Abstract:
A 5 th -generation (5G) or pre-5G communication system which is to support a higher data transfer rate beyond a 4G communication system such as a long term evolution (LTE) is provided. The method for transmitting a downlink signal by a base station in a wireless communication system supporting non-orthogonal multiple access (NOMA) includes the steps of selecting a pair of terminals including one short-distance terminal and at least one long-distance terminal which will share an identical downlink transmission resource, generating a superimposed signal in which a signal for the short-distance terminal and a signal for the long-distance terminal are superimposed on one another, generating information necessary for cancelling the signal of the long-distance terminal from the superimposed signal, transmitting the generated information necessary for cancelling the signal of the long-distance terminal to the short-distance terminal, and transmitting the generated superimposed signal to the pair of terminals.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application is a U.S. National Stage application under 35 U.S.C. §371 of an International application filed on Apr. 4, 2016 and assigned application number PCT/KR2016/003456, which claimed the benefit of U.S. Provisional application filed on Apr. 2, 2015 in the U.S. Patent and Trademark Office and assigned Ser. No. 62/142,245, the entire disclosure of each of which is hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure relates to a method and apparatus for transmitting downlink (DL) control information in a wireless communication system. 
       BACKGROUND 
       [0003]    To satisfy demands for wireless data traffic having increased since commercialization of 4th generation (4G) communication systems, efforts have been made to develop improved 5 th  generation (5G) communication systems or pre-5G communication systems. For this reason, the 5G communication system or the pre-5G communication system is also called a beyond-4G-network communication system or a post-long term evolution (LTE) system. 
         [0004]    To achieve a high data rate, implementation of the 5G communication system in an ultra-high frequency (mmWave) band (e.g., a 60 GHz band) is under consideration. In the 5G communication system, beamforming, massive multi-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), an array antenna, analog beamforming, and large-scale antenna technologies have been discussed to alleviate a propagation path loss and to increase a propagation distance in the ultra-high frequency band. 
         [0005]    For system network improvement, in the 5G communication system, techniques such as an evolved small cell, an advanced small cell, a cloud radio access network (RAN), an ultra-dense network, a device to device (D2D) communication, a wireless backhaul, a moving network, cooperative communication, coordinated multi-points (CoMPs), and interference cancellation have been developed. 
         [0006]    In the 5G system, advanced coding modulation (ACM) schemes including hybrid frequency-shift keying (FSK) and quadrature amplitude modulation (QAM) modulation (FQAM) and sliding window superposition coding (SWSC), and advanced access schemes including filter bank multi carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA) have been developed. 
         [0007]    NOMA is a technique for allowing a plurality of user equipments (UEs) to use identical non-orthogonal time/frequency resources, thereby improving the performance of a system and the fairness of scheduling of the UEs. When compared to NOMA, orthogonal frequency divisional multiple access (OFDMA) used in a general communication system may be referred to as orthogonal multiple access (OMA). 
         [0008]    In a NOMA system, an evolved NodeB (eNB) allocates identical time/frequency resources to multiple UEs, and transmits downlink (DL) signals for respective UEs in a superposed manner. Each UE cancels a signal of another UE from its received signal (successive interference cancellation) to restore its signal. 
         [0009]      FIGS. 1A, 1B, and 1C  illustrates an example to compare communication schemes between an eNB and a UE between a NOMA system and an OMA system according to the related art. 
         [0010]    Referring to  FIGS. 1A to 1C , it is assumed that when identical time/frequency resources are allocated to two UEs, UE 1   103  and UE 2   105 , an eNB  101  allocates low power (e.g., ⅕ of available power) to a signal  1  for the UE 1   103  that is the nearer UE located closer to the eNB  101  than the UE 2   105 , and allocates high power (e.g., ⅘ of the available power)  133  to a signal  2  for the terminal UE 2   105  that is the far UE located farther from the eNB  101  than the UE 1   103 , and transmits the two signals to the UE 1   103  and the UE 2   105  in a superposed manner. 
         [0011]    When the UE 1   103 , which is the near UE, receives the superposed signal, attenuation of the signal  1  and the signal  2  may not be large because the UE 1   103  is located close to the eNB  101 . Herein, since a component of the signal  2  may occupy a large part of the superposed signal received by the UE 1   103 , a signal-to-noise and interference ratio (SINR) of the superposed signal received by the UE  1   103  is relatively high. Referring to  FIGS. 1A to 1C , for example, an SINR is expressed as 20 dB. 
         [0012]    On the other hand, if the UE 2   105 , which is the far UE, receives the superposed signal, the power strength of the signal  1  is low and the UE 2   105  is located far from the eNB  101 , such that the signal  1  may arrive at the UE 2   103  after being mostly attenuated. Thus, the superposed signal received by the UE 2   103  may include a component of the signal  1  with power of a level that is similar to noise. As a result, most components of the superposed signal received by the UE 2   105  may be occupied by the signal  2 . Moreover, the signal  2  may be attenuated while arriving at the UE 2   105 , such that the magnitude of the SINR of the signal received by the UE 2   105  is small. Referring to  FIGS. 1A to 1C , for example, an SINR is expressed as 0 dB. 
         [0013]    In this example, the superposed signal received by the UE 1   103  includes the signal  1  and the signal  2 , and the power of the signal  2  is much higher than that of the signal  1 , such that the UE 1   103  may easily distinguish the signal  1  from the signal  2 . Thus, the UE 2  cancels the interference of the signal  2  from the superposed signal and receives the signal  1 . Meanwhile, in the signal received by the UE 2   105 , the signal  1  may be processed as noise and only the signal  2  may be processed as a signal component, such that the UE 2   105  may receive the signal  2  without a need to perform interference cancellation with respect to the signal  1 . 
         [0014]      FIG. 1B  shows system performance in OMA such as OFDMA. That is,  FIG. 1B  shows DL transmission performance for the UE 1   103  and the UE 2   105  when ½ of an available bandwidth  121  and full available power  123  are allocated to the UE 1   103  and the UE 2   105 , respectively. A data rate R 1  of the UE 1   103  is 3.33 bps/Hz, and a DL data rate R 2  of the UE 2   105  is 0.50 bps/Hz. Thus, in case of OFDMA, the transmission speed of the entire system is 3.83 bps/Hz. 
