configured to determine a quasi-co-location (QCL) assumption for reception of a physical layer shared channel (PDSCH) based on one of the one or more first and second unified TCI states and the beam application time. The transceiver is configured to receive the PDSCH according to the QCL assumption. Receptions of the first and second PDCCHs are in control resource sets (CORESETs) configured with same or different values of a coresetPoollndex. 
     In another embodiment, a base station (BS) is provided. The BS includes a transceiver configured to transmit: a first PDCCH including a first DCI format indicating one or more first unified TCI states; information on a beam application time; and a PDSCH for reception according to a QCL assumption that is based on (i) the beam application time and (ii) one of the one or more first unified TCI states or one or more second unified TCI states indicated in a second DCI format included in a second PDCCH. The first and second PDCCHs are in CORESETs configured with same or different values of a coresetPoollndex. 
     In yet another embodiment, a method for operating a UE is provided. The method includes receiving a first PDCCH including a first DCI format indicating one or more first unified TCI states, receiving a second PDCCH including a second DCI format indicating one or more second unified TCI states, and receiving information on a beam application time. The method further includes determining a QCL assumption for reception of a PDSCH based on one of the one or more first and second unified TCI states and the beam application time and receiving the PDSCH according to the QCL assumption. Receptions of the first and second PDCCHs are in CORESETs configured with same or different values of a coresetPoollndex. 
     Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims. 
     Before undertaking the DETAILED DESCRIPTION below, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The terms “transmit,” “receive,” and “communicate,” as well as derivatives thereof, encompass both direct and indirect communication. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrase “associated with,” as well as derivatives thereof, means to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, have a relationship to or with, or the like. The term “controller” means any device, system, or part thereof that controls at least one operation. Such a controller may be implemented in hardware or a combination of hardware and software and/or firmware. The functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. The phrase “at least one of,” when used with a list of items, means that different combinations of one or more of the listed items may be used, and only one item in the list may be needed. For example, “at least one of: A, B, and C” includes any of the following combinations: A, B, C, A and B, A and C, B and C, and A and B and C. 
     Moreover, various functions described below can be implemented or supported by one or more computer programs, each of which is formed from computer readable program code and embodied in a computer readable medium. The terms “application” and “program” refer to one or more computer programs, software components, sets of instructions, procedures, functions, objects, classes, instances, related data, or a portion thereof adapted for implementation in a suitable computer readable program code. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. A “non-transitory” computer readable medium excludes wired, wireless, optical, or other communication links that transport transitory electrical or other signals. A non-transitory computer readable medium includes media where data can be permanently stored and media where data can be stored and later overwritten, such as a rewritable optical disc or an erasable memory device. 
     Definitions for other certain words and phrases are provided throughout this patent document. Those of ordinary skill in the art should understand that in many if not most instances, such definitions apply to prior as well as future uses of such defined words and phrases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the present disclosure and its advantages, reference is now made to the following description taken in conjunction with the accompanying drawings, in which like reference numerals represent like parts: 
         FIG. 1  illustrates an example of wireless network according to embodiments of the present disclosure; 
         FIG. 2  illustrates an example of gNB according to embodiments of the present disclosure; 
         FIG. 3  illustrates an example of UE according to embodiments of the present disclosure; 
         FIGS. 4 and 5  illustrate example of wireless transmit and receive paths according to this disclosure; 
         FIG. 6A  illustrate an example of wireless system beam according to embodiments of the present disclosure; 
         FIG. 6B  illustrate an example of multi-beam operation according to embodiments of the present disclosure; 
         FIG. 7  illustrate an example of antenna structure according to embodiments of the present disclosure; 
         FIG. 8  illustrates an example of multi-TRP system according to embodiments of the present disclosure; 
         FIG. 9  illustrates an example of unified TCI state indication according to embodiments of the present disclosure; 
         FIG. 10  illustrates an example of unified TCI state indication in a multi-DCI based multi-TRP system according to embodiments of the present disclosure; 
         FIG. 11  illustrates another example of unified TCI state indication in a multi-DCI based multi-TRP system according to embodiments of the present disclosure; 
         FIG. 12  illustrates yet another example of unified TCI state indication in a multi-DCI based multi-TRP system according to embodiments of the present disclosure; 
         FIG. 13  illustrates yet another example of unified TCI state indication in a multi-DCI based multi-TRP system according to embodiments of the present disclosure; 
         FIG. 14  illustrates yet another example of unified TCI state indication in a mult-DCI based multi-TRP system according to embodiments of the present disclosure; 
         FIG. 15  illustrates yet another example of unified TCI state indication in a multi-DCI based multi-TRP system according to embodiments of the present disclosure; 
         FIG. 16  illustrates an example of a signaling flow between a UE and a gNB according to embodiments of the present disclosure; 
         FIG. 17  illustrates an example of a signaling flow for configuring and determining a default TCI state according to embodiments of the present disclosure; 
         FIG. 18  illustrates an example of a signaling flow between a UE and a gNB according to embodiments of the present disclosure; 
         FIG. 19  illustrates an example of priority rule for configuring and determining default TCI state according to embodiments of the present disclosure; 
         FIG. 20  illustrates another example of priority rule for configuring and determining default TCI state according to embodiments of the present disclosure; 
         FIG. 21  illustrates a flowchart of a UE method for receiving and decoding PDSCH according to embodiments of the present disclosure; 
         FIG. 22  illustrates another flowchart of a UE method for receiving and decoding PDSCH according to embodiments of the present disclosure; 
         FIG. 23  illustrates yet another flowchart of a UE method for receiving and decoding PDSCH according to embodiments of the present disclosure; 
         FIG. 24  illustrates an example of unified TCI state indication in a single-DCI based multi-TRP system according to embodiments of the present disclosure; 
         FIG. 25  illustrates another example of unified TCI state indication in a single-DCI based multi-TRP system according to embodiments of the present disclosure; 
         FIG. 26  illustrates yet another example of unified TCI state indication in a single-DCI based multi-TRP system according to embodiments of the present disclosure; 
         FIG. 27  illustrates an example of configuring and determining default TCI states according to embodiments of the present disclosure; 
         FIG. 28  illustrates another example of configuring and determining default TCI states according to embodiments of the present disclosure; 
         FIG. 29  illustrates an example of priority rule for configuring and determining default TCI state according to embodiments of the present disclosure; and 
         FIG. 30  illustrates a flowchart of a method for configuring and determining a default beam according to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  through  FIG. 30 , discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged system or device. 
     The following documents are hereby incorporated by reference into the present disclosure as if fully set forth herein: 3GPP TS 38.211 v16.1.0, “NR; Physical channels and modulation”; 3GPP TS 38.212 v16.1.0, “NR; Multiplexing and Channel coding”; 3GPP TS 38.213 v16.1.0, “NR; Physical Layer Procedures for Control”; 3GPP TS 38.214 v16.1.0, “NR; Physical Layer Procedures for Data”; 3GPP TS 38.321 v16.1.0, “NR; Medium Access Control (MAC) protocol specification”; and 3GPP TS 38.331 v16.1.0, “NR; Radio Resource Control (RRC) Protocol Specification.” 
       FIGS. 1-3  below describe various embodiments implemented in wireless communications systems and with the use of orthogonal frequency division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA) communication techniques. The descriptions of  FIGS. 1-3  are not meant to imply physical or architectural limitations to the manner in which different embodiments may be implemented. Different embodiments of the present disclosure may be implemented in any suitably-arranged communications system. 
       FIG. 1  illustrates an example wireless network according to embodiments of the present disclosure. The embodiment of the wireless network shown in  FIG. 1  is for illustration only. Other embodiments of the wireless network  100  could be used without departing from the scope of this disclosure. 
     As shown in  FIG. 1 , the wireless network includes a gNB  101  (e.g., base station, BS), a gNB  102 , and a gNB  103 . The gNB  101  communicates with the gNB  102  and the gNB  103 . The gNB  101  also communicates with at least one network  130 , such as the Internet, a proprietary Internet Protocol (IP) network, or other data network. 
     The gNB  102  provides wireless broadband access to the network  130  for a first plurality of user equipments (UEs) within a coverage area  120  of the gNB  102 . The first plurality of UEs includes a UE  111 , which may be located in a small business; a UE  112 , which may be located in an enterprise (E); a UE  113 , which may be located in a WiFi hotspot (HS); a UE  114 , which may be located in a first residence (R); a UE  115 , which may be located in a second residence (R); and a UE  116 , which may be a mobile device (M), such as a cell phone, a wireless laptop, a wireless PDA, or the like. The gNB  103  provides wireless broadband access to the network  130  for a second plurality of UEs within a coverage area  125  of the gNB  103 . The second plurality of UEs includes the UE  115  and the UE  116 . In some embodiments, one or more of the gNBs  101 - 103  may communicate with each other and with the UEs  111 - 116  using 5G/NR, long term evolution (LTE), long term evolution-advanced (LTE-A), WiMAX, WiFi, or other wireless communication techniques. 
     Depending on the network type, the term “base station” or “BS” can refer to any component (or collection of components) configured to provide wireless access to a network, such as transmit point (TP), transmit-receive point (TRP), an enhanced base station (eNodeB or eNB), a 5G/NR base station (gNB), a macrocell, a femtocell, a WiFi access point (AP), or other wirelessly enabled devices. Base stations may provide wireless access in accordance with one or more wireless communication protocols, e.g., 5G/NR 3GPP NR, long term evolution (LTE), LTE advanced (LTE-A), high speed packet access (HSPA), Wi-Fi 802.11a/b/g/n/ac, etc. For the sake of convenience, the terms “BS” and “TRP” are used interchangeably in this patent document to refer to network infrastructure components that provide wireless access to remote terminals. Also, depending on the network type, the term “user equipment” or “UE” can refer to any component such as “mobile station,” “subscriber station,” “remote terminal,” “wireless terminal,” “receive point,” or “user device.” For the sake of convenience, the terms “user equipment” and “UE” are used in this patent document to refer to remote wireless equipment that wirelessly accesses a BS, whether the UE is a mobile device (such as a mobile telephone or smartphone) or is normally considered a stationary device (such as a desktop computer or vending machine). 
     Dotted lines show the approximate extents of the coverage areas  120  and  125 , which are shown as approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the coverage areas associated with gNBs, such as the coverage areas  120  and  125 , may have other shapes, including irregular shapes, depending upon the configuration of the gNBs and variations in the radio environment associated with natural and man-made obstructions. 
     As described in more detail below, one or more of the UEs  111 - 116  include circuitry, programing, or a combination thereof, for configuring and determining default beams in a wireless communication system. In certain embodiments, and one or more of the gNBs  101 - 103  includes circuitry, programing, or a combination thereof, for configuring and determining default beams in a wireless communication system. 
     Although  FIG. 1  illustrates one example of a wireless network, various changes may be made to  FIG. 1 . For example, the wireless network could include any number of gNBs and any number of UEs in any suitable arrangement. Also, the gNB  101  could communicate directly with any number of UEs and provide those UEs with wireless broadband access to the network  130 . Similarly, each gNB  102 - 103  could communicate directly with the network  130  and provide UEs with direct wireless broadband access to the network  130 . Further, the gNBs  101 ,  102 , and/or  103  could provide access to other or additional external networks, such as external telephone networks or other types of data networks. 
