Patent Publication Number: US-2023141941-A1

Title: Method and apparatus for determining control resource set

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to the determination of control resource set, and relates more particularly to the determination of control resource set for New Radio apparatus. 
     BACKGROUND OF THE INVENTION 
     In conventional network, Physical Downlink Control Channel (PDCCH) detection may be performed between user equipment and base station according to some configurations of network resources. These configurations may include control resource set configuration, search space set configuration and demodulation reference symbol position. 
     For some networks which are compatible with New Radio (NR) protocol, NR apparatus with reduced capabilities (i.e., NR-Light apparatus) may be introduced. Because the capabilities of NR-Light apparatus may be limited, the configurations for performing PDCCH detection by NR-Light apparatus need to be re-configured. However, specific details of the configurations for the NR-Light apparatus to perform PDCCH detection have not been discussed yet and there are still some issues that need to be solved. 
     BRIEF SUMMARY OF THE INVENTION 
     One embodiment of the present disclosure provides a method of a user equipment. The method includes: receiving a configuration of a first control resource set (CORESET) from a base station; and determining a second CORESET based on the first CORESET, wherein an initial physical resource block (PRB) of the second CORESET is allocated as an initial PRB of a control channel element (CCE) of the first CORESET. 
     Another embodiment of the present disclosure provides a method of a base station. The method includes: transmitting a configuration of a first CORESET to a user equipment; and determining a second CORESET based on the first CORESET, wherein an initial PRB of the second CORESET is allocated as an initial PRB of a CCE of the first CORESET. 
     Yet another embodiment of the present disclosure provides an apparatus. According to an embodiment of the present disclosure, the apparatus includes: at least one non-transitory computer-readable medium having computer executable instructions stored therein; at least one receiving circuitry; at least one transmitting circuitry; and at least one processor coupled to the at least one non-transitory computer-readable medium, the at least one receiving circuitry and the at least one transmitting circuitry, wherein the at least one non-transitory computer-readable medium and the computer executable instructions are configured to, with the at least one processor, cause the apparatus to perform a method according to an embodiment of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to describe the manner in which advantages and features of the disclosure can be obtained, a description of the disclosure is rendered by reference to specific embodiments thereof, which are illustrated in the appended drawings. These drawings depict only exemplary embodiments of the disclosure and are not therefore to be considered limiting of its scope. 
         FIG.  1    illustrates a wireless communication system according to an embodiment of the present disclosure. 
         FIG.  2 A  illustrates configuration transmission in a wireless communication system according to an embodiment of the present disclosure. 
         FIGS.  2 B to  2 I  are schematic views of the CORESETs according to an embodiment of the present disclosure. 
         FIGS.  3 A to  3 B  are schematic views of the CORESETs according to an embodiment of the present disclosure. 
         FIG.  4    is a schematic view of the CORESETs according to an embodiment of the present disclosure. 
         FIGS.  5 A to  5 B  are schematic views of the CORESETs according to an embodiment of the present disclosure. 
         FIG.  6    is a schematic view of the CORESETs according to an embodiment of the present disclosure. 
         FIG.  7    is a schematic view of the CORESETs according to an embodiment of the present disclosure. 
         FIG.  8    illustrates flow chart of a method for wireless communications according to an embodiment of the present disclosure. 
         FIG.  9    illustrates an example block diagram of an apparatus according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The detailed description of the appended drawings is intended as a description of preferred embodiments of the present disclosure and is not intended to represent the only form in which the present disclosure may be practiced. It should be understood that the same or equivalent functions may be accomplished by different embodiments that are intended to be encompassed within the spirit and scope of the present disclosure. 
     Referring to  FIG.  1   , a wireless communication system  100  may include a user equipment (UE)  101 , a base station (BS)  102  and a core network (CN)  103 . Although a specific number of UE  101 , BS  102  and CN  103  are depicted in  FIG.  1   , it is contemplated that any number of UEs  101 , BSs  102  and CNs  103  may be included in the wireless communication system  100 . 
     CN  103  may include a core Access and Mobility management Function (AMF) entity. BS  102 , which may communicate with CN  103 , may operate or work under the control of the AMF entity. CN  103  may further include a User Plane Function (UPF) entity, which communicatively coupled with the AMF entity. 
     BS  102  may be distributed over a geographic region. In certain embodiments of the present application, BS  102  may also be referred to as an access point, an access terminal, a base, a base unit, a macro cell, a Node-B, an evolved Node B (eNB), a gNB, a Home Node-B, a relay node, or a device, or described using other terminology used in the art. BS  102  is generally part of a radio access network that may include one or more controllers communicably coupled to one or more corresponding BS(s). 
     UE  101  may include, for example, but is not limited to, computing devices, such as desktop computers, laptop computers, personal digital assistants (PDAs), tablet computers, smart televisions (e.g., televisions connected to the Internet), set-top boxes, game consoles, security systems (including security cameras), vehicle on-board computers, network devices (e.g., routers, switches, and modems), Internet of Thing (IoT) devices, or the like. 
     According to some embodiments of the present application, UE  101  may include, for example, but is not limited to, a portable wireless communication device, a smart phone, a cellular telephone, a flip phone, a device having a subscriber identity module, a personal computer, a selective call receiver, or any other device that is capable of sending and receiving communication signals on a wireless network. 
     In some embodiments of the present application, UE  101  may include, for example, but is not limited to, wearable devices, such as smart watches, fitness bands, optical head-mounted displays, or the like. Moreover, UE  101  may be referred to as a subscriber unit, a mobile, a mobile station, a user, a terminal, a mobile terminal, a wireless terminal, a fixed terminal, a subscriber station, a user terminal, or a device, or described using other terminology used in the art. UE  101  may communicate directly with BS  102  via uplink communication signals. 
     The wireless communication system  100  may be compatible with any type of network that is capable of sending and receiving wireless communication signals. For example, the wireless communication system  100  is compatible with a wireless communication network, a cellular telephone network, a Time Division Multiple Access (TDMA)-based network, a Code Division Multiple Access (CDMA)-based network, an Orthogonal Frequency Division Multiple Access (OFDMA)-based network, a Long Term Evolution (LTE) network, a 3GPP-based network, a 3GPP 5G network, a satellite communications network, a high altitude platform network, and/or other communications networks. 
     In some embodiments of the present application, the wireless communication system  100  is compatible with the 5G New Radio (NR) of the 3GPP protocol or the 5G NR-light of the 3GPP protocol, wherein BSs  102  transmit data using an OFDM modulation scheme on the downlink (DL) and UE  101  transmit data on the uplink (UL) using a single-carrier frequency division multiple access (SC-FDMA) or OFDM scheme. More generally, however, the wireless communication system  100  may implement some other open or proprietary communication protocols, for example, WiMAX, among other protocols. 
     In some embodiments of the present application, BS  102  may communicate using other communication protocols, such as the IEEE 802.11 family of wireless communication protocols. Further, in some embodiments of the present application, BS  102  may communicate over licensed spectrums, whereas in other embodiments BS  102  may communicate over unlicensed spectrums. The present application is not intended to be limited to the implementation of any particular wireless communication system architecture or protocol. In yet some embodiments of present application, BS  102  may communicate with UE  101  using the 3GPP 5G protocols. 
     According to some existed agreements, UE  101  and BS  102  included in the wireless communication system  100  may be compatible with NR-Light of the 3GPP protocol. However, because the capabilities of NR-Light UE  101  may be limited, the configurations for performing Physical Downlink Control Channel (PDCCH) detection by UE  101  and BS  102  need to be re-configured. 
     In some embodiments, a general configuration of control resource set (CORESET) may be used for UE  101  and BS  102  to determine another configuration of CORESET proper to NR-Light protocol. In detail, referring to  FIG.  2 A , BS  102  may broadcast master information block (MIB)  102 A which may include a configuration of a first CORESET CT 1 . Then, UE  101  may receive the MIB  102 A including the configuration of the first CORESET CT 1  through detecting synchronization signal blocks (SSBs). 
     Next, UE  101  may retrieve the configuration of the first CORESET CT 1  from the MIB  102 A. UE  101  and BS  102  may then determine the first CORESET CT 1  according to the configuration respectively. Specifically, please refer to  FIG.  2 B , the configuration of the first CORESET CT 1  may include a frequency domain size and a time domain size for defining the first CORESET CT 1 . 
     In some implementations, the first CORESET CT 1  may include a CORESET zero (i.e., CORESET 0 ) specified in 3GPP Technical Specification #38.213 (the entirety of which are incorporated herein by reference), and the frequency domain size and the time domain size for defining the first CORESET CT 1  may be selected from:
     (1) 24 physical resource blocks (PRBs) for frequency domain and 2 Orthogonal Frequency Division Multiplexing (OFDM) symbols in time domain;   (2) 24 PRBs for frequency domain and 3 OFDM symbols in time domain;   (3) 48 PRBs for frequency domain and 1 OFDM symbols in time domain;   (4) 48 PRBs for frequency domain and 2 OFDM symbols in time domain;   (5) 48 PRBs for frequency domain and 3 OFDM symbols in time domain;   (6) 96 PRBs for frequency domain and 1 OFDM symbols in time domain;   (7) 96 PRBs for frequency domain and 2 OFDM symbols in time domain; or   (8) 96 PRBs for frequency domain and 3 OFDM symbols in time domain.   

