Abstract:
The present disclosure relates to fifth generation (5G) or pre-5G communication systems provided to support a higher data rate than that given by long term evolution (LTE) or other post-fourth generation (4G) communication systems. A method for performing a sidelink communication by a terminal is provided. The method includes sending, to a base station, a request for multiple grants for the sidelink communication and a first indicator indicating whether the terminal supports multiple transmissions of the sidelink communication to different destinations in a sidelink control (SC) period, receiving the multiple grants from the base station, and performing the multiple transmissions to the different destinations in the SC period.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit under 35 U.S.C. §119(a) of an Indian patent application filed on Oct. 29, 2015 in the Indian Patent Office and assigned Serial number 5843/CHE/2015, the entire disclosure of which is hereby incorporated by reference. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to sidelink communication methods and apparatuses in wireless communication systems. More particularly, the present disclosure relates to sidelink communication methods and apparatuses for processing grants on side link communications. 
       BACKGROUND 
       [0003]    In order to meet the demand for wireless data traffic soaring since the fourth generation (4G) communication system came to the market, there are ongoing efforts to develop enhanced fifth generation (5G) communication systems or pre-5G communication systems. The 5G communication system or pre-5G communication system is called the beyond 4G network communication system or post long term evolution (LTE) system. 
         [0004]    For higher data transmit rates, 5G communication systems are considered to be implemented on ultra-high frequency bands (mmWave), such as, eg., 60 GHz. To mitigate pathloss on the ultra-high frequency band and increase the reach of radio waves, the following techniques are taken into account for the 5G communication system: beamforming, massive multi-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamfoming, and large scale antenna. 
         [0005]    Also being developed are various technologies for the 5G communication system to have an enhanced network, such as evolved or advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-point (CoMP), and interference cancellation. 
         [0006]    There are also other various schemes under development for the system including, e.g., hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) (FQAM) and sliding window superposition coding (SWSC), which are advanced coding modulation (ACM) schemes, and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA), which are advanced access schemes. 
         [0007]    The advent of smartphones led to a sharp increase in data traffic. As the population of using smartphones and application services through smartphones are likely to sharply grow up, mobile data traffic is anticipated to increase even more. In particular, if intelligent communications utilizing things come into play, such as communications between human beings and things or inter-thing communications, which are regarded as a brand-knew market as beyond communications between human beings, traffic forwarded to base stations may increase to the extent difficult for them to handle. 
         [0008]    A noticeable technique to address such issues s direct inter-device communication technology. Such technology also called D2D communication or sidelink communication draws attention for both licensed bands used for cellular mobile communications and unlicensed bands used for Wi-Fi or other similar communications. 
         [0009]    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 
       [0010]    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 grant processing method and apparatus enabling multiple transmissions to different destinations using multiple grants. 
         [0011]    Another aspect of the present disclosure is to provide a grant processing method and apparatus enabling multiple transmissions to one destination using multiple grants. 
         [0012]    Another aspect of the present disclosure is to provide a grant processing method and apparatus enabling a user equipment (UE) having a plurality of source identifications (IDs) to relay data using multiple grants. 
         [0013]    In accordance with an aspect of the present disclosure, a method for performing a sidelink communication by a terminal is provided. The method includes sending, to a base station, a request for multiple grants for the sidelink communication and a first indicator indicating whether the terminal supports multiple transmissions of the sidelink communication to different destinations in a sidelink control (SC) period, receiving the multiple grants from the base station, and performing the multiple transmissions to the different destinations in the SC period. 
         [0014]    In accordance with another aspect of the present disclosure, a method for processing a grant in a sidelink communication by a base station is provided. The method includes receiving, from a terminal, a request for multiple grants allowing the terminal to perform multiple transmissions for the sidelink communication and a first indicator indicating whether the terminal supports multiple transmissions of the sidelink communication to different destinations in a SC period, allocating the multiple grants for the terminal, and sending the multiple grants to the terminal. 
         [0015]    In accordance with another aspect of the present disclosure, a terminal for performing a sidelink communication is provided. The terminal includes a transmitter configured to send, to a base station, a request for multiple grants for the sidelink communication and a first indicator indicating whether the terminal supports multiple transmissions of the sidelink communication to different destinations in a SC period, a receiver configured to receive the multiple grants from the base station, and at least one processor configured to perform the multiple transmissions to the different destinations in the SC period. 
         [0016]    In accordance with another aspect of the present disclosure, a base station for performing a sidelink communication is provided. The base station includes a receiver configured to receive, from a terminal, a request for multiple grants allowing the terminal to perform multiple transmissions for the sidelink communication and a first indicator indicating whether the terminal supports multiple transmissions of the sidelink communication to different destinations in a SC period, at least one processor configured to allocate the multiple grants for the terminal, and a transmitter configured to send the multiple grants to the terminal. 
         [0017]    According to the present disclosure, multiple grants all may be accommodated, preventing waste of sidelink communication resources. 
         [0018]    According to the present disclosure, a UE may perform sidelink communication only when a grant is provided and may accommodate multiple grants, preventing unnecessary transmission attempt and transmission interruption for neighbor devices. 
         [0019]    According to the present disclosure, an evolved node B (eNB) may send multiple grants only to UEs attempting multiple transmissions while allowing the UEs to perform sidelink communication, thereby allowing for efficient management of sidelink communication resources 
         [0020]    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 THE DRAWINGS 
         [0021]    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: 
           [0022]      FIG. 1  is a view illustrating a concept of communication using a base station and sidelink communication according to an embodiment of the present disclosure; 
           [0023]      FIG. 2  is a view illustrating an example of a grant received by a user equipment (UE) for a sidelink control (SC) period according to an embodiment of the present disclosure; 
           [0024]      FIG. 3  is a view illustrating an example of performing sidelink communication using a grant according to an embodiment of the present disclosure; 
           [0025]      FIG. 4  is a view illustrating an example of processing multiple grants received by a UE for a SC period according to an embodiment of the present disclosure; 
           [0026]      FIG. 5  is a view illustrating an example of multiple grants received by a UE for a SC period according to an embodiment of the present disclosure; 
           [0027]      FIGS. 6A and 6B  are views illustrating multiple grants received in different radio frames including subframes according to various embodiments of the present disclosure; 
           [0028]      FIG. 7  is a view illustrating an example of processing multiple grants in sidelink communication using a first indicator and a second indicator according to an embodiment of the present disclosure; 
           [0029]      FIG. 8  is a view illustrating an example of processing multiple grants in sidelink communication using a first indicator included in a UE capability message according to an embodiment of the present disclosure; 
           [0030]      FIG. 9  is a view illustrating an example of receiving and processing multiple grants by a UE according to an embodiment of the present disclosure; 
           [0031]      FIG. 10  is a view illustrating an example of processing multiple grants in sidelink communication using multiple sidelink resource pools (SC pools) according to an embodiment of the present disclosure; 
           [0032]      FIG. 11  is a view illustrating an example of processing multiple grants in sidelink communication using a first indicator and multiple SC pools according to an embodiment of the present disclosure; 
           [0033]      FIG. 12  is a view illustrating an example of processing multiple grants in sidelink communication using multiple SC pools and multiple sidelink radio network temporary identities (RNTIs) according to an embodiment of the present disclosure; 
           [0034]      FIG. 13  is a view illustrating an example of transmitting media access control packet data units (MAC PDUs) to multiple destinations by multi-scheduling assignment (multi-SA) transmission or multi-data transmission according to an embodiment of the present disclosure; 
           [0035]      FIG. 14  is a view schematically illustrating a configuration of a UE according to an embodiment of the present disclosure; and 
           [0036]      FIG. 15  is a view schematically illustrating a configuration of an evolved node B (eNB) according to an embodiment of the present disclosure. 
       