       FIG. 2  illustrates an example gNB  102  according to embodiments of the present disclosure. The embodiment of the gNB  102  illustrated in  FIG. 2  is for illustration only, and the gNBs  101  and  103  of  FIG. 1  could have the same or similar configuration. However, gNBs come in a wide variety of configurations, and  FIG. 2  does not limit the scope of this disclosure to any particular implementation of a gNB. 
     As shown in  FIG. 2 , the gNB  102  includes multiple antennas  205   a - 205   n , multiple RF transceivers  210   a - 210   n , transmit (TX) processing circuitry  215 , and receive (RX) processing circuitry  220 . The gNB  102  also includes a controller/processor  225 , a memory  230 , and a backhaul or network interface  235 . 
     The RF transceivers  210   a - 210   n  receive, from the antennas  205   a - 205   n , incoming RF signals, such as signals transmitted by UEs in the network  100 . The RF transceivers  210   a - 210   n  down-convert the incoming RF signals to generate IF or baseband signals. The IF or baseband signals are sent to the RX processing circuitry  220 , which generates processed baseband signals by filtering, decoding, and/or digitizing the baseband or IF signals. The RX processing circuitry  220  transmits the processed baseband signals to the controller/processor  225  for further processing. 
     The TX processing circuitry  215  receives analog or digital data (such as voice data, web data, e-mail, or interactive video game data) from the controller/processor  225 . The TX processing circuitry  215  encodes, multiplexes, and/or digitizes the outgoing baseband data to generate processed baseband or IF signals. The RF transceivers  210   a - 210   n  receive the outgoing processed baseband or IF signals from the TX processing circuitry  215  and up-converts the baseband or IF signals to RF signals that are transmitted via the antennas  205   a - 205   n.    
     The controller/processor  225  can include one or more processors or other processing devices that control the overall operation of the gNB  102 . For example, the controller/processor  225  could control the reception of UL channel signals and the transmission of DL channel signals by the RF transceivers  210   a - 210   n , the RX processing circuitry  220 , and the TX processing circuitry  215  in accordance with well-known principles. The controller/processor  225  could support additional functions as well, such as more advanced wireless communication functions. For instance, the controller/processor  225  could support beam forming or directional routing operations in which outgoing/incoming signals from/to multiple antennas  205   a - 205   n  are weighted differently to effectively steer the outgoing signals in a desired direction. Any of a wide variety of other functions could be supported in the gNB  102  by the controller/processor  225 . 
     The controller/processor  225  is also capable of executing programs and other processes resident in the memory  230 , such as an OS. The controller/processor  225  can move data into or out of the memory  230  as required by an executing process. 
     The controller/processor  225  is also coupled to the backhaul or network interface  235 . The backhaul or network interface  235  allows the gNB  102  to communicate with other devices or systems over a backhaul connection or over a network. The interface  235  could support communications over any suitable wired or wireless connection(s). For example, when the gNB  102  is implemented as part of a cellular communication system (such as one supporting 5G/NR, LTE, or LTE-A), the interface  235  could allow the gNB  102  to communicate with other gNBs over a wired or wireless backhaul connection. When the gNB  102  is implemented as an access point, the interface  235  could allow the gNB  102  to communicate over a wired or wireless local area network or over a wired or wireless connection to a larger network (such as the Internet). The interface  235  includes any suitable structure supporting communications over a wired or wireless connection, such as an Ethernet or RF transceiver. 
     The memory  230  is coupled to the controller/processor  225 . Part of the memory  230  could include a RAM, and another part of the memory  230  could include a Flash memory or other ROM. 
     Although  FIG. 2  illustrates one example of gNB  102 , various changes may be made to  FIG. 2 . For example, the gNB  102  could include any number of each component shown in  FIG. 2 . As a particular example, an access point could include a number of interfaces  235 , and the controller/processor  225  could support routing functions to route data between different network addresses. As another particular example, while shown as including a single instance of TX processing circuitry  215  and a single instance of RX processing circuitry  220 , the gNB  102  could include multiple instances of each (such as one per RF transceiver). Also, various components in  FIG. 2  could be combined, further subdivided, or omitted and additional components could be added according to particular needs. 
       FIG. 3  illustrates an example UE  116  according to embodiments of the present disclosure. The embodiment of the UE  116  illustrated in  FIG. 3  is for illustration only, and the UEs  111 - 115  of  FIG. 1  could have the same or similar configuration. However, UEs come in a wide variety of configurations, and  FIG. 3  does not limit the scope of this disclosure to any particular implementation of a UE. 
     As shown in  FIG. 3 , the UE  116  includes an antenna  305 , a radio frequency (RF) transceiver  310 , TX processing circuitry  315 , a microphone  320 , and receive (RX) processing circuitry  325 . The UE  116  also includes a speaker  330 , a processor  340 , an input/output (I/O) interface (IF)  345 , a touchscreen  350 , a display  355 , and a memory  360 . The memory  360  includes an operating system (OS)  361  and one or more applications  362 . 
     The RF transceiver  310  receives, from the antenna  305 , an incoming RF signal transmitted by a gNB of the network  100 . The RF transceiver  310  down-converts the incoming RF signal to generate an intermediate frequency (IF) or baseband signal. The IF or baseband signal is sent to the RX processing circuitry  325 , which generates a processed baseband signal by filtering, decoding, and/or digitizing the baseband or IF signal. The RX processing circuitry  325  transmits the processed baseband signal to the speaker  330  (such as for voice data) or to the processor  340  for further processing (such as for web browsing data). 
     The TX processing circuitry  315  receives analog or digital voice data from the microphone  320  or other outgoing baseband data (such as web data, e-mail, or interactive video game data) from the processor  340 . The TX processing circuitry  315  encodes, multiplexes, and/or digitizes the outgoing baseband data to generate a processed baseband or IF signal. The RF transceiver  310  receives the outgoing processed baseband or IF signal from the TX processing circuitry  315  and up-converts the baseband or IF signal to an RF signal that is transmitted via the antenna  305 . 
     The processor  340  can include one or more processors or other processing devices and execute the OS  361  stored in the memory  360  in order to control the overall operation of the UE  116 . For example, the processor  340  could control the reception of DL channel signals and the transmission of UL channel signals by the RF transceiver  310 , the RX processing circuitry  325 , and the TX processing circuitry  315  in accordance with well-known principles. In some embodiments, the processor  340  includes at least one microprocessor or microcontroller. 
     The processor  340  is also capable of executing other processes and programs resident in the memory  360 , such as processes for configuring and determining default beams in a wireless communication system. The processor  340  can move data into or out of the memory  360  as required by an executing process. In some embodiments, the processor  340  is configured to execute the applications  362  based on the OS  361  or in response to signals received from gNBs or an operator. The processor  340  is also coupled to the I/O interface  345 , which provides the UE  116  with the ability to connect to other devices, such as laptop computers and handheld computers. The I/O interface  345  is the communication path between these accessories and the processor  340 . 
     The processor  340  is also coupled to the touchscreen  350  and the display  355 . The operator of the UE  116  can use the touchscreen  350  to enter data into the UE  116 . The display  355  may be a liquid crystal display, light emitting diode display, or other display capable of rendering text and/or at least limited graphics, such as from web sites. 
     The memory  360  is coupled to the processor  340 . Part of the memory  360  could include a random access memory (RAM), and another part of the memory  360  could include a Flash memory or other read-only memory (ROM). 
     Although  FIG. 3  illustrates one example of UE  116 , various changes may be made to  FIG. 3 . For example, various components in  FIG. 3  could be combined, further subdivided, or omitted and additional components could be added according to particular needs. As a particular example, the processor  340  could be divided into multiple processors, such as one or more central processing units (CPUs) and one or more graphics processing units (GPUs). Also, while  FIG. 3  illustrates the UE  116  configured as a mobile telephone or smartphone, UEs could be configured to operate as other types of mobile or stationary devices. 
     To meet the demand for wireless data traffic having increased since deployment of  4 G communication systems and to enable various vertical applications, 5G/NR communication systems have been developed and are currently being deployed. The 5G/NR communication system is considered to be implemented in higher frequency (mmWave) bands, e.g., 28 GHz or 60 GHz bands, so as to accomplish higher data rates or in lower frequency bands, such as 6 GHz, to enable robust coverage and mobility support. To decrease propagation loss of the radio waves and increase the transmission distance, the beamforming, massive multiple-input multiple-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, an analog beam forming, large scale antenna techniques are discussed in 5G/NR communication systems. 
     In addition, in 5G/NR communication systems, development for system network improvement is under way based on advanced small cells, cloud radio access networks (RANs), ultra-dense networks, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), reception-end interference cancellation and the like. 
     The discussion of 5G systems and frequency bands associated therewith is for reference as certain embodiments of the present disclosure may be implemented in 5G systems. However, the present disclosure is not limited to 5G systems or the frequency bands associated therewith, and embodiments of the present disclosure may be utilized in connection with any frequency band. For example, aspects of the present disclosure may also be applied to deployment of 5G communication systems,  6 G or even later releases which may use terahertz (THz) bands. 
     A communication system includes a downlink (DL) that refers to transmissions from a base station or one or more transmission points to UEs and an uplink (UL) that refers to transmissions from UEs to a base station or to one or more reception points. 
     A time unit for DL signaling or for UL signaling on a cell is referred to as a slot and can include one or more symbols. A symbol can also serve as an additional time unit. A frequency (or bandwidth (BW)) unit is referred to as a resource block (RB). One RB includes a number of sub-carriers (SCs). For example, a slot can have duration of 0.5 milliseconds or 1 millisecond, include 14 symbols and an RB can include 12 SCs with inter-SC spacing of 15 KHz or 30 KHz, and so on. 
     DL signals include data signals conveying information content, control signals conveying DL control information (DCI), and reference signals (RS) that are also known as pilot signals. A gNB transmits data information or DCI through respective physical DL shared channels (PDSCHs) or physical DL control channels (PDCCHs). A PDSCH or a PDCCH can be transmitted over a variable number of slot symbols including one slot symbol. For brevity, a DCI format scheduling a PDSCH reception by a UE is referred to as a DL DCI format and a DCI format scheduling a physical uplink shared channel (PUSCH) transmission from a UE is referred to as an UL DCI format. 
     A gNB transmits one or more of multiple types of RS including channel state information RS (CSI-RS) and demodulation RS (DMRS). A CSI-RS is primarily intended for UEs to perform measurements and provide CSI to a gNB. For channel measurement, non-zero power CSI-RS (NZP CSI-RS) resources are used. For interference measurement reports (IMRs), CSI interference measurement (CSI-IM) resources associated with a zero power CSI-RS (ZP CSI-RS) configuration are used. A CSI process includes NZP CSI-RS and CSI-IM resources. 
     A UE can determine CSI-RS transmission parameters through DL control signaling or higher layer signaling, such as radio resource control (RRC) signaling, from a gNB. Transmission instances of a CSI-RS can be indicated by DL control signaling or be configured by higher layer signaling. A DM-RS is transmitted only in the BW of a respective PDCCH or PDSCH and a UE can use the DMRS to demodulate data or control information. 
