Patent Publication Number: US-11659561-B2

Title: Wireless communication method, eNode B, and user equipment

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to the field of wireless communication, and in particular, to wireless communication methods, an eNode B (eNB), and a user equipment (UE). 
     2. Description of the Related Art 
     Machine-Type Communication (MTC) is a new type of communication in 3GPP in release 12 and an important revenue stream for operators. The coverage enhancement technique is quite useful for some MTC UEs like sensors in the basement which has large loss on signal strength due to penetration loss. For MTC with coverage enhancement, repetition is a basic solution to enhance the coverage. 
     SUMMARY 
     One non-limiting and exemplary embodiment provides an approach to design downlink control information (DCI) for a UE which may need coverage enhancement. 
     In one general aspect, the techniques disclosed here feature a wireless communication method performed by an eNode B (eNB), including: transmitting downlink control information (DCI) to a user equipment (UE), wherein the DCI is designed based on a coverage enhancement level for the UE. 
     It should be noted that general or specific embodiments may be implemented as a system, a method, an integrated circuit, a computer program, a storage medium, or any selective combination thereof. 
     Additional benefits and advantages of the disclosed embodiments will become apparent from the specification and drawings. The benefits and/or advantages may be individually obtained by the various embodiments and features of the specification and drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    schematically illustrates a flowchart of a wireless communication method for an eNB according to an embodiment of the present disclosure; 
         FIG.  2    schematically illustrates a flowchart of a wireless communication method for a UE according to an embodiment of the present disclosure; 
         FIG.  3    schematically illustrates a block diagram of an eNB for wireless communication according to an embodiment of the present disclosure; and 
         FIG.  4    schematically illustrates a block diagram of a UE for wireless communication according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings, which form a part thereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. It will be readily understood that the aspects of the present disclosure can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure. 
     In the present disclosure, MTC may be taken as an example to describe the principle of the present disclosure; however, it is noted that the wireless communication methods disclosed in the present disclosure can not only be applied to MTC, but also be applied to other wireless communications such as other communications conforming to LTE specifications as long as those wireless communications may require coverage enhancement (CE). Accordingly, the UEs are not limited to MTC UEs, but can be any other UEs that can perform the communication methods described in the present disclosure. 
     For wireless communication with coverage enhancement (for example, 15 dB for MTC), repetitions of a channel to be transmitted (e.g. Physical Downlink Shared Channel (PDSCH) or Physical Uplink Shared Channel (PUSCH)) can be a basic solution to enhance the coverage. The downlink control information (DCI) for a channel with coverage enhancement may need to indicate resource assignment in both time and frequency domains. How to design DCI with relatively small size to for example assign resources for such a channel with coverage enhancement becomes an important issue of the wireless communication with coverage enhancement. 
     For example, for a MTC UE, DCI size is quite important as it heavily impacts active time of the UE. Active time means the period that the UE&#39;s RF/baseband is keeping working status to transmit or receive physical signals. It reflects the UE&#39;s power consumption and is mainly related with repetitions in the time domain. Smaller DCI size can mean that the UE will use less time to receive the DCI. For example, assuming each repetition of a small DCI is transmitted by one ECCE (Enhanced Control Channel Element, 36 REs (Resource Element) per ECCE), QPSK (Quadrature Phase Shift Keying), ⅓ coding rate and full occupation of narrowband (6 PRBs) are used, and total repetition times are 96, then the UE only needs 4 subframes to receive such DCI. 
     However, assuming one PRB pair transmits each repetition of DCI with larger size, full occupation of narrowband is used, and total repetition times are 96, then the UE will need 16 subframes to receive such DCI. So it is meaningful to design DCI with smaller size. Such DCI could also be transmitted by less resource like one ECCE instead of one PRB pair. 
     Furthermore, one ECCE can only carry 24 bits, which also means it can only support 8-bit payload size assuming CRC (Cyclic Redundancy Check) uses 16 bits. So DCI payload size requirement is quite tight assuming less resource like one ECCE to transmit DCI. A 1-bit or 2-bit increase will require more ECCEs for DCI transmission. 
     In view of the above, how to design DCI with relatively small size for such a channel with coverage enhancement is an important issue for the wireless communication with coverage enhancement. 
     An embodiment of the present disclosure provides a wireless communication method  100  performed by an eNB, as shown in  FIG.  1    which schematically illustrates a flowchart of the wireless communication method  100  according to an embodiment of the present disclosure. The wireless communication method  100  can include step  101  of transmitting DCI to a UE, wherein the DCI is designed based on a coverage enhancement level for the UE. 
     Situations of UEs with CE may be different due to environment, distance to the eNB, penetration loss, and so on. Therefore, the wireless communication design may need to consider different coverage enhancement levels like 5 dB, 10 dB, and 15 dB. Accordingly, the DCI can be designed based on the coverage enhancement level for the UE. It is noted that, if any field (for example, a resource assignment field) in the DCI is designed based on the coverage enhancement level, the DCI is considered to be designed based on the coverage enhancement level. For example, as described later in detail, a resource assignment field in DCI contains an index associated with the coverage enhancement level, and thus such DCI is considered to be designed based on the coverage enhancement level. 
     In an exemplary embodiment, the DCI can use different sizes for different sets of coverage enhancement levels. For example, the coverage enhancement levels can be divided into two sets by comparing the coverage enhancement levels with a predetermined level. If a coverage enhancement level is larger than the predetermined level, the coverage enhancement level is considered to be a large coverage enhancement level and is assigned to a large CE level set. If a coverage enhancement level is smaller than the predetermined level, the coverage enhancement level is considered to be a small coverage enhancement level and is assigned to a small CE level set. The coverage enhancement level of a UE can be configured by the RRC layer, and the predetermined level can be specified or configured by the RRC layer. 
     For example, for a small coverage enhancement level, a payload size of 26 bits for the DCI can be used; and for a large coverage enhancement level, a payload size of 11 bits for the DCI can be used. 
     Table 1 indicates that two different DCIs (DCI 1 and DCI 2) are designed for small coverage enhancement levels and large coverage enhancement levels respectively. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 DCI 2 (large enhancement 
               