    
    
       [0037]    Throughout the drawings, like reference numerals will be understood to refer to like parts, components, and structures. 
       DETAILED DESCRIPTION 
       [0038]    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, descriptions of well-known functions and constructions may be omitted for clarity and conciseness. 
         [0039]    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. 
         [0040]    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. 
         [0041]    Sidelink communication for enabling data communication services between user equipments (UEs) is being researched by communication standardization groups. During such sidelink communication, a transmitting IT may send data packets to a group of UEs, broadcast the data packets to all the UEs, or send unicast data packets to a particular LIE The sidelink communication between the transmitting IT and a receiving LT is essentially connnectionless. In other words, before the transmitting UE starts to send data packets, no link is established between the transmitting UE and the receiving UE, and no control messages are exchanged therebetween. 
         [0042]    During transmission, the transmitting UE may include a source identifier and destination identifier in data packets. The source identifier may be set as the UE identification (ID) of the transmitting LTE. The destination identifier is an identifier for a receiving UE targeted for packet transmission. The destination identifier indicates whether the packet is a broadcast packet, unicast packet, or a packet intended for one group. For the broadcast packet, the destination identifier may be set as a broadcast group identifier. For the group cast packet, the destination identifier may be set as a group identifier of its intended group. For the unicast packet, the destination identifier may be set as the UE ID. 
         [0043]    During the sidelink communication, a normal UE performs one sidelink transmission with another destination UE. For a sidelink transmission, a UE should receive a grant from an evolved node B (eNB). Meanwhile, the UE may perform multiple transmissions. The multiple transmissions may include simultaneously transmitting a plurality of data packets to several destinations or one or more transmitting single data packets to one destination over several times. 
         [0044]    Thus, the UE needs to receive several grants. However, upon receiving several grants, the UE cannot perform efficient sidelink multiple transmissions under grant processing methods of the related art. Such approaches may delay transmissions to other destinations. Further, as per the approaches of the related art, during sidelink communication, the LIE may have multiple source IDs and may use only one sidelink grant to transmit one or more medium access control (MAC) protocol data units (PDUs) corresponding to the same source ID and destination IDs. Thus, the approaches of the related art may delay transmission of data along with other source IDs and/or destination IDs. To address the above issues, a need exists for a method enabling transmission using multiple sidelink grants. Hereinafter, preferred embodiments of the present disclosure are described in detail with reference to the accompanying drawings. The same reference denotations may be used to refer to the same or similar elements throughout the specification and the drawings. When making the gist of the present disclosure unclear, the detailed description of known functions or configurations is skipped. The terms as used herein are defined considering the functions in the present disclosure and may be replaced with other terms according to the intention or practice of the user or operator. Therefore, the terms should be defined based on the overall disclosure. 
         [0045]    Before detailing the present disclosure, some terms as used herein may be interpreted as follows, for example. However, it should be noted that the present disclosure is not limited thereto. 
         [0046]    The base station (BS) is an entity communicating with a LE and may be denoted a nodeB (NB), eNB, or access point (AP). 
         [0047]    The mobile station (MS) is an entity communicating with a base station and may be denoted a UE, mobile equipment (ME), device, or terminal. 
         [0048]    Sidelink communication also known as device to device (D2D) communication is a direct communication scheme, meaning a technique enabling communication with other device within a short range without passing through a network infrastructure such as a base station. Sidelink communication is long term evolution (LTE)-based direct communication. 
         [0049]      FIG. 1  is a view illustrating a concept of communication using abase station and sidelink communication according to an embodiment of the present disclosure. 
         [0050]      FIG. 1  illustrates a method in which a UE  1   a  communicates with another UE  1   b.    
         [0051]    Wireless communication may include network communication and direct communication depending on whether a network comes in use. The network communication uses a network while the direct communication uses wireless connections for neighboring user devices. For example, Bluetooth communication and sidelink communication may be direct communication methods. 
         [0052]    The UE  1   a  may communicate with the other UE  1   b  via an eNB  2 . Path I may represent a path through which data is transmitted in the network communication. Further, the UE  1   a  may directly communicate with the other UE  1   b . The UE  1   a  may perform sidelink communication with the other UE  1   b . Path II represents a path through data transmitted in the sidelink communication. The sidelink communication may provide two types of proximity based services (ProSe), i.e., direct discovery and direct communication. 
         [0053]      FIG. 2  is a view illustrating an example of a grant received by a UE for a sidelink control (SC) period according to an embodiment of the present disclosure. 
         [0054]    Referring to  FIG. 2 , a UE  10  may perform sidelink communication on specified subframes during duration of an SC period  210 . SC data and sidelink data may he transmitted using subframes  200  of the SC period  210 . The SC period  210  may be the period over which resources allocated in a cell for the transmissions of the SC data and sidelink data occur. The SC period  210  may be defined as a period from a time when the SC data is generated to a time when next SC data is generated and may include an SC region  211 -N and a sidelink data region  212 -N. The SC region  211 -N may be configured of one or more SC subframes for transmitting the SC data, and the sidelink data region  212 -N may be configured of data subframes for transmitting sidelink data. Taking  FIG. 2  as an example, the SC period  210  may be a period from the subframe of the SC region  211 -N of the SC period  210 -N to a last data subframe (a subframe positioned right before an SC region  211 -N+1 of an SC period  210 -N+1) of the sidelink data region  212 -N. In the SC period  210 , the UE  10  may transmit SC data included in the SC region  211 -N in an SC subframe and subsequently transmit sidelink data included in the sidelink data region  212 -N in a data subframe. The SC period  210  may continuously be followed by other SC periods. For example, as shown in  FIG. 2 , the SC period  210  may be continuously repeated as the SC period N ( 210 -N) and the SC period ( 210 -N+1). The SC period N+1 ( 210 -N+1) is a period continuously subsequent to the SC period N ( 210 -N). The UE  10  performs sidelink communication during the SC period N ( 210 -N) and the SC period N+1 ( 210 -N+1). 