       FIG. 4  and  FIG. 5  illustrate example wireless transmit and receive paths according to this disclosure. In the following description, a transmit path  400  may be described as being implemented in a gNB (such as the gNB  102 ), while a receive path  500  may be described as being implemented in a UE (such as a UE  116 ). However, it may be understood that the receive path  500  can be implemented in a gNB and that the transmit path  400  can be implemented in a UE. In some embodiments, the receive path  500  is configured to support the codebook design and structure for systems having 2D antenna arrays as described in embodiments of the present disclosure. 
     The transmit path  400  as illustrated in  FIG. 4  includes a channel coding and modulation block  405 , a serial-to-parallel (S-to-P) block  410 , a size N inverse fast Fourier transform (IFFT) block  415 , a parallel-to-serial (P-to-S) block  420 , an add cyclic prefix block  425 , and an up-converter (UC)  430 . The receive path  500  as illustrated in  FIG. 5  includes a down-converter (DC)  555 , a remove cyclic prefix block  560 , a serial-to-parallel (S-to-P) block  565 , a size N fast Fourier transform (FFT) block  570 , a parallel-to-serial (P-to-S) block  575 , and a channel decoding and demodulation block  580 . 
     As illustrated in  FIG. 4 , the channel coding and modulation block  405  receives a set of information bits, applies coding (such as a low-density parity check (LDPC) coding), and modulates the input bits (such as with quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM)) to generate a sequence of frequency-domain modulation symbols. 
     The serial-to-parallel block  410  converts (such as de-multiplexes) the serial modulated symbols to parallel data in order to generate N parallel symbol streams, where N is the IFFT/FFT size used in the gNB  102  and the UE  116 . The size N IFFT block  415  performs an IFFT operation on the N parallel symbol streams to generate time-domain output signals. The parallel-to-serial block  420  converts (such as multiplexes) the parallel time-domain output symbols from the size N IFFT block  415  in order to generate a serial time-domain signal. The add cyclic prefix block  425  inserts a cyclic prefix to the time-domain signal. The up-converter  430  modulates (such as up-converts) the output of the add cyclic prefix block  425  to an RF frequency for transmission via a wireless channel. The signal may also be filtered at baseband before conversion to the RF frequency. 
     A transmitted RF signal from the gNB  102  arrives at the UE  116  after passing through the wireless channel, and reverse operations to those at the gNB  102  are performed at the UE  116 . 
     As illustrated in  FIG. 5 , the down-converter  555  down-converts the received signal to a baseband frequency, and the remove cyclic prefix block  560  removes the cyclic prefix to generate a serial time-domain baseband signal. The serial-to-parallel block  565  converts the time-domain baseband signal to parallel time domain signals. The size N FFT block  570  performs an FFT algorithm to generate N parallel frequency-domain signals. The parallel-to-serial block  575  converts the parallel frequency-domain signals to a sequence of modulated data symbols. The channel decoding and demodulation block  580  demodulates and decodes the modulated symbols to recover the original input data stream. 
     Each of the gNBs  101 - 103  may implement a transmit path  400  as illustrated in  FIG. 4  that is analogous to transmitting in the downlink to UEs  111 - 116  and may implement a receive path  500  as illustrated in  FIG. 5  that is analogous to receiving in the uplink from UEs  111 - 116 . Similarly, each of UEs  111 - 116  may implement the transmit path  400  for transmitting in the uplink to the gNBs  101 - 103  and may implement the receive path  500  for receiving in the downlink from the gNBs  101 - 103 . 
     Each of the components in  FIG. 4  and  FIG. 5  can be implemented using only hardware or using a combination of hardware and software/firmware. As a particular example, at least some of the components in  FIGS. 4  and  FIG. 5  may be implemented in software, while other components may be implemented by configurable hardware or a mixture of software and configurable hardware. For instance, the FFT block  570  and the IFFT block  515  may be implemented as configurable software algorithms, where the value of size N may be modified according to the implementation. 
     Furthermore, although described as using FFT and IFFT, this is by way of illustration only and may not be construed to limit the scope of this disclosure. Other types of transforms, such as discrete Fourier transform (DFT) and inverse discrete Fourier transform (IDFT) functions, can be used. It may be appreciated that the value of the variable N may be any integer number (such as 1, 2, 3, 4, or the like) for DFT and IDFT functions, while the value of the variable N may be any integer number that is a power of two (such as 1, 2, 4, 8, 16, or the like) for FFT and IFFT functions. 
     Although  FIG. 4  and  FIG. 5  illustrate examples of wireless transmit and receive paths, various changes may be made to  FIG. 4  and  FIG. 5 . For example, various components in  FIG. 4  and  FIG. 5  can be combined, further subdivided, or omitted and additional components can be added according to particular needs. Also,  FIG. 4  and  FIG. 5  are meant to illustrate examples of the types of transmit and receive paths that can be used in a wireless network. Any other suitable architectures can be used to support wireless communications in a wireless network. 
       FIG. 6A  illustrate an example wireless system beam  600  according to embodiments of the present disclosure. An embodiment of the wireless system beam  600  shown in  FIG. 6A  is for illustration only. 
     As illustrated in  FIG. 6A , in a wireless system a beam  601 , for a device  604 , can be characterized by a beam direction  602  and a beam width  603 . For example, a device  604  with a transmitter transmits radio frequency (RF) energy in a beam direction and within a beam width. The device  604  with a receiver receives RF energy coming towards the device in a beam direction and within a beam width. As illustrated in  FIG. 6A , a device at point A  605  can receive from and transmit to the device  604  as Point A is within a beam width of a beam traveling in a beam direction and coming from the device  604 . 
     As illustrated in  FIG. 6A , a device at point B  606  cannot receive from and transmit to the device  604  as Point B is outside a beam width of a beam traveling in a beam direction and coming from the device  604 . While  FIG. 6A , for illustrative purposes, shows a beam in 2-dimensions (2D), it may be apparent to those skilled in the art, that a beam can be in 3-dimensions (3D), where the beam direction and beam width are defined in space. 
       FIG. 6B  illustrate an example multi-beam operation  650  according to embodiments of the present disclosure. An embodiment of the multi-beam operation  650  shown in  FIG. 6B  is for illustration only. 
     In a wireless system, a device can transmit and/or receive on multiple beams. This is known as “multi-beam operation” and is illustrated in  FIG. 6B . While  FIG. 6B , for illustrative purposes, is in 2D, it may be apparent to those skilled in the art, that a beam can be 3D, where a beam can be transmitted to or received from any direction in space. 
     Rel.14 LTE and Rel.15 NR support up to 32 CSI-RS antenna ports which enable an eNB to be equipped with a large number of antenna elements (such as 64 or 128). In this case, a plurality of antenna elements is mapped onto one CSI-RS port. For mmWave bands, although the number of antenna elements can be larger for a given form factor, the number of CSI-RS ports—which can correspond to the number of digitally precoded ports—tends to be limited due to hardware constraints (such as the feasibility to install a large number of ADCs/DACs at mmWave frequencies) as illustrated in  FIG. 7 . 
       FIG. 7  illustrate an example antenna structure  700  according to embodiments of the present disclosure. An embodiment of the antenna structure  700  shown in  FIG. 7  is for illustration only. 
     In this case, one CSI-RS port is mapped onto a large number of antenna elements which can be controlled by a bank of analog phase shifters  701 . One CSI-RS port can then correspond to one sub-array which produces a narrow analog beam through analog beamforming  705 . This analog beam can be configured to sweep across a wider range of angles  720  by varying the phase shifter bank across symbols or subframes. The number of sub-arrays (equal to the number of RF chains) is the same as the number of CSI-RS ports N CSI-PORT . A digital beamforming unit  710  performs a linear combination across N CSI-PORT  analog beams to further increase precoding gain. While analog beams are wideband (hence not frequency-selective), digital precoding can be varied across frequency sub-bands or resource blocks. Receiver operation can be conceived analogously. 
     Since the aforementioned system utilizes multiple analog beams for transmission and reception (wherein one or a small number of analog beams are selected out of a large number, for instance, after a training duration—to be performed from time to time), the term “multi-beam operation” is used to refer to the overall system aspect. This includes, for the purpose of illustration, indicating the assigned DL or UL TX beam (also termed “beam indication”), measuring at least one reference signal for calculating and performing beam reporting (also termed “beam measurement” and “beam reporting”, respectively), and receiving a DL or UL transmission via a selection of a corresponding RX beam. 
     The aforementioned system is also applicable to higher frequency bands such as &gt;52.6 GHz (also termed the FR 4 ). In this case, the system can employ only analog beams. Due to the O2 absorption loss around 60 GHz frequency (˜10 dB additional loss @ 100 m distance), larger number of and sharper analog beams (hence larger number of radiators in the array) may be needed to compensate for the additional path loss. 
     A UE receives from the network downlink control information through one or more PDCCHs. The UE would use the downlink control information to configure one or more receive parameters/settings to decode subsequent downlink data channels (i.e., PDSCHs) transmitted from the network. Under certain settings, the UE could start receiving and/or decoding the PDSCH after the UE has decoded the PDCCH and obtained the corresponding control information. 
     In this case, the time offset between the reception of the PDCCH and the reception of the PDSCH exceeds a preconfigured threshold, which, e.g., could correspond to the time required for decoding the PDCCH and adjusting the receive parameters. The time offset between the receptions of the PDCCH and the PDSCH could be smaller than the threshold (e.g., the network could send the PDSCH close to the PDCCH in time or even overlapping with the PDCCH in time). 
     In this case, the UE may not be able to decode the PDSCH because the UE does not have enough time to decode the PDCCH to set appropriate receive parameters such as the receive spatial filter for receiving/decoding the PDSCH. Hence, there is a need to configure one or more default TCI states for the PDSCH transmission, and therefore, one or more default receive beams for the UE to buffer the PDSCH when the UE is in the process of receiving and/or decoding the PDCCH control information. In a multi-TRP system (depicted in  FIG. 8 ), wherein the UE could simultaneously receive multiple PDSCHs from multiple physically non-co-located TRPs, the configuration of the default TCI state(s)/receive beam(s) could be different from that for the single-TRP operation. Further, the configurations of the default TCI state(s)/receive beam(s) could also be different between single-DCI (or single-PDCCH) and multi-DCI (or multi-PDCCH) based multi-TRP systems. 
       FIG. 8  illustrates an example of multi-TRP system  800  according to embodiments of the present disclosure. An embodiment of the multi-TRP system  800  shown in  FIG. 8  is for illustration only. 
     For the single-PDCCH or single-DCI based multi-TRP operation, if the time offset between the reception of the PDCCH and the reception of the PDSCH is less than the threshold, the UE could assume that the DMRS ports of the PDSCH follow the QCL parameters indicated by the default TCI state(s), which could correspond to the lowest codepoint among the TCI codepoints containing two different TCI states activated for the PDSCH. For the multi-PDCCH or multi-DCI based multi-TRP operation (assuming that the CORESETPOOLIndex is configured), if the time offset between the reception of the PDCCH and the reception of the PDSCH is less than the threshold, the UE could assume that the DMRS ports of the PDSCH follow the QCL parameters indicated by the default TCI state(s), which could be used for the PDCCH with the lowest CORESET index among the CORESETs configured with the same value of CORESETPOOLIndex. 