               
                   
                   
                 level) 
               
               
                   
                 DCI 1 (small coverage 
                 Target is to reduce DCI size as 
               
               
                   
                 enhancement level) 
                 much as possible 
               
               
                   
               
             
            
               
                 Contents 
                 Resource indication (6 bits); 
                 Resource indication (6 bits); 
               
               
                   
                 MCS (5 bits); 
                 New data indicator (1 bit); 
               
               
                   
                 New data indicator (1 bit); 
                 MCS (2 bits); 
               
               
                   
                 Redundancy version (2 bits); 
                 HARQ process number (1 bit); 
               
               
                   
                 HARQ process number (3 
                 Antenna port(s), scrambling 
               
               
                   
                 bits); 
                 identity and number of layers  
               
               
                   
                 TPC command for PUCCH 
                 (1 bit) 
               
               
                   
                 (2 bits); 
                   
               
               
                   
                 Antenna port(s), scrambling 
                   
               
               
                   
                 identity and number of layers 
                   
               
               
                   
                 (3 bits); 
                   
               
               
                   
                 SRS request (1 bit); 
                   
               
               
                   
                 HARQ-ACK resource offset (2 
                   
               
               
                   
                 bits) 
                   
               
               
                 Payload  
                 26 bits 
                 11 bits 
               
               
                 size 
               
               
                   
               
            
           
         
       
     
     In the example of Table 1, DCI 2 for large CE level has much smaller size since many features like SRS request are not required. 
     Table 2 indicates that common DCI is designed for both small coverage enhancement levels and large coverage enhancement levels, but the field interpretation is different among different CE levels. 
     
       
         
           
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                 Common DCI (applied to all CE UEs) 
               
               
                   
               
             
            
               
                 Contents 
                 Resource indication (6 bits); 
               
               
                   
                 MCS (5 bits for small coverage enhancement level; 2 bits 
               
               
                   
                 for large coverage enhancement level); 
               
               
                   
                 New data indicator (1 bit); 
               
               
                   
                 Redundancy version (2 bits) - such field does not exist for 
               
               
                   
                 large coverage enhancement; 
               
               
                   
                 HARQ process number (3 bits for small coverage 
               
               
                   
                 enhancement level and 1 bit for large coverage 
               
               
                   
                 enhancement level); 
               
               
                   
                 TPC command for PUCCH (2 bits for small coverage 
               
               
                   
                 enhancement level and such field does not exist for large 
               
               
                   
                 coverage enhancement); 
               
               
                   
                 Antenna port(s), scrambling identity and number of layers 
               
               
                   
                 (3 bits for small coverage enhancement level and 1 bit for 
               
               
                   
                 large coverage enhancement); 
               
               
                   
                 SRS request (1 bit for small coverage enhancement level 
               
               
                   
                 and such field does not exist for large coverage 
               
               
                   
                 enhancement); 
               
               
                   
                 HARQ-ACK resource offset (2 bits for small coverage 
               
               
                   
                 enhancement level and such field does not exist for large 
               
               
                   
                 coverage enhancement) 
               
               
                 Payload size 
                 26 bits or 11 bits depending on the coverage 
               
               
                   
                 enhancement level 
               
               
                   
               
            
           
         
       
     
     As exemplarily shown in Table 1 and Table 2, when the DCI uses different sizes for different sets of coverage enhancement levels, the DCI for the large coverage enhancement levels can use much less bits. It is noted that the small coverage enhancement level herein also includes the case of no coverage enhancement. 
     In addition or alternatively, in an embodiment of the present disclosure, the coverage enhancement of a channel (e.g., PUSCH or PUSCH) scheduled by the DCI with the coverage enhancement level can be realized at least by repetitions in the time domain and/or repetitions in the frequency domain with a repetition number which represents the total number of repetitions of the channel, and a resource assignment field in the DCI uses a single index associated with the repetition number to jointly indicate resource assignment in both the time domain and the frequency domain. This embodiment is another exemplary way of designing the DCI based on the coverage enhancement level for the UE. 
     Repetition is an effective way to enhance the coverage of a channel. The repetition can happen in the time domain, for example, multiple subframes can be used to transmit a transport block repeatedly. The repetition can also happen in the frequency domain, for example, multiple PRBs in the frequency domain are used to transport a transport block. Aggregation in the frequency domain is a way of repetitions in the frequency domain. Obviously, the repetition can also happen in both the time domain and the frequency domain. The DCI scheduling a channel (e.g. PUSCH or PDCCH) requiring coverage enhancement may need to indicate resource assignment in both the time domain and the frequency domain. The resource assignment can be indicated in a resource assignment field. For example, the resource assignment field may need to indicate how many subframes and how many PRBs in the frequency domain are used for repetition. Optionally, the resource assignment field may also need to indicate the resource positions in the frequency domain. The total number of repetitions (the repetition number) can be the product of the subframe number in the time domain and the PRB number in the frequency domain in unit of PRB pair. For example, 100 repetitions (PRB pairs) can be reflected by 2 PRB×50 subframes, that is, the repetition number is 100. Alternatively, the repetition number can also be in unit of PRB. For example, 200 repetitions (PRBs) can be reflected by 2 PRB×100 slots (50 subframes). In the present disclosure, the unit of PRB pair is used to present the repetition number. 
     An example of resource assignment field design is separate indications for the time domain and the frequency domain. For example, one field is used to indicate the number of subframes in the time domain and another field is used to indicate the number and/or positions of PRBs in the frequency domain for example within the narrowband (6 PRBs). Table 3 illustrates one example of such separate indications. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                 Repetitions in 
                 Number of PRBs in 
                 Total PRB pair number 
               
