Patent Publication Number: US-11032789-B2

Title: Method and apparatus for calculating ranging information by terminal in wireless communication system supporting device to device communication

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the National Stage filing under 35 U.S.C. 371 of International Application No. PCT/KR2018/008849, filed on Aug. 3, 2018, which claims the benefit of U.S. Provisional Application No. 62/541,047 filed on Aug. 3, 2017, the contents of which are all hereby incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a method and apparatus for calculating ranging information by a user equipment (UE) in a wireless communication system supporting device to device (D2D) communication, and more particularly, to a method and apparatus for calculating ranging information by a UE. 
     BACKGROUND ART 
     Wireless communication systems have been widely deployed to provide various types of communication services such as voice or data. In general, a wireless communication system is a multiple access system that supports communication of multiple users by sharing available system resources (a bandwidth, transmission power, etc.) among them. For example, multiple access systems include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, and a multi-carrier frequency division multiple access (MC-FDMA) system. 
     Device-to-device (D2D) communication is a communication scheme in which a direct link is established between user equipments (UEs) and the UEs exchange voice and data directly without intervention of an evolved Node B (eNB). D2D communication may cover UE-to-UE communication and peer-to-peer communication. In addition, D2D communication may be applied to machine-to-machine (M2M) communication and machine type communication (MTC). 
     D2D communication is under consideration as a solution to the overhead of an eNB caused by rapidly increasing data traffic. For example, since devices exchange data directly with each other without intervention of an eNB by D2D communication, compared to legacy wireless communication, network overhead may be reduced. Further, it is expected that the introduction of D2D communication will reduce procedures of an eNB, reduce the power consumption of devices participating in D2D communication, increase data transmission rates, increase the accommodation capability of a network, distribute load, and extend cell coverage. 
     At present, vehicle-to-everything (V2X) communication in conjunction with D2D communication is under consideration. In concept, V2X communication covers vehicle-to-vehicle (V2V) communication, vehicle-to-pedestrian (V2P) communication for communication between a vehicle and a different kind of terminal, and vehicle-to-infrastructure (V2I) communication for communication between a vehicle and a roadside unit (RSU). 
     DISCLOSURE 
     Technical Problem 
     An object of the present disclosure is to provide a method and apparatus for calculating ranging information by a user equipment (UE) in a wireless communication system, in which the UE determines a resource region corresponding to its geographical information in a plurality of resource regions divided in accordance with the geographical information and transmits ranging signals from the determined resource region to a road side unit to cancel interference between the ranging signals and reduce a position estimation error. 
     Another object of the present disclosure to provide a method and apparatus for calculating ranging information by a user equipment (UE) in a wireless communication system, in which a UE moving at a fast speed calculates its ranging information and position information through signal exchange with a road side unit fixed to a specific position to quickly acquire exact position information and ranging information. 
     It will be appreciated by persons skilled in the art that the objects that could be achieved with the present disclosure are not limited to what has been particularly described hereinabove and the above and other objects that the present disclosure could achieve will be more clearly understood from the following detailed description. 
     Technical Solution 
     According to one aspect of the present disclosure, a method for calculating ranging information by a user equipment (UE) in a wireless communication system supporting device to device (D2D) communication comprises determining a resource region corresponding to geographical information of the UE, based on ranging resource information of a resource region set per geographical information, and transmitting a ranging signal for calculating ranging information from the determined resource region; receiving, from a road side unit (RSU) which has received the ranging signal, a response signal including information which is the basis for calculation of the ranging information; and calculating ranging information, which is distance information with the RSU, based on the response signal. 
     According to an embodiment, the ranging signal is transmitted using at least one resource element selected based on ID of the UE within the determined resource region. 
     Otherwise, the geographical information on the UE is determined based on coordinate information of the UE, which is measured using a global positioning system (GPS) included in the UE. 
     Otherwise, the geographical information is determined based on intensity of a signal received from the RSU. 
     Otherwise, a size of the resource region corresponding to the geographical information is previously determined considering the intensity of the received signal. 
     Otherwise, the response signal is transmitted using a resource and sequence associated with at least one of a resource and sequence to which the ranging signal is transmitted. 
     Otherwise, the response signal is transmitted from the RSU which has received the ranging signal at receiving intensity of a preset threshold value or more. 
     The information which is the basis for calculation of the ranging information includes at least one of information on the time when the RSU receives the ranging signal and information on a phase difference according to propagation delay between tones of the ranging signal received by the RSU. 
     Otherwise, the response signal is received from a resource region that is not overlapped with a resource region to which the ranging signal is transmitted. 
     Otherwise, the response signal further includes information on a position of the RSU. 
     Otherwise, the UE further measures AoA information on a direction where the response signal is received, and calculates its position based on the measured AoA information, the ranging information and the position of the RSU. 
     Otherwise, the UE retransmits the ranging signal by changing the determined resource region or changing a transmission power when the response signal is not received. 
     Otherwise, a transmission power of the ranging signal is determined based on intensity of the signal received from the RSU. 
     Otherwise, a sequence index or ID of the ranging signal is determined based on intensity of the signal received from the RSU. 
     Otherwise, the ranging resource information is signaled to the UE by a network through a physical layer signal or a higher layer signal. 
     Advantageous Effects 
     In the present disclosure according to various embodiments, the UE may determine a resource region corresponding to its geographical information in a plurality of resource regions divided in accordance with the geographical information and transmit ranging signals from the determined resource region to a road side unit to cancel interference between the ranging signals and reduce a position estimation error. 
     Also, according to the present disclosure, even though the UE moves at a fast speed, the UE may calculate its ranging information and position information through signal exchange with a road side unit fixed to a specific position, thereby more exactly and quickly measuring its position information and ranging information. 
     Effects obtainable from the present invention are non-limited by the above-mentioned effects. And, other unmentioned effects can be clearly understood from the following description by those having ordinary skill in the technical field to which the present invention pertains. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate embodiments of the disclosure and together with the description serve to explain the principle of the disclosure. In the drawings: 
         FIG. 1  is a view illustrating the structure of a radio frame; 
         FIG. 2  is a view illustrating a resource grid during the duration of one downlink slot; 
         FIG. 3  is a view illustrating the structure of a downlink subframe; 
         FIG. 4  is a view illustrating the structure of an uplink subframe; 
         FIG. 5  is a view illustrating the configuration of a wireless communication system having multiple antennas; 
         FIG. 6  is a view illustrating a subframe carrying a device-to-device (D2D) synchronization signal; 
         FIG. 7  is a view illustrating relay of a D2D signal; 
         FIG. 8  is a view illustrating an exemplary D2D resource pool for D2D communication; 
         FIG. 9  is a view referred to for describing transmission modes and scheduling schemes for vehicle-to-everything (V2X); 
         FIG. 10  is a view illustrating a method of selecting resources in V2X; 
         FIG. 11  is a view referred to for describing a scheduling assignment (SA) and data transmission in D2D; 
         FIG. 12  is a view referred to for describing an SA and data transmission in V2X; 
         FIGS. 13 and 14  are views illustrating a new radio access technology (NRAT) frame structure; 
         FIG. 15  is a view illustrating a method for determining a resource region in accordance with geographical information of a UE according to an embodiment; 
         FIG. 16  is a view illustrating a method for calculating a position of a UE according to an embodiment; 
         FIG. 17  is a flow chart illustrating a method for calculating ranging information according to an embodiment of the present disclosure; and 
         FIG. 18  is a view illustrating a configuration of a transceiving apparatus. 
     