     The default TCI state(s)/receive beam(s) configurations in the 3GPP Rel. 15/16 assume that the PDCCH and the PDSCH could employ different beams, and therefore, the UE could use different spatial filters to receive the PDCCH and the PDSCH beams. If a common TCI state/beam is used/configured for various types of channels such as PDCCH and PDSCH, the configuration of the default TCI state(s)/receive beam(s) could be different from the existing solutions (described above, relying on lowest CORESET ID/TCI codepoint). Further, whether the UE could simultaneously receive the PDSCHs transmitted from the coordinating TRPs may also be considered when configuring the default TCI state(s) for the multi-TRP operation. 
     The present disclosure considers various design options for configuring default TCI state(s)/receive beam(s) in both single-DCI and multi-DCI based multi-TRP systems. Specifically, the common TCI state/beam indication is used as the baseline framework to configure the default TCI state(s). The UE could also follow the legacy behavior(s) defined in the 3GPP Rel. 15/16 to determine the default receive beam(s) under certain settings/conditions, which are also discussed in this disclosure. 
     Furthermore, throughout the present disclosure, a common TCI state/beam is equivalent to a unified TCI state/beam or a Rel. 17 unified TCI state/beam. Under the Rel. 17 unified TCI framework, a UE could receive from the network a DCI format (e.g., DCI format  1 _ 1  or  1 _ 2  with or without DL assignment) indicating one or more Rel. 17 unified TCI states for various DL/UL channels and/or signals such as UE-dedicated reception on PDSCH/PDCCH or dynamic-grant/configured-grant based PUSCH and all of dedicated PUCCH resources. 
     For instance, the DCI format could include one or more “Transmission Configuration Indication” fields. A “Transmission Configuration Indication” field could carry a codepoint from the codepoints activated by a MAC CE activation command, and the codepoint could indicate at least one of: M≥1 joint DL and UL Rel. 17 unified TCI states or M≥1 separate UL Rel. 17 unified TCI states or a first combination of M≥1 joint DL and UL Rel. 17 unified TCI states and separate UL Rel. 17 unified TCI states or N≥1 separate DL Rel. 17 unified TCI states or a second combination of N≥1 joint DL and UL Rel. 17 unified TCI states and separate DL Rel. 17 unified TCI states or a third combination of N≥1 joint DL and UL Rel. 17 unified TCI states, separate DL Rel. 17 unified TCI states and separate UL Rel. 17 unified TCI states. 
       FIG. 9  illustrates an example of unified TCI state indication  900  according to embodiments of the present disclosure. An embodiment of the unified TCI state indication  900  shown in  FIG. 9  is for illustration only. 
     The UE could be configured/indicated by the network a common TCI state/beam for various types of channels such as PDCCH and PDSCH. In  FIG. 9 , a conceptual example of using a DCI to indicate the common TCI for both the PDCCH and the PDSCH is presented. The common TCI signaled in the DCI at time t would become effective at t+timeDurationForQCL. As illustrated in the example shown in  FIG. 9 , the UE could be able to first decode PDCCH_A (conveying the DCI that indicates the common TCI) and obtain the necessary QCL parameters. 
     The UE could then follow the QCL parameters and set appropriate receive parameters such as the receive spatial filter to receive and decode PDCCH_ 0  and PDSCH_ 0 . The UE, however, is not able to set the receive parameters according to the QCL configured in PDCCH_B (conveying the DCI that indicates the common TCI) to decode PDSCH_ 1  because the time offset between the reception of PDCCH_B and that of PDSCH_ 1  is less than timeDurationForQCL. 
     Hence, the UE may need to follow the QCL indications in the default TCI state to set appropriate receive parameters such as the receive spatial filter (default receive beam). For example, the default TCI state could correspond to the common TCI indicated/configured in PDCCH_A. There could be various other means to configure the default TCI state(s)/receive beam(s) depending on whether/how the common TCI state/beam is indicated and/or simultaneous PDSCH reception requirement for the multi-TRP operation. 
       FIG. 10  illustrates an example of unified TCI state indication for a multi-DCI based multi-TRP system  1000  according to embodiments of the present disclosure. An embodiment of the unified TCI state indication for a multi-DCI based multi-TRP system  1000  shown in  FIG. 10  is for illustration only. 
     In the multi-DCI based multi-TRP system, different coordinating TRPs (e.g., TRP- 1  and TRP- 2  in  FIG. 8 ) could transmit to the UE separate PDCCHs (and therefore, separate PDSCHs) associated with different values of the higher layer signaling index CORESETPOOLIndex (if configured). For example, TRP- 1  in  FIG. 8  could transmit PDCCH- 1  to the UE, and TRP- 2  could transmit PDCCH- 2  to the UE; PDCCH- 1  could be associated with “CORESETPOOLIndex=0” while PDCCH- 2  could be associated with “CORESETPOOLIndex=1.” Further, if the common TCI state/beam indication is enabled for the multi-TRP operation, the UE could be configured with multiple common TCI states/beams (N_tci&gt;1), each corresponding to a coordinating TRP. Under the multi-DCI framework, the common TCI states/beams, and therefore, their indicating PDCCHs, could also be associated with the CORESETPOOLIndex. 
     In  FIG. 10 , a conceptual example characterizing the common TCI states/beams indication in a multi-TRP system comprising of two coordinating TRPs is provided. As illustrated in  FIG. 10 , PDCCH- 1 _A is from TRP- 1  and indicates to the UE the common TCI state/beam from TRP- 1  (TCI- 1 _A). Further, PDCCH- 1 _A is associated with “CORESETPOOLIndex=0.” PDCCH- 1 _B indicates to the UE the common TCI state/beam from TRP- 2  (TCI- 2 _A), and is associated with “CORESETPOOLIndex=1.” The UE could set the receive spatial filter based on TCI- 1 _A for receiving and/or decoding PDCCH- 1 _ 0  and PDSCH- 1 _ 0  because the time offsets between them and PDCCH- 1 _A are less than timeDurationForQCL- 1 . 
     Similarly, the UE could also be able to set appropriate receive spatial filter to receive and/or decode PDCCH- 2 _ 0  and PDSCH- 2 _ 0  from TRP- 2  as the UE could have enough time (time offsets are less than timeDurationForQCL- 2 ) to decode PDCCH- 2 _A first and extract the necessary QCL configurations/assumptions for decoding the subsequent PDCCH/PDSCH transmissions. The two thresholds timeDurationForQCL- 1  and timeDurationForQCL- 2  for TRP- 1  and TRP- 2  could be common or different. For instance, the UE could use different receive panels with different array configurations to receive the PDCCHs/PDSCHs from different coordinating TRPs, resulting in different thresholds for different TRPs. 
       FIG. 11  illustrates another example of unified TCI state indication for a multi-DCI based multi-TRP system  1100  according to embodiments of the present disclosure. An embodiment of the unified TCI state indication for a multi-DCI based multi-TRP system  1100  shown in  FIG. 11  is for illustration only. 
     In  FIG. 11 , another example depicting the common TCI states/beams indication in a multi-TRP system is presented. In this example, prior to fully decoding PDCCH- 1 _A, the UE would receive PDSCH- 1 _ 1  from TRP- 1  (their time offset is less than timeDurationForQCL- 1 ), and prior to fully decoding PDCCH- 2 _A, the UE would receive PDSCH- 2 _ 1  from TRP- 2  (their time offset is less than timeDurationForQCL- 2 ). In this case, the UE would need to set appropriate spatial receive filters (default receive beams) to buffer PDSCH- 1 _ 1  and PDSCH- 2 _ 1  without relying on the common TCI states/beams indicated in PDCCH- 1 _A and PDCCH- 2 _A. In the following, various design options to configure default TCI states/beams for the PDSCH transmissions (or equivalently, to determine default receive beams for the UE to buffer the PDSCHs) in the multi-DCI based multi-TRP system are presented. 
     In one example of Option-1, if the CORESETPOOLIndex is configured and the time offset between the reception of a first PDCCH carrying the common TCI state/beam indication (e.g., PDCCH- 1 _A in  FIG. 11 ) and the reception of the PDSCH (e.g., PDSCH- 1 _ 1  in  FIG. 9 ) is less than the threshold (e.g., timeDurationForQCL- 1  in  FIG. 11 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCH follow those of the default TCI state/beam, which could correspond to the previous common TCI state/beam indicated in a second PDCCH, which is associated with the same CORESETPOOLIndex (value) as that associated with the first PDCCH. 
       FIG. 12  illustrates yet another example of unified TCI state indication for a multi-DCI based multi-TRP system  1200  according to embodiments of the present disclosure. An embodiment of the unified TCI state indication for a multi-DCI based multi-TRP system  1200  shown in  FIG. 12  is for illustration only. 
     In  FIG. 12 , a conceptual example illustrating Option-1 is given. As indicated in  FIG. 12 , the UE cannot use the common TCI state/beam indicated in PDCCH- 1 _C (the first PDCCH in Option-1) to set the receive parameter(s) for decoding PDSCH- 1 _ 1  because their time offset is less than timeDurationForQCL- 1 . According to Option-1, the default TCI state for PDSCH- 1 _ 1  in this example is the common TCI state (TCI- 1 _B) indicated in PDCCH- 1 _B (the second PDCCH in Option-1). This is because the time offset between the reception of PDCCH- 1 _B and that of PDSCH- 1 _ 1  is beyond timeDurationForQCL- 1 , and PDCCH- 1 _B and PDCCH- 1 _C share the same CORESETPOOLIndex (“0”), i.e., both of them are transmitted from the same TRP- 1 . 
     Furthermore, PDCCH- 1 _B is the closest to PDSCH- 1 _ 1  in time among all PDCCHs from TRP- 1  that carry the common TCI state/beam indications and have been decoded by the UE. Note that in this case, the common TCI state/beam indicated in PDCCH- 2 _A cannot be configured as the default TCI state/beam for PDSCH- 1 _ 1  because the common TCI state/beam is associated with a different value of CORESETPOOLIndex (“1”). 
     In one example of Option-2, if the time offset between the reception of the PDCCH carrying the common TCI state/beam indication (e.g., PDCCH- 1 _A in  FIG. 11 ) and the reception of the PDSCH (e.g., PDSCH- 1 _ 1  in  FIG. 11 ) is less than the threshold (e.g., timeDurationForQCL- 1  in  FIG. 11 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCH follow those of the default TCI state/beam, which could correspond to the previous common TCI state/beam indicated to the UE regardless of the transmitting TRP. This design option does not depend on whether the CORESETPOOLIndex is configured. 
       FIG. 13  illustrates yet another example of unified TCI state indication for a multi-DCI based multi-TRP system  1300  according to embodiments of the present disclosure. An embodiment of the unified TCI state indication for a multi-DCI based multi-TRP system  1300  shown in  FIG. 13  is for illustration only. 
     In  FIG. 13 , a conceptual example characterizing Option-2 is provided. Different from the example for Option-1 shown in  FIG. 12 , the CORESETPOOLIndex is not configured for the multi-DCI based multi-TRP system. Hence, the default TCI state/beam for PDSCH- 1 _ 1  from TRP- 1  could correspond to the previous common TCI state/beam indicated to the UE. In this example, the previous common TCI state/beam indicated to the UE is TCI- 2 _A indicated in PDCCH- 2 _A from TRP- 2 . That is, PDCCH- 2 _A is the closest PDCCH to PDSCH- 1 _ 1  in time among all the PDCCHs from both TRP- 1  and TRP- 2  that carry the common TCI state/beam indications and have been decoded by the UE. 