               
                   
                 time domain 
                 frequency domain 
                 (repetition number) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                   
                 1 
                 1 
                 1 
               
               
                   
                 1 
                 2 
                 2 
               
               
                   
                 1 
                 3 
                 3 
               
               
                   
                 1 
                 4 
                 4 
               
               
                   
                 1 
                 5 
                 5 
               
               
                   
                 1 
                 6 
                 6 
               
               
                   
                 2 
                 1 
                 2 
               
               
                   
                 2 
                 2 
                 4 
               
               
                   
                 2 
                 3 
                 6 
               
               
                   
                 2 
                 4 
                 8 
               
               
                   
                 2 
                 5 
                 10 
               
               
                   
                 2 
                 6 
                 12 
               
               
                   
                 4 
                 1 
                 4 
               
               
                   
                 4 
                 2 
                 8 
               
               
                   
                 4 
                 3 
                 12 
               
               
                   
                 4 
                 4 
                 16 
               
               
                   
                 4 
                 5 
                 20 
               
               
                   
                 4 
                 6 
                 24 
               
               
                 Required  
                 2 bits 
                 3 bits 
                   
               
               
                 field size 
               
               
                   
               
            
           
         
       
     
     In the example of Table 3, 2 bits are used to indicate repetitions in the time domain and 3 bits are used to indicate repetitions in the frequency domain. Thus, totally 5 bits are needed for the resource assignment field. It is noted that, in this example, only PRB number in the frequency domain is indicated, but the resource position(s) in the frequency domain is not indicated. The resource position(s) can be for example configured by the RRC layer or based on identity (ID) of the UE. 
     Table 4 illustrates another example of separate indications, in which the resource position(s) in the frequency domain is indicated. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                   
                 Total PRB pair 
               
               
                   
                 Repetitions 
                 Number of PRBs 
                 Position in 
                 number 
               
               
                   
                 in time 
                 in frequency 
                 frequency 
                 (repetition 
               
               
                   
                 domain 
                 domain 
                 domain 
                 number) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 
                 1 
                 6 candidates 
                 1 
               
               
                   
                 1 
                 2 
                 5 candidates 
                 2 
               
               
                   
                 1 
                 3 
                 4 candidates 
                 3 
               
               
                   
                 1 
                 4 
                 3 candidates 
                 4 
               
               
                   
                 1 
                 5 
                 2 candidates 
                 5 
               
               
                   
                 1 
                 6 
                 1 candidates 
                 6 
               
               
                   
                 2 
                 1 
                 6 candidates 
                 2 
               
               
                   
                 2 
                 2 
                 5 candidates 
                 4 
               
               
                   
                 2 
                 3 
                 4 candidates 
                 6 
               
               
                   
                 2 
                 4 
                 3 candidates 
                 8 
               
               
                   
                 2 
                 5 
                 2 candidates 
                 10 
               
               
                   
                 2 
                 6 
                 1 candidates 
                 12 
               
               
                   
                 4 
                 1 
                 6 candidates 
                 4 
               
               
                   
                 4 
                 2 
                 5 candidates 
                 8 
               
               
                   
                 4 
                 3 
                 4 candidates 
                 12 
               
               
                   
                 4 
                 4 
                 3 candidates 
                 16 
               
               
                   
                 4 
                 5 
                 2 candidates 
                 20 
               
               
                   
                 4 
                 6 
                 1 candidates 
                 24 
               
               
                 Required  
                 2 bits 
                   
                 5 bits 
                   
               
               
                 field size 
               
               
                   
               
            
           
         
       
     