     Please refer to  FIG.  2 C . After determining the first CORESET CT 1  based on the selected frequency domain size and time domain size, UE  101 /BS  102  may determine a second CORESET CT 2  according to the first CORESET CT 1 . In detail, in frequency domain, UE  101 /BS  102  may allocate an initial PRB P 2  of the second CORESET CT 2  as an initial PRB P 1  of the first CORESET CT 1 . Particularly, the initial PRB P 2  of the second CORESET CT 2  may be allocated as the initial PRB P 1  of a specific control channel element (CCE) C 1  of the first CORESET CT 1 . In some implementations, when the first CORESET CT 1  includes the CORESET 0 , the specific CCE C 1  of the first CORESET CT 1  may include CCE zero (CCE 0 ) or CCE one (CCE 1 ) of the CORESET 0 . 
     More specifically, when UE  101 /BS 102  determines that a pre-defined frequency domain size of the second CORESET CT 2  is smaller than the frequency domain size of the first CORESET CT 1 , UE  101 /BS 102  then determines whether the initial PRB of the second CORESET CT 2  should be allocated as the initial PRB of CCE 0  of the CORESET 0  or as the initial PRB of CCE 1  of the CORESET 0 . It should be noted that the pre-defined frequency domain size of the second CORESET CT 2  may be a default setting stored in UE  101 /BS 102  or the pre-defined frequency domain size of the second CORESET CT 2  may be determined by BS  102  and included in the configuration of the first CORESET CT 1 . In some embodiments, the size of second CORESET CT 2  in time domain and/or in frequency domain may be determined by the configuration of the first CORESET CT 1 . 
     Please refer to  FIG.  2 D . If frequency band of the second CORESET CT 2  is determined within frequency band of the CORESET 0  when the initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 0  of the CORESET 0 , UE  101 /BS  102  determines that the initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 0  of the CORESET 0 . 
     Please refer to  FIGS.  2 E to  2 F . As shown in  FIG.  2 E , if frequency band of the second CORESET CT 2  is determined not within (e.g., partially overlapped) frequency band of the CORESET 0  when an initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 0  of the CORESET 0 , UE  101 /BS  102  determines that the initial PRB P 2  of the second CORESET CT 2  is allocated as an initial PRB P 1  of CCE 1  of the CORESET 0  as shown in  FIG.  2 F . 
     Please refer to  FIG.  2 G . Similarly, if frequency band of the second CORESET CT 2  is determined within frequency band of the CORESET 0  when an initial PRB P 2  of the second CORESET CT 2  is allocated as an initial PRB P 1  of CCE 1  of the CORESET 0 , UE  101 /BS  102  determines that the initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 1  of the CORESET 0 . 
     Please refer to  FIGS.  2 H to  2 I . As shown in  FIG.  2 H , if frequency band of the second CORESET CT 2  is determined not within (e.g., partially overlapped) frequency band of the CORESET 0  when the initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 1  of the CORESET 0 , UE  101 /BS  102  determines that the initial PRB P 2  of the second CORESET CT 2  is allocated as an initial PRB P 1  of CCE 0  of the CORESET 0  as shown in  FIG.  2 I . 
     Further, in time domain, UE  101 /BS  102  may determine at least one resource unit for the second CORESET CT 2  according to a pre-defined time domain size. It should be noted that the pre-defined time domain size of the second CORESET CT 2  may be a default setting stored in UE  101 /BS  102  or the pre-defined time domain size of the second CORESET CT 2  may be determined by BS  102  and included in the configuration of the first CORESET CT 1 . 
     In some implementations, each resource unit of the second CORESET CT 2  may include at least one OFDM symbol(s). The number of the OFDM symbol(s) of each resource unit may be same as the number of the OFDM symbol(s) of the first CORESET CT 1 . For example, please refer to  FIG.  3 A , when the first CORESET CT 1  includes the CORESET 0  and the time domain size is selected as 2 OFDM symbols, the number of the OFDM symbols of each resource unit is configured as 2 OFDM symbols. 
     In some implementations, each of first “N−1” resource units of the second CORESET CT 2  may include at least one OFDM symbol(s), and the number of the OFDM symbol(s) of each of first “N−1” resource units may be same as the number of the OFDM symbol(s) of the first CORESET CT 1 . The N th  resource unit of the second CORESET CT 2  may include at least one OFDM symbol(s), and the number of the OFDM symbol(s) of the N th  resource unit may be configured as less than the number of the OFDM symbol(s) of the first CORESET CT 1 . 
     For example, please refer to  FIG.  3 B , when the first CORESET CT 1  includes the CORESET 0 , the time domain size is selected as 3 OFDM symbols and the second CORESET CT 2  includes 3 resource units, the number of the OFDM symbols of each of the first two (i.e., “3−1=2”) resource units is configured as 3 OFDM symbols. The number of the OFDM symbols of the third resource unit is configured less than 3 OFDM symbols (e.g., 2 OFDM symbols). 
     In some embodiments, in the resource units of the second CORESET CT 2  that have same time domain duration (i.e., include same number of OFDM symbols) of the first CORESET CT 1 , a resource element group bundle (REGB) may include a plurality of resource element groups (REGs). In some implementations, the number of the REGs in one REGB of the second CORESET CT 2  may be same as the number of REGs in one REGB of the first CORESET CT 1 . For example, when the first CORESET CT 1  includes the CORESET 0  and one REGB of CORESET 0  includes six REGs, the number of the REGs in one REGB of the second CORESET CT 2  is also six. 
     In some embodiments, the REGB of the second CORESET CT 2  may be: (1) sequentially indexed in each resource unit; and (2) sequentially indexed from one resource unit to another resource unit. 
     In some implementations of that the number of the OFDM symbols of each resource unit is configured as the same as the number of the OFDM symbols of the first CORESET CT 1 , the indexes of the REGB of the second CORESET CT 2  may be configured as the following rule:
         REGBs of resource unit “x” is indexed as: REGB{x*N_RegBundle_unit, x*N_RegBundle_unit+1, . . . , x*N_RegBundle_unit+N_RegBundle_unit−1}, wherein N_RegBundle_unit represents the number of REGBs per resource unit.       