     In one example of Option-3, if the CORESETPOOLIndex is configured and the time offset between the reception of a first PDCCH carrying the common TCI state/beam indication (e.g., PDCCH- 1 _A in  FIG. 11 ) and the reception of the PDSCH (e.g., PDSCH- 1 _ 1  in  FIG. 11 ) is less than the threshold (e.g., timeDurationForQCL- 1  in  FIG. 11 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCH follow those of the default TCI state/beam, which could be used for the latest PDCCH carrying the common TCI state/beam indication (a third PDCCH) associated with the same CORESETPOOLIndex (value) as that associated with the first PDCCH. 
       FIG. 14  illustrates yet another example of unified TCI state indication for a multi-DCI based multi-TRP system  1400  according to embodiments of the present disclosure. An embodiment of the unified TCI state indication for a multi-DCI based multi-TRP system  1400  shown in  FIG. 14  is for illustration only. 
     In  FIG. 14 , a conceptual example of Option-3 default TCI state/beam configuration in a multi-DCI based multi-TRP system is presented. In this example, the UE cannot set the receive spatial filter to receive and/or decode PDSCH- 1 _ 1  according to the common TCI state/beam indicated in PDCCH- 1 _A because their time offset is less than timeDurationForQCL- 1 . The UE, however, could use the same spatial receive filter as that used for receiving PDCCH- 1 _B to receive and/or decode PDSCH- 1 _ 1 . This is because for PDSCH- 1 _ 1 , PDCCH- 1 _B is the latest PDCCH carrying the common TCI state/beam indication and shares the same CORESETPOOLIndex (value) with PDCCH- 1 _A. 
     Hence, based on Option-3, the UE would assume the same TCI state (and therefore the corresponding QCL parameters) for the DMRS ports of PDSCH- 1 _ 1  as that used for PDCCH- 1 _B (TCI′- 1 _B). Note that TCI′- 1 _B for PDCCH- 1 _B could be activated by MAC CE from a pool of TCI states configured by RRC signaling. Further, in this example, if PDCCH- 1 _B is not present, the TCI state used for PDCCH- 1 _A could be the default TCI state for PDSCH- 1 _ 1  because now PDCCH- 1 _A becomes the “third PDCCH” in Option-3. 
     In one example of Option-4, if the time offset between the reception of a first PDCCH carrying the common TCI state/beam indication (e.g., PDCCH- 1 _A in  FIG. 11 ) and the reception of the PDSCH (e.g., PDSCH- 1 _ 1  in  FIG. 11 ) is less than the threshold (e.g., timeDurationForQCL- 1  in  FIG. 11 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCH follow those of the default TCI state/beam, which could be used for the latest PDCCH carrying the common TCI state/beam indication (a fourth PDCCH) regardless of the transmitting TRP. This design option does not depend on whether the CORESETPOOLIndex is configured. 
       FIG. 15  illustrates yet another example of unified TCI state indication for a multi-DCI based multi-TRP system  1500  according to embodiments of the present disclosure. An embodiment of the unified TCI state indication for a multi-DCI based multi-TRP system  1500  shown in  FIG. 15  is for illustration only. 
     The example shown in  FIG. 15  assumes that the CORESETPOOLIndex is not configured, and the latest PDCCH that conveys the common TCI state/beam with respect to the PDSCH of interest, i.e., PDSCH- 1 _ 1  from TRP- 1 , is PDCCH- 2 _A from TRP- 2 . Based on Option-4, the default TCI state for PDSCH- 1 _ 1  could therefore be configured as TCI′- 2 _A used for PDCCH- 2 _A. That is, the UE could use the same receive parameters to receive PDSCH- 1 _ 1  as those used for receiving PDCCH- 2 _A. 
     In one example of Option-5, the configuration of the default TCI state/beam for PDSCH follows the legacy procedure defined in the 3GPP Rel. 16 for multi-DCI based multi-TRP. If the CORESETPOOLIndex is configured and the time offset between the reception of a first PDCCH carrying the common TCI state/beam indication (e.g., PDCCH- 1 _A in  FIG. 11 ) and the reception of the PDSCH (e.g., PDSCH- 1 _ 1  in  FIG. 11 ) is less than the threshold (e.g., timeDurationForQCL- 1  in  FIG. 11 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCH follow those of the default TCI state/beam, which could be used for the latest PDCCH with the lowest CORESET index among the CORESETs configured with the same value of CORESETPOOLIndex as that associated with the first PDCCH. 
     In one example of Option-6, the configuration of the default TCI state/beam for PDSCH follows the legacy procedure defined in the 3GPP Rel. 15. If the time offset between the reception of a first PDCCH carrying the common TCI state/beam indication (e.g., PDCCH- 1 _A in  FIG. 11 ) and the reception of the PDSCH (e.g., PDSCH- 1 _ 1  in  FIG. 11 ) is less than the threshold (e.g., timeDurationForQCL- 1  in  FIG. 11 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCH follow those of the default TCI state/beam, which could be used for the PDCCH with the lowest CORESET index among the CORESETs associated with a monitored search space in the latest slot. This design option does not depend on whether the CORESETPOOLIndex is configured. 
       FIG. 16  illustrates an example of a signaling flow  1600  between a UE and a gNB according to embodiments of the present disclosure. For example, the signaling flow  1600  as may be performed by a UE (e.g.,  111 - 116  as illustrated in  FIG. 1 ) and a BS (e.g.,  101 - 103  as illustrated in  FIG. 1 ). An embodiment of the signaling flow  1600  shown in  FIG. 16  is for illustration only. One or more of the components illustrated in  FIG. 16  can be implemented in specialized circuitry configured to perform the noted functions or one or more of the components can be implemented by one or more processors executing instructions to perform the noted functions. 
     As illustrated in  FIG. 16 , in step  1601 , a gNB indicates to a UE to apply one or more options from Option-1, Option-2, Option-3, Option-4, Option-5 and Option-6 presented in the present disclosure along with other necessary indications. In step  1602 , a UE follows the configured one or more options (and other necessary indications) to determine the default beam(s) for receiving and/or decoding the PDSCH(s) from the coordinating TRPs. 
     The UE could be configured by the network one or more design options described above to configure the default beam(s) for receiving the PDSCH(s) in a multi-DCI based multi-TRP system (see  FIG. 16 ). In the following, four configuration embodiments are discussed. 
     In one embodiment of Method-I: the UE is indicated by the network to follow only one design option, e.g., Option-1 in the present disclosure, to configure the default receive beam(s) for receiving and/or decoding the PDSCH(s). The configured design option applies to all of the coordinating TRPs in the multi-TRP system. 
       FIG. 17  illustrates an example of a signaling flow  1700  for configuring and determining a default TCI state according to embodiments of the present disclosure. For example, the signaling flow  1700  as may be performed by a UE (e.g.,  111 - 116  as illustrated in  FIG. 1 ) and BSs (e.g.,  101 - 103  as illustrated in  FIG. 1 ). An embodiment of the signaling flow  1700  shown in  FIG. 17  is for illustration only. One or more of the components illustrated in  FIG. 17  can be implemented in specialized circuitry configured to perform the noted functions or one or more of the components can be implemented by one or more processors executing instructions to perform the noted functions. 
     In  FIG. 17 , the signaling procedure of configuring and determining the default TCI state(s)/beam(s) following Option-1 for both coordinating TRPs (TRP- 1  and TRP- 2 ) in a multi-DCI based multi-TRP system is depicted. In this example, the UE is indicated by the network to only follow Option-1 to configure the default receive beams for receiving and/or decoding the PDSCHs from both TRP- 1  and TRP- 2 . For instance, according to Option-1, the UE would configure the receive spatial filter following the QCL parameters of the common TCI state/beam indicated in PDCCH_ 1 -A to buffer PDSCH_ 1 - 1  from TRP- 1 . This is because the scheduling offset between PDCCH_ 1 -B and PDSCH_ 1 - 1  is less than timeDurationForQCL- 1  and PDCCH_ 1 -A is the previous PDCCH that carries a common TCI state/beam indication. Similarly, the UE would configure the receive spatial filter following the QCL parameters of the common TCI state/beam indicated in PDCCH_ 2 -A to buffer PDSCH_ 2 - 1  from TRP- 2 . 
     As illustrated in  FIG. 17 , in step  1701 , a UE is configured by the network with Option-1 to set default receive beam(s) for receiving and/or decoding the PDSCH(s). In step  1702 , a TRP- 1  sends a PDCCH- 1 _A common TCI state/beam indication to the UE. In step  1703 , a TRP- 2  sends a PDCCH- 2 _A common TCI state/beam indication to the UE. In step  1704 , the TRP- 1  sends PDCCH- 1 _B common TCI state/beam indication to the UE. In step  1705 , TRP- 1  sends PDSCH- 1 _ 1  to the UE. In step  1706 , the UE uses the default receive beam configured based on the common TCI state/beam indicated in PDCCH- 1 _A to buffer PDSCH- 1 _ 1 . In step  1707 , the TRP- 2  sends PDCCH- 2 _B common TCI state/beam indication to the UE. In step  1708 , the TRP- 2  sends PDSCH- 2 _ 1  to the UE. In step  1709 , the UE uses the default receive beam configured based on the common TCI state/beam indicated in PDCCH- 2 _A to buffer PDSCH- 2 _ 1 . 
       FIG. 18  illustrates an example of a signaling flow  1800  between a UE and a gNB according to embodiments of the present disclosure. For example, the signaling flow  1800  as may be performed by a UE (e.g.,  111 - 116  as illustrated in  FIG. 1 ) and a BS (e.g.,  101 - 103  as illustrated in  FIG. 1 ). An embodiment of the signaling flow  1800  shown in  FIG. 18  is for illustration only. One or more of the components illustrated in  FIG. 18  can be implemented in specialized circuitry configured to perform the noted functions or one or more of the components can be implemented by one or more processors executing instructions to perform the noted functions. 
     As illustrated in  FIG. 18 , in step  1801 , a UE receives an indication from a gNB to use Option-1 for TRP- 1  (associated with “CORESETPOOLIndex=0”). In step  1802 , the gNB indicates to the UE to use Option-2 for TRP- 2  (associated with “CORESETPOOLIndex=1”). In step  1803 , the UE follows Option-1 to determine the default beam(s) for receiving and/or decoding the PDSCH(s) from TRP- 1 ; and follows Option-2 to determine the default beam(s) for receiving and/or decoding the PDSCH(s) from TRP- 2 . 
     In one embodiment of Method-II, the UE is indicated by the network to follow only one design option per TRP, or per CORESETPOOLIndex, to configure the default receive beam(s) for receiving and/or decoding the PDSCH(s). The design options configured for different TRPs (or different values of CORESETPOOLIndex) could be different. For instance, for a multi-DCI based multi-TRP system comprising of two coordinating TRPs (TRP- 1  and TRP- 2 ), the UE could be indicated by the network to follow Option-1 to configure the default receive beam for buffering the PDSCH from TRP- 1 , and Option-2 to configure the default receive beam for buffering the PDSCH from TRP- 2  (see  FIG. 18 ). 
     For another example, assuming that the common TCI state/beam indication is enabled for TRP- 1  but not for TRP- 2 , the UE could be indicated by the network to follow Option-1 to configure the default receive beam for buffering the PDSCH from TRP- 1 , and Option-5 to configure the default receive beam for buffering the PDSCH from TRP- 2 . 