     In the example of Table 4, 2 bits are used to indicate repetitions in the time domain and 5 bits are used to indicate repetitions in the frequency domain. Thus, totally 7 bits are needed for the resource assignment field. 
     The benefit of such a separate indication approach as exemplarily shown in Table 3 and Table 4 is flexibility on resource assignment. However, it has the problem that the field size for resource assignment is relatively large so that the DCI size may be large as well, and the UE&#39;s active time to for example receive PDSCH is not optimized. 
     In an embodiment of the present disclosure, a joint indication of resource assignment is proposed, that is, a resource assignment field in the DCI uses a single index associated with the repetition number to jointly indicate resource assignment in both the time domain and the frequency domain. It is noted that one repetition number can correspond to one or more indexes to represent one or more specific resource assignment ways for the one repetition number. Joint indication may reduce the field size for resource assignment. For example, in the example of Table 3, if two more repetition possibilities (for example, 6 and 8 repetitions) are added in the time domain, then there needs 3 bits to indicate 5 possibilities (1, 2, 4, 6 and 8). Therefore, totally 6 bits (3 bits for the time domain and 3 bits for the frequency domain) are needed if the separation indication approach is used. However, if a joint indication is used, then only 5 bits are needed to indicate 30 possibilities (5 in the time domain×6 in the frequency domain). One bit is saved. The 5 bits constitute an index associated with the repetition number. Optionally, in this embodiment, transport block size can also be determined by the index associated with the repetition number in the resource assignment field. For example, a smaller repetition number can indicate a smaller transport block size, and a larger repetition number can indicate a larger transport block size. 
     In a further embodiment, the same number of repetitions in the time domain is used for one and the same value of the repetition number. In other words, only one combination of repetition number in the time domain and repetition number (number of PRBs) in the frequency domain is used for one repetition number. For example, assuming the repetition number is 8, the resource assignment may be 2 PRBs in the time domain×4 subframes in the time domain (simplified as 2 PRBs×4 subframes) or 4 PRBs×2 subframe. However, according to this embodiment, for the repetition number of 8, only one possibility of repetition number in the time domain can be used and the UE knows it in advance. For example, the repetition number in the time domain can be either 4 subframes or 2 subframes, and accordingly the repetition number in the frequency domain can be either 2 PRBs or 4 PRBs. The selection of repetition number in the time domain or the frequency domain for each repetition number can be for example configured by the RRC layer or specified in the standard. Therefore, when the UE receives an index corresponding to the repetition number, it can determine the repetition number in the time domain and the repetition number in the frequency domain. In this way, the size of the resource assignment filed can be reduced since only one combination of repetition number in the time domain and repetition number in the frequency domain needs to be indicated for one repetition number. Table 5 illustrates a specific example of the embodiment that each repetition number only has one combination of repetition number in the time domain and repetition number in the frequency domain in the context of Table 3. 
     
       
         
           
               
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                 Repetitions 
                 Number of PRBs 
                 Total PRB pair 
                 Index  
               
               
                   
                 in 
                 in frequency 
                 number (repetition 
                 in 
               
               
                   
                 time domain 
                 domain 
                 number) 
                 DCI 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 1 
                 1 
                 1 
                 0 
               
               
                   
                 1 
                 2 
                 2 
                 1 
               
               
                   
                 1 
                 3 
                 3 
                 2 
               
               
                   
                 1 
                 4 
                 4 
                 3 
               
               
                   
                 1 
                 5 
                 5 
                 4 
               
               
                   
                 1 
                 6 
                 6 
                 5 
               
               
                   
                 2 
                 4 
                 8 
                 6 
               
               
                   
                 2 
                 5 
                 10 
                 7 
               
               
                   
                 2 
                 6 
                 12 
                 8 
               
               
                   
                 4 
                 4 
                 16 
                 9 
               
               
                   
                 4 
                 5 
                 20 
                 10 
               
               
                   
                 4 
                 6 
                 24 
                 11 
               
               
                 Required 
                   
                   
                   
                 3 bits 
               
               
                 field size 
               
               
                   
               
            
           
         
       
     
     In Table 5, each repetition number only has one combination of repetition number in the time domain and repetition number in the frequency domain; therefore, only 3 bits are needed for the resource assignment field, which saves 2 bits compared with the approach show in Table 3. 
     Table 6 illustrates another specific example of the embodiment that each repetition number only has one combination of repetition number in the time domain and repetition number in the frequency domain in the context of Table 4. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                   
                   
                 Number of 
                   
                 Total PRB pair 
                   
               
               
                   
                 Repetitions 
                 PRBs in 
                 Position in 
                 number 
                 Index 
               
               
                   
                 in time 
                 frequency 
                 frequency 
                 (repetition 
                 in 
               
               
                   
                 domain 
                 domain 
                 domain 
                 number) 
                 DCI 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 1 
                 1 
                 6 candidates 
                 1 
                 0-5 
               
               
                   
                 1 
                 2 
                 5 candidates 
                 2 
                  6-10 
               
               
                   
                 1 
                 3 
                 4 candidates 
                 3 
                 11-14 
               
               
                   
                 1 
                 4 
                 3 candidates 
                 4 
                 15-17 
               
               
                   
                 1 
                 5 
                 2 candidates 
                 5 
                 18-19 
               
               
                   
                 1 
                 6 
                 1 candidates 
                 6 
                 20 
               
               
                   
                 2 
                 4 
                 3 candidates 
                 8 
                 21-23 
               
               
                   
                 2 
                 5 
                 2 candidates 
                 10 
                 24-25 
               
               
                   
                 2 
                 6 
                 1 candidates 
                 12 
                 26 
               
               
                   
                 4 
                 4 
                 3 candidates 
                 16 
                 27-29 
               
               
                   
                 4 
                 5 
                 2 candidates 
                 20 
                 30-31 
               
               
                   
                 4 
                 6 
                 1 candidates 
                 24 
                 32 
               
               
                 Required 
                   
                   
                   
                   
                 5 bits 
               
               
                 field size 
               
               
                   
               
            
           
         
       
     