         [0055]    To support the sidelink communication of the LIE  10 , the eNB  20  may allocate resources and send a grant to the UE  10 . Here, the grant may be valid during a particular SC period. After receiving the grant, the UE  10  may determine an SC period  210  corresponding to the grant. Preferably, the received grant may remain valid for a first SC period starting, at least some (e.g., at least four) subframes after the subframe where the grant is received. Here, such offset is necessary as a processing time for the UE  10  to perform sidelink communication. Hence, the first SC period starting after the offset is rendered valid and available. The UE  10  may perform transmission during the first SC period using the received grant. For example, the UE  10  receiving the grant during the first SC period may perform sidelink communication with a destination UE by sending the SC data and sidelink data. Here, the UE  10  would transmit a scheduling assignment (SA) in resources of scheduling control region and data in resources of sidelink data region marked by the grant to one destination having a destination ID  1  using the received grant. 
         [0056]    In the case shown in  FIG. 2 , the UE  10  receives a single grant  201 . The single grant  201  may be transmitted using a particular subframe  200  within a grant allocation period  220 . There may be continuous grant allocation periods  220 . For example, the SC period  220  may be continuously repeated as a grant allocation period N ( 220 -N) and a grant allocation period N+1 ( 220 -N+1). The grant allocation period N+1 ( 220 -N+1) is a period continuously subsequent to the grant allocation period N ( 220 -N). In the grant allocation period N ( 220 -N), the UE  10  may receive the single grant  201  from the eNB  20  for transmitting SC data and sidelink data during the SC period N ( 210 -N). The grant allocation period N ( 220 -N) may be a period during which grants for the SC period N ( 210 -N) may be received and may be represented as corresponding to the SC period N ( 210 -N). The grant allocation period N+1 ( 220 -N+1) may be a period during which grants for the SC period N+1 ( 210 -N+1) may be received and may be represented as corresponding to the SC period N+1 ( 210 -N+1). 
         [0057]    The UE  10  may perform sidelink communication using the single grant  201  received in a particular subframe in the grant allocation period N ( 220 -N). Here, the grant allocation period N ( 220 -N) may be offset from the SC period N ( 210 -N) for transmission in the SC period N ( 210 -N). The offset subframe  213 -N−1 for the offset interval may be at least four subframes (e.g., 4 ms). Thus, the grant allocation period N ( 220 -N) may begin at least four subframes earlier than the SC period N ( 210 -N). The duration of each grant allocation period  220  may be the same as that of the SC period  210 . If the grant allocation period  220  and the SC period  210  has the same duration, and the SC period N ( 210 -N) starts delayed by the offset subframe  213 -N−1, the UE  10  may transmit SC data and sidelink data during the same SC period N+ 1  ( 210 -N+1) as the grant allocation period N ( 220 -N), from a subframe after the time when the grant allocation period N ( 220 -N) plus the offset subframe ( 213 -N). Here, the UE  10  may be permitted to do sidelink communication by the grant received during the grant allocation period N ( 220 -N). The offset subframes  213 -N−1,  213 -N, and  213 -N+1 are not limited to four in number, and more or less offset subframes may be included. 
         [0058]      FIG. 3  is a view illustrating an example of performing sidelink communication using a grant according to an embodiment of the present disclosure. 
         [0059]    Referring to  FIG. 3 , to transmit packets, the transmitting-side UE  10  requires resources (e.g., time and frequency) for transmitting SC data and sidelink data. To obtain resources, the UE  10  interested in sidelink communication may transmit a destinationInfoList, i.e., a sidelink UE information (SidelinkUEInformation) message including a list of destinations, to a base station, i.e., the eNB  20  at operation S 305 . 
         [0060]    The eNB  20  may allocate a sidelink resource pool (SC pool) and sidelink radio network temporary identity (SL-RNTI) for transmitting SC data through a radio resource control (RRC)connection reconfiguration message at operation S 310 . The SC pool represents time and frequency resources by which SC (scheduling) data may be transmitted, i.e., at least one or more subframes and the respective physical resource blocks of the subframes. The time and frequency may periodically be allocated by the SC period  210 . 
         [0061]    Thereafter, the UE  10  may request dedicated resources for transmission of SC data and sidelink data by transmitting a sidelink buffer status report (BSR) at operation S 315 . 
         [0062]    The eNB  20  may allocate dedicated resources and send a grant  201  for sidelink communication, i.e., information about the dedicated resources at operation S 320 . The received single grant  201  may be one for an SC period first available as starting predetermined subframes after the subframe of the end point of the grant allocation period N ( 220 -N) during which the single grant  201  has been received. The LTE  10  may perform transmission during the first available SC period  210  using the single grant  201  at operation S 325 . 
         [0063]      FIG. 4  is a view illustrating an example of processing multiple grants received by a UE for an SC period according to an embodiment of the present disclosure. 
         [0064]    When the LTE  10  receives multiple grants corresponding to the SC period  210 , the UE  10  may use one of the grants, but not the rest. For example, the UE  10  may use the grant received latest but not its previous grants. 
         [0065]    Referring to  FIG. 4 , the UE  10  may receive multiple grants, e.g., a first grant  401  and a second grant  402  and may use the second grant  402  which has been received latest while not using the first grant  401 . 
         [0066]    Based on the received sidelink grant, the UE  10  may send MAC PDUs to one destination having destination ID  1 . The reason is that SC data may represent only one destination ID. In order to transmit MAC PDUs corresponding to the same source ID and destination ID, the UE  10  may use only grant received latest corresponding to the SC period. The source ID and destination ID may be included in the MAC headers of the MAC PDUs. A UE playing a role as a relay (hereinafter, “relaying UE”) may have other source IDs for other packet data network (PDN) connections. The relaying UE may relay packets from other remote UEs to other PDN connections or from other PDN connections to other remote UEs and may communicate with remote UEs using other source IDs. Hence, the relaying UE may have a more need for a scheme for processing multiple grants. 
         [0067]      FIG. 5  is a view illustrating an example of multiple grants received by a UE for an SC period according to an embodiment of the present disclosure. 
         [0068]    Referring to  FIG. 5 , all grants received for the SC period  210  are valid grants. The UE  10  may use all of the grants received for the SC period  210  for transmission during the SC period  210 . The UE  10 , absent a sufficient amount of data to be transmitted, may use only some of the multiple grants allocated. 
         [0069]    In the case shown in  FIG. 5 , two grants  401  and  402  may be received. The multiple grants  401  and  402  may be transmitted using any one subframe  200  in the grant allocation period  220 . In the grant allocation period N ( 220 -N), the UE  10  may receive the multiple grants  401  and  402  from the eNB  20  for transmitting SC data and sidelink data during the SC period N ( 210 -N). 
         [0070]    The multiple grants  401  and  402  may allow for transmission of SC data and sidelink data in the SC period N ( 210 -N). Preferably, the first grant  401  is one for a SC period first available starting at least some pre-defined subframes after the subframe where the first grant  401  has been received. Here, the SC period first available may occur after the grant allocation period N ( 220 -N), Preferably, the second grant  402  may be one for a SC period first available starting at least a predetermined number of subframes after the subframe where the second grant  402  has been received. Here, the SC period first available may also occur after the grant allocation period N ( 220 -N) and may be the same as an SC period corresponding to the first grant  401 . The first grant  401  and the second grant  402  both correspond to the SC period N ( 210 -N), and thus, the UE  10  may determine that the first grant  401  and the second grant  402  are valid during the SC period N ( 210 -N). The UE  10  may use the first grant  401  and the second grant  402  for sidelink transmission during the SC period N ( 210 -N). 