         [0015]      FIG. 1C  shows system performance in a NOMA scheme. When a full available bandwidth is allocated to the UE 1   103  and the UE 2   105  and ⅕ of available power,  131 , and ⅘ of the available power,  133 , are allocated to the UE 1   103  and the UE 2   105 , respectively, the DL data rate R 1  of the UE 1   103  is 4.39 bps/Hz and the DL data rate R 2  of the UE 2   105  is 0.74 bps/Hz. Thus, in case of NOMA, the transmission speed of the entire system is 5.11 bps/Hz. As such, it can be seen that the entire system performance of NOMA is better than the entire system performance of OFDMA. 
         [0016]    In the NOMA system, the overall system performance gain increases as an SINR difference between DL superposed signals received by the UEs that share resources increases. Thus, in the NOMA system, the eNB selects UEs having a large SINR difference between received signals and allocates an identical resource to the UEs. Although it is assumed that two UEs share a resource in  FIGS. 1A to 1C , the number of UEs sharing an identical resource may be greater than or equal to 2. However, it is known that a performance gain is not large for three or more UEs even if the number of UEs sharing an identical resource increases. 
         [0017]    Meanwhile, the 3 rd  generation partnership project (3GPP) LTE Rel-13 is discussing application for NOMA to the LTE system. However, to support NOMA in LTE, a detailed scheme for transmitting DL information has not yet been determined. 
         [0018]    In particular, in the LTE standard specifications, UEs may have different transmission modes (TMs) and different precoding information. If an identical resource is allocated to UEs having different precoding information and/or different TMs, a performance gain increases largely. Therefore, there is a need for a scheme in which UEs having different TMs and/or different precoding information share resources by using NOMA in the LTE communication system. 
         [0019]    The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure. 
       SUMMARY 
       [0020]    Aspects of the present disclosure are to address at least the above-mentioned problems and/or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present disclosure is to provide a method and apparatus for transmitting downlink (DL) information by an evolved node B (eNB) in a non-orthogonal multiple access (NOMA) system. 
         [0021]    Another aspect of the present disclosure is to provide a method and apparatus for providing, by an eNB to a near user equipment (UE), information needed to cancel a signal (hereinafter, referred to as a far UE signal) for a far UE, by using downlink control information (DCI) defined in the long-term evolution (LTE) standard in a NOMA system. 
         [0022]    Another aspect of the present disclosure is to provide a method and apparatus for providing, by an eNB to a near UE, information needed to cancel a signal (hereinafter, referred to as a far UE signal) for a far UE, by using a radio resource control (RRC) message defined in the LTE standard in a NOMA system. 
         [0023]    In accordance with an aspect of the present disclosure, a method for transmitting a downlink (DL) signal by an evolved NodeB (eNB) in a wireless communication system supporting non-orthogonal multiple access (NOMA) is provided. The method includes selecting a user equipment (UE) pair including at least one near UE and at least one far UE among a plurality of UEs which are to share an identical DL transmission resource, generating a superposed signal by superposing a signal for the at least one near UE and a signal for the far UE, generating information necessary for canceling the signal for the at least one far UE, transmitting the generated information necessary for canceling the signal for the at least one far UE to the at least one near UE, and transmitting the generated superposed signal to the UE pair. 
         [0024]    In accordance with another aspect of the present disclosure, a method for receiving a DL signal by a near UE in a wireless communication system supporting NOMA is provided. The method includes receiving, from an eNB, information necessary for canceling a signal for at least one far UE from a superposed signal generated by superposition of a signal for the near UE and a signal for the at least one far UE, receiving the superposed signal, and canceling the signal for the at least one far UE from the superposed signal by using the information necessary for canceling the signal for the at least one far UE. 
         [0025]    In accordance with another aspect of the present disclosure, an eNB for transmitting a DL signal in a wireless communication system supporting NOMA is provided. The eNB includes at least one processor (i.e. controller) configured to select a UE pair including at least one near UE and at least one far UE among a plurality of UEs which are to share an identical DL transmission resource and generate a superposed signal by superposing a signal for the at least one near UE and a signal for the at least one far UE, an information generator configured to generate information necessary for canceling the signal for the at least one far UE, and a transceiver configured to transmit the generated information necessary for canceling the signal for the at least one far UE to the at least one near UE and to transmit the generated superposed signal to the UE pair. 
         [0026]    In accordance with another aspect of the present disclosure, a UE for receiving a DL signal in a wireless communication system supporting NOMA is provided. The UE includes a transceiver configured to receive, from an eNB, information necessary for canceling a signal for at least one far UE from a superposed signal generated by superposition of a signal for the near UE and a signal for the at least one far, and receive the superposed signal, and an interference canceller configured to cancel the signal for the at least one far UE from the superposed signal by using the information necessary for canceling the signal for the at least one far UE. 
         [0027]    Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses various embodiments of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0028]    The above and other aspects, features, and advantages of certain embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
           [0029]      FIGS. 1A, 1B, and 1C  illustrates an example to compare communication schemes between an evolved node B (eNB) and a user equipment (UE) between a non-orthogonal multiple access (NOMA) system and an orthogonal multiple access (OMA) system according to the related art; 
           [0030]      FIG. 2  illustrate downlink control information (DCI) formats for scheduling defined in the current long term evolution (LTE) standard according to an embodiment of the present disclosure; 
           [0031]      FIG. 3  illustrates an example of a DCI format for a near UE newly defined according to a first embodiment of the present disclosure; 
           [0032]      FIG. 4  is a view for describing operations of an eNB according to first and second embodiments of the present disclosure; 
           [0033]      FIG. 5  is a view for describing operations of an eNB according to third through fifth embodiments of the present disclosure; 
           [0034]      FIG. 6  is a view for describing operations of a near UE according to the first and second embodiments of the present disclosure; 
           [0035]      FIG. 7  is a view for describing operations of a near UE according to the three through fifth embodiments of the present disclosure; 
           [0036]      FIG. 8  is a block diagram of an eNB that performs operations according to various embodiments of the present disclosure; and 
           [0037]      FIG. 9  is a block diagram of an UE that performs operations according to various embodiments of the present disclosure. 
       