     In Table 6, each repetition number only has one combination of repetition number in the time domain and repetition number in the frequency domain; therefore, only 5 bits are needed for the resource assignment field, which saves 2 bits compared with the approach show in Table 4. 
     It is reasonable that each repetition number has only one combination of repetition number in the time domain and repetition number in the frequency domain based on the reason that there is almost no performance difference between different combinations of repetition number in the time domain and repetition number in the frequency domain. For example, there is almost no performance difference between 2 PRBs×4 subframes and 4 PRB×2 subframe for resource assignment. First, frequency hopping is disabled within “multiple subframes” to realize symbol-level combining based on current 3GPP agreements (refer to “Draft Report of 3GPP TSG RAN WG1 #80 v0.2.0”). In other words, the resources should keep the same position in the frequency domain within “multiple subframes”. For example, the value of “multiple subframes” can be 4. Second, the total repetition times are the same, for example, 2 PRBs×4 subframes can realize 8 repetitions and 4 PRB×2 subframe can also realize 8 repetitions. Therefore, the embodiment that each repetition number has only one combination of repetition number in the time domain and repetition number in the frequency domain can reduce the field size of resource assignment while remaining the performance almost unchanged. 
     In a further embodiment, the least possible repetitions in the time domain can be assigned for one and the same value of the repetition number. In other words, repetitions in the time domain should be used as less as possible to reduce the UE&#39;s active time and thus reduce the UE&#39;s power consumption. The UE&#39;s active time is related to repetition number in the time domain. The smaller the repetition number in the time domain is, the less the UE&#39;s active time is. For example, for the total repetition number of 8, the resource assignment of “4 PRBs×2 subframes” should be used assuming narrowband of total 6 PRBs in the frequency domain according to the embodiment since repetitions of 2 subframes in the time domain are the least possible repetitions and the UE&#39;s active time is the least in this case. For example, “2 PRBs×4 subframes” has more repetitions in the time domain but less repetitions in the frequency domain, and “4 PRBs×2 subframes” has more repetitions in the frequency domain but less repetitions in the time domain. Therefore, the UE&#39;s active time caused by receptions is larger in the case of “2 PRBs×4 subframes” than in the case of “4 PRBs×2 subframes”. The UE keeps active for 4 subframes in the case of “2 PRBs×4 subframes” but only needs to keep active for 2 subframes in the case of “4 PRBs×2 subframes”. As specific examples, the embodiment can be applied to Table 5 and Table 6. 
     In a further embodiment, only a proper subset of all possible resource positions in the frequency domain are considered as frequency position candidates of the resource assignment for at least one value of the repetition number. In other words, only limited resource candidates (not all possible resource positions) are kept in the frequency domain since there is no much scheduling gain within narrowband. In this way, the size of the resource assignment field can be further reduced. Table 7 is an example of limited resource candidates in the frequency domain in the context of Table 6. 
     
       
         
           
               
               
               
               
               
               
             
               
                 TABLE 7 
               
               
                   
               
               
                   
                   
                 Number of 
                   
                 Total PRB  
                   
               
               
                   
                 Repetitions 
                 PRBs in 
                 Position in 
                 pair number 
                 Index 
               
               
                   
                 in time 
                 time 
                 frequency 
                 (repetition 
                 in 
               
               
                   
                 domain 
                 domain 
                 domain 
                 number) 
                 DCI 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 1 
                 1 
                 X1, Y1, Z1 
                 1 
                 0-2 
               
               
                   
                 1 
                 2 
                 X2, Y2, Z2 
                 2 
                 3-5 
               
               
                   
                 1 
                 3 
                 X3, Y3 
                 3 
                 6-7 
               
               
                   
                 1 
                 4 
                 X4 
                 4 
                 8 
               
               
                   
                 1 
                 5 
                 X5 
                 5 
                 8 
               
               
                   
                 1 
                 6 
                 X6 
                 6 
                 10 
               
               
                   
                 2 
                 4 
                 X7 
                 8 
                 11 
               
               
                   
                 2 
                 5 
                 X8 
                 10 
                 12 
               
               
                   
                 2 
                 6 
                 X9 
                 12 
                 13 
               
               
                   
                 4 
                 4 
                  X10 
                 16 
                 14 
               
               
                   
                 4 
                 5 
                  X11 
                 20 
                 15 
               
               
                   
                 4 
                 6 
                  X12 
                 24 
                 16 
               
               
                 Required 
                   
                   
                   
                   
                 4 bits 
               
               
                 field size 
               
               
                   
               
            
           
         
       
     
     In Table 7, for the repetition number 1, only 3 candidates (X1, Y1 and Z1) out of 6 candidates (assuming narrowband) are considered; for the repetition number 2, only 3 candidates (X2, Y2 and Z2) out of 5 candidates are considered; and so on. In this example, only 4 bits are needed and thus 1 bit is further saved compared with Table 6. The set of resource candidates (i.e., proper subset of all possible resource positions) can be configured by the RRC layer or determined based on ID of the UE. 
     The above embodiments can be used to any uplink channel (e.g. PUSCH) or downlink channel (e.g. PDSCH) for any enhancement level or repetition number. In an example, the above embodiments are used to a downlink channel for a small enhancement level or repetition number. Whether the coverage enhancement level is large or small can be determined by comparing it with a predetermined level. The predetermined level can be configured by the RRC layer or specified. In some embodiments, the coverage enhancement level can also be configured by the RRC layer. It is noted that the above coverage enhancement level also includes the case of no enhancement, and the repetition number also includes the case of no repetition. For example, the first lines in Tables 3-7 represent no repetition. 
     In a further embodiment, if the coverage enhancement level is larger than a predetermined level and the channel scheduled by the DCI is a downlink channel, all possible resources in the frequency domain are assigned in the resource assignment. In other words, if the coverage enhancement level is large, full occupation of the resources (for example 6 PRBs of narrowband) in the frequency domain can be used in a downlink channel in order to reduce the UE&#39;s active time. Table 8 illustrates an example of full occupation of frequency resources. 
     