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The embodiments of the present disclosure described hereinbelow are combinations of elements and features of the present disclosure. The elements or features may be considered selective unless otherwise mentioned. Each element or feature may be practiced without being combined with other elements or features. Further, an embodiment of the present disclosure may be constructed by combining parts of the elements and/or features. Operation orders described in embodiments of the present disclosure may be rearranged. Some constructions or features of any one embodiment may be included in another embodiment and may be replaced with corresponding constructions or features of another embodiment. 
     In the embodiments of the present disclosure, a description is made, centering on a data transmission and reception relationship between a base station (BS) and a user equipment (UE). The BS is a terminal node of a network, which communicates directly with a UE. In some cases, a specific operation described as performed by the BS may be performed by an upper node of the BS. 
     Namely, it is apparent that, in a network comprised of a plurality of network nodes including a BS, various operations performed for communication with a UE may be performed by the BS or network nodes other than the BS. The term ‘BS’ may be replaced with the term ‘fixed station’, ‘Node B’, ‘evolved Node B (eNode B or eNB)’, ‘Access Point (AP)’, etc. The term ‘relay’ may be replaced with the term ‘relay node (RN)’ or ‘relay station (RS)’. The term ‘terminal’ may be replaced with the term ‘UE’, ‘mobile station (MS)’, ‘mobile subscriber station (MSS)’, ‘subscriber station (SS)’, etc. 
     The term “cell”, as used herein, may be applied to transmission and reception points such as a base station (eNB), a sector, a remote radio head (RRH), and a relay, and may also be extensively used by a specific transmission/reception point to distinguish between component carriers. 
     Specific terms used for the embodiments of the present disclosure are provided to help the understanding of the present disclosure. These specific terms may be replaced with other terms within the scope and spirit of the present disclosure. 
     In some cases, to prevent the concept of the present disclosure from being ambiguous, structures and apparatuses of the known art will be omitted, or will be shown in the form of a block diagram based on main functions of each structure and apparatus. Also, wherever possible, the same reference numbers will be used throughout the drawings and the specification to refer to the same or like parts. 
     The embodiments of the present disclosure can be supported by standard documents disclosed for at least one of wireless access systems, Institute of Electrical and Electronics Engineers (IEEE) 802, 3rd Generation Partnership Project (3GPP), 3GPP long term evolution (3GPP LTE), LTE-advanced (LTE-A), and 3GPP2. Steps or parts that are not described to clarify the technical features of the present disclosure can be supported by those documents. Further, all terms as set forth herein can be explained by the standard documents. 
     Techniques described herein can be used in various wireless access systems such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier-frequency division multiple access (SC-FDMA), etc. CDMA may be implemented as a radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. TDMA may be implemented as a radio technology such as global system for mobile communications (GSM)/general packet radio service (GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may be implemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved-UTRA (E-UTRA) etc. UTRA is a part of universal mobile telecommunications system (UMTS). 3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA for downlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE. WiMAX can be described by the IEEE 802.16e standard (wireless metropolitan area network (WirelessMAN)-OFDMA Reference System) and the IEEE 802.16m standard (WirelessMAN-OFDMA Advanced System). For clarity, this application focuses on the 3GPP LTE and LTE-A systems. However, the technical features of the present disclosure are not limited thereto. 
     LTE/LTE-A Resource Structure/Channel 
     With reference to  FIG. 1 , the structure of a radio frame will be described below. 
     In a cellular orthogonal frequency division multiplexing (OFDM) wireless packet communication system, uplink and/or downlink data packets are transmitted in subframes. One subframe is defined as a predetermined time period including a plurality of OFDM symbols. The 3GPP LTE standard supports a type-1 radio frame structure applicable to frequency division duplex (FDD) and a type-2 radio frame structure applicable to time division duplex (TDD). 
       FIG. 1( a )  illustrates the type-1 radio frame structure. A downlink radio frame is divided into 10 subframes. Each subframe is further divided into two slots in the time domain. A unit time during which one subframe is transmitted is defined as a transmission time interval (TTI). For example, one subframe may be 1 ms in duration and one slot may be 0.5 ms in duration. A slot includes a plurality of OFDM symbols in the time domain and a plurality of resource blocks (RBs) in the frequency domain. Because the 3GPP LTE system adopts OFDMA for downlink, an OFDM symbol represents one symbol period. An OFDM symbol may be referred to as an SC-FDMA symbol or symbol period. An RB is a resource allocation unit including a plurality of contiguous subcarriers in a slot. 
     The number of OFDM symbols in one slot may vary depending on a cyclic prefix (CP) configuration. There are two types of CPs: extended CP and normal CP. In the case of the normal CP, one slot includes 7 OFDM symbols. In the case of the extended CP, the length of one OFDM symbol is increased and thus the number of OFDM symbols in a slot is smaller than in the case of the normal CP. Thus when the extended CP is used, for example, 6 OFDM symbols may be included in one slot. If channel state gets poor, for example, during fast movement of a UE, the extended CP may be used to further decrease inter-symbol interference (ISI). 
     In the case of the normal CP, one subframe includes 14 OFDM symbols because one slot includes 7 OFDM symbols. The first two or three OFDM symbols of each subframe may be allocated to a physical downlink control channel (PDCCH) and the other OFDM symbols may be allocated to a physical downlink shared channel (PDSCH). 
       FIG. 1( b )  illustrates the type-2 radio frame structure. A type-2 radio frame includes two half frames, each having 5 subframes, a downlink pilot time slot (DwPTS), a guard period (GP), and an uplink pilot time slot (UpPTS). Each subframe is divided into two slots. The DwPTS is used for initial cell search, synchronization, or channel estimation at a UE. The UpPTS is used for channel estimation and acquisition of uplink transmission synchronization to a UE at an eNB. The GP is a period between an uplink and a downlink, which eliminates uplink interference caused by multipath delay of a downlink signal. One subframe includes two slots irrespective of the type of a radio frame. 
     The above-described radio frame structures are purely exemplary and thus it is to be noted that the number of subframes in a radio frame, the number of slots in a subframe, or the number of symbols in a slot may vary. 
       FIG. 2  illustrates the structure of a downlink resource grid for the duration of one downlink slot. A downlink slot includes 7 OFDM symbols in the time domain and an RB includes 12 subcarriers in the frequency domain, which does not limit the scope and spirit of the present disclosure. For example, a downlink slot may include 7 OFDM symbols in the case of the normal CP, whereas a downlink slot may include 6 OFDM symbols in the case of the extended CP. Each element of the resource grid is referred to as a resource element (RE). An RB includes 12×7 REs. The number of RBs in a downlink slot, NDL depends on a downlink transmission bandwidth. An uplink slot may have the same structure as a downlink slot. 
       FIG. 3  illustrates the structure of a downlink subframe. Up to three OFDM symbols at the start of the first slot in a downlink subframe are used for a control region to which control channels are allocated and the other OFDM symbols of the downlink subframe are used for a data region to which a PDSCH is allocated. Downlink control channels used in the 3GPP LTE system include a physical control format indicator channel (PCFICH), a physical downlink control channel (PDCCH), and a physical hybrid automatic repeat request (HARQ) indicator channel (PHICH). The PCFICH is located in the first OFDM symbol of a subframe, carrying information about the number of OFDM symbols used for transmission of control channels in the subframe. The PHICH delivers an HARQ acknowledgment/negative acknowledgment (ACK/NACK) signal in response to an uplink transmission. Control information carried on the PDCCH is called downlink control information (DCI). The DCI transports uplink or downlink scheduling information, or uplink transmission power control commands for UE groups. The PDCCH delivers information about resource allocation and a transport format for a downlink shared channel (DL-SCH), resource allocation information about an uplink shared channel (UL-SCH), paging information of a paging channel (PCH), system information on the DL-SCH, information about resource allocation for a higher-layer control message such as a Random Access Response transmitted on the PDSCH, a set of transmission power control commands for individual UEs of a UE group, transmission power control information, voice over Internet protocol (VoIP) activation information, etc. A plurality of PDCCHs may be transmitted in the control region. A UE may monitor a plurality of PDCCHs. A PDCCH is formed by aggregating one or more consecutive control channel elements (CCEs). A CCE is a logical allocation unit used to provide a PDCCH at a coding rate based on the state of a radio channel. A CCE includes a plurality of RE groups. The format of a PDCCH and the number of available bits for the PDCCH are determined according to the correlation between the number of CCEs and a coding rate provided by the CCEs. An eNB determines the PDCCH format according to DCI transmitted to a UE and adds a cyclic redundancy check (CRC) to control information. The CRC is masked by an identifier (ID) known as a radio network temporary identifier (RNTI) according to the owner or usage of the PDCCH. If the PDCCH is directed to a specific UE, its CRC may be masked by a cell-RNTI (C-RNTI) of the UE. If the PDCCH is for a paging message, the CRC of the PDCCH may be masked by a paging indicator Identifier (P-RNTI). If the PDCCH carries system information, particularly, a system information block (SIB), its CRC may be masked by a system information ID and a system information RNTI (SI-RNTI). To indicate that the PDCCH carries a random access response in response to a random access preamble transmitted by a UE, its CRC may be masked by a random access-RNTI (RA-RNTI). 
       FIG. 4  illustrates the structure of an uplink subframe. An uplink subframe may be divided into a control region and a data region in the frequency domain. A physical uplink control channel (PUCCH) carrying uplink control information is allocated to the control region and a physical uplink shared channel (PUSCH) carrying user data is allocated to the data region. To maintain the property of a single carrier, a UE does not transmit a PUSCH and a PUCCH simultaneously. A PUCCH for a UE is allocated to an RB pair in a subframe. The RBs of the RB pair occupy different subcarriers in two slots. Thus it is said that the RB pair allocated to the PUCCH is frequency-hopped over a slot boundary. 
     Reference Signal (RS) 
     In a wireless communication system, a packet is transmitted on a radio channel. In view of the nature of the radio channel, the packet may be distorted during the transmission. To receive the signal successfully, a receiver should compensate for the distortion of the received signal using channel information. Generally, to enable the receiver to acquire the channel information, a transmitter transmits a signal known to both the transmitter and the receiver and the receiver acquires knowledge of channel information based on the distortion of the signal received on the radio channel. This signal is called a pilot signal or an RS. 
     In the case of data transmission and reception through multiple antennas, knowledge of channel states between transmission (Tx) antennas and reception (Rx) antennas is required for successful signal reception. Accordingly, an RS should be transmitted through each Tx antenna. 
     RSs may be divided into downlink RSs and uplink RSs. In the current LTE system, the uplink RSs include: 
     i) Demodulation-reference signal (DM-RS) used for channel estimation for coherent demodulation of information delivered on a PUSCH and a PUCCH; and 
     ii) Sounding reference signal (SRS) used for an eNB or a network to measure the quality of an uplink channel in a different frequency. 
     The downlink RSs are categorized into: 
     i) Cell-specific reference signal (CRS) shared among all UEs of a cell; 
     ii) UE-specific RS dedicated to a specific UE; 
     iii) DM-RS used for coherent demodulation of a PDSCH, when the PDSCH is transmitted; 
     iv) Channel state information-reference signal (CSI-RS) carrying CSI, when downlink DM-RSs are transmitted; 
     v) Multimedia broadcast single frequency network (MBSFN) RS used for coherent demodulation of a signal transmitted in MBSFN mode; and 
     vi) Positioning RS used to estimate geographical position information about a UE. 
     RSs may also be divided into two types according to their purposes: RS for channel information acquisition and RS for data demodulation. Since its purpose lies in that a UE acquires downlink channel information, the former should be transmitted in a broad band and received even by a UE that does not receive downlink data in a specific subframe. This RS is also used in a situation like handover. The latter is an RS that an eNB transmits along with downlink data in specific resources. A UE can demodulate the data by measuring a channel using the RS. This RS should be transmitted in a data transmission area. 
     Modeling of MIMO System 
       FIG. 5  is a diagram illustrating a configuration of a wireless communication system having multiple antennas. 
     As shown in  FIG. 5( a ) , if the number of Tx antennas is increased to N T  and the number of Rx antennas is increased to N R , a theoretical channel transmission capacity is increased in proportion to the number of antennas, unlike the case where a plurality of antennas is used in only a transmitter or a receiver. Accordingly, it is possible to improve a transfer rate and to remarkably improve frequency efficiency. As the channel transmission capacity is increased, the transfer rate may be theoretically increased by a product of a maximum transfer rate Ro upon utilization of a single antenna and a rate increase ratio Ri.
 