    
    
       [0038]    Throughout the drawings, it should be noted that like reference numbers are used to depict the same or similar elements, features, and structures. 
       DETAILED DESCRIPTION 
       [0039]    The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the present disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the present disclosure. In addition, description of well-known functions and constructions may be omitted for clarity and conciseness. 
         [0040]    The terms and words used in the following description and claims are not limited to the bibliographical meanings, but, are merely used by the inventor to enable a clear and consistent understanding of the present disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the present disclosure is provided for illustration purpose only and not for the purpose of limiting the present disclosure as defined by the appended claims and their equivalents. 
         [0041]    It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to “a component surface” includes reference to one or more of such surfaces. 
         [0042]    The following embodiments will be separately described for convenience, but at least two embodiments may be implemented in combination without colliding with each other. 
         [0043]    Further, the terminologies to be described below are defined in consideration of functions in the various embodiments of the present disclosure and may vary depending on a user&#39;s or operator&#39;s intention or practice. Therefore, the definitions should be made based on the contents throughout the entire description of the present disclosure. 
         [0044]    Various changes may be made to various embodiments of the present disclosure and the present disclosure may have various embodiments which will be described in detail with reference to the drawings. However, the various embodiments according to the concept of the present disclosure are not construed as limited to specified disclosures, and include all changes, equivalents, or substitutes that do not depart from the spirit and technical scope of the present disclosure. 
         [0045]    Although the terms such as “first” and “second” used in the various embodiments of the present disclosure may modify various elements of the various embodiments, these terms do not limit the corresponding elements. These terms may be used for the purpose of distinguishing one element from another element. For example, a first element may be named as a second element without departing from the right scope of the various embodiments of the present disclosure, and similarly, a second element may be named as a first element. The term “and/or” includes a combination of a plurality of related provided items or any one of the plurality of related provided items. 
         [0046]    Herein, the term “include”, “have”, or the like used in the present disclosure is to indicate the presence of features, numbers, operations, elements, parts, or a combination thereof described in the specifications, and does not preclude the presence or addition of one or more other features, numbers, operations, elements, parts, or a combination thereof. 
         [0047]    The apparatus and method proposed in the present disclosure are applicable to various communication systems such as a Long-Term Evolution (LTE) mobile communication system, an LTE-Advanced (LTE-A) mobile communication system, a high speed downlink packet access (HSDPA) mobile communication system, a high speed uplink packet access (HSUPA) mobile communication system, a high rate packet data (HRPD) mobile communication system of the 3 rd  generation partnership project (3GPP) 2, a wideband code division multiple access (WCDMA) mobile communication system of the 3GPP 2, a code division multiple access (CDMA) mobile communication system of the 3GPP 2, the Institute of Electrical and Electronics Engineers (IEEE) 802.16m communication system, an evolved packet system (EPS), a mobile Internet Protocol (IP) system, and so forth. 
         [0048]    Before the present disclosure is described in detail, the main concept of the present disclosure will be described in brief. 
         [0049]    The present disclosure proposes schemes for transmitting information needed for removing or canceling a far-user equipment (UE) signal included in a non-orthogonal multiple access (NOMA) signal received by a near or short-distance UE to the near UE in a NOMA system. The information needed for canceling the far UE signal may vary with an embodiment, and a detailed description thereof will be described later. 
         [0050]    A first scheme proposed in the present disclosure defines a new downlink control information (DCI) format for NOMA and includes information needed for canceling a far UE signal in the NOMA DCI format to support NOMA in an LTE system. The first scheme will be described in first and second embodiments. 
         [0051]    A second scheme proposed in the present disclosure includes information needed for canceling a far UE signal in a radio resource control (RRC) message to support NOMA in an LTE system. The second scheme will be described in third through fifth embodiments. 
         [0052]    In the first embodiment using the DCI format, the evolved node B (eNB) provides information needed for canceling a far UE signal to the near UE through the newly defined DCI format. In the first embodiment, the information needed for canceling the far UE signal may include modulation and coding scheme (MCS) information of the far UE, transmission mode (TM) information of the far UE, and precoding information of the far UE. 