     For example, when there are two resource unit “0” and “1” in the second CORESET CT 2  and N_RegBundle_unit is 8:
         REGBs of resource unit “0” are indexed as: REGB(0*8), REGB(0*8+1), REGB(0*8+2), REGB(0*8+3), REGB(0*8+4), REGB(0*8+5), REGB(0*8+6) and REGB(0*8+7), i.e., the REGBs of resource unit “0” are indexed as: REGB 0 , REGB 1 , REGB 2 , REGB 3 , REGB 4 , REGB 5 , REGB 6  and REGB 7 ; and   REGBs of resource unit “1” are indexed as: REGB(1*8), REGB(1*8+1), REGB(1*8+2), REGB(1*8+3), REGB(1*8+4), REGB(1*8+5), REGB(1*8+6) and REGB(1*8+7), i.e., the REGBs of resource unit “1” are indexed as: REGB 8 , REGB 9 , REGB 10 , REGB 11 , REGB 12 , REGB 13 , REGB 14  and REGB 15 .       

     In some implementations of that: (1) the number of the OFDM symbols of each of first “N−1” resource units is configured as the same as the number of the OFDM symbols of the first CORESET CT 1 ; and (2) the number of the OFDM symbols of the N th  resource unit is configured as less than the number of the OFDM symbols of the first CORESET CT 1 , the indexes of the REGB of the second CORESET CT 2  may be configured as following rules:
         REGBs of first N−1 resource units “x” is indexed as: REGB {x*N_RegBundle_unit, x*N_RegBundle_unit+1, . . . , x*N_RegBundle_unit+N_RegBundle_unit−1}, wherein N_RegBundle_unit represents the number of REGBs per resource unit; and   REGBs of N th  resource unit “y” is indexed as: {y*N_RegBundle_unit+N_RegBundle_unit, y*N_RegBundle_unit+N_RegBundle_unit+1, . . . , N_RegBundle}, wherein N_RegBundle represents the number of REGBs of the second CORESET CT 2 .       

     For example, when there are three resource unit “0”, “1” and “2” in the second CORESET CT 2 , N_RegBundle_unit is 8 and N_RegBundle is 20:
         REGBs of resource unit “0” are indexed as: REGB(0*8), REGB(0*8+1), REGB(0*8+2), REGB(0*8+3), REGB(0*8+4), REGB(0*8+5), REGB(0*8+6) and REGB(0*8+7), i.e., the REGBs of resource unit “0” are indexed as: REGB 0 , REGB 1 , REGB 2 , REGB 3 , REGB 4 , REGB 5 , REGB 6  and REGB 7 ;   REGBs of resource unit “1” are indexed as: REGB(1*8), REGB(1*8+1), REGB(1*8+2), REGB(1*8+3), REGB(1*8+4), REGB(1*8+5), REGB(1*8+6) and REGB(1*8+7), i.e., the REGBs of resource unit “1” are indexed as: REGB 8 , REGB 9 , REGB 10 , REGB 11 , REGB 12 , REGB 13 , REGB 14  and REGB 15 ; and   REGBs of resource unit “2” are indexed as: REGB(2*8), REGB(2*8+1), REGB(2*8+2) and REGB(2*8+3), i.e., the REGBs of resource unit “2” are indexed as: REGB 16 , REGB 17 , REGB 18  and REGB 19 .       

     In some embodiments, when the first CORESET CT 1  includes the CORESET 0 , a mapping relation of CCE-to-REGB of the first CORESET CT 1  may be defined as the following rules:
         CCE 0  of CORESET 0  maps to REGB“X” while X=n shift  mod (N REG   CORESET /L), wherein n shift  represents an offset, N REG   CORESET  represents the number of REGs of the CORESET 0  and L represents the number of REGs in one REGB;   When the number of REGBs of the CORESET 0  is K and an interleaver size is R:
           CCE“R*i” maps to REGB“X+i”, i=0,1,2, . . . ,(K/2)−1, wherein if “X+i” is greater than “K−1”, then CCE numbering is continued in a wraparound way from REGB 0 ;   CCE“R*i+1” maps to REGB“X+i+K/2”, i=0,1,2, . . . , (K/2)−1, wherein if “X+i+K/2” is greater than “K−1”, then CCE numbering is continued in a wraparound way from REGB 0 .   
               

     In some embodiments, when frequency band of the first CORESET CT 1  is greater than frequency band of the second CORESET CT 2 , a mapping relation of CCE-to-REG of the second CORESE CT 2  may be re-defined. In detail, when the first CORESET CT 1  includes the CORESET 0  and the initial PRB of the second CORESET CT 2  is allocated as the initial PRB of CCE 0  of the CORESET 0 , a mapping relation of CCE-to-REG of the second CORESET CT 2  may be defined as the following rules
         CCE 0  of CORESET 0  maps to REGB“X” while X=n shift  mod (N REG   CORESET /L), wherein n shift =0, and N REG   CORESET  represents the number of REGs of the CORESET 0  and L represents the number of REGs in one REGB;   When the number of REGBs of the CORESET 0  is K and an interleaver size is R:
           CCE“R*i” maps to REGB“X+i”, i=0,1,2, . . . ,(K/2)−1, wherein if “X+i” is greater than “K−1”, then CCE numbering is continued in a wraparound way from REGB 0 ;   CCE“R*i+1” maps to REGB“X+i+K/2”, i=0,1,2, . . . , (K/2)−1, wherein if “X+i+K/2” is greater than “K−1”, then CCE numbering is continued in a wraparound way from REGB 0 .   
               

     When the first CORESET CT 1  includes the CORESET 0  and the initial PRB of the second CORESET CT 2  is allocated as the initial PRB of CCE 1  of the CORESET 0 , a mapping relation of CCE-to-REG of the second CORESET CT 2  may be defined as the following rules
         CCE 0  of CORESET 0  maps to REGB“X” while X=n shift  mod (N REG   CORESET /L), wherein n shift =N_RegBundle/2, and N_RegBundle represents the number of REGBs of the CORESET 0 , N REG   CORESET  represents the number of REGs of the CORESET 0  and L represents the number of REGs in one REGB;   When the number of REGBs of the CORESET 0  is K and an interleaver size is R:
           CCE“R*i” maps to REGB“X+i”, i=0,1,2, . . . ,(K/2)−1, wherein if “X+i” is greater than “K−1”, then CCE numbering is continued in a wraparound way from REGB 0 ;   CCE“R*i+1” maps to REGB“X+i+K/2”, i=0,1,2, . . . , (K/2)−1, wherein if “X+i+K/2” is greater than “K−1”, then CCE numbering is continued in a wraparound way from REGB 0 .   
               