 R   i =min( N   T   ,N   R )  [Equation 1]
 
     For instance, in an MIMO communication system, which uses four Tx antennas and four Rx antennas, a transmission rate four times higher than that of a single antenna system can be obtained. Since this theoretical capacity increase of the MIMO system has been proved in the middle of 1990s, many ongoing efforts are made to various techniques to substantially improve a data transmission rate. In addition, these techniques are already adopted in part as standards for various wireless communications such as 3G mobile communication, next generation wireless LAN, and the like. 
     The trends for the MIMO relevant studies are explained as follows. First of all, many ongoing efforts are made in various aspects to develop and research information theory study relevant to MIMO communication capacity calculations and the like in various channel configurations and multiple access environments, radio channel measurement and model derivation study for MIMO systems, spatiotemporal signal processing technique study for transmission reliability enhancement and transmission rate improvement and the like. 
     In order to explain a communicating method in an MIMO system in detail, mathematical modeling can be represented as follows. It is assumed that there are N T  Tx antennas and N R  Rx antennas. 
     Regarding a transmitted signal, if there are N T  Tx antennas, the maximum number of pieces of information that can be transmitted is N T . Hence, the transmission information can be represented as shown in Equation 2.
 
 s=└s   1   ,s   2   , . . . ,s   N     T   ┘ T   [Equation 2]
 
     Meanwhile, transmit powers can be set different from each other for individual pieces of transmission information s 1   , s   2 , . . . , s N     T   , respectively. If the transmit powers are set to P 1 , P 2 , . . . , P N     T   , respectively, the transmission information with adjusted transmit powers can be represented as Equation 3.
 
 ŝ =[ ŝ   1   ,ŝ   2   , . . . ,ŝ   N     T   ] T =[ P   1   s   1   ,P   2   s   2   , . . . ,P   N     T     s   N     T   ] T   [Equation 3]
 
     In addition, ŝ can be represented as Equation 4 using diagonal matrix P of the transmission power. 
     
       
         
           
             
               
                 
                   
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     Assuming a case of configuring N T  transmitted signals x 1 , x 2 , . . . , x N     T   , which are actually transmitted, by applying weight matrix W to the information vector S having the adjusted transmit powers, the weight matrix W serves to appropriately distribute the transmission information to each antenna according to a transport channel state. x 1 , x 2 , . . . , x N     T    can be expressed by using the vector X as follows. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     In Equation 5, w ij  denotes a weight between an i th  Tx antenna and j th  information. W is also called a precoding matrix. 
     If the N R  Rx antennas are present, respective received signals y 1 , y 2 , . . . , y N     R    of the antennas can be expressed as follows.
 
 y =[ y   1   ,y   2   , . . . ,y   R     T   ] T   [Equation 6]
 
     If channels are modeled in the MIMO wireless communication system, the channels may be distinguished according to Tx/Rx antenna indexes. A channel from the Tx antenna j to the Rx antenna i is denoted by h ij . In h ij , it is noted that the indexes of the Rx antennas precede the indexes of the Tx antennas in view of the order of indexes. 
       FIG. 5( b )  is a diagram illustrating channels from the N T  Tx antennas to the Rx antenna i. The channels may be combined and expressed in the form of a vector and a matrix. In  FIG. 5( b ) , the channels from the N T  Tx antennas to the Rx antenna i can be expressed as follows.
 