     In one embodiment of Method-III, the UE is configured by the network more than one (N_opt&gt;1) design options, e.g., Option-1 and Option-2. Further, the UE is configured by the network a priority rule and/or a set of conditions. Based on the priority rule and/or the set of conditions, the UE could determine an appropriate design option (out of all the configured design options) to follow to configure the default receive beam(s) for buffering the PDSCH(s). The configured design options along with the priority rule and/or the set of conditions are common for all the coordinating TRPs in the multi-TRP system. 
       FIG. 19  illustrates an example of priority rule for configuring and determining default TCI state  1900  according to embodiments of the present disclosure. An embodiment of the priority rule for configuring and determining default TCI state  1900  shown in  FIG. 19  is for illustration only. 
     In  FIG. 19 , one example depicting the priority rule/order is presented. In the diagram shown in  FIG. 19 , Priority 0 is the highest priority and Priority 5 is the lowest priority. Option-3 has the highest priority in this example, followed by Option-1, Option-4, Option-2, Option-5, and Option-6 has the lowest priority. For instance, if the UE is configured by the network with both Option-3 and Option-2, the UE would follow Option-3 to set the default receive beam(s) for buffering the PDSCH(s) if the CORESETPOOLIndex is configured. Otherwise, if the CORESETPOOLIndex is not configured, the UE would follow Option-2 to set the default receive beam(s) for buffering the PDSCH(s). 
     For another example, assume that the UE is configured by the network with Option-2, Option-5 and Option-6. If the common TCI state/beam indication is configured/enabled, regardless of whether the CORESETPOOLIndex is configured, the UE would follow Option-2 to configure the default receive beam(s). If the common TCI state/beam indication is not configured/enabled but the CORESETPOOLIndex is configured, the UE would follow Option-5 to set the default receive beam(s). Otherwise, the UE would fall back to Option-6 to set the default receive beam(s) for buffering the PDSCH(s). Other priority rules/orderings than that shown in  FIG. 19  are also possible. 
       FIG. 20  illustrates another example of priority rule for configuring and determining default TCI state  2000  according to embodiments of the present disclosure. An embodiment of the priority rule for configuring and determining default TCI state  2000  shown in  FIG. 20  is for illustration only. 
     In  FIG. 20 , another example of priority rule/ordering is given. In this example, Option-1 and Option-3 have the same priority, and Option-2 and Option-4 have the same priority. Hence, the network may be better not to configure the design options with the same priority (e.g., Option-1 and Option-3) to the UE, unless the UE could rely on other criteria/conditions to prioritize them. 
     Based on the above embodiments and examples, in addition to the priority rule/ordering, the UE could also be indicated by the network a set of conditions. The UE could decide the appropriate design option (out of the total configured design options) based on the indicated conditions to set the default receive beam(s) for receiving/buffering the PDSCH(s). As indicated in  FIG. 20 , Condition A is associated with Priority 0 to differentiate between Option-1 and Option-3, and Condition B is associated with Priority 1 to differentiate between Option-2 and Option-4. For instance, if Condition A is satisfied, the UE would choose Option-1 over Option-3 as the design option to follow to set the appropriate default receive beam(s). Otherwise, the UE would follow Option-3. 
     Similarly, if Condition B is satisfied, the UE would follow Option-2 to configure the default receive beam(s) for buffering the PDSCH(s). 
       FIG. 21  illustrates a flowchart of a UE method  2100  for receiving and decoding PDSCH according to embodiments of the present disclosure. For example, the UE method  2100  as may be performed by a UE (e.g.,  111 - 116  as illustrated in  FIG. 1 ). An embodiment of the UE method  2100  shown in  FIG. 21  is for illustration only. One or more of the components illustrated in  FIG. 21  can be implemented in specialized circuitry configured to perform the noted functions or one or more of the components can be implemented by one or more processors executing instructions to perform the noted functions. 
     In  FIG. 21 , an algorithm flowchart illustrating the above described procedures is presented assuming that the UE is configured by the network with Option-1, Option-2, Option-3 and Option-4 as the candidate design options to set the default receive beam(s) for receiving and/or decoding the PDSCH(s). 
     As illustrated in  FIG. 21 , in step  2101 , a UE is configured by the network with Option-1, Option-2, Option-3, and Option-4 as the candidate design options to set default receive beam(s) for buffering the PDSCH(s). In step  2102 , the UE is configured by the network with the priority rule/ordering shown in  FIG. 20  along with Condition A and Condition B. In step  2103 , the UE determines whether the CORESETPOOLIndex is configured. In step  2104 , the UE determines that Option-1 and Option-3 with Priority 0 as the candidate design options to set default receive beam(s) for buffering the PDSCH(s). In step  2105 , the UE determines that Option-2 and Option-4 with Priority 1 as the candidate design options to set default receive beam(s) for buffering the PDSCH(s). In step  2106 , the UE determines whether the Condition A is satisfied. In step  2107 , the UE determines whether the Condition B is satisfied. In step  2108 , the UE follows Option-1 to configure default receive beam(s) for buffering the PDSCH(s). In step  2109 , the UE follows Option-3 to configure default receive beam(s) for buffering the PDSCH(s). In step  2110 , the UE follows Option-2 to configure default receive beam(s) for buffering the PDSCH(s). In step  2111 , the UE follows Option-4 to configure default receive beam(s) for buffering the PDSCH(s). 
       FIG. 22  illustrates another flowchart of a UE method  2200  for receiving and decoding PDSCH according to embodiments of the present disclosure. For example, the UE method  2200  as may be performed by a UE (e.g.,  111 - 116  as illustrated in  FIG. 1 ). An embodiment of the UE method  2200  shown in  FIG. 22  is for illustration only. One or more of the components illustrated in  FIG. 22  can be implemented in specialized circuitry configured to perform the noted functions or one or more of the components can be implemented by one or more processors executing instructions to perform the noted functions. 
     In  FIG. 22 , another algorithm flowchart is depicted assuming that the UE is configured by the network with Option-1, Option-2, Option-5 and Option-6 as the candidate design options. As can be seen from  FIG. 22 , besides checking whether the CORESETPOOLIndex is configured or not, no additional conditions are needed to prioritize between Option-5 and Option-6. 
     As illustrated in  FIG. 22 , in step  2201 , a UE is configured by the network with Option-1, Option-2, Option-5, and Option-6 as the candidate design options to set default receive beam(s) for buffering the PDSCH(s). In step  2202 , a UE is configured by the network with the priority rule/ordering shown in  FIG. 20  along with Condition A. In step  2203 , the UE determines whether the common TCI state/beam indication is configured/enabled. In step  2204 , the UE determines that Option-1 and Option-3 with Priority 0 as the candidate design options to set default receive beam(s) for buffering the PDSCH(s). In step  2205 , the UE determines whether the Condition A is satisfied. In step  2206 , the UE follows Option-1 to configure default receive beam(s) for buffering the PDSCH(s). In step  2207 , the UE follows Option-3 to configure default receive beam(s) for buffering the PDSCH(s). In step  2208 , the UE determines whether the CORESETPOOLIndex is configured. In step  2209 , the UE follows Option-2 to configure default receive beam(s) for buffering the PDSCH(s). In step  2210 , the UE follows Option-4 to configure default receive beam(s) for buffering the PDSCH(s). 
     Condition A and/or Condition B shown in  FIG. 20  could correspond to a variety of possible conditions as shown below. 
     In one embodiment, Condition A is used for prioritizing between Option-1 and Option-3 under Priority 0 in  FIG. 20 . 
     In one example of Condition A.1, if the time offset between the PDSCH of interest and the previous PDCCH (the second PDCCH in Option-1, which shares the same CORESETPOOLIndex with the first PDCCH and has been decoded by the UE) carrying the common TCI state/beam indication is below a threshold (e.g., X ms/slots/symbols), Option-1 has a higher priority than Option-3. 
     In one example of Condition A.2, if the time offset between the PDSCH of interest and the previous PDCCH (the second PDCCH in Option-1, which shares the same CORESETPOOLIndex with the first PDCCH and has been decoded by the UE) carrying the common TCI state/beam indication is below a threshold (e.g., X ms/slots/symbols), but the receive beam configured according to the common TCI state/beam indicated in the second PDCCH and that used for receiving the latest PDCCH that carries the common TCI state/beam indication (the third PDCCH in Option-3) are from different panels, Option-3 has a higher priority than Option-1. 
     In one example of Condition A.3, if the UE could simultaneously receive the common beam indicated in the second PDCCH and the current beam from a different CORESETPOOLIndex (TRP), Option-1 has a higher priority than Option-3. 
     In one example of Condition A.4, if the UE could simultaneously receive the third PDCCH and the current beam from a different CORESETPOOLIndex (TRP), Option-3 has a higher priority than Option-1. 
     In one embodiment, Condition B is used for prioritizing between Option-2 and Option-4 under Priority 1 in  FIG. 20 . 
     In one example of Condition B.1, if the time offset between the PDSCH of interest and the previous PDCCH carrying the common TCI state/beam indication (which has been decoded by the UE) is below a threshold (e.g., X ms/slots/symbols), Option-2 has a higher priority than Option-4. 
     In one example of Condition B.2, if the time offset between the PDSCH of interest and the previous PDCCH carrying the common TCI state/beam indication (which has been decoded by the UE) is below a threshold (e.g., X ms/slots/symbols), but the receive beam configured according to the common TCI state/beam indicated in the previous PDCCH and that used for receiving the latest PDCCH that carries the common TCI state/beam indication (the fourth PDCCH in Option-4) are from different panels, Option-4 has a higher priority than Option-2. 
     Note that other conditions to Condition A.1, Condition A.2, Condition A.3, Condition B.1, and Condition B.2 are also possible. For Condition A.2 and Condition B.2, the UE may report to the network the receive antenna panel information such as panel ID along with the channel measurement report. For Condition A.3 and Condition A.4, a certain level of backhaul coordination between the TRPs is needed as one TRP may need to know the current transmit beam from another TRP (associated with a different value of CORESETPOOLIndex). 
     The UE could be configured by the network with all necessary conditions described above. The UE could then be indicated by the network to use one or more of them. For instance, the UE could be indicated by the network to only use Condition A.1 if both Option-1 and Option-3 are configured, though the UE could be configured by the network with Condition A.1, Condition A.2, Condition A.3, Condition A.4, Condition A.5, Condition B.1 and Condition B.2. 
     In some cases, the UE may not be configured by the network any priority rule/ordering (e.g.,  FIG. 19  and  FIG. 20 ), but instead a set of explicit conditions along with the configured design options. 
     For instance, the UE could be first configured by the network three options, Option-1, Option-3 and Option-5. Further, the UE could be configured by the network three conditions, denoted by Condition X, Condition Y and Condition Z. If Condition X is satisfied, the UE would follow Option-1 over Option-3. If Condition Y is satisfied, the UE would follow Option-3 over Option-5. If Condition Z is satisfied, Option-5 has a higher priority than Option-1. One example charactering how the UE would determine the appropriate design option (from Option-1, Option-3 and Option-5) according to the configured conditions (Condition X, Condition Y and Condition Z) is shown in  FIG. 23 . 