         [0071]    Preferably, the first grant  401  and the second grant  402  may be received during the grant allocation period N ( 220 -N). The multiple grants  401  and  402  received in the grant allocation period N ( 220 -N) may correspond to the SC period N ( 210 -N). The UE  10  may perform sidelink communication using the multiple grants  401  and  402  of the grant allocation period N ( 220 -N). Here, the grant allocation period N ( 220 -N) may be offset from the SC period N ( 210 -N) for transmission in the SC period N ( 210 -N). The offset subframe  213 -N−1 for the offset interval may be at least four subframes (e.g., 4 ms). Thus, the grant allocation period N ( 220 -N) may begin at least four subframes earlier than the SC period N ( 210 -N). The duration of each grant allocation period  220  may be the same as that of the SC period  210 . If the grant allocation period  220  and the SC period  210  has the same duration, and the SC period N ( 210 -N) starts delayed by the offset subframe  213 -N−1, the UE  10  may transmit SC data and sidelink data during the same SC period N+1 ( 210 -N+1) as the grant allocation period N ( 220 -N), from a subframe after the time when the grant allocation period N ( 220 -N) plus the offset subframe ( 213 -N). The UE  10  may be permitted to do sidelink communication by the grant received during the grant allocation period N ( 220 -N). The offset subframes  213 -N- 1 ,  213 -N, and  213 -N+1 are not limited to four in number, and more or less offset subframes may be included. Here, the UE  10  may perform single/multiple transmissions to a plurality of destinations having a plurality of destination IDs or multiple transmissions to a single destination having one destination ID by the first grant  401  and the second grant  402 . 
         [0072]    According to an embodiment of the present disclosure, when multiple grants are received by the UE  10  for an SC period, the UE  10  may use only some of the grants. Not all of the received grants are multiple valid grants. The UE  10  may determine whether the multiple grants are valid and may perform multiple transmissions corresponding to the multiple valid grants. In the embodiment, the UE  10  may determine that amongst the multiple sidelink(SL) grants received in same subframe number of distinct radio frames the SL grant received in latest radio frame is a valid grant. In the embodiment, the UE  10  also may determine that amongst the multiple SL grants received in a radio frame, the SL grant which is received in latest subframe is a valid grant. 
         [0073]      FIGS. 6A and 6B  are views illustrating multiple grants received in different radio frames including subframes according to various embodiments of the present disclosure. 
         [0074]    The UE  10  may determine that amongst the multiple SL grants received in same subframe number of distinct radio frames, the SL grant received in latest radio frame is a valid grant. 
         [0075]    Referring to  FIG. 6A , the UE  10  may select some of the five grants received in five different subframes for the SC period N ( 210 -N) or SC period N+1 ( 210 -N+1). It may be assumed that the multiple grants include a grant  1 - 1  ( 601 - 1 ), a grant  1 - 2  ( 601 - 2 ), a grant  1 - 3  ( 601 - 3 ), a grant  2  ( 602 ), and a grant  3  ( 603 ), and the plurality of radio frames include a radio frame  1 , a radio frame  2 , and a radio frame  3 . According to an embodiment of the present disclosure, the grant  1 - 1  ( 601 - 1 ) may be received in subframe  0  of the radio frame  1 , the grant  1 - 2  ( 601 - 2 ) in subframe  0  of the radio frame  2 , the grant  2  ( 602 ) in subframe  2  of the radio frame  2 , the grant  1 - 3  ( 601 - 3 ) in subframe  0  of the radio frame  3 , and the grant  3  ( 603 ) in subframe  3  of the radio frame  3 . Here, the radio frame  2  may come after the radio frame  1 , and the radio frame  3  after the radio frame  2 . Subframes  0  to  3 , which are smaller units than a radio frame, are not limited for absolute timings by logical symbols. The grant  1 - 1  to the grant  1 - 3  ( 601 - 1 ,  601 - 2 , and  601 - 3 ), respectively, may be received in subframe  0  of the radio frame  1 , subframe  0  of the radio frame  2 , and subframe  0  of the radio frame  3 . The UE  10  may prioritize the grant included in the latest radio frame, determining that, among the grants  1 - 1  to  1 - 3  ( 601 - 1 ,  601 - 2 , and  601 - 3 ) received in different radio frames but the same subframe, the grant  1 - 3  ( 601 - 3 ), which is circulated, is valid while excluding the grant  1 - 1  and the grant  1 - 2  ( 601 - 1  and  601 - 2 ) from use. Since the grant  2  and the grant  3  ( 603 ) are received in distinct subframes in the radio frame  2  and radio frame  3 , respectively, they may immediately be selected without determination as to whether they are valid. Thus, the UE  10  may select and use the grants  1 - 3 ,  2 , and  3  ( 601 - 3 ,  602 , and  603 ) and perform transmissions corresponding thereto. The eNB  20  may send the same grants in the same subframes of different radio frames. Thus, the UE  10 , if missing reception of multiple grants belonging to any one radio frame, may receive multiple grants belonging to the same subframes of other different radio frames. The eNB  20  may use this method to overwrite the grants with new grants. 
         [0076]    According to an embodiment of the present disclosure, the eNB  20  may present flexibility by which it allocates multiple grants for SC period and repeat and overwrite grants for reliability. Here, the maximum number of available grants which are allocated to the UE  10  and are valid may be the same as the number of subframes of a radio frame. When the subframes of one radio frame are numbered 0 to 9, the number of the subframes or the maximum number of available grants would be 10, 
         [0077]    According to an embodiment of the present disclosure, the UE  10  may determine that amongst the multiple SL grants received in a radio frame, the SL grant which is received in latest subframe is a valid grant. 
         [0078]    Referring to  FIG. 6B , under the condition shown in  FIG. 6A , the UE  10  receives only one grant  601 - 1  in radio frame  1  and considers it as a valid grant. The UE  10  receives two grants  601 - 2  and  602  in radio frame  2 , and considers the latest i.e. grant  602  among these two grants as a valid grant. The UE  10  receives two grants  601 - 3  and  603  in radio frame  3 , and considers the latest i.e. grant  603  among these two grants as a valid grant. Thus, the LT  10  may select and use the grants  1 - 1 ,  2 , and  3  ( 601 - 1 ,  602 , and  603 ) and perform transmissions corresponding thereto. 
         [0079]      FIG. 7  is a view illustrating an example of processing multiple grants in sidelink communication using a first indicator and a second indicator according to an embodiment of the present disclosure. 
         [0080]    In the legacy system, when the UE  10  receives multiple grants and each grant received corresponds to any particular SC period  210 , the UE  10  may perform transmission using the latest grant. In other words, the UE  10  may replace or disregard the previous grant for a certain SC period  210 . Similarly, from an eNB  20  standpoint, whenever the eNB  20  sends new grants, the eNB  20  may release previous grants. A relevant issue is represented in Table 1 below: 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 UE 
                 eNB 
                 Issue 
               