       
         
           
               
               
               
             
               
                 TABLE 8 
               
               
                   
               
               
                 Repetitions in time 
                 Number of PRBs in 
                   
               
               
                 domain 
                 frequency domain 
                 Index in DCI 
               
               
                   
               
             
            
               
                   8 
                 6 
                 0 
               
               
                  20 
                 6 
                 1 
               
               
                  40 
                 6 
                 2 
               
               
                  100 
                 6 
                 3 
               
               
                  200 
                 6 
                 4 
               
               
                  400 
                 6 
                 5 
               
               
                  800 
                 6 
                 6 
               
               
                 1000 
                 6 
                 7 
               
               
                 Required field size 
                   
                 3 bits 
               
               
                 Resource assignment size 
                   
                 6 bits 
               
               
                 in separation indications 
                   
                 Time domain: 4 bits 
               
               
                 (time + frequency) 
                   
                 Frequency domain: 2 bits 
               
               
                   
               
            
           
         
       
     
     In Table 8, all 6 PRBs of narrowband are occupied in the time domain, and only 3 bits are needed to indicate resource assignment, which saves 3 bits compared with the separate indication approach. In addition, according to this embodiment, the UE&#39;s active time can be reduced. 
     In a further embodiment, if the coverage enhancement level is larger than a predetermined level and the channel scheduled by the DCI is an uplink channel, only one resource in the frequency domain is assigned in the resource assignment. One PRB transmission in the frequency domain can realize the largest power spectral density (PSD) in uplink. Optionally, the one resource in the frequency domain can be configured by the RRC layer or based on ID of the UE. Alternatively, limited resource candidates in the frequency domain can be configured for the resource assignment of the one resource. Table 9 illustrates an example of one PRB transmission combined with limited resource candidates in the frequency domain. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 9 
               
               
                   
               
               
                   
                 Number of PRBs 
                 Position in  
                 Index  
               
               
                 Repetitions in 
                 in frequency 
                 frequency 
                 in  
               
               
                 time domain 
                 domain 
                 domain 
                 DCI 
               
               
                   
               
             
            
               
                   8 
                 1 
                 X, Y, Z 
                  0-2 
               
               
                  20 
                 1 
                 X, Y, Z 
                  3-5 
               
               
                  40 
                 1 
                 X, Y, Z 
                  6-8 
               
               
                  100 
                 1 
                 X, Y, Z 
                  9-11 
               
               
                  200 
                 1 
                 X, Y, Z 
                 12-14 
               
               
                  400 
                 1 
                 X, Y, Z 
                 15-17 
               
               
                  800 
                 1 
                 X, Y, Z 
                 18-20 
               
               
                 1000 
                 1 
                 X, Y, Z 
                 21-23 
               
               
                 Required field 
                   
                   
                 5 bits 
               
               
                 size 
                   
                   
                   
               
               
                 Resource 
                   
                   
                 6 bits 
               
               
                 assignment 
                   
                   
                 Time domain: 
               
               
                 size in 
                   
                   
                 4 bits 
               
               
                 separate 
                   
                   
                 Frequency 
               
               
                 indications 
                   
                   
                 domain: 2 bits 
               
               
                 (time + 
                   
                   
                   
               
               
                 frequency) 
               
               
                   
               
            
           
         
       
     
     In Table 9, one PRB transmission and three resource candidates in the frequency domain are used in the uplink for each large repetition number. In other words, only repetitions in the time domain have multiple options, for example 8, 20, 40, 100 and so on. The field size for resource assignment is reduced from 6 bits to 5 bits. It is noted that the set of resource candidates {x, y, z} can be configured by the RRC layer or determined based on ID of the UE. 
     In an embodiment, the resource assignment field can be interpreted based on whether the coverage enhancement level is large or small. In other words, different sets of coverage enhancement levels can use different designs of the resource assignment field. For example, for a small coverage level, the interpretation of the resource assignment field can use any of Tables 5-7; for a large coverage level, the interpretation of the resource assignment field can use Table 8 for downlink and Table 9 for uplink. In this example, it assumes that the UE knows the coverage enhancement level in advance in order to determine which table should be used. For example, the UE can know the information by RRC configuration. 
     In another embodiment, all possible repetition numbers should be covered in one table in case the UE does not know the coverage enhancement level for example during system information block (SIB) acquisition or random access period as it is common information that should be used for all UEs. For example, Table 10 illustrates an exemplary table that contains all possible repetition numbers (from 1 repetition in the time domain to 1000 repetitions in the time domain). Therefore, the UE can interpret the resource assignment field even if it does not know the coverage enhancement level. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 10 
               
               
                   
               
               
                 Repetitions 
                 Number of PRBs  
                 Position in  
                   
               
               
                 in 
                 in frequency 
                 frequency 
                 Index  
               