 h   i   T =[ h   i1   ,h   i2   , . . . ,h   iN     T   ]  [Equation 7]
 
     Accordingly, all channels from the N T  Tx antennas to the N R  Rx antennas can be expressed as follows. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     An AWGN (Additive White Gaussian Noise) is added to the actual channels after a channel matrix H. The AWGN n 1 , n 2 , . . . n N     R    respectively added to the N R  Rx antennas can be expressed as follows.
 
 n =[ n   1   ,n   2   , . . . ,n   N     R   ] T   [Equation 9]
 
     Through the above-described mathematical modeling, the received signals can be expressed as follows. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     Meanwhile, the number of rows and columns of the channel matrix H indicating the channel state is determined by the number of Tx and Rx antennas. The number of rows of the channel matrix H is equal to the number N R  of Rx antennas and the number of columns thereof is equal to the number N T  of Tx antennas. That is, the channel matrix H is an N R ×N T  matrix. 
     The rank of the matrix is defined by the smaller of the number of rows and the number of columns, which are independent from each other. Accordingly, the rank of the matrix is not greater than the number of rows or columns. The rank rank(H) of the channel matrix H is restricted as follows.
 
rank( H )≤min( N   T   ,N   R )  [Equation 11]
 
     Additionally, the rank of a matrix can also be defined as the number of non-zero Eigen values when the matrix is Eigen-value-decomposed. Similarly, the rank of a matrix can be defined as the number of non-zero singular values when the matrix is singular-value-decomposed. Accordingly, the physical meaning of the rank of a channel matrix can be the maximum number of channels through which different pieces of information can be transmitted. 
     In the description of the present document, ‘rank’ for MIMO transmission indicates the number of paths capable of sending signals independently on specific time and frequency resources and ‘number of layers’ indicates the number of signal streams transmitted through the respective paths. Generally, since a transmitting end transmits the number of layers corresponding to the rank number, one rank has the same meaning of the layer number unless mentioned specially. 
     Synchronization Acquisition of D2D UE 
     Now, a description will be given of synchronization acquisition between UEs in D2D communication based on the foregoing description in the context of the legacy LTE/LTE-A system. In an OFDM system, if time/frequency synchronization is not acquired, the resulting inter-cell interference (ICI) may make it impossible to multiplex different UEs in an OFDM signal. If each individual D2D UE acquires synchronization by transmitting and receiving a synchronization signal directly, this is inefficient. In a distributed node system such as a D2D communication system, therefore, a specific node may transmit a representative synchronization signal and the other UEs may acquire synchronization using the representative synchronization signal. In other words, some nodes (which may be an eNB, a UE, and a synchronization reference node (SRN, also referred to as a synchronization source)) may transmit a D2D synchronization signal (D2DSS) and the remaining UEs may transmit and receive signals in synchronization with the D2DSS. 
     D2DSSs may include a primary D2DSS (PD2DSS) or a primary sidelink synchronization signal (PSSS) and a secondary D2DSS (SD2DSS) or a secondary sidelink synchronization signal (SSSS). The PD2DSS may be configured to have a similar/modified/repeated structure of a Zadoff-chu sequence of a predetermined length or a primary synchronization signal (PSS). Unlike a DL PSS, the PD2DSS may use a different Zadoff-chu root index (e.g., 26, 37). And, the SD2DSS may be configured to have a similar/modified/repeated structure of an M-sequence or a secondary synchronization signal (SSS). If UEs synchronize their timing with an eNB, the eNB serves as an SRN and the D2DSS is a PSS/SSS. Unlike PSS/SSS of DL, the PD2DSS/SD2DSS follows UL subcarrier mapping scheme.  FIG. 6  shows a subframe in which a D2D synchronization signal is transmitted. A physical D2D synchronization channel (PD2DSCH) may be a (broadcast) channel carrying basic (system) information that a UE should first obtain before D2D signal transmission and reception (e.g., D2DSS-related information, a duplex mode (DM), a TDD UL/DL configuration, a resource pool-related information, the type of an application related to the D2DSS, etc.). The PD2DSCH may be transmitted in the same subframe as the D2DSS or in a subframe subsequent to the frame carrying the D2DSS. A DMRS can be used to demodulate the PD2DSCH. 
     The SRN may be anode that transmits a D2DSS and a PD2DSCH. The D2DSS may be a specific sequence and the PD2DSCH may be a sequence representing specific information or a codeword produced by predetermined channel coding. The SRN may be an eNB or a specific D2D UE. In the case of partial network coverage or out of network coverage, the SRN may be a UE. 
     In a situation illustrated in  FIG. 7 , a D2DSS may be relayed for D2D communication with an out-of-coverage UE. The D2DSS may be relayed over multiple hops. The following description is given with the appreciation that relay of an SS covers transmission of a D2DSS in a separate format according to a SS reception time as well as direct amplify-and-forward (AF)-relay of an SS transmitted by an eNB. As the D2DSS is relayed, an in-coverage UE may communicate directly with an out-of-coverage UE. 
     D2D Resource Pool 
       FIG. 8  shows an example of a first UE (UE 1 ), a second UE (UE 2 ) and a resource pool used by UE 1  and UE 2  performing D2D communication. In  FIG. 8( a ) , a UE corresponds to a terminal or such a network device as an eNB transmitting and receiving a signal according to a D2D communication scheme. A UE selects a resource unit corresponding to a specific resource from a resource pool corresponding to a set of resources and the UE transmits a D2D signal using the selected resource unit. UE 2  corresponding to a receiving UE receives a configuration of a resource pool in which UE 1  is able to transmit a signal and detects a signal of UE 1  in the resource pool. In this case, if UE 1  is located at the inside of coverage of an eNB, the eNB can inform UE 1  of the resource pool. If UE 1  is located at the outside of coverage of the eNB, the resource pool can be informed by a different UE or can be determined by a predetermined resource. In general, a resource pool includes a plurality of resource units. A UE selects one or more resource units from among a plurality of the resource units and may be able to use the selected resource unit(s) for D2D signal transmission.  FIG. 8( b )  shows an example of configuring a resource unit. Referring to  FIG. 8( b ) , the entire frequency resources are divided into the N F  number of resource units and the entire time resources are divided into the N T  number of resource units. In particular, it is able to define N F *N T  number of resource units in total. In particular, a resource pool can be repeated with a period of N T  subframes. Specifically, as shown in  FIG. 8 , one resource unit may periodically and repeatedly appear. Or, an index of a physical resource unit to which a logical resource unit is mapped may change with a predetermined pattern according to time to obtain a diversity gain in time domain and/or frequency domain. In this resource unit structure, a resource pool may correspond to a set of resource units capable of being used by a UE intending to transmit a D2D signal. 
     A resource pool can be classified into various types. First of all, the resource pool can be classified according to contents of a D2D signal transmitted via each resource pool. For example, the contents of the D2D signal can be classified into various signals and a separate resource pool can be configured according to each of the contents. The contents of the D2D signal may include a scheduling assignment (SA or physical sidelink control channel (PSCCH)), a D2D data channel, and a discovery channel. The SA may correspond to a signal including information on a resource position of a D2D data channel, information on a modulation and coding scheme (MCS) necessary for modulating and demodulating a data channel, information on a MIMO transmission scheme, information on a timing advance (TA), and the like. The SA signal can be transmitted on an identical resource unit in a manner of being multiplexed with D2D data. In this case, an SA resource pool may correspond to a pool of resources that an SA and D2D data are transmitted in a manner of being multiplexed. The SA signal can also be referred to as a D2D control channel or a physical sidelink control channel (PSCCH). The D2D data channel (or, physical sidelink shared channel (PSSCH)) corresponds to a resource pool used by a transmitting UE to transmit user data. If an SA and a D2D data are transmitted in a manner of being multiplexed in an identical resource unit, D2D data channel except SA information can be transmitted only in a resource pool for the D2D data channel. In other word, REs, which are used to transmit SA information in a specific resource unit of an SA resource pool, can also be used for transmitting D2D data in a D2D data channel resource pool. The discovery channel may correspond to a resource pool for a message that enables a neighboring UE to discover transmitting UE transmitting information such as ID of the UE, and the like. 