     In some embodiments, BS  102  may transmit the configuration of the first CORESET CT 1  further with a first search space set. The first search space set corresponds to a first set of aggregation levels. In some implementations, when the first CORESET CT 1  includes the CORESET 0 , the configuration of the first CORESET CT 1  may be associated with search space zero specified in 3GPP Technical Specification #38.213 and the first set of aggregation levels may include aggregation level 4, 8 and 16 which correspond to number of CCE candidates 4, 2 and 1 respectively. 
     Next, UE  101  may receive the configuration of the first CORESET CT 1  and the first search space set. UE  101 /BS  102  may determine a second set of aggregation levels for a second search space set of the second CORESET CT 2 . In some implementations, the aggregation levels in the second set may be equal to or higher than those in the first set of aggregation levels. 
     Please refer to  FIG.  4    for some implementations of determining the second CORESET CT 2  based on the first CORESET CT 1  including the CORESET 0 . In detail, after UE  101  receives MIB information including a configuration of the CORESET 0  from BS  102 , UE  101  can retrieve the following information from the configuration: (1) the frequency domain size of the CORESET 0  includes 48 PRBs; and (2) the time domain size of the CORESET 0  includes 2 OFDM symbols. Then, UE  101 /BS  102  respectively determines the second CORESET CT 2  according to: (1) the configuration of CORESET 0 ; (2) a pre-defined frequency domain size, which includes 24 PRBs, of the second CORESET CT 2 ; and (3) a pre-defined time domain size, which includes 4 OFDM symbols of 2 resource units, of the second CORESET CT 2 . 
     Particularly, as for the CORESET 0  of these implementations, n shift  is configured as 5, N REG   CORESET  is configured as 48*2=96 and L is configured as 6, i.e., one REGB contains 6 REGs, as shown in  FIG.  4   . Therefore, CCE 0  of the CORESET 0  maps to REGB 5 . Further, the mapping relation of CCE-to-REG of the CORESET 0  is defined as:
         CCE 0  (C 0  as shown in  FIG.  4   ) maps to REGB 5  (R 5  as shown in  FIG.  4   )   CCE 2  (C 2  as shown in  FIG.  4   ) maps to REGB 6  (R 6  as shown in  FIG.  4   )   CCE 4  (C 4  as shown in  FIG.  4   ) maps to REGB 7  (R 7  as shown in  FIG.  4   )   CCE 6  (C 6  as shown in  FIG.  4   ) maps to REGB 8  (R 8  as shown in  FIG.  4   )   CCE 8  (C 8  as shown in  FIG.  4   ) maps to REGB 9  (R 9  as shown in  FIG.  4   )   CCE 10  (C 10  as shown in  FIG.  4   ) maps to REGB 10  (R 10  as shown in  FIG.  4   )   CCE 12  (C 12  as shown in  FIG.  4   ) maps to REGB 11  (R 11  as shown in  FIG.  4   )   CCE 14  (C 14  as shown in  FIG.  4   ) maps to REGB 12  (R 12  as shown in  FIG.  4   )   CCE 1  (C 1  as shown in  FIG.  4   ) maps to REGB 13  (R 13  as shown in  FIG.  4   )   CCE 3  (C 3  as shown in  FIG.  4   ) maps to REGB 14  (R 14  as shown in  FIG.  4   )   CCE 5  (C 5  as shown in  FIG.  4   ) maps to REGB 15  (R 15  as shown in  FIG.  4   )   CCE 7  (C 7  as shown in  FIG.  4   ) maps to REGB 0  (R 0  as shown in  FIG.  4   )   CCE 9  (C 9  as shown in  FIG.  4   ) maps to REGB 1  (R 1  as shown in  FIG.  4   )   CCE 11  (C 11  as shown in  FIG.  4   ) maps to REGB 2  (R 2  as shown in  FIG.  4   )   CCE 13  (C 13  as shown in  FIG.  4   ) maps to REGB 3  (R 3  as shown in  FIG.  4   )   CCE 15  (C 15  as shown in  FIG.  4   ) maps to REGB 4  (R 4  as shown in  FIG.  4   )       

     Accordingly, as for the second CORESET CT 2 : (1) in time domain, UE  101 /BS  102  determines that a first OFDM symbol s 0  of the second CORESET CT 2  starts from a first OFDM symbol S 0  of the CORESET 0 ; and (2) in frequency domain, because frequency band of the second CORESET CT 2  is within frequency band of the CORESET 0  when the initial PRB P 2  of the second CORESET CT 2  is allocated as an initial PRB P 1  of CCE 0  of the CORESET 0 , UE  101 /BS  102  determines that the initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 0  of the CORESET 0 . 
     Further, the second CORESET CT 2  includes two resource units RU 0  and RU 1 . The number of OFDM symbols of each resource unit is the same as the number of OFDM symbols of the CORESET 0 , which is 2 in these implementations. Each resource unit includes 8 REGBs. Therefore, resource units RU 0  and RU 1  include 16 REGBs. The REGBs of the second CORESET CT 2  are: (1) sequentially indexed in each resource unit; and (2) sequentially indexed from one resource unit to another resource unit. Accordingly, 16 REGBs are indexed as REGB 0  to REGB 15  as shown in  FIG.  4    (i.e., r 0  to r 15  as shown in  FIG.  4   ). 
     Next, because the initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 0  of the CORESET 0 , n shift  is configured as 0. Therefore, a mapping relation of CCE-to-REG of the second CORESET CT 2  is defined as:
         CCE 0  (c 0  as shown in  FIG.  4   ) maps to REGB 0  (r 0  as shown in  FIG.  4   )   CCE 2  (c 2  as shown in  FIG.  4   ) maps to REGB 1  (r 1  as shown in  FIG.  4   )   CCE 4  (c 4  as shown in  FIG.  4   ) maps to REGB 2  (r 2  as shown in  FIG.  4   )   CCE 6  (c 6  as shown in  FIG.  4   ) maps to REGB 3  (r 3  as shown in  FIG.  4   )   CCE 8  (c 8  as shown in  FIG.  4   ) maps to REGB 4  (r 4  as shown in  FIG.  4   )   CCE 10  (c 10  as shown in  FIG.  4   ) maps to REGB 5  (r 5  as shown in  FIG.  4   )   CCE 12  (c 12  as shown in  FIG.  4   ) maps to REGB 6  (r 6  as shown in  FIG.  4   )   CCE 14  (c 14  as shown in  FIG.  4   ) maps to REGB 7  (r 7  as shown in  FIG.  4   )   CCE 1  (c 1  as shown in  FIG.  4   ) maps to REGB 8  (r 8  as shown in  FIG.  4   )   CCE 3  (c 3  as shown in  FIG.  4   ) maps to REGB 9  (r 9  as shown in  FIG.  4   )   CCE 5  (c 5  as shown in  FIG.  4   ) maps to REGB 10  (r 10  as shown in  FIG.  4   )   CCE 7  (c 7  as shown in  FIG.  4   ) maps to REGB 11  (r 11  as shown in  FIG.  4   )   CCE 9  (c 9  as shown in  FIG.  4   ) maps to REGB 12  (r 12  as shown in  FIG.  4   )   CCE 11  (c 11  as shown in  FIG.  4   ) maps to REGB 13  (r 13  as shown in  FIG.  4   )   CCE 13  (c 13  as shown in  FIG.  4   ) maps to REGB 14  (r 14  as shown in  FIG.  4   )   CCE 15  (c 15  as shown in  FIG.  4   ) maps to REGB 15  (r 15  as shown in  FIG.  4   )       

     In these implementations, a first search space set corresponding to a first set of aggregation levels is designated to the CORESET 0 . In detail, because the CORESET 0  includes 16 REGBs, the first aggregation level set supports aggregation level 16 at most (i.e., the first aggregation level set supports aggregation level 4, 8 and 16). Accordingly, since the aggregation levels in a second aggregation level set should be equal to or higher than those in the first aggregation level set, UE  101  determines the maximum aggregation level as 16 for a second search space set of the second CORESET CT 2 . The CCE indices for each candidate of each aggregation level of the second aggregation level set are listed in the following table: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 CCE indices 
                 CCE indices 
                 CCE indices 
                 CCE indices 
               
               
                 Aggregation 
                 of 1 st   
                 of 2 nd   
                 of 3 rd   
                 of 4 th   
               
               
                 Level 
                 candidate 
                 candidate 
                 candidate 
                 candidate 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 4 
                 0, 1, 2, 
                 4, 5, 6, 
                 8, 9, 10, 
                 12, 13, 14, 
               
               
                   
                 3 
                 7 
                 11 
                 15 
               
               
                 8 
                 0, 1, 2, 
                 8, 9, 10, 
                 null 
                 null 
               
               
                   
                 3, 4, 5, 
                 11, 12, 13, 
               
               
                   
                 6, 7 
                 14, 15 
               
               
                 16 
                 0, 1, 2, 
                 null 
                 null 
                 null 
               
               
                   
                 3, 4, 5, 6, 
               
               
                   
                 7, 8, 9, 10, 
               
               
                   
                 11, 12, 13, 14, 
               
               
                   
                 15 
               
               
                   
               
            
           
         
       
     