               
                 time domain 
                 domain 
                 domain 
                 in DCI 
               
               
                   
               
             
            
               
                   1 
                 1 
                 X1, Y1, Z1 
                 0-2 
               
               
                   1 
                 2 
                 X2, Y2, Z2 
                 3-5 
               
               
                   1 
                 4 
                 Only one  
                  6 
               
               
                   
                   
                 candidate in 
                   
               
               
                   
                   
                 the following 
                   
               
               
                   1 
                 6 
                   
                  7 
               
               
                   2 
                 4 
                   
                  8 
               
               
                   2 
                 6 
                   
                  9 
               
               
                   4 
                 4 
                   
                 10 
               
               
                   4 
                 6 
                   
                 11 
               
               
                   8 
                 6 
                   
                 12 
               
               
                  20 
                 6 
                   
                 13 
               
               
                  40 
                 6 
                   
                 14 
               
               
                  100 
                 6 
                   
                 15 
               
               
                  200 
                 6 
                   
                 16 
               
               
                  400 
                 6 
                   
                 17 
               
               
                  800 
                 6 
                   
                 18 
               
               
                 1000 
                 6 
                   
                 19 
               
               
                 Required field 
                   
                   
                 5 bits 
               
               
                 size 
                   
                   
                   
               
               
                 Resource 
                   
                   
                 6 bits 
               
               
                 assignment 
                   
                   
                 Time domain: 4 
               
               
                 size in 
                   
                   
                 bits 
               
               
                 separate 
                   
                   
                 Frequency 
               
               
                 indications 
                   
                   
                 domain: 2 bits 
               
               
                 (time + 
                   
                   
                   
               
               
                 frequency) 
               
               
                   
               
            
           
         
       
     