     Despite the same contents, D2D signals may use different resource pools according to the transmission and reception properties of the D2D signals. For example, despite the same D2D data channels or the same discovery messages, they may be distinguished by different resource pools according to transmission timing determination schemes for the D2D signals (e.g., whether a D2D signal is transmitted at the reception time of a synchronization reference signal or at a time resulting from applying a predetermined TA to the reception time of the synchronization reference signal), resource allocation schemes for the D2D signals (e.g., whether an eNB configures the transmission resources of an individual signal for an individual transmitting UE or the individual transmitting UE autonomously selects the transmission resources of an individual signal in a pool), the signal formats of the D2D signals (e.g., the number of symbols occupied by each D2D signal in one subframe or the number of subframes used for transmission of a D2D signal), signal strengths from the eNB, the transmission power of a D2D UE, and so on. In D2D communication, a mode in which an eNB directly indicates transmission resources to a D2D transmitting UE is referred to as sidelink transmission mode  1 , and a mode in which a transmission resource area is preconfigured or the eNB configures a transmission resource area and the UE directly selects transmission resources is referred to as sidelink transmission mode  2 . In D2D discovery, a mode in which an eNB directly indicates resources is referred to as Type 2, and a mode in which a UE selects transmission resources directly from a preconfigured resource area or a resource area indicated by the eNB is referred to as Type 1. 
     In V2X, sidelink transmission mode  3  based on centralized scheduling and sidelink transmission mode  4  based on distributed scheduling are available.  FIG. 9  illustrates scheduling schemes according to these two transmission modes. Referring to  FIG. 9 , in transmission mode  3  based on centralized scheduling, when a vehicle requests sidelink resources to an eNB (S 901   a ), the eNB allocates the resources (S 902   a ), and the vehicle transmits a signal in the resources to another vehicle (S 903   a ). In the centralized transmission scheme, resources of another carrier may be also scheduled. In distributed scheduling corresponding to transmission mode  4  illustrated in  FIG. 9( b ) , a vehicle selects transmission resources (S 902   b ), while sensing resources preconfigured by the eNB, that is, a resource pool (S 901   b ), and then transmits a signal in the selected resources to another vehicle (S 903   b ). When the transmission resources are selected, transmission resources for a next packet are also reserved, as illustrated in  FIG. 10 . In V2X, each MAC PDU is transmitted twice. When resources for an initial transmission are reserved, resources for a retransmission are also reserved with a time gap from the resources for the initial transmission. For details of the resource reservation, see Section  14  of 3GPP TS 36.213 V14.6.0, which is incorporated herein as background art. 
     Transmission and Reception of SA 
     A UE in sidelink transmission mode  1  may transmit a scheduling assignment (SA) (a D2D signal or sidelink control information (SCI)) in resources configured by an eNB. A UE in sidelink transmission mode  2  may be configured with resources for D2D transmission by the eNB, select time and frequency resources from among the configured resources, and transmit an SA in the selected time and frequency resources. 
     In sidelink transmission mode  1  or  2 , an SA period may be defined as illustrated in  FIG. 9 . Referring to  FIG. 9 , a first SA period may start in a subframe spaced from a specific system frame by a specific offset, SAOffsetIndicator indicated by higher-layer signaling. Each SA period may include an SA resource pool and a subframe pool for D2D data transmission. The SA resource pool may include the first subframe of the SA period to the last of subframes indicated as carrying an SA by a subframe bitmap, saSubframeBitmap. The resource pool for D2D data transmission may include subframes determined by a time-resource pattern for transmission (T-RPT) (or a time-resource pattern (TRP)) in mode  1 . As illustrated, when the number of subframes included in the SA period except for the SA resource pool is larger than the number of T-RPT bits, the T-RPT may be applied repeatedly, and the last applied T-RPT may be truncated to include as many bits as the number of the remaining subframes. A transmitting UE performs transmission at T-RPT positions corresponding to 1 s in a T-RPT bitmap, and one MAC PDU is transmitted four times. 
     Unlike D2D, an SA (PSCCH) and data (PSSCH) are transmitted in FDM in V2X, that is, sidelink transmission mode  3  or  4 . Because latency reduction is a significant factor in V2X in view of the nature of vehicle communication, an SA and data are transmitted in FDM in different frequency resources of the same time resources. Examples of this transmission scheme are illustrated in  FIG. 12 . An SA and data may not be contiguous to each other as illustrated in  FIG. 12( a )  or may be contiguous to each other as illustrated in  FIG. 12( b ) . Herein, a basic transmission unit is a subchannel. A subchannel is a resource unit including one or more RBs on the frequency axis in predetermined time resources (e.g., a subframe). The number of RBs included in a subchannel, that is, the size of the subchannel and the starting position of the subchannel on the frequency axis are indicated by higher-layer signaling. 
     In V2V communication, a cooperative awareness message (CAM) of a periodic message type, a decentralized environmental notification message (DENM) of an event triggered message type, and so on may be transmitted. The CAM may deliver basic vehicle information including dynamic state information about a vehicle, such as a direction and a speed, static data of the vehicle, such as dimensions, an ambient illumination state, details of a path, and so on. The CAM may be 50 bytes to 300 bytes in length. The CAM is broadcast, and its latency should be shorter than 100 ms. The DENM may be generated, upon occurrence of an unexpected incident such as breakdown or an accident of a vehicle. The DENM may be shorter than 3000 bytes, and received by all vehicles within a transmission range. The DENM may have a higher priority than the CAM. When it is said that a message has a higher priority, this may mean that from the perspective of one UE, in the case of simultaneous transmission of messages, the higher-priority message is transmitted above all things, or earlier in time than any other of the plurality of messages. From the perspective of multiple UEs, a message having a higher priority may be subjected to less interference than a message having a lower priority, to thereby have a reduced reception error probability. Regarding the CAM, the CAM may have a larger message size when it includes security overhead than when it does not. 
     NR (New RAT(Radio Access Technology)) 
     As more and more communication devices require a larger communication capacity, there is a need for enhanced mobile broadband communication beyond legacy RAT. In addition, massive Machine Type Communications (MTC) capable of providing a variety of services anywhere and anytime by connecting multiple devices and objects is another important issue to be considered for next generation communications. Communication system design considering services/UEs sensitive to reliability and latency is also under discussion. As such, introduction of new radio access technology considering enhanced mobile broadband communication (eMBB), massive MTC, and ultra-reliable and low latency communication (URLLC) is being discussed. In the present disclosure, for simplicity, this technology will be referred to as NR. 
       FIGS. 13 and 14  illustrate an exemplary frame structure available for NR. Referring to  FIG. 13 , the frame structure is characterized by a self-contained structure in which all of a DL control channel, DL or UL data, and a UL control channel are included in one frame. The DL control channel may deliver DL data scheduling information, UL data scheduling information, and so on, and the UL control channel may deliver ACK/NACK information for DL data, CSI (modulation and coding scheme (MCS) information, MIMO transmission-related information, and so on), a scheduling request, and so on. A time gap for DL-to-UL or UL-to-DL switching may be defined between a control region and the data region. A part of a DL control channel, DL data, UL data, and a UL control channel may not be configured in one frame. Further, the sequence of channels in one frame may be changed (e.g., DL control/DL data/UL control/UL data, UL control/UL data/DL control/DL data, or the like). 
     Meanwhile, carrier aggregation may be used even in case of D2D communication to improve a data transmission rate or reliability. For example, a receiving UE may receive a signal from aggregated carriers, perform combining or joint decoding or deliver a decoded signal to a higher layer, thereby performing (soft) combining for signals transmitted from different carriers. However, for this operation, since the receiving UE needs to identify what carriers are aggregated, that is, carriers of which signals should be combined, it is required to indicate radio resources of the aggregated carriers. In the legacy 3GPP Rel. 14 V2X, a transmitting UE directly indicates a time frequency position to which data (PSSCH) is transmitted, by using a control signal (PSCCH). However, if carrier aggregation is indicated through PSCCH, additional bit field is required for this indication. However, reserved bits remaining in the current PSCCH are 5 to 7 small bits, approximately. Therefore, a method for indicating radio resources of effectively aggregated carriers is required. Hereinafter, detailed methods related to this case will be described. 
     UE Initiates Ranging Signal Transmission 
     The present disclosure suggests a method for determining transmission and reception resources and transmission signals for ranging/positioning in D2D communication. Hereinafter, a unit of which position is fixed or previously delivered to a UE or peripheral UEs through a physical layer signal or a higher layer signal will be defined as a road side unit (RSU). The RSU may be a UE type (network access by wireless) or an eNB type (network access by wire). Meanwhile, among UEs, a UE of which position information is determined to be relatively exact may perform an operation equal to or similar to that of the RSU suggested in the following description. 