       FIG. 23  illustrates yet another flowchart of a UE method  2300  for receiving and decoding PDSCH according to embodiments of the present disclosure. For example, the UE method  2300  as may be performed by a UE (e.g.,  111 - 116  as illustrated in  FIG. 1 ). An embodiment of the UE method  2300  shown in  FIG. 23  is for illustration only. One or more of the components illustrated in  FIG. 23  can be implemented in specialized circuitry configured to perform the noted functions or one or more of the components can be implemented by one or more processors executing instructions to perform the noted functions. 
     As indicated in  FIG. 23 , the UE could follow Option-5 instead of Option-1 and Option-3 to configure the default receive beam(s) for receiving the PDSCHs, which is not possible if the UE is configured and follows the priority rules/orderings in  FIG. 19  and  FIG. 20 . 
     As illustrated in  FIG. 23 , in step  2301 , a UE is configured by the network with Option-1, Option-3, and Option-5, along with Condition X, Condition Y and Condition Z. In step  2302 , the UE determines whether Condition X is satisfied. In step  2303 , the UE determines Option-1 as one candidate design option. In step  2304 , the UE determines whether Condition Z is satisfied. In step  2305 , the UE follows Option-5 to configure default receive beam(s) for buffering the PDSCH(s). In step  2306 , the UE follows Option-1 to configure default receive beam(s) for buffering the PDSCH(s). In step  2307 , the UE determines Option-3 as one candidate design option. In step  2308 , the UE determines whether Condition Y is satisfied. In step  2309 , the UE follows Option-3 to configure default receive beam(s) for buffering the PDSCH(s). In step  2310 , the UE follows Option-5 to configure default receive beam(s) for buffering the PDSCH(s). 
     For example, Condition Z in  FIG. 23  could be: if the time offset between the PDSCH of interest and the previous PDCCH (the second PDCCH in Option-1, which shares the same CORESETPOOLIndex with the first PDCCH and has been decoded by the UE) carrying the common TCI state/beam indication is below a threshold (e.g., X ms/slots/symbols), Option-1 has a higher priority than Option-5. Otherwise, the UE would follow Option-5 over Option-1 to configure the default receive beam(s), which was used for receiving the latest PDCCH with the lowest CORESET index among the CORESETs configured with the same value of CORESETPOOLIndex as that associated with the first PDCCH. 
     In one embodiment of Method-IV, the UE is configured by the network more than one (N_opt&gt;1) design options per TRP (or per CORESETPOOLIndex). The design options configured for different TPRs could be mutually exclusive. For instance, if the CORESETPOOLIndex is configured, the UE could be configured with Option-1 and Option-3 for TRP- 1  (associated with “CORESETPOOLIndex=0”) and Option-2 and Option-5 for TRP- 2  (associated with “CORESETPOOLIndex=1”). Similar to Method-III, the UE could be indicated by the network one or more priority rules/orderings and/or one or more sets of conditions to help UE determine appropriate design option for each coordinating TRP. The priority rules/orderings and/or the sets of conditions could be common for all TRPs, are customized on a per TRP basis. Detailed methods of configuring and using the priority rules/orderings and/or the sets of conditions follow those described in  FIG. 19 ,  FIG. 20 ,  FIG. 21 ,  FIG. 22 , and  FIG. 23  in the present disclosure. 
     In the single-DCI based multi-TRP system, the UE could be configured by the network a single PDCCH/DCI to schedule the PDSCH transmissions from different coordinating TRPs. For common TCI state(s)/beam(s) indication, the corresponding PDCCH could signal N_tci&gt;1 common TCI states/beams, each corresponding to a coordinating TRP. For instance, for a multi-TRP system comprising of two coordinating TRPs (e.g., TRP- 1  and TRP- 2  in  FIG. 8 ), the TCI codepoint in the PDCCH that indicates the common TCI state(s)/beam(s) to the UE could be formulated as (TCI #a, TCI #b), where TCI #a could represent the common TCI state for TRP- 1 , and TCI #b could be the common TCI state for TRP- 2 . Similar to the example shown in  FIG. 11  for the multi-DCI based multi-TRP system, the UE would also need to set the default receive beam(s) for buffering the PDSCH(s) in the single-DCI based multi-TRP system if the scheduling offset between the PDSCH(s) of interest and the PDCCH carrying the common TCI state(s)/beam(s) indication is less than a predetermined threshold. 
       FIG. 24  illustrates an example of unified TCI state indication in a single-DCI based multi-TRP system  2400  according to embodiments of the present disclosure. An embodiment of the unified TCI state indication in a single-DCI based multi-TRP system  2400  shown in  FIG. 24  is for illustration only. 
     In  FIG. 24 , a conceptual example depicting the common TCI state/beam indication in the single-DCI based multi-TRP system is presented. It is shown in  FIG. 24  that the scheduling offset between PDSCH- 1 _ 0 /PDSCH- 2 _ 0  and PDCCH-A carrying the common TCI states/beams for both TRP- 1  and TRP- 2  is beyond timeDurationForQCL. Hence, the UE could configure the receive spatial filters for receiving and/or decoding PDSCH- 1 _ 0  and PDSCH- 2 _ 0  based on the QCL parameters in TCI-A_ 1  and TCI-A_ 2  indicated in PDCCH-A. The scheduling offset between PDSCH- 1 _ 1 /PDSCH- 2 _ 1  and PDCCH-B carrying the common TCI states/beams for both TRP- 1  and TRP- 2 , however, is below the threshold timeDurationForQCL. 
     In this case, the UE is not able to set the receive spatial filters for receiving and/or decoding PDSCH- 1 _ 1  and PDSCH- 2 _ 1  according to the QCL parameters of TCI-B_ 1  and TCI-B_ 2  indicated in PDCCH-B. Hence, the UE needs to configure appropriate default receive beams for buffering PDSCH- 1 _ 1  and PDSCH- 2 _ 1 . In the following, several design options of configuring and determining default TCI states/receive beams in the single-DCI based multi-TRP system with common TCI state/beam indication are discussed. 
     In one example of Option-A, if the time offsets between the reception of a first PDCCH carrying the common TCI states/beams for all the coordinating TRPs (e.g., PDCCH-B in  FIG. 24 ) and the receptions of the PDSCHs (e.g., PDSCH- 1 _ 1  and PDSCH- 2 _ 1  in  FIG. 24 ) are less than the threshold (e.g., timeDurationForQCL in  FIG. 24 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCHs follow those of the default TCI states/beams, which could correspond to the previous N_tci (&gt;1) TCI states/beams (not common TCI states/beams) indicated in a single DCI for all the PDSCHs transmitted from the coordinating TRPs. 
       FIG. 25  illustrates another example of unified TCI state indication in a single-DCI based multi-TRP system  2500  according to embodiments of the present disclosure. An embodiment of the unified TCI state indication in a single-DCI based multi-TRP system  2500  shown in  FIG. 25  is for illustration only. 
     In  FIG. 25 , a conceptual example describing the provided Option-A is presented. In this example, PDCCH-a is the previous PDCCH with respect to PDCCH-B that signals the DCI that indicates two TCI states, i.e., TCI-a_ 1  and TCI-a_ 2 , for the PDSCHs transmitted from TRP- 1  and TRP- 2 . For instance, (TCI-a_ 1 , TCI-a_ 2 ) could correspond to one of the TCI codepoints (e.g., a total of eight TCI codepoints specified in the 3GPP Rel. 16) activated by MAC CE from a pool of TCI states configured by RRC. 
     As the scheduling offsets between PDSCH- 1 _ 1  and PDCCH-B, and PDSCH- 2 _ 1  and PDCCH-B, are less than timeDurationForQCL, the UE cannot configure the receive spatial filters for receiving PDSCH- 1 _ 1  and PDSCH- 2 _ 1  according to the QCL parameters of the common TCI states/beams indicated in PDCCH-B. According to Option-A, the UE would set the default receive beams for buffering PDSCH- 1 _ 1  and PDSCH- 2 _ 1  based on the QCL parameters of the TCI states/beams indicated in PDCCH-a. 
     In one example of Option-B, if the time offsets between the reception of a first PDCCH carrying the common TCI states/beams for all the coordinating TRPs (e.g., PDCCH-B in  FIG. 24 ) and the receptions of the PDSCHs (e.g., PDSCH- 1 _ 1  and PDSCH- 2 _ 1  in  FIG. 24 ) are less than the threshold (e.g., timeDurationForQCL in  FIG. 24 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCHs follow those of the default TCI states/beams, which could correspond to the previous N_tci (&gt;1) common TCI states/beams indicated in a single DCI for all the coordinating TRPs. 
       FIG. 26  illustrates yet another example of unified TCI state indication in a single-DCI based multi-TRP system  2600  according to embodiments of the present disclosure. An embodiment of the unified TCI state indication in a single-DCI based multi-TRP system  2600  shown in  FIG. 26  is for illustration only. 
     A conceptual example illustrating the provided Option-B in configuring and determining the default receive beams is given in  FIG. 26 . Different from the example for Option-A shown in  FIG. 25 , the UE in  FIG. 26  would configure the default receive beams for buffering PDSCH- 1 _ 1  and PDSCH- 2 _ 1  based on the QCL parameters of the two common TCI states, TCI-A_ 1  and TCI-A_ 2 , indicated in PDCCH-A. This is because in this example, TCI-A_ 1  and TCI-A_ 2  are the previous common TCI states (with respect to those indicated in PDCCH-B) indicated in a single DCI (PDCCH-A) for all the coordinating TRPs (TRP- 1  and TRP- 2 ). 
     In one example of Option-C, if the time offsets between the reception of a first PDCCH carrying the common TCI states/beams for all the coordinating TRPs (e.g., PDCCH-B in  FIG. 24 ) and the receptions of the PDSCHs (e.g., PDSCH- 1 _ 1  and PDSCH- 2 _ 1  in  FIG. 24 ) are less than the threshold (e.g., timeDurationForQCL in  FIG. 24 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCHs follow those of the default TCI states/beams, which could correspond to the lowest codepoint among the TCI codepoints containing N_tci (&gt;1) different TCI states activated for the PDSCH. This design option is similar to the configuration of the default TCI state specified in the 3GPP Rel. 16 for the single-DCI based multi-TRP system. 
       FIG. 27  illustrates an example of configuring and determining default TCI states  2700  according to embodiments of the present disclosure. An embodiment of configuring and determining the default TCI states  2700  shown in  FIG. 27  is for illustration only. 
     As can be seen from the example shown in  FIG. 27 , a total of  8  TCI codepoints are activated for PDSCH by MAC CE from a pool of TCI states configured by RRC. Each TCI codepoint corresponds to one or two TCI states. According to Option-C, the default TCI states/beams would correspond to the lowest TCI codepoint containing two different TCI states. In this example, the default TCI states are then TCI # 1  and TCI # 4 , and the corresponding TCI codepoint is “010.” The UE would configure the default receive beams for buffering the PDSCHs (e.g., PDSCH- 1 _ 1  and PDSCH- 2 _ 1  in  FIG. 24 ) based on the QCL parameters of TCI # 1  and TCI # 4 . 