         [0053]    In the second embodiment using the DCI format, the eNB provides an identifier of the far UE (and the TM mode information of the far UE) to the near UE through the newly defined DCI format. The near UE obtains the identifier of the far UE (and the TM mode information of the far UE), receives a DCI (defined in the existing LTE standard) for the far UE by using the identifier of the far UE (and the TM mode information of the far UE), and obtains information needed for canceling the far UE signal, which is additionally required, e.g., MCS information of the far UE, precoding information of the far UE, and so forth, from the DCI for the far UE. For reference, the identifier of the UE may be a cell-radio network temporary identifier (C-RNTI), etc. 
         [0054]    In the third embodiment using the RRC message, the eNB provides information needed for canceling a far UE signal to the near UE through an RRC message. The information needed for canceling the far UE signal may include MCS information of the far UE, TM mode information of the far UE, and precoding information of the far UE. 
         [0055]    In a fourth embodiment using the RRC message, the eNB provides the identifier of the far UE to the near UE through the RRC message. The near UE having received the identifier of the far UE receives a DCI (defined in the existing LTE standard) for the far UE and additionally obtains needed information, i.e. the MCS information of the far UE, the precoding information of the far UE, etc., from the DCI for the far UE. 
         [0056]    In a fifth embodiment using the RRC message, the eNB provides various identifiers of candidate far UEs capable of sharing resources with near UEs to the near UEs through the RRC message in NOMA. The near UE attempts to decode the DCI (defined in the existing LTE standard) for a far or long-distance UE actually scheduled as a NOMA UE pair by using the identifier of each candidate far UE and additionally obtains needed information from the DCI of the actually scheduled far UE if the decoding is successful. 
         [0057]    Hereinbelow, various embodiments of the present disclosure will be described. 
         [0058]    In the following description, UEs sharing an identical resource in NOMA may be referred to as a NOMA UE pair or a UE pair. The UE pair means not only two UEs, but also three or more UEs. 
         [0059]    Generally, in a NOMA system, the eNB&#39;s operation of selecting a UE pair by using information of UEs in a cell may be referred to as pairing. For reference, the eNB pairs a UE pair capable of maximizing a NOMA performance gain by using feedback information received from UEs in a cell, e.g., a channel quality indicator (CQI), a precoding matrix indicator (PMI), transmission mode (TM) mode, etc., and allocates an identical resource to the paired UE pair. The eNB transmits information needed for NOMA operations to the paired UE pair. 
         [0060]    The far UE perceives a near UE signal as noise as described with reference to  FIGS. 1A to 1C , and thus may receive a signal in a typical way for a UE to receive a DL signal in an orthogonal multiple access (OMA) system. 
         [0061]    The near UE performs interference cancellation with respect to a far UE signal. More specifically, the near UE demodulates a far UE signal of a received superposed signal at a symbol level or decodes the far UE signal at a codeword level and cancels the demodulated or decoded far UE signal from the received superposed signal. Thereafter, the near UE decodes its (near UE) signal from the received signal from which the far UE signal is cancel. Thus, in the NOMA system, in order for the near UE to demodulate or decode the far UE signal, information needed for canceling the far UE signal is provided to the near UE. 
         [0062]    However, as stated above, in the current 3GPP LTE standard, DL signaling for supporting NOMA is not prescribed. According to the current LTE standard, the eNB transmits information needed for decoding data transmitted in a physical downlink shared channel (PDSCH) through a DCI and transmits the needed information to the UE in a physical downlink control channel (PDCCH). In the current LTE standard, a plurality of formats for a DCI are defined. For example, formats  1 ,  1 A,  1 B,  1 C,  1 D,  2 ,  2 A,  2 B,  2 C, etc., are defined as DCI formats for DL scheduling, and information included in different DCI formats are different and a DCI format to be used may be determined according to a set transmission mode (TM). 
         [0063]      FIG. 2  illustrates DCI formats for scheduling defined in the current LTE standard according to an embodiment of the present disclosure. 
         [0064]    To add information needed for NOMA operations to the DCI formats, a separate DCI format for the NOMA operations needs to be defined. However, when DCI formats are changed simply by adding the information for the NOMA operations to the formats, the number of DCI formats with respect to which the UE has to perform blind decoding increases, significantly increasing the reception complexity of the UE. Moreover, in the current LTE standard, resources are allocated to the UE through the UE-specific PDCCH signaling, and thus, there is no way to identify information required for the near UE to identify information needed for canceling a far UE signal without changing a DCI format. 
         [0065]    The present disclosure newly defines a DCI format for providing information needed for canceling a far UE signal to the near UE for NOMA without changing DCI formats defined in the existing LTE standard. A scheme using a DCI format will be described in the first and second embodiments. 
         [0066]    However, various embodiments using a DCI format proposed in the present disclosure (as will be described later) are limited to a case where the number of UE pairs in NOMA is  2  and a fixed resource is used, and thus proposes a scheme for providing information needed for canceling a far UE signal to the near UE by using an RRC message instead of a new DCI format. A scheme using an RRC message will be described in the third through fifth embodiments. 
         [0067]    Meanwhile, information needed for supporting NOMA is shown in Table 1. 
         [0000]    
       