     Meanwhile, in case of V2X, position measurement of the UE through TDoA from a plurality of eNBs may not be proper in view of fast movement. In detail, in order to estimate a position of the UE based on TDoA, a series of procedures are required as follows. The plurality of eNBs need to receive a feedback signal from the UE and transmit the received feedback signal to a location server, and the location server needs to analyze the position of the UE and then feed the analyzed position of the UE back to the eNB. However, in V2X of which position is quickly varied, since the position is varied even for a time period required for feedback according to the series of procedures, an error between the position information which is fed back and the current position of the UE is increased. Also, in case of V2X of which position should be measured per short time period, since a PRS period is too long, position measurement may not be proper. In this respect, position measurement of the UE through a new method is required. Hereinafter, a detailed method for position measurement will be described. 
     Basically, a signal for ranging and/or positioning may have a short transmission length in a time domain. Hereinafter, although a time unit for transmitting a signal for ranging and/or positioning is assumed as a subframe unit unless mentioned separately, a transmission time interval (TTI) length less than the subframe unit may be applied to the present disclosure. 
     Ranging may be performed in such a manner that a signal is directly transmitted or received between UEs or between a UE and an RSU. For example, if a signal is transmitted at a subframe n, the UE which has received the signal may transmit a feedback signal at a subframe n+k. At this time, if at least one or more UEs or RSUs simultaneously perform signal transmission and reception, it may be required to perform time division multiplexing (TDM) for transmission and reception resources between the UEs or RSUs. 
     First of all, the UE may transmit a signal for ranging and/or positioning from a resource region where the signal for ranging and/or positioning is transmitted or received. In this case, the UE which transmits or receives the signal for ranging and/or positioning may be a UE of which position information is not exact or position error is a certain threshold value or more. The UE of which position information is not exact or position error is a certain threshold value or more may transmit a transmission signal to request the RSU or another UE of which position is exact to transmit a feedback signal (or response signal). 
     The UE may determine RSU to which a signal will be transmitted, and may select a resource region. In this case, all or some of time and frequency resources, sequence index or ID, comb repetition factor, comb index, and tone position (in case of phase difference of arrival (PDoA)), which are used for signal transmission for ranging and/or positioning per UE, may previously be determined, or may be determined by the UE. 
     For example, some of the above attributes (transmission resources, sequence, etc.) may be determined depending on the position of the UE. The position of the UE may be identified based on GNSS. This is to transmit signals between UEs arranged differently from each other by using different transmission resources. To this end, a resource region used per position of the UE may previously be determined, or may be signaled by a network through a physical layer signal or a higher layer signal. In this case, a resource region used for ranging and/or positioning by UEs which belong to a region A and a resource region used for ranging and/or positioning by UEs which belong to a region B may be separated from each other. 
     Some of the above attributes may be determined depending on receiving intensity of RSU signal. For example, a transmission resource used by a UE having receiving intensity of a signal received from RSU A, which is a certain threshold value or more, may be set differently from a transmission resource used by another UE having receiving intensity of a signal received from RSU B, which is a certain threshold value or more. To this end, resources used for each RSU, conditions of transmission resources used per receiving intensity of RSU signals, etc. may previously be determined, or may be signaled by a network or RSU to the UE through a physical layer signal or a higher layer signal. 
     According to an embodiment, a transmission power for ranging and/or positioning may be determined in accordance with receiving intensity of RSU signal. For example, open loop power control may be applied to the transmission power. This is to reduce inband emission effect when the RSU receives signals from several UEs. In this case, if open loop power control is applied, UE specific parameter P related to SINR which is used and a weight value alpha for pathloss may previously be determined, or may be signaled by the network through a physical layer signal or a higher layer signal. At this time, P0 and alpha which are used may be indicated separately unlike a value used for data transmission. This is because that attributes (TTI, subcarrier spacing) of signals used for ranging and/or positioning may be different from those of signals used for data and an interference status of resources for data transmission may be different from that of transmission resources of a ranging signal. 
     Next, the UE may select a detailed resource and signal in a resource region. If the UE transmits a signal to a specific RSU or a UE of which position is exact in accordance with the above methods, a plurality of UEs not one UE may transmit the signal. At this time, attributes (position of transmission resources, sequence ID, etc.) of signals may be set differently between individual UEs. This is because that all or some of attributes of signals should be set differently to be identified per UE when the RSU transmits a feedback signal. 
     The UE needs to vary a detailed position of transmission resources even within a resource region. For example, the UE may randomly select a position of transmission resources, derive a position of transmission resources from ID of the UE, determine a position of transmission resources by sensing (method for measuring a receiving power or energy and selecting the receiving power or energy from resources of which energy is less than a certain threshold value) of the UE, or determine a position of transmission resources in accordance with indication of the RSU. Also, all or some of attributes (sequence ID, etc.) of a transmission signal as well as a position of transmission resources may be selected by one or combination of more of the above methods. 
     Next, the RSU which has received a signal from the UE may transmit a response signal by using resource/sequence information associated with the signal transmitted from the UE. The response signal may be used by the UE to measure a distance between the UE and the RSU. In detail, in case of phase difference of arriving (PDoA), the response signal may be used to indicate information on a phase difference between tones when the RSU receives a signal of the UE. Alternatively, in case of time difference of arrival (TDoA), the response signal may be used to indicate information on the time when a signal is received from a specific UE. 
     At this time, the RSU may differently determine resources which will transmit the response signal, to avoid resource collision between RSUs. For example, the RSU may determine a position of transmission resources/sequences of the response signal based on resources/sequences which have received the signal of the UE if the UE successfully receives the signal of the UE. In this case, in order to avoid resource collision or signal collision between RSUs, all or some of attributes of resources or signals used between the RSUs may previously be determined, or this information may be shared between the RSUs by using a backhaul between the RSUs. A rule which allows transmission of a feedback signal may be determined only if the RSU receives a signal of a specific UE at a certain threshold value or more. In this case, the RSU may not perform a feedback for the signal transmitted from a UE which is far away therefrom, so as to cancel interference between response signals and reduce a position estimation error. 
     A rule may be determined such that a resource region used when the RSU transmits a signal may not be used by another UE. For example, a resource region used by the RSU and a resource region used by the UE may previously be separated from each other, or may be indicated by the network through a physical layer signal or a higher layer signal. 
     The RSU may be configured to transmit a feedback signal (or response signal) for a signal of which receiving power is the largest or a signal having a certain threshold value or more among the signals which are received when the signals of the UE are received at a specific time. In this case, the threshold value may be set by the network or previously be determined. If the RSU follows this method, the RSU may use the feedback signal (or response signal) as a purpose of use of response indicating that the signal of the specific UE has been received well. That is, if the specific UE has transmitted a signal but has not received a feedback signal from the RSU, the specific UE may trigger an operation for changing transmission resources or a resource region by assuming that its signal has not been delivered well. 
     The RSU may signal its position information as well as the response signal to a peripheral UE through a physical layer signal or a higher layer signal. This is to allow the UE to estimate its exact position by using the position of the RSU after measuring a distance. 
     Next, the UE may calculate a distance from the RSU by receiving the response signal. The UE may estimate a distance and direction from the RSU by estimating angles of arrival (AoA) from the RSU. If the RSU has transmitted its position information, the UE may estimate its position based on the position information of the RSU. 