               
                   
               
             
             
               
                 Legacy UE 
                 Enhanced 
                             eNB may send multiple grants for 
               
               
                   
                 eNB 
                 transmission to the same destination or 
               
               
                   
                   
                 multiple destinations in SC period 210. 
               
               
                   
                   
                 UE may replace or discard previous grants 
               
               
                   
                   
                 for the same SC period using the latest 
               
               
                   
                   
                 grant. 
               
               
                   
                   
                             Results, waste of resources 
               
               
                 Enhanced UE 
                 Legacy eNB 
                             eNB may replace previous grants for 
               
               
                   
                   
                 any particular SC period 210 by sending 
               
               
                   
                   
                 revised grants. UE may use multiple 
               
               
                   
                   
                 grants for transmission to multiple 
               
               
                   
                   
                 destinations or same destination. 
               
               
                   
                   
                             Results, interference with wide area 
               
               
                   
                   
                 network (WAN) or other UE&#39;s sidelink 
               
               
                   
                   
                 transmission. 
               
               
                   
               
             
          
         
       
     
         [0081]    The legacy UE may perform sidelink communication in the cell of the enhanced eNB (the eNB supporting the above-features of allocating resources to the legacy UE for any particular SC period  210  and transmitting multiple grants). In such case, the eNB sends multiple grants for transmission to a plurality of destinations in the SC period  210 . However, the legacy UE uses the latest grant and cannot replace (or overwrite) previous grants for the SC period  210 . This may result in waste resources, causing some grants, although allocated, not to be used by the UE. 
         [0082]    Likewise, the enhanced LIE may perform sidelink communication in the cell of the legacy eNB. The legacy eNB may be transmitting multiple grants to revise previous grants. In such case, the legacy eNB may send multiple grants revising the previous grants. However, the UE uses both the previous grants and revised grants. This allows the UE to perform transmission with resources not allocated, causing interference with other transmissions. 
         [0083]    The above issues may be addressed by introducing a first indicator and second indicator as described below. 
         [0084]    The first indicator (indication  1 ) may indicate that the UE  10  may perform multiple transmissions using multiple grants corresponding to the SC period  210  through a UE capability message or sidelink UE information (SidelinkUEInformation) message or whether the UE  10  supports transmission to a plurality of destinations using multiple grants in the SC period  210 . The first indicator may represent information about multiple transmissions by the UE  10 . Specifically, the UE  10  may indicate the number of multiple transmissions that may be performed and may indicate the number of hybrid automatic repeat and request (HARQ) processes supported for multiple transmissions. Here, the term “transmission” means transmission of an SA and transmission of one or more MAC PDUs in the SC period. The first indicator may be transmitted by the UE  10  to the eNB  20 . The first indicator may be included and transmitted in the sidelink UE information message, or instead in the UE capability message. The UE capability message containing the first indicator may be sent before or after transmitting the sidelink UE information message is transmitted and may not necessarily be accompanied with transmission of the sidelink UE information message. 
         [0085]    The second indicator (indication  2 ) may be a UE capability message, radio resource control connection reconfiguration (RRCConnectionReconfiguration) message or broadcast signaling for mode  1  (non-contention-based resource al location mode) resource allocation and allows the eNB  20  to indicate whether multiple grants for the SC period  210  transmitted by the eNB  20  are ones for multiple transmissions. In other words, the eNB  20  may indicate that the UE  10  performs transmissions to a plurality of destinations during the SC period  210  using multiple grants allocated through an RRCConnectionReconfiguration message for mode  1  resource allocation. Here, mode  1  means an environment where the eNB  20  itself may set up a resource pool necessary for sidelink communication in the coverage. The second indicator may represent information about multiple transmissions by the UE  10 . Specifically, the eNB  20  may include the UE  10  where multiple transmissions are performed, whether to permit the multiple transmissions by the UE  10 , and/or characteristics of multiple transmissions performed by the UE  10  in the second indicator and instruct the UE  10  to perform multiple transmissions. The eNB  20  may send multiple grants for UEs indicating to support transmission to a plurality of destinations or the UE  10  capable of perform multiple transmissions using multiple grants corresponding to the SC period  210 . 
         [0086]    Operations of the UE  10  based on the first indicator and second indicator are shown in the following Table 2: 
         [0000]    
       
         
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 First 
                 Second 
                 Operation of UE 10 when multiple grants are 
               
               
                 indicator 
                 indicator 
                 received in SC period 210 
               
               
                   
               
             
             
               
                 Yes 
                 No 
                 UE 10 uses latest grant and replaces previous 
               
               
                   
                   
                 grant during any particular SC period 210 
               
               
                 No 
                 No 
                 UE 10 uses latest grant and replaces previous 
               
               
                   
                   
                 grant during any particular SC period 210 
               
               
                 Yes 
                 Yes 
                 UE 10 uses all grants for transmission to 
               
               
                   
                   
                 multiple destinations or same destination 
               
               
                 No 
                 Yes 
                 UE 10 cannot perform sidelink communication 
               
               
                   
               
             
          
         
       
     
         [0087]    The first indicator may indicate whether the UE  10  support multiple transmissions of sidelink communication to other destinations during one SC period  210 . The first indicator may have a structure as in the following Table 3: 
         [0000]    
       
         
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
               
               
             
           
               
                 TABLE 3 
               
               
                   
               
             
             
               
                 -- ASN1START 
               
               
                 UE-evolved universal mobile telecommunications system (UMTS) 
               
               
                 terrestrial radio access 
               
             
          
           
               