         
               
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Information 
                 Description 
               
               
                   
               
             
             
               
                 NOMA Indication 
                 NOMA Indication indicates that 
               
               
                   
                 corresponding transmission is NOMA 
               
               
                   
                 transmission. 
               
               
                 NOMA Power Allocation 
                 PA Information indicates a ratio of a 
               
               
                 (PA) Information 
                 transmission power allocated to a signal of 
               
               
                   
                 each UE in NOMA transmission. 
               
               
                   
                 PA Information may be indicated by a 
               
               
                   
                 power offset value that is a difference than 
               
               
                   
                 an existing transmission power value. 
               
               
                   
                 PA Information is information needed not 
               
               
                   
                 only for far UE as well as for Near UE. 
               
               
                   
                 However, for a fixed PA value, PA may not 
               
               
                   
                 be separately provided. In this case, NOMA 
               
               
                   
                 Indication may substitute for PA 
               
               
                   
                 Information. 
               
               
                 Successive Interference 
                 SIC Level indicates the number of signals 
               
               
                 Cancellation (SIC) Level 
                 of far UE for which Near UE is to perform 
               
               
                   
                 SIC operation with respect to corresponding 
               
               
                   
                 resource. 
               
               
                   
                 If the number of UEs sharing resources in 
               
               
                   
                 NOMA is set to 2, SIC Level is fixed to 1, 
               
               
                   
                 such that SIC Level may not be separately 
               
               
                   
                 provided. In this case, NOMA Indication or 
               
               
                   
                 PA may substitute for SIC Level. 
               
               
                   
                 In case of non-NOMA in an identical 
               
               
                   
                 resource, SIC Level for each resource has to 
               
               
                   
                 be indicated. 
               
             
          
           
               
                 Far UE 
                 Resource 
                 Indicate allocated resource information to 
               
               
                 Information 
                 Allocation 
                 far UE. 
               
               
                 Necessary 
                 Information 
                 There is a method for using resource 
               
               
                 for SIC 
                 of far UE 
                 allocation or reducing the size of indication 
               
               
                 Operation of 
                   
                 in existing OMA. 
               
               
                 Near UE 
                 MCS 
                 Indicate MCS Information for far UE 
               
               
                   
                 Information 
                 signals. 
               
               
                   
                 of far UE 
                 There is a method for transmitting this 
               
               
                   
                 (For 
                 information identically to existing 
               
               
                   
                 CW-SIC) 
                 Modulation and Coding Scheme (MCS) 
               
               
                   
                   
                 information or a method for reducing the 
               
               
                   
                   
                 size of data for MCS indication. 
               
               
                   
                 Precoding 
                 Precoding matrix index (PMI) used for DL 
               
               
                   
                 Information 
                 transmission for far UE 
               
               
                   
                 of Far UE 
                 3 bits or 6 bits according to the number of 
               
               
                   
                   
                 used antennas 
               
               
                   
                 Transmission 
                 TM Information indicates a transmission 
               
               
                   
                 Mode (TM) 
                 mode (TM) defined in the LTE standard. 
               
               
                   
                 of Far UE 
                 The TM information is provided to the UE 
               
               
                   
                   
                 through RRC Message in the current LTE 
               
               
                   
                   
                 standard. 
               
               
                   
               
             
          
         
       
     