     Please refer to  FIG.  5 A  for some implementations of determining the second CORESET CT 2  based on the first CORESET CT 1  including the CORESET 0 . In detail, after UE  101  receives MIB information including a configuration of the CORESET 0  from BS  102 , UE  101  can retrieve the following information from the configuration: (1) the frequency domain size of the CORESET 0  includes 48 PRBs; and (2) the time domain size of the CORESET 0  includes 2 OFDM symbols. Then, UE  101 /BS  102  respectively determines the second CORESET CT 2  according to: (1) the configuration of CORESET 0 ; (2) a pre-defined frequency domain size, which includes 24 PRBs, of the second CORESET CT 2 ; and (3) a pre-defined time domain size, which includes 4 OFDM symbols of 2 resource units, of the second CORESET 
     Particularly, as for the CORESET 0  of these implementations, n shift  is configured as 12, N REG   CORESET  is configured as 48*2=96 and L is configured as 6. Therefore, CCE 0  of the CORESET 0  maps to REGB 12 . Further, the mapping relation of CCE-to-REG of the CORESET 0  is defined as:
         CCE 0  (C 0  as shown in  FIG.  5 A ) maps to REGB 12  (R 12  as shown in  FIG.  5 A )   CCE 2  (C 2  as shown in  FIG.  5 A ) maps to REGB 13  (R 13  as shown in  FIG.  5 A )   CCE 4  (C 4  as shown in  FIG.  5 A ) maps to REGB 14  (R 14  as shown in  FIG.  5 A )   CCE 6  (C 6  as shown in  FIG.  5 A ) maps to REGB 15  (R 15  as shown in  FIG.  5 A )   CCE 8  (C 8  as shown in  FIG.  5 A ) maps to REGB 0  (R 0  as shown in  FIG.  5 A )   CCE 10  (C 10  as shown in  FIG.  5 A ) maps to REGB 1  (R 1  as shown in  FIG.  5 A )   CCE 12  (C 12  as shown in  FIG.  5 A ) maps to REGB 2  (R 2  as shown in  FIG.  5 A )   CCE 14  (C 14  as shown in  FIG.  5 A ) maps to REGB 3  (R 3  as shown in  FIG.  5 A )   CCE 1  (C 1  as shown in  FIG.  5 A ) maps to REGB 4  (R 4  as shown in  FIG.  5 A )   CCE 3  (C 3  as shown in  FIG.  5 A ) maps to REGB 5  (R 5  as shown in  FIG.  5 A )   CCE 5  (C 5  as shown in  FIG.  5 A ) maps to REGB 6  (R 6  as shown in  FIG.  5 A )   CCE 7  (C 7  as shown in  FIG.  5 A ) maps to REGB 7  (R 7  as shown in  FIG.  5 A )   CCE 9  (C 9  as shown in  FIG.  5 A ) maps to REGB 8  (R 8  as shown in  FIG.  5 A )   CCE 11  (C 11  as shown in  FIG.  5 A ) maps to REGB 9  (R 9  as shown in  FIG.  5 A )   CCE 13  (C 13  as shown in  FIG.  5 A ) maps to REGB 10  (R 10  as shown in  FIG.  5 A )   CCE 15  (C 15  as shown in  FIG.  5 A ) maps to REGB 11  (R 11  as shown in  FIG.  5 A )       

     Accordingly, as for the second CORESET CT 2 : (1) in time domain, UE  101  determines that a first OFDM symbol s 0  of the second CORESET CT 2  starts from a first OFDM symbol S 0  of the CORESET 0 ; and (2) in frequency domain, because frequency band of the second CORESET CT 2  is not within (i.e., partially overlapped) frequency band of the CORESET 0  when the initial PRB P 2  of the second CORESET CT 2  is allocated as an initial PRB P 1  of CCE 0  of the CORESET 0 , UE  101  determines that the initial PRB P 2  of the second CORESET CT 2  is allocated as an initial PRB P 1  of CCE 1  of the CORESET 0  as shown in  FIG.  5 B . 
     Further, the second CORESET CT 2  includes two resource units RU 0  and RU 1 . The number of OFDM symbols of each resource unit is the same as the number of OFDM symbols of the CORESET 0 , which is 2 in these implementations. Each resource unit includes 8 REGBs. Therefore, resource units RU 0  and RU 1  include 16 REGBs. The REGBs of the second CORESET CT 2  are: (1) sequentially indexed in each resource unit; and (2) sequentially indexed from one resource unit to another resource unit. Accordingly, 16 REGBs are indexed as REGB 0  to REGB 15  as shown in  FIG.  5 B  (r 0  to r 15  as shown in  FIG.  5 B ). 
     Next, because the initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 1  of the CORESET 0 , n shift  is configured as N_RegBundle/2 which is 16/2=8. Therefore, a mapping relation of CCE-to-REG of the second CORESET CT 2  is defined as:
         CCE 1  (c 1  as shown in  FIG.  5 B ) maps to REGB 0  (r 0  as shown in  FIG.  5 B )   CCE 3  (c 3  as shown in  FIG.  5 B ) maps to REGB 1  (r 1  as shown in  FIG.  5 B )   CCE 5  (c 5  as shown in  FIG.  5 B ) maps to REGB 2  (r 2  as shown in  FIG.  5 B )   CCE 7  (c 7  as shown in  FIG.  5 B ) maps to REGB 3  (r 3  as shown in  FIG.  5 B )   CCE 9  (c 9  as shown in  FIG.  5 B ) maps to REGB 4  (r 4  as shown in  FIG.  5 B )   CCE 11  (c 11  as shown in  FIG.  5 B ) maps to REGB 5  (r 5  as shown in  FIG.  5 B )   CCE 13  (c 13  as shown in  FIG.  5 B ) maps to REGB 6  (r 6  as shown in  FIG.  5 B )   CCE 15  (c 15  as shown in  FIG.  5 B ) maps to REGB 7  (r 7  as shown in  FIG.  5 B )   CCE 0  (c 0  as shown in  FIG.  5 B ) maps to REGB 8  (r 8  as shown in  FIG.  5 B )   CCE 2  (c 2  as shown in  FIG.  5 B ) maps to REGB 9  (r 9  as shown in  FIG.  5 B )   CCE 4  (c 4  as shown in  FIG.  5 B ) maps to REGB 10  (r 10  as shown in  FIG.  5 B )   CCE 6  (c 6  as shown in  FIG.  5 B ) maps to REGB 11  (r 11  as shown in  FIG.  5 B )   CCE 8  (c 8  as shown in  FIG.  5 B ) maps to REGB 12  (r 12  as shown in  FIG.  5 B )   CCE 10  (c 10  as shown in  FIG.  5 B ) maps to REGB 13  (r 13  as shown in  FIG.  5 B )   CCE 12  (c 12  as shown in  FIG.  5 B ) maps to REGB 14  (r 14  as shown in  FIG.  5 B )   CCE 14  (c 14  as shown in  FIG.  5 B ) maps to REGB 15  (r 15  as shown in  FIG.  5 B )       

     In these implementations, a first search space set corresponding to a first set of aggregation levels is designated to the CORESET 0 . In detail, because the CORESET 0  includes 16 REGBs, the first aggregation level set supports aggregation level 16 at most (i.e., the first aggregation level supports aggregation level 4, 8 and 16). Accordingly, since the aggregation levels in a second aggregation level should be equal to or higher than those in the first aggregation level set, UE  101  determines the maximum aggregation level as 16 for a second search space set of the second CORESET CT 2 . The CCE indices for each candidate of each aggregation level of the second aggregation level are listed in the following table: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 CCE indices 
                 CCE indices 
                 CCE indices 
                 CCE indices 
               
               
                 Aggregation 
                 of 1 st   
                 of 2 nd   
                 of 3 rd   
                 of 4 th   
               
               
                 Level 
                 candidate 
                 candidate 
                 candidate 
                 candidate 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 4 
                 0, 1, 2, 
                 4, 5, 6, 
                 8, 9, 10, 
                 12, 13, 14, 
               
               
                   
                 3 
                 7 
                 11 
                 15 
               
               
                 8 
                 0, 1, 2, 
                 8, 9, 10, 
                 null 
                 null 
               
               
                   