                 (EUTRA)-Capability ,,= 
                 SEQUENCE { 
               
               
                 , 
               
               
                 , 
               
             
          
           
               
                 SL-Parameters-v1310 ,,= 
                 SEQUENCE { 
               
             
          
           
               
                   discSysInfoReporting-r13 
                 ENUMERATED 
               
               
                 {supported}  OPTIONAL, 
               
             
          
           
               
                   commMultipleTx-r13 
                 ENUMERATED {supported} 
               
             
          
           
               
                   OPTIONAL,  discInterFreqTx-r13 
                 ENUMERATED 
               
               
                 {supported}  OPTIONAL, 
               
             
          
           
               
                   discPeriodicSLSS-r13 
                 ENUMERATED 
               
               
                 {supported}  OPTIONAL 
               
               
                 } 
               
               
                   
               
             
          
         
       
     
         [0088]    The first indicator may be included in the UE-EUTRA-Capability field. Specifically, the first indicator may be specified to indicate whether in the commMultipleTx-r13 field the UE  10  supports multiple transmissions of sidelink communication to different destinations during one SC period  210 . 
         [0089]    The second indicator may indicate that the UE  10  is to perform multiple transmissions for sidelink communication to different destinations during one SC period  210 . The second indicator may have a structure as in the following Table 4: 
         [0000]    
       
         
               
               
             
           
               
                 TABLE 4 
               
               
                   
               
             
             
               
                 SL-CommConfig-r12 ,,= 
                 SEQUENCE  { 
               
               
                 [[  commTxResources-v1310 
                      CHOICE { 
               
               
                       release 
                    NULL, 
               
               
                       setup 
                    CHOICE { 
               
               
                        scheduled-v1310 
                        SEQUENCE { 
               
               
                     logicalChGroupInfoList-r13 
                 , 
               
               
                        multipleTx-r13 
                      BOOLEAN 
               
               
                        }, 
               
               
                        ue-Selected-v1310 
                      SEQUENCE { 
               
               
                 , 
               
               
                   ]] 
               
               
                   
               
             
          
         
       
     