         [0068]    Among the information of Table 1, information needed for the far UE is only PA information. To provide the PA information to the far UE, another DCI format having another size has to be defined. Thus, it is not efficient to define a DCI format only for the far UE for the PA information needed for the far UE. To this end, it is assumed that in NOMA according to the present disclosure, the PA value is fixed. Thus, in Table 1, the PA value does not need to be provided to either the near UE or the far UE. 
         [0069]    In Table 1, an SIC level is assumed to be  1 . That is, in NOMA, the number of UEs sharing one resource is assumed to be  2 . In this case, the SIC level value does not need to be provided to the UE any longer. 
         [0070]    As to resource allocation information of the far UE, if a resource allocatable to the far UE is fixed to a preset particular resource, the resource allocation information of the far UE may not need to be provided to the near UE. 
         [0071]    In the present disclosure, under the foregoing assumptions, in Table 1, PA information, an SIC level, and resource allocation information of the far UE do not need to be provided to the near UE. Eventually, among the information of Table 1, a NOMA indicator, MCS information of the far UE, precoding information of the far UE, and TM mode information of the far UE are included in information for performing NOMA reception by the near UE. Herein, such information is referred to as information for canceling a far UE signal. 
         [0072]    As discussed above, the first embodiment and the second embodiment use newly defined NOMA DCI formats. However, to use the DCI format, a fixed resource needs to be allocated to the far UE and an SIC level value needs to be fixed to  1 , such that the first embodiment and the second embodiment are intended for NOMA operations under such restrictions. 
         [0073]    The third through fifth embodiments use an RRC message instead of a DCI format. To the various embodiments using the RRC message, the restrictions in the first and second embodiments are not applied. Thus, there is no limitation in the number of NOMA UE pairs, and an allocated resource is not fixed. Each embodiment will be described in detail. 
       First Embodiment 
       [0074]    The first embodiment according to the present disclosure newly defines a DCI format for the near UE and provides information needed for canceling a far UE signal to the near UE through the newly defined DCI format. The information needed for canceling the far UE signal may include MCS information of the far UE, TM mode information of the far UE, and precoding information of the far UE. For reference, in the first embodiment, the newly defined DCI format is the NOMA indicator of Table 1. 
         [0075]      FIG. 3  illustrates an example of a DCI format for the near UE newly defined in the first embodiment of the present disclosure. 
         [0076]    Referring to  FIG. 3 , in the bottom three lines of  FIG. 3 , MCS information of the far UE, TM mode information of the far UE, and precoding information of the far UE are indicated. 
         [0077]    According to the first embodiment, once the eNB provides the MCS information of the far UE, the TM mode information of the far UE, and the precoding information of the far UE to the near UE through the newly defined DCI format, the near UE may cancel interference of the far UE signal by performing successive interference cancellation (SIC) with respect to the far UE signal by using the foregoing information, thereby successfully receiving a signal transmitted to the near UE. 
       Second Embodiment 
       [0078]    The second embodiment of the present disclosure includes an identifier of the far UE and TM mode information of the far UE in a newly defined NOMA DCI format. However, the TM mode information of the far UE is included when a TM mode of the near UE and a TM mode of the far UE are different. The MCS information of the far UE and the precoding information of the far UE, which are included in the DCI format in the first embodiment, are not included in the NOMA DCI format in the second embodiment. 
         [0079]    According to the second embodiment, the eNB provides the identifier of the far UE and the TM mode information of the far UE to the near UE through the newly defined DCI format. The near UE receives a DCI (defined in the existing LTE standard) for the far UE by using the identifier of the far UE and the TM mode information of the far UE, and additionally obtains the MCS information of the far UE and the precoding information of the far UE from the DCI for the far UE. Thereafter, the near UE cancels the interference of the far UE signal by performing SIC with respect to the far UE signal using information needed for canceling the far UE signal, which includes the received information and the additionally obtained information, thereby successfully receiving the transmitted signal. 
       Third Embodiment 
       [0080]    The third embodiment of the present disclosure includes the information needed for canceling the far UE signal, i.e. the MCS information of the far UE, the TM mode information of the far UE, and the precoding information of the far UE in the RRC message. However, the RRC message has to be transmitted to the UE before the eNB performs NOMA transmission to the UE, such that a time interval (i.e. a predetermined number of subframes) between a point in time when the RRC message is transmitted (i.e. a subframe) and a point in time when the NOMA transmission is performed has to be set in advance or information about the time interval has to be included in the RRC message. 
         [0081]    According to the third embodiment of the present disclosure, the eNB transmits the RRC message including the information needed for canceling the far UE signal to the near UE. The UE receives the information through the RRC message, and performs operations for NOMA reception by using the information obtained from the RRC message upon the elapse of a preset time or a predetermined time (i.e. a predetermined subframe) corresponding to time interval information included in the RRC message. More specifically, the near UE performs SIC with respect to the far UE signal included in a NOMA signal received from the eNB through the PDSCH by using the information needed for canceling the far UE signal. In this way, by canceling the interference of the far UE signal, a signal transmitted to the near UE may be successfully received. 
       Fourth Embodiment 
       [0082]    The fourth embodiment of the present disclosure includes an identifier of the far UE and TM mode information of the far UE in an RRC message. However, the TM mode information of the far UE is included when a TM mode of the near UE and a TM mode of the far UE are different. In addition, the RRC message has to be transmitted to the UE before the eNB performs NOMA transmission to the UE, such that a time interval (i.e. a predetermined subframe) between a point in time when the RRC message is transmitted (i.e. a subframe) and a point in time when the NOMA transmission is performed (i.e. a subframe) has to be set in advance or has to be included in the RRC message. 