                 3, 4, 5, 
                 11, 12, 13, 
               
               
                   
                 6, 7 
                 14, 15 
               
               
                 16 
                 0, 1, 2, 
                 null 
                 null 
                 null 
               
               
                   
                 3, 4, 5, 
               
               
                   
                 6, 7, 8, 
               
               
                   
                 9, 10, 11, 
               
               
                   
                 12, 13, 14, 15 
               
               
                   
               
            
           
         
       
     
     Please refer to  FIG.  6    for some implementations of determining the second CORESET CT 2  based on the first CORESET CT 1  including the CORESET 0 . In detail, after UE  101  receives MIB information including a configuration of the CORESET 0  from BS  102 , UE  101  can retrieve the following information from the configuration: (1) the frequency domain size of the CORESET 0  includes 48 PRBs; and (2) the time domain size of the CORESET 0  includes 3 OFDM symbols. Then, UE  101 /BS  102  respectively determines the second CORESET CT 2  according to: (1) the configuration of CORESET 0 ; (2) a pre-defined frequency domain size, which includes 24 PRBs, of the second CORESET CT 2 ; and (3) a pre-defined time domain size, which includes 4 OFDM symbols of 2 resource units, of the second CORESET CT 2 . 
     Particularly, as for the CORESET 0  of these implementations, n shift  is configured as 8, N REG   CORESET  is configured as 48*3=144 and L is configured as 6, i.e., one REGB contains 6 REGs. Therefore, CCE 0  of the CORESET 0  maps to REGB 8 . Accordingly, the mapping relation of CCE-to-REG of the CORESET 0  is defined as:
         CCE 0  (C 0  as shown in  FIG.  6   ) maps to REGB 8  (R 8  as shown in  FIG.  6   )   CCE 2  (C 2  as shown in  FIG.  6   ) maps to REGB 9  (R 9  as shown in  FIG.  6   )   CCE 4  (C 4  as shown in  FIG.  6   ) maps to REGB 10  (R 10  as shown in  FIG.  6   )   CCE 6  (C 6  as shown in  FIG.  6   ) maps to REGB 11  (R 11  as shown in  FIG.  6   )   CCE 8  (C 8  as shown in  FIG.  6   ) maps to REGB 12  (R 12  as shown in  FIG.  6   )   CCE 10  (C 10  as shown in  FIG.  6   ) maps to REGB 13  (R 13  as shown in  FIG.  6   )   CCE 12  (C 12  as shown in  FIG.  6   ) maps to REGB 14  (R 14  as shown in  FIG.  6   )   CCE 14  (C 14  as shown in  FIG.  6   ) maps to REGB 15  (R 15  as shown in  FIG.  6   )   CCE 16  (C 16  as shown in  FIG.  6   ) maps to REGB 16  (R 16  as shown in  FIG.  6   )   CCE 18  (C 18  as shown in  FIG.  6   ) maps to REGB 17  (R 17  as shown in  FIG.  6   )   CCE 20  (C 20  as shown in  FIG.  6   ) maps to REGB 18  (R 18  as shown in  FIG.  6   )   CCE 22  (C 22  as shown in  FIG.  6   ) maps to REGB 19  (R 19  as shown in  FIG.  6   )   CCE 1  (C 1  as shown in  FIG.  6   ) maps to REGB 20  (R 20  as shown in  FIG.  6   )   CCE 3  (C 3  as shown in  FIG.  6   ) maps to REGB 21  (R 21  as shown in  FIG.  6   )   CCE 5  (C 5  as shown in  FIG.  6   ) maps to REGB 22  (R 22  as shown in  FIG.  6   )   CCE 7  (C 7  as shown in  FIG.  6   ) maps to REGB 23  (R 23  as shown in  FIG.  6   )   CCE 9  (C 9  as shown in  FIG.  6   ) maps to REGB 0  (R 0  as shown in  FIG.  6   )   CCE 11  (C 11  as shown in  FIG.  6   ) maps to REGB 1  (R 1  as shown in  FIG.  6   )   CCE 13  (C 13  as shown in  FIG.  6   ) maps to REGB 2  (R 2  as shown in  FIG.  6   )   CCE 15  (C 15  as shown in  FIG.  6   ) maps to REGB 3  (R 3  as shown in  FIG.  6   )   CCE 17  (C 17  as shown in  FIG.  6   ) maps to REGB 4  (R 4  as shown in  FIG.  6   )   CCE 19  (C 19  as shown in  FIG.  6   ) maps to REGB 5  (R 5  as shown in  FIG.  6   )   CCE 21  (C 21  as shown in  FIG.  6   ) maps to REGB 6  (R 6  as shown in  FIG.  6   )   CCE 23  (C 23  as shown in  FIG.  6   ) maps to REGB 7  (R 7  as shown in  FIG.  6   )       

     Accordingly, as for the second CORESET CT 2 : (1) in time domain, UE  101  determines that a first OFDM symbol s 0  of the second CORESET CT 2  starts from a first OFDM symbol S 0  of the CORESET 0 ; and (2) in frequency domain, because frequency band of the second CORESET CT 2  is within frequency band of the CORESET 0  when the initial PRB P 2  of the second CORESET CT 2  is allocated as an initial PRB P 1  of CCE 0  of the CORESET 0 , UE  101 /BS  102  determines that the initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 0  of the CORESET 0 . 
     Further, the second CORESET CT 2  includes two resource units RU 0  and RU 1 . The number of OFDM symbols of the first resource unit RU 0  is the same as the number of OFDM symbols of the CORESET 0 , which is 3 in these implementations. The first resource unit RU 0  includes 12 REGBs. The number of OFDM symbols of the second resource unit RU 1  is 1 in these implementations. The second resource unit RU 1  includes 4 REGBs. Therefore, resource units RU 0  and RU 1  include 16 REGBs. The REGBs of the second CORESET CT 2  are: (1) sequentially indexed in each resource unit; and (2) sequentially indexed from one resource unit to another resource unit. Accordingly, 16 REGBs are indexed as REGB 0  to REGB 15  (r 0  to r 15  as shown in  FIG.  6   ). 
     Next, because the initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 0  of the CORESET 0 , n shift  is configured as 0. Therefore, a mapping relation of CCE-to-REG of the second CORESET CT 2  is defined as:
         CCE 0  (c 0  as shown in  FIG.  6   ) maps to REGB 0  (r 0  as shown in  FIG.  6   )   CCE 2  (c 2  as shown in  FIG.  6   ) maps to REGB 1  (r 1  as shown in  FIG.  6   )   CCE 4  (c 4  as shown in  FIG.  6   ) maps to REGB 2  (r 2  as shown in  FIG.  6   )   CCE 6  (c 6  as shown in  FIG.  6   ) maps to REGB 3  (r 3  as shown in  FIG.  6   )   CCE 8  (c 8  as shown in  FIG.  6   ) maps to REGB 4  (r 4  as shown in  FIG.  6   )   CCE 10  (c 10  as shown in  FIG.  6   ) maps to REGB 5  (r 5  as shown in  FIG.  6   )   CCE 12  (c 12  as shown in  FIG.  6   ) maps to REGB 6  (r 6  as shown in  FIG.  6   )   CCE 14  (c 14  as shown in  FIG.  6   ) maps to REGB 7  (r 7  as shown in  FIG.  6   )   CCE 1  (c 1  as shown in  FIG.  6   ) maps to REGB 8  (r 8  as shown in  FIG.  6   )   CCE 3  (c 3  as shown in  FIG.  6   ) maps to REGB 9  (r 9  as shown in  FIG.  6   )   CCE 5  (c 5  as shown in  FIG.  6   ) maps to REGB 10  (r 10  as shown in  FIG.  6   )   CCE 7  (c 7  as shown in  FIG.  6   ) maps to REGB 11  (r 11  as shown in  FIG.  6   )   CCE 9  (c 9  as shown in  FIG.  6   ) maps to REGB 12  (r 12  as shown in  FIG.  6   )   CCE 11  (c 11  as shown in  FIG.  6   ) maps to REGB 13  (r 13  as shown in  FIG.  6   )   CCE 13  (c 13  as shown in  FIG.  6   ) maps to REGB 14  (r 14  as shown in  FIG.  6   )   CCE 15  (c 15  as shown in  FIG.  6   ) maps to REGB 15  (r 15  as shown in  FIG.  6   )       