         [0090]    The second indicator may be included in the SL-CommConfig-r12 field. Specifically, the second indicator may be specified in the multipleTx-r13 field to indicate whether the UE  10  is to perform multiple transmissions to different destinations during one SC period  210 . For example, the second indicator in the multipleTx-r13 field may have a TRUE value, which may indicate that multiple transmissions are to be performed. 
         [0091]    Referring to  FIG. 7 , operations for processing multiple grants in an SC period using the first indicator and the second indicator are described below. 
         [0092]    The transmitting-side UE  10  requires resources (e.g., time and frequency) for transmitting SC data and sidelink data. To obtain resources, the UE  10  interested in sidelink communication sends the first indicator and sidelink UE information message including a destination list to the eNB  20  at operation S 705 . The first indicator represents information about multiple transmissions by the UE  10 . 
         [0093]    The eNB  20  allocates, to the UE  10 , an SC pool for transmission of SC data, SL-RNTI, and second indicator, through an RRC connection reconfiguration message at operation S 710 . Here, the second indicator may be allocated and transmitted to the UE  10 , included in a UE capability message or broadcast signaling for mode  1  resource allocation. The operation of transmitting the second indicator may be performed in any operation before sending grant. 
         [0094]    The UE  10  may request dedicated resources for SC and sidelink data transmission by sending a sidelink buffer status report at operation S 715 . 
         [0095]    The eNB  20 , when the UE  10  indicates that it may perform multiple transmissions using the first indicator, may allocate dedicated resources to the UE  10  for transmission of multiple grants at operation S 720 . 
         [0096]    The eNB  20  sends multiple grants for sidelink communication, i.e., information about the dedicated resources at operation S 725 , When receiving the second indicator from the eNB  20 , the UE  10  may perform single/multiple transmissions using the multiple grants at operation S 730 . 
         [0097]      FIG. 8  is a view illustrating an example of processing multiple grants in sidelink communication using a first indicator included in a UE capability message according to an embodiment of the present disclosure. 
         [0098]      FIG. 8  shows operations for processing multiple grants similar to those shown in  FIG. 7  except that the first indicator sent from the UE  10  to the eNB  20  is included in the UE capability message. 
         [0099]    The UE  10  may send the first indicator to the eNB  20  through a LTE capability message before or after sending a sidelink LTE information message to the eNB  20  in order to obtain resources for transmitting SC data and sidelink data at operation S 805 . 
         [0100]    The UE  10  may send a sidelink UE information message including a destination list to the eNB  20  at operation S 810 . 
         [0101]    The eNB  20  may allocate, to the UE  10 , the second indicator, sidelink RNTI, and SC pool for transmitting SC data through a RRC connection reconfiguration message at operation S 815 . Here, the second indicator may be allocated and transmitted to the UE  10 , included in a UE capability message or broadcast signaling for mode  1  resource allocation. The operation of transmitting the second indicator may be performed in any operation before sending grant. 
         [0102]    The UE  10  may request dedicated resources for SC and sidelink data transmission by sending a sidelink buffer status report at operation S 820 . 
         [0103]    The eNB  20 , when the UE  10  indicates that it may perform multiple transmissions using the first indicator, may allocate dedicated resources to the UE  10  for transmission of multiple grants at operation S 825 . 
         [0104]    The eNB  20  may send multiple grants for sidelink communication, i.e., information about the dedicated resources at operation S 830 . When receiving the second indicator from the eNB  20 , the UE  10  may perform single/multiple transmissions using the multiple grants at operation S 835 . 
         [0105]      FIG. 9  is a view illustrating an example of receiving and processing multiple grants by a UE  10  according to an embodiment of the present disclosure. 
         [0106]      FIG. 9  illustrates operations of the UE  10  supporting multiple transmissions for the same destination in the SC period  210  or transmission to a plurality of destinations when the UE  10  receives multiple grants. 
         [0107]    The UE  10  may receive multiple grants for the SC period  210  from the eNB  20  at operation S 905 . 
         [0108]    The UE  10  may determine whether there is an indication as to whether the multiple grants from the eNB  20  are ones for multiple transmissions at operation S 910 . The UE  10 , when allocated with sidelink resources through a RRC connection reconfiguration message from the eNB  20 , may also receive the second indicator included in the RRC connection reconfiguration message. The UE  10  may receive from the eNB  20  the second indicator included in broadcast signaling for mode  1  resource allocation or a UE capability message through a separate operation. The UE  10  may determine whether the second indicator has been received which indicates whether transmission is performed to one destination or a plurality of different destinations during the SC period  210  using multiple grants received by the UE  10  from the eNB  20  at operation S 910 . 
         [0109]    Upon receiving the second indicator, the UE  10  may perform single/multiple transmissions to the same or different destinations using the multiple grants received at operation S 915 . 
         [0110]    When the UE  10  fails to receive the second indicator, the UE  10  may use the latest grant. The latest grant may be one grant, and the UE  10  may replace or disregard the previous grant at operation S 920 . The UE  10  may perform single transmission using one grant. Since the UE  10  accommodates only one grant, only one sidelink transmission may be performed accordingly at operation S 925 . 
         [0111]      FIG. 10  is a view illustrating an example of processing multiple grants in sidelink communication using multiple SC pools according to an embodiment of the present disclosure. 
         [0112]    The eNB  20  may allocate resources for different transmissions from different SC pools. In this case, the eNB  20  may configure multiple SC pools in a RRC connection reconfiguration message in response to the sidelink UE information message. The eNB  20  may display sidelink resource full indexes for each grant. The UE  10  may perform multiple transmissions in the SC period in association with the SC pool of the received grant. 
         [0113]    Referring to  FIG. 10 , operations for processing multiple grants including SC pool indexes and associated with multiple SC pools are described as an example. 
         [0114]    The UE  10  may send a sidelink UE information message including a destination list to the eNB  20  at operation S 1005 . 
         [0115]    The eNB  20  may allocate SC pools and a sidelink RNTI for transmitting SC data to the UE  10  at operation S 1010 . 
         [0116]    The UE  10  may request dedicated resources for SC and sidelink data transmission by sending a sidelink buffer status report at operation S 1015 . 
         [0117]    For the UE  10 , the eNB  20  allocate dedicated resources and multiple grants which are information about the dedicated resources at operation S 1020 . 
         [0118]    The eNB  20  may send multiple grants each including the SC pool index to the UE  10  at operation S 1025 . 
         [0119]    The UE  10  may perform multiple transmissions using each grant in the relevant SC period considering the SC pool index at operation S 1030 . 
         [0120]      FIG. 11  is a view illustrating an example of processing multiple grants in sidelink communication using a first indicator and multiple SC pools according to an embodiment of the present disclosure. 
         [0121]    Referring to  FIG. 11 , the UE  10  may perform sidelink communication by sending the first indicator and multiple SC pools to the eNB  20 . When processing multiple grants in the sidelink communication using multiple SC pools, the first indicator and the second indicator may also be used. Here, an example of using the first indicator is described. 
         [0122]    The UE  10  may send a sidelink UE information message including a destination list to the eNB  20  at operation S 1105 . 
         [0123]    The eNB  20  may allocate SC pools and a sidelink RNTI for transmitting SC data to the UE  10  at operation S 1110 . 
         [0124]    The UE  10  may request dedicated resources for SC and sidelink data transmission by sending a sidelink buffer status report at operation S 1115 . 
         [0125]    When it is indicated that the UE  10  may perform transmission using multiple transmissions using the first indicator, the eNB  20  may allocate dedicated resources and multiple grants that are information about the dedicated resources at operation S 1120 . 
         [0126]    The eNB  20  may send multiple grants each including the SC pool index to the UE  10  at operation S 1125 . 
         [0127]    The UE  10  may perform multiple transmissions using each grant n the relevant SC period at operation S 1130 . 
         [0128]      FIG. 12  is a view illustrating an example of processing multiple grants in sidelink communication using multiple SC pools and multiple sidelink RNTIs according to an embodiment of the present disclosure. 
         [0129]    The eNB  20  may allocate sidelink RNTIs for each SC pool besides the SC pools when allocating resources for different transmissions from different SC pools. In this case, the grant corresponding to the SC pool may be indicated by masking the cyclic redundancy check (CRC) of physical downlink control channel (PDCCH) to the sidelink RNTI corresponding to the SC pool. The UE  10  may perform multiple transmissions in the SC period associated with the SC pool in the received grant. 
         [0130]    Referring to  FIG. 12 , operations for processing multiple grants including multiple sidelink RNTIs specifying SC pool and associated with multiple SC pools are described as an example. 
         [0131]    The UE  10  may send a sidelink UE information message including a destination list to the eNB  20  at operation S 1205 . 
         [0132]    The eNB  20  may allocate SC pools and multiple sidelink RNTIs for transmitting SC data to the UE  10  at operation S 1210 . 
         [0133]    Thereafter, the UE  10  may request dedicated resources for SC and sidelink data transmission by sending a sidelink buffer status report at operation S 1215 . 
         [0134]    The eNB  20  may allocate dedicated resources and multiple grants which are information about the dedicated resources at operation S 1220 . 
         [0135]    The eNB  20  may send multiple grants each including a sidelink RNTI specifying the SC pools to the LIE  10  at operation S 1225 . 