       FIG. 15  is a view illustrating a method for determining a resource region in accordance with geographical information of a UE according to an embodiment. 
     Referring to  FIG. 15( a ) , a resource region to which the ranging signal is transmitted may be determined based on geographical information. In detail, the UE may previously receive ranging resource information which is information on the previously configured resource region. For example, the UE may previously receive ranging resource information for mapping each of region A, region B, region C, region D and region E into region of a first resource region, a second resource region, a third resource region, a fourth resource region, and a fifth resource region in a one-to-one relationship. In this case, the first to fifth resource regions may be configured as resource regions which are not overlapped with one another, or may be configured as partially overlapped resource regions. 
     In this case, the UE  200  may determine a corresponding resource region from the ranging resource information based on the geographical information acquired by itself. In this case, the geographical information may be coordinate information of the UE, which is measured using a global positioning system (GPS) included in the UE. For example, if a second resource region is previously configured as a resource region corresponding to the region B and it is determined that the second resource region is arranged in the region B based on the geographical information acquired through the GPS, the UE may determine the second resource region previously configured to correspond to the region B as a resource region for transmitting the ranging signal. 
     Also, referring to  FIG. 15( b ) , the UE may determine a corresponding resource region based on the geographical information and ranging resource information acquired by itself, wherein the geographical information may be determined based on signal intensity of the RSU  101 . That is, peripheral regions may be identified in accordance with receiving intensity of the signal of the RSU. In detail, the peripheral regions may be divided into a region A where receiving intensity of the signal of the RSU is more than a first threshold value, a region B where receiving intensity of the signal of the RSU is smaller than the first threshold value but is more than a second threshold value, and a region C where receiving intensity of the signal of the RSU is smaller than the second threshold value but is more than a third threshold value. The ranging resource information may include receiving intensity of the signal, information on a region corresponding to the receiving intensity, and information on a resource region corresponding to the region. In this case, the UE may determine geographical information (or region information) corresponding to receiving intensity of a signal received from the RSU and a resource region corresponding to the geographical information considering the ranging resource information. For example, if the signal of the RSU of intensity smaller than the second threshold value and more than the third threshold value is received, the UE may determine its geographical information as the region B and determine the resource region corresponding to the region B as a resource region for transmitting the ranging signal. 
     Meanwhile, a size of the resource included in the resource region determined in each region may be set to be increased if the intensity of the signal becomes smaller. For example, the size of the resource region may previously be set such that the resource region corresponding to the region A may include 10 resource blocks, the resource region corresponding to the region B may include 20 resource blocks, and the resource region corresponding to the region C may include 40 resource blocks. 
     In this way, the resource region for ranging may previously be divided into a plurality of resource regions based on GPS information, or may previously be divided into a plurality of resource regions in accordance with the receiving intensity of the signal of the RSU  101 . In this case, the UE may acquire its geographical information based on the intensity of the signal received from the RSU or its GPS information and determine a corresponding resource region as a resource region for transmitting the ranging signal based on the acquired geographical information. Meanwhile, the UE may determine a resource region by any one of the aforementioned two methods depending on what the geographical information is, or may previously be indicated by the network as to how the geographical information should be determined. 
     Next, the UE may determine specific resource elements in the determined resource region based on its ID information. For example, in case of time difference of arrival (TDoA), the UE may specify a position of resources or sequence used in the determined resource region based on its ID information. Alternatively, in case of phase difference of arriving (PDoA), the UE may specify different frequency resources (REs, tones) used in the determined resource region based on its ID information. Also, the UE may randomly determine specific resource elements within the resource region. In this method, the UE may transmit a ranging signal by selecting resources which are not overlapped with peripheral UEs, whereby interference and collision between ranging signals of the UEs may be minimized. 
       FIG. 16  is a view illustrating a method for calculating a position of a UE according to an embodiment. 
     Referring to  FIG. 16 , the UE may receive a response signal of the RSU, and may measure a receiving direction of the response signal by using multi-antennas. 
     In detail, the UE may receive the response signal of the RSU through multi-antennas. The UE may estimate AoA which is a receiving angle of the response signal of the RSU. Also, the UE may calculate distance information with the RSU from information which is the basis for calculation of ranging information included in the response signal. In this case, the UE may exactly determine its position in a circle having the distance information as a radius based on the receiving angle. That is, if the receiving angle of the response signal is measured through multi-antennas, the UE may calculate and estimate its exact position based on the calculated ranging information, the receiving angle and the position of the RSU. 
     In this case, the UE may correct GPS coordinate information acquired from its GPS device based on its position information which is calculated. In this way, the UE may calculate or acquire more exact position by correcting the position information according to the GPS device to the position information calculated by signal exchange through the RSU. Particularly, if the UE is a UE included in an autonomous vehicle, the vehicle may autonomously drive based on position information more exact than the GPS, whereby safety of autonomous driving may effectively be improved. 
       FIG. 17  is a flow chart illustrating a method for calculating ranging information according to an embodiment of the present disclosure. 
     Referring to  FIG. 17 , the UE may transmit a ranging signal for calculating ranging information based on geographical information to the RSU. Particularly, it is determined that the UE cannot exactly measure its position (for example, the UE passes through a tunnel, is arranged in a place where high buildings are concentrated, or error operation of the GPS device, etc.), the UE may transmit the ranging signal to the RSU. In this case, the UE may transmit a ranging signal requesting transmission of a response signal, which includes information for calculating ranging information, to RSU of which position is exact, to exactly measure its position. At this time, the UE may determine a transmission region, to which the ranging signal will be transmitted, based on the geographical information of the UE. In this case, the geographical information may be brief coordinate information determined directly by the UE through GPS, or may be region information determined based on receiving intensity of a signal (signal received from the RSU before the ranging signal is transmitted) received from the RSU. In detail, the UE may determine a resource region corresponding to the determined geographical information based on the geographical information. The resource region may be determined as at least one of a plurality of resource regions divided in accordance with the geographical information as shown in  FIGS. 15( a ) and 15( b )  (S 301 ). 
     According to an embodiment, the UE may previously acquire ranging resource information, which includes information on a corresponding resource region, from the RSU or the network in accordance with the geographical information. 
     Next, the UE may select a specific resource element within the determined resource region corresponding to its geographical information based on UE ID or randomly. The UE may transmit the ranging signal by using the determined specific resource element. This is to minimize collision and interference with ranging signals of different UEs that transmit ranging signals in the same resource region. 
     According to an embodiment, the UE may determine a transmission power of the ranging signal based on receiving intensity of the signal of the RSU received before the ranging signal is transmitted. For example, the UE may measure pathloss between the RSU and the UE based on the receiving intensity of the signal of the RSU, and may determine the transmission power of the ranging signal in accordance with an open loop power control method. In this case, when each of a plurality of UEs transmits the ranging signal at a similar timing, even though the RSU receives the ranging signals at a similar timing, a difference in the receiving power between the ranging signals is not great. That is, the transmission power of the ranging signal is determined based on the receiving intensity of the signal of the RSU as above, whereby an inband emission problem caused by the difference in the receiving power between the ranging signals may be solved. 