         [0083]    According to the fourth embodiment, once the eNB provides the identifier of the far UE and the TM mode information of the far UE to the near UE through the RRC message, the near UE receives a DCI (defined in the existing LTE standard) for the far UE by using the identifier of the far UE and the TM mode information of the far UE after the predetermined subframe, and additionally obtains the MCS information of the far UE and the precoding information of the far UE from the DCI for the far UE. Thereafter, the near UE cancels the interference of the far UE signal by performing SIC with respect to the far UE signal included in the NOMA signal received through the PDSCH using information needed for canceling the far UE signal, thereby successfully receiving the transmitted signal. 
       Fifth Embodiment 
       [0084]    In the third embodiment and the fourth embodiment, the eNB has to send an RRC message including information about the far UE to the near UE before performing NOMA transmission. Thus, the eNB needs to perform pairing between the far UE and the near UE for NOMA before sending the RRC message. In this way, once a UE pair is paired in advance for NOMA and a resource is previously scheduled to the UEs, a greater performance loss due to previous scheduling may occur than a performance gain based on NOMA. 
         [0085]    Thus, in the fifth embodiment of the present disclosure, not to previously perform pairing and scheduling with respect to UEs for NOMA, an identifier of each of a plurality of candidate far UEs capable of NOMA pairing is provided to the near UE through the RRC message. However, if the TM modes of the candidate far UEs are different from the TM mode of the near UE, the TM mode information of the far UE is also included in the RRC message. In addition, the RRC message has to be transmitted to the UE before the eNB performs NOMA transmission to the UE, such that a time interval (i.e. a predetermined subframe) between a point in time when the RRC message is transmitted (i.e. a subframe) and a point in time when the NOMA transmission is performed (i.e. a subframe) has to be set in advance or has to be included in the RRC message. 
         [0086]    That is, according to the fifth embodiment of the present disclosure, the eNB provides identifier information (and TM mode information of the candidate far UEs) to the near UE through the RRC message. The near UE performs decoding with respect to a DCI (defined in the existing LTE standard) for the far UE by using the identifier information (and the TM mode information of the candidate far UEs) after the predetermined subframe. If decoding with respect to the DCI for the far UE is successful, the MCS information of the actual far UE and the precoding information of the actual far UE may be additionally obtained from the DCI. Thereafter, the near UE cancels the interference of the far UE signal by performing SIC with respect to the far UE signal using information needed for canceling the actual far UE signal, thereby successfully receiving the transmitted signal. 
         [0087]    Hereinbelow, operations of the eNB according to various embodiments of the present disclosure will be described in detail. 
         [0088]      FIG. 4  is a view for describing operations of an eNB according to the first and second embodiments of the present disclosure. 
         [0089]    Referring to  FIG. 4 , in operation  401 , the eNB collects channel quality information like CQI, precoding information like PMI, TM mode information, MCS information, and so forth. The information may be received from UEs or may be determined by the eNB. 
         [0090]    In operation  403 , the eNB determines a NOMA UE pair by using the collected information and performs NOMA scheduling that allocates resources to the determined UE pair. To determine the UE pair, for example, a UE pair having a large CQI difference may be selected. The precoding information, the TM mode information, the MCS information, and so forth may also be considered for the determination. However, as described above, in the first embodiment and the second embodiment, it is assumed that the resource is fixed and 2 UEs are included in the UE pair. 
         [0091]    In operation  405 , the eNB generates information necessary for canceling a far UE signal for the determined UE pair by using a DCI according to the above-described embodiment. That is, the information necessary for canceling a far UE signal is generated using a DCI format. 
         [0092]    In operation  407 , the eNB transmits the generated information necessary for canceling the far UE signal to the near UE through a PDCCH. In operation  409 , the eNB generates a NOMA signal by superposing signals for the respective UEs of the UE pair and sends the generated NOMA signal through the PDSCH. For reference, in the various embodiments of the present disclosure, it is assumed that transmission power allocation (PA) for the signals for the respective UEs of the UE pair uses a fixed value. 
         [0093]      FIG. 5  is a view for describing operations of an eNB according to third through fifth embodiments of the present disclosure. 
         [0094]    Referring to  FIG. 5 , operation  501  is identical to operation  401  of  FIG. 4  and operation  503  is identical to operation  403  of  FIG. 4 . However, in the third through fifth embodiments, it is assumed that the resource is fixed and the number of UEs included in the UE pair is not limited to two (2). 
         [0095]    In operation  505 , the eNB generates the information necessary for canceling the far UE signal using the RRC message. The information necessary for canceling the far UE signal may include the MCS information of the far UE, the TM mode information of the far UE, and the precoding information of the far UE in the third embodiment, includes the identifier of the far UE and the TM mode information of the far UE in the fourth embodiment, and includes an identifier of each candidate far UE in the fifth embodiment. 
         [0096]    In operation  507 , the eNB sends the generated RRC message to the near UE through a higher layer. 
         [0097]    In operation  509 , the eNB generates a NOMA signal by superposing signals for the respective UEs of the UE pair and sends the generated NOMA signal through the PDSCH. For reference, in the various embodiments of the present disclosure, it is assumed that transmission PA for the signals for the respective UEs of the UE pair uses a fixed value. Meanwhile, the NOMA signal is sent in a subframe upon the elapse of a preset time or a predetermined time (i.e. a predetermined subframe) corresponding to time interval information included in the RRC message. 
         [0098]      FIG. 6  is a view for describing operations of a near UE according to the first and second embodiments of the present disclosure. 
         [0099]    Referring to  FIG. 6 , in operation  601 , the near UE receives its DCI including information necessary for canceling interference of a far UE signal through the PDCCH. 
         [0100]    In operation  603 , the near UE obtains the information necessary for canceling the interference of the far UE signal from the received DCI. The information necessary for canceling the far UE signal may include the MCS information of the far UE, the TM mode information of the far UE, and the precoding information of the far UE in the first embodiment, and includes the identifier of the far UE and the TM mode information of the far UE in the second embodiment. 
         [0101]    In operation  605 , the near UE receives a NOMA signal generated by superposition of signals of a UE pair through the PDSCH. 
         [0102]    In operation  607 , the near UE cancels the far UE signal from the NOMA signal by using the information necessary for canceling the interference of the far UE signal. More specifically, the near UE demodulates a far UE signal of a received superposed signal at a symbol level or decodes the far UE signal at a codeword level and cancels the demodulated or decoded far UE signal from the received superposed signal. 