         [0136]    The UE  10  may perform multiple transmissions using each grant in the relevant SC period at operation S 1230 . 
         [0137]      FIG. 13  is a view illustrating an example of transmitting MAC PDUs to multiple destinations by multi-SA transmission or multi-data transmission according to an embodiment of the present disclosure. 
         [0138]    According to the present disclosure, there is provided a method for handling collisions in multiple transmissions when multiple transmissions are performed after receiving multiple grants. The multiple transmissions may include multiple SA transmissions or multiple data transmissions. 
         [0139]    In the multiple SA transmissions, SA resources in the case of mode  2  (contention-based resource allocation mode) may randomly be selected from an SA resource pool. An SA may he transmitted over at least one or more subframes. When the UE  10  selects multiple SA resources randomly from the SA resource pool, one or two subframes for SA transmission to one destination may be the same as one or two subframes for SA transmission to another destination. The term “overlap” may mean using one or more subframes in separate transmissions. The overlap operation may arise even when the SA resources for transmitting SAs to the plurality of destinations are selected from different SA resource pools when the SA resource pools overlap each other. 
         [0140]    The UE  10  cannot send multiple SAs in one subframe due to the single carrier frequency division multiple (SC-FDM) limitation. To address such issue, two available methods are present. 
         [0141]    First, in case of discovery, the UE  10  may be permitted to select a plurality of discovery resources from a discovery resource pool to send a plurality of discovery messages. Collision may be avoided by excluding discovery resources belonging to the subframes of the discovery resources already selected for transmission. Similarly, this may be applicable to SA transmissions. In other words, the UE  10  may select SA resources from the SA resource pool while excluding any resources belonging to the subframes of the SA resources already selected for SA transmissions. 
         [0142]    Second, when the SA transmission for one destination overlaps the SA transmission for another destination, the UE  10  transmits only one SA while stopping (or dropping) the other. The SA transmission dropped may be left as a matter regarding a UE implementation as based on the data priority. Each SA may be transmitted over one subframe and may be repeated in another subframe. According to an embodiment of the present disclosure, when two subframes overlap each other, the SA transmission drops, and when they partially overlap, only the SA transmission in the subframes overlapping each other may be dropped. According to an embodiment of the present disclosure, when one or two subframes overlap, SA transmission may drop, 
         [0143]    In multiple data transmissions corresponding to multiple SA transmissions, in case of mode  2 , a time-resource pattern of transmission (T-RPT) index may randomly be selected from a set of T-RPTs by the UE  10 . For data transmission, the T-RPT index may determine subframes available to the UE  10  in the data resource pool. When the UE  10  selects a plurality of T-RPT indexes randomly from the data resource pool, one or multiple subframes for data transmission to one destination may be the same as one or multiple subframes for data transmission to another destination. The term “overlap” may mean using one or more subframes in separate transmissions. The overlap operation may arise even when the data resources for transmitting data to the plurality of destinations are selected from different data resource pools when the data resource pools overlap each other. 
         [0144]    The UE  10  cannot send multiple data PDUs in one subframe due to SC-FDM limitations. To address such issue, two available methods are present. 
         [0145]    First, the UE  10  may select a T-RPT index from a T-RPT set while excluding any T-RPT index resulting in the data subframe overlapping the subframes already selected for data transmission. 
         [0146]    Second, when the subframe for data transmission to one destination is the same as the data transmission to another destination, the UE  10  may transmit one but drop the other. The dropping data transmission may be left as a matter regarding a HE implementation. 
         [0147]    When the UE  10  sends transmissions to several destinations, the first approach above may limit the number of T-RPT indexes available for selection. Further, there may be a plurality of chances depending on the number of data subframes in the data resource pool and T-RPT index, and the UE  10  might not use all of them for a predetermined destination. For example, it is assumed that the UE  10  selects the same T-RPT index corresponding to two different data transmissions or SA transmissions in the SA period. Then, as shown in  FIG. 13 , the UE  10  selects subframes for transmission based on the T-RPT index from the data subframe  1301  for mode  2 . The UE  10  has a chance to transmit four MAC PDUs  1303  using the T-RPT subframes  1302  which are data subframes corresponding to the selected T-RPT index. The UE  10  may send MAC PDU  1  ( 1303 - 1 ) and MAC MU  2  ( 1303 - 2 ) corresponding to destination  1  and MAC PDU  3  ( 1303 - 3 ) and MAC PDU  4  ( 1303 - 4 ) corresponding to destination  2 . In this case, the first approach above need not be carried out. In the case of mode  2 , once the SC period and its corresponding data all are SC-FDM limited and sent dependently, multiple transmissions may be performed for different destinations in the SC period. 
         [0148]      FIG. 14  is a view schematically illustrating a configuration of a UE according to an embodiment of the present disclosure. 
         [0149]    Referring to  FIG. 14 , a UE  1400  may perform sidelink communication with neighboring UEs  1400 - 1 ,  1400 - 2 , . . . , and  1400 -n and receive resources and grants for sidelink communication from an eNB  1500  ( FIG. 15 ). The UE  1400  may include a transmitter  1410 , a receiver  1420 , and a controller  1430 . 
         [0150]    The transmitter  1410  sends a request for single or multiple grants to the eNB  1500 . However, by way of example, and not as a limitation, resources, data, and signals for sidelink communication as described above in detail may be sent to another entity, according to the present disclosure. 
         [0151]    The receiver  1420  receives single or multiple grants from the eNB  1500 . However, by way of example, and not as a limitation, resources, data, grants, and signals for sidelink communication as described above in detail may be received from another entity, according to the present disclosure, 
         [0152]    The controller  1430  may perform multiple transmissions to the same destination or multiple destinations corresponding to the received single or multiple grants. However, by way of example, and not as a limitation, the controller  1430  may make the determination for sidelink communication as described above and may transmit commands as per the determination to the transmitter  1410  and the receiver  1420 . 
         [0153]    All of the operations of the transmitter  14   0  and the receiver  1420  may be appreciated as performed under the control of the controller  1430 . The transmitter  1410 , the receiver  1420 , and the controller  1430  are not necessarily implemented as separate devices, respectively, but may be implemented in a single configuration unit in the form of e.g., a single chip. 
         [0154]      FIG. 15  is a view schematically illustrating a configuration of an eNB according to an embodiment of the present disclosure. 
         [0155]    Referring to  FIG. 15 , the eNB  1500  may send resources, grants, and data to the UE  1400  to allow the UE  1400  to perform sidelink communication. The eNB  1500  may include a transmitter  1510 , a receiver  1520 , and a controller  1530 . 
         [0156]    The transmitter  1510  may send single or multiple grants to the UE  1400 . However, without limited thereby, resources, data, and signals for sidelink communication as described above in detail may be sent to another entity, according to the present disclosure. 
         [0157]    The receiver  1520  receives a request for single or multiple grants from the UE  1400 . However, by way of example, and not as a limitation, data and signals for sidelink communication as described above in detail may be received from another entity, according to the present disclosure. 
         [0158]    The controller  1530  may allocate single or multiple grants to allow the UE  1400  to perform multiple transmissions to the same or multiple destinations corresponding to the single or multiple grants. However, by way of example, and not as a limitation, the controller  1430  may make the determination for sidelink communication as described above and may transmit commands as per the determination to the transmitter  1510  and the receiver  1520 . 
         [0159]    All of the operations of the transmitter  1510  and the receiver  1520  may be appreciated as performed under the control of the controller  1530 . The transmitter  1510 , the receiver  1520 , and the controller  1530  are not necessarily implemented as separate devices, respectively, but may be implemented in a single configuration unit in the form of e.g., a single chip. 
         [0160]    It should be noted that the device configurations or examples of processing grants shown and described in connection with  FIGS. 1 to 5, 6A and 6B, and 7 to 15  are not intended to limit the scope of the present disclosure. In other words, all the components or operations illustrated in  FIGS. 1 to 5, 6A and 6B, and 7 to 15  should not be construed as essential components to practice the present disclosure, and the present disclosure may be rather implemented with only some of the components without departing from the gist of the present disclosure. An embodiment according to the present disclosure may be applicable to vehicle-to-vehicle(V2V) communication. Devices applicable to the present invention may be vehicles. 
         [0161]    The above-described operations may be realized by equipping at least one memory device retaining their corresponding program codes in any component of the UE or eNB. That is, the controller in the eNB or UE may execute the above-described operations by reading and running the program codes stored in the at least one memory device by at least one processor or central processing unit (CPU). 
         [0162]    As described herein, various components or modules in the UE or eNB may be operated using a hardware circuit, e.g., a complementary metal oxide semiconductor-based logic circuit, firmware, software, and/or using a hardware circuit such as a combination of hardware, firmware, and/or software embedded in a machine-readable medium. As an example, various electric structures and methods may be executed using electric circuits such as transistors, logic gates, or application-specific integrated circuits (ASICs). 
         [0163]    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.