     Otherwise, the UE may determine sequence index or ID of the feedback signal based on the receiving intensity of the signal of the RSU. For example, considering that it is not likely to be a line of sight (LOS) state if the receiving intensity of the signal of the RSU becomes weaker, the UE may determine a proper sequence that may solve this problem. 
     Otherwise, the UE may change a CP and frequency band for the ranging signal in accordance with the receiving intensity of the signal of the RSU. For example, if the receiving intensity of the signal of the RSU becomes weaker, the UE may make the CP be longer or the frequency band to which the ranging signal is transmitted may be increased. 
     Next, the UE may receive the response signal from the RSU in response to the ranging signal. The response signal may include information which is the basis for calculation of the ranging information calculated by the RSU on the basis of the ranging signal. In detail, the information which is the basis for calculation of the ranging information includes information on the time when the ranging signal is received or phase rotation information according to propagation delay acquired from the ranging signal (S 303 ). 
     According to an embodiment, the response signal may be transmitted from the RSU only if a specific condition is satisfied. In detail, the response signal may be transmitted when the RSU receives the ranging signal at receiving intensity of a previously set threshold value or more. For example, if the receiving intensity of the ranging signal is weak, even though the RSU transmits the response signal because the RSU is not likely to be LOS with the UE which has transmitted the ranging signal, the UE may calculate inexact ranging information based on the response signal. Therefore, if the receiving intensity of the ranging signal is less than a preset threshold value, transmission of the response signal to the ranging signal to the RSU is limited, whereby unnecessary resource waste and collision between signals may be minimized. 
     Also, the response signal may be transmitted using resources and sequence associated with at least one of resources and sequence to which the ranging signal is transmitted. The UE may identify the response signal to the ranging signal based on any one of resources and sequence used to transmit the ranging signal. Meanwhile, the resource region to which the response signal is transmitted is previously separated from the resource region used to transmit the ranging signal. That is, the transmission resources used by the RSU to transmit a signal may previously configured as those different from the transmission resources used by the UEs to transmit the ranging signal. Also, the response signal may include position information on the RSU. This is to allow the UE to determine a reference position of the ranging information based on the position information of the RSU when calculating the ranging information from the response signal. 
     Next, the UE may acquire distance information with the RSU from information which is the basis for calculation of ranging information included in the response signal. For example, if the response signal includes information on the time when the ranging signal is received, the UE may calculate time delay with the RSU, and may calculate ranging information which is distance information with the RSU corresponding to the calculated time delay in accordance with a method according to TDoA. Alternatively, if the response signal includes phase rotation information on the ranging signal, the UE may calculate ranging information with the RSu corresponding to the phase rotation information in accordance with a method according to PDoA (S 305 ). 
     Also, the UE may measure a receiving angle of the response signal, and may calculate and estimate its exact position based on the measure receiving angle, the calculated ranging information and the position information of the RSU. Meanwhile, if the response signal transmitted in response to the ranging signal is not received, the UE may retransmit the ranging signal by changing the determined resource region or changing a transmission power. 
       FIG. 18  is a view illustrating a UE that performs D2D communication according to the present disclosure. 
       FIG. 18  is a block diagram of a transmission point and a UE according to an embodiment of the present disclosure. 
     Referring to  FIG. 18 , a transmission point  10  according to the present disclosure may include a receiving device  11 , a transmitting device  12 , a processor  13 , a memory  14 , and a plurality of antennas  15 . Use of the plurality of antennas  15  means that the transmission point  10  supports MIMO transmission and reception. The receiving device  11  may receive various UL signals, data, and information from a UE. The transmitting device  12  may transmit various DL signals, data, and information to a UE. The processor  13  may provide overall control to the transmission point  10 . 
     The processor  13  of the transmission point  10  according to an embodiment of the present disclosure may process requirements for each of the foregoing embodiments. 
     The processor  13  of the transmission point  10  may function to compute and process information received by the transmission point  10  and information to be transmitted to the outside. The memory  14  may store the computed and processed information for a predetermined time, and may be replaced by a component such as a buffer (not shown). 
     With continued reference to  FIG. 18 , a UE  20  according to the present disclosure may include a receiving device  21 , a transmitting device  22 , a processor  23 , a memory  24 , and a plurality of antennas  15 . Use of the plurality of antennas  25  means that the UE  20  supports MIMO transmission and reception. The receiving device  21  may receive various DL signals, data, and information from an eNB. The transmitting device  22  may transmit various UL signals, data, and information to an eNB. The processor  23  may provide overall control to the UE  20 . 
     The processor  23  of the UE  20  according to an embodiment of the present disclosure may process the necessary matters in each of the above-described embodiments. In detail, the processor may determine a resource region corresponding to geographical information on the UE based on ranging resource information on a resource region configured per geographical information, transmit a ranging signal for calculating ranging information from the determined resource region, receive a response signal including information which is the basis for calculation of the ranging information, from a road side unit (RSU) which has received the ranging signal, and calculate ranging information which is distance information with the RSU based on the response signal. 
     The processor  23  of the UE  20  may also perform a function of computationally processing information received by the UE  20  and information to be transmitted to the outside, and the memory  24  may store the computationally processed information and the like for a predetermined time and may be replaced by a component such as a buffer (not shown). 
     The specific configuration of the transmission point and the UE may be implemented such that the details described in the various embodiments of the present disclosure may be applied independently or implemented such that two or more of the embodiments are applied at the same time. For clarity, a redundant description is omitted. 
     In the example of  FIG. 18 , the description of the transmission point  10  may also be applied to a relay as a DL transmission entity or a UL reception entity, and the description of the UE  20  may also be applied to a relay as a DL reception entity or a UL transmission entity. 
     The embodiments of the present disclosure may be implemented through various means, for example, in hardware, firmware, software, or a combination thereof. 
     In a hardware configuration, the methods according to the embodiments of the present disclosure may be achieved by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, etc. 
     In a firmware or software configuration, the methods according to the embodiments of the present disclosure may be implemented in the form of a module, a procedure, a function, etc. Software code may be stored in a memory unit and executed by a processor. The memory unit is located at the interior or exterior of the processor and may transmit and receive data to and from the processor via various known means. 
     As described before, a detailed description has been given of preferred embodiments of the present disclosure so that those skilled in the art may implement and perform the present disclosure. While reference has been made above to the preferred embodiments of the present disclosure, those skilled in the art will understand that various modifications and alterations may be made to the present disclosure within the scope of the present disclosure. For example, those skilled in the art may use the components described in the foregoing embodiments in combination. The above embodiments are therefore to be construed in all aspects as illustrative and not restrictive. 
     Those skilled in the art will appreciate that the present disclosure may be carried out in other specific ways than those set forth herein without departing from the spirit and essential characteristics of the present disclosure. The above embodiments are therefore to be construed in all aspects as illustrative and not restrictive. The scope of the disclosure should be determined by the appended claims and their legal equivalents, not by the above description, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein. It is obvious to those skilled in the art that claims that are not explicitly cited in each other in the appended claims may be presented in combination as an embodiment of the present disclosure or included as a new claim by a subsequent amendment after the application is filed. 
     INDUSTRIAL APPLICABILITY 
     The above-described embodiments of the present disclosure are applicable to various mobile communication systems.