         [0103]      FIG. 7  is a view for describing operations of a near UE according to the three through fifth embodiments of the present disclosure. 
         [0104]    Referring to  FIG. 7 , in operation  701 , the near UE receives an RRC message including information necessary for canceling interference of the far UE signal through a higher layer. The information necessary for canceling the far UE signal may include the MCS information of the far UE, the TM mode information of the far UE, and the precoding information of the far UE in the third embodiment, includes the identifier of the far UE and the TM mode information of the far UE in the fourth embodiment, and includes an identifier of each candidate far UE in the fifth embodiment. 
         [0105]    In operation  703 , the near UE receives the NOMA signal generated by superposition of signals of the UE pair from the eNB upon the elapse of a preset time or a predetermined time (i.e. a predetermined subframe) corresponding to time interval information included in the RRC message. 
         [0106]    In operation  705 , the near UE cancels interference of the far UE signal at a symbol level or a codeword level by performing SIC with respect to the far UE signal in the received NOMA signal using the information necessary for canceling the far UE signal, which is obtained from the RRC message. 
         [0107]      FIG. 8  is a block diagram of an eNB that performs operations according to various embodiments of the present disclosure. 
         [0108]    Referring to  FIG. 8 , the eNB may include a transceiver  801 , a controller  803  (i.e. at least one processor), and an information generator  805 . 
         [0109]    The transceiver  801  receives channel quality information like CQI, precoding information like PMI, TM mode information, MCS information, and so forth. The information may be received from UEs or may be determined by the eNB. 
         [0110]    The controller  803  determines a NOMA UE pair by using the collected information, performs NOMA scheduling that allocates resources to the determined UE pair, and controls overall operations corresponding to the description of the foregoing embodiments. For example, the controller  803  may generate a NOMA signal by superposing signals for respective UEs of the UE pair and send the NOMA signal to the UE pair through the transceiver  801 . 
         [0111]    The information generator  805  generates information necessary for canceling a far UE signal for the determined UE pair by using a DCI according to the above-described embodiment. The generated DCI or RRC message is sent to the near UE through the transceiver  801 . 
         [0112]    The description made with reference to  FIG. 8  regards only to main operations of the various embodiments of the present disclosure for convenience, and even operations not described with reference to  FIG. 8  may be included in the operations of the near UE described in the various embodiments of the present disclosure. 
         [0113]      FIG. 9  is a block diagram of an UE that performs operations according to various embodiments of the present disclosure. 
         [0114]    Referring to  FIG. 9 , the UE may include a transceiver  901 , a controller  903  (i.e. at least one processor), and an interference canceller  905 . 
         [0115]    The transceiver  901  receives its DCI through the PDCCH or receives an RRC message through a higher layer. The DCI or the RRC message may include information necessary for canceling interference of the far UE signal. The transceiver  901  receives a NOMA signal generated by superposition of signals of a UE pair through the PDSCH. 
         [0116]    The controller  903  detects the information necessary for canceling the interference of the far UE signal from the DCI or the RRC message and controls overall operations of the UE according to the various embodiments of the present disclosure. 
         [0117]    The interference canceller  905  cancels the far UE signal from the NOMA signal by using the information necessary for canceling the interference of the far UE signal. 
         [0118]    The description made with reference to  FIG. 9  regards only to main operations of the various embodiments of the present disclosure for convenience, and even operations not described with reference to  FIG. 9  may be included in the operations of the near UE described in the various embodiments of the present disclosure. 
         [0119]    Particular aspects of the present disclosure may be implemented with a computer-readable code on a computer-readable recording medium. The computer readable recording medium may be any type of data storage device that may store data readable by a computer system. Examples of record-mediums readable by the computer may include a read-only memory (ROM), a random-access memory (RAM), compact disc ROM (CD-ROM), magnetic tapes, floppy disks, optical data storage devices, carrier waves (such as data transmission through the Internet). The computer readable recording medium may be distributed through computer systems connected over a network, and thus the computer readable code is stored and executed in a decentralized manner. Further, functional programs, codes and code segments for achieving the present disclosure may be easily interpreted by programmers skilled in the art which the present disclosure pertains to. 
         [0120]    The apparatus and method according to an embodiment of the present disclosure may be implemented by hardware, software, or a combination of hardware and software. Such arbitrary software may be stored, for example, in a volatile or non-volatile storage device (e.g., a ROM, etc.), a memory (e.g., a RAM, a memory chip, a memory device, or a memory IC), or a machine (e.g., computer) recordable optical or magnetic storage medium (e.g., a CD, a digital versatile disc (DVD), a magnetic disc, a magnetic tape, etc.) regardless of its ability to erase or rewrite. It can be seen that the method according to the present disclosure may be implemented by a computer or a portable terminal which includes a controller and a memory, and the memory is an example of a machine-readable storage medium which is suitable for storing a program or programs including instructions for implementing the embodiment of the present disclosure. 
         [0121]    Therefore, the present disclosure includes a program including codes for implementing an apparatus or method claimed in an arbitrary claim and a machine (computer)-readable storage medium for storing such a program. The program may be electronically transferred through an arbitrary medium such as a communication signal delivered through a wired or wireless connection, and the present disclosure properly includes equivalents thereof. 
         [0122]    The apparatus according to an embodiment of the present disclosure may receive and store the program from a program providing device connected in a wired or wireless manner. The program providing device may include a memory for storing a program including instructions for instructing the apparatus to execute a preset method, information necessary for the method, a communication unit for performing wired or wireless communication with the apparatus, and a controller for transmitting a corresponding program to the apparatus at the request of the apparatus or automatically. 
         [0123]    While the present disclosure has been shown and described with reference to various embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the appended claims and their equivalents.