     In these implementations, a first search space set corresponding to a first set of aggregation levels is designated to the CORESET 0 . In detail, because the CORESET 0  includes 24 REGBs, the first aggregation level supports aggregation level 16 at most (i.e., the first aggregation level supports aggregation level 4, 8 and 16). Accordingly, since the aggregation levels of a second aggregation level should be equal to or higher than those in the first aggregation level set, UE  101  determines the maximum aggregation level as 16 for a second search space set of the second CORESET CT 2 . The CCE indices for each candidate of each aggregation level of the second aggregation level are listed in the following table: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 CCE indices 
                 CCE indices 
                 CCE indices 
                 CCE indices 
               
               
                 Aggregation 
                 of 1 st   
                 of 2 nd   
                 of 3 rd   
                 of 4 th   
               
               
                 Level 
                 candidate 
                 candidate 
                 candidate 
                 candidate 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 4 
                 0, 1, 2, 
                 4, 5, 6, 
                 8, 9, 10, 
                 12, 13, 14, 
               
               
                   
                 3 
                 7 
                 11 
                 15 
               
               
                 8 
                 0, 1, 2, 
                 8, 9, 10, 
                 null 
                 null 
               
               
                   
                 3, 4, 5, 
                 11, 12, 13, 
               
               
                   
                 6, 7 
                 14, 15 
               
               
                 16 
                 0, 1, 2, 
                 null 
                 null 
                 null 
               
               
                   
                 3, 4, 5, 
               
               
                   
                 6, 7, 8, 
               
               
                   
                 9, 10, 11, 
               
               
                   
                 12, 13, 14, 15 
               
               
                   
               
            
           
         
       
     
     Please refer to  FIG.  7    for some implementations of determining the second CORESET CT 2  based on the first CORESET CT 1  including the CORESET 0 . In detail, after UE  101  receives MIB information including a configuration of the CORESET 0  from BS  102 , UE  101  can retrieve the following information from the configuration: (1) the frequency domain size of the CORESET 0  includes 24 PRBs; and (2) the time domain size of the CORESET 0  includes 2 OFDM symbols. Then, UE  101 /BS  102  respectively determines the second CORESET CT 2  according to: (1) the configuration of CORESET 0 ; (2) a pre-defined frequency domain size, which includes 24 PRBs, of the second CORESET CT 2 ; and (3) a pre-defined time domain size, which includes 3 OFDM symbols of 2 resource units, of the second CORESET CT 2 . 
     Particularly, as for the CORESET 0  of these implementations, n shift  is configured as 5, N REG   CORESET  is configured as 24*2=48 and L is configured as 6. Therefore, CCE 0  of the CORESET 0  maps to REGB 5 . Further, the mapping relation of CCE-to-REG of the CORESET 0  is defined as:
         CCE 0  (C 0  as shown in  FIG.  6   ) maps to REGB 5  (R 5  as shown in  FIG.  6   )   CCE 2  (C 2  as shown in  FIG.  6   ) maps to REGB 6  (R 6  as shown in  FIG.  6   )   CCE 4  (C 4  as shown in  FIG.  6   ) maps to REGB 7  (R 7  as shown in  FIG.  6   )   CCE 6  (C 6  as shown in  FIG.  6   ) maps to REGB 0  (R 0  as shown in  FIG.  6   )   CCE 1  (C 1  as shown in  FIG.  6   ) maps to REGB 1  (R 1  as shown in  FIG.  6   )   CCE 3  (C 3  as shown in  FIG.  6   ) maps to REGB 2  (R 2  as shown in  FIG.  6   )   CCE 5  (C 5  as shown in  FIG.  6   ) maps to REGB 3  (R 3  as shown in  FIG.  6   )   CCE 7  (C 7  as shown in  FIG.  6   ) maps to REGB 4  (R 4  as shown in  FIG.  6   )       

     Accordingly, as for the second CORESET CT 2 : (1) in time domain, UE  101  determines that a first OFDM symbol s 0  of the second CORESET CT 2  starts from a first OFDM symbol S 0  of the CORESET 0 ; and (2) in frequency domain, because frequency band of the second CORESET CT 2  is equal to frequency band of the CORESET 0  when the initial PRB P 2  of the second CORESET CT 2  is allocated as an initial PRB P 1  of CCE 0  of the CORESET 0 , UE  101  determines that the initial PRB P 2  of the second CORESET CT 2  is allocated as the initial PRB P 1  of CCE 0  of the CORESET 0 . 
     In some implementations, when frequency band of the second CORESET CT 2  is equal to frequency band of the CORESET 0 , a mapping relation of CCE-to-REG of the second CORESET CT 2  in a first resource unit RU 0  is the same as the mapping relation of CCE-to-REG of the CORESET 0 , which is as following:
         CCE 0  (c 0  as shown in  FIG.  6   ) maps to REGB 5  (r 5  as shown in  FIG.  6   )   CCE 2  (c 2  as shown in  FIG.  6   ) maps to REGB 6  (r 6  as shown in  FIG.  6   )   CCE 4  (c 4  as shown in  FIG.  6   ) maps to REGB 7  (r 7  as shown in  FIG.  6   )   CCE 6  (c 6  as shown in  FIG.  6   ) maps to REGB 0  (r 0  as shown in  FIG.  6   )   CCE 1  (c 1  as shown in  FIG.  6   ) maps to REGB 1  (r 1  as shown in  FIG.  6   )   CCE 3  (c 3  as shown in  FIG.  6   ) maps to REGB 2  (r 2  as shown in  FIG.  6   )   CCE 5  (c 5  as shown in  FIG.  6   ) maps to REGB 3  (r 3  as shown in  FIG.  6   )   CCE 7  (c 7  as shown in  FIG.  6   ) maps to REGB 4  (r 4  as shown in  FIG.  6   )       

     In some implementations, CCEs and REGBs in a second resource unit RU 1  are sequentially indexed and a mapping relation of CCE-to-REG of the second CORESET CT 2  in the second resource unit RU 1  is defined as following:
         CCE 8  (c 8  as shown in  FIG.  6   ) maps to REGB 8  (r 9  as shown in  FIG.  6   )   CCE 9  (c 9  as shown in  FIG.  6   ) maps to REGB 9  (r 9  as shown in  FIG.  6   )   CCE 10  (c 10  as shown in  FIG.  6   ) maps to REGB 10  (r 10  as shown in  FIG.  6   )   CCE 11  (c 11  as shown in  FIG.  6   ) maps to REGB 11  (r 11  as shown in  FIG.  6   )       

     In these implementations, a first search space set corresponding to a first set of aggregation levels is designated to the CORESET 0 . In detail, because the CORESET 0  includes 8 REGBs, the first aggregation level set supports aggregation level 8 at most (i.e., the first aggregation level supports aggregation level 4 and 8). Accordingly, since the aggregation levels in a second aggregation level should be equal to or higher than those in the first aggregation level set, UE  101  determines the maximum aggregation level as 8 for a second search space set of the second CORESET CT 2 . The CCE indices for each candidate of each aggregation level of the second aggregation level are listed in the following table: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 CCE indices 
                 CCE indices 
                 CCE indices 
                 CCE indices 
               
               
                 Aggregation 
                 of 1 st   
                 of 2 nd   
                 of 3 rd   
                 of 4 th   
               
               
                 Level 
                 candidate 
                 candidate 
                 candidate 
                 candidate 
               
               
                   
               
             
            
               
                 4 
                 0, 1, 2, 
                 4, 5, 6, 
                 null 
                 null 
               