     In one example of Option-D, if the time offsets between the reception of a first PDCCH carrying the common TCI states/beams for all the coordinating TRPs (e.g., PDCCH-B in  FIG. 24 ) and the receptions of the PDSCHs (e.g., PDSCH- 1 _ 1  and PDSCH- 2 _ 1  in  FIG. 24 ) are less than the threshold (e.g., timeDurationForQCL in  FIG. 24 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCHs follow those of the default TCI states/beams, which could be configured by the network and indicated to the UE. 
     For instance, the UE could be explicitly configured/indicated by the network N_tci (&gt;1) common TCI states/beams as the default TCI states/beams, upon which the UE could configure the receive spatial filters for buffering the PDSCHs transmitted from the coordinating TRPs. For a multi-TRP system comprising of two TRPs (TRP- 1  and TRP- 2 ), the UE could be configured by the network (TCI # 1 , TCI # 4 ) as the default common TCI states. The UE would configure the default receive beams for buffering the PDSCHs (e.g., PDSCH- 1 _ 1  and PDSCH- 2 _ 1  in  FIG. 24 ) based on the QCL parameters of TCI # 1  and TCI # 4  until the default common TCI states are updated/reconfigured by the network. 
     For another example, the UE could be configured by the network via higher layer signaling such as RRC a pool of default TCI sets. Each default TCI set could correspond to a single common TCI state, or N_tci (&gt;1) common TCI states. The MAC CE could activate one of the default TCI sets, and the UE could configure the default receive beam(s) for buffering the PDSCH(s) according to the QCL parameters of the common TCI state(s) indicated in the activated default TCI set. 
       FIG. 28  illustrates another example of configuring and determining default TCI states  2800  according to embodiments of the present disclosure. An embodiment of configuring and determining the default TCI states  2800  shown in  FIG. 28  is for illustration only. 
     In  FIG. 28 , two examples of the default TCI sets are presented. On the upper-half of  FIG. 27 , a default TCI set could contain a single common TCI state (e.g., for the single-TRP operation) or two common TCI states (e.g., for the multi-TRP operation). One the lower-half of  FIG. 27 , a default TCI set contains two common TCI states. If the MAC CE activates the default TCI set # 2  as shown on the lower-half of  FIG. 27 , the UE would configure the default receive beams for buffering the PDSCHs (e.g., PDSCH- 1 _ 1  and PDSCH- 2 _ 1  in  FIG. 24 ) based on the QCL parameters of TCI # 1  and TCI # 4  until the MAC CE activates a new default TCI set. 
     In one example of Option-E, the configuration of the default TCI state(s)/beam(s) for PDSCH follows the legacy procedure defined in the 3GPP Rel. 15. If the time offset between the reception of a first PDCCH carrying the common TCI states/beams for all the coordinating TRPs (e.g., PDCCH-B in  FIG. 24 ) and the receptions of the PDSCHs (e.g., PDSCH- 1 _ 1  and PDSCH- 2 _ 1  in  FIG. 24 ) are less than the threshold (e.g., timeDurationForQCL in  FIG. 24 ), the UE could assume that the QCL parameters for the DMRS ports of the PDSCHs follow those of the default TCI state(s)/beam(s), which could be used for the PDCCH with the lowest CORESET index among the CORESETs associated with a monitored search space in the latest slot. 
     The UE could be configured by the network one or more design options described above to configure the default beam(s) for receiving the PDSCH(s) in a single-DCI based multi-TRP system. For instance, the UE could be indicated by the network to follow only one design option, e.g., Option-A, to configure the default receive beam(s) for receiving and/or decoding the PDSCH(s). For another example, the UE could be indicated by the network more than one design options along with a priority rule/ordering and/or a set of conditions, upon which the UE could determine and follow an appropriate design option to configure the default receive beam(s) for buffering the PDSCH(s). 
       FIG. 29  illustrates an example of priority rule for configuring and determining default TCI state  2900  according to embodiments of the present disclosure. An embodiment of the priority rule for configuring and determining default TCI state  2900  shown in  FIG. 29  is for illustration only. 
     A priority rule/ordering example is given in  FIG. 29 , in which Priority 0 has the highest priority while Priority 3 has the lowest priority. In this example, Option-B and Option-D belong to Priority 0, Option-A and Option-C belong to Priority 1, and Option-E corresponds to Priority 3. For instance, if the UE is indicated by the network Option-A and Option-B, the UE would follow Option-B to configure the default receive beam(s) as long as the common TCI state/beam indication is configured/enabled. For another example, assume that the UE is indicated by the network Option-C and Option-E. The UE would follow Option-E to set the default receive beam(s) if all of the TCI codepoints activated by the MAC CE comprise of a single TCI state. 
     Under certain settings, the UE could be indicated/configured by the network the design options that belong to the same priority order, e.g., Option-B and Option-D in the example shown in  FIG. 29 . In this case, the UE needs additional indications/conditions from the network so that the UE could prioritize one option over the other. In this example, the UE would be indicated by the network Condition 1 if the UE is configured with both Option-B and Option-D. Similarly, the UE would be indicated by the network Condition 2 if the UE is configured with both Option-A and Option-C. In the following, several possibilities for Condition 1 and Condition 2 are presented. 
     In one embodiment, Condition 1 is used for prioritizing between Option-B and Option-D under Priority 0 in  FIG. 29 . 
     In one example of Condition 1.1, if the UE is explicitly configured by the network the default (common) TCI states/beams (e.g., activating a default TCI set from a pool of default TCI sets each comprising of N_tci&gt;1 common TCI states), Option-D has a higher priority than Option-B. 
     In one example of Condition 1.2, it may be assumed that the UE is explicitly configured by the network the default (common) TCI states/beams. If the previous N_tci (&gt;1) common TCI states/beams (indicated in the single DCI for all the coordinating TRPs) are different from the explicitly configured default (common) TCI states and/or configured at a later time, Option-B has a higher priority than Option-D. 
     In one example of Condition 1.3, if the receive default beam(s) configured according to Option-B and the beam for receiving the first PDCCH are from different panels, meanwhile the receive default beam(s) configured following Option-D and the beam for receiving the first PDCCH are from the same panel, Option-D has a higher priority than Option-B. 
     In one example of Condition 1.4, if the receive default beam(s) configured according to Option-D and the beam for receiving the first PDCCH are from different panels, meanwhile the receive default beam(s) configured following Option-B and the beam for receiving the first PDCCH are from the same panel, Option-B has a higher priority than Option-D. 
     In one embodiment, Condition 2 is used for prioritizing between Option-A and Option-C under Priority 1 in  FIG. 29 . 
     In one example of Condition 2.1, if there is at least one TCI codepoint activated for PDSCH comprising of N_tci (&gt;1) TCI states, Option-A has a higher priority than Option-C. 
     In one example of Condition 2.2, it may be assumed that there is at least one TCI codepoint activated for PDSCH comprising of N_tci (&gt;1) TCI states. If the previous N_tci (&gt;1) TCI states/beams (not common TCI states/beams) indicated in the single DCI for all the coordinating TRPs are different from those corresponding to the lowest TCI codepoint among all the TCI codepoints comprising of N_tci (&gt;1) TCI states and/or configured at a later time, Option-C has a higher priority than Option-A. 
     In one example of Condition 2.3, if the receive default beam(s) configured according to Option-A and the beam for receiving the first PDCCH are from different panels, meanwhile the receive default beam(s) configured following Option-C and the beam for receiving the first PDCCH are from the same panel, Option-C has a higher priority than Option-A. 
     In one example of Condition 2.4, if the receive default beam(s) configured according to Option-C and the beam for receiving the first PDCCH are from different panels, meanwhile the receive default beam(s) configured following Option-A and the beam for receiving the first PDCCH are from the same panel, Option-A has a higher priority than Option-C. 
     Other priority rules/orderings than that shown in  FIG. 29  are also possible. Further, other conditions than those described above can be implemented as well. Note that for Condition 1.3, Condition 1.4, Condition 2.3 and Condition 2.4, the UE may need to report to the network their receive panel information such as panel ID along with the channel measurement report. The UE could be configured by the network with all necessary conditions described above. The UE could then be indicated by the network to use one or more of them. For instance, the UE could be indicated by the network to only use Condition 1.1 if both Option-B and Option-D are configured, though the UE could be configured by the network with Condition 1.1, Condition 1.2, Condition 1.3, Condition 1.4, Condition 2.1, Condition 2.2, Condition 2.3 and Condition 2.4 in the first place. 
     In some cases, the UE may not be configured by the network any priority rule/ordering (e.g.,  FIG. 29 ), but instead a set of explicit conditions along with the configured design options. For instance, the UE could be first configured by the network three options, Option-A, Option-B and Option-D. Further, the UE could be configured by the network three conditions, denoted by Condition I, Condition II and Condition III. If Condition I is satisfied, the UE would follow Option-A over Option-B. If Condition II is satisfied, the UE would follow Option-A over Option-D. If Condition III is satisfied, Option-B has a higher priority than Option-D. One example charactering how the UE would determine the appropriate design option (from Option-A, Option-B and Option-D) according to the configured conditions (Condition I, Condition II and Condition III) is shown in  FIG. 30 . 
       FIG. 30  illustrates a flowchart of a method  3000  for configuring and determining a default beam according to embodiments of the present disclosure. For example, the method  3000  as may be performed by a UE (e.g.,  111 - 116  as illustrated in  FIG. 1 ). An embodiment of the method  3000  shown in  FIG. 30  is for illustration only. One or more of the components illustrated in  FIG. 30  can be implemented in specialized circuitry configured to perform the noted functions or one or more of the components can be implemented by one or more processors executing instructions to perform the noted functions. 
     As indicated in  FIG. 30 , the UE could follow Option-A instead of Option-B and Option-D to configure the default receive beam(s) for receiving the PDSCHs, which is not possible if the UE is configured and follows the priority rule/ordering in  FIG. 29 . For example, Condition II in  FIG. 30  could be: the previous N_tci (&gt;1) TCI states/beams (not common TCI states/beams) indicated in the single DCI for all the coordinating TRPs are different from the explicitly configured default (common) TCI states and/or configured at a later time. 
     As illustrated in  FIG. 30 , in step  3001 , a UE is configured by the network with Option-A, Option-B, and Option-D, along with Condition I, Condition II, and Condition III. In step  3002 , the UE determines whether Condition I is satisfied. In step  3003 , the UE determines Option-A as one candidate design option. In step  3004 , the UE determines whether Condition II is satisfied. In step  3005 , the UE follows Option-A to configure default receive beam(s) for buffering the PDSCH(s). In step  3006 , the UE follows Option-D to configure default receive beam(s) for buffering the PDSCH(s). In step  3007 , the UE determines Option-B as one candidate design option. In step  3008 , the UE determines whether Condition III is satisfied. In step  3009 , the UE follows Option-B to configure default receive beam(s) for buffering the PDSCH(s). In step  3010 , the UE follows Option-D to configure default receive beam(s) for buffering the PDSCH(s). 
     The above flowcharts illustrate example methods that can be implemented in accordance with the principles of the present disclosure and various changes could be made to the methods illustrated in the flowcharts herein. For example, while shown as a series of steps, various steps in each figure could overlap, occur in parallel, occur in a different order, or occur multiple times. In another example, steps may be omitted or replaced by other steps. 
     Although the present disclosure has been described with exemplary embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims. None of the description in this application should be read as implying that any particular element, step, or function is an essential element that must be included in the claims scope. The scope of patented subject matter is defined by the claims.