     As shown in Table 10, the field size for resource assignment is reduced from 6 bits to 5 bits compared with the separate indication approach. It is noted that Table 10 is only an example of the solution covering all possible repetition numbers. The technical features described in the other embodiments can also be applied to the solution covering all possible repetition numbers unless the context indicates otherwise. 
     According to embodiments of the present disclosure, the DCI size can be reduced. In some embodiments, the active time of the UE can be reduced and/or the PSD can be increased. It is noted that the above embodiments can be combined unless the context indicates otherwise. For example, the embodiments of different DCI size for different sets of coverage enhancement levels can be combined with any of the other embodiments. 
     In addition, at the UE side, an embodiment of the present disclosure provides a wireless communication method  200  performed by a UE, as shown in  FIG.  2    which schematically illustrates a flowchart of the wireless communication method  200  according to an embodiment of the present disclosure. The wireless communication method includes step  201  of receiving downlink control information (DCI) transmitted from an eNB, wherein the DCI is designed based on a coverage enhancement level for the UE. It is noted that the above descriptions for the wireless communication can also be applied to the wireless communication method  100 , which will not be repeated here. 
     Further, embodiments of the present disclosure also provide an eNB and a UE to perform the above described communication methods.  FIG.  3    schematically illustrates a block diagram of an eNB  300  for wireless communication according to an embodiment of the present disclosure. The eNB  300  can include a transmitting unit  301  configured to transmit downlink control information (DCI) to a UE, wherein the DCI is designed based on a coverage enhancement level for the UE. 
     The eNB  300  according to the present disclosure may optionally include a CPU (Central Processing Unit)  310  for executing related programs to process various data and control operations of respective units in the eNB  300 , a ROM (Read Only Memory)  313  for storing various programs required for performing various process and control by the CPU  310 , a RAM (Random Access Memory)  315  for storing intermediate data temporarily produced in the procedure of process and control by the CPU  310 , and/or a storage unit  317  for storing various programs, data and so on. The above transmitting unit  301 , CPU  310 , ROM  313 , RAM  315  and/or storage unit  317  etc. may be interconnected via data and/or command bus  320  and transfer signals between one another. 
     Respective units as described above do not limit the scope of the present disclosure. According to one implementation of the disclosure, the functions of the above transmitting unit  301  may be implemented by hardware, and the above CPU  310 , ROM  313 , RAM  315  and/or storage unit  317  may not be necessary. Alternatively, the functions of the above transmitting unit  301  may also be implemented by functional software in combination with the above CPU  310 , ROM  313 , RAM  315  and/or storage unit  317  etc. 
       FIG.  4    schematically illustrates a block diagram of a UE  400  for wireless communication according to an embodiment of the present disclosure. The UE  400  can include a receiving unit configured to receive downlink control information (DCI) transmitted from an eNB, wherein the DCI is designed based on a coverage enhancement level for the UE. 
     The UE  400  according to the present disclosure may optionally include a CPU (Central Processing Unit)  410  for executing related programs to process various data and control operations of respective units in the UE  400 , a ROM (Read Only Memory)  413  for storing various programs required for performing various process and control by the CPU  410 , a RAM (Random Access Memory)  415  for storing intermediate data temporarily produced in the procedure of process and control by the CPU  410 , and/or a storage unit  417  for storing various programs, data and so on. The above receiving unit  401 , CPU  410 , ROM  413 , RAM  415  and/or storage unit  417  etc. may be interconnected via data and/or command bus  420  and transfer signals between one another. 
     Respective units as described above do not limit the scope of the present disclosure. According to one implementation of the disclosure, the functions of the above receiving unit  401  may be implemented by hardware, and the above CPU  410 , ROM  413 , RAM  415  and/or storage unit  417  may not be necessary. Alternatively, the functions of the above receiving unit  401  may also be implemented by functional software in combination with the above CPU  410 , ROM  413 , RAM  415  and/or storage unit  417  etc. 
     It is noted that the above descriptions for the communication methods can also be applied to the UE or eNB, which will not be repeated herein. 
     The present disclosure can be realized by software, hardware, or software in cooperation with hardware. Each functional block used in the description of each embodiment described above can be realized by an LSI as an integrated circuit, and each process described in each embodiment may be controlled by LSI. They may be individually formed as chips, or one chip may be formed so as to include a part or all of the functional blocks. They may include a data input and output coupled thereto. The LSI here may be referred to as an IC, a system LSI, a super LSI, or an ultra LSI depending on a difference in the degree of integration. However, the technique of implementing an integrated circuit is not limited to the LSI and may be realized by using a dedicated circuit or a general-purpose processor. In addition, a FPGA (Field Programmable Gate Array) that can be programmed after the manufacture of the LSI or a reconfigurable processor in which the connections and the settings of circuits cells disposed inside the LSI can be reconfigured may be used. 
     It is noted that the present disclosure intends to be variously changed or modified by those skilled in the art based on the description presented in the specification and known technologies without departing from the content and the scope of the present disclosure, and such changes and applications fall within the scope that claimed to be protected. Furthermore, in a range not departing from the content of the disclosure, the constituent elements of the above-described embodiments may be arbitrarily combined. 
     Embodiments of the present disclosure can at least provide the following subject matters. 
     According to an embodiment of the present disclosure, there is provided a wireless communication method performed by an eNode B (eNB), including: 
     transmitting downlink control information (DCI) to a user equipment (UE), wherein 
     the DCI is designed based on a coverage enhancement level for the UE. 
     In the foregoing wireless communication method, 
     coverage enhancement of a channel scheduled by the DCI with the coverage enhancement level is realized at least by repetitions in a time domain and/or repetitions in a frequency domain with a repetition number which represents a total number of repetitions of the channel, and 
     a resource assignment field in the DCI uses a single index associated with the repetition number to jointly indicate resource assignment in both the time domain and the frequency domain. 
     In the foregoing wireless communication method, 
     the same number of repetitions in the time domain is used for one and the same value of the repetition number. 
     In the foregoing wireless communication method, 
     the least possible repetitions in the time domain are assigned for one and the same value of the repetition number. 
     In the foregoing wireless communication method, 
     only a proper subset of all possible resource positions in the frequency domain is considered as frequency position candidates of the resource assignment for at least one value of the repetition number. 
     In the foregoing wireless communication method, 
     if the coverage enhancement level is larger than a predetermined level and the channel scheduled by the DCI is a downlink channel, all possible resources in the frequency domain are assigned in the resource assignment. 
     In the foregoing wireless communication method, 
     if the coverage enhancement level is larger than a predetermined level and the channel scheduled by the DCI is an uplink channel, only one resource in the frequency domain is assigned in the resource assignment. 
     In the foregoing wireless communication method, 
     if the coverage enhancement level is smaller than the predetermined level, the least possible repetitions in the time domain are assigned for one and the same value of the repetition number. 
     In the foregoing wireless communication method, 
     a transport block size is determined by the index associated with the repetition number in the resource assignment field. 
     In the foregoing wireless communication method, 
     the DCI uses different sizes for different sets of coverage enhancement levels. 
     According to another embodiment of the present disclosure, there is provided a wireless communication method performed by a user equipment (UE), including: 
     receiving downlink control information (DCI) transmitted from an eNode B (eNB), wherein 
     the DCI is designed based on a coverage enhancement level for the UE. 
     In the foregoing wireless communication method, 
     coverage enhancement of a channel scheduled by the DCI with the coverage enhancement level is realized at least by repetitions in a time domain and/or repetitions in a frequency domain with a repetition number which represents a total number of repetitions of the channel, and 
     a resource assignment field in the DCI uses a single index associated with the repetition number to jointly indicate resource assignment in both the time domain and the frequency domain. 
     According to another embodiment of the present disclosure, there is provided an eNode B (eNB) for wireless communication, including: 
     a transmitter that transmits downlink control information (DCI) to a user equipment (UE), wherein 
     the DCI is designed based on a coverage enhancement level for the UE. 
     In the foregoing eNB, 
     coverage enhancement of a channel scheduled by the DCI with the coverage enhancement level is realized at least by repetitions in a time domain and/or repetitions in a frequency domain with a repetition number which represents a total number of repetitions of the channel, and 
     a resource assignment field in the DCI uses a single index associated with the repetition number to jointly indicate resource assignment in both the time domain and the frequency domain. 
     According to another embodiment of the present disclosure, there is provided a user equipment (UE) for wireless communication, including: 
     a receiver that receives downlink control information (DCI) transmitted from an eNode B (eNB), wherein 
     the DCI is designed based on a coverage enhancement level for the UE. 
     In addition, embodiments of the present disclosure can also provide an integrated circuit which includes module(s) for performing the step(s) in the above respective communication methods. Further, embodiments of the present disclosure can also provide a computer readable storage medium having stored thereon a computer program containing a program code which, when executed on a computing device, performs the step(s) of the above respective communication methods.