               
                   
                 3 
                 7 
               
               
                 8 
                 0, 1, 2, 
                 null 
                 null 
                 null 
               
               
                   
                 3, 4, 5, 
               
               
                   
                 6, 7 
               
               
                   
               
            
           
         
       
     
     In some implementations, because the number (i.e., 12) of CCEs of the second CORESET CT 2  is greater than 8, another aggregation level may be introduced as following: 
     
       
         
           
               
               
               
               
               
             
               
                   
               
               
                   
                 CCE indices 
                 CCE indices 
                 CCE indices 
                 CCE indices 
               
               
                 Aggregation 
                 of 1 st   
                 of 2 nd   
                 of 3 rd   
                 of 4 th   
               
               
                 Level 
                 candidate 
                 candidate 
                 candidate 
                 candidate 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 4 
                 0, 1, 2, 
                 4, 5, 6, 
                 null 
                 null 
               
               
                   
                 3 
                 7 
               
               
                 8 
                 0, 1, 2, 
                 null 
                 null 
                 null 
               
               
                   
                 3, 4, 5, 
               
               
                   
                 6, 7 
               
               
                 12 
                 0, 1, 2, 
                 null 
                 null 
                 null 
               
               
                   
                 3, 4, 5, 
               
               
                   
                 6, 7, 8, 
               
               
                   
                 9, 10, 11 
               
               
                   
               
            
           
         
       
     
       FIG.  8    illustrates a flow chart of a method for wireless communications in accordance with some embodiments of the present application. Referring to  FIG.  8   , method  800  is performed by a UE (e.g., UE  101 ) and a BS (e.g., BS  102 ) in some embodiments of the present application. 
     Operation S 801  is executed to transmit, by BS, configuration of a first CORESET to UE. Operation S 802  is executed to receive, by UE the configuration information from BS. Operations S 803  and S 804  are executed to determine, by UE and BS respectively, a second CORESET based on the first CORESET. In some embodiments, an initial PRB of the second CORESET may be allocated as an initial PRB of a specific CCE of the first CORESET. It should be noted that BS  102  may execute operation S 804  after executing S 801 . 
     In some embodiments, the initial PRB of the second CORESET may be allocated as the initial PRB of the specific CCE of the first CORESET when a frequency band of the second CORESET is within a frequency band of the first CORESET. 
     In some implementations, the first CORESET may include a CORESET 0  and the specific CCE of the first CORESET include an initial CCE of the CORESET 0  (i.e., CCE 0  of CORESET 0 ). In the second CORESET, an initial CCE of the second CORESET is mapped to an initial REGB of the second CORESET. 
     In some embodiments, the CCEs of the second CORESET may be mapped to the CCEs of the first CORESET. The mapping could be either 1-to-1 mapping or many-to-one mapping. 
     In some implementations, the first CORESET may include the CORESET 0  and the specific CCE of the first CORESET may have a CCE offset from the initial CCE of the CORESET 0 . In these implementations, the CCE offset is 1 and the specific CCE is CCE 1 . In the second CORESET, an initial CCE of the second CORESET is mapped to an REGB of the second CORESET and the index of the initial CCE maps to an index of the REGB based on the following formula:
         REGBindex=(N_RegBundle/2) mod (N REG   CORESET /L)
 
wherein REGBindex represents the index of the REGB, N_RegBundle represents a number of REGBs of the first CORESET, N REG   CORESET  represents a number of REGs of the first CORESET and L represents a number of REGs in one REGB.
       

     In some implementations, the initial PRB of the second CORESET may be allocated as the initial PRB of an REGB of the first CORESET. In detail, the initial PRB of the second CORESET may be allocated as the initial PRB of the REGB of the first CORESET when a frequency band of the second CORESET is within a frequency band of the first CORESET. In these implementations, the first CORESET may include a CORESET 0  and the REGB may include an initial REG of the CORESET 0  (i.e., REGB 0  of CORESET 0 ). 
     In some implementations, the second CORESET may include at least one resource unit defined in time domain. In detail, a time duration (i.e., OFDM symbols) of one of the at least one resource unit may the same as a time duration (i.e., OFDM symbols) of the first CORESET. The second CORESET may include a plurality of REGBs, and the REGBs are sequentially indexed in the at least one resource unit. In addition, a first REGB of the REGBs of the second CORESET may include same number of REGs as an REGB in the first CORESET in time domain and in frequency domain respectively. 
     Further, the at least one resource unit includes a first resource unit and a mapping relation of CCE-to-REG of the first resource unit of the second CORESET may be the same as a mapping relation of CCE-to-REG of the first CORESET. The at least one resource unit may include a second resource unit and a mapping relation of CCE-to-REGB of the second resource unit of the second CORESET is with same index. 
     In some implementations, BS may transmit the configuration of the first CORESET further with a first search space set. The first search space set corresponds to a first aggregation level. For example, when the first CORESET includes the CORESET 0 , the configuration of the first CORESET may include search space zero and the first aggregation level may include aggregation level 4, 8 and 16 which correspond to number of CCE candidates 4, 2 and 1 respectively. Next, UE may receive the configuration of the first CORESET and the first search space set. UE/BS may determine a second aggregation level for a second search space set of the second CORESET. In these implementations, the second aggregation level may be equal to or higher than the first aggregation level. 
       FIG.  9    illustrates an example block diagram of an apparatus  9  according to an embodiment of the present disclosure. 
     As shown in  FIG.  9   , the apparatus  9  may include at least one non-transitory computer-readable medium (not illustrated in  FIG.  9   ), a receiving circuitry  91 , a transmitting circuitry  93 , and a processor  95  coupled to the non-transitory computer-readable medium (not illustrated in  FIG.  9   ), the receiving circuitry  91  and the transmitting circuitry  93 . The apparatus  9  may be a user equipment or a base station. 
     Although in this figure, elements such as processor  95 , transmitting circuitry  93 , and receiving circuitry  91  are described in the singular, the plural is contemplated unless limitation to the singular is explicitly stated. In some embodiments of the present disclosure, the receiving circuitry  91  and the transmitting circuitry  93  are combined into a single device, such as a transceiver. In certain embodiments of the present disclosure, the apparatus  9  may further include an input device, a memory, and/or other components. 
     In some embodiments of the present disclosure, the non-transitory computer-readable medium may have stored thereon computer-executable instructions to cause a processor to implement the method with respect to the base station as described above. For example, the computer-executable instructions, when executed, cause the processor  95  interacting with receiving circuitry  91  and transmitting circuitry  93 , so as to perform the operations with respect to BS depicted in  FIGS.  1  to  2 A . 
     In some embodiments of the present disclosure, the non-transitory computer-readable medium may have stored thereon computer-executable instructions to cause a processor to implement the method with respect to the user equipment as described above. For example, the computer-executable instructions, when executed, cause the processor  9  interacting with receiving circuitry  91  and transmitting circuitry  93 , so as to perform the operations with respect to UE depicted in  FIGS.  1  to  2 A . 
     Those having ordinary skill in the art would understand that the operations of a method described in connection with the aspects disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. Additionally, in some aspects, the steps of a method may reside as one or any combination or set of codes and/or instructions on a non-transitory computer-readable medium, which may be incorporated into a computer program product. 
     While this disclosure has been described with specific embodiments thereof, it is evident that many alternatives, modifications, and variations may be apparent to those skilled in the art. For example, various components of the embodiments may be interchanged, added, or substituted in the other embodiments. Also, all of the elements of each figure are not necessary for operation of the disclosed embodiments. For example, one of ordinary skill in the art of the disclosed embodiments would be enabled to make and use the teachings of the disclosure by simply employing the elements of the independent claims. Accordingly, embodiments of the disclosure as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the disclosure. 
     In this document, the terms “includes”, “including”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “a”, “an”, or the like does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that includes the element. Also, the term “another” is defined as at least a second or more. The term “having” and the like, as used herein, are defined